PALLADIN'S 

PLANT  PHYSIOLOGY 

EDITED  BY 

BURTON  E.  LIVINGSTON 


Prof.  V.  I.  Palladin 
i  9  i  i 


/ 


PLANT  PHYSIOLOGY 


BY 

VLADIMIR  I.  PALLADIN 

PROFESSOR   IN   THE    UNIVERSITY    OF    PETROGRAD 

AUTHORIZED  ENGLISH  EDITION 

Based  on  the  German  Translation  of  the  Sixth  Russian 
Edition  and  on  the  Seventh  Russian  Edition   (1914) 

EDITED  BY 

BURTON  EDWARD  LIVINGSTON,  Ph.  D. 

PROFESSOR  OF   PLANT   PHYSIOLOGY  AND   DIRECTOR   OF   THE   LABORATORY 
OF   PLANT   PHYSIOLOGY   OF   THE   JOHNS   HOPKINS   UNIVERSITY 


Second  American  Edition 
With  a  Biographic  Note  and  Chapter  Summaries  by  the  Editor 


173  ILLUSTRATIONS 


PHILADELPHIA 

P.   BLAKISTON'S   SON   &   CO 

1012   WALNUT   STREET 


Copyright,  1923,  by  P.  Blakiston's  Son  &  Co. 


PRINTED  IN  U.  S.  A. 
BY  THE  MAPLE  PRESS  YORK  PA 


A  NOTE  OF  APPRECIATION1 

Doctor  V.  I.  Palladin,  Academician  of  the  Russian  Academy  of  Sciences 
and  author  of  this  book,  died  in  Petrograd  on  February  3,  1922,  after  a  pro- 
longed illness  that  culminated  in  aortic  aneurism.  His  life  work  was  a  fine 
contribution  to  physiological  science  in  general,  and  especially  to  plant  physio- 
logy. His  text-book  on  plant  physiology  was  published  in  Russian,  German, 
French,  and  English,  and  the  marked  excellencies  of  the  book  have  made  his 
name  well  known  wherever  this  science  is  studied.  But  his  greatest  contribu- 
tion lies  in  his  research  publications. 

Palladin  was  born  July  11,  1859,  in  Moscow  and  received  his  education  in 
the  First  Gymnasium  of  Moscow  and  in  the  University  of  Moscow.  He 
studied  botany  under  Timiriazev  and  Gorozhankin,  and  published  his  first 
research  contribution,  "On  the  structure  and  capacity  for  swelling  of  cell 
walls  and  starch  grains,"  in  1883  (Zapiski  Moskovskogo  Univ.).  His  disser- 
tation for  the  master's  degree,  conferred  at  the  University  of  Moscow  in  1887, 
is  on  "The  significance  of  oxygen  for  plants"  (Bull.  Soc.  Nat.  Moscow,  1886), 
and  that  for  the  doctor's  degree,  conferred  at  the  same  university  in  1888,  is 
on  "The  influence  of  oxygen  on  the  decomposition  of  proteinaceous  substances 
in  plants"  (Dissert.  Moscow  Univ.,  1889). 

The  first  teaching  position  held  by  the  great  Russian  physiologist  was  in  the 
Institute  of  Rural  Economics  and  Forestry  at  Novaya  Alexandria,  whither  he 
went  in  1886.  Three  years  later,  after  receiving  the  doctor's  degree,  he  became 
professor  of  plant  anatomy  and  physiology  in  the  University  of  Kharkov.  In 
1897  he  was  appointed  to  a  professorship  in  the  University  of  Warsaw  and  was 
made  director  of  the  Pomological  Garden  of  Warsaw.  He  was  called  to  the 
University  of  Petrograd  in  1900,  as  professor  of  plant  physiology,  where  he 
remained  until  191 7.  In  the  last-named  year  Palladin  removed  to  the  Crimea, 
giving  lectures  in  the  newly  founded  university  at  Simferopol.  Later  he  became 
director  of  the  Nikitskii  Botanical  Garden  at  Jalta. 

He  was  elected  to  the  Russian  Academy  of  Sciences  in  1906,  and  took  active 
part  in  the  work  of  the  Academy,  publishing  many  papers  in  its  proceedings. 
Election  as  academician  is  the  highest  honor  conferred  on  Russian  scientists, 
and  only  a  few  receive  this  mark  of  great  distinction. 

1  This  note  is  mainly  based  on  a  biographical  sketch  of  Palladin.  by  Professor  X.  I.  Kuz- 
netzov,  in  the  ninth  Russian  edition  of  the  Physiology.  I  have  been  helped  in  its  preparation 
by  Dr.  Selman  A.  Waksman,  of  the  New  Jersey  Agricultural  Experiment  Station,  and  by  Mr. 
L.  J.  Pessin,  of  the  Mississippi  Agricultural  and  Mechanical  College,  as  well  as  by  Mr.  D.  X. 
Borodin,  of  the  Xew  York  Office  of  the  Russian  Bureau  of  Applied  Botany  and  Prof.  X. 
Ivanov,  of  the  University  of  Petrograd. — B.  E.  L. 

vii 


viii  A    NOTE    OF    APPRECIATION 

Palladin's  lectures  were  always  precise  and  unusually  clear.  His  text-books 
—on  plant  anatomy,  plant  physiology,  and  systematic  botany— show  his  excel- 
lent style  of  presentation.  In  his  teaching  positions  Palladin  always  attracted 
a  group  of  enthusiastic  students.  He  was  a  calm  and  polished  leader,  always 
pleasant  to  work  with,  who  would  not  quarrel  over  unessential  matters  but 
who  understood  how  to  lead  the  advance  persistently  toward  the  finer  and 
greater  things.  The  remarkable  precision  of  his  scientific  thinking,  together 
with  his  indefatigable  application,  placed  him  at  the  head  of  a  school  of  plant 
physiology  that  extends  far  beyond  the  boundaries  of  Russia. 

Although  he  was  interested  in  and  contributed  to  many  different  lines  of 
botanical  study,  Palladin's  main  research  publications  were,  from  the  time  of 
his  master's-degree  dissertation  at  Moscow,  devoted  to  the  fundamental  phe- 
nomena of  respiration.  His  many  papers  on  this  subject — and  those  that 
appeared  under  joint  authorship,  with  one  or  more  of  his  colleagues  or  students 
—were  not  confined  to  the  Russian  language,  and  Palladin's  name  became 
familiar  to  readers  of  the  leading  French  and  German  journals  devoted  to 
botany  and  to  physiological  chemistry.  To  the  scientific  world  at  large,  as 
well  as  to  plant  physiologists  of  all  nations  Palladin's  thorough  elucidation  of 
some  of  the  most  fundamental  and  baffling  aspects  of  the  respiration  process 
will  stand  as  his  greatest  achievement.  Step  by  step,  he  and  his  followers 
gradually  built  up  a  new  and  clear  picture  of  the  chemistry  of  respiration  as  it 
apparently  occurs  in  all  living  cells. 

The  main  points  of  the  Palladin  theory  of  respiration  are  somewhat  as 
follows:  Under  the  influence  of  enzymes,  carbohydrates  and  similar  sub- 
stances are  anaerobically  decomposed  into  carbon  dioxide  and  incompletely 
oxidized  organic  compounds,  these  partial  oxidations  occurring  partly  at  the 
expense  of  oxygen  derived  from  the  decomposition  of  water.  The  hydrogen 
produced  by  aqueous  decomposition  may  sometimes  be  set  free,  or  it  may  dis- 
appear in  the  reduction  of  some  of  the  incompletely  oxidized  compounds  just 
mentioned,  but  it  is  regularly  oxidized  in  aerobic  respiration,  with  the  formation 
of  water.  The  aerobic  oxidation  of  hydrogen  occurs  by  two  stages:  (i)  This 
element  combines  with  respiration  pigments  (acceptors  of  hydrogen),  thus 
forming  respiration  chromogens.  (2)  The  chromogens,  in  turn,  are  oxidized  by 
free  oxygen,  under  the  influence  of  oxidizing  enzymes,  forming  water  and  respira- 
tion pigments.  Thus,  in  normal,  or  aerobic,  respiration,  the  carbon  dioxide 
produced  is  a  product  of  anaerobic  respiration  (fermentation),  while  the  water 
produced  is  a  product  of  the  oxidation,  by  free  oxygen,  of  anaerobically  pro- 
duced hydrogen.  Anaerobic  respiration  occurs  in  all  living  cells,  of  animals  as 
well  as  plants,  while  aerobic  respiration  is  confined  to  those  forms  that  are  sup- 
plied with  free  oxygen  and  possess  adequate  oxidizing  enzymes.  This  theory, 
with  all  the  details  that  it  implies,  must  be  regarded  as  one  of  the  most  bril- 
liant achievements  of  physiological  science,  and  it  may  be  said  to  represent 
the  main  contribution  Palladin  made  to  the  advance  of  appreciative  human 


A   NOTE    OF    APPRECIATION  IX 

knowledge.     It  is  remarkable  that  the  great  scholar  was  able  to  bring  this  phase 
of  his  studies  to  such  a  logical  completeness  within  his  lifetime. 

Palladin's  inspiration  still  works  in  the  minds  and  lives  of  his  students,  and 
his  contributions  to  science  have  become  a  permanent  part  of  the  mental  equip- 
ment of  mankind.  The  results  of  his  studies  and  the  bent  and  trend  of  his 
clear  thought  have  left  a  lasting  effect,  even  upon  dwellers  in  far  countries. 
The  publication  of  this  second  printing  of  the  English  edition  of  the  Physiology 
furnishes  a  significant  illustration  of  the  unity  of  science,  in  space  as  well  as  in 
time,  and  of  the  true  immortality  of  the  scientific  spirit. 

Burton  E.  Livingston. 
Desert  Laboratory, 
Tucson,  Arizona. 
August,  15,  1922. 


AUTHOR'S  PREFACE  TO  THE  GERMAN  EDITION 


This  text-book  constitutes  an  improved  and  enlarged  translation  of  the 
sixth  Russian  edition  of  mv  Plant  Physiology.  There  are  already  several  ex- 
cellent text-books  on  this  subject  in  German,  but  I  venture  to  hope  that  the 
present  volume  will  not  be  without  worth,  especially  on  account  of  the  atten- 
tion here  given  to  the  chemical  aspect  of  physiological  processes,  and  also  be- 
cause of  certain  peculiarities  in  the  presentation  of  the  subject-matter  itself. 

It  is  my  pleasant  duty  to  express  my  hearty  thanks  to  Professor  E.  Abder- 
halden,  through  whose  friendly  offices  the  publication  of  this  edition  was 
undertaken.  For  the  translation  of  the  book,  my  thanks  are  due  to  Messrs. 
Nicolai  von  Adelung,  S.  Kostytschew,  Georg  Ritter  and  O.  Walther,  and  I  am 
also  indebted  to  the  last  three  gentlemen  for  valuable  advice. 

W.  Palladin. 


XI 


EDITOR'S  NOTE  TO  THE  SECOND  AMERICAN  EDITION 


In  this,  the  second  American  edition  of  Palladin's  book,  a  few  typo- 
graphical and  other  errors  that  have  come  to  the  editor's  attention  have 
been  corrected.  In  a  very  few  cases  the  wording  of  the  text  has  been  somewhat 
improved,  especially  where  the  old  wording  was  not  quite  clear.  Several  new 
notes  by  the  editor  have  been  added,  notably  in  Part  II,  Chapters  V  and  VI. 
While  a  small  number  of  additional  references  to  the  literature  have  been 
inserted,  no  attempt  has  generally  been  made  to  enlarge  the  scope  or  increase 
the  number  of  the  citations.  The  text  and  notes  are  generally  the  same  as  in 
the  first  Edition.  The  editor  is  glad  to  acknowledge  valuable  assistance  re- 
ceived from  Dr.  Sam  F.  Trelease,  and  also  to  express  his  thanks  to  those  readers 
who  have  called  his  attention  to  errors  occurring  in  the  first  Edition.  The 
publishers  have  assumed  the  responsibility  for  the  index. 

One  new  feature  has  been  added,  in  the  form  of  a  summary  for  each  chapter. 
In  preparing  the-  summaries  it  has  been  attempted  to  present  a  succinct  but 
rather  complete  statement  of  the  main  features  dealt  with  in  the  respective 
chapters,  with  the  idea  that  these  resumes  may  be  useful  to  the  student,  espe- 
cially in  reviewing  the  subject.  It  is  suggested,  also,  that  the  summary  of  a 
chapter  may  be  read  with  profit  before  reading  the  chapter  itself,  the  summary 
thus  serving  as  a  sort  of  general  background  for  the  more  detailed  information 
gained  by  perusing  the  fuller  presentation.  In  some  cases  new  material  has 
been  introduced  into  the  summaries,  mainly  to  clear  up  a  few  vague  transitions 
from  one  topic  to  another  that  occur  in  the  text,  and  generally  to  help  the  stu- 
dent gain  a  logical  and  consistent  view-point  for  the  subject  as  a  whole.  The 
editor  is  alone  responsible  for  the  summaries. 


The  Desert  Laboratory, 
Tucson,  Arizona, 
July  15,  1922. 


xin 


EDITOR'S  NOTE  TO  THE  FIRST  EDITION 


The  German  edition  of  this  book  has  gained  many  friends  in  institutions 
where  plant  physiology  is  taught  and  has  supplied  a  need  for  elementary  students 
not  otherwise  met.  Its  small  size,  together  with  its  generally  excellent  arrange- 
ment and  manner  of  presentation  render  it  very  well  suited  to  the  use  of  begin- 
ning students  who  really  desire  to  obtain  a  general  grasp  of  the  subject  in  a 
comparatively  short  time.  Its  brevity,  its  conciseness  and  the  readableness  of 
its  story  are  its  first  attractions,  but  a  further  examination  reveals  the  facts  that 
Palladin  has  been  exceptionally  thorough  in  much  of  his  treatment,  and  that  a 
wealth  of  well-chosen  citations  from  the  literature  of  plant  physiology  places 
in  the  reader's  hands  a  ready  guide  to  original  sources.  In  the  latter  regard  the 
text-books  originating  in  our  own  language  are  usually  deficient,  thereby  depriv- 
ing the  student  of  one  of  his  most  important  rights  at  the  very  start— the  right 
to  appreciate  that  the  key  to  the  science  he  is  entering  really  lies  in  its  literature, 
contributed  to  by  many  hundreds  of  serious  workers  writing  in  many  languages. 

Palladin  approaches  the  subject  from  the  point  of  view  of  a  student  of  physio- 
logical chemistry,  and  it  is  the  chemical  aspects  of  plant  physiology  that  here 
receive  greatest  emphasis.  Most  workers  in  the  science  will  doubtless  agree 
that  this  is  an  excellent  method  of  approach.  One  who  has  read  the  book  under- 
standingly  should  be  able  to  plan  his  own  further  development,  with  the  aid  of 
the  current  journals  and  other  contributions,  and  he  will  hardly  miss  the  main 
general  idea  of  present-day  physiology,  that  the  future  of  the  subject  must  rest 
largely  in  the  development  and  application  of  the  technique  and  methods  of 
thinking  that  characterize  the  more  fundamental  sciences  of  chemistry  and 

physics. 

If  the  German  translation  has  proved  to  be  well  suited  to  the  use  of  serious 
elementary  students,  it  follows  that  they  should  make  use  of  it.  Here,  however, 
lies  a  difficulty.  It  appears  to  be  the  present  fashion  for  graduates  of  American 
colleges  to  be  able  to  really  read  only  the  English  language,  so  that  the  drudgery 
of  virtually  digging  their  way  through  a  German  text  militates  strongly  against 
their  becoming  familiar  with  the  subject-matter  involved ;  they  are  apt  to  fail  to 
grasp  the  ideas  because  of  a  sort  of  blind  struggle  to  understand  the  language. 
This  being  all  too  commonly  the  case,  those  who  take  up  plant  physiology  or  its 
applications  need,  especially,  just  such  a  short  and  scientific  treatise  as  Palladin's 
book  offers,  but  they  need  it  in  their  own  language,  so  that  they  may  revert  to  it 
now  and  again  without  distraction.  In  this  way  the  student's  physiological 
habits  of  thought  may  continue  to  advance  steadily  while  he  is  learning  to  read 
the  foreign  tongues  that  will  be  requisite  for  his  future  work.  It  was  to  fill  this 
sort  of  need  among  students  aiming  to  make  some  branch  of  plant  physiology 
their  specialty  that  an  English  translation  of  the  German  edition  was  originally 


XV 


Xvi  EDITOR  S    NOTE    TO    THE   FIRST   EDITION 

undertaken  by  Miss  Aleita  Hopping,  working  in  this  Laboratory.  Out  of  her 
translation  the  present  book  has  developed. 

Aside  from  its  usefulness  to  university  students,  Palladin's  treatise  ought  to 
be  of  great  value  to  more  advanced  investigators,  especially  as  it  furnishes  a 
summary  of  a  large  amount  of  the  literature  of  the  subject,  and  it  is  hoped  that 
the  present  edition  may  prove  helpful  to  the  many  English-speaking  workers 
who  are  engaged  in  physiological  research  as  applied  to  agriculture  and  forestry. 
To  specialists  in  its  own  field  the  book  may  serve  as  a  convenient  means  of 
approach  to  Palladin's  general  interpretations.  Finally,  the  numerous  Russian 
references  may  help  to  open  the  domain  of  Russian  science  to  English-speaking 
students  and  to  emphasize  the  rapidly  growing  importance  of  Russian  research 
in  this  subject. 

As  this  translation  was  nearing  completion,  Prof.  Palladin  very  kindly 
furnished  the  editor  with  a  copy  of  the  seventh  Russian  edition,  with  those 
passages  marked  in  which  the  latter  differs  from  the  sixth  Russian  edition  (from 
which  the  German  was  directly  derived),  and  it  seemed  desirable  to  make  the 
present  book  conform  with  the  author's  latest  alterations  as  far  as  possible. 
Dr.  E.  E.  Free,  also  of  this  Laboratory,  has  made  the  necessary  translations 
from  the  Russian,  following  Prof.  Palladin's  notations,  and  these  alterations  are 
included  in  the  English  text  as  here  brought  forth. 

The  body  of  the  text  aims  to  be  primarily  a  true  translation  of  the  German 
edition,  and  the  original  forms  of  expression  have  been  retained  in  practically 
all  cases  where  this  was  at  all  possible  in  English.  The  general  attitude  of  the 
author  is  so  obviously  opposed  to  teleological  reasoning  that  the  non-teleological 
point  of  view  has  been  made  unmistakable  in  those  few  places  where  the  German 
text  might  leave  the  reader  uncertain  in  this  regard.  Palladin's  writing  is  more 
free  from  teleological  misinterpretations  of  the  relations  between  conditions  and 
results  than  is  that  in  most  of  the  text-books  hitherto  available,  and  this  fact 
was  one  of  the  reasons  for  the  undertaking  of  the  present  translation.  It  will 
doubtless  be  a  long  time  before  teleology  may  be  deleted  from  physiological 
writing  and  thinking,  but  readers  with  a  teleological  point  of  view,  who  may  still 
be  satisfied  with  the  consideration  of  results  or  effects,  in  place  of  conditions  or 
causes  that  may  be  as  yet  unknown,  will  perhaps  not  object  seriously  to  an  em- 
phasis upon  the  conviction  that  permanent  progress  does  not  lie  in  this  direction. 
Few  other  alterations  have  been  made,  these  consisting  mainly  in  some  modifica- 
tions in  the  order  of  presentation,  some  slight  additions  that  render  certain 
statements  more  easily  understood,  and  a  very  few  changes  in  terminology  that 
seemed  desirable.  Slight  additions  are  sometimes  indicated  by  being  enclosed 
in  brackets. 

Editorial  notes  have  been  added  here  and  there,  in  the  form  of  footnotes, 
which  are  uniformly  signed  "Ed."  Footnotes  not  thus  designated  are  Palladin's 
own.  The  editorial  notes  give  such  additional  matter  as  has  seemed  desirable, 
either  for  completeness  of  presentation  or  for  a  better  understanding  by  English- 
speaking  readers.  They  constitute,  in  the  aggregate,  only  a  small  portion  of 
the  volume. 


editor's  note  to  the  first  edition  xvn 

Palladin's  treatment  of  the  topics  Growth,  Movement  and  Reproduction  (which 
make  up  the  subject  matter  of  Part  II)  is  much  less  complete  than  is  his  treat- 
ment of  Nutrition  (Part  I),  and  no  attempt  has  been  made  by  the  editor  to  alter 
this  characteristic  of  the  book.  The  reader  will  appreciate  the  fact  that  there 
is  available  an  enormous  wealth  of  knowledge  not  seriously  touched  upon  in 
Part  II,  which  he  will  be  able  to  approach  through  such  other  treatises  as  are 
mentioned  in  the  list  of  books  that  follows  this  note. 

The  entire  manuscript  has  been  read  and  criticised  by  Dr.  H.  E.  Pulling,  of 
this  Laboratory,  who  has  contributed  much  valuable  advice  in  regard  to  some 
of  the  editorial  additions. 

Since  literature  references  are  of  prime  importance  in  a  book  of  this  kind,  and 
since  the  citations  are  not  always  clearly,  fully,  nor  uniformly  given,  either  in 
the  German  or  in  the  Russian,  it  became  necessary  to  verify  these  and  correct 
them  when  necessary.  This  arduous  task  has  been  carried  out  by  Mrs.  Grace 
J.  Livingston.  Nearly  all  of  the  references  have  thus  been  verified,  and  the 
form  of  citation  has  been  rendered  uniform,  as  far  as  possible,  throughout  the 
work.  Dr.  Free  has  cared  for  the  Russian  citations.  No  attempt  has  been 
made  to  indicate  what  portions  of  any  of  the  citations  are  due  to  correction  or 
completion.  Citations  that  it  has  been  impossible  to  verify  are  given  just  as 
they  appear  in  the  German  (or  Russian),  and  are  followed  by  an  asterisk(*)  to 
signify  this.  Some  additional  literature  references  have  been  inserted  by  the 
editor,  these  being  generally  enclosed  in  brackets,  unless  they  occur  in  editorial 
notes. 

The  rapidly  increasing  frequency  of  references  to  Russian  authors  in  scien- 
tific literature  is  accompanied  by  much  discrepancy  in  the  English  spelling  of 
Russian  proper  names.  This  matter  will  require  more  serious  attention  from 
scholarly  scientific  writers  in  the  future  than  has  been  accorded  it  in  the  past, 
and  an  attempt  is  here  made  at  least  to  avoid  the  exacerbation  of  a  condition 
that  is  already  bad  enough.  The  difficulty  has  perhaps  arisen  mainly  through 
the  fact  that  our  acquaintance  with  Russian  science  is  almost  wholly  based  on 
writings  in  other  foreign  languages,  especially  in  French  and  German.  We 
have  too  frequently  taken  the  German  or  French  transliteration,  as  the  case 
maybe,  without  regard  to  the  fact  that  this  almost  always  leads  to  mispronuncia- 
tion by  the  English  reader.  Thus,  Pavlov  often  appears  as  Pawlow,  which  is 
as  incorrect  in  English  as  it  is  correct  in  German.  The  name  of  the  author  of 
the  present  volume  furnishes  another  example;  we  have  W.  Palladin  where  we 
should  have  V.  Palladin.  (In  this  particular  case,  the  silent  final  e  of  the  Rus- 
sian and  of  the  French  form  of  this  name  should  be  dropped  in  English,  to 
avoid  the  resulting  lengthening  of  the  last  syllable  and  even  the  misplacing  of 
the  accent,  which  is  penultimate.  The  name  is  pronounced  Pai-lad'-in,1  like 
Aladdin.) 

In  those  cases  where  it  is  quite  clear  that  a  proper  name  ought  to  be  regarded 
as  Russian,  an  English  spelling  is  here  adopted  that  will  lead  to  no  serious  ambig- 
uity as  to  pronunciation  and  that  can  be  readily  retransformed  into  the  Rus- 

1  This  is  authoritative,  from  Professor  Palladin  himself. 


xviii  editor's  note  to  the  first  edition 

sian.  In  these  transliterations  of  Russian  words  into  English  the  rules  of  the 
U.  S.  Library  of  Congress  have  been  followed,  with  a  few  slight  modifications, 
as  follows: ia,  tu,  ie  are  all  given  as  ia,  in,  ie;  i,  'i  and  i  are  all  given  as  i;  the  sign 
of  the  silent  letter  between  two  others  (')  is  omitted  (Krasnoselskaia  is  used 
instead  of  KrasnoseV skaia)  and  Yegunov  is  employed  instead  of  Egunov,  to  insure 
proper  pronunciation.  When  the  name  is  not  certainly  Russian  and  when  sev- 
eral spellings  occur,  the  commonest  form  occurring  in  the  German  book  is 
adopted.  In  those  cases  where  the  paper  cited  is  in  Russian  the  author's  name 
is  transliterated  into  English  in  the  citation,  as  well  as  in  the  text,  the  title  of  the 
paper  being  translated  into  English  unless  a  title  in  French  or  German  is  avail- 
able. In  citations  from  languages  other  than  Russian,  author's  names  are  given 
just  as  they  occur  in  the  publications  cited.  The  two  or  three  spellings  that 
thus  occur  for  the  same  Russian  name  are  all  given  in  the  index,  with  the  requi- 
site cross-references.  Thus,  references  to  Ivanov  are  all  given  under  this 
spelling,  but  Ivanojj and  Iwanow  are  also  given,  with  the  notation,  "  see  Ivanov." 
The  index  is  somewhat  more  comprehensive  than  is  the  case  with  the  orig- 
inal, and  authors'  names  have  been  inserted  in  the  same  alphabet  with  the 
names  of  subjects.  This  feature  of  the  index  amounts  practically  to  a  bibliog- 
raphy; references  are  given  to  all  pages  where  the  name  in  question  is  men- 
tioned, and  those  pages  that  bear  footnote  citations  of  this  name  are  indicated 

by  full-face  type. 

A  note  on  the  form  of  citation  employed  in  this  volume,  and  a  selected  list 
of  books  bearing  on  plant  physiology,  are  added  after  the  present  note.  It  is 
hoped  that  these  additions,  as  well  as  the  citations  of  the  book  itself,  may  prove 
serviceable  to  those  who  wish  to  acquire  familiarity  with  the  far-flung  literature 
of  a  subject  that  embraces  the  principles  of  many  separately  named  sciences, 
that  brings  into  a  single  narrative  such  topics  as  ionization,  adsorption,  photo- 
synthesis, fermentation,  the  forcing  of  azalias  and  the  keeping-qualities  of 
apples. 

Laboratory  of  Plant  Physiology 
of  the  Johns  Hopkins  University. 


FORM  OF  CITATION 


The  form  of  citation  employed  in  the  footnotes  uses  (i)  an  Italic  Roman 
numeral  (followed  by  a  comma)  for  the  series  number,  (2)  a  black-face  Arabic 
numeral  (followed  by  a  colon)  for  the  volume  number,  (3)  a  superscript 
numeral  for  a  subdivision  of  the  volume,  (4)  Arabic  numerals,  in  ordinary 
type,  for  the  first  and  last  page  of  the  article  cited  (separated  by  a  dash,  and  the 
second  number  followed  by  a  period),  and  (5)  an  ordinary  Arabic  numeral  for 
the  year  of  publication  (followed  by  a  period).  When  several  pairs  of  page 
numbers  are  given,  as  when  an  article  is  continued  through  several  issues  of  the 
serial,  these  pairs  are  separated  by  commas.  Where  there  is  no  volume  number 
the  volume  has  to  be  designated  by  its  year  number,  and  this  is  given  in  the  place 
that  would  be  occupied  by  the  volume  number,  and  in  black-face  type.  Some- 
times this  year  number,  for  which  the  volume  stands,  is  not  the  same  as  the 
rear  of  publication.  In  cases  where  a  volume  extends  into  more  than  one  year, 
the  year  of  publication  of  the  volume  frequently  gives  place,  to  two  year  numbers 
(separated  by  a  dash).  When  adequate  information  was  available  a  single 
year  number  is  given  in  the  cases  just  mentioned,  referring  to  the  year  of  pub- 
lication of  the  article  cited  rather  than  to  the  two  or  more  years  of  the  volume 
as  a  whole. 

Author's  names  are  given  in  black-face  type,  the  surname  preceding  the 
initials  or  given  name  Idem  (black-face  type)  denotes  a  repetition  of  the 
author's  name,  or  of  the  authors'  names,  next  preceding.  Ibid.  (Italics)  de- 
notes repetition  of  the  name  of  the  serial  next  preceding. 

The  rather  customary  promiscuous  scattering  of  capital  letters  through 
citations  has  been  avoided;  words  or  their  abbreviations  begin  with  capital 
letters  only  (1)  when  they  are  considered  as  beginning  a  sentence,  (2)  when  they 
are  proper  names,  (3)  when  they  begin  the  proper  name  of  a  serial  (as,  Bot.  gaz., 
Plant  world),  (4)  when  they  are  important  words  in  the  proper  name  of  a  society, 
institution,  etc.  (as,  Roy.  Soc.  London,  Missouri  Bot.  Gard.),  or  (5)  when  they 
are  German  nouns  (compare  Ann.  bot.,  Compt.  rend.,  Bot.  Zeitsch.,  Jahrb.wiss. 
Bot.).  The  abbreviations  employed  for  the  names  of  serials  appearing  in  the 
citations  are,  it  is  hoped,  self-explanatory. 

When  a  citation  appears  more  than  once,  it  is  given  in  full  only  in  the  first 
instance,  and  later  occurrences  include  simply  the  author's  name,  the  year,  and 
(in  brackets)  a  reference  to  the  page  of  this  book  where  the  full  citation  may  be 
found. 


XIX 


A  CLASSIFIED  LIST  OF  BOOKS  FOR  REFERENCE 
IN  PLANT  PHYSIOLOGY 


Physics,  General  Chemistry  and  Mathematics 

Bernthsen,  A.,  A  Text-book  of  Organic  Chemistry,  English  translation,  edited  by  J.  J. 
Sudborough.     674  p.     New  York,  1907. 

Comstock,  Daniel  F.,  and  Troland,  Leonard  T.,  The  Nature  of  Matter  and  Electricity,  an 
Outline  of  Modern  Views.     203  p.     New  York,  191 7. 

Davenport,  C.  B.,  Statistical  Methods,  with  Special  Reference  to  Biological  Variation. 
3d  ed.     225  p.     New  York,  1914. 

Holleman,  A.  F.,  and  Cooper,  H.  C,  A  Text-book  of  Inorganic  Chemistry.  6th  Eng. 
ed.     527  p.     Philadelphia,  1921. 

Holleman,  A.  F.,  and  Walker,  A.  J.,  A  Text-book  of  Organic  Chemistry.  5th  Eng.  ed. 
642  p.     New  York,  1920. 

Mellor,  J.  W.,  Higher  Mathematics  for  Students  of  Chemistry  and  Physics,  with  Special 
Reference  to  Practical  Work.     641  p.     London,  1909. 

Northrup,  E.  F.,  Laws  of  Physical  Science,  a  Reference  Book.     210  p.     Philadelphia,  191 7. 

Nutting,  P.  G.,  Outlines  of  Applied  Optics.     234  p.     Philadelphia,  191 2. 

Ostwald,  Wilhelm,  The  Principles  of  Inorganic  Chemistry.  Translated  by  Alexander  Find- 
lay.     3d  ed.     801  p.     London,  1908. 

■ — — — ,  The  Fundamental  Principles  of  Chemistry.  Translated  by  Harry  W.  Morse. 
349  p.     New  York,  1909. 

,  Introduction  to  Chemistry.  Translated  by  William  T.  Hall  and  Robert  S.  Wil- 
liams.    36S  p.     New  York,  1911. 

Willows,  R.  S.,  and  Hatschek,  E.,  Surface  Tension  and  Surface  Energy  and  their  Influence 
on  Chemical  Phenomena.     114  p.     2d  ed.     London,  1919. 

Physical  Chemistry  and  Colloid  Chemistry 

Clark,  W.  M.,  The  Determination  of  Hydrogen  Ions.     2d  ed.     480  p.     Baltimore,  1922. 

Cohen,  Ernst,  Physical  Chemistry  for  Physicians  and  Biologists.  Translated  by  Martin 
Fischer.     343  p.     New  York,  1903. 

Findlay,  Alexander,  Osmotic  Pressure.     84  p.     London,  1913. 

Freundlich,  Herbert,  Kapillarchemie,  eine  Darstellung  der  Chemie  der  Kolloide  und  ver- 
wandter  Gebiete.     591  p.     Leipzig,  1909. 

Hatschek,  E.,  An  Introduction  to  the  Physics  and  Chemistry  of  Colloids.  172  p.  4th  (re- 
vised) ed.     London",  1922. 

Jellinek,  Karl,  Lehrbuch  der  physikalischen  Chemie.  Vol.  I,  715  p.  Stuttgart,  1914. 
Vol.  II,  909  p.     Stuttgart,  1915.     [Two  more  volumes  to  follow.] 

Lewis,  William  C.  McC,  A  System  of  Physical  Chemistry.  2d  ed.  3  vols.  494,  403  and 
209  p.     London  and  New  York,  1918,  1919,  1921. 

Nernst,  Walther,  Theoretical  Chemistry  from  the  Standpoint  of  Avogadro's  Rule  and 
Thermodynamics.     Translated  by  Chas.  Skeele  Palmer.     697  p.     London  and  New  York, 

1895. 

Ostwald,  Wolfgang,  A  Handbook  of  Colloid  Chemistry.  2d  Eng.  ed.,  translated  from 
the  3d  Ger.  ed.  by  Martin  Fischer,  with  notes  by  Emil  Hatschek.  266  p.  Philadelphia, 
1919. 

xxi 


X.xii  A    CLASSIFIED    LIST    OF   BOOKS 

,  An  Introduction  to  Theoretical  and  Applied  Colloid  Chemistry,  "The  World  of 


Neglected  Dimensions."     Translation  by  Martin  H.  Fischer.     232  p.     New  York,  1917. 

,  Die  Welt  der  Vernachlassigten  Dimensionen.     219  p.     Dresden  andLeipzig,  1915. 

Philip,  J.  C,  Physical  Chemistry,  Its  Bearing  on  Biology  and  Medicine.  326  p.  London, 
1920. 

Taylor,  W.  W.,  The  Chemistry  of  Colloids  and  Some  Technical  Applications.  3d  impres- 
sion.    328  p.     London, 1918. 

van't  Hoff,  J.  H.,  Lectures  on  Theoretical  and  Physical  Chemistry.  Translated  by  R.  A. 
Lehfeldt.  Part  I,  Chemical  Dynamics.  254  p.  Part  II,  Chemical  Statics.  156  p.  Part 
III,  Relations  Between  Properties  and  Composition.     143  p.     London,  1898,  1899,  and  1900. 

Washburn,  Edward  W.,  An  Introduction  to  the  Principles  of  Physical  Chemistry  from  the 
Standpoint  of  Modern  Atomistics  and  Thermodynamics.     2d  ed.     516  p.     New  York,  1921. 

Zsigmondy,  Richard,  Kolloidchemie.     281  p.     Leipzig,  1912. 

Zsigmondy,  Richard,  Spear,  Ellwood  B.,  and  Norton,  John  Foote,  The  Chemistry  of 
Colloids.  [Part  I  is  an  English  translation  of  Zsigmondy's  Kolloidchemie,  translated  by 
Spear.  Part  II  consists  of  Industrial  Colloid  Chemistry  (by  Spear)  and  a  chapter  on  Col- 
loidal Chemistry  and  Sanitation  (by  Norton).]     288  p.     New  York,  191 7. 

Soil  Science  and  Climatology 

Cameron,  F.  K.,  The  Soil  Solution,  the  Nutrient  Medium  for  Plant  Growth.  136  p. 
Easton,  Pa.,  191 1. 

Clements,  F.  E.,  Aeration  and  Air-content,  the  Role  of  Oxygen  in  Root  Activity.  Carnegie 
Inst.  Wash.  Publ.  No.  315.     183  p.     1921. 

Ehrenberg,  Paul,  Die  Bodenkolloide.     563  p.     Dresden  andLeipzig,  1915. 

Hall,  A.  D.,  The  Soil,  an  Introduction  to  the  Scientific  Study  of  the  Growth  of  Crops.  3d 
ed.     352  p.     London,  1920. 

Hann,  Julius,  Handbuch  der  Klimatologie.  3  vols.  394,  426  and  713  p.  Stuttgart, 
1 908-1 1. 

,  Handbook  of  Climatology.     Part  I,  General  Climatology.     Translated  from  2d 

Ger.  ed.,  with  additional  references  and  notes,  by  Robert  De  Courcy  Ward.     437  p.     New 
York  and  London,  1903. 

Hilgard,  E.  W.,  Soils,  Their  Formation,  Properties,  Composition,  and  Relations  to  Climate 
and  Plant  Growth.     593  p.     New  York,  1906. 

Mitscherlich,  Eilh.  Alfred,  Bodenkunde  fur  Land  und  Forstwirte.  2teAufL  317  p.  Ber- 
lin, 1913. 

Russell,  Edward  J.,  Soil  Conditions  and  Plant  Growth.  4th  ed.  406  p.  London  and  New 
York,  192 1. 

Ward,  Robert  De  Courcy,  Climate,  Considered  Especially  in  Relation  to  Man.  372  p. 
New  York,  1908. 

Warrington,  Robert,  Lectures  on  Some  of  the  Physical  Properties  of  Soil.  231  p.  Oxford, 
1900. 

General  Physiology,  Physiological  Chemistry  and  Physiological  Physics 

Abderhalden,  Emil,  Handbuch  der  biochemischen  Arbeitsmethoden.  9  vols.  Berlin, 
1910-19. 

,  Biochemisches  Handlexikon.     Vols.  1-7,  Berlin,  191 1.     Vol.  8,  1913;  vol.  9,  1915. 

[Includes  very  extensive  literature  references.] 

Bayliss,  William  Maddock,  Principles  of  General  Physiology.  3d  ed.  862  p.  London 
and  New  York,  1920.     Includes  an  extensive  bibliography. 

Czapek,  Friedrich,  Biochemie  der  Pflanzen.  ite  Aufl.  2  vols.  Jena,  1905.  [Includes 
very  extensive  citations  of  the  literature.]  2te  Aufl.  3  vol.,  (828  p.).  Jena,  1913.  [Only 
first  vol.  has  appeared.] 

Effront,  Jean,  Enzymes  and  Their  Applications.  Translated  by  Samuel  C.  Prescott. 
322  p.     New  York,  1902. 


A    CLASSIFIED    LIST    OF   BOOKS  XX1U 

Euler,  H.,  General  Chemistry  of  the  Enzymes.  Translated  by  T.  H.  Pope.  323  p.  New 
York,  1912. 

,  Grundlagen  und  Ergebnisse  der  Pflanzenchemie,  nach  der  Schwedischen  Aus- 

gabe  bearbeitet.  I  Teil,  Das  chemische  Material  der  Pflanzen.  239  p.  Braunschweig, 
1908.  II  Teil,  Die  allgemeinen  Gesetze  des  Pflanzenlebens.  Ill  Teil,  Die  chemischen  Vor- 
gange  im  Pflanzenkorper.     The  last  2  parts  in  one  vol.     298  p.     Braunschweig,  1909. 

Haas,  P.,  and  Hill,  T.  G.,  An  Introduction  to  the  Chemistry  of  Plant  Products.  3d  ed. 
414  p.     London, 1921. 

Henry,  Thomas  Anderson,  The  Plant  Alkaloids.     466  p.     Philadelphia,  1913. 

Hober,  Rudolf,  Physikalische  chemie  der  Zelle  und  der  Gewebe.  4th  (revised)  ed.  S08  p. 
Leipzig  and  Berlin,  19 14. 

Loeb,  J.,  The  Dynamics  of  Living  Matter.     233  p.     New  York,  1906. 

,  The   Mechanistic  Conception  of  Life:  Biological  essays.     232  p.     Chicago,  191 2. 

,  The  Organism  as  a  Whole,  from  the  Physicochemical  Viewpoint.     379  p.     New 

York  and  London,  1916. 

Mathews,  Albert  P.,  Physiological  Chemistry.     3d  ed.     1154P.     New  York,  1920. 

McClendon,  J.  F.,  Physical  Chemistry  of  Vital  Phenomena,  for  Students  and  Investi- 
gators in  the  Biological  and  Medical  Sciences.  240  p.  Princeton,  191 7.  [Includes  an  ex- 
tensive bibliography.] 

Onslow,  M.  W.,  Practical  Plant  Biochemistry.     178  p.     Cambridge,  1920. 

Putter,  August,  Vergleichende  Physiologic     721  p.     Jena,  191 1. 

Verworn,  Max,  Allgemeine  Physiologie,  ein  Grundriss  der  Lehre  vom  Leben.  6  ed.  766  p. 
Jena,  191 5. 

,  General  Physiology,  an  Outline  of  the  Science  of  Life.  Translated  from  the  2d  Ger- 
man edition  by  F.  S.  Lee.     599  p.     London,  1899. 

Plant  Morphology  and  General  Botany 

Chamberlain,  C.  J.,  Methods  in  Plant  Histology.     3d  ed.     314  p.     Chicago,  1915. 
De  Bar}-,  Heinrich  Anton,  Comparative  Anatomy  of  the  Vegetative  Organs  of  the  Phanero- 
gams and  Ferns.     Translated  and  annotated  by  F.  O.  Bower  and  D.  H.  Scott.     659  p.     Oxford, 

1884. 

Ganong,  Wm.  F.,  A  Text-book  of  Botany  for  Colleges.     604  p.     New  York,  191 7. 

Haberlandt,  G.,  Physiological  Plant  Anatomy.  Translated  by  M.  Drummond.  777  p. 
London,  1914. 

Jordan,  Edwin  O.,  A  Text-book  of  General  Bacteriology.  7th  ed.  744  p.  Philadelphia 
and  London,  19  21. 

Martin,  J.  N.,  Botany  with  Agricultural  Applications.     2d  ed.     604  p.     New  York,  1920. 

Molisch,  Hans,  Mikrochemie  der  Pflanze.     2d  ed.     434  p.     Jena,  1921. 

Palladin,  W.  I.  [V.  I.],  Pflanzenanatomie.  Nach  der  sten  Russischen  Aufl.,  iibersetzt 
und  bearbeitet  von  S.  Tschulok.     195  p.     Leipzig  and  Berlin,  1914. 

Zimmermann,  A.,  Botanical  microtechnique.  Translated  by  J.  E.  Humphrey.  296  p. 
New  York,  1893. 

Schimper,  A.  F.  W.,  Plant  Geography  Upon  a  Physiological  Basis.  Translated  by  W.  R. 
Fischer.     839  p.     Oxford,  1903. 

Stevens,  W.  C,  Plant  Anatomy  from  the  Standpoint  of  the  Development  and  Functions  of 
the  Tissues,  and  Handbook  of  Microtechnic.     3d  ed.,  399  p.     Philadelphia,  1916. 

Plant  Physiology 

Atkins,  W.  R.  G.,  Some  Recent  Researches  in  Plant  Physiology.  328  p.  London  and 
New  York,  1916. 

Barnes,  C.  R.,  "Physiology."  Vol.  I,  Part  II  (p.  295-484)  of:  Coulter,  J.  M.,  Barnes,  C. 
R.,  and  Cowles,  H.  C,  A  Text-book  of  Botany  for  Colleges  and  Universities.     New  York,  1910. 


XXIV  A    CLASSIFIED    LIST    OF    BOOKS 

Brenchley,  Winifred  E.,  Inorganic  Plant  Poisons  and  Stimulants,     no  p.     Cambridge, 
1014. 

Darwin,  Francis,  and  Acton,  E.  Hamilton,  Practical  Physiology  of  Plants.     3d  ed.     340  p. 
Cambridge,  1901. 

Detmer,  W.,  Das  Pflanzenphysiologische  Praktikum,  Anleitung  zu  pflanzenphysiolo- 
gischen  Untersuchungen.     456  p.     Jena,  1865. 

,  Practical  Plant  Physiology.     Translated  by  S.  A.  Moor.     555  p.     London,    1909. 

Dixon,  H.  H.,  Transpiration  and  the  Ascent  of  Sap  in  Plants.     216  p.     London,  1914. 

Duggar,  B.  M.,  Plant  Physiology  with  Special  Reference  to  Plant  Production.     516  p. 
New  York,  191 1. 

Errera,  Leo,  Cours  de  Physiologie  moleculaire  Recueillies  et  redigees  par  H.  Schouteden. 
(Extrait  du  Recueil  de  l'lnst.  Bot.  de  Bruxelles,  tome  VII.)     153  p.     Bruxelles,  1907. 

Ganong,  William  E.,  A  Laboratory  Course  in  Plant  Physiology.     2d  ed.     265  p.     New 

York,  1908. 

,  The  Living  Plant,  a  Description  and  Interpretation  of  Its  Functions  and  Structure. 

47S  p.     New  York,  1913. 

Goodale,  George  L.,  Physiological  Botany.     499  P-     New  York,  1885. 

Grafe,  Viktor,    Ernahrungsphysiologisches    Praktikum    der    hoheren  Pflanzen.     494   p. 

Berlin,  1914. 

Green,  J.  R.,  An  Introduction  to  Vegetable  Physiology.     3d  ed.     47°  P-     London,  191 1. 

Jorgensen,  Ingvar,  and  Stiles,  Walter,  Carbon  Assimilation,  a  Review  of  Recent  Work  on 
the  Pigments  of  the  Green  Leaf  and  the  Processes  Connected  with  Them.  New  Phytologist 
Reprint  No.  10.     180  p.     London,  191 7. 

Jost,  Ludwig,  Lectures  on  Plant  Physiology.  Translated  by  R.  J.  H.  Gibson.  564  p. 
Oxford,  1907.  [This  is  translated  from  the  1st  German  edition;  the  following  is  to  be  used  with 
it:  Jost,  Ludwig,  Plant  Physiology.  Translated  by  R.  J.  H.  Gibson.  Supplement,  incor- 
porating the  alterations  of  the  second  edition  of  the  German  original.     168  p.     Oxford,  1913-] 

Keeble,  Frederick,  assisted  by  M.  C.  Rayner,  Practical  Plant  Physiology.     250  p.     London, 

1911. 

Kolkwitz,  R.,  Pflanzenphysiologie,  Versuche  und  Beobachtungen  an  hoheren  und  niederen 
Pflanzen,  einschliesslich  Bakteriologie  und  Hydrobiologie  mit  Planktonkunde.     258  p.     Jena, 

1914. 

Linsbauer,  Ludw.,  and  Linsbauer,   Karl,  Vorschule  der  Pflanzenphysiologie.     2te  Aufl. 

255  p.     Wien,  191 1. 

Livingston,  Burton  E.,  The  Role  of  Diffusion  and  Osmotic  Pressure  in  Plants.     149  p. 

Chicago,  1903. 

Livingston,  B.  E.,  and  Shreve,  F.,  The  Distribution  of  Vegetation  in  the  United  States, 
as  Related  to  Climatic  Conditions.  Carnegie  Inst.  Wash.  Pub.  No.  284.  590  p.,  75  pl-» 
including  2  colored  maps.     1921. 

MacDougal,  D.  T.,  Practical  Text-book  of  Plant  Physiology.     352  p.     New  York,  1908. 

Nathansohn,  A.,  Der  Stoffwechsel  der  Pflanzen.     472  P-     Leipzig,  1910. 

Osterhout,  W.  J.  V.,  Experiments  with  Plants.     492  p.     New  York,  1908. 

Peirce,  G.  J.,  A  Text-book  of  Plant  Physiology.     2d  ed.     291  p.     New  York,  1909. 

Pfeffer,  W.,  The  Physiology  of  Plants,  a  Treatise  upon  the  Metabolism  and  Sources  of 
Energy  in  Plants.  Translated  by  A.  J.  Ewart.  Vol.1.  632  p.  Oxford,  1900.  Vol.  II,  296 
p.  Oxford,  1906.  Vol.  III.  451  p.  Oxford,  1906.  [This  is  the  standard  reference  for  the 
whole  subject.] 

Pringsheim,  Ernst  G.,  Die  Reizbewegungen  der  Pflanzen.     326  p.     Berlin,  191 2. 

Sablon,  LeClerc  du,  Traite  de  physiologie  vegetale  et  agricole.     610  p.     Paris,  1911. 

Timiriazeff,  C.  A.,  [Timiriazev,  K.  A.],  The  Life  of  the  Plant.  Translated  from  the  7th 
Russian  edition  by  Anna  Cheremeteff.     355  p.     London,  191 2. 

Vines,  Sydney  Howard,  Lectures  on  the  Physiology  of  Plants.     710  p.     Cambridge,  1886. 


TABLE  OF  CONTENTS 


PART  I— PHYSIOLOGY  OF  NUTRITION 
CHAPTER  I 

Assimilation  of  Carbon  and  of  the  Radiant  Energy  of  the  Sun  by 

Green  Plants 

Page 

i.  Importance  of  the  assimilation  of  carbon  by  green  plants i 

2.  Exchange  of  gases 2 

3.  Chlorophyll 5 

4.  Pigments  accompanying  chlorophyll 19 

5.  Influence  of  light  upon  the  decomposition  of  carbonic  acid  by  plants 21 

6.  Products  of  photosynthesis 28 

7.  Assimilation  of  solar  radiant  energy  by  green  plants 32 

S.  Influence  of  external  and  internal  conditions  upon  photosynthesis 34 

9.  Nutrition  of  green  plants  by  organic  compounds 36 

Summary 39 

CHAPTER  II 

Assimilation  of  Carbon  and  of  Energy  by  Plants  without  Chlorophyll 

1.  General  discussion 42 

2.  Assimilation  of  energy  from  organic  compounds  by  plants  without  chlorophyll.    ...  42 

3.  Assimilation  of  energy  from  inorganic  substances  by  plants  without  chlorophyll.    ...  47 

4.  Distribution  of  microorganisms  in  nature 52 

5.  Sterilization  and  disinfection 56 

6.  Pure  cultures 58 

Summary 61 


CHAPTER  III 

Assimilation  of  Nitrogen 

1.  The  nitrogen  of  the  air 64 

2.  The  nitrogen  of  the  soil 65 

3.  Nitrification  in  soils 67 

4.  Circulation  of  nitrogen  in  nature 72 

5.  Fixation  of  atmospheric  nitrogen  by  the  Leguminosae 73 

6.  Assimilation  of  atmospheric  nitrogen  by  bacteria 78 

7.  Assimilation  of  nitrogen  compounds  by  lower  plants 79 

Summary 79 

17*7  1. 


XXVI  TABLE    OF    CONTENTS 

CHAPTER  IV 

Absorption  of  Ash-constituents 

Page 

i.  Cultures  in  artificial  media 82 

2.  Importance  of  the  essential  ash-constituents 84 

3.  Importance  of  the  non-essential  ash-constituents 85 

4.  Ash-analysis  of  plants 88 

5.  Microchemical  ash-analysis 9° 

6.  The  plant  and  the  soil 92 

Summary io2 

CHAPTER  V 

Absorption  of  Materials  in  General 

1.  Materials  absorbed  by  plants io4 

2.  Diffusion  of  gases io4 

3.  Absorption  of  gases io5 

4.  Diffusion  of  dissolved  substances io9 

5.  Absorption  of  dissolved  substances 119 

Summary .126 

CHAPTER  VI 

Movement  of  Materials  in  the  Plaxt 

1.  General  occurrence  of  movement  of  materials 13° 

2.  Movement  of  gases I3° 

j.  Movement  of  water  and  dissolved  substances 133 

4.  The  transpiration  stream r34 

(a)  Transpiration T34 

(b)  Exudation  pressure 140 

(c)  Movement  of  water  in  the  stem I43 

5.  Movement  of  organic  substances v  .    .    .  I48 

Summary r5° 

CHAPTER  VII 

Material  Transformations  in  the  Plant 

1.  The  cell  as  the  physiological  unit x54 

2.  Proteins r55 

3.  Enzymes z^3 

4.  Protein  decomposition  in  plants x7° 

5.  Nitrogenous  products  of  protein  decomposition i?5 

6.  Protein  synthesis  in  plants I78 

7.  Alkaloids,  toxins  and  antitoxins I8i 

8.  Lipoids  and  phosphatides x83 

9.  Carbohydrates I85 

10.  Glucosides J87 

11.  Organic  acids x88 

12.  The  importance  of  water  in  plants x88 

13.  The  germination  of  seeds l&9 

Summary I92 


TABLE    OF    CONTENTS  XXV11 

CHAPTER  VIII 

Fermentation  and  Respiration 

Page 

General  discussion 10S 

2.  Alcoholic  fermentation 201 

3.  Other  kinds  of  fermentation 209 

4.  Plant  respiration 210 

Apparatus  for  measuring  plant  respiration 215 


1 


0 


6.  Formation  of  water  during  respiration 217 

7.  Liberation  of  heat  during  respiration 218 

8.  Anaerobic,  or  intramolecular,  respiration 220 

9.  Respiration  chromogens 

10.  Respiratory  enzymes 223 

11.  Materials  consumed  in  respiration 227 

12.  Special  cases  of  respiration  in  lower  plants 230 

13.  Circulation  of  energy  in  nature 232 

Summary 232 

PART  II— PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

CHAPTER  I 

General  Discussion  of  Growth 


1 


Anatomical  relations  of  cell  growth 241 

2.  Conditions  favorable  to  growth 242 

3.  Apparatus  for  the  study  of  growth 245 

Summary 246 


CHAPTER  II 
Growth  Phenomena  That  are  Controlled  by  Internal  Conditions 

1.  The  grand  period  of  growth 247 

2.  Growth  of  root,  stem  and  leaf .              247 

3.  Tissue  strains 251 

Summary 251 

CHAPTER  III 

Influence  of  External  Conditions  on  Growth  and  Configuration 

1.  Dependence  of  growth  and  configuration  upon  temperature 253 

2.  Dependence  of  growth  and  configuration  upon  the  oxygen  content  of  the  surroundings  258 

3.  Influence  of  other  gases  on  growth  and  configuration 260 

4.  Influence  of  moisture  on  growth  and  configuration 263 

5.  Dependence  of  growth  and  configuration  upon  light 274 

6.  Influence  of  gravitation  on  growth  and  configuration 292 

7.  Influence  of  nutrition  on  growth  and  configuration 299 

8.  Influence  of  wounding,  traction  and  pressure  on  growth  and  configuration.  ' 300 

Summary 3°5 


XXV111  TABLE    OF    CONTENTS 

CHAPTER  IV 

Twiners  and  Other  Climbing  Plants 

Page 
i.  Twiners 311 

2.  Non-twining  climbers 312 

3.  Circumnutation 314 

Summary 315 

CHAPTER  V 

Movements  of  Variation 

1.  General  survey  of  plant  movements 316 

2.  Autonomic  movements  of  variation 316 

3.  Paratonic  movements  of  variation 316 

Summary 320 

CHAPTER  VI 

Development  and  Reproduction 

1.  Influence  of  external  and  internal  conditions  on  development 322 

2.  Influence  of  internal  conditions  on  development 329 

3.  Reproduction 331 

Summary 337 

Index 341 


INTRODUCTION 


La  physiologie  est  une  des  sciences  les  plu 
dignes  de  l'attention  des  esprits  eleves  par 
l'importance  des  questions,  qu'elle  traite,  et 
de  toute  la  sympathie  des  hommes  de  progrds 
par  l'influence,  qu'elle  est  destines  a  exercer 
sur  le  bienetre  de  lhumanite. 

— Claude  Bernard. 

The  aim  of  plant  physiology  is  to  gain  a  complete  and  thorough  knowledge 
of  all  the  phenomena  occurring  in  plants,  to  analyze  the  complex  life  processes 
so  as  to  interpret  them  in  terms  of  simpler  ones  and  to  reduce  them  finally  to 
the  principles  of  physics  and  chemistry.  It  is  evident  from  this  statement  that 
physiology  is  dependent  upon  physics  and  chemistry,  and  that  progress  in 
physiology  depends,  in  great  measure,  upon  progress  in  these  two  other  sciences. 
Only  since  the  end  of  the  eighteenth  century,  when  the  principle  of  the  con- 
servation of  mass  was  formulated  by  Lavoisier,  and  chemistry  became  an  exact 
science,  did  it  become  possible  for  physiology  also  to  begin  to  assume  this 
character.  Since  that  time  it  has  been  possible  to  employ  the  balance  in  pre- 
cise studies  of  the  materials  that  enter  and  leave  plants.  The  well-known 
experiment  of  van  Helmont  (1577-1644),  performed  long  before  those  of  Lavoi- 
sier, may  be  cited  as  an  early  though  but  partially  successful  attempt  to  use  the 
balance  for  determining  the  source  of  the  materials  found  in  the  plant  body. 
A  willow  branch  weighing  5  pounds  was  potted  in  200  pounds  of  dry  soil  and 
watered  with  rain-water.  After  five  years  the  weight  of  the  rooted  branch 
was  estimated  to  be  164  pounds,  while  the  dried  earth  showed  a  loss  in  weight  of 
only  2  ounces.  Van  Helmont  concluded  from  this  that  the  material  of  the  plant 
was  formed  from  water,  but  this  inference  is  incorrect,  since  the  surrounding  air 
was  not  considered.  He  would  have  been  justified  in  concluding,  however,  that 
the  greater  part  of  the  non-aqueous  material  of  plants  does  not  come  from  the  soil. 

Besides  the  discoveries  of  Lavoisier,  another  important  event  in  the  history 
of  chemistry  must  be  alluded  to  here,  the  synthesis  of  urea,  accomplished  by 
Wohler  in  1828.  Up  to  that  time  organic  compounds  had  been  obtained  only 
from  living  organisms,  and  the  idea  prevailed  that  the  synthetic  preparation  of 
such  compounds  from  inorganic  materials  was  impossible  and  that  their  forma- 
tion presupposed  the  participation  of  a  special  vital  activity.  Wohler's  dis- 
covery, together  with  subsequently  successful  syntheses  of  various  other  organic 
compounds,  have  shown  that  no  vital  force  is  essential  to  the  formation  of 

such  substances. 

The  organic  and  inorganic  compounds  of  carbon  are  often  combined  in  a 
single  group,  but  there  is  an  essential  difference  between  them  for  the  physi- 
ologist; all  organic  substances  contain  a  store  of  energy,  since  they  give  off  heat 

xx  ix 


XXX  INTRODUCTION 

when  burned,  while  the  inorganic  carbon  compounds  cannot  be  burned.  The 
heat  of  combustion,  measured  in  calories,  serves  as  an  index  of  the  energy 
content  of  organic  compounds.  By  a  large  calory,  or  kilogram-calory  (Cal., 
or  kg.-cal.)  is  meant  the  amount  of  heat  necessary  to  raise  the  temperature  of 
iooo  g.  of  water  from  o°  to  i°C;  by  a  small  calory,  or  gram-calory  (cal.  or 
g.-cal.)  is  meant  the  amount  of  heat  necessary  to  raise  the  temperature  of  i  g. 
of  water  the  same  amount." 

The  following  table  shows  the  amounts  of  heat  obtained  from  the  combustion 
of  i  g.  of  various  substances,  expressed  in  kilogram-calories. 

Hydrogen 34-6 

Carbon 8.0 

Linseed  oil • 9.3 

Ethyl  alcohol  (C2H60) 7.1 

Gluten  flour 5.9 

Ammonia  (NHs) 5  ' 

Starch  (CeHioOs) 4 

Glucose  (C6G12O6) 3 

Asparagin  (C4H2N2O3) 3.3 

It  is  evident  from  this  table  that  hydrogen  develops  much  more  heat 
during  combustion  than  does  carbon.  The  more  oxygen  the  molecule  of  a 
substance  contains,  the  less  is  its  heat  of  combustion,  and  it  is  for  this  reason 
that  ethyl  alcohol  develops  more  heat  than  starch.  The  introduction  of  hy- 
drogen into  the  molecule,  on  the  contrary,  produces  a  great  increase  in  the  heat 
of  combustion;  thus,  oil  develops  more  heat  than  does  pure  carbon,  while 
ammonia,  without  any  carbon  at  all — but  because  of  its  high  hydrogen  content 
— produces  a  far  greater  amount  of  heat  than  does  either  starch  or  glucose. 

Wohler's  discovery  led  to  a  great  advance  in  the  physico-chemical  interpreta- 
tion of  physiological  processes.  But  there  were  still  other  difficulties  to 
overcome^  Many  chemical  reactions  go  on  in  plants  and  animals  at  the  tempera- 
ture of  the  organism  (i.e.,  about  ordinary  room  temperatures),  while  the  same 
reactions  outside  the  organism  occur  only  at  much  higher  temperatures  or  with 
the  aid  of  strong  acids.  For  instance,  as  will  be  seen  later,  plant  respiration 
is  a  process  of  oxidation  or  combustion,  but  it  proceeds  at  medium  temperatures, 
while  ordinary  combustion  requires  a  very  high  temperature.  While  plant 
and  animal  substances  outside  of  the  organism  generally  undergo  oxidation 
slowly  at  ordinary  temperatures,  with  the  oxygen  of  the  air,  they  are  oxidized 
much  more  rapidly  in  the  organism,  at  the  same  temperatures.  This  dis- 
crepancy was  explained  by  the  theory  of  catalysis,  advanced  by  Berzelius  in 
1836.  Catalytic  action,  according  to  this  author,  is  a  process  wherein  certain 
substances  (called  catalyzers)  are  capable  of  accelerating  chemical  reactions  be- 
tween other  substances,  by  the  presence  of  the  catalyzer  alone,  independently 

a  The  gram-calory  is  frequently  defined  as  the  heat  required  to  raise  the  temperature  of  a 
gram  of  water  one  degree  Centigrade,  but  this  is  not  precise,  since  the  specific  heat  and  the 
heat  of  vaporization  of  water  vary  with  its  temperature.  The  definition  given  in  the  text 
is  that  of  the  o-degree  gram-calory.  Other  calories  are  in  use,  as  the  15-degree  gram-calory,  the 
heat  needed  to  alter  the  temperature  of  a  gram  of  water  from  14. 50  to  i5.5°C,  etc.— Ed. 


INTRODUCTION  XXXI 

of  its  chemical  affinities  and  without  its  being  used  up  in  the  reaction.  A 
substance  is  regarded  as  a  catalyzer  if  it  alters  the  velocity  of  a  chemical  reac- 
tion without  itself  appearing  in  the  end-products.  For  instance,  if  a  weak 
solution  of  sulphuric  acid  is  allowed  to  act  upon  metallic  zinc,  the  evolution 
of  hydrogen  is  very  slow  if  both  reagents  are  very  pure,  but  the  addition  of  a 
few  drops  of  platinic  chloride  is  sufficient  to  cause  a  stormy  evolution  of  the 
gas.  The  reaction  proceeds,  either  in  the  presence  or  in  the  absence  of  the 
platinum  salt,  according  to  the  equation, 

Zn  +  H2S04  =  ZnS04  +  H2. 

The  platinic  salt  does  not  enter  into  the  reaction  and  so  acts  simply  as  a 
catalyzer. 

Various  kinds  of  catalyzers  have  now  been  shown  to  exist  in  plants  and  ani- 
mals, and  these  are  called  ferments6  or  enzymes.  Enzymes,  according  to  Wilhelm 
Ostwald,  are  catalyzers  formed  in  the  organism  during  the  life  of  the  cell,  and 
it  is  with  their  help  that  the  living  organism  effects  most  of  its  chemical  processes. 
Not  only  are  digestion  and  assimilation  regulated  entirely  by  enzymes,  but  the 
production  of  chemical  energy  by  oxidation,  at  the  expense  of  the  oxygen  of 
the  air — a  process  forming  the  basis  for  the  life  activity  of  most  organisms — 
is  also  made  possible  and  directed  by  these  catalyzers.  It  is  well  known  that 
oxygen  is  a  very  inactive  substance  at  the  temperature  of  organisms  and  that 
the  maintenance  of  the  life  process  would  be  impossible  without  an  acceleration 
of  chemical  reaction  velocities.  In  plants  special  enzymes  (oxydases)  are  indeed 
found  that  act,  either  within  or  without  the  organism,  to  produce  the  oxida- 
tion of  various  substances  at  room  temperature. 

The  attention  of  scientists  was  especially  attracted  by  the  enzymes  of  lower 
plants,  such  as  yeasts  and  bacteria,  these  plants  having  been  themselves  desig- 
nated as  "organized  ferments."  The  most  important  discoveries  in  the  physi- 
ology of  yeasts  and  bacteria  are  due  to  Pasteur,0  who  proved  the  absence  of 
spontaneous  generation  in  the  lower  organisms,  developed  a  clear  conception 
of  the  various  kinds  of  fermentation,  and  devised  perfect  methods  for  the  con- 
trol of  infectious  diseases.  The  worker  in  the  shop,  as  well  as  the  farmer  in 
the  field,  the  physician  at  the  bedside,  the  veterinarian  treating  domestic  ani- 
mals, the  brewer  handling  his  yeast,  are  all  now  guided  by  the  ideas  of  Pasteur. 

A  physical  discovery  that  was  very  important  to  physiology  must  here  be 
mentioned,  the  formulation  of  the  principle  of  the  conservation  of  energy,  by 
Julius  Robert  Mayer,  in  1840.     Mayer  demonstrated  that  no  energy  is  lost  in 

6  The  noun  ferment  should  be  dropped,  as  unnecessary  and  apt  to  be  misleading.  What 
were  once  called  unorganized  ferments  are  enzymes,  and  organized  ferments  (such  as  yeasts, 
bacteria,  etc.)  may  be  called  by  name  or  referred  to  as  fermentation  organisms.  The  word 
enzyme  is  frequently  mispronounced;  it  should  be  pronounced  as  if  spelled  enzim,  with  the 
first  vowel  accented  and  the  second  short.  The  spelling  enzym  is  better,  but  has  not  yet  come 
into  general  use  in  English. — Ed. 

c  Students  of  chemical  physiology  should  be  well  acquainted  with  Pasteur's  life  and  work. 
See:  Vallery-Radot,  Rene,  The  Life  of  Pasteur.  Translated  by  Mrs.  R.  L.  Devonshire. 
ix  -f-  484  p.     New  York,  1915. — Ed. 


XXX11  INTRODUCTION 

the  various  chemical  reactions,  but  that  it  is  transformed  from  the  potential 
into  the  kinetic  condition,  or  vice  versa.  In  the  combustion  of  coal,  for  example, 
heat  is  liberated,  while  by  the  reverse  process,  the  decomposition  of  carbon 
dioxide,  heat  is  stored.  Since  combustibility  is  a  characteristic  of  all  organic 
compounds,  their  formation  from  carbonic  acid  must  therefore  be  accompanied 
by  an  intake  of  heat  and  a  storing  of  potential  energy,  which  may  be  subse- 
quently liberated  during  combustion.  In  all  investigations  concerning  the 
transformations  of  materials  in  plants  it  must  be  clearly  stated  whether  energy 
is  stored  or  released,  since  only  thus  can  it  be  clear  what  is  the  meaning  and  im- 
portance of  such  transformations  in  the  general  activity  of  the  organism. 

At  first  glance,  some  phenomena  seem  to  present  exceptions  to  the  principle 
of  the  conservation  of  energy  and  to  exhibit  no  quantitative  relation  between 
cause  and  effect.  For  example,  a  small  spark  may  cause  the  explosion  of  an 
enormous  amount  of  gunpowder  and  thus  produce  tremendous  destruction.  It 
might  seem  here  that  a  small  cause  has  entailed  a  great  effect;  in  reality,  however, 
the  same  amount  of  energy  was  liberated  in  the  explosion  as  was  originally 
present — in  a  potential  form — in  the  gunpowder.  The  spark  served  only  to 
initiate  the  change  of  this  energy  from  one  condition  to  the  other.  A  small 
concussion  of  the  air  is  often  sufficient  to  cause  the  fall  of  a  huge  boulder  from 
a  great  height,  but  the  work  thereby  performed  is  exactly  equal  to  the  amount 
necessary  to  replace  the  boulder  in  its  original  position.  The  pressure  of  the 
air  serves  here  as  the  trigger  that  produces  the  discharge. 

In  considering  the  great  importance  of  enzymes  in  the  chemical  processes  of 
plants  it  must  be  realized  that  their  part  in  the  various  reactions  does  not  con- 
sist in  a  simple  release.  Bredig  was  quite  right  when  he  said,  "We  still  find 
much  vagueness  in  the  text-books  as  to  whether,  in  this  matter  of  the  contact 
action  of  substances  such  as  acids  and  enzymes  in  the  hydrolysis  of  esters, 
carbohydrates,  glucosides,  etc.,  we  have  to  do  with  the  initiation  of  a  reaction 
incapable  of  occurring  by  itself,  or  only  with  the  acceleration  of  a  reaction  that 
takes  place  so  slowly  (in  the  absence  of  the  catalyzer)  as  to  be  almost  imper- 
ceptible, but  that  is  nevertheless  already  in  operation.  The  question  is,  there- 
fore, to  use  a  mechanical  figure,  whether  the  enzyme  sets  into  operation  a 
machine  previously  held  at  rest  by  a  trigger-pin,  or  whether  the  enzyme  serves 
only  as  a  lubricant  to  hasten  the  action  of  the  machine  (the  chemical  reaction), 
which  would  otherwise  be  very  slow  and  almost  imperceptible,  because  of  great 
resistance."1  Enzymes  accelerate  reactions  that  would  otherwise  progress  but 
slowly  (Wilh.  Ostwald)  and  they  are  thus  comparable  only  to  the  "  lubricant. "d 
On  the  other  hand,  the  touch  that  causes  a  reaction-movement  of  the  leaves 
of  Mimosa  pndica  (the  sensitive  plant)  may  be  regarded  as  a  typical  example  of 
a  discharge  or  release. 

The  causes  that  produce  certain  phenomena  and  the  conditions  that  first 
render  them  possible  must  also  be  differentiated.     For  instance,  if  solid  calcium 

1  Bredig,  G.,  Die  Elemente  der  chemischen  Kinetik,  mit  besonderer  Beriicksichtigung  der  Katalyse 
und  der  Fermentwirkung,  Ergeb.  Physiol,  i:   134-212.      1902. 

d  Enzymes  frequently  appear  to  alter  the  end-point  of  a  reaction,  so  that  it  proceeds 
farther  in  their  presence  than  without  them. — Ed. 


INTRODUCTION  XNX111 

sulphate  is  mixed  with  solid  barium  chloride  there  is  no  reaction;  when  water 
is  added,  however,  barium  sulphate  and  calcium  chloride  are  formed.  This 
reaction  is  caused  by  the  chemical  attraction  of  the  elements,  the  water  acting 
only  as  a  necessary  condition.  Thus  releases,  which  are  conditioning  factors, 
must  be  distinguished  from  real  causes/ 

Plants  have  an  internal  structure,  being  composed  of  cells  of  various  forms 
and  sizes.  The  life  of  an  organism  is  the  sum-total  of  the  life  activities  of  the 
individual  cells  composing  it,  and  the  study  of  plant  physiology  presupposes  an 
acquaintance  with  the  internal  structure  or  anatomy  of  the  plant.  Familiarity 
with  the  miscroscope  is  essential  in  physiological  study,  since  many  important 
physiological  questions  can  be  solved  by  its  use. 

For  the  study  of  many  physiological  phenomena — those  of  growth  and  en- 
largement, for  example — a  knowledge  of  the  structure  of  the  given  plant  and  an 
acquaintance  with  the  external  conditions  affecting  it,  are  not  sufficient;  it  must 
also  be  remembered  that  the  plant  has  developed  from  a  long  series  of  ancestors 
whose  form  and  mode  of  living  have  not  been  without  effect  upon  the  offspring. 
In  these  cases,  therefore,  heredity  must  be  taken  into  account/ 

e  The  definition  of  the  term  cause  involves  difficulties.  It  is  probably  best  to  consider  that 
all  changes  are  determined  (in  quantity,  rate  and  direction)  by  a  set  of  controlling  conditions, 
the  cause — in  the  ordinary  sense — being  simply  the  last  one  of  these  necessary  conditions  to  be 
fulfilled.  For  a  discussion  of  this  matter  see:  Verworn,  Max,  Kausale  und  Konditionale  Welt- 
anschauung, Jena,  191 2. — Ed. 

f  This  is  somewhat  vague;  the  phenomena  in  question  are  assuredly  conditioned  at  any 
given  time  by  the  internal  and  external  conditions  then  prevailing.  The  nature  of  the  ances- 
tors of  a  plant  and  the  surroundings  under  which  these  lived  are  but  secondary  conditions, 
which  have  been  influential  in  determining  what  are  the  present  internal  conditions  (what  the 
plant  is  now),  but  which  are,  in  themselves,  without  any  present  direct  influence  upon  its 
processes.  The  phenomena  connoted  by  the  term  heredity  have  played  an  important  role  in 
determining  the  present  internal  conditions,  and  these  latter,  together  with  the  present  sur- 
roundings, are  now  influential  in  the  determination  of  physiological  phenomena. — Ed. 


PART  I 
PHYSIOLOGY  OF  NUTRITION 

CHAPTER  I 

ASSIMILATION  OF  CARBON  AND   OF  THE  RADIANT 

ENERGY  OF  THE  SUN  BY  GREEN  PLANTS 

§i.  Importance  of  the  Assimilation  of  Carbon  by  Green  Plants.— Plants 
may  be  classified  according  to  their  color  into  two  groups,  those  that  are 
green  and  those  that  are  not.  The  green  color  forms  such  a  conspicuous  char- 
acteristic of  many  plants  that  certain  ones  are  sometimes  spoken  of  as  "greens." 
The  general  distribution  of  the  green  coloring  would  itself  suggest  that  some 
important  property  must  be  connected  with  it,  and  such  is  indeed  the  fact;  upon 
this  green  coloring  depends  one  of  the  main  cosmic  functions  of  plants,  the 
building  up  of  organic  compounds  from  inorganic  substances.  A  simple  ex- 
periment will  show  this.  A  seed  is  placed  in  quartz  sand  and  is  watered  from 
time  to  time  with  a  solution  of  mineral  salts.  A  plant  grows  from  the  seed, 
blooms  and  bears  fruit.  Comparison  of  the  amount  of  organic  material  origi- 
nally present  in  the  seed,  with  the  corresponding  amount  found  in  the  grown 
plant,  shows  that  the  latter  amount  is  very  much  greater.  If  follows  that  green 
plants  are  able  to  form  organic  compounds  from  inorganic  ones.  Animals,  and 
plants  without  green  pigment,  generally  lack  this  power;  they  obtain  organic 
compounds  only  after  these  have  been  already  manufactured  by  green  plants. 
The  formation  of  organic  substances  by  green  plants  is  thus  not  only  important 
from  the  standpoint  of  plant  physiology,  but  it  acquires  a  much  broader  interest, 
since  the  whole  animal  kingdom,  including  even  mankind,  is  dependent  upon 
green  plants.  In  a  physiological  sense,  green  plants  form  the  connecting  link 
between  the  animal  and  mineral  kingdoms. 

Since  all  organic  compounds  are  characterized  by  their  carbon  content  and 
by  their  combustibility — the  latter  property  implying  that  energy  was  stored 
up  in  their  formation— the  study  of  plant  physiology  may  begin  with  an  in- 
quiry as  to  the  sources  of  the  carbon  and  the  energy  necessary  for  the  formation 
of  organic  compounds  in  the  organism.  The  answer  is  derived  mainly  from  the 
study  of  the  assimilation  of  carbon  dioxide.  This  process  consists,  essentially,  in 
the  absorption  of  carbon  dioxide  by  the  green  parts  of  plants  and  in  the  elimination 
of  oxygen,  in  sunlight.  Since  the  volumes  of  the  two  gases  involved  in  this  proc- 
ess are  found  to  be  about  equal,  it  follows  that  for  each  molecule  of  carbon 
dioxide  absorbed  a  molecule  of  oxygen  is  eliminated;  C02  =  02  +  C  (principle 
of  Avogadro).  The  carbon  remains  in  the  plant  and  thus  produces  an  increase 
in  its  weight,  this  process  being  a  part  of  what  is  called  nutrition. 


2  PHYSIOLOGY    OF    NUTRITION 

Since  the  formation  of  carbon  dioxide  in  the  combustion  of  carbon  is  ac- 
companied by  the  liberation  of  heat,  energy  must  be  stored  in  the  reverse 
process,  the  decomposition  of  carbon  dioxide.  From  this  it  is  clear  why  sun- 
light is  so  important  in  this  decomposition;  the  energy  of  the  sunshine  ab- 
sorbed by  the  plant  is  partly  used  in  the  decomposition  of  carbon  dioxide  and  in 
the  synthesis  of  other  carbon  compounds.  The  green  coloring  matter,  chlo- 
rophyll, serves  as  a  screen  which  absorbs  the  sun's  rays  and  makes  this  energy 
fixation  possible. 

§2.  Exchange  of  Gases. — Our  first  knowledge  of  the  elimination  of  oxygen 
by  green  plants  was  obtained  by  Priestley,1  in  1772.  Since  animals  utilize 
''dephlogisticated  air"  (as  Priestley,  its  discoverer,  called  oxygen)  and  thus 
render  the  atmosphere  unfit  for  the  maintenance  of  combustion  and  respiration, 
he  sought  a  reverse  process  by  which  the  air  might  be  improved,  and  he  found 
this  process  in  plants.  He  placed  plants  under  a  bell-jar  of  air  that  had  been 
vitiated  by  animal  respiration  and  was  thus  unfit  for  the  maintenance  of  com- 
bustion and  respiration,  and  found  that  after  some  time  the  air  became  again 
capable  of  supporting  these  processes.  Unfortunately,  however,  subsequent 
repetition  of  this  experiment  did  not  always  give  the  same  result.  Sometimes 
the  plants  improved  the  air,  often  they  did  not,  and  Priestley  did  not  know  the 
reason  for  these  variations.  It  remained  for  Ingen-Housz2  to  show  that  the 
purifying  of  the  air  was  effected  only  by  the  green  parts  of  plants,  and  only  in 
sunlight.  The  importance  of  this  process  in  the  life  of  the  plant  was  still  un- 
explained; it  was  regarded  as  a  purposeful  arrangement  for  the  improvement  of 
the  air  for  animals.  Ingen-Housz  had  no  clear  idea  as  to  what  gas  is  taken  in  by 
the  plant,  and  even  thought  that  the  gas  given  off  by  metals  under  the  action 
of  acids  might  be  thus  improved  by  plants.  Senebier3  was  later  able  to  show 
that  carbon  dioxide  alone  is  absorbed,  and  that  this  absorption  is  a  nutritive 
process.  De  Saussure4  then  found  that  the  volume  of  oxygen  given  out  was 
equal  to  that  of  carbon  dioxide  taken  in,  that  the  decomposition  of  the  last- 
named  gas  was  most  rapid  when  one  part  of  it  was  present  in  eleven  parts  of  air, 
and,  finally,  that  an  increase  in  the  weight  of  the  plant  occurred  as  a  result  of 
this  absorption  and  decomposition.  All  these  questions  were  finally  taken  up 
by  Boussingault,5  in  a  series  of  precise  experiments.  The  equality  of  the  vol- 
umes of  the  exchanged  gases  was  established.  By  an  experiment  upon  the  de- 
composition of  carbon  dioxide  by  green  plants  in  a  mixture  of  this  gas  and  hy- 
drogen or  nitrogen,  Boussingault  was  able  to  show  that  the  decomposition  in 
question  began  immediately  after  the  illumination  of  the  apparatus,  and  ceased 
as  soon  as  it  was  darkened.     Phosphorus  was  used  to  show  the  presence   of 

1  Priestley,  Joseph,  Experiments  and  observations  on  different  kinds  of  airs.     324  p.     London,  1774. 

2  Ingen-Housz,  Jan,  Experiments  upon  vegetables,  discovering  their  great  power  of  purifying  common 
air  in  the  sunshine,  and  of  injuring  in  the  shade  and  at  night.  London,  1779.  [Ref.  in  Ger.  ed.  is  ap- 
parently to  Scherer's  translation,  3  v.,  Vienna,  1786,  178S,  1790.  This  was  from  author's  French  ed., 
1780.] 

3  Senebier,  J.,  Memoires  physico-chimiques  sur  l'influence  de  la  lumiere  solaire  pour  modifier  les  etres 
des  trois  regnes  de  la  nature  et  sur-tout  ceux  du  regne  vegetal.  Geneve,  1782.  Idem,  Physiologie  v6g6tale. 
Geneve,  1800. 

<  Saussure,  Nicolas  Theodore  de,  Recherches  chimiques  sur  la  vegetation.     Paris,  1804. 

5  Boussingault,  JeanB.  J.  D.,  Agronomie,  chimie  agricole  et  physiologie.     2nd  ed.  Paris,  1860-1891. 


ASSIMILATION    OF    CARBON  3 

oxygen,  a  piece  of  this  substance  being  exposed  in  the  experiment  chamber. 
As  soon  as  light  was  allowed  to  enter  the  apparatus  the  formation  of  a  white 
vapor  indicated  the  presence  of  oxygen,  and  when  the  apparatus  was  darkened 
the  fumes  already  formed  disappeared  and  no  more  appeared,  showing  that 
the  elimination  of  oxygen  had  ceased.  [The  fumes  are  suspended  phosphorus 
pentoxide  (P205),  which  dissolves  in  water,  forming  phosphoric  acid  (H3P04), 
and  thus  disappears  soon  after  the  apparatus  is  darkened.] 

Since  this  experiment  was  performed  in  a  closed  chamber  with  a  high  car- 
bon dioxide  content,  it  was  questionable  whether  the  results  obtained  might 
justify  the  conclusion  that  plants  can  utilize  the  small  amount  of  carbon  di- 
oxide in  the  air  under  natural  conditions  (0.028-0.04  percent.).  To  clear  up 
this  point,  Boussingault  placed  a  plant  in  a  jar  through  which  a  current  of  air 
was  passed.  Analysis  of  the  entering  air  and  of  that  passing  out  showed  that 
the  plant  was  able,  under  favorable  conditions  of  light,  to  absorb  almost  all  of 
the  carbon  dioxide  that  entered  the  jar.  Regarding  this  experiment  of  Boussin- 
gault, Timiriazev  says: 

To  what  degree  the  precision  of  this  experiment  aroused  the  wonder  of  his  contemporaries 
(as  did  most  of  Boussingault's  researches)  can  best  be  shown  by  an  anecdote  which  I  heard 
from  Boussingault  himself.  "The  investigation  was  undertaken  jointly  with  Dumas,  with 
weighings  and  records  independently  made  by  each  worker,  in  order  to  secure  more  reliable 
results.  At  first  all  went  well,  and  the  plants  decomposed  carbon  dioxide  as  they  were  ex- 
pected to  do.  Then  things  suddenly  changed.  On  a  bright,  sunny  day,  the  plants  began  to 
produce  carbon  dioxide  instead  of  decomposing  it.  In  the  evening  we  examined  the  result  with 
astonishment  and  stared  at  each  other  in  blank  amazement.  Involuntarily  we  remembered 
the  misfortune  that  had  attended  Priestley  when  he  attempted  to  repeat  his  famous  experiment. 
Several  days  passed  by.  Then,  one  fine  morning,  Regnault,  the  famous  physicist,  who  had 
been  watching  our  experiment  with  much  interest,  began  to  laugh  at  our  long  faces  and 
admitted  that  he  had  been  to  blame  for  our  misfortune.  Every  day,  while  we  were  at  lunch- 
eon, he  had  sneaked  over  to  our  apparatus  and  breathed  into  it,  'in  order,'  as  he  explained, 
'to  be  convinced  that  you  were  not  taking  a  u  for  an  x,  and  could  really  determine  such  small 
amounts  of  carbon  dioxide.'  "l 

C02 

De  Saussure  and  Boussingault  showed  that  the  ratio   ^—    is   generally   equal 

to  unity.  However,  it  must  be  remembered  that  green  plant  parts  also  respire 
while  they  are  assimilating  carbon  dioxide;  that  is,  they  carry  on  the  reverse 
process,  wherein  carbon  dioxide  is  eliminated  and  oxygen  is  combined.  Al- 
though the  process  of  respiration  is  much  weaker  than  that  of  photosynthesis 
(or  "carbon  assimilation""),  still  each  must  be  kept  distinct  and  it  must  be 

1  Timiriazev,  K.  A.,  From  the  field  of  plant  physiology.  Public  lectures  and  addresses.  [Russian.] 
Moscow,  1888.     P.  245. 

"  The  term  photosynthesis  has  now  come  into  very  general  use  among  English  and  French 
physiologists,  in  place  of  the  more  cumbersome  expressions  previously  employed,  and  there 
seems  to  be  little  room  for  doubt  that  it  will  eventually  become  universal.  The  word  is  of 
American  origin.  Barnes  (Barnes,  C.  R.,  On  the  food  of  green  plants.  Bot.  gaz.  18:  403- 
411.  1893)  suggested  photosyntax,  and  the  other  and  better  form  is  due  to  McMillan,  and  it> 
general  introduction  to  MacDougal.  Ewart  is  partly  right  in  the  footnote  he  appended  to  his 
translation  of  Pfeffer's  Plant  Physiology  (1  :  302.  Oxford,  1900),  but  his  objections  do  not 
appear  valid  as  against  the  use  of  photosynthesis.  Of  course,  this  should  include  all  possible 
forms  of  chemical  synthesis  brought  about  through  the  action  of  light,  but  the  formation  of 


4  PHYSIOLOGY    OF    NUTRITION 

CO 

found  out  how  the  ratio  -^r-2  varies,  independently  of  respiration.     Bonnier 

U2 

and  Mangin1  investigated  this  and  found  the  value  of  the  ratio  to  be  really 

somewhat  less  than  unity.     So  the  plant  gives  off  not  only  the  equivalent  of  all 

the  oxygen  originally  contained  in  the  absorbed  carbon  dioxide,  but  also  a 

smaller   portion    of    oxygen    arising   from    the    water    that  is  decomposed  in 

photosynthesis.2 

As  to  methods  of  investigation,  the  decomposition  of  carbon  dioxide  can  be 

detected  in  the  following  manner.     A  cut  leaf  is  placed  in  a  calibrated  glass 

tube  (Fig.  1),  the  upper  end  closed  and  the  lower,  open  end  dipping  into  mercury. 

Then  a  part  of  the  air  is  removed  by  a  rubber  tube  and  the  level  of  the  mercury 

rises.     The  volume  of  the  remaining  air  is  read,  after  which  some  carbon  dioxide 

is  admitted  from  a  gasometer  and  the  gas  volume  is  again  determined.     The 

apparatus  is  not  placed  in  light  and  after  some  time  the  gas  volume  is  once 

more  recorded.     The  remaining  carbon  dioxide  is  removed  by  injecting  some 

concentrated  potassium  hydroxide  solution,  and  the  diminished  gas  volume  is 

again  read;  pyrogallol  is  next  introduced,  and  a  final  reading,  after  the  removal 

of  oxygen  by  the  pyrogallol,  gives  the  amount  of  nitrogen  that  remains.     The 

numbers  obtained  permit  the  determination  of  the  amounts  of  carbon  dioxide 

absorbed  and  of  oxygen  liberated.3 

A    less    exact    method    consists    in    counting   the    number   of   gas   bubbles 


carbohydrate  out  of  carbon  dioxide  and  water  is  by  far  the  most  important  form  of  photosyn- 
thesis, and  the  term  may  readily  be  qualified  whenever  need  arises.  Thus,  we  may  distinguish 
chlorophyll  photosynthesis  of  carbohydrate  from  other  photosyntheses.  The  word  assimilation 
has  been  employed  in  so  many  different  senses  that  to  attempt  its  use  as  a  precise  term  in  this 
connection  here  seems  unadvisable. — Jorgensen  and  Stiles  prefer,  however,  to  employ  the 
"rather  non-committal  expression,"  carbon  assimilation,  and  they  do  so  in  their  recent 
very  excellent  monograph  on  this  subject,  which  should  be  referred  to  in  connection  with 
this  entire  chapter,  and  which  should  become  familiar  to  every  student  of  plant  physiology. 
See:  Jorgensen,  Ingvar,  and  Stiles,  Walter,  Carbon  assimilation,  a  review  of  recent  work 
on  the  pigments  of  the  green  leaf  and  the  processes  connected  with  them.  New  phytolo- 
gist  reprint  No.  10.  London,  191 7.  (This  is  reprinted  from  a  series  of  articles  having  same 
title,  in  New  phytol.  14-16.     1015-17.) — Ed. 

1  Bonnier,  Gaston,  and  Mangin,  Louis,  L'action  chlorophyllienne  separde  de  la  respiration.  Ann. 
sci.  nat.  Bot.  VII,  3  :  5-44-      1886. 

2  It  will  be  seen  later  that  hydrogen  and  oxygen  are  actually  assimilated,  as  well  as  carbon,  in  the 
photosynthetic  process,  the  source  of  the  hydrogen  and  of  some  of  the  oxygen  being  water,  taken  up  from 

the  soil. 

s  For  precise  methods  of  gas  analysis  see:  Bunsen,  Robert  W.  E.,  Gasometrische  Methoden.  2te 
Aufl.  Braunschweig,  1877.  Winkler,  C  A.,  Lehrbuch  der  technischen  Gasanalyse.  1885.  [Idem, 
Handbook  of  technical  gas-analysis  containing  concise  instructions  for  carrying  out  gas-analytical  methods 
of  proved  utility.  Translated  with  a  few  additions  by  George  Lunge.  London,  1885.  Idem,  same  title, 
2d  English  ed.  from  3d  German  ed.  London,  1902.]  For  physiological  experiments,  see  especially:  Doyere, 
M.  L.,  Etudes  sur  la  respiration.  Ann.  chim.  et  phys.  Ill,  28:  5-50.  1850.  Blackman,  F.  Frost,  Experi- 
mental researches  on  vegetable  assimilation  and  respiration.  I.  On  a  new  method  for  investigating  the 
carbonic  acid  exchanges  of  plants.  Phil,  trans.  Roy  Soc.  London  B186:  485-502.  1896.  [Idem,  same  title. 
II.  On  the  paths  of  gaseous  exchange  between  aerial  leaves  and  the  atmosphere.  Ibid.  B186:  503-562. 
1896.]  Palladin,  W.,  and  Kostytschew,  S.,  in  Abderhalden's  Handbuch  der  biochemischen  Arbeitsmethoden 
3  :  479-     Berlin,  1910. 


ASSIMILATION    OF    CARBOX  5 

(comparatively  pure  oxygen1)  given  off,  in  light,  from  the  cut  end  of  a  piece  of 
the  water  plant  Elodea,  submerged  in  water  saturated  with  carbon  dioxide, 
as  shown  in  Fig.  2.  If  a  number  of  such  green  water  plants  are  placed  under 
water  in  sunlight  and  are  covered  by  an  inverted  funnel,  over  the  neck  of 
which  is  inverted  a  test-tube  of  water  (Fig.  3),  the  test-tube  soon  becomes 
filled  with  a  gas  that  is  nearly  pure  oxygen. 

Schutzenberger's  reagent  (a  solution  of  indigo  carmine  or  nigrosine,  de- 
colorized by  sodium  sulphite)  can  also  be  used  to  demonstrate  that  oxygen  is 


r~\ 


W 


Fig.  2. — Elimina- 
tion of  oxygen  bubbles 
by  Elodea  in  sunlight. 


Fig.  3. — Collection    of    oxygen  from 
water  plants  in  light. 


Fig.  I. — Leaf  in 
position  in  a  measuring 
tube,  for  demonstration 
of  absorption  of  carbon 
dioxide  and  elimination 
of  oxygen  during  photo- 
synthesis. 

liberated  by  water  plants;  this  solution  is  yellow  when  prepared,  but  turns  blue 
in  the  presence  of  oxygen.  If  a  shoot  of  Elodea,  or  other  aquatic,  is  placed 
in  a  dilute  solution  of  this  reagent  and  exposed  to  sunlight,  the  solution  surround- 
ing the  leaves  becomes  blue  in  a  few  minutes.2 

§3.  Chlorophyll.— Since  the  decomposition  of  carbon  dioxide  is  effected  exclu- 
sively by  the  green  parts  of  plants,  the  properties  of  the  green  pigment — called 

1  This  method  was  perfected  by  Kohl.  See:  Kohl,  F.  G.,  Die  assimilatorische  Energie  der  blauen  und 
violetten  Strahlen  des  Spektrums.     Ber.  Deutsch.  Bot.  Ges.  IS :  111-124.     1897. 

'  Kny,  L.,  Die  Abhangigkeit  der  Chlorophyllfunction  von  den  Chromatophoren  und  vom  Cytoplasma. 
Ber.  Deutsch.  Bot.  Ges.  15:  388-403.  1897.  [See  also:  Kolkwitz,  R.,  Pflanzenphysiologie.  Jena,  1914- 
P.  3-1 


6  PHYSIOLOGY    OF    NUTRITION 

chlorophyll  by  Pelletier  and  Caventou1— must  be  studied.  Chlorophyll  can  be 
extracted  from  leaves  by  alcohol,  but  the  solution  thus  obtained  also  contains 
several  other  pigments,  as  well  as  colorless  substances,  for  the  removal  of  which 
various  methods  have  been  devised.2  The  method  of  Fremy  involves  the 
precipitation  of  the  alcoholic  extract  with  barium  hydroxide;  the  green  precipi- 
tate is  collected  upon  a  filter  and  treated  with  alcohol  until  the  yellow  pigments, 
xanthophyll  and  carotin,  are  completely  removed.  The  remaining  precipitate 
is  then  decomposed  by  potassium  hydroxide,  according  to  the  method  of 
Timiriazev.3  The  green  solution  thus  obtained  is  treated  with  ether,  and  dilute 
acetic  acid  is  gradually  added,  with  shaking,  to  neutralize  the  potassium 
hydroxide.  As  long  as  the  reaction  is  alkaline  the  ether  remains  without 
color,  but  as  soon  as  the  hydroxide  is  neutralized  the  lower  layer  becomes  yellow, 
since  all  the  green  pigment  passes  into  solution  in  the  ether  above.  The  color 
of  the  ether  solution  is  emerald  green,  more  intense  than  that  of  the  alcoholic 
solution;  it  is  cherry  red,  however,  in  reflected  light,  while  the  yellow  solution 
shows  no  fluorescence.  Timiriazev  was  the  first  to  succeed  in  separating  chlo- 
royhyll  from  yellow  pigments,  out  of  the  alcoholic  chlorophyll  extract.  This 
chlorophyll  is  not  the  normal  pigment,  however,  for  it  has  been  changed  by  the 
treatment  employed  in  separating  it. 

The  method  of  Kraus4  is  based  upon  the  relative  solubilities  of  the  pig- 
ments in  alcohol  and  benzine.  If  benzine  is  gradually  added,  with  shaking, 
to  the  green  alcoholic  extract  diluted  with  water  so  as  to  be  about  an  85 -per 
cent,  solution  of  alcohol,  two  sharply  distinct  layers  are  finally  formed,  an 
upper,  green  layer  (benzine)  and  a  lower,  golden-yellow  one  (alcohol  and 
water).  By  renewed  shaking  of  the  former  solution,  with  further  additions  of 
alcohol,  the  green  pigment  can  be  practically  freed  from  the  yellow  coloring 
matter. 

The  green  pigments6  form  an  amorphous  mass,  readily  soluble  in  alcohol, 
ether  and  naphtha.  The  solution  is  intensely  fluorescent,  appearing  cherry 
red  by  reflected  light  and  green  by  transmitted  light.  The  chemistry  of  chloro- 
phyll has  been  largely  worked  out  by  Willstatter  and  his  co-workers.  Two 
closely  related  pigments  are  always  associated  to  form  chlorophyll,  these  having 
been  termed  chlorophyll  a  and  chlorophyll  b. 

1  [Pelletier,  [Joseph],  and  Caventou,  [J.  B.],  Sur  la  matiere  verte  des  feuilles.  Ann.  chim.  et  phys. 
11,9:  194-196.     1818.]  f 

2  Willstatter,  Richard,  Chlorophyll  und  seine  wichtigsten  Abbauprodukte.  Abderhalden  s  Handb. 
biochem.  Arbeitsmeth.  2:  671-716.  Berlin,  1910.  Willstatter,  Richard,  and  Hug,  Ernst,  Isolierung  des 
Chlorophylls.     Liebig's  Ann.  Chem.  u.  Pharm.  380:  177-21 1.      1911. 

s  Timiriazev,  K.  A.,  Spectral  analysis  of  chlorophyll.  [Russian.]  St.  Petersburg,  1871.*  [Haas  and 
Hill  give  methods  for  obtaining  chlorophyll,  and  present  a  good  discussion.  See:  Haas,  Paul,  and  Hill, 
T.  G.,  An  introduction  to  the  chemistry  of  plant  products.     London,  192 1.] 

■>  Kraus,  Gregor,  Zur  Kenntnis  der  Chlorophyllfarbstoff e  und  ihrer  Verwandten.     Stuttgart,  1872. 

b  Some  modifications  have  been  made  in  this  discussion  of  chlorophyll,  so  that  it  does  not 
agree  entirely  with  Palladin's  presentation.  .  An  attempt  has  been  made  to  bring  it  more  into 
accord  with  Willstatter  and  Stall's  monograph.  (Willstatter,  Richard,  and  Stall,  Arthur, 
Untersuchungen  liber  Chlorophyll,  Methoden  und  Ergebnisse.  Berlin,  1913-)  For  English 
resumes  of  this  work,  see:  West,  Clarence  J.,  A  review  of  Willstatter's  researches  on  chloro- 
phyll. Biochem.  bull.  3:  229-258.  1914.  Willstatter,  R.,  Chlorophyll.  Jour.  Amer.  Chem. 
Soc.  38:  323-345.     1915—  Ed. 


ASSIMILATION    OF    CARBON  7 

Alcoholic  solution  of  chlorohyll  a  is  blue-green  by  transmitted  light  and 
blood-red  by  reflected  light;  it  is  said  to  fluoresce  blood-red.  Alcoholic  solu- 
tion of  chlorophyll  b  is  yellow-green  by  transmitted  light  and  fluoresces  brown- 
red.  This  phenomenon  of  fluorescence  (seen  also  in  a  solution  of  the  red  dye 
eosin,  which  fluoresces  green)  appears  to  be  due  to  an  alteration  in  the  wave- 
length of  radiant  energy,  brought  about  by  a  peculiar  action  on  the  part  of  the 
molecules  in  the  solution.  By  this  action  the  chlorophyll  solution  gives  off 
energy  of  long  wave-lengths  (red  light)  when  it  is  illuminated  by  energy  of 
much  shorter  wave-lengths  (green  and  blue  light)/ 

Of  the  total  green  pigment,  as  obtained  from  leaves,  about  72  per  cent,  is 
chlorophyll  a  and  the  rest  chlorophyll  b.  The  proportions  vary  somewhat,  but 
the  variation  is  not  over  10  perc  ent.  Both  form  crystals.  The  two  chloro- 
phylls'' have  the  following  formulas,  as  so  far  known: 

Chlorophyll  a,  C55H7206N4Mg 
Chlorophyll  b,  C55H7o06N4Mg 

It  is  seen  that  both  contain  magnesium,  the  content  of  this  element  being  about 
5.6  per  cent.,  by  weight.  Iron  is  apparently  necessary  for  the  formation  of 
chlorophyll  in  plants,  but  it  is  not  a  part  of  the  pigment.  Iron  does  occur, 
however,  in  the  molecule  of  hemoglobin,  which  is  somewhat  closely  related  to 
chlorophyll,  chemically.  An  explanation6  of  this  is  to  be  found  in  the  fact  that 
the  actions  of  these  two  substances  in  the  cell  are  directly  opposed;  for  the 
analytic  action  of  hemoglobin,  iron  is  essential,  while  magnesium  seems  to 
take  part  in  the  synthetic  processes  effected  by  chlorophyll.1 

1  Willstatter,  Richard,  Zur  Kenntniss  der  Zusammensetzung  des  Chlorophylls.  Liebig's  Ann.  Chem.  u. 
Pharm.  350:  48-82.  1906.  Willstatter,  Richard,  and  Benz,  Max,  Ueber  krystallisirtes  Chlorophyll. 
Ibid.  358:  267-287.     1908. 

c  This  explanation  is  not  given  by  Palladin.  For  a  discussion  of  the  various  theories  regard- 
ing the  color  and  fluorescence  of  plant  pigments,  see :  Horowitz,  B.,  Plant  pigments.  Biochem. 
bull.  4:  161-172.     1915. — Ed. 

d  Stokes  had  long  ago  suspected  that  chlorophyll  is  a  mixture  of  two  green  pigments.  In 
this  connection  see:  Stokes,  G.  G.,  On  the  supposed  identity  of  biliverdin  with  chlorophyll, 
with  remarks  on  the  constitution  of  chlorophyll.  Proc.  Roy.  Soc.  London  13  :  144-145.  1864. 
Sorby,  H.  C,  On  comparative  vegetable  chromatology.     Ibid.  21  :  442-483.     1873. 

On  an  interesting  method  for  separating  the  yellow  and  green  pigments  by  absorption  in 
paper  or  in  a  column  of  calcium  carbonate,  see:  Tswett,  M.,  Physikalisch-chemische  Studien 
liber  das  Chlorophyll.  Die  Adsorptionen.  Ber.  Deutsch.  Bot.  Ges.  24:  316-323-  ia°6- 
Idem,  Adsorptionsanalyse  und  chromatographische  Methode.  Anwendung  auf  die  Chemie 
des  Chlorophylls.  Ibid.  24 :  384-393.  1906.  Idem,  Ueber  die  nachsten  Saurederivate  der 
Chlorophylline.     Ber.  Deutsch.  Chem.  Ges.  41/:  1352-1354.     1908.— Ed. 

e  It  is  difficult  to  understand  this  as  an  explanation.  It  must  not  be  understood  that 
hemoglobin  and  chlorophyll  are  really  very  much  alike;  they  differ  very  markedly,  but  give 
some  of  the  same  decomposition  products.  It  is  true  that  both  are  related  to  the  interchange, 
between  the  organism  and  its  surroundings,  of  carbon  dioxide  and  oxygen,  but  the  actions  of 
the  two  substances  do  not  appear  to  be  similar  in  detail.  The  author  refers  here  to  the  fact 
that  they  have  similar  component  atomic  groups,  which  may  suggest  that,  in  the  phylogeny 
of  animals  and  plants,  both  groups  of  organisms  may  have  developed  from  a  common  ancestral 
form  having  a  substance  with  the  characters  that  are  common  to  hemoglobin  and  chlorophyll. 
This  is  as  far  as  such  a  theory  may  go  at  present.     But  see  below,  page  u,  ct  seq.—Ed. 


8  PHYSIOLOGY    OF    NUTRITION 

Almost  a  third  of  the  chlorophyll  molecule  is  composed  of  phytyl,  the  radical 
of  phytol,1  an  unsaturated  mono-hydric  primary  alcohol  of  the  aliphatic  series, 
having  the  composition  C20H40O  and  the  probable  structure  shown  by  the 
following  diagram: 

CH3— CH— CH— CH— CH— CH— CH— C=C CH— CHoOH 

I  I         I  I  I  I         I       I  I 

CH3   CH3  CH3   CH3   CH3   CH3  CH3CH3  CH3 

Phytol  is  readily  oxidized  in  the  presence  of  air.  Willstatter  suggests  that  it 
may  be  obtained  from  isoprene  in  the  following  way: 

4C5H8  (isoprene)  -f-  H20  +  3H2  =  C2oH400  (phytol). 

Carotin  appears  also  to  be  related  to  isoprene.  The  phytyl  of  chlorophyll 
may  be  replaced  by  the  ethyl  group  if  the  leaves  are  treated  with  ethyl  alcohol. 
This  replacement  is  effected  by  an  enzyme  known  as  chlorophyllase.2 

Another  alcohol  radical  is  present  in  both  the  chlorophylls,  namely,  methyl 
(CH3).  They  thus  appear  to  be  esters  of  a  complex,  dicarboxylic  acid,  one  of 
the  two  carboxyls  (COOH)  being  joined  to  phytyl  and  the  other  to  methyl. 

Regarding  the  complex  acids  that  form  the  basis  of  the  chlorophylls,  there  still 
remain  some  uncertainties,  but  it  appears  to  be  related  to  a  tricarboxylic  acid 
that  may  be  represented  by  the  formula  (C3iH29N4Mg)  (COOH)3,  but  one  of  the 
carboxyls  is  inactive,  so  that  a  dicarboxylic  acid  results.  A  general  idea  of  the 
manner  in  which  the  magnesium  atom  is  probably  related  to  the  other  compo- 
nents of  the  molecule  may  be  obtained  from  the  following  structural  formula 
for  etiophyllin,  to  which  this  fundamental  acid  is  apparently  closely  related. 

CH=CH 

I       I 
CH3— C— CH  C— C 


C2H5— C— C  C— CH 

yC  Cx_ 

C2Ho — C — C  /C — C — C2H.-j 


>N— Mg— N 
CH3— C=C  C=rC— CH3 

!  I 

CH3  CH3 

When  the  phytyl  group  of  chlorophyll  a  is  replaced  by  the  ethyl  group 
(C2H5),  a  substance  is  obtained  (C37H3806N4Mg)  which  Willstatter  called 
ethyl  chlorophyllide.  This  forms  beautiful  crystals,  which  were  earlier  mistaken 
for  pure  chlorophyll.     Chlorophyll  b  reacts  in  a  similar  way.     According  to  the 

1  Willstatter,  Richard,  and  Hocheder,  Ferdinand,  Ueber  die  Einwirkung  von  Sauren  und  Alkalien  auf 
Chlorophyll.  Liebig's  Ann.  Chem.  u.  Pharm.  354:  205-258.  1007.  Willstatter,  Richard,  Mayer,  Erwin 
W.,  and  Huni,  Ernst,  Ueber  Phytol.  I.    7&j'<2.  378:  73-152.     1011. 

2  Willstatter,  Richard,  and  Stoll,  Arthur,  Ueber  Chlorophyllase.  Liebig's  Ann.  Chem.  u.  Pharm. 
378:  18-72.     1911. 


ASSIMILATION    OF    CARBON  9 

method  of  Monteverde,1  these  crystals  may  be  obtained  by  treatment  of  tritu- 
rated leaves  with  95  per  cent,  ethyl  alcohol;  after  an  hour  the  extract  is  filtered 
and  the  alcohol  is  removed  by  evaporation,  either  in  air  or  in  hydrogen.  The 
crystals  are  separated  from  impurities  and  from  the  yellow  pigments  by  means 
of  distilled  water  and  benzine.  In  the  pure  condition  they  form  a  dark  green, 
almost  black  powder,  with  a  bluish  metallic  luster.  Their  alcoholic  solution  is 
green,  with  a  beautiful  red  fluorescence.  Although  the  solution  is  unstable  in 
light,  the  crystals  can  endure  intense  light  for  a  long  time  without  change.  The 
following  plants  serve  especially  well  as  sources  of  ethyl  chlorophyllide  in  the 
crystalline  condition:  Dianthns  barbatus,  Lathyrus  odoratus,  Galeopsis  versicolor, 
G.  tetrahit,  Acacia  lophantha,  and  Dahlia  variabilis.  Amorphous  chlorophyll 
may  be  obtained  from  many  other  plants.  Willstatter  and  Benz2  obtained 
over  2  g.  of  ethyl  chlorophyllide  from  1  kg.  of  dry  leaves. 


afiC 


Fig.  4. — -Absorption  spectrum  of  ethyl  chlorophyllide,  0.1  g.  in  5  1.  of  alcohol.  (After 
Willstatter.)  The  thickness  of  the  layer  employed  is  shown  (in  millimeters)  at  the  left,  the 
conventional  letters  of  the  Fraunhofer  lines  are  at  the  top,  and  the  wave-lengths  (in  10  m**) 
are  indicated  below. 


The  absorption  spectrum  of  chlorophyll  deserves  special  attention.  Light 
of  certain  ranges  of  wave-length  is  more  or  less  completely  absorbed  by  the 
solution,  so  that  dark  bands  appear  in  the  spectrum.  The  absorption  spectrum 
of  every  colored  solution  changes  with  its  concentration.  On  this  account  the 
spectrum  of  chlorophyll  solution  must  be  determined  either  throughout  a  range 
of  concentrations  or  by  using  layers  of  various  thicknesses.  Six  absorption 
bands  are  found  in  the  spectrum  (Fig.  4)  of  ethyl  chlorophyllide;  arranged  ac- 
cording to  their  intensities,  they  form  the  series:  I,  VI,  V,  II,  III,  IV.  The 
first  band,  lying  between  the  Fraunhofer  lines  B  and  C,  is  the  most  distinct;  it 
appears  in  solutions  of  weaker  concentration  than  are  necessary  to  make  the 
others  evident.     The  absorption  bands  become  broader  with  increasing  con- 

1  Monteverde,  N.  A.,  Ueber  das  Protochlorophyll.  Acta  Horti  Petropolitani  13:  190-217.  1894. 
Borodin  had  obtained  crystals  from  chlorophyll  before  they  were  described  by  Monteverde.  See:  Borodin, 
J.,  Ueber  Chlorophyllkrystalle.     Bot.  Zeitg.  40:  608-610,  622-626.     1882. 

2  Willstatter  and  Benz,  1908.     [See  note  1,  p.  7-1 


IO 


PHYSIOLOGY   OF    NUTRITION 


centration  and  finally  merge  into  one  another,  so  that  only  the  red  rays,  between 
.  1  and  B,  and  a  part  of  the  green  can  pass  through  a  concentrated  solution  or  a 
thick  layer;  finally,  with  still  further  increase  in  concentration  or  thickness 


1 

■i  ■  i 

f             '             1             1              1 

1    '    1 

'    I    ' 

1    i 

'       1 

1           1 

'    « 

Q 

o 

o 

& 

3 

O 

o 

in 

C 

r 

o 

o 

m 

t-i 

*t 

-J- 

B 

I 

1  ll 

1 

ll 

B 

,1 

F 

i 

|| 

G 

Pig.  5. — Absorption  spectra  of  five  different  concentrations  of  chlorophyll  a.     {After  Willstatter 

and  Sloll.) 


Fig.    6. — Absorption    spectra    of    five    different    concentrations    of    chlorophyll    b.      {After 

Willstatter  and  Sloll.) 


of  layer,  the  green  rays  are  also  completely  absorbed  and  only  the  rays  between 
A  and  B  are  transmitted.  All  objects  appear  red  when  seen  through  a  very 
concentrated  solution  or  a  very  thick  layer. 


ASSIMILATION    OF    CARBON 


II 


The  absorption  spectra  of  chlorophyll  a  and  chlorophyll  b,  in  acetone,  are 
shown  in  Figs.  5  and  6,  reproduced  photographically,  these  being  taken  from 
Willstatter  and  S toll's  monograph  (Tafel  VIII).  Five  different  concentrations 
are  employed,  the  strongest  being  represented  by  the  lowest  spectrum  in  each 
case.     The  Fraunhofer  lines  and  wave-lengths  (in  mm)  are  shown  above/ 

The  spectrum  of  living  leaves  shows  the  same  absorption  bands  as  does  the 
spectrum  of  an  alcoholic  solution  of  chlorophyll  (ethyl  chlorophyllide) ;  in  the 
former  case  the  bands  are  merely  displaced  a  little  toward  the  infra-red  end  of 
the  spectrum.9 

The  researches  of  Schunck  and  Marchlewski1  have  contributed  much  to  an 
understanding  of  the  chemical  character  of  chlorophyll.  The  action  of  hydro- 
chloric acid  upon  an  alcoholic  chlorophyll  solution  produces  first  chlorophyllan, 
then  phylloxanthin,  and  finally  phyllocyanin.  The  interesting  substance  phyl- 
lo porphyrin2  (C16H1SN20,  or  C32H36N4O0)3  is  obtained  by  treating  phyllocyanin 
with  strong  alkalies.     Phylloporphyrin  crystallizes  in  beautiful,  dark  red-violet 


pIG  » — Absorption  spectra  of  phylloporphyrin  (i,  3,  5)  and  of  hematoporphyrin  (2,  4,  6); 
1  and  2  in  ether;  3  and  4  in  hydrochloric  acid;  5  and  6  in  zinc  chloride  solution.  (After  Schunck 
and  Marchlewski.) 

crystals,  is  slightly  soluble  in  alcohol  and  ether,  and  more  readily  soluble 
in  chloroform.  The  absorption  spectrum  of  its  ethereal  solution  (Fig.  7) 
exhibits  seven  absorption  bands,  the  first  of  which  lies  to  the  right  of  the  red 
region  of  the  spectrum,  between  C  and  D,  and  is  very  distinct. 

Phylloporphyrin  is  of  great  interest  because  of  its  close  relationship  to 

1  Schunk,  E.,  and  Marchlewski,  L.,  Zur  Chemie  des  Chlorophylls.     Liebig's  Ann.  Chem.  u.  Pharm. 

278:  329-345-     1894. 

* Schunck,  E.  and  Marchlewski ;  L.,  Zur  Chemie  des  Chlorophylls.  (Zweite  Abhandlung.)  Liebig's 
Ann.  Chem.  u.  Pharm.  284:  81-107.      1805. 

'Willstatter,  Richard,  and  Fritzsche,  Hermann,  Ueber  den  Abbau  von  Chlorophyll  durch  Alkalien. 
Liebig's  Ann.  Chem.  u.  Pharm.  371:  33-124-     1909. 

'  These  two  figures  are  added  by  the  editor. — Ed. 

0  It  seems  highly  probable  that  the  chlorophyll  of  living  leaves  exists  in  colloidal  solution. 
(Herlitzka,  A.,  Neben  den  Zustand  des  Chlorophylls  in  der  Pflanze  und  iiber  kolloidales 
Chlorophyll.  Biochem.  Zeitsch.  38:  321-330.  1912.  Iwanowski,  [D.],  Ueber  das  Verhalten 
des  lebenden  Chlorophylls  zum  Lichte.  Ber.  Deutsch.  Bot.  ges.  31:  600-612.     1913). — Ed. 


12 


PHYSIOLOGY    OF    NUTRITION 


hematoporphyrin,  which  was  obtained  by  Nentskii  and  Sieber  from  hemoglobin 
of  animal  blood.  Hematoporphyrin  has  the  composition  Ci6Hi8N20i,  the  dif- 
ference between  it  and  phylloporphyrin,  as  represented  by  these  formulas,  con- 
sisting in  the  lower  oxygen  content  of  the  latter.1  The  method  used  in  the 
isolation  of  hematoporphyrin  is  also  analogous  to  that  employed  for  phyllopor- 
phyrin. The  spectra  of  these  two  substances,  in  various  solvents,2  are  almost 
identical,  except  that  the  absorption  bands  of  hematoporphyrin  sometimes 
appear  slightly  displaced  toward  the  red  (Fig.  7). 

Both  hematoporphyrin  and  phylloporphyrin,  when  heated  in  a  test-tube, 
form  a  vapor  which  gives  a  red  color  to  pine  sawdust  moistened  with  hydro- 
chloric acid,  a  characteristic  indication  of  the  presence  of  the  pyrrol  ring 
(C4H5N):  the  characteristic  odor  of  pyrrol  may  also  be  plainly  recognized  in 
this  vapor.3  It  thus  appears  that  chlorophyll  (acting  synthetically)  and  hemo- 
globin (acting  analytically)  are  closely  related,  in  that  the  pyrrol  ring  is  common 
to  both.  It  is  of  great  interest  also  to  note  that  the  bile  pigment  bilirubin 
has  the  same  percentage  formula  as  hematoporphyrin  (Ci6Hi8N20,j).  Further- 
more, Nentskii  and  Zaliesskii4  succeeded  in  obtaining  mesoporphyrin  ivom  hemin, 
the  latter  substance  being  formed  by  the  action  of  acids  upon  hemoglobin. 
Mesoporphyrin  has  the  composition  Ci6Hi8N202,  and  stands  between  hemato- 
porphyrin and  phylloporphyrin  in  oxygen  content.  By  a  further  decomposition 
of  hemin  these  authors  obtained  hemopyrrol  (Ci3H8N),  a  volatile  oil  that  turns 
red  in  air  and  changes  into  urobilin,  which  is  also  obtained  from  bilirubin. 
When  Nentskii  and  Marchlewski5  succeeded  in  obtaining  hemopyrrol  and 
urobilin  from  phylloporphyrin,  the  relationship  between  chlorophyll  and 
hemoglobin  was  conclusively  established.  The  atomic  group  common  to 
both,  as  in  the  case  of  the  bile  pigments,  occurs  in  hemopyrrol.  The  following 
diagram  represents  the  relationship  existing  between  these  three  groups  of 
substances. 

Chlorophyll  Hemoglobin 


Hematoporphyrin 


Phylloporphyrin 


Hemopyrrol 

! 

Urobilin 


Bilirubin 

1  For  the  difference  in  structure  between  the  two  compounds  see:  Willstatter,  Richard,  and  Asahina, 
Yasuhiko,  Oxydation  der  Chlorophyllderivate.     Liebig's  Ann.  Chem.  u.  Pharm.  373  :  227-238.     1910. 

2  Schunck,  E.,  and  Marchlewski,  L.,  Zur  Chemie  des  Chlorophylls.  (Vierte  Abhandlung.)  Liebig's 
Ann.  Chem.  u.  Pharm.  290:  306-313.     1896. 

3  Schunck,  E.,  and  Marchlewski,  L.,  Zur  Chemie  des  Chlorophylls.  (Dritte  Abhandlung.)  Liebig's 
Ann.  Chem.  u.  Pharm.  288:  200-218.     1895. 

4  Nencki,  M.,  and  Zaleski,  J.  Ueber  die  Reduclionsproducte  des  Hamins  durch  Jodwasserstoff  and 
Phosphoniumjodid  und  iiber  die  Constitution  des  Hamins  and  seiner  Derivate.  Ber.  Deutsch.  Chem.  Ges. 
341'  997-IOIO.     1901. 

6  Nencki,  M.,  and  Marchlewski,  L.,  Zur  Chemie  des  Chlorophylls.  Abbau  des  Pyhllocyanins  zum 
Hamopyrrol.     Ber.  Deutsch.  Chem.  Ges.  34";  1687-1693.     1901. 


ASSIMILATION    OF    CARBON'  1 3 

Results  of  this  kind  are  exceedingly  important  in  biochemistry,  since  they 
seem  to  illuminate  the  most  remote  period  in  the  evolutionary  development  of 
organisms,  and  point  to  a  common  origin  of  the  plant  and  animal  worlds.  Dar- 
win's theory  of  the  origin  of  species  is  based  upon  the  conception  of  variability 
in  structure,  influenced  by  environmental  conditions  in  the  struggle  for  existence. 
But  the  differences  between  organisms  lie,  not  only  in  the  form  and  structure 
of  the  various  organs,  but  also  in  the  chemical  properties  of  the  substances  con- 
stituting the  living  cells.  The  character  of  the  metabolic  processes  is  dependent 
upon  the  nature  of  the  intracellular  substances,  and  these  processes,  in  their 
turn,  determine  the  configuration  of  the  cells  and  their  differentiation  into 
organs.  In  other  words,  the  form  of  the  cell-complexes  composing  the  different 
organs  is  determined  by  metabolism  as  this  has  been  developed  by  the  various 
organs  in  the  struggle  for  existence,  relative  to  various  environmental  condi- 
tions. With  a  change  of  conditions,  their  chemical  constitution  and  their 
metabolism  are  modified,  which  explains  why  they  frequently  change  their 
form  also.  Thus,  to  obtain  a  fundamental  conception  of  the  evolution  of  the 
organic  world,  not  only  the  structure  but  also  the  chemical  composition  of  the 
cells  and  the  products  of  their  metabolism  must  be  considered.  From  this 
viewpoint  the  work  of  Schunck  and  Marchlewski,  whereby  the  leaf  and  blood 
pigments  are  shown  to  be  related  chemically,  though  widely  different  as  to 
function,  is  of  great  scientific  interest.1 

According  to  Nentskii,2  chlorophyll  and  hemoglobin  arise  from  chromogens 
that  are  protein  decomposition  products.  A  substance  called  tryptophan  is 
formed  in  protein  decomposition  by  pancreatic  juice;  tryptophan  is  colored  red 
by  bromine  and  is  related,  in  its  percentage  composition,  to  hematoporphyrin 
and  the  melanins. 

The  decomposition  products  of  chlorophyll  can  be  separated,  according  to 
Willstatter,3  into  two  groups.  Those  obtained  by  the  action  of  acids  contain 
no  magnesium;  the  action  of  alkalies,  on  the  other  hand,  results  in  such  deriva- 
tives as  glaucophyllin,  rhodophyllin,  pyrrophyllin,  and  phyllophyllin,  all  of  which 
contain  magnesium.  If  acids  are  allowed  to  act  upon  these  latter  substances, 
new  compounds  without  magnesium  arise,  which  are  related  to  hematoporphyrin ; 
in  this  way  phylloporphyrin  is  obtained  from  phyllophyllin.  The  action  of 
acids  upon  chlorophyll  itself  gives  phaophytin,  in  which  the  phytyl  can  be  re- 
placed by  the  ethyl  group,  giving  ethyl  phceophorbide;  chlorophyllin  modified  by 
the  action  of  acid  is  designated  as  phseophorbide,  and  phseophytin  may  thus 
be  termed  phytyl-phaeophorbide. 

i  Nencki,  M.,  Sur  les  rapports  biologiques  entre  la  matiere  colorante  des  feuilles  ct  celle  du  sang.  Arch, 
sci.  biol.  St.-Petersbourg  5:  254-260.     1897. 

2  Nencki,  M.,  Ueber  die  biologischen  Beziehungen  des  Blatt-  und  des  Blutfarbstoffes.  Ber.  Deutsch. 
Chem.  Ges.  2o7//:  2877-2883.     1896. 

»  Willstatter,  Richard,  and  Pfannenstiel,  Adolf,  Ueber  Rhodophyllin.  Liebig's  Ann.  Chem.  u.  Pharm. 
358:  205-265.  1908.  Willstatter  and  Fritzsche,  1909.  [See  note  3.  P-  "•]  Willstatter  and  Hocheder, 
1907.  [See  note  1,  p.  8.]  Willstatter,  Richard,  and  Stoll,  Arthur,  Spaltung  und  Bildung  von  Chlorophyll. 
Liebig's  Ann.  Chem.  u.  Pharm.  380:  148-154-  I9H.  Willstatter,  Richard,  and  Isler,  Max.,  Vergleichende 
Untersuchung  des  Chlorophylls  verschiedener  Pflanzen.  III.  Ibid.  380:  154-176.  I9H-  [The  whole 
series  of  studies  is  summarized  by  Willstatter  and  Stoll,  1913-     (See  note  6,  p.  6-^ 


14  PHYSIOLOGY    OF    NUTRITION 

Among  the  other  transformation  products  of  chlorophyll,  protophyllin  de- 
serves attention;  Timiriazev1  obtained  this  by  the  action  of  nascent  hydrogen. 
It  is  yellow  or  red  in  solution,  according  to  the  concentration.  It  is  very  easily 
oxidized,  going  over  into  chlorophyll;  for  this  reason  it  must  be  preserved  under 
carbon  dioxide  or  hydrogen  in  sealed  tubes.  It  is  stable  in  hydrogen,  in  light 
as  well  as  in  darkness,  but  in  carbon  dioxide  it  is  stable  only  in  darkness;  in 
light,  with  carbon  dioxide,  it  becomes  green  and  is  transformed  into  chlorophyll. 
It  must  be  supposed  that  carbon  dioxide  is  decomposed  in  this  case  and  that 
oxygen  is  liberated,  at  the  expense  of  which  the  transformation  and  greening  of 
the  protophyllin  occurs.  Absorption  bands  in  the  orange  and  green  regions  of 
the  spectrum,  corresponding  to  bands  II  and  IV  of  chlorophyll,  are  character- 
istic of  protophyllin. 

It  appears  from  many  investigations  that  the  formation  of  chlorophyll  in 
plants  is  a  very  complicated  process.  Until  the  publication  of  the  work  of 
Liro2  most  authors  failed  to  distinguish  between  the  beginning  of  chlorophyll 
formation  and  the  visible  accumulation  of  this  pigment  in  plants  as  they  become 
green.     This  distinction  is  quite  necessary. 

We  shall  first  turn  our  attention  to  the  conditions  requisite  for  the  formation 
of  chlorophyll .  Light  may  be  mentioned  as  the  first  of  these.  Leaves  of  angio- 
sperms  grown  in  darkness  are  always  yellow,  but  such  etiolated  plants  soon  turn 
green  when  exposed  to  light.  Seedlings  of  some  conifers,3  young  fern  fronds  and 
some  one-celled  algae4  are  exceptions,  for  they  become  green  in  darkness;  still, 
according  to  Liubimenko,  conifer  seedlings  form  much  less  chlorophyll  in  dark- 
ness than  in  light.  Very  weak  light  is  sufficient  for  chlorophyll  formation,  and 
light  of  medium  intensity  is  most  favorable.  Famintsyn5  exposed  a  part  of  an 
etiolated  plant  to  direct  sunlight,  while  the  intensity  of  the  light  falling  upon  the 
remaining  portion  was  reduced  by  interposing  sheets  of  paper;  greening  always 
occurred  first  in  the  reduced  light.  According  to  Wiesner  this  phenomenon  is 
to  be  explained  by  supposing  that  decomposition  and  formation  of  chlorophyll 
occur  simultaneously.  In  light  of  low  or  medium  intensity  the  decomposition 
process  is  nearly  absent,  while  in  strong  light  active  formation  is  accom- 
panied by  rapid  breaking  down  of  chlorophyll,  which  results  in  less  pronounced 
greening  than  occurs  in  diffuse  light. 

Various  parts  of  the  spectrum  have  different  effects  upon  the  formation  of 
chlorophyll,   a   matter  which   was   carefully  investigated   by  Wiesner.6     He 

1  Timiriazeff,  C,  La  chlorophylle  et  la  reduction  de  l'acide  carbonique  par  les  vegetaux.  Compt. 
rend.  Paris  102:  686-689.  1886.  Idem,  La  protophylline  dans  les  plantes  etiolees.  Ibid.  109:  414-416. 
1889.     Idem,  La  protophylline  naturelle  et  la  protophylline  artificielle.     Ibid.  120:  467-470.     1895. 

2  Liro,  J.  Ivar,  Ueber  die  photochemische  Chlorophyllbildung  bei  den  Phanerogamen.  Ann.  Acad. 
Sci.  Fennicae  (Helsinki)  Ai:  1-147.      1909. 

8  Lubimenko,  W.,  Influence  de  la  lumiere  sur  le  developpement  des  fruits  et  des  graines  chez  les  vegetaux 
superieurs.     Rev.  gen.  hot.  22:  145-175.     1910. 

4  Artari,  A.,  Ueber  die  Entwicklung  der  griinen  Algen  unter  Ausschluss  der  Bedingungen  der  Kohlen- 
saure-Assimilation.  Bull.  Soc.  Imp.  Nat.  Moscou  13:  3Q—47.  1900.  Idem,  Zur  Ernahrungs-physiologie 
der  grunen  Algen.  Ber.  Deutsch.  Bot.  Ges.  19:  7-9       1901. 

'  Famintzin,  A.,  Die  Wirkung  des  Lichts  auf  das  Ergunen  der  Pflanzen  ("aus  dem  Bulletin  10:  548- 
552.")     Melanges  biol.  Acad.  Imp.  Sci.  St.-P6tersbourg  6:  94-100.     1866. 

«  Wiesner,  Julius,  Untersuchungen  uber  die  Beziehungen  des  Lichtes  zum  Chlorophyll.  Sitzungsber. 
(math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien  69':  327-385.  1874.  Idem,  Die  Entstehung  des  Chloro- 
phylls in  der  Pflanze.     Wien.  1877. 


ASSIMILATION    OF    CARBON 


15 


employed  double-walled  bell- jars  with  colored  liquids,  as  light  screens  for  isolat- 
ing certain  regions  of  the  spectrum  (Fig.  8).  Solutions  of  potassium  dichromate 
and  of  ammoniacal  copper  oxide  [copper  sulphate  solution  to  which  an  excess  of 
ammonia  water  is  added]  were  most  frequently  used;  the  first,  in  medium  con- 
centration, permits  the  passage  of  the  rays  of  the  less  refrangible  half  of  the 
spectrum  (red,  orange,  yellow  and  a  part  of  the  green),  while. the  second  trans- 
mits the  remainder  of  the  visible  rays  (the  rest  of  the  green  and  all  of  the  blue 
and  violet).  Thus,  by  the  use  of  these  liquids,  the  spectrum  is  separated  into 
two  parts.  [Of  course  the  intensity  of  the  light  transmitted  is  considerably 
decreased.] 

In  weak  light  plants  become  green  sooner  under  the  yellow  solution,  but  in 
strong  light  more  quickly  under  the  blue.  This  may  be  explained  by  supposing 
that  in  weak  light  the  formation  of  chlorophyll  occurs  almost  exclusively,  under 
the  influence  of  the  less  refrangible  rays,  which  are  most  favorable,  while  in 
strong  light,  besides  chlorophyll  formation,  an  active  de- 
composition also  takes  place.  Experiments  upon  the  de- 
composition of  alcoholic  solutions  of  chlorophyll  under 
colored  bell-jars  have  shown  that  this  process  is  especially 
pronounced  in  the  less  refrangible  half  of  the  spectrum; 
greening  in  plants  is  thus  seen  to  be  weaker  in  strong  yellow- 
red  fight  because  a  very  rapid  destruction  here  accompa- 
nies the  formation  of  chlorophyll.  But  another  explana- 
tion is  also  possible:  strong  light  may  not  act  directly  upon 
chlorophyll  that  has  already  been  formed  but  may,  some- 
how, have  a  harmful  effect  upon  some  process  antecedent 
to  chlorophyll  formation;  this  might  explain  why  less 
chlorophyll  accumulates  in  strong  light. 

Plants  do  not  become  green  under  the  non-luminous 
heat  rays.     In  order  to  separate  this  portion  of  the  spec- 
trum, Tyndall's  solution  is  used,  iodine  in  carbon  bisul- 
phide; in  low  concentrations  the  rays  between  Fraunhofer  lines  A  and  B  are 
transmitted,  but  these,  produce  no  green  color.     In  ultra-violet  light  green- 
ing is  very  slight. 

The  production  of  chlorophyll  is  dependent  upon  temperature.  Medium 
temperatures  are  most  favorable,  and  no  greening  occurs  at  very  low  or  at  very 
high  temperatures.     Wiesner  obtained  the  following  results  from  experiments 

with  etiolated  barlev  seedlings. 

Time  Required 

Temperature  F0R  Greening 

Deg.C.  Hours 

2_  4  (No  greening) 

4-5-'^' 7-2S 

10 3-50 

18-19 l6? 

30 -s8 

37-38 4.oo 

4C (No  greening) 


S3! 


S3! 


Pig.  8. — Double- 
walled  bell-jar  with 
colored  solution  filling 
the  space  between 
the  walls. 


i6 


PHYSIOLOGY    OF    NUTRITION 


The  autumn  coloration  of  leaves  is  dependent  upon  light  and  upon  the  tem- 
perature of  the  air;  chlorophyll  is  decomposed  by  sunlight  in  autumn,  while  its 
re-formation  is  hindered  by  the  low  temperatures  then  prevailing.  According 
to  Batalin,1  the  conifer  Chamacyparis  obtusa  is  especially  interesting  in  this 
connection.  Branches  in  sunshine  have  a  golden-yellow  color  in  the  cold  sea- 
son, while  shaded  ones  remain  green;''  at  the  margin  between  the  shaded  and  un- 
shaded regions  the  different  colors  may  often  be  seen  in  neighboring  cells. 

The  products  of  chlorophyll  decomposition  do  not  remain  in  the  leaf  but  dif- 
fuse away.2  This  is  shown  by  the  following  experiment:  if  an  incision  is  made 
in  a  leaf  in  the  autumn,  while  it  is  still  green,  so  that  the  chlorophyll  decomposi- 
tion-products are  prevented  from  diffusing  away,  the  part  of  the  leaf  above  the 
cut  remains  green  while  the  other  parts  turn  yellow  (Fig.  9). 

The  presence  of  iron  is  a  third  condition  necessary  for  the  formation  of 
chlorophyll.3  Without  iron,  plants  remain  bright  yellow,  thus  suffering  from 
chlorosis. 


Pig.  9. — Gingko  leaf  in  which  autumnal  coloration  has  been  prevented  in  the  upper  part, 

by  an  incision.      {After  Stahl.) 


The  presence  of  oxygen  is  an  additional  condition  necessary  for  greening. 
Etiolated  leaves  in  an  oxygen-free  chamber  remain  yellow,  even  in  light.  This 
is  also  true  when  the  amount  of  oxygen  is  small;  greening  demands  an  excess 
of  this  gas. 

Ville1  was  able  to  show  that  the  absence  of  necessary  mineral  salts  in  the 
soil  results  in  the  diminution  of  the  chlorophyll  and  carotin  contents  of  leaves. 

1  Batalin,  A.,  Ueber  die  Zerstorung  des  Chlorophylls  in  lebenden  Organen.     Bot.  Zeitg.  32 :  433-439. 

1874- 

-  Stahl,  Ernst,  Zur  Biologie  des  Chlorophylls;  Laubfarbe  und  Himmelslicht,  Vergilbung  und  Etiole- 
ment.     Jena,  1909. 

3  Gris,  Eusebe,  Nouvelles  experiences  sur  Taction  des  composes  ferrugineux  solubles,  appliques  h.  la 
veg6tation,  et  specialement  au  traitement  de  la  chlorose  et  de  la  debilite  des  plantes.  Compt.  rend.  Paris 
19:1118-1119.  1844.  Molisch,  Hans,  Die  pflanze  in  ihren  Beziehungen  zum  Eisen.  Eine  physiologische 
Studie.     Jena,  1892. 

*  Ville,  Georges,  Recherches  sur  les  relations  qui  existent  entre  la  couleur  des  plantes  et  la  richesse  des 
terres  en  agents  de  £ertilit6.     Compt.  rend.  Paris  109:  397-400.     1889. 

h  This  may  also  be  seen  in  the  arbor  vitae  (Thuja  occidentalis)  of  the  northeastern  United 
States  in  very  cold,  bright  winter  weather. — Ed. 


ASSIMILATION    OF    CARBON  1 7 

Lesage  and  Schimper1  found  that  an  excess  of  mineral  substances  reduces  the 
chlorophyll  content,  an  effect  that  may  be  observed  not  only  in  halophytes, 
growing  normally  upon  soils  rich  in  salts,  but  also  in  other  plants  when  watered 
with  strong  salt  solutions. 

Finally,  Palladin2  pointed  out  that  carbohydrates  are  essential  to  the 
formation  of  chlorophyll.  As  will  be  seen  farther  on,  plants  fall  into  twTo 
groups  according  to  the  carbohydrate  content  of  their  etiolated  leaves;  in  one 
group  (for  example,  wheat),  such  leaves  contain  much  soluble  carbohydrate 
material,  while  in  etiolated  leaves  of  the  other  group  (such  as  bean  and  lupine) 
carbohydrates  are  almost  entirely  absent.  If  etiolated  leaves  of  these  plants 
are  removed  and  floated  upon  water  in  light,  those  of  barley  become  green,  while 
almost  all  the  bean  leaves  and  all  those  of  lupine  remain  yellow.  In  the  latter 
are  floated,  not  upon  water  but  upon  a  saccharose  or  glucose  solution,  then 
they  also  all  become  green.  The  greening  of  entire,  completely  etiolated  bean 
plants  in  light  is  explained  in  this  way,  that  carbohydrates  migrate  into  the 
leaves  from  the  stems.  Besides  saccharose  and  glucose,  such  substances  as 
raffinose,  fructose,  maltose,  glycerine,  and  some  others,  also  produce  greening3 
under  these  conditions.  The  concentration  of  these  substances  is  important 
in  this  connection.4  Greening  occurs  quickly  with  a  saccharose  solution  of 
low  or  medium  concentration.  If  the  concentration  is  previously  increased 
to  35  per  cent.,  in  darkness,  the  leaves  remain  yellow  for  several  days  when 
subsequently  brought  into  the  light,  but  greening  occurs  quickly  in  these  leaves 
if  they  are  transferred  from  the  strong  solution  to  one  having  a  concentration 
of  from  5  to  io  per  cent. 

Single-celled  algae  are  particularly  well  adapted  to  the  study  of  the 
importance  of  various  substances  in  the  formation  of  chlorophyll.  Cultures  in 
light  exhibit  a  considerable  range  of  color  (from  yellow-green  to  intense,  dark 
green)  according  to  the  composition  of  the  nutrient  solution  used.5 

Thus  greening,  or  the  accumulation  of  chlorophyll,  is  a  physiological  process 
that  proceeds  only  in  living  cells  and  under  conditions  favorable  to  life.  The 
substance  from  which  chlorophyll  arises  has  not  yet  been  isolated,  but  the 
existence  of  such  a  substance  may  be  inferred  from  various  observations. 
According  to  Monteverde  and  Liubimenko,6  a  pigment  called  chlorophyllogen  is 
formed,  independently  of  light,  in  the  chromatophores  of  all  green  plants.  It  is 
said  to  arise  from  a  colorless  chromogen,  leucophyllj  of  which  little  more  is 

1  Schimper,  A.  F.  W.,  Die  Indo-Malayische  Strandflora.     Jena,  1891.     P.  9. 

2  Palladin,  W.,  Ergrunen  und  Wachsthum  der  etiolirten  Blatter.  Ber.  Deutsch.  Bot.  Ges.  9:  229-232. 
1891. 

3  Palladin,  W.,  Recherches  sur  la  formation  de  la  chlorophylle  dans  les  plantes.  Rev.  g6n.  Bot.  9 :  385- 
394-      1897. 

4  Palladin,  W.,  Einfluss  der  Concentration  der  Losungen  auf  die  Chlorophyllbildung  in  etiolirten  Blat- 
tern.     Ber.  Deutsch.  Bot.  Ges.  20:  224-228.     1902. 

5  Artari,  Alexander,  Ueber  die  Bildung  des  Chlorophylls  durch  griine  Algen.  Ber.  Deutsch.  Bot.  Ges. 
20:  201-207.  1902.  Matruchot,  L.,  and  Molliard,  M.,  Variations  de  structure  d'une  algue  verte  sous 
l'influence  du  milieu  nutritif.     Rev.  gen.  bot.  40:  1 14-130,  254-268.     1902. 

6  Monteverde,  N.  A.,  and  Lubimenko,  V.  N.,  Recherches  sur  la  formation  de  la  chlorophylle  chez  les 
plantes.     [Text  in  Russian.]     Bull.  Acad.  Imp.  Sci.  St.-Petersbourg  VI,  5:  73-100.     191 1. 

7  Sachs,  J.,  Ueber  das  Vorhandensein  eines  farblosen  Chlorophyll-Chromogens  in  Pflanzentheilen,  welche 
fahig  sind  griin  zu  werden.     Lotos  9:  6-14.     1859.     Idem,  same  title.     Chem.  Centralbl.,  n.  F.  4:  145- 

IS3.     1859. 
o 


l8  PHYSIOLOGY    OF    NUTRITION 

known.  Chlorophyllogen  is  a  very  unstable  substance,  and  its  absorption  spec- 
trum shows  a  great  similarity,  in  the  red  region,  to  that  of  chlorophyll. 
Attempts  to  isolate  it  result  in  an  artificial  transformation-product,  the  proto- 
chlorophyll of  Monteverde.1  Like  chlorophyll,  protochlorophyll  is  a  deep  green 
pigment,  which  is  fluorescent,  appearing  red  by  reflected  light.  The  spectrum 
shows  four  absorption  bands.  The  absorption  spectra  of  alcoholic  solutions  of 
protochlorophyll  on  the  one  hand,  and  of  alcoholic  chlorophyll  on  the  other, 
are  different  in  that  the  absorption  band  between  B  and  C  in  the  second  is  absent 
in  the  first,  and  the  one  between  C  and  D  in  the  first  appears  slightly  displaced 
toward  the  left  in  the  second;  the  other  bands  practically  agree.  Although 
protochlorophyll  is  a  transformation-product,  it  is  still  of  interest,  in  so  far  as 
its  existence  indicates  the  presence  of  a  mother-substance  for  chlorophyll; 
protochlorophyll  itself  cannot  change  into  chlorophyll.  Protochlorophyll 
arises  independently  of  light,  from  chlorophyllogen.  As  to  its  presence  in 
living  cells,  it  is  normally  found  in  large  quantities  in  the  inner  seed-coats  of 
the  Cucurbitaceae,  especially  inLuffa. 

A  rapid  transformation  of  chlorophyllogen  into  chlorophyll  occurs  in  living 
plant  cells  under  the  influence  of  light.  This  process  can  also  be  observed  in 
plants  that  have  been  killed.  According  to  Liro,  if  etiolated  leaves  are  care- 
fully killed  so  that  at  least  some  of  the  chlorophyllogen  remains,  and  if  they  are 
then  exposed  to  light,  some  formation  of  chlorophyll  can  still  be  observed.  For 
the  transformation  of  chlorophyllogen  into  chlorophyll,  Liro  and  Isachenko2 
have  shown  that  neither  oxygen,  favorable  temperature  conditions,  nor  even 
the  presence  of  carbohydrates  are  necessary,  but  since  greening  is  possible  only 
with  these  conditions  they  are  evidently  necessary  for  the  formation  of  chloro- 
phyllogen, or  of  the  chromogen  that  gives  rise  to  it.  Chlorophyll  may  be  formed 
from  chlorophyllogen  in  the  absence  of  light,  as  is  exemplified  by  plants  that 
turn  green  in  darkness;  in  such  cases  the  influence  of  chemical  agents  must 
replace  the  action  of  light.3 

Such  are  the  chief  results  of  the  researches  thus  far  carried  out  upon  chloro- 
phyll and  its  formation.  As  to  the  role  it  plays  in  the  chemical  decomposition 
of  carbonic  acid  and  the  formation  of  the  first  products  of  photosynthesis 
almost  nothing  is  known.  Schryver4  suggests  that  the  formaldehyde  arising 
in  the  decomposition  of  carbon  dioxide  and  water  enters  into  combination  with 
the  chlorophyll. 

»  Monteverde,  1894.  [See  Note,  1,  p.  9.]  Monteverde,  N.  A.,  Der  Einfluss  des  Lichts  auf  die  Gesch- 
windingkeit  deT  Chlorophyllbildung  in  Blattern  etiolirter  Pflanzen.  Trav.  Soc.  Imp.  Nat.  St.-P6tersbourg 
27' ':  131-142  [Russian],  143-145  [German  abstract].  1896.  Idem,  Das  Protochlorophyll  und  Chlorophyll. 
[Title  and  abstract  in  German,  article  in  Russian.]  Bull.  Jard.  Imp.  Bot.  St.-Petersbourg  2:  179-182. 
[Abstract,  p.  181-182.]  1902.  Idem,  Ueber  das  Absorptionsspectrum  des  Protochlorophylls.  I.  [Title 
and  abstract  in  German,  article  in  Russian.]  Ibid.  7:  37-42  [Abstract,  p.  42],  47-58.  [Abstract,  p.  5S~58]. 
1907. 

'  Issatchenko,  B.,  Sur  les  conditions  de  la  formation  de  la  chlorophylle.  [Title  and  abstract  in 
French,  article  in  Russian.]  Bull.  Jard.  Imp.  Bot.  St.-Petersbourg  6:  20-28  [Abstract,  p.  27-28].  1906. 
Idem,  same  title.  Ibid.  7:  59-64  [Abstract,  p.  64].  1907.  Idem,  same  title.  Ibid.  9:  106-120  [Ab- 
stract, p.  119-120].      1909. 

3  Monteverde  and  Liubimenko,  1911.     [See  note  6,  p.  17.] 

4  Schryver,  S.  B.,  Photochemical  formation  of  formaldehyde  in  green  plants.  Chem.  news  101  :  64. 
19TO. 


ASSIMILATION    OF    CARBON  1 9 

As  to  the  physics  of  the  action  of  chlorophyll,  it  behaves  as  a  sensitizer1  and 
renders  the  energy  of  the  absorbed  light  effective  in  the  decomposition  of  car- 
bon dioxide.  In  an  analogous  manner  the  red  light  rays  between  lines  B  and  C 
of  the  spectrum  rapidly  decompose  silver  salts  in  the  presence  of  chlorophyll, 
although  these  salts  are  otherwise  decomposed  only  by  blue  and  violet  rays. 

§4.  Pigments  Accompanying  Chlorophyll. — Among  the  other  pigments 
accompanying  chlorophyll,  special  attention  should  be  given  to  carotin.2  Boro- 
din3 was  able  to  show  that  carotin  (called  erythrophyll  by  him)  regularly  ap- 
peared in  alcoholic  leaf  extract  when  he  allowed  this  to  form  crystals  under  the 
microscope. 

The  chemical  nature  of  carotin,  and  also  some  of  the  conditions  of  its  forma- 
tion in  leaves,  were  first  made  clear  by  the  investigations  of  Arnaud4  and  of 
Willstatter  and  Mieg.5  This  pigment  forms  flat,  rhombic  crystals,  which,  with 
one-sided  illumination,  appear  blue-green  on  the  illuminated  side  and  orange- 
red  on  the  other.  It  is  readily  soluble  in  ether,  chloroform  and  carbon  bisul- 
phide, less  so  in  benzine,  slightly  soluble  in  hot  alcohol,  almost  insoluble  in  cold 
alcohol  and  insoluble  in  water.  A  carbon  bisulphide  solution  of  carotin  is 
blood-red;  dissolved  in  concentrated  sulphuric  acid,  carotin  is  bluish-violet.  It 
is  a  hydrocarbon,  with  the  formula  C4oH56,  which  is  easily  oxidized.  It  may  be 
transformed  into  cholesterin.  The  carotin  content  of  leaves  varies  with  the 
season  of  the  year.  A  series  of  experiments  continued  throughout  the  summer 
upon  the  leaves  of  stinging  nettle  and  horse-chestnut  showed  that  the  carotin 
content  is  greatest  during  the  flowering  season,  for  both  plants.  The  formation 
of  carotin  is  also  dependent  upon  light;  green  leaves  of  vetch  contained  178.8 
mg.  of  carotin,  as  compared  to  34.0  mg.  in  the  same  quantity  of  etiolated  leaves. 

It  was  shown  by  the  work  of  Kohl6  that  carotin  is  widely  distributed.  It 
is  not  limited  to  the  green  parts  of  plants  but  occurs  also  in  flowers,  fruits,  seeds 
and  subterranean  organs,  and  also  in  fungi.  It  may  be  extracted  in  large  quan- 
tities from  carrots. 

The  function  of  carotin  is  not  yet  clear,  but  its  tendency  to  unite  with  oxygen 
appears,  at  any  rate,  to  be  significant  in  connection  with  the  photosynthetic 
process,  where  reduction  of  compounds  containing  oxygen  is  known  to  occur. 

•  Tappeiner,  H.  von,  Die  photodynamische  Erscheinung  (Sensibilisierung  durch  fluoreszierende  Stoffe). 

Ergeb.  Physiol.  8:  698-741.     1909- 

2  Escher,  Heinr.  H.,  Zur  Kenntnis  des  Carotins  und  des  Lycopins.  Zurich,  1909.  104  p.  (Zurich  Poly- 
techn.  Dissert.  1909-10.)  [For  a  general  discussion  of  the  yellow  pigments,  see  Haas  and  Hill,  1921. 
(See  note  3,  p.  6.)] 

'Borodin,  J.,  Ueber  krystallinische  Nebenpigmente  des  Chlorophylls.  Bull.  Acad.  Imp.  Sci.  St.- 
Petersbourg  28:  328-350.     1883. 

4  Arnaud,  A.,  Recherches  sur  les  matieres,  colorantes  des  feuilles;  identite  de  la  matiere  rouge  orange 
avec  la  carotine,  Cj8H240.  Compt.  rend.  Paris  100:  75 1-753-  1885.  Idem,  Recherches  sur  la  composi- 
tion de  ia  carotine,  sa  fonction  chimique  et  sa  formule.  Ibid.  102 :  1119-1122.  1886.  Idem,  Sur  la  pres- 
ence de  la  cholesterine  dans  la  carotte;  recherches  sur  ce  principe  immediat.  Ibid.  102  :  1310-1322.  1886. 
Idem,  Recherches  sur  la  carotine;  son  role  physiologique  probable  dans  la  feuille.  Ibid.  109:  911-914. 
1889. 

s  Willstatter,  Richard,  and  Mieg,  Walter,  Ueber  die  gelben  Begleiter  des  Chlorophylls.  Liebig's  Ann. 
Chem.  u.  Pharm.  355:  1-28.     1907. 

«  Kohl,  Friedrich  Georg,  Untersuchungen  uber  das  Karotin  und  seine  physiologische  Bedeutung  in 
der  Pflanze.     Leipzig,  1902. 


20 


PHYSIOLOGY   OF   NUTRITION 


The  absorption  spectrum  of  carotin  has  two  dark  bands  in  the  green-blue  half  of 
the  spectrum  (Fig.  10). 

A  second  yellow  pigment  accompanying  chlorophyll  is  xanthophyll,  an  oxida- 
tion product  of  carotin,  with  the  formula  C4oH5602.1 


Lycopin    ■ 


Karoiin  . 


70    85 


Fig.  io.— Absorption  spectra  of  carotin  and  lycopin.  (After  Escher.)  The  Fraunhofer 
lines  are  indicated  by  the  letters  above  and  the  wave-lengths  (in  io  nn)  are  shown  below;  the 
thickness  of  layer  employed  is  given  (in  mm.)  at  the  left. 

Lycopin1  is  closely  related  to  carotin  and  has  the  same  percentage  formula 
(C4oH56) ;  it  is  found  in  the  fruit  of  the  tomato  {Solatium  ly coper sicum).  Three 
dark  bands  occur  in  the  right  half  of  its  absorption  spectrum  (Fig.  10). 


700  B   C 

J L 


GOOD 


E  500  F 


400 


700  B   C 

J L 


eooD 

I  1 


500  F 


G   400 


pIG  II# Absorption  spectra  of  carotin  (above)  and  xanthophyll  (below).  (After  Will- 
statter and  Stoll.)  The  Fraunhofer  lines  and  the  wave-lengths  (in  /i/i)  are  shown  on  the  upper 
line  of  each  diagram. 

Red  alga?  contain  phycoerythrin,  a  protein-like  substance,  which  is  readily 
soluble  in  water  but  insoluble  in  alcohol,  ether,  and  carbon  bisulphide.     The 

1  Montanari,  Carlo,  Materia  colorante  rossa  del  pomodoro.  Le  Stazioni  Sperimentali  Agrarie  Italiane 
37:  909-919.  1904.  [Willstatter,  Richard,  and  Escher,  Heinr.  H.,  Ueber  den  Farbstoff  der  Tomate. 
Zeitsch.  physiol.  Chem.  64:  47-61.     1910.] 

i  The  absorption  spectra  of  carotin  and  xanthophyll,  as  given  by  Willstatter  and  Stoll 
(1913)  [see  note  b,  p.  6]  are  here  reproduced  as  Fig.  11.  It  is  questionable  whether  xanthophyll 
is  actually  formed  by  the  oxidation  of  carotin. — Ed. 


ASSIMILATION    OF    CARBON  21 

dark,  bluish-red  solution  shows  an  orange-yellow  fluorescence.     It  crystallizes 
from  salt  solutions  in  hexagonal  red  crystals.7' 

Phycocyanin,1  the  blue  pigment  of  the  blue-green  algae,  Cyanophyceae,  is 
likewise  of  protein  nature;  it  is  soluble  in  water  and  glycerine  but  insoluble  in 
ether  and  alcohol,  its  crystals  are  indigo  blue  in  color. 

The  brown  algae  contain  a  pigment,  phycophcein,2  which  is  easily  soluble  in 
water;  in  concentrated  solutions  it  is  dark  reddish-brown.fc 

Engelmann3  studied  the  absorption  spectra  of  bright-colored  leaves  of  vari- 
ous plants,  and  Stahl4  investigated  the  biological  importance  of  their  coloring/ 

§5.  Influence  of  Light  upon  the  Decomposition  of  Carbonic  Acid  by  Plants. 
An  acquaintance  with  the  properties  of  the  different  rays  of  the  sun's  spectrum 
(Fig.  12)  is  prerequisite  to  an  understanding  of  the  researches  devoted  to  this 
subject.  Only  the  central  part  of  the  spectrum,  approximately  that  portion 
lying  between  lines  A  and  H,  is  visible  to  the  human  eye;  on  either  side  are  in- 
visible rays,  infra-red  to  the  left  and  ultra-violet  to  the  right.  Of  the  visible 
rays,  the  yellow  are  the  brighest,  the  brightness  reaching  a  maximum  at  line 
D  and  decreasing  to  zero  beyond  A  and  H.  Brightness  does  not,  however, 
represent  the  character  of  the  rays,  but  only  that  of  the  human  eye.  The  en- 
ergy maximum  in  the  prismatic  solar  spectrum  is  usually  shown  as  falling  in  the 
region  of  the  infra-red,  as  in  Fig.  12.  Nevertheless,  recent  work  upon  the  dis- 
tribution of  heat  in  the  ordinary  diffraction  spectrum  of  sunlight  shows  the 

1  Molisch,  Hans,  Das  Phycocyan,  ein  krystallisirbarer  Eiweisskorper.     Bot.  Zeitg.  53:  I3I-I35-     1895. 

2Schiirt,  Franz,  Ueber  das  Phycophasin.     Ber.  Deutsch.  Bot.  Ges.  5:  259-274.     1887. 

aEnglemann,  Th.  W.,  Die  Farben  bunter  Laubblatter  und  ihre  Bedeutung  fur  die  Zerlegung  der 
Kohlensaure  im  Lichte.     Bot.  Zeitg.  45 :  393-398,  409-419.  425-436,  44i-4SO.  457-469-     1887. 

*  Stahl,  E.,  Ueber  bunte  Laubblatter.  Ein  Beitrag  zur  Pflanzenbiologie.  II.  Ann.  Jard.  Bot.  Buitenzorg 
13:  137-216.     1896. 

■»  On  phycoerythrin,  see  Haas  and  Hill,  1921.  [See  note  3,  p.  6.]  The  best  study  of  this 
pigment  is  that  of  Hanson.  (Hanson,  E.  K.,  Observations  on  phycoerythrin,  the  red  pigment 
of  deep-water  alga?.     New  phytol.  8:  337-344.     1909.) — Ed. 

k  But  it  seems  to  have  been  shown  that  there  is  no  such  pigment  as  phycophasin  in  the  living 
cells,  this  being  a  post-mortem  product  of  the  decomposition  of  a  colorless  chromogen.  The 
brown  color  of  the  brown  algae  is  at  least  partly  due  to  the  presence  of  carotin.  In  this  con- 
nection see  the  following:  Molisch,  Hans,  Das  Phycoerythyrin,  seine  Krystalisirbarkeit 
und  chemische  Natur.  Bot.  Zeitg.  52:  177-189.  1894.  Idem,  Das  Phycocyan  ein  Krystal- 
lisirbarer Eisweisskorper.  Ibid.  53:  131-135-  1895.  Idem,  Ueber  den  braunen  Farbstoff 
der  Pha;ophyceen  und  Diatomeen.  Ibid.  63' ':  131-144-  1905-  Tswett,  M.,  Zur  Kenntnis 
der  Phaeophyceenfarbstoffe.     Ber.  Deutsch.  Bot.  Ges.  24:  235-244.     1906.— Ed. 

1  The  antliocyanins,  or  anthocyans,  are  other  pigments  that  may  be  mentioned  here.  They 
occur  very  commonly  in  flowers,  leaves,  stems,  fruits,  and  even  in  roots,  giving  them  a  red, 
blue  or  purple  color  and  frequently  masking  the  green  of  the  chlorophyll  in  leaves.  They  are 
red  when  acid  and  blue  when  alkaline.  The  color  of  red  apples  and  many  other  fruits,  of 
many  red,  blue  and  purple  flowers,  of  the  beet-root,  of  red  cabbage,  of  young  leaves  of  many 
plants,  and  of  the  bronze-colored  leaves  of  the  copper  beech,  are  due  to  the  presence  of  these 
pigments.  They  are  often  present  along  with  chlorophyll,  as  in  the  case  of  red  cabbage  and  the 
copper  beech,  and  still  other  pigments  frequently  accompany  them.  They  are  soluble  in  water, 
alcohol  and  ether,  and  the  color  of  the  solution  alters  from  red  to  purple  or  blue  as  the  reaction 
is  altered  from  acid  to  neutral  or  alkaline.  For  further  information  see:  Haas  and  Hill,  1921. 
[See  note  3,  p.  6.]  West,  Clarence  J.,  Plant  pigments:  The  chemistry  of  plant  pigments  other 
than  chlorophyll.     Biochem.  bull.  4:  151-160.     1915. — Ed. 


2  2  •  PHYSIOLOGY    OF    NUTRITION 

energy  maximum  to  lie  between  lines  B  and  C;1  and,  according  to  the  latest 
researches,  the  position  of  this  maximum  is  not  constant  but  varies  from  the 
region  of  the  red  to  that  of  the  yellow-green,  according  to  the  hour  of  the  day. 
Finally,  chemically  active  or  "actinic"  rays,  with  a  maximum  in  the  violet 
region,  are  frequently  differentiated.  The  term  actinic  rays  really  refers  to 
the  power  of  light  to  decompose  silver  salts,  which  is  most  pronounced  in  the 
blue-violet  region  of  the  solar  spectrum.  Many  other  compounds  are  decom- 
posed by  light,  however,  frequently  in  other  regions  than  the  blue-violet,  and 
the  wave-lengths  producing  such  decomposition  are  those  that  are  absorbed 
by  the  substances  decomposed:  thus,  chlorophyll  is  most  rapidly  decomposed 
by  rays  between  B  and  C,  exactly  the  ones  most  completely  absorbed  by 
chlorophyll.  Therefore,  the  curve  of  chemical  intensity,  as  usually  given,  has 
no  importance  excepting  with  reference  to  silver  salts:  there  are  no  specific 
"chemical"  rays. 


Fig.  12. — Graphs  of  the  prismatic  solar  spectrum.  PA,  infra-red;  AH,  visible;  HS, 
ultra-violet  rays;  PTS,  temperature  curve;  ALH,  curve  of  light  intensity;  DKS,  curve  of  effect 
of  light  upon  the  decomposition  of  silver  salts. 

Researches  upon  the  influence  of  light  on  the  decomposition  of  carbon  di- 
oxide and  water  by  plants  fall  into  two  groups.  One  group  includes  studies 
dealing  with  the  qualitative  side  of  the  question,  as  to  which  rays  or  wave- 
lengths are  most  effective  in  the  process.  The  other  includes  quantitative  in- 
vestigations, as  to  how  much  energy  is  needed  for  this  decomposition.  The 
first  qualitative  work  was  done  by  Daubeny™  and  Draper"  the  former  using 

i  Langley,  [S.  P.],  Observations  du  spectre  solaire.  Compt.  rend.  Paris  95:  482-487.  1882.  Idem, 
Energy  and  vision.  Phil.  mag.  V,  27 :  1-23.  1889.  [Sunlight  as  it  reaches  plants  is  so  variable  in  both 
quality  and  intensity  that  each  quantitative  experiment  on  photosynthesis,  etc.,  in  natural  illumination, 
should  be  carried  out  with  very  careful  measurements  of  solar  radiation.  Nutting  states  that  the  sun's 
total  radiation  varies  over  a  range  of  8  per  cent,  of  the  mean,  while  the  earth's  atmosphere,  even  with  a  clear 
sky,  absorbs  from  20  to  50  per  cent.,  and  this  varies  from  minute  to  minute  and  from  hour  to  hour  of  the 
day.  Nutting  gives  a  table  (p.  202)  of  mean  solar  energy  quantities  reaching  the  surface  of  the  earth  at 
Washington  at  noon,  for  26  different  wave-lengths,  from  38s  to  428^.  (See  Nutting,  P.  G.,  Outlines  of 
applied  optics.  Philadelphia,  191 2.)  The  wave-length  showing  the  maximum  energy  value  also  varies 
markedly  in  natural  sunlight.  For  further  information  see:  Abbot,  C.  G.,  and  Fowle,  F.  E.,  Jr.,  Primary 
standard  pyrheliometer.  Ann.  Astrophys.  Observ.  Smithsonian  Inst.  2:  39-47-  1908.  Idem,  The 
value  of  the  solar  constant  of  radiation.  Astrophys.  jour.  33:  191-196.  19".  Also  see  Pulling,  H.  E.,  Sun- 
light and  its  measurement.     Plant  World  22:  151-171,  187-209.      1919—  Ed 

••'  Daubeny,  Charles,  On  the  action  of  light  upon  plants,  and  of  plants  upon  the  atmosphere. 
Phil,  trans.  Roy.  Soc.  London  126:  149-175.     1836. — Ed. 

"  Draper,  John  W.,  On  the  decomposition  of  carbonic  acid  gas  and  the  alkaline  carbonates 
by  the  light  of  the  sun.  Phil.  mag.  Ill,  23:  161-175-  l843-  Idem,  Scientific  memoires. 
473  p.     New  York,  1878.     P.  184-185.— Ed. 


ASSIMILATION    OF    CARBON 


23 


light  screens  and  the  latter  the  prismatic  spectrum.  Both  came  to  the  con- 
clusion that  plants  decompose  carbon  dioxide  most  readily  under  the  influence 
of  the  yellow  light  rays.  Sachs1  divided  the  spectrum  into  two  nearly  equal 
portions,  by  using  a  solution  of  potassium  dichromate  and  one  of  ammoniacal 
copper  oxide,  and  found  that  decomposition  of  carbon  dioxide  proceeded  almost 
as  energetically  in  the  yellow  portion  of  the  spectrum  as  in  direct  sunlight, 
while  very  little  decomposition  occurred  in  the  blue-violet  region.  It  is  seen, 
therefore,  that  it  is  not  the  so-called  "chemical"  rays  that  are  needed  for  this 
process,  but  chiefly  the  less  refrangible  rays  of  the  first  half  of  the  spectrum. 
Sachs  determined  the  amount  of  oxygen  given  off,  using  the  method  of  counting 
ing  gas  bubbles  (Fig.  2). 

The  next  problem  was  to  discover  in  what  rays  of  the  first  half  of  the 
spectrum  the  decomposition  of  carbonic  acid  was  most 
rapid.  The  most  exact  studies  upon  this  point  were 
carried  out  by  Timiriazev,2  who  arranged  his  experi- 
ments as  follows:  Sunlight  was  reflected  from  a  helio- 
stat  into  a  dark  chamber  and  was  then  broken  up  by 
a  carbon  bisulphide  prism.  Pieces  of  bamboo  leaves 
were  enclosed  in  glass  tubes,  with  air  containing  5  per 
cent,  of  carbon  dioxide,  and  these  tubes  were  placed  in 
various  regions  of  the  spectrum — in  the  red  between 
A  and  B,  in  the  chlorophyll  absorption  band  between 
B  and  C,  in  the  orange,  in  the  yellow,  and  in  the  green. 
At  the  conclusion  of  the  experiment  analyses  of  the 
gas  were  made,  by  means  of  a  very  sensitive  appa- 
ratus capable  of  measuring  extremely  small  amounts 
of  gas.  Timiriazev's  results  are  graphically  repre- 
sented in  Fig.  13.  The  ends  of  the  five  ordinates,  for 
the  five  positions  in  the  spectrum  where  the  tubes  were 

exposed,  are  joined  to  form  a  curve,  which  represents  ^onof  carbon  dioxide  in 
the  relative  rates  of  decomposition  of  carbon  dioxide  different  parts  of  the  spec 

,     .  ~,  trum.     {After  Txmniazev.) 

in  these  different  regions  of  the  spectrum.     1  he  maxi- 
mum decomposition  occurs  in  the  red,  between  B  and  C,  in  the  region  where  light 
is  most  strongly  absorbed  by  chlorophyll.     No  decomposition  occurs  between  A 
and  B  (the  line  m  represents  the  amount  of  carbon  dioxide  eliminated  during 
the  experiment).     These  results  were  confirmed  by  Engelmann3  and  Reinke.4 

1  Sachs,  J.,Wirkungen  farbigen  Lichts  auf  Pflanzen.      Bot.  Zeitg.  22  :  353-358.  361-367.  369-372.    1864. 

2  Timiriazev,  K.  A.,  (C.)  On  the  assimilation  of  light  by  plants.  [Russian.)  St.  Petersburg.  1875. 
Timiriazeff,  C,  Recherches  sur  la  decomposition  de  l'acide  carbonique  dans  le  spectre  solaire.  par  les 
parties  vertes  des  vegetaux.  (Extrait  d'un  Ouvrage  "Sur  l'assimilation,  de  la  lumiere  par  les  vegetaux," 
St.-Petersbourg,  1875;  publie  en  languerusse.)     Ann.  chim.  et  phys.     V,  12:  355-396.     1877. 

s  Engelmann,  Th.  W.,  Ueber  Sauerstoffausscheidung  von  Pflanzenzellen  im  Mikrospectrum.  Bot. 
Zeitg.  40  :  419-426.     1882. 

*  [Reinke,  J.,  Untersuchungen  uber  die  Einwirkung  des  Lichtes  auf  die  Sauerstoffausscheidung  per  Pflan- 
zen. II.  Die  Wirkung  der  einzelnen  Strahlengattungen  des  Sonnenlichtes.  Bot.  Zeitg.  42:  17-29.  33~46. 
40-59.  1884.  See  column  27.  Idem,  Die  Zerstorung  von  Chlorophyll osungen  durch  das  Licht  und  eine 
neue  Methode  zur  Erzeugung  des  Normalspectrums.  Ibid.  43:  65-70,  81-89,  97-ioi,  113-117,  129-137 
1885.  See  column  84.  Idem,  Die  Abhangigkeit  des  Ergrunens  von  der  Wellenlange  des  Lichts 
ungsber  (Math.-Naturw.  Mitth.).  K.  Preuss.  Akad.  Wiss.  Berlin.      1893  :  301-314-     1893I 


Fig.     13. — Graphs     show- 
;   relative   rates   of   decom- 


Sitz- 


24 


PHYSIOLOGY    OF    NUTRITION 


Engelmann  was  the  originator  of  the  bacterial  method  for  the  study  of 
photosynthesis.  It  is  well  known  that  many  bacteria  are  active  only  in  the 
presence  of  oxygen,  and  that  their  movement  ceases  as  soon  as  there  is  no 
oxygen  present.  If  a  filament  of  a  green  alga  is  placed  in  a  culture  of  such 
bacteria,  upon  a  slide,  and  if  the  preparation  is  protected  by  a  cover  glass  and 
darkened,  the  movement  of  the  bacteria  eventually  ceases  because  of  lack  of 
oxygen.  If  a  solar  spectrum  is  now  projected  upon  the  alga  filament,  under  the 
microscope,  it  is  seen  that  the  movement  of  the  bacteria  is  renewed  in  the  neigh- 
borhood of  both  of  the  main  chlorophyll  absorption  bands  (Fig.  14),  being  espe- 
cially pronounced  in  the  red  and  appreciably  weaker  in  the  blue.  It  is  only  in 
the  spectral  regions  thus  undicated,  therefore,  that  an  evolution  of  oxygen 
occurs,  to  which  the  bacteria  respond. 

The  degree  of  difference  between  the  efficiences  of  the  blue  and  red  spectral 
regions  was  established   by  Timiriazev.1     For  this  purpose  he  divided  the 


aB  C         D 


Eb         F 


I_ 


Fig.  14. — Bacterial  movement  in  the  regions 
of  the  absorption  bands  of  chlorophyll.  (After 
Englemann.)  The  dots  indicate  moving  bacteria 
and  the  letters  denote  the  Fraunhofer  lines. 


700 


600 


500 


WO 


Fig.  15. — AB,  distribution  of  heat 
energy  in  the  solar  spectrum.  (After 
Langley.)  100—14,  relative  rates  of  car- 
bon-dioxide decomposition  by  leaves  in 
red  and  in  blue  light. 


spectrum  into  two  equal  parts  by  means  of  a  cylindrical  lens  and  a  prism  with 
a  very  small  angle  of  refraction.  Flat-sided  glass  tubes  containing  pieces  of 
leaves  of  equal  area  were  placed  in  the  bright  bands  of  blue  and  yellow  light 
thus  obtained,  and  a  gas  analysis  of  the  tube  contents  was  made  after  three- 
quarters  of  an  hour  or  an  hour.  If  the  intensity  of  carbon  dioxide  decomposi- 
tion in  the  less  refrangible  (red-yellow)  light  be  taken  as  100,  then  the  corre- 
sponding intensity  in  the  more  refrangible  (blue)  light  is  54.  Thus  the  light 
absorbed  by  the  leaves  in  the  blue  half  of  the  spectrum  is  only  about  half  as 
effective  as  that  absorbed  in  the  other  half.  The  absorption  spectrum  of  the 
leaves  used  in  Timiriazev's  experiment  is  presented  in  Fig.  15.  It  must  be 
noted,  however,  that  the  two  absorption  bands  are  not  of  equal  width,  the  one 
in  the  blue-violet  region  of  the  normal  spectrum  being  more  than  three  times 
as  wide  as  the  band  between  B  and  C.     If  each  of  the  ratios  mentioned  above  is 


1  Timiriazev,  C,  Photochemische  Wirkung  der  am  Rande  des  sichtbaren  Spektrums  liegenden  Strahlen. 
1893.     (Russian.)* 


ASSIMILATION    OF    CARBON  25 

divided  by  the  breadth  of  the  corresponding  effective  absorption  band,  there 
is  obtained  for  an  average  wave-length  of  the  red  region,  100,  and  for  a  similar 
average  in  the  blue-violet,  14,  a  relation  which  is  graphically  represented  in 
Fig.  15.  Thus  red  light  is  relatively  much  more  effective  than  blue-violet  light. 
How  can  this  difference  be  explained?  Obviously  the  explanation  is  to  be  found 
in  a  consideration  of  the  energy  of  the  different  wave-lengths  expressed  in 
terms  of  their  respective  heat  values,  and  (as  will  be  seen  from  comparison  of 
the  curve  of  decomposition  of  carbon  dioxide  with  the  Langley  curve,  AB, 
representing  the  heating  effect  of  the  various  parts  of  the  solar  spectrum) 
both  of  these  increase  in  the  same  direction.  So  the  blue  and  violet  rays  have 
only  a  comparatively  slight  effect  in  the  decomposition  of  carbon  dioxide,  be- 
cause, even  though  they  are  absorbed  by  chlorophyll,  they  represent  only  a  very 
small  amount  of  energy.0 

The  dependence  of  the  process  of  decomposition  of  carbon  dioxide  upon  the 
energy  of  the  light  rays  was  demonstrated  in  a  still  more  detailed  manner  by 
the  experiments  of  Rikhter.1  Only  light  that  is  absorbed  can  decompose 
carbon  dioxide,  and  those  wave-lengths  of  the  absorbed  light  are  most  effective 
which  furnish  the  greatest  amount  of  heat  energy.  Rikhter  used  solutions  of 
potassium  dichormate,  ammoniacal  copper  oxide  and  potassium  permanganate 
as  light  filters.  The  plant  received  the  following  relative  amounts  of  light  when 
placed  behind  the  various  filters: 

Potassium  Dichro-    Ammoniacal  Copper   Potassium  Perman- 
Water  mate  Solution  Oxide  Solution  ganate  Solution 

1000  491  *77  233° 

100  3&  47-5 

The  corresponding  relative  rates  of  carbon  dioxide  decomposition  behind  the 
same  light  screens  proved  to  be,  on  the  average,  as  follows: 

Potassium  Dichro-    Ammoniacal  Copper    Potassium  Perman- 
Water  mate  Solution  Oxide  Solution  ganate  Solution 

1000  494  168.0  249 

100  34-4  48 

The  numbers  in  the  two  series  agree  so  closely  as  to  suggest  that  the  amount 
of  photosynthetic  work  accomplished  by  a  ray  of  light  is  proportional  to  the 
amount  of  energy  absorbed  by  the  leaf,  and  is  independent  of  the  wave  length 
of  the  ray  and  of  its  position  in  the  spectrum.2 

1  Richter,  Andre,  Etude  sur  la  photosynthese,  et  sur  1'absorption  par  la  feuille  verte  des  rayons  de 
differentes  longueurs  d'onde.     Rev.   gen.  bot.    14:    151-169.     211-218.      1902.     Kohl,   1897.     [See  p.  5. 

note  1.] 

2  See  also:  Kniep,  H.,  and  Minder,  F.,  Ueber  den  Einfluss  verschiedenfarbigen  Lichtes  auf  die  Koblen- 
saureassimilation.  Zeitsch.  Bot.  1  :  619-650.  1909.  [Puriewitsch,  K.,  Untersuchungen  iiber  Photosyn- 
these.    Jahrb.  wiss.  Bot.  53:  210-254.     I9I3-1 

0  These  statements  apply  to  leaves  and  should  not  be  interpreted  as  necessarily  applying 
to  chlorophyll,  for  leaves  contain  carotin,  etc.,  which  surely  affect  their  power  to  absorb 
radiation.  Some  referencess  on  sunlight  have  been  given  in  note  1,  p.  22.  See  also: 
Iwanowski,  D.,  Ein  Beitrag  zur  physiologischen  Theorie  des  Chlorophylls.  Ber.  Deutsch. 
Bot.  Ges.     32:433-447-     1914-— Ed. 


26  PHYSIOLOGY    OF    NUTRITION 

Carbon  dioxide  is  thus  seen  to  be  decomposed  most  rapidly  in  green  plants  by 
the  light  rays  between  lines  B  and  C.  But  when  other  pigments  besides  chloro- 
phyll are  present,  the  maximum  of  this  decomposition  may  fall  in  another  part 
of  the  spectrum.1  In  the  Cyanophyceae  the  maxumim  occurs  at  D;  the  brown 
algae  show  a  maximum  between  D  and  E,  although  the  decomposition  between 
B  and  C  is  here  almost  as  great;  finally,  the  red  algae  have  a  maximum  between 
D  and  E  also,  but  the  decomposition  between  B  and  C  is  here  very  weak. 
These  facts  are  in  agreement  with  the  distribution  of  the  various  algae,  accord- 
ing to  depth,  in  the  ocean;  while  the  surface  layer  of  water  is  mainly  inhabited 
by  green  algae,  the  red  forms  are  found  at  very  great  depths.  Spectroscopic 
investigations  have  shown  that  red  light,  which  is  essential  to  green  algae,  is 
quickly  absorbed  by  water  and  that  this  light  is  entirely  absent  at  no  great 
distance  below  the  surface.  On  the  other  hand,  the  green  and  blue  rays,  which 
are  absorbed  by  the  red  algae,  attain  great  depths. 

According  to  Engelmann,2  plants  that  contain  no  chlorophyll  may  also 
decompose  carbon  dioxide,  provided  they  contain  another  pigment;  as,  for  in- 
stance, the  purple  bacteria. p 

Engelmann's  theory  of  complementary  pigments  found  confirmation  in  the 
interesting  researches  of  Gaidukov3  upon  the  influence  of  colored  light  upon 
the  color  of  Oscillaria.  This  alga  tends  to  assume  the  color  complementary  to 
that  of  the  light  acting  upon  it,  and  the  longer  the  organism  remains  in  the 
colored  light  the  more  pronounced  is  the  response.  The  following  kinds  of 
illumination  produced  the  following  colorations  in  the  organism. 

Color  of  Light  Color  of  Alga 

Red Green 

Brownish-yellow Blue-green 

Green Reddish 

Blue Brownish-yellow 

The  principle  illustrated  by  this  phenomenon  was  designated  by  Gaidukov  as 
the  law  of  complementary  chromatic  adaptation. 

The  amount  of  light6  necessary  for  the  decomposition  of  carbon  dioxide  is 

1  Engelmann,  Th.  W.,  Farbe  und  Assimilation.     Bot.  Zeitg.  41  :  1-13.  17-29.     1883. 

-Engelmann,  Th.  W.,  Die  Purpurbacterien  und  ihre  Beziehungen  zum  Licht.  Bot.  Zeitg.  46:  661-669, 
677-689,  693-710,  709-720.     1888. 

3  Gaidukov,  N.,  Ueber  den  Einfluss  farbigen  Lichts  auf  die  Farbung  lebender  Oscillarien.  Abh.  K. 
Preuss.  Akad.  Wiss.     Berlin,  1902.     Anhang,  Phys.  Abh.  V.,  p.  1-36. 

*  Kreusler,  U.,  Ueber  eine  Methode  zur  Beotachtung  der  Assimilation  und  Athmung  der  Pflanzen  und 
iiber  einige  diese  Vorgange  beeinflussende  Momente.  Landw.  Jahrb.  14:  913-065.  1885.  Timriazeff, 
C,  Sur  le  rapport  entre  l'intensit6  des  radiations  solaires  et  la  decomposition  de  l'acide  carbonique  par  les 
vegetaux.  Compt.  rend.  Paris  109:  370-382.  1889.  Pantanelli,  Enrico,  Abhangigkeit  der  Sauerstoff- 
ausscheidung  belichteter  Pflanzen  von  ausseren  Bedingungen.  Jahrb.  wiss.  Bot.  39:  167-228.  1904. 
Lubimenko,  W.,  Sur  la  sensibility  de  1'  appareil  chlorophyllien  des  plantes  ombrophiles  et  ombrophobes. 
Rev.  g6n.  Bot.  17:  381-415.  1915.  Idem,  concentration  du  pigment  vert  et  l'assimilation  chlorophyl- 
lienne.  Ibid.  20:  162-177,  217-238,  253-267;  285-297.  1908.  Idem,  Production  de  la  substance  seche 
et  de  la  chlorophylle  chez  les  vegfitaux  superieurs  aux  differentes  intensites  lumineuses.  Ann.  sci.  nat. 
Bot.  IX,  7:  321-415.      1908. 

p  But  Molisch's  studies  indicate  that  the  purple  bacteria  are  not  capable  of  the  photo- 
synthesis of  carbohydrates  from  carbon  dioxide  and  water.  See:  Molisch,  Hans,  Die  Purpur- 
bakterien  nach  neuen  Untersuchungen,  eine  mikrobiologische  Studie.  92  p.  ]ena,  1907. 
(A  misstatement  occurred  here  in  the  first  printing.) — Ed. 


ASSIMILATION    OF    CARBON 


27 


closely  related  to  the  individual  properties  of  the  plant,  some  forms  needing 
more  and  other  less  light.  Trees  were  long  ago  differentiated  by  students  of 
forestry  into  two  types,  heliophobous  (shade  plants)  and  heliophilous  (non-shade 
plants);  among  the  first  are  included,  for  example,  Abies  (fir),  Taxus  (yew), 
Fagus  (beech),  Tilia  (linden);  among  the  latter,  Pinus  (pine),  Larix  (larch), 
Betula  (birch),  Robina  (locust). 

Schistostega  osmundacea,  a  moss  that  grows  in  dark  caves,  may  be  mentioned 
as  an  example  of  plants  that  can  thrive  in  extremely  weak  light.  Its  protonema 
has  a  very  peculiar  structure  (Fig.  16),  and,  although  existing  in  semi-darkness, 
it  appears  emerald  green.  Single  filaments  of  the  protonema,  as  they  grow 
upward,  each  form  a  plate  of  cells  lying  at  right  angles  to  the  direction  of  the 
impinging  light.  Each  cell  of  this  plate  has  the  form  of  a  lens  and  the  chloro- 
plasts  lie  in  the  prolonged  basal  region.  Acting  like  biconvex  lenses,  these 
cells  concentrate  the  light  of  the  half-dark  cave  sufficiently  to  allow  carbon 


.4  B 

Pig.  16. — Schistostega  osmundacea:  A,  protonema;  B,  diagram  representing  the  path  taken  by 
rays  of  light  as  they  enter  and  leave  the  cells  of  the  protonema. 

dioxide  decomposition  by  the  chloroplasts.     A  part  of  the  light  is  reflected, 
thus  rendering  the  protonema  luminous. 

In  general,  plants  are  adapted  to  the  minimum  of  available  light  (Wiesner, 
Liubimenko).  In  heliophilous  plants  (which  thrive  best  in  bright  sunshine) 
the  rate  of  carbon  dioxide  decomposition  increases  continuously  with  increase 
in  light  intensity;5  on  the  other  hand,  for  heliophobous  plants  (which  thrive 
in  shade  or  in  regions  of  low  light  intensity)  there  exists  an  optimum  light 
intensity,  and  any  increase  beyond  this  optimum  results  in  a  decrease  in  the 
amount  of  carbon  dioxide  decomposed.  This  difference  is  related  to  the 
different  amounts  of  chlorophyll  contained  in  the  two  kinds  of  plants.  Liubi- 
menko was  able  to  show  that  heliophobous  plants  are  richer  in  chlorophyll 
than  are  heliophilous  ones.     Within  limits,  the  greater  the  amount  of  light 

« It  is  not  to  be  understood  that  there  are  no  optimum  light  intensities  for  carbon-dioxide 
decomposition  in  plants  that  grow  best  in  bright  sunshine,  only  that  such  optima  are  markedly 
higher  than  those  for  plants  that  grow  best  in  shade.— Ed. 


28 


PHYSIOLOGY    OF    NUTRITION 


and  the  higher  the  temperature,  the  smaller  is  the  amount  of  chlorophyll  formed 
by  the  plant. 

§6.  Products  of  Photosynthesis.1 — The  simplest  equation  that  may  repre- 
sent the  exchange  of  gases  in  photosynthesis  is  CO"  =  C  +  Oo.  The  carbon  is 
retained  by  the  plant,  combined  with  other  elements  in  the  form  of  organic  sub- 
stances. The  question  now  arises  as  to  what  are  to  be 
considered  as  the  first  products  of  photosynthesis.  The 
investigations  of  Sachs2  showed  that  the  first  visible  product 
is  starch.  If  leaves  are  kept  for  several  days  in  darkness 
the  starch  completely  disappears  from  the  chlorophyll 
bodies,  and  if  the  leaves  are  then  returned  to  light  starch 
soon  appears  again.  Small  traces  of  starch  may  be  recog- 
nized by  the  method  of  Bohm,  whereby  leaves  are  first 
decolorized  by  alcohol  and  then  treated  with  caustic 
potash  and  iodine  solution;  the  starch  grains,  greatly  swollen 
by  potassium  hydroxide,  are  stained  by  iodine  and  thus 
become  visible.  If  a  part  of  the  leaf  is  covered  with  tinfoil 
before  it  is  exposed  to  light,  and  if,  after  the  exposure,  the 
leaf  is  decolorized  with  alcohol  and  then  treated  with 
iodine,  the  portion  that  was  shaded  becomes  yellowish 
brown,  while  the  rest  of  the  leaf  is  blue  or  black,  accord- 
ing to  the  amount  of  starch  present  (Fig.  17).  The 
experiment  becomes  particularly  striking  if  the  whole  leaf 
is  covered  with  a  piece  of  tinfoil,  or  cardboard,  from  which 
the  letters  of  the  word  starch,  etc.,  have  been  cut  out  as  in  a  stencil;  after 
the  treatment  described  above,  the  letters  stand  out  blue  against  a  brown 
background/ 

According  to  Famintsyn,3  algae  may  be  very  satisfactorily  employed  in  this 
connection;  the  presence  of  starch  may  be  shown  after  only  half  an  hour's 
illumination  from  a  bright  lamp.  According  to  Kraus,4  algae  may  form  starch 
in  sunlight  within  a  period  of  five  minutes.     As  Godlewski5  has  shown,  starch 

1  Brown,  H.  T.,  and  Morris,  G.  H.,  A  contribution  to  the  chemistry  and  physiology  of  foliage  leaves. 
Jour.  Chem.  Soc.  London  63:  604-677.     1893. 

2  Sachs,  J.,  Ueber  den  Einfluss  des  Lichtes  auf  die  Bildung  des  Amylums  in  den  Chlorophyllkornern. 
Bot.  Zeitg.  20:  365—373.  1862.  Idem,  Ueber  die  Auflosung  und  Wiederbildung  des  Amylums  in  den 
Chlorophyllkornern  bei  wechselnder  Beleuchtung.     Ibid.  22:  280-294.     1864. 

3  [Famintzin,  A.,  Die  Wirkung  des  Lichtes  auf  Algen  und  einige  andere  ihnen  nahe  venvandte  Organismen. 
Jahrb.  wiss.  Bot.  6:  1-44.     1867.     See  P.  34.] 

4  [Kraus,  Gregor,  Einige  Beobachtungen  uber  den  Einfluss  des  Lichts  und  der  Warme  aud  die  Starkeer- 
zeugung  im  Chlorophyll.     Jahrb.  wiss  Bot.  7:  511-531.     1868.] 

6  Godlewski,  Emil,  Abhangigkeit  der  Starkebildung  in  den  Chlorophyllkornern  von  dem  Kohlensaurege- 
halt  der  Luft.     Flora,  n.  R.  31:  378-383.     1873. 

T  The  experiment  should  be  performed  in  such  manner  that  access  of  the  carbon  dioxide  of 
the  air  to  the  stomata  is  clearly  not  hindered;  otherwise  the  conclusion  given  is  not  logically 
substantiated.  (See  Ganong,  W.  F.,  A  laboratory  course  in  plant  physiology.  2  ed.,  New- 
York,  1908.  P.  86-90.)  It  is  usually  best  to  transfer  the  decolorized  leaves  from 
alcohol  to  water,  then  to  an  aqueous  solution  of  potassium  hydroxide,  after  which  an  aqueous 
solution  of  potassium  iodide  and  iodine  is  added  to  bring  out  the  color  reaction.  The  iodine 
solution  may  be  prepared  by  dissolving  5  g.  of  the  iodide  in  water,  then  dissolving  1  g.  of 
iodine  in  this,  and  diluting  the  resulting  double  solution  to  a  volume  of  1000  cc.  or  less. — Ed. 


Fig.  17. — Accu- 
mulation of  starch 
in  the  illuminated 
portion  of  a  leaf. 
The  light-colored 
portion  was  shaded 
by  tinfoil  and  the 
starch  has  been 
stained  by  iodine. 


ASSIMILATION    OF    CARBOX  20 

can  be  formed  in  light  only  in  the  presence  of  carbon  dioxide.  In  a  closed 
chamber,  illuminated  but  free  from  this  gas,  no  starch  was  formed;  indeed, 
if  starch  had  been  originally  present  its  amount  decreased  under  these  con- 
ditions. The  chloroplasts  of  some  plants  do  not  form  starch  at  all,  as  is  the 
case  with  laves  of  Allium  cepa  (onion),  A.fistulosum,  Asphodelns  luteus,  Orchis 
militaris,  and  Lactuca  sativa  (lettuce),  but  in  all  these  instances  glucose  is 
formed  instead  of  starch. 

According  to  whether  starch  ((C6Hio05)n)  or  glucose  (C6Hi206)  is  con- 
sidered as  the  first  product  of  photosynthesis,  the  chemical  equation  represent- 
ing the  process  may  take  one  or  the  other  of  the  two  forms  given  below: 

(1)  6  C02  +  5  H20  =  C6H10O5  +  6  02. 

(2)  6  COo  +  6  H20  =  C6H1206  +  6  02. 

Timiriazev1  showed  by  direct  experiment  that  the  formation  of  starch  in  light 
is  brought  about  by  the  same  rays  of  the  spectrum  as  are  effective  in  the  decom- 
position of  carbon  dioxide.  By  means  of  a  heliostat,  a  spectrum  was  thrown 
upon  a  leaf  of  a  plant  that  had  been  previously  exposed  to  darkness  so  as  to 
free  the  leaves  of  starch;  two  strips  of  paper  were  fastened  across  the  leaf  with 
the  spectrum  falling  between  them,  and  upon  these  strips  were  recorded  the 
positions  of  the  Fraunhofer  lines  in  the  spectrum.  At  the  end  of  the  experi- 
ment, after  the  leaf  had  been  decolorized  by  alcohol  and  stained  with  iodine,  it 
became  evident  that  starch  formation  had  occurred  exactly  in  the  regions  cor- 
responding to  the  absorption  bands  of  chlorophyll.  In  such  an  experiment  the 
band  between  lines  B  and  C  is  especially  pronounced,  and  a  fainter  iodine- 
starch  color  is  noticeable  in  the  orange-yellow  region,  this  coloration  gradually 
decreasing  in  intensity  and  ceasing  not  far  beyond  the  D  line.  Thus  starch 
is  produced  by  those  wave-lengths  of  light  that  cause  the  decomposition  of 
carbon  dioxide,  the  rays  between  B  and  C  being  most  effective  in  both  cases. 

Briosi2  was  unable  to  find  starch  in  the  leaves  of  Musa  (banana)  and  Strelitzia, 
but  found  oil  instead,  and  expressed  the  opinion  that  the  latter  was  the  first 
product  of  photosynthesis  in  these  plants.  Holle3  and  Godlewski4  were  able 
to  prove,  however,  that  this  supposition  is  untenable. 

Baeyer5  advanced  the  hypothesis  that  formaldehyde  is  really  the  first  prod- 
uct of  photosynthesis,  and  that  carbohydrates  arise  from  this  by  progressive 
condensation  or  polymerization.  The  formation  of  formaldehyde  thus  supposed 
is  represented  by  the  equation,  C02  +  H20  =  CH20  +  0>.  Baeyer  based  his 
supposition  upon  a  discovery  by  Butlerow6  that  oxymethylene  (C3H603)  is  con- 

1  Timiriazeff,  C,  Enregistrement  photographique  de  la  fonction  chlorophyllienne  par  la  plante  vivante. 
Compt.  rend.  Paris  no:  1346-1347.      1890. 

-  [Briosi,  Giovani,  Ueber  normale  Bildung  von  Fettartiger  Substanz  im  Chlorophyll.  Bot.  Zeitg.  31 : 
520-533,  545-550.     1873-] 

3  Holle,  H.  G.,  Ueber  die  Assimilationsthatigkeit  von  Strelitzia  regina.  Flora,  n.  R.  35 :  113-120,  154- 
160.  161-168,  184-192.     1877. 

'  Godlewski,  Emil,  1st  das  Assimilationsprodukt  der  Musaceen  Oel  oder  Starke?  Flora,  n.  R.  35 :  215- 
220.     1877. 

5  Baeyer,  Adolf,  Ueber  die  Wasserentziehung  und  ihre  Bedeutung  fur  das  Pflanzenleben  und  die  Gah- 
rung.     Ber.  Deutsch.  Chem.  Ges.  3:  63-75-     1870. 

«  [Butlerow,  A.,  Bildung  einiger  Zuckerarten  durch  Synthese.  Liebig's  Ann.  Chem.  u.  Pharm.  120:  295- 
298.     1861.     Idem,  Formation  synthetique  d'une  substance  sucree.  Compt.  rend.  Paris  53:  145-147.      1861.] 


30  PHYSIOLOGY    OF    NUTRITION 

verted  into  a  sugar-like  substance  in  the  presence  of  calcium  and  barium 
hydroxides. 

Reinke  is  of  the  opinion  that  the  hydrate  of  carbonic  acid  and  not  the 
anhydride,  is  decomposed  in  the  light,  as  indicated  by  the  equation,  H2C03  = 
CH20  +  O2.  The  same  author1  was  successful  in  showing  that  substances 
possessing  aldehyde  characters  generally  occur  in  green  plants,  and  Curtius 
and  Reinke2  succeeded  in  isolating  a  material  of  this  sort  and  in  identifying  it 
chemically.  Curtius  and  Franzen3  isolated  a-/3-hexylene-aldehyde  from  the 
leaves  of  Carpinus  (horn-beam).  This  aldehyde  shows  the  same  carbon 
skeleton  as  does  glucose,  as  becomes  evident  from  a  comparison  of  their  struc- 
tural formulae: 

CH3— CH2— CH2— CH— CH— Cf       (a-0-Hexylene-aldehyde) 

\H 

CHo— CH— CH— CH— CH— Cf       (d-glucose). 
I  I  I  I  I  XH 

OH      OH    OH    OH    OH 
Pollacci4  found,  furthermore,  that  the  green  parts  of  plants  gave  a  positive 
aldehyde  reaction  with  Schiff 's  reagent  only  if  they  had  been  previously  exposed 
to  light  and  carbon  dioxide ;  if  the  plants  had  previously  been  deprived  of  both 
light  and  this  gas  they  gave,  as  did  also  fungi,  no  reaction  for  aldehyde.8 

Formaldehyde  can  be  utilized  by  green  plants  in  the  formation  of  carbohy- 
drates, but  none  is  absorbed  in  darkness.5 

Walther  Lob's6  interesting  researches  have  furnished  experimental  evidence 
in  favor  of  Baeyer's  hypothesis.  He  used  a  silent  electric  discharge  as  source 
of  energy,  instead  of  sunlight,  and  established  the  following  principal  reactions 
between  carbon  dioxide  and  water,  etc. 

1.  2  C02  =  2  CO  +  02 

2.  CO  +  H20  =  C02  +  H2 

3.  H2  +  CO  =  H2CO 

4.  CO  +  H20  =  HCOOH 

5.    3  02   =    20d 

6.  2  H2  +  2O3  =  2  H»02  +  02 

1  Reinke,  J.,  Studien  uber  das  Protoplasma.  I— III.  Untersuch.  Bot.  Lab.  Gottingen  2  :  1-202.  i88r. 
Idem,  Studien  uber  das  Protoplasma.     2te  Folge.     Ibid.  3:  1-76.     1883. 

2  Curtius,  Theodor,  and  Reinke,  J.,  Die  fluchtige,  reducirende  Substanz  der  griinen  Pflanzentheile.  Ber. 
Deutsch.  Bot.  Ges.  15:  201—210.     1897. 

3  Curtius,  Theodor,  and  Franzen,  Hartwig,  Aldehyde  aus  grunen  Pflanzenteilen.  I.  Mitteilung.  Ueber 
a-0-Hexylenaldehyd.  Sitzungsber.  (math.-naturw.  Kl.)  Heidelberg.  Akad.  Wiss.  Jahrgang  1910,  Abhandl. 
20.      13  p.      IQIO. 

«  Pollacci,  Gino,  Intorno  all'  assimilazione  clorofilliana  delle  plante.  Atti  1st.  Bot.  Univ.  Pavia  //, 
7:  1-21.  1902.  On  the  synthesis  of  carbohydrates  in  chloroplasts  see:  Fischer,  Emil,  Synthesen  in  der 
Zuckergruppe.  II.     Ber.  Deutsch.  Chem.  Ges.  27111 :  3189-3232.     1894.     P«  323°- 

5  Grafe,  Viktor,  Untersuchungen  uber  das  Verhalten  gruner  Pflanzen  zu  gasformigen  Formaldehyd.  II. 
Ber.  Deutsch.  Bot.  Ges.  29:  10-26.  191 1.  Idem,  Die  biochemische  Seite  der  Kohlensaure-Assimila- 
tion  durch  die  grune  Pflanze.  Biochem.  Zeitsch.  32:  114-129.  1911.  [Baker,  Sarah  M.,  Quantitative 
experiments  on  the  effect  of  formaldehyde  upon  living  plants.     Ann.  bot.  27:  411-442.     1913.] 

6  Lob,  Walther,  Zur  Kenntnis  der  Assimilation  der  Kohlensaure.     Landw.  Jahrb.  35 :  541-378.     1906. 

*  On  reactions  for  identifying  formaldehyde  in  plant  parts,  see  Haas  and  Hill,  1921.  [See 
note  3,  p.  6.] — Ed. 


ASSIMILATION    OF    CARBON  3 1 

The  formation  of  formaldehyde  was  limited  by  the  last  three  (secondary) 
reactions;  hydrogen  combined  more  easily  with  oxygen,  to  form  hydrogen 
peroxide,  than  with  carbon  monoxide.  To  obtain  formaldehyde  in  greater 
quantity  Lob  added  a  reducing  agent  (salicylic  aldehyde,  pyrogallol  or 
chlorophyll.  Glycolic  aldehyde  (which  represents  the  simplest  sugar),  as  well 
as  formic  acid  and  formaldehyde,  arises  from  the  action  of  the  silent  discharge 
upon  carbon  monoxide,  water,  and  hydrogen;  2(H2  +  CO)  =  CH2OH  — 
CHO  (glycolic  aldehyde).  By  the  concentration  of  its  solution  in  vacuo  this 
substance  is  readily  transformed  into  a  tetrose  or  hexose.1 

Stoklasa  and  Zdobnicky2  found  that  formaldehyde  was  formed  by  the  action 
of  ultra-violet  light  upon  water  vapor  and  carbon  dioxide  in  the  presence  of 
potassium  hydroxide,  but  no  carbohydrates  were  thus  produced.  Sugar  was 
formed,  however,  under  these  same  conditions,  when  hydrogen  was  present  in 
the  nascent  state.' 

Sorbose  is  formed  by  the  action  of  light  upon  a  mixture  of  formaldehyde 
and  oxalic  acid.3 

Bonnier  and  Mangin,  as  has  already  been  mentioned  (see  page  4),  have 

shown  that  if  the  interchange  of  gases  accompanying  the  process  of  photosyn- 

C02.    ,  , 

thesis  is  determined  independently  of  respiration,  the  ratio  -q-  is  found  to  be 

somewhat  less  than  unity.  From  this  we  must  suppose  that  substances  other 
than  carbohydrates  and  less  easily  oxidized  than  these,  are  formed  in  the  leaves 
under  the  influence  of  sunlight.  The  supposition  that  proteins  also  arise  in  the 
process  of  photosynthesis  has  been  frequently  advanced.  This  is  supported 
by  the  quantitative  researches  of  Sapozhnikov,4  in  which  he  established  the 
fact  that  an  increase  in  protein  occurs  parallel  with  the  accumulation  of  carbo- 
hydrates in  light.  Posternak5  is  of  the  opinion  that  oxymethyl-phosphoric 
acid  is  also  formed  in  leaves  in  the  presence  of  light. 

'Bach,  A.,   Sur  1'evolution   biochimique  du  carbone.     Arch.  sci.  phys.  et  nat.  5:  401-415.  520-535 
1898.     This  deals  with  the  theory  of  photosynthesis. 

2  Stoklasa,  J.,  and  Zdobnicky,  W.,  Photochemische  Synthese  der  Kohlenhydrate  aus  Kohlensaurean- 
hydrid  und  Wasserstoff  in  Abwesenheit  von  Chlorophyll.     Biochem.  Zeitsch.  30:  433-456.     1011. 

'Inghilleri,  Giuseppe,  Photochemische  Synthese  der  Kohlenhydrate.  I.  Mitteilung.  Bildung  von 
Sorbose.     Zeitsch.  physiol.  Chem.  71 :  105-109.     1911. 

*  Saposchnikoff,  W.,  Bildung  und  Wanderung  der  Kohlenhydrate  in  den  Laubblattem.  Ber.  Deutsch. 
Bot.  Ges.  8:  233-242.  1890.  Idem,  Beitrag  zur  Kenntniss  der  Grenzen  der  Anhaufung  von  Kohlenhy- 
draten  in  den  Blattern.  Ibid.  11:  391-393.  1893-  Idem,  Eiweissstoffe  und  Kohlenhydrate  der  grunen 
Blatter  als  Assimilations-producte.  61  p.  Tomsk,  1894-  [Russian.]  [Rev.  by  Rothert  in:  Bot.  Centralbl. 
63:  246-251.     1895. 

s  Posternak,  S.,  Contribution  a  l'6tude  chimique  de  l'assimilation  chlorophyllienne.  Sur  le  premier 
produit  d  organization  de  l'acide  phosphorique  dans  les  plantes  a  chlorophylle  avec  quelques  remarques  sur 
le  r&le  physiologique  de  l'inosite.     Rev.  gin.  bot.  12:  5-24.  65-73-     1900. 

(  Further,  on  the  artificial  formation  of  formaldehyde,  etc.,  from  carbon  dioxide  and  water, 
see:  Berthelot,  D.,  and  Gaudichon,  H.,  Synthese  photochimique  des  hydrates  de  carbone  aux 
depens  des  elements  de  l'anhydride  carbonique  et  de  la  vapeur  de  l'eau,  en  l'absence  de  chloro- 
phylle; synthese  photochimique  des  composes  quartenaires.  Compt.  rend.  Paris  150:  1690- 
1693.  1910.  For  a  review  of  this  general  subject,  see:  Spoehr,  H.  A.,  Theories  of  photosyn- 
thesis. Plant  world  19:  1-16.  1916.  It  should  be  remembered  that  the  reactions  that  take 
place  in  leaves  may  not  be  the  same  as  those  studied  in  vitro.  Very  little  experimental  work 
has  been  done  on  the  photochemical  changes  to  which  chlorophyll  itself  is  subject. — Ed. 


$2  PHYSIOLOGY   OF   NUTRITION 

According  to  Krasheninnikov1  a  definite  relation  holds  between  the  amount 
of  carbon  dioxide  decomposed  and  the  concomitant  increase  in  dry  weight,  as  is 
evident  from  the  following  average  values:  for  a  square  meter  of  leaf  surface  the 
amount  of  carbon  dioxide  decomposed  was  2286  cc.  or  4.48  g.,  while  the  corre- 
sponding increase  in  dry  weight  was  2.94  g.  The  increase  in  dry  weight  for 
each  weight  unit  of  carbon  dioxide  decomposed  was  found  to  have  the  values 
given  below,  for  the  different  plant  forms  considered. 

Bamboo o .  60 

Cherry-laurel o .  60 

Sugar  cane 0.67 

Linden 0.74 

Tobacco 0.68 

It  is  seen  that  this  ratio  appears  to  be  fairly  constant.  The  formation  of  a 
carbohydrate  with  the  composition  C12H22O11  (like  cane  sugar)  would  give 
this  ratio  a  value  of  0.64. 

Investigations  upon  the  first  products  of  photosynthesis  agree  with  plant 
analyses  in  showing  that  an  assimilation  of  water  occurs  simultaneously  with 
that  of  carbon  dioxide.  In  every  green  plant  the  formation  of  organic  substance 
in  sunlight  is  accompanied  by  assimilation  of  carbon,  hydrogen  and  oxygen. 
The  bulk  of  the  dry  weight  of  the  plant  is  due  to  these  three  elements;  this  dry 
weight  is  made  up  of  about  45  per  cent,  carbon,  42  per  cent,  oxygen,  6.5  per  cent, 
hydrogen,  1.5  per  cent,  nitrogen,  and  5  per  cent,  mineral  constituents.  Thus 
plants  obtain  more  than  90  per  cent,  of  their  dry  weight  from  the  carbon  dioxide 
of  the  air  and  the  water  of  the  soil. 

§7.  Assimilation  of  Solar  Radiant  Energy  by  Green  Plants. — We  have 

already  seen  that  green  plants  are  able,  with  absorption  of  sunlight,  to  build  up 

combustible  organic  compounds  out  of  non-combustible  inorganic  substances. 

The  chloroplasts  of  green  plants  furnish  conditions  for  this  process.     Animal 

heat  and  movement,  the  heat  of  fuels,  the  work  of  steam  engines,  are  all  due  to 

the  freeing  of  the  radiant  energy  of  the  sun  which  was  previously  fixed  by  the 

chloroplasts. 

Julius  Robert  Mayer  stated  very  clearly  the  role  of  green  plants  when  he 

said: 

Nature  has  set  for  herself  the  task  of  seizing  the  sunlight  in  its  flight,  as  it  streams  upon  the 
earth,  and  of  accumulating  the  most  swiftly  moving  of  all  forms  of  energy  by  transforming  it 
into  a  potential  state.  To  accomplish  this  purpose  she  has  covered  the  surface  of  the  earth 
with  living  organisms  that  absorb  sunlight  into  themselves  and  thus  generate  a  permanent 
store  of  potential  chemical  energy.  These  organisms  are  plants,  and  the  plant  world  forms  a 
reservoir  in  which  the  fleeting  rays  of  light  are  caught  and  cleverly  hoarded  for  future  use.2 

The  following  interesting  anecdote  is  taken  from  the  biography  of  the  engi- 
neer Stephenson,  and  shows  that  he  also  was  well  acquainted  with  this  role 
played  by  plants. 

On  Sunday  as  people  were  returning  from  church,  with  Stephenson  and  Buckland  among 

1  Krascheninnikoff,  Th.,  Ansammlung  der  Sonnenengergie  in  den  Pflanzen.     Moskow,  1901.     [Russian. ]• 

2  Mayer,  Julius  Robert,  Die  Mechanik  der  Warme.  P.  34.  Leipzig,  1911.  (Ostwald's  Klassiker  no. 
180.) 


ASSIMILATION    OF    CARBOX  33 

them,  the  whole  company  stopped  upon  the  terrace  beside  Drayton  Castle  to  watch  a  railway 
train  as  it  vanished  rapidly  in  the  distance,  with  a  trail  of  white  smoke  behind  it. 

"Well,  Buckland,"  said  Stephenson  as  he  turned  to  the  famous  geologist,  "Answer  me  a 
question,  not  a  very  easy  one,  perhaps.  Can  you  tell  me  what  sort  of  force  it  is  that  drives 
yonder  train  along?'' 

"Well,"  answered  the  geologist,  "I  should  think  that  the  force  was  one  of  your  great 
engines." 

"Yes  but  what  moves  the  engine?" 

'Why,  one  of  your  Newcastle  engineers,  of  course." 

"No,  sunlight." 

"How  can  that  be?"  asked  the  doctor. 

"I  assure  you  it  is  nothing  else,"  replied  the  engineer.  "It  is  light  that  has  lain  stored  in 
the  earth  for  many  thousands  of  years;  the  light  absorbed  by  the  plant  during  its  growth  is 
essential  for  the  condensation  of  carbon,  and  this  light,  which  has  been  buried  in  the  coal 
measures  for  so  many  years,  is  now  unearthed  and,  being  freed  again  as  in  this  locomotive, 
serves  great  human  ends."1 

Along  with  the  accumulation  of  starch  there  occurs  also  a  storage  of  poten- 
tial energy  in  the  plant.  Krasheninnikov2  was  able  to  demonstrate  this  rela- 
tion by  direct  experiment.  Half-leaves  were  removed  from  the  plant  and  their 
areas  were  measured,  after  which  they  were  dried  and  burned,  to  determine  the 
heat  of  combustion  of  their  dry  substance.  The  remaining  half-leaves,  also 
removed  from  the  plant  but  still  alive,  were  exposed  to  light  for  a  time,  and  the 
amount  of  carbon  dioxide  which  they  decomposed  was  measured.  They  were 
then  dried  and  their  heat  of  combustion  was  also  determined.  Below  are  given 
the  average  values  of  all  the  determinations,  calculated  for  an  area  of  1  sq.  m. 
of  leaf  surface  exposed  to  the  light. 

Increase  in  dry  weight 3 .  51  g. 

Increase  in  carbohydrates 2 .46  g. 

Increase  in  carbon 1 .  58  g. 

Increase  in  heat  of  combustion i5>35°  g.-cal. 

Amount  of  carbon  dioxide  decomposed 5 .  626  g. 

From  the  data  of  this  experiment  Krasheninnikov  calculated  that  there  was 
an  increase  of  from  2.2  to.  3.6.  g.-cal.  for  each  gram  of  carbon  dioxide  decom- 
posed." 

It  is  also  desirable  to  know  what  proportion  of  the  radiant  energy  falling 
upon  the  leaf  is  assimilated.  The  first  calculation  bearing  upon  this  question 
was  made  by  Becquerel,3  with  the  following  results,  which  represent  the  yearly 
amounts  of  assimilation  for  three  different  types  of  vegetation,  per  hectare 
(2.5  acres). 

1  Mayer,  Adolf  Eduard,  Lehrbuch  der  Agrikulturchemie.   5   Aufl.     Heidelberg,    1001-1902.     P.   35. 

;  Krascheninnikoff,  1001.     [See  note  1,  p.  32.] 

3  Becquerel,  Alexandre  E.,  La  lumiere,  ses  causes  et  ses  effects.     Paris,  1 867-1 868. 

u  On  alterations  in  the  areas  of  leaves  when  the  latter  are  transferred  from  shade  to  sun- 
light, which  may  possibly  have  some  influence  on  the  magnitudes  of  such  values  as  these, 
see:  Thoday,  D.,  Experimental  researches  on  vegetable  assimilation  and  respiration.  V.  A 
critical  examination  of  Sachs'  method  for  using  increase  of  dry  weight  as  a  measure  of 
carbon  dioxide  assimilation  in  leaves.  Proc.  Roy.  Soc.  London  B82:  1-55.  1909. — Ed. 
3 


34  PHYSIOLOGY    OF    NUTRITION 

Kilograms  of 
Carbon  Assimilated 
Kind  of  Vogetatbon  per  Hectare 

Forest  in  Central  Europe 1800 

Well  fertilized  meadow 3500 

Helianthus  tuberosus  (Jerusalem  artichoke) 6coo 

From  a  series  of  calculations,  Becquerel  came  to  the  conclusion  that,  in  France, 
plants  assimilate  less  than  1  per  cent,  of  the  radiant  energy  that  reaches  them. 
Timiriazev  arrived  at  the  same  result,  and  Brown's1  more  recent  determinations 
give  a  still  smaller  value.  In  the  latter  case  a  Helianthus  leaf  received  on 
a  sunny  day  600,000  g.-cal.  per  square  meter  of  leaf  surface  per  hour. 
In  the  same  time  an  equal  surface  of  leaf  produced  0.8  g.  of  carbohydrates,  for 
the  formation  of  which  3200  g.-cal.  were  necessary.  Thus  the  leaf  accu- 
mulated, by  the  photosynthetic  process,  barely  0.5  per  cent,  of  the  solar  energy 
reaching  it;  viewed  as  a  machine  designed  to  produce  organic  compounds,  its 
efficiency  is  thus  seen  to  be  far  from  high/ 

An  excess  of  light  has  a  retarding  effect  upon  increase  in  dry  weight.  It 
appears  that  different  rays  of  the  spectrum  are  effective  in  different  stages  of 
the  photosynthetic  process.2 

The  importance  of  light  to  plants  is  not  confined  to  the  photosynthesis  of 
carbohydrate  from  carbon  dioxide  and  water;  light  is  necessary  for  very  many 
kinds  of  chemical  reactions  taking  place  in  plants.  Among  the  investigations 
that  already  testify  to  this  are  those  upon  the  influence  of  light  in  protein 
formation.  Numerous  other  reactions  that  are  influenced  by  light  and  that 
are  purely  chemical  in  nature  furnish  additional  evidence  upon  this  point. 
Ciamician  and  Silber3  were  able  to  establish  the  fact  that  very  many  oxidations, 
reductions,  hydrolyses,  polymerizations  and  condensations  are  effected  by  light; 
such  changes  may  progress  very  rapidly  when  an  inorganic  substance  is  involved.4 

§8.  Influence  of  External  and  Internal  Conditions  upon  Photosynthesis  — 
One  of  the  most  important  of   the   external   conditions  upon  which  various 
physiological  processes  depend  is  the  temperature  of  the  surroundings.     The 
influence  of  temperature  upon  the  velocity  of  the  greening  process  has  been 
shown  above.     Photosynthesis,  on  the  other  hand,  is  only  very  slightly  affected 

1  Brown,  H.  T.,  Recherches  sur  la  fixation  du  carbone  par  les  feuilles  et  sur  la  diffusion  de  l'acide 
carbonique.  Traduit  librement  de  l'Anglais  par  M.  E.  Demoussy.  Ann.  agron.  27:  428-438.  1901. 
[The  original  paper  is:  Brown,  Horace  T.,  Opening  address  by  the  President  of  Section  B  (Chemistry), 
Brit.  Assoc.  Adv.  Sci.,  Nature  60:  474-483.  1899.  (See  also  correction:  ibid.  60:  544.  1899.)  Also 
published  in:  Rept.  Brit.  Assoc.  Adv.  Sci.  1899:  664-683.  1900.  See  also:  Brown,  H.  T.,  and  Escombe 
F.,  Static  diffusion  of  gases  and  liquids  in  relation  to  the  assimilation  of  carbon  and  translocation  in 
plants.     Phil',  trans.  Roy.  Soc.  London  B193:  223-292.     1900. 1 

2  Liubimenko,  V.  N.,  La  quantite  de  pigment  vert  dans  le  grain  de  chlorophylle  et  l'energie  de  la  photo- 
synthese.  [Abstract  in  French,  p.  263-266;  text  in  Russian.]  Trav.  Soc.  Imp.  Nat.  St.-Petersbourg  Ser. 
///,  Sect.  Bot.  41:  1—266.      1910. 

s  Ciamician,  G.,  Sur  les  actions  chimiques  de  la  lumiere.  Bull.  Soc.  chim.  France  4  (fasc.  is):  i-xxvii. 
1908.     [A  special  appendix  to  this  fasc,  bound  at  end  of  vol.,  separately  paged. 1     [See  also  note  1,  p.  180.] 

*  Neuberg,  Carl,  Chemische  Umwandlungen  durch  Strahlenarten.  I.  Mitteilung.  Katalytische  Reak- 
tionen  des  Sonnenlichtes.  Biochem.  Zeitsch.  13:  305-320.  1908.  Idem,  Ueber  die  Reaktion  der  Gallen- 
sauren  mit  Rhamnose  bzw.  <5-Methyl-furfurol.  Ibid.  14:  349-350.  1908.  Idem,  Bemerkung  iiber  die 
"Glucothionsauren."     Ibid.  16:  25c—  253.     1909.     Idem,  Notiz  iiber  Phytin.     Ibid.  16:  406-410.     1909. 

"  In  such  calculations  as  this  it  is  to  be  noted  that  the  plant  does  not  absorb  nearly  all  the 
energy  reaching  it  and  that  all  the  organic  material  formed  does  not  appear  in  the  final  deter- 
minations.— Ed. 


ASSIMILATION   OF    CARBON  35 

by  temperature.  According  to  the  investigations  of  Kreusler,1  the  decomposi- 
tion of  carbon  dioxide  begins  at  temperatures  almost  as  low  as  the  freezing  point 
and  continues  up  to  5o°C.     His  data  are  presented  below. 

Tempera-         Amount  of   Tempera-         Amount  of  Tempera-         Amount  of 

ture  CO2  De-     ture  C02  De-    ture  CO2  De- 

Deg.  C.  composed    Deg.  C.  composed    Deg.  C.  composed 

2.3 1.0  20.6 2.6  37.3 2.3 

7.5 1.7  25.0 2.9  41.7 2.0 

11. 3 2.4  29.3 2.4  46.6 1.3 

15.8 2.8  33.0 2.4 

If  the  amount  of  carbon  dioxide  decomposed  in  a  unit  of  time  at  2.30  be  repre- 
sented by  unity  it  is  seen  that  this  rate  is  not  yet  equal  to  3  at  250.  Such  a  rise 
of  temperature  increases  the  rate  of  respiration  to  many  times  its  original  value."' 

Great  fluctuations  in  atmospheric  pressure  exert  a  marked  influence  upon 
photosynthesis.2 

The  process  of  photosynthesis  is  dependent  upon  the  amount  of  chlorophyll 
present  in  the  leaves.3  The  anatomical  structure  of  these  organs  is  also  of 
importance,  the  stomata  playing  a  particularly  pronounced  role.      Mangin4 

1  Kreusler,  U.,  Beobachtungen  uber  die  Kohlensaure-Aufnahme  und  -Ausgabe  (Assimilation  und 
Athmung)  der  Pflanzen.  II.  Mittheilung:  Abhangigkeit  vom  Entwicklungszustand — Einfluss  der  Tem- 
peratur.  Landw.  Jahrb.  16  :  711-755.  1887.  [Idem,  same  title.  III.  Mittheilung:  Einfluss  der  Tempera- 
tur;  untere  Grenze  der  Wirkung.  Ibid.  17:  161-175.  1888.  Idem,  Beobachtungen  uber  Assimilation 
und  Athmung  der  Pflanzen.  IV.  Mittheilung:  Verhalten  bei  hoheren  Temperaturen;  Kohlensaure-ausschei- 
dung  seitens  getodterer  Exemplare;  Kohlensaure  Verbrauch,  wenn  Ober-  und  Unterseite  der  Blatter  dem 
Licht  Zugewendet.     Ibid.  19:  649-668.     1890.] 

2  Friedel,  Jean,  L'assimilation  chlorophyllienne  aux  pressions  inferieures  a  la  pression  atmospherique. 
Rev.  gen.  bot.  14:  337-355,  369-390.     1902. 

s  Liubimenko,  1910.     [See  note  2,  p.  34.] 

4  Mangin,  L.,  Sur  le  rdle  des  stomates  dans  l'entree  ou  la  sortie  des  gaz.  Compt.  rend.  Paris  105  : 
879-881.      1887. 

w  But  Gabrielle  Matthaei's  very  careful  studies  (Matthaei,  Gabrielle  L.  C,  Experimental 
researches  on  vegetable  assimilation  and  respiration.  III.  On  the  effect  of  temperature 
on  carbon  dioxid  assimilation.  Phil,  trans.  Roy.  Soc.  London  B197:  47-105.  1905)  show- 
that  the  influence  of  temperature  upon  photosynthesis  in  leaves  of  Primus  laurocerasus 
(cherry-laurel)  is  much  more  pronounced  than  is  indicated  by  Kreusler's  numbers.  Her  re- 
sults are  shown  below,  the  amounts  representing  hourly  rates  per  50  sq.  cm.  of  leaf. 
Temperature,  deg.  C,  -6  8.8  11.4  15  23^7  30.5  37.5  4Q-5  43-Q 
CO-j  assimilated,  g.  0.0002  0.0038  0.0048  0.00700.0102  0.0157  0.0238  0.0149  0.0102 
From  these  data  it  appears  that  the  process  in  question  about  doubles  for  each  increase  in 
temperature  of  io°C,  thus  agreeing  with  a  large  number  of  chemical  reactions.  (Van't  Hoff, 
J.  H.,  Lectures  on  theoretical  and  physical  chemistry,  translated  by  R.  A.  Lehfeldt.  London, 
no  date — author's  preface  dated  1898.  Part  I,  p.  227  et  seq.)  See  also:  Blackman,  F.  F., 
and  Matthaei,  G.  L.  C,  Experimental  researches  on  vegetable  assimilation  and  respira- 
tion. IV.  A  quantitative  study  of  carbon-dioxide  assimilation  and  leaf  temperature  in 
natural  illumination.  Proc.  Roy.  Soc.  London  B76.  402-460.  1905.  Blackman,  F.  F., 
Optima  and  limiting  factors.  Ann.  bot.  19:  281-295.  *9°5-  Idem,  The  metabolism  of  the 
plant  considered  as  a  catalytic  reaction.  Presidential  Address,  Bot.  Sect.  British  Assoc, 
Dublin  meeting,  1908.  Also  published  in:  Science,  n.s.  28:  628-636.  1908.  Two  criticial 
reviews  of  published  data  on  photosynthesis  may  also  be  mentioned  here;  the  first  (Brown, 
W.  H.,  and  Heise,  G.  W.,  The  application  of  photochemical  temperature  coefficients  to  the 
velocity  of  carbon  dioxide  assimilation.  Philippine  Jour.  Sci.  12,  C  (botany):  1-25. 
1917.)  interprets  the  data  as  indicating  that  temperature  has  little  effect  on  the  rate  of 
the  process,  while  the  second  (Smith,  A.  M.,  The  temperature  coefficient  of  photosynthesis  : 
a  reply  to  criticism.  Ann.  bot.  33:  517-536.  1919.)  corroborates  the  interpretation  that 
temperature  has  a  pronounced  effect  on  the  rate. — Ed. 


36 


PHYSIOLOGY    OF    NUTRITION 


was  able  to  show  that  when  the  stomatal  pores  are  artificially  plugged  exchange 
of  gases  is  retarded.  A  privet  leaf  (Ligustrum  vulgaris),  the  upper  surface 
of  which  was  coated  with  petrolatum,  decomposed  6.26  g.  of  carbon  dioxide, 
but  only  1.92  g.  was  decomposed  by  a  similar  leaf  coated  on  the  under  surface. 
[Privet  leaves  have  stomata  only  below,  so  that  coating  the  upper  surface 
did  not  close  the  pores.]  Stahl1  arrived  at  the  same  result.  Parts  of  the  lower 
surfaces  of  leaves  that  had  been  rendered  free  from  starch  were  covered  with  a 
mixture  of  one  part  of  beeswax  and  three  parts  of  cocoa  butter,  and  the  leaves 
were  then  exposed  to  light;  after  being  bleached  with  alcohol  and  then  treated 
with  iodine,  the  part  that  had  been  covered  was  brown,  while  the  remainder  of 
the  leaf  was  dark  blue  (Fig.  18).  Blackman's2  results  point  to  the  same 
conclusion.     The  size  of  the  stomatal  openings  is  also  important.3 

An  adequate  supply  of  water  in  the  leaves  is  essential 
to  the  normal  progress  of  photosynthesis;  according  to 
Sachs  and  Nagamatsz4  no  starch  is  formed  by  wilting 
leaves,  a  fact  which  Stahl  believed  to  be  due  to  the 
stomatal  closure  that  accompanies  wilting.  This  interpre- 
tation is  supported  by  the  observation  that  leaves  in  which 
the  stomata  remain  open  even  in  the  wilted  condition 
(Rumex  aquaticus,  Caltha  palustris,  Hydrangea  hortensis, 
Calla  palustris)  still  continue  to  accumulate  starch  after 
wilting  has  occurred. 

Finally,  an  excess  of  salts  in  the  soil  has  a  retarding 
effect  upon  the  rate  of  carbon  dioxide  decomposition. 
Schimper  found  that  watering  with  sodium  chloride  solu- 
tion caused  development  to  cease  in  most  plants  (non- 
halophytes),  through  a  checking  of  photosynthesis.  Ac- 
F  1  g  .  18  .—Privet  cording  to  Stahl  this,  also,  is  due  to  stomatal  closure, 
leaf,  the  unshaded  Por-  caused    Dy   excess  0f   saits.     if   the  leaves  are   slightly 

tion    ofwhichwas  J  ..... 

covered      with      cocoa  wounded  so  as  to  facilitate  entrance  of  carbon  dioxide  into 
butter   during   exposure  tke  tissue  starch  accumulates  about  the  wound  margins. 

to    light.     This    portion  '  .  "    . 

shows   no    starch   reac-  True  halophytes  grow,  though  slowly,  upon  soils  rich  in 
tion  with  iodine.  sajtSj  since  ^^  stomata  do  not  close  at  all. 

§9.  Nutrition  of  Green  Plants  by  Organic  Compounds. — Green  plants 
can  also  use  as  food  organic  compounds  that  are  supplied  from  without.5  This 
form  of  nutrition  may  go  on  simultaneously  with  the  assimilation  of  carbon 

1  Stahl,  Ernst.,  Einige  Versuche  uber  Transpiration  und  Assimilation.  Bot.  Zeitg.  52  :  11 7-146. 
1894. 

-  Blackman,  F.  Frost,  Experimental  researches  on  vegetable  assimilation  and  respiration. — No.  I.  On 
a  new  method  for  investigating  the  carbonic  acid  exchanges  of  plants.  Phil,  trans.  Roy.  Soc.  London 
Bi867:  485-502.  1895.  Idem,  same  title,  No.  11.  On  the  paths  of  gaseous  exchange  between  aerial 
leaves  and  the  atmosphere.     Ibid.  B:  1867:  503-562.     1895.     See  Sect.  IV. 

3  Kolkunov,  V.,  Ueber  die  Abhangigkeit  der  Assimilation  von  der  Grosse  der  Spaltoffnungen  bei  den 
Gramineen.     [Abstract    in    German,    pp.    381-382;    text    in  Russian.]     Jour.  exp.  Landw.  8:  369-382. 

1907. 

*  Nagamatsz,  Atsusuke,  Beitrage  zur  Kenntnis  der  Chlorophyllfunktion.  Arbeit.  Bot.  Inst.  Wurzburg 
3:     389-407.     1888. 

5  Apparently  carbon  monoxide  cannot  be  assimilated;  see :  Krascheninnikoff,  Th.,  La  plante  verte  assimile- 
t-elle  l'oxyde  de  carbone?     Rev.  gen.  bot.  21:  177-193.     1909- 


ASSIMILATION    OF    CARBON 


37 


dioxide  from  the  air,  which  is  especially  true  in  the  case  of  insectivorous  plants.1 
These  latter  are  green  and  can  assimilate  carbon  dioxide,  but,  at  the  same  time, 
they  are  provided  with  a  characteristic  mechanism  for  catching  and  digesting 
insects  (Fig.  19).  In  this  class,  for  instance,  belongs  the  widely  distributed 
sundew  {Drosera  rotundi folia),  which  grows  in  bogs.  Its  leaves  are  covered 
with  pin-shaped  tentacles  or  glands,  which  secrete  a  sticky  fluid.  As  an  insect 
alights  upon  the  leaf,  the  tentacles  bend  toward  it,  a  copious  flow  of  an  acid  liquid 


Fig.  19. — Above,  a  leaf  of  Drosera  rotundifolia,  whose  tentacles  on  the  left  side  have 
responded  to  a  stimulus,  and  one  of  Nepenthes  gracilis.  Below,  a  leaf  of  Dionaea  muscipula; 
A,  open;  B,  closed,  with  an  imprisoned  earwig.     (After  Pfeffer.) 

containing  a  pepsin-like  enzyme  takes  place,  and  the  insect  is  digested.  Sundew- 
can  also  digest  and  absorb  lean  meat  and  white  of  egg.  In  Nepenthes'2  a  part 
of  the  petiole  is  modified  into  a  tankard-shaped  structure  with  the  leaf-blade 
acting  as  a  cover.  The  hollow  portion  contains  a  weakly  acid  solution,  in 
which  imprisoned  insects  are  digested.  Each  leaf  of  Dionaea  muscipula  con- 
sists of  a  flattened  petiole  and  a  round  leaf-blade  divided  by  the  midrib  into 
halves,  like  the  halves  of  an  open  mussel,  separated  by  an  angle  of  from  60  to 

1  Darwin,  Charles  R.,  Insectivorous  Plants.     London,  1875. 

-  Clautriau,  G.,  La  digestion  dans  les  urnes  de  Nepenthes.  Recueil  Inst.  Bot.  Bruxelles  5:  89-133. 
1902.     Vines,  S.  H.,  The  proteolytic  enzyme  of  Nepenthes  (III).     Ann.  bot.  15  :  563-573-     1901. 


38  PHYSIOLOGY   OF   NUTRITION 

90  degrees.  The  free  margin  of  each  lobe  is  extended  into  sharp,  slender  teeth, 
and  each  lobe  bears  on  its  upper  surface  near  the  center  three  very  elastic 
bristles.  When  an  insect  alights  upon  the  leaf  and  touches  a  bristle,  the  valves 
quickly  close  together  and  a  digestive  fluid  is  secreted  into  the  space  between 
them. 

If  the  ability  to  derive  nutrition  from  complex  organic  compounds,  inde- 
pendently of  photosynthesis,  is  a  special  characteristic  of  the  insectivores, 
nevertheless  other  plants  that  utilize  the  carbon  dioxide  of  the  air  can  also 
assimilate  complex  organic  substances.  Green  water-plants  thrive  especially 
well  in  harbors  where  the  water  is  very  rich  in  organic  compounds,  in  the 
neighborhood  of  canals  and  sewer  outlets;  for  example,  the  algae,  Ulva  lactuca, 
some  species  of  the  genera  Bangia  and  Ceramium,  and  Cystoseira  barbata. 
Also,  some  single-celled  green  algae  are  known  to  grow  excellently  and  retain 
their  green  color  in  pure  culture  in  darkness,  with  organic  substances  supplied. 
Finally,  it  was  proved  by  Bohm  and  other  observers1  that  even  green  leaves 
that  have  been  previously  deprived  of  starch  are  able  to  assimilate  various 
organic  substances  from  solution  and  thus  to  form  starch  in  darkness.  In 
this  manner  starch  can  be  formed  from  saccharose,  glucose,  fructose,  lactose, 
glycerine,  dextrine,  mannite,  melampyrite,  and  adonite.2  Sapozhnikov'5 
investigated  this  matter  quantitatively.  Leaves  of  Astrapcea  wallichii, 
previously  rendered  starch-free,  formed  in  seven  days  from  4.6  to  5.3  g.  of 
starch,  per  square  meter  of  leaf  surface,  when  floating  upon  a  20-per  cent,  solu- 
tion of  cane  sugar  in  darkness.  Here  assimilation  is  not  limited  for  forma- 
tion of  starch,  however;  the  amount  of  proteins  also  increases  when  leaves  are 
grown  upon  cane-sugar  solution  in  darkness,  and  respiration  is  accelerated.  The 
ability  to  absorb  organic  compounds  is  even  more  pronounced  in  roots  than 
in  leaves.  Many  green  plants  possess  mycorhiza  (see  Chapter  IV)  and  grow 
on  humus  soils,  and  these  probably  assimilate  organic  materials.  Light 
influences  the  absorption  of  organic  compounds  by  green  plants.4 

According  to  the  experiments  of  Reinhardt  and  Sushkov5  the  accumulation 
of  starch  in  leaves  floating  upon  cane-sugar  solution  depends  upon  a  variety  of 
conditions.  This  process  occurs  rapidly  only  at  medium  temperatures,  while 
starch  that  was  previously  present  disappears  at  higher  or  lower  temperatures, 
in  spite  of  the  supply  of  sugar.  Among  poisons,  some  (quinin)  hasten  the  first 
appearance  of  starch  but  prevent  its  continued  accumulation;  others  (0.5  per 
cent,  of  caffein)  favor  the  accumulation  of  starch. 

1  [Boehm,  Josef.  Ueber  Starkebildung  aus  Zucker.  Bot.  Zeitg.  41 :  33-38,  49~54-  1883.  P.  35-  Idem, 
Starkebildung  in  den  Blattern  von  Sedum  spectabile  Boreau.  Bot.  Centralbl.  37  :  193-201,  225-232.  1889. 
P.  200.]  Nadson,  G.,  The  formation  of  starch  from  organic  substances  by  chlorophyll-bearing  plant  cells 
[Russian].    Trav.  Soc.  Imp.  Nat.  St-P6tersbourg  20:  (Sect,  bot.):  73-122.      1889. 

2  Treboux,  O.,  Starkebildung  aus  Adonit  im  Blatte  von  Adonis  vernalis.  Ber.  Deutsch.  Bot.  Ges. 
27:  428-430.     1909. 

3  Saposchnikoff,  W.,  Ueber  die  Grenzen  der  Anhaufung  der  Kohlenhydrate  in  den  Blattern  der  Weinrebe 
und  anderer  Pflanzen.  (Vorlaufige  Mittheilung.)  Ber.  Deutsch.  Bot.  Ges.  9:  293-300.  1891.  P.  298. 
Idem,  1890,  1893.     [See  note  4,  p.  31.] 

1  Lubimenko,  W.,  Influence  de  la  lumiere  sur  l'assimilation  des  matieres  organiques  par  les.  plantes 
vertes.     Bull.  Acad.  Imp.  Sci.  St.-Petersbourg  VI,  1:  395-426.      1907. 

6  Reinhard,  [L.  V.|  and  Suschkoff,  Beitrage  zur  Starkebildung  in  der  Pflanze.  Beih.  Bot.  Centralbl. 
18:  133-146.     1904-1905- 


ASSIMILATION    OF    CARBON  39 

Experiments  in  which  green  plants  were  supplied  with  organic  nitrogenous 
compounds,  in  a  chamber  free  from  carbon  dioxide,  gave  negative  results.1 

Summary 

i.  Importance  of  Carbon  Assimilation  by  Green  Plants.— Green  plants  form 
organic  compounds  from  inorganic  ones.  Non-green  plants  and  animals  are  unable  to 
do  this  and  are  therefore  all  ultimately  dependent  on  green  plants  for  organic  sub- 
stances. .  The  study  of  plant  physiology  may  begin  by  inquiring  about  photosynthesis 
of  carbohydrates  by  the  green  parts  of  plants.  These  organic  compounds  are  formed 
from  carbon  dioxide  and  water,  by  means  of  solar  energy  that  is  absorbed  and  trans- 
formed in  the  green  tissues.  Carbon  dioxide  is  of  course  a  carbon  compound,  but  it  is 
not  combustible  and  is  usually  classed  as  inorganic.  Combustible  carbon  compounds 
derived  from  organisms  are  capable  of  being  burned  in  air  because  they  are  incom- 
pletely oxidized;  when  completing  their  oxidation  these  compounds  absorb  oxygen  and 
produce  carbon  dioxide  and  water,  and  this  process  of  combustion  liberates  energy 
(heat  or  light  or  both).  A  certain  amount  of  sunlight  energy  is  absorbed,  and  a 
corresponding  amount  of  oxygen  is  eliminated,  when  carbon  dioxide  and  water  are 
combined  by  green  plants,  with  the  formation  of  carbon  compounds. 

2.  Exchange  of  Gases. — Photosynthesis  is  accompanied  by  taking  in  of  carbon 
dioxide  and  giving  out  of  oxygen,  as  well  as  by  absorption  of  solar  energy,  and  the  ratio 
of  the  amount  of  absorbed  carbon  dioxide  to  the  amount  of  oxygen  eliminated  in  the 
same  period  has  been  found  to  have  a  value  somewhat  less  than  unity.  The  process 
results  in  decomposition  of  carbon  dioxide  and  water,  and  in  the  union  of  the  carbon, 
the  hydrogen,  and  some  of  the  oxygen,  to  form  carbohydrates;  the  rest  of  the  oxygen  is 

given  off. 

3.  Chlorophyll. — The  two  green  pigments  that  make  it  possible  for  carbohydrate 
photosynthesis  to  occur  in  green  plant  tissues  when  light  is  properly  supplied  are 
called  chlorophyll,  or,  more  correctly,  the  chlorophylls.  Photosynthesis  of  carbo- 
hydrates from  carbon  dioxide  and  water  does  not  occur  in  tissues  that  do  not  contain 
these  pigments.  The  green  pigments  are  named  chlorophyll  a  and  chlorophyll  b. 
They  occur  in  green  leaves  in  about  the  proportions  72  to  28,  by  weight.  Dissolved  in 
ethyl  alcohol,  the  first  appears  blue-green,  the  second  yellow-green,  by  transmitted 
light.  Both  are  fluorescent,  the  first  appearing  blood-red,  the  second  brown-red,  by 
reflected  light.  The  two  are  alike  in  that  each  molecule  contains  55  atoms  of  C,  4 
atoms  of  N,  and  a  single  atom  of  Mg.  The  molecule  of  chlorophyll  a  contains  72 
atoms  of  H  and  5  atoms  of  O,  while  that  of  chlorophyll  b  contains  70  atoms  of  H  and 
6  atoms  of  O.  Iron  is  necessary  for  the  formation  of  the  chlorophylls  in  plants,  but 
does  not  occur  in  the  pigments  themselves. 

The  chlorophylls  absorb  light  more  or  less  completely  according  to  the  wave- 
lengths of  the  light  that  is  supplied.  Light  of  wave-lengths  from  about  640  to  about 
680  ft  (red)  is  most  completely  absorbed.  With  wave-lengths  shorter  than  about 
475  fj.  (blue  to  ultra-violet)  absorption  is  almost  as  complete.  The  spectrum  of 
chlorophyll  solution  shows,  between  these  two,  several  other  ranges  of  wave-lengths, 
with  less  complete  absorption,  and  very  strong  solutions  show  complete  absorption 
throughout  the  entire  range  of  visible  light.— The  chlorophylls  are  chemically  some- 

«  Grafe,  Victor,  Untersuchungen  iiber  die  Aufnahme  yon  Stickstoffhaltigen  organischen  Substanzen 
durch  die  Wurzel  von  Phanerogamen  bei  Ausschluss  der  Kohlensaure.  Sitzungsber.  (math.-naturw.  Kl.) 
K.  Akad.  Wiss.  Wien  118':  II35-"S3.      1000. 


40  PHYSIOLOGY    OF    NUTRITION 

what  related  to  hemoglobin  (which  occurs  in  red  blood-corpuscles  of  animals) ;  they 
give  several  of  the  same  decomposition  products. 

For  the  formation  of  chlorophyll  in  leaves,  etc.,  the  following  conditions  are  essen- 
tial: (i)  light  (within  the  limits  of  the  visible  spectrum  and  with  different  intensities 
for  different  kinds  of  plants);  (2)  temperature  (from  about  o°C.  to  about  45°C.  as 
general  limits;  the  range  is  usually  narrower,  differing  for  different  kinds  of  plants); 
(3)  iron  (but  the  supply  must  be  very  small  or  poisoning  results);  (4)  oxygen;  (5)  salts 
derived  from  the  soil  (containing  K,  Ca,  Mg,  N,  P,  S) ;  (6)  water-soluble  carbohydrates. 

4.  Pigments  Accompanying  Chlorophyll. — Several  other  pigments  accompany 
the  chlorophylls,  especially  carotin  and  xanthophyll,  which  are  generally  present  in 
cells  with  the  green  pigments,  but  often  occur  in  the  absence  of  the  latter.  Carotin  is 
a  hydrocarbon,  with  the  formula  C40H56.  It  forms  crystals  that  appear  blue-green  by 
reflected  light  and  orange-red  by  transmitted  light.  It  is  insoluble  in  water,  readily 
soluble  in  ether,  carbon  bisulphide,  etc.,  and  is  readily  oxidized.  In  leaves  it  varies 
in  amount,  according  to  the  light  intensity,  temperature,  etc.  It  occurs  in  all  parts  of 
plants. — Xanthophyll  resembles  carotin  but  contains  some  oxygen;  it  has  the  formula 
4oCH5609. 

5.  Influence  of  Light  in  Carbohydrate  Photosynthesis. — Light  impinging  on  leaves 
is  partly  reflected,  partly  absorbed,  and  partly  transmitted.  Only  that  which  is 
absorbed  can  influence  chemical  processes  within  the  leaves.  The  absorbed  portion 
may  have  various  qualities  (according  to  the  proportions  of  the  different  ranges  of 
wave-length  that  are  present)  and  various  total  intensities.  The  range  of  wave- 
lengths approximately  corresponding  to  our  visual  range  of  red  and  orange  appears 
usually  to  be  most  effective  in  furnishing  energy  for  photosynthesis,  but  the  rest  of 
the  visible  range  of  wave-lengths  is  not  without  effect.  The  proportional  distribution 
of  total  light  energy  among  the  several  ranges  of  wave  length  varies  greatly  in  nature. 
When  the  relations  between  light  quality  and  carbohydrate  photosynthesis  are  to  be 
dealt  with,  it  is  necessary  to  consider  the  energy-supplying  power  of  any  wave-length 
range  of  absorbed  light.  It  has  been  suggested  that  the  rate  of  the  process  may  be 
proportional  to  the  energy  value  of  the  absorbed  light,  other  conditions  being  adequate 
and  constant  throughout  the  series  of  comparisons.  The  absorbing  power  of  chloro- 
phyll-bearing tissue,  for  the  different  ranges  of  wave-lengths,  is  greatly  influenced  by 
the  amount  of  chlorophyll  present  and  by  the  presence  of  pigments  other  than  chloro- 
phyll— also  by  the  cell  structures  of  the  tissues. — Considering  simply  the  total  intensity 
of  sunlight,  carbohydrate  photosynthesis  proceeds  with  intensities  between  a  minimum 
and  a  maximum,  with  an  optimum  intensity  somewhere  within  the  range.  Shade- 
plants  (as  beech)  have  a  low  range  of  intensities  for  the  process,  while  sun-plants  (as 
pine)  have  a  high  range.     Cave  mosses  thrive  with  very  weak  illumination. 

6.  Products  of  Carbohydrate  Photosynthesis. — If  a  living  green  plant  that  forms 
starch  be  kept  in  darkness  till  all  starch  has  disappeared  from  the  chlorophyll-bearing 
cells,  and  if  it  be  then  exposed  to  suitable  light,  starch  grains  soon  appear  in  the  cells. 
But  starch  is  not  the  first  product  of  the  photosynthetic  process,  for  starch  is  formed 
from  a  water-soluble  sugar  (such  as  dextrose),  not  directly  from  carbon  dioxide  and 
water.  There  are  plants  that  do  not  form  starch,  and  these  show  an  increased  amount 
of  sugar  when  they  are  brought  into  light  after  a  prolonged  period  in  darkness.  A 
supply  of  carbon  dioxide  is  of  course  necessary,  in  the  surrounding  air,  and  the  form- 
ation of  sugar  or  starch  proceeds  parallel  to  the  absorption  of  carbon  dioxide  by  the 
plant  in  this  kind  of  a  test.  Of  course  the  active  cells  are  plentifully  supplied  with 
water,  which  is  the  other  necessary  material.     Besides  sugar,  a  prominent  product  of 


ASSIMILATION   OF   CARBON  4 1 

this   process  is   oxygen,   most  of  which   escapes  from   the   green   tissues  into   the. 
surroundings. 

6a.  Chemistry  of  Carbohydrate  Photosynthesis. — Baeyer's  hypothesis  supposes 
that  carbon  dioxide  and  water  are  decomposed,  that  some  free  oxygen  is  produced,  and 
that  the  remaining  carbon,  hydrogen,  and  oxygen  are  combined  to  form  formalde- 
hyde (CH2O),  the  latter  being  polymerized,  with  the  formation  of  dextrose  (C6Hi2  06). 
The  hypothesis  is  represented  by  the  equations:  (1)  CO2  +  H20  =  CH20  +  02 
and  (2)  6CH2O  =  C6Hi206.  Traces  of  formladehyde  have  been  found  in  green 
tissues,  and  green  plants  in  light  have  been  experimentally  shown  to  be  able  to  increase 
their  carbohydrate  content  when  supplied  with  this  substance  as  the  only  source  of 
carbon.  But  formaldehyde  is  a  violent  poison  and  can  never  accumulate  considerably 
in  living  tissues.  It  is  supposed  that  this  substance  generally  polymerizes  as  rapidly 
as  it  is  formed.  If  the  hypothesis  is  true,  light  appears  necessary  for  the  polymeriza- 
tion of  formaldehyde,  as  well  as  for  its  formation  and  for  the  antecedent  decomposition 
of  carbon  dioxide  and  water.  Many  other  hypotheses  have  been  suggested,  and  the 
chemistry  of  this  photosynthetic  process  is  still  to  be  worked  out. — More  than  90  per 
cent,  of  the  dry  weight  of  the  plant  is  derived  from  the  carbon  dioxide  and  water 
used  in  the  process  here  considered;  the  rest  is  derived  from  mineral  salts  absorbed  from 
the  soil  solution. 

7.  Assimilation  of  Solar  Radiant  Energy  by  Green  Plants. — The  formation  of 
carbohydrates  in  green  plants  necessarily  results  in  the  storage  of  potential  energy,  in 
an  amount  equivalent  to  the  energy  that  would  be  freed  by  the  complete  oxidation 
or  burning  of  the  carbohydrates  formed.  The  fuel  values  of  wood  and  coal  are  pro- 
portional to  the  potential  energy  stored  in  these  substances  and  set  free  when  they  are 
burned.  This  energy  is  a  part  of  that  which  was  absorbed  from  sunlight  when  the 
plants  from  which  these  fuels  have  been  derived  were  growing.  The  stored  solar 
energy  of  coal  has  lain  dormant  for  ages,  that  of  wood  generally  for  years.  Cal- 
culations indicate  that  2.2-3.6  gram-calories  of  energy  is  stored  for  each  gram  of 
carbon  dioxide  decomposed  in  photosynthesis.  Experiments  have  shown,  however, 
that  plants  accumulate,  as  potential  energy  in  their  carbon  compounds,  less  than  0.5 
per  cent,  of  the  radiant  energy  that  reaches  them  as  sunlight. 

8.  Influence  of  Conditions  on  Carbohydrate  Photosynthesis. — Internal  conditions 
influencing  the  rate  of  carbohydrate  photosynthesis  are:  (a)  the  amount  of  chlorophyll 
present;  (b)  anatomical  and  histological  structure,  especially  arrangement  and  size 
of  stomata;  (c)  condition  of  stomata — whether  open,  closed,  partly  closed,  etc.;  (d) 
turgor  condition— whether  the  leaf  is  wilted,  etc.  (this  is  perhaps  covered  by  c) ;  (e) 
the  rate  at  which  products  of  the  process  leave  the  leaf;  (/)  the  ability  of  the  leaf  to 
absorb  light  (may  be  included  under  b) ;  (g)  leaf  temperature. 

External  conditions  influencing  the  rate  of  this  process  are:  (a)  the  rate  of  supply  of 
carbon  dioxide;  (b)  the  quality — wave-lengths — of  the  light  received;  (c)  the  rate  of 
light-energy  absorption — intensity  of  each  group  of  wave-lengths  and  time  during 
which  leaf  is  exposed  to  them;  (d)  the  temperature  of  the  surroundings — which  mainly 
controls  leaf  temperature;  (c)  other  external  conditions  whose  influence  is  not  yet  so 
well  understood. 

9.  Nutrition  of  Green  Plants  by  Organic  Compounds. — Some  green  plants  (as,  for 
example,  the  insectivorous  forms,  Drosera,  Nepenthes,  Dionaea,  etc.)  are  able  to 
absorb  considerable  amounts  of  ready-made  carbohydrates,  etc.,  from  the  surround- 
ings. Many  other  green  plants  have  this  ability  to  a  smaller  degree.  Of  course  the 
non-chlorophyll-bearing  parts  of  green  plants,  regularly,  derive  their  carbohydrates 
from  the  tissues  that  bear  chlorophyll. 


CHAPTER   II 

ASSIMILATION  OF  CARBON  AND  OF  ENERGY  BY  PLANTS 

WITHOUT  CHLOROPHYLL 

§i.  General  Discussion. — Most  plants  that  are  without  chlorophyll  and  are, 
in  consequence,  unable  to  assimilate  the  energy  of  sunlight,  do  not  have  the  power 
to  transform  non-combustible  inorganic  substances  into  organic  compounds. 
As  will  appear  later,  in  order  to  form  their  various  organic  substances,  green 
plants  require  (besides  carbon  dioxide  from  the  air  and  water  from  the  soil) 
nitrogen,  potassium,  calcium,  magnesium,  iron,  sulphur  and  phosphorus,  all  of 
which  occur  in  the  form  of  various  salts  in  the  soil.  From  the  preceding  dis- 
cussion of  chlorophyll  (see  Chapter  I)  it  appears  that  no  plant  without  chloro- 
phyll can  utilize  the  energy  of  sunlight  to  manufacture  combustible  organic 
matter  out  of  such  substances.  Most  non-green  plants  must  use,  as  sources 
of  both  energy  and  material,  organic  compounds  that  have  already  been 
formed;  they  are  thus  more  nearly  related  to  animals  than  to  green  plants,  as 
far  as  their  nutrition  is  concerned.  But  organic  compounds  are  not  the  only 
substances  that  can  be  oxidized.  This  property  belongs  also  to  various  inorganic 
substances,  such  as  ammonia,  hydrogen  sulphide  and  hydrogen,  which  thus 
contain  stored  energy.  As  we  have  previously  seen  (page  xxviii),  the  heat  of 
combustion  of  ammonia  is  greater  than  that  of  starch.  The  researches  of  recent 
years  have  shown  that  such  substances  can  serve  as  sources  of  nutrition  for 
certain  plants  without  chlorophyll.  On  the  basis  of  their  mode  of  nutrition, 
plants  without  chlorophyll  may  be  divided  into  two  groups:  (i)  plants  that 
derive  their  energy  from  organic  compounds,  and  (2)  plants  that  derive  it  from 
inorganic  substances. 

§2.  Assimilation  of  Energy  from  Organic  Compounds  by  Plants  without 
Chlorophyll. — Most  bacteria,  yeasts,  fungi  and  the  non-green  seed-plants  obtain 
their  nutrition  from  previously  formed  organic  compounds.  To  study  the  nutri- 
tional requirements  of  these  forms,  culture  media  containing  various  nutritive  sub- 
stances are  employed.  It  was  formerly  thought  that  the  same  nutrient  medium 
should  be  suitable  for  all  the  simpler  non-green  forms,  but  this  is  not  so.  In 
higher  plants,  specialization — i.e.,  adaptation  to  surrounding  conditions— is 
accompanied  by  peculiarities  of  external  form  as  well  as  of  anatomical  structure. 
On  the  other  hand,  the  lower  plants,  such  as  bacteria  and  yeasts,  are  marked  by 
their  structural  similarity  and  simplicity.  It  was  supposed,  therefore,  that  such 
similarity  of  structure  was  accompanied  by  a  similarity  in  the  characteristic  life 
processes,  and  this,  in  turn,  led  to  the  supposition  that  the  nutritive  processes  must 
be  more  or  less  uniform  in  these  lower  forms.  The  most  recent  investigations 
have  shown,  however,  that,  in  spite  of  the  simple  structure  of  microorganisms 

42 


ASSIMILATION    OF    CARBON  43 

(more  properly,  just  because  of  this  very  simplicity)  they  usually  exhibit  far- 
reaching  physiological  peculiarities.     Each  one  of  these  organisms  carries  out  its 
own  little  work,  but  it  constitutes  a  very  important  link  in  the  processes  of  nature. 
For  example,  the  presence  of  two  kinds  of  bacteria  appears  to  be  requisite  for  the 
oxidation  into  nitric  acid  of  the  ammonia  present  in  the  soil.     One  of  these 
(Nitrosomonas)  carries  the  oxidation  as  far  as  nitrous  acid,  the  other  (Nitro- 
bacter)  oxidizes  this  to  nitric  acid.     Ammonia  is  essential  as  nutrient  material 
for  the  first  form  and  nitrous  acid  is  a  waste.     But  this  by-product  constitutes 
an  essential  food  substance  for  the  other  form.     Is  it  possible,  then,  to  conceive 
of  some  nutrient  medium  that  would  be  equally  well  suited  for  the  nutrition  of 
both  these  bacteria?     This  question  must  receive  a  negative  answer;  a  medium 
must  be  used  that  is  favorable  only  to  the  microorganism  under  investigation, 
and  that  is  especially  adapted  to  its  particular  requirements.     The  use  of  such 
media  is  highly  important  if  pure  cultures  are  desired.     This  use  has  been  desig- 
nated by  Vinogradskii  as  the  method  of  "selective  culture."     A  culture  is 
selective  if  it  promotes  only  a  certain  func- 
tion, or  if  it  promotes  a  function  which  is 
as  restricted  as  possible.     The  more  closely 
limited  or  exclusive  are  the  conditions,  the 
more  favorable  will  these  conditions  be  for 
one  species  possessing  a  particular  property 
or  function,  in  contrast  to  others  not  so 
endowed,  and  the  growth  of  these  latter 
in  a  medium  thus  alien  to  them  will  be 
quite  impossible  or  at  least  very  difficult. 
In  thus  assisting  the  desired  microorgan- 
isms in  their  struggle  for  existence,  we  in- 
crease their  numbers  in  our  cultures  and       Fig.  20.— Various  forms  of  bacteria, 
thereby  render  their  discovery  easier.     When  a  specific  bacterium  has  once  been 
found,  it  is  thus  usually  possible  to  discover  also  the  method  by  which  it  may 
be  isolated  in  pure  culture.     On  this  general  principle  is  based  the  now  frequent 
employment  of  many  different  kinds  of  nutrient  substrata,  both  liquid  and  solid. 
The  first  attempt  to  prepare  an  artificial  nutrient  medium  for  microorganisms, 
was  made  by  Pasteur,1  whose  solution  for  the  culture  of  yeast  had  the  following 
composition:  water,  100  g.;  ammonium  tartrate,  1  g.;  saccharose,  10  g.;  and 
yeast  ash,  0.075  g. 

Meat  extract  is  used  most  commonly  for  the  culture  of  bacteria  (Fig.  20). 
The  addition  of  gelatine  to  peptone  bouillon  (10  per  cent,  of  gelatine  in  winter 
and  15  per  cent,  in  summer)  produces  a  solid  substratum.  Agar-agar  may  be 
used  instead  of  gelatine.  Besides  the  various  kinds  of  meat  extracts,  milk, 
blood  serum,  yeast  water,  beer-wort  and  other  similar  materials  may  be  used. 
Among  other  things,  cylinders  cut  from  potato  tubers  may  be  employed  as 
solid  media. 

1  Pasteur,  Louis,   Memoire  sur  la  fermentation  alcoolique.     Ann.  chim.  et  phys.   ///,   58:  323-426. 

i860. 


44  PHYSIOLOGY   OF   NUTRITION 

Beer-wort  is  the  best  nutrient  medium  for  the  culture  of  yeast.1  Other 
liquids  are  used,  however,  among  which  may  be  mentioned  Pasteur's  solution 
as  given  above,  grape  juice,  the  juice  of  various  other  fruits  and  berries,  and  other 
materials  containing  sugar.  Hansen  has  carried  out  very  exhaustive  studies 
upon  yeasts  and  has  established,  among  others,  the  following  important  species.2 

Saccharomyces  cerevisice  I.  Hansen.  An  English  top-fermentation  yeast, 
which  produces,  in  beer-wort  at  room  temperature,  from  4  to  6  per  cent,  of 
alcohol.  In  the  resting  condition  the  plant  consists  of  single  cells,  which  begin 
to  multiply  by  budding  when  placed  in  beer- wort.  The  young  generation  con- 
sists of  large  spherical  or  oval  cells  (Fig.  21).  After  the  temination  of  the 
primary  fermentation  a  scum  appears  on  the  surface  of  the  fermenting  liquid 
and  on  this  a  continuous  membrane  of  yeast-cells  is  formed.  The  general 
appearance  of  these  cells  is  different  from  that  of  the  sedimentary  forms;  much 
elongated  cells  are  found  here  (Fig.  22).  In  the  surface  membrane  of  old  cul- 
tures occur  very  much  elongated  cells  that  are  entirely  unlike  the  young  sedi- 
ment cells  from  which  they  have  developed  (Fig.  23).     This  film    formation 


Pig.  21. — Saccharomyces  cerevisice  I.  Fig.  22. — Saccharomyces  cerevisice  I.  Sur- 
Young  cells  from  the  sediment  of  the  beer-  face  film  at  i5-i6°C.      {After  E.  Hansen.) 

vat.      {After  E.  Hansen.) 

furnishes    a  striking    example    of    the    great    variability    in    form,    that    is 
characteristic  of  yeast  cells. 

In  order  to  obtain  ascospores  young  cultures  must  be  used,  and  it  is 
also  essential  that  air  be  plentifully  supplied.  Little  plaster  of  Paris  disks 
prepared  with  special  moulds  are  used  for  this  purpose.  These  are  placed 
in  small,  shallow  glass  pans  (Petri  dishes),  covered  with  similar  pans  of  slightly 
greater  diameter,  and  then  sterilized.  A  few  drops  from  a  day-old  culture  of 
yeast  cells  are  placed  upon  one  of  these  plaster  disks.  Sterilized  water  is 
poured  into  a  dish  around  the  disk,  to  keep  the  latter  constantly  moist.  x\fter 
some  time  the  ascospores  are  formed.  Temperature  exerts  a  pronounced  in- 
fluence upon  their  formation.  With  the  same  temperature,  ascospores  of 
different  species  develop  at  different  rates,  and  this  fact  is  made  use  of  in  indenti- 

1  Jorgensen,  Alfred  P.  C,  Die  Mikroorganismen  der  Garungsindustrie.  4te  Aufl.  Berlin,  1898.  Idem, 
Microorganisms  and  fermentation.  Philadelphia,  191 1.  Lindner,  Paul,  Mikroskopische  Betriebskontrolle 
in  den  Garungsgewerben.  2te  Aufl.,  Berlin,  1898.  (ste  Aufl.,  Berlin,  1909.)  [Hansen,  Emil  Chr.,  Prac- 
tical studies  in  fermentation.  Transl.  by  Alex.  K.  Miller.  227  p.  London  and  New  York,  1896. — See 
also  the  references  on  brewing,  etc.,  given  on  p.  181.] 

The  Carlsberg  Laboratory  in  Copenhagen  is  especially  interested  in  the  study  of  fermentation  organisms. 
It  publishes  a  journal  devoted  to  this  study,  entitled  "  Meddeledser  fra  Carlsberg  Laboratories" 

2  More  information  upon  top  and  bottom  fermentation  will  be  found  in  Chapter  VIII  of  this  Part. 


ASSIMILATION   OF   CARBnX 


45 


Fig.  23. — Saccharomyces  cerevisice  I.     Film  of  an  old  culture.     (After  E.  Hansen.) 


EM 


Fig.      24. — Saccharomyces      pastorianus      I.  Fig.     25. — Saccharomyces         pastorianus 

Ascospores.     (After  E.  Hansen.)  III.     Young  cells  of  the  sediment.      (After 

E.  Hansen.) 


46 


PHYSIOLOGY    OF    NUTRITION 


fying  the  different  yeasts,  particularly  in  technical  analysis  for  distinguishing 
wild  from  cultivated  forms. 

Saccharomyces  pastorianus  I.  Hansen  (Fig.  24).  This  is  a  bottom-fermenta- 
tion yeast  and  consists  mainly  of  elongated  cells,  but  round  and  oval  cells  also 
occur.  This  yeast  is  frequently  present  in  the  air  in  breweries.  It  imparts  to 
the  beer  a  disagreeable,  bitter  taste  and  an  unpleasant  odor. 

Saccharomyces  pastorianus  III.  Hansen.  This  top-fermentation  yeast 
produces  a  turbid  condition  in  beer  (Fig.  25). 

Saccharomyces  anomalus  Hansen.  This  species  is  distinguished  by  its  char- 
acteristic ascospores,  which  have  the  form  of  hemispheres,  with  projecting  rims 
at  their  bases  (Fig.  26). 

Besides  the  species  mentioned  here,  which  are  among  those  thoroughly 
investigated  by  Hansen,  a  great  many  other  yeasts,  both  wild  and  cultivated, 
are  known.  Some  of  the  cultivated 
varieties  are  employed  in  the  brew- 
ing industry,  some  in  distilleries, 
some  in  the  manufacture  of  berry 
or  fruit  wines,  and  still  others  in  the 
preparation  of  compressed  yeast  for 
bakers'  use. 

The  moulds  (Fig.   27)   are  not 
very  exacting  as  to  their  nutrition, 


Pig.      26.- 


-Saccharomyces 
oospores. 


anomalus.     As- 


A  B 

Fig.  27. — A,  Penicillium  glaucum;  B,  Asper- 
gillus glaucus.      A  conidiophore,  in  each  case. 

for  they  can  grow  upon  a  very  great  variety  of  materials.  Among  artificial 
liquid  media  for  mould  culture,  Raulin's1  solution  is  the  best  known;  its  formula 
follows: 

Water 1 500 .  o  g. 

Saccharose 70 .  o  g. 

Tartaric  acid 4  •  o  g. 

Ammonium  nitrate 4  ■  o  g. 

Ammonium  phosphate o.6g. 

Ammonium  sulphate o .  25  g. 

Potassium  silicate o .  07  g. 

Potassium  carbonate o.6g. 

Magnesium  carbonate o .  4  g. 

Zinc  sulphate o .  07  g. 

Ferric  sulphate o .  07  g. 

Fermentation  phenomena  often  accompany  the  nutrition  of  the  moulds 
and  bacteria.  There  is  still  very  little  known  concerning  the  nutrition  of  the 
higher  fungi. 

1  Raulin,  Jules,  Etudes  chimiques  sur  la  vegetation.     Ann.  sci.  nat.  Bot.  V,  1 1 :  93-299.     1 869. 


ASSIMILATION    OF    CARBON 


47 


Almost  the  only  definitely  known  fact  concerning  the  nutrition  of  seed- 
plants  without  chlorophyll  is  that  some  are  saprophytes  and  others  parasites. 
The  former  utilize  decomposition  products  from  plants  and  animals,  while  the 
latter  attach  themselves  to  living  plants  and  derive  nourishment  therefrom. 
»  The  widely  distributed  dodder  (species  of  Cuscuta)  is  an  example  of  a  para- 
site. It  is  parasitic  upon  nettles,  hops  and  many  other  plants  (Fig.  28). 
Parasitism  exhibits  such  a  high  state  of  development  in  some  flowering 
plants  without  chlorophyll  that  they  possess  neither  root  nor  stem,  nor  have 
they  any  leaves.  The  entire  plant  body  here  resembles  a  fungus  in  its  struc- 
ture, consisting  of  branching  filaments  each  composed  of  a  row  of  cells,  very 
similar  to  fungus  hyphae.  The  Balanophorese,  Hydnoreae  and  Rafflesiaceae, 
are  examples  of  such  plants.  The  hypha-like  body  of  these  plants  develops 
within  various  trees  and  derives  nourishment  therefrom  after  the  manner  of 


Fig.  28. — Section  of  stem  of  Cuscuta  europaa,  attached,  by  means  of  its  haustorium,  to  the 
stem  of  a  nettle.     E  represents  the  epidermis  of  the  nettle. 

many  fungi.  The  flower  buds  and  flowers  of  these  non-green  parasites  appear 
upon  the  branches  of  the  host  only  during  the  flowering  season  of  the  latter. 
It  then  appears,  at  first  glance,  as  though  the  plant  infested  by  the  parasite  were 
bearing  two  kinds  of  flowers.  In  reality,  however,  some  of  these  are  the  true 
flowers  of  the  host  plant,  while  the  others  belong  to  the  parasite.  Fig.  29  shows 
a  portion  of  an  underground  stem  of  a  host  plant,  bearing  its  own  flower  buds 
and  a  mature  flower  of  a  parasite,  Hydnora  africana. 

§3.  Assimilation  of  Energy  from  Inorganic  Substances  by  Plants  without 
Chlorophyll. — Some  bacteria  are  so  constituted  as  to  be  able  to  obtain  their 
energy  from  oxidizable  inorganic  substances  that  are  common  on  the  earth. 
Of  these  the  nitrifying  bacteria,  which  oxidize  ammonia  into  nitric  acid,  are  the 
most  important.  The  absence  of  organic  substances  is  necessary  for  their 
successful  growth.     Vinogradskii  succeeded   in  obtaining  a  pure  culture  of 


48 


PHYSIOLOGY    OF    NUTRITION 


nitrifying  bacteria  only,  by  preparing  a  nutrient  solution  containing  no  organic 
substances.  This  nutrient  medium1  contained  i  g.  of  ammonium  sulphate  and 
i  g.  of  potassium  phosphate,  dissolved  in  a  liter  of  water.  From  0.5  to  1.0  g. 
of  basic  magnesium  carbonate  was  added  to  each  100  cc.  of  this  solution. 
Nitrifying  bacteria  were  able  to  develop  excellently  in  this  medium;  they 
oxidized  ammonia  to  nitric  acid  and  formed  an  appreciable  quantity  of  organic 
substance,  thus  assimilating  the  carbon  dioxide  of  the  air  without  the  agency 
of  sunlight.  Bacteria  that  need  organic  substances  for  their  nutrition  could 
not  develop  in  such  a  medium. 


Fig.  29. — Hydnora  africana.     t,  part  of  the  underground  stem  of  the  host  plant;  bl,  one  of 
the  mature  flowers;  bl',  bl",  flower  buds  of  the  parasite.      (H  natural  size.)      {After  Sachs.) 

Without  the  agency  of  sunlight  as  source  of  energy,  green  plants  are  unable  to 
produce  organic  substance  from  the  inorganic  materials  that  serve  as  nutrients 
for  these  forms.  As  has  been  said,  there  are  other  inorganic  substances, 
however  (such  as  ammonia  and  hydrogen  sulphide)  that  can  serve  as  sources  of 
energy  for  such  plants  as  the  bacteria  just  mentioned.  These  substances  are 
common  in  nature,  being  frequently  of  organic  origin  as  decomposition  products 
of  complex  organic  compounds,  and,  although  they  do  not  contain  carbon 
(which  is  present  in  all  organic  compounds),  yet  they  do  possess  the  power 

1  [Winogradsky,  S.,  Recherches  stir  les  organismes  de  la  nitrification.  I.  Ann.  Inst.  Pasteur  4  :  213-231 
1890.  Idem,  same  title,  II.  76^.4:257-275.  1890.  Idem,  same  title.  III.  Ibid.  4:  760-771.  1890. 
Idem,  same  title,  IV.  Ibid.  5 :  52-100.  1891.  [Idem,  same  title,  V.  Ibid.  5:  577-616.  1891.  See  No. 
IV,  especially.] 


ASSIMILATION    OF    CARBON  49 

to  burn  readily;  i.e.,  to  liberate  heat.  On  this  account  these  oxidizable  in- 
organic substances  can  supply  energy  for  these  bacteria.  Thus,  nitrifying 
bacteria  utilize  ammonia,  and  sulphur  bacteria  make  use  of  hydrogen  sulphide. 

To  obtain  a  solid  substratum  for  cultures  where  organic  substances  must  be 
avoided,  silicic  acid1  may  be  used  instead  of  gelatine  or  agar-agar. 

Vinogradskii2  also  proved  that  bacteria  living  in  sulphur  springs,  as  Beggia- 
toa  and  some  other  species,  use  hydrogen  sulphide  as  a  source  of  energy.  This 
is  first  oxidized  only  to  sulphur  and  water;  H2S  +  O  =  H20  +  S.  The  sul- 
phur thus  formed  accumulates  within  the  cells,  to  be  further  oxidized,  in  the 
presence  of  carbonates  (e.g.,  calcium  carbonate),  to  form  calcium  sulphate  and 
carbonic  acid.  The  sulphur  bacteria  play  a  very  important  role  in  the 
economy  of  nature;  without  them  the  circulation  of  sulphur  might  be  impossible. 

In  order  to  obtain  sulphur  bacteria,  freshly  cut  pieces  of  roots  of  Butomus 
umbellalus .  with  the  mud  clinging  to  them,  are  placed  in  a  deep  vessel,  in  from 
3  to  5  1.  of  water;  some  calcium  sulphate  is  added  and  the  vessel  is  left  uncovered 
at  room  temperature.  After  several  days  the  formation  of  hydrogen  sulphide 
is  evident,  consequent  upon  the  decomposition  of  calcium  sulphate  by  various 
bacteria  contained  in  the  mud.  Some  time  after  the  appearance  of  hydrogen 
sulphide  the  development  of  sulphur  bacteria  begins.  They  usually  collect  at 
some  distance  from  the  free  surface  of  the  liquid  and,  as  they  move  upwards 
and  downwards,  they  sometimes  absorb  hydrogen  sulphide  and  sometimes 
oxygen. 

When  grown  upon  a  microscope  slide,  in  a  liquid  containing  hydrogen  sul- 
phide, the  sulphur  bacteria  assemble  to  form  a  ring,  about  a  millimeter  from  the 
edge  of  the  cover  glass.  If  the  drop  of  liquid  is  not  covered  they  do  not  develop 
at  all.  There  is  therefore  a  definite  optimum  of  oxygen  supply  for  these  bac- 
teria. According  to  the  researches  of  Yegunov,3  this  point  is  well  brought  out 
by  growing  them  in  deep  vessels.  A  bacterial  membrane  is  formed  at  a  cer- 
tain distance  from  the  surface  of  the  liquid  and  short,  tassel-like  outgrowths 
project  downwards  from  this  membrane.  A  part  of  such  a  membrane  with  its 
projections  is  shown,  enlarged,  in  Fig.  30.  If  these  outgrowths  are  examined 
with  a  horizontal  microscope  it  becomes  evident  that  they  consist  of  bacterial 
cells  that  are  moving  up  and  down  with  a  boiling  motion,  like  water  in  a  spring. 

The  occurrence  of  hydrogen  sulphide  is  not  confined  to  bogs  and  sulphur 
springs,  for  this  substance  is  also  found  in  the  sea.  The  water  of  the  Black  Sea 
below  a  depth  of  about  200  m.  becomes  richer  in  hydrogen  sulphide  as  the  depth 
increases.  One  hundred  liters  of  water,  collected  at  the  depths  given,  contained 
the  following  amounts  of  hydrogen  sulphide. 

1  Omeliansky,  V.,  Sur  la  culture  des  microtes  mitrificateurs  du  sol.  Arch.  sci.  biol.  St.-Petersbourg 
7:  291-302.     iSoo- 

-  Winogradsky,  Sergius,  Ueber  Schwefelbacterien.  Bot.  Zeitg.  45:  480-507.  513-523.  520-539, 
545-559.  569-576,  585-594,  606-610.  1887.  Nathansohn,  Alexander,  Ueber  eine  neue  Gruppe  von  Schwe- 
felbacterien und  ihren  Stoffwechsel.  Mittheil.  Zool.  Sta.  Neapel  15:  655-680.  1902.  Beijerinck, 
M.  W.,  Ueber  die  Baketerien  welche  sich  im  Dunkeln  mit  Kohlensaure  als  Kohlenstoffquelle  ernahren 
konnen.  Centralbl.  Bakt.  II.  11:  493-599.  1904.  Omelianski,  W.,  Ueber  eine  neue  Art  farbloser 
Thiospirillen.     Ibid.  II.  14:  769-772.     1905. 

!  Yegounow,  M.,  Sur  les  sulfobacteries  des  limans  d'Odessa.     Arch.  sci.  biol.  St.-Petersbourg  3:  381- 
397.     1895.     Idem,  Die  Mechanik  und  Typen  der  Teilung  der  Bakterienscharen.     Centralbl.  Bakt.  //, 
4:  97-109.     1898. 
4 


5° 


PHYSIOLOGY    OF    NUTRITION 


Depth  in  the  Black  Sea, 
meters 

215 

432 

2040 

2525 


H2S  Context  per  100  l. 
cc. 

33 
222 

555 
655 


In  the  mud  of  the  sea-bottom  are  therefore  going  on  various  kinds  of  fermenta- 
tion, which  are  accompanied  by  the  elimination  of  hydrogen  sulphide."  Only 
because  of  the  presence  of  sulphur  bacteria  is  the  hydrogen  sulphide  prevented 
from  reaching  the  upper  layers  of  water. 

Nitrifying  and  sulphur  bacteria  use  ammonia  and  hydrogen  sulphide,  which 
are  injurious  to  other  organisms,  and  aid  in  preventing  the  accumulation  of  these 
substances  upon  the  surface  of  the  earth;  oxidizing  them  to  nitric  and  sulphuric 


Fig.  30. — Part  of  a  membrane  of  sulphur  bacteria,  magnified   n    times.     (After  Yegunow.) 

acids,  they  bring  these  substances  again  into  the  general  circulation  of  materials 
in  nature. 

Besides  ammonia  and  hydrogen  sulphide,  hydrogen  is  also  produced  in 
large  amounts  by  the  decomposition  of  complex  organic  compounds,  and  yet 
it  is  present  only  in  minimal  quantities  in  the  atmosphere.  According  to  various 
determinations,  the  amount  of  hydrogen  in  the  air  varies  between  0.0003  and 
0.0 1  per  cent.  It  therefore  appears  that  processes  must  occur  on  the  earth, 
by  which  hydrogen  is  combined  and  so  started  anew  in  the  general  circulation 
of  materials. 

The  researches  of  Kaserer1  have  shown  that  there  are  special  bacteria  that 
utilize  hydrogen.  Viewed  from  the  standpoint  of  thermo-chemistry,  hydrogen 
represents  the  best  nutrient  substance.  Its  heat  of  combustion  is  eight  times 
that  of  starch;  a  gram  of  starch  gives  out  during  combustion  but  4.0  kg.-cal.,  of 
heat,  while  a  gram  of  hydrogen  gives  out  34.6  kg.-cal.  (see  page  xxviii).  Certain 
soil  bacteria,  such    as  Bacillus    pantotrophus    and    Bacillus   oligocarbophilus, 

1  Kaserer,  Hermann,  Die  Oxydation  des  Wasserstoffes  durch  Mikroorganismen.  Centralbl.  Bakt.  // 
16:  681-696,  769-775.  1906.  Lebedeff,  A.  F.,  Ueber  die  Assimilation  des  Kohlenstoffes  bei  wasserstoff- 
oxydierenden  Bakterien.  Ber.  Deutsch.  Bot.  Ges.  27:  598-602.  1909.  Nabokich,  A.  J.,  and  Lebedeff, 
A.  F.,  Ueber  die  Oxydation  des  Wasserstoffes  durch  Bakterien.     Centralbl.  Bakt.  11,  17  :  350-355-     1907. 

"  This  deduction  is  of  course  not  strictly  accurate;  although  perhaps  most  of  the  hydrogen 
sulphide,  ammonia  and  hydrogen  in  nature  is  of  organic  origin,  these  substances  are  also  pro- 
duced,  to  some  extent  at  least,  quite  independently  of  organisms. — Ed. 


ASSIMILATION    OF    CARBON  5 1 

utilize  hydrogen.1  The  former  can  derive  its  nourishment  from  organic  com- 
pounds but  it  can  also  grow  in  purely  inorganic  media,  in  which  case  it 
assimilates  carbon  dioxide  and  hydrogen  from  the  atmosphere  and  forms  for- 
maldehyde according  to  the  equation,  H2C03  +  2H2  =  CH20  +  2H0O. 
Niklevskii2  has  isolated  two  bacteria  (Hydrogenomonas  nitrea  and  H.  flava) 
that  can  live  upon  an  inorganic  substratum  with  an  atmosphere  of  hydrogen 
and  oxygen  containing  some  carbon  dioxide.  They  form  organic  compounds 
from  hydrogen  and  carbon  dioxide,  which  are  then  oxidized  to  carbon  dioxide 
and  water  during  respiration.  The  assimilation  of  hydrogen  ceases  when  they 
are  grown  upon  organic  substances. 

In  all  cases  here  described,  of  nutrition  of  bacteria  by  inorganic  substances, 
the  production  of  organic  compounds  occurs  without  the  agency  of  sunlight. 
The  formation  of  hydrogen,  hydrogen  sulphide  and  ammonia  (by  reduction  of 
oxidized  compounds  existing  in  nature,  such  as  water,  sulphuric  acid  and 
nitric  acid),  goes  on  at  the  expense  of  radiant  energy  assimilated  in  green  leaves, 
however.  Therefore  it  is  indirectly  at  the  expense  of  this  energy  that  nitrifying 
bacteria,  sulphur  bacteria  and  hydrogen  bacteria  are  able  to  exist.6 

1  Methane  (CH4),  which  is  frequently  given  off  during  the  putrefaction  of  organic  substances,  can  also 
serve  as  a  nutrient  material  for  some  bacteria.  [See:  Sohngen,  N.  L.,  Ueber  Bakterien,  welche  Methan 
als  Kohlenstoff nahrung  und  Energiequelle  gebrauchen.     Centralbl.Bakt.il,  15:513-517.     1906.] 

2  Niklewski,  Bronislaw,  Ueber  die  Wasserstoffoxydation  durch  Mikroorganismen.  Jahrb.  wiss.  Bot. 
47:  113-142-      1910. 

6  In  the  foregoing  discussion  the  terms  "combustible"  or  " oxidizable "  and  "non-combus- 
tible" or  "non-oxidizable"  substances  should  be  considered  as  synonymous  with  the  more  ac- 
curate ones  "substances  of  high  energy  content"  and  "substances  of  low  energy  content." 
Although  plant  physiology  has  never  yet  received  adequate  treatment  from  the  standpoint  of 
energy  transformations,  some  of  the  more  general  principles  of  such  a  treatment  are  well  recog- 
nized and  are  pertinent  in  the  present  connection.  Energy  can  no  more  be  destroyed  or 
created  than  can  matter,  so  that  when  compounds  of  high  energy  content  (carbohydrates, 
proteins,  etc.)  are  formed  from  compounds  of  lower  energy  content  (carbon  dioxide,  water, 
inorganic  salts,  etc.)  energy  must  be  supplied  from  some  source  other  than  the  reacting  sub- 
stances themselves.  Since  the  reverse  process  yields  energy  it  is  conceivable  that  some  of  the 
energy  obtained  by  the  oxidation  of  large  organic  molecules  may  enter  into  reaction  by  which 
other  complex  compounds  may  be  formed.  This  appears  to  take  place  to  some  extent  in 
green  plants,  in  the  formation  of  proteins,  cellulose,  etc.,  and  in  parasites  and  saprophytes.  It 
is  also  conceivable  that  other  substances  that  yield  energy  upon  oxidation  may  enter  into 
analogous  reactions.  That  this  possibility  is  realized  in  the  cases  of  some  bacteria  seems  to  be 
true,  and  is  one  of  the  chief  contributions  that  the  investigation  of  these  forms  has  made  to 
general  physiology.  Beggiatoa,  which  the  author  mentions,  appears  to  be  able  to  form 
complex  organic  molecules  from  carbonates  by  means  of  the  energy  derived  from  the  oxida- 
tion of  hydrogen  sulphide.  (See:  Keil,  Friedrich,  Beitrage  zur  Physiologie  der  farblosen 
Schwefelbakterien.     Cohn's  Beitrage  zur  Biol.  d.  Pflanzen  2:  335-372-     1912.) 

Bacteria  that  produce  hydrogen  sulphide  must  derive  the  necessary  energy  from  other  reac- 
tions that  yield  energy,  as  from  the  oxidation  of  carbohydrates.  Many  other  colorless  bacteria  are 
similar  in  this  respect.  Besides  the  authors  already  cited  in  the  text,  see:  Keil,  1912  (just  cited). 
Hinze,  G.,  Thiophysa  volutans,  ein  neues  Schwefelbakterium.  Ber.  Deutsch.  Bot.,  Ges. 
21:  309-316.  1903.  Molisch,  Hans,  Neuc  farblose  Schwefelbakterien.  Centralbl.  Bakt. 
H-  33 :  55-02-  191 2.  Lauterborn,  Robert,  Eine  neue  Gattung  der  Schwefelbakterien 
(Thyoploca  schmidlei.  nov.  gen.,  nov.  spec.).     Ber.  Deutsch.  Bot.  Ges.  25:   238-242.     1907. 

Other  bacteria  oxidize  sulphites,  the  liberated  energy  apparently  enabling  them  to  form 


;> 


2  PHYSIOLOGY    OF    NUTRITION 


§4.  Distribution  of  Microorganisms  in  Nature. — The  study  of  microorganisms 
is  possible  only  with  the  aid  of  the  microscope,  and  their  discovery  was  impos- 
sible until  magnifying  glasses  became  available.  The  Columbus  who  discovered 
the  world  of  the  lowest  organisms,  which  are  ordinarily  invisible,  was  a  Dutch 
lens-maker  of  Delft,  Anton  van  Leeuwenhoek.  He  succeeded  in  making  mag- 
nifying glasses  that  magnified  100  and  even  150  diameters.  When,  in  1675,  he 
examined  a  drop  of  rain  water  that  had  stood  for  several  days  in  a  barrel,  using 
one  of  his  glasses,  he  observed  a  vast  number  of  extremely  small  organisms 
moving  hither  and  thither  in  the  water.  The  number  of  these  organisms  ap- 
proached 10,000  in  a  single  drop.  No  such  organisms  were  to  be  seen  in  freshly 
collected  rain  water,  and  Leeuwenhoek  therefore  concluded  that  the  germs  of 
these  must  have  fallen  into  the  water  from  the  air. 

The  question  then  arose  as  to  the  origin  of  these  extremely  small  organisms, 
and  this  became  the  subject  of  a  very  lively  polemic.  It  is  well  known  that 
infusions  of  most  organic  materials,  such  as  meat  and  vegetable  matter,  de- 
compose very  easily.  Microscopical  examination  of  material  undergoing  de- 
composition always  shows  the  presence  of  microorganisms.  The  promptness 
with  which  they  appear  led  to  the  conclusion  that  we  have  here  a  spontaneous 
generation  (generatio  spontenea)  of  the  lowest  forms  of  life  out  of  various 
organic  substances. 

The  theory  of  spontaneous  generation  has  had  many  adherents,  even  until 
recent  times.  Thus,  van  Helmont  (1 577-1644)  was  the  author  of  a  recipe  for 
the  production  of  mice  from  meal.  It  was  maintained  that  maggots  (fly  larvae) 
arise  by  spontaneous  generation  in  meat.  Even  after  it  had  been  provided  by 
exact  experimentation  that  neither  mice  nor  maggots  can  be  produced  de  novo, 
and  that  such  forms  must  arise  by  propagation,  still  the  conviction  persisted 
for  a  long  time  that  the  tiny,  microscopic  organisms  may  develop  by  spon- 
taneous generation.  As  early  as  1776  Spallanzani  proved  experimentally  that 
this  theory  was  incorrect.  He  showed  that  no  animalcules  appeared  in  an  her- 
metically sealed  vessel  containing  an  infusion  of  organic  material,  no  matter 
how  long  this  was  allowed  to  stand,  provided  the  infusion  had  been  first  boiled 
for  three-quarters  of  an  hour.  After  such  a  vessel  had  been  opened,  however, 
the  contents  soon  began  to  putrefy;  because  germs  entered  from  the  air,  as 
Spallanzani  maintained.     Although  the  adherents  of  the  theory  of  spontaneous 

complex  carbon  compounds  from  mineral  carbonates  and  bicarbonates.  (See  Nathansohn, 
1902,  and  Beijerinck,  1004.  [Note  2,  p.  49.])  In  addition  to  these  there  are  still  others 
that  oxidize  ferrous  compounds  to  the  ferric  form.1  See:  Winogradsky,  S.,  Ueber  Eisenbak- 
terien.  Bot.  Zeitg.  46:  261-270.  1888.  Molisch,  Hans.  Die  Eisenbakterien.  Jena,  1910. 
Lieske,  Rudolf,  Beitrage  zur  Kenntnis  der  Physiologie  von  Spirophyllum  ferrugineum  Ellis, 
einen  typischen  Eisenbakterium.  Jahrb.  wiss.  Bot.  49:  91-127.  1911.  Idem,  Untersuch- 
ungen  uber  die  Physiologie  eisenspeichernder  Hyphomyceten.     Ibid.  50:  328-354.     1911. 

Since  the  forms,  or  kinds,  of  energy  are  mutually  transformable  it  is  possible  that  energy  for 
the  syntheses  that  occur  in  organisms  may  be  derived  not  only  from  chemical  reactions  and 
light  but  also  from  other  immediate  sources,  such  as  the  radiant  energy  of  heat  and  electri- 
city. The  heat  of  the  medium  in  which  the  reactions  occur  is  of  course  a  very  important 
source  of  energy,  not  generally  discussed  in  this  connection. — Ed. 


ASSIMILATION    OF    CARBON 


53 


generation  were  not  convinced  by  the  experiment  of  Spallanzani,  nevertheless  it 
received  a  practical  application  at  the  hands  of  a  French  cook,  Francois  Appert. 
who  started  a  factory  for  making  preserves.  He  found  that  it  was  possible  to 
keep  meats,  vegetables  and  liquids  unspoiled  for  unlimited  periods  of  time,  if 
these  materials  were  placed  in  hermetically  sealed  jars  and  then  heated  in 
boiling  water.  Appert  published  his  experiments  in  a  book  which  passed 
through  many  editions;1  the  book  brought  him  fame,  the  preserves  brought  him 
a  fortune.  We  have  here  a  conspicuous  example  of  the  dependence  of  technical 
arts  upon  theoretical  knowledge;  Spallanzani,  in  solving  the  purely  philosophical 
question  of  the  origin  of  living  things  on  the  earth,  thereby  gave  Appert  the 
opportunity  to  found  a  new  industry. 

Since  the  objection  was  raised  against  Spallanzani's  experiment,  that  the 
closed  vessels  contained  an  inadequate  supply  of  air  and  that  the  quality  of  what 
air  there  was  must  be  greatly  impaired  by  the  high  temperature,  Franz  Schultze 
performed  the  following  experiment  in  1836.     A  glass  flask  (Fig.  31)  half  full 


Fig.  31. — Arrangement  of  bottle  and  potash  bulbs  in  Schultze's  experiment. 

of  an  organic  infusion  and  tightly  closed  with  a  cork  stopper,  through  which 
two  bent  glass  tubes  were  passed,  was  subjected  to  active  boiling  for  some 
time.  While  hot  steam  was  still  escaping  from  both  tubes  he  attached  a  potash 
bulb  to  each,  one  filled  with  potassium  hydroxide  solution  and  the  other  with 
sulphuric  acid,  after  which  the  apparatus  was  allowed  to  cool.  Twice  a  day, 
for  three  months  thereafter,  air  was  drawn  through  the  flask,  entering  through 
the  sulphuric  acid  and  passing  out  through  the  alkali.  No  organisms  of  any 
kind  were  found  in  the  solution.  All  the  germs  present  in  the  entering  air  were 
removed  by  the  sulphuric  acid.  In  this  experiment  the  air  retained  its  usual 
composition  and  was  not  heated. 

But  this  experiment  did  not  seem  to  be  entirely  convincing,  and  it  was 
only  by  the  remarkable  investigations  of  Pasteur  that  the  question  of  spon- 
taneous generation  was  finally  and  conclusively  settled  in  the  negative.     Pas- 

1  [Appert,  Charles,  L'art  de  conserver  pendant  plusieurs  annees  toutes  les  substances  animales  et  veg£- 
tales.  2nd  ed.  Paris,  1811.  Idem,  Le  livre  de  tout  les  menages  ou  l'art  de  conserver  pendant  plusieurs 
anees  les  substances  animales  et  vcgetales.  3rd  ed.  Paris,  1813.  A  5th  ed.  was  published  in  1842,  or 
earlier.  Xone  of  these  has  been  seen  in  preparing  this  note;  the  references  are  taken  from:  Catalogue 
gen6ral  des  livres  imprimes  de  la  Bibliotheque  Xationale,  Paris  3:  736.      1899. — Ed. 


54 


PHYSIOLOGY    OF    NUTRITION 


teur  (1857)  closed  glass  flasks  of  various  solutions  with  cotton  plugs  and  sub- 
jected them  to  prolonged  boiling.  If  the  boiling  had  been  continued  sufficiently 
long  the  solution  in  the  flasks  remained  unchanged  and  free  from  microorganisms 
for  an  indefinite  period  of  time.  The  air  that  entered  the  flasks  during  cooling 
was  filtered  through  the  cotton  plugs,  in  which  all  the  germs  that  it  originally 
held  were  left  behind.  Since  the  spores  of  some  bacteria  withstand  a  single, 
though  long-continued  boiling,  this  operation  must  sometimes  be  repeated 
several  times,  and  even  under  pressure,  in  order  to  kill  all  organisms  originally 
present.  Pasteur  carried  out  a  number  of  his  experiments  in  glass  flasks  espe- 
cially arranged  with  two  necks  (Fig.  32).  One  of  the  necks  bore  a  short  piece 
of  rubber  tubing,  which  was  closed  by  a  bit  of  glass  rod.  The  other  neck  was 
drawn  out  into  a  narrow  tube,  bent  twice  upon  itself.  Both  were  open  during 
the  boiling  of  the  liquid.  While  boiling  was  still  going  on  the  wide  tube  was 
plugged,  after  which  boiling  was  stopped  and  the  apparatus  was  cooled,  air 

entering  through  the  narrow  tube.  The  solution  re- 
mained unchanged  indefinitely,  since  all  spores  con- 
tained in  the  entering  air  were  caught  in  the  narrow 
bend  of  the  tube.  However,  if  the  glass  stopper  was 
momentarily  removed,  thus  allowing  a  very  small 
number  of  microorganisms  to  enter  the  flask,  then 
the  solution  immediately  began  to  decompose.  De- 
composition is  brought  about  in  such  an  experiment 
as  a  result  of  the  rapid  multiplication  of  the  micro- 
organisms that  have  been  introduced. 

To  demonstrate  conclusively  that  the  theory  of 
spontaneous  generation  is  untenable,  it  remained 
still  to  prove  that  microorganisms  and  their  spores 
really  do  occur  in  the  air  in  great  abundance.  This 
question  was  also  worked  out  by  Pasteur  in  the  most 
exact  manner.  He  took  a  series  of  flasks,  filled  to  a 
third  of  their  volume  with  nutrient  solution,  brought  the  contents  to  boiling 
and  then  sealed  them  by  fusing  the  glass  of  their  narrow  necks.  The  flasks 
were  then  placed  in  positions  where  he  wished  to  investigate  the  air,  and  the 
sealed  ends  were  then  broken  off,  thus  allowing  air  to  enter.  The  flasks  were 
then  resealed.  If  the  air  entering  a  flask  was  free  from  germs,  then  the  liquid 
remained  unchanged,  but  if  the  entering  air  contained  microorganisms  or  their 
spores,  then  decomposition  began.  In  this  way  Pasteur  proved  that  the  air  of 
deep  cellars  and  high  mountains  is  most  nearly  pure.  It  need  not  be  con- 
cluded, however,  that  the  air  is  absolutely  free  from  organisms  in  those  cases 
where  the  liquid  remains  unchanged  in  such  experiments;  it  is  quite  possible 
that  spores  may  be  contained  in  the  air  but  they  may  be  able  to  develop  in 
the  particular  nutrient  medium  chosen. 

Many  exact  investigations  have  now  been  made  upon  the  distribution  of 
microorganisms  in  the  air.  The  table  given  below  presents  the  average  results 
from  ten  years  of  observation  (1885-1894)  upon  the  number  of  microorganisms 


Fig.  32. — Pasteur  flask. 


ASSIMILATION    OF    CARBON 


;>;> 


in  a  cubic  centimeter  of  air  in  the  Park  of  Montsourie.  In  the  same  table  are 
shown  the  corresponding  numbers,  averages  from  ten  years  of  observations, 
in  one  of  the  squares  in  Paris  (Place  Saint-Gervais).  The  numbers  are  much 
larger  in  cities  than  in  the  country. 


Season  of  Year 


Bacteria 


Winter. . 
Spring. 
Summer 
Autumn. 


170 

295 
345 
195 


Place  Saint  Gervais 
(Paris) 


Moulds 


Bacteria 


i4S 
i95 
246 
230 


43°S 
8080 

9845 
S665 


Moulds 


1345 
2275 
2500 
2185 


Microorganisms  occur  not  only  in  the  air  but  also  in  water  and  soil.  The 
water  of  rivers  always  contains  bacteria,  these  being  especially  numerous  in  the 
vicinity  of  cities.  The  following  numbers  of  bacteria  were  found  in  a  cubic 
centimeter  of  water  from  the  rivers  and  at  the  localities  cited  below. 


River  Rhone 


River  Spree 


above  Lyons 75 

below  Lyons 800 

above  Berlin 4,3°° 

below  Berlin 97>4oo 


Microorganisms  also  occur  in  rain  water,  in  snow  and  in  hail. 

The  soil  always  contains  microorganisms,  their  number  naturally  depending 
upon  the  amount  of  organic  material  present.  Many  more  are  found  near  the 
surface  than  in  the  deeper  layers.  The  following  table  gives  an  idea  of  their 
distribution  at  various  depths  in.  a  soil  covered  with  forest  growth  (at  Pfingst- 
berg,  in  the  vicinity  of  Potsdam).  These  are  the  numbers  of  microorganisms 
found  in  a  cubic  centimeter  of  soil  from  various  depths  at  different  times  of  the 


vear. 


Depth  below  Soil  Surface, 

meters 

May  27 

June  15 

Nov.  3 

0.0 

150,000 

140,000 

55,ooo 

0.5 

200,000 

145,000 

75,000 

1 .0 

2,000 

1,000 

7,000 

2 .0 

2,000 

0 

100 

3-o 

3,000 

700 

1,500 

4-5 

100 

100 

0 

PHYSIOLOGY    OF    NUTRITION 


Bacteria  are  present  in  all  foods,  milk  furnishing  especially  favorable  condi- 
tions for  their  development.  When  fresh  this  liquid  generally  contains  no  bac- 
teria, but  they  develop  very  quickly  from  spores  that  fall  from  the  air.  Thus 
a  cubic  centimeter  of  milk  that  had  stood  since  milking  at  a  temperature  of 
i5.5°C,  contained  the  following  numbers  of  bacteria  per  cubic  centimeter. 


Hours  after  Milking 

4 

9 

24 


Bacteria  per  cc. 

34,000 

1 00,000 

4,000,000 


The  intestinal  tract  of  man  is  densely  populated  with  bacteria,  which  fre- 
quently cause  decomposition  of  foods  in  the  intestine.  We  are  thus  not  only 
externally  surrounded  by  bacteria,  but  are  even  internally  infested  with  them. 
This  seems  to  explain  why  these  organisms  appear  so  promptly  in  all  kinds  of 
organic  material  that  they  decompose. 

§5.  Sterlization  and  Disinfection.1— In  view  of  the  fact  that  microorganisms 
are  so  universally  present,  all  objects  used  in  handling  them  must  be  absolutely 
free  from  spores  or  germs  of  any  kind,  especially  if  pure  cultures  of  a  certain 
species  are  desired.     This  is  accomplished  by  sterilization.     Such  small  objects 


Fig.  33. — Dry-air  sterilizer  heated  by  gas. 

as  knives,  scissors,  glass  rods,  forceps,  slides  and  cover  glasses,  platinum  needles, 
etc.,  may  be  sterilized  by  heating  in  a  gas  or  alcohol  flame.  Platinum  instru- 
ments may  be  brought  to  a  red  heat  but  for  other  objects  a  few  moments  in  the 
flame  suffices,  so  that  germs  clinging  to  the  surface  may  be  destroyed.  A  dry- 
ing oven,  or  dry-air  sterilizer,  is  used  for  the  sterilization  of  larger  objects  (Fig. 
33).     This  is  usually  equipped  with  double  walls,  the  products  of  combustion 

1  Abel,  Rudolf  V.  L.,  Taschenbuch  fur  den  bakteriologischen  Praktikanten.  [Abel's  Laboratory  hand- 
book of  bacteriology.  Tr.  from  10th  German  ed.  by  M.  H.  Gordon.  London,  1907.]  Kiister,  Ernst, 
Anleitung  zur  Kultur  der  Mikroorganismen  fur  den  Gebrauch  in  zoologischen,  botanischen,  medizinischen 
und  landwirtschaftlichen  Laboratorien.     Leipzig  and  Berlin,  1907- 


ASSIMILATION    OF    CARBON 


57 


from  the  gas  flame  below  passing  between  the  two  walls  and  thus  rendering  the 
heating  uniform.0 

Objects  that  cannot  endure  dry  heat  are  sterilized  in  a  steam  sterilizer, 
such  as  Koch's  apparatus.  This  is  a  cylinder  of  tinned  sheet  iron  or  copper 
with  a  cover  above.  The  lower  part  is  filled  with  water  and  the  objects  to  be 
sterilized  are  placed  upon  a  perforated  rack  in  the  upper  part.  A  burner  below 
the  cylinder  heats  the  water  to  boiling  and  the  contained  objects  are  sterilized 
by  water  vapor  at  ioo°C.  The  apparatus  is  covered  with  felt  or  asbestos,  to 
retard  the  escape  of  heat.d 


Fig.  34. — Arnold  steam  sterilizer. 


Instead  of  a  steam  sterilizer  the  autoclave  is  frequently  used  for  steriliza- 
tion (Fig.  35).  This  is  nothing  more  than  a  Papin's  digester,  operating  with 
superheated  steam,  under  pressure  up  to  two  atmospheres  or  more  and  at 
temperatures  of  from  ioo°  to  i34°C.  or  higher.  At  a  temperature  of  i2o°C. 
sterilization  need  last  only  fifteen  minutes.  At  a  temperature  of  1300  all 
germs  are  instantly  killed,  so  that  repeated  treatment,  necessary  in  the  case 
of  steam  sterilization,  is  here  superfluous. 

c  For  most  satisfactory  work  the  oven  should  have  an  automatic  temperature-regulator, 
various  forms  of  which  are  available  for  gas.  Electrically  heated,  automatically  regulated 
ovens  are  also  obtainable,  some  of  which  are  so  well  insulated  that  but  little  heat  escapes  to  the 
exterior. — Ed. 

d  One  of  the  various  forms  of  the  Arnold  type  of  steam  sterilizer  is  most  convenient  and 
efficient  in  operation.  (Fig.  34.)  This  keeps  but  a  small  amount  of  water  boiling  at  any  one 
time  and  a  large  portion  of  the  water  that  is  boiled  away  is  condensed  and  returned  to  the 
reservoir. — Ed. 


53 


PHYSIOLOGY    OF    NUTRITION 


Liquids  may  also  be  sterilized  by  filtration.  The  most  convenient  arrange- 
ment for  this  purpose  is  the  Chamberland  filter,  a  hollow  cylinder  of  porous 
porcelain,  closed  at  one  end.  The  liquid  to  be  sterilized  is  passed,  under  pres- 
sure, through  the  porous  walls  of  the  previously  sterilized  filter. 

Various  disinfecting  materials  are  also  used  for  the  chemical  destruction  of 
microorganisms.  The  most  effective  of  these  is  corrosive  sublimate,  or  mercuric 
chloride  (HgCl2).  A  solution  of  i  g.  of  mercuric  chloride  in  a  liter  of  distilled 
water  is  thus  used  in  bacteriological  laboratories.     The  hands  of  the  worker  and 

also  his  implements  are  disinfected  with  this  solu- 
tion, which  is  also  employed  to  destroy  cultures 
that  are  not  needed.  A  solution  of  one  part  of 
the  salt  in  300,000  parts  of  water  prevents  the 
development  of  the  bacillus  of  splenic  fever, 
Bacillus  anthracis.  Sulphurous  acid,  chlorinated 
lime  [also  known  as  bleaching  powder;  it  con- 
tains calcium  hypochlorite],  hydrofluoric  acid 
and  its  salts,  boric  acid,  ozone,  hydrogen  per- 
oxide, milk  of  lime,  and  phenol,  or  carbolic 
acid,  are  also  suitable  for  use  as  disinfectants.6 
§6.  Pure  Cultures. — To  study  microorgan- 
isms with  respect  to  their  developmental  history 
and  their  physiological  process  it  is  necessary 
to  obtain  them  in  a  pure  culture.1  A  pure 
culture  is  one  known  to  contain  only  a  single, 
definite  species  of  organism.  Such  a  culture 
can  be  obtained  only  by  fulfilling  two  conditions. 
The*  first  consists  in  the  exercise  of  sufficient 
precaution  to  prevent  the  entrance  of  germs 
from  the  air  into  the  sterilized  culture  medium; 
the  second  is  the  derivation  of  the  culture  from 
a  single  cell.  A  culture  in  which  all  the  micro- 
organisms are  quite  similar  is  nevertheless  not 
to  be  termed  a  pure  culture  unless  it  has  been  derived  from  a  single  cell, 
since  very  many  microorganisms  with  entirely  different  physiological  properties 

1  Pure  cultures  may  be  purchased  from  several  establishments,  among  which  may  be  mentioned  the 
following:  Krals  Bakteriologisches  Laboratorium,  Prag  I,  Kleiner  Ring  II;  Institut  fur  Garungsgewerbe, 
Berlin  N,  Seest:asse  6s;  Jorgensens  Laboratorium,  Kopenhagen,  Frydendalsvej  30;  Zentralstelle  fur  Pilz- 
kulturen,  Amsterdam.  [They  may  be  obtained  from  the  Laboratory  of  the  American  Museum  of  Natural 
History,  New  York,  and  from  Parke,  Davis  and  Co.,  Detroit.  —Ed.] 

'To  the  substances  mentioned  in  the  text  may  be  added:  iodine,  sodium  sulphite  and 
Dakin's  recent  discovery,  paratoluene-sodium-sulphochloramide  (on  the  American  market 
under  the  trade-name  chlorazene,  though  it  was  called  "chloramine"  by  Dakin  [British 
med.  jour.,  Aug.  25,  1915,  also  Jan.  29,  1916]).  Chlorine,  bromine,  and  potassium  per- 
manganate are  also  used  as  disinfectants.  It  should  be  noted,  however,  that  antiseptics 
or  disinfectants  that  are  useful  in  some  cases  may  be  useless  or  even  harmful  in  others. 
Numerous  references  on  this  subject  are  given  in  the  Index  Medicus,  Carnegie  Inst.,  Wash. — 
Ed. 


Fig.  35. — Autoclave.  The  top 
is  hinged  and  may  be  raised  after 
releasing  the  locking  clamps. 


ASSIMILATION    OF    CARBON 


59 


have  exactly  the  same  form.  On  the  other  hand,  a  culture  obtained  from  a 
single  cell  is  called  a  pure  culture,  even  though  the  microorganisms  therein 
contained  exhibit  diverse  forms,  since  we  now  know  that  one  and  the  same 
species  of  bacterium  or  yeast  can  assume  different  forms,  according  to  its 
developmental  stage  and  the  influence  of  the  medium  in  which  it  is  grown. 

The  method  most  frequently  used  for  the  production  of  pure  cultures  is 
that  of  dilution.  This  method  was  first  used,  in  its  original  form,  by  Lister1 
in  1878,  to  obtain  a  pure  culture  of  lactic  acid  bacteria.  It  was  carefully 
elaborated  for  yeasts  by  the  Danish  bacteriologist,  Hansen  in  1881/ 

Let  it  be  supposed  that  we  have  a  fermenting  beer-wort  with  many  different 
species  of  yeasts,  and  that  these  are  to  be  separated,  so  that  each  species  may 
be  had  in  pure  culture.  After  shaking  the  liquid,  several  drops  are  taken  up  in 
a  sterilized  pipette  and  transferred  to  a  Freudenreich  flask  (Fig.  36)  partly  filled 
with  sterilized  water.  This  flask  is  of  glass,  with  a  capacity  of 
from  25  to  30  cc,  and  is  closed  by  means  of  a  glass  cap  shaped 
like  a  short,  inverted  thistle-tube,  the  small  opening  of  which  is 
plugged  with  cotton.  To  obtain  a  uniform  distribution  of  the 
yeast  cells  throughout  the  liquid,  the  flask  is  thoroughly  shaken, 
after  which  a  drop  of  the  contents  is  transferred,  upon  the  bent 
end  of  a  platinum  wire,  to  the  surface  of  a  microscope  cover  glass 
which  is  marked  off  into  small  squares.  Here  the  drop  is  spread 
out  into  a  thin  layer,  and  the  number  of  cells  present  is  determined 
by  counting.  A  van  Tieghem  cell,  or  moist  chamber,  is  used  for 
this  purpose  (Fig.  37).  This  consists  of  a  slide  upon  which  a  glass 
ring  (c)  is  sealed  with  vaseline.  A  small  quantity  of  water  (d)  is 
introduced  into  the  chamber  so  that  microorganisms  clinging  to 
the  under  side  of  the  cover  glass  (a)  may  not  become  desiccated. 
The  cross-ruled  cover  glass  is  sealed  to  the  glass  ring  with  vaseline,  the  culture 
drop  hanging  from  its  lower  surface  (b).  The  divisions  marked  upon  the 
cover  glass  facilitate  the  counting  of  the  cells  under  the  microscope. 

Suppose  that  twenty  cells  are  found  upon  the  cover  glass.  The  drop  of 
liquid  is  again  transferred,  by  means  of  the  platinum  hook,  to  a  fresh  Freunden- 
reich  flask  containing  40  cc.  of  sterilized  water.     After  vigorous  shaking  about  1 

cc.  of  this  liquid  is  transferred  (with  a  pipette) 
into  each  of  forty  Freudenreich  flasks  containing 
sterilized  beer-wort.     Since  the  original  drop  con- 


Fig.  36  — 

Freudenreich 
flask. 


a- 


c- 


mm 


7     T  tained  only  twenty  cells,  we  should  expect  that 

Fig.  37. — Moist  chamber,  or  J  J  '  ^  . 

van  Tieghem  cell,  for  microscopic  the  yeast  would,  in  all  probability,  develop  only  in 

work,     a,  cover  glass;  b,  position  twenty  0f  the  flasks  while  the  other  twenty  would 
01    drop    of   medium;    c,    wall    of  .  . 

chamber  made  of  section  of  glass  remain  sterile.     It  is  also  highly  probable  that  the 
bottom^of  Ihambe0/  solution  in  new  generation  has  arisen  from  only  a  single  cell 

in   those   flasks   where   growth   does   occur.     All 

1  Lister,  Joseph,  On  the  lactic  fermentation  and  its  bearings  on  pathology.      Trans.  Pathol.  Soc.  London 
20:  425-467.      1878. 

'Hansen,  1896.     [See  note  1,  p.  44.]. — Ed. 


6o 


PHYSIOLOGY    OF    NUTRITION 


this  is  only  highly  probable,  however,  and  not  definitely  established.  Hansen 
employed  this  method  in  his  work  with  yeasts.  Flasks  containing  freshly 
inoculated  beer-wort  are  vigorously  shaken  and  then  allowed  to  stand.  The 
cells  sink  to  the  bottom  and  begin  to  multiply,  so  that,  after  a  time,  whitish 
colonies  of  cells  become  visible  with  the  unaided  eye.  If  a  flask  shows  but 
one  such  colony  it  follows  that  only  a  single  cell  was  introduced,  since  it  is 
highly  improbable  that  two  cells  might  have  settled  together  after  the  shaking. 
If,  on  the  other  hand,  two  or  three  cells  have  been  introduced  into  the  flask, 
then  two  or  three  colonies,  respectively,  develop. 

In  order  to  secure  pure  yeast  cultures,  solid  substrata  may  also  be  em- 
ployed, which  make  it  possible  to  follow,  under  the  microscope,  the  development 
of  a  colony  from  a  single  cell.  For  this  purpose  a  drop  from  a  young  yeast  cul- 
ture—previously shaken — is  introduced  into  a  small  flask  of  sterilized  water. 
From  this  is  inoculated,  by  means  of  the  tip  of  a  platinum  wire,  another  flask 
containing  beer-wort  and  gelatine,  warmed  to  45°C.  The  latter  is  vigorously 
shaken  and  then  a  drop  of  the  liquid  is  transferred  to  a  circular  cover  glass  (30  mm. 
in  diameter),  which  has  been  marked  off  into  numbered  squares,  and  the  cover 
is  laid  over  a  glass  ring  to  form  a  moist  chamber  or  van  Tieghem  cell.  The 
yeast  cells  are  held  immovable  in  the  hardened  gelatine  so  that  it  may  now  be 


Fig.  38. — Pasteur  flask; 
a  slightly  different  form  from 
that  of  Fig.  32,  p.  54. 


Fig.  39. — Petri  dish. 


Fig.  40. — Showing  insertion 
of  needle  into  solid  medium  in 
inverted  tube,  to  make  stab 
inoculation. 


noted  in  which  squares  single  ones  lie,  and  the  development  of  colonies  from  these 
may  be  readily  followed.  When  the  colonies  become  clearly  visible  to  the  un- 
aided eye,  one  of  them  is  removed  from  the  cover  glass  and  placed  in  a  flask  of 
nutrient  solution.  The  colony  is  lifted  on  the  end  of  a  bit  of  flame-sterilized 
platinum  wire,  held  by  means  of  forceps,  and  the  wire,  with  its  colony,  is  dropped 
into  the  flask.  During  this  operation  the  cover  glass  must  be  held  with  the  drop 
on  its  under  side,  to  prevent  infection  from  the  air.  If  a  large  quantity  of  pure 
culture  is  desired,  a  portion  of  a  young  culture  a  day  old,  obtained  as  just  de- 


ASSIMILATION    OF    CARBON  6 1 

scribed,  is  transferred  with  a  pipette  to  a  Pasteur  flask  (capacity  about  200  cc.) 
of  sterilized  beer- wort  (Fig.  38).  After  a  day  the  contents  of  this  flask  are 
poured  into  second  flask  (capacity  about  500  cc.)  also  filled  with  sterile  beer- 
wort. 

Solid  as  well  as  liquid  nutrient  media  are  used  for  pure  cultures  of  bacteria. 
In' the  case  of  liquid  media  the  dilution  method  described  above  is  used  to 
separate  the  cells.  With  solid  media,  which  are  very  valuable  for  the  pro- 
duction of  pure  cultures,  Petri  dishes  are  used  for  this  purpose  (Fig.  39).  Each 
dish  consists  of  two  shallow  glass  pans  (9  or  10  cm.  in  diameter),  one  being  a 
little  larger  than  the  other  and  forming  a  cover  for  it.  A  trace  of  the  mixed 
culture  is  introduced  into  a  flask  containing,  for  instance,  a  mixture  of  bouillon 
and  gelatine,  at  3o°C,  after  which  the  flask  is  shaken,  and  the  contents  are  then 
poured  into  the  dish  and  the  latter  is  covered.  After  some  time  each  bacterial 
cell  builds  a  colony  around  itself,  which  can  be  seen  by  the  unaided  eye  or  with 
a  simple  magnifying  glass. 

When  a  pure  culture  of  a  certain  microorganism  is  finally  obtained,  then 
any  number  of  pure  cultures  of  that  form  may  be  readily  prepared.  Inoculations 
of  liquid  nutrient  media  are  effected  by  means  of  a  glass  rod,  a  platinum  wire  or 
a  pipette,  with  all  the  requisite  precautions.  Inoculations  of  solid  media  may 
take  the  form  of  either  stab  or  streak  cultures.  To  make  a  stab  culture  a 
platinum  needle  is  dipped  in  the  original  culture  and  is  then  thrust  upward  into 
the  solid  medium  held  in  an  inverted  test-tube  (Fig.  40).  F6r  a  streak  cul- 
ture, a  test-tube  of  solid  medium  with  a  slanting  surface  is  prepared,  and  the 
point  of  the  inoculating  needle  is  drawn  across  this  surface. 

Summary 

1.  General. — Plants  without  chlorophyll  cannot  form  carbohydrates  from  carbon 
dioxide  and  water  by  means  of  the  energy  of  sunlight.  They  derive  energy,  as  well 
as  material,  from  chemical  compounds.  Such  plants  may  be  divided  into  two  groups: 
those  of  one  group  get  energy  from  organic  compounds  alone  (these  compounds  having 
been  previously  made  by  green  plants),  those  of  the  other  group  derive  energy  from 
inorganic  substances.  Cells  with  chlorophyll  utilize  sunlight  energy  to  form  carbo- 
hydrates (and  oxygen)  out  of  carbon  dioxide  and  water,  while  cells  without  chlorophyll 
either  get  carbohydrates  (or  related  organic  compounds)  ready-made  from  their 
surroundings,  being  unable  to  utilize  either  sunlight  energy  or  carbon  dioxide,  or  else 
they  derive  energy  from  inorganic  compounds  and  thereby  form  their  carbohydrates 
and  related  compounds  out  of  carbonates  or  carbon  dioxide  and  water. 

2.  Non-green  Plants  That  Derive  Energy  Only  from  Organic  Compounds.— Yeasts, 
fungi,  non-green  seed  plan  s,  the  non-green  portions  of  ordinary  green  plants,  and 
most  bacteria,  derive  their  energy  supply  exclusively  from  ready-made  organic  com- 
pounds. These  ompounds  also  supply  carbon,  which  is  of  course  as  essential  for 
non-green  cells  as  for  cells  with  chlorophyh1.- 

The  microorganisms  of  this  group  are  very  important  in  nature,  being  largely 
responsible  for  decay  and  putrefaction.  They  live  by  decomposing  the  organic  sub- 
stances produced  by  other  organisms,  including  green  plants.  They  may  be  dis- 
tinguished from  one  another  by  the  nature  of  the  substances  required  for  their  growth, 
and  they  may  be  grown  in  artificial  nutrient  media,  such  as  Pasteur's  culture  solution 


62  PHYSIOLOGY    OF    NUTRITION 

for  yeast.  These  organisms  are  either  saprophytic  (living  on  dead  material  from  other 
organisms)  or  parasitic  (living  on  tissues  that  are  still  alive).  There  are  also  a  few 
saprophytes  and  parasites  among  flowering  plants.  Dodder  (Cuscuta)  is  an  example 
of  a  parasite  of  this  kind.     Mushrooms  are  examples  of  large  saprophytic  forms. 

3.  Non-green  Plants  That  Derive  Energy  from  Inorganic  Compounds. — This 
group  is  composed  of  certain  kinds  of  bacteria  that  are  able  to  oxidize  inorganic  com- 
pounds and  thus  secure  a  supply  of  energy.  Of  these,  nitrifying  bacteria  are  very 
important.  They  oxidize  ammonia  to  nitric  acid.  They  must  be  grown  in  surround- 
ings free  from  carbohydrates  and  other  organic  substances,  but  they  require  carbon 
dioxide  (or  carbonates)  and  oxygen.  They  form  carbohydrates  and  other  organic  com- 
pounds out  of  water  and  carbonates  or  carbon  dioxide,  somewhat  as  do  green  plants, 
but  their  source  of  energy  is  very  different.  Another  example  of  this  group  is  furnished 
by  the  sulphur  bacteria  (as  Beggiatoa),  which  oxidize  hydrogen  sulphide  to  sulphur 
and  water,  thus  securing  an  energy  supply.  The  sulphur  produced  is  finally  oxidized 
into  sulphates,  such  as  calcium  sulphate.  The  sulphur  bacteria  grow  in  the  presence  of 
organic  material.  Some  hydrogen  bacteria  (Hydrogenomonas)  can  form  organic  material 
from  hydrogen,  oxygen,  and  carbon  dioxide,  in  the  absence  of  organic  compounds. 
Hydrogen  is  oxidized,  thus  supplying  energy.  In  the  presence  of  organic  compounds 
hydrogen  is  not  oxidized,  and  these  bacteria  are  then  to  be  considered  as  belonging  to 
the  preceding  group. 

This  whole  matter  of  the  carbon  nutrition  of  plants  may  be  stated  as  follows: 
Apparently  all  organic  compounds  in  plants  are  formed,  directly  or  indirectly,  from 
carbohydrates  (such  as  sugars).  (1)  The  carbohydrates  used  may  be  formed  in  cells 
with  chlorophyll,  out  of  carbon  dioxide  and  water,  and  by  means  of  sunlight  energy 
(2)  The  carbohydrates  used  may  be  formed  in  cells  without  chlorophyll,  out  of  carbon 
dioxide  (or  carbonates)  and  water,  by  means  of  energy  obtained  through  the  oxidation 
of  inorganic  substances  such  as  ammonia,  sulphur  dioxide,  hydrogen,  etc.  (3)  The 
carbohydrates  used  may  be  derived  from  the  surroundings,  either  ready-made  or  else 
by  the  decomposition  of  other  organic  compounds  that  are  themselves  supplied  ready- 
made  in  the  surroundings.  These  other  organic  compounds  may  also  be  used  directly, 
without  the  preliminary  step  of  forming  carbohydrates.  There  are  just  two  general 
sources  of  energy  for  plant  activities,  (a)  sunlight  and  (b)  energy  derived  from  the 
oxidation  of  substances;  and  the  substances  oxidized  may  be  either  organic  or  inorganic. 

4.  Microorganisms  in  Nature. — Since  Spallanzani's  time  it  has  been  known  that  all 
organisms  are  formed  by  the  reproduction  of  other  organisms,  and  that  the  micro- 
organisms found  everywhere  in  nature  arise  in  this  way.  On  the  basis  of  this  principle 
Appert  originated  the  art  of  preserving  foods  by  sterilization.  If  all  organisms  in  a 
preparation  are  killed  at  the  start,  and  if  no  more  are  allowed  to  enter  from  without, 
there  will  be  no  living  ones  in  the  preparation.  Fermentation  and  the  decay  of  foods 
are  caused  by  microorganisms,  and  these  substances  may  therefore  be  preserved  by 
sterilizing  and  then  hermetically  sealing  them.  This  whole  proposition  was  finally 
clearly  worked  out  by  Pasteur,  who  showed,  among  many  other  things,  that  the  micro- 
organisms that  cause  fermentation  in  foods,  etc.,  originate  from  individuals  of  the 
same  forms,  which  fall  in  from  the  air,  etc.  The  air  generally  contains  large  numbers 
and  many  kinds  of  microorganisms  as  do  also  soil,  water,  the  human  alimentary  tract, 
etc. 

5.  Sterilization  and  Disinfection.— To  obtain  objects  or  material  absolutely  free 
from  living  microorganisms  sterilization  is  necessary.  In  many  cases  this  is  done  by 
dry  heat.     In  other  cases  steam  is  used,  especially  in  a  closed  chamber,  such  as  the 


ASSIMILATION    OF    CARBON  63 

autoclave.  The  heat  must  be  applied  for  an  adequate  period,  and  the  temperature 
must  be  sufficiently  high.  Liquids  are  frequently  sterilized  by  passing  them  through 
a  suitable  filter  (such  as  the  Chamberland),  which  retains  the  bacteria,  etc.  Steril- 
ization may  also  be  accomplished  by  the  use  of  antiseptics  or  disinfectants,  such  as 
mercuric  bichloride,  phenol,  etc.     These  simply  poison  the  microorganisms. 

6.  Pure  Cultures. — Pure  cultures  of  any  given  kind  of  microorganism  may  be 
obtained  by  inoculating  a  suitable  sterile  medium  with  a  single  cell  of  the  form  desired, 
and  allowing  this  to  develop  without  the  entrance  of  any  other  cells.  Unless  obtained 
in  this  way,  a  culture  cannot  be  surely  considered  as  pure.  Single-spore  inoculation  is 
generally  accomplished  by  repeated  dilution  of  a  liquid  medium  that  contains  the 
particular  form  desired.     For  this  sort  of  work  special  technique  has  been  devised. 


CHAPTER  III 
ASSIMILATION  OF  NITROGEN1 

§i.  The  Nitrogen  of  the  Air. — Atmospheric  air  is  fourth-fifths  free  nitrogen 
and  it  contains  very  small  amounts  of  ammonia.  We  owe  the  first  experiments 
upon  the  assimilation  of  free  nitrogen  to  Boussingault,a  who  grew  various  plants 
from  the  seed  in  nitrogen-free,  ignited  sand  to  which  was  added  some  ash  from 
seeds  of  the  kind  of  plants  employed.     He  placed  the  porous  culture  pot  in  a 

shallow  glass  dish  supported  above  the 
bottom  of  a  larger  glass  pan,  in  which 
stood  a  large  bell-jar,  covering  the  cultures. 
(See  Fig.  41.)  Some  sulphuric  acid  was 
placed  in  the  large  pan,  to  prevent  the  en- 
trance of  ammonia  from  the  outside  air 
into  the  bell- jar.  Two  glass  tubes  were 
introduced  under  each  jar,  one  to  supply 
distilled  water6  to  the  dish  in  which  the 
pot  stood,  the  other  to  provide  the  necessary 
carbon  dioxide  to  the  air-space  within  the 
bell-jar.  There  was  thus  no  source  of 
nitrogen  within  the  bell-jar,  other  than 
the  free  nitrogen  of  the  air.  The  amount 
of  nitrogen  in  the  seed  was  determined,  at 
the  beginning  of  the  experiment,  by  analy- 
sis of  a  control  portion  of  the  same  kind 
of  seed.  The  apparatus  was  exposed  to 
light,  and  at  the  close  of  the  experiment 
(after  two  or  three  months)  the  nitrogen 
content  of  the  mature  plant  was  deter- 
mined, and  no  increase  in  this  element 
could  be  detected.  It  follows  from  this 
that  free  nitrogen  is  not  assimilated  by  ordinary  higher  plants  when  these 
are  cultivated  in  the  soil  without  microorganisms. 

1  A  complete  summary  of  the  work  upon  nitrogen  assimilation  up  to  1879  is  given  in:  Grandeau,  L.. 
Cours  d'agriculture  de  l'ecole  forestiere.  Chimie  et  physiologie  applies  a  l'agriculture  et  a  la  sylviculture 
I.  La  nutrition  de  la  plante.     Paris,  187c-* 

a  Boussingault,  1860-91.  [see  note  5,  p.  2.]  Idem,  De  Taction  du  salpetre  sur  la  vege- 
tation. Ann.  sci.  nat.  Bot.  IV,  4:  32-46.  1855.  Idem,  Recherches  sur  l'influence  que  l'azote 
assimilable  des  engrais  exerce  sur  la  production  de  la  matiere  vegetale.  Ibid.  IV,  7:  5-20. 
1857.— Ed. 

6  It  should  be  mentioned,  however,  that,  while  distilled  water  should  not  add  anything  but 
water  and  the  atmospheric  gases  to  the  organism,  yet  it  may  extract  other  materials.  Thus 
seedlings  grown  in  distilled  water  give  off  salts,  etc.,  by  diffusion  into  the  surrounding  medium. 
(See,  further,  note  b,  p.  83.) — Ed. 

64 


Fig.  41. — Arrangement  of  Boussin- 
gault, for  growing  a  plant  in  nitrogen-free 
soil,  without  access  of  ammonia  from  the 
air.  The  large  pan  contains  sulphuric 
acid  (forming  a  seal) ;  water  is  supplied 
through  the  tube  at  the  right  and  carbon 
dioxide  through  the  one  at  the  left. 


ASSIMILATION    OF    NITROGEN 


65 


Experiments  upon  the  assimilation  of  ammonia  from  the  air  by  leaves  were 
carried  out  by  Sachs,c  by  Schlosing^  and  by  Adolf  Mayer.e  The  upper  parts 
of  the  plant  were  isolated  from  the  soil  and  received  the  ammonia  as  the  car- 
bonate, in  solution.  All  the  plant  parts  so  treated  exhibited  a  higher  nitrogen 
content  than  the  corresponding  organs  in  the  controls  without  ammonia  thus 
supplied.  This  kind  of  nitrogen  assimilation  is  of  almost  no  importance  under 
natural  conditions,  however,  since  the  ammonia  content  of  the  air  is  exceedingly 
small.  According  to  Schlosing  a  volume  of  100  cu.  m.  of  air  contains,  on  the 
average,  only  2.4  mg.  of  ammonia. 

§2.  The  Nitrogen  of  the  Soil. — The  nitrogen  of  the  soil  occurs  as  organic 
compounds,  ammonium  salts  and  nitrates/  The  experiments  of  Boussingault 
and  those  of  many  agricultural  chemists  have  shown  that  ordinary  plants 
(with  the  exception  of  certain  forms,  especially  the  legumes,  which  will  be  dis- 
cussed later)  obtain  their  nitrogen  exclusively  from  the  soil,  and  that  all  three 
kinds  of  nitrogen  compounds  of  the  soil  are  beneficial  to  plants.  Soils  poor 
in  nitrogen,  and  thus  unproductive,  can  often  be  made  productive  by  addition 
of  any  of  these  three  forms  of  nitrogen  compounds,  but  this  result  can  usually 
be  best  and  most  quickly  attained  by  the  addition  of  nitrates.  Therefore,  the 
various  nitrates  generally  serve  as  the  best  source  of  nitrogen  for  higher  plants. 

The  question  arises  whether  all  nitrogen  compounds  of  the  soil  are  taken 
up  directly  by  the  plant  or  first  undergo  some  alteration.  In  order  to  answer 
this  question  we  must  consider  some  of  the  properties  of  soils. 

According  to  Boussingault  1  kg.  of  soil  contained  the  following  amounts  of 
nitrogen: 


Source  of  Soil 

Kind  of  N-compoxjnd 

LlEBFRAUENBERG 

Nancy 

Mettais 

Organic  nitrogen 

gravis 
2 .  101 
0.019 
0.029 

grams 

1-432 
0.004 
0.040 

grams 
1.223 
0.004 
0  0?^ 

Nitrogen  of  ammonium  salts 

Nitrate  nitrogen 

5 

• 

Most  of  the  soil  nitrogen  thus  has  the  form  of  organic  compounds,  which  are 
decomposition  products  from  the  decay  of  animal  and  plant  materials.     The 

e  Sachs,  J.,  as  cited  by  Robert  Hoffman,  Ueber  die  Aufnahme  des  Kohlensauren  Ammoniaks 
der  Luft  durch  die  Pflanzenblatter.     Jahresb.  Agrikulturchem.  3:  78-80.     1862. — Ed. 

d  Mayer,  Adolf,  Ueber  die  Aufnahme  von  Ammoniak  durch  oberirdische  Pflanzentheile. 
Landw.  Versuchsst.  17:  329-397.     1874. — Ed. 

'  Schloesing,  Th.,  Sur  l'absorption  de  l'ammoniaque  de  l'air  par  les  vegetaux.  Compt. 
rend.  Paris  78:  1 700-1 703.  1874.  Also  see:  Atwater,  W.  O.  Ueber  die  Assimilation  von 
Stickstoff  aus  der  Atmosphare  durch  die  Blatter  der  Pflanzen.  Landw.  Jahrb.  14:  621-632. 
1885.— Ed. 

f  Nitrites  also  occur,  but  in  small  amount. — Ed. 
5 


66 


PHYSIOLOGY    OF    NUTRITION 


nitrogen  of  ammonium  salts  forms  the  smallest  part.  The  ammonia  of  the  soil 
is  derived  partly  from  the  decomposition  or  organic  nitrogenous  compounds 
and  partly  from  the  air.  According  to  Schlosing's  investigations,  ammonia 
gas  is  vigorously  absorbed  from  the  air  by  both  dry  and  moist  soils.  Dry  soils, 
it  is  true,  soon  become  saturated  with  ammonia,  but  this  is  not  so  for  moist 
soils,  for  the  ammonia  absorbed  is  gradually  converted  into  nitric  acid.  A  soil 
surface  of  i  hectare  (2.5  acres)  can  absorb  yearly  from  53  to  63  kg.  of  ammonia 
from  the  air. 

Besides  organic  compounds  and  ammonia,  every  soil  also  contains  nitric 
acid  or  its  salts.  According  to  Boussingault's  exact  investigations  nitric  acid 
is  formed  in  the  soil  at  the  expense  of  other  nitrogenous  compounds.  A  known 
quantity  of  damp  soil,  of  known  composition,  was  placed  in  a  large  carboy, 
which  was  sealed  in  1859  and  not  reopened  until  1871.  At  the  conclusion  of  the 
experiment  the  soil  in  the  carboy  was  again  analyzed.  The  results  are  presented 
in  the  following  table. 


Year 


1859 

1871 

Difference 


Total  nitrogen 


grams 
0.4722 
0.4520 
-0.0202 


Nitric  acid  nitrogen 


grams 
0.0029 
0.6178 
+0.6149 


grams 
0.00075 
0.16000 
+  0.15925 


The  nitric  acid  was  at  least  mainly  formed  from  other  nitrogenous  compounds 
present  in  the  soil.  Moreover,  during  the  progress  of  the  experiment  a  part 
of  the  nitrogen  of  the  soil  diffused  into  the  air  of  the  enclosed  space.  Bous- 
singault  showed  in  later  experiments  that  very  many  kinds  of  organic  materials 
(e.g.,  meat,  blood,  horn,  bone,  wool,  etc.),  if  added  to  the  soil,  serve  as  sources 
for  the  formation  of  nitrates.  Conditions  thus  exist  in  the  soil  which  render 
possible  the  transformation  of  a  great  many  kinds  of  nitrogen  compounds 
into  nitric  acid  or  nitrates. 

Now  the  question  arises,  how  is  it  that,  in  spite  of  the  continuous  formation 
of  nitric  acid,  there  is  never  more  than  a  small  quantity  of  this  substance  present 
in  the  soil?  An  answer  is  obtained  from  a  consideration  of  the  phenomena 
of  absorption  of  various  compounds  by  the  soil.17  The  soil  takes  substances 
out  of  solution  and  retains  them,  so  that  a  solution  filtered  through  a  soil  layer 
becomes  less  concentrated.  The  first  investigator  to  direct  his  attention  to 
this  phenomenon  and  to  recognize  its  importance  in  agriculture  was  Bronner 
(1836),  who  describes  the  following  experiment.  A  bottle  with  a  small  opening 
in  the  bottom  is  filled  with  fine  sand  or  with  half-dry,  sifted  garden-soil.  Dark 
ill-smelling  manure  extract  is  gradually  poured  into  the  bottle  until  the  entire 
soil-mass  is  saturated.     The  liquid  issuing  below  is  almost  entirely  odorless  and 

*  This  is  partly  the  phenomenon  now  generally  termed  adsorption.- — Ed. 


ASSIMILATION   OF   NITROGEN  67 

colorless  and  has  lost  all  the  readily  recognizable  characteristics  of  manure 
extract. 

More  exact  studies  show  that  not  all  compounds  are  thus  retained  by  the 
soil;  while  ammonium  salts  are  absorbed,  nitrates  easily  pass  through.  This 
characteristic  of  nitrates,  their  ability  to  be  washed  out  of  soils,  explains  the 
small  nitrate  content  of  the  soil.  All  of  the  nitrates  not  absorbed  by  plants  are 
washed  down  by  the  rain  into  the  deeper  soil  layers.  Of  all  the  nitrogenous 
substances  occurring  in  the  soil,  the  organic  materials  and  ammonium  salts 
form,  so  to  speak,  the  nitrogen  stock  of  the  soil.  These  are  firmly  held  and  so 
act  as  a  constant  source  of  nitrates,  which  may  be  absorbed  by  plant  roots. 

The  investigations  of  Kostychev1  have  shown  that  organic  nitrogenous 
compounds  of  humus  do  not  consist  solely  of  decomposition  products  of  plant 
and  animal  substances  but  are  mainly  proteins,  such  as  are  the  constituents  of 
living  organisms.  In  the  leaf-mould  formed  by  oak  leaves  that  had  been  de- 
composing for  twelve  months  the  nitrogen  content  was  2.98  per  cent.,  of  which 
2.73  per  cent,  was  protein  nitrogen  and  only  0.25  per  cent,  was  made  up  of 
simpler  nitrogenous  compounds.  These  experiments  constitute  a  new  proof 
that  the  processes  going  on  in  the  soil  are  not  exclusively  chemical,  without 
the  intervention  of  living  cells,  but  are  also  physiological  in  their  nature,  being 
connected  with  the  life-processes  of  organisms.  The  same  author  has  shown 
that  the  phosphorus  of  the  soil  appears  mainly  in  complex  organic  compounds 
such  as  are  constituents  of  the  lowest  organisms.  By  virtue  of  its  abundant 
bacterial  life,  the  soil  is  practically  a  living  mass.* 

§3.  Nitrification  in  Soils.— The  ability  of  the  soil  to  produce  nitric  acid 
or  nitrates  from  various  more  complex  nitrogenous  compounds  depends  upon 
various  conditions.  One  of  these,  according  to  Schlosing,  is  free  access  of 
oxygen.  Equal  amounts  of  the  same  soil  were  confined  in  five  vessels,  and  a 
current  of  gas  was  passed  through  each  vessel.  The  gas  passed  through  the 
first  vessel  was  pure  nitrogen,  so  that  this  soil  was  without  oxygen.  The  other 
vessels,  II,  III,  IV  and  V,  received  mixtures  of  nitrogen  and  oxygen  containing 
6,  n,  16,  and  21  per  cent,  of  the  latter  gas,  respectively.  The  amount  of 
nitrate  present  in  the  soil  was  determined  for  each  vessel  at  the  beginning  and 
end  of  the  experiment.     The  results  of  these  determinations,  expressed  as  nitric 

1  Kostytschew,  P.,  Ueber  die  Mikroorganismen  des  Bodens.     Kurlandische  Land-  und  Forstwirtsch. 
Zeitg.  (Riga)  5:  13-14.     1890. 

A  On  the  nature  of  the  organic  matter  of  the  soil  see  the  following:  Schreiner,  Oswald, 
and  Shorey,  Edmund  C,  The  isolation  of  harmful  organic  substances  from  soils.  U.  S. 
Dept.  Agric,  Bur.  Soils,  Bull.  53.  53  p.  Washington,  1909.  Idem,  Chemical  nature  of 
soil  organic  matter.  Ibid.  Bull.  74,  48  p.  Washington,  1910.  Schreiner,  Oswald,  and 
Skinner,  J.  J.,  Nitrogenous  soil  constituents  and  their  bearing  on  soil  fertility.  Ibid.  Bull. 
87.  84  p.  Washington,  191 2.  Trusov,  A.,  The  formation  of  humus  by  means  of  vegeta- 
ble substances.  [Russian.]  Selskoie  khoziaistvo  i  liesovodstvo  (Economie  agricole  et  syl- 
viculture) Petrograd  246:  233-245.  1914.  Rev.  in:  Month,  bull,  agric.  intell.  and  pi. 
diseases  6:  540-541.  1915-  Abo  rev.  in:  Exp.  sta.  rec.  34:  619.  1916.  Idem,  same  title. 
[Russian.]  Selskoie  khoziaistvo  i  liesovodstvo  (Economic  agricole  et  sylviculture)  Petro- 
grad 248:  409-437.  1915.  Rev.  in:  Month,  bull,  agric.  intell.  and  pi.  diseases  7:  46-47. 
1916.     Also  rev.  in:  Exp.  sta.  rec.  34:  516.     1916. — Ed. 


68 


PHYSIOLOGY    OF    NUTRITION 


acid,  are  presented  below.  The  soil  without  oxygen  thus  lost  its  whole  content 
of  nitrate,  and  those  supplied  with  oxygen  formed  additional  amounts,  the 
quantity  formed  increasing  with  the  amount  of  oxygen  supplied. 


Vessel  Number  and  Oxygen 
Content  of  Gas 

Nitric  Acid  Present  in 
the  Soil 

Loss 

Gain 

Nov.  18,  1872 

July  3,  1873 

mg. 
64 
64 
64 
64 
64 

mg. 
00 
263 
286 
267 
289 

mg. 
64 

mg. 

II.  6  per  cent,  oxygen 

III.  ii  per  cent,  oxygen 

IV.  16  per  cent,  oxygen 

V.  21  per  cent,  oxygen 

199 

222 
203 
225 

Nitrification  in  soils  is  due  to  bacterial  action,  as  Schlosing  and  Mlintz1  have 
shown.  These  authors  took  a  large-bore  glass  tube  a  meter  long,  filled  it  with 
a  mixture  of  sand  and  lime  and  allowed  sewage  water  containing  ammonia  to 
percolate  slowly  through  it.  After  some  days  nitrate  could  be  indentified  in 
the  filtrate.  The  ammonia  of  the  water  was  oxidized  in  its  passage  through 
the  tube.  They  also  subjected  the  soil  contained  in  the  tube  to  the  action  of 
chloroform  vapor  during  the  percolation,  to  determine  whether  this  oxidation 
was  effected  by  the  soil  itself  or  by  microorganisms  contained  therein.  The  re- 
sult was  a  cessation  of  nitrification,  the  filtrate  containing  ammonia  instead 
of  nitrates  in  this  case.  Since  the  chloroform  probably  only  repressed  the 
vitality  of  the  soil  bacteria,  without  influencing  purely  chemical  processes, 
Schlosing  and  Muntz  concluded  that  the  process  of  nitrification  in  the  soil  is 
caused  by  bacteria. 

After  many  investigators  had  vainly  endeavored  to  obtain  the  nitrifying 
bacteria  of  soil  in  the  pure  culture,  Vinogradskii2  was  at  length  successful  in 
this,  as  have  been  mentioned  above  (page  48). 

Further  investigations  by  Vinogradskii  showed  that  the  nitrification  of 
ammonia  and  ammonium  salts  to  nitrates  is  effected  in  the  soil  not  by  one 
but  by  two  species  of  bacteria.  One  form  produces  nitrites  (N02)  from 
ammonium  salts,  and  the  other  produces  nitrates  from  nitrites.  Vinogradskii 
proposed  to  reserve  the  term  Nitrobacteria  for  all  those  bacteria  that  have  to 
do  with  converting  ammonium  into  nitrate.  Investigation  of  the  morpho- 
logical characteristics  of  nitrite-formers  from  different  sources  shows  that  they 
belong  to  different  species.     The  difference  between  the  nitrite-formers  of 

1  [Schloesing,  Th.,  and  Muntz,  A.,  Sur  la  nitrification  par  les  ferments  organis6s.     Compt.  rend.  Paris 
84:301-303.     1877.     Idem,  same  title.     Ibid.  85 :  1018-1020.     1877.     Idem,  same  title.     Jbtd.  86:  892- 

9Ss  Winog'radsky,  S.,  Recherches  sur  les  organismes  de  la  nitrification.  I,  II,  III.  IV  and  V.  : 1890.  [See 
note  I,  p.  48.]  Idem.  Contributions  a  la  morphologie  des  organismes  de  la  nitrification.  [Russian  and 
French.]     Arch.  sci.  biol.  St.-Petersbourg  1 :  87-137.     1892. 


ASSIMILATION    OF    NITROGEN 


69 


the  Old  World  and  of  the  New  is  so  great  that  it  has  even  been  necessary  to 
distinguish  two  different  genera,  each  with  several  species.  The  nitrite  bac- 
teria of  the  Old  World  constitute  the  genus  Nitrosomonas,  with  two  species 
(N.  europaa,  N.javanensis)  and  local  varieties.  Those  of  the  New  World  form 
the  genus  Nitrosococcus.  A  third  genus,  Nitrobader,1  includes  those  bacteria 
that  oxidize  nitrites  to  nitrates. 

The  work  of  Vinogradskii  led  to  the  supposition  that  these  organisms  might 
get  their  carbon  as  magnesium  carbonate,  but  Godlewski2  showed  that  such  is 
not  the  case.  Even  with  magnesium  carbonate  (MgC03)  present,  no  carbon 
assimilation  occurs  in  an  atmosphere  devoid  of  carbon  dioxide.  The  nitrify- 
ing bacteria  are  thus  shown  to  obtain  their  carbon  from  the  carbon  dioxide  of 
the  air. 

Further  investigations  of  Vinogradskii  and  Omelianskii3  cleared  up  the  re- 
lation of  nitrifying  organisms  to  various  organic  compounds  that  check  their 
growth.  In  the  following  table  are  given,  for  each  of  the  two  kinds  of  bacteria 
and  for  several  organic  compounds,  the  concentrations  of  the  latter  that  just 
begin  to  retard  growth  and  those  that  check  it  completely. 


Nitrite  Formers 


Concentration 


Just  Retard- 
ing Growth 


Inhibiting 
Growth 


Nitrate  Formers 


Concentration 


Just  Retard- 
ing Growth 


Inhibiting 
Growth 


Glucose. . . 
Peptone . . . 
Asparagin . 
Ammonia . 


0.025-0.050 

0.025 

0.05 


0.2 
0.2 

o-3 


0.05 
0.8 
0.05 
0.0005 


0.2-0.3 

0.5-1.0 
0.015 


Vinogradskii  and  Omelianskii  state:  "The  action  of  the  above-named  sub- 
stances, in  preventing  nitrification,  is  so  pronounced  and  becomes  evident  at 
such  low  concentrations,  that  these  substances  are  not  to  be  considered  even  as 
neutral  in  this  case,  although  they  are  usually  regarded  as  nutrients  in  bacteri- 
ology; on  the  contrary,  their  action  is  quite  analogous  to  that  of  the  substances 
that  are  known  as  antiseptics." 

If  the  presence  of  organic  substances  checks  the  process  of  nitrification,  then 
no  nitrifying  of  organic  nitrogenous  compounds  is  to  be  expected  in  pure  cul- 
tures of  nitrobacteria.  According  to  Omelianskii4  these  organisms  are  entirely 
lacking  in  ability  either  to  break  down  organic  nitrigenous  compounds  by  split- 
ting off  ammonia,  or  to  oxidize  the  nitrogen  of  these  compounds  directly.     Or- 

*  On  methods  for  pure  cultures  of  nitrifying  bacteria,  see:  Omeliansky,  1899.     [See  note  I,  p.  49.1 
2  Godlewski,  Emil,  O  nitryfikacyi  ammoniaku.     Krakow.     1896.* 

»  Winogradsky,  S.,  and  Omeliansky,  V.,  L'influence  des  substances  organiques  sur  le  travail  des  microbes 
nitrificateurs.     Arch.  sci.  biol.  St.-P6tersbourg  7:  233-271.     1899. 

»  Omeliansky,  V.,  Sur  la  nitrification  de  l'azote  organique.     Arch.  sci.  biol.  St.-Petersbourg  7 :  272-290. 

1899- 


7° 


PHYSIOLOGY    OF    NUTRITION 


ganic  nitrogen  can  be  nitrified  by  nitrobacteria  only  after  it  has  been  changed 
into  ammonia  or  ammonium  salts.  The  cooperation  is  thus  necessary,  of  at 
least  one  of  the  bacterial  forms  that  give  rise  to  ammonia  from  organic  com- 
pounds. Omelianskii  was  able  to  obtain  nitrification  of  bouillon  if  he  inocu- 
lated the  medium  with  three  species  of  bacteria  at  the  same  time:  Bacillus 
ramosus,  Nitrosomonas  and  Nitrobacter.  If  only  B.  ramosus  and  Nitrosomonas 
are  introduced  the  process  is  limited  to  the  formation  of  nitrous  acid  (nitrites), 
while  B.  ramosus  and  Nitrobacter  produce  only  ammonia.  Inoculation  with 
Nitrosomonas  and  Nitrobacter  leaves  the  bouillon  unchanged.  All  these  rela- 
tions may  be  shown  by  a  diagram,  reproduced  below,  in  which  the  bacteria 
that  decompose  organic  compounds  to  form  ammonia  are  represented  by  a, 
those  that  form  nitrites  are  represented  by  b,  and  those  that  oxidize  nitrous 
to  nitric  acid  (nitrites  to  nitrates)  are  represented  by  c. 


Organic 
Nitrogen 


Ammonia 
Nitrogen 


Nitrite 
Nitrogen 


Nitrate 
Nitrogen 


a  +  b  -f-  c 

a  +  b 

a  -f-  c 

b  +  c 


No  alteration  of  organic  nitrogen. 


Fig.  42. — Comparison  of  the  effect  of  nitrate  and  of  ammonium  salts  on  growth  of  plants 
in  bog-soil,  which  is  poor  in  lime.  O,  no  fertilizer;  NO 3,  nitrate  added;  NH3.  ammonium 
salts  added.      (After  P.  Wagner.) 


Now  that  we  have  become  acquainted  with  the  process  of  nitrification,  we 
may  consider  the  question  whether  higher  plants  are  able  to  obtain  their  nitro- 
gen only  as  nitrates  or  whether  they  can  assimilate  ammonium  salts  directly, 
without  previous  nitrification  of  the  latter.  Recent  discoveries  favor  the  view 
that  nitrates  act  chiefly,  if  not  exclusively,  as  the  source  of  nitrogen  for  such 
plants.  The  experiments  of  Wagner1  have  shown  that  nitrates  and  ammo- 
nium salts  have  different  effects  according  to  the  nature  of  the  soil  employed. 
Turnips  were  grown  in  vessels  of  a  bog-soil  very  poor  in  calcium.  In  one  series 
of  experiments  some  of  the  vessels  contained  no  nitrogen  fertilizer,  others  each 

1  Wagner,  Paul,  Dimgungsfragen  unter  Beriicksichtigung  neuer  Forschungsergebnisse.  Heft.  IV.  Ber- 
lin, 1898.     72  p. 


ASSIMILATION    OF    NITROGEN 


71 


contained  2  g.  of  nitrogen  as  nitrates,  and  still  others  each  contained  about  2  g. 
of  nitrogen  as  ammonium  salts.  In  a  second  series  calcareous  marl  was  added 
throughout,  in  addition  to  the  fertilizers  mentioned  above.  The  results  of  this 
experiment  are  brought  together  in  the  following  table  (see  also  Fig.  42). 


Fertilizer 


Dry  Yield 


Increase  in  Yield, 
Compared  with  Cul- 
ture without 
Nitrogen 


Without  lime 


With  lime 


grams 

Without  addition  of  nitrogen  ....  6.3 

2  g.  of  nitrogen  as  nitrate 94-4 

2  g.  of  nitrogen  as  ammonium  salt.  29.4 

Without  addition  of  nitrogen 9.6 

\  2  g.  of  nitrogen  as  nitrate 92 .0 

I  2  g.  of  nitrogen  as  ammonium  salt .  .  86 . 7 


grams 

88.1 
23.1 

82.4 

77.1 


Thus,  ammonium  salts  have  but  little  value  as  fertilizers  for  soils  poor  in  lime. 
But  soils  rich  in  lime  show  almost  as  good  yields  with  ammonium  salts  as  with 
nitrates  (Fig.  43).     These  experiments  show  that  nitrate  fertilizer  is  suitable 


Pig.  43. — Comparison  of  the  effect  of  nitrate  and  ammonium  salts  on  growth  of  plants  in 
soil  rich  in  lime.  O,  no  fertilizer;  NO3,  nitrate  added;  NHi,  ammonium  salts  added.  (After 
P.  Wagner.) 

for  many  different  kinds  of  soils  whereas  ammonia  fertilizer  is  suitable  for  only 
a  limited  number.  There  are  two  reasons  for  this:  first,  if  we  suppose  that 
the  ammonia  is  all  oxidized  to  nitric  acid  before  assimilation,  then  free  nitric 
acid  may  be  produced  in  the  soil  that  lacks  calcium  (as  in  the  first  series  of  ex- 
periments just  described),  and  this  acid  retards  the  growth  of  the  plants  as  well 
as  the  nitrification  process.  Secondly,  if  we  suppose  that  a  part  of  the  ammonia 
is  assimilated  unchanged,  then  free  acid  may  again  accumulate  in  the  soil  lack- 
ing calcium;  for  ammonium  salts  are  physiologically  acid,  their  basic  radicals 
being  absorbed  by  the  plants  to  a  greater  extent  than  are  their  acid  radicals.1 

1  This  is  more  fully  considered  in  Chapter  IV. 


72  PHYSIOLOGY   OF   NUTRITION 

The  presence  of  calcium  carbonate  prevents  the  accumulation  of  free  acid  in 
both  cases. 

Such  experiments  with  natural  soils  cannot  answer  the  question  regarding 
the  direct  assimilation  of  ammonia.  Sterilized  soils  must  be  used,  in  which  the 
nitrifying  process  is  eliminated.  The  experiments  of  Pitsch,1  Breal,2  and  Kos- 
sovich,3  who  used  sterilized  soils,  gave  positive  results. 

§4.  Circulation  of  Nitrogen  in  Nature. — The  investigations  of  Boussingault 
and  of  Schlosing  and  Mtintz  [see  note  c,  page  64,  and  notes  c,  d,  e,  page  65] 
established  the  view  that  higher  plants  can  assimilate  only  combined  nitrogen. 
Free  nitrogen  should  thus  have  absolutely  no  value  for  green  plants,  in  spite  of 
the  enormous  amount  of  it  present  in  the  air.  Schlosing  pictures  the  circula- 
tion of  nitrogen  in  nature  in  the  following  way.  Nitric  acid  (HN03)  formed  in 
the  soil  is  taken  up  by  plants  and  transformed  into  proteins  and  other  organic 
compounds,  which,  in  their  turn,  serve  for  the  nutrition  of  animals.  These 
compounds  of  nitrogen  finally  return  to  the  soil  as  decomposition  products  of 
plants  and  animals,  and  are  there  again  oxidized  to  nitrates.  The  nitrate  of  the 
soil,  that  is  not  assimilated  by  plants,  is  washed  into  the  deep  soil  layers  by  pre- 
cipitation water  and  finally  reaches  the  sea,  where  it  is  changed  back  into  am- 
monium salts  by  the  life  activities  of  marine  organisms.  Ammonia  evaporates, 
with  water  vapor,  from  the  surface  of  the  sea,  and  is  again  taken  up  from  the 
atmosphere  by  plant  leaves  or  by  the  soil,  and  in  this  way  re-enters  the  general 
circulation.  All  these  transformations  of  combined  nitrogen  have  no  effect 
upon  the  total  amount  of  it  occurring  in  nature.  Natural  processes  are  known, 
however,  which  lead  to  the  decomposition  of  nitrogenous  compounds  and  to  the 
liberation  of  molecular  nitrogen.  Thus,  in  the  complete  combustion  of  nitroge- 
nous organic  compounds  the  total  nitrogen  is  eliminated  as  nitrogen  gas. 
The  decomposition  of  organic  compounds  in  the  soil  is  also  accompanied  by 
the  liberation  of  free  nitrogen. 

The  total  amount  of  combined  nitrogen  in  nature  is  diminished  by  these 
processes  and,  for  this  reason,  many  authors  have  sought  some  natural  process 
that  might  lead  to  fixation  of  free  nitrogen.  Nitrogen  is  one  of  the  elements  that 
form  only  weak  combinations  with  other  elements.  Until  recently  chemistry 
could  name  but  three  kinds  of  nitrogen  fixation  that  might  be  of  importance  in 
nature:  (1)  An  electric  spark  discharge  effects  the  union  of  nitrogen  and  oxygen 
(Cavendish).  (2)  A  silent  electrical  discharge  causes  the  union  of  nitrogen 
with  organic  substances  (Berthelot).  (3)  During  the  evaporation  of  water  a 
small  amount  of  nitrogen  combines  with  hydrogen  from  the  water  and  produces 
ammonium  nitrate  (Schonbein).  Only  the  first  of  these  three  possibilities  has 
real  significance  in  nature,  namely  the  fixation  of  atmospheric  nitrogen  during 
thunderstorms. 

1  Pitsch,  Otto,  Versuche  zur  Entscheidung  der  Frage  ob  saltpetersaure  Salze  fur  die  Entwicklung  der 
landw.  Kulturgewacb.se  unentbehrlich  sind.  II.  Landw.  Versuchsst.  42:  i~95-  i893-  Pitsch,  O.,  and 
Haarst,  J.  Van,  same  title  as  above,  III.     Ibid.  46:  357-382.     1896. 

2  Breal,  E.,  Contribution  a  l'etude  de  l'alimentation  azot6e  des  vegetaux.     Ann.  agron.  19:  274-293. 

1893.  . 

3  Kossowitch,  P.,  Ammoniaksalze  als  unmittelbare  Stickstoff  Quelle  fur  pflanzen.  [Abstract  in  German, 
p.  637-638.     Text  in  Russian.]     Jour  exp.  Landw.  2  :  625-638.      190 1. 


ASSIMILATION    OF    NITROGEN  73 

Recent  technical  advance  has  made  it  possible  to  obtain  larger  amounts  of 
nitrogen  compounds  from  atmospheric  nitrogen.  By  oxidation  of  the  latter, 
with  the  electric  current,  nitric  acid  is  obtained  on  a  large  scale.  By  passing 
nitrogen  through  glowing  calcium  carbide,  calcium  cyanamide  is  formed,  accord- 
ing to  the  equation:  CaC2  +  2N  =  CaCN2  +  C.  The  German  commercial 
name  of  this  product  in  the  raw  state  is  "  Kalkstickstoff ,n  and  it  is  used  as  a 
nitrogen  fertilizer. 

What  has  been  attained  by  man  only  after  much  travail  is  commonly  ac- 
complished by  plants,  however,  for  we  now  know  a  number  of  plants  that  can 
assimilate  atmospheric  nitrogen. 

§5.  Fixation  of  Atmospheric  Nitrogen  by  the  Leguminosae.— All  legumes  are 
able  to  develop  normally,  producing  a  rich  harvest  with  a  high  nitrogen  content, 
without  the  addition  of  any  nitrogenous  compounds  to  the  soil,  as  the  exact 
studies  of  Lawes  and  Gilbert  have  shown.  If  we  cultivate  some  sort  of  grain 
or  legume  for  many  years  in  succession  on  the  same  field  without  applying  fer- 
tilizer, the  nitrogen  content  of  the  crop  finally  reaches  a  certain  minimum, 
beyond  which  it  does  not  alter.  Addition  of  mineral  fertilizers  without  nitrogen 
is  almost  without  effect  upon  the  yield  of  grain,  the  nitrogen  content  remaining 
almost  the  same  as  before.  This  is  entirely  different  in  the  case  of  the  legumes; 
the  same  mineral  fertilizer  without  nitrogen  produces  a  marked  increase  in  the 
nitrogen  content  of  this  crop. 

Two  series  of  experiments  by  P.  Wagner2  are  illustrated  in  Figs.  44  and  45, 
one  with  peas  and  the  other  with  oats,  the  experimental  conditions  being  the 
same  in  both  cases.  The  containers  marked  O  contained  no  fertilizer  at  all, 
those  marked  KP  contained  potassium  and  phosphoric  acid  (P04),  and  those 
marked  KPN  contained  potassium,  phosphoric  acid  and  nitrogen  as  nitrate. 
Comparison  of  these  figures  reveals  a  distinct  difference  between  the  legumes  and 
the  grains  in  their  relation  to  fertilizers.  The  growth  of  oat  plants  is  seen  to 
be  very  slight  in  the  unfertilized  culture,  and  the  addition  of  potassium  and 
phosphoric  acid  produces  no  improvement;  while  the  addition  of  these  together 
with  potassium  nitrate  produces  excellent  growth  (Fig.  44) .  The  behavior  of  the 
pea  plants  is  entirely  different.     These  do  not  need  nitrate  fertilizer,  addition 

«  Frank,  A.,  Die  Nutzbarmachung  des  freien  Stickstoffs  der  Luft  fur  Landwirtschaft  und  Industrie. 
Zeitsch.  angew.  Chem.  16:  536-539-  1903.  Gerlach,  M.,  Die  Nutzbarmachung  des  atmospharischen 
Stickstoffes.  Illustr.  landw.  Zeitg.  1904.  Nos.  5  and  7.*  Review  by  Vogel  in:  Centralbl.  Bakt. //.  12  : 
495-497-     1904.     [See  also  review  in:  Exp.  sta.  rec.  15:  25.     1003-C4.] 

2  Wagner,  P.,  Ergebnisse  von  Dunungungsversuchen  in  Lichtdruckbildern  mit  erlauterndem  Vortrage 
viber  die  rationelle  Dungung  der  land  wirtschaftlichen  Kulturpflanzen.     2te  Aufl.     Darmstadt,  1891. 

•Lawes  J.  B.,  and  Gilbert,  J.  H.,  The  sources  of  the  nitrogen  of  our  leguminous  crops. 
Jour.  Roy.  Agric.  Soc.  England  III,  2:  657-702.  London,  1891.  Idem,  The  Rothamsted 
memoirs  on  agricultural  chemistry  and  physiology.  7  v.  London,  1886-1899.  Idem,  same 
title.  3  v.London,  1 890-1 893.  Hall,  A.  D.,  The  book  of  the  Rothamsted  experiments.  294  p. 
New  York,  1905.  For  a  brief  discussion  of  this  whole  matter  see:  Russell,  E.  J.,  Soil  condi- 
tions and  plant  growth.  4  th  ed.  London  and  New  York  406  p.,  192 1.  Russell's  ex- 
cellent bibliography  includes  references  to  a  number  of  the  papers  of  Lawes  and  Gilbert. 
These  papers  have  all  been  collected  and  published  in  the  Rothamsted  Memoirs,  and 
Lawes  and  Gilbert's  results  are  summarized  by  Hall. — Ed. 


74 


PHYSIOLOGY    OF    NUTRITION 


Fig.  44. — Growth  of  oats  with  various  fertilizers.  O,  without  addition  to  the  soil;  KP 
with  addition  of  potassium  and  phosphoric  acid;  KPN,  with  addition  of  potassium,  phosphoric 
acid  and  potassium  nitrate.      (After  P.  Wagner.)      Compare  with  Fig.  45- 


Fig.  45. — Growth  of  peas  with  various  fertilizers.  0,  without  addition  to  the  soil;  KP, 
with  addition  of  potassium  and  phosphoric  acid;  KPN,  with  addition  of  potassium,  phos- 
phoric acid  and  potassium  nitrate.      (After  P.  Wagner.)      Compare  with  Fig.  44. 


ASSIMILATION    OF    NITROGEN 


75 


of  potassium  and  phosphoric  acid  being  sufficient  to  produce  normal  growth. 
In  this  case  the  total  need  of  nitrogen  is  supplied  from  the  air  (Fig.  45). 

The  results  of  Lawes  and  Gilbert  and  those  of  Wagner  thus  seem  to  dis- 
agree with  the  conclusions  reached  by  Boussingault  (see  page  64).  This  is 
explained  by  the  fact  that  Boussingault  used  sterilized  soils,  whereas  the  other 
authors,  just  referred  to,  worked  with  unsterilized  soil  under  natural  condi- 
tions. The  reason  for  the  entirely  different  behavior  of  legumes  in  sterilized 
soils  and  in  unsterilized  soils  has  been  discovered  in  a  series  of  remarkable  in- 
vestigations conducted  by  Hellriegel  and  Wilfarth.1  In  their  experiments, 
various  legumes  grew  quite  normally  in  soils  that  lacked  nitrogen,  provided  these 
soils  were  not  previously  sterilized.  Growth  was  checked,  however,  in  sterilized, 
nitrogen-free  soils,  because  of  lack  of  nitrogen.  Addition  to  the  sterilized 
soil  of  a  small  quantity  of  an  infusion  from  unsterilized  soil  produced  normal 
growth  of  the  plants  and  resulted  in  a  crop  rich  in  nitrogen.  If  the  added 
infusion  was  previously  boiled,  however, 
then  its  addition  produced  no  effect  at  all; 
the  plants  were  retarded  in  their  develop- 
ment and  the  harvest  showed  no  increase 
in  nitrogen.  The  soil  used  in  preparing 
the  infusion  must  be  taken  from  a  field 
upon  which  plants  of  the  kind  used  in  the 
experiment  have  been  cultivated;  for  ex- 
ample, if  peas  are  employed  the  soil  used 
for  the  water  extract  must  be  obtained 
from  a  field  where  peas  have  previously 
been  grown. 

Legumes  growing  under  natural  condi- 
tions have  small  tubercles  upon  their  roots 
(Fig.  46).  Hellriegel  and  Wilfarth  ob- 
served that  these  tubercles  developed  only 
in  unsterilized  soil,  or  in  sterilized  soil  only 
if  it  had  been  treated  with  infusion  of  un- 
sterilized soil.  Tubercles  never  develop  in 
uninoculated  sterilized  soils. 

From  their  studies  Hellriegel  and 
Wilfarth  came  to  the  conclusion  that  the 
formation  of  root  tubercles  is  the  result  of 
a  symbiosis  between  the  legumes  and  lower 
organisms,  and  that  these  very  tubercles  are  directly  influential  in  the  assimila- 
tion of  atmospheric  nitrogen  by  leguminous  plants. 

A  cross-section  of  a  legume  root,  through  one  of  these  tubercles,  shows  that 
the  greater  part  of  the  tubercle  consists  of  parenchymatous  tissue  (Fig.  47). 
The  inner  cells  are  very  different  from  the  outer  ones.     The  former  constitute 

1  Hellriegel,  H.,  and  Wilfarth,  H.,  Untersuchungen  uber  die  Stickstoffnahrung  der  Gramineen  und 
Leguminosen.     Beilage  Zeitschr.  Rubenzucker-Indust.  d.  deutsch.  Reich.     234  p.      November,  1888. 


Fig.  46. — Root  system  of  pea  plant,  with 
tubercles  (if.) 


76  PHYSIOLOGY    OF    NUTRITION 

the  so-called  bacterioid  tissue  and  are  characterized  by  thin  cell  walls  and  high 
content  of  protein.  The  protein  substances  occur  in  the  cells  as  small,  bacteria- 
like  rods,  which  are  branched  in  the  older  tubercles.  These  are  the  so-called 
bacterioids.  The  cells  of  the  outer  parenchyma  layers  contain  little  reserve 
material,  and  only  those  adjacent  to  the  bacterioid  tissue  are  filled  with  starch 
grains.  The  tubercle  is  covered  on  the  outside  by  a  layer  of  cork,  and  branches 
of  the  vascular  bundles  of  the  root  extend  into  the  tubercle. 

Beijerinck1  and  Prazmovskii2  have  succeeded  in  securing  tubercle  bacteria 
in  pure  culture.  When  transferred  to  a  nutrient  solution,  the  young  bacteria, 
or  the  modified  cells  called  bacterioids,  begin  to  divide  and  multiply  rapidly. 
The  newly  formed  organisms  appear  to  be  in  no  way  different  from  ordinary 
bacteria,  and  they  show  the  same  kind  of  movement.  Prazmovskii  has  given 
them  the  name  Bacterium  radicicola. 

This  writer  has  studied  the  developmental  history  of  the  tubercles  of  the 
pea  plant.  If  sterilized  soil  in  which  young  pea  seedlings  are  growing  is  inocu- 
lated with  a  pure  culture  of  Bacterium  radicicola,  an  accumulation  of  bacteria 
in  the  root-hairs  becomes  noticeable  after  several  days.  This  mass  of  bacteria 
then  becomes  enclosed  in  a  sheath,  forming  a  sack-like  body  that  enlarges  and 


Fig.  47. — Cross-section  of  a  root  tubercle  of  lupine,  showing  bacterioid  tissue  (the  elon- 
gated area  below)  surrounded  by  root  parenchyma.  The  dark  lines  above  the  bacterioid  area 
represent  vessels  that  penetrate  from  the  uninjured  root  to  the  hypertrophied  tubercle. 

penetrates  through  the  root-hair  into  the  root  parenchyma  as  a  bacterial  fila- 
ment. Having  advanced  into  the  root,  this  filament  begins  to  branch  rapidly. 
A  lively  division  of  the  cells  of  the  root  parenchyma  proceeds  at  the  same  time, 
in  the  neighborhood  of  the  bacterial  filament,  which  results  in  a  swelling  in  this 
region  of  the  root  and  in  the  formation  of  a  tubercle.  The  branches  of  the  fila- 
ment occupy  the  central  portion  of  the  tubercle.  The  filament  sheath  finally 
disintegrates  and  the  bacteria  thus  liberated  enter  the  cell  sap.     Here  they 

beijerinck,  M.  W.,  Die  Bacterien  der  Papilionaceen-Knollchen.  Bot.  Zeitg.  46:  725-735.  741-750, 
757-77L  781-790,  797-802.     1888. 

2  Prazmowski,  Adam,  Die  Wurzelknollchen  der  Erbse.  I.  Teil.  Die  Aetiologie  und  Entwickelungs- 
geschichte  der  Knollchen.     Landw.  Versuchsst.  37 :  161-238.     1890. 


ASSIMILATION  OF  NITROGEN  77 

enlarge  and  become  branched,  thus  becoming  mature  bacterioids.  At  this  time 
the  vascular  bundles  develop  in  the  tubercle.  The  bacterioid  tissue  becomes 
depleted  after  a  time,  its  contents  being  used  up  by  the  plant.  The  bacterial 
cells  collect  in  groups  in  the  remaining  portions  of  the  infection-filaments  and 
become  enclosed  in  a  hard  sheath.  The  spore-like  colonies  thus  formed  fall 
away  after  the  destruction  of  the  tubercle  and  are  capable  of  infecting  other 
roots  the  following  spring. 

Kossovich1  sought  to  solve  the  question  as  to  what  organs  of  legumes 
absorb  atmospheric  nitrogen.  He  carried  out  two  series  of  experiments,  in 
one  case  depriving  the  leaves,  and  in  the  other  case  the  roots,  of  nitrogen.  He 
came  to  the  conclusion  that  nitrogen  is  absorbed  by  the  roots. 

Infection  of  legumes  with  cultures  of  Bacterium  radicicola  does  not  always 
have  a  favorable  influence  upon  the  growth  of  these  plants.  If  the  inoculation 
occurs  late  in  the  growing  season  (in  July),  the  result  is  an  abundant  formation 
of  root  tubercles,  but  the  plants,  instead  of  growing  better,  grow  more  poorly 
than  do  uninfected  individuals.  The  action  of  the  bacteria  is  merely  parasitic 
in  this  case.  Microscopic  investigation  shows  that  the  transformation  of 
bacteria  into  bacterioids  does  not  occur  here,  and  it  was  for  this  reason  that 
Nobbe  and  Hiltner2  believed  assimilation  of  atmospheric  nitrogen  to  be  corre- 
lated with  the  formation  of  the  bacterioids.  Long-continued  cultivation  upon 
nutrient  gelatine  (from  spring  until  midsummer)  is  said  to  make  Bacterium 
radicicola  more  vigorous  and  to  deter  its  transformation  into  bacterioids  after 
it  enters  the  root.  Plants  inoculated  late  in  the  season,  being  already  partially 
exhausted  at  this  time,  are  too  weak  to  produce  this  change  in  the  infecting 
organism. 

Investigation  of  the  tubercle  bacteria  of  various  legumes  leads  to  the  conclu- 
sion that  there  are  many  varieties  of  these  organisms.  In  order  to  obtain  a 
healthy  development  of  Robinia  pseudacacia  in  soil  without  available  nitrogen, 
inoculations  must  be  made  with  cultures  from  Robinia  tubercles;  infection  with 
bacteria  from  pea  and  lupine  tubercles  has  no  effect  at  all.  But  inoculation 
with  cultures  from  Cytisus  tubercles  has  almost  as  good  an  effect  as  inoculation 
with  cultures  of  the  bacteria  of  Robinia  itself.3 

Certain  non-leguminous  plants  also  assimilate  atmospheric  nitrogen  by 
symbiosis  with  bacteria,  and  the  tubercles  may  be  formed  in  other  regions  of 
the  plant  besides  the  root  system.  For  example,  the  leaves  of  some  of  the 
tropical  Rubiaceae  are  characterized  by  numerous  rounded,  tubercle-like  thicken- 
ings, which  contain  peculiar  bacterial  cells  (Mycobacterium  rubiacearum) .  These 
bacteria  fix  nitrogen  from  the  air  in  the  same  general  manner  as  do  the  root- 
tubercle  bacteria  of  legumes.4     (See  Fig.  48.) 

1  Kossowitsch,  P.,  Durch  welche  Organe  nehmen  die  Leguminosen  den  freien  Stickstoff  auf ?  Bot. 
Zeitg.  50:  697-702,  713-723,  720-738,  745-756,  771-774-      1892. 

2  Nobbe,  F.,  and  Hiltner,  L.,  Wodurch  werden  die  knollchenbesitzenden  Leguminosen  befahigt,  den 
freien  atmospharischen  Stickstoff  fur  sich  zu  verwerten?     Landw.  Versuchsst.  42  :  450-478.     1893. 

8  Nobbe,  F.,  Schmid,  E.,  Hiltner,  L.,  and  Hotter,  E.,  Versuche  iiber  die  Stickstoff-Assimilation  der 
Leguminosen.  Landw.  Versuchsst.  39:  327-359.     1891. 

*  [Faber,  F.  C.  von,  Das  erbliche  Zusammenleben  von  Bakterien  und  tropischen  Pnanzen.  Jahrb. 
wiss.  Bot.  51:  285-375.     19 1 2.] 


•8 


PHYSIOLOGY   OF   NUTRITION 


§6.  Assimilation  of  Atmospheric  Nitrogen  by  Bacteria. — The  work  of 
Berthelot1  rendered  assimilation  of  free  nitrogen  by  the  bacteria  of  the  soil 
very  probable,  but  we  owe  the  final  solution  of  this  problem  to  Vinogradskii2 
and    Beijerinck.3    Vinogradskii    caused    the    development    of    nitrogen-fixing 


A 


Pig.  48. — A.  Leaves  of  Pavetla  indica,  showing  nodules,  which  contain  nitrogen-fixing 
bacteria.  B.  Cells  of  Mycobacterium  rubiacearum  from  leaf  nodules  of  Pavetta  zimmermanniana. 
Magnified  to  3000  diameters.      (After  Faber.) 

1  Berthelot,  Marcellin,  Fixation  de  l'azote  atmospherique  sur  la  terre  vegetale.  Ann.  chim.  et  phys. 
13:  S-14.  15-73.  74-78,  78-92,  93-H9.     1888. 

8  Winogradsky,  S.,  Sur  l'assimilation  de  l'azote  gazeux  de  l'atmosphere  par  les  microbes.  Compt.  rend. 
Paris  116:  1385-1388.     1893.     Idem,  same  title.     Ibid.  118:  353-355-     1894. 

'Beijerinck,  M.  W.,  Ueber  oligonitrophile  Mikroben.  Centralbl.  Bakt.  //,  7:  561-582.  1901.  Freund- 
enreich,  Ed.  von,  Ueber  stickstoffbindende  Bakterien.  Ibid.  II,  10:  514-522.  1903.  Lohnis,  F.,  Beitrage 
zur  Kenntnis  der  Stickstoffbakterien.  Ibid.  II,  14:  582-604,  713-723.  1905.  Christensen,  Harald,  R., 
Ueber  das  Vorkommen  und  die  Verbreitung  des  Azotobacter  chroococcum  in  verschiedenen  Boden.  Ein 
BeitragzurMethodikdermikrobiologischen  Bodenforschung.  Ibid.  II,  17:  100-119,  161-165,  378-383,  528. 
1907.  Bredemann,  G.  Regeneration  der  Fahigkeit  zur  Assimilation  von  freiem  Stickstoff  des  Bacillus 
amylobacter  A.  M.  et  Bredemann  und  der  zu  dieser  Spezies  gehorenden  bisher  als  Granulobacter,  Clos- 
tridium usw.  bezeichneten  anaeroben  Bakterien.  Ber.  Deutsch.  Bot.  Ges.  26:  362-367.  1908.  Idem., 
Bacillus  amylobacter  A.  M.  et  Bredemann  in  morphologischer,  physiologischer  und  systematitscher  Bezie- 
hung.  Mit  besonderer  Berucksichtigung  des  StickstofTverbindungsveimogens  dieser  Spezies.  Centralbl, 
Bakt.  II,  23:385-568.     1909. 


ASSIMILATION    OF   NITROGEN  79 

microorganisms  by  inoculating  a  grape-sugar  solution  with  garden  soil.  In 
spite  of  the  fact  that  this  solution  contained  no  nitrogenous  compounds,  a 
vigorous  fermentation  began  immediately,  with  the  formation  of  carbon  dioxide, 
much  hydrogen,  and  butyric  and  acetic  acids,  the  process  being  accompanied 
by  the  fixation  of  atmospheric  nitrogen.  The  amount  of  nitrogen  combined  was 
related  to  the  amount  of  sugar  used  up,  as  is  shown  in  the  following  table: 

Experiment  number 1  2  3  4 

Grams  of  sugar  consumed 2.0  2.0  4.0  20 . o 

Milligrams  of  nitrogen  fixed 3.9  5.9  9.7  28.o 

Addition  of  ammonium  salts  in  very  small  amounts  acted  favorably;  larger 
amounts  retarded  the  fixation  of  nitrogen  and  finally  stopped  it  altogether. 
The  fixation  of  atmospheric  nitrogen  is  possible  only  in  substrata  which 
are  either  entirely  deficient  in  nitrogenous  compounds  or  contain  these  only 
in  very  small  amounts.  The  bacterium  to  which  this  fixation  is  due  was 
named  by  its  discoverer,  Vinogradskii,  Clostridium  pasteurianum.  It  is  an- 
aerobic, living  without  free  oxygen. 

More  recently  Beijerinck  has  found  another  nitrogen-fixing  bacterium, 
Azotobacter  chroococum.  Unlike  the  forms  previously  mentioned,  this  is  aerobic 
and  thrives  best  in  the  presence  of  air,  where  it  also  exhibits  its  ability  to  fix 
nitrogen.  Furthermore,  other  investigators  have  found  other  soil  microorgan- 
isms that  possess,  to  a  smaller  degree,  this  power  to  assimilate  free  nitrogen. 
The  fixation  of  atmospheric  nitrogen  is  therefore  a  process  that  occurs  commonlv 
in  nature. 

§7.  Assimilation  of  Nitrogen  Compounds  by  Lower  Plants. — We  have  seen 
that  nitrates  usually  furnish  the  best  source  of  nitrogen  for  higher  plants.  Of 
the  lower  plants  without  chlorophyll  (moulds,  yeasts,  bacteria)  not  nearly 
all  are  capable  of  utilizing  nitrates.  To  be  sure,  this  property  is  possessed  by 
most  of  the  common  moulds  (Penicillium,  Aspergillus  and  some  species  of 
Mucor)  and  one  group  of  bacteria  is  sufficiently  specialized  to  utilize  nitrates 
as  a  source  of  nitrogen,  at  the  same  time  reducing  them  vigorously,  with  elimi- 
nation of  free  nitrogen  (denitrifying  bacteria1).  Nevertheless,  most  lower 
plants  require  organic  nitrogenous  substances,  or  at  least  ammonium  salts. 
Suitable  culture  media  for  such  forms  have  already  been  referred  to,  and  it 
has  also  been  mentioned  that  these  organisms  are  in  great  variety,  as  far  as 
their  nutrition  is  concerned. 

Summary 

1.  The  Nitrogen  of  the  Air.— By  volume  measurement,  about  four-fifths  of  the  air 
is  free  nitrogen.  Air  also  generally  contains  very  small  amounts  of  nitrogen  in  the 
form  of  ammonia.  Free  nitrogen  cannot  be  assimilated  by  ordinary  higher  plants. 
Under  natural  conditions  these  plants  may  assimilate  minute  quantities  of  nitrogen 
from  the  ammonia  of  the  air,  but  this  source  of  nitrogen  is  generally  quite  negligible. 

1  Laurent,  E.,  Recherches  sur  le  polymorphisme  du  Cladosporium  herbarum.  Ann.  Inst.  Pasteur  2  : 
558-566,  581-603.  1888.  Idem,  Recherches  sur  la  valeur  comparee  des  nitrates  et  des  sels  ammomiacaux 
comme  aliment  de  la  levure  de  biere  et  de  quelques  autres  plantes.  Ibid.  3 :  362-374.  1889.  Ritter.'G., 
Ammoniak  und  Nitrate  als  Stickstoffquelle  fur  Schimmelpilze.  Ber.  Deutsch.  Bot.  Ges.  27:  582-588. 
1909. 


8o  PHYSIOLOGY   OF   NUTRITION 

2.  The  Nitrogen  of  the  Soil. — The  soil  contains  free  nitrogen  (which  cannot  be 
assimilated  by  ordinary  plants),  ammonia  and  ammonium  compounds,  nitrates, 
nitrites,  and  organic  nitrogenous  substances.  Nitrates  in  the  soil  are  the  main  source 
of  nitrogen  for  ordinary  plants,  though  some  forms  are  apparently  able  to  assimilate 
some  nitrogen  in  the  form  of  nitrites  or  in  the  form  of  ammonia  or  ammonium  salts. 
Organic  nitrogen  compounds  are  first  decomposed  (by  soil  microorganisms),  giving 
nitrates,  and  then  the  resulting  nitrates  are  assimilated  by  higher  plants.  Ammonium 
salts  are  similarly  converted  to  nitrates  in  the  soil,  by  microorganisms,  as  also  are 
nitrites.  Ammonium  compounds  and  organic  nitrogenous  substances  (arising  from 
the  decay  of  animal  and  plant  tissues,  etc.)  are  held  in  the  soil  in  considerable  amounts, 
but  nitrates  are  readily  washed  out  by  percolating  rain  water,  and  carried  away  in  the 
soil  drainage.  More  nitrates  are  gradually  formed,  so  that  there  is  always  a  supply  of 
these  salts  that  may  be  absorbed  through  the  roots  of  ordinary  plants  and  assimilated. 

3.  Nitrification  in  Soils. — The  production  of  nitrates  in  the  soil,  from  other  nitro- 
genous compounds  (and  from  free  nitrogen),  occurs  through  the  action  of  soil  bacteria. 
For  the  activity  of  these  nitrifying  organisms  a  continuous  supply  of  oxygen  is  neces- 
sary in  the  soil.  According  to  Vinogradskii's  work,  ammonia  and  ammonium  salts  are 
assimilated  by  nitrite  bacteria  in  the  soil,  which  give  off  nitrites,  and  nitrites  are  assimil- 
ated by  nitrate  bacteria  in  the  soil,  which  give  off  nitrates.  These  two  groups  of  soil 
bacteria  derive  their  carbon  compounds  by  synthesis,  from  carbon  dioxide  or  carbo- 
nates as  source  of  carbon.  The  energy  for  this  synthesis  is  derived  from  the  oxidation  of 
ammonia  or  of  nitrites;  the  nitrites  and  nitrates  that  are  produced  may  be  considered 
as  by-products.  In  the  presence  of  organic  compounds  that  may  be  readily  oxidized 
(like  sugars),  these  bacteria  secure  their  carbon  compounds  directly,  without  synthesis 
from  carbon  dioxide,  and  they  do  not  alter  the  organic  nitrogenous  compounds  that 
may  be  present,  nor  does  nitrification  occur.  Nitrogenous  organic  compounds  are 
not  assimilated  by  the  nitrite  and  nitrate  bacteria,  but  they  are  used  by  another  group 
of  soil  bacteria,  the  ammonifying  forms,  which  give  off  ammonia  as  a  by-product. 
When  bacteria  of  all  three  groups  are  present,  the  nitrogen  of  other  nitrogenous 
compounds  is  ultimately  converted,  by  three  steps,  into  nitrate  nitrogen.  (1)  The 
ammonifiers  produce  ammonium  compounds  (NH4)  from  nitrogenous  organic  sub- 
stances. (2)  The  nitrite  bacteria  produce  nitrites  (N02)  from  ammonium  compounds. 
(3)  The  nitrate  bacteria  produce  nitrates  (N03)  from  nitrites. 

Ammonium  salts  are  generally  not  largely  assimilated  by  ordinary  plants,  and 
ammonium  nitrogen  usually  becomes  readily  assimilable  only  after  nitrification,  with 
formation  of  nitrates.  Wagner  found  that  ammonium  salts  were  beneficial,  as  fertil- 
izer, in  lime  soils,  but  not  in  other  soils.  In  lime  soils  the  lime  prevents  the  develop- 
ment of  any  considerable  acidity.  Nitrites  are  generally  not  largely  assimilated  by 
ordinary  plants. 

4.  [6]  Assimilation  of  Atmospheric  Nitrogen  by  Soil  Bacteria.— Still  another  group 
of  soil  bacteria  assimilate  free  nitrogen,  as  was  shown  by  Vinogradskii  and  Beijerinck, 
and  these  bacteria  form  organic  nitrogen  compounds  or  nitrates.  The  energy  for  this 
nitrogen  fixation  is  derived  from  the  oxidation  or  fermentation  of  organic  compounds, 
such  as  sugars.  Some  of  these  nitrogen-fixing  bacteria  thrive  in  the  presence  of 
oxygen,  others  are  inhibited  by  oxygen.  There  are  also  soil  bacteria,  thriving 
under  special  conditions,  that  convert  nitrate  nitrogen  into  nitrite  or  ammonium 
nitrogen,  or  even  into  free  nitrogen,  these  being  denitrifying  processes. 

5.  Fixation  of  Free  Nitrogen  by  Tubercle  Bacteria. — Although  ordinary  plants  are 
not  able  to  assimilate  free  nitrogen,  there  are  certain  groups  of  them  (especially  the 


ASSIMILATION  OF  NITROGEN  8 1 

legumes)  that  appear  to  do  so.  Hellriegel  and  Wilfarth  showed  that  the  roots  of 
legumes  are  normally  infected  with  nodule  or  tubercle  bacteria,  which  remain  in  the  soil 
from  season  to  season,  infecting  the  new  plants  each  year.  The  same  experimenters 
showed  that  these  microorganisms  carry  on  nitrogen  fixation  in  the  structurally 
characteristic  root-tubercles  that  result  from  their  invasion  of  the  legume  root  tissues. 
The  tubercle  bacteria  apparently  derive  carbohydrates  from  the  host,  secure  utiliz- 
able  energy  through  the  oxidation  of  these  substances,  and  use  some  of  this  energy  for 
the  formation  of  nitrates  or  nitrogenous  organic  compounds  from  carbohydrates  and 
free  nitrogen.  Nitrates,  or  organic  nitrogenous  compounds,  are  given  off  by  the 
bacteria  and  these  substances  are  assimilated  by  the  host  plant.  Legumes  may  thus 
grow  well  in  soils  with  very  small  supplies  of  nitrates,  or  none  at  all,  deriving  their 
nitrogen  from  the  free  nitrogen  of  the  soil,  through  the  activities  of  the  tubercle 
bacteria.  In  the  presence  of  considerable  supplies  of  soil  nitrates  this  fixation  of  free 
nitrogen  is  slight  or  does  not  occur.  Different  legumes  have  different  nodule  bacteria; 
the  right  form  of  the  latter  must  be  present  in  the  soil  for  any  given  legume.  Free 
soil  nitrogen  may,  therefore,  be  fixed  (as  nitrates,  etc.)  (i)  through  the  action  of 
nitrogen-fixing  bacteria  in  the  soil  (see  4,  above),  or  (2)  through  the  action  of  tubercle 
bacteria  in  root  nodules.  Some  other  groups  of  higher  plants  have  tubercles  with 
nitrogen-fixing  bacteria;  for  example,  Pavetta  (Rubiaceae),  with  lea}  tubercles  in 
which  atmospheric  nitrogen  becomes  fixed. 

6.  [4].  Circulation  of  Nitrogen  in  Nature. — Free  nitrogen  is  converted  into  the 
nitrogen  of  nitrates  and  organic  nitrogen  compounds  by  the  nitrogen-fixing  bacteria 
of  the  soil  and  by  tubercle  bacteria.  Some  free  nitrogen  is  converted  into  ammonia 
nitrogen  by  the  action  of  atmospheric  electricity,  the  ammonia  finding  its  way  into 
the  soil,  where  its  nitrogen  is  converted  into  nitrite  nitrogen  by  the  nitrite  bacteria. 
Nitrites  are  changed  to  nitrates  by  nitrate  bacteria  in  the  soil.  Nitrates  (and,  to  some 
extent,  ammonium  compounds  and  nitrites)  are  assimilated  by  higher  plants  and 
disappear  in  the  formation  of  complex  nitrogenous  organic  compounds.  Animals 
secure  their  nitrogen  from  these  complex  plant  compounds,  or  from  other  animals. 
When  animal  and  plant  tissues  decay,  ammonia  and  free  nitrogen  result.  Free 
atmospheric  nitrogen  can  be  combined  with  other  elements  artifically,  as  in  the 
production  of  calcium  cyanamide  (CaCN2). 

7.  Assimilation  of  Nitrogen  Compounds  by  Lower  Plants. — Many  representatives 
of  the  moulds,  yeasts,  and  bacteria  are  unable  to  assimilate  nitrates,  and  must  be 
supplied  with  organic  nitrogenous  substances,  or  at  least  with  ammonium  salts. 
Animals  require  organic  nitrogen  compounds,  which  they  secure  from  plants  or  other 
animals. 


CHAPTER  IV 


ABSORPTION  OF  ASH-CONSTITUENTS 

§i.  Cultures  in  Artificial  Media. — Besides  the  four  elements,  carbon, 
hydrogen,  oxygen  and  nitrogen,  every  organ  of  the  plant  contains  many  other 
elements,  the  so-called  ash-constituents.  The  four  constituents  just  named 
volatilize  and  are  lost  during  incineration,  but  more  or  less  ash  always  remains. 
According  to  Knop,  the  average  amount  of  ash  left  after  burning  plant  tissue 
is  about  5  per  cent,  of  the  original  dry  weight.  The  following  elements  have 
been  found  in  the  ash  of  plants: 


Sulphur 

Potassium 

Zinc 

Selenium 

Phosphorus 

Sodium 

Mercury 

Manganese 

Chlorine 

Lithium 

Aluminium 

Iron 

Bromine 

Rubidium 

Thallium 

Cobalt 

Iodine 

Magnesium 

Titanium 

Nickel 

Fluorine 

Calcium 

Tin 

Copper 

Boron 

Strontium 

Lead 

Silver 

Silicon 

Barium 

Arsenic 

Experiments  with  plant  cultures  in  artificial  media  show  that  only  a  few 
of  these  elements  of  ash  are  essential  to  normal  growth.  Cultures  may 
be  prepared  by  using  either  a  neutral  solid  medium  to  which  various  salts  are 
added,  or  by  dissolving  the  respective  salts  in  water  and  employing  the  solu- 
tion thus  formed.  Clean  quartz  sand,  ground  pumice  or  ground  charcoal 
may  be  used  as  solid  media,  or  even  finely  divided  platinum-wire,  but  the  latter 
is  very  expensive.  Quartz  sand  with  various  salts  is  most  frequently  used. 
The  method  of  water-cultures  has  been  well  worked  out  in  many  researches 
dealing  with  the  necessity  of  various  substances  for  plant  growth,  but  espe- 
cially in  the  work  of  Knop  and  Nobbe.1 

The  study  of  artificially  controlled  cultures  has  shown  that  plants  need  the 
following  elements  in  salts,  for  normal  growth:  nitrogen,  sulphur,  phosphorus, 
potassium,  calcium,  magnesium  and  iron,  and  sometimes  chlorine  also. 

These  essential  elements  may  be  supplied  to  the  plant  as  salts  in  water  solu- 
tion, in  the  following  proportions  by  weight:  one  part  of  KNO3,  one  part  of 
KH2PO$,  one  part  of  MgS04,  and  four  parts  of  Ca(N03)2.  A  trace  of  ferric 
phosphate  is  also  added.  The  addition  of  a  nitrogen  compound  to  the  culture 
medium  is  necessary  although  nitrogen  is  not  one  of  the  ash-constituents,  for 
plants  obtain  their  nitrogen  from  the  soil,  as  has  been  seen  in  the  preceding 
chapter.  This  particular  nutrient  solution  is  known  as  Knop's  solution.  The 
concentration  must  be  very  low ;  as  long  as  the  plants  are  still  young,  o.  1  per  cent . 

'  Knop,  Wilh.,  Der  Kreislauf  des  Stoffes.     Lehrbuch  der  Agrikulturchemie.     Leipzig  and  St.  Petersburg. 
1868.     P.  572-663. » 

82 


ABSORPTION    OF    ASH-CONSTITUENTS 


83 


suffices,  but  the  concentration  may  be  raised  later  to  0.5  per  cent."  The  seed 
for  the  experiment  may  be  germinated  in  distilled  water.6  As  soon  as  the  root 
has  reached  a  suitable  length,  the  seedling  is  transferred  to  the  nutrient  solution, 
being  fixed  in  a  perforated  cork  stopper  with  cotton  packing,  so  that  only  the 
root  reaches  into  the  solution  (Fig.  49).  The  culture-bottle  should  be  protected 
from  light,  to  retard  or  prevent  the  development  of  algae  and  other  organisms, 
and  the  vessel  is  therefore  covered  with  a  paper  cylinder.  Care  must  be  taken 
that  the  culture  solution  does  not  become  alkaline  during 
the  growth  of  the  plants.  To  prevent  alkalinity  a  solution 
of  phosphoric  acid  may  be  added  to  the  culture  solution  so 
as  to  make  it  weakly  acid.c  Normal  plants,  producing 
flowers  and  fruit,  can  be  obtained  in  such  water  cultures 
by  observing  all  the  necessary  precautions. 

Salts  that  may  be  used  in  water-cultures  are  divided 
into  two  groups,  those  that  are  physiologically  alkaline  and 
those  that  are  physiologically  acid.  To  the  first  group  be- 
long salts  whose  anions  are  absorbed  by  the  plant  more 


Fig.  49. — Water 
culture  of  maize 
seedling. 


0  This  means  0.5  g.  of  all  the  salts  taken  together,  dissolved  to  make 
100  cc.  of  solution. — Various  other  four-salt,  and  some  five-salt,  solu- 
tions have  been  employed  by  various  workers.  For  a  list  of  these, 
see:  Grafe,  Viktor,  Ernahrungsphysiologisches  Praktikum  der  hoheren 
Pflanzen.  Berlin,  1914,  p,  56  el  seq.  The  simplest  solution  yet  de- 
vised for  this  sort  of  experiment  is  that  of  Shive,  which  contains 
but  three  salts  (calcium  nitrate,  mono-potassium  phosphate  and 
magnesium  sulphate)  besides  the  iron  phosphate.  See:  Shive,  J.  W., 
A  three-salt  nutrient  solution  for  plants.  Amer.  jour.  bot.  2:  157- 
160.  1915.  Idem,  A  study  of  physiological  balance  in  nutrient 
media.     Physiol,  res.  1:  327-397.     1915. — Ed. 

b  Distilled  water  is  unsuitable  for  seed  germination  and  for  the 
growth  of  plants,  because  (1)  it  may  contain  small  traces  of  toxic  sub- 
stances— which  are  more  influential  in  the  absence  of  nutrient  salts 
than  in  their  presence — and  (2)  it  acts  to  remove  salts  from  the  seeds 
and  young  seedlings  by  outward  diffusion.  See,  in  this  connection:  True,  R.  H.,  and  Bartlett, 
H.  H.,  Absorption  and  excretion  of  salts  by  roots,  as  influenced  by  concentration  and  composi- 
tion of  culture  solutions.  U.  S.  Dept.  Agric,  Bur.  Plant  Industry.  Bull.  231.  1912.  True, 
R.  H.,  Harmful  action  of  distilled  water.  Amer.  jour.  bot.  1 :  255-273.  1914.  Merrill,  M.  C, 
Some  relations  of  plants  to  distilled  water  and  certain  dilute  toxic  solutions.  Ann.  Missouri 
Bot.  Gard.  2:  459-506.  1915.  Idem,  Electrolytic  determination  of  exosmosis  from  the 
roots  of  plants  subjected  to  the  action  of  various  agents.  Ibid.  2:  507-572.  1915.  For 
earlier  work  on  the  physiological  properties  of  distilled  water,  see:  Livingston,  B.  E.,  Further 
studies  on  the  properties  of  an  unproductive  soil.  U.  S.  Dept.  Agric,  Bur.  Soils.  Bull.  36. 
1907.  It  is  probably  best  to  allow  germination  to  occur  in  a  properly  balanced  nutrient 
solution,  frequently  renewed. — Ed. 

0  Frequent  renewal  of  the  solution  is  necessary  in  any  case,  and  this  avoids  any  need  for 
adding  acid.  The  salt  proportions  and  total  concentration  of  a  nutrient  solution  may  be 
maintained  throughout  the  period  of  a  solution-culture  experiment  by  allowing  the  solution 
to  flow  continuously  through  the  culture  jar.  (See:  Trelease,  Sam  F.,  and  Livingston, 
Burton  E.,  Continuous  renewal  of  nutrient  solution  for  plants  in  water-cultures.  Science  n.s. 
55  :  483-486.     iQ22.).—Ed. 


84 


PHYSIOLOGY    OF    NUTRITION 


rapidly  than  are  their  kations,  thereby  rendering  the  culture  solution  alkaline. 
Potassium  nitrate  (KN03)  is  an  example  of  these.  To  the  second  group 
belong  those  salts  whose,  kations  are  absorbed  more  rapidly  than  are  the 
anions,  thus  giving  the  nutrient  medium  an  acid  reaction.  Ammonium 
chloride  (NH4C1)  and  ammonium  sulphate  [(NH4)2S04]  are  physiologically 
acid.  The  injurious  effects  of  these  salts  are  prevented  by  certain  reactions 
in  complex  agricultural  soils,  but  in  sand  or  water  cultures  account  must  be 
taken  of  these  phenomena. 

§2.  Importance  of  the  Essential  Ash-constituents.1— Not  much  is  known 
concerning  the  importance  of  the  single  ash-constituents. d     Of  some  it  can  be 

said  only  that  their  absence  results  in  re- 
tardation of  plant  development.  Two 
buckwheat  plants  are  shown  in  Fig.  50, 
one  of  which  has  been  grown  in  a  solution 
containing  all  the  essential  elements  and 
exhibits  an  entirely  healthy  appearance, 
while  the  other,  cultivated  in  a  nutrient 
solution  lacking  potassium,  has  hardly 
developed  at  all.  The  difference  in 
growth  is  very  great,  although  the  dry 
substance  of  the  normally  grown  buck- 
wheat plant  contains  only  about  2.5  per 
cent,  of  potassium. 

1  Berthelot,  M.,  Chimie  vegetale  et  agricole.  Paris, 
1899.  Tome  IV.*  Mayer,  A.,  1901-1902.  [See  note  1, 
P-  33- 

d  For  modern  studies  on  the  relation  between 

plant  growth  and  the  salt  proportions  and  total 
concentration  of  the  nutrient  solution  see:  Totting  - 
ham,  W.  E.,  A  quantitative  chemical  and  physio- 
logical study  of  nutrient  solutions  for  plant  cultures. 
Physiol,  res.  1  :  133-245.  1914.  (This  includes  a 
very  thorough  study  of  Knop's  solution  and  a  re- 
view of  the  literature.)  Shive,  1915,  1,  2.  [See 
note  a,  p.  83.]  The  whole  subject  of  the  necessity 
of  the  various  elements  for  plant  growth  is  well 
discussed  by  Russell,  1915.     [See  note  i,  p.  73.] 

The  relations  between  plant  growth  and  the 
supply  of  mineral  salts  may  be  studied  also  by 
using  the  solution-culture  method  and  three  or 
more  single-salt  solutions  supplied  separately,  in 
rotation.  This  had  been  attempted,  without  suc- 
cess, at  the  Laboratory  of  Plant  Physiology  of  the 
Johns  Hopkins  University,  and  it  remained  for 
Gericke  to  succeed  at  the  University  of  California. 
(See  Gericke,  W.  F.,  Water  culture  experimentation.  Science  n.s.  56:421-422.  1922.) 
Gericke  obtained  good  growth  of  wheat  with  0.0 1  volume-molecular  solutions  for  KNO3, 
CaS04,  and  MgHP04,  the  solution  rotation  being  four  days  for  the  first  solution  and  one 
day  for  each  of  the  other  two.  A  very  small  amount  of  iron  was  supplied  in  the  otherwise 
single-salt  solutions.     This  method  deserves  further  attention. 


B  A 

Fig.  50. — Buckwheat  plants  in  water- 
culture.  A,  with  potassium;  B,  without 
potassium. 


ABSORPTION    OF   ASH-COXSTITUENTS 


85 


Sulphur  is  a  necessary  element  because  it  is  essential  to  the  formation  of 
proteins,  which  are  so  important  in  plants.  It  must  be  supplied  as  the  sulphate 
of  one  of  the  essential  metals;  all  other  compounds  of  sulphur  are  injurious. 
It  cannot  be  replaced  by  any  other  element. 

Phosphorus  also  is  necessary.  It  is  a  constituent  of  nucleins  (a  special 
group  of  proteins),  and  of  phosphatides.  It  may  be  introduced  in  the  solution 
only  as  one  of  the  phosphates 
of  the  tribasic  acid  (H3PO4), 
since  other  phosphorus  com- 
pounds have  been  found  to 
be  harmful.  It  cannot  be  re- 
placed by  any  other  element. 
Potassium  is  also  abso- 
lutely essential.  It  accom- 
panies carbohydrates  and  is 
supposed  to  promote  their 
formation. 

Calcium  is  likewise  neces- 
sary, especially  for  normal 
leaf  development.  Some 
plants  without  chlorophyll 
(moulds)  can  exist  without 
calcium,1  and  non-green 
phanerogams  contain  much 
less  calcium  than  do  green 
plants.2 

Magnesium  is  also  neces- 
sary; it  accompanies  pro- 
teins and  is  contained  in 
chlorophyll. 

Finally,  plants  need  iron,  the  lack  of  which  prevents  chlorophyll  formation; 
they  become  pale  and  chlorotic,3  even  in  the  light,  when  grown  without  this 
element. 

§3.  Importance  of  the  Non-essential  Ash-constituents. — Plant  ash  contains 
appreciable  quantities  of  other  elements  than  the  absolutely  essential  ones,  and 
these  are  not  to  be  considered  as  entirely  without  physiological  effects.  Each 
ash-constituent  must  be  considered  as  exerting  some  slight  effect  in  the  plant, 
either  injurious  or  beneficial.  If  plants  develop  apparently  normally  in  a  nutri- 
ent solution  without  a  given  element,  it  does  not  necessarily  follow  that  this 
element,  if  present  might  not  exert  some  beneficial  influence. 

Silicon,  for  example,  is  abundant  in  many  plants.  Nevertheless,  experi- 
ments with  various  plants  in  artificial  media  have  shown  that  even  the  grasses 

1  Loew,  Oscar,  Liming  of  soils  from  a  physiological  standpoint.     U.  S.  Dept.  Agric.     Bull.  I.     27  p. 
Washington,  1901. 

2  Aso,  K.,  On  the  lime  content  of  phanerogamic  parasites.     Bull.  Coll.  Agric.     Imp.  Univ.  Tokyo  4: 
387-389-     1900-1002. 

«  Molisch,  1892.     [See  note  b,  p.  51.] 


Pig.  51. — Portion  of  a  cross-section  through  a  rye  stalk. 
At  left,  lodged;  at  right,  normal.     (After  Koch.) 


86  PHYSIOLOGY    OF    NUTRITION 

(Gramineae)  can  develop  without  this  element.  The  lodging  of  grain  (when  the 
plants  fail  to  stand  erect  in  the  field),  which  was  earlier  ascribed  to  a  deficiency 
of  silicic  acid  (H2Si03)  in  the  soil,  is  a  result  of  insufficient  illumination.  This, 
in  turn,  is  due  to  too  thick  planting.  Anatomical  study1  of  the  stalks  of  lodged 
grain  shows  that  they  have  all  the  characteristics  of  etiolated  stems  (Fig.  51). 
In  healthy  stems  we  find  small,  thick-walled  cells,  while  in  etiolated  stalks, 
whether  lodged  or  not,  the  cells  are  very  large  and  have  much  thinner  walls. 

In  laboratory  experiments,  where  plants  are  protected  from  some  of  the 
unfavorable  conditions  of  the  field,  silicon  is  not  essential,  but  this  is  not  true 
when  plants  develop  under  natural  conditions.  Here  silicon  appears  to  play  a 
very  important  role,  protecting  the  plant  from  attacks  of  various  parasites. 
Fungus  hyphae  cannot  easily  penetrate  cell  walls  that  are  impregnated  with 
silica.  Wheat,  rye,  etc.,  grown  in  nutrient  solutions  deficient  in  silicic  acid 
often  suffer  so  severely  from  rust  that  only  great  care  can  prevent  their  complete 
destruction.  The  hardness  of  silicated  cell  walls  is  also  a  very  good  protection 
against  animal  attack.  Thus,  for  instance,  one  plant  of  Lithospermum  arvense, 
grown  in  a  nutrient  solution  without  silicic  acid,  suffered  severely  from  plant- 
lice  even  though  these  were  removed  daily,  while  two  similar  plants,  standing 
near  by  and  grown  in  similar  solutions  but  not  tended  so  carefully,  were 
completely  killed  by  these  insects. 

The  distribution  of  silicic  acid  in  different  parts  of  seeds2  is  another  indi- 
cation of  its  protective  action.  Millet  seeds  without  the  seed-coats  contain 
only  from  4.8  to  7.1  per  cent,  of  the  total  silicic  acid  of  the  seed,  all  the  re- 
mainder (from  92.6  to  95.1  per  cent.)  being  deposited  in  the  seed-coats.  Such 
a  marked  accumulation  of  silicic  acid  in  the  seed-coats  suggests  the  impor- 
tance of  this  substance  to  plants  growing  under  natural  conditions.  The 
investigations  of  Sabanin  upon  ripening  seeds  of  millet  show  that  this  plant 
hastens,  as  it  were,  to  accumulate  enough  silicic  acid  in  the  peripheral  parts  of 
the  grain  (as  in  the  palea)  to  protect  the  increasing  reserve  material  from 
unfavorable  external  conditions. 

Most  plants  can  live  without  chlorine,  but  buckwheat  deprived  of  this 
element  did  not  attain  complete  development  in  Nobbe's  experiments,  and  it 
was  his  opinion  that  chlorine  favors  the  translocation  of  carbohydrates  from 
the  leaves  into  other  organs.  Knop,  however,  obtained  normal  development 
of  buckwheat  plants  in  a  solution  without  chlorine,  and  so  the  question  of  the 
role  of  chlorine  is  still  unsettled/     It  is  advisable  to  add  chlorine  to  the  nutrient 

1  Koch,  L.,  Welche  abnorme  Aenderungen  werden  durch  Beschattung  in  wachsenden  Pflanzenorganen 
hervorgerufen?     Landw.  Centralbl.  Deutschl.  20:  202.      1872. 

=  Sabanin,  A.  N.,  Ueber  Kieselsaure  in  den  Kornern  der  Hirse  (Panicum  miliaceum  L.)  [Abstract  in 
German,  pp.  295-302.     Text  in  Russian.]     Jour.  exp.  Landw.  2:  257-302.     1001. 

e  Buckwheat  has  been  repeatedly  grown  to  maturity,  with  production  of  seed,  in  water- 
cultures  without  any  more  chlorine  than  might  have  been  present  in  spite  of  all  ordinary  pre- 
cautions to  exclude  this  element,  in  the  Laboratory  of  Plant  Physiology  of  the  Johns  Hopkins 
University;  but  the  possibility  remains  that  the  presence  of  chlorine  might  produce  more 
vigorous  growth.  Trelease's  results  strengthen  the  idea  that  this  element  is  not  beneficial 
to  wheat  in  its  early  stages  of  growth.  It  exerted  no  injurious  influence,  however,  in  his 
cultures.  (See:  Trelease,  Sam  F.,  The  relation  of  salt  proportions  and  concentrations  to  the 
growth  of  young  wheat  plants  in  nutrient  solutions  containing  a  chloride.  Philippine  jour. 
sci.  17:527-603.     1920.). — Ed. 


ABSORPTION   OF   ASH-CONSTITUENTS  87 

solution  when  experimenting  with  plants  whose  relation  to  chlorine  is  not  under- 
stood; potassium  chloride  is  best  for  this  purpose.  Observations  of  agri- 
culturists favor  the  idea  that  chlorine  influences  the  translocation  of  carbo- 
hydrates under  natural  conditions.  Potatoes  grown  in  soil  rich  in  chlorine 
contain  less  starch  than  those  cultivated  in  soil  deficient  in  this  element.  So, 
when  potatoes  with  the  highest  possible  starch  content  are  desired  chlorine 
fertilizers  are  to  be  avoided.1 

Zinc  is  one  of  the  less  common  ash-constituents.  It  is  contained  in  a 
variety  of  violet  (Viola  calaminaria  or  V.  lutea  var.  muUicaulis),  which  grows 
exclusively  in  soils  containing  zinc.  The  differences  by  which  these  "calamin" 
violets  are  distinguished  from  the  ordinary  Viola  tricolor  are  probably  due  to 
the  effect  of  the  zinc  salt/  Also,  Raulin  used  zinc  in  his  nutrient  solution 
(see  page  46)  for  Aspergillus  niger.  Rikhter's2  investigations  showed  that  zinc 
promoted  growth  and  the  accumulation  of  organic  substances  during  the 
early  period  of  development  of  this  mould,  but  prevented  the  formation  of 
spores.     Kostychev3  also  found  that  zinc  influenced  metabolism  in  moulds. 

Aluminium  occurs  in  plant  ash  rather  infrequently.  It  influences  the 
color  of  the  flowers  in  Hydrangea  (II.  hortensis).*  Gardeners  had  long  since 
noticed  that  the  ordinary  reddish-flowered  hydrangea  bore  blue  flowers  when 
grown  in  certain  soils,  such  as  some  forest  and  moor  soils.  Tests  of  many 
different  substances  showed  that  blue  flowers  always  appeared  if  the  soil  con- 
tained soluble  aluminium  compounds.  At  first  ordinary  alum  (  made  up  of 
aluminium  and  potassium  sulphate,  A12S04  +  K2SOi  +  24H2O)  was  used, 
being  introduced  into  the  soil  in  pieces  varying  from  the  size  of  a  pea  to  that  of 
a  hazel-nut,  and  blue  flowers  were  always  obtained.  In  another  series  of  experi- 
ments, some  plants  were  treated  with  aluminium  sulphate  and  others  with 
potassium  sulphate.  The  cultures  with  potassium  sulphate  gave  the  usual 
red  color,  while  those  with  aluminium  sulphate  always  produced  blue  flowers, 
and  the  color  appearing  with  this  salt  was  more  intense  than  that  obtained  by 
the  alum  treatment.  The  alum  therefore  produced  the  blue  color  because  of 
the  presence  of  aluminium,  the  potassium  being  without  influence.  This  case 
shows  clearly  how  the  presence  of  a  non-essential  element  may  influence 
metabolism  in  a  specific  manner. 

Researches  in  recent  years  have  shown  that  various  elements,  such  as 
manganese,  boron,  rubidium,  etc.,  are  more  or  less  favorable  to  plant  growth. 

1  Budrin,  Die  kiinstlichen  Dungemittel  mit  besonderer  Berucksichtigung  der  Stickstoffdunger.  WTarsaw, 
1888.  (Russian.)*  [See  also:  Tottingham,  Wm.  E.,  A  preliminary  study  of  the  influence  of  chlorides 
upon  the  growth  of  certain  agricultural  plants.     Jour.  Amer.  Soc.  Agron.  11:  1-32.     1019.] 

-  Richter,  Andreas,  Zur  Frage  der  chemischen  Reizmittel.  Die  Rolle  des  Zn  and  Cu  bei  der  Ernahrung 
von  Aspergillus  niger.     Centralbl.  Bakt.  //.  7-  417-429.     iQOi. 

3  Kostytschew,  S.,  Der  Einfluss  des  Substrates  auf  die  anaerobe  Athmung  der  Schimmelpilze.  Ber. 
Deutscb,.  Bot.  Ges.  20:  327-334-     1902. 

1  Molisch,  Hans,  Der  Einfluss  des  Bodens  auf  die  Bluthenfarbe  der  Hortensien.     Bot.  Zeitg.  55  :  40-61. 

1897. 

'But  the  studies  of  Hoffmann  appear  to  controvert  this  statement.  According  to  this 
author  the  calamin  violet  is  the  same  whether  grown  with  or  without  zinc,  and  Viola  tricolor 
does  not  take  the  calamin  form  when  supplied  with  zinc.  See:  Hoffmann,  H.,  Culturver- 
suche.  Bot.  Zeitg.  33:  601-605,  617-628.  1875.  Idem,  Untersuchungen  iiber  Variation. 
Ber.  Oberhess.  Ges.  Giessen  16:    1-37.     1877. — Ed. 


88 


PHYSIOLOGY    OF    NUTRITION 


These  elements  act  like  catalyzers,1  while  the  plastic  ash-constituents  (phos- 
phorus, sulphur,  potassium,  magnesium,  calcium)  have  to  do  with  the  structure 
of  the  cell  and  its  parts;  these  latter  may  also  act  as  catalyzers,  however. 

§4.  Ash-analysis  of  Plants.- — Besides  the  growing  of  plants  in  artificial 
media,  the  analysis  of  plants  grown  under  natural  conditions  is  also  useful  in 
the  determination  of  the  relative  importance  of  the  various  mineral  elements. 
Large  numbers  of  such  analysis  have  been  carried  out,  and  the  results  obtained 
up  to  1880  have  been  assembled  and  arranged  in  a  very  helpful  way  by  Wolff.2 

The  ash-analyses  of  entire  plants  show  that  the  amount  of  each  individual 
ash-constituent  is  different  with  different  plants.  The  agriculturist,  for  ex- 
ample, recognizes  three  groups  of  cultivated  forms,  silicon  plants,  calcium  plants 
and  potassium  plants,  according  to  which  one  of  these  three  elements  is  most 
abundant  in  the  ash.  The  following  table  (after  Liebig)  contains  the  results 
of  ash-analyses  of  some  of  the  plants  belonging  to  these  three  classes. 


Salts  of  K  and 

Na 


Silicon 
plants 

Calcium 
plants 

Potassium 
plants 


f  Oat  straw  and  grain . . . 
\  Rye  straw 

Havanna  tobacco 

Stems  and  leaves  of  pea 

Sugar  cane 

Artichoke 


per  cent. 
34.00 
18.65 

24-34 
27.82 

88.80 
84.30 


Salts  of  Ca  and 
Mg 


per  cent. 

4.00 

16.52 

67.44 
63-74 

12.00 
i5-7o 


Silicic  Acid 


per  cent. 
62.08 
63.89 

S.30 
7.81 


The  total  amount  of  ash  is  also  known  to  be  different  in  different  species. 
Water  plants  are  richest,  woody  plants  are  among  the  poorest,  and  herbs  take 
a  middle  place,  with  reference  to  the  amount  of  ash  they  contain.  A  comparison 
of  the  ash-analyses  of  the  alga  Chara  and  the  tree  Fagus  (beech)  is  shown  in 
the  next  table. 


Entire  Ash 

Content, 
Per  Cent,  of 
Dry  Weight 


Amounts  of  Various  Elements  in  Ash 

Calculated  as  Oxides,  Per  Cent,  of  Total 

Ash 


K20 


CaO 


MgO 


Fe20 


2^3 


P20 


2^5 


SO3 


SlOo 


Chara  fcetida . . . 
Fagus  sylvalica 

Wood 

Bark 

Leaves 


39.080 

0-355 
5.860 

5-i4o 


0.40 

96.23 

1-39 

0.28 

0.28 

0.49 

14.40 

60.20 

4-5o 

2.30 

2.70 

3-50 

5.10 

83.40 

3.60 

0.70 

2.10 

1 .00 

21.80 

44-30 

7.20 

2.30 

7.80 

2.40 

0.58 

10.00 

3 -7o 

10.50 


1  Agulhon,  H.,  Recherches  sur  la  presence  et  le  role  du  bore  chez  les  v6g6taux.     Paris,  1910. 

*  Wolff,  Emil,  Aschen-Analysen  von  landwirthshaftlichen  Producten,  Fabrik-abfallen  und  wildwach- 
senden  Pflanzen.  I  Theil.  Berlin,  1871.  Idem,  Aschen-Analysen  von  land-  and  forstwirtschaftlichen 
Producten      II  Theil.     Berlin,  1880. 


ABSORPTION    OF    ASH-CONSTITUENTS 


89 


This  distribution  of  the  ash  shows  that  the  tissues  richest  in  ash  are  those 
in  which  living  cells  are  most  numerous,  such  as  those  of  algae  and  the  leaves 
and  cortex  of  the  beeech.  Dead  cells  contain  much  less  ash,  since  the  salts 
begin  to  pass  out  at  about  the  time  death  occurs;  thus,  the  hard  wood  of 
the  beech  contains  much  less  than  does  the  dry  substance  of  the  living  leaf 
tissue. 

Different  amounts  of  ash  occur  in  different  organs  of  the  same  plant.  Leaves 
are  richer  in  ash  than  stems  and  roots.  The  amounts  of  the  different  chemical 
elements  likewise  vary;  calcium,  for  instance,  predominates  in  leaves. 

The  ash  content  of  each  organ  changes  during  the  course  of  its  development; 
in  leaves  it  increases  with  age,  while  in  roots  and  stems  it  decreases.  In  the 
case  of  roots  and  stems  the  number  of  dead  cells,  poor  in  ash,  increases  with  age. 
The  following  table  gives  the  total  ash  content  and  the  proportions  of  the  vari- 
ous elements  in  the  ash,  for  beech  leaves  (Fagus  sylvatica)  at  three  different 
stages  of  their  development. 


Date 


Total  Ash, 
Per  Cent,  of 
Dry  Weight 


May  16 
July  18. 
Oct.  15. 


41 
4-7 

7-1 


Amounts  of  Various  Elements  in  Ash,   Cal- 
culated as  Oxides,  Per  Cent,  of  Total  Ash 


K20 


42.1 

17. 1 

7-i 


CaO 


13-8 

42.3 
50.6 


MgO 

Fe203 

P205    j 

4-3 

0.8 

32-4 

5-6 

1.4 

8.2 

4-i 

i-3 

5-i 

Si02 


1.6 
21.3 
30-5 


These  analyses  of  beech  leaves  show  how  strikingly  the  amount  of  the  differ- 
ent ash-constituents  alter  with  the  age  of  the  leaves.  Calcium  and  silicon  show 
a  marked  increase  in  amount  while  potassium  and  phosphorus  decrease  as  the 
leaves  become  older.  But,  as  has  been  well  pointed  out  by  Wehmer,1  it  is  not 
to  be  concluded  from  these  analyses  that  the  absolute  amounts  of  potassium 
and  phosphoric  acid  diminish  in  such  leaves.  For  example,  if  50  g.  of  potassium 
and  50  g.  of  other  elements  were  present  in  a  certain  quantity  of  young  leaves, 
we  should  then  find  50  per  cent,  of  potassium  in  the  ash.  If  we  suppose  that 
the  leaves  take  up  100  g.  more  of  the  other  elements  but  that  the  amount  of 
potassium  remains  unchanged,  then  we  should  expect  to  find  only  25  per  cent, 
of  potassium  in  the  ash  of  the  older  leaves.  According  to  Riesmuller's  anal- 
yses, the  ash  of  1000  beech  leaves  contained,  at  different  times  of  the  year, 
the  percentages  and  absolute  amounts  of  potassium  shown  in  the  following 
table. 


1  Wehmer,  C,  Zur  Frage  nach  der  Entleerung  absterbender  Organe,  insbesondere  der  Laubblatter. 
Unter  Beruchsichtigung  der  vorliegenden  Aschenanalysen  vom  kritischen  Standpunkte  beleuchtet. 
Landw.  Jahrb.  21 :  513-569-     1892. 


9° 


PHYSIOLOGY    OF    NUTRITION 


Time  of    Analysis 


May 

June 

July 

August.  .  . 
October. . . 
November 


Absolute  Amount  of 
Potassium 


grams 
0.7 
1.2 
1 .2 
1 . 1 
0.8 
0.7 


The  percentage  content  of  potassium  in  the  ash  underwent  a  marked  decrease 
during  the  course  of  the  summer,  but  no  corresponding  decrease  in  the  absolute 
amount  of  potassium  is  apparent.  The  absolute  amount  is  maintained  fairly- 
constant  during  the  growing  period,  and  undergoes  a  marked  decrease  only 
in  late  autumn.     Similar  results  were  also  obtained  for  phosphoric  acid  (PO4). 

§5.  Microchemical  Ash-analysis.3 — Ash-analyses  of  the  kind  just  referred 
to  can  be  carried  out  only  with  large  amounts  of  material,  but  in  exact  studies 
of  the  distribution  and  translocation  of  ash-constituents  small  quantities  must 
suffice,  and  microchemical  analysis  is  resorted  to  in  such  cases.1  Platinic 
chloride  is  used  for  the  identification  of  potassium,  beautiful  crystals  of  potas- 
sium chloroplatinate  being  formed  (Fig.  52).     To  identify  calcium,  dilute  sul- 

1  Haushofer,  K.,  Mikroskopische  Reaktionen.  Braunschweig,  1885.  Kle merit,  Constantin,  and 
Renard,  A.,  R6actions  microchimiques  a  cristaux  et  leur  application  en  analyse  qualitative.  132  p.  Brux- 
elles,  1886.  Schimper,  A.  F.  W.,  Zur  Frage  der  Assimilation  der  Mineralsalze  durch  die  gnine  Pflanze. 
Flora  73:  207-261.  1890.  P.  207.  [Zimmerman,  A.,  Die  botanischen  Mikrotechnik.  Tubingen,  1892. 
Idem.  Botanical  microtechnique,  a  handbook  of  methods  for  the  preparation,  staining,  and  microscopical 
investigation  of  vegetable  structures.  Translated  by  J.  E.  Humphrey.  XII  +  296  p.  New  York,  1893. 
Richter,  O.,  Die  Fortschritte  der  botanischen  Mikrochemie  seit  Zimmermann's  Botanische  Mikrotechnik. 
Sammelreferat  Zeitsch  wiss.  Mikroskopie  22  :  1904-261.  1905.  Emich,  F.,  Lehrbuch  der  Mikrochemie. 
Wiesbaden,  1911.     Molisch,  Hans,  Mikrochemie  der  Pflanze.     Jena,  1913.] 

0  On  these  methods  for  ash-analysis  the  reader  is  referred  to  Molisch,  1913,  cited  just 
below.  The  following  points  may  be  of  value  in  connection  with  the  discussion  given  in  the 
text.  The  reaction  given  for  potassium  fails  to  distinguish  between  potassium  and  ammonium. 
(On  this  difficulty  see:  Weevers,  Th.  I.,  Untersuchungen  iiber  die  Lokalization  und  Funktion 
des  Kaliums  in  der  Pflanze.  Recueil  trav.  bot.  neerland.  8:  289.  1911.)  When  calcium 
is  plentiful  the  crystals  mentioned  occur  in  dense  masses,  so  that  their  individual  form  is  seen 
only  at  the  periphery  of  the  mass.  The  reaction  here  given  for  iron  serves  only  to  identify  it 
when  in  the  ferrous  condition.  For  other  tests  for  this  element  in  inorganic  compounds  see 
Molisch,  1913.  In  organic  compounds  {masked  iron)  it  cannot  be  identified  by  any  known 
microchemical  methods.  (See:  Wiener,  Adele,  Microchemical  proof  of  iron,  especially 
masked,  in  plants.  Rev.  in:  Chem.  abstracts  11:  615-616.  1917.  [Original  not  seen; 
cited  as:  Biochem.  Zeitsch.  77:  27-50.  1916].)  To  identify  phosphorus  in  organic  com- 
pounds it  is  necessary  first  to  incinerate  the  material,  after  which  the  test  given  may  be  applied. 
The  precipitation  of  the  phosphate  ion  as  ammonium-magnesium  phosphate  (see  under 
magnesium)  offers  a  more  sensitive  method,  not  affected  by  the  presence  of  organic  substances. 
(See  Molisch,  1913.)  The  tests  for  sulphur  given  in  the  text  apply  only  to  sulphates  and 
are,  moreover,  not  reliable  for  plant  tissues.  There  is  no  microchemical  test  available  for 
sulphur  as  it  is  usually  encountered  in  plant  cells.  A  more  reliable  test  for  chlorides  is  that 
of  Macallum.  (See:  Macallum,  A.  B.,  On  the  nature  of  the  silver  reaction  in  animal  and 
vegetable  tissues.     Proc.  Roy.  Soc,  London  B  76:  217-229.     1905.) — Ed. 


ABSORPTION    OF    ASH-CONSTITUENTS 


91 


phuric  acid  is  added,  which  forms  needle-like  crystals  of  calcium  sulphate  (gyp- 
sum) in  the  presence  of  this  element  (Fig.  53).  Magnesium  crystallizes, 
as  ammonium-magnesium  phosphate  (in  a  great  variety  of  forms),  upon  the 


Fig.  52.— Crystals  of  potassium  chloroplatinate.  Fig.  53.— Crystals  of  calcium  sulphate. 


addition  of  sodium  phosphate  and  ammonia  (Fig.  54) .  Iron  is  identified  by  the 
blue  color  produced  with  potassium  ferrocyanide.  Phosphates  are  identified 
by  treatment  with  a  solution  of  ammonium  molybdate  in  nitric  acid,  greenish- 


Fig.  54. — Crystals  of  ammonium  magnesium 
phosphate. 


Fig.    55. — Crystals  of   ammonium   phospho- 
molybdate. 


yellow  crystals  of  ammonium  phospho-molybdate  being  formed  and  gradually 
becoming  bright  green  (Fig.  55).  Upon  addition  of  strontium  nitrate,  sulphur 
separates  out  as  small  rounded  crystals  of  strontium  sulphate  (Fig.  56).     An- 


^0  0°^ 


Fig.  56— Crystals  of  strontium  sulphate.  Fig.     57.— Crystals     of    thallium     chloride. 

other  test  for  sulphuric  acid  is  the  addition  of  caesium  chloride  and  aluminium 
chloride,  which  leads  to  the  formation  of  large  crystals  of  caesium-alum.  Chlor- 
ides may  be  identified  by  adding  thallium  sulphate,  with  the  formation  of 
characteristic  crystals  of  thallium  chloride  (Fig.  57). 


92 


PHYSIOLOGY   OF   NUTRITION 


§6.  The  Plant  and  the  Soil.* — Plants  obtain  all  their  essential  ash-constitu- 
ents from  the  soil.  The  following  table  gives  an  idea  of  the  compositions  of 
several  different  kinds  of  soil,  the  numbers  representing  the  amounts  of  usual 
soil  bases,  calculated  as  oxides  and  expressed  as  percentages  of  the  total  dry 
weight  of  the  soil. 


Loam 


Loamy  Marl 

Lime  Marl 

40.70 

11.80 

32.00 

10.60 

8.90 

1.50 

6.00 

47.00 

1 .20 

0.20 

0.05 

O.IO 

Si02. 
Al2Oa 
Fe20; 
CaO. 
MgO 
K20. 


51-52 

17-93 
7.42 

i-57 
7.27 
4.10 


Every  soil  covered  with  vegetation  contains  organic  as  well  as  mineral  sub- 
stances. Bog  soils  are  particularly  rich  in  organic  materials,  as  is  evident  from 
the  following  table,  which  again  presents  percentages  on  the  basis  of  the  dry 
weight  of  the  soil. 


P205 

N 

Humus 

Black  soil,  Government  of  Orlov,  Russia 

Black  soil,  Government  of  Saratov,  Russia 

Soil  of  low  moor 

Soil  of  high  moor 

0.128 
0.223 
0.250 
0.090 

0.268 
0.607 
3-230 
1 .060 

13.080 
14.580 
82.560 
91.470 

The  chemical  analysis  of  a  soil  can  give  no  definite  idea  of  its  properties, 
however.*  In  order  to  predict  a  good  crop  from  a  given  soil,  it  is  not  enough  to 
know  that  it  contains  potassium,  phosphorus  and  the  other  essential  elements; 
it  must  also  be  known  whether  these  elements  occur  in  compounds  that  plants 
can  assimilate.  Nile  silt,  famous  for  its  fertility,  contains  only  0.5  per  cent,  of 
potassium  and  needs  no  further  addition  of  this  element,  but  mica-schist  soil 
contains  3  per  cent,  of  potassium  and  remains  unproductive  unless  a  potassium 
fertilizer  is  added. 

To  obtain  a  better  idea  of  the  productiveness  of  a  soil,  the  analysis  of  its 
water  or  hydrochloric  acid  extract  is  carried  out,  in  addition  to  determining  the 
essential  minerals  present.  The  necessary  elements  for  plant  growth  are  con- 
tained in  very  small  quantities  in  the  extract,  but  it  must  be  borne  in  mind  that 


*  An  excellent  treatise  on  the  soil  is:  Mitscherlich,  E.  A.,  Bodenkunde  fur  Land-  und 
Forstwirte.  2  Aufl.  317  p.  Berlin,  1913.  A  less  scientific  treatise  is:  Hilgard,  E.  W.,  Soils, 
their  formation,  properties,  composition,  and  relations  to  climate  and  plant  growth  in  the 
humid  and  arid  regions.  593  p.  New  York,  1912.  Best  of  all  presentations  of  the  soil,  from 
the  standpoint  of  plant  physiology,  is  that  of  Russell  (1921).     [See  note  i,  p.  73I. — Ed. 

1  Cameron,  F.  K.,  The  soil  solution.     136  p.     Easton,  Pa.     191 1. — Ed. 


ABSORPTION    OF    ASH-CONSTITUENTS 


93 


not  nearly  all  of  the  materials  thus  extracted  from  the  soil  can  be  assimilated  by 
the  plant,  and  also  that  much  material  that  the  plant  might  eventually  absorb 
is  not  thus  extracted.  It  must  also  be  emphasized  that  plant  species  differ 
very  greatly  in  their  power  to  absorb  salts  from  the  soil. 

If  the  soil  does  not  contain  the  essential  elements  in  a  sufficient  amount  and 
in  the  proper  form  for  assimilation  by  plants,  its  productiveness  may  be  in- 
creased by  the  addition  of  suitable  fertilizers.  The  gain  that  may  be  obtained 
from  the  use  of  the  fertilizer  depends  not  only  upon  the  properties  of  the  latter 
but  also  upon  those  of  the  soil  and  upon  the  plant  species  that  is  to  be  culti- 


63  39  36  2 

Fig.  58. — Effect  of  fertilizing  oats  with  different  kinds  of  Thomas  slag  (1-3)  and  with 
phosphorite  (4),  all  showing  different  solubilities  of  their  phosphates  in  ammonium  citrate 
solution.  The  relative  solubilities  of  the  phosphates  are  shown  by  the  numbers  below  the 
pots.     Culture  5  received  no  addition.     (After  P.  Wagner.) 

vated.  For  example,  let  us  consider  phosphatic  fertilizers.  Thomas  slag  is 
one  of  the  best  of  these.  It  is  a  by-product  derived  from  the  manufacture  of 
steel  out  of  pig  iron.  The  latter  contains  silicic  acid,  sulphur  and  phosphorus, 
which  are  oxidized,  through  the  addition  of  lime  in  the  process,  to  calcium  salts, 
and  these  rise  to  the  surface  of  the  molten  steel  as  slag.  Such  slag  varies  accord- 
ing to  the  solubility  of  its  phosphoric  acid  in  an  acid  solution  of  ammonium 
citrate.  The  varieties  with  large  amounts  of  phosphates  that  are  soluble  in 
ammonium  citrate  are  good  fertilizers,  while  other  varieties  are  not  useful  in 
this  way. 


94 


PHYSIOLOGY    OF    NUTRITION 


This  is  shown  by  Wagner's  experiments1  with  oats  (Fig.  58).  Three  culture 
vessels  received  equal  amounts  of  phosphoric  acid  (0.5  g.)  as  pulverized  Thomas 
slag;  but  different  kinds  of  slag  were  used,  showing  different  solubilities  of  their 
phosphates  in  ammonium  citrate  solution.  The  fourth  vessel  received  twice 
as  much  phosphoric  acid  (1.0  g.),  in  the  form  of  pulverized  phosphate  rock 
(phosphorite),  and  the  fifth  received  no  phosphorus  fertilizer  at  all.  The  fol- 
lowing table  shows  the  effects  of  these  fertilizers  upon  the  growth  of  the  plants. 


Culture 
No. 


1 
2 

3 

4 
5 


Phosphoric 
Acid  Added 


grams 
0.5 
0.5 

1 .0 


Kind  of 
Fertilizer 


Thomas  slag 
Thomas  slag 
Thomas  slag 
Phosphorite . 
No  fertilizer. 


Solubility  in 

Ammonium 

Citrate 


per  cent. 
65 
39 
36 


Yield 


grams 

416.7 

306.9 

281. 1 

1590 

144.0 

Gain  Due  to 
Fertilizer 


per  cent. 

272.7 

162.9 

137.1 

15.0 


This  experiment  shows  very  clearly  how  fertilizers  may  differ  in  quality. 
Although  the  fourth  culture  contained  more  phosphoric  acid  than  any  of  the 
others,  its  yield  exceeded  that  of  the  unfertilized  plants  by  only  about  15  g. ; 
the  plants  could  not  assimilate  this  particular  phosphorus  compound.  It 
appears  that  the  greater  the  amount  of  phosphorus  compounds  that  can  be 
dissolved  out  of  the  fertilizer  by  ammonium  citrate  solution,  the  better  can  the 
fertilizer  be  utilized  by  the  plant  and  the  greater  is  the  yield. 

Not  only  the  properties  of  the  fertilizer,  but  also  the  peculiarities  of  the 
plants  under  cultivation  must  receive  attention.  The  same  fertilizer,  added  to 
a  gTven  soil,  may  be  beneficial  to  one  plant  and  entirely  useless  to  another.  In 
Prianishnikov's  experiments,2  for  instance,  various  plants  were  cultivated  in 
sand  supplied  with  the  necessary  nutrient  salts.  In  one  series  of  experiments 
phosphorus  was  supplied  as  mono-sodium  phosphate  (NaEUPOO,  in  the  other 
as  phosphate  rock  (phosphorite),  which  contains  calcium  phosphate,  calcium 
carbonate,  sand,  loam,  iron  oxide,  and  aluminium.  Millet  grown  in  these  two 
media  gave  a  yield  of  29.07  g.  with  the  soluble  phosphate  and  one  of  only  0.57  g. 
with  phosphate  rock  (Fig.  59).  Millet  and  other  grains  either  cannot  utilize 
phosphorite  in  sand  cultures  at  all,  or  else  they  can  utilize  it  only  to  a  very  slight 
degree.  The  Papilionaceag  (peas,  beans,  etc.),  however,  show  an  entirely  dif- 
ferent behavior  toward  phosphate  fertilizers.  Scarcely  any  difference  can  be 
discovered  between  pea  cultures  supplied  with  soluble  phosphates  and  those 
supplied  with  phosphorite  (Fig.  59). 

The  value  of  phosphate  rock  as  a  fertilizer  depends  not  only  upon  the  nature 

1  Wagner,   Paul,    Dungungsfragen    unter    Beriicksichtigung   neuer   Forschungsergebnisse.     Heft   III. 
56  p.     Berlin,  1896. 

2  Prianishnikov,  D.  N.,  1st  die  Phosphorsaure  der  Mineralphosphate  der  Kulturpflanzen  zuganglich? 
[Russian,  with  German  abstract.]     Ann.  Inst.  Agron.  Moscou  5  (Partie  non  officielle):  90-110.     1899. 


ABSORPTION   OF   ASH-CONSTITUENTS 


95 


of  the  plant  but  also  upon  that  of  the  soil.  That  the  small  grains  fail  to  assimi- 
late phosphorite  in  sand  cultures  does  not  necessarily  mean  that  they  behave 
in  the  same  way  in  cultures  with  other  kinds  of  soil.  In  Prianishnikov's  experi- 
ments summer-rye  was  grown  in  black  soil  from  the  Government  of  Voronezh, 
in  light  sandy  loam  from  the  Government  of  Minsk,  and  in  two  light-colored, 
uncultivated  sands  ("Podsol")  from  the  vicinity  of  Moscow,  all  four  soils  being 
fertilized  with  phosphate  rock.     His  results  are  presented  in  the  following  table. 


NaH2P04       Phosphorite  NaH2PO*  Phosphorite 

Fig.  59. — Comparative  effects  of  sodium  phosphate  and  of  phosphorite  upon  millet  and  pea 

in  sand  cultures.      (After  Prianishnikov.) 


Soil 


Yield  of  Grain 


Unferti- 
lized 


Fertilized 

with 

Phosphorite 


Total  Weight  of  Grain 
and  Straw 


Unferti- 
lized 


Fertilized 

with 

Phosphorite 


grams 

grams 

grams 

grams 

Black  soil 

1-95 

2.30 

5.6s 

5-8o 

Sandy  loam .... 

1-25 

1  -5° 

3-55 

4.40 

Sand  No.  1 

0.40 

4-75 

3-3° 

10.75 

Sand  No.  2 

1 .40 

3-3° 

2-35 

11 .10 

Increase 

in  Yield 

Due  to 

Fertilizer 


per  cent. 
3 

24 
226 

372 


96 


PHYSIOLOGY   OF   NUTRITION 


Phosphorite  fertilizers  had  very  good  effects  upon  the  uncultivated  sands 
(Podsol),  but  no  effect  at  all  upon  the  black  soil.  The  sands  apparently  in- 
creased the  solubility  of  phosphate  rock,  since  summer-rye  cannot  assimilate 
phosphoric  acid  in  the  form  in  which  it  occurs  in  this  fertilizer,  and  the  black 
soil  appears  to  have  had  no  such  effect. 

In  sand  cultures  phosphorite  can  be  made  available  for  the  small  grains  by 
supplying  them  with  a  complementary  fertilizer,  such  as  ammonium  salts, 
which  are  physiologically  acid.  Since  adequate  amounts  of  ammonium  salts 
are  usually  injurious  to  plants  in  water  and  sand  cultures,  Prianishnikov1  re- 
placed only  a  part  of  the  requisite  sodium  nitrate  in  his  sand  cultures  by  an 
equivalent  amount  of  ammonium  sulphate.     This  gives  a  medium  that  tends 


Fig.  60. — Effect  of  ammonium  salts  upon  the  availability  of  phosphorite  for  oats  in  sand 
cultures.     {After  Prianishnikov.)     See  text  for  explanation. 

to  become  more  acid  with  increase  in  its  content  of  the  ammonium  salt,  and  so 
phosphate  rock  supplied  to  such  cultures  might  be  expected  to  become  soluble 
and  thus  available  to  the  plants.  This  expectation  was  realized  in  experiments 
with  oats.  The  results  of  such  an  experiment  are  given  in  the  table  below.  The 
appearance  of  the  first  six  cultures,  in  the  order  followed  in  the  table,  is  shown  in 
Fig.  60. 
Culture  Weight  of  Tops 


No. 

1 
2 

3 
4 
5 
6 


Treatment  grams 

Control,  KH2PO4  +  NaN03 19- 7 

Phosphorite           +  NaN03 6.9 

Phosphorite           +  K(NH4)2S04  +  %NaN03 22.0 

Phosphorite           +  K(NH4)2S04  +  KNaN03 20.5 

Phosphorite           +  M(NH4)2S04  +  MNaN03 19.2 

Phosphorite           +  (NH4)2S04 1.6 


1  Prianishnikov,  T>.   N.,  Results    of    vegetation  experiments  for  1899  and   1900. 
Moscow  Agric.  Inst.  7  (non-official  part):  85-129.     1901. 


[Russian.]     Bull. 


ABSORPTION   OF   ASH-CONSTITUENTS 


97 


These  results  support  the  idea  that  partial  replacement  of  sodium  nitrate 
by  ammonium  salts  renders  the  phosphoric  acid  of  the  phosphate  rock  available 
for  oats;  when  one-fourth  or  one-half  of  the  NaN03  was  replaced  by  (NH4)2S04 
the  yield  did  not  fall  below  that  of  the  control,  as  it  did  in  the  other  cases. 

It  is  clear  that  the  nutrient  materials  in  the  soil  are  utilized  to  unequal  degrees 
by  different  plants.  As  we  shall  see  later,  roots  excrete  acid  substances  that  favor 
the  solution  of  soil  materials  otherwise  practically  insoluble  in  water.  Further- 
more, many  plants  are  characterized  by  having  their  roots  covered  with  fungus 

hyphae,  a  fact  discovered  by  Kami- 
enski.1  Frank2  gave  the  name  myco- 
rhiza  to  this  weft  of  fungus  hyphae  growing 
upon  roots,  and  emphasized  the  impor- 
tance of  this  whole  phenomenon  in  the 
physiology  of  nutrition.  Plants  that  have 
mycorhiza  are  said  to  be  mycotrophic.  We 
owe  extended  investigations  upon  the 
physiological  importance  of  mycorhiza  to 
Stahl.3  In  some  cases  the  fungus  hyphae 
cover  the  surface  of  the  roots  (ectotrophic 
mycorhiza),  as  is  shown  in  the  case  of 
beech  roots  (Fig.  61).     The  tip  region  of 


Pig.  6i. — Ectotrophic  mycorhiza  of  the 
beech;  a,  humus  particles;  b,  strands  of 
fungus  hyphae  penetrating  the  soil. 


Pig.  62. — Endotrophic  mycorhiza  in  epider- 
mal cells  of  the  root  of  Andromeda  poll folia, 
the  root  shown  in  cross-section. 


the  root  is  covered  with  hyphae  some  of  which  branch  out  into  the  soil  and 
attach  themselves  to  particles  of  humus.  In  other  cases  the  fungus  hyphas  are 
found  within  the  cells  of  the  root  (endotrophic  mycorhiza),  as  in  the  case  of 
Andromeda  polifolia  (Fig.  62).  Here  the  hypas  occur  in  the  large  cells  of  the 
root  epidermis. 

Mycorhiza  is  of  common  occurrence,  being  found  on  the  majority  of  vascular 
plants,  not  only  trees,  shrubs  and  herbs,  but  even  mosses.     Some  plants  cannot 

1  Kamienski,  Fr.,  Die  Vegetationsorgane  der  Monotropa  hypopitys  L.  Vorlauf.   Mitth.     Bot.  Zeitg. 
39=  4S7-46I.     1881. 

-  Frank,  B.,  Ueber  die  auf  Wurzelsymbiose  beruhende  Ernahrung  gewisser  Baume  durch  unterirdische 
Pilze.     Ber.  Deutsch.  Bot.  Ges.  3:  128-145.     1885. 

3  Stahl,   E.,    Der    Sinn   der    Mycorhizenbildung.     Ein    vergleichend-biologische   Studie.     Jahrb.  wiss. 
Bot.  34:  539-668.     1900. 
7 


98 


PHYSIOLOGY   OF   NUTRITION 


thrive  without  mycorhiza,  others  are  never  found  with  it,  and  still  others  occur 
sometimes  with  and  sometimes  without.  The  non-green  seed-plants  appear 
generally  to  belong  to  the  first  group.  Mycorhiza  develops  mainly  in  soils  rich 
in  humus,  where  the  fungus  hyphae  facilitate  the  entrance  of  nutrient  substances 
into  the  plant. 

Non-green  seed-plants  draw  organic  as  well  as  inorganic  substances  from  the 
soil  by  means  of  their  mycorhiza.  The  importance  of  mycorhiza  to  green  plants 
is  probably  most  pronounced  in  connection  with  the  absorption  of  the  ash-con- 
stituents, although  these  may  be  taken  up  first  in  organic  compounds.  The 
properties  of  humus  soils  are  not  by  any  means  to  be  considered  only  from  a 
purely  chemical  standpoint.  The  abundance  of  bacterial  and  fungous  organisms 
in  the  soil  makes  it  almost  like  a  living  thing,  and  all  the  microorganisms  of  the 
soil  require  large  amounts  of  mineral  substances.  If  a  higher  green  plant  grows 
in  humus  soil  it  must  compete  with  these  microorganisms  for  its  nutrition,  and 
this  competition  is  especially  active  since  the  nutrient  materials  in  humus  are 
not  as  well  suited  to  the  needs  of  green  plants  as  are  those  in  mineral  soils. 


pIG   £., Cultures  of  Lepidium  sativum  in  humus  soil.     On  the  left,  two  vessels  with  sterilized 

•    soil-  on  the  right,  two  vessels  with  unsterilized  soil.     {After  Stahl.) 

It  appears  that  plants  with  an  associated  fungus,  forming  mycorhiza,  are 
thus  enabled  to  compete  with  soil  microorganisms  not  associated  with  them 
much  more  successfully  than  can  plants  without  mycorhiza.  How  difficult  the 
growth  of  these  latter  may  be  in  humus  soil  is  shown  by  the  following  experiment 
of  Stahl.  Humus  soil  from  a  beech  forest  was  placed  in  four  vessels,  two  of 
which  were  sterilized  with  ether  and  chloroform  vapor,  thus  killing  all  the  micro- 
organisms of  the  soil  without  otherwise  altering  it.  Seeds  of  Lepidium  sativum, 
a  plant  without  mycorhiza,  were  then  planted  in  all  four  vessels.  Healthy 
plants  developed  in  the  sterilized  vessels,  while  the  plants  grew  but  poorly  in 
those  that  were  not  sterilized  (Fig.  63).  The  microorganisms  of  the  soil  are 
thus  seen  to  have  retarded  the  growth  of  Lepidium  to  a  very  marked  degree. 

No  trace  of  nitric  acid  or  nitrates  can  be  found  in  the  mycorhiza,  nor  is  any 
usually  found  in  soils  in  which  mycotrophic  plants  are  growing.  This  fact  con- 
firms the  opinion  that  mycotrophic  plants  differ  from  those  without  mycorhiza 
in  their  manner  of  nutrition.  If  fact,  the  experiment  with  ammonium  fertilizers, 
mentioned  above,  shows  that  such  fertilizers  have  no  effect  in  soils  rich  in  humus 
and  poor  in  lime  (which  are  usually  occupied  by  mycotrophic  plants),  and  that 
intrification  progresses  with  great  difficulty  in  these  soils. 


ABSORPTION    OF    ASH-CONTITUENTS  99 

If  a  particular  kind  of  plant  is  grown  for  several  years  in  succession  upon  the 
same  soil,  the  crop  gradually  decreases,  in  spite  of  the  addition  of  plenty  of 
fertilizers.  This  is  the  well-known  phenomenon  of  "soil  sickness."  In  this 
case  we  do  not  have  to  deal  with  an  inadequate  supply  of  mineral  nutrients, 
but  with  something  entirely  different.  The  work  of  Whitney  and  Cameron, 
and  that  of  Livingston,  Schreiner,  and  other  American  investigators,1  has  indi- 
cated that  plants  produce  poisonous  substances  (toxins)  in  the  soil.7'  These 
toxins  appear,  in  many  cases,  to  be  poisonous  only  to  the  particular  kind  of  plant 
in  connection  with  which  they  were  produced,  and  this  may  explain  the  fact  that 

»  Whitney,  Milton,  and  Cameron,  F.  K.,  Investigations  in  soil  fertility.  U.  S.,  Dept.  Agric.  Bur.  Soils- 
Bull.  23.  48  p.  Washington,  1904.  Livingston,  B.  E.,  Britten  J.  C,  and  Reid,  F.  R.,  Studies  on  the  prop- 
erties of  an  unproductive  soil.  Ibid.  Bull.  28.  39  p.  Washington,  1905.  Livingston,  1907.  [See 
note  6,  p.  83.]  Schreiner,  Oswald,  Reed,  Howard  S.,  and  Skinner,  J.  J.,  Certain  organic  constituents  of 
soils  in  relation  to  soil  fertility.  Ibid.  Bull.  47.  52  p.  Washington,  1907.  Schreiner,  Oswald,  and 
Shorey,  Edmond  C,  The  isolation  of  picoline  carboxylic  acid  from  soils  and  its  relation  to  soil  fertility. 
Jour.  Amor.  Chem.  Soc.  30:  1295-1307.  1908.  Idem,  The  isolation  of  dihydroxy-stearic  acid  from  soils. 
Ibid.  30:  1590-1607.  1908.  Idem,  The  isolation  of  harmful  organic  substances  from  soils.  U.  S.  Dept. 
Agric,  Bur.  Soils.  Bull.  53.     53  p.     Washington,  1909. 

'  A  discussion  of  some  of  the  earlier  literature  regarding  this  general  idea  of  soil  toxins  is 
given  by  Livingston,  1907.  [See  note  b,  p.  83.]  This  earlier  literature  (not  considered  by 
Whitney  and  Cameron,  1904,  nor  by  Livingston  ei  al.,  1905  [note  1,  just  above])  is  rather 
extensive.  The  idea  that  plants  may  excrete  into  the  soil  substances  that  may  be  poisonous 
to  other  plants,  appears  to  have  originated  with  A.  P.  DeCandolle  (Physiologie  vegetale. 
Paris,  1832),  but  the  experimentation  invoked  by  this  writer's  suggestion  seemed  to  dis- 
prove the  hypothesis,  and  the  whole  matter  was  laid  aside  until  it  was  taken  up  again,  in 
a  modern  way,  by  the  Duke  of  Bedford  and  S.  U.  Pickering  (at  the  Woburn  Experimental 
Fruit  Farm,  near  Bedford,  England)  and  by  the  American  students  mentioned  above.  On  the 
Woburn  work  see :  Pickering,  Spencer  U.,  The  effect  of  grass  on  apple  trees.  Jour.  Roy.  Agric. 
Soc.  England  64  (of  entire  series):  365-376.  London,  1903.  Also  see  the  Reports  of  the 
Woburn  Experimental  Fruit  Farm  after  1897. 

In  later  years  the  general  hypothesis  that  unproductiveness  in  agricultural  soils  is  frequently 
due  to  soil  toxins  has  been  well  established  by  workers  in  various  parts  of  the  world,  and  it  is 
now  generally  accepted.  Evidence  that  agricultural  plants  do  actually  excrete  toxic  substances 
into  the  soil  is  not  very  strong  in  any  of  this  work,  however.  Better  than  to  assert  that  they 
are  so  excreted  is  to  state  that  there  is  evidence  that  the  soil  frequently  contains  toxins  and 
that  these  sometimes  result,  directly  or  indirectly,  from  the  growth  of  higher  plants.  As  to  the 
manner  in  which  these  poison  substances  arise  in  the  soil,  no  definite  statements  can  yet  be 
made,  but  they  are  surely  not  generally  excreted  as  such  from  plant  roots..  There  is  physio- 
logical evidence,  however,  that  such  substances  are  given  off  by  living  roots  when  the  latter  are 
practically  deprived  of  oxygen.  (See  p.  1 26.)  It  seems  highly  probable  that  soil  microorgan- 
isms play  an  important  part  in  the  production  of  the  toxic  substances  here  considered.  Ex- 
creted substances,  the  materials  of  dead  root-cap  cells,  root-hairs,  roots,  etc.,  or  even  substances 
carried  down  into  the  soil  by  rain  (as  from  the  bark  of  trees  and  fallen  leaves)  may  become 
altered  by  the  action  of  microorganisms  so  as  to  produce  poisons.  That  such  poisons  are 
present  in  many  soils  has  now  been  established  without  question  by  Schreiner  and  his  co- 
workers, and  also  that  their  deleterious  effect  upon  plants  may  often  be  removed  by  oxidation, 
or  by  the  addition  of  proper  substances. 

The  general  acceptance  of  the  hypothesis  of  toxic  soil  constituents  as  a  frequent  cause  of 
unproductiveness  was  much  retarded  by  the  form  of  its  original  statement,  by  Whitney  and 
Cameron  (1904),  which  emphasized  actual  root  excretion  at  the  expense  of  all  the  other  logical 
possibilities.  It  was  of  course  to  be  expected  that  such  poisons  might  arise  in  the  soil  in  a 
great  variety  of  ways,  and  the  theory  of  soil  toxins  is  not  to  be  considered  without  continual 
reference  to  the  microbiology  of  the  soil.  Russell  (1921.  [see  note  i,  p.  73.])  gives  a  clear  dis- 
cussion of  this  whole  matter,  from  the  standpoint  of  field  experiments. — Ed. 


IOO 


PHYSIOLOGY    OF    NUTRITION 


pIG  64- — Wheat  plants  grown  in  extract  of  toxic  soil.  I  and  2,  undiluted  extract;  3  and 
4,  equal  parts  of  extract  and  distilled  water;  5  and  6,  one  part  extract  diluted  with  nine  parts 
of  distilled  water.  (After  Schreiner  and  Shorey.  Reproduced  by  permission  of  U.  S.  Dept. 
Agric,  1909.) 


Fig.  65. — Vicia  faba  (Windsor  bean)  plants  grown  in  water  extract  of  bog-soil  and  in  bog 
water.  1,  extract;  2,  bog  water;  4,  bog  water  neutralized  with  calcium  carbonate;  5,  bog 
water  treated  with  carbon-black  and  filtered.     (After  Dachnowski.) 


.ABSORPTION   OF   ASH-CONSTITUENTS  IOI 

a  soil  that  is  unproductive  for  tomatoes  may  still  produce  a  good  crop  of 
grain.  Cultures  in  water  extracts  of  unproductive  soil  give  but  poor  growth, 
but  growth  is  improved  proportionally  with  the  dilution  of  the  extract  with 
distilled  water  (Fig.  64).  Addition  of  lime  frequently  neutralizes  the  toxic 
effect.  To  secure  a  good  crop  in  an  unproductive  soil  that  contains  toxins,  it  is 
necessary  to  find  substances  or  treatments  that  render  the  soil  toxins  harmless. 

The  effects  of  water  extract  from  bog-soil  and  those  of  bog  water,  upon  the 
development  of  Vicia  faba1  (Windsor  or  broad  bean),  are  shown  in  Fig.  65. 
The  addition  of  calcium  carbonate  and  the  adsorptive  action  of  carbon- 
black  have  been  very  effective  here.  In  this  case  the  toxic  action  of  the  bog 
water  was  probably  due  to  toxins  arising  from  the  microorganisms  of  the  soil,2 
rather  than  to  toxins  emanating  from  the  bog  plants.fc 

Toxins  of  some  agricultural  soils  are  organic  in  nature,  as  is  indicated  by  the 
following  experiment.3  Water  extract  of  a  soil  that  had  become  alfalfa-sick 
was  toxic  to  this  plant,  but  if  the  soil  was  brought  to  a  red  heat  before  making 
the  extract  the  latter  was  not  toxic.  Water  extracts  of  other  soils,  which  had 
not  been  in  alfalfa  culture,  had  no  injurious  effect  upon  the  growth  of  this 
plant. 

Experiments  have  also  been  made  to  determine  the  effects  of  various  plant 
substances  upon  plant  growth.  Such  substances  are  sometimes  injurious  and 
sometimes  beneficial.  Watering  with  a  3-per  cent,  solution  of  nicotin,  for 
instance,  produces  good  growth  in  tobacco,  and  is  likewise  beneficial  to  potatoes.4 

1  Dachnowski,  Alfred,  The  toxic  properties  of  bog  water  and  bog  soil.     Bot.  gaz.  46:  130-143.     1908. 

•  Lohnis,  F.,  Handbuch  der  landwirtschaftlichen  Bakteriologie.     Berlin,  1910. 

'  Pouget,  I.,  and  Chouchak,  D.,  Sur  la  fatigue  des  terres.     Compt.  rend.  Paris  14s:  1200-1203.     1907. 

«  Otto,  R.,  and  Kooper,  W.  D.,  Untersuchungen  iiber  der  Einfluss  giftiger,  alkaloidfuhrender  Losungen 
auf  Boden  und  Pflanzen.     Landw.  Jahrb.  39:  397-407.     1910. 

k  That  bog  waters  are  toxic  to  ordinary  plants  (at  least,  in  that  they  have  an  acid  reaction), 
has  long  been  suspected.  Schimper  (Schimper,  A.  F.  W.,  Plant  geography  upon  a  physiologi- 
cal basis.  Translated  by  W.  R.  Fisher.  Oxford,  1903)  considers  bogs  as  physiologically  dry, 
but  is  not  clear  as  to  just  what  physiological  dryness  may  be  due  to.  Livingston  tested  the 
two  logical  possibilities  in  this  case.  He  found  (Livingston,  B.  E.,  Physical  properties  of  bog 
water.  Bot.  gaz.  37:  383-385.  1904)  that  high  osmotic  concentration  of  bog  water  is 
not  a  possible  explanation  of  physiological  dryness;  bog  water  has  a  freezing-point  no  lower 
than  that  of  water  from  drained  swamps  and  rivers  of  the  vicinity.  By  the  use  of  an  alga 
as  a  physiological  indicator,  the  same  author  showed  very  clearly  that  bog  waters  usually 
contain  toxic  substances.  (Livingston,  B.  E.,  Physiological  properties  of  bog  water.  Bot. 
gaz.  39:  348-355.  1905.)  It  appeared  also  that  this  toxicity  (for  the  alga  used)  was  surely 
not  directly  related  to  acidity,  the  degree  of  acidity  being  measured  with  phenolphthalein 
as  indicator.  It  is  interesting  to  note  that  this  first  step  toward  an  analysis  of  the  bog-water 
problem  occurred  at  almost  exactly  the  same  time  as  the  general  problem  of  toxic  substances 
in  arable  soils  was  opened  up  (in  its  modern  sense)  by  Whitney  and  Cameron  (1904)  [see 
note  1,  p.  99]  and  by  Belford  and  Pickering  (1903)  [see  note  j,  p.  99].  The  three  lines  of 
work  were  entirely  independent.  Transeau  also  (Transeau,  E.  N.,  On  the  development 
of  palisade  tissue  and  resinous  deposits  in  leaves.  Science,  n.  s.  19:  866-867.  i*)1^)  bad 
shown  that  bog  water  is  toxic,  to  Rumex  at  least,  before  the  excellent  studies  of  Dachnow- 
ski (cited  here  in  text),  and  those  of  Rigg  were  published.  (Rigg,  G.  B.,  The  effect  of  some 
Puget  Sound  bog  waters  on  the  root  hairs  of  Tradescantia.  Bot.  gaz.  55:  314-326.  1913- 
Idem,  The  toxicity  of  bog  water.  Araer.  jour.  bot.  3:  436-437.  1916.  Idem,  A  summary 
of  bog  theories.  Plant  world  10 :  310-325.  1916.)  It  seems  probable  that  microorganisms 
and  lack  of  oxygen  have  to  do  with  the  production  of  these  bog  toxins. — Ed. 


102  PHYSIOLOGY   OF   NUTRITION 

Summary 

i.  Cultures  in  Artificial  Media. — The  essential  chemical  elements  for  plants  in 
general  are:  Carbon,  hydrogen,  oxygen,  nitrogen,  sulphur,  phosphorus,  potassium, 
calcium,  magnesium,  and  iron  (C,  H,  O,  N,  S,  P,  K,  Ca,  Mg,  Fe).  Carbon  and  oxygen 
enter  ordinary  green  plants  as  carbon  dioxide  (C02),  while  hydrogen  and  oxygen 
enter  as  water  (H20) .  As  already  seen,  these  two  compounds  are  decomposed  in  chlo- 
rophyll-bearing cells,  by  the  action  of  sunlight,  forming  carbohydrates  ([CH20]„) 
and  free  oxygen.  From  carbohydrates  and  other  substances  the  plant  cells  form  the 
many  different  organic  compounds  found  in  the  plant  body.  Tissues  without  chloro- 
phyll must  absorb  their  carbohydrates  (and  often  many  other  organic  compounds  from 
their  surroundings,  including  the  green  tissues  of  the  same  plant.  As  has  also  been, 
seen,  nitrogen  enters  the  ordinary  plant  mainly  as  nitrates  (sometimes  as  nitrites, 
ammonium  salts,  or  organic  nitrogenous  substances),  and  these  become  combined  with 
carbohydrates,  etc.,  to  form  many  of  the  most  complex  substances  occurring  in  plants. 
When  plants  are  completely  burned  all  of  the  carbon,  hydrogen,  oxygen,  and  nitro- 
gen are  given  off  as  gases,  but  there  remain  small  amounts  of  many  other  essential 
and  non-essential  elements  in  the  form  of  incombustible  ash.  The  total  ash  of  ordinary 
plants  constitutes  only  about  5  per  cent,  of  the  total  dry  weight,  or  about  0.02  per 
cent,  of  the  green  weight.  The  other  essential  elements  (S,  P,  K,  Ca,  Mg,  Fe)  of  the 
ash  are  absorbed  by  ordinary  plants  from  the  soil,  just  as  are  water  and  nitrates,  and 
the  supply  is  in  the  form  of  inorganic  salts:  mainly  nitrates  (N03),  sulphates  (S04), 
and  phosphates  (P04),  of  potassium,  calcium,  magnesium,  and  iron. 

The  elements  absorbed  through  the  roots  may  be  studied  by  artificially  controlled 
cultures  in  water  solutions  or  in  pure  quartz  sand,  etc.,  the  latter  of  course  containing 
water  solution  in  its  interstices.  Numerous  different  solutions  have  been  tested  by 
many  workers.  A  very  good  medium  for  solution  cultures  may  be  prepared  with  cal- 
cium nitrate  [Ca(N03)2],  mono-  or  di-potassium  phosphate,  (KH2P04  or  K2HP04), 
and  magnesium  sulphate  (MgS04),  about  seven  thousandths  of  a  gram-molecule  (the 
molecular  weight  expressed  in  grams)  of  each  salt,  all  dissolved  together  in  a  liter  of 
water,  with  addition  of  a  very  small  amount  (about  3  mg.)  of  an  iron  salt  such  as 
ferrous  sulphate  (FeS04.7H20).  This  is  one  of  Shive's  nutrient  solutions.  Three 
single-salt  solutions  (with  trace  of  an  iron  salt)  may  be  used  in  rotation,  if  concen- 
trations and  time  periods  are  properly  chosen. 

2.  Importance  of  Essential  Ash-constituents.— Little  is  known  as  to  just  how  the 
small  amounts  of  essential  ash  constituents  are  used  in  the  plant,  but  all  must  be 
supplied.  Sulphur  occurs  in  proteins,  phosphorus  in  nucleins  (a  special  group  of 
protein-like  substances),  magnesium  occurs  in  chlorophyll,  and  iron  is  essential  for 
the  formation  of  chlorophyll. 

3.  Importance  of  Non-essential  Ash-constituents. — Although  plants  grow  well 
with  only  the  essential  elements  supplied,  yet  they  generally  contain  many  non-essen- 
tial elements,  and  these  are  not  without  influence  upon  growth  and  development  when 
they  are  present  in  the  right  amounts.  Grasses  accumulate  silica  in  the  epidermis  and 
are  thus  more  or  less  protected,  from  fungi,  etc.,  by  a  glassy  layer  on  the  exterior. 

4.  Ash  Analysis  of  Plants. — The  chemical  analysis  of  the  ash  of  a  plant  shows  what 
elements  are  present  and  in  what  proportions  they  occur.  Different  species  differ  in 
these  respects,  and  also  in  the  amount  of  total  ash  per  unit  of  weight,  etc.  The  nature 
of  the  soil  influences  the  ash  content  of  the  plant.  Different  parts  of  the  same  indi- 
vidual plant  differ  in  ash  content.  Leaves  are  generally  richer  in  ash  than  stems  and 
roots.     The  ash  content  alters  with  the  age  of  the  organ  or  tissue. 


ABSORPTION   OF    ASH-CONSTITUENTS  103 

5.  Microchemical  Ash  Analysis. — Small  amounts  of  plant  tissue  may  be  studied  by 
microchemical  methods,  to  determine  what  chemical  elements  are  present. 

6.  The  Plant  and  the  Soil. — Ordinary  plants  obtain  all  their  ash  constituents  from 
the  soil,  but  a  chemical  analysis  of  the  soil  is  of  little  value  in  determining  whether  a 
plant  can  thrive  in  any  given  soil.  The  essential  elements  must  be  present  as  the 
proper  salts,  and  these  must  be  supplied  to  the  obsorbing  roots  at  proper  rates. 
Soils  may  generally  be  much  improved  for  growing  plants  by  the  addition  of  certain 
inorganic  salts,  or  of  material  that  will  produce  these  when  it  is  decomposed  by  soil 
microorganisms.  To  determine  the  value  of  a  fertilizer,  it  must  generally  be  actually 
tested  with  the  given  soil  and  with  the  kind  of  plant  that  is  under  consideration. 

Many  plant  roots  are  normally  accompanied  by  fungus  hyphae  as  mycorhiza, 
these  hyphae  either  forming  a  weft  about  the  root  or  occurring  in  the  cavities  of  the 
superficial  cells.  Mycorhiza  is  necessary  for  many  plants,  especially  when  growing  in 
humus  soils.  It  appears  that  the  fungus  hyphae  facilitate  the  movement  of  substances 
from  the  soil  into  the  roots.  There  is  little  or  no  nitrification  in  humus  soils,  and  it  is 
possible  that  the  mycorhiza  in  such  soils  may  furnish  the  roots  with  some  nitrogenous 
substances  other  than  nitrates. 

A  soil  may  be  unproductive  because  it  contains  too  much  (or  too  little)  of  the 
soluble  mineral  salts,  or  because  it  contains  very  injurious  substances  in  toxic  amounts. 
"Soil  sickness,"  often  resulting  from  repeatedly  growing  the  same  crop  on  the  same 
soil,  appears  to  furnish  an  example  of  this,  the  toxic  materials  being  probably  organic 
in  such  cases.  They  seem  to  be  produced  from  the  decay  of  plant  roots,  etc.,  or  from 
substances  emanating  from  the  roots,  and  they  appear  often  to  be  related  to  the  activi- 
ties of  microorganisms  in  the  soil.  Such  a  "  toxic  "  soil  may  produce  good  growth  of  one 
kind  of  plant  (as  wheat)  while  it  is  very  injurious  to  another  kind  (as  tomato).  Bog 
soils  are  toxic  to  many  forms  of  plants,  although  characteristic  bog  plants  thrive  in 
them. 


CHAPTER  V 

ABSORPTION  OF  MATERIALS  IN  GENERAL 

§i.  Materials  Absorbed  by  Plants. — We  have  seen  in  the  preceding  chapter 
that  only  a  few  inorganic  materials  are  needed  in  the  construction  of  the  plant 
body.  These  essential  substances  are  carbon  dioxide,  water,  and  certain  salts 
containing  the  elements  N,  S,  P,  K,  Ca,  Mg,  and  Fe,  these  salts  being  dissolved 
in  the  soil  water.  From  these  substances  [including  the  ten  essential  elements, 
C,  H,  O,  N,  S,  P,  K,  Ca,  Mg,  and  Fe]  various  kinds  of  organic  compounds 
are  built  up  by  the  green  plants.  Atmospheric  oxygen  is  also  absorbed  by  plants. 
Absorption  of  free  oxygen  does  not  generally  result  in  an  increase  in  dry  weight, 
however,  but  is  generally  accompanied  by  the  elimination  of  water  and  carbon 
dioxide,  and  thus  results  in  a  loss  of  plant  material.  Some  of  the  organic 
compounds  thus  undergo  oxidation  through  the  respiratory  process,  which 
will  be  discussed  later. 

Some  of  the  materials  that  enter  the  plant  are  commonly  met  with  in  the 
gaseous  form  (carbon  dioxide  and  oxygen),  others  are  generally  encountered 
as  solids  (the  salts  of  the  soil,  including  nitrogen  compounds),  but  they  all  enter 
plant  cells  as  substances  dissolved  in  water.  In  entering,  they  must  all  pass 
through  the  cell  wall,  as  well  as  the  outer  layer  of  the  protoplasm.  The 
mechanics  of  the  absorption  of  materials  by  plant  cells  is  thus  based  upon  the 
laws  of  controlling  the  migration  of  substances  dissolved  in  other  substances." 

§2.  Diffusion  of  Gases.— If  two  gases  are  separated  by  a  membrane  per- 
meable to  them  they  pass  through  the  spectum  and  mix.  Whether  there  is  a 
septum  between  them  or  not,  this  mixing  process  is  termed  diffusion.  Two 
cases  may  be  differentiated  here.  The  first  case  refers  to  septa  in  which  the 
gases  are  not  dissolved  (e.g.,  a  dry  porous  clay  plate).  The  other  case  relates 
to  septa  in  which  the  gases  are  dissolved  (e.g.,  moist  animal  bladder).6     The 

°  Of  course  the  oxygen  of  the  air  and  of  the  soil  and  the  carbon  dioxide  of  the  air  cannot 
enter  plant  cells  without  being  first  dissolved  in  water;  if  not  dissolved  at  a  greater  distance  they 
go  into  solution  in  the  water  of  the  cell,  which  extends  to  the  exterior  surface  of  each  exposed 
cell  wall,  these  walls  being  impregnated  with  water  of  imbibition.  The  distinctions  between 
solids,  liquids  and  gases  have  nothing  to  do,  primarily,  with  the  kind  of  matter  considered,  but 
only  with  its  state,  which  generally  depends  upon  temperature.  The  author's  presentation  is 
here  departed  from  to  a  certain  extent,  to  avoid  his  apparent  implication  that  gases  enter 
plant  cells  in  a  manner  different  from  that  by  which  substances  that  are  usually  solid  or  liquid 
make  their  entrance. — Ed. 

b  The  term  dialysis  refers  to  the  process  of  separating  two  dissolved  substances  by  letting 
one  diffuse  through  a  septum  that  is  impermeable  to  the  other — a  common  laboratory  opera- 
tion— and  follows  the  same  principles,  whether  the  diffusing  substance  is  commonly  met  with  in 
the  gas,  liquid,  or  solid  form.  The  word  osmosis,  frequently  encountered  in  connection  with 
the  diffusion  of  substances  through  membranes,  should  be  dropped,  for  it  does  not  add  to 

104 


AB SORPTION    OF   MATERIALS    IN    GENERAL  105 

velocity  of  diffusion  of  undissolved  gases  depends  upon  the  density  of  the  dif- 
fusing gas  (temperature  and  pressure  being  the  same)  and  is  inversely  propor- 
tional to  the  square  root  of  this  density.  For  instance,  the  density  of  hydrogen 
is  approximately  1,  while  that  of  oxygen  is  16,  and  the  velocities  of  diffusion 
of  these  two  gases  are  to  each  other  as  1  is  to  4;  i.e.,  hydrogen  passes  through 
a  dry  porous  clay  septum  four  times  as  rapidly  as  does  oxygen  when  the  t  w<  1 
gases  have  the  same  temperature  and  pressure. 

In  the  diffusion  of  dissolved  gases  the  density  of  the  gas  plays  no  direct 
part.  Here  the  velocity  of  the  movement  is  directly  proportional  to  the  co- 
efficient of  solubility  of  the  gas  in  the  solvent  contained  in  the  septum.  In 
the  absorption  of  gases  by  plant  cells,  it  is  diffusion  of  dissolved  gases  that  is 
encountered,  since  the  cell  walls  are  impregnated  with  water.  According  to 
the  law  of  gas  diffusion,  carbon  dioxide  should  enter  plant  cells  more  slowly 
than  do  any  of  the  other  gases  encountered;  on  the  basis  of  the  principle  of 
diffusion  of  dissolved  gases,  it  should  enter  more  quickly  that  the  others,  since 
it  possesses  the  greatest  solubility  in  water  (and  in  water-impregnated  mem- 
branes). Thus  it  happens  that  carbon  dioxide,  in  spite  of  the  small  amount  of 
it  in  the  air,  is  still  absorbed  by  plant  cells  in  adequate  amounts/ 

§3.  Absorption  of  Gases.— Plants  possess  various  structures  that  favor  gas 
absorption  and  gas  movement,  among  which  are  stomata,  lenticels,  and  numer- 
ous intercellular  passages   traversing   the  plant  body  in  all  directions.     The 

clearness  and  is  frequently  confusing.  We  have  two  kinds  of  diffusion  with  which  to  deal  here, 
one  being  the  intermingling  of  gases  as  such  and  the  other  that  of  substances  (such  as  carbon 
dioxide,  alcohol,  potassium  nitrate,  etc.)  while  dispersed  (dissolved)  in  a  solvent;  the  solvent  is 
usually  liquid  (water),  but  substances  may  dissolve  in  solid  material — as  carbon  dioxide  in  the 
wax-like,  cuticular  material  of  many  exterior  cell  walls.  Diffusion  of  undissolved  gases  is  met 
with  in  the  inward  and  outward  movement  of  water  vapor,  carbon  dioxide  and  oxygen  through 
stomatal  openings  and  from  place  to  place  in  the  plant  body  through  gas-filled  intercellular 
spaces,  but  gases  do  not  pass  through  the  cell  walls  or  protoplasm  of  active  cells,  and  therefore 
cannot  get  inside  the  cells,  unless  they  are  first  dissolved,  usually  in  water.  (See  below,  in 
text.)  Of  course,  when  water  vapor  is  dissolved  in  liquid  water  it  simply  becomes  a  part  of 
the  liquid,  being  condensed  from  the  gaseous  to  the  liquid  state.  This  and  the  following  para- 
graphs have  been  subjected  to  some  modification,  in  accordance  with  these  principles.  It 
may  be  added  at  this  point  that,  besides  the  diffusion  of  gases  and  that  of  dissolved  sub- 
stances, there  is  another  kind  of  movement  met  with  in  plants,  namely  that  of  molar  stream- 
ing. This  occurs  with  gases  and  liquids  and  also  (but  not  commonly  in  the  plant)  with 
suitably  sub-divided  solids  (as  sand).  When  a  gas  or  liquid  is  forced  through  openings,  by 
pressure,  it  is  this  molar  movement  that  has  to  be  considered.  Diffusion  may  go  on  at  the 
same  time,  in  the  liquid  or  gas  stream,  its  direction  being  independent  of  the  direction  of 
the  streaming.  If  diffusion  and  streaming  are  in  the  same  direction,  the  rate  of  movement 
is  the  sum  of  the  rates  of  diffusion  and  streaming;  if  they  are  in  opposite  directions  the 
difference  is  the  rate  of  movement. — Ed. 

c  Carbon  dioxide  is  about  three  times  as  soluble  in  water  as  is  oxygen.  It  is  as  a  gas, 
however  (undissolved  in  either  liquid  or  solid),  that  carbon  dioxide  first  enters  the  ordinary 
green  plant  through  stomatal  openings.  See:  Blackman,  1895.  [See  note  2,  p.  36.]  Brown, 
1899.  [See  note  1,  p.  34.]  Brown  and  Escombe,  1900.  [See  note  1,  p.  34.]  Having  entered 
by  gas  diffusion,  carbon  dioxide  soon  passes  into  solution  in  the  water  with  which  the  cell  walls 
abutting  on  the  sub-stomatal  intercellular  spaces  are  impregnated,  and  it  diffuses  as  a  dissolved 
substance  through  these  walls  and  into  the  cells. — Ed. 


106  PHYSIOLOGY   OF   NUTRITION 

• 
migration  of  gases  through  different  kinds  of  plant  septa  has  been  investigated 
by  many  authors.  The  most  recent  and  extensive  studies  on  the  molar  or 
streaming  movement  and  the  diffusion  of  gases  through  plant  cell  walls  are  due 
to  Wiesner  and  Molisch.1  In  these  experiments  a  piece  of  dry  plant  tissue  was 
fastened  over  one  end  of  a  straight  glass  tube  (6  mm.  in  internal  diameter  and 
50  to  100  cm.  long)  with  sealing  wax,  and  the  joint  was  then  covered  with  a 
mixture  of  equal  parts  of  resin  and  beeswax.  When  soft,  succulent  tissues 
were  employed,  the  tissue  was  kept  in  place  by  a  perforated  metal  cap,  and  was 
kept  from  being  crushed  by  rubber  rings,  the  openings  of  which  just  fitted  the 
end  of  the  glass  tube.  The  tube  was  partly  or  entirely  filled  with  mercury  and 
the  open  end  was  closed  with  the  finger  while  the  tube  was  inverted,  the  open 
end  being  then  placed  in  a  vessel  of  mercury.  The  tube  was  finally  ar- 
ranged in  an  upright  position,  with  the  mercury  below.  After  a  number  of 
days  the  height  of  the  mercury  column  in  the  tube  was  measured. 

An  experiment  with  birch  bark  may  serve  as  an  example.  A  piece  of  white 
periderm,  0.09  mm.  thick,  was  used.  The  height  of  the  mercury  column  in  the 
tube  was  400  mm.  at  the  beginning  of  the  experiment  and  remained  the  same, 
after  fourteen  days,  the  usual  corrections  for  temperature  and  pressure  having 
been  applied.  Wiesner  and  Molisch  came  to  the  following  conclusions  from 
the  result  of  these  experiments. 

1.  Plant  cell  walls,  either  wet  or  dry,  whether  the  cells  are  alive  or  dead,  are 
impermeable  to  the  molar  movement  of  gases  under  ordinary  pressures. 

2.  Protoplasm  and  cell  sap  are  likewise  impermeable  to  this  kind  of  gas 
movement,  so  that  there  is  no  movement  of  air  as  such  through  tissue  without 
intercellular  passages.  This  experiment  explains  how  negative  gas  pressure 
(i.e.,  pressure  less  than  that  of  the  surrounding  atmosphere)  in  wood  may 
be  maintained,  which  will  be  discussed  later. 

Similar  tubes  filled  partly  with  mercury  and  partly  with  various  gases  were 
employed  in  experiments  upon  the  diffusion  of  gases  through  dry  and  moist 
plant  membranes.  The  velocity  of  outward  diffusion  was  indicated  by  the  rate 
of  rise  of  the  mercury  column  in  the  tube.  An  experiment  with  periderm  of  the 
potato  tuber  may  be  taken  as  an  example.  Two  tubes  were  filled  with  carbon, 
dioxide,  one  being  closed  with  a  dry,  the  other  with  a  moist  piece  of  periderm. 
In  the  tube  with  the  dry  membrane  the  mercury  rose  only  5  mm.  during  a  period 
of  thirty  days,  while  the  tube  with  moist  membrane  showed  a  corresponding  rise 
of  about  40  mm.  This  experiment  shows  that  the  interchange  of  gases  through 
the  wet  membrane  occurred  according  to  the  principles  of  diffusion  of  dissolved 
gases;  carbon  dioxide  passed  outward  through  the  membrane  more  rapidly  than- 
air  passed  inward,  thus  causing  the  mercury  to  rise  in  the  tube.  If  the  septa 
to  be  studied  were  permeable  to,  but  did  not  dissolve  the  gas  (as  in  the  case  of 
a  dry  porous  clay  plate),  then,  according  to  the  law  of  gas  diffusion,  the 
mercury  column  should  fall.  From  a  series  of  experiments  similar  to  this,  these 
authors  came  to  the  following  conclusions: 

1  Wiesner,  J.,  and    Molisch,  H.,  Untersuchungen   uber  die  Gasbewegung  in  der  Pflanze.     Sitzungsber. 
(math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien.  o8^ :  670-713.      1890. 


ABSORPTION   OF   MATERIALS   IN   GENERAL  I07 

1.  Gases  move  through  cell  walls  only  in  solution  in  the  water  imbibed  in  the 
wall;  when  intercellular  spaces  are  present,  they  of  course  facilitate  the  move- 
ment through  the  tissue. 

2.  Gases  pass  through  cell  walls  the  more  easily,  the  more  thoroughly  the 
latter  are  impregnated  with  water.  Diffusion  is  most  rapid  through  cell  walls 
of  algae  and,  in  general,  through  those  of  submerged  plant  parts. 

3.  Cell  walls  that  are  neither  lignified  nor  suberized  do  not  permit  the 
passage  of  some  gases  when  the  walls  are  dry,  but  carbon  dioxide  and  oxygen 
pass  through  practically  dry  walls  if  the  latter  are  lignified  or  ssuberized. d 

These  Experiments  suggest  an  important  ecological  consideration  as  regards 
suberization  and  cutinization  in  plant  tissues.  If  the  entire  surface  of  the  plant 
were  covered  by  a  dry  membrane  of  pure  cellulose,  then  the  interior  cells  would 
be  suffocated,  but  the  presence  of  cork  and  cutin,  in  the  absence  of  lenticels  and 
while  the  stomata  are  closed,  protects  plants  from  desiccation  without  at  the 
same  time  preventing  gaseous  exchange. 

4.  Carbon  dioxide  passes  out  of  plant  cells  more  rapidly  into  air  than  into 
water. 

Since  Wiesner's  experiments  indicate  that  gases  may  pass  through  the  cuticle, 
the  question  arises,  to  what  extent  do  open  stomata  increase  the  rate  of  gaseous 
exchange  through  the  epidermis?  To  answer  this  question  F.  F.  Blackman1 
constructed  a  special  apparatus  described  below  (Fig.  66).  Two  brass  rings, 
each  prolonged  into  two  tubes  at  opposite  points  and  each  with  a  glass  plate 
attached  to  one  side,  were  used  as  gas  chambers,  each  chamber  being  about 
5  mm.  deep  and  36  mm.  broad.  A  leaf  was  clamped  between  two  chambers  of 
this  kind  and  the  joints  were  sealed  with  wax.  Oblong  chambers  were  used  for 
narrow  leaves  (Fig.  66,  A).  Gas  of  known  composition  was  passed  simulta- 
neously, but  separately,  through  both  chambers  and  then  analyzed.  Experi- 
ments with  leaves  having  stomata  only  on  the  lower  surface  showed  that  the 
respiratory  gas  exchange  occurred  almost  entirely  through  these  openings. 
For  example,  a  leaf  of  Nerium  oleander  gave  out  0.002  g.  of  CO2  from  its  upper 
surface  while  0.065  g-  escaped  from  the  lower;  thus  the  two  sides  gave  off  this 
gas  in  the  ratio  of  3  to  100. 

Further  experiments  upon  the  assimilation  of  carbon  dioxide  in  light  showed 
that  leaves  absorb  this  gas  from  the  air  almost  exclusively  through  the  stomata. 
Leaf  surfaces  without  stomata  practically  fail  to  absorb  carbon  dioxide.  When 
the  lower  surface  alone  is  provided  with  stomata,  coating  this  surface  with 
petrolatum  greatly  decreases  gaseous  exchange  without  wholly  stopping  it,  as 
•  Mangin  has  shown  (see  page  35).     When  stomata  occur  on  both  sides  of  the 

1  Blackman,  F.  F.,  1895,  No.  II.     [See  note  2,  p.  36.] 

d  Molar  movement  of  gases  can  occur  only  through  intercellular  spaces  and  relatively  large 
openings  in  plant  membranes  (stomatal  openings,  etc.),  and  gas  diffusion  can  occur  through 
such  openings  and  through  dry  membranes  with  relatively  large  pores  (porous  porcelain,  etc.). 
The  diffusion  of  dissolved  gases  is  possible  if  the  gas  is  soluble  in  the  membrane.  When  the 
latter  contains  water  this  kind  of  diffusion  can  occur,  for  the  gas  dissolves  in  the  water.  When 
the  membrane  contains  little  or  no  water,  but  contains  suberin,  etc.,  the  action  is  similar  to 
that  of  a  wet  membrane,  if  the  gas  dissolves  in  the  wax-like  material  as  it  does  in  water. — Ed. 


io8 


PHYSIOLOGY   OF   NUTRITION 


leaf,  the  amount  of  carbon  dioxide  absorbed  is  greater  on  the  side  where  these 
openings  are  most  abundant.  In  the  case  of  Alisma  plantago,  the  number  of 
stomata  on  the  upper  is  to  the  number  on  the  lower  surface  as  135  is  to  100. 
While  the  upper  surface  was  absorbing  0.10  or  0.15  g.  of  the  gas  the  lower  sur- 
face absorbed  0.06  or  o.n  g. 

These  experiments  led  Brown  and  Escombe1  to  carry  out  the  following  inter- 
esting investigations.  The  Catalpa  leaf  has  stomata  only  on  the  lower  surface, 
through  which  carbon  dioxide  is  absorbed  in  the  presence  of  light.  Under  the 
most  favorable  conditions  700  cc.  of  this  gas  is  absorbed  per  hour,  per  square 
meter  of  leaf  surface.  If  it  is  assumed  that  absorption  proceeds  equally  over 
the  entire  leaf  surface,  then  each  molecule  of  carbon  dioxide  enters  the  leaf 
with  an  average  velocity  of  3.8  cm.  per  minute.  This  velocity  is  only  half  of 
that  with  which  carbon  dioxide  is  absorbed  by  the  exposed  surface  of  a  sodium 


Fig.  66. — Apparatus  for  the  study  of  gaseous  exchange  through  the  upper  and  lower  surfaces 

of  leaves.      (After  Blackmail.) 

hydroxide  solution.  But  since  the  gas  is  absorbed  only  through  the  stomata, 
and  since  the  total  area  of  the  stomatal  openings  is  not  greater  than  one-one- 
hundredth  of  the  entire  leaf  surface,  then  a  surprisingly  large  number  (380  cm.) 
is  obtained  as  the  average  velocity  of  absorption  of  carbon  dioxide  through  the 
stomata.  This  number  is  fifty  times  as  great  as  that  representing  the  absorp- 
tion of  CO2  by  the  free  surface  of  sodium  hydroxide  solution.  These  results 
led  to  the  following  experiment.  Test-tubes  were  filled  with  aqueous  solution 
of  sodium  hydroxide  and  covered  with  thin,  perforated  plates,  different  plates 

1  Brown,  1899.     [Brown  and  Escombe,  1900.]     [See  note  1,  p.  34.] 


ABSORPTION    OF    MATERIALS    IX    GENERAL 


IO9 


having  openings  of  different  diameters.  Some  of  the  results  are  tabulated 
below.  The  velocity  of  carbon  dioxide  diffusion  was  found  to  be  proportional, 
not  to  the  area  of  the  opening  in  the  plate,  but  to  its  diameter. 


Diffusion  of  CO2 

Ratio  of 
Areas  of 
Openings 

Ratio  of 

Diameters  of 

Openings 

Ratio  of 

Amounts 

of  C02 

Diameter 
of  Opening 

Per  Hour 

Per  Hour, 

per  Square 

Centimeter 

mm. 

cc. 

cc. 

22 .  70 

0. 2380 

0.0588 

1 .000 

1 .000 

1 .00 

6.03 

0.0625 

0.2186 

0.070 

0. 260 

0.  26 

3-25 

0.0399 

0.48SS 

0.023 

0. 140 

0. 16 

2.12 

0.0261 

0.8253 

0.008 

0.093 

0. 10 

While  the  area  of  the  smallest  opening  (diameter  2.12  mm.)  was  less  than  a 
hundredth  of  that  of  the  largest  (diameter  22.7  mm.),  the  amount  of  gas  passing 
the  former  was  one-tenth,  rather  than  one-hundredth,  of  the  amount  passing  the 
latter.  From  this  it  follows  that  if  a  vessel  of  sodium  hydroxide  solution  is 
covered  with  a  thin  plate  perforated  with  very  small  openings,  the  quantity  of 
carbon  dioxide  absorbed  may  be  as  great  as  though  no  cover  were  present  at 
all.  The  total  area  of  all  the  openings  may  be  only  a  small  fraction  of  the  total 
surface  of  the  plate,  however.  It  was  found  that  diffusion  was  most  rapid  when 
the  distances  between  the  openings  were  each  ten  times  as  great  as  the  diameter. 
This  proportion  holds  approximately  for  the  distribution  of  stomata  in  most 
leaves.  Therefore  the  velocity  of  gas  absorption  is  as  great  when  the  stomata 
are  open  as  it  would  be  if  no  cuticle  were  present  and  if  the  whole  leaf  were  cov- 
ered with  a  wet  membrane  of  pure  cellulose. 

Investigations  of  movements  of  gases  in  water  plants1  have  shown  that  the 
air  of  the  intercellular  spaces  has  about  the  same  composition  as  that  of  the  ex- 
ternal atmosphere. 

§4.  Diffusion  of  Dissolved  Substances.2 — Many  substances  that  are  not 
gases  at  ordinary  temperatures  are  soluble  in  water,  but  not  all  substances  are 
appreciably  so;  oils,  for  example,  are  generally  practically  insoluble  in  water.6 

1  Devaux,  Henri,  Du  mecanisme  des  6changes  gazeux  chez  les  plantes  aquatiques  submergdes.  Ann  ■ 
sci.  nat.  Bot.  VII  9:  35-179-      1889. 

-  Dastre,  M.  A.,  Traite  de  physique  biologique  1  :  466.     Paris,  1901. 

e  The  following  discussion  of  osmotic  pressure  and  related  phenomena  is  largely  due  to  the 
editor,  but  the  spirit  and  apparent  intent  of  the  author  is  followed  as  closely  as  possible,  at  the 
same  time  avoiding  the  author's  curious  conceptions  that  dissolved  substances  are  liquids  and 
that  "osmosis"  and  diffusion  are  essentially  different.  For  another  attempt  at  presenting 
these  phenomena  to  the  student  of  physiology,  see:  Livingston,  B.  E.,  The  role  of  diffusion 
and  osmotic  pressure  in  plants.  Chicago,  1903.  Also  see:  Findlay,  Alexander,  Osmotic  pres- 
sure. London,  1913.  Washburn,  Edward  W.,  An  introduction  to  the  principles  of  physical 
chemistry.  2d  ed.  516  p.  New  York,  19  21.  The  last-named  discussion  is  the  most 
thorough  from  the  physical  and  mathematical  point  of  view. — Ed. 


I  IO  PHYSIOLOGY   OF   NUTRITION 

Whether  the  dissolved  substance  is  a  gas,  liquid  or  solid  under  ordinary 
conditions,  it  forms  an  aqueous  solution  when  it  is  dissolved  in  water.  The 
dissolved  substance  is  usually  called  the  solute  and  the  water  in  which  it 
dissolves  is  the  solvent.  A  solution  may  contain  many  different  kinds  of  solutes, 
all  dissolved  in  the  common  solvent.  All  dissolved  substances  diffuse  in  all 
directions  within  the  limits  of  the  solution  or  solvent,  and  tend  to  become  equally 
distributed  throughout  its  volume.  If  two  solutions  having  a  common  solvent 
but  different  solutes  be  brought  into  contact,  the  two  solutes  diffuse  into  each 
other's  region  and  they  eventually  become  completely  mixed,  so  as  to  form  a 
single  solution  of  two  solutes.  The  solvent  itself  exhibits  a  corresponding 
tendency  to  diffuse  in  all  directions;  if  a  mass  of  pure  water  be  brought  into 
contact  with  an  aqueous  solution,  water  enters  the  solution  and  dilutes  it,  while 
the  solute  or  solutes  enter  the  water  and  convert  it  into  a  solution,  this  process 
continuing  until  the  resulting  solution  becomes  uniform  throughout.  (If  the 
solute  be  another  liquid — as  alcohol,  glycerine,  etc. — the  solute  may  become 
the  solvent  when  it  predominates.  Thus  we  may  have  a  solution  of  glycerine 
in  water  or  a  solution  of  water  in  glycerine,  etc.).  It  appears  that  the  solute 
and  solvent  attract  each  other  and  that  the  latter  enters  between  the  particles 
of  the  former,  thus  hastening  their  outward  diffusion.  If  a  membrane  that  is 
permeable  to  water  but  relatively  impermeable  to  the  solute  be  placed  around 
the  solution  and  be,  in  turn,  surrounded  by  the  pure  solvent,  a  pressure,  called 
osmotic  pressure,  is  developed,  which  tends  to  drive  the  membrane  outward 
before  the  outwardly  diffusing  solute,  thus  stretching — or  even  rupturing — the 
membrane.  This  phenomenon  of  osmotic  pressure  was  discovered  by  Dut- 
rochet,1  as  early  as  1827,  who  observed  the  escape  of  zoospores  from  an  alga  and 
tried  to  arrive  at  an  explanation  for  the  bursting  of  the  sporangium.  He 
supposed  that  an  increased  absorption  of  water  by  the  sporangium  was  brought 
about  by  water-attracting  substances  within,  and  that  this  caused  the  rupture. 
If  an  animal  bladder  filled  with  aqueous  sugar  or  salt  solution  is  placed  in  water, 
the  solvent  enters,  and  the  outwardly  directed  osmotic  pressure  simultaneously 
developed  may  become  so  great  as  to  rupture  the  membrane  itself.  The  rupture 
of  the  alga  sporangium  as  observed  by  Dutrochet,  was  caused  in  a  similar  way  f 

[l  Dutrochet,  Rene  Joachim  Henri,  Nouvelles  observation  sur  l'endosmose  et  l'exosmose,  et  sur  la  cause 
de  ce  double  phenomene.     Ann.  chim.  et  phys.  35:  393-400.     1827.] 

{  It  is  still  commonly  stated  or  implied  that  the  entering  water  turns  on  itself  after  entrance, 
and,  thus  tending  to  return,  presses  outwardly  upon  the  membrane  and  causes  the  rupture. 
But  the  bladder  membrane  is,  in  itself,  as  permeable  to  water  diffusing  in  one  direction  as  to  the 
same  substance  diffusing  in  the  other,  and  more  water  enters  than  passes  out,  so  that  if  there  is 
a  pressure  of  water  in  either  direction  it  should  tend  to  collapse  the  bladder,  not  to  explode  it 
from  within.  A  logical  picture  may  represent  the  osmotic  pressure  causing  the  rupture  as 
directly  due  to  a  tendency  of  the  solute  particles  (as  of  sugar  or  salt,  or  ions),  or  of  any  combina- 
tions of  solute  particles  with  water  particles  (in  so  far  as  these  are  unable  to  pass  the  septum),  to 
diffuse  outward  into  the  surrounding  solvent.  This,  in  turn,  may  be  considered  as  brought 
about  or  made  possible  by  the  entrance  of  water  (at  least  it  cannot  occur  without  this  entrance), 
which,  finally,  may  be  due  to  an  attraction  exerted  upon  the  water  by  the  solute.  Such  a 
simple  picture  may  still  serve  the  purposes  of  physiology,  although  serious  complications  appear 
to  arise  sometimes  when  a  complete  appreciation  of  osmotic  and  related  phenomena  is 
attempted.  The  most  thorough  discussion  of  osmotic  pressure  so  far  available  is  that  given 
by  Washburn  [see  note  e,  p.  109]. — Ed. 


.ABSORPTION   OF   MATERIALS   IN   GENERAL  III 

Briicke  (1843)  advanced  a  theory  of  diffusion  through  septa,  based  upon 
the  observation  that  if  two  liquids  are  separated  by  a  membrane,  the  one  that 
wets  the  membrane  more  thoroughly  (i.e.,  in  which  the  latter  swells 
more  rapidly)  penetrates  more  rapidly.  For  example,  if  a  membrane  of  rubber 
or  collodion  be  employed,  then  alcohol  passes  through  more  rapidly  than  water, 
but  with  a  membrane  of  animal  bladder  the  opposite  is  true.  Rubber  and 
collodion  membranes  imbibe  alcohol  more  rapidly  than  water  and  they  also 
swell  more  in  alcohol.  Thus  alcohol  passes  through  such  septa  more  rapidly. 
But  animal  bladder  swells  in  water  and  shrinks  in  alcohol,  and  water  passes 
through  such  a  membrane  more  quickly  than  does  alcohol.  Animal  bladder 
swells  more  in  pure  water  than  in  salt  solution,  and  the  former  passes  through 
such  a  septum  more  rapidly  than  does  the  latter.  These  facts  indicate  that  the 
water  is  more  forcibly  attracted  by  the  membrane  substance  than  are  the  salts, 
so  that  the  concentration  of  the  imbibed  solution  in  the  pores  of  the  membrane 
increases  as  the  distance  from  the  pore  walls  becomes  greater.  Ludwig1  has 
shown  further  that  if  dry  pieces  of  animal  bladder  are  placed  in  a  solution  of 
sodium  sulphate  or  sodium  chloride,  the  solution  that  is  imbibed  is  less  concen- 
trated than  what  remains.  By  means  of  a  hand  press  he  pressed  some  of  the 
liquid  out  of  such  impregnated  pieces  of  bladder,  and  found  that  the  expressed 
solution  possessed  a  concentration  higher  than  the  average  concentration  of 
the  solution  originally  within  the  pores  of  the  bladder." 

Osmotic  pressure  is  studied  by  various  kinds  of  osmometers.  BaranetskiiV2 
osmometer  consists  of  two  chambers  separated  by  a  membrane,  one  containing 
a  salt  solution,  which  is  to  increase  in  volume,  while  the  other  contains  water 
introduced  through  a  funnel  that  is  attached  by  a  rubber  tube.  As  the  solution 
increases  in  volume  a  rubber-tube  outlet  from  the  solution  chamber  allows 
the  overflow  to  be  caught  in  a  graduated  flask.  The  surface  of  the  water  in 
the  funnel  must  be  kept  at  the  same  height  as  that  of  the  solution  in  the  exit 
tube.  The  movement  of  liquids  through  the  membrane  continues  until  the 
concentration  of  the  two  solutions  is  the  same  on  both  sides. 

Experiments  upon  diffusion  of  dissolved  substances  through  membranes 
have  shown  that  all  water-soluble  substances  may  be  classified  into  two  groups 
according  to  their  relation  to  the  membrane,  those  which  can  pass  through  the 
membrane  (crystalloids)  and  those  which  cannot  (colloids).  Upon  these  dif- 
ferent properties  of  colloids  and  crystalloids  depends  the  method  of  dialysis, 
by  which  colloid  material  may  be  separated  from  crystalloids.  Many  plant 
substances  are  colloids  and  they  cannot,  therefore,  diffuse  out  of  the  cells.* 

1  Ludwig,  C,  Ueber  die  endosmotischen  Aequivalente  und  die  endosmotische  Theorie.  Poggendorff's 
Ann.  Phys.  u.  Chem.  154  ("der  ganzen  Folge")  :  307-326.     1849. 

2  Baranetskii,  I.  Investigations  on  diosmosis  as  related  to  plants.  [Russian.]  Inaug.  Dissertation. 
St.  Petersburg,  1870.  Barenetzky,  J.,  Diosmotische  Untersuchungen,  Poggendorff's  Ann.  Phys.  u.  Chem. 
223  ("der  ganzen  Folge")  :  195-245.      1872. 

0  These  considerations  give  the  reason  why  the  membrane  is  more  permeable  to  one  sub- 
stance than  to  the  other,  or,  they  merely  state  this  fact  in  other  terms. — Ed. 

h  But  the  matter  is  not  so  simple  as  this.  Many  water-soluble  crystalloids  fail  to  pass  cer- 
tain membranes  that  are  permeable  to  water,  and  some  colloids  do  pass  them.  Colloids  and 
crystalloids  are  difficult  to  distinguish  accurately,  these  terms  referring  to  the  state  rather  than 


112 


PHYSIOLOGY    OF    NUTRITION 


Membranes  of  animal  bladder,  parchment  paper  and  collodion,  as  well  as 
the  so-called  precipitation-membranes,  are  all  used  for  osmotic  experiments. 
Cellulose  membranes,  giving  the  cellulose  reaction  with  zinc  chloride  and  iodine 
(Baranetskii,  1870)  can  be  produced  by  treatment  of  collodion  membranes 
with  ferric  chloride.     Of  the  above-mentioned  membranes,  animal  bladder  is 

much  like  the  plant  cell  wall  in  its  osmotic 
properties,  while  precipitation  membranes 
are  only  very  slightly  permeable  to  many 
substances  and  can  give  rise  to  high  osmotic 
pressures.  Suitable  supports  must  be  pro- 
vided for  these  delicate  membranes.  Pfeffer1 
employed  porous  clay  cylinders  such  as  are 
used  in  electric  batteries.  When  such  a 
porous  cell  is  filled  with  a  copper  sulphate 
(CuS04)  solution  and  placed  in  a  solution 
of  potassium  ferrocyanide  (K4Fe(CN)6),  a 
membrane  of  copper  ferrocyanide  (Cu-2Fe- 
(CN)6)  is  precipitated  in  the  porous  wall. 
Similar  precipitation  membranes  may  be  ob- 
tained with  other  substances,  such  as  iron 
silicate.  To  measure  osmotic  pressure  the 
porous  cylinder,  with  its  membrane,  is  filled 
with  the  solution  to  be  studied  and  is  con- 
nected with  a  mercury  manometer,  the 
cylinder  being  submerged  in  water  (Fig.  67). 
The  magnitude  of  the  pressure  exerted  at 
-     equilibrium  is  then  read  upon  the  manometer. % 


to  the  nature  of  the  substance  considered.     In  this 

connection  see:  Weimarn,  P.  P.  von,  Grundziige  der 

Dispersoidcheme.      12  7  p.     Dresden,,  1915.     For   a 

clear    and  very    readable    discussion    of  colloids    in 

general,   see-    Ostwald,    Wolfgang,    Die    Welt    der 

vernachlassigten  Dimensionen.     x  +  219  p.     Dresden 

and  Leipzig    191 5.     Also  see:  Hatschek,  Emil.     An 

Pig.    67. — Pfeffer    osmometer    (z),    introduction  to  the  physics  and  chemistry  of  colloids. 

with     closed     mercury     manometer.    4th   ed.     i7<;    p.     London,    1922.     Other  books    on 

(After  Pfeffer.)  this  subjec  1    are    mentioned   in  the  List  of   Books, 

p.  xix. — Ed 
1  Pfefier,     W.,     Osmotische     Untersuchungen.     Leipzig    1877. 

i  The  most  perfect  precipitation  membranes  yet  made  are  those  of  Morse  and  his 
coworkers,  who  have  been  engaged  for  many  years  in  very  thorough  studies  on  the  osmotic 
pressures  developed  by  concentrated  solutions.  This  work  has  been  carried  out  in  the 
Chemical  Laboratory  of  the  Johns  Hopkins  University.  Much  improved  forms  of  the 
Pfeffer  cell  have  been  employed  and  the  copper  ferrocyanide  membranes  of  these  writers 
have  proved  quite  impermeable  to  cane  sugar  for  many  days,  even  with  very  high 
pressures.  For  accounts  of  this  work  see:  Morse,  H.  N.,  and  Horn,  D.  W.,  The 
preparation  of  osmotic  membranes  by  electrolysis.     Amer.  chem.  jour.  26:  80-86.     1901. 


ABSORPTION   OF   MATERIALS   IN   GENERAL  113 

Walden1  obtained  semi-permeable  precipitation  membranes  in  the  following 
manner.  The  upper  end  of  a  glass  tube  5  cm.  long  and  1  cm.  wide  is  closed  by 
the  finger  and  the  lower  end  is  dipped  into  a  solution  containing  50  g.  of  water, 
10  g.  of  gelatine,  and  1  g.  of  ammonium  chromate.  When  the  tube  is  lifted 
from  the  solution,  the  lower  end  remains  closed  by  a  thin  membrane,  which  is 
rendered  insoluble  in  water  by  the  action  of  light.  A  precipitation  membrane 
of  copper  ferrocyanide  is  then  deposited  in  the  hardened  gelatine  film,  according 
to  the  method  employed  by  Pfeffer. 

Experiments  with  precipitation  membranes  have  given  the  general  results 
summarized  below.     Other  conditions  remaining  the  same: — 

1.  Osmotic  pressure  is  proportional  to  the  concentration  of  the  solution. 
Thus  1-,  2-  and  4-per  cent,  solutions  of  cane  sugar  developed  osmotic  pressures 
equivalent  to  53.2  cm.,  1 01. 6  cm.  and  208.2  cm.  of  a  mercury  column,  respectively. 

2.  Osmotic  pressure  increases  with  rise  in  temperature.  A  i-per  cent, 
saccharose  solution  at  temperatures  6.8°,  13. 70  and  2  2°C.  gave  osmotic  pressures 
of  50.5  cm.,  52.5  cm.  and  56.7  cm.  of  a  mercury  column,  respectively. 

3.  Osmotic  pressure  depends  upon  the  nature  of  the  dissolved  substance. 
Six-per  cent,  solutions  of  (1)  gum  arabic,  (2)  gelatine,  (3)  saccharose  and  (4) 
potassium  nitrate  gave  osmotic  pressures  of  (1)  25.9  cm.,  (2)  23.8  cm.,  (3)  287.7 
cm.  and  (4)  700  cm.  of  a  mercury  column,  respectively.  Colloids  (such  as 
gum  arabic  and  gelatine)  thus  produce  much  lower  osmotic  pressures  than  do 
crystalloids. » 

4.  Osmotic  pressure  depends  upon  the  nature  of  the  membrane.  Six-per 
cent,  solutions  of  the  four  substances  named  above  gave  the  following  osmotic 
pressures  (in  centimeters  of  a  mercury  column)  with  membranes  of  copper 
ferrocyanide,  parchment  paper  and  animal  bladder,  respectively. 


Morse,  H.  N.,  The  osmotic  pressure  of  cane  sugar  solutions  at  high  temperatures.  Ibid. 
48:  29-94.  191 2.  Idem,  The  osmotic  pressure  of  aqueous  solutions.  Carnegie  Inst.  Wash. 
Pub.  198.  222  p.  1914.  During  the  same  period  other  very  important  experimental  studies 
on  the  osmotic  pressure  developed  by  concentrated  solutions  have  been  prosecuted  by  Berkeley 
and  Hartley,  in  England.  See:  Berkeley,  Earl  of,  and  Hartley,  E.  G.  J.,  On  the  osmotic 
pressure  of  some  concentrated  solutions.  Phil,  trans.  Roy  Soc.  London  A206 :  481-507. 
1906.  For  a  general  discussion,  see  Findlay,  1913,  also  Washburn,  1921.  (See  note  e,  p. 
109.)— Ed. 

1  Walden,  Paul,  Ueber  Diffusionserscheinungen  an  Niederschlagsmembranen.  Zeitsch.  physik. 
Chem.  10:699-732.     1892. 

'  As  is  brought  out  a  little  farther  on,  the  concentration  of  the  solutions  should  not  be 
stated  in  terms  of  percentage  for  such  comparisons;  they  should  be  given  in  terms  of  a  volume- 
molecular,  or  still  better,  of  a  weight-molecular  solution.  The  former  gives  the  number  of 
gram-molecules  of  solute  dissolved  in  a  liter  of  solution  (at  a  stated  temperature)  and  the  latter 

gives  the  number  of  gram-molecules  of  solute  dissolved  in  1000  g.  (  —5—  =  55.56  g.-mol.)  of 

Io 

water  taken  as  H20.  For  a  valuable  discussion  of  the  relation  of  volume-molecular  and 
weight-molecular  solutions  to  physiological  considerations,  see:  Renner,  O.,  Ueber  die  Berech- 
nung  des  osmotischen  Druckes.  Biol.  Centralbl.  32  :  486-504.  1912.  The  general  principle 
holds,  as  stated  in  the  text,  however.     See  also  note  n,  below  (p.  123). — Ed. 

8 


114 


PHYSIOLOGY   OF   NUTRITION 


Substance,  in  6-Per 
Cent.  Solution 

Kind  of  Membrane 

Copper 
Ferrocyanide 

Parchment 
Paper 

Animal 
Bladder 

Gum  arabic 

cm.  Hg 

25-9 

23.8 

287.7 

700.0 

cm.  Hg 
17.7 
21.3 
29.0 

20.4 

cm.  Hg 
14. 2 

Gelatine 

Saccharose 

Potassium  nitrate 

15-4 

14-5 

8.0 

The  crystalloids,  saccharose  and  potassium  nitrate,  produced  lower  pressures 
than  did  the  colloids,  gum  arabic  and  gelatine,  when  plant  or  animal  membranes 
were  used.  This  seems  to  be  in  disagreement  with  statement  3,  above,  but  it 
is  explained  by  the  fact  that  these  two  crystalloids  readily  pass  through  such 
membranes,  while  the  precipitation  membranes  are  almost  impermeable  to 
them. 

IV. 


N- 


1  2 

Pig.  68. — Successive  stages  of  plasmolysis. 


N,  nucleus;  V,  vacuole.     (After  deVries.) 


Pfeffer's  experiments  indicated  that,  other  conditions  remaining  the  same, 
the  magnitude  of  the  osmotic  pressure  differed  according  to  the  nature  of  the 
dissolved  substance,  and  the  question  arose  whether  this  phenomenon  obeyed 
any  law.  This  question  was  answered  by  deVries,1  who  used  living  plant  cells 
instead  of  the  artificial  cells  employed  by  Pfeffer.  He  determined  the  isosmotic 
(or  isotonic)  coefficients  of  various  substances  by  means  of  the  plasmolytic 
method. 

As  is  well  known,  plasmolysis  occurs  when  a  living  plant  cell  is  placed  in  a 
sufficiently  strong  (10-per  cent.)  solution  of  such  substances  as  cane  sugar,  sodium 
chloride,  etc.  At  first  there  is  a  decrease  in  cell  volume,  to  a  certain  point, 
after  which  the  protoplasm  separates  from  the  cell  wall  and  withdraws  inward 
(Fig.  68).     The  cell  gradually  regains  its  earlier  form  if  the  salt  solution  is 

1  Vries,  Hugo  de,  Eine  Methode  zur  Analyze  der  Turgorkraft.     Jahrb.  wiss.  Bot.  14:  427-601.     1884. 


ABSORPTION   OF   MATERIALS   IN   GENERAL  115 

replaced  by  water.  Cells  with  colored  sap  are  very  good  for  plasmolytic  ex- 
periments, since  the  coloring  matter  is  retained  within  the  shrinking  vacuole, 
leaving  the  space  between  the  protoplasm  and  the  cell  wall  filled  with  colorless 
solution.  By  the  use  of  such  cells  plasmolysis  may  be  readily  detected, 
even  in  its  incipient  stages.  DeVries  used  mature  cells  with  colored  sap  and 
determined  the  concentration  of  the  plasmolyzing  solution  when  the  latter  was 
just  strong  enough  to  cause  separation  of  the  protoplasm  from  the  wall  at  the 
corners  of  the  cell  (Fig.  68,  3).  If  no  further  contraction  of  the  protoplasm 
occurs  it  follows  that  the  osmotic  pressure  within  the  vacuole  just  equals  that 
of  the  external  solution.  The  same  experiment  was  repeated  with  various 
substances,  and  the  limiting  concentration  (i.e.,  that  concentration  which  is 
just  strong  enough  to  cause  incipient  plasmolysis)  was  determined  for  each. 
In  this  way  concentrations  of  various  substances  were  found  that  produced  the 
same  osmotic  pressure  with  the  same  membrane.  Such  solutions  are  termed 
isosmotic  or  isotonic. 

The  colored  epidermal  cells  of  the  leaf  sheath  of  Curcuma  rubricaidis,  of 
the  leaves  of  Tradescantia  discolor,  and  of  the  petiolaf  scales  of  Begonia  manicata, 
are  all  very  well  suited  to  such  experiments  as  that  just  described.  Twelve 
preparations  may  be  made  for  each  experiment,  six  being  placed  in  various 
concentrations  of  the  substance  to  be  studied,  and  the  other  six  in  corresponding 
concentrations  of  potassium  nitrate.  All  preparations  must  be  taken  from  the 
same  region  of  the  leaf  or  other  plant  organ.  To  accomplish  this,  a  narrow 
rectangle  is  marked  on  the  leaf,  and  divided  longitudinally  into  halves  and 
transversely  into  six  divisions,  the  area  of  each  of  the  resulting  sections  being 
about  1  sq.  mm.  Each  piece  of  epidermis  is  removed  with  a  razor  and  placed 
in  a  glass  cylinder  (about  10  cm.  tall  and  2  cm.  in  diameter^')  containing  the 
solution  to  be  tested.  The  cylinders  are  loosely  stoppered  to  prevent  evapora- 
tion, and  the  preparations  are  left  in  the  solutions  about  two  hours. 

Volume-molecular  solutions  were  employed,  containing  the  molecular  weight 
of  the  solute  in  grams  (called  a  gram-moleCule  or  a  mol)1  per  liter  of  solution. 
[See  note  j.  p.  113.]  A  volume-molecular  solution  (m)  of  potassium  nitrate 
contains,  for  example,  1  g.-mol.  (101.1  g.)  of  the  salt  in  a  liter  of  solution,  and 
a  tenth-molecular  solution  (0.1 '  m.)  contains  10. n  g.  of  the  salt  per  liter.  In 
physiological  studies  it  is  generally  more  convenient  to  calculate  solution  con- 
centrations as  gram-molecules  per  liter  than  to  consider  them  in  terms  of 
percentage. 

DeVries  compared  the  osmotic  pressures  developed  by  equimolecular  solu- 
tions of  various  substances,  and  found  that  the  substances  tested  fell  into  four 
groups  according  to  the  amount  of  pressure  developed,  the  four  different  pres- 
sures obtained  being,  relatively,  0.066,  o.  100,  0.133,  and  0.166.  The  second 
group  represents  the  pressure  caused  by  potassium  nitrate.  These  numbers 
are  approximately  in  the  proportion  of  2 :  3:  4:  5,  so  that  if  the  pressure  produced 

1  Ostwald,  Wilhelm,  Lehrhuch  der  allgemeinen  Chemie.     2te  Aufl.  2:   212.     Leipzig,   1906.     [Idem, 
Outlines  of  general  chemistry.     Translated  by  James  Walker.     London,  1895.] 

k  Much  shorter  vials  are  more  convenient,  about  1  cm.  in  diameter  and  2  cm.  high.  —  Ed. 


u6 


PHYSIOLOGY   OF   NUTRITION 


by  a  volume-molecular  solution  of  potassium  nitrate  be  considered  as  3,  then 
the  pressure  developed  by  a  volume-molecular  solution  of  any  other  substance 
not  in  the  same  group  is  2,  4,  or  5,  according  to  the  group  in  which  the  given 
substance  belongs.  On  this  account  deVries  adopted  as  his  unit  of  osmotic 
pressure  one-third  of  the  pressure  produced  by  a  volume-molecular  solution  of 
potassium  nitrate,  so  that  a  volume-molecular  solution  of  this  salt,  or  of  any 
other  salt  belonging  to  the  same  group,  always  produced  a  pressure  of  3,  and  the 
three  other  groups  of  substances  gave  pressure  of  2,  4  and  5,  respectively.  The 
numbers  2,  3,  4  and  5  were  termed  isosmotic  coefficients;  they  represent  the 
relative  osmotic  pressures  developed  by  equimolecular  solutions  of  the  various 
substances. 

The  isosmotic  coefficients  were  determined  in  the  following  manner.  Three 
cane  sugar  solutions,  0.20-,  0.22-  and  0.24-volume-molecular,  and  three  solu- 
tions of  potassium  nitrate,  0.12-,  0.13-  and  0.14- volume-molecular,  were  em- 
ployed, for  plasmolytic  experiments  with  epidermal  cells  of  Curcuma 
rubricaulis.  Each  experiment  lasted  seven  hours.  The  results  obtained 
in  three  such  tests  are  given  in  the  following  table,  where  n  denotes  that 
no  plasmolysis  occurred,  hp  denotes  that  about  half  of  the  cells  were 
plasmolyzed  and  p  denotes  that  most  of  the  cells  were  plasmolyzed.  IC 
denotes  the  isosmotic  concentration,  taken  to  be  osmotically  equal  to  the  cell 
sap.     Volume-molecular  concentration  is  denoted  by  m. 


Saccharose 

Potassium  Nitrate 

Experiment 

Ratio  of 

no. 

ICi  TO   ICi 

0.2OWJ 

0.22m 

0.24m 

Id 

0.12/K 

0.13m 

0.14m 

IC2 

m 

m 

1 

n 

hp 

P 

0.22 

n 

hp 

P 

0.130 

0.591 

2 

n 

P 

P 

0.21 

n 

P 

P 

0.125 

o.595 

3 

n 

P 

P 

0.21 

n 

P 

P 

0.130 

0.610 

0. 602 

Since  the  osmotic  pressure  produced  by  a  volume-molecular  potassium 
nitrate  solution  is  taken  as  3,  the  numbers  in  the  last  column  are  to  be  multi- 
plied by  3,  and  the  average  ratio  thus  becomes  1.81,  which  is  the  isosmotic 
coefficient  of  saccharose  when  that  of  potassium  nitrate  is  considered  as  3. 

A  list  of  substances  thus  tested  by  deVries  is  given  in  the  next  table,  together 
with  their  isosmotic  coefficients,  as  actually  derived  from  experiment  and  also 
in  round  numbers.  The  next  to  the  last  column  gives  the  percentage  concen- 
trations thus  found  to  be  isosmotic  with  a  one-tenth  volume-molecular  solution 
of  KNO3,  and  the  last  column  gives  the  osmotic  pressure  produced  by  a  i-per 
cent,  solution  of  each  substance. 


ABSORPTION    OF    MATERIALS    IN    GENERAL 


117 


Substance 


Chemical 
Formula 


Molecular 
Weight 


Isosmotic 
Coefficient 


Ob- 
served 


In  Round 
Numbers 


Concentration 

Isosmotic 

with  0.1  m 

KXO3 


Osmotic 

Pressure 

Produced  by 

i.o-Per  Cent. 

Solution 


Saccharose 

Glucose  

Glycerine 

Citric  acid 

Oxalic  acid 

Potassium  nitrate 
Ammonium  chloride  . . 
Potassium  sulphate  . .  . 
Magnesium  sulphate  .  . 
Magnesium  chloride  .  . 
Potassium  citrate 


C12H22O11 

C6Hi206 

C3H8O3 

C6Hs07 

C2H2O4 

KNOa 

NH4CI 

K2S04 

MgS04 

MgCh 

X3C6H5O7 


342.0 
180.0 

92.0 
192.0 

90.0 
101 .0 

53- S 
174-0 
120.0 

95-0 
306.0 


1.88 

2 

1.88 

2 

1.78 

2 

2.02 

2 

2 

3-00 

3 

3-00 

3 

3-90 

4 

1.96 

2 

4-33 

4 

5. 01 

5 

per  cent. 
5. 13 
2.70 
1.39 
2.88 


35 
01 
S3 
30 

80 


0.71 
1.84 


atmospheres 

0.69 
.      1. 25 

2.54 

1.23 

2.62 

3-50 

6.67 

2.72 

1.93 

4.98 

1.92 


In  the  above  table  the  isosmotic  coefficients  are  seen  to  be  about  2,  3,  4 
and  5.  If  the  coefficient  for  saccharose  and  the  other  organic  compounds  be 
taken  as  unity,  then  the  remaining  ones  become  %,  2,  and  %. 

It  is  also  evident  from  this  table  that  the  osmotic  pressures  produced  by  the 
non-electrolytes  (saccharose,  glycerine  and  the  other  organic  compounds)  are  re- 
lated to  their  molecular  weights.  A  solution  containing  92  g.  of  glycerine  per 
liter  produces  the  same  osmotic  pressure  as  one  of  cane  sugar  containing  342  g. 
per  liter.  These  two  solutions  contain  very  different  amounts  of  substance 
by  weight,  but  they  contain  equal  numbers  of  molecules  (i.e.,  they  are  equi- 
molecular).  Here  all  molecules  produce  the  same  osmotic  pressure,  and  the 
osmotic  pressure  of  a  solution  is  thus  proportional  to  its  molecular  concentra- 
tion. This  agrees  with  Avogadro's  law  for  gases,  which  states  that  gas  pressure 
is  proportional  to  the  number  of  molecules  occurring  in  a  given  volume.  Van't 
Hoff  compared  solutions  of  solid  bodies  in  liquids,  with  gases,  and  concluded 
that  osmotic  pressure  follows  the  same  law  as  does  gas  pressure.  One  gram- 
molecule  of  any  gas  (e.g.,  44  g.  of  C02)  occupies  a  volume  of  22.4  1.,  with  a  pres- 
sure of  760  mm.  and  at  a  temperature  of  o°C.  When  this  volume  of  gas  is  re- 
duced to  1  1.,  the  pressure  becomes  22.4  atmospheres.  If  the  van't  Hoff  theory 
is  correct,  a  molecular  solution  of  cane  sugar  containing  342  g.  per  liter,  should 
produce  22.4  atmospheres  of  osmotic  pressure,  and  a  i-per  cent,  solution  of 
the  same  substance  should  give  an  osmotic  pressure  of  0.69  atmospheres  at 
i5°C.  The  pressure  actually  produced  by  a  i-per  cent,  solution  of  cane  sugar 
lies  between  0.62  and  0.71  atmospheres  according  to  Pfeffer's  measurements, 
which  constitutes  a  brilliant  confirmation  of  the  theory. 

The  following  table  gives  a  summary  of  other  osmotic  values  for  cane- 
sugar  solutions,  as  observed  by  Pfeffer  and  as  calculated  by  the  van't  Hoff 
theory. 


n8 


PHYSIOLOGY    OF    NUTRITION 


Concentration  of  Cane  Sugar 


Osmotic  Value 


Observed 


Calculated 


per  cent. 

atmospheres 

atmospheres 

I.O 

0.664 

0.665 

2.0 

I-336 

I-336 

2-5 

1.997 

1.639 

4.0 

2-739 

2.742 

6.0 

4.046 

4.050 

It  is  different  with  electrolytes;  from  the  table  given  on  page  117  it  is  clear 
that,  of  the  crystalloids,  isosmotic  solutions  of  electrolytes  (metallic  salts)  and 
non-electrolytes  are  not  equimolecular,  the  molecular  concentrations  of  the  former 
being  much  lower.  Furthermore,  there  is  no  constant  relation  between  the 
isosmotic  concentrations  of  solutions  of  electrolytes  on  the  one  hand  and  of  non- 
electrolytes  on  the  other,  so  that  electrolytes  do  not  agree  with  the  gas-pressure 
theory  of  osmotic  pressure.  For  example,  a  0.1-volume-molecular  solution 
of  KNO3  ought,  according  to  this  theory,  to  give  a  pressure  of  0.235  atmos- 
pheres, but  it  actually  gives  one  of  0.352  atmospheres.  If  the  value  derived 
directly  from  the  van't  Ffoff  theory  be  multiplied  by  %,  the  isosmotic  coeffi- 
cient of  this  salt  (considering  the  coefficient  of  cane  sugar  as  unity),  the  value 
0.352  is  obtained,  which  is  the  same  as  that  found  experimentally.  Equimole- 
cular solutions  of  potassium  nitrate  and  of  organic  substances  are  thus  not 
isosmotic.  To  obtain  a  solution  of  potassium  nitrate  that  shall  produce  the 
same  osmotic  pressure  as  does  a  0.1-molecular  cane-sugar  solution  it  is  necessary 
to  prepare  a  Ms  (%  X  Mo)  molecular  solution  of  the  salt.  Salts  with  other 
isosmotic  coefficients  must  be  employed  in  corresponding  concentrations.  Thus, 
a  0.05-molecular  solution  of  potassium  sulphate  is  isosmotic  with  a  0.1-molecular 
solution  of  cane  sugar.  The  osmotic  pressure  of  a  weak  solution  of  an  electrolyte 
is  thus  equal  to  the  theoretical  pressure  multiplied  by  the  isosmotic  coefficient 
of  the  electrolyte  in  question.  This  departure  from  the  theory  is  explained  by 
Arrhenius'  hypothesis,  which  supposes  that  electrolytes  in  solution  dissociate 
into  ions.  In  a  sodium  chloride  solution,  for  example,  sodium  and  chlorine  ions 
are  both  present  as  well  as  molecules  of  sodium  chloride.  The  more  dilute  the 
solution,  the  greater  is  the  degree  of  dissociation. 

According  to  the  Arrhenius  theory  of  electrolytic  dissociation,  the  isosmotic 
coefficient  of  potassium  nitrate  indicates  that  the  number  of  particles  in  a  solu- 
tion of  this  salt  is  increased  by  dissociation,  and  if  half  of  the  molecules  be  con- 
sidered as  dissociated  the  total  number  of  particles  ought  to  be  %  of  what  it 
would  be  without  dissociation,  and  the  osmotic  pressure  should  be  correspond- 
ingly increased.  A  dissociated  molecule  of  KNO;i,  in  the  form  of  two  ions,  K  and 
NO3,  produces  twice  as  much  osmotic  pressure  as  does  an  undissociated  molecule. 


ABSORPTION   OF   MATERIALS   IN   GENERAL  Iig 

Potassium  sulphate  has  an  isosmotic  coefficient  of  2  at  the  concentrations 
employed  by  de  Vries,  the  molecule  of  this  electrolyte  dissociates  into  three  ions, 
K,  K  and  S04,  and  the  coefficient  2  indicates,  in  this  case  also,  that  half  the  total 
number  of  molecules  are  to  be  considered  as  dissociated.  The  number  of  par- 
ticles in  solution  would  thus  be  about  doubled,  for  K  +  3  X  H  =  2-1 

DeVries  used  salt  solutions  of  about  0.1 -volume-molecular  concentration, 
these  being  about  half  dissociated.  The  degree  of  dissociation  varies  with  the 
concentration,  and  so  the  osmotic  coefficients  obtained  by  deVries  cannot  be 
used  for  solutions  of  other  concentrations,  the  coefficients  for  which  must  be 
obtained  through  the  use  of  isosmotic  solutions,1  employing  a  solution  of  an 
undissociated  and  unhydrated  substance  as  a  standard. 

Errera2  proposed  the  myriotonie  as  a  unit  for  the  measurement  of  osmotic 
pressure,  to  replace  the  arbitrary  one  of  an  atmosphere.  A  tonie  is  the  pressure 
exerted  upon  a  surface  of  1  sq.  cm.  by  1  dyne  (the  well-known  unit  representing 
the  force  necessary  to  give  a  velocity-acceleration  of  1  cm.  per  second  to  a  mass 
of  1  g.).  The  terms  dekatonie,  hectotonie,  kilotonie  and  myriotonie  (10,000 
tonies)  are  employed  for  greater  pressures.  A  myriotonie  (M)  is  about  one 
one-hundredth  of  an  atmosphere."1 

§5.  Absorption  of  Dissolved  Substances. — Only  a  few  direct  experiments 
upon  the  entrance  of  dissolved  substances  into  the  cell  are  available.  Some  con- 
clusions concerning  the  mechanism  of  absorption  may  be  drawn  from  plasmoly tic 
experiments  with  salt  solutions.  Every  substance  entering  the  cell  must  pass 
through  two  membranes,  the  cell  wall  and  the  protoplasmic  membrane.  Most 
dissolved  substances  easily  penetrate  the  cell  wall,  but  the  protoplasm  is  imper- 
meable, or  nearly  so,  to  many  of  these. 

The  osmotic  properties  of  the  protoplasmic  membrane  are  similar  to  those 
of  Pfeffer's  precipitation  membranes.  Only  the  living  protoplasm  is  here 
meant,  however;  dead  protoplasmic  membranes  have  entirely  different  proper- 
ties. Thus  pigments  are  persistently  retained  within  the  cell  sap  by  the  living 
protoplast,  but  these  and  other  dissolved  substances  diffuse  out  very  rapidly 
after  the  cell  is  dead.  Like  precipitation  membranes,  the  protoplasmic  mem- 
brane is  not  completely  impermeable  to  most  substances.     For  example,  Pfeffer3 

1  Hamburger,  H.  J.,  Osmotischer  Druck  und  Ionenlehre  in  den  medicinisctun  Wissenschaften.  3  v. 
Wiesbaden,  1902-1904.  Hober,  Rudolf,  Physikalische  Chemie  derZelleund  der  Gewebe.  2  Aufl.  Leipzig.. 
1906.  [4  Aufl.  Leipzig,  1914-]  Brasch,  Richard,  Die  Anwendung  der  physikalischen  Chemie  auf  die  Phy- 
siologic und  Pathologie.     Wiesbaden,  1901. 

2  Errera,  L.,  Sur  la  myriotonie  comme  unite  dans  les  mesures  osmotiques.  Recueil  Inst.  Bot. 
Bruxelles  5:  193-208.     1902. 

3  Pfeffer,  W.,  Ueber  Aufnahme  von  Anilinfarben  in  lebenden  Zellen.  Untersuch.  Bot.  Inst.  Tubingen 
2:  179-331.     1886-1888. 

1  The  degrees  of  dissociation  are  actually  much  greater,  however,  than  are  assumed  in 
this  discussion.  DeVries's  isosmotic  coefficients  are  now  to  be  regarded  as  of  historical 
interest  only.  The  best  discussion  of  the  calculation  of  osmotic  values  of  solutions  is  that 
of  Washburn,  1921.     [See  note  e,  p.  ioo.| — Ed. 

m  This  unit  has  never  come  into  general  use  and  it  is  now  highly  improbable  that  it  ever 
will.  Pressures  are  generally  stated  in  terms  of  millimeters  or  centimeters  of  a  mercury  column 
or  in  atmospheres,  an  atmosphere  being  760  cm.  of  mercury.  It  seems  undesirable  to  state 
osmotic  pressure  in  any  other  terms  than  those  already  used  for  other  kinds  of  pressure. — Ed. 


120 


PHYSIOLOGY    OF    NUTRITION 


■  '',,'    '_'    '  I'  '  i  i  i    i  j_ 


Fig.  69. — Cell  of  Zygnema 
with  crystals  formed  by 
methylene  blue. 


succeeded  in  introducing  useless  and  even  injurious  substances  (such  as  aniline 
dyes)  into  the  living  cell.  He  found  that  the  following  pigments  penetrated: 
methylene  blue,  methyl  violet,  bismarck  brown,  fuchsin,  cyanin,  safranin, 
methyl  green,  methyl  orange,  tropaeolin  00  and  rosolic  acid.  The  concentra- 
tions of  the  solutions  employed  were  very  low  (from  0.001  to  0.00001  per  cent.). 
Some  of  the  dyes,  (e.g.  methylene  blue)  first  enter  the  cell  sap  and  color  it,  but 
form  crystals  after  a  time;  Fig.  69  shows  an  alga  cell  (Zygnema)  with  crystals 
formed  by  methylene  blue.  Other  dyes  (e.g.,  methyl  violet)  stain  the  proto- 
plasm itself.     In  neither  case  is  the  cell  fatally  injured. 

Overton1  studied  a  number  of  different  dyes  and  found  that  the  permeability 

of  the  protoplasm  to  these  varied  according  to 
their  chemical  constitution.  Basic  aniline  dyes 
readily  enter  the  cell,  but  most  of  their  sulphuric 
acid  derivatives  penetrate  either  not  at  all  or  very 
slowly.  Dyes  that  have  accumulated  in  the  cells 
diffuse  out  when  the  cells  are  placed  in  water,  this 
outward  passage  being  accelerated  by  the  addition 
of  0.01  per  cent,  of  citric  acid  to  the  water.2 
Citric  acid  thus  appears  to  change  the  osmotic  properties  of  the  protoplasm. 
No  dye  accumulates  in  the  cell  if  the  solution  contains  0.01  per  cent,  of  citric 
acid,  but  the  dye  is  absorbed  from  the  surrounding  solution  in  the  absence  of 
the  acid.     It  is  thus  possible  to  alter  at  will  the  osmotic  properties  of  cells. 

It  is  well  known  that  plants  can  absorb  and  accumulate  the  essential  chemical 
elements  from  very  dilute  solutions.  Some 
non-essential  elements  enter  the  plant  cell  only 
until  their  effective  concentration  becomes  the 
same  within  and  without,  but  some  others,  as 
well  as  the  essential  elements,  continue  to  enter 
and  accumulate  in  the  cell,  even  from  a  weak- 
solution,  since  they  are  converted  into  new  com- 
pounds after  entrance  and  so  the  internal  con- 
centration never  becomes  equal  to  the  external. 
An  illustration  of  continued  absorption  may 
be  found  in  the  accumulation  of  iron  tannate 
in  an  artificial  cell  of  collodion  or  animal  bladder 
filled  with  tannin  solution  and  surrounded  by 
one  of  ferric  chloride.  Tannin  does  not  escape 
through  the  membrane,  but  ferric  chloride 
diffuses  into  the  cell  and  there  enters  into  combi- 
nation with  the  tannin  to  form  iron  tannate, 

which  also  remains  in  the  cell.  Ferric  chloride  is  continually  consumed  in  the 
formation  of  the  iron  tannate,  and  its  concentration  within  the  cell  never  becomes 
the  same  as  that  outside.     If  the  tannin  solution  is  sufficiently  concentrated 

1  Overton,  E.,  Studien  uber  die  Aufnahme  der  Anilinfarbe  durch  die  lebende  Zelle.     Jahrb.  wiss.  Bot. 


Fig.  70. — Apparatus  for  show- 
ing diffusion  of  copper  sulphate 
through  a  membrane  into  a  tube 
containing  zinc. 


34:  669-701.     1900. 
»  Pfeffer,  1886-88. 


[See  note  1,  page  121.] 


ABSORPTION    OF    MATERIALS    IN    GENERAL 


121 


all  of  the  ferric  chloride  will  pass  from  the  outer  solution  into  the  cell.  In 
a  similar  way  plant  roots  appear  to  absorb  the  essential  elements,  as  well  as 
other  substances,  from  the  surrounding  solution. 

The  following  experiment  also  illustrates  this  phenomenon  of  continued 
absorption  (Fig.  70).  A  roll  of  sheet  zinc  is  placed  in  a  short  glass  tube  of 
large  diameter,  the  tube  being  filled  with  water  and  having  both  ends  closed 
with  animal  bladder  or  parchment  paper.  The  tube  is  placed  in  a  dilute 
solution  of  copper  sulphate,  which  passes  through  the  membranes  into  the 
tube.  Here  the  copper  of  the  salt  is  replaced  by  zinc,  and  the  zinc  sulphate 
thus  formed  diffuses  into  the  outer  solution.  Copper  sulphate  continues  to  enter 
until  all  of  it,  or  all  of  the  zinc,  has  been  used  up.  The  same  phenomenon 
occurs  in  the  growth  of  bacteria  and  moulds  on  various  organic  compounds. 
Of  two  substances  having  different  nutritive  values,  the  cells  take  up  mostly 
the  one  with  the  higher  value,  frequently  leaving  the  other  entirely  untouched. 
For  instance,  Aspergillus  niger  absorbs  only  glucose  from  a  mixture  of  this 
substance  and  glycerine,  so  long  as  the  former  is  present  in  the  solution.1 

Outward  diffusion  through  the  cell  membranes  is  also  subject  to  regulation. 
Nathansohn's  experiments2  indicate  that  sodium  chloride  easily  penetrates  the 
cells  of  Codium  tomentosum  (a  marine  alga)  but  that  this  salt  cannot  be  com- 
pletely withdrawn  from  the  cells  after  it  has  once  entered.  When  the  alga  is 
placed  in  an  isosmotic  solution  (4  per  cent.)  of  sodium  nitrate,  the  chloride  con- 
tent of  the  cell  sap  rapidly  decreases  at  first,  but  the  outward  diffusion  of  chloride 
ceases  after  a  time,  as  is  clear  from  the  following  table.  The  figures  denote 
chlorine  content,  calculated  as  per  cent,  of  HC1. 


Original 

Chlorine  Content  after  a  Period  of 

Chlorine 
Content 

I  DAY 

3  DAYS 

8  DAYS 

15  DAYS 

25  DAYS 

2.24 

0.92 

0.93 

0.90 

O.84 

O.76 

Plasmolysis  of  cells  has  already  been  described  (Fig.  68).  DeVries3  plas- 
molyzed  whole  plant  organs  as  well  as  cells,  and  showed  that  growing  parts 
(such  as  stems,  roots  and  flower  stalks)  are  noticeably  shortened  after  immer- 
sion in  a  plasmolyzing  solution,  but  regain  their  original  stiffness  and  elas- 
ticity when  returned  to  pure  water.  This  rigidity,  which  is  a  result  of  osmostic 
pressure,  is  called  turgidity. 

The  rate  at  which  water  and  dissolved  substances  penetrate  the  protoplasm 

>  Pfeffer,  W.,  Ueber  Election  organischer  Nahrstoffe.     Jahrb.  wiss.  Bot.  28:   206-268.     1895. 

2  Nathansohn,  Alexander,  ZurLehre  vom  StoSaustausch.     Ber.  Qputsch,  Bot  Ges.  19:  500-513.     1901. 

3  Vries,  Hugo  de,  Untersuchungen  uber  die  mechanischen  Ursachen  der  Zellstreckung.  ausgehend  von 
der  Einwirkung  von  Salzlosungen  auf  den  Turgor  wachsender  Pflanzenzellen.  Leipzig,  1877.  Idem, 
Untersuchungen  uber  die  mechanischen  Ursachen  der  Zellstreckung.     Halle,  1877. 


122 


PHYSIOLOGY   OF   NUTRITION 


is  influenced  by  external  conditions.  Van  Rysselberghe1  studied  the  effect  of 
temperature  upon  this  rate.  In  one  series  of  experiments  pieces  of  pith  from 
young  twigs  of  Sambucus  nigra  (elder)  were  placed  in  water  and  then  trans- 
ferred to  26-per  cent,  solutions  of  cane  sugar  at  different  temperatures.  Each 
piece  was  114  mm.  in  length  at  the  outset,  and  their  lengths  were  redetermined 
at  stated  intervals.  The  lower  the  temperature,  the  more  slowly  did  plasmolysis 
occur.  The  amounts  of  shrinkage  observed  for  such  pieces  of  Sambucus  pith, 
with  different  temperatures  and  after  different  periods  of  time,  are  shown  in  the 
following  table. 


Temperature. 

deg.  C. 

0 

6 

12 

16 

20 

25 

Time  Period 

hours 

mm. 

mm. 

mm. 

mm. 

mm. 

mm. 

2 

4-5 

8.5 

20.0 

33-0 

40.5 

40.5* 

4 

7-5 

135 

25.0 

38.0 

42.0* 

6 

10. 0 

17.0 

28.0 

42.0* 

8 

12.5 

20.0 

30.0 

10 

14.0 

21-5 

3i-5 

24 

21 .0 

310 

40.0 

*No  further  shrinkage.  * 

In  another  series  of  experiments  plasmolyzed  pieces  of  Sambucus  pith  were 
placed  in  water  at  various  temperatures,  with  the  same  result;  the  return  of 
turgidity  was  more  rapid  as  the  temperature  of  the  water  was  higher.  These 
results  are  shown  graphically  in  the  curve  of  Fig.  71,  where  the  abscissas  are 
the  temperatures  and  the  ordinates  are  the  velocities  of  the  movement  of 
water  through  the  protoplasmic  membrane  (both  inward  and  outward.) 


8 

7 

n 
.5 
7 
J 

2 


z?c 


16c 


SOc 


26' 


30* 


Fig.  71. — Graph  representing  relation  of  temperature  to  velocity  of  penetration  of  water  through 

the  protoplasmic  membrane. 

The  rates  at  which  dissolved  substances  diffuse  through  the  protoplasm 
also  depend  on  temperature.  If  the  velocity  of  movement  at  o°C,  be  taken  as 
unity,  then  the  following  relative  velocities  are  obtained  for  potassium  nitrate, 
glycerine  and  urea,  for  various  higher  temperatures. 

1  Van  Rysselberghe,  Fr.,  Influence  de  la  temperature  sur  la  permeabilite  du  protoplasme  vivant  pour 
l'eau  et  les  substances  dissoutes.  Recueil  Inst.  Bot.  Bruxelles  5:  200-249.  1902.  [Idem,  Reaction 
osmotique  des  cellules  vegetales  a  la  concentration  du  milieu.  Mdm.  cour.  Acad.  Roy.  Belgique  58:  1-101. 
1898.] 


ABSORPTION    OF    MATERIALS    IX    GENERAL 


123 


Temperature, 
deg.  C. 
Substance 

0 

6 

12 

16 

20 

25 

1 .0 
1 .0 
1 .0 

1.8 
1.9 
2.1 

4-4 
4.2 

4-5 

6.0 
5-6 
5-3 

7-3 
7.0 

7.0 

7-3 

7.0 
7.6 

The  cell  sap  frequently  exhibits  high  osmotic  values.71  DeVries  found  that 
sap  expressed  from  young  plant  organs  showed  the  osmotic  values  given  in 
the  table  below. 


Source  of  Expressed  Sap 


Csmotic  Value 


Gunnera  scabra  (petioles) . . . 
Solatium  tuberosum  (leaves) 
Sorbtis  arcuparia  (berries) . . 
Beta  vulgaris  (roots) 


atmospheres 

3-5 

5-5 

9.0 

21 .0 


The  moulds  Aspergillus  niger  and  Penicillium  may  develop  osmotic  pres- 
sures as  great  as  157  atmospheres,  when  they  are  grown  in  concentrated 
sugar  or  salt  solutions.0 

n  A  solution  alone  has  no  osmotic  pressure,  this  being  produced  by  two  solutions  (or  a  solu- 
tion and  the  pure  solvent)  and  a  membrane,  all  acting  together.  When  the  "osmotic  pres 
sure"  of  a  solution  is  spoken  of,  the  maximum  osmotic  pressure  that  might  be  obtained  with 
that  solution,  at  the  given  temperature,  is  meant.  To  obtain  this  maximum  the  membrane  em- 
ployed must  be  quite  impermeable  to  all  the  solutes  (dissolved  substances)  of  the  solution,  and 
the  membrane  must  be  in  contact  with  the  solution  on  one  side  and  with  the  pure  solvent 
(water)  on  the  other.  These  conditions  are  probably  never  actually  fulfilled  in  the  case  of  plant 
cells.  If  we  employ  the  term  osmotic  value  for  the  maximum  pressure,  then  the  actual  pressure 
developed  in  any  cell  is  usually  of  somewhat  lower  magnitude  than  is  the  osmotic  value 
of  the  cell  sap.  Diffusion  tension  of  the  solute  is  another  term  that  may  be  employed  for 
the  osmotic  value,  with  reference  to  the  solution  itself,  but  this  is  not  without  objection. 
These  measurements  of  deVries'  were  made  by  means  of  cell  membranes  (plasmolytic  method), 
so  that  the  nature  and  condition  of  the  cells  used  as  indicators  enter  into  the  argument  here,  and 
he  was  not  really  measuring  the  osmotic  values  of  these  expressed  solutions. — Ed. 

0  Fitting  has  studied  the  osmotic  pressures  of  the  cells  of  plant  leaves,  by  the  plasmolytic 
method,  using  potassium  nitrate  solutions,  in  a  very  thorough  way.  He  dealt  especially  with 
desert  plants.  See:  Fitting,  Hans,  Die  Wasserversorgung  und  die  osmotischen  Druckver- 
haltnisse  der  Wustenpflanzen.  Zeitsch.  Bot.  3 :  209-275.  1911.  Livingston,  B.  E.,  The  rela- 
tion of  the  osmotic  pressure  of  the  cell  sap  in  plants  to  arid  habitats.  Plant  world  14:  153-164. 
1911.  (This  is  a  somewhat  critical  review  of  Fitting's  paper.)  While  plant  cells  in  general 
have  osmotic  pressures  of  from  5  to  n  atmospheres,  Fitting  found  pressures  much  exceeding 
100  atmospheres  in  the  leaves  of  some  desert  plants.     This  value  is  greater  for  plants  growing  in 


124 


PHYSIOLOGY   OF   NUTRITION 


DeVries  determined  the  partial  osmotic  pressure  developed  by  some  of  the 
constituents  of  the  cell  sap.  The  following  table  gives  an  idea  as  to  what  sub- 
stances are  instrumental  in  the  production  of  osmotic  pressure  in  plants.  The 
figures  denote  percentage  of  the  total  pressure. 


Source  of  Expressed 
Sap 

Potassium. 
Salts  of  Or- 
ganic Acids 

Malic 
Acid 

Glucose 

Sodium 
Chloride 

Other 
Sub- 
stances 

Heracleum  spondilium 
(petioles) 

5-9 

9.1 

69.1 

6.4- 

9-5 

Rochea  falcata  (leaves) 

3-i 

42-3 

23.1 

n-5 

20.0 

Diffusion  in  solution  is  very  important  in  the  absorption  of  materials  by 
plants  but  it  cannot  account  for  the  transfer  of  absorbed  substances  within  the 
plant,  for  movement  by  diffusion  alone  is  much  too  slow.1  For  example,  it 
would  take  319  days  for  1  mg.  of  sodium  chloride,  a  rapidly  diffusing  substance, 
to  diffuse  1  m.  out  of  a  10  per  cent,  solution  of  that  salt.  A  period  of  fourteen 
years  would  be  required  for  the  same  amount  of  albumin  to  migrate  the  same  dis- 
tance. Since  diffusion  progresses  rapidly  in  gelatine  and  agar  as  well  as  in  water, 
these  substances  may  be  employed  in  diffusion  experiments,  being  poured  into 
a  glass  cylinder  while  hot  and  then  covered,  after  cooling,  with  a  solution  of  the 
substance  to  be  studied  {e.g.,  indigo).  Intercellular  protoplasmic  connections, 
like  thin  threads  reaching  through  the  cell  walls,  are  now  known  to  be  of  common 
occurrence  in  plants  (Fig.  72).  How  these  structures  may  influence  exchange 
of  materials  between  the  cells  is  still  unknown,  however. 


very  dry  habitats  than  for  those  growing  in  more  moist  situations.  For  further  studies  bearing 
on  this  and  related  matters,  see:  Dixon,  H.  H.,  and  Atkins,  W.  R.  G.,  On  osmotic  pressures  in 
plants  and  on  a  thermo-electric  method  of  determining  freezing  points.  Proc.  Roy.  Dublin 
Soc,  n.s.  12:  275-311.  1910.  Idem,  Osmotic  pressures  in  plants.  I.  Methods  of  extracting 
sap  from  plant  organs.  Ibid,  n.s  13:  422-433.  1913.  (Reprinted  in:  Notes  from  Bot.  Sch., 
Trinity  Coll.,  Dublin  2  :  154-165.  1913.)  Idem,  same  title,  II.  Cryoscopic  and  conductivity 
measurements  on  some  vegetable  saps.  Ibid.  n.s.  13:  434-440.  1913.  (Reprinted  in:  Notes 
from  Bot.  Sch.,  Trinity  Coll.,  Dublin  2:  166-172.  1913.)  Harris,  J.  Arthur,  and  Lawrence, 
John  V.,  assisted  by  Gortner,  R.  A.,  The  cryoscopic  constants  of  expressed  vegetable  saps 
as  related  to  local  environmental  conditions  in  the  Arizona  deserts.  Physiol,  res.  2:  1-49. 
1916.  (Other  papers  are  there  referred  to.)  Hibbard,  R.  P.,  and  Harrington,  O.  E. ,  De- 
pression of  the  freezing-point  in  triturated  plant  tissues  and  the  magnitude  of  this  depression 
as  related  to  soil  moisture.  Ibid.  1 :  441-454.  1916.  For  a  general  discussion  of  the  osmotic 
relations  of  cells  see:  Atkins,  W.  R.  G.,  Some  recent  researches  in  plant  physiology,  xi  + 
328  p.     London,  1916. — Ed. 

1  Stefan,  J.,  Ueber  die  Diffusion  der  Fliissigkeiten.  II.  Berechnung  der  Grahamschen  Versuche. 
Sitzungsber.  (math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien  79II :  161-214.  1879.  Vries,  Hugo  de,  Ueber  die 
Bedeutung  der  Circulation  und  der  Rotation  des  Protoplasma  fur  den  Stofftransport  in  der  Pflanze.  Bot. 
Zeitg.  43:  1-6,  17-26.      1885. 


ABSORPTION   OF   MATERIALS   IN   GENERAL 


125 


Plants  can  absorb  solid  soil  constituents  but  these  must  first  be  dissolved  in 
water.  If  a  polished  marble  plate  is  placed  in  the  bottom  of  a  box  in  which 
seedlings  are  grown,  many  of  the  roots  come  into  close  contact  with  the  plate, 


Pig.  73. 

a,  thick  cell  wall;  b,  canals  piercing  cell 


Fig.   72. 

Fig.  72. — Cells  of  endosperm  of  Areca  oleracea. 
walls  and  containing  protoplasmic  strands. 

Fig.  73. — A  piece  of  calcium  carbonate  dissolving  in  hydrochloric  acid  as  this  diffuses 
upward  through  the  bladder  membrane  M. 


and  if  the  latter  is  removed  after  a  time  the  imprint  of  the  roots  may  be  seen  on 
the  polished  surface,  etched  by  acid  root  excretion.  The  acid  character  of  root 
excretion  may  also  be  shown  by  the  reddening  of  blue  litmus  paper  against 
which  the  roots  are  induced  to  grow. 

The  following  experiment  illustrates  the  solution  of  soil  particles  and  their 
absorption  after  being  dissolved.  A  broad  glass  tube  with  its  lower  end  firmly 
bound  with  animal  bladder  (Fig.  73)  is  filled  with  and  inverted  over  a  weak  solu- 
tion of  hydrochloric  acid,  so  that  the  cylinder  remains  filled.  A  piece  of  marble 
is  placed  upon  the  smooth  surface  of  the  bladder.  The  marble  gradually  becomes 
smaller  and  smaller  as  it  is  dissolved  by  the  acid  imbibed  in  the  membrane. 
Calcium  chloride  is  formed  during  the  process  and  diffuses  slowly  through  the 
membrane  into  the  solution  below,  where  it  can  be  identified  with  suitable 
chemical  reagents. 

Czapek1  studied  the  nature  of  root  excretions.  He  employed  plates  made 
of  a  mixture  of  aluminium  phosphate  and  plaster  of  Paris.  These  are  soluble 
in  many  acids  (hydrochloric,  nitric,  sulphuric,  phosphoric,  formic,  oxalic,  suc- 
cinic, lactic,  malic,  citric,  and  tartaric)  but  they  are  insoluble  in  carbonic, 
acetic,  propionic  and  butyric  acids.     Various  kinds  of  roots  produced  no  effect 

1  Czapek,  Friedrich,  Zur  Lehre  von  den  Wurzelausscheidungen.     Jahrb.  wiss.  Bot.  29:  321-390.      1896. 


126  PHYSIOLOGY   OF   NUTRITION 

upon  these  plates,  when  they  were  exposed  to  the  roots  as  was  the  marble  men- 
tioned above,  and  it  therefore  follows  that  acids  belonging  to  the  first  list  just 
given  are  not  noticeably  present  in  root  excretions.  In  other  experiments  by 
the  same  writer  Congo  red  was  employed,  which  becomes  brownish-red  through 
the  action  of  carbonic  acid  and  bright  blue  through  the  action  of  acetic,  pro- 
pionic and  butyric  acid.  The  roots  turned  the  Congo  red  only  brownish-red, 
without  any  tendency  toward  blue,  from  which  it  appears  that  the  corrosion 
of  the  marble  (in  the  experiment  described  above)  and  of  soil  particles, 
is  to  be  attributed  to  the  action  of  carbonic  acid  excreted  by  the  roots. 
According  to  Stoklasa  and  Ernest1  roots  excrete  organic  acids  only  when 
inadequately  supplied  with  oxygen. 

The  following  examples  indicate  how  much  may  be  accomplished  by  plants 
in  dissolving  soil  particles.  Lind2  showed  that  the  hyphae  of  certain  fungi  in 
pure  culture  were  able  to  penetrate  through  marble  plates  and  bones.  Nadson3 
described  a  considerable  number  of  algae  that  penetrate  somewhat  deeply  into 
limestone  and  shells,  dissolving  the  material.  These  forms  experience  severe 
competition  with  many  other  algae  on  the  surface  of  the  substratum,  but  their 
ability  to  grow  in  solid  limestone,  which  is  impenetrable  to  their  competitors, 
gives  them  a  definite  advantage  in  the  struggle  for  existence.  Nadson  found 
that  these  algae  excrete  oxalic  acid.p 

It  is  also  well  known  that  parasitic  fungi  penetrate  the  cell  walls  of  their 
host  plants.  Miyoshi4  found  that  fungus  hyphae  can  pierce  membranes  of  very 
different  kinds.  The  membranes  to  be  studied  were  placed  over  nutrient  gela- 
tine and  inoculated  with  spores.  As  germination  took  place  the  hyphae  bored 
through  the  membranes  and  reached  the  nutrient  media  below. 

Summary 

i.  Materials  Absorbed  by  Plants. — From  the  air  the  ordinary  plant  absorbs 
carbon  dioxide  (and  also  oxygen  sometimes,  especially  at  night).  From  the  soil  it 
absorbs  water,  and  inorganic  salts  that  contain  nitrogen  and  the  six  essential  ash 
constituents  (S,  P,  K,  Ca,  Mg,  Fe) .  As  stated  in  Chapter  III,  free  nitrogen  is  absorbed 
by  some  lower  forms  and  by  the  nodule  bacteria  in  the  tubercles  of  legume  roots,  etc. 
Small  amounts  of  oxygen  appear  to  be  absorbed  from  the  soil  by  active  roots.  All 
these  substances,  supplying  the  ten  essential  elements,  and  also  many  that  supply 
non-essential  elements,  are  absorbed  by  diffusion  in  solution,  generally  in  aqueous 
solution.     (When  the  transpiration  rate  is  high,  however,  it  appears  that  these  sub- 

i  Stoklasa,  Julius,  and  Ernest,  Adolf,  Beitrage  zur  Losung  der  Frage  der  chemischen  Natur  des  Wur- 
zelsekretes.     Jahrb.  wiss.  Bot.  46  :  55-102.     1909. 

2  Lind,  K.,  Ueber  das  Eindringen  von  Pilzen  in  Kalkgesteine  und  Knochen.  Jahrb.  wiss.  Bot.  32  : 
603-634.     1898. 

3  Nadson,  G.,  Die  perforierenden  (kalkbohrenden)  Algen  und  ihre  Bedeutung  in  der  Natur.  [Abstract 
in  German,  pp.  35-40.  Text  in  Russian.]  Scripta  Botanica  Hort.  Univ.  Imp.  St.  Petersburg  18:  1-40. 
1900-1902. 

*  Miyoshi,  Manabu,  Die  Durchbohrung  von  Membranen  durch  Pilzfaden.  Jahrb.  wiss.  Bot.  28: 
260-289.      1895. 

p  Also  sec:  Diels,  L.,  Die  Algen-Vegetation  der  Siidtyroler  Dolomitenriffe.  Ber.  Deutsch. 
Bot.  Ges.  32  :  502-526.     1914. — Ed. 


ABSORPTION    OF    MATERIALS    IN    GENERAL  12  7 

stances  may  enter  roots  from  the  soil  by  a  mass  streaming  a|id  nitration  of  the  soil 
solution  through  the  peripheral  cells,  to  the  xylem  vessels.)  To  enter  plant  cells, 
these  substances  must  be  dissolved  in  water  (or  some  other  substance  in  the  cell  wall). 
They  diffuse  through  the  peripheral,  water-impregnated  cell  walls,  into  the  proto- 
plasm. Carbon  dioxide  and  oxygen  diffuse  through  the  suberin  or  lignin  of  cell  walls 
that  are  impregnated  with  one  of  these  substances,  as  well  as  through  the  imbibed 
water. 

2.  Diffusion  of  Gases. — The  ultimate  particles  of  every  gas,  and  of  every  mixture 
of  gases,  are  considered  as  always  in  motion  (somewhat  as  the  individuals  of  a  swarm 
of  gnats  in  the  air)  and  as  always  tending  to  spread  outward  in  all  directions,  until 
some  impermeable  wall  is  encountered.  They  tend  to  distribute  themselves  uni- 
formly throughout  all  the  space  that  is  available.  This  spreading  movement  of  the 
individual  gas  particles  is  called  diffusion  of  the  gas ;  it  is  not  to  be  confused  with  mass 
flow  and  convection,  by  which  the  gas  streams  or  flows  as  a  whole,  like  wind.  If  two 
masses  of  different  gases  are  brought  into  contact  (as  in  the  two  halves  of  a  closed 
chamber)  and  if  no  convection  or  stirring  motion  is  present,  the  particles  of  both 
kinds  of  gas  diffuse  outward,  each  kind  into  the  space  of  the  other  kind,  as  though  the 
other  kind  were  not  present,  and  they  eventually  become  uniformly  mixed.  Rates  of 
diffusion  of  different  kinds  of  gases  are  proportional  to  the  square  roots  of  their  respect- 
ive densities;  hydrogen  diffuses  four  times  as  rapidly  as  oxygen  (densities,  1:16), 
temperature  and  pressure  being  the  same  for  both.  If  septum  or  wall  separates  the 
two  original  gas  masses,  diffusion  takes  place  in  both  directions  through  the  septum 
if  that  is  permeable  to  both  gases;  if  the  septum  is  permeable  to  but  one  of  the  gases, 
diffusion  occurs  in  one  direction  only.  If  the  material  of  the  septum  is  such  that  the 
gas  dissolves  in  it,  then  the  gas  diffuses  through  this  material  in  the  dissolved  state 
(as  a  solute) ,  Solutes  (whether  they  are  gases,  liquids,  or  solids  under  ordinary  con- 
ditions) diffuse  through  the  solvent  in  a  manner  analogous  to  that  of  gas  diffusion,  but 
the  rate  of  diffusion  here  is  proportional  to  the  concentration  gradient  in  the  liquid. 
With  a  liquid-water  septum  separating  two  different  gases  (which  are  at  the  same 
pressure  and  temperature),  the  rates  of  diffusion  through  the  septum  are  proportional 
to  the  solubilities  of  the  two  gases  in  water.  There  may  also  be  mass  streaming  of  the 
septum  material  itself,  which  would  apparently  alter  the  rate  of  this  diffusion,  the  solute 
being  carried  by,  rather  than  diffusing  in,  the  solvent. 

3.  Entrance  of  Gases  into  Plants. — Gases,  as  such,  diffuse  into  (and  out  of)  ordinary 
plants  through  stomata  and  lenticels  (openings  in  the  peripheral  layer  of  cells,  con- 
necting directly  with  gas-filled,  irregular,  intercellular  channels  in  the  tissues).  Gas 
diffusion  continues  in  the  intercellular  spaces.  There  is  also  some  mass  streaming  of 
gases  through  intercellular  spaces  and  their  external  openings.  But  beyond  the  cell 
walls  bounding  these  channels  gas  diffusion  and  gas  streaming  do  not  reach.  Through 
suberized,  lignified,  or  cutinized  cell  walls,  substances  that  are  ordinarily  gases  diffuse 
in  solution  in  the  substance  of  the  walls,  as  well  as  in  the  small  amounts  of  water  held 
by  imbibition.  Through  ordinary,  water-impregnated  walls  (and  also  through  the 
cell  contents)  they  diffuse  as  solutes  in  the  water. 

Most  of  the  carbon  dioxide  and  oxygen  exchange  of  ordinary  plants  occurs  through 
the  stomata  or  lenticels,  the  true  absorption  (or  elimination)  occurring,  however,  at 
the  peripheries  of  the  intercellular  channels,  where  the  gases  pass  into  (or  out  of) 
solution  in  the  imbibed  water  of  the  cell  walls  that  bound  these  channels.  Gas  diffu- 
sion through  stomata  occurs  at  a  rate  proportional  to  the  linear  dimensions  of  the 
openings  or  pores,  other  conditions  being  constant;  the  rate  is  therefore  relatively 


128  PHYSIOLOGY   OF   NUTRITION 

much  greater  for  these  small  openings  than  would  be  the  case  if  it  were  proportional  to 
the  areas  of  the  cross  sections  of  the  openings. 

4.  Diffusion  of  Dissolved  Substances. — Solute  particles  diffuse  outward  in  the 
solvent,  much  as  do  gas  particles  in  space,  and  tend  to  become  equally  distributed 
throughout  its  volume  Solute  diffusion  does  not  extend  beyond  the  spatial  limits  of 
the  solvent.  Mass  streaming  or  convection  accelerates  or  retards  the  apparent  rate 
of  diffusion,  just  as  is  true  for  gases.  Solute  and  solvent  particles  attract  each  other. 
If  pure  water  is  separated  from  an  aqueous  solution  by  a  septum  permeable  to  both 
solvent  and  solute,  diffusion  of  both  substances  occurs  through  the  septum  and  a 
uniform  solution  on  both  sides  finally  results.  If  the  septum  is  permeable  only  to  the 
solvent  (water),  then  diffusion  takes  place  only  in  the  direction  from  solvent  to  solu- 
tion, and  osmotic  pressure  is  developed  in  the  latter.  This  is  like  gas  pressure  in 
many  respects,  being  proportional  to  the  outward-diffusing  tendency  of  the  solute 
particles.  Salts  dissociate  or  ionize  to  some  extent  in  solution,  and  the  osmotic 
pressure  that  can  be  developed  by  a  given  solution  (its  osmotic  value)  is  nearly 
proportional  to  the  total  number  of  particles  contained  in  a  unit  of  volume;  more 
precisely,  it  is  proportional  to  the  quotient  of  the  number  of  solute  particles  present 
divided  by  the  total  number  of  particles  (solvent  and  solute). 

When  a  septum — such  as  the  outer  surface  of  the  protoplasm  of  a  cell — separates, 
two  different  aqueous  solutions,  each  containing  many  kinds  of  solutes  as  well  as 
water,  the  septum  may  retard  the  diffusion  of  water  or  that  of  any  of  the  solutes,  but 
its  presence  does  not  render  diffusion  any  more  rapid  than  it  would  be  if  the  septum 
were  not  present.     Retardation  may  be  greater  for  some  substances  than  for  others. 

Plasmolysis  is  the  tearing  of  the  protoplasmic  lining  away  from  the  cell  wall, 
frequently  due  to  the  presence  of  more  non-permeating  solute  particles,  per  unit  of 
volume,  on  the  outside  of  the  protoplasmic  periphery  than  on  the  inside.  Turgor 
results  largely  from  the  reverse  condition,  being  generally  due  to  osmotic  pressure 
developed  within  the  cell,  by  solutes  to  which  the  protoplasm  is  impermeable.  This 
results  in  the  protoplasm  being  pushed  outward  against  the  cell  wall,  which  becomes 
stretched. 

5.  Absorption  of  Dissolved  Substances. — Most  dissolved  substances  diffuse 
through  cell  walls  rather  rapidly,  but  the  protoplasm  is  frequently  impermeable  to 
many  solutes  that  are  present  and  it  retards  the  inward  (or  outward)  diffusion  of 
others.  The  permeability  of  the  protoplasm  of  a  cell  to  the  various  solutes  within  and 
without,  alters  from  time  to  time,  according  to  conditions  in  the  surroundings  and 
within  the  cell.  Carbon  dioxide  and  oxygen  (and  other  gases  in  the  air)  pass  into 
solution  in  the  water,  etc.,  of  cell  walls  and  then  diffuse  as  other  dissolved  substances. 
These  materials,  and  also  salts,  etc.,  dissolved  in  the  soil  solution,  diffuse  through  the 
cell  walls  and  protoplasm  of  roots.  (It  appears  that  they  may  also  be  carried  in  by 
mass  streaming  when  the  transpiration  rate  is  high ;  if  this  occurs,  the  peripheral  cells 
of  the  roots  may  act  somewhat  as  filters,  allowing  the  soil  water  and  some  of  its  solutes 
to  enter  with  the  stream  but  causing  other  solutes  to  remain  outside  or  to  enter  more 
slowly  than  do  water  and  the  solutes  that  penetrate  the  membranes  readily.) 

A  solute  may  accumulate  in  the  interior  of  a  living  cell  until  its  concentration  there 
is  higher  than  that  in  the  solution  from  which  it  diffuses.  This  phenomenon  is  some- 
times to  be  explained  on  the  ground  that  the  accumulating  solute  is  chemically  altered 
upon  passing  into  the  cell,  in  which  case  it  only  apparently  surpasses  the  concentration 
of  the  solution  from  which  it  comes.  In  other  cases  the  physical  explanation  is  still 
uncertain.     The  osmotic  value  of  cell  sap  is  generally  between  two  and  six  atmos- 


ABSORPTION    OF    MATERIALS    IN    GENERAL  1 29 

pheres,  but  it  may  be  much  higher,  as  much  as  157  atmospheres  having  been  reported 
for  moulds.  The  actual  osmotic  pressure  in  a  cell  is  generally  much  lower  than  the 
osmotic  value  of  its  sap. 

The  rate  of  diffusion  of  water  and  solutes  through  protoplasm  is  influenced  by 
temperature,  by  the  condition  of  the  protoplasm,  etc.,  as  well  as  by  the  concentration 
difference  (or  gradient)  between  the  interior  and  exterior  of  the  cell.  Carbon  dioxide 
continually  diffuses  out  of  roots  into  the  soil  solution  (excepting  when  the  transpira- 
tion rate  is  so  high  that  the  flow  of  water  into  the  root's  is  more  rapid  than  the  diffusion 
rate  of  carbon  dioxide).  This  substance  (forming  carbonic  acid  when  dissolved  in 
water)  acts  as  a  solvent  on  many  solid  soil  constituents.  Organic  acids  appear  to 
diffuse  out  of  roots  when  the  latter  are  poorly  supplied  with  oxygen,  and  these  acids 
may  have  a  similar  action  on  solid  materials  in  the  soil.  Some  fungi  and  algae 
normally  give  off  organic  acids,  as  do  many  bacteria  also. 


CHAPTER  VI 

MOVEMENT  OF  MATERIALS  IN  THE  PLANT 

§i.  General  Occurrence  of  Movement  of  Materials. — From  previous 
statements  it  is  clear  that  the  essential  materials  are  not  always  directly  ab- 
sorbed by  the  plant  organs  in  which  they  are  ultimately  used.  Organic  materials 
are  produced  from  inorganic  substances  in  the  green  leaf,  but  the  leaf  itself  can 
absorb  only  carbon  dioxide.  The  other  materials  (water  and  mineral  constitu- 
ents) that  are  necessary  in  the  formation  of  organic  compounds  are  absorbed 
by  the  roots,  and  usually  travel  long  distances  before  finally  reaching  the  leaves. 
Similarly,  organic  materials  are  frequently  used  in  large  quantities  in  organs 
where  they  are  not  produced;  for  instance,  in  all  growing  parts  that  lack  chloro- 
phyll. This  is  especially  true  of  organic  materials  that  are  elaborated  from 
inorganic  compounds;  new  kinds  of  organic  substances  may  of  course  be  pro- 
duced in  any  region  of  the  plant,  from  other  organic  substances  that  have  been 
previously  formed  there,  or  that  come  from  elsewhere.  The  organic  substances 
that  are  requisite  for  the  formation  of  new  cells  come  to  these  cells  from 
the  leaves,  and  they  also  frequently  travel  long  distances  before  reaching  the 
point  where  they  are  used,  as  in  the  case  of  growing  root-tips.  It  is  clear, 
therefore,  that  there  is  a  general  movement  of  materials  within  the  plant. 

The  compounds  occurring  in  plants  may  be  in  the  solid  as  well  as  in  the 
liquid  or  gaseous  condition.  Solid  substances,  however,  must  first  pass  into 
solution  before  translocation  can  occur,  since  otherwise  they  cannot  pass 
through  cell  walls.  The  study  of  the  movement  of  materials  in  plants  may, 
accordingly,  be  reduced  to  a  consideration  of  the  movement  of  gases  and 
of  water  and  dissolved  substances. 

§2.  Movement  of  Gases. — Many  air  passages  (intercellular  spaces)  are 
always  present  in  the  cortex  of  stems  and  roots  as  well  as  in  the  parenchymatous 
tissues  of  leaves.  The  lenticels,  small  openings  in  the  bark,  and  the  stomata 
also,  bring  these  passages  into  direct  connection  with  the  external  air,  and  the 
internal  atmosphere  is  thus  always  under  the  same  pressure  as  that  of  the  air 
outside,  while  renewal  of  the  internal  air  may  readily  occur  through  openings 
to  the  outside. 

Gas  exchange  through  the  cortex  of  water  plants  is  greatly  hastened  by 
differential  diffusion  of  air,  which  was  first  observed  in  the  leaves  oiNelumbium 
speciosum.1  The  leaf  of  this  plant  consists  of  a  round  leaf-blade,  from  the 
center  of  the  lower  surface  of  which  the  petiole  projects.     Stomata  occur  only 

1  Barthelemy,  A.,  De  la  respiration  et  de  la  circulation  des  gaz  dans  les  vegetaux.  Ann.  sci.  nat.  Bot.  V . 
19:  131-175.  1874.  [See  also,  for  observations  and  a  better  explanation:  Ohno,  N.,  Ueber  lebhafte 
Gasausscheidung  aus  den  Blattern  von  Nelumbo  nucifera.  Zeitschr.  Bot.  2:  641-664.  1010.  [Rev. 
by  Livingston  in:  Plant  world  14:  7-2-73-     ion) 

130 


MOVEMENT    OF    MATERIALS    IN    THE    PLANT  13I 

on  the  upper  surface.  If  water  happens  to  lie  upon  the  upper  leaf  surface 
gas  bubbles  are  observed  to  be  given  off  rapidly  on  sunny  days,  these  bubbles 
arising  from  the  stomata  and  from  any  chance  openings  in  the  surface  of  the 
petiole.  This  evolution  of  gas  is  so  violent  at  times  that  the  water  appears  to  be 
boiling.  This  phenomenon  is  unrelated  to  life  processes,  since  it  occurs  also  with 
dead  leaves.  A  similar  elimination  of  gas  may  be  artificially  produced  by  a  special 
arrangement.  This  consists  of  a  cylindrical  porous  clay  cell  rilled  with  finely 
powdered  chalk,  or  simply  with  air.  A  glass  tube  is  inserted  through  a  stopper 
closing  the  open  end;  this  tube  corresponds  to  the  petiole  of  the  Nelumbium 
leaf,  while  the  cell  corresponds  to  the  leaf-blade.  The  porous  cell  is  first  dipped 
in  water  and  is  then  supported  obliquely,  the  tube  ending  in  a  vessel  of 
water  below.  When  the  clay  cell  is  heated,  gas  is  given  out  in  large  quantities 
from  the  open  end  of  the  glass  tube.  This  gas  is  air,  practically  saturated  with 
water  vapor.  Frequently  the  volume  of  gas  thus  eliminated  is  as  much  as 
forty  times  as  great  as  that  of  the  cell  itself,  so  that  gas  must  enter  the  cell 
through  the  porous  wall  during  the  experiment.  This  phenomenon  is  caused 
by  unequal  heating,  both  in  the  case  of  the  porous  clay  cell  and  in  that  of  the 
Nelumbium  leaf.a 

The  underground  portions  of  many  plants  growing  in  submerged,  swampy, 
or  poorly  aerated  soils,6  possess  root  outgrowths  that  grow  upward  into  the  air 

0  Ohno  found  the  pressure  under  which  gas  escapes  from  Nelumbo  leaves  to  rise  sometimes 
to  more  than  40  mm.  of  a  mercury  column.  The  explanation  is  somewhat  complicated.  The 
gas  pressure  outside  the  clay  chamber  is  due  to  a  large  partial  pressure  of  oxygen  and  nitrogen 
and  a  very  much  smaller  one  of  water  vapor,  the  magnitude  of  the  latter  depending  upon 
the  humidity  of  the  air.  The  conditions  are  reversed  on  the  inside,  where  the  larger  partial 
pressure  is  due  to  water  vapor  and  that  due  to  the  other  gases  of  the  air  is  smaller.  The  wet 
porous  clay  wall,  being  permeable  to  the  other  gases  as  well  as  water,  movement  takes  place 
in  both  directions;  water  moves  outward  and  evaporates,  and  nitrogen  and  oxygen  diffuse 
inward.  Since  there  is  an  excess  of  liquid  water,  the  partial  pressure  of  water  vapor  on  the 
inside  remains  constant  in  spite  of  the  outward  movement.  Also,  the  water  vapor  that  evap- 
orates from  the  external  surface  of  the  porous  clay  is  quickly  removed  from  the  vicinity  by  air 
currents,  so  that  the  partial  gas  pressure  due  to  water  vapor  on  the  outside  also  remains  nearly 
constant.  The  external  partial  pressure  of  nitrogen  and  oxygen  is  also  constant,  in  spite 
of  the  inward  diffusion,  for  there  is  here  an  excess  of  these  gases  and  the  whole  atmosphere  is 
available.  But,  as  these  gases  diffuse  into  the  chamber  they  raise  the  partial  pressure  of 
non-aqueous  gases  within,  and  so  increase  the  total  gas  pressure  on  the  inside.  Since  the  cham- 
ber opens  to  the  outside  through  the  tube,  this  internal  gas  pressure  can  never  rise  much  above 
what  it  was  at  the  start,  for  bubbles  escape  from  the  open  end  of  the  tube.  The  arrangement  is 
a  sort  of  osmometer,  with  a  concentrated  solution  of  water  vapor  in  the  other  gases  on  the  inside 
and  a  very  dilute  solution  of  the  same  sort  on  the  outside,  the  wet  wall  being  more  permeable 
to  nitrogen  and  oxygen  than  to  water  vapor.  A  relatively  large  amount  of  water  vapor  is 
contained  in  the  gas  that  exudes  from  the  tube.  The  heating  of  the  tube  seems  to  accelerate 
the  process  partly  because  it  tends  to  remove  the  water  vapor  as  it  evaporates  from  the  tube,  so 
as  to  keep  the  external  partial  pressure  of  the  other  air  gases  near  its  original  high  value.  It 
thus  acts  like  a  stirrer  in  an  osmometer  cell,  which  keeps  the  internal  solution  from  becoming 
too  much  diluted  next  to  the  membrane.  Also,  at  higher  temperature  the  vapor  pressure  of 
water  inside  the  chamber  is  higher. — Ed. 

b  These  structures  (called  "knees")  are  characteristic  of  Taxodium  distichum  (bald  cypress), 
of  the  swamps  of  the  southeastern  United  States.  For  an  excellent  photograph  showing  these 
see:  Schimper-Fisher,  1903.     [See  note  k,  p.  ior.]     Fig.  48,  facing  p.  74. — Ed. 


132 


PHYSIOLOGY    OF    NUTRITION 


(Fig.  74).  The  tips  of  these  are  composed  of  spongy  tissue  and  readily  allow 
the  entrance  of  air.  These  outgrowths  are  like  ventilation  pipes  in  that  they 
promote  the  movement  of  air  to  the  roots  below.  The  air  spaces  of  the  cortex 
are  thus  always  directly  or  indirectly  in  communication  with  the  external 
atmosphere.1 

The  central  woody  cylinder  of  the  stem  also  contains  air.  HohnePs2  ex- 
periments indicate  that  the  air  in  the  wood  and  that  in  the  cortex  are  not  at  all 
continuous.  In  these  experiments  (Fig.  75)  a  leaf  is  fastened,  by  means  of  a 
rubber  stopper,  in  a  wide-mouth  bottle  (g),  which  has  a  lateral  opening  below, 
the  latter  fitted  with  a  tube  and  funnel  (/)  through  which  mercury  is  introduced. 
The  air  in  the  cylinder,  compressed  by  the  mercury,  is  forced  through  the  sus- 
pended leaf  and  rises  in  bubbles  through  the  water  in  the  glass  vessel  above  (/). 


Fig.    74. — Part  of   stem  of  Jussicea  repens,    with 
ventilation  roots  (w);  surface  of  water,  O. 


Fig.    75. — Hohnel's   apparatus. 
Pfeffer.) 


(After 


Microscopic  study  shows  that  bubbles  are  extruded  only  from  the  cortex,  not 
from  the  central  cylinder.  Air  enters  the  leaf  through  the  stomata  and  air 
spaces  of  the  leaf  cortex  and  is  given  out  from  the  cortical  region  of  the  stem, 
without  entering  the  wood.  The  aeration  system  of  the  wood  is  a  closed 
system  and  does  not  communicate  at  all  with  that  of  the  cortex. 

Hbhnel  demonstrated  the  existence  of  negative  gas  pressure  in  the  wood  of 
stems.  If  a  twig,  or  the  petiole  of  a  leaf,  is  cut  under  mercury  on  a  sunny  day 
in  summer,  mercury  rises  very  rapidly  through  the  cut  surface  into  the  vessels 
(Fig.  76),  which  then  appear  gray  in  cross-section,  from  the  presence  of  the 


1  Goebel,  K.,  Ueber  die  Luftwurzeln  von  Sonneratia.  Ber.  Deutsch.  Bot.  Ges.  4:  240-255.  1886. 
Jost,  Ludwig,  Ein  Beitrag  zur  Kenntniss  der  Athmungsorgane  der  Pflanzen.  Bot.  Zeitg.  45 :  601-606, 
617-627,  633-642.     1887. 

*  Hohnel,  Franz  Xavier  R.  von,  Einige  anatomisehe  Bemerkungen  uber  das  raumliche  Verhaltniss  der 
Intercellularraume  zu  den  Gefassen.  Bot.  Zeitg.  37:  541-545.  1879.  Idem,  Beitrage  zur  Kenntniss  der 
Luft-  und  Saftbewegung  in  der  Pflanze.     Jahrb.  wiss.  Bot.  12:  47-131.     1870-1881. 


MOVEMENT    OF    MATERIALS    IN    THE    PLANT 


133 


metal.  Occasionally  vessels  may  thus  be  injected  with  mercury  for  a  distance 
of  from  50  to  60  cm.  above  the  cut  surface.  Experiments  of  this  kind  show  that 
the  attenuation  of  the  air  in  the  vessels  may  be  very  considerable.  Negative 
pressure  in  wood  may  be  demonstrated  in  still  another  way.  A  leafy  branch 
with  two  or  more  twigs  (Fig.  77)  is  placed  with  its  cut  end  in  water.  One  of 
the  twigs  is  cut  off  and  the  cut  end  (b)  is  connected  with  rubber  tubing  to  a  glass 
tube  (a),  the  lower  end  of  which  dips  into  mercury.  After  some  time  the  mer- 
cury rises  in  the  tube  indicating  that  the  air  in  the  wood  is  rarefied.  The  air 
of  the  stem  is  most  attenuated  when  the  activity  of  the  plant  is  greatest.0  As 
will  be  seen  later,  this  phenomenon  of  negative  gas  pressure  bears  an  important 
relation  to  the  movement  of  water  in  the  stem. 


Fig.  76. — The  cutting  of  a  stem  under  mercury 


§3.  Movement  of  Water  and  Dissolved  Substances.— The  first  experiments 
upon  the  movement  of  water  and  solutes  in  plants  were  carried  out  by  Malpighi 
in  1 67 1.  He  removed  a  ring  of  bark  from  a  woody  stem  and  found  that  the 
region  above  the  wound  continued  alive  and  grew  even  more  rapidly  than  be- 
fore, producing  an  annular  swelling  (Fig.  78),  while  the  region  below  the  wound 
failed  to  develop  further.  The  girdling  operation  is  thus  seen  to  have  no  effect 
at  all  upon  the  movement  of  water  from  the  soil  into  the  upper  portion  of  the 
plant,  although  it  stops  the  movement  of  organic  materials  into  the  lower 
regions.  Malpighi  concluded  from  this  experiment  that  the  soil  solution  moves 
upward  through  the  wood,  while  the  organic  substances  produced  in  the  leaves 
pass  downward  through  the  cortex.  The  movement  of  water  is  sometimes 
spoken  of  as  the  ascending  current,  and  that  of  organic  (or  plastic)  substances 
as  the  descending  current.  The  expressions  ascending  and  descending  are  not 
to  be  interpreted  literally,  however;  in  the  drooping  branches  of  the  weeping 
willow,  for  example,  the  ascending  stream  descends  and  the  descending  one 

cThe  phenomenon  is  mainly  dependent  upon  the  rate  of  loss  of  water  by  transpiration 
from  the  leaves  and  upon  the  rate  at  which  water  reaches  the  leaves  from  below.  The  word 
activity,  as  used  in  the  text,  is  rather  indefinite,  but  it  may  be  taken  to  refer  to  conditions 
promoting  high  transpiration  rates. — Ed. 


134 


PHYSIOLOGY    OF    NUTRITION 


ascends.  If  a  ring  of  bark  is  removed  from  a  drooping  branch  of  this  willow, 
the  swelling  develops  not  above  but  below  the  wound. 

§4.  The  Transpiration  Stream. — The  upward  movement  of  the  soil  solution 
in  the  plant  depends  upon  a  large  number  of  conditions.  Water  can  enter  the 
plant  only  if  a  part  of  the  water  already  present  be  lost.d  Water  is  removed 
from  the  plant  by  evaporation  from  the  leaves,  the  process  being  called  trans- 
piration, and  this  is  the  main  condition  determining  the  movement  of  water. 

(a)  Transpiration.e — Transpiration  may  be  studied  in  a  number  of  ways, 
some  of  which  will  now  receive  attention. 


»-JP 


Fig.  77. — Apparatus  for  showing  negative  gas 
pressure  in  wood.      {After  Pfeffer.) 


Fig.      78. — Malpighi's     girdling     experi- 
ment; the  twig  is  immersed  in  water  to   the 

line  h. 


i.  The  quantity  of  water  transpired  may  be  found  by  determining  the  loss  in 
weight  of  the  plant  and  its  container.  The  pot  in  which  the  plant  is  rooted  is 
hermetically  sealed  in  a  sheet-metal  container.  The  seal  (which  may  be  of 
plastiline  or  of  a  mixture  of  paraffine  and  petrolatum,  etc.)  should  have  three 

d  While  this  is  the  main  consideration,  it  may  be  remembered  that  enlargement  alone,  with- 
out any  loss  of  water,  must  necessitate  water  entrance  into  the  enlarging  cells.  Also,  water  may 
be  removed  from  a  cell  and  still  not  pass  out  of  it,  as  when  it  becomes  chemically  combined 
within  (formation  of  carbohydrate  from  water  and  carbon  dioxide,  formation  of  glucose  from 
starch,  etc.). — Ed. 

e  For  an  excellent  review  of  the  literature  of  transpiration,  see:  Burgerstein,  A.,  Die 
Transpiration  der  Pflanzen.  Jena,  1904.  Also:  Zweiter  Teil  (Erganzungsband).  Jena, 
1920. — Ed. 


MOVEMENT    OF    MATERIALS    IN    THE    PLANT 


135 


openings,  through  one  of  which  the  stem  of  the  plant  projects.  The  second 
opening  is  usually  closed  and  bears  a  tube  through  which  water  may  be  added 
to  the  pot,  and  the  third  bears  a  small  glass  tube  drawn  to  a  fine,  open  point 
above.  Through  the  capillary  opening  of  this  tube  the  air  in  the  apparatus 
remains  in  equilibriuin  with  that  of  the  external  atmosphere.  The  loss  in  weight 
of  the  apparatus  is  due  almost  entirely  to  the  loss  of  water  from  the  plant  by 
evaporation.1  A  tall  cylindrical  vessel  of  water  may  be  used  for  small  plants  in 
experiments  of  short  duration.  The  plants  are  fastened,  by. means  of  silk- 
wrapped  wire,  with  their  roots  in  the  water  and  their  green  parts  projecting  into 
the  air,  a  thin  layer  of  oil  being  placed  over  the  water  surface  to  prevent  evapora- 
tion/    The  loss  in  weight  of  the  apparatus,  in  this  case  also,  is  due  almost 


Fig.  70. — Kohl's  apparatus  for  the  study  of  plant  transpiration. 


wholly  to  evaporation  of  water  from  the  plant.2 

2.  The  amount  of  water  absorbed  by  the  plant  may  be  measured,  Kohl's3 

1  Hales,  Stephen,  Vegetable  Staticks.     London,  1727. 

-  Wiesner,  Julius,  Untersuchungen  iiber  den  Einfluss  des  Lichtes  und  der  strahlenden  Warme  auf  die 
Transspiration  der  Pflanze.     Sitzungsber.  (math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien  741 :  477-531-     1877. 

3  Kohl,  F.  G.,  Die  Transpiration  der  Pflanzen  and  ihre  Einwirkung  auf  die  Ausbildung  pflanzlicher 
Gewebe.     Braunschweig,      1886. 

*  Oil  is  apt  to  penetrate  into  the  stem,  and  the  wax  seal  is  muck  to  be  preferred.  For  a 
short  distance  above  and  below  the  water  surface,  the  stem  may  be  covered  with  some  material 
(as  plastiline,  chicle — the  base  of  the  common  chewing-gum  of  the  American  market — etc.) 
that  does  not  absorb  water  and  prevents  the  oil  from  coming  into  contact  with  the  plant,  in 
which  case  the  oil-seal  method  may  be  satisfactory.  Some  of  the  plastilineon  the  American 
market  is  unsuitable,  however,  for  it  injures  some  plants. — Ed. 


136  PHYSIOLOGY    OF    NUTRITION 

apparatus,  shown  in  Fig.  79,  being  well  suited  to  such  studies.  The  roots  of 
the  plant,  together  with  a  thermometer,  are  placed  in  a  tube  of  water  (r),  which 
communicates  below  with  a  long  capillary  glass  tube  and  also  with  a  rubber 
tube  closed  with  a  glass  plug  (gl).  As  transpiration  proceeds,  the  water  menis- 
cus advances  along  the  capillary  tube.  To  refill  the  latter,  the  glass  plug  is 
simply  inserted  somewhat  farther  into  the  rubber  tube.  By  placing  a  bell-jar 
over  the  plant  the  atmosphere  surrounding  the  latter  may  be  kept  either  moist 
or  dry.  To  keep  it  moist  a  sponge  saturated  with  water  may  be  placed  under  the 
bell-jar,  the  walls  of  which  may  also  be  moistened.  To  keep  the  atmosphere 
dry,  air  may  be  drawn  by  an  aspirator  through  a  series  of  wash  bottles  filled 
with  concentrated  sulphuric  acid  or  with  pieces  of  pumice  saturated  with  this 
acid.  The  plant  may  be  kept  in  darkness  by  covering  the  bell-jar  with  an 
opaque  paper  cylinder. 

3.  Finally,  the  amount  of  liquid  water  absorbed  and  the  amount  of  water 
vapor  lost  at  the  same  time  may  be  determined.  In  this  connection,  Vesque's1 
apparatus  may  be  used,  which  consists  of  a  U-shaped  tube,  one  arm  of  which  is 
broad  and  the  other  narrow.  This  is  filled  with  water  and  the  roots  of  the  plant 
are  placed  in  the  broad  arm  with  a  tightly  fitting  stopper  about  the  stem.  Loss 
in  weight  of  the  entire  apparatus  gives  the  quantity  of  water  evaporated, 
while  the  depression  of  the  water  in  the  narrow  arm  indicates  the  amount  of 
water  absorbed  by  the  plant." 

In  addition  to  the  apparatus  already  described,  cobalt  paper  was  employed 
by  Stahl2  to  study  transpiration.  Swedish  filter  paper  is  dipped  in  a  5-per  cent. 
solution3  of  cobalt  chloride,  and  is  then  dried  in  the  sun  or  in  an  oven.  It 
should  be  stored  in  a  dry  place.  This  paper  is  intensely  blue  when  dry  but  the 
color  changes  to  a  bright  pink  as  water  is  absorbed.  The  paper  is  placed  upon 
the  leaf  surface  that  is  to  be  studied,  and  is  covered  with  a  small  glass  or  mica 
plate.  For  example,  a  slip  of  dry  cobalt  paper,  placed  against  the  lower  sur- 
face of  a  leaf  with  stomata  on  this  side  only,  turns  pink  in  a  few  seconds  on  a 
sunny  day,  but  may  remain  blue  for  several  hours  when  placed  against  the  upper 
leaf  surface,  where  stomata  are  lacking.  This  experiment  shows  clearly  the 
influence  of  stomata  upon  transpiration.* 

1  Vesque,  Julien,  L'Absorption  comparee  directement  a.  la  transpiration.  Ann.  sci.  nat.  Bot.  VI,  6  : 
201-222.     1877. 

2  Stahl,  1894.     [See  note  1,  p.  36.] 

3  Weaker  solutions  (1-  or  2-per  cent.)  are  more  suitable  in  delicate  tests,  where  the  differences  in  trans- 
piration are  small. 

0  It  is  not  strictly  true  that  loss  of  weight  in  these  experiments  is  to  be  interpreted 
solely  as  loss  of  water,  though  other  losses  are  generally  negligible.  Perhaps  the  only  case 
where  significant  errors  may  be  involved  on  account  of  this  assumption  is  that  in  which 
leaves,  etc.,  fall  from  the  plant  during  an  experiment.  For  a  complete  picture  of  the 
meaning  of  loss  of  weight,  however,  aside  from  such  obvious  accidents  as  the  fall  of  leaves, 
it  should  be  remembered  that  carbon  dioxide  and  oxygen  leave  the  plant  in  the  same  way 
as  does  water  vapor,  that  absorption  of  these  two  gases  also  occurs,  and  that  many  vola- 
tile oils,  etc.,  also  evaporate  into  the  air  to  some  extent. — Ed. 

h  The  cobalt-chloride  method  really  furnishes  a  means  for  measuring  only  the  power  of  the 
leaf  to  retard  water  loss  by  transpiration,  the  transpiration  rate  itself  depending  upon  the 
evaporating  power  of  the  air  and  upon  the  intensity  of  absorbed  radiant  energy  as  well  as 
upon  this  power.     On  various  improvements  upon  Stahl 's  method  and  upon  the  transpiring 


MOVEMENT    OF    MATERIALS    IN    THE    PLANT 


137 


The  amount  of  water  lost  from  plants  by  evaporation  is  very  large;  in 
Wiesner's  experiments,  for  instance,  three  maize  seedlings  weighing  1.6  g.  lost 
0.198  g.  of  water  during  a  single  hour  in  sunlight.  Wollny1  measured  the 
amount  of  water  lost  by  evaporation  from  several  plants  during  their  entire 
vegetative  period  and  also  determined  the  dry  weights  of  the  harvested  plants 
and  the  amounts  of  water  evaporated  for  each  gram  of  dry  material  for  the 
entire  period  of  growth.*     These  values,  in  grams,  appear  in  the  table  below. 


Kind 

Loss  from  Plants  and  Soil  Together 

Total  Loss  For 
Whole  Period 

Plant  Loss, 

OF 

Plant 

June 

July 

Aug. 

Sept. 

Oct. 

Total 

From 
Soil 

From 

Plants 

per  Gram  of 
Dry  Weight 

Maize 

Oats 

Pea 

647 
482 
773 

3"3 
2095 

978 

576i 

2733 
917 

2754 

2008 

941 

801 

12,275 
7,3i8 
4,410 

1063 
178 
234 

11. 212 

7,140 
4,176 

grams 

233 
665 
416 

Although  plants  evaporate  large  amounts  of  water,  as  is  evident  from 
the  data  just  given,  the  amount  of  water  lost  from  a  certain  area  of  leaf  is  con- 
siderably less  than  that  lost  from  an  equal  area  of  a  free  water  surface.  Ac- 
cording to  Hartig,  1  sq.  m.  of  free  water  surface  lost  2000  cc.  of  water  in 
twenty-four  hours,  while  an  equal  area  of  beech  leaves  lost  only  210  cc.1' 

power  of  leaves,  see:  Livingston,  B.  E.,  The  resistance  offered  by  leaves  to  transpirational 
water  loss.  Plant  world  16  :  1-35.  1913.  Bakke,  A.  L.,  Studies  on  the  transpiring  power  of 
plants  as  indicated  by  the  method  of  standardized  hygrometric  paper.  Jour.  ecol.  2  :  145- 
173.  1914.  Livingston,  B.  E.,  and  Shreve,  Edith  B.,  Improvements  in  the  method  for 
determining  the  transpiring  power  of  plant  surfaces  by  hygrometric  paper.  Plant  world  19  : 
287-309.     1 91 6. — Ed. 

1  Sachsse,  Robert,  Lehrbuch  der  Agriculturchemie.  Leipzig,  1888.  P.  423.  [Whollny,  E.,  Der  Einfluss 
der  Pflanzendecke  und  der  Beschattung  auf  die  physikalischen  Eigenschaften  und  die  Fruchtbarkeit  des 
Bodens.     197  p.  Berlin,  1877.     P.  126.] 

*  This  ratio  has  been  called  the  water  requirement.  For  an  excellent  review  of  the  literature 
of  this  subject  see:  Briggs,  L.  J.,  and  Shantz,  H.  L.,  The  water  requirement  of  plants.  II.  A 
review  of  the  literature.     U.  S.  Dept.  Agric,  Bur.  Plant  Ind.,  Bull.  285.     1913. — Ed. 

'  Such  comparisons  are  without  very  much  significance  unless  the  two  surfaces  that  are  com- 
pared have  the  same  shape  and  the  same  exposure.  In  such  studies  as  that  here  referred  to  it 
has  frequently  been  the  practice  to  compare  evaporation  rates  from  circular,  horizontally 
exposed,  free  water  surfaces  with  the  corresponding  rates  of  transpiration  from  an  equivalent 
area  of  plant  leaves.  The  form  and  exposure  of  the  latter  surface  is  generally  exceedingly  com- 
plex, while  these  characters  of  the  water  surface  are  relatively  simple,  and  no  very  useful  com- 
parison is  possible  by  such  methods.  The  evaporating  surface  of  the  physical  apparatus  must 
resemble  the  plant  surface,  in  form,  size,  color,  etc.,  as  nearly  as  is  practicable.  In  this  connec- 
tion, see  Renner,  O.,  Experimentelle  Beitrage  zud  Kenntnisder  Wasserbewegung.  Flora  103  : 
171-247.  1911.  Idem,  Zur  Physik  der  Transpiration.  Ber.  Deutsch.  Bot.  Ges.  29  :  125-132. 
1911.  Idem,  Zur  Physik  der  Transpiration  II.  Ibid.  30:  572-575.  1912.  Perhaps  the 
Livingston  spherical  porous-cup  atmometer  furnishes  the  best  evaporating  surface  for  com- 
parison with  plants  in  general,  but  for  detailed  study  a  special  atmometer  constructed  after  the 
pattern  of  the  particular  plant  used  should  be  employed.  On  the  porous-cup  atmometer 
see:  Livingston,  B.  E.,  Atmometry  and  the  porous-cup  atmometer.  Plant  world  18  :  21-30, 
51-74,  95-111,  143-149.  1915.  Livingston,  B.  E.  and  Thone,  Frank,  A  simple  non-absorb- 
ing mounting  for  porous  porcelain  atmometers.     Science,  n.  s.  52:  85-86.  1920. — Ed. 


138  PHYSIOLOGY    OF    NUTRITION 

Leaves  removed  from  the  plant  lose  much  more  water  than  those  still 
attached  to  the  plant.  Krutizky1  found  that  a  single  leaf  of  Cyssus  antarcticus 
lost  10.6  cc.  of  water  in  one  day,  while  a  branch  of  the  same  plant  with  six 
leaves,  lost  only  10.8  cc.  Results  obtained  from  studies  with  cut  leaves  are  thus 
not  to  be  applied  directly  to  entire  plants. 

After  the  foregoing  introductory  remarks,  the  influence  of  external  conditions 
upon  the  rate  of  transpiration  will  now  be  considered. 

Light  exerts  a  pronounced  influence  upon  the  amount  of  water  evaporated.2 
For  instance,  three  maize  seedlings  weighing  1.6  g.  transpired  in  one  day,  198 
mg.  in  sunlight,  68  mg.  in  diffuse  light  and  27  mg.  in  darkness.  Plants  trans- 
pire much  more  actively  in  light  than  in  darkness.  If  they  are  transferred 
from  darkness  to  light,  or  the  reverse,  the  rate  of  transpiration  is  not  suddenly 
increased  or  decreased,  but  the  change  in  rate  takes  place  gradually. 

The  daily  periodicity  of  transpiration  also  depends  upon  light.3  The  amount 
of  water  absorbed  during  the  whole  period  of  twenty-four  hours  is  practically 
equal  to  that  lost  by  transpiration  in  the  same  period,  but  there  is  no  such  agree- 
ment between  the  rates  of  absorption  and  transpiration  for  the  various  hours  of 
the  day;  plants  are  generally  nearly  saturated  with  water  at  night  but  during  the 
day  there  is  a  saturation  deficit/" 

All  rays  of  the  spectrum  are  not  equally  effective  in  promoting  transpiration 
from  green  plants,  the  maximum  effect  is  produced  in  the  blue  and  violet  regions. 
The  red  rays  between  the  Fraunhofer  lines  B  and  C  are  next,  in  order  of  their 
influence.  The  same  wave-lengths  of  light  that  are  most  absorbed  by  chloro- 
phyll are  thus  also  most  effective  in  promoting  transpiration. 

Of  all  the  external  factors  influencing  transpiration,  light  is  undoubtedly  the 
most  important.  The  question  arises  as  to  how  much  light  is  used  in  this  proc- 
ess. An  experiment4  showed  that  sunflower  leaves  transpired  on  a  sunny 
day  275  cc.  per  square  meter  of  leaf  surface  per  hour.  To  evaporate  this 
amount  of  water  requires  166,800  gram-calories  of  heat  per  hour.  This  leaf  area 
received  600,000  calories  per  hour,  so  that  it  appears  that  27.5  per  cent,  of  the 
total  amount  of  radiant  energy  received  was  used  up  in  transpiration;  as  will  be 
remembered,  only  about  0.5  per  cent,  is  used  up  in  the  assimilation  of  carbon. 

1  Famintsyn,  A.,  Exchange  of  materials  and  transformation  of  energy  in  plants.  [Russian.]  Zapiski 
Akad.  Sci.  St.  Petersburg  46,  Appendix,     xvi  +  816  p.     1883. 

2  Baranetsky,  J.,  Ueber  den  Einfluss  einiger  Bedingungen  auf  die  Transpiration  der  Pflanzen.  Bot.  Zeitg. 
30:  65-73,  8ib-8ob,  97-109.  1872.  Wiesner,  1877.  [See  note  2,  p.  135-]  Kohl,  1886.  [See  note  3. 
P.  135] 

3Eberdt,  O.,  Die  Transpiration  der  Pflazen  und  ihre  Abhangigkeit  von  ausseren  Bedingungen.  Mar- 
burg, 1889. 

4  Brown  and  Escombe,  1900.     [See  note  1,  p.  34.] 

*  Renner,  O.,  Beitrage  zur  Physik  der  Transpiration.  Flora  100  :  451-547.  1910.  Idem 
Versuche  zur  Mechanik  der  Wasserversorgung.  1.  Der  Druck  in  den  Leitungsbahnen  von 
Freilandpflanzen.  Ber.  Deutsch.  Bot.  Ges.  30:  576-580.  1912.  Idem,  same  title.  2. 
Ueber  Wurzeltatigkeit.  Ibid.  30:  642-648.  191 2.  Livingston,  B.  E.,  and  Brown,  W.  H., 
Relation  of  the  daily  march  of  transpiration  to  variations  in  the  water  content  of  foliage  leaves. 
Bot.  gaz.  53  :  309-330.  191 2.  Lloyd,  F.  E.,  Leaf  water  and  stomatal  movement  in  Gossy- 
pium  and  a  method  of  direct  visual  observation  of  stomata  in  situ.  Bull.  Torrey  Bot.  Club. 
40:  1-26.  1913.  Shreve,  Edith  B.,  The  daily  march  of  transpiration  in  a  desert  perennial. 
Carnegie  Inst.  Wash.  Pub.  194.     1914. — Ed. 


MOVEMENT  OF  MATERIALS  IN  THE  PLANT  139 

Although  leaves  removed  from  the  plant  evaporate  much  more  water  than  do 
apparently  similar  attached  leaves,  nevertheless  this  experiment  shows  that  con- 
siderably more  solar  energy  disappears  in  the  process  of  transpiration  than  in 
the  decomposition  of  carbon  dioxide. 

The  humidity  of  the  surrounding  air  is  a  second  condition  markedly  influenc- 
ing the  rate  of  transpiration.  The  less  water  vapor  the  air  contains,  the  more 
rapid  is  transpiration,  and  the  transpiration  rate  decreases  as  the  water-vapor 
content  of  the  air  increases. l 

Temperature  also  influences  transpiration,  but  the  relation  here  is  compli- 
cated by  the  fact  that  life-processes  in  general  are  greatly  affected  by  tempera- 
ture. 

Movement  of  the  air  also  increases  transpiration.  Finally,  the  chemical 
properties  of  the  soil  exert  a  marked  influence  upon  the  amount  of  water  evapo- 
rated from  leaves.  Experiments  with  water  cultures  show  that  transpiration 
is  controlled  both  by  the  concentration  of  the  solution  and  by  the  presence  or 
absence  of  certain  substances.  Thus,  acids  may  accelerate,  while  alkalies  may 
retard  transpiration.  Addition  of  a  small  amount  of  some  salt  to  distilled 
water  in  which  plants  are  rooted  produces  an  increased  rate  of  transpiration, 
but  addition  of  larger  amounts  causes  a  gradual  decrease  in  the  rate.  The 
transpiration  of  plants  grown  in  solution  containing  the  essential  mineral 
elements  becomes  less  as  the  concentration  of  the  solution  is  increased.'" 

Besides  the  external  factors  mentioned  above,  there  are  also  internal  condi- 
tions that  control  transpiration,  these  being  related  to  the  organization  of  the 
plant.  First,  the  age  of  the  plant  is  important.  During  the  period  of  greatest 
activity  of  the  leaf,  while  it  is  still  growing,  the  rate  of  transpiration  is  highest. 
The  reason  for  this  is  that  the  epidermis  of  young  leaves  is  very  permeable  to 
water;  transpiration  decreases  later,  but  a  second  maximum  is  reached  when  the 
stomata  begin  to  function.  Thereafter  the  rate  of  transpiration  gradually 
decreases  as  the  epidermis  hardens,  in  spite  of  the  influence  of  the  stomata. 

The  rate  of  transpirational  water  loss  from  leaves  is  also  correlated  with 
the  form  and  character  of  their  anatomical  structures  (e.g.,  number  of  stomata, 
thickness  or  permeability  of  the  epidermis,  etc.).  A  discussion  of  the  resistance 
offered  by  plants  to  transpiration  will  be  presented  later,  in  Part  II,  Chapter  III. 

Liquid  water,  as  well  as  water  vapor,  is  given  out  from  many  plants,  through 
hydathodes.'1     The  exudation  of  liquid  water  may  partly  replace  transpiration, 

1  The  best  study  of  the  influence  of  air  humidity  as  such  is:  Darwin,  F.,  On  a  method  of 
studying  transpiration.  Proc.  Roy.  Soc.  London  B87  :  269-280.  1914.  Reviewed  by  Liv- 
ingston in:  Plant  world  17:   216-219.     1914. — Ed. 

m  On  the  influence  of  chemicals  upon  transpiration  see:  Reed,  Howard  S.,  The  effect  of 
certain  chemical  agents  upon  the  transpiration  and  growth  of  wheat  seedlings.  Bot.  gaz.  49  : 
81-109.  1910.  On  the  influence  of  the  osmotic  concentration  of  the  medium  see:  Briggs  and 
Shantz,  1913  [see  note  i,  p.  137];  Tottingham,  1914,  [see  note  d,  p.  84];  Shive,  1915,  2  [see 
note  a,  p.  83];  Trelease,  1920,  [see  note  c,  p.  86]. — Ed. 

"  Moll,  J.  W.,  Ueber  Tropfenausscheidung  und  Injection  bei  Blattern.  Bot.  Zeitg.  38 : 
49-54.  1S80.  Idem,  Untersuchungen  liber  Tropfenausscheidung  und  Injection  von  Blat- 
tern.    Verslag.  en  Meded.     K.  Akad.  Wettensch.  Naturk.  Amsterdam  2  R.,  15:  237-337. 


140 


PHYSIOLOGY    OF    NUTRITION 


occurring  mostly  when  transpiration  is  retarded  for  some  reason,  as  for  example, 
in  the  case  of  the  Aroidea?  and  other  plants  living  in  moist  places  (Fig.  80) ." 

(b)  Exudation  Pressure; — The  second  condition  determining  the  movement 
of  water  in  stems  is  the  so-called  root  pressure,  sap  pressure,  or  exudation  pres- 
sure, which  produces  bleeding.  This  phenomenon  was  first  investigated  bv 
Hales.1  If  a  branch  is  cut  from  a  grapevine  in  the  spring,  before  the  buds  open,  a 
watery  fluid  is  extruded  from  the  wound.  Hales  bound  a  piece  of  animal  bladder 
over  the  cut  end  and  found  that  the  sap  was  excreted  with  such  force  that  the 
bladder  was  much  swollen  at  first  and  was  finally  broken.  To  measure  the  force 
with  which  the  sap  was  extruded,  Hales  connected  the  cut  end  of  a  branch  with 


Fig.  80. — Guttation  from  hydathodes 
at  the  edge  of  a  leaf  of  Impatiens  sultani. 
(After  Pfeffer.) 


Fig.   81. — Arrangement  for  measuring  exu- 
dation pressure.      (After  Pfeffer.) 


1880.  Volkens,  G.,  Ueber  Wasserausscheidung  in  liquider  Form  an  den  Blattern  hoherer 
Pflanzen.  Jahrb.  K.  Bot.  Gart.  u.  Bot.  Mus.  Berlin  2 :  166-209.  1883.  Gardiner,  Walter, 
On  the  physiological  significance  of  waterglands  and  nectaries.  Proc.  Cambridge  Phil. 
Soc  5:  35-50.  1883.  Wieler,  A.,  Das  Bluten  der  Pflanzen.  Cohn's  Beitrage  zur  Biol.  d. 
Pflanzen  6:  1-211.  1893.  Haberlandt,  G.,  Anatomisch-physiologische  Untersuchungen 
iiber  das  tropische  Laubblatt.  II.  Ueber  wassersecernirende  und-absorbirende  Organe.  (I. 
Abhandlung.)  Sitzungsber.  (math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien  I03r.  489-538. 
1894.  Idem,  same  title  (II.  Abhandlung.)  Ibid.  1 04/:  55-116.  1895.  Idem,  Zur  Kenntniss 
der  Hydathoden.  Jahrb.  wiss.  Bot.  30  :  511-528.  1897. — Ed. 
"Hales,  1735-     [See  note  i,  p.  135.] 

0  Guttation,  as  Burgerstein  terms  this  excretion  of  liquid  water  [see  note  e,  p.  134],  may  be  in- 
duced in  many  plants  by  injecting  the  cut  stem  or  petiole  with  water  under  pressure.  A  simple 
way  is  to  attach  a  cut  branch,  by  a  rubber  tube  (properly  reinforced  with  cloth  wrapping),  to 
the  water-tap,  having  first  filled  the  tube  with  water,  and  then  to  open  the  tap.  Fuchsia, 
.Impatiens  sultani,  and  Tropaolum  majus  (garden  nasturtium)  serve  very  well.  This  phe- 
nomenon was  first  described  by  deBary  (Bot.  Zeitg.  27:  883.  1869).  See  also,  for  another 
early  description:  Prantl,  K.,  Die  Ergebnisse  der  neueren  Untersuchungen  iiber  die  Spal- 
toffnungen.     Flora  55:  305-312,  321-328,  337-346,  369-382.     1872.— Ed. 


MOVEMENT  OF  MATERIALS  IN  THE  PLANT  1 4 1 

a  mercury  manometer  (Fig.  81).  The  mercury  is  forced  up  in  the  free  arm  of 
the  tube  by  the  pressure  of  the  exuding  sap,  attaining  a  height,  in  one  of  Hales' 
experiments,  of  103  cm.  or  about  1.5  atmospheres.  Instead  of  removing  a 
branch,  an  incision  may  be  made  in  the  stem.  Bleeding  is  characteristic  of 
many  woody  plants  in  the  spring;  this  is  called  spring  bleeding,  since  it  occurs 
only  in  the  spring  before  the  leaves  expand.  After  the  leaves  expand  an  incision 
in  the  stem  or  the  removal  of  a  branch  usually  fails  to  produce  bleeding;  water 
is  then  being  lost  from  the  leaves  by  transpiration.  Under  these  conditions 
bleeding  may  be  induced  at  the  surface  of  the  stump  of  a  cut  stem,  the  leafy 
portion  having  been  entirely  removed.  Bleeding  may  be  demonstrated  in 
this  way  throughout  the  entire  vegetative  period,  in  both  woody  and  herbaceous 
plants,  but  the  same  plant  may  not  show  it  at  all  times  during  its  period. 

To  measure  the  force  with  which  sap  is  extruded,  a  mercury  manometer 
is  connected  to  the  cut  stump  of  the  plant.  To  measure  the  amount  of  liquid  ex- 
creted the  manometer  may  be  replaced  by  a  glass  tube  connecting  with  a 
graduate.  The  recording  apparatus  of  Baranetskii  serves  the  same  purpose. 
Here  the  liquid  flows  into  a  U-shaped  tube,  lifting  a  float  in  the  free  arm.  The 
float  is  fastened  to  one  end  of  a  silk  thread  that  passes  over  a  pulley,  and  a 
pointer  attached  to  the  other  end  of  the  thread  traces  a  curve  on  a  smoked,  rotat- 
ing drum.  In  another  apparatus  constructed  by  Baranetskii,  the  excreted 
liquid  is  caught  in  separate  tubes,  each  tube  remaining  beneath  the  outlet  tube 
from  the  plant  for  a  single  hour.  The  tubes  are  arranged  on  the  rim  of  a  wooden 
disk  with  vertical  axis,  and  this  is  rotated,  by  clockwork,  just  far  enough  every 
hour  to  place  a  fresh  tube  under  the  outlet. 

Exudation  pressure,  as  indicated  by  the  height  of  a  mercury  column,  varies 
in  different  plants,  being  less  in  herbaceous  than  in  woody  forms.  Thus,  in 
Hofmeister's1  experiments  the  height  attained  by  the  mercury  column  was 
66  mm.  with  Atriplex  hortensis,  and  461  mm.  with  Digitalis  media. 

The  amount  of  sap  excreted  by  herbaceous  plants  greatly  exceeds  the  total 
volume  of  their  roots.  Much  of  the  excreted  liquid  must  therefore  enter  the 
roots  after  the  cut  is  made.  A  plant  of  Urtica  urens  excreted  3025  cc.  of  sap, 
and  the  total  volume  of  its  root  system  proved  to  be  only  1350  cc.  Similarly, 
the  root  volume  of  a  plant  of  Helianthus  animus  was  only  3370  cc,  and  yet 
this  plant  excreted  from  its  cut  stump  5830  cc.  of  liquid. p 

There  is  a  daily  periodicity  in  the  rate  of  bleeding2  and  this  has  no  relation 
to  temperature.  The  time  of  occurrence  of  the  maximum  and  of  the  minimum 
rate  of  liquid  excretion  is  not  the  same  for  different  plants.  Etiolated  plants 
exhibit  no  periodicity.     Analyses  of  the  sap  extruded  by  bleeding  stems  are 

1  Hofmeister,  W.,  Ueber  das  Steigen  des  Saftes  der  Pflanzen.  Flora,  n.  R.  16:  1-12.  1858.  Idem, 
Ueber  Spannung,  Ausflussmenge  und  Ausflussgeschwindigkeit  von  Saften  lebender  Pflanzen.  Ibid.  n.  R. 
20:  97-108.     1862. 

2  Baranetzky,  J.,  Untersuchungen  uber  die  Periodicitat  des  Blutens  der  Krautigen  Pflanzen  und  deren 
Ursachen.    (Besonders  abgedruckt  aus  den  Abhandl.  Naturf.  Ges.  Halle  13/)     63  p.    Halle,  1873. 

pIn  this  connection  see:  Hofmeister,  W.,  Ueber  Spannung,  Ausflussmenge  und  ausfluss- 
geschwindigkeit von  Saften  lebender  Pflanzen.  Flora  45 :  97-108,  113-120,  138-144,  145- 
152,  170-175.     1862.     The  numbers  given  in  the  text  are  from  this  paper. — Ed. 


142 


PHYSIOLOGY    OF    NUTRITION 


very  interesting.  In  Ulbricht's1  experiments,  potato  tubers  planted  on  April 
ii,  produced  stems  that  bloomed  on  July  5.  On  July  9  the  stems  were  cut  off 
at  from  4  to  6  cm.  above  the  soil.  The  sap  that  exuded  during  the  next  five 
days  was  collected,  the  exudation  for  each  day  being  kept  separate,  so  that 
five  portions  of  sap  were  available  for  analysis,  the  results  of  which  are  shown 
in  the  following  table.  The  quantities  (stated  in  milligrams)  refer  to  a  liter  of 
sap  in  all  cases. 


First  Day     Second  Day 


Third  Day 


Fourth  Day 


Fifth  Day 


Combustible  material  ',  450 

Ash I         1160 

Total  dry  weight j         1610 


310 

980 

1290 


220 

960 

1180 


280 

910 

1 190 


295 
945 

1240 


These  numbers  show  plainly  that  the  total  solids  consisted  mainly  of  mineral 
substances,  but  this  statement  is  still  further  emphasized  by  the  fact  that  the 
combustible  material  does  not  represent  organic  matter  alone,  for  nitric  acid 
and  some  other  inorganic  substances  are  vaporized  during  incineration,  so  that 
it  is  certain  that  the  sap  always  contained  more  inorganic  substances  than  the 
data  show.  This  result  was  to  be  expected,  since  the  ascending  water  current 
distributes  absorbed  soil  solution  throughout  the  plant.  The  presence  of  organic 
substances  in  sap  extruded  from  the  xylem  may  be  explained  by  the  fact  that 
the  soil  solution  does  not  enter  this  tissue  directly,  but  is  transferred  into  the 
wood  soon  after  its  entrance.  It  can  hardly  be  supposed  that  parenchymatous 
cells,  which  are  so  rich  in  organic  substances,  should  excrete  nothing  but  inor- 
ganic materials  into  the  vessels. 

The  composition  of  sap  excreted  in  early  spring  is  very  different  from  that 
of  sap  excreted  in  summer.  Birch  sap  was  collected  from  an  opening  in  the 
tree  trunk  just  above  the  soil  surface,  on  each  of  six  different  days,  between 
April  5  and  May  2  2.2  The  sugar,  protein,  malic  acid,  and  ash  contents  per  liter 
of  sap  are  given  below,  in  milligrams,  together  with  the  dates  on  which  the  sap 


April  5. 
April  1 1 . 
April  17. 
May  2. 
May  19. 
May  22 . 


Date  of  Flow 


Sugar 


12,500 
13,500 
10,900 

IO,IOO 

9,400 

6,900 


Protein 


21 
6 
6 


Malic  Acid 


Ash 


33? 


437 


500 

640 

1080 


>Ulbricht,  R.,  Ein  Beitrag  zur  Kenntniss  der  Blutungssafte  einjahriger  Pflanzen.  Landw.  Versuchsst. 
6:468-474.     1864.     [Idem,  same  title.     Ibid.  7 :  185-192.     1865] 

*Schroeder,  Julius,  Die  Fruhjahrsperiode  der  Birke  (Belula  alba  L.)  und  des  Ahorn  (Acer  plalanoides  L.) 
Landw.     Versuchsst.  14:  1 18-146.     187 1. 


MOVEMENT  OF  MATERIALS  IN  THE  PLANT  1 43 

was  collected.  It  is  apparent  from  these  analyses  that  the  sap  contains  less  in- 
organic substances  and  more  organic  materials  in  the  earlier  part  of  the  season 
than  at  the  later  dates.  This  is  explained  by  the  facts  that  organic  materials 
accumulate  in  the  woody  tissue  of  perennial  plants  during  the  summer,  and  that 
they  are  rapidly  removed  to  the  growing  regions  with  the  opening  of  the  follow- 
ing spring;  it  is  at  the  expense  of  this  accumulated  food  that  spring  leaves  are 
formed.  After  the  leaves  develop,  the  sap  contains  inorganic  substances 
mainly,  and  spring  bleeding  thus  becomes  transformed  into  summer  bleeding. 

The  term  bleeding  thus  denotes  the  exudation  of  sap  from  the  woody  tissues 
of  wounded  plants,  brought  about  by  the  absorption  of  water  and  dissolved 
mineral  substances  by  the  parenchymatous  cells  of  the  root,  and  the  movement 
of  this  solution  into  the  vessels  of  the  xylem,  in  which  it  is  carried  upward  to 
the  wound.  The  causes  upon  which  this  phenomenon  is  dependent  have  not  yet 
been  found  out.'' 

(c)  Movement  of  water  in  the  stem1  depends  upon  a  number  of  conditions. 
Water  moves  upward  in  the  xylem,  as  was  shown  in  Malpighi's  girdling  experi- 
ment. Sach's  theory,  which  supposed  that  it  traverses  the  vessel  walls,  was 
proved  untenable  and  is  no  longer  upheld.  The  ascending  current  moves  in 
the  lumina  of  the  vesssels  and  tracheides,  as  is  shown  by  the  fact  that  wilting 
promptly  occurs  when  these  are  plugged.  The  following  experiment  demon- 
strates this.  A  mixture  of  20  parts  of  gelatine  in  100  parts  of  water,  melting  at 
330  and  still  liquid  at  28°C.  (at  which  temperatures  plant  tissues  is  not  at  all  in- 
jured) is  prepared,  and  enough  India  ink  is  added  to  make  the  preparation 
readily  visible  in  the  vessels.  The  stem  of  a  leafy  shoot  is  cut  under  this  prepa- 
ration, the  latter  having  been  warmed  to  33°C.  The  liquid  rises  in  the  vessels 
and  is  allowed  to  harden  by  cooling.  A  small  piece  is  then  cut  from  the  base 
of  the  stem,  to  give  a  fresh  absorbing  surface,  and  the  cut  end  is  placed  in  water. 
After  several  hours  wilting  occurs  in  the  leaves,  while  the  leaves  of  a  similar 

1  Votchal,  Ueber  die  Bewegung  des  Wassers  in  den  Pflanzen.  Moscow,  1897  (Russian).*  Bohm, 
Joseph,  Ueber  die  Ursache  des  Saftsteigens  in  den  Pflanzen.  Sitzungsber.  (math.-naturw.  Kl.)  K.  Akad. 
Wiss.  Wien.  48*:  10-24.  1863.  Hartig,  R.,  Die  Gasdrucktheorie  und  die  Sachs'sche  Imbibitions-Theorie. 
Berlin,  1883.  Strasburger,  Eduard,  Ueber  den  Bau  und  die  Verrichtungen  der  Leitungsbahnen  in  den 
Pflanzen.  (Histologische  Beitrage,  Heft  3.)  Jena,  1891.  Askenasy,  E.,  Ueber  das  Saftsteigen.  Verhandl. 
Naturhist.-Med.  Ver.  Heidelberg,  n.  F.  5 :  325-345-  [Gesammtsitzung  vom  7-  Dez.,  1894,  und  1.  Febr., 
1895.  Heft  4,  dated  1896.]  Idem,  Beitrage  zur  Erklarung  des  Saftsteigens.  Ibid,  5:  429-448.  [Ge- 
sammtsitzung vom  6.  Marz,  1896.  Heft  4.  Vol.  dated  Heidelberg,  1897.]  Godlewski,  E.,  Zur  Theorie 
der  Wasserbewegung  in  den  Pflanzen.  Jahrb.  wiss  Bot.  15;  5  69-630.  1884.  [Schwendener,  S.,  Unter- 
suchungen  uber  das  Saftsteigen.  Sitzungsber.  (math.-naturw.  Mitth.)  K.  Preuss.  Akad.  Wiss.  Berlin 
1886;  355-396.     1886.     Idem,  Vorlesungen  uber  mechanischen  Probleme  der  Botanik.     Leipzig,   1909.] 

«  Molisch  showed  that  the  phenomenon  of  sap  exudation  from  holes  and  cuts  in  the  upper 
regions  of  palm  stems  is  not  due  to  a  pressure  normally  present  in  the  plant,  but  that  the  pres- 
sure here  indicated  is  brought  about  as  a  result  of  wounding.  The  cells  near  the  cut  surface 
undergo  an  alteration,  and  bleeding  begins  only  after  enough  time  has  elapsed  to  allow  this 
alteration  to  occur.  The  altered  cells  resemble  gland  cells  and  secrete  the  liquid.  But  it 
appears  improbable  that  all  the  cases  of  bleeding  are  to  be  thus  explained.  See:  Molisch, 
Hans,  Botanische  Beobachtungen  auf  Java.  (III.  Abhandlung.)  Die  Secretion  des  Palm- 
weins  und  ihre  Ursachen.  Sitzungsber.  (math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien  I07z:  1247- 
1271.  1898.  Idem,  Ueber  localen  Blutungsdruck  und  seine  Ursachen.  Bot.  Zeitg.  60: 
45-63.     1902. 


144  PHYSIOLOGY   OF   NUTRITION 

branch,  the  vesesls  of  which  are  not  thus  plugged,  may  remain  turgid  for  a 
number  of  days.1 

Air  as  well  as  water  is  present  in  the  vessels  and  is  very  much  rarefied  at 
times,  as  was  shown  by  Hohnel's  experiments.  To  show  the  presence  of  water 
in  the  vessels,  a  piece  is  removed  from  a  young  stem  by  means  of  a  double  pair 
of  shears,  so  arranged  that  the  two  cuts  are  made  at  the  same  time.  From  the 
piece  thus  obtained,  longitudinal  sections  are  prepared  and  examined  under  the 
microscope,  of  course  without  any  addition  of  water.  If  the  two  cuts  are  not 
made  simultaneously  no  water  is  observed  in  the  vessels,  for,  because  of  nega- 
tive pressure  in  the  gases  of  the  wood,  air  rushes  into  the  vessels  at  the  cut 
surface  as  soon  as  the  incision  is  made,  driving  the  water  before  it  into  other 
regions  of  the  plant.  The  water  columns  in  the  vessels  are  frequently  interrupted 
by  air  bubbles  and  these  may  be  demonstrated  under  the  microscope.  To 
accomplish  this  the  parenchymatous  tissue  is  carefully  removed  from  one  of  the 
woody  bundles  of  a  young  stem  with  but  little  wood  (e.g.,  Begonia  or  Dahlia). 
Thus  the  bundle  is  exposed,  but  is  uninjured  and  is  still  in  connection  with  the 
rest  of  the  plant  at  both  ends  of  the  preparation.  Study  of  such  preparations 
shows  that  the  vessels  are  nearly  filled  with  water  and  contain  but  few  air  bub- 
bles in  moist,  cloudy  weather,  but  that  they  contain  less  water  and  consequently 
a  greater  amount  of  air2  on  sunny  days. 

All  the  investigations  that  have  so  far  been  made  indicate  that  the  water 
columns  in  the  vessels  are  not  completely  broken  by  air  bubbles.  Cross-sec- 
tions of  the  vessels  show  that  they  are  not  perfectly  cylindrical  but  are  more  or 
less  prismatic  and  many-sided  and  that  this  irregularity  in  form  is  further  in- 
creased by  circular,  spiral  and  other  secondary  thickenings  of  the  walls.  Air 
bubbles  tend  to  assume  a  spherical  form  and  the  irregularly  shaped  portions  of 
the  vessels  are  thus  not  completely  filled  with  air,  so  that  a  continuous  water 
column  results,  the  air  bubbles  being  wholly  surrounded  by  water/ 

1  Errera,  Leo,  Ein  Transpirationsversuch.     Ber.  Deutsch.  Bot.  Ges.  4:  16-18.      1886. 

2  Capus,  Guillaume,  Sur  l'observation  directe  du  mouvement  de  l'eau  dans  les  plantes.  Compt.  rend. 
Paris  97:  1087-1080.     1883. 

r  It  is  doubtful  whether  this  is  true  when  the  transpiration  rate  is  considerable  and  the  soil 
fairly  dry.  Wherever  a  gas  bubble  occurs  in  a  vessel  it  should  enlarge,  under  these  conditions, 
until  it  fills  that  entire  vessel  segment  from  the  cross-wall  below  to  the  one  above.  The  gas- 
liquid  surface  tension  in  such  a  case  as  is  postulated  in  the  text  would  have  to  be  as  great  as  the 
sum  of  the  gas  pressure  in  the  enlarged  bubble  and  the  tensile  stress  exerted  upon  the  water  by 
the  transpiration  process  going  on  above.  The  gas  pressure  in  the  bubble  must  be  less  than  a 
single  atmosphere,  but  the  magnitude  of  the  tensile  stress  is  at  least  more  than  equivalent 
to  an  atmosphere.  Thus  the  sum  just  mentioned  is  frequently  of  the  order  of  several  atmos- 
pheres and  is  surely  of  greater  magnitude  than  the  gas-liquid  surface  tension.  It  follows  that 
the  bubble  must  enlarge  until  its  surface  film  comes  into  contact  with  the  surrounding  vessel 
walls  at  every  point;  thus  reinforced,  the  surface  layer  of  the  liquid  can  withstand  the  great 
attraction  exerted  by  the  stressed  water-mass,  and  the  gas  bubble  does  not  expand  farther. 
When  the  water  has  been  under  stress  for  a  sufficient  time  there  should  be  no  free  water 
between  cell  walls  and  gas  at  any  point  in  the  entire  plant  body;  all  such  surfaces  should  be 
cell-wall  surfaces,  at  which  the  liquid  surface  is  held  by  the  force  of  imbibition.  Indeed,  this 
condition  would  probably  be  attained  by  the  action  of  the  gas  pressure  within  the  bubble, 
before  any  stress  developed  in  the  liquid  at  all.     The  picture  presented  in  the  text  at  this 


MOVEMENT  OF  MATERIALS  IN  THE  PLANT  145 

Votchal  has  carried  out  a  thorough  investigation  upon  the  transmission  of 
pressure  by  wood  containing  both  air  and  water.  [See  note  1,  p.  131  for 
reference].  Portions  about  2  m.  in  length,  from  saplings  or  branches,  were 
placed  in  a  horizontal  position  and  water  was  forced  through  them  from  one  end 
to  the  other,  by  means  of  water  or  mercury  pressure  applied  through  glass  tubes 
suitably  attached.  The  rate  of  entrance  of  water  at  one  end  and  that  of  exit  at 
the  other  vary  in  a  regular  manner  for  a  time  after  pressure  is  first  applied. 
VotchaFs  representation  of  these  variations  is  reproduced  in  the  diagram  of 
Fig.  82.  The  variation  in  the  entrance  rate,  at  the  end  where  pressure  is 
applied,  is  shown  by  the  line  a.  This  rate  first  increases  with  remarkable 
rapidity  and  soon  attains  a  rather  high  value  (a),  but  this  high  rate  is  maintained 
only  during  several  hundredths  of  a  second  after  the  pressure  is  applied.  The 
next  stage  (a(S)  shows  a  decreasing  rate  and  is  of  longer  duration,  continuing 
for  from  one-half  to  two  minutes.  In  the  third  stage  (fiy)  the  velocity  continues 
to  fall,  but  more  slowly  and  gradually,  and  it  finally  assumes  a  constant  value. 
In  short  pieces  of  stem  the  final  constant  rate  is  attained  after  five  minutes,  but 


Fig.  82. — Diagram  showing  variations  in  rates  of  entrance  and  exit  of  water  moving  under 
pressure  through  a  section  of  woody  stem.      (After  Votchal.) 


with  longer  pieces  this  period  may  be  prolonged.  The  simultaneous  variation 
in  the  rate  of  exit,  at  the  opposite  end  of  the  piece  of  stem,  is  shown  by  the 
line  a! &'.  The  velocity  of  movement  here  increases  very  slowly,  gradually 
attaining  a  value  equal  to  that  of  the  rate  of  entrance  at  the  other  end. 
When  the  two  rates  become  equal,  the  two  curves  become  coincident,  and  water 

point  can  be  true  only  with  comparatively  low  transpiration  rates,  and  with  comparatively 
ready  entrance  of  water  into  the  vessels  below.  The  compound  water  column  of  the  stem 
is  not  broken  in  all  vessels  at  the  same  level,  however,  and  the  transpiration  stress  is  trans- 
mitted laterally  from  the  water  of  one  vessel  to  that  of  adjoining  ones,  around  the  gas-filled 
vessel  segments.  These  matters  have  been  very  thoroughly  treated  by  Dixon,  and  Overton 
and  Renner  have  each  brought  forward  additional  convincing  arguments  in  favor  of  the 
general  interpretation  adopted  in  the  present  note.  See:  Dixon,  H.  H.,  Transpiration  and 
the  ascent  of  sap.  Prog,  rei  bot.  3 :  1-66.  1909.  Idem,  Transpiration  and  the  ascent  of  sap 
in  plants.  London,  1914.  Renner,  1910.  [See  note  k,  p.  138.]  Idem,  1911,^,^.  [Seenotej, 
p.  137-]  Idem,  191 2,  1,  2.  [See  note  k,  p.  138.]  Idem,  Theoretisches  und  Experimentelles 
zur  Kohasions-theorie  der  Wasserbewegung.  Jahrb.  wiss.  Bot.  56 :  617-667.  1915.  Holle, 
H.,  Untersuchungen  iiber  Welken,  Vertrocknen  und  Wider-straff werden.  Flora  108 :  73-126. 
1915.  Overton,  J.  B.,  Studies  on  the  relation  of  the  living  cells  to  the  transpiration  and 
sap-flow  in  Cyperus.     Bot.  gaz.  51  :  2S-63,  102-120.     1911. — Ed. 


10 


146  PHYSIOLOGY    OF    NUTRITION 

is  then  moving  through  the  piece  at  a  uniform  rate  throughout.  Similar 
experiments  with  tubes  filled  with  sand  containing  air  and  impregnated  with 
water  gave  concordant  results  with  those  obtained  with  the  pieces  of  stem. 
Votchal  conceives  that  air  bubbles  in  the  wood  act  simply  as  resilient  springs 
that  transmit  and  distribute  the  thrust  imparted  to  them  more  slowly  and 
evenly  than  would  a  continuous,  homogeneous  water  column.  The  effective 
forces  applied  at  the  ends  of  the  conducting  channels — i.e.,  the  force  of  foliar 
transpiration  and  that  of  root  pressure — furnish  energy  to  account  for  the 
ascending  water  current  in  plants.  Root  pressure,  produced  by  osmotic  forces, 
exerts  a  pressure  upon  one  end  of  the  water  column  in  the  wood,  while  evapo- 
ration of  water  from  the  leaves  establishes  traction  at  the  opposite  end.8 

A  simple  experiment  (Fig.  83)  indicates  the  magnitude  of  the  force  that 
draws  water  into  the  leaves  to  replace  that  lost  by  evaporation.  If  the  cut  end 
of  a  leafy  branch  or  stem  is  carefully  sealed  to  the  upper  end  of  a  glass  tube  filled 
with  water,  and  if  the  lower  end  of  the  tube  dips  into  mercury,  then  mercury 
is  drawn  up  into  the  tube,  replacing  the  water  absorbed  at  the  cut  surface, 
which  in  turn  replaces  that  lost  by  evaporation  from  the  leaves.  In  Bohm's1 
experiments  the  mercury  column  rose  86  and  even  90  cm.  in  the  tube,  thus 
considerably  exceeding  the  height  of  mercury  column  supported  by  atmospheric 
pressure  upon  the  free  mercury  surface  below.  AskenasyV  experiments  indi- 
cate that  the  rise  of  the  mercury  column  here  shown  has  a  simple  physical  cause. 
In  these  experiments  the  upper,  broad  portion  of  a  glass  funnel,  the  neck  of 
which  was  fused  to  a  long  glass  tube,  was  filled  with  a  thick  layer  of  plaster  of 
Paris;  when  the  plaster  hardened  the  apparatus  was  filled  with  water,  the  glass 
tube  dipping  into  mercury  below.  As  water  evaporated  from  the  plaster 
surface  the  mercury  rose  in  the  tube  and  attained  a  height  of  82  cm.,  which  is, 
here  also,  noticeably  greater  than  that  attained  under  the  action  of  atmospheric 
pressure.  The  funnel  may  be  covered  with  animal  bladder  instead  of  being 
filled  with  plaster  (Fig.  84)." 

These  experiments  indicate  the  great  magnitude  of  the  force  of  cohesion 
existing  between  the  molecules  of  water;  the  water  column  is  not  broken 
even  when  it  is  subjected  to  a  considerable  stress.  These  experiments 
also  give  some  idea   of   the   magnitude   of   the  imbibition  force  resident  in 

1  [Bohm,  J.,  Capillaritat  und  Saftsteigen.     Ber.  Deutsch.  Bot.  Ges.  n  :  203-212,  1893-! 

8  Root  pressure  is  not  to  be  considered  as  generally  important  in  the  ascent  of  water  through 
plant  stems.  The  mere  existence  of  "negative  gas  pressure"  in  the  vessels  shows  that  the 
liquid  above  the  gas  bubbles  is  not  being  forced  upward  by  a  pressure  applied  below.  Perhaps 
the  simplest  argument  in  favor  of  dismissing  root  pressure  from  consideration  in  the  general 
problem  of  rise  of  sap  lies  in  the  fact  that  this  pressure  is  found  to  be  highest  when  water 
movement  is  slowest  and  lowest  when  movement  is  most  rapid. — Ed. 

1  Askenasy,  1896,  1897  [See  note  1,  p.  143.]     Dixon,  1914-     [See  note  r,  144-1- — Ed. 

"  But  the  bladder  membrane  has  not  been  recorded  as  ever  showing  a  rise  of  the  mercury 
column  above  the  height  of  the  barometer.  The  experiment  usually  fails  to  demonstrate  this 
important  point,  even  with  porous  porcelain  or  plaster  of  Paris;  the  water  column  almost 
always  breaks  before  a  stress  of  one  atmosphere  is  developed.  In  this  connection  see:  Ur- 
sprung,  A.,  Zur  Demonstration  der  Fliissigkeits-Kohasion.  Ber.  Deutsch.  Bot.  Ges.  31 :  388- 
400.  1913.  Idem,  Ueber  die  Blasenbildung  in  Tonometern.  Ibid.  33:  140-153.  1915. 
Idem,  Ueber  die  Kohiision  des  Wassers  im  Farnannulus.     Ibid.  33:  153-162.     1915. — Ed. 


MOVEMENT  OF  MATERIALS  IN  THE  PLANT 


147 


cell  walls  of  plants  and  also  in  plaster  of  Paris;  this  force  is  so  great  that  when 
water  is  removed  from  the  cell  wall  by  evaporation  more  water  is  immediately 
withdrawn  from  the  interior  of  the  cell  in  spite  of  the  osmotic  force  that  opposes 
such  movement.  Transpiration  from  the  leaves,  the  force  of  imbibition  in  the 
cell  walls,  and  the  cohesion  of  liquid  water,  are  therefore  the  main  causes 

underlying  the  movement  of  water  in 
plant  stems.  The  so-called  root  pres- 
sure, which  causes  bleeding  in  plants, 
may  also  be  involved  here  to  some 
extent/ 

The  amount  of  water  passing  through 
the  plant  is  important  in  the  distribu- 
.  tion  of  mineral  substances  throughout 
the  organism,  as  well  as  in  their  absorp- 
tion. Schlosing's  studies  with  tobacco 
plants   may   serve   as   an   illustration1 


Pig.  83. — Arrangement  to  show  rise  of  a 
mercury  column  caused  by  evaporation  of  water 
from  the  leaves  of  a  cut  twig. 


Fig.  84. — Evaporation  of  water  through 
a  membrane,  causing  rise  of  mercury  in 
tube  below. 


Compt.  rend.  Paris  69: 


1  Schloesing,  Th.,  Vegetation  comparee  du  tabac  sous  glocke  et  a.  l'air  libre. 
353-356.     1869. 

"  The  discussion  here  given  of  the  physics  of  the  rise  of  the  transpiration  stream  is  fragmen- 
tary and  incomplete,  but  it  has  not  seemed  advisable  to  attempt  to  render  it  much  more 
thorough  in  the  limited  space  to  which  editorial  notes  should  be  restricted  in  a  translation  such 
as  the  present  volume.  The  notes  that  have  been  added  to  this  section  aim  to  place  before  the 
student  the  main  points  omitted  by  the  author,  and  to  give  references  to  the  literature,  so  that 
the  best  treatments  of  the  modern  phase  of  this  much-discussed  problem  may  be  read.  The 
writings  of  Dixon,  Renner,  and  J.  B.  Overton,  cited  in  note  r,  p.  144,  should  be  referred  to,  at 
any  rate.  The  existing  text-books  are  all  unsatisfactory  in  regard  to  this  subject,  the  Dixon 
theory  not  yet  having  been  adequately  incorporated  into  any  of  them. — Ed. 


148  PHYSIOLOGY   OF   NUTRITION 

of  this.  A  portion  of  a  plant  was  allowed  to  grow  in  a  water-saturated  atmos- 
phere, under  a  bell-jar,  while  the  remainder  was  exposed  to  natural  condi- 
tions. The  ash  content  in  the  leaves  grown  in  the  moist  atmosphere  was 
lower  than  that  of  the  other  leaves,  the  former  being  only  13  per  cent.,  while  the 
latter  was  21.8  per  cent.,  of  the  total  dry  weight.1" 

§5.  Movement  of  Organic  Substances. — Malpighi's  girdling  experiment, 
already  described  (page  133),  indicates  that  organic  substances  move  through 
plant  stems  only  in  the  cortex.  This  region,  however,  includes  many  different 
kinds  of  tissue  and  the  question  arises  whether  the  movement  here  considered 
occurs  equally  throughout  the  cortex  or  only  through  special  parts  of  it.  Han- 
stein1  carried  out  a  series  of  experiments  in  this  connection  and  found  that  the 
removal  of  a  ring  of  cortex  did  not  always  stop  growth  in  the  region  below  the 
lesion.  Anatomical  study  of  the  plants  that  were  not  injured  showed  that  some 
of  these  possessed  vascular  bundles  in  the  pith  as  well  as  in  the  ring  of  vessels 
always  found  in  dicotyledonous  plants,  while  others  possessed  no  collateral 
bundles  and  had  only  bicollateral  ones.  Girdling  had  no  effect  upon  the  growth 
of  monocotyledonous  plants.  Hanstein  concluded,  therefore,  that  this  dif- 
ference between  different  plants,  in  regard  to  the  effect  of  girdling,  is  due  to  the 
fact  that  all  the  sieve-tubes  are  removed  in  the  girdling  of  most  dicotyledonous 
plants,  while  only  a  part  of  them  are  removed  in  those  dicotyledons  that  have 
vascular  bundles  in  the  pith,  and  in  monocotyledons  with  bicollateral  bundles. 
Sieve-tubes  are  therefore  the  main  channels  through  which  the  movement  of  or- 
ganic material  occurs.  By  virtue  of  their  anatomical  structure  these  tubes  are 
better  suited  for  this  movement  than  are  any  of  the  other  tissues  of  the  cortex. 
This  conclusion  does  not  at  all  exclude  the  possibility  that  organic  substances 
may  move  by  diffusion  through  any  other  living  cells,  especially  through  the  very 
small  pores  by  which  many  cell  walls  are  perforated.  A  peculiarity  of  the  move- 
ment of  organic  materials  is  that  it  is  regulated  exclusively  by  the  activity  of 
living  cells  and  that  it  is  a  result  of  this  activity.  In  other  words,  this  move- 
ment is  controlled  by  internal  conditions.  External  conditions  affect  transloca- 
tion only  as  they  affect  the  life-processes  of  the  cells  in  general.  With  the  upward 
movement  of  the  soil  solution  it  is  quite  different,  for,  as  has  been  seen,  this  is 
very  largely  dependent  upon  such  external  conditions  as  light,  humidity,  wind, 
etc.  The  movement  of  the  soil  solution  has  been  somewhat  thoroughly  investi- 
gated in  its  general  aspects,  but  our  knowledge  of  the  translocation  of  organic 
materials  rests  upon  only  a  few  well-known  facts  and  is  largely  hypothetical. 

The  movement  of  organic  materials  has  been  extensively  studied  in  connec- 

1  Hanstein,  Johannes,  Versuche  iiber  die  Leitung  des  Saftes  durch  die  Rinde  und  Folgerungen  daraus. 
Jahrb.  wiss.  Bot.  2:  392-467.     i860. 

"  But  see:  Hasselbring,  Heinrich,  The  relation  between  the  transpiration  stream  and  the 
absorption  of  salts.  Bot.  gaz.  57:  72-73.  1914.  Hasselbring's  conclusion  is  the  direct 
opposite  of  the  one  reached  by  Schlosing.  The  question  as  to  what  rates  of  transpiration 
are  necessary  to  elevate  the  requisite  amount  of  salts  in  tall  plants  deserves  further  atten- 
tion at  the  hands  of  experimenters.  It  appears  clear  enough,  on  a  priori  grounds,  that  some 
transpiration  must  generally  give  better  growth  than  none  at  all,  but  the  rates  generally 
experienced  by  ordinary  plants  are  probably  much  higher  than  the  optimum. — Ed. 


MOVEMENT  OF  MATERIALS  IN  THE  PLANT  1 49 

tion  with  seed  germination.  The  most  important  work  in  this  field  was  done 
by  Sachs.1  By  means  of  microchemical  tests  applied  to  hand  sections  of  seeds 
and  seedlings,  he  investigated  the  most  important  organic  substances  (such  as 
proteins,  sugars,  fats,  acids,  tannins),  with  regard  to  their  distribution  in  the 
tissues.  By  comparing  the  distribution  of  these  substances  as  shown  in  the 
seed  with  that  exhibited  in  the  seedling  and  in  different  regions  of  the  older  plant, 
Sachs  reached  his  conclusions  as  to  the  paths  of  translocation.  He  found,  for 
example,  that  the  cortex  contains  cells  that  are  filled  with  starch  grains  during 
germination,  and  that  these  cells  form  a  continuous  series  (which  he  called  the 
starch  sheath)  reaching  outward  from  the  cotyledons  into  all  parts  of  the 
plantlet.  From  these  observations  he  concluded  that  it  is  in  this  sheath  that 
starch  moves  from  the  cotyledons  into  other  regions,  as  growth  proceeds.  The 
sort  of  observations  on  which  this  conclusion  was  based  bear,  however,  only 
upon  the  distribution  and  accumulation  of  the  substances  in  question,  in  the 
various  organs  of  the  plant;  the  fact  that  a  continuous  series  of  cells  all  contain 
a  certain  substance  does  not  indicate  that  the  substance  in  question  is  moving 
through  those  cells.  In  the  case  of  the  starch-filled  cells  above  mentioned,  the 
subsequent  experiments  of  Heine2  showed  that  this  material  is  not  there  in 
process  of  translocation,  but  that  the  contents  of  these  cells  represent  merely 
local  accumulations.  This  author  removed  rings  of  tissue  from  stems  of  young 
seedlings,  so  as  to  remove  the  starch  sheath  at  the  region  of  girdling,  and  found 
that  such  treatment  neither  hindered  the  development  of  the  plants  nor  lessened 
the  amount  of  starch  in  those  regions  of  the  sheath  beyond  the  wound.  There- 
fore, in  this  case  also,  the  organic  materials  must  have  moved  through  the  phloem 
(leptome)  of  the  bundles,  which  was  not  injured  by  the  girdling  operation. 
Some  of  the  plastic  material  passing  through  the  uninjured  phloem  found  its 
way  to  the  sheath  cells  and  there  accumulated  locally  as  starch. 

There  are  also  available  some  studies,  by  Sachs,  Sapozhnikov,3  and  others, 
bearing  upon  the  translocation  of  organic  substances  from  the  leaves,  where  they 
are  formed,  to  other  portions  of  the  plant.  As  carbohydrates  are  produced  in 
the  leaves  they  continually  move  into  the  stem.  Comparison  of  the  loss  of 
carbohydrates  from  attached  leaves  with  the  loss,  in  the  same  time,  from  similar 
leaves  that  have  been  detached  from  the  plant,  shows  that  this  rate  of  loss  is 
more  than  five  times  as  great  in  the  first  case  as  it  is  in  the  second.  This  obser- 
vation indicates  clearly  that  translocation  of  carbohydrates  from  leaves  to  stem 
actually  occurs.  Carbohydrates  disappear  from  the  detached  leaves  only 
through  local  consumption,  and  the  rate  of  its  disappearance  is  much  lower 
than  in  the  case  of  leaves  that  remain  attached  to  the  plant.     This  movement 

1  Sachs,  J.,  Uebersicht  der  Ergebnisse  der  neueren  Untersuchungen  uber  das  Chlorophyll.  Flora,  n.  R. 
20:  120-137.  1862.  Idem,  Mikrochemische  Untersuchungen.  Ibid.,  n.  R.  20:  289-301.  1862.  Idem. 
Ueber  die  Stoffe,  welche  das  Material  zum  Wachsthum  der  Zellhaute  liefern.  Jahrb.  wiss.  Bot.  3  :  186-188. 
1863.  Idem,  Ueber  die  Leitung  der  plastischen  Stoffe  durch  verschiedene  Gewebeformen.  Flora,  n.  R. 
21:  33-42.     1863.     Idem,  Beitrage  zur  Physiologie  des  Chlorophylls.     Ibid.,  n.  R.  ax:  193-204.     1863. 

2  Heine,  H.,  Die  physiologische  Bedeutung  der  sogenannten  Starkescheide.  Landw.  Versuchsst.  35 : 
161-193.     1888. 

s  Sapozhnikov,  Die  Bildung  der  Kohlehydrate  in  den  Blattern  and  ihre  Bewegung  in  der  Pflanze.  Moscow , 
1890.  (Russian.)*  Idem,  1890.  [See  note  4,  p.  31.]  Idem,  1891.  [See  note  3,  p.  38. |  Idem,  1893- 
[See  note  4,  p.  31.] 


150  PHYSIOLOGY    OF    NUTRITION 

of  carbohydrates  takes  place  through  the  phloem.1  There  is  a  daily  periodicity 
in  the  movement  of  carbohydrates  out  of  the  leaf;  the  maximum  rate  of 
movement  occurs,  according  to  Sapozhnikov,  during  the  early  hours  of  the 
night,  between  7  :?,o  and  1 1 :3c 

In  perennial  plants  the  accumulated  material  formed  during  the  summer 
in  never  wholly  consumed  in  the  same  season;  a  large  part  is  accumulated  and 
remains  in  the  plant  until  the  following  spring.  The  renewed  activity  of  early 
spring  and  the  development  of  new  shoots  and  leaves  occurs  at  the  expense  of 
organic  material  accumulated  in  the  preceding  year.  Accumulation  begins 
very  early  in  the  season  in  some  plants — in  May,  for  instance,  in  the  case  of  the 
maple;  in  other  plants  it  begins  later — in  the  oak,  for  example,  in  July,  and  in 
the  Scotch  pine,  in  September.  The  material  first  accumulates  in  the  young 
twigs,  from  which  it  gradually  moves  down  the  stem  until  the  roots  also  are 
rilled.  Accumulation  ceases  at  the  end  of  the  summer  or  in  the  autumn — 
not  until  the  middle  of  October  in  the  case  of  the  pine,  for  example.  In  winter 
the  accumulated  material,  consisting  mainly  of  oil  and  starch,  fills  all  the 
pith,  the  medullary  rays,  the  cortex  and  some  parts  of  the  xylem. 

The  solution  of  the  accumulated  material  begins  in  early  spring.  As  it 
dissolves  it  passes  through  the  medullary  rays  into  the  vessels  of  the  xylem,  in 
which  it  moves  to  the  growing  regions,  as  has  been  pointed  out.  If  the  young 
twigs  are  killed  by  a  late  spring  frost,  after  the  winter  reserve  has  been  used  up, 
the  death  of  the  tree  may  follow. 

Organic  materials  are  removed  from  storage  tissues  into  other  tissues  only 
when  they  are  being  consumed  in  the  latter  or  are  moving  through  these  tissues 
into  still  more  distant  regions.2  If  the  embryo  is  removed  from  a  seed  of 
maize  or  barley,  for  example,  and  if  the  remaining  endosperm  is  planted  in  moist 
soil,  then  the  starch  of  the  endosperm  is  neither  removed  nor  converted  into 
sugar.  If,  however,  the  endosperm  is  placed  on  the  point  of  a  little  cone  of 
plaster  of  Paris,  the  lower  end  of  which  dips  into  water,  the  starch  is  then  dis- 
solved and  the  resulting  sugar  diffuses  into  the  water  below.  Maize  endo- 
sperm is  thus  completely  emptied  of  starch  in  from  thirteen  to  eighteen  days  and 
a  considerable  quantity  of  carbohydrates  appears  in  the  water.  Similar  experi- 
ments may  be  performed  with  bulbs,  roots,  rhizomes  and  branches.  Lack  of 
oxygen  in  the  atmosphere  about  the  endosperm,  or  the  presence  of  ether  or 
chloroform  vapor,  terminates  this  process. 

Summary 

1.  Movement  of  Materials  in  General. — Substances  enter  the  plant  body  at  certain 
parts  of  its  periphery,  and  then  move  to  distant  regions,  being  in  many  cases  decom- 
posed and  their  elements  being  recombined  in  various  ways  during  their  stay  in  the 
plant.  Some  materials  remain  in  the  plant  until  its  death,  while  others  are  continuously 
or  intermittently  given  off  to  the  surroundings. 

1  Czapek,  Friedrich,  Ueber  die  Leitungswege  der  organischen  Baustoffe  im  Pflanzenkorper.  Sitzungsber. 
(math,  naturw.  Kl.)  K,  Akad.  Wiss.  Wien  106:  117-170.     1897. 

2  Puriewitsch,     K.,    Physiologsche    Untersuchungen    iiber    die    Entleerung    der    Reservestoffbehalter. 
lahrb.  wiss.  Bot.  31 :  1-76.     1898. 


MOVEMENT  OF  MATERIALS  IN   THE  PLANT  151 

2.  Movement  of  Gases. — The  internal  gas  spaces  (the  intercellular  channels 
mentioned  in  Chapter  V,  Section  3)  are  continuous  with  the  external  atmosphere 
(through  stomata  and  lenticels)  and  gas  streaming  as  well  as  gas  diffusion  may  occur 
through  these  channels.  Gases  enter  into  solution  and  diffuse  through  cell  walls, 
protoplasm,  etc.,  just  as  do  other  dissolved  substances.  Dissolved  gas  may  go  out  of 
solution  and  enter  the  gas  spaces  in  any  region  of  the  plant.  Thus,  dissolved  nitrogen, 
oxygen,  etc.,  may  diffuse  from  the  soil  into  the  roots  and  may  subsequently  pass  out  of 
solution  into  an  intercellular  channel.  Dissolved  oxygen,  produced  in  the  chlorophyll- 
bearing  cells  of  a  leaf  during  a  period  of  sunlight,  diffuses  as  a  solute,  mainly  to  the 
periphery  of  a  sub-stomatal  gas  space,  where  it  passes  out  of  solution  and  then  diffuses 
as  a  gas  through  the  stomatal  pore  into  the  surrounding  atmosphere.  Of  course  it 
may  also  diffuse  in  other  directions  through  the  tissues.  The  gas  spaces  of  the  xylem 
are  not  continuous  with  those  of  the  cortex,  but  gases  may  move  from  one  system  of 
channels  to  the  other,  first  passing  into  solution,  then  diffusing  as  solutes,  and  finally 
passing  out  of  solution  again.  These  gas  spaces  of  the  xylem  are  generally  not  inter- 
cellular; they  occupy  portions  of  the  vascular  channels  (that  is,  the  interiors  of  much 
elongated  cells  that  are  dead  and  without  protoplasm  and  that  have  lost  their  end 
walls  in  many  cases  where  adjacent  cells  were  originally  in  contact).  The  pressure  of 
the  gas  in  the  vessels  is  frequently  much  lower  (especially  when  the  transpiration  rate 
is  high)  than  that  of  the  environmental  atmosphere  and  of  the  intercellular  cortical 
channels.  On  the  other  hand,  the  gas  pressure  in  the  xylem  may  sometimes  be  higher 
than  that  in  the  cortical  channels  (when  there  is  sap  pressure). 

3.  Movement  of  Water  and  Dissolved  Substances. — Girdling  experiments  show 
(1)  that  water  and  soil  solutes  move  from  the  roots  to  other  parts  of  the  plant  body 
through  the  xylem  vessels  that  are  not  blocked  with  gas;  and  (2)  that  organic  solutes 
(such  as  sugar)  move  from  the  leaves,  and  from  regions  where  such  substances  have 
been  accumulated,  to  other  regions,  through  the  phloem  of  the  vascular  tissue. 

4.  The  Transpiration  Stream. — Water  evaporates  from  the  water-impregnated 
cell  walls  that  bound  the  sub-stomatal  gas  spaces  of  leaves,  and  it  then  diffuses,  as 
water  vapor,  through  the  stomatal  openings  into  the  external  atmosphere.  This 
process  is  called  stomatal  transpiration.  Water  also  evaporates  directly  into  the 
atmosphere,  but  at  a  slower  rate,  from  the  cutinized  epidermal  cell  walls  which  always 
contain  some  imbibed  water.  This  process  is  cuticular  transpiration.  Transpiration 
tends  to  dry  the  cell  walls  from  which  the  water  evaporates,  and  thus  to  increase  the 
imbibitional  attraction  they  exert  on  the  liquid  water  within  the  cells  and  farther  back 
in  the  tissues.  Equilibrium  tends  to  be  reestablished  by  movement  of  water  out  of 
the  xylem  vessels,  through  intervening  cells,  to  the  evaporating  surfaces.  The  forces 
drawing  water  out  of  the  vessels  are  very  great,  and  they  tend  to  stretch  the  whole 
-water  mass  of  the  plant  body.  The  vessels  are  sufficiently  rigid  to  prevent  their  being 
collapsed  by  this  inward  pull  on  their  walls,  and  the  strain  (by  virtue  of  the  cohesion  of 
water)  is  transmitted  to  all  parts,  tending  to  remove  some  water  from  all  cell  walls 
whose  outer  surfaces  are  in  contact  with  gas.  At  root  surfaces  this  tendency  results 
in  the  drawing  in  of  water  from  the  soil  (probably  carrying  dissolved  salts  with  it,  in 
so  far  as  the  cell  membranes  are  permeable  to  these  solutes).  As  transpiration  pro- 
ceeds, so  long  as  the  water  supply  is  maintained  at  the  absorbing  root  surfaces  (espe- 
cially root-hairs),  there  is  a  flow  of  water  into  the  roots,  through  the  xylem  vessels,  and 
into  the  cell  walls  from  which  evaporation  is  occurring.  This  mass  flow  of  water 
(carrying  solutes)  through  the  plant  is  called  the  transpiration  stream.  Some  of  the 
water  drawn  into  the  roots  is  used  in  tissue  enlargement  (which  is  primarily  imbibi- 


152  PHYSIOLOGY    OF    NUTRITION 

tional  and  osmotic  swelling),  in  the  photosynthesis  of  carbohydrates,  etc.,  and  con- 
sequently the  rate  of  water  absorption  by  the  root  system  is,  on  the  whole,  for  long 
periods,  a  little  greater  than  the  rate  of  transpiration.  Also,  some  water  is  lost,  in 
some  plants,  by  being  excreted  to  the  exterior  in  the  liquid  form,  as  from  hydathodes 
and  nectaries,  which  excrete  aqueous  solution  at  leaf  margins,  on  flower  parts,  etc. 
This  glandular  excretion  of  aqueous  solution  by  hydathodes  is  termed  guttation. 
Compared  with  transpiration,  guttation  is  a  slow  and  not  very  important  process; 
it  is  encountered  in  comparatively  few  plants  and  is  not  maintained  for  long  periods. 
Water  loss  through  nectaries  is  still  less  significant  in  this  connection.  Sap  pressure, 
by  which  the  water  solution  of  the  vessels  is  sometimes  under  pressure  instead  of 
under  tension  (it  is  under  pressure  only  when  the  transpiration  rate  is  very  low  and 
the  soil  water  supply  is  plentiful),  appears  to  be  due  to  a  sort  of  gland  action  (some- 
what like  that  of  hydathodes  on  leaf  margins)  in  the  tissues  of  the  roots,  etc.,  resulting 
in  the  active  forcing  of  solution  from  the  cortex  into  thexylem  vessels;  the  water  thus 
forced  into  the  xylem  is  derived  from  the  surrounding  tissue,  and  ultimately  from  the 
soil.  Bleeding,  as  of  cut  grape  shoots  in  early  spring,  is  partly  or  wholly  due  to  sap 
pressure.  Sap  pressure  does  not  occur  when  the  transpiration  stream  is  rapid;  at 
such  times  the  solution  in  the  xylem  vessels  is  under  tension;  therefore  this  pheno- 
menon cannot  generally  be  the  cause  of  the  rise  of  sap  in  stems.  This  rise  is  directly 
due  to  the  removal  of  water  from  the  xylem  above,  to  the  tensile  or  stretching  strain 
transmitted  through  the  water  of  walls,  protoplasm,  vacuoles,  etc.,  in  all  directions, 
and  to  the  inward  flow  from  the  soil  adjacent  to  the  root  surfaces.  The  molecular 
physics  of  sap  pressure,  gland  secretion,  etc.,  is  not  yet  understood. 

The  rate  of  transpiration  nearly  controls  the  rate  of  water  absorption  in  ordinary 
plants  with  a  plentiful  water  supply.  When  plants  are  well  supplied  with  water  at  the 
absorbing  surfaces  of  the  roots,  the  rate  at  which  water  is  evaporated  from  leaves  and 
stems  is  dependent  on  several  conditions,  which  may  be  grouped  as  internal  and 
external.  Among  the  internal  conditions  are:  The  structure  of  the  plant,  the  kind 
of  epidermis,  the  distribution,  size,  and  open  or  closed  condition  of  stomata,  the 
degree  of  water  saturation  of  the  tissues,  the  power  of  the  foliage  to  absorb  solar  radia- 
tion, the  rate  of  water  movement  from  roots  to  transpiring  surfaces,  etc.  Many 
(but  not  nearly  all)  stomata  open  and  close  according  to  conditions.  Such  stomata 
usually  open  when  the  light  intensity  increases  about  dawn,  and  close  more  or  less 
completely  with  the  diminution  of  light  intensity  in  the  evening.  They  also  usually 
close  when  wilting  approaches.  Generally  the  guard  cells  are  more  turgid  when  the 
pores  are  open.  Stomatal  movement  is  due  to  changes  in  the  turgor  relations  (ten- 
sions) between  the  guard  cells  and  the  other  epidermal  cells. 

External  conditions  influencing  the  transpiration  rate,  when  the  root  surfaces  are 
well  supplied  with  water,  are  the  evaporating  power  of  the  air  (air  temperature,  air 
humidity,  air  movement)  and  the  intensity  of  absorbed  sunlight.  Over  25  per  cent, 
of  the  radiant  energy  absorbed  may  be  converted  into  the  latent  heat  of  water  vapor  in 
this  way,  without  considerable  change  in  the  temperature  of  the  foliage.  When  the 
supply  of  water  to  the  absorbing  roots  is  not  adequate,  the  rate  of  this  supply  greatly 
influences  the  transpiration  rate  by  limiting  the  rate  of  absorption  by  the  roots. 
Plants  usually  transpire  more  than  they  absorb  during  the  day  and  absorb  more  than 
they  transpire  during  the  night. 

There  are  usually  several  hundred  stomata  per  square  millimeter  of  leaf  surface, 
the  stomata  being  frequently  more  numerous  on  one  leaf  surface  than  on  the  opposite 
one.     For  plants  of  the  same  kind,  all  with  the  same  environment  and  all  having 


MOVEMENT  OF  MATERIALS  IN  THE  PLANT  1 53 

been  grown  under  the  same  condition  complex,  the  amount  of  water  lost  per  day 
is  about  proportional  to  the  extent  of  the  leaf  surface.  According  to  Wollny,  a  maize 
plant  transpired  nearly  13  liters  of  water  during  its  entire  growing  season.  A  pea 
plant  correspondingly  gave  off  nearly  4.5  liters.  The  transpiration  rate  is  very 
important  in  determining  the  rate  at  which  dissolved  salts,  as  well  as  water,  enter  the 
roots  from  the  soil,  also  in  determining  the  rate  at  which  dissolved  salts  are  earried 
to  the  leaves.  The  dissolved  material  is  left  in  the  leaves  when  the  water  evapor- 
ates, and  old  leaves  generally  have  a  large  salt  content. 

5.  Movement  of  Organic  Substances. — Organic  materials  (such  as  sugars,  etc.) 
must  be  in  aqueous  solution  to  move  from  one  region  of  the  plant  to  another.  Evi- 
dence points  to  the  sieve-tubes  of  the  phloem  as  the  main  path  of  movement  of  these 
solutes.  They  may  diffuse,  however,  in  all  directions,  so  far  as  the  protoplasmic  mem- 
branes and  cell  walls  are  permeable  to  them.  Also,  some  organic  materials  move  in 
the  transpiration  stream,  through  the  xylem  vessels. 

Carbohydrates  produced  by  photosynthesis  in  the  cells  of  green  leaves,  in  sunlight, 
diffuse  outward  and  move  to  other  parts  of  the  plant  through  the  phloem.  They,  and 
other  organic  materials,  frequently  accumulate  in  storage  tissues,  often  going  out  of 
solution  there  (e.g.,  starch).  Such  accumulations  usually  dissolve  again  later,  and 
move  once  more  when  new  growth  begins.  The  molecular  physics  of  this  movement 
through  the  phloem  is  not  understood;  the  rate  of  the  movement  is  too  great  to  be 
accounted  for  by  simple  diffusion. 

Materials  enter  the  plant  body  and  move  about  therein  according  to  the  principles 
and  considerations  that  have  been  briefly  stated.  It  remains  to  consider  their  exit 
from  the  plant  body.  As  has  been  shown,  water  is  almost  continually  being  given  off 
to  the  surrounding  air  by  ordinary  plants  (transpiration,  guttation).  It  has  also 
been  mentioned  that  salts,  sugars,  etc.,  are  given  off  to  a  small  degree  through  gut- 
tation and  gland  action.  Oxygen  passes  from  green  leaves  into  the  air  during  sunlight 
periods,  and  some  carbon  dioxide  escapes  in  a  similar  way  during  periods  of  darkness. 
Very  small  amounts  of  volatile  materials  besides  water,  carbon  dioxide,  and  oxygen, 
are  given  off  by  transpiration  (volatile  oils  recognized  as  odors,  etc.).  Salts  and 
organic  substances  are  given  off  when  flowers,  fruits,  leaves,  bark  fragments,  etc., 
fall  away.  Roots  regularly  give  off  carbon  dioxide,  sometimes  organic  acids  and  their 
salts.  Numerous  materials  are  given  off  to  the  soil  when  roots,  root  hairs,  and  the 
tissues  of  the  root-caps  die  and  decay.  The  amount  of  nitrogenous  material  in  the 
soil  is  often  markedly  increased  in  this  manner  by  the  growth  and  decay  of  legume 
roots  with  tubercles.  Finally,  the  material  in  the  plant  body  is  ultimately  released 
to  the  environment  after  the  death  of  the  plant,  the  various  substances  being 
subsequently  decomposed  by  the  action  of  other  organisms,  such  as  bacteria,  animals, 
etc. 


CHAPTER  VII 

MATERIAL  TRANSFORMATIONS  IN  THE  PLANT1 

§i.  The  Cell  as  the  Physiological  Unit.2 — livery  plant  is  composed  of  one 
or  more  cells,  each  of  which  consists  essentially  of  cytoplasm  and  nucleus. 
Observations  and  experiments  have  shown  that  the  life  of  the  cell  depends  upon 
the  activities  of  these  two  parts  and  that  the  other  parts  of  the  cell  are  formed 
by  these.  The  life  of  a  many-celled  plant  is  thus  nothing  but  the  sum 
total  of  the  lives  of  its  individual  cells.  For  this  reason  the  cell  may  be  charac- 
terized, as  the  elementary  organism.3  We  know  of  no  organism  with  a  structure 
simpler  than  that  of  a  single  cell. 

The  nucleus  and  the  cytoplasm  both  have  peculiar  internal  structures,  and 
their  chemical  nature  is  very  complicated  and  not  well  understood.  The  dried 
Plasmodium  of  the  slime-mould  Mthalium  septicum,  consisting  almost  entirely 
of  cytoplasm  and  nuclei,  has  the  following  chemical  composition  expressed,  in 
percentage  of  dry  weight:4 

Proteins 40  Cholesterin 2.0 

Albumins  and  enzymes 15  Resins , 1.2 

Other  nitrogenous  compounds 2  Calcium  salts  (except  CaC03) 0.5 

Fats 12  Other  salts 6.5 

Carbohydrates 12  Undetermined  materials 6.5 

The  cytoplasm  and  nucleus  thus  consist  mostly  of  proteins — very  compli- 
cated nitrogenous  compounds,  many  of  which  contain  phosphorus.  After 
treatment  of  proteins  with  gastric  juice  or  trypsin  there  remains  an  undissolved 
residue  containing  nucleic  acid.  The  nucleus,  the  cytoplasm,  chloroplasts, 
leucoplasts,  and  all  other  living  constituents  of  the  cell  are  only  partially  dis- 
solved in  gastric  juice  (exceptions  to  this  statement  are  very  rare).  On  the  other 
hand,  the  simple  proteins  (constituents  of  aleurone  grains,  albumin  crystals, 
etc.),  are  completely  soluble  in  gastric  juice.  The  amount  of  simple  proteins 
in  cytoplasm  and  nucleus  is  so  small  that  it  cannot  be  determined  at  all  by  micro- 
chemical  methods,  or  this  is  possible  only  with  special  precautions. 

1  Euler,  H.,  Grundlagen  und  Ergebnisse  der  Pflanzenchemie.     2  v.  Braunschweig,  1908-1909. 

2  Verworn,  M.,  Allgemeine  Physiologie.  5  Aufl.  Jena,  1909.  [Idem,  General  physiology.  Translated 
by  F.  S.  Lee,  from  the  2nd  Ger.  ed.  XVI  +  599  p.  London,  1899.]  Reinke,  J.,  Einleitung  in  die  theo- 
retische  Biologie.  2  Aufl.  578  p.  Berlin,  1911..  Hofmeister,  F.,  Die  chemische  Organisation  der  Zelle. 
Braunschweig,  1901.     [Hober,  1914.     (See  note  1,  p.  119.)] 

3  Briicke,  Ernst,  Die  Elementarorganismen.  Sitzungsber.  (math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien 
447/:  381-406.     1861. 

4  Reinke,  1S81.     [See  note  I,  p.  30. 1 

154 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT 


155 


§2.  Proteins. — -The  proteins  are  chemically  the  most  complicated  consti- 
tuents of  the  plant.1  They  accumulate  to  the  greatest  extent  in  the  protoplasm 
of  resting  cells  and  cells  where  physiological  activity  is  just  beginning.  The 
diagrams  of  Fig.  85  represent  stages  in  the  development  of  a  dicotyledonous 
seedling:  7  is  a  young  embryo,  II  is  a  developed  embryo,  and  777  is  a  germinated 
seedling.  The  parts  rich  in  proteins  are  shown  in  black.  These  parts  are  the 
voungest  organs  of  the  plant,  and  are  either  in  the  resting  condition  or  are  just 
beginning   to   grow.     The   shaded   areas   represent   parts   containing   smaller 


Fig.   85. — Diagrams  showing  stages  in  the  development  of  a  dicotyledonous  seedling,   and 

distribution  of  proteins.      (After  Sachs.) 


'  For  the  literature  of  proteins  see:  Hammarsten,  O.,  Lehrbuch  der  physiologischen  Chemie.  4  te  Aufl. 
Wiesbaden,  1899.  [Idem,  A  text-book  of  physiological  chemistry.  Tr.  by  J.  A.  Mandel  from  8th  Ger.  ed. 
(7th  Eng.  ed.)  New  York,  1914.I  Haliburton  W.  D.  A  text-book  of  chemical  physiology  and  pathology. 
874  p.  London,  1891.  See  p.  111-142.  Cohnheim,  Otto,  Chemie  der  Eisweisskorper.  315  p.  Braun- 
schweig, 1900.  Griessmayer,  Victor,  Die  Proteide  der  Getreidearten.  Heidelberg,  1897.  [Czapek,  F., 
BiochemiederPflanzen.  1  te  Aufl.  2  v.  Jena.  1903.  Idem,  same  title.  2  te  Aufl.  Jena,  1913.  (Only 
1st  v.  (828  p.)  has  appeared.)]  Abderhalden,  E.,  Lehrbuch  der  physiologischen  Chemie  in  dreissig  Vorles- 
ungen.  Berlin,  1906.  Idem,  Handbuch  der  biochemischen  Arbeitsmethoden.  8v.  Berlin,  1910-1915. 
[Euler,  1908-1909.  [See  note  I,  p.  154.]  Hofmeister,  1901.  [See  note  2,  p.  154.]  Grafe,  1914.  [See 
note  o,  p.  83.]  Haas  and  Hill,  1921.  [See  note  3,  p.  6-1  Osborne,  Thomas  B.,  The  vegetable  proteins. 
London  and  New  York,  1909.  Plimmer,  R.  H.  Aders,  The  chemical  constitution  of  the  proteins.  London 
and  New  York.     1908.] 


156  PHYSIOLOGY   OF   NUTRITION 

amounts  of  proteins  and  these  are  the  regions  of  most  active  growth.  The 
unshaded  parts  represent  fully  grown  tissues,  which  contain  only  a  very  small 
amount  of  proteins,  these  substances,  having  disappeared  during  the  growth 
process.  An  exception  to  this  statement  are  full-grown  leaves,  which  contain 
much  protein  material  in  their  chloroplasts.  These  diagrams  show  not  only 
the  protein  contents  but  also  the  growth  activities  of  the  different  parts  of  the 
plant. 

The  principal  chemical  reactions  of  proteins  are  given  below. a 

1.  With  copper  sulphate  and  caustic  potash  solution,  a  dark  violet  color  is 
produced  (biuret  reaction).  Albumoses  and  peptones  give  a  red  color  with  this 
reagent.  This  reaction  is  of  special  importance,  since  it  serves  as  a  means  of 
distinguishing  the  albumins  from  their  cleavage  products.  Excess  of  copper 
sulphate  is  to  be  avoided,  since  the  blue  color  of  this  salt  may  obscure  the 
result. 

2.  Heating  with  strong  nitric  acid  gives  a  deep  yellow  color,  which  changes 
to  orange-red  upon  treatment  with  an  excess  of  ammonia  (xanthoproteic  reac- 
tion). 

3.  Heating  with  Millon's  reagent  gives  a  red  color  (Millon's  reaction). 

4.  With  a-napthol  and  concentrated  sulphuric  acid  a  blue-violet  color  is 
produced  (Molisch's  furfurol  reaction). 

5.  Boiling  with  fuming  hydrochloric  acid  gives  a  bluish-violet  color  (Lieber- 
mann's  reaction). 

0  The  following  additions  may  be  useful.  (1)  For  the  biuret  test,  add  strong  KOH  solu- 
tion and  follow  with  weak  CuS04  solution.  A  partially  decomposed  protein — such  as  pep- 
tones— gives  a  pink  or  purplish-red  color.  Gies  and  Kantor  give  directions  for  a  single  solution 
suitable  for  this  test.  (Gies,  W.  J.,  and  Kantor,  J.  L.,  Methods  of  applying  the  biuret  test. 
Biochem.  bull  1:  264-269.  1911.)  To  1000  cc.  of  10-per  cent,  aqueous  solution  of  NaOH 
add  25  cc.  of  a  3-per  cent,  solution  of  CuSO*,  a  few  cubic  centimeters  at  a  time,  with  thorough 
shaking  after  each  addition.  Filter  through  glass  wool  if  necessary.  The  biuret  test,  as 
well  as  many  other  microchemical  reactions,  may  be  influenced  by  other  reactions,  the  possible 
occurrence  of  which  must  be  considered.  (See:  Mathewson,  C.  A.,  A  study  of  some  of  the 
more  important  biochemical  tests.  Biochem.  bull.  2:  181.  1912.)  Biuret  is  represented 
by  the  formula,  NH2CO-NH-CONH2.  In  treating  sections,  a  solution  of  copper  hydrate 
in  KOH  solution  may  be  used.  It  is  sometimes  better  to  warm  the  section  in  weak  KOH 
solution,  wash  in  water  and  treat  with  CUSO4  solution,  after  which  it  is  again  washed  and 
then  examined  in  KOH  solution.  (3)  Millon's  reagent  is  a  solution  of  mercuric  nitrate  and 
nitrous  acid.  To  prepare  it,  dissolve  (in  fume  cupboard)  mercury  in  twice  its  weight  of  strong 
HNO3  (spec.  grav.  1.42),  and  then  dilute  the  solution  to  three  times  its  volume,  with  water. 
This  reaction  and  the  xanthoproteic  reaction  are  dependent  on  the  tyrosin  or  tryptophan  group 
in  the  protein  molecule.  (4)  For  the  furfurol  reaction,  add  a  few  drops  of  10-20-per  cent,  alco- 
holic solution  of  et-naphthol,  and  then  slowly  add  concentrated  H2SO4.  The  color  reaction 
appears  at  junction  of  the  two  liquids.  If  thymol  is  used  instead  of  a-naphthol  a  carmine  color 
is  produced.  (5)  Liebermann's  reaction  is  used  with  material  that  has  previously  been 
extracted  with  alcohol  and  ether,  and  it  appears  to  be  due  to  glyoxylic  (glyoxalic)  acid  present 
in  the  ether,  this  acid  reacting  with  the  tryptophan  group  of  protein.  (6)  For  Adamkiewicz's 
reaction,  material  is  extracted  with  ether  to  remove  fat,  dried  and  then  extracted  with  glacial 
acetic  acid.  The  concentrated  H2SO4  is  added  slowly  and  the  color  appears  at  the  junction  of 
the  two  liquids.  Here,  also,  the  reaction  seems  due  to  glyoxylic  acid  (present  in  the  acetic 
acid). — Ed. 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT  1 57 

6.  Glyoxylic  acid  and  concentrated  sulphuric  acid  produce  a  beautiful 
bluish- violet  color  (Adamkiewicz  and  Hopkin's  tryptophan  reaction). 

The  method  of  Stutzer1  may  be  used  for  the  quantitative  determination  of 
proteins.  This  depends  upon  the  fact  that  with  copper  hydroxide  these  sub- 
stances form  a  compound  that  is  insoluble  in  water.  The  determination  is  carried 
out  as  follows.  The  triturated  plant  tissue  is  boiled  with  water  and  the  ex- 
tract is  then  treated  with  copper  hydroxide.  The  precipitate  is  filtered  off 
with  hot  water  and  is  then  washed  with  alcohol  and  dried.  This  precipitate 
contains  all  the  protein  material.  The  other  nitrogenous  substances  of  plants 
form  water-soluble  compounds  with  copper  hydroxide  and  are  thus  removed 
in  the  filtrate.  For  the  determination  of  nitrogen  in  the  precipitate  the  well- 
known  method  of  Kjeldahl  may  be  used.  The  nitrogen  of  most  organic  sub- 
stances is  converted  into  ammonia  by  boiling  with  fuming  sulphuric  acid 
and  thus  remains  in  the  flask  as  ammonium  sulphate,  which  may  then  be  deter- 
mined by  any  of  the  usual  methods.  From  the  result  is  calculated  the  amount 
of  protein  nitrogen  originally  present. 

If  the  entire  nitrogen  content  is  determined  for  one  portion  of  the  material 
and  the  content  in  protein  nitrogen  is  determined  for  another  portion,  the  differ- 
ence between  these  two  numbers  gives  the  amount  of  the  non-protein  nitrogen. 

The  following  table  may  serve  to  show  the  relative  amounts  of  protein  nitro- 
gen and  of  non-protein  nitrogen  contained  in  different  plants.  The  quantities 
are  given  as  percentages  of  total  nitrogen  present.  A  considerable  amount  of 
nitrogen  is  seen  to  be  present  in  simple  compounds. 

Protein  Non-protein 

Nitrogen  Nitrogen 

Vetch 67.2  32.8 

Young  alfalfa 73.1  26.9 

Potato  tubers  (July  7) 58.7  413 

From  a  physiological  viewpoint  one  must  distinguish  between  two  groups  of 
proteins:  the  simple  proteins  or  albuminous  bodies,  and  the  conjugated  proteins 
or  combination  of  simple  proteins  with  other  substances.  The  simple  proteins 
are  reserve  foods  (as,  for  example,  the  albumin  of  aleurone  grains),  and  the 
compound  proteins  are  essential  in  the  life  of  the  cell.  The  latter  form  the 
principal  non-aqueous  component  of  protoplasm,  as  is  evident  from  the 
analysis  given  on  page  154.6 

The  simple  proteins  may  be  grouped  as  follows.0 

1  Stutzer,  A.,  Untersuchungen  iiber  die  quantitative  Bestimmung  des  Protein  Stickstoffs  und  die  Tren. 
nung  der  Proteinstoffe  von  anderen  in  Pflanzen  vorkommenden  Stickoff-Verbindungen.  Jour.  exp.  Landw. 
28:  103-123.  1881.  Idem,  Untersuchungen  iiber  die  Verdaulichkeit  und  die  quantitative  Bestimmung 
der  Eiwissstofle.     7&i<f.  29:  473-492.     1881. 

6  Since  our  knowledge  of  plant  proteins  rests  almost  wholly  upon  the  investigation  of  seeds, 
a  general  classification  based  on  physiological  properties  is  not  yet  possible.  For  a  discussion 
of  this  point  see:  Osborne,  1909.     [See  note  1,  p.  155.] — Ed. 

e  This  discussion  is  mainly  based  on  our  knowledge  of  animal  proteins;  plant  proteins  appear 
to  differ  from  these  in  many  respects.  See  Osborne,  1909.  [See  note  1,  p.  155].  Haas  and 
Hill,  1921.     [See  note  3,  p.  6.] — Ed. 


158  PHYSIOLOGY    OF    NUTRITION 

i.  Albumins. — The  albumins  are  soluble  in  pure  water  and  may  be  precipi- 
tated by  saturation  of  the  solution  with  ammonium  sulphate.  They  are  coagu- 
lated by  boiling  or  by  treatment  with  alcohol. 

2.  Globulins. —  The  globulins  are  insoluble  in  pure  water  but  are  soluble  in 
solutions  of  neutral  salts  (sodium  chloride,  ammonium  chloride,  magnesium 
sulphate,  etc.).  They  are  completely  precipitated  by  a  half-saturated 
solution  of  ammonium  sulphate  and  are  coagulated  by  boiling  or  by  addition 
of  alcohol. 

3.  Albuminates. — These  are  formed  when  albumins  and  globulins  are  treated 
with  weak  alkalies  (alkali  albuminates),  or  with  weak  acids  (acid  albuminates, 
or  syntonins).  They  are  insoluble  in  water  and  in  solutions  of  neutral  salts 
but  are  soluble  in  weak  acids  and  alkalies;  they  are  not  precipitated  by  boiling 
but  are  salted  out  by  saturation  with  ammonium  sulphate.  They  coagulate 
with  excess  of  alcohol. 

4.  Albumoses  and  Peptones. — These  compounds  are  the  first  products  of  the 
hydrolytic  cleavage  of  proteins  by  enzymes.  The  albumoses  are  precipitated 
by  ammonium  sulphate,  while  the  peptones  remain  in  solution. 

The  proteins  occurring  in  plants  have  been  only  partially  worked  out,1  even 
for  seeds.  The  simple  ones  may  be  illustrated  by  the  phy toalbumins,  the  phy  to- 
globulins,  and  the  peptones.d 

The  phytoalbumins  are  not  of  common  occurrence2  and  in  most  cases  have 
not  been  identified  with  absolute  certainty.  The  proteins  present  in  the  cell 
sap  are  usually  globulins,  since  they  are  soluble  only  in  the  presence  of  salts  and 
are  obtained  as  a  precipitate  by  dialysis. 

The  phytoglobulins  are  better  understood.3  They  appear  to  compose  the 
principal  reserve  proteins  of  some  seeds.  Seeds  of  Lupinus  luteus  may  be  men- 
tioned as  one  of  the  best  materials  for  the  demonstration  of  phytoglobulin. 

1  Abderhalden,  Emil,  Biochemisches  Handlexikon.     Berlin,  1911.     Vol.  4. 

2  Martin,  Sidney  H.  C,  The  nature  of  papain  and  its  action  on  vegetable  proteid.  Jour.  Physiol. 
6:  336-360.  1884-1885..  Green,  J.  R.,  Proteid  substances  in  latex.  Proc.  Roy.  Soc.  London  40:  28-39. 
1886.     Vines,  S.  H.,  and  Green,  J.  R.,  The  reserve  proteid  of  the  asparagus  root.     76j'<2.  52 :  130-132.     1893. 

3  Weyl,  Th.,  Beitrage  zur  Kenntniss  thierischer  und  pnanziicher  Eiweisskorper.  Zeitsch.  physiol. 
Chem.  1 :  72-100.  1877-1878.  Palladin,  W.,  Beitrage  zur  Kenntniss  der  pflanzlichen  Eiweissstoffe. 
Zeitsch.  Biol.  31:  191-202.  1895.  Abderhalden,  Lehrbuch,  1906.  [See  note  1.  p,  155.]  [Also  see  Os- 
borne, 1909.     [See  note  I,  p.  155.] 

d  The  following  additional  information  may  help  the  reader  to  fom  a  more  concrete  picture. 

(1)  Albumins  are  plentiful  in  animals  but  generally  seem  to  occur  only  in  small  quantities  in 
plants.  Examples  of  plant  albumins  are  legumelin,  from  pea  seeds,  and  leucosin,  from  the 
seeds  of  wheat  and  other  grains.  (2)  Globulins  are  the  main  reserve  proteins  in  seeds,  except- 
ing those  of  the  cereals.  Examples  are:  excelsin,  from  the  Brazil  nut  {Bertholetia  excelsa); 
legumin  from  pea  seeds  and  seeds  of  other  legumes;  edestin,  from  hemp  seeds  (Canna- 
bis saliva);  conglutin,  from  lupine  seeds.  (3)  Metaproteins  is  a  better  term  than  albuminates. 
(4)  Proteose  is  the  general  term,  so  that  albumose  results  from  splitting  of  albumin,  and 
globulose  from  splitting  of  globulin.  It  may  be  mentioned  that  the  gluten  of  wheat,  etc.,  is 
largely  composed  of  glutelins  and  gliadins,  two  other  groups  that  might  be  inserted  between 

(2)  and  (3)  in  the  text.  To  the  latter  group,  besides  gliadin  proper  (which  occurs  in  wheat 
and  rye),  belong  also  hordein  (in  barley),  and  zein  (in  wheat  and  maize).  It  should  be  re- 
membered that  the  classifications  of  proteins  are  based  on  temporary  needs  of  description; 
the  chemical  knowledge  necessary  for  a  really  satisfactory  classification  is  still  lacking. — Ed. 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT 


J59 


The  finely  powdered  seeds  are  treated  with  a  io-per  cent,  solution  of  sodium 
or  ammonium  chloride  and  the  solution  is  filtered  off  after  twenty-four  hours. 
The  filtrate  is  then  dialysed,  Kuhne's  dialyser  being  well  suited  to  this  purpose 
(Fig.  86).  The  solution  is  placed  in  a  tube  of  parchment  paper  surrounded  by 
running  water.  The  water  enters  through  the  funnel,  in  the  diagram,  and  es- 
capes through  the  lateral  tube.  After  two  or  three  day's  the  globulin  is  found 
to  have  settled  upon  the  bottom  of  the  parchment  paper  tube,  as  a  tough,  viscous 
mass,  insoluble  in  pure  water  but  soluble  in  solutions  of  neutral  salts.  The 
globulins  obtained  from  different  plants  are  not  identical.  So  are  distinguished, 
for  example,  edestin  (from  fatty  seeds,  such  as  those  of  hemp,  Cannabis  saliva) , 
legumin  (from  pea  and  other  legume  seeds),  and  conglutin  (from  lupine  seeds). 
The  phytoglobulins  are  not  altogether  the  same  as  the  typical  animal  globulins. 

Peptones  are  present  in  plants  only  in  very  small  amounts.  To  isolate  these 
Neumeister1  has  made  use  of  their  solubility  in  saturated  ammonium  sulphate 
solution.  All  other  proteins  are  precipitated  by  this  salt.  Aqueous  extracts 
of  seeds  and  plants  are  saturated  with  solid  ammonium  sul- 
phate and  then  filtered.  The  filtrate  gives  the  color  reaction 
of  the  biuret  test  for  peptones.  The  plants  studied  by 
Neumeister  may  be  assorted  into  two  groups  according  to 
their  peptone  content.  Seeds  of  Papaver  (poppy),  Beta 
(beet),  Hordeum  (barley),  Zea  (maize),  and  Triticum  (wheat), 
contain  no  trace  of  peptones;  these  substances  being  here  de- 
tected only  during  germination.  In  seeds  of  Lupinus  (lupine), 
Vicia  (vetch),  and  Avena  (oats),  however,  which  belong  to  the 
second  group,  peptones  are  more  plentiful  than  in  the  seedlings. 
The  peptones  thus  act  here  as  reserve  food  and  are  gradually 
used  up  during  germination. 

An  idea  of  the  structure  of  the  proteins  may  be  derived 
from  the  study  of  their  cleavage  products.  The  products  of 
complete  hydrolysis,2  obtained  by  continued  boiling  with  concentrated  acids 
and  alkalis,  or  through  enzymatic  decomposition,  are  mainly  amino  acids.  The 
following  principal  products  of  the  hydrolysis  of  simple  proteins  have  already 
been  isolated  and  identified. e 


W 


Fig.  86. — Kuhne's 
dialyser. 


i.  Aliphatic  Compounds 

A.  Monoamino  acids 

Glycocoll  (a-amino-acetic  acid),  CH2NH0COOH. 

d-Alanin  (a-amino-propionic  acid),  CH3CHNH2  COOH. 

/-Serin  (a-amino-/3-hydroxypropionic  acid,  a-amino-(3-lactic  acid), 

CH2OHCHNH2COOH. 

i  Neumeister,  R.,  Ueber  das  Vorkommen  und  die  Bedeutung  eines  eiweisslosenden  Enzyms  in  jugend- 
lichen  Pflanzen.     Zeitsch.  Biol.  30:  447-463.     1894. 

-  Abderhalden.  E.,  Keuere  Ergebnisse  auf  dem  Gebiete  der  speziellen  Eiweisschemie.     Jena.  1909. 

e  The  classification  has  been  made  clearer  than  in  the  German  text,  and  the  formulas  are 
here  introduced.  Formulas  are  more  clearly  given  in:  Mathews,  Albert  P.,  Physiological 
Chemistry.     3d  ed.     n  54  p.     New  York,  1920. — Ed. 


l6o  PHYSIOLOGY   OF   NUTRITION 

d-Valin  (a-amino-iso valeric  acid),  „3  />CHCHNH2COOH. 

/-Leucin  (a-amino-isocaproic  acid,  a-amino-isobutyl-acetic  acid), 

^aN^CHCH2CHNH2COOH. 
CH3/ 


d-Isoleucin  (/3-methyl-/3-ethyl-a:-ammo-propionic  acid), 

i^'N  CHCHNH2COOH. 
C2XI5/ 

/-Aspartic  acid  (a-amino-succinic  acid),  COOHCH2CHNH2COOH. 

^-Glutamic  acid  (a-amino-glutaric  acid),  COOHCH2CH2CHNH2COOH. 

B.  Diamino  acids 

Lysin  (a-e-diamino-caproicacid),  NH2CH2CH2CH2CH2CHNH2COOH. 

J-arginin  (5-guanidin-a-amino- valeric  aci),d 

HN  -  c/NH2 

N  '  '     \NHCH2CH2CH2CHNH2COOH. 

Cystin  (a-diamino-/3-dithio-dilactylic  acid), 

CH2CHNH2COOH— S— S— CH2CHNH2COOH. 

Aromatic  Compounds 

/-Phenyl  alanin  ((3-phenyl-a-amino-propionic  acid), 

C6H5CH2CHNH2COOH. 

/-Tyrosin  (/3-para-hydroxyphenyl-a-amino-propionic  acid), 

HOC6H4CH2CHNH2COOH. 

Heterocyclic  Compounds,  Derivatives  of  Imidazol,  Pyrrol  and  Indol 

/-Histidin  (/3-imidazol-a-amino-propionic  acid), 
CH  =  C— CH2CHNH2COOH 

N        NH 

V 

CH 

/-Prolin  (a-pyrrolidin-carboxylic  acid), 
CH2— CH2 

CH2     CHCOOH 


NH 

/-Hydroxyprolin  (hydroxy -a-pyrrolidin-carboxylic  acid) , 
/-Tryptophan  (/3-indol-a-amino-propionic  acid). 
C— CH2CHNH2COOH 


CeH^v     /CH 


NH 

The  relative  amounts  of  the  various  amino  acids  obtained  from  different 
proteins  are  not  constant,  as  is  evident  from  the  following  table,  which  shows 
these  amounts  for  seeds  of  wheat  and  oats. 


MATERIAL    TRANSFORMATIONS    IX   THE   PLANT 


161 


i.   Monoamino 
acids 


2.  Diamino 

acids 

3.  Heterocylic 
compounds 


Glycin 

Alanin 

Serin 

Leucin 

Aspartic  acid. 
Glutamic  acid. 
Phenyl  alanin. 

Tyrosin 

Cystin/ 

Total 

Lysin 

Arginin 

Total 

Histidin 

Prolin 

Tryptophan . . . 
Total 


Wheat 

0.90 

4-65 
0.74 
6.00 
0.90 
23.40 
2.00 
4-25 
0.02 


42.86 

1 .90 
4-7Q 
6.60 

1 .76 
4.20 
trace 

596 


Oats 

1 .0 
2-5 

15.0 

4.0 

18.4 

3-2 

45-6 


5-4 
5-4 


The  greater  part  of  the  simple  proteins  is  thus  seen  to  be  composed  of  mono- 
amino  acids. 

After  numerous  analyses  had  firmly  established  the  fact  that  the  various 
ammo  acids  are  to  be  considered  as  the  building-stones  out  of  which  proteins 
are  formed,  Emil  Fischer*  took  up  the  synthesis  of  these  complicated  substances 
irom  the  ammo  acids.  We  now  know  many  compounds  that  are  produced  by 
an  amid-hke  linking  of  amino  acids  and  Fischer  has  called  these  polypeptides 
These  compounds  are  classified  according  to  the  number  of  amino  acids  asso^ 
ciated  in  their  formation  as  dipeptides,  tripeptides,  tetrapeptides,  pentapeptides, 
etc.  The  simplest  polypeptides  are  crystalline  compounds,  but  the  more  com- 
plicated ones,  with  great  molecular  weights,  have  colloidal  properties,  give  the 
biuret  reaction  and  are  similar  to  peptones. 

It  is  hardly  to  be  doubted  that  Fischer's  reasoning  and  methods  point  the 
way  to  the  synthesis  of  proteins.  The  partial  hydrolysis  of  the  simple  proteins 
has  demonstrated  the  fact  that  polypeptides  are  undoubtedly  concerned  in  the 
building  up  of  these  substances.  This  partial  hydrolysis  is  effected  by  acids 
at  room  temperature  or,  at  most,  at  temperatures  not  higher  than  37°C  In  this 
way  polypeptides  may  be  obtained  from  various  simple  proteins  2  It  thus 
appears  that  the  simple  proteins  are  to  be  considered  as  built  up  from  polv- 
peptides,  which,  in  their  turn,  are  products  of  amid-like  linkings  of  various  amino 
acids. 


Berlin.   1906.     Ab- 


1  Cystm  is  a  diamino  acid.— Ed. 


1 62  PHYSIOLOGY   OF   NUTRITION 

The  simple  proteins  just  considered  act  as  reserve  materials.  The  complex 
proteins,  on  the  other  hand,  which  are  contained  in  protoplasm,  sperms  and  egg 
cells,  are  differently  constructed.  Here  belong  nucleo-proteins,  histones  and 
protamins.  Nucleo-proteins  are  combinations  of  simple  proteins  with  other 
substances,  they  split  up  into  simple  proteins  and  nucleins.  Nucleins  are  soluble 
in  water  to  a  considerable  degree;  they  often  fail  to  exhibit  either  the  biuret  or  the 
Millon  reaction.  They  are  acid,  and  are  not  decomposed  by  gastric  juice. 
Treatment  with  alkalies  produces  a  splitting  up  of  nucleins  into  simple  proteins1 
and  nucleic  acids.  These  latter  are  rich  in  phosphorus  and  have  very  large 
molecular  weights.  The  simplest  formula  of  the  nucleic  acid  derived  from  yeast 
cells  is  C40H59N14O22-2P2O6;  another  nucleic  acid,  from  salmon  sperm,  maybe 
expressed  in  simplest  form  as  C40H56N14O16-2P2O5.  The  hydrolysis  of  nucleic 
acids  gives  phosphoric  acid,  pyrimidin  and  purin  derivatives,  pentoses  and 
levulinic  acid.  Among  these  decomposition  products,  phosphoric  acid  and 
the  purin  bases — xanthin,  hypoxanthin,  guanin  and  adenin — are  especially 
noteworthy. 

For  an  understanding  of  the  physiological  role  of  the  nucleo-proteins  quan- 
titative determinations  of  these  compounds  are  requisite,  but,  unfortunately, 
no  exact  methods  are  available  for  the  determination  of  nucleins.  Treatment  of 
nucleo-proteins  with  gastric  juice  leaves  an  insoluble  residue  which  contains 
nitrogen  and  phosphorus.  From  the  amount  of  either  one  of  these  two  elements 
can  be  approximated  the  amount  of  nucleo-proteins.  This  method  is  useful  only 
in  qualitative  studies,  however,  since  different  nucleo-proteins  are  differently 
affected  bv  gastric  juice.  The  determination  of  the  purine  bases  contained  in 
nucleo-proteins  is  complex  and  tedious.  The  method  of  Plimmer2  has  hitherto 
proved  to  be  the  best  for  this  purpose.  After  the  nucleo-proteins  have  been 
treated  for  from  twenty-four  to  forty-eight  hours  with  a  i-per  cent,  solution 
of  sodium  hydroxide,  at  37°C,  the  nucleic  acid  remains  unchanged  while  the 
entire  phosphorus  content  of  other  organic  compounds  is  split  off  in  the  form  of 
phosphoric  acid.  The  determination  of  the  remaining  phosphorus  thus  gives 
a  starting  point  for  the  estimation  of  the  nucleic  acids.  In  the  tips  of  etiolated 
stems  of  Viciafaba,  for  example,  57  per  cent,  of  the  total  protein-phosphorus  is 
present  in  nucleic  acids  and  37  per  cent,  is  present  in  the  indigestible  protein 
residue.3 

Histones  and  protamins  have  hitherto  not  been  found  in  plants.  These 
compounds  can  best  be  isolated  from  fish  sperm.  It  thus  seems  legitimate  to 
suppose  that  they  may  also  be  present  in  plant  sperms.  The  decomposition 
products  of  the  histones  and  protamins  are  mainly  diamino  acids.  Among  the 
protamins  arginin  is  most  frequently  encountered  (from  58  to  84  per  cent.). 

1  Altmann,  Richard,  Ueber  Nucle'insauren.  Arch.  Anat.  Physiol.  (Physiol.  Abt.)  1889:  524-536. 
1889. 

2  Plimmer,  R.  H.  Aders,  The  proteins  of  egg  yolk.  Jour.  Chem.  Soc.  London  (Transactions)  93" : 
1500-1506.  1908.  Plimmer,  R.  H.  Aders,  and  Scott,  F.  H.,  A  reaction  distinguishing  phosphoprotein 
from  nucleoprotein  and  the  distribution  of  phosphoproteins  in  tissues.  Ibid.  93  :  1699-1721.  1908. 
Abstracted  in  Biochem.  Centralbl.  8s7//:  109.     1909. 

3  Zaleski,  W.,  Ueber  den  Umsatz  des  Nucleoproteid-phosphors  in  den  Pflanzen.  Ber.  Deutsch.  Bot. 
Ges.  27:  202-210.     1909. 


MATERIAL   TRANSFORMATIONS   IX   THE    PLANT  163 

It  is  manifest  that  the  proteins  that  are  most  important  in  the  life  processes 
are  peculiarly  constituted.  The  hydrolysis  of  these  proteins  does  not  primarily 
result  in  mono-amino  acids,  but  gives,  to  a  much  greater  degree,  heterocyclic 
basic,  derivatives  of  purin,  pyrimidin  and  imidazol.  The  structural  formulas 
of  these  three  substances  are  given  below. 
N=CH  N=CH 

CH    C— NH^  CH   CH  HC— NJT 

CH        'I  rw 

r       J         N~-CH  S 

C        W  HC        W 

Purin  Pyrimidin  Imidazo! 

Mono-amino  acids  are  especially  scarce  in  fish  sperms.     These  acids,  which 
are  so  predominant  in  reserve  proteins  (following  the  terminology  of  A.  Kossel1) 
are  practically  without  importance  in  the  formative  proteins. 

§3-  Enzymes.2— Most  biochemical  reactions  occurring  in  plants  and  ani- 
mals can  now  be  interpreted  in  terms  of  enzymatic  activity.     To  be  sure   suc- 
cess has  not  yet  attended  the  effort  to  isolate  enzymes  in  the  free  state,  and  the 
presence  of  an  enzyme  is  only  inferred  from  its  specific  activity.     The  plants  in 
question  must  be  killed  in  such  a  way  that  their  enzymes  are  not  destroyed 
One  of  the  most  useful  methods  involves  the  use  of  a  water  or  glycerine  extract 
of  the  finely  divided  plant  material.     Brown  and  Morris3  dried  the  plants  at 
from  400  to  So°C.  (higher  temperatures  are  injurious  to  the  enzymes)  and  showed 
that  the  powder  obtained  by  pulverizing  the  dried  tissues  exhibited  enzymatic 
activity.     In  the  isolation  of  zymase,  which  accelerates  alcoholic  fermentation 
E.  Buchner  found  that  the  juice  expressed  from  triturated  yeast  cells,  by  means 
of  a  hydraulic  press,  possessed  the  properties  of  the  enzvme.     He  also  em- 
ployed acetone  in  killing  the  yeast  cells.     Palladia  employed  a  method  of  killing 
by  low  temperature,  to  demonstrate  enzymes  in  seed-plants.     The  frozen  plants 
are  dead  when  thawed  out,  but  the  efficiency  of  the  various  enzymes  has  not 
been  decreased. 

As  to  the  mechanism  of  their  action,  enzymes  are  to  be  regarded  as  cataly- 
zers. Catalysis  may  be  defined  as  the  acceleration  or  retardation  of  an 
otherwise  slow  or  limited  chemical  change,  through  the  influence  of  a  foreign 
substance.  Many  cases  of  the  catalytic  acceleration  of  various  reactions  are 
known  in  general  chemistry.  For  example,  hydrogen  is  but  slowly  formed  by 
the  action  of  pure  sulphuric  acid  upon  zinc.  When  a  drop  of  platinic  chloride 
solution   is   added,  however,  an  energetic  evolution  of  the  gas  ensues.     The 

Che^Z:  34t3S^ni8ie9oBrerkUngen  *""  ^  ^^  *"  Vr0t™™  in  Tierkorper.     Zeitsch.  physio.. 

OnlDr-aUX'  En  T1^-6  de  microbiol°eie-  Paris.  1898,  1899.  1900.  Disastases.  toxines  et  renins  in  v  2 
Oppenhcmer.  Carl,  D,e  Fermente.  3te  Aufl.  Le.pzig.  I90p.  Abderhalden's  Handb.  I9io  Tee  note  \ 
P.  ISS.  Green  J  Reynolds,  The  solub.e  ferments  and  fermentat.on.  Cambridge.  1899  J Ted  Cam ' 
£2*  M*""  r         ^  T8--    (SCe  n°te  ''  P'  I54°     Id6m'  AllBemeine  Chemie  der  knzyme.     wfesbadeT 

po1;;.  STir,HtTS2  tt enzymes-  Tr- from  revised  and  en,arged  Ger-  "d- b" Th—  h- 

3  Brown  and  Morris,  1893.     [See  note  1.  p.  28. 1 
^^^J-'C^.^t-::,At^SenZymedeT    PflanZCn    Unt6r    VCrSC  hied6nen  Verhlltni™, 


164  PHYSIOLOGY    OF   NUTRITION 

velocity  of  the  decomposition  of  hydrogen  peroxide  by  alkalies  is  distinctly  in- 
creased by  a  very  small  amount  of  platinum  or  other  metals.  In  both  cases 
platinum  plays  the  part  of  the  inorganic  catalyzer.1  The  catalytic  activity,  of 
both  organic  and  inorganic  catalyzers,  depends  upon  the  amount  of  catalyzer 
present,  upon  the  temperature  and  upon  the  properties  of  the  surrounding 
medium.  Chemical  reactions  can  not  only  be  accelerated  by  foreign  substances, 
but  they  can  also  be  retarded.  As  an  instance  of  this,  the  catalytic  effect  of 
platinum  upon  the  decomposition  of  hydrogen  peroxide  by  alkalies  is  greatly 
reduced  by  the  presence  of  a  trace  of  hydrocyanic  acid,  arsenic  acid,  hydrogen 
sulphide  or  other  poisons. 

Diastase  is  the  most  widely  distributed  of  the  plant  enzymes.  It  causes  the 
transformation  of  starch  into  glucose.  A  very  slight  amount  of  the  enzyme  is 
able  to  hydrolyze  large  amounts  of  starch;  one  part  by  weight  of  the  powder 
called  diastase  decomposed  2000  parts  of  starch. 

Diastase,  according  to  investigations  carried  out  by  Baranetskii,2  is  very 
widely  distributed  in  plants.  It  is  found  in  especially  large  amounts  during 
the  germination  of  starchy  seeds.  The  approximate  isolation  of  diastase  is  best 
effected  from  barley  malt.  The  malt  is  first  digested  with  water,  the  extract 
is  then  filtered,  and  the  enzyme  is  finally  precipitated  in  the  filtrate  by  the  addi- 
tion of  alcohol.  The  white  precipitate  obtained  in  this  way  is  purified  by  being 
repeatedly  dissolved  in  water  and  reprecipitated  with  alcohol.  The  precipitate 
from  alcohol  is  soluble  in  water,  and  when  thus  dissolved,  possesses  the  ability 
to  hydrolyze  starch.  The  chemical  composition  of  diastase  appears  to  be  very 
similar  to  that  of  the  proteins. 

The  first  stage  of  starch  hydrolysis  is  indicated  by  the  fact  that  addition  of 
iodine  to  the  mixture  fails  to  give  the  usual  blue  color  of  starch  with  this  reagent. 
In  a  somewhat  early  stage  of  the  process,  the  color  produced  by  addition  of 
iodine  is  violet,  but  at  a  later  stage  of  the  hydrolysis  a  brown  color  is  produced. 
Finally,  there  is  no  color  change  at  all  with  addition  of  iodine.  The  reaction  is 
hastened  by  higher  temperature,  up  to  450  or  5o°C.  The  decomposition  of  undis- 
solved starch  (starch  grains)  occurs  only  in  the  presence  of  acids  (hydrochloric, 
formic,  acetic,  and  citric  acid),  formic  acid  being  especially  active,  according  to 
Baranetskii's  results.  The  action  of  diastase  on  starch  grains  in  vitro,  shows  the 
same  peculiarities  as  appear  when  the  starch  grains  are  dissolved  in  the  seed  dur- 
ing germination.  The  diastase  attacks  only  portions  of  each  grain  first;  these 
portions  becoming  transparent,  glassy  and  giving  no  color  with  iodine;  the  whole 
starch  grain  becomes  transparent  at  length,  showing  only  a  sort  of  framework, 
and  finally  even  this  is  dissolved.  Much  information  is  now  available  upon  the 
formation  and  distribution  of  diastase  in  germinating  barley.  The  following 
table  shows  the  relative  amounts  and  distribution  of  diastase  in  Hordeum 
(barley)  seedlings  four  days  old.3 

'  Bredig,  Georg,  Anorganische  Fermente.     Leipzig,  1901.     Idem,  1902.     [See  note  1,  p.  xxx.] 
-  Baranetzky,  J.,  Die  Starkeumbildenden  Fermente  in  den  Pflanzen.     Leipzig,  1878. 
:  Moritz.,  E.  R.,  and  Morris,  G.  H.,  Handbuch  der  Brauwissenschaft  (German  transl.  by  Windisch). 
P.  142.     Berlin,  1893.*     [Idem,  Textbook  of  the  science  of  brewing.     London,  1891.] 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT  1 65 

In  the  half  of  the  endosperm  nearest  to  the  embryo 9. 7970 

In  the  half  of  the  endosperm  farthest  from  the  embryo 3 .5310 

In  the  roots 0.0681 

In  the  leaves o .  0456 

In  the  scutellum o .  5469 

Total 13.9886 

It   thus  appears   that,   in  such   seedlings,   diastase  is    most  plentiful  in  the 
endosperm. 

Diastase  is  less  easily  demonstrated  in  leaves  of  mature  plants  than  in 
germinating  seeds.  Extracts  of  fresh  leaves  contain  almost  no  diastase,  since 
the  enzyme  diffuses  hardly  at  all  through  cell  walls.  Brown  and  Morris1 
recommended  the  following  method  for  obtaining  it  from  leaves.  The  leaves 
are  dried  at  400  to  5o°C,  after  which  they  are  ground  to  a  fine  powder,  which  is 
allowed  to  act  upon  starch  in  water.  Different  leaves  have  different  diastatic 
powers,  as  may  be  seen  from  the  table  given  below,  in  which  the  relative  effi- 
ciencies of  leaf  powders  from  five  different  plants  are  presented. 

Pisum  sativum  (pea) 240 .  30 

Lathyrus  odoratiis 100.37 

Helianthus  annuus  (sunflower) 3-97 

Syringa  vulgaris  (lilac) 2.52 

Hydrocharis  morsus-rana o. 26 

The  greater  is  the  tannin  content  of  leaves,  the  weaker  is  the  diastatic  power. 
Detailed  researches  have  shown  that  diastase  consists  of  a  mixture  of  at  least 
two  different  enzymes,  amylase  and  maltase.  Amylase  effects  the  transforma- 
tion of  starch  to  maltose,  which  in  turn  is  transformed  into  glucose  through  the 
action  of  maltase. 

Starch  is  replaced  by  inulin  in  the  tubers  of  some  plants,  such  as  Inula, 
Helianthus,  Dahlia.  The  cleavage  of  inulin  takes  place  through  the  agency  of 
a  specific  enzyme,  inulase.  For  the  isolation  of  inulase  a  glycerine  extract  is 
prepared  from  dried  sprouting  tubers  and  the  extract  is  dialyzed.  The  solution 
of  inulase  thus  obtained  produces  hydrolytic  cleavage  of  inulin. 

Saccharase  (invertase)  hydrolyzes  saccharose  and  is  especially  abundant  in 
yeast.  It  is  concentrated  in  the  following  way.  Yeast  that  has  been  dried 
at  4o°C.  is  heated  for  six  hours  at  ioo°  and  is  then  placed  in  water  and  left  undis- 
turbed for  twelve  hours  at  400.  The  preparation  is  then  filtered  and  alcohol  is 
added  to  the  filtrate.  A  precipitate  is  thus  formed,  which  is  purified  by  being 
repeatedly  dissolved  in  water  and  reprecipitated  with  alcohol.  One  part  of  the 
dry  precipitate  is  capable  of  inverting  700  parts  of  saccharose  when  in  solution. 

Emulsin  is  found  in  sweet  almonds.  It  splits  the  glucoside  amygdalin 
into  glucose,  hydrocyanic  acid  and  benzaldehyde."7 

1  Brown  and  Morris,  1893.     [See  note,  I,  p.  28.] 

9  The  complete  hydrolysis  is  represented  by  the  equation : 

Hydrocyanic 
Amygdalin  Glucose  acid  Benzaldehyde 

C20H27NOii  +  2H20  =  C6H1206  +      HCN      +      C6H5CHO.— Ed. 


1 66  PHYSIOLOGY    OF    NUTRITION 

Myrosin  occurs  in  the  seeds  of  black  mustard.  It  decomposes  sinigrin 
into  mustard  oil  (allyl  isothiocyanate),  glucose  and  monopotassium  sulphate.* 

The  decomposition  of  simple  proteins  is  brought  about  through  the  agency 
of  proteolytic  enzymes.  Glycerine  extraction  of  this  type  of  enzymes  is  not 
always  successful  and  the  method  of  Neumeister1  is  to  be  recommended  here. 
Fresh  fibrin  (from  blood),  which  has  the  power  to  absorb  proteolytic  enzymes 
from  their  solution,  is  placed  in  an  aqueous  extract  of  the  plant  material  to  be 
studied.  After  two  hours  the  fibrin  is  removed,  washed  with  water,  and  left 
in  a  weak  solution  of  oxalic  acid,  in  a  warm  place.  If  proteolytic  enzymes  were 
present  in  the  original  extract,  the  fibrin  is  completely  dissolved  after  five  or  six 
hours.  In  the  control  preparation  the  fibrin  remains  practically  unchanged 
after  two  days  in  the  weak  oxalic  acid  solution. 

No  proteolytic  enzymes  are  present  in  resting  seeds,  but  Butkevich2  has 
isolated  this  kind  of  enzyme  from  germinating  seeds.  The  sprouted  seeds  are 
dried  at  a  temperature  of  from  35  to  4o°C,  and  then  pulverized,  after  which  the 
mass  is  extracted  with  ether  and  placed  in  water  with  an  antiseptic  (thymol). 
The  preparation  is  allowed  to  remain  in  a  thermostat,  with  a  temperature  of 
from  350  to  400,  for  several  days.  Auto-digestion  results,  accompanied 
by  a  decrease  in  the  amount  of  protein  material  present.  The  proteolytic 
enzyme  is  extracted  with  glycerine  and  the  extract  effects  a  cleavage  of  proteins, 
with  the  formation  of  tryosin  and  leucin.  Butkevich  was  unable  to  isolate 
asparagin,  but  this  is  readily  understood,  since  it  is  not  a  primary  product  in 
the  hydrolysis  of  proteins  (see  pp.  1 59-1 61). 

Saponification  of  fats  and  oils  occurs  in  plants  through  the  agency  of 
specific  enzymes,  the  so-called  lipases.3  Lipase  is  now  obtained  for  technical 
purposes  from  fatty  seeds.4 

The  enzymes  thus  far  mentioned  cause  various  hydrolytic  decompositions, 
but  oxidizing  enzymes  also  occur,  in  plants  as  well  as  in  animals.  Laccase  was 
the  first  of  these  oxidases  to  be  discovered.  It  causes  the  formation  of  laccol 
in  the  latex  of  various  species  of  Rhus.  The  latex,  which  is  originally  white, 
changes  very  quickly  in  the  presence  of  air  and  becomes  black.  Laccase  is 
soluble  in  water  and  may  be  precipitated  with  alcohol.  Its  oxidizing  effect 
disappears  after  heating  to  ioo°C.  Laccase  oxidizes  various  aromatic  com- 
pounds by  means  of  molecular  oxygen.  The  presence  of  this  enzyme  is  shown 
by  a  blue  color-reaction  with  a  solution  of  gum  guaiac  in  60  to  80  per  cent, 
alcohol. 

1  Neumeister,  1894.     [See  note  1,  p.  159-1 

-  Butkewitsch,  Wl.,  Ueber  das  Vorkommen  eines  proteolytischen  Enzymes  in  gekeimten  Samen  und 
iiber  seine  Wirkung.     Zeitsch.  physiol.  Chem.  32:  1-53-     1901. 

3  Nicloux,  Maurice,  Contribution  a  l'etude  de  la  saponification  des  corps  gras.     Paris,  1906. 

*  Hoyer,  E.,  Ueber  fermentative  Fettspaltung  (2te  Mittheilung.)  Ber.  Deutsch.  Chem.  Ges.  377/ : 
1436-1447.     1904.     Idem,  same  title.     Zeitsch.  physiol.  Chem.  50:  414-435.     1906-1907. 

h  Sinigrin  is  potassium  myronate,  a  glucoside,  myronic  acid  being  C10H17O9NS2.     The 
hydrolysis  is  represented  by  the  equation: 

Monopotassium 
Potassium  myronate  Glucose  sulphate  Allyl  isothiocyanate 

CioHi6K09NS,+  H20  =  C6H180«  +    KHS04    +    CH.  =  CHCH2NCS—  Ed. 


5 


MATERIAL   TRANSFORMATIONS    IN    THE    PLANT  1 67 

According  to  the  theory  of  Bach  and  Chodat1  the  oxidases  are  not  to  be  con- 
sidered as  simple  substances;  they  consist  of  peroxidases  (oxidizing  enzymes) 
and  oxygenases  (organic  peroxides).  Frequently  the  blue  color  with  tincture 
of  gum  guaiac  appears  only  after  addition  of  hydrogen  peroxide,  in  which  cases 
it  is  evident  that  only  peroxydase  is  present;  hydrogen  peroxide  here  takes  the 
place  of  oxygenases,  which  are  absent. 

E.  Buchner  and  his  co-workers2  have  isolated  an  enzyme  from  yeast,  which 
splits  glucose  into  ethyl  alcohol  and  carbon  dioxide,  the  so-called  zymase.  If 
compressed  yeast  is  triturated  in  water  with  quartz  sand  and  infusorial  earth 
(kieselguhr),  and  is  then  subjected  to  high  pressure  with  a  hydraulic  press,  a 
liquid  is  obtained  that  is  free  from  cells,  and  that  produces  a  very  active  alcoholic 
fermentation.  For  example,  from  26  g.  of  glucose  were  obtained  12.4  g.  of 
alcohol  and  12.2  g.  of  carbon  dioxide.  Thus,  as  the  theory  demands,  almost 
equal  amounts  of  alcohol  and  of  carbon  dioxide  are  produced;  160  g.  C6H1206 
=  92  g.  C2H60  +  88  g.  C02. 

Zymase  has  also  been  isolated3  by  treating  yeast  with  acetone.  The  yeast 
is  first  pressed  to  remove  most  of  the  water  and  is  then  placed  in  a  sieve  and 
plunged  in  a  flat  dish  of  acetone  for  ten  minutes.  The  material  is  then  pressed 
again,  treated  with  acetone  and  washed  with  ether,  after  which  it  is  pulverized 
and  dried  (beginning  at  room  temperature  and  ending  at  65°C).  This  prepara- 
tion, which  possesses  keeping-qualities,  is  on  the  market  under  the  name  of 
zymin*  In  sugar  solutions  it  produces  alcoholic  fermentation.  Lebedev' 
gives  a  good  method  for  obtaining  a  very  active  enzyme  from  thoroughly 
macerated  dry  yeast.6 

More  extended  researches*  upon  alcoholic  fermentation  have  shown  that 
zymase,  like  diastase,  is  not  a  single  enzyme.7  It  is  supposed  that  glucose  is 
split  up  by  dextrase  into  two  molecules  of  dihydroxy acetone,  CH2OH — CO 

1  Bach,  A.,  and  Chodat,  R.,  Zerlegung  der  sogennanten  Oxydasen  in  Oxygenasen  und  Peroxygenasen 
Ber.  Deutsch.  Chem.  Ges.  36 :  606-609.  1904-  Chodat  R.,  and  Bach,  A.,  Recherches  sur  les  ferments  oxy- 
dants.  Arch.  sci.  phys.  et  nat.  IV.  17:  477-510.  1904.  Idem,  Untersuchungen  liber  die  Rolle  der 
Peroxyde  in  der  Chemie  der  lebenden  Zelle.  VII.  Einiges  uber  die  chemische  Natur  der  oxydasen. 
Ber.  Deutsch.  Chem.  Ges.  377:  36-43-  1904.  Idem,  same  title.  VIII.  Ueber  die  Wirkungsweise  der 
Peroxydase.  Ibid.  37":  1342-1348.  1904.  Engler,  C,  and  Weissberg,  J.,  Kritische  Studien  uber  die 
Vorgange  der  Autoxydation.  204  p.  Braunschweig.  1904.  Haar,  A.  W.  van  der,  Untersuchungen  uber 
Pflanzen-Peroxydasen.  I.  Eine  neue  Methode  der  Peroxydasen-Gewinnung.  Ibid.  43  :  1321-1327. 
1910.  Idem,  same  title.  II.  Die  Hedera-Peroxydase,  ein  .Glucoproteid.  Ibid.  43":  1327-1329.  1010. 
Bach,  A.,  Die  langsame  Verbrennung  und  die  Oxydationsfermente.  Fortschr.  naturw.  Forsch.  1 :  85-140, 
1910.  Palladine,  W.,  und  Iraklionoff,  P.,  La  peroxydase  et  les  pigments  respiratoires  chez  les  plantes. 
Rev.  gen.  bot.     23:225-247.     1911.     [For  more  recent  literature  see  Atkins,  1916.       [See  note  o,  p.  11 5- ] 

°-  Buchner,  Eduard,  Buchner,  Hans,  and  Hahn,  Martin,  Die  Zymasegarung.  Untersuchungen  uber 
den  Inhalt  der  Hefezellen  und  die  biologische  Seite  des  Garungsproblems.     Miinchen  and  Berlin.  1903- 

3  Albert,  R.,  Buchner,  E.,  and  Rapp,  R.,  Herstellung  von  Dauerhefe  mittels  Aceton.  Ber.  Deutsch. 
Chem.  Ges.  357/:  2376-2382.     1902. 

5  It  may  be  obtained  from  A.  Schroder,  Miinchen,  Landwehrstrasse  45- 

•  Lebedew,  A.,  Darstellung  des  aktiven  Hefensaftes  durch  Maceration.  Zeitsch.  physiol.  Chem.  73 : 
447-452.     191 1. 

s  This  is  also  to  be  obtained  from  Schroder,  as  "  Trocken-Hefe  nach  A.  Lebedew." 

1  Jensen,  P.  Boysen,  Die  Zersetzung  des  Zuckers  wahrend  des  Respirationsprozesses.  Ber.  Deutsch. 
Bot.  Ges.  26a:  666-667.  1908.  Idem,  Sokkersonderdelingen  under  respirationsprocessen  hos  hojere 
planter.  Kjobenhavn.  1910.*  Buchner,  Edward,  and  Meisenheimer,  Jakob,  Die  chemischen  Vorgange 
bei  der  alkoholischen  Garung.     (IV.    Mitteilung.)     Ber.   Deutsch.   Chem.   Ges.  43":   I773-I79S-     I9™. 

'This  paragraph  is  omitted  in  the  7th  Russian  edition. — Ed. 


1 68  PHYSIOLOGY    OF   NUTRITION 

CH2OH;  dihydroxyacetone  is  then  changed  by  dihydroxyacetonase  into  alcohol 
and  carbon  dioxide.  The  process  of  alcoholic  fermentation  may  therefore  be 
represented  in  the  following  way: 

C6H1206  =  2C3H603  =  2C2H5OH  +  2CO2 

The  parts  of  the  plant  that  are  rich  in  protoplasm  usually  contain  appre- 
ciable amounts  of  catalase,  which  splits  hydrogen  peroxide  into  molecular  oxygen 
and  water.  The  physiological  role  of  catalase  is  not  well  understood  at  present; 
it  is  probably  connected  with  anaerobic  processes,  to  which  the  common  reduc- 
tion processes1  seem  also  to  be  related.  Whether  the.  latter  are  caused  by  specific 
enzymes  (reductase,  hydrogenase)  is  still  undetermined.  The  process  of  reduc- 
tion may  be  demonstrated  if  plant  tissues  are  placed  in  a  solution  of  methylene 
blue  or  sodium  selenite,  in  the  absence  of  oxygen.  Methylene  blue  is  thus 
bleached,  while  sodium  selenite  is  decomposed  with  the  formation  of  red  metallic 
selenium.  While  oxidase  is  to  be  conceived  as  a  system  consisting  of  peroxidase 
with  a  peroxide-former  (oxygenase),  Bach2  considers  reductase  as  a  combination 
of  an  enzyme  with  a  water-splitting  substance. ; 

Only  the  most  important  of  the  enzymes  thus  far  discovered  have  been  de- 
scribed in  the  preceding  paragraphs,  but  it  is  probable  that  the  living  protoplasm 
produces  specific  enzymes  for  most  of  the  biochemical  reactions.  The  same 
organism  may  produce  different  enzymes  according  to  the  chemical  nature  of 
the  nutritive  material  at  its  disposal.  Thus,  Penicillium  glaucum  produces 
saccharase  when  grown  in  a  medium  containing  calcium  lactate,  casease  when 
cultivated  in  milk,  and  lipase  when  supplied  with  monobutyrin. 

Synthetic  processes,  as  well  as  those  of  decomposition,  can  be  brought  about 
by  enzymes.  Hill,3  for  example,  has  found  that  the  inversion  of  maltose  by  mal- 
tase  is  not  complete,  but  proceeds  to  a  definite  equilibrium  point  as  the  velocity 
of  the  process  is  reduced  by  the  accumulation  of  glucose.  From  this  it  is  at 
least  apparent  that  this  is  a  reversible  reaction.  Hill  proved  that  a  concen- 
trated glucose  solution  is  actually  transformed,  in  the  presence  of  maltase, 
into  a  maltose  solution.  It  seems  plausible  to  suppose,  in  the  light  of  the  studies 
on  this  subject  so  far  available,  that  enzymatic  processes  in  general  may  be  thus 
reversible.4 

It  is  now  possible  to  produce  death  in  plants  without  destroying  the  enzymes 
of  their  tissues.  Plants  that  have  been  so  treated  are  not  the  same  as  those  that 
have  been  killed  in  such  a  way  as  to  render  their  enzymes  inactive.     (Enzymes 

1  Ehrlich,  Paul,  Das  Sauerstoff-Bedurfniss  des  Organismus.  167  p.  Berlin,  1885.  Palladin,  W., 
Beteiligung  der  Reduktase  im  Prozesse  der  Alkoholgarung.  Zeitsch.  physiol.  Chem.  56:  81-88.  1908. 
Zaleski,  W.,  Ueber  die  Rolle  der  Reduktionsprozesse  bei  der  Atmung  der  Pflanzen.  (Vorlaufige  Mitteil- 
ung.)  Ber.  Deutsch.  Bot.  Ges.  28:  319-329.  1910.  [Appleman,  Charles  O.,  Relation  of  oxidases  and 
catalase  to  respiration  in  plants.     Amer.  jour.  bot.  5  :  223-233.      1916.      (Other  references  are  there  given.)! 

2  Bach,  A.,  Zur  Kenntnis  der  Reduktionsfermente.  I.  Mitteilung.  Ueber  das  Schardinger-Enzym 
(Perhydridase).     Biochem.  Zeitsch.  31 :  443-449.      191 1. 

3  Hill,  Arthur  Croft,  Reversible  zymohydrolysis.     Jour.  Chem.  Soc.  London  73:  634-658.     1898. 

4  Dietz,  Wilhelm,  Ueber  eine  umkehrbare  Fermentreaktion  im  heterogenen  System.  Esterbildung  und 
Esterverseifung.  Zeitsch.  physiol.  Chem.  52:  279-325.  1907.  Loeb,  Jacques,  The  dynamics  of  living 
matter.      233  p.     New  York,  1906. 

;  The  considerations  of  this  paragraph  receive  more  detailed  attention  in  the  following 
chapter. — Ed. 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT  1 69 

lose  their  power  with  temperatures  about  ioo°C.)  Trommsdorff1  called  the 
former  " abgetotet"  and  the  latter  " abgestorben."k  If  plants  are  killed  in  the 
proper  way,  the  enzymes  of  their  tissues  still  exhibit  their  characteristic  proper- 
ties, in  the  presence  of  air,  water,  and  substances  that  are  poisonous  to  bacteria 
but  not  injurious  to  the  enzymes.  It  may  seem,  at  first  thought,  that  such 
plants  should  continue  to  carry  out  their  general  life-processes  in  the  same  man- 
ner as  do  living  ones,  so  that  the  latter  might  be  hard  to  distinguish  from  the 
former.  Deeper  study,  however,  reveals  important  differences.  When  plants 
are  killed  without  the  destruction  of  their  enzymes  the  physiological  system  of 
the  cells  appear  to  become  completely  disarranged,  with  the  destruction  of  the 
interrelations  that  obtain  between  the  different  constituents  of  the  living  cell. 
In  the  living  organism  the  different  cells  and  cell  components  appear  to  be  bound 
together  and  interrelated  so  as  to  form  a  harmonious  whole — somewhat  as  our 
solar  system  is  unified — but  the  component  units  of  a  dead  cell,  even  though  its 
enzymes  still  retain  their  proper  powers,  appears  to  be  a  mass  of  unrelated  compo- 
nents enclosed  within  a  common  membrane;  a  tissue  composed  of  such  cells  is 
without  the  interrelations  that  make  it  a  living  tissue.  Just  as  an  atom  of 
radium  breaks  down  into  its  component  particles,  so  does  the  living  cell  break 
down  at  death,  it  being  the  largest  physiological  unit  of  the  organism.  The 
following  important  differences  may  be  noted  between  the  enzymatic  processes 
of  dead  cells  and  those  of  living  ones.2 

1.  There  is  no  correlation  in  activity  between  the  different  enzymes  in  dead 
cells.  In  living  cells  an  enzyme  remains  active  only  so  long  as  the  products  of  its 
activity  are  used.  In  dead  cells  the  activity  of  an  enzyme  is  not  regulated  by 
that  of  the  other  enzymes.  Enzyme  activity  is  apt  to  be  prolonged  even  after 
its  products  have  ceased  to  be  removed. 

2.  In  dead  cells  enzymes  are  decomposed  by  other  enzymes.  This  was 
clearly  demonstrated  by  the  experiments  of  Petrushevskaia.3  As  is  well  known, 
the  respiratory  activity  of  living  yeast  is  increased  by  a  rise  in  temperature.  On 
the  other  hand,  the  enzymatic  activity  of  zymin  (yeast  killed  with  acetone)  is 
retarded  by  increased  temperature.  So,  for  example,  10  g.  of  zymin  produced 
706.5  mg.  of  C02  at  from  22  to  23°C,  while  only  285.3  mg-  were  formed  at  from 
^^  to  34°C.  This  difference,  amounting  to  59.7  per  cent.,  may  be  explained  by 
supposing  that  the  velocity  of  protein  decomposition  in  the  acetone  preparation 
increases  with  higher  temperature.  According  to  Petrushevskaia  only  35.9  per 
cent.  of  the  protein  nitrogen  of  the  zymin  was  decomposed  in  three  days  at 
from  15  to  i6°C,  while  81.5  per  cent,  was  broken  down  in  the  same  time  at 
3 20.  The  proteolytic  enzyme  appears  to  decompose  the  zymase,  which  is  of 
protein  nature. 

1  Trommsdorff,  Richard,  Ueber  die  Beziehungen  der  Gram'schen  Farbung  zu  chemischen  Vorgangen  in 
der  abgetoteten  Hefezelle.     Centralbl.  Bakt.  //,  8:  82-87.     1902. 

2  Palladin,  W.,   Die  Eigentumlichkeiten  der  Fermentarbeit  in  lebenden  und  abgetoteten  Pflanzen. 
Fortschr.  naturw.  Forsch.  1:  253-268.      1910. 

3  Petruschewsky,  Anna,  Einfluss  der  Temperatur  auf  die  Arbeit  des  proteolytischen  Ferments  und  der 
Zymase  in  abgetoteten  Hefezellen.     Zeitsch.  physiol.  Chem.  50:  251—262.      1906-1907. 

*  While  there  is  some  usage  of  killed  and  dead,  as  corresponding  to  these  German   words, 
such  a  usage  seems  undesirable  and  is  here  avoided. — Ed. 


170  PHYSIOLOGY   OF   NUTRITION 

3.  Enzymes  in  dead  cells  are  destroyed  by  various  poisons  and  bacteria,  that 
have  no  effect  upon  them  in  the  living  cell.  Korsakova1  showed  that  living  yeast 
cells  exhibit  alcoholic  fermentation  in  the  presence  of  considerable  amounts  of 
sodium  selenite,  but  the  production  of  carbon  dioxide  in  yeast  killed  with  ace- 
tone is  stopped  at  once  by  a  trace  of  this  substance. 

The  experiments  described  above  show  that  life -processes  are  not  to  be  inter- 
preted simply  as  enzymatic  activity.  Enzymatic  activities  are  regulated  in 
riving  cells,  and  the  apparently  unregulated  processes  carried  out  by  the  enzymes 
of  dead  cells  indicate  that  enzymes  really  play  a  subordinate  role  in  the  life  of  the 
organism. 

Living  protoplasm  is  not  to  be  considered  merely  as  a  complex  of  heterogene- 
ous enzymes.  Enzymes  are,  in  a  manner  of  speaking,  workers  in  the  service 
of  the  protoplasm;  they  are  formed  by  the  protoplasm,  used  in  the  work  that  is 
in  hand,  and  then  imprisoned  or  destroyed  as  soon  as  their  activities  are  no 
longer  required.'  Enzymes  that  have  become  unnecessary  are  rendered  inactive 
by  specific  anti-enzymes;  they  are  imprisoned,  as  it  were,  and  when  they  once 
more  become  necessary  they  are  rendered  active  again,  from  the  condition  of 
proenzymes,  by  activators  or  kinases.  Activators  or  kinases  on  the  one  hand, 
and  anti-enzymes  on  the  other,  are  thus  the  agents  through  which  the  regulating 
power  exerted  by  the  protoplasm  is  effected. 

In  the  animal  organism,  moreover,  special  substances  are  found  that  not 
only  modify  the  activities  of  the  various  enzymes  but  also  regulate  the  processes 
of  the  whole  body,  and  even  initiate  the  development  of  new  organs.  These 
substances  arise  in  some  particular  organ  and  then  migrate  into  far-distant 
regions,  where  they  set  up  whole  series  of  definite  chemical  reactions.  Such 
chemical  messengers  have  been  called  hormones  by  Starling.2 

§4.  Protein  Decomposition  in  Plants. "' — As  has  been  stated  above,  proteins 
do  not  remain  unchanged  in  plants,  but  are  continually  being  broken  down  and 
again  reformed.3  Some  life-processes  depend  upon  protein  decomposition  and 
others  upon  protein  synthesis.  Etiolated  seedlings  and  actively  growing  plant 
organs  are  very  satisfactory  subjects  for  the  study  of  protein  decomposition. 
We  owe  our  first  information  regarding  this  decomposition  to  Theodor  Hartig.4 
This  author  found  an  important  nitrogenous  substance  in  seedlings,  which  he 
designated  by  the  name  "Gleis."  It  developed  later  that  Hartig's  "Gleis"  is 
identical  with  asparagin.     Boussingault5  asserted  that  asparagin  appears  in  all 

1  Korsakoff,  Marie,  Ueber  die  Wirkung  des   Natriumselenits  auf  die  Ausscheidung  der  Kohlensaure 
lebenderund  abgetoteter  Hefe.  Ber.  Deutsch.  Bot.  Ges.  28:  334-338.      1910. 

2  Bayliss,  W.  M.  and  Starling,  E.  H.,  Die  chemische  Koordination  der  Funktionen  des  Korpers.     Ergeb. 
Physiol.  5:  664-697.     1906. 

3  Lusk,  Graham,  The  elements  of  the  science  of  nutrition.     2nd  ed.  402  p.     London  and  Philadelphia, 
1909. 

*  Hartig,  Theodor,  Entwickelungsgeschichte  des  Pflanzenkeims,  dessen  Stoffbildung  und  Stoffwandlung 
wahrend  der  Vorgange  des  Reifens  und  des  Keimens.     Leipzig,  1858. 

6  Boussingault,  1860-1861.     [See  note  5.  P-  2.]     Vol.  4,  p.  265. 

1  Of  course  this  is  a  figurative  way  of  describing  these  phenomena.  The  "necessity"  for  an 
enzyme,  or  the  need  of  the  work  it  can  do  is  not  a  reason  for  its  being  produced. — Ed. 

m  This  section  is  numbered  §6  in  the  German.  The  numbering  of  the  7th  Russian  edition  is 
here  followed. — Ed. 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT  171 

plants  that  are  subjected  to  illumination.  Respiration  in  plants  is  connected 
with  protein  decomposition,  and  asparagin  is  formed  as  one  of  the  main  ni- 
trogenous products.  This  process  is  to  be  considered  as  strictly  analogous  to  the 
formation  of  urea  in  animals,  but  urea  is  eliminated  from  the  animal  body  while 
asparagin  is  again  utilized  in  the  plant  body,  by  means  of  the  energy  of  sunlight. 
Pfeffer1  has  demonstrated  by  microchemical  observation,  that  asparagin  dis- 
appears as  carbohydrates  accumulate  during  the  process  of  photosynthesis 
in  sunlight,  being  used  in  protein  synthesis.  When  seeds  germinate  in  the 
dark,  however,  protein  decomposition  predominates,  and  asparagin  therefore 
accumulates.  Under  usual  conditions  the  synthesis  and  decomposition  of 
proteins  occur  simultaneously,  but  it  should  be  mentioned  that  the  influence 
of  light  becomes  apparent  only  in  the  later  stages  of  germination.  In 
the  earlier  stages  asparagin  accumulates,  in  light  as  well  as  in  darkness. 
Afterwards  asparagin  increases  in  amount  only  in  darkened  plants,  while  lighted 
plants  gradually  lose  all  the  asparagin  that  has  previously  been  formed. 
These  relations  were  long  ago  pointed  out  by  Boussingault  and  were  later  verified 
by  Meunier.2  The  following  table  shows  some  of  Meunier's  results  with 
phaseolus  coccineus.  The  numbers  denote  the  relative  amounts  of  asparagin 
found  in  plants  of  three  different  ages,  in  darkness  and  in  light. 

Relative  Amounts  of  Asparagin  in  Plants  Grown  in 
Age  of  Plants                             Darkness  Light 

days 
13  1. 13  J-18 

18  2.28  2.25 

38  5-18  1 .41 

Of  the  seedlings  eighteen  days  old,  those  in  light  contained  as  much  asparagin 
as  those  in  darkness.  In  the  oldest  seedlings,  however,  the  asparagin  content 
had  markedly  increased  in  the  darkened  plants  but  had  decreased  in  the 
illuminated  ones. 

Pfeffer  has  confined  his  researches  upon  asparagin  exclusively  to  the  legumes, 
which  are  rich  in  this  substance,  but  Borodin3  showed  that  asparagin  is  very 
widely  distributed  and  is  probably  present  in  the  majority  of  plants.  Under  the 
usual  conditions  of  plant  life  the  detection  of  asparagin  is  frequently  either  very 
difficult  or  even  impossible,  but  if  the  plants  to  be  studied  are  placed  in  water 
culture  in  darkness  for  several  days,  then  the  carbohydrates  necessary  for  pro- 
tein formation  become  entirely  used  up  and  asparagin  accumulates,  as  Borodin 
was  able  to  show  by  microchemical  tests.  Along  with  asparagin,  Borodin  also 
found  ty rosin  and  leucin. 

Borodin's    conclusions    were    afterwards    quantitatively    substantiated  by 

1  Pfeffer,  W.,  Untersuchungen  iiber  die  Proteinkorper  und  die  Bedeutung  des  Asparagins  beim  Keimen 
der  Samen.  Jahrb.  wiss.  Bot.  8:  429-574-     1872. 

-  Meunier,  Fernand.,  Etude  sur  l'asparagine.     Ann.  agron.  6:  275-28 1.     1880. 

3  Borodin,  J.,  Ueber  ide  physiologische  Rolle  und  die  Verbreitung  des  Asparagins  im  Pfianzenreiche 
Bot.  Zeitg.  36:     801-832.     1878. 


172  PHYSIOLOGY    OF    NUTRITION 

Ernst  Schulze.1  The  following  experiment  with  oat  seedlings  may  serve  as  an 
illustration  of  his  work.  The  seedlings  were  first  grown  in  light,  then  some  of 
them  were  used  for  analysis  while  the  rest  were  placed  in  darkness.  After  a 
week  these  also  were  analyzed.     The  numbers  given  below  show  the  relative 

Original  After  a  Week 

Plants  in  Darkness 

Total  nitrogen 4.12  450 

Nitrogen  of  proteins 3.51  1.46 

Non-protein  nitrogen 0.61  3 .  04 

amounts  of  protein  and  non-protein  nitrogen  found  in  each  of  the  two  lots  of 
seedlings.  During  the  course  of  seven  days  in  darkness  more  than  half  the 
total  amount  of  protein  material  is  thus  seen  to  have  been  broken  down. 

The  chemical  nature  of  the  protein  decomposition  products  is  dependent 
upon  various  conditions;  with  different  environmental  conditions  very  different 
decomposition  products  are  produced.  Oxygen  is  very  important  for  the 
progress  of  protein  decomposition,  but  Palladin2  has  shown  that  this  process 
goes  on  also  in  the  absence  of  oxygen.  The  following  table  shows  the  relative 
rates  at  which  protein  decomposition  occurred  in  wheat  seedlings  grown  with 
and  without  oxygen.  The  numbers  denote  percentages  of  total  original  protein 
decomposed  during  the  corresponding  time  periods. 

Percentage  of  Original  Protein  Decomposed 

Time  Period  Without  Oxygen  With  Oxygen 

22  hours  1.1  .... 

1  day  3.9  7.9 

2  days  15.4  17.2 

3  days  26.1  

7  days  ....  54.3 

The  quantitative  relations  of  the  individual  decomposition  products  are  not 
the  same  in  the  absence  of  oxygen  as  in  its  presence.  In  the  latter  case  asparagin 
is  the  main  product  while  tyrosin  and  leucin  are  formed  only  in  very  small 
quantities.  In  the  absence  of  oxygen,  however,  tyrosin  and  leucin  accumulate 
to  a  marked  degree  while  the  amount  of  asparagin  formed  is  quite  negligible. 
This  fact  shows  that  the  primary  products  of  protein  hydrolysis  are  formed  only 
in  the  absence  of  oxygen.  As  long  as  asparagin  was  considered  as  one  of  these 
primary  products  it  was  impossible  to  understand  how  protein  hydrolysis 
within  the  plant  body  results  in  the  formation  of  asparagin,  while  the  hydrolysis 
of  plant  proteins  with  acids  produces  but  a  negligible  amount  of  aspartic  acid 
(see  page  161).  The  experiments  described  above  explain  this;  it  has  been 
shown  that  asparagin  arises  during  synthetic  processes.     Borodin3  had  already 

>  Schulze,  E.,  Steiger  E.,  and  Bossard,  E.  Untersuchungen  uber  die  stickstoffhaltigen  Bestandtheile 
einiger  Rauhfutterstoffe.  Landw.  Versuchsst.  33:  89-123.  1887.  [Schulze,  E.,  Ueber  die  Methoden, 
welche  zur  quantitative  Bestimmung  der  stickstoffhaltigen  Pflanzenbestandtheile  verwendbar  sind.  Ibid. 
33:  124-145.     1887.] 

2  Palladin,  W.,  Ueber  Eiweisszersetzung  in  den  Pflanzen  bei  Abwesenheit  von  freiem  Sauerstoff.  Ber. 
Deutsch.  Bot.  Ges.  6:  205-212.  1888.  Idem,  Ueber  Zersetzungsproducte  der  Eiweissstoffe  in  den  Pflan- 
zen bei  Abwesenheit  von  freiem  Sauerstoff.     Ibid.  6:  296-304.     1888. 

3  Borodin,  I.  P.,  On  the  conditions  for  the  accumulation  of  leucin  in  plants.  [Russian.]  Trav.  Soc. 
Imp.  Nat.  St.-Petersbourg  16  (Protocole):  69-73.     1885. 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT  173 

observed  that  no  asparagin  is  formed  in  the  absence  of  oxygen.  The  researches 
of  Palladin  have  recently  been  repeated  and  substantiated  by  Godlewski,1  and 
Butkevich2  also  obtained  similar  results.  Aspergillus  niger  decomposes 
peptones  to  ammonia  in  the  presence  of  oxygen,  but  only  to  amino  acids  in  the 
absence  of  this  element.  It  still  remains  uncertain  in  what  way  asparagin  is 
formed  from  the  primary  products  of  protein  cleavage,  but  it  seems  possible 
that  here,  also,  an  enzymatic  process  is  involved. 

The  formation  of  the  various  nitrogenous  cleavage  products  of  proteins  is 
also  dependent  upon  the  chemical  nature  of  the  nutrient  medium  in  which  the 
organism  is  grown.  Butkevich3  showed  that  different  moulds  do  not  produce 
the  same  cleavage  products  when  grown  in  peptone  solution.  Aspergillus 
niger  produces  ammonia  mainly,  while  Penicillium  glaucum  forms  tyrosin  and 
leucin  for  the  most  part.  This  difference  is  correlated  with  the  acid  or  alkaline 
reaction  of  the  substratum.  Aspergillus  forms  a  considerable  amount  of  oxalic 
acid  and  this  renders  the  nutrient  solution  acid.  Penicillium  produces  no  oxalic 
acid  and  the  solution  in  which  it  is  growing  soon  becomes  alkaline,  as  a  result 
of  ammonia  formation.  If,  however,  Aspergillus  is  cultivated  with  an  excess 
of  calcium  carbonate  in  the  medium,  then  it  forms  considerable  amounts  of 
tyrosin  and  leucin,  while  Penicillium  produces  ammonia  in  considerable  amount 
when  the  nutrient  solution  is  rendered  acid  by  addition  of  phosphoric  acid. 

Not  only  the  simple  or  reserve  proteins  but  also  the  so-called  formative 
proteins,  are  broken  down  in  the  plant.  When  seeds  germinate  in  darkness 
adenin,  guanin,  xanthin  and  hypoxanthin  are  produced,  as  cleavage  products 
of  nucleic  acid.  The  studies  of  Karapetova  and  Sobashnikova,4  who  employed 
seedlings  of  rye  and  barley  grown  with  inadequate  nutrition,  show  that  the 
proteins  found  to  be  indigestible  in  gastric  juice  are  not  as  easily  broken  down 
in  the  plant  as  are  the  ones  that  are  digestible  in  gastric  juice.  In  the  early 
stages  of  development  the  amount  of  indigestible  proteins  actually  increases, 
while  the  total  amount  of  protein  decreases.  Decomposition  of  the  indigestible 
proteins  occurs  later.  Zaliesskii5  has  also  pointed  out  that  nucleo-proteins  are  to 
he  considered  as  formative  (non-reserve)  materials,  on  account  of  their  relative 
stability  as  revealed  by  their  behavior  when  the  organism  is  in  a  starved  condi- 
tion. It  may  be  supposed  that  those  substances  that  are  first  decomposed  dur- 
ing starvation  are  nutrient  materials,  while  those  remaining  unchanged  are 
constituents  of  the  protoplasm.  Pronounced  decomposition  of  the  nucleo- 
proteins  is  to  be  observed  only  in  dead  plants  that  still  possess  active  enzymes. 

The   decomposition   of   formative   proteins    (nucleo-proteins   and   nucleo- 
albumins)  may  be  estimated  from  the  decrease  in  phosphorus-containing  pro- 

1  Godlewski,  E.,  Nouvelle  contribution  a  l'etude  de  la  respiration  intramoleculaire  des  plantes.  [Title 
in  Polish,  German  and  French.]  Bull.  Int.  Acad.  Sci.  Cracovie  (Math.-nat.  CI.)  (Anz.  Akad.  Wiss. 
Krakau.)      1904:  115-158.     1904. 

-  Butkewitsch,  Wl.,  Umwandlung  der  Eiweissstoffe  durch  die  niederen  Pilze  im  Zusammenhange  mit 
einigen  Bedingungen  ihrer  Entwickelung.     Jahrb.  wiss.  Bot.  38:  147-240.      1903- 

3  Butkevich,  1903.     [See  note  2,  this  page.] 

4  Karapetoff,  H.,  and  Sabachnikoff,  M.,  Sur  le  d6composition  des  matieres  proteiques  dans  les  plantes. 
Rev.  gen.  bot.  14:  483-486.      1902. 

5  Zaleski,  W.,  Ueber  die  Rolle  der  Nucleoproteide  in  den  Pflanzen.     Ber.  Deutsch.  Bot.  Ges.  29:  146- 

JS5-      ion- 


J74 


PHYSIOLOGY   OF   NUTRITION 


teins.  Ivanov1  determined  the  amounts  of  phosphorus  of  various  kinds  of 
compounds,  in  seeds  and  etiolated  seedlings  of  Vicia  faba,  and  obtained  the 
results  given  in  the  table  below,  where  the  numbers  are  percentages,  on  the  basis 
of  total  phosphorus  content. 


Seeds 


Seedlings 
5  Days  Old 


Phosphorus  of  inorganic  phosphates 11.4 

Phosphorus  of  lecithin 11. 6 

Phosphorus  of  proteins 52.5 

Phosphorus  of  organic  phosphates 25 . 7 


48.1 

37-4 
9.8 


Seedlings 
20  Days  Old 

80.2 

6.6 
13  -7 

5-i 


Germination  in  darkness  thus  appears  to  be  correlated  with  a  pronounced 
decomposition  of  phosphorus-containing  proteins.  In  resting  seeds  protein 
phosphorus  amounted  to  52.5  per  cent,  of  the  total  phosphorus  content,  while 
seedlings  twenty  days  old  contained  protein  phosphorus  amounting  to  only 
13.7  per  cent.;  in  the  latter  case  most  of  the  phosphorus  occurred  as  inorganic 
phosphates.2  Zaliesskii3  obtained  results  similar  to  these.  He  found,  for  ex- 
ample, that  the  phosphorus-containing  proteins  disappear  from  the  cotyledons 
of  germinating  seeds,  while  the  amount  of  these  proteins  increases  markedly 
in  the  axial  organs,  since  growth  is  accompanied  by  synthetic  processes. 
Thus,  in  the  axial  parts  of  Vicia  faba  seedlings  three  days  old,  the  ratio  of 
protein  phosphorus  to  protein  nitrogen  was  found  to  be  0.0125:0.0850(1:6.8), 
while  the  corresponding  ratio  for  seedlings  nine  days  old  was  0.0337:0.3755 
(1:11.1). 

The  researches  of  Burkevich,  Zaliesskii,4  Ivanov,5  Kovshov6  and  Gromow7 
show  that  the  cleavage  of  phosphorus-containing  as  well  as  that  of  phosphorus- 
free  nitrogens  is  dependent  upon  enzymatic  processes. 

1  Ivanow,  Leonid,  Ueber  die  Umwandlungen  des  Phosphors  beim  Keimen  der  Wicke.  (Vorlaufige 
Mittheilung.)  Ber.  Deutsch.  Bot.  Ges.  20:  366-372.  1902.  Idem,  Ueber  die  Umwandlungen  des  Phos- 
phors in  der  Pflanze  im  Zusammenhange  mit  der  Eiweissstoffmetamorphose.  Arbeit.  Naturforscherges. 
St.  Petersburg  34:  1-170.      1905.     [Russian.]     [Rev.  in:  Bot.  Centralbl.  103:  83.     1906.] 

2  Vorbrodt,  Wlad.,  Untersuchungen  uber  die  Phosphorverbindungen  in  den  Pflanzensamen,  mit  be- 
sonderer  Berucksichtigung  des  Phytins.  [Title  also  in  Russian.  Text  in  German.]  Bull,  internat. 
(classe  sci.  math,  et  nat.,  ser  A.)     Acad.  Sci.  Cracovie  1910:  414-511.     1910. 

s  Zaelski,  W.,  Beitrage  zur  Verwandlung  des  Eiweissphosphors  in  den  Pflanzen.  Ber.  Deutsch.  Bot. 
Ges.  20:  426 — 433.  1922.  Idem,  Ueber  den  Umsatz  der  Nucleinsaure  in  keimenden  Samen.  Ibid.,  25: 
349-356.      1907. 

4  Zaleski,  W.,  Beitrage  zur  Kenntnis  der  Eiweissbildung  in  reifenden  Samen.  (Vorlaufige  Mitteilung.) 
Ber.  Deutsch.  Bot.  Ges.  23:  126-133.  1905.  Idem,  Zur  Kenntnis  der  proteolytischen  Enzyme  der  rei- 
fenden Samen.  Ibid.  23:  133-142.  1905.  Idem,  Ueber  den  Umsatz  der  Phosphorverbindungen  in 
reifenden  Samen.  Ibid.  25:  58-66.  1907.  Idem,  Ueber  die  autolytische  Ammoniakbildung  in  den  Pflan- 
zen.    Ibid.  25:357-360.      1907.     Idem,  1907.     [See  note  3,  this  page.] 

5  Ivanov,  1902,  1905.     [See  note  1,  this  page.] 

6  Kovshov,  I.  D.,  Fermentative  Eisweisszersetzung  in  erfrorenen  Pflanzen.  [Russian,  with  German 
abstract.]  Trav.  Soc.  Imp.  Nat.  St.-Petersbourg  35s  (Jour.  bot.  1) :  180-185.  1906.  [German  abstract, 
p.  187.] 

7  Gromow,  T.,  and  Grigoriew,  O.,  Die  Arbeit  der  Zymase  und  der  Endotryptase  in  den  abgetoteten 
Hefezellen  unter  verschiedenen  Verhaltnissen.     Zeitsch.  physiol.  Chem.  42:  299-329.     1904. 


MATERIAL  TRANSFORMATIONS  IN  THE  PLANT  175 

§5.  Nitrogenous  Products  of  Protein  Decomposition— Asparagin  (NH2- 
CO — CH2 — €HNH2)  is  the  most  important  product  of  protein  decomposition  in 
plants.  Germinated  legumes  that  have  beeen  kept  in  the  dark,  especially  Lupi- 
nus  luteus,  are  notably  rich  in  this  substance.  According  to  Borodin,1  asparagin 
is  not  present  in  the  Caryophyllaceae,  in  which  glutamin  occurs,  however. 
Glutamin  (NH2CO— CH2— CH2— CHNH2— COOH)  is  a  product  similar  to 
asparagin,  but  it  is  known  only  in  isolated  cases,  since  it  is  difficult  to  bring  to 
crystallization  and  gives  no  definite  reaction.  This  substance  is  present  in  sugar 
beets  and  is  abundant  in  Curcurbita  seedlings.  It  takes  the  place  of  asparagin 
in  the  Caryophyllaceae  and  in  ferns.2 

The  following  amino  acids  and  basic  substances  may  be  mentioned  as  other 
products  of  protein  decomposition  in  plants. 

Monoamino  Acids 
Leucin,  (CH3)2.CH— CH2— CHNH2— COOH. 
Tyrosin,  C6H4OH— CH2— CHNH2— COOH. 
Valin,  (CH3)2— CH— CHNH2— COOH. 

Basic  Substances3 

Lysin,  NH2CH2— CH2— CH,— CH2— CHNH2— COOH. 

/NH2 

Arginin,  HN=C^ 

XNHCH2— CH.— CH2— CHN2H— COOH. 

Histidin,      /       \ 
NH  N 

I  I 

CH-  C— CHo— CHNH2— COOH. 

Large  amounts  of  arginin  are  present4  in  conifer  seedlings.  The  purin  bases," 
xanthin,  hypoxanthin,  adenin  and  guanin,  the  formulas  for  which  are  given 
below,  arise  from  the  decomposition  of  the  nucleo-proteins. 

1  Borodin,  1885.     [See  note  3,  p.  172.] 

2  Schulze,  E.,  Ueber  die  Verbreitung  des  Glutamins  in  den  Pflanzen.     Landw.  Versuchsst.  48:  33~55. 

1897. 

»  Schulze,  E.,  and  Winterstein,  E.,  Ueber  die  bei  der  Spaltung  der  Eiweisssubstanzen  entstehenden 

basischen  Produkte.     Ergeb.  Physiol.  1:  32-61.     1902. 

«  Schulze,  E.,  Ueber  die  beim  Umsatz  der  Proteinstoffe  in  den  Keimpflanzen  einiger  Coniferen-Arten 
entstehenden  Stickstoffverbindungen.     Zeitsch.  physiol.  Chem.  22:  435-448.      1896-1897. 

"  The  purin  bases  may  be  considered  as  derived  from  purin,  which  is  not  found  in  nature, 
but  which  has  been  synthetized.  It  may  be  represented  as  follows,  the  various  atomic  posi- 
tions in  the  two  rings  being  numbered. 

(1)  N  =  (6)    CH 

I  I 

(2)  CH    (5)   C— (7)   NH. 

II  II  J>  (8)CH 

(3)  N-(4)    C-(o)N- 

Referring  to  the  numbers,  xanthin  is  called  2-6-dioxypurin.     Adenin  is  6-aminopurin,  hypo- 
xanthin is  6-oxypurin,  and  guanin  is  2-amino-oxypurin. — Ed. 


176  PHYSIOLOGY   OF   NUTRITION 

NH— CO  NH— CO 


1 


CO      C— NH.  CH      C— NH 

I          II           >H                          ||     ||  >H 

NH— C W  N— C W 

Xanthin  Hypoxanthin 

N  =     C.NH2  NH— CO 

CH      C— NH  NH2.C         C-NR 

II  I!  >H  II  I!  \CH 

N € W  N C W 

Adenin  Guanin 

Among  these  decomposition  products  are  also  the  xanthin  derivatives,  caffein 
(1-3-7-trimethyl-xanthin)  and  theobromin  (3-7-dimethyl-xanthin1)- 

Recent  accounts  of 'the  formation  of  polypeptids  in  plants  are  very  inter- 
esting.2 These  products  may  be  either  primary  or  secondary,  the  latter  being 
formed  by  secondary  synthetic  processes.  Tryosin  and  leucin  are  among  the 
primary  products  and  are  formed  by  protein  hydrolysis  due  to  proteolytic  en- 
zymes. Asparagin,  on  the  contrary,  is  a  secondary  product,  arising  through  the 
transformation  of  primary  products.  Tyrosin  and  leucin,  for  example,  occur 
only  in  the  first  stages  of  the  development  of  seedlings  of  Lupinus  lulens, 
while  asparagin  practically  replaces  these  substances  in  later  stages.  The 
following  analyses3  of  lupine  seedlings  fifteen  and  eighteen  days  old  show  the 
increase  in  asparagin  content  as  the  seedlings  become  older.  [The  values  are 
percentages  on  the  basis  of  the  total  dry  weight  of  the  seeds  before  germination. 

Seedlings  Seedlings 

15  Days  Old  18  Days  Old 

Nitrogen  of  proteins 1 .  49  1 .  51 

Nitrogen  of  asparagin 385  4-23 

Nitrogen  of  other  compounds 1.27  o.  77 

Both  groups  of  seedlings  are  seen  to  contain  similar  quantities  of  proteins, 
but  the  amount  of  asparagin  in  the  older  seedlings  is  greater  that  that  in  the 
younger  ones.  The  increase  in  asparagin  content  arises  at  the  expense  of  the 
lower  decomposition  products,  the  amount  of  which  is  seen  to  be  correspondingly 
decreased. 

The  amino  acids  formed  in  the  primary  decomposition  of  proteins  are  further 
transformed  without  oxidation,  and  the  transformation  products  thus  produced 
have   been    called    aporrhegmas.4     Furthermore,   methylation  and  splitting 

!  Weevers,  Th.,  Die  physiologische  Bedeutung  des  Kaffeins  und  des  Theobromins.  Ann.  Jard. 
Bot.  Buitenzorg  //,  6:  1-78.     1907. 

-  Schulze,  E.,  Neue  Beitrage  zur  Kenntnis  der  Zusammensetzung  und  des  Stoffwechsels  der  Keim- 
pflanzen.     Zeitsch.  physiol.  Chem.  47:  507-569.     1906. 

3  Merlis,  M.,  Ueber  die  Zusammensetzung  der  Samen  und  der  etiolierten  Keimpflanzen  von  Lupinus 
augustifolius  L.     Landw.  Versuchsst.  48:  419-454.     1897. 

4  Ackermann,  D.,  and  Kutscher,  Fr.,  Ueber  die  Aporrhegmen.  Zeitsch.  physio.  Chem.  69:  265-272. 
1910.  Ackermann,  D.,  Ueber  ein  neues,  auf  bakteriellem  Wege  gewinnbares,  Aporrhegma.  Ibid.,  69  : 
273-281.  1910.  Engeland,  R.,  and  Kutscher,  Fr.,  Ueber  ein  methyliertes  Aporrhegma  des  Tierkorpers. 
Ibid.  69:  282-285.      1910. 


MATERIAL   TRANSFORMATIONS   IN   THE    PLANT  1 77 

by  oxidation  alter  the  composition  of  the  aporrhegmas.     The  end   product  of 
these  processes  is  ammonia,  which  is  then  used  in  the  synthesis  of  asparagin.1 
The  following  method  is  employed  in  the  quantitative  study  of  the  various 
nitrogenous  substances  that  have  been  mentioned  in  the  preceding  paragraphs.2 
The  total  nitrogen  content  is  determined  from  one  portion  of  the  material,  and 
the  protein  nitrogen  is  determined  from  an  other  portion,  the  difference  between 
these  two  quantities  being  the  amount  of  the  non-protein  nitrogen.     For  the 
determination  of  the  separate  nitrogen  compounds,  the  plants  to  be  studied  are 
extracted  with  water  and  the  extract  is  precipitated  with  lead  acetate.     The 
precipitate  contains  proteins,  pigments  and  other  compounds,  while  the  crys- 
talline nitrogenous  substances  are  in  the  filtrate.     The  filtrate  is  treated  with 
mercuric  nitrate,  which  precipitates  asparagin,  glutamin  and  allantoin;  also, 
in  part,  xanthin,  hypoxanthin,  guanin,  arginin,  tvrosin.     The  precipitate  is 
suspended  in  water,  treated  with  hydrogen  sulphide  and  the  mercuric  sul- 
phide thus  formed  is  filtered  out.     The  filtrate  is  neutralized  with  ammonia 
and  concentrated  by  evaporation,  after  which  it  is  allowed  to  stand  for  some 
time.     Crystals  of  the  nitrogenous  compounds  separate  out  and  may  be  further 
dealt  with  by  suitable  methods.     If  no  material  is  precipitated  by  mercuric 
nitrate,  then  the  plant  extract  is  treated  with  lead  acetate  and  filtered    the 
filtrate  being  treated  directly  with  hydrogen  sulphide.     The  lead  sulphide  is 
filtered  off,  the  filtrate  is  neutralized  with  ammonia  and  then  concentrated  bv 
evaporation  over  a  water  bath. 

The  method  of  Sachsse3  is  used  especially  in  the  determination  of  asparagin 
and  glutamin.  This  procedure  depends  upon  the  fact  that  these  amides  break 
down,  upon  being  boiled  with  weak  hydrochloric  acid  and  water,  into  amino 
acids  and  ammonia,  as  is  illustrated  by  the  following  equation. 

(Asparagin) 

NH2.CO.CH2.CHNH2.COOH  +  H20  = 

(Aspartic  acid)      (Ammonia) 

COOH.CH2.CHNH2.COOH  +  NH3. 

Half  of  the  asparagin  nitrogen  is  thus  split  off.  The  ammonia  nitrogen  is 
then  determined,  according  to  the  usual  methods,  and  the  number  thus  obtained 
is  doubled,  to  give  the  asparagin  nitrogen.  The  same  method  is  of  course  also 
available  for  the  determination  of  glutamin  nitrogen. 

For  microchemical  identification  of  asparagin  the  method  of  Borodin4  is 
employed.  The  sections  to  be  studied  are  mounted  in  alcohol  under  a  cover 
glass  and  the  alcohol  is  allowed  slowly  to  evaporate  out  at  the  margin  of  the 
cover.     If  asparagin  is  present  it  crystallizes  during  this  process.     The  crystals 

Pflan^BS^*-,0^   A"lm°n!ak  als  Umwandlungsprodukt  stickstoffhaltiger  Stoffe  in  hoheren 
("Me,n'     Biochem    Z-.tsch.  16:  411-452.     1909.     Prianischnikow,  D.,  and  Schulow,  J.,  Ueber  die  svn 
thet  sche  Asparagmb.ldung  in  den  Pflanzen.     Ber.  Deutsch.  Bot.  Ges.  28 :  253-264.       oI0 
-  Abderhalden,  Handbuch.     [See  note  I.  p.  155  ] 

C^T^tlZTml"  Meth°de  ZUr  QUantitatiVen  B«*™™»*  des  Aparagin,     Jour,  prakt. 
*  Borodin,  1878.     [See  note  3,  p.  171.] 


12 


178  PHYSIOLOGY    OF    NUTRITION 

are  tested  for  solubility  in  a  saturated  solution  of  asparagin,  which  dissolves 
all  crystals  but  those  of  this  substance.0 

§6.  Protein  Synthesis  in  Plants.*'— It  has  already  been  stated  (page  31) 
that  the  primary  protein  synthesis  occurs  in  leaves.  The  nitrogen  necessary 
for  such  synthesis  is  mainly  derived  from  the  soil,  as  nitrates.  Investigations 
upon  the  distribution  of  nitrates1  in  the  plant  have  shown  that  they  reach  the 
leaves  through  the  water-conducting  system.  Nitrates  are  found  in  leaves 
only  in  exceedingly  small  amounts,  however,  or  else  they  are  entirely  absent,  and 
it  is  therefore  suggested  that  a  transformation  of  nitrates  must  take  place  in 
these  organs.  Schimper2  has  proved,  moreover,  that  the  transformation  of 
nitrates  in  leaves  is  connected  with  the  photosynthetic  assimilation  of  carbon. 
Accumulation  of  nitrates  occurs  in  plants  that  have  been  kept  in  darkness, 
and  these  salts  are  used  up  afterwards,  when  the  plants  are  exposed  to  light. 
Also,  in  chlorotic  leaves,  which  are  incapable  of  photosynthesis,  no  transforma- 
tion of  nitrates  occurs  in  the  light.  Experiments  with  variegated  leaves  are 
especially  convincing  in  this  connection.  The  green  as  well  as  the  white  parts 
of  such  leaves  are  filled  with  nitrates  in  the  dark.  After  subsequent  illumination 
only  the  green  portions  are  found  to  be  without  nitrates;  in  the  colorless  parts 
the  amount  of  nitrate  remains  unchanged. 

From  such  experiments  it  has  been  concluded  that  protein  synthesis  in  leaves 
occurs  only  in  light.  It  must  be  noted,  however,  that  in  these  experiments  of 
Schimper  a  deficiency  of  carbohydrates  surely  occurred  in  the  absence  of  light. 
This  consideration  is  of  great  importance,  since  Zaliesskii3  was  able  to  demon- 
strate protein  synthesis  from  carbohydrates  and  nitrates  when  darkened  leaves 
were  supplied  with  carbohydrates  by  means  of  a  nutrient  solution.  It  thus 
appears  that  protein  synthesis  in  leaves  is  only  indirectly  dependent  upon  light. 
Only  in  light  is  the  formation  of  carbohydrates  possible,  and  these  substances 
are  necessary  for  the  formation  of  proteins.  It  is  quite  possible,  however,  that 
with  an  adequate  supply  of  carbohydrates,  protein  synthesis  may  go  on  more 
rapidly  in  light  than  in  darkness. 

1  Wulfert,  H.,  Ueber  die  Bestimmung  der  Salpetersaure  bei  Gegenwart  organischer  Substanzen.  Landw. 
Versuchsst.  12:  164-184.  1869.  Monteverde,  Arbeit.  Naturforscherges  St.  Petersburg.  1882.*  Berthe- 
lot,  [Marcellin],  and  Andre,  [Gustave],  Sur  l'existence  et  stir  la  formation  des  azotates  dans  le  regne  vege- 
tal. Ann.  chim.  et  phys.  VI,  8:  5-8.  1886.  Idem,  Les  azotates  dans  les  veg6taux.  I.  Methodes 
2'analyze.  Ibid.  VI,  8:  8-25.  1886.  Idem,  same  title.  II.  Leur  presence  universelle.  Ibid.  VI,  8: 
d6-3i.  1886.  Idem,  Les  azotates  dans  les  plantes  aux  diverses  periodes  de  la  v£g6tation.  Plante 
totale.  Ibid.  VI,  8:  32-63.  1886.  Idem,  Les  azotates  dans  les  difterentes  parties  des  plantes.  Ibid. 
VI,  8:  64-115.  1886.  Idem,  Sur  la  formation  de  salpetre  dans  les  v6g6taux.  Ibid.  VI,  8:  116-128. 
1886. — Berthelot,  [Marcelin],  and  Andre,  [Gustave],  Recherches  sur  la  vegetation.  Sur  les  carbonates  dans 
les  plantes  vivantes.  Ann.  chim.  et  phys.  VI,  10:  85-107.  1887.  Idem,  Recherches  sur  l'acide  oxalique 
dans  la  vegetation.  I.  Methodes  d'analyze.  Ibid.  VI,  10:  289-308.  1887.  Idem,  same  title.  II. 
Etude  de  diverses  plantes.  bid.  VI,  10:  308-350.  1887.  Idem,  Sur  une  relation  entre  la  formation  de 
l'acide  oxalique  et  celle  des  principes  albuminoides  dans  certains  v6g£taux.     Ibid.  VI,  10:  350-353-     1887. 

2  Schimper,  A.  F.  W.,  Ueber  Kalkoxalatbildung  in  den  Laubblattern.  Bot.  Zeitg.  46:  65-69,  81-89. 
97-107.  113-123.  129-139,  145-153-     1888. 

s  Zaleski,  W.,  Die  Bedingungen  der  Eiweisssynthese  in  Pflanzen,  p.  53-  1900.*  Idem,  Zur  Kenntniss 
der  Eiweissbildung  in  den  Pflanzen.     Ber.  Deutsch.  Bot.  Ges.  15:  536-542.     1897. 

o  This  method  is  very  unsatisfactory  for  several  reasons.  For  better  methods  see  Molisch, 
1013.     [See  note  i,  p.  90.] — Ed. 

p  The  section  is  numbered  §7  in  German;  the  numbering  of  the  7th  Russian  edition  is 
here    followed. — Ed.  • 


M  \TERIAL    TRANSFORMATIONS    IN    THE    PLANT 


J79 


J<. 


- 


Treub1  has  developed  the  hypothesis  that  hydrocyanic  acid  is  an  interme- 
diate product  in  protein  synthesis.  It  is  well  known  that  many  leaves  contain 
appreciable  amounts  of  hydrocyanic  acid  (in  the  form  of  glucosides).  With 
suitable  .treatment  such  leaves  give  a  chemical  test  for  this  acid  by  becoming 
intensely  blue,  with  the  formation  of  Prussian  blue  (Fig.  87,  a).  If  the  leaves  are 
left  several  days  in  darkness  the  hydrocyanic  acid  disappears  completely,  as 
is  shown  by  the  complete  absence  of  Prussian  blue  after  application  of  the  test. 
The  leaf  shown  in  Fig.  87  was  divided  along  the  midrib  and  one  portion  (a)  was 
subjected  to  the  test,  after  which  the  remaining  portion  (b)  was  kept  in  the  dark 
for  a  time,  the  test  being  finally  applied  to  this  part  also,  without  the  formation 
of  any  Prussian  blue.9 

Leaves  that  have  thus  been  depleted  of  hydrocyanic  acid  again  produce  it  in 
considerable    quantity    when    supplied    with 
nitrate  and  sugar  in  darkness,  or  when  supplied  /,. L 

with  nitrate  in  light.  Considerable  amounts  of 
hydrocyanic  acid  are  also  contained  in  axial 
organs  (young  bamboo  sprouts).2 

Protein  decomposition  occurs  in  germinat- 
ing seeds  in  darkness,  while  the  later  stages  of 
germination  in  light  exhibit  protein  synthesis. 
In  this  case  also,  light  is  directly  necessary  only 
for  the  formation  of  carbohydrates.  Protein 
formation,  out  of  carbohydrates  and  nitrog- 
enous organic  substances,  is  independent  of 
light.  Leek  bulbs,  for  instance,  contain  little 
protein,  but  much  carbohydrate  and  or- 
ganic  nitrogen.     Consequently,  according    to 

Zaliesskii,3    the   sprouting   of   these   bulbs   in 

r  °  Pig.    87. — Leaf   of    Phaseolus 

darkness  is  not  accompanied  by  protein  de-   lunatus,    showing    coloration    with 

composition,  but  bv  its  synthesis.     The  follow-    pprussian  blue  (°).  due  to  presence 

.         "  of  hydrocyanic  acid. 

ing  data  referring  to  leek  bulbs  in  the  dormant 

condition  and  after  having  grown  for  a  month  in  darkness,  may  serve  as  an 
illustration  of  this.  The  numbers,  excepting  the  last  two,  show  the  relative 
amounts  of  the  various  materials  mentioned  that  were  found  in  the  two  stages 
of  development. 

1  Treub,  M.,  Nouvelles  recherches  sur  le  r6Ie  de  l'acide  cyanhydrique  dans  les  plantes  vertes.  Ann. 
Jard.  Bot.  Buitenzorg //,4:  86-147.      1904.     Idem,  same  title.     Ibid,  II,  6:  79-1 14.      1907. 

2  Walther,  O.,  Krasnosselsky,  T.  Maximow,  N.  A.,  and  Malcewsky,  W.,  Ueber  den  Blausauregehalt 
dcx  Bambusschoszlinge.     Bull.  Deparetment  Agric.  Indes  X6erlandaises.  No.  42.     4  p.  1910. 

3  Zaleski,  W.,  Zur  Keimung  der  Zweibel  von  Allium  cepa  und  Eiweissbildung.  (Vorlaufige  Mittheil- 
ung.)     Ber.  Deutsch.  Bot.  Ges.  16:  146-151.     1898. 

5  The  test  for  hydrocyanic  acid  here  referred  to  is  carried  out  as  follows:  The  leaf  is  punched 
full  of  minute  holes  by  means  of  a  bunch  of  fine  needles  and  is  then  placed  in  5  per  cent,  solu- 
tion of  potassium  hydrate  for  a  minute  or  two.  It  is  then  transferred  to  a  warm  (6o°C.) 
aqueous  solution  of  ferrous  sulphate  (2.5  per  cent.)  and  ferric  chloride  (1  per  cent.),  where  it 
remains  about  ten  minutes.  It  is  finally  placed  in  hydrochloric  acid  (1  part  of  ordinary  con- 
centrated acid  to  5  or  6  parts  of  water).  The  color  develops  after  from  five  to  fifteen 
minutes. — Ed. 


\y> 


4\ 


,**'\ 


L-'l 


> 


jSo  physiology  of  nutrition 

Dormant  Sprouted 

Bulbs  Bulbs 

Total  dry  weight 5-8246  4- 77i6 

Total  nitrogen 0.1614  0.1595 

Nitrogen  of  protein 0.0517  0.0838 

Nitrogen  of  substances  precipitated  by  phospho- 

tungstic    acid 0.0252  0.0244 

Nitrogen  of  asparagin 0.0121  0.0163 

Nitrogen  of  other  compounds 0.0744  0.0350 

Protein  nitrogen  (percentage  of  total  nitrogen) . .           32.0  52.5 

Hettlinger1  and  Zaliesskii2  showed  also  that  a  formation  of  protein  is  brought 
about  by  the  wounding  of  onion  bulbs  and  that  this  proceeds  with  considerable 
velocity.  The  same  amount  of  protein  was  formed  in  four  days  after  wounding 
as  was  found  after  a  month  of  normal  sprouting  in  darkness.  The  sprouted 
bulb  was  cut  into  four  equal  parts,  one  part  being  dried  and  the  three  others 
being  left  in  darkness  for  four  days.  Analysis  showed  that  the  protein  nitrogen 
of  the  dried  portion  amounted  to  32.0  per  cent,  of  the  total  nitrogen,  while  the 
corresponding  percentages  for  the  other  portions  were  from  49.4  to  51.8. 

Hansteen3  showed  that  various  nitrogenous  substances  are  suited  to  the 
formation  of  protein.  Zaliesskii  and  Kovshov4  showed  that  protein  formation 
in  wounded  onion  bulbs  occurs  only  in  the  presence  of  oxygen.  According  to 
Zaliesskii,5  the  process  of  protein  transformation  is  altered  when  the  surrounding 
atmosphere  contains  ether  vapor.  He  showed  that  the  axial  organs  of  Lupinus 
augustifolius,  when  the  cotyledons  had  been  removed,  were  able  to  carry  on  pro- 
tein synthesis  in  darkness  if  supplied  with  carbohydrates  and  nitrogen  by  means 
of  a  nutrient  solution,  and  that  this  process  was  accelerated  by  the  presence  of 
ether  vapor. 

Present  knowledge  regarding  the  formation  of  nucleins  in  plants  is  very  in- 
complete. It  is  well  known  that  growth  is  generally  accompanied  by  nuclein 
synthesis.  Although  the  total  protein  content  decreases  during  the  germination 
of  seeds  in  darkness,  nevertheless  the  nucleo-proteins  increase  during  the  first 
stages  of  germination.6  Fig.  88  shows  that  the  germination  of  wheat  in  dark- 
ness is  correlated  with  an  increase  in  proteins  indigestible  in  gastric  juice,  the 
amount  of  which  is  nearly  proportional  to  the  amount  of  nucleo-proteins. 

Wounding  produces  increased  vital  activity.  The  work  of  Kovshov7  shows 
that  the  formation  of  protein  is  accelerated  in  wounded  onions.  This  increased 
synthesis  results  mainly  in  proteins  indigestible  in  gastric  juice,  but  there  is  no 

1  Hettlinger,  A.,  Influence  des  blessures  sur  la  formation  des  matieres  proteiques  dans  les  plantes.     Rev. 
gen.  bot.  13:  248-250.     1001. 

2  Zaleski,  W.,  Beitrage  zur  Kenntniss  der  Eiweissbildung  in  den  Pflanzen.     Ber.  Deutsch.  Bot.  Ges.  19: 

331-339.     1901. 

3  Hansteen,  Barthold,  Ueber  Eiweisssynthese  in  grunen  Phanerogamen.     Jahrb.  wiss.  Bot.  33 :  417-486. 

1899. 

*  Kovchoff,  J.,  L'influence  des  blessures  sur  la  formation  des  matieres  proteiques  non  digestibles    dans 
les  plantes.     Rev.  g6n.  bot.  14:  440-462.     1902. 

6  Zaleski,  W.,  Zur  Aetherwirkung  auf  die  Stoffumwandlung  in  den  Pflanzen.      (Vorlaufige  Mittheilung.) 
Ber.  Deutsch.  Bot.  Ges.  18:  292-296.      1900. 

»  Palladin,  W.,  Recherches  sur  la  correlation  entre  la  respiration  des  plantes  et  les  substances  azotfies 
actives.     Rev.  g6n.  bot.  8 :  225-248.     1896.     Zaliesskii,  1907.     [See  note  3.  P-  1  74-1 

7  Kovchoff,  1902.     [See  note  4,  this  page.] 


MATERIAL   TRANSFORMATIONS    IX    THE    PLANT 


iSl 


corresponding  increase  in  the  amount  of  protein  phosphorus  in  the  tissues,  and 
it  appears  that  the  observed  increase  in  these  indigestible  proteins  is  mainly 
made  up  of  phosphorus-free  compounds.1 

In  leaves  the  formation  of  proteins  indigestible  in  gastric  juice  is  dependent 
upon  the  presence  of  carbohydrates  and  upon  illumination.  Palladin2  found 
that  such  indigestible  proteins  increase  in  etiolated  bean  leaves  when  these  are 
supplied  with  saccharose,  more  of  these  proteins  being  formed  in  light  than  in 
darkness.  The  following  table  presents  the  results  of  two  experiments  in  this 
connection,  the  numbers  representing  milligrams. 


2     3      *     6     6      7      S     9      10    11    12    13    Hh 

Fig.  88. — Graphs  showing  metabolic  changes  during  germination  of  wheat  seeds  in  darkness. 
n-u-c-l,  indigestible  protein  content;  p-r-t,  total  protein  content;  c-a-r,  carbon  dioxide  elimi- 
nated; s-u,  sugar  content. 


Nitrogen  of  Proteins  Indigestible  in  Gastric  Juice,  Contained  in  ioo  g.  of 

Etiolated  Leaves 


Freshly  Gathered 
18.6 
i8.6 


After  Srx  Days  on  Saccharose  Solution 
in  Darkness  in  Light 

82.6  166.4 

5i-9  1154 


§7.  Alkaloids,  Toxins  and  Antitoxins/ — Plants  often  contain  various  poison- 
ous substances,3  among  which  alkaloids  and  some  glucosides  are  especially 

1  Kovchoff,  J.,  Ueber  den  Einfluss  von  Verwundlungen  auf  Bildung  von  Nucleoproteideh  in  den  Pflanzen. 
Ber.  Deutsch.  Bot.  Ges.  21:  165-175.  1903-  Zaleski,  W.,  Ueber  den  Umsatz  der  Nucleinsaure  in  Keim- 
enden  Samen.  Ibid.  25:  349-356.  1907.  Idem,  Ueber  den  Aufbau  der  Eiweissstoffe  in  den  Pflanzen. 
Ibid.  25:  360-367.  1907.  Idem,  1907  (Ammoniakbildung).  [See  note  4,  p.  174.]  Ivanov,  1902,  1905. 
[See  note  1,  p.  174.] 

2  Palladin,  W.,  Influence  de  la  lumiere  sur  la  formation  des  matieres  prot&ques  actives  et  sur  l'energie 
de  la  respiration  des  parties  vertes  des  vegdtaux.     Rev.  gen.  bot.  ir:  81-105.     1899. 

8  Gauthier,  A.,  Les  toxines  microbiennes  et  animals.  Paris,  1896.  Briihl,  Julius,  Die  Pflanzenalka- 
loide.  Braunschweig,  1900.  Rijnn,  J.  J.  L.  van,  Die  Glykoside;  Chemische  Monographie  der  Pflanzengly- 
koside  nebst  systematischer  Darstellung  der  kunstlichen  Glykoside.  Berlin,  1900.  Winterstein  Ernst 
and  Trier,  Georg,  Die  Alkaloide,  eine  Monographie  der  naturlichen  Basen.  Berlin,  1910.  Faust,  Die 
tierischen  Gifte.     248.  p.     Braunschweig,  1906. 

r  This  section  is  numbered  §4  in  the  German;  the  numbering  of  the  7th  Russian  edition  is 
here  followed. — Ed. 


1 82  PHYSIOLOGY    OF    NUTRITION 

worthy  of  note.  These  poisons  may  be  effective  as  accelerators  of  material 
exchange.  According  to  Votchal,1  solanin,  which  is  a  very  poisonous  alka- 
loid, is  formed  in  various  parts  of  the  potato  tuber,  especially  during  the  period 
of  active  growth.  When  the  tuber  is  wounded  a  considerable  amount  of  the 
solanin  accumulates  in  the  neighborhood  of  the  wound.  It  will  be  shown  later 
that  respiration,  as  well  as  other  metabolic  processes,  is  increased  by  injury 
of  plant  tissues.  Solanin  thus  seems  to  be  a  stimulant  that  increases  metabolism 
in  wounded  regions. 

Extremely  active  poisons  are  formed  by  bacteria.  These  organisms  not 
only  destroy  dead  bodies,  but  many  of  them  infest  even  living  plants  and  ani- 
mals, thus  giving  rise  to  various  infectious  diseases.  They  are  the  so-called 
pathogenic  forms.  Bacillus  tetani,  the  form  that  produces  the  disease  known 
as  tetanus  or  lockjaw,  is  a  typical  example  of  the  anaerobic  pathogenic  bacteria, 
which  develop  only  in  the  absence  of  oxygen.  Many  other  pathogenic  bacteria 
are  aerobic,  however,  and  attain  their  full  development  only  in  the  presence  of 
oxygen.  Bacillus  anthracis,  which  produces  splenic  fever,  belongs  in  the  latter 
group.  It  was  by  the  study  of  anthrax  that  Pasteur  first  made  the  discovery 
that  infectious  diseases  are  caused  and  propagated  by  bacteria.  It  had  long 
been  known  that  many  bacteria  are  present  in  the  blood  of  animals  suffering 
from  splenic  fever.  Pasteur  placed  a  drop  of  such  blood  in  broth  and  obtained 
an  abundant  development  of  bacteria.  Re-inoculations  were  made,  from  the 
first  culture  to  a  second,  from  the  second  to  a  third,  etc.,  and  the  twentieth 
culture  was  still  capable  of  producing  the  disease  when  an  animal  was  infected 
with  the  liquid.  Pasteur  deserves  credit  also  for  working  out  the  method  of 
immunization  by  vaccination.  In  1870.  he  began  his  work  on  the  bacillus  of 
chicken  cholera.  Pure  cultures  of  this  organism  proved  to  have  become  greatly 
weakened  by  standing  in  a  thermostat  during  the  summer;  inoculation  there- 
from produced  only  a  local  effect  and  failed  to  cause  the  death  of  the  fowl.  It 
also  became  evident  that  subsequent  inoculation  with  extremely  virulent,  fresh 
cultures  was  without  fatal  effect  if  the  fowls  had  previously  been  inoculated 
with  the  weakened  culture.  Generalizing  from  these  observations,  Pasteur 
arrived  at  vaccination  as  a  protection  against  anthrax.  He  found  that  the 
virulence  of  the  anthrax  bacillus  becomes  weakened  under  the  influence  of  high 
temperature,  gradually  losing  its  poisonous  properties  at  from  42  to  43°C. 
Animals  inoculated  with  such  weakened  cultures  endure  this  inoculation,  and 
are  then  no  longer  susceptible  to  injury  from  inoculation  with  stronger  cultures; 
they  are  thus  protected  against  anthrax.  This  leads  to  the  supposition  that 
toxins  are  neutralized  by  antitoxins  that  are  produced  in  the  animal  tissues. 
A  number  of  such  antitoxins  have  been  actually  isolated.  Vaccination  protects 
against  infection,  but  after  the  disease  is  already  developed  it  may  be  controlled 
by  direct  injection  of  antitoxin.  As  is  well  known,  diphtheria  is  combated  by 
means  of  diphtheria  antitoxin,  which  is  obtained  from  the  blood  serum  of  horses 

1  Votchal,  E.,  Zur  Frage  von  der  Verbreitung,  Vertheilung  und  Rolle  des  Solanins  in  den  Pflanzen.  II. 
Das  Geschick  des  Solanins  in  der  Pflanze  and  seine  Bedeutung  fur  das  Leben  derselben.  [Title  in 
Russian  and  German,  article  in  Russian.]  Trav.  Soc.  Nat.  Univ.  Imp.  Kazan.  195:  i~74-  1889.  Clau- 
triau,  G.,  Nature  et  signification  des  alcolo'ides  veg6taux.     Rec.  Inst.  Bot.  Bruxelles  5:  1-87.      1902. 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT  1 83 

that  have  been  previously  immunized  by  vaccination.  This  method  of  treat- 
ment of  diseases  is  called  serumtherapy. 

In  many  cases  the  pathogenic  bacteria  are  distributed  throughout  the  whole 
body  of  the  infected  animal  or  human  being;  in  other  cases  they  are  localized 
in  some  special  region.  The  bacilli  of  diphtheria  and  tetanus  are  thus  local- 
ized. In  such  cases  the  injurious  action  of  the  bacteria  is  manifestly  not  directly 
due  to  their  number  but  to  their  poisonous  excretions.  Although  diphtheria 
bacilli  develop  only  in  the  throats  of  human  beings,  nevertheless  the  entire 
body  is  poisoned  by  the  toxins  excreted  by  the  bacterial  cells.  Diphtheria 
toxin  may  be  obtained  from  bouillon  cultures  of  the  diphtheria  bacillus  by  filter- 
ing the  liquid  through  a  Chamberland  filter,  the  filtrate  being  very  poisonous. 
Tetanus  bacilli  are  present  in  many  soils.  If  a  wound  is  infected  with 
tetanus,  the  bacteria  develop  only  in  the  immediate  neighborhood  of  the  lesion 
but,  even  so,  the  disease  is  deadly,  since  tetanus  toxin  is  extraordinarily  poi- 
sonous. One  gram  of  this  toxin  is  capable  of  bringing  about  the  death,  by 
poisoning,  of  75,000  men. 

§8.  Lipoids  and.  Phosphatides. —The  term  " lipoid,"  which  was  introduced 
by  Overton,1  may  be  understood  to  include2  all  tissue  and  cell  constituents  that 
may  be  extracted  by  ether  and  similar  solvents.  Here  belong  not  only  fats 
and  fatty  acids  but  also  various  other  substances,  among  which  cholesterin  and 
complex  phosphatides  are  especially  important.  Thudichum3  designates  as 
phosphatides  those  organic  compounds  containing  phosphorus,  that  are  soluble 
in  alcohol  and  ether.  These  substances  are  very  unstable  and  are  chemically 
very  active;  they  constitute  an  indispensable  part  of  the  protoplasm  of  all  living 
cells.     Many  complex  phosphatides  undergo  auto-oxidation. 

.Recent  investigation  shows  that  phosphorus  is  not  the  only  mineral  sub- 
stance contained  in  lipoids.  Thus,  Glikin-  found  that  half  of  the  total  iron 
content  of  human  and  cow's  milk  is  contained  in  lipoids.  Winterstein  and 
Stegmann5  have  found,  in  the  leaves  of  Ricinus  (castor  bean),  a  phosphatide  that 
contains  6.74  per  cent,  of  calcium.  Phosphatides  containing  carbohydrates  are 
present  in  some  plants.6     It  may  be  suggested  that  lipoids  form  combinations 

1  Overton,  Ernst,  Studien  uber  die  Narkose,  zugleich  ein  Beitrag  zur  allgemeinen  Pharmakologie.  Jena, 
1901. 

-  Bang,  Ivar,  Biochemie  der  ZelHpoide.     Ergeb.  Physiol.  6:  131-186.      IO07- 

3  Thudichum,  John  L.  W.,  Die  chemische  Konstitution  des  Gehirns  des  Menschen  und  der  Tiere.  Tu- 
bingen, 1001. 

*  Glikin,  W.,  Zur  biologischen  Bedeutung  des  Lecithins.  III.  Mitteilung.  Ueber  den  Lecithin-  und 
Eisengehalt  in  der  Kuh-  und  Frauenmilch.     Biochem.  Zeitsch.  21 :  348-354-      iooo- 

5  Winterstein,  E.,  and  Stegmann,  L.,  Ueber  einen  eigenartigen  phosphorhaltigen  Bestandteil  der  Blatter 
von  Ricinus.     VI.   Mitteilung.     Ueber  Phosphatide.     Zeitsch.  physiol.  Chem.  58:  527-528.      1908-1909. 

«  Hiestand,  O.,  Historische  Entwickelung  unserer  Kenntnisse  uber  die  Phosphatide.  Beitrage  zur 
Kenntnis  der  pflanzlichen  Phosphatide.  Zurich,  1906.*  Winterstein,  E.,  and  Hiestand,  O.,  Beitrage  zur 
Kenntnis  der  pflanzlichen  Phosphatide.  II.  Mitteilung.  Zeitsch.  physiol.  Chem.  54=  288-330.  1907-08. 
Winterstein,  E.,  Beitrage  zur  Kenntnis  pflanzlicher  Phosphatide.  III.  Mitteilung.  Ibid.  58:  500-505. 
1908-09.  Winterstein,  E.,  and  Smolenski,  K.,  Beitrage  zur  Kenntnis  der  aus  Cerealien  darstellbaren  Phos- 
phatide. IV.  Mitteilung.  Ueber  Phosphatide.  Ibid.  58:  506-521.  1909.  Smolenski,  K.,  Zur  Kenntnis 
der  aus  Weizenkeimen  darstellbaren  Phosphatide.  V.  Mitteilung.  Ueber  Phosphatide.  Ibid.  58  :  522-526. 
1908-09. 

8  For  a  recent  discussion  of  these  substances  see:  Rosenbloom,  Jacob,  and  Gies,  W.  J.,  A 
proposed  chemical  classification  of  the  lipins,  with  a  note  on  the  intimate  relation  between 
cholesterols  and  bile  salts.  Biochem.  bull.  1:  51-56.  1911.  Rosenbloom,  J.,  Intracellular 
lipins.     Ibid.i:  75-79.     1912. — Ed. 


1 84 


PHYSIOLOGY   OF   NUTRITION 


with  proteins,  in  plants  as  well  as  in  animals,  the  labile,  complex  substances 
thus  produced  being  split  up  by  hot  alcohol.  The  results  of  Bondi  and  Eissler1 
support  this  suggestion.  They  obtained  lipoid-proteins  soluble  in  alcohol,  by 
the  linking  together  of  fatty  acids  and  amino  acids;  these  substances  are  broken 
down  by  hydrolyzing  enzymes.  Since  the  chemical  composition  of  lipoids  is 
very  complex  and  since  they  show  marked  adsorption  phenomena,  no  reliable 
method  for  the  isolation  of  lipoids  and  phosphatides  is  as  yet  available.2  Never- 
theless numerous  investigations  already  show  that  lipoids  play  an  extremely 
important  role  in  the  activity  of  the  cell.3  Studies  upon  the  distribution  of 
lipoids  as  determined  microchemically  have  been  carried  out  by  Ciaccio.4 
Kossel5  states  that  lecithin  is  always  present  in  every  protoplast.  The  extended 
researches  of  Schulze6  and  his  school,  and  those  of  Stoklasa7  and  other  authors, 
have  demonstrated  beyond  question  that  phosphatides  are  widely  distributed 
in  plants.  According  to  Stoklasa,  lecithin  accompanies  proteins  in  plants, 
and  seeds  rich  in  protein  also  contain  an  appreciable  amount  of  phosphatides. 
The  relative  protein,  phosphatide  and  fat  contents  of  various  seeds  are  shown 
below. 


Kind  of  Seed                            Protein 

Phosphatides 

Fats 

Lupinus  luteus  (yellow  lupine) 

Pisum  sativum  (pea) 

Cannabis  saliva  (hemp) 

Helianthus  annuus  (sunflower) 

38.25 

23-13 

18.23 

14.22 

9.12 

i-59 

1.23 
0.88 
0.44 
0.28 

4-38 

1.89 

32.58 

32.26 

4-36 

The  researches  of  Palladin  and  Stanevich8  show  that  plant  respiration  is 
dependent  upon  lipoids.  Wheat  seedlings  were  treated  with  various  solvents, 
toluol,  benzene,  acetone,  benzine,  turpentine,  chloroform,  ether,  alcohol. 
The  greater  the  amount  of  lipoids  extracted,  the  smaller  was  the  quantity  of 


1  Bondi,  S.,  and  Eissler,  Franz,  Ueber  Lipoproteide  und  die  Deutung  der  degenerativen  Zellverfettung 
VI.  Weitere  Spaltungsversuche  mit  Lipopeptiden.     Biochem.  Zeitsch.  23:  510-513.      1910. 

2  Schulze,  E.,  and  Winterstein,  E.,  Phosphatide.  In:  Abderhalden,  Handbuch  2:  256.  1909.  [See 
note  i,  p.  155.] 

3  Bang,  Ivar,  Biochemie  der  Zellipoide  II.     Ergeb.  Physiol.  8:  463-523.      1909. 

*  Ciaccio,  Carmelo,  Ueber  das  Vorkommen  von  Lecithin  in  den  zellularen  Entziindungsprodukten  und 
uber  besondere  lipoidbildende  Zellen  (Lecithinzellen) .  Centrlbl.  allg.  Pathol,  u.  pathol.  Anat.  20 :  385-390. 
1909. 

5  Kossel,  A.,  Chemische  Zusammensetzung  der  Zelle.  Arch.  Physiol.  1891:  181-186.  1891.  (Review 
by  Sachsse  in  Chem.  Centralbl.  627//:  37-38.     1891.) 

6  Schulze  E.,  and  Steiger,  E.,  Ueber  den  Lecithingehalt  der  Pflanzensamen.  Zeitsch.  physiol.  Chem. 
13:  365-384.  1889.  Schulze,  E.,  and  Likiernik,  A.,  Ueber  das  Lecithin  der  Pflanzensamen.  Ibid.  15: 
405-414.  1891.  Schulze,  E.,  and  Winterstein,  E.,  Beitrage  zur  Kenntnis  der  aus  Pflanzen  darstellbaren 
Lecithine.  (Erste  Mitteilung.)  Ibid.  40:  101-119.  1903-04.  Schulze,  E.,  and  Frankfurt,  S.,  Ueber 
den  Lecithingshalt  einiger  vegetabilischen  Substanzen.     Landw.  Versuchsst.  43:  307-318.     1894. 

7  Stoklasa,  Julius,  Die  Assimilation  des  Lecithins  durch  die  Pflanze.  Sitzungsber.  (math.-naturw.  Kl.) 
K.  A  kad.  Wiss.  Wien  I047:  712-722.  1895.  Idem,  Ueber  die  Entstehung und  Umwandlung  des  Lecithins 
in  der  Pflanze.     Zeitsch.  physiol.  Chem.  25:  398-405.     1898. 

8  Palladin,  W.,  and  Stanewitsch,  E..  Die  Abhangigkeit  der  Pflanzenatmung  von  den  Lipoiden.  Bio- 
chem. Zeitsch.  26:  351-369.     1910. 


MATERIAL   TRANSFORMATIONS    IN   THE   PLANT 


iS; 


carbon  dioxide  formed.  Korsakova1  has  shown  that  lipoids  likewise  influence 
the  activity  of  proteolytic  enzymes. 

Among  the  phosphatides,  phytin2  is  especially  noteworthy;  it  probably 
represents  the  first  product  in  the  assimilation  of  phosphoric  acid. 

§9.  Carbohydrates. — The  carbohydrates  cellulose  and  starch  are  especially 
widely  distributed  in  plants.  Anatomical  observation  shows  that  the  growth 
of  cell  walls  and  the  formation  of  starch  grains  occur  only  in  the  immediate 
presence  of  protoplasm  or  leucoplasts.  Starch  and  cellulose  thus  appear  to  be 
transformation  products  of  proteins.3  Physiological  studies  also  support  this 
supposition.  The  formation  of  starch  and  cellulose  is  accompanied  by  a  de- 
composition of  proteins,  whereby  nitrogenous  compounds,  especially  asparagin, 
are  formed.  Thus,  for  example,  the  experiments  of  Hungerbuhler4  upon  ripen- 
ing potatoes  gave  the  following  results,  which  show  that  starch  formation  is  ac- 
companied by  splitting  of  proteins  and  a  formation  of  nitrogenous  decomposition 
products. 


Date  Starch,  Per  Cent.     Protein  Nitrogen, 

of  Test  of  Total  Dry  Weight  Per  Cent,  of  Total  N 


Non-protein  Nitro- 


gen, Per  Cent,  of 
Total  N 


June  23. 
June  30. 
July  7- • 


56.7 

61.3 
66.3 


70.9 

64.4 
58.7 


29. 1 
35-6 
4i-3 


On  theoretical  grounds  Palladin5  supposes  that  the  formation  of  cell  walls 
and  of  starch  grains  is  accompanied  by  oxygen  absorption,  a  supposition  that 
is  supported  by  anatomical  observations. 

Starch,  which  is  insoluble  in  water,  acts  as  a  reserve  material,  the  cells 
being  frequently  quite  filled  with  it.  If  this  reserve  material  were  stored  as 
water-soluble  compounds  (such  as  glucose),  the  cell  walls  would  not  then  be 
able  to  withstand  the  enormous  osmotic  pressures  that  would  develop. 

The  cell  wall  was  long  considered  as  made  up  of  a  single  substance  and  as 
having  a  simple  structure,  but  it  was  later  shown  that  it  is  complex.  Schulze6 
has  classified  the  cell-wall  constituents  into  two  groups.  The  first  group  in- 
cludes hemicelluloses,  which  can  be  extracted  by  heating  in  a  i-per  cent,  solu- 
tion of  hydrochloric  or  sulphuric  acid.  Among  these  substances  is  paragalactan, 
which  is  insoluble  in  water  and  is  transformed  by  oxidation  into  mucic  acid;  it 

1  Korsakow,  Marie,  Ueber  den  Einfluss  der  Zelllipoide  auf  die  Autolyse  der  Weizenkeime.  Biochem. 
Zeitsch.  28:  121-126.     1910. 

'  Vorbrodt,  1910.     [See  note  2,  p.  174.] 

3  Langstein,  Leo,  Die  Bildung  von  Kohlehydraten  aud  Eiweiss.     Ergeb.  Physiol.  1:  63-109.     1902. 

'  Hungerbuhler,  J.,  Zur  Kenntniss  der  Zusammensetzung  nicht  ausgereifter  Kartoffelknollen.  Landw. 
Versuchsst.  32:  381-388.     1886. 

5  Palladin,  W.,  Kohlehydrate  als  Oxydationsproducte  der  Eiweissstoffe.  Ber.  Deutsch.  Bot.  Ges.  7 : 
126-130.     1889. 

6  Schulze,  E.,  Steiger,  E.,  and  Maxwell,  W.,  Zur  Chemie  der  Pflanzenzellmembranen.  (I.  Abhandlung.) 
Zeitsch.  physiol.  Chem.  14:  227-273-  1890.  Schulze,  E.,  Zur  Chemie  der  pflanzlichen  Zellmembranen. 
(II.  Abhandlung.)  Ibid.  16:  387-438.  1892.  Idem,  Zur  Chemie  der  pflanzlichen  Zellmembranen.  (III. 
Abhandlung.)      Ibid.  19:  38-69.      1894. 


1 86  PHYSIOLOGY    OF    NUTRITION 

forms  galactose  by  hydrolysis.  Other  hemicelluloses  of  the  cell  wall  are  hydro- 
lyzed  to  mannose,  arabinose,  and  xylose.  The  second  group  of  cell-wall  con- 
stituents contains  the  true  celluloses,  which  do  not  go  into  solution  on  being 
warmed  with  i-per  cent.  acid.  By  hydrolysis  they  produce  glucose  only,  and 
by  oxidation  they  give  saccharic  acid. 

Cellulose  does  not  always  serve  only  as  mechanical  support;  in  many  seeds 
thickenings  of  the  cell  walls  are  simply  reserve  materials,  which  are  resorbed 
during  germination.1  This  reserve  cellulose  consists  of  hemicelluloses,  especially 
of  mannans  and  galactans.' 

The  cell  walls  of  many  fungi  differ  from  those  of  other  plants  in  that  they 
contain  nitrogen.  Those  of  Boletus  edulis,  Agaricus  campestris,  Morchella  es~ 
culenta,  Botrytis  cinerea,  and  Polyporus  officinalis  furnish  illustrations  of  this 
characteristic.  The  nitrogen  content  may  be  as  great  as  5.5  per  cent.2  If  the 
cell  walls  of  such  fungi  are  hydrolyzed  by  heating  with  hydrochloric  acid,  glu- 
cosamin  chlorhydrate  is  obtained  as  a  decomposition  product.  It  is  represented 
as  follows: 

,COH 
CH2OH— CHOH— CHOH— CHOH— CH^ 

XNH2— HC1 

The  same  substance  results  from  the  hydrolysis  of  the  chitin  of  insects.  The 
cell  walls  of  fungi  thus  contain  substances  that  are  very  similar  to  chitin. 

Grape  sugar  (glucose)  is  present  in  many  active  cells,3  and  therefore  merits 
particular  attention,  especially  since  it  is  one  of  the  simplest  carbohydrates. 
The  structural  formula  of  dextro-glucose,  or  dextrose  (which,  in  solution,  rotates 
the  plane  of  polarized  light  to  the  right)  is  as  follows: 

CHO— HCOH— HOCH— HCOH— HCOH— CH2OH. 

Cane  sugar  (saccharose)  was  formerly  considered  to  be  of  limited  distribution. 
With  refinement  of  methods,4  however,  considerable  amounts  of  this  sugar  have 
been  found  in  growing  organs.5  Brown  and  Morris6  have  identified  cane  sugar 
in  leaves  and  consider  it  to  be  the  first  product  of  the  photosynthetic  assimila- 
tion of  carbon  dioxide."     Only  after  the  accumulation  of  considerable  amounts  of 

1  Elfert,  Th.,  Ueber  die  Auflospungsweise  der  sekundaren  Zellmembranen  der  Samen  bei  ihrer  Keimung. 
Bibliotheca  botanica,  Heft.  30,  viii  +  26  p.     Stuttgart,  1894. 

2  Winterstein,  E.,  Ueber  ein  stickstoffhaltiges  Spaltungsproduct  der  Pilzcellulose.  Ber.  Deutsch.  Chem. 
Ges.  277//:  3113-3115.     1894.     Idem,  Ueber  die  Spaltungsproducte  der  Pilzcellulose.      Ibid.  28   :  167-169. 

189S. 

3  Armstrong,  E.  F.     The  simple  carbohydrates  and  glucosides.     London,  1910. 

*  Schulze,  E.,  Ueber  den  Nachweis  von  Rohrzucker  in  vegetabilischen  Substanzen.  Landw.  Versuchsst. 
34:  408-413.  1887.  Schulze,  E.,  and  Frankfurt,  S.,  Ueber  die  Verbreitung  des  Rohrzuckers  in  den 
Pflanzen,  uber  seine  physiologische  Rolle  und  uber  losliche  Kohlenhydrate,  die  ihn  begleiten.  Zeitsch. 
physiol.  Chem.  20:  Si  1-555-      1895. 

*  Seliwanoff,  Th.,  Ein  Beitrag  zur  Kenntnis  der  Zusammensetzung  etiolierter  Kartoffelkeime.  Landw. 
Versuchsst.  34:  414-417.  1887.  Frankfurt,  Solomon,  Ueber  die  Zusammensetzung  der  Samen  und  der 
etiolierten  Keimpflanzen  von  Cannabis  sativa  und  Helianthus  annuus.     Ibid.  43:  143-182.      1894. 

*  Brown  and  Morris,  1893.     [See  note  1,  p.  28.] 

'  This  sentence  is  omitted  in  the  7th  Russian  edition. — Ed. 

"On  this  point,  however,  see:  Dixon,  H.  H.,  and  Mason,  T.  G.,  The  primary  sugar 
of  photosynthesis.     Nature  97:   160.     1916. — Ed. 


MATERIAL   TRANSFORMATIONS    IN   THE    PLANT  1 87 

cane  sugar  is  there  any  transformation  of  the  latter  into  starch;  Bohm  obtained 
quite  analogous  results  by  artificially  supplying  sugar  to  the  plant. 

§10.  Glucosides.1 — Glucosides1  are  chemical  combinations  of  glucose  (some- 
times of  other  sugars)  with  various  other  substances,  and  they  are  split  into  their 
component  parts  by  the  action  of  acids  or  glucoside-splitting  enzymes.  For 
example,  under  the  influence  of  emulsin,  arbutin  takes  up  water  and  produces 
hydroquinone  and  glucose.     This  reaction  is  shown  below:"' 

i O f 

CH2OH— CHOH— CH— CHOH— CHOH— CH— OCBH4OH    (arbutin)    + 

-        -o 

H20  (water)  =  CH2OH— CHOH— CH— CHOH— CHOH— CHOH  (glucose)  + 
HOCeHjOH  (hydroquinone). 

Indican,  a  glucoside  of  the  indigo  plant,  etc.,  forms  glucose  and  indoxyl, 
with  the  taking  up  of  water: 

C7H6NC— O— CeHnOs  (indican)  +  H20  (water  = 

/C0H\ 
C6Hi20e  (glucose)  +  CfiH/  ,CH  (indoxyl). 

^NH^ 

Indoxyl  oxidizes  in  the  air,  forming  dark  blue  indigotin  (indigo  blue)  and  water: 

2C8H7ON  +  02  =  2H20  +  Ci6H10O2N2. 
Indigotin  has  the  structural  formula, 

/co\  _  /co\ 

CeHu  C — C.  .CeH4. 

XNHX  XNHX 

As  a  third  example  may  be  mentioned  amygdalin,  an a-$ glucoside  of  almond, 
peach,  etc.,  which  takes  up  water  and  splits  into  glucose,  benzaldehyde  and 
hydrocyanic  acid: 

-o-  - 

CH2OH— CHOH— CH— CHOH— CHOH— CH—0—CH2— CHOH— 

C  6H  5 

CH— CHOH— CHOH— CH—O—CH  (amvgdalin)  +  H20  (water)  =  2C6H1206 

-  -o- 

CN 

(glucose)  +  C6H6 — CHO   (benzaldehyde)  +  HCN   (hydrocyanic  acid). 

Glucosides  may  undergo  autolysis  in  the  tissues.  Thus,  if  leaves  of  Polygo- 
num tinctorium  are  exposed  to  an  atmosphere  saturated  with  chloroform 
vapor  (which  kills  the  cells), blue  indigotin  is  formed  in  the  tissues.  The  chlor- 
ophyll may  then  be   extracted  by  alcohol,  leaving   the  leaves  blue.     When 

1  Rijn,  van,  1900.     [See  note  2,  p.  333.] 

"  This  section  appears  for  the  first  time  in  the  7th  Russian  edition. — Ed. 

"  For  this  and  similar  statements  of  formulas  and  reactions,  see  Haas  and  Hill,  1913.  '[See 
note  3,  p.  6.]  Also  see  works  on  organic  chemistry;  an  excellent  short  treatise  for  physio- 
logical students  is  Bernthsen,  A.,  A  text-book  of  organic  chemistry.  Translated  and  edited 
by  J-  J-  Sudborough.     New  York.     1907. — Ed. 


1 88  PHYSIOLOGY    OF    NUTRITION 

autolysis  occurs  in  plant  parts  containing  amygdalin,  a  strong  odor  of  hy- 
drocyanic acid  is  developed. 

Some  of  the  glucosides  that  accumulate  in  plants  appear  to  be  respiratory 
chromogens,  others  are  very  efficient  activators  (hormones). 

§11.  Organic  Acids. x — All  living  cells  always  contain  some  organic  acids, 
the  cell  sap  always  giving  an  acid  reaction.  It  is  supposed  that  these  acids 
arise  through  incomplete  oxidation  of  carbohydrates.  Numerous  studies  have 
been  carried  out  upon  oxalic  acid  in  the  form  of  its  calcium  salt,1  and  it  appears 
that  marked  accumulation  of  this  salt  occurs  in  most  plants  only  in  light  and 
with  normal  or  high  transpiration,  while  very  little  is  formed  in  darkness  and 
when  transpiration  is  low. 

Various  external  and  internal  conditions  have  great  influence  upon  the  forma- 
tion and  decomposition  of  organic  acids  in  plants.2  The  amounts  of  these  acids 
decrease  somewhat  in  light,  as  is  shown  by  the  table  below,  which  presents  the 
relative  acid  contents  of  several  plants,  in  darkness  and  in  light. 

Relative  Acid  Content 

Plant                                                           In  Darkness  In  Light 

Convallaria  majalis  (rhizome) 72  68 

Phaseolus  multiflorus  (roots) 60  64 

Etiolated  wheat  seedlings 238  230 

The  acid  content  is  lower  with  higher  temperatures.  Thus,  for  example, 
plants  of  Sempervivum  tectorum,  with  an  acid  content  of  358,  were  placed  in 
diffuse  light  for  three  hours,  with  temperatures  of  4-6°C,  22-25°C,  and  35- 
38°C,  and  at  the  end  of  this  period  the  acid  content  had  fallen  to  336,  to  327, 
and  to  301,  respectively. 

If  carbohydrates  are  artificially  supplied,  an  increase  in  the  acid  content 
occurs.  The  roots  were  removed  from  etiolated  seedlings  of  Phaseolus  and 
some  were  placed  in  distilled  water,  others  in  a  solution  of  glucose,  in  dark- 
ness. After  three  days  the  acid  content  of  those  on  water  was  185,  while  that 
of  the  plants  in  glucose  solution  was  257.  Grape  sugar  thus  produces  an  in- 
crease in  the  acid  content  of  seedlings. 

[Active  roots  appear  to  give  off  organic  acids,  into  the  soil,  when  the  supply 
of  oxygen  is  low.  With  a  plentiful  supply  of  oxygen  they  appear  to  give  off 
only  carbon  dioxide.] 

§12.  The  Importance  of  Water  in  Plants. y — Physiological  processes  can- 

1  Kohl,  Friedrich  Georg,  Anatomisch-physiologische  Untersuchung  der  Kalksalze  und  Kiesels&ure  in 
der  Pflanze.  Ein  Beitrag  zur  Kenntnis  der  Mineralstoffe  im  lebenden  Pflanzenkorper  Marburg,  1889. 
Monte verde,  N.  A.,  On  the  deposition  of  the  oxalates  of  calcium  and  magnesium  in  plants.  [Russian.} 
81  p.  St.  Petersburg,  1889.  Rev.  in  Bot.  Centralbl.  43:  327-333,  1890.  Wehmer,  Carl,  Entstehung  und 
physiologische  Bedeutung  der  Oxalsaure  im  Stoffwechsel  einiger  Pilze.  Bot.  Zeitg.  49:  233-246,  240-257, 
271-280,  289-298,  305-313.  321-332,  337-346.  3S3-363,  369-374.  385-396,  401-407,  4I/-428,  433-439. 
449-456,  465-478,  511-518,  531-539,  547-554.  563-569,  579-584,  596-602,  611-620,  630-638.     1891. 

2  Puriewitsch  Konstantin  A.,  Bildung  und  Zersetzung  der  organischen  Sauren  in  Samenpflanzen.  Kiev, 
1893. 

x  This  section  is  numbered  §10  in  the  German;  the  numbering  of  the  7th  Russian 
edition  is  here  followed. — Ed. 

v  This  section  appears  for  the  first  time  in  the  7th  Russian  edition. — Ed. 


MATERIAL  TRANSFORMATIONS   IN   THE   PLANT  1 89 

not  go  on  without  water  in  the  cells.1  About  80  or  90  per  cent,  (by  weight)  of 
the  active  plant  cell  is  water,  and  the  water  content  is  small  only  in  so-called 
resting  tissues,  such  as  those  of  dry  seeds.  When  such  relatively  inactive  tissues 
become  active,  the  acceleration  of  the  physiological  processes  is  preceded  or 
accompanied  by  pronounced  absorption  of  water.  At  the  same  time  much  of 
the  insoluble  material  of  the  inactive  cells  (starch,  oil,  etc.)  is  modified  so  as  to 
become  soluble  in  water,  and  this  dissolves  with  the  advance  of  renewed  activity. 
Also,  with  the  entrance  of  water  many  colloidal  substances  in  the  cell  (which 
are  not,  or  do  not  become,  truly  soluble  in  water)  absorb  this  liquid  to  a  marked 
degree  and  swell  to  a  corresponding  extent,  even  becoming  so  completely  dis- 
persed in  the  water  that  the  hydrosol  thus  formed  becomes  liquid  and  assumes 
many  of  the  properties  of  a  true  solution.  In  nearly  dry  cells  these  cell  colloids 
are  largely  in  the  hydrogcl  phase  and  are  virtually  solid. 

As  the  cell  colloids  pass  into  the  sol  phase  and  the  crystalloids  dissolve, 
those  of  the  latter  that  are  electrolytes  become  increasingly  dissociated,  so 
that  they  become  much  more  active  chemically.  The  water  also  is  dissociated 
and  a  cell  well  supplied  with  water  thus  contains  many  different  kinds  of 
kations  and  anions,  the  concentrations  of  which  determine  the  rates  and  direc- 
tions of  many  chemical  changes.  Especially  are  the  hydrogen  ion  (kation) 
and  hydroxyl  ion  (anion)  concentrations  important  in  this  way.2 

Aside  from  being  the  medium  of  solution  and  dispersion  of  the  non-aqueous 
cell  substances,  and  aside  from  its  influence  on  ionization  and  chemical  action, 
water  is  also  an  essential  material  in  the  synthesis  of  organic  compounds.  The 
hydrogen  and  oxygen  of  the  plant  body  are  to  be  considered  as  derived  from 
water  (see  Part  I,  Chapter  I).  Water  is  also  a  necessary  material  for  the 
hydrolysis  of  many  complex  carbohydrates,  proteins,  fats,  etc.,  into  simpler 
compounds  {e.g.,  starch  and  cellulose  into  sugar,  cane  sugar  into  glucose). 
Of  course  water  is  produced  by  the  opposite  process  (e.g.,  the  polymerization  of 
glucose  to  form  cane  sugar),  and  also  by  the  complete  oxidation  of  carbohy- 
drates, fats,  etc.,  in  respiration.  But  water  apparently  disappears  in  the  earlier 
chemical  steps  of  respiration  (see  page  225  and  compare  page  217). 

§13.  The  Germination  of  Seeds/ — In  the  above  discussion,  some  of  the  ques- 
tions concerning  various  material  changes  and  other  physiological  processes 

1  Kraus,  Gregor,  Ueber  die  Wasserverteilung  in  der  Pflanze.  Halle,  1879-1884.  [This  vol.  is  reprinted 
from  Naturforscherges  Halle;  Festschr.  (1879),  71  p.;  Abhandl.  15:  40-120  (1880);  15:  220-319  (1881); 
16:  141-20S  (1884).]  Babcock,  S.  M.,  Metabolic  water:  its  production  and  role  in  vital  phenomena. 
Univ.  Wisconsin  Agric.  Exp.  Sta.  Research  Bull.  22.  1912.  (Also  Ann.,  rept.  Wisconsin  Agric.  Exp.  Sta. 
292:  87-181.     1912.) 

2  [The  true  acidity"  of  a  solution  depends,  not  upon  the  total  quantity  of  acid  present,  but  upon  the 
concentration  of  hydrogen  ions;  similarly,  the  "true  alkalinity  "  depends  upon  the  concentration  of  hydroxyl 
ions.  Which  concentration  is  in  excess  determines  the  reaction  of  the  solution.  It  is  necessary  to  remem- 
ber that  ion  concentrations  may  be  different  in  different  parts  of  the  same  cell;  for  example,  the  protoplasm 
is  generally  alkaline  while  the  cell-sap  is  acid.  On  the  reactions  of  cell  solutions,  see:  Michaelis,  L.,  Die 
allgemeine  Bedeutung  der  Wasserstoffionenkonzentration  fur  die  Biologie.  In  Oppenheimer's  Handbuch 
der  Biochemie  des  Menschen  und  der  Tiere.  Jena,  1909-n.  Erganzungsband,  1913.  (See  Erganzbd., 
p.  10.)  SSrensen,  S.  P.  L.,  Ueber  die  Messung  und  Bedeutung  der  Wasserstoffionenkonzentration  bei 
biologischen  Prozessen.     Ergeb.  Physiol.  12:  393-532.     1912.] 

2  This  section  is  numbered  §11  in  the  German  edition.  It  appears  unnumbered,  at  the 
end  of  the  chapter,  in  the  7th  Russian  edition. — Ed. 


190 


PHYSIOLOGY    OF    NUTRITION 


have  been  considered  with  reference  to  changes  that  occur  in  germinating  seeds. 
The  important  factors  in  seed  germination  will  now  be  considered  more  in  detail. 
Considerable  amounts  of  organic  reserve  food  materials  are  stored  in  all  seeds, 
either  in  the  cotyledons  or  in  the  endosperm.  Consequently,  the  first  phases 
of  germination  can  occur  without  light  or  mineral  substances.  During 
germination  in  darkness  stored  substances  alone  are  utilized,  the  chemical 
nature  and  amount  of  which  can  be  determined  by  exact  analysis.  Quite 
similar  phenomena  occur  also  in  plants  growing  in  light;  but  matters  are  com- 
plicated in  this  case  by  the  fact  that  the  process  is  accompanied  by  the  assimila- 
tion of  carbon  dioxide  and  mineral  constituents.  This  assimilation  results  in 
the  formation  of  new  substances,  of  external  origin,  which  obscure  the  trans- 
formations occurring  in  the  reserve  materials.  By  studying  germination  in 
darkness  and  in  distilled  water  we  may  eliminate  the  absorption  of  all  materials 
except  water  and  atmospheric  oxygen,  and  may  thus  study  the  changes  of 
reserve  materials  already  within  the  plant. 

It  is  generally  observed  that  the  dry  weight  of  seedlings  of  various  plants  is 
considerably  less  than  the  dry  weight  of  the  ungerminated  seeds.  This  is  illus- 
trated by  the  following  analyses  of  46  wheat  seeds  and  of  the  same  number  of 
seedlings.     The  numbers  represent  grams. 


Total  Dry 
Weight 


Carbon 


Hydrogen 


Oxygen 


Nitrogen 


Total 
Ash 


Seeds 

Seedlings 

Loss  during  germina- 
tion   


1.665 
o.  722 


o.943 


0.758 
0.293 

0.465 


0.095 

0.043 

0.052 


0.718 
o.  282 


0.436 


0.057 
0.057 


0.000 


0.038 

0.038 

0.000 


The  chemical  processes  of  germination  are  not  identical  in  different  kinds 
of  seeds;  they  depend  largely  upon  the  chemical  nature  of  the  stored  reserve 
materials.  Seeds  are  grouped  into  three  classes  according  to  the  nature  of 
the  reserve  materials  that  predominate  in  them:  starchy  seeds,  proteinaceous 
seeds  and  fatty  seeds. 

From  the  table  given  above  it  is  evident  that  the  loss  of  material  during  the 
germination  of  starchy  seeds  (such  as  those  of  the  Gramineae1)  occurs  through 
loss  of  carbon,  oxygen  and  hydrogen.  The  amount  of  nitrogen  and  of  ash  con- 
stituents remains  unchanged.  The  nature  of  the  transformations  occurring  in 
the  germination  of  maize  is  shown  in  the  following  table,  which  presents  the 
results  of  analyses  of  22  maize  seeds  and  of  as  many  seedlings.  The  numbers 
represent  grams.  It  thus  appears  that  most  of  the  starch  is  decomposed  by 
diastase,  with  the  formation  of  glucose  and  cellulose. 

During  the  germination  of  proteinaceous  seeds  also  (such  as  those  of  the 


1  Boussingault,  1860-1891.      [See  note  5,  p.  2.]     Vol.  4. 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT 


IQI 


Leguminosae1),  the  decrease  in  dry  weight  is  due  to  loss  of  carbon,  hydrogen 
and  oxygen.  Protein  decomposition  occurs  at  the  same  time,  with  the  formation 
of  asparagin  and  amino  acids.     Glucose  is  formed  from  the  non-nitrogenous 


Total  Dry 
Weight 


Starch  and 
Dextrine 


Glucose  and 
Saccharose 


Seeds 8.636 

Seedlings 4 .  529 

Gain   or  loss  during 

germination —4.107 


6.386 
0.777 

-5.609 


0.000 
Q-953 

+  o.953 


Fats 


0.463 
0.150 

-0.313 


Cellulose 


0.516 
1. 316 

+0.800 


substances,  and  the  cellulose  content  increases.  The  table  given  below  shows 
analyses  of  seeds  and  seedlings  of  Lupinus  luteus,  the  quantities  being  percent- 
ages of  the  total  dry  weight  of  the  seeds.     Sulphates  also  appear,  as  a  by- 


Total  Dry 
Weight 

Proteins 

Aspara- 
gin 

Other  Nitro- 
genous Sub- 
stances 

Glu- 
cose 

Cellu- 
lose 

Seeds 

Seedlings 

100.00 
81.70 

-18.30 

45-07 
11 .06 

-34.01 

0.00 
18.22 

-f  18.22 

11. 6 
23-97 

+  12.31 

0.00 
2.10 

+  2.10 

3-24 
6.47 

Gain  or  loss  during 
germination 

+3-23 

product  of  protein  decomposition  in  the  germination  of  proteinaceous  seeds; 
lupine  seeds  with  an  equivalent  sulphuric  acid  content  of  0.385  g.  were  germi- 
nated and  showed  a  corresponding  content  of  0.610  g.  when  seven  days  old,  and 
one  of  1.323  g.  when  fifteen  days  old. 

In  the  germination  of  fatty  seeds  (such  as  those  of  Helianthus,  Cucurbita, 
Ricinus,  etc.2)  the  loss  in  dry  weight  occurs  almost  entirely  through  loss  of  car- 
bon and  hydrogen,  while  the  amount  of  oxygen  actually  increases  through 
absorption.  The  stored  fats  decrease  during  this  process  and  are  replaced  by 
starch,  which  shows  how  the  absorption  of  oxygen  is  to  be  interpreted.  Fats 
are  much  poorer  in  oxygen  than  starch,  and  the  formation  of  starch  from  fats  is 
therefore  possible  only  with  addition  of  oxygen.  The  hydrolysis  of  fat  results 
in  an  increase  in  the  fatty  acid  content  of  the  seeds  during  germination.  The 
following  experiment  may  serve  as  an  illustration  of  this.  Twenty  grams  of 
poppy  seed  contained  8.915  g.  of  fat  and  0.975  g-  °f  free  fatty  acids.  After 
germination  for  four  days  3.77  g.  of  free  fatty  acids  were  present,  and  only  3.90 
g.  of  fat.     Glycerine,  however,  was  not  found  in  the  seedlings. 

The  following  table  illustrates  the  changes  that  occur  during  the  germination 
of  sunflower  seeds.  The  numbers  represent  percentages,  on  the  basis  of  the 
original  total  dry  weight  of  the  seeds.3 

1  Schulze,  E.,  and  Umlauft,  W.  Untersuchungen  iiber  einige  chemische  Vorgange  bei  der  Keimung  der 
gelben  Lupine.     Landw.  Jahrb.  5:  821-858.      1876. 

'  Laskovsky,  Die  Keimung  der  Kurbissamen  in  chemischer  Bezielhung.      Moscow,  1874.* 
3  Frankfurt,  1894.     [See  note  5,  p.  186.] 


192 


PHYSIOLOGY    OF   NUTRITION 


Seeds 


Total  dry  weight 

Simple  proteins 

Nuclein  and  plastin .... 
Asparagin  and  glutamin 

Lecithin 

Fats 

Sugars 

Soluble  organic  acids. .  . 

Cellulose 

Hemicelluloses 


100.00 
24.06 
0.96 
0.00 
0.44 
55-32 
3-78 
0.56 

2-54 
0.00 


Seedlings 


88.98 

13-34 
4-05 
3.60 
0.71 

21.82 

13.12 
2 .  16 

10.25 
3-4i 


Gain  or  Loss 

During 
Germination 


—  11 .12 

—  10.72 

+  3-09 
+  3-60 
+  0.27 
-33-5o 

+  9-34 
+   1.60 

+  7-7i 
+  3-4i 


The  main  facts  regarding  germination  may  of  course  be  most  readily  demon- 
strated from  the  study  of  seeds  germinated  in  darkness.  Germination  in  light 
is  identical  with  that  in  darkness  except  for  the  additional  assimilation  of  carbon 
and  mineral  constituents.1 

Summary 

1.  The  Cell  as  Physiological  Unit. — The  life  activities  of  a  plant  are  the  summed 
activities  of  its  cells.  Cell  activities  are  due  to  protoplasm,  influenced  by  the  sur- 
roundings. In  all  but  the  very  simplest  forms,  the  protoplasm  of  each  cell  consists 
of  the  nucleus  and  the  cytoplasm,  and  both  parts  are  necessary  for  the  life  of  the  cell. 
Plastids  are  special  parts  of  the  protoplasm.  Chemically,  the  protoplasm  consists 
largely  of  water  and  proteins.  Over  90  per  cent,  of  the  weight  of  active  protoplasm 
is  water.  Among  the  non-aqueous  substances  in  protoplasm  the  proteins  predominate, 
forty  per  cent,  of  the  dry  weight  of  slime-mould  Plasmodium  (protoplasm  mainly) 
being  proteins. 

2.  Proteins. — The  proteins  are  chemically  the  most  complex  substances  in  the 
plant.  They  are  very  plentiful  in  resting  tissue  (such  as  seeds),  less  plentiful  in  active 
tissue,  and  least  plentiful  in  mature  tissue  that  has  nearly  ceased  its  activities.  Full- 
grown  leaves  that  are  still  active  photosynthetically  contain  much  protein  in  their 
chloroplasts.     There  are  several  chemical  tests  generally  used  for  identifying  proteins. 

The  proteins  of  plants  are  considered  as  belonging  to  two  groups,  the  simple 
proteins  (such  as  the  albumin  of  aleurone  in  seeds)  and  the  compound  proteins  (which 
are  essential  in  the  protoplasm  itself).  The  simple  proteins  contain  carbon,  hydrogen, 
oxygen,  nitrogen,  and  often  sulphur.  They  are  combinations  or  complexes  of  much 
simpler  nitrogenous  organic  compounds,  the  amino  acids.  About  seventeen  different 
amino  acids  enter  into  the  simple  proteins  of  plants  (and  animals  also).  The  simplest 
of  these  acids  is  glycocoll  (alpha-amino-acetic  acid,  CH2NH2COOH).  As  examples  of 
the  most  complicated  amino  acids  may  be  mentioned  cystin  (alpha-diamino-beta- 
dithio-dilactic  acid)  and  triptophan  (beta-indol-alpha-amino-propionic  acid).  The 
constituent  amino  acid  molecules  are  joined  into  groups  called  polypeptides,  and 
polypeptide  groups  are  united  to  form  the  simple  protein  molecule.  The  simple 
proteins,  of  which  there  are  a  large  number,  act  as  foods  and  are  not  considered  here 

1  For  a  treatise  on  seed  germination  see:  Detmer,  Wilhelm,  Vergleichende  Physiologie  des  Keimungs- 
processes  der  Samen.     Jena,  1880. 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT  1 93 

as  really  constituents  of  the  protoplasm,  though  they  occur  in  the  cytoplasm  of  cells. 
They  mainly  occur  as  protein  grains  or  dissolved  in  the  cell  sap  (which  is  the  more 
liquid  material  lying  within  the  cytoplasm  of  ordinary  plant  cells). 

The  nucleo-proteins  furnish  examples  of  the  complex  proteins.  They  are  com- 
binations of  simple  proteins  with  nucleins,  and  nucleins  are  combinations  of  the  more 
complex  simple  proteins  with  nucleic  acids.  The  latter  are  rich  in  phosphorus.  The 
simplest  nucleic  acid  (derived  from  yeast)  has  the  formula,  C40H59N14O22 — 2P0O5. 
These  acids  give  phosphoric  acid,  on  being  decomposed. 

3.  Enzymes. — Enzymes  are  catalyzers  that  occur  in  plant  cells.  They  are  organic 
in  their  nature  and  act,  like  other  catalyzers,  to  accelerate  (or  retard)  chemical  changes 
or  to  alter  the  equilibrium  point  at  which  a  chemical  change  ceases.  In  their  presence 
many  chemical  reactions  go  on  that  would  not  go  on  appreciably  without  their  aid,  or 
would  soon  come  to  equilibrium  and  cease.  The  rate  of  change  depends  on  the  amount 
of  enzyme  present,  as  well  as  upon  the  temperature  and  the  other  substances  in  the 
medium.  The  enzyme  is  not  used  up  in  the  process  that  it  promotes.  The  chemical 
nature  of  enzymes  is  not  yet  known;  they  are  known  by  their  effects. 

Diastase  is  a  widely  distributed  plant  enzyme.  It  causes  the  transformation  of 
starch  into  glucose,  with  the  consumption  of  water.  It  may  be  obtained  from  germin- 
ating seeds,  such  as  those  of  barley  (malt),  from  leaves,  etc.  Diastase,  as  here  defined, 
consists  of  a  mixture  of  two  enzymes,  amylase  and  maltase.  Amylase  transforms 
starch  to  maltose,  and  maltase  forms  dextro-glucose  (dextrose)  out  of  maltose. — Sac- 
charose (or  invertase)  is  another  common  enzyme  in  plants.  It  converts  saccharose 
(cane  sugar)  into  dextro-glucose  (dextrose)  and  dextro-fructose  (levulose),  with  the 
consumption  of  water. — Proteins  are  transformed  and  rendered  soluble  in  water  by  the 
action  of  proteolytic  enzymes,  which  decompose  proteins,  with  consumption  of  water, 
into  simpler  compounds. — Fats  are  decomposed  into  glycerine  and  fatty  acids,  with 
consumption  of  water,  by  lipases. 

Besides  these,  and  other,  hydrolytic  enzymes  (operating  with  consumption  of 
water),  oxidases  are  present  in  plant  cells.  These  cause  the  oxidation  of  organic 
substances,  with  molecular  oxygen. — Another  non-hydrolytic  enzyme  is  zymase, 
which  promotes  the  formation  of  alcohol  and  carbon  dioxide  from  glucose.  It  occurs 
plentifully  in  active  yeast  cells. 

Living  protoplasm  is  supposed  to  contain  specific  enzymes  that  promote  the  various 
chemical  changes  of  vital  activity,  not  only  decompositions  but  syntheses.  Hill 
showed  that  maltase  acts  in  either  direction,  to  form  glucose  from  maltose  (with  addi- 
tion of  water)  or  to  form  maltose  from  glucose  (with  production  of  water),  according  to 
the  concentrations  of  maltose  and  glucose  in  the  mixture. 

Tissues  may  be  killed  without  destroying  all  of  their  enzymes,  as  follows  from  the 
fact  that  many  enzymes  may  be  extracted  from  tissues  that  have  been  killed  in  the 
process  of  extraction.  Enzymes  may  remain  active  in  dead  tissues  for  a  considerable 
time,  but  enzyme  activity  in  dead  cells  is  nol  automatically  regulated  and  coordinated 
as  it  is  in  living  cells.  The  enzymes  are  very  important  agents  in  vital  processes,  and 
perhaps  catalysis  furnishes  a  key  to  vital  processes  in  general,  but  the  nice  coordination 
of  all  the  various  catalytic  actions  that  is  the  main  characteristic  of  living  protoplasm 
remains  still  to  be  understood. 

4.  Protein  Decomposition  in  Plants. — Proteins  are  continually  broken  down  and 
re-formed  in  living  tissues,  apparently  by  the  action  of  enzymes.  In  germinating 
seeds,  the  decomposition  of  simple  proteins  gives  amino  acids  such  as  tyrosin  (beta-para- 
hydroxyphenyl-alpha-amino-propionic  acidl  and  leucin  (alpha-amino-isobutyl-acetic 

13 


1 94  PHYSIOLOGY   OF   NUTRITION 

acid).  Asparagin  (NH2COCH2CHNH2)  appears  to  be  formed  from  these  in  most 
plants,  in  the  presence  of  oxygen,  so  that  the  amino  acids  do  not  accumulate  except 
when  oxygen  is  absent.  In  the  presence  of  oxygen  asparagin  appears  as  the  main 
nitrogenous  waste  of  plants  (somewhat  as  urea  (NH2CONH2)  does  in  animals).  But 
this  waste  is  not  given  off  to  the  exterior  of  the  plant;  in  green  leaves,  in  sunlight 
(apparently  because  of  a  plentiful  supply  of  sugars),  asparagin  is  combined  with  carbo- 
hydrates, forming  simple  proteins,  and  thus  returns  to  the  metabolic  system.  Only  in 
very  young  seedlings  (in  the  presence  of  oxygen)  does  asparagin  accumulate  consider- 
ably, since  it  is  used  up  in  protein  synthesis  about  as  rapidly  as  it  is  formed;  but  it 
becomes  clearly  evident  in  older  plants  kept  for  a  time  in  darkness,  where  protein 
formation  is  stopped  because  of  lack  of  carbohydrates. — The  decomposition  of  proteins, 
and  the  products  formed,  are  influenced  by  the  chemical  nature  of  the  substances 
supplied  to  the  living  cells.  The  mould  Aspergillus  forms  oxalic  acid  when  grown  in 
acid  media,  but  when  there  is  an  excess  of  calcium  carbonate  it  forms  tyrosin  and 
leucin  instead  of  oxalic  acid. 

The  compound  proteins  are  also  broken  down  in  active  tissues,  and  their  decomposi- 
tion products  appear,  especially  in  darkness  and  when  the  plants  are  starved.  Appar- 
ently the  simple  proteins  are  attacked  first  (and  as  long  as  the  supply  lasts),  and  the 
complex  proteins  are  considerably  decomposed  only  when  the  supply  of  simple  pro- 
teins is  about  exhausted.  Compound  proteins  appear  in  many  instances  to  be  formed 
at  the  expense  of  simple  proteins. 

5.  Nitrogenous  Products  of  Protein  Decomposition. — As  has  been  said,  asparagin 
appears  as  the  most  important  decomposition  protuct  of  simple  proteins.  In  some 
plants  its  place  is  taken  by  a  similar  substance,  glutamin.  Tyrosin,  leucin,  and  some 
other  amino-acids  are  also  formed  in  plants,  from  simple  proteins.  The  purin  bases 
(xanthin,  hypoxanthin,  adenin,  guanin),  as  well  as  their  derivatives  (such  as  caffein 
— the  main  alkaloid  of  coffee  and  tea,  and  theobromin — the  main  alkaloid  of 
chocolate)  result  from  the  decomposition  of  the  nucleo-proteins. 

6.  Protein  Synthesis  in  Plants. — The  primary  synthesis  of  simple  proteins  in 
ordinary  green  plants  appears  to  occur  in  the  leaves,  where  carbohydrates  (formed  in 
the  chlorophyll-bearing  tissues  by  photosynthesis)  are  combined  with  the  nitrogen 
of  nitrates  (which  reach  the  leaves  through  the  xylem  vessels,  from  the  absorbing 
regions  of  the  roots).  Nitrates  are  usually  found  in  leaves  only  in  very  small  amounts, 
and  it  appears  that  they  are  ordinarily  used  up  as  rapidly  as  they  arrive.  In 
prolonged  darkness,  however,  the  supply  of  carbohydrates  is  stopped,  and  nitrates  accu- 
mulate in  leaves  to  considerable  amounts.  Also,  nitrates  have  been  found  to  accumu- 
late in  the  chlorotic  parts  of  white-green  variegated  leaves,  even  in  light.  In  these 
parts  no  carbohydrates  are  formed.  Light  is  apparently  not  directly  necessary  for  the 
synthesis  of  simple  proteins  from  carbohydrates  and  nitrates,  but  it  is  of  course  neces- 
sary for  the  photosynthesis  of  carbohydrates,  and  it  is  thus  indirectly  necessary  for  these 
protein  syntheses. 

Hydrocyanic  acid  (HCN)  has  been  supposed  to  be  an  intermediate  product  in 
simple  protein  synthesis  from  carbohydrates  and  nitrates.  Many  leaves  ordinarily 
contain  this  acid  (combined  with  sugars)  in  detectable  quantities.  It  disappears, 
however,  after  prolonged  darkness  (being  probably  used  up  in  protein  formation), 
but  it  reappears  when  the  leaves  are  supplied  with  nitrate  and  sugar  in  darkness 
or  when  they  are  supplied  with  nitrate  in  light. 

Decomposition  of  simple  proteins  occurs  in  germinating  seeds,  in  darkness,  as 
has  been  said,  while  the  later  growth  of  the  plantlets  (in  light  and  with  photosynthesis 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT  1 95 

going  on)  shows  protein  synthesis.     Light  is  here,  again,  apparently  necessary  only  for 
the  formation  of  the  necessary  carbohydrates. 

As  to  the  nucleins  (of  compound  proteins),  active  growth  is  generally  accompanied 
by  nuclein  synthesis.  The  nucleo-proteins  increase  during  the  first  stages  of  seed 
germination,  doubtless  being  formed  at  the  expense  of  the  simple  proteins,  which 
decrease  during  these  stages.  Compound  proteins  are  formed  in  leaves  when  sugars 
are  plentiful,  and  the  process  seems  to  be  more  rapid  in  light  than  in  darkness,  as 
though  light  exerted  a  direct  influence  in  this  case. 

7  [8].  Lipoids  and  Phosphatides. — Lipoids  are  substances  that  can  be  dissolved  out 
of  plant  or  animal  cells  by  treatment  with  ether  or  similar  solvents.  Here  belong  not 
only  fats  and  fatty  acids,  but  also  phosphatides.  The  latter  may  be  defined  as  lipoids 
containing  phosphorus;  they  are  very  active  chemically  and  are  present  in  all  proto- 
plasm. Lipoids  apparently  form  labile  compounds  with  the  proteins,  on  the  one  hand 
and  with  iron,  calcium,  etc.,  on  the  other  hand. 

8  [9].  Carbohydrates. — The  carbohydrates  of  plants  are  either  water-soluble 
(glucose,  saccharose,  inulin,  etc.)  or  insoluble  in  water  (starches,  celluloses,  etc.). 
Starch  and  cellulose  appear  to  be  formed  in  plant  cells  by  a  sort  of  decomposition  of 
proteins.  Protoplasm  is  necessary  for  their  formation,  and  they  form  as  solid  masses 
in  leucoplasts  (starch  grains)  or  at  the  protoplasmic  periphery  (cell  walls).  There  is 
evidence  that  their  formation  is  accompanied  by  the  production  of  nitrogenous  sub- 
stances such  as  asparagin.  (These  nitrogenous  products  appear  to  be  then  combined 
with  sugar,  forming  more  proteins,  so  that  cellulose  and  starch  are  said  to  be  formed  by 
a  sort  of  condensation  of  sugar,  although  proteins  seem  to  be  involved  in  the  process.) 
Cellulose  forms  the  main  mechanical  support  of  plant  tissues,  but  the  thickened  cell 
walls  of  some  forms  (as  the  endosperm  of  date  seeds)  are  subsequently  dissolved,  by  the 
action  of  the  enzyme  cytase,  and  furnish  sugar  that  is  used  in  later  growth.  Ordinary 
cell  walls  contain  hemicelluloses{  which  can  be  extracted  with  hot  1  per  cent,  solution 
of  hydrochloric  or  sulphuric  acid)  and  true  celluloses  (which  cannot  be  extracted  in 
that  way).  The  cell  walls  of  many  fungi  (ordinary  mushrooms)  are  composed  of 
fungus  cellulose,  which  contains  considerable  nitrogen  and  is  similar  to  the  chitin  of  the 
external  skeleton  of  insects,  crabs,  etc. 

Grape  sugar  (dextrose  or  dextro-glucose)  is  a  glucose  sugar  very  generally  present 
in  plant  cells.  It  is  one  of  the  simplest  of  the  carbohydrates,  being  represented  by 
the  formula  C6Hi206.  As  has  been  said,  it  is  freely  soluble  in  water  and  always  occurs 
in  aqueous  solution  in  the  tissues.  Saccharose  (cane  sugar)  is  a  more  complex  water- 
soluble  carbohydrate,  represented  by  the  formula  Ci2H220ii.  It  is  very  common  in 
plants  (in  fruits,  roots,  stems,  etc.,  in  large  amounts)  and  forms  dextrose  (grape  sugar) 
and  levulose  (fruit  sugar,  fructose)  upon  partial  decomposition,  as  by  the  enzyme 
invertase. 

9  [10].  Glucosides. — Glucosides  are  chemical  combinations  of  glucose,  or  other 
sugars,  with  various  organic  substances,  and  they  decompose  into  these  constituents, 
with  the  consumption  of  water,  when  acted  upon  by  glucoside-splitting  enzymes  or  by 
acids.  For  example,  amygdalin  is  a  glucoside  occurring  in  leaves,  seeds,  etc.,  of  almond, 
peach,  etc.  Under  the  influence  of  the  enzyme  emulsin,  amygdalin  takes  up  water 
and  produces  glucose  sugar,  benzaldehyde,  and  hydrocyanic  acid. 

10  [11].  Organic  Acids. — Organic  acids  and  their  calcium  salts,  etc.,  occur  com- 
monly in  plant  cells.  They  are  apparently  formed  by  the  incomplete  oxidation  of 
sugars.  In  some  plants  and  in  some  tissues  (leaves  of  Oxalis,  petioles  of  rhubarb, 
fruit  of  lemon)  they  accumulate  in  large  quantities.     Various  conditions  influence 


196  PHYSIOLOGY    OF    NUTRITION 

their  formation;  sugar  must  be  plentifully  supplied  and,  in  some  cases  at  least  (as 
in  some  roots),  oxygen  must  not  be  too  plentiful. 

11  [7].  Alkaloids,  Toxins,  Antitoxins. — A  very  large  number  of  different  kinds  of 
substances,  some  of  which  are  very  poisonous,  are  formed  in  plants.  Here  may  be 
mentioned  solanin,  an  alkaloid  that  is  formed  in  the  potato,  especially  in  wounded  or 
actively  growing  regions.  Bacteria  form  poisonous  substances  called  toxins,  which 
diffuse  out  of  the  cells  into  the  surroundings.  Some  bacteria  are  parasitic  and  develop 
in  the  bodies  of  living  higher  plants  and  animals,  these  being  the  pathogenic  forms. 
Pathogenic,  as  well  as  other,  bacteria  are  generally  grouped  as  aerobic  or  anaerobic, 
accordingly  as  they  require  free  oxygen  or  are  poisoned  by  it.  Some  forms  (the  faculta- 
tive anaerobes)  can  live  without  free  oxygen  but  are  not  injured  by  its  presence. 

The  tetanus  bacillus  is  an  anaerobic  form.  Its  development  in  the  human  body  is 
confined  to  the  neighborhood  of  the  infected  wound,  but  the  very  active  toxin  that  it 
produces  spreads  throughout  the  body  of  the  victim,  causing  death  by  lock-jaw.  The 
anthrax  bacillus,  which  causes  splenic  fever  of  cattle,  etc.,  is  aerobic  and  can  be  grown 
in  bouillon.  It  was  through  Pasteur's  studies  of  this  organism  that  he  discovered  the 
bacterial  nature  of  infectious  diseases.  He  also  laid  the  foundations  of  serum  therapy, 
vaccination  for  immunization,  etc.,  from  experiments  with  anthrax  bacillus.  The 
peculiar  toxin  emanating  from  the  cells  of  the  parasitic  bacillus  stimulates  the  cells  of 
the  diseased  animal  to  give  off,  into  the  blood-stream,  a  specific  antitoxin.  This  tends 
to  counteract  the  poisonous  influence  of  the  toxin,  and  if  sufficient  antitoxin  can  be 
formed  soon  enough  (or  is  supplied  from  the  blood  serum  of  another  animal  that  has 
been  immunized  by  previous  vaccination  with  a  weakened  strain  of  the  parasite),  the 
disease  is  cured.  Diphtheria  and  tetanus  are  treated  in  this  way.  The  solution 
obtained  by  filtering  (through  a  Chamberland  filter)  a  bouillon  culture  of  the 
diphtheria  bacillus  is  very  poisonous  because  of  the  toxin  that  is  present. 

12.  Water.— Physiological  processes  cannot  go  on  without  a  plentiful  supply  of 
water;  the  chemistry  of  life  is  almost  entirely  that  of  aqueous  solution.  Active  plant 
tissues  contain  80  or  90  per  cent,  (by  weight)  of  water.  Resting  cells  (as  in  seeds) 
become  very  dry,  but  they  must  be  freely  supplied  with  water  before  they  become 
active.  The  water-soluble  substances  of  the  organism  are  largely  dissolved  in  the  water 
of  active  cells,  and  many  insoluble  materials  swell  in  water  until  the  colloid  dispersion 
formed  has  many  of  the  properties  of  a  true  solution.  Electrolytes  become  ionized 
(and  consequently  more  active  chemically)  when  in  aqueous  solution.  Furthermore, 
water  itself  enters  into  numerous  chemical  reactions  in  living  cells;  for  example,  the 
photosynthesis  of  carbohydrates,  and  the  hydrolytic  decompositions  of  carbohydrates, 
proteins,  etc.,  by  enzymes.  Practically  all  of  the  hydrogen  of  the  plant  is  derived 
from  water.  Some  water  is  produced  in  living  cells,  through  respiration,  through  the 
formation  of  the  complex  carbohydrates,  proteins,  etc.,  from  simpler  substances, 
but  by  far  the  greater  part  of  the  water  in  a  plant  has  entered  as  such,  from  the  soil. 
Much  water  escapes  from  ordinary  plants  by  transpiration,  some  by  guttation,  glandu- 
lar secretion,  etc. 

13.  Germination  of  Seeds. — The  resting  seed  contains  all  the  substances  needed 
for  a  considerable  amount  of  growth,  excepting  water  and  oxygen;  the  latter  substances 
are  absordeb  as  germination  starts  and  proceeds.  The  earlier  stages  of  germination, 
until  the  photosynthesis  of  carbohydrates  becomes  pronounced,  result  in  the  using  up 
of  the  non-aqueous  materials  of  the  seed;  thus  the  dry  weight  of  a  young  seedling  is 
smaller  than  that  of  the  ungerminated  seed. 


MATERIAL    TRANSFORMATIONS    IN    THE    PLANT  1 97 

The  chemical  processes  of  germination  are  different  in  different  kinds  of  seeds. 
Seeds  may  be  grouped  into  three  classes  according  to  the  substances  that  predominate 
in  them :  starchy  seeds,  proteinaceous  seeds,  and  fatty  seeds.  In  starchy  seeds  (such  as 
the  cereal  grains)  carbon,  hydrogen,  and  oxygen  are  lost  during  germination.  Germinat- 
ing proteinaceous  seeds  (such  as  those  of  the  legumes)  also  give  of  carbon,  hydrogen, 
and  oxygen,  but  they  are  specially  characterized  by  the  production  of  asparagin,  amino 
acids,  and  some  sulphates.  Fatty  seeds  (such  as  those  of  sunflower)  do  not  lose  oxygen 
during  germination ;  the  oxygen  content  actually  increases.  The  original  supply  of  fats 
is  depleted  and  carbohydrates  appear,  these  being  apparently  formed  by  the  oxidation 
of  the  fats.     Free  fatty  acids  increase  in  amount. 


CHAPTER  VIII 

FERMENTATION  AND  RESPIRATION 

§i.  General  Discussion. — -Plants  grow,  and  in  growing  they  produce  various 
metabolic  changes  and  movements  of  materials.  It  thus  comes  about  that 
work  of  various  kinds  is  performed  in  living  plants,  and  this  necessitates  the 
consumption  of  energy.  The  organic  substances  produced  by  green  plants  in 
sunlight  are  sources  of  energy  to  the  plant,  just  as  wood,  gasoline  or  coal  may 
act  as  the  source  of  energy  for  the  operation  of  a  manufactory,  the  energy  neces- 
sary for  the  running  of  the  machinery  being  supplied  by  the  combustion  of  such 
materials.  The  processes  of  living  plants  in  which  organic  reserve  substances 
are  oxidized  by  oxygen  are  quite  analogous  to  combustion,  and  this  vital 
oxidation  is  known  as  respiration. 

The  material  changes  that  constitute  respiration  may  be  considered  as  con- 
sisting typically  in  the  absorption  of  oxygen  and  the  formation  of  carbon  dioxide 
and  water,  the  latter  remaining  in  the  plant  body.a  The  general  process  may 
be  represented  by  the  equation: 

Carbon 
Glucose  Oxygen        dioxide  Water 

C6H1206  +  6  02  =  6  C02  +  6  H20. 

It  is  thus  clear  that  these  material  changes  of  respiration  proceed  in  a  direc- 
tion opposite  to  that  of  the  photosynthetic  process.  Respiration  results  in  the 
decomposition  of  material  by  oxidation.  It  is  really  a  kind  of  slow  com- 
bustion and,  like  other  kinds  of  combustion,  it  is  accompanied  by  the  liberation 
of  energy.  This  liberated  energy  is  used  in  other  processes  that  go  on  within 
the  plant,  or  some  of  it  may  escape  to  the  surroundings.  The  loss  of  material 
from  seeds  germinating  in  darkness  is  due  to  this  process.  A  part  of  the  reserve 
material  of  the  seed  is  oxidized,  and  the  energy  thus  liberated  is  largely  used 
in  the  construction  of  the  young  plant  out  of  the  remaining  material. 

Normal  respiration  does  not  occur  everywhere  in  nature.  Atmospheric 
oxygen  fails  to  penetrate  into  many  places  where  organisms  may  develop,  as 
in  the  case  of  stagnant  water  and  especially  in  flooded  soils.  Hoppe-Seyler1 
has  suggested  some  simple  criteria  for  judging  whether  or  not  a  soil  contains 
oxygen.  Moor  soil  that  is  nearly  free  from  oxygen  is  peculiarly  colored. 
Also,  the  formation  of  methane,  hydrogen  sulphide,  ferrous  carbonate  and 

1  Hoppe-Seyler,  Uber  die  Einwirkung  des  Sauerstoffs  auf  Garungen.  Strassburg,  1881.  P.  26.* 
0  There  seems  to  be  no  reason  for  supposing  that  respiration  water  is  less  apt  to  pass  out  of 
the  plant  body  than  is  water  from  any  other  source.  This  water  must  simply  become  a  part  of 
the  general  water  mass  of  the  organism  and  the  water  lost  by  transpiration  and  excretion,  as 
well  as  that  chemically  fixed  in  photosynthesis  and  hydrolysis,  is  supplied  from  this  general 
mass.  In  this  connection  it  may  be  recalled  that  the  ordinary  plant  loses  very  much  more 
water  than  any  other  substance,  during  its  growth. — Ed. 

198 


FERMENTATION   AND    RESPIRATION  1 99 

ferrous  sulphate  takes  place  in  the  absence  of  oxygen.  On  the  other  hand, 
the  presence  of  ferric  hydrate  in  a  soil  indicates  an  adequate  supply  of  oxygen 
for  plant  growth. 

Various  simple  plant  forms  always  abound  in  soil  and  water  that  lack 
oxygen.  Since  the  absorption  of  free  oxygen  is  impossible  under  such  condi- 
tions, the  energy  requirements  of  these  organisms  must  be  supplied  by  processes 
other  than  those  of  simple  oxidation.  As  a  matter  of  fact,  such  processes — 
which  are  those  of  fermentation,  in  general — do  occur  in  organisms  that  exist 
without  free  oxygen. 

It  is  well  known  that  energy  is  liberated  by  the  decomposition  of  many 
organic  substances  in  other  ways,  as  well  as  by  oxidation  processes.  Berthelot1 
showed  that  formic  acid  is  decomposed  by  platinum  black,  into  carbon  dioxide 
and  hydrogen,  with  liberation  of  heat,  the  reaction  being  represented  by  the 
equation: 

Carbon     Hydro- 
Formic  acid        dioxide        gen 

HCOOH  =  C02  +  H2. 

On  the  basis  of  this  observation  he  concluded  that  heat  production  may  occur 
in  living  organisms  without  any  relation  to  oxidation  processes. 

Oxidation,6  with  liberation  of  heat,  may  occur  also  in  the  absence  of  molecular 
oxygen,  this  element  being  derived  from  water.  Wieland2  showed  that,  in  the 
presence  of  palladium-black,  aldehydes  are  oxidized  by  water,  to  form  the  corre- 
sponding acids.  Hydrogen  is  liberated  and  absorbed  by  the  palladium  black. 
The  reaction  is  represented  as  follows: 

Hydro- 
Aldehyde         Water  Acid  gen 

R-COH  +H20  =  R-COOH  +H2. 

Loew3  showed  that  much  hydrogen  is  freed  from  an  alkaline  solution  of  formalde- 
hyde in  the  presence  of  cuprous  oxide,  formic  acid  being  formed.  This  reaction 
explains  the  formation  of  fatty  acids,  with  evolution  of  hydrogen,  by  anaerobic 
bacteria.  These  bacteria  effect  oxidation  in  the  absence  of  molecular  oxygen, 
deriving  this  element  from  water.  Favorskii4  cites  a  series  of  oxidations  of 
organic  compounds  at  the  expense  of  water. 

Finally,  oxidation  in  the  absence  of  free  oxygen  may  occur  as  the  result  of 
the  removal  of  hydrogen  from  a  molecule,  so  as  to  form  carbon  dioxide.  Thus, 
by  the  action  of  sunlight  on  a  mixture  of  formic  acid  and  quinone,  Ciamician 

1  Berthelot,  Marcellin,  Sur  le  synthase  de  l'acide  formique.  Compt.  rend.  Paris,  59:  616-618.  1864. 
Idem,  Sur  l'acide  formique.  /bid.  59:  817-819.  1864.  Idem,  Sur  la  decomposition  de  l'acide  formique. 
/!»<*.  59:  861-865,  901-904.     1864. 

2  Wieland,  Heinrich,  Studien  uber  den  Mechanismus  der  Oxydationsvorgange.  Ber.  Deutsch.  Chem. 
Ges.  45r/:  2606-2615.     1912. 

3  Loew,  O.,   Ueber  einige  katalytische  Wirkungen.     Ber.  Deutsch.  Chem.  Ges.  20J:    144-145.     1887. 

4  Favorskii,  A.  E.,  Ueber  Isomerisationserscheinungen  in  den  Reihen  der  Carbonylverbindungen  ge- 
chlorter  Alcohole  und  haloidsubstituirter  Oxyde  der  Aethylenekohlenwasserstoffe.  (Original  in  Russian. 
St.  Petersburg,  1895.)  Rev.  in  Jour,  prakt.  Chem.  51:  533-563.  1895.  Rev.  also  in  Bull.  Soc.  Chim. 
Paris  14:  1188-1206.     1895. 

6  This  and  the  next  following  paragraph  are  introduced  from  the  7th  Russian  edition. — Ed. 


200  PHYSIOLOGY    OF    NUTRITION 

and  Silber1  obtained  hydroquinone  and  carbon  dioxide,  according  to  the 
following  equation: 

Carbon 
Formic  acid  Quinone        Hydroquinone       dioxide 

HC02H  +  C6H402  =  C6H602  +  C02. 

Bredig  and  Sommer2  also  obtained  carbon  dioxide  by  the  action  of  methylene 
blue  on  formic  acid  in  the  presence  of  a  catalyzer,  the  reaction  being: 

(C16H18N3S)2S04  +  HC02H  =  (C]6H2oN3S)2S04  +  C02. 

Fermentation  processes  are  really  processes  of  decomposition  accompanied 
by  the  liberation  of  heat,  and  they  may  take  the  place  of  respiration  when 
free  oxygen  is  not  absorbed.  Pasteur  regarded  fermentation  as  "life  without 
oxygen."  Economically  these  decompositions  are  less  efficient  for  the  organism 
than  are  oxidations,  for  more  energy  is  always  liberated  in  the  latter.  It  is 
obvious,  for  example,  that  the  oxidation  of  formic  acid  must  produce  a  greater 
amount  of  heat  than  does  the  simple  decomposition  of  this  substance  into  car- 
bon dioxide  and  hydrogen,  since  the  heat  of  combustion  of  hydrogen  does  not 
appear  in  the  latter  case.  An  analogous  result  is  reached  by  comparing  the 
equation  representing  oxygen  respiration  with  that  for  alcoholic  fermentation, 
from  the  thermo-chemical  point  of  view. 

Respiration:  C6H1206  +  6  02  =  6  C02  +  6  H2  0. 
Fermentation:  C6Hi206  =  2  C2H5OH  +  2  C02. 

In  the  first  case  the  total  heat  of  combustion  of  the  glucose  is  liberated,  which 
amounts  to  709  kg.-cal.  per  gram-molecule  (180  g.).  The  amount  of  heat  liber- 
ated in  the  second  case  must  be  less  than  in  the  first,  because  one  of  the  end 
products  of  fermentation  is  ethyl  alcohol,  which  is  easily  oxidized.  This  alco- 
hol gives  a  heat  of  total  combustion  of  326  kg.-cal.  per  gram-molecule,  and, 
since  there  are  two  molecules  of  alcohol  produced  from  each  molecule  of 
glucose,  we  must  subtract  2  X  326  from  709,  thus  obtaining  57  kg.-cal.  as  the 
amount  of  heat  set  free  by  the  fermentation  of  a  gram-molecule  of  glucose 
according  to  the  second  equation  given  above.  It  follows  that  more  than 
twelve  times  as  much  glucose  must  be  decomposed  in  fermentation  as  is  oxidized 
in  respiration,  to  give  equal  amounts  of  free  heat.  The  difference  between  the 
two  processes  is  practically  even  more  pronounced  than  is  thus  indicated.  All 
kinds  of  fermentation  require  relatively  very  large  amounts  of  material,  as 
compared  with  the  corresponding  complete  oxidations. 

Fermentation  consists  in  the  decomposition  of  organic  compounds  with- 
out the  agency  of  atmospheric  oxygen,  while  respiration  is  essentially  an 
oxidation  process.     The  question  now  arises  whether  there  may  be  a  relation- 

1  Ciamician,  G.,  and  Silber,  P.,  Chemische  Lichtwirkungen,  (I  Mitteilung.)  Ber.  Deutsch.  Chem.  Ges. 
347/:  1530-1543-     1001. 

2  Bredig,  G.,  and  Sommer,  Fritz,  Anorganische  Fermente.  V.  Die  Schardingersche  Reaktion  und 
ahnliche  enzymartige  Katalysen.  I.  Die  Schardingersche  Reaktion  mit  anorganischen  Fermenten.  [Re- 
duktion  von  Methylenblau  mit  Formaldehyd   durch    Metallkatalyse.]     Zeitsch.  physik,  Chem.  70:  34-65. 

Iqio. 


FERMENTATION    AND    RESPIRATION  201 

ship  between  the  two,  as  they  occur  in  organisms;  this  question  was  first 
answered  in  the  affirmative  by  Pfliiger,1  whose  conclusions  in  this  regard  are  now 
generally  accepted.  In  living  animals  and  plants  various  kinds  of  organic  de- 
compositions are  always  going  on,  under  the  influence  of  specific  intracellular 
enzymes.  In  some  cases,  as  in  the  microorganisms  that  produce  various  kinds 
of  fermentation,  the  entire  energy  requirement  is  supplied  in  this  way.  Oxida- 
tion of  the  decomposition  products  thus  formed  may  fail  to  occur  here,  either 
because  the  organisms  in  question  live  in  the  absence  of  oxygen  or  because 
they  lack  the  necessary  oxidation  enzymes.  It  may  also  occur  that  the  fermen- 
tation products  diffuse  out  of  the  cells  before  oxidation  can  occur,  especially  in 
the  case  of  organisms  that  develop  in  a  liquid  medium.  Most  plants,  however, 
absorb  oxygen  by  means  of  their  oxidizing  enzymes,  thus  allowing  the  complete 
oxidation  (to  water  and  carbon  dioxide)  of  the  decomposition  products  that 
arise  from  the  breaking  down  of  complex  nutrient  materials.  This  constitutes 
aerobic  or  normal  respiration.  If  ordinary  plants  are  deprived  of  free  oxygen, 
then  their  respiratory  processes  become  restricted  to  those  of  fermentation, 
which  is  thus  seen  to  be  a  fundamental  process  characteristic  of  all  plants. 

§2.  Alcoholic  Fermentation.2— Alcoholic  fermentation  consists  essentially 
in  the  splitting  of  various  sugars  into  ethyl  alcohol  and  carbon  dioxide  through 
the  specific  activities  of  organisms  such  as  the  Saccharomycetes;  negligible 
amounts  of  succinic  acid  and  glycerine  are  also  formed.  This  kind  of  fermenta- 
tion occurs  especially  in  the  presence  of  yeast  fungi.  At  first  thought,  it  may 
appear  that  the  fermentation  of  grape  juice  is  an  exception  to  this  statement, 
since  yeast  is  not  added  to  the  juice,  but  Pasteur  showed  that  yeast  fungi  are 
also  effective  here.  Microscopic  examination  demonstrates  the  presence  of 
various  kinds  of  yeasts  upon  the  outer  surface  of  the  fruit  of  the  grape,  and  when 
the  berries  are  pressed  these  pass  into  the  juice,  where  they  multiply  and  give 
rise  to  alcoholic  fermentation.  Yeast  cells  are  not  numerous  on  uninjured 
grapes,  but  berries  that  have  been  perforated  by  wasps  often  exhibit  large  colo- 
nies of  well-nourished,  budding  cells.  The  yeasts  find  here  a  very  favorable 
substratum  for  growth  and  reproduction,  and  the  cells  are  carried  from  one 
bunch  to  another  by  the  wasps.  All  of  these  insects  are  found  to  be  carriers 
of  yeast  cells  during  the  grape  season,  as  may  be  shown  either  by  direct  micro- 
scopical examination  of  the  wasps  or  by  placing  them  in  sterilized  beer- wort 
and  noting  the  subsequent  fermentation  that  is  set  up.  Wortmann  performed 
many  experiments  of  this  kind,  always  with  the  same  result;  after  the  introduc- 

1  Pfliiger,  E.,  F.  W.,  Beitrage  zur  Lehre  von  der  Respiration.  I.  Ueber  die  physiologische  Verbrennung 
in  den  lebendigen  Organismen.  Pfluger's  Arch.  Physiol.  10:  251-367,  641-644.  1875.  Pfeffer,  W., 
Das  Wesen  und  die  Bedeutung  der  Athmung  in  der  Pflanze.  Landw.  Jahrb.  7:  805-834.  1878.  Wort- 
mann, Julius,  Ueber  die  Beziehungen  der  intramolecularen  zur  normalen  Athmung  der  Pflanzen.  Arbeit. 
Bot.  Inst.  Wurzburg.  2:  500-520.      1882. 

2  Pasteur,  L.,  Etudes  sur  la  biere.  Paris,  1876.*  Mortiz,  and  Morris,  i8or.  [See  note  3,  p.  164.] 
Lafar,  Franz,  Technische  Mykologie.  Ein  Handbuch  der  Garungsphysiologia  fur  technische  Chemiker, 
nahrungsmittelchemiker  usw.  Jena,  1807-1907.  Idem,  Technical  Mycology;  the  utilization  of  micro- 
organisms in  the  arts  and  manufactures.  A  practical  handbook,  etc.  Translated  by  Charles  T.  C.  Salter. 
(2  vols,  in  3.)  London,  1003-1010.  Buchner,  Buchner  and  Hahn,  1903.  [See  note  2,  p.  167.]  Duclaux, 
1899-1900.  [See  note  2,  p.  163. 1  Hansen,  1896.  [See  note  1,  p.  44.]  Oppenheimer,  1909.  [See  note 
2,  p.  163.]  Wahl  and  Henius,  American  handy  book  of  brewing,  malting  and  auxiliary  trades.  [Chicago, 
1902.] 


202  PHYSIOLOGY   OF   NUTRITION 

tion  of  the  wasp  the  medium  soon  began  to  ferment.  The  yeast  cells  pass  the 
winter  in  the  soil  and  find  their  way  to  the  young  fruits  the  following  season. 

Fermentation  results  in  an  increase  in  the  dry  weight  of  the  yeast.  If  a 
fermentable  liquid  is  inoculated  with  a  slight  amount  of  yeast,  the  cells  rapidly 
increase  by  budding,  and  if  enough  of  the  liquid  has  been  used  a  considerable 
amount  of  dry  substance  is  finally  obtained.  Fermentation  is  thus  a  physio- 
logical process  connected  with  the  growth  and  reproduction  of  the  yeast  cells. 

Glucose  and  other  varieties  of  sugar  are  suitable  material  for  fermentation. 
Saccharomyces  cerevisice  7,  S.  pastorianus  7,  77  and  777,  and  S.  ellipsoideus  I  and 
77,  all  contain  the  enzyme  invertase,  which  hydrolyzes  cane  sugar  to  form  fruc- 
tose and  glucose,  the  latter  being  subject  to  fermentation.  Maltose  is  fer- 
mented in  the  same  way,  but  lactose  is  not  affected.  Saccharomyces  marxi- 
anus,  S.  ludwigii  and  S.  exiguus  attack  only  glucose  and  saccharose,  without 
affecting  lactose  or  maltose;  S.  apiculatus  ferments  only  glucose,  but  S.  kiphyr 
and  S.  lactis  are  able  to  hydrolyze  lactose. 

Sugar  solution  alone  fails  to  produce  an  abundant  growth  of  yeast;  nitrogen 
and  mineral  substances  are  necessary  for  these  cells  just  as  in  the  case  of  other 
plants.  These  other  substances  are  plentiful  in  grape  juice  and  beer-wort,  but 
must  of  course  be  included  in  artificial  nutrient  media  if  yeasts  are  to  be 
cultivated  therein.  Among  the  ash-constituents  of  yeast,  phosphates  play  a 
conspicuous  role. 

The  researches  by  Harden  and  Young1  indicate  that  alcoholic  fermentation 
proceeds  by  two  stages,  as  follows: 

Carbon 
Glucose  Phosphate  dioxide  Alcohol  Water  Hexose  phosphate 

i.  2C6H1206  +  2M"HP04  =  2CO2  +  2C2H5OH  +  2H20  +  C6H10O4(M"PO4)2 

Hexose  phosphate  Water  Glucose  Phosphate 

2.  C6H10O6(M"PO4)2  +  2H20  =  C6H1206  +  2M"HP04 

Hexose-phosphate  is  thus  formed  and  again  decomposed  during  the  process,  and 
it  is  for  this  reason  that  the  addition  of  soluble  phosphates  accelerates  fermenta- 
tion. The  phosphate  may  therefore  be  considered  as  a  co-enzyme  of  zymase. 
Harden  and  Young  showed  that  after  the  filtration  of  yeast  through  a  gelatine 
filter  neither  the  filtrate  nor  the  precipitate  is  capable  of  producing  alcoholic 
fermentation,  but  fermentation  does  occur  if  the  filtrate  and  precipitate  are 
again  brought  together.  The  necessary  phosphates  occur  in  the  filtrate  in  this 
experiment. 

Yeast  cells  may  also  develop  in  a  medium  without  nutrient  material,  under 
otherwise  suitable  conditions,  and  they  still  produce  carbon  dioxide  and  alcohol. 
This  is  the  so-called  auto-fermentation  of  yeast,  which  results  in  a  decrease 
rather  than  in  an  increase  of  dry  substance.  Here  the  carbon  dioxide  and 
alcohol  are  formed  at  the  expense  of  the  yeast  material  itself.     A  similar  phe- 

1  Harden,  Arthur,  and    Young,   William  J.,   The  alcoholic  ferment  of  yeast-juice.  Proc.   Roy.    Soc. 

London   77:   405-420.     1906.     Idem,   same   title.     Ibid.   78:   360-375.      1906.     Idem,  same   title.     Ibid. 

80:  299-311.  1908.  Idem,  The  function  of  phosphates  in  alcoholic  fermentation.  Centralbl.  Bakt., 
//,  26:  178-184.      1910. 


FERMENTATION    AND    RESPIRATION 


203 


nomenon  appears  in  the  germination  of  seeds  in  darkness,  where  the  loss  in  dry 
weight  is  due  to  respiration  in  the  absence  of  the  photosynthetic  process. 

Great  interest  is  attached  to  the  question  of  the  role  of  oxygen  in  alcoholic 
fermentation.  Pasteur  devised  the  apparatus  shown  in  Fig.  89  for  experi- 
ments upon  the  development  of  yeast  in  the  complete  absence  of  oxygen.  A 
fermentable  liquid  is  placed  in  the  flask  A ,  which  has  two  glass  necks  (a  and  b) 
with  narrow  openings.  One  of  these  is  provided  with  a  glass  stop-cock  and  a 
glass  funnel  while  the  other  bends  downward  into  a  dish  (c)  filled  with  some 
of  the  same  liquid  as  is  in  the  flask.  Both  masses  of  liquid  are  brought  to  boil- 
ing, to  expel  air  from  the  liquid.  After  cooling,  the  liquid  in  the  dish  is  replaced 
with  mercury.  Resting  yeast  cells  are  then  introduced  into  the  glass  funnel  and 
admitted  into  the  flask  through  the  stop-cock.  It  was  found  that  such  resting 
yeast  cells  (called  "old"  cells 
by  Pasteur)  produce  no  fer- 
mentation when  air  is  entirely 
lacking.  In  another  series  of 
experiments  a  small  amount  of 
the  fermentable  liquid  was  in- 
troduced into  the  funnel,  in- 
oculated with  yeast,  and  fer- 
mentation was  allowed  to  take 
place.  A  little  of  the  ferment- 
ing liquid,  containing  a  very 
few  of  the  young,  budding 
cells  was  then  allowed  to  pass 
from  the  funnel  into  the  flask, 
the  cock  being  immediately  re- 
closed.  Vigorous  fermenta- 
tion occurred  in  the  flask,  more 
than  a  gram  of  dry  substance 
being  obtained  from  the  very 

slight  amount  of  yeast  that  was  introduced.  It  is  clear,  therefore,  that  oxygen 
is  essential  to  the  development  of  resting  yeast  cells,  while  young  cells  can  de- 
velop when  oxygen  is  entirely  lacking,  if  nutrient  materials  are  present. 

In  connection  with  the  relation  of  oxygen  to  fermentation,  it  is  of  great  im- 
portance to  discover  whether  normal  respiration  occurs  in  yeast  abundantly 
supplied  with  oxygen.  Ivanovskii,1  who  took  up  this  question,  grew  a  pure 
culture  of  yeast  upon  a  sterilized  porous  clay  plate  half  immersed  in  sterilized 
nutrient  solution,  the  whole  being  in  an  air  chamber  formed  by  a  bell-jar. 
The  yeast  was  thus  abundantly  supplied  with  oxygen,  and  the  nutrient  solu- 
tion reached  the  cells  only  through  the  capillary  passages  of  the  clay  plate. 
After  three  days  a  gas  analysis  showed  that  the  ratio  between  the  amount  of 

carbon  dioxide  eliminated  and  the  amount  of  oxygen  absorbed,  (   ~ j,    w 

1  Ivanovskii,  D.,  On  the  influence  of  oxygen  on  alcoholic  fermentation.  [Russian.]  Works  of  the  Botan- 
ical Laboratory,  Acad.  Sci.  St.  Petersburg.  No.  4.  In  Zapiski  Acad.  Sci.  St.  Petersburg  732.  28  p.  1804. 
(Pagination  of  parts  in  vol.  is  separate.] 


Fig. 


89. — Apparatus  for  showing   fermentation  in 
the   absence  of  oxygen. 


as 


204  PHYSIOLOGY   OF   NUTRITION 

2.0 

equal  to  — >  or  10.     It  thus  appears  that  but  very  little  oxygen  is  absorbed, 

even  with  an  abundance  of  this  gas,  while  much  carbon  dioxide  is  produced; 
oxygen  respiration  is  here  very  weak  but  the  decomposition  of  sugar  into 
alcohol  and  carbon  dioxide  is  very  pronounced.  Another  series  of  experiments 
by  Ivanovskii  gave  concordant  results.  Equal  amounts  of  nutrient  solution 
were  placed  in  two  vessels,  the  space  above  the  liquid  being  filled  with  air  in 
one  case  and  with  nitrogen  in  the  other,  and  equal  quantities  of  yeast  were 
added  to  the  vessels.  At  the  end  of  the  experiment  the  rate  of  sugar  fermen- 
tation, per  gram  of  dry  yeast,  per  day,  was  determined.  In  one  test,  for  ex- 
ample, where  the  yeast  introduced  into  each  vessel  had  a  dry  weight  of 
0.16  g.,  this  weight  increased  to  0.516  g.  in  the  presence  of  air  and  to  0.497  g- 
in  its  absence.  With  air,  6.009  S-  °f  sugar  was  decomposed  in  twenty-four 
hours  and  without  air  5.804  g.  Thus,  the  amount  of  sugar  decomposed  in 
twenty-four  hours  per  gram  of  dry  yeast  was  8.9  g.  in  both  cases.  A  marked 
difference  between  the  two  cultures  is  to  be  noted,  however,  in  regard  to  their 
reproduction;  with  access  of  air  the  yeast  multiplied  considerably  faster  than 
in  the  absence  of  oxygen.  With  a  long  exposure  to  oxygen-free  air,  growth  ceases 
entirely,  but  the  cells  still  remain  alive  and  capable  of  decomposing  sugar. 
Reproduction  continues  indefinitely  when  the  supply  of  oxygen  is  not  cut  off. 

The  researches  of  Gromow  and  Grigoriew  ^how  that  zymin  (acetone-treated 
yeast,  see  page  174)  produces  carbon  dioxide  at  the  same  rate  in  a  stream  of 
air  as  in  a  stream  of  hydrogen,  and  these  results  were  substantiated  by 
Buchner  and  Antoni.2 

Palladin3  showed  that  oxidation  enzymes  are  present  in  yeast  in  but  slight 
amount,  and  this  explains  the  fact,  which  seems  remarkable  at  first,  that  yeast 
produces  alcoholic  fermentation  even  with  an  abundant  supply  of  oxygen.  It 
is  on  account  of  the  absence  of  these  enzymes  that  yeast  is  unable  to  oxidize 
alcohol  in  the  presence  of  air,  but  this  organism  usually  develops  in  the  absence 
of  oxygen,  where  oxidation  enzymes  are  not  needed.  Moreover,  alcohol 
readily  diffuses  out  of  the  cells  and  thus  becomes  inaccessible  to  the  action  of 
intracellular  enzymes. 

In  the  industries,  it  is  well  to  carry  out  the  fermentation  process  under  condi- 
tions of  good  aeration,  since  the  multiplication  of  the  yeast  is  hastened  by  the 
presence  of  oxygen  and  the  process  is  thus  accelerated.  Although  each  individ- 
ual cell  produces  the  same  amount  of  alcohol  in  the  absence  as  in  the  presence 
of  air,  the  number  of  active  cells  is  larger  when  oxygen  is  supplied.  Oxygen 
thus  exerts,  indirectly,  an  accelerating  influence  upon  fermentation. 

The  concentration  of  alcohol  in  the  solution  influences  the  rate  of  fermenta- 
tion; with  increasing  alcoholic  concentration  an  anesthesia  of  the  yeast  cells 
finally  sets  in,  and  the  rate  of  sugar  decomposition  is  diminished.  If  the  alco- 
holic concentration  reaches  16  per  cent,  fermentation  ceases  altogether. 

1  Gromow  and  Grigoriew,  1904.     [See  note  7,  p.  174.] 

-  Buchner,  Eduard,  and  Antoni,  Wilhelm,  Weitere  Versuche  iiber  die  Zellfreie  Garung.     Zeitsch.  physiol. 
Chem.  44:  206-228.     1905. 

3  Palladin,  W.,  Ueber  das  Wesen  der  Pflanzenatmung.     Biochem.  Zeitsch.  18:  151—206.     1909. 


FERMENTATION    AND    RESPIRATION 


205 


Two  kinds  of  fermentation  are  distinguished  in  the  brewing  industry:  top- 
fermentation,  which  occurs  at  high  temperatures,  and  bottom-fermentation, 
which  occurs  at  lower  ones,  these  two  kinds  of  fermentation  being  produced  by 
two  different  groups  of  yeast  races.  Experiments  aiming  to  change  bottom  into 
top  yeasts,  or  the  reverse,  have  never  been  successful. 

Pasteur  called  attention  to  the  fact  that  the  properties  of  beer  depend  upon 
the  character  of  the  yeast  employed  in  its  manufacture.  Since  bacteria  cause  a 
deterioration  in  beer,  Pasteur  suggested  a  method  for  yeast  purification,  by 
means  of  cultures  with  tartaric  acid  or  phenol.  Hansen  proved,  however  (1883), 
that  the  most  widespread  and  injurious  "diseases"  of  beer  are  not  caused  by 
bacteria  but  are  due  to  wild  species  of  yeasts.0  The  same  writer  has  also  shown 
that  treatment  of  yeast  with  tartaric  acid  fails  to  have  any  good  effect  and  is 
positively  harmful  when  wild  species  are  present;  such  treatment  weakens  the 
cultivated  yeast  and  the  wild  forms  become  ascendant  in  the  culture.  To  ob- 
tain a  perfect  product  pure  cultures  of  yeast  must  be  employed.  Comparative 
studies  have  shown  that  different  varieties  of  beer  are  produced  from  the  same 
beer- wort  by  different  forms  of  yeast.  Thus,  Saccharomyces  pastor ianus  I 
produces  a  bitter  taste  and  an  umpleasant  odor,  while  the  use  of  S.  pastorianus 
III  or  S.  ellipsoideus  II  results  in  cloudy  beers. 

In  a  mixture  of  yeasts  the  wild  forms  may  be  identified  by  the  time  required 
for  ascospore  production  at  a  temperature  of  i5°C,  as  is  brought  out  by  the 
following  scheme. 


Wild  Yeasts 

Cultivated  Yeasts, 

Fermentation  Rate 

Temperature 

Rapid 

Slow 

deg.  C. 
15° 

25° 

Ascospores  after  72 

hours 
Ascospores  after  40 

hours 

No  ascospores  after 

72  hours 
Ascospores  after  40 

hours 

No  ascospores  after 

72  hours 
Ascospores  after  40 

hours 

If  a  drop  of  a  yeast  culture  a  day  old  is  thinly  spread  on  a  sterilized  plaster 
plate  impregnated  with  beer-wort,  and  if  the  preparation  is  kept  at  a  tempera- 
ture of  i5°C,  no  ascospores  are  found  after  seventy- two  hours  unless  wild  yeasts 
were  present  in  the  original  culture;  ascospore  formation  does  not  occur  till 
later.  If  spores  are  found,  on  the  other  hand,  then  wild  yeasts  are  present,  and 
the  amount  of  these  may  be  estimated  by  the  number  of  ascospores  that  have 
been  formed.  It  is  possible  in  this  way  to  detect  the  presence  of  wild  yeasts  in 
mixtures  where  they  comprise  no  more  than  one  two-hundredth  of  the  total 
amount  of  yeast  present. 

Another  method  of  identifying  yeasts  is  based  on  the  forms  of  their  "giant 
colonies,"1  which  are  formed  from  cell  masses/     A  drop  of  a  young  yeast  cul- 

1  Lindner,  1909.     [See  note  1,  p.  44.] 

c  See  Hansen,  1896.     [See  note  1,  p.  44.]  — Ed. 

d  This  paragraph  is  omitted  in  the  7th  Russian  edition. — Ed. 


206 


PHYSIOLOGY   OF   NUTRITION 


ture  in  beer-wort  is  transferred  to  gelatine  and  the  cells  multiply  and  develop 
into  giant  colonies  upon  the  gelatine  surface.  The  form  of  colony  is  always  con- 
stant for  the  same  species  and  different  forms  of  colonies  are  produced  by 
different  kinds  of  yeast.  The  drawings  of  Fig.  90  show  how  distinct  are  the 
giant  colonies  of  various  different  yeasts. 

It  has  been  seen  that  alcoholic  fermentation  is  a  process  involving  the  action 
of  enzymese  (see  page  204).  Besides  carbohydrates,  such  ketonic  acids  as  pyro- 
tartaric  acid  may  also  be  decomposed  in  this  way,  as  was  shown  by  Neuberg1 
and  his  co-workers.     Pyrotartaric  acid  is  split  into  carbon  dioxide  and  acetic 


S.  pastorianus  I.  S.  pastorianus  II. 


S.  pastorianus  III. 


S.  ellipsoideus  I. 

Fig.  90.- 


5.  ellipsoideus  II.  Bottom-Fermentation  Yeasts. 

-Giant  colonies  of  different  yeasts.      {After  P.  Lindner.) 


aldehyde,  by  a  special  enzyme,  carboxylase,  the  reaction  being  represented  by 
the  following  equation : 


Pyrotartaric  acid 
CH3COCOOH 


Carbon 

dioxide      Acetic  aldehyde 

=   C02  +  CH3COH. 


The  acetic  aldehyde  thus  formed  is  reduced  to  ethyl  alcohol.  Kostychev2  re- 
ports that  pyrotartaric  acid  is  apparently  one  of  the  intermediate  products  in  the 
breaking  down  of  glucose.  Zaliesskii3  found  the  enzyme  carboxylase  in  higher 
plants. 

Reductase  is  plentiful  in  yeast,  and  this  enzyme  has  been  shown  to  play  an 

1  Neuberg,  C,  and  Karczag,  L.,  Ueber  zuckerfreie  Hefegarungen.  IV.  Carboxylase,  ein  neues  Enzym 
der  Hefe.  Biochem.  Zeitsch.  36:  68-75.  1911.  Idem,  same  title.  V.  Zur  Kenntnis  der  Carboxylase 
Ibid.  36:  76-81.  191 1.  Neuberg,  Carl,  and  Kerb,  J.,  Entsteht  bei  Zuckerfreien  Hefegarungen  .lEthyl- 
alkohol?     Zeitsch.  Garungsphysiol.     1:  114— 120.      1912. 

2  Kostytchew,  S.,  Ueber  Alkoholgarung.  (I  Mitteilung.)  Ueber  die  Bildung  von  Acetaldehyd  bei  der 
alkoholischen  Zuckergarung.  Zeitsch.  physiol.  Chem.  79:  130-145.  1912.  Kostyschew,  S.,  and  Hub- 
benet,  E.  (II  Mitteilung.)  Ueber  Bildung  von  Aethylalkohol  aus  Acetaldyhyd  durch  lebende  und  getotete 
Hefe.     Ibid.  79:  359-374-     1912. 

a  Zaleski,  W.,  Ueber  die  Verbreitung  der  Carboxylase  in  den  Pflanzen.  Ber.  Deutsch.  Bot.  Ges.  31 : 
349-353-     1913- 

eThis  and  the  next  following  paragraph  are  not  in  the  German  edition  and  are 
translated  from  the  7th  Russian  edition. — Ed. 


FERMENTATION    AND    RESPIRATION  207 

important  role  in  alcoholic  fermentation.1  Palladin  and  Lvov2  were  able  to 
retard  the  process  of  alcoholic  fermentation  by  employing  the  respiration  pig- 
ment of  the  white  beet  to  remove  the  active  hydrogen  as  it  was  formed.  The 
production  of  alcohol  was  thus  decreased,  as  well  as  that  of  carbon  dioxide. 
They  then  employed  methylene  blue  in  place  of  the  respiration  pigment,  and 
found  that  for  each  atom  of  hydrogen  removed  by  the  methylene  blue  there 
occurred  a  decrease  of  one  molecule  in  the  production  of  alcohol  and  of  carbon 
dioxide.  This  dependence  of  alcoholic  fermentation  upon  reduction  processes 
may  be  represented  by  the  following  simplified  scheme,  in  which  M  denotes 
methylene  blue. 

2  C6H]206  +  M  =  2  C02  +  2  C2H5OH  +  C6H10O6  +  M-H2. 

The  methylene  blue  is  reduced  to  the  leuco-compound.  In  this  scheme  no  ac- 
count is  taken  of  Palladin's3  opinion  that  alcoholic  fermentation  involves  the 
chemical  action  of  water,  nor  of  Bach's  idea  that  reduction  also  depends  upon 
such  action  (see  page  225). 

The  action  of  reductase  consists  in  the  removal  of  hydrogen  from  one  sub- 
stance (de-hydrogenation)  and  its  transmission  to  another  substance  (hydro- 
genation)/  The  substance  that  gives  up  hydrogen  is  oxidized  and  is  called 
the  reducer,  reductor  or  reducing  agent  (R-H2).  The  other  substance,  said  to 
be  an  oxidizer  or  oxidizing  agent,  which  receives  the  hydrogen,  is  called  the 
acceptor  of  hydrogen  (A).     The  reaction  is  shown  by  the  general  equation, 

R-H2  +  A  =  R  +  A-H2. 

An  example  of  this  is  the  decomposition  of  lactic  acid  by  the  reductase  of  yeast, 
in  the  presence  of  methylene  blue  (M)  as  a  hydrogen  acceptor,  as  shown  by  the 
equation: 

CH3-CHOH-COOH  (lactic  acid)  +  M  = 
CHji-CO-COOH  (pyrotartaric  acid)  +  MH2. 

The  pyrotartaric  acid  produced  is  decomposed  by  carboxylase,  into  acetic 
aldehyde  and  carbon  dioxide.4 

If  it  is  granted  that  reduction  takes  place  with  the  participation  of  water, 
then  the  hydrogen  of  the  water  must  unite  with  the  acceptor  of  hydrogen,  while 

«  Griiss,  J.,  Untersuchungen  uber  die  Atmung  und  Atmungsenzyme  der  Hefe.  Zeitsch.  ges.  Brauwesen 
27:686-692,699-704,721-724,734-739.752-755.769-772.     1904.     Palladin,  1908.     [See  note  1.  p.  168.] 

2  Palladin,  V.  I.  (W.),  and  L'vov,  S.  D.,  Sur  l'influence  des  chromogenes  respiratoires  sur  la  fermentation 
alcooliqtie.  [Text  in  Russian.]  Bull.  Acad.  Imp.  Sci.  St. -Petersbourg  VI,  7:  241-252.  1913.  Palladin, 
W.,  and  L'vov,  Sergius,  Ueber  die  Einwirkung  der  Atmungschromogene  auf  die  alkoholische  Garung. 
Zeitsch.  Garungsphysiol.  2:  326-337.     1913. 

8  Palladin,  V.  I.  (W).,  Sur  le  r61e  des  pigments  respiratoires  dans  le  respiration  des  plantes  et  les  ani- 
maux.  [Russian.]  Bull.  Acad.  Imp.  Sci.  St.-Petersbourg,  VI,  6:  437-451.  1912.  Palladin,  W.,  Ueber 
die  Bedeutung  der  Atmungspigmente  in  den  oxydationsprocessen  der  Pflanzen  und  Tiere.  Zeitsch.  Garungs- 
physiol. 1 :  91-105.      1912. 

'Palladin,  Sabanin  and  Lochinovskaia,  Bull.  Acad.  Imp.  Sci.  St.-Petersbourg,  1915.     P.  701.* 
*  This  and  the  four  following  paragraphs  are  translated  from  separate  pages  in  Russian, 
received  from  Prof.  Palladin.     For  another  statement  of  these  considerations  and  a  report  of 
some  later  work;  see:  Palladin,  W.,  and  Sabinin,  D.,  The  decomposition  of  lactic  acid  by  killed 
yeast.     Biochem.  jour.  10:  183-196.     1916. — Ed. 


208  PHYSIOLOGY    OF    NUTRITION 

the  oxygen  unites  with  the  substance  being  oxidized,  reacting  with  it  either  by 
the  splitting  off  of  hydrogen  to  form  water  or  by  some  other  oxidizing  reaction. 
An  example  of  a  reaction  in  which  water  participates  is  furnished  by  the  work 
of  Wieland1  on  the  oxidation  of  alcohol  to  form  acetic  acid  by  living  or  dead 
acetic  bacteria  in  an  oxygen-free  atmosphere  but  in  the  presence  of  methylene 
blue  (M).  This  reaction  is  represented  by  the  equation: 
CH3CH0OH  (ethyl  alcohol)  +  H20  +  2  M  =  CH3COOH  (acetic  acid)  +  2  M-H2. 

It  is  possible,  also,  for  water  to  be  formed  as  a  result  of  the  union  of  hydrogen 
with  an  acceptor  of  hydrogen;  for  example,  with  potassium  nitrate  as  acceptor, 
as  represented  by  the  equation: 

R-H2  +  KNO3  =  R  +  KNO2  +  HoO. 

It  follows  that,  after  reduction,  the  molecule  of  the  acceptor  of  hydrogen 
may  become  either  richer  by  two  atoms  of  hydrogen  (methylene  blue)  or 
poorer  by  one  atom  of  oxygen  (potassium  nitrate). 

The  action  of  reductase,  in  causing  anerobic  oxidation  by  means  of  the 
splitting  off  of  hydrogen,  may  be  accompanied  by  the  production  of  carbon 
dioxide.  Thus  Bredig  and  Sommer2  showed  (see  page  200)  that,  in  the 
presence  of  a  catalyzer  and  of  methylene  blue,  formic  acid  is  decomposed 
into  carbon  dioxide  and  hydrogen : 

HC02H  (formic  acid)  +  M  =  C02  +  M-H2. 

Until  recently  the  presence  of  reductase  in  plants  was  determined  on  the 
basis  of  the  effect  produced  upon  various  acceptors  of  hydrogen.  If  no  effect 
on  these  acceptors  was  observed,  reductase  was  inferred  to  be  absent,  but  this 
is  not  correct.  In  addition  to  a  hydrogen  acceptor  there  must  be  present  a  sub- 
stance that  may  be  oxidized,  in  order  that  the  reductase  may  act.  This  was 
shown  by  Harden  and  Norris,3  who  found  that  reductase  makes  itself  evident, 
in  the  dried  yeast  of  Lebedev,  only  after  the  addition  of  both  an  oxidizer  and 
a  reducer. 

Various  bacteria  and  moulds  (e.g.,  the  Mucoracese),  as  well  as  yeasts,  pro- 
duce alcoholic  fermentation.  Moulds  generally  form  thick  masses  of  mycelium 
upon  the  surface  of  the  substratum  and  usually  absorb  considerable  oxygen  from 
the  air.  If  the  mycelium  of  such  a  mould  is  submerged  in  a  fermentable  liquid, 
alcoholic  fermentation  occurs,  and  the  further  development  of  the  mycelium  in 
the  liquid  is  very  characteristic.  The  long  hyphae  divide  to  form  cells  that  are 
very  similar  to  those  of  yeast.  It  has  recently  been  shown  that  the  most  active 
of  these  mucor  yeasts  produce  alcoholic  fermentation  even  in  the  presence  of  an 
abundance  of  oxygen4  just  as  do  ordinary  yeasts. 

1  Wieland,  Heinrich,  Ueber  den   Mechanismus  der  Oxydationsvorgange.     Ber.   Deutsch.   Chem.  Ges. 

461'1:  3327-3342-      1913- 

-  Bredig  and  Sommer,  ioio.     [See  note  2,  p.  200.] 

3  Harden,  Arthur,  and  Norris,  Roland  Victor,  The  reducing  enzymes  of  dried  yeast  (Lebedeff)  and  of 
rabbit  muscle.     Biochem.  jour.  9:  330-336.      ioi5- 

«  Kostytschew,  S.,  Untersuchungen  iiber  die  Atmung  und  alkoholische  Garung  der  Mucoraceen.  Cen- 
tralbl.  Bakt.  //,  13:  490-503.  1904.  Wehmer,  C,  Versuche  uber  Mucorineengarung.  Ibid.  II,  14: 
.556-572.      1905.     Idem,  same  title.     Ibid.  II,  15:  8-19.     1906. 


FERMENTATION    AND    RESPIRATION  2O0 

^3.  Other  Kinds  of  Fermentation. . — Lactic  acid  fermentation  (the  souring 
of  milk)  is  caused  by  Bacillus  lactici  acidi,  which  has  the  form  of  small  paired 
rods  from  1.0  to  1.7  micra  long  and  from  0.3  to  0.4  micron  broad.  Many  other 
bacteria  are  able  to  produce  lactic  acid  fermentation;  such  as  Bacterium  lactis 
acidi,  Bacillus  lactis  acidi,  Bacterium  limbatum  lactis  acidi,  Micrococcus  lactis 
acidi,  Spharococcus  lactis  acidi,  Streptococcus  acidi  lactici  and  Bacillus  acidificans 
longissimus. 

The  process  of  lactic  acid  fermentation  is  represented  by  the  following 
equation: 

Lactose  Water  Lactic  acid 

C12H22On  +  H20  =  4  C3H603. 

This  fermentation  occurs  when  milk  is  simply  exposed  to  a  temperature  of 
from  350  to  42°C.  for  a  short  time.  The  process  stops  when  a  certain  amount  of 
acid  has  accumulated,  but  if  the  acidity  thus  produced  is  neutralized  with 
calcium  carbonate  fermentation  begins  again.  Some  acetic  acid  and  other 
volatile  acids  usually  occur,  as  well  as  lactic  acid,  the  amount  of  these  being 
dependent  both  upon  the  kind  of  bacterium  and  upon  the  composition  of  the 
nutrient  medium.  Besides  lactose,  other  kinds  of  sugars,  such  as  cane  sugar, 
fructose  and  maltose,  can  be  fermented  to  lactic  acid  if  the  proper  kind  of 
bacteria  is  used. 

Lactic  acid  may  also  be  obtained  if  a  mixture  of  100  g.  of  cane  sugar  and  10  g. 
of  casein  or  old  cheese,  in  a  liter  of  water  saturated  with  calcium  carbonate,  is  al- 
lowed to  stand  in  an  open  vessel  at  a  temperature  of  from  350  to  4o°C,  with 
occasional  shaking.  After  fermentation  has  ceased  the  liquid  is  evaporated  and 
calcium  lactate  is  deposited,  from  which  free  lactic  acid  is  obtained  by  decompos- 
ing the  lactate  with  sulphuric  acid.  The  optically  inactive  variety  of  lactic 
acid  is  obtained  in  this  process,  but  in  some  cases  the  optically  active  isomers 
arise.  When  Micrococcus  acidi  paralactici  acts  in  a  medium  containing  sugar, 
appreciable  amounts  of  the  dextro-rotatory  paralactic  acid  are  formed;  Bacillus 
acidi  levolactici  forms  the  levo-rotatory  acid.  The  different  powers  possessed 
by  different  bacteria  to  form  optically  active  isomers  of  lactic  acid  may  be  used 
in  identifying  related  species  of  these  organisms;  thus,  Bacterium  coli  commune 
decomposes  grape  sugar,  giving  dextro-lactic  acid,  but  Bacillus  typhi  abdominalis 
produces  levo-lactic  acid  under  the  same  conditions.  Lactic  acid  bacteria  have 
been  widely  applied  in  the  industries;  for  example,  Berlin  white  beer  is  obtained 
by  the  action  of  these  forms. 

Butyric  acid  fermentation  is  produced  by  the  bacterium,  Clostridium  butyri- 
cutn,  which  has  recently  been  shown  to  consist  of  a  mixture  of  at  least  three 
different  species.  There  are  also  many  other  bacteria  that  produce  butyric 
acid.  Butyric  acid  fermentation  occurs  in  the  complete  absence  of  oxygen, 
and  both  hydrogen  and  carbon  dioxide  always  arise  as  gaseous  products  of  the 
process.     The  reaction  is  represented  by  the  following  equation: 

Glucose  Hydro-       Carbon        Butyric  acid 

gen  dioxide 

C6H1206  =  2  H2  +  2  C02  -f  CJJsOz. 

14 


2IO  PHYSIOLOGY   OF   NUTRITION 

When  lactic  acid  is  fermented  instead  of  sugar  the  reaction  becomes  the 
following: 

Hydro-        Carbon 
Lctica  acid         gen  dioxide        Butyric  acid 

2  C3H603  =  2  H2  +  2  C02  +  C4H802. 

To  obtain  butyric  acid  fermentation  a  mixture  is  prepared  containing  2  1. 
of  water,  100  g.  of  potato  starch  (or  dextrin),  1  g.  of  ammonium  chloride  and 
other  nutrient  salts,  and  50  g.  of  chalk,  and  this  is  allowed  to  stand  at  4o°C. 

Numerous  bacteria  are  known  that  cause  different  kinds  of  fermentation, 
but  an  account  of  each  separate  process  is  not  here  possible.  It  should  be  men- 
tioned, however,  that  these  various  bacteria  produce  numerous  and  diverse 
chemical  reactions,  far  surpassing  the  well-known  chemical  reagents  in  sensi- 
tiveness and  specificity.1 

§4.  Plant  Respiration.2 — Ingen-Housz  (1779)  was  the  first  to  demonstrate 
that  living  plants  respire.  In  repeating  the  experiments  of  Priestley  upon  the  im- 
provement of  air  by  plants,  Ingen-Housz  showed  that  this  alteration  of  the  air 
is  accomplished  only  by  the  green  parts  of  plants  and  that  it  occurs  only  in  sun- 
light; the  non-green  parts  of  plants  are  like  animals,  as  far  as  their  effect  upon 
the  air  is  concerned,  and  unilluminated  green  plant  parts  also  act  in  the  same 
way,  to  "poison"  the  air.  (See  p.  2.)  This  poisoning  of  the  air  is  due  to  the 
elimination  of  carbon  dioxide  and  is  the  result  of  respiration.  The  first  exact 
experimentation  upon  plant  respiration  was  carried  out  by  Saussure  in  1804. 

The  influence  of  external  conditions  upon  the  respiratory  activity  of  plants 
has  received  the  attention  of  many  investigators.  The  effect  of  temperature 
has  been  studied  with  unusual  care,3  thermostats  of  various  kinds  being  used  to 
keep  the  temperature  constant  during  the  period  of  an  experiment.  The  rate 
of  gaseous  exchange  is  nearly  proportional  to  the  temperature,  for  medium  tem- 
peratures, but  a  maximum  rate  is  reached  at  about  4o°C.  and  further  rise  in 
temperature  is  without  influence  upon  this  rate,  which  remains  constant  until 
death  supervenes.  The  value  of  the  respiratory  ratio  (the  amount  of  carbon 
dioxide  given  off  divided  by  the  amount  of  oxygen  absorbed  in  a  unit  of  time, 

CO 

~?^~ )  reaches  a  minimum  at  about  io°  or  i5°C,  and  increases  with  higher  as 
U2 

well  as  with  lower  temperatures,  the  increase  being  more  rapid  in  the  first  case. 
This  is  illustrated  by  the  following  table  of  experimental  results,  taken  from  the 
work  of  Purievich.4 

1  Omeliansky,  W.,  De  la  m6thode  bact6riologique  dans  les  recherches  de  chimie.  Arch.  sci.  biol. 
St.  P6tersbourg  12:  224-247.     1907. 

2  Palladin,  1909.  [See  note  2,  p.  204.]  Czapek,  Friedrich,  Die  Atmung  der  Pflanzen,  Ergeb.  Physiol. 
9:  587-613.  1910.  Nicolas,  G.,  Recherches  sur  la  respiration  des  organes  vegdtatifs  des  plantes  vascu- 
laires.  Ann.  sci.  nat.  Bot.  IX,  10:  1-113.  1909.  Reinitzer,  Fr.,  Ueber  Atmung  der  Pflanzen.  (Antritts- 
rede.)      17  p.       Graz,  1909.     Rev.  in:  Bot.  Centralbl.      115:  52.      1910. 

3  Wolkoff,  A.  v.,  and  Mayer,  Adolf,  Beitrage  zur  Lehre  iiber  die  Athmung  der  Pflanzen.  Landw.  Jahrb. 
3:  481-527.  1874.  Bonnier,  Gaston,  and  Mangin,  Louis,  Recherches  sur  la  respiration  et  la  transpira- 
tion des  champignons.  Ann.  sci.  nat.  Bot.  VI  17:  210-305.  1884.  Kuijper,  J.,  Ueber  den  Einfluss 
der    Temperatur  auf  die  Atmung  der  hoheren  Pflanzen.     Recueil  trav.  bot.  Neerland.  7     131-240.  1910. 

4  Puriewitsch,  1893.     [See  note  2,  p.  188.] 


FERMENTATION    AND    RESPIRATION 


211 


Plant 


Sedum  hybrid  urn 


Pelargonium  zonule. 


Temperature,       Respiratory  Ratio, 
deg.  C.  C02 

0, 

2-4  0.45 

10-12  o-37 

25-26  0.48 

4-5  0.75 

12-14  0.54 

34-35  0.95 

Temperature  fluctuations  themselves  exert  great  influence  upon  plant  respi- 
ration, aside  from  the  effect  produced  by  altered  temperature.  Palladin1 
exposed  three  similar  lots  of  tips  of  etiolated  bean  seedlings  to  three  different 
temperatures,  respectively,  and  then  brought  them  all  to  the  same  medium  tem- 
perature and  determined  the  rate  of  evolution  of  carbon  dioxide  in  each  case. 
The  following  table  illustrates  the  kind  of  results  obtained. 


Previous 

Temperature, 

deg.  C. 


Relative  Amounts  of  C02  Produced  per 
Unit  of  Time,  i8-2  2°C. 


Average 


Excess, 
Per  Cent. 


Medium,  17-20 
Low,  7—1 2 

High         36-37 


54-5>  53-5,  55o,  44.9,  58.1,  65.3,  59.8, 
89.8,  73.6,  80.2,  53.9,  78.9,  87.4,  82.9 
81.4, 89.4, 


40 
53 


The  tips  that  remained  at  medium  temperature  formed  the  least  carbon  dioxide, 
but  those  that  had  been  recently  transferred  from  lower  to  higher  or  from  higher 
to  lower  temperature  produced  much  more  of  this  gas. 

A  very  peculiar  influence  of  temperature  upon  the  respiration  and  vital 
activity  of  Aspergillus  niger  was  observed  by  A.  Rikhter.2  Frozen  mycelium 
of  this  fungus,  when  allowed  to  thaw  at  room  temperature,  appeared  to  have 
been  killed,  and  produced  no  trace  of  carbon  dioxide.  When  the  frozen  filaments 
were  transferred  directly  to  a  temperature  of  30°C,  however,  this  gas  began  to 
be  given  off.  The  rate  of  evolution  of  the  gas  increased  gradually  and  spores 
were  formed.  This  shows  that  freezing  is  not  fatal,  per  se;  death  is  of  later  oc- 
currence, with  the  thawing  of  the  organism,  under  unfavorable  temperature 
conditions. 

An  indirect  relation  between  light  conditions  and  respiration  was  discovered 
by  Borodin,3  who  found  that  the  intensity  of  respiratory  activity  in  leafy  twigs 
gradually  decreases  after  the  twigs  are  placed  in  darkness,  and  rises  again  after 
they  have  been  once  more  illuminated.  These  phenomena  may  be  interpreted 
as  follows:  Carbohydrates  are  necessary  for  respiration  and  are  gradually  used  up 

1  Palladin,  W.,  Influence  des  changements  de  temperature  sur  la  respiration  des  plantes.  Rev.  g6n 
bot.  11:  241-257.     1899. 

-  Richter,  A.,  Zur  Frage  uber  den  Tod  von  Pflanzen  infolge  niedriger  Temperatur.  (Kalteresistenz  von 
Aspergillus  niger.)      Centralbl.  Bakt.  //,  28:  617-624.      1910. 

3  Borodin,  J.  P.,  Physiologische  Untersuchungen  uber  die  Atmung  beblatterter  Sprosse.  St.  Petersburg, 
1876.        (Idem,  Sur  la  respiration  des  plantes  pendant  leur  germination.     Florence,  1875.] 


212  PHYSIOLOGY    OF    NUTRITION 

during  the  period  of  darkness,  so  that  respiration  is  at  length  retarded'  because 
of  lack  of  material.  When  the  plants  are  returned  to  the  light  the  supply  of 
available  carbohydrates  is  again  increased  and  the  respiratory  process  returns 
to  its  usual  rate.  Such  an  interpretation  finds  further  support  in  the  observa- 
tion that  the  change  from  darkness  to  light  is  accompanied  by  an  acceleration 
in  the  evolution  of  carbon  dioxide  only  when  the  light  contains  the  less  refran- 
gible wave-lengths  (which  are  especially  active  in  photosynthesis),  and  when  the 
surrounding  air  is  supplied  with  carbon  dioxide  (without  which  photosynthesis 
cannot  occur). 

Bonnier  and  Mangin1  state  that  there  is  also  a  direct  influence  of  light  upon 
plant  respiration,  but  that  this  is  very  slight.  If  plants  are  placed  alternately 
in  darkness  and  in  light  a  retarding  effect  of  light  is  observed,  and  this  bears 
no  relation  to  the  photosynthetic  process,  since  it  is  demonstrable  in  plants 
without  chlorophyll.     The  value  of  the  respiratory  ratio  is  independent  of  light.9 

Maksimov2  came  to  the  conclusion  that  the  effect  of  light  upon  the  respira- 
tion of  Aspergillus  niger  varies  with  the  age  of  the  culture  and  with  the  nature  of 
the  nutrient  medium.  He  found  that  light  exerted  no  influence  upon  the 
respiration  of  young,  well-nourished  cultures,  but  that  the  respiration  of  old 
cultures  was  increased  by  illumination.  The  stimulating  effect  became  more 
marked  if  the  culture  was  deficient  in  nutrient  material.  Levshin,3  however, 
could  observe  no  influence  of  diffuse  light  upon  the  rate  of  respiration  in  various 
fungi. 

The  partial  pressure  of  oxygen  in  the  surrounding  atmosphere  also  influences 
plant  respiration.  In  this  case,  also,  the  value  of  the  respiratory  ratio  does 
not  change. 

According  to  the  results  of  Kosinski4  and  Palladin,5  the  concentration  of 
the  nutrient  solution  exerts  great  influence  upon  the  rate  of  respiration.  If 
plants  are  transferred  from  a  more  concentrated  to  a  more  dilute  solution  respira- 
tion becomes  more  active,  and  a  change  in  the  opposite  direction  decreases 
respiratory  activity.  Thus,  ioo  g.  of  etiolated  bean  leaves,  with  their  petioles 
dipping  into  a  cane-sugar  solution  that  was  altered  in  concentration  from  time 
to  time,  gave  the  following  mean  hourly  rates  of  evolution  of  carbon  dioxide, 
for  the  different  exposure  periods. 

1  Bonnier,  Gaston,  and  Mangin,  Louis,  Recherches  sur  la  respiration  des  tissus  sans  chlorophylle- 
Ann.  sci.  nat.  Bot.  VI,  18:  293-382.      1884. 

2  Maximow,  N.  A.,  Ueber  den  Einfluss  des  Lichtes  aud  die  Atmung  der  niederen  Pilze.  Centralbl. 
Bakt.  //,  9:  193-205,  261-272.      1902. 

3  Lbwschin,  A.,  Zur  Frage  iiber  den  Einfluss  des  Lichtes  auf  die  Atmung  der  niederen  Pilze.  Beih. 
Bot.  Centralbl.  23:  54—64.     1908. 

4  Kosinski,  Ignacy,  Die  Athmung  bei  Hungerzustanden  und  unter  Einwirkung  von  mechanischen  und 
chemischen  Reizmitteln,  bei  Aspergillus  niger.     Jahrb.  wiss.  Bot.  37:  137-204.      1902. 

5  Palladin,  W.,  and  Komleff,  A.,  Influence  de  la  concentration  des  solutions  sur  l'energie  respiratoire  et 
sur  la  transformation  des  substances  dans  les  plantes.      Rev.  g6n.  bot.  14:  497-516.      1902. 

"  The  respiratory  activity  of  plant  parts  containing  chlorophyll  is  of  course  difficult  to 
study  as  long  as  light  is  present,  because  of  the  fact  that  photosynthesis  reverses  the  respira- 
tion process,  as  far  as  the  absorption  of  oxygen  and  the  elimination  of  carbon  dioxide  is  con- 
cerned. In  this  connection,  as  well  as  with  regard  to  the  influence  of  light  on  respiration  itself, 
see:  Spoehr,  H.  A.,  Photochemical  processes  in  the  diurnal  deacidification  of  the  succulent 
plants.  Biochem.  Zeitsch.  57:  95-111.  1914.  Idem,  Variations  in  respiratory  activity 
in  relation  to  sunlight.     Bot.  gaz.  59:  366-386.     1915. — Ed. 


FERMENTATION    AND    RESPIRATION 


213 


Concentration 
of  Medium 

Period  of 
Exposure 

CO2  Produced         Change  in  Respira- 
per  Hour                     tory  Rate 

per  cent. 

15 

25 

5° 

0 

days 
3 
3 

1 

1 

mg.                                 per  cent. 
122.7 

79-4                                 -32.5 
69. 7                                    —12.2 

154.0                                 +120.9 

Zaliesskii1  found  that  if  the  bulbs  of  Gladiolus  are  immersed  in  water  for  a 
short  time  their  respiratory  activity  is  considerably  increased. 

Changes  in  concentration  of  the  nutrient  solution  affect  the  value  of  the 
respiratory  ratio.  Purievich2  obtained  the  following  values  of  this  ratio  for 
Aspergillus  niger  with  different  concentrations  of  cane-sugar  solution. 

Concentration  of  the  medium,  per  cent 1  5         10         20         25 

.,      •  •    /co2\ 

Respiratory  ratio,  I  V)     I 0-85     o .  96     1 .  04     o .  93     0.73 

Respiration  is  influenced  by  various  toxic  substances.3  Morkovin4  studied 
this  effect  in  the  case  of  various  alkaloids,  glucosides,  alcohols  and  other  sub- 
stances, such  as  ethyl  ether,  formaldehyde  and  paraldehyde,  and  found  that 
these  increase  respiratory  activity  when  present  in  very  weak  concentration. 
For  example,  of  two  similar  groups  of  shoots  of  etiolated  bean  seedlings  one 
group  was  grown  in  cane-sugar  solution,  and  the  other  in  the  same  solution  with 
the  addition  of  1  per  cent,  of  isobutyl  alcohol.  Without  the  poison,  100  g. 
of  shoots  produced  65.0  mg.  of  carbon  dioxide  per  hour  during  the  first  twenty- 
four  hours  of  the  experiment,  and  72.4  mg.  per  hour  during  the  first  thirty-seven 
hours.  With  the  poison,  191. 7  mg.  of  carbon  dioxide  was  produced  per  hour  for 
the  first  twenty-four  hours  and  124.5  mg.  per  hour  for  the  first  thirty-seven 
hours.  Isobutyl  alcohol,  in  this  concentration,  is  thus  seen  to  exert  a  definitely- 
accelerating  effect  upon  respiration.  Zaliesskii5  has  shown  that  ether  accelerates 
respiration  in  resting  plant  organs  to  a  marked  degree;  in  the  case  of  Gladiolus 
bulbs  exposed  to  an  atmosphere  containing  ether,  respiration  is  first  increased, 
but  later  decreases  to  below  the  normal  rate. 

Wounding  markedly  increases  the  rate  of  respiration.6     In  one  experiment 

1  Zaliesskii,  V.,  Influence  de  l'excitation  sur  la  respiration  des  plantes.  [Russian,  French  sub-title  only.] 
Mem.  Inst.  Agron.  et  Forest.  Novo-Alexandria  15? :  1-41.     1902.     [Parts  of  vol.  are  separately  paged.] 

-  Puriewitsch,  K.,  Physiologische  Untersuchungen  iiber  Pflanzenatmung.  Jahrb.  wiss.  Bot.  35:  573- 
610.     1900. 

3  Palladin,  W.,  Ueber  die  Wirkung  von  Giften  auf  die  Atmung  lebender  und  abgetoteter  Pflanzen, 
sowie  auf  Atmungsenzyme.     Jahrb.  wiss.  Bot.  47:  431—461.      1910. 

*  Morkowin,  N.,  Recherches  sur  l'influence  des  anesthetiques  sur  la  respiration  des  plantes.  Rev. 
gen.  bot.  n:  289-303,  341-352.  1899.  Idem,  Recherches  sur  l'influence  des  alcaloides  sur  la  respiration 
des  plantes.     Ibid.  13:  100-126,  177-192,  212-226,  265-275.     1901. 

»  Zaliesskii,  1902.     [See  note  1,  this  page.) 

*  Stich,  Conrad,  Die  Athmung  der  Pflanzen  bei  verminderter  Sauerstoffspannung  und  bei  Verletzungen. 
Flora  74:  1-57.  1891.  P.  15.  Pfeffer,  W.,  Ueber  die  Steigerung  der  Athmung  und  der  Warme- 
production  nach  Verletzung  lebensthatiger  Pflanzen.  Ber.  ii.  d.  Verh.  d.  K.  Sachs.  Ges.  Wiss.  Leipzig 
(Math.-phys.  CI.)  48:  384-389.  1896.  Smirnoff,  Influence  des  blessures  sur  la  respiration  normale  et 
intramol6culaire  (fermentation)  des  bulbes.     Rev.  g6n.  bot.  115:  26-38.     1903. 


214  PHYSIOLOGY    OF    NUTRITION 

300  g.  of  uninjured  potato  tubers  produced  from  1.2  to  2  nig.  of  carbon  dioxide 
per  hour.  After  this  rate  had  been  determined  each  tuber  was  quartered,  and 
the  pieces  were  left  at  the  same  temperature  and  in  the  same  surroundings  as 
before.  For  the  second  hour  after  cutting,  the  rate  of  evolution  of  carbon  dioxide 
was  9  mg.;  for  the  fifth,  14.4  mg.;  for  the  tenth,  16.8  mg.;  and  for  the  twenty- 
eighth,  18.6  mg.  Then  the  rate  began  to  decrease.  For  the  fifty-first  hour 
after  cutting  it  was  13.6  mg.,  after  four  days  it  was  3.2  mg.,  and  after  six  days  it 
had  fallen  to  1.6  mg.,  the  original  average  rate  obtained  before  wounding. 

Phosphates,*  which  markedly  accelerate  alcoholic  fermentation,  have  the 
same  effect  upon  respiration,  which,  as  has  been  seen,  is  related  to  alcoholic 
fermentation.1  These  salts  thus  accelerate  both  the  anaerobic  and  the  oxida- 
tion phase  of  the  respiratory  process.2 

The  rate  of  plant  respiration  depends,  furthermore,  upon  various  internal 
conditions,  within  the  organism.  In  the  first  place  may  be  mentioned  the 
relation  between  respiration  and  growth.  The  more  rapidly  a  plant  grows,  the 
more  oxygen  does  it  absorb  and  the  more  carbon  dioxide  does  it  give  off.  As 
will  appear  in  the  sequel  (page  247) ,  all  plants  exhibit  the  so-called  grand  period  of 
growth,  which  may  be  represented  by  the  grand  curve  of  growth.  A  germinating 
seedling  grows  slowly  at  first,  but  with  increasing  rapidity  as  it  becomes  older,  until 
a  maximum  growth  rate  is  attained,  after  which  growth  proceeds  more  and 
more  slowly.  The  intensity  of  respiration  is  found  also  to  be  very  low  during 
the  early  stages  of  growth;  with  increasing  growth  rates  the  respiratory  process 
is  accelerated  and  this  also  reaches  a  maximum  intensity  and  then  declines. 
Thus  may  be  constructed  a  grand  curve  of  respiration,  the  form  of  which  is 
practically  identical  with  that  of  the  grand  curve  of  growth.  This  grand  curve 
of  respiration  was  first  shown  by  A.  Mayer,  who  measured  the  oxygen  absorbed. 
Like  results  were  obtained  by  Borodin  and  Rischavi,3  who  determined  the 
amount  of  carbon  dioxide  eliminated. 

The  value  of  the  respiratory  ratio (  q~)  does  not  remain  constant  during 

seed  germination.  Bonnier  and  Mangin4  showed  that  this  value  is  unity  for  the 
first  phase  of  germination,  but  that  it  becomes  smaller  with  increasing  growth 
rates.  Palladin5  came  to  a  similar  conclusion  from  a  study  of  the  value  of  the 
respiratory  ratio  for  actively  growing  internodes  cut  from  the  stems  of  various 
kinds  of  plants.  In  all  these  experiments  the  value  of  the  ratio  was  less  than 
unity,  which  shows  that  growing  organs  absorb  more  oxygen  than  they  give  off 

1  Iwanoff,  Leonid,  Ueber  die  Wirkung  der  Phosphate  auf  die  Ausscheidung  der  Kohlensaure  durch 
Pflanzen.  Biochem.  Zeitsch.  25:  171-186.  1010.  Iwanoff,  Nicolaus,  Die  Wirkung  der  nutzlichen  und 
schadlichen  Stimulatoren  aud  die  Atmung  der  lebenden  und  abgetoteten  Pflanzen.     Ibid  32. :  74-96-     191 1- 

2  Zaleski,  W.,  and  Reinhard,  A.,  Zur  Frage  der  Wirkung  der  Salze  auf  die  Atmung  der  Pflanzen  und 
auf  die  Atmungsenzyme.     Biochem.  Zeitsch.  27:  450-473-  iqio. 

a  Mayer,  A.,  Ueber  den  Verlauf  der  Athmung  beim  keimenden  Weizen.  Landw.  Versuchsstat.,  18:  245- 
279.  1875.  Borodin,  1875.  [See  note  3,  p.  211.]  Rischavi,  L.,  Einige  Versuche  uber  die  Athmung  der 
Pflanzen.  Landw.  Versuchsstat.  19:  321-340.     1876. 

4  Bonnier  and  Mangin,  1884.     [See  note  1,  p.  212.} 

5  Palladin,  W.,  Athmung  und  Wachsthum.  (Auszug  aus  einer  russisch  erscheinenden  Arbeit.)  Ber. 
Deutsch.  Bot.  Ges.  4:  322-328.     1886. 

*  This  paragraph  is  omitted  in  the  7th  Russian  edition. — Ed. 


FERMENTATION  AND   RESPIRATION  215 

in  the  carbon  dioxide  eliminated.  In  such  organs  cellulose  is  accumulating  and 
asparagin  is  being  formed,  and  both  of  these  processes  are  dependent  upon 
the  assimilation  of  oxygen. 

Respiration  is  closely  related  to  all  of  the  other  processes  occurring  in  living 
cells.  The  relation  of  fat  and  carbohydrate  content  to  the  respiration  of 
germinating  seeds  may  serve  as  an  illustration  of  this.  Many  studies  agree  in 
showing  that  the  germination  of  fatty  seeds  exhibits  respiratory  ratio  values 
that  are  exceptionally  low.  It  is  thus  suggested  that  the  germinal  activity  of 
such  seeds  is  connected  with  a  fixation  of  oxygen.  It  has  been  pointed  out 
(page  191)  that  the  loss  during  the  germination  of  fatty  seeds  is  made  up  only 
of  carbon  and  hydrogen,  while  the  amount  of  oxygen  in  the  seeds  increases. 
This  becomes  clear  in  connection  with  the  fact  that  the  respiration  of  these 
seeds  involves  the  oxidation  of  fats,  whose  oxygen  content  is  much  smaller 

CO? 

than  that  of  cabohydrates.     Therefore,  the  value  of  the  ratio  -~r-  must  be 

markedly  less  than  unity  in  this  case.  The  complete  oxidation  of  triolein  may 
be  represented  by  the  following  equation; 

Carbon 
Triolein  Oxygen  dioxide  Water 

C3H603  (C18H330)i  +  80O2  =  57  C02  +  52  H20. 

57 
Here  the  value  of  the  oxidation  ratio  is  z-»  which  is  less  than  unity.    Polovtzov1 

has  shown  that  fatty  seeds  germinating  in  cane-sugar  solution  produce  a  direct 
oxidation  of  sugar,  the  respiratory  ratio  being  equal  to  unity  in  this  case. 

The  gas  exchange  accompanying  respiration  in  ripening  fruits  that  have 
oily  seeds,  after  the  fats  have  begun  to  accumulate,  presents  a  very  different 
picture.  The  formation  of  oils  from  carbohydrates  (the  direct  products  of  photo- 
synthesis) is  possible  only  with  the  elimination  of  the  superfluous  oxygen.  Thus, 
the  rate  of  carbon  dioxide  production  increases  in  these  ripening  fruits,  without  any 
corresponding  increase  in  the  rate  of  oxygen  absorption,  and  the  value  of  the  res- 
piratory ratio  becomes  greater  than  unity.  An  experiment  with  ripening  poppy 
fruits2  showed  a  rate  of  oxygen  absorption  of  21.72  cc.  while  the  corresponding 

CO 

rate  of  carbon  dioxide  production  was  32.62.     Thus,  ~r-    =  1.5,  which  is  greater 

U2 

than  unity. 

§5.  Apparatus  for  Measuring  Plant  Respiration.3 — In  respiration  studies  it 
is  necessary  to  measure  one  or  both  of  the  gases  involved.  When  the  determina- 
tion of  the  rate  of  elimination  of  carbon  dioxide  is  sufficient,  Pettenkoffer  tubes 
(Fig.  91)  are  serviceable.  These  are  glass  tubes  about  1.5  cm.  in  diameter  and 
about  a  meter  long,  filled  with  titrated  baryta  water  [preferably  barium 
hydroxide  dissolved  in  an  aqueous  solution  of  barium  chloride]  and  supported 
in  an  oblique  position.     A  water  aspirator  is  used  to  produce  a  slow  current  of 

1  Polovtsov,  V.,  fitudes  sur  la  respiration  des  plantes.      Mem.  Acad.  Imp.  Sci.  St.-Petersbourg  VIII, 
127 :  1-69.      1902. 

2  Godlewski,  Emil,  Beitriige  zur  Kenntniss    der    Pflanzenathmung.     Jahrb.    wiss.  Bot.   13:    491-543. 
1882. 

3Palladin,  W.,  and  Kostytschew,  S.,  Methoden  zui  Bestimmung  der  Athmung  der  Pflanzen.    Abder- 
halden's  Handbuch  3:  479-515-     1910 


2l6 


PHYSIOLOGY    OF    NUTRITION 


air,  which  enters  the  plant  chamber  (a,  Fig.  91)  after  having  been  freed  of  carbon 
dioxide  through  the  action  of  soda  lime.  From  the  plant  chamber  the  air 
passes  into  the  lower  end  of  the  Pettenkoffer  tube,  forming  small  bubbles  which 
ascend  slowly  through  the  baryta  water.  The  air,  again  freed  of  carbon  dioxide, 
passes  out  to  the  aspirator  from  the  upper  end  of  the  tube.  Since  the  aspirator 
would  usually  produce  a  more  rapid  air  stream  than  can  be  passed  through  the 
Pettenkoffer  tube,  a  pressure  regulator  (b,  Fig.  91)  is  introduced,  which  also 
prevents  too  great  rarification  of  the  air  in  the  plant  chamber.  The  carbon 
dioxide  produced  by  the  plants  is  precipitated  in  the  tube  as  barium  carbonate. 
After  a  suitable  time  the  air  stream  is  turned  into  a  second  Pettenkoffer  tube 
and  the  solution  is  removed  from  the  first  and  titrated  [with  standard  oxalic 
acid  solution  and  phenolphthalein  as  indicator].  Thus  the  amount  of  unprecipi- 
tated  barium  hydroxide  that  remains  is  determined,  and  a  simple  calculation 
gives  the  weight  of  the  carbon  dioxide  produced  by  the  plants  during  the  given 
period.  The  temperature  of  the  plant  chamber  is  maintained  constant  by 
immersing  it  in  a  large  vessel  of  water  which  is  warmed  as  necessary. 


Fig.  91. — Respiration  apparatus.      (After  Petlenkofer.) 


The  amount  of  oxygen  absorbed  by  a  plant  may  be  measured  by  means 
of  the  apparatus  of  Wolkoff  and  Mayer  (see  note  3,  p.  210),  which  consists  essen- 
tially of  a  large  inverted  U-tube  with  one  arm  broad  and  the  other  narrow  and 
graduated  for  volume  readings.  In  the  broad  arm  of  this  tube  are  placed  the 
seedlings,  etc.,  to  be  studied,  and  also  a  small,  open  vessel  of  potassium  hydroxide 
solution,  and  the  larger  opening  is  tightly  closed  with  a  glass  stopper.  The 
other,  narrow  arm  of  the  tube  is  closed  by  dipping  into  mercury  below.  The 
carbon  dioxide  produced  by  the  plant  is  absorbed  by  the  potassium  hydroxide 
solution  and  the  volume  of  the  oxygen  absorbed  is  measured  by  the  rise  of  the 
mercury  meniscus  in  the  narrow,  graduated  arm. 

For  the  simultaneous  determination  of  the  oxygen  absorbed  and  the  carbon 
dioxide  given  off,  the  apparatus  of  Bonnier  and  Mangin  may  be  employed  (Fig. 
92).  The  bell-jar,  A,  serves  as  plant  chamber,  into  which  air  passes  through 
the  tube  a,  having  first  been  freed  of  carbon  dioxide  by  bubbling  through  potas- 
sium hydroxide  solution  in  the  wash-bottle,  F.  A  vessel  of  water  in  the  chamber 
keeps  the  atmosphere  moist.  The  chamber  is  first  filled  with  air  that  has  been 
freed  from  carbon  dioxide,  suction  being  applied  through  tube  b,  by  means  of 
an  aspirator.     Then  the  two  cocks,  r  and  2,  are  closed.     From  time  to  time  a 


FERMENTATION    AND    RESPIRATION 


2  I  7 


gas  sample  is  removed  from  the  plant  chamber  and  analyzed,  the  removal 
of  this  sample  being  accomplished  as  follows:  The  three-way  cock  R  is  so 
set  as  to  bring  the  tube  b  into  communication  with  the  container  I,  after  which 
the  similar  container  V  is  lowered,  so  that  some  mercury  flows  fron  /  to  V,  thus 
drawing  air  from  the  plant  chamber  into  /.  Then  the  cock  R  is  reset  so  that  I 
communicates  with  tube  d  and  the  sample  tube  beyond,  and  the  container  V  is 
again  raised,  thus  forcing  into  the  sample  tube  some  of  the  gas  that  has  just 
been  removed  from  the  plant  chamber. 

The  volume  of  the  gas  in  the  plant  chamber  is  determined  as  follows:  Some 
gas  is  removed  and  its  volume  (V)  is  determined  at  atmospheric  pressure  (H). 
If  p  is  the  gas  pressure  in  the  apparatus  before,  and  p'  is  the  pressure  after,  the 
removal  of  this  gas  (these  pressures  being  determined  by  means  of  the  mano- 


Fig.  92. — Respiration  apparatus.      {After  Bonnier  and  Mangin.) 


meter,  M),  then  the  original  gas  volume  (A')  contained  in  the  chamber  is  found 
from  the  equation: 

X~  p-p" 

If  the  absolute  amounts  of  oxygen  absorbed  and  of  carbon  dioxide  given  off 
are  not  important,  then  the  determination  of  the  total  gas  volume  is  not  required. 

COo 

In  such  a  case  the  value  of  the  ratio  -7^—  is  derived  from  the  proportions  of  these 

two  gases  found  in  the  samples  taken  at  the  beginning  and  end  of  the  experiment. 
§6.  Formation  of  Water  during  Respiration. — During  germination  in  dark- 
ness all  seeds  lose  an  appreciable  amount  of  hydrogen,  in  the  form  of  the  water 
vapor  produced  by  the  respiratory  process.  Very  few  direct  determinations  of 
respiration  water  are  available.  Liaskovskii1  studied  the  formation  of  water 
during  the  germination  of  pumpkin  seeds.  The  seeds  were  germinated  under  a 
bell-jar,  through  which  a  current  of  air  was  drawn,  the  entire  apparatus  being 
weighed  from  time  to  time.     The  amount  of  water  produced  by  the  respira- 

1  Liaskovskii,  1874.  [See  note  2,  p.  191.] — Also,  in  this  connection,  see:  Babcock,  1912.  [See  note  3. 
p.  189.] — [Babcock  deals  with  the  water  of  respiration  in  insects  (such  as  the  common  clothes  moth,  which 
lives  on  dry  wool)  as  well  as  in  germinating  seeds. — Ed.] 


2l8 


PHYSIOLOGY   OF   NUTRITION 


tory  process  was  obtained  from  five  measured  values,  as  follows:  the  total 
weight  of  the  apparatus  at  the  beginning  (.4)  and  at  the  end  (B)  of  the  experi- 
ment, the  dry  weight  of  the  seeds  before  (m)  and  after  germination  (n)  and  the 
amount  of  water  actually  given  off  (O).  The  water  eliminated  during  the 
experiment,  was  collected  in  calcium  chloride  tubes.  Supposing  that  the 
weight  of  the  empty  apparatus  (S)  and  the  air  therein  contained  (U)  suffered 
no  change  during  the  experiment,  the  amount  of  water  formed  by  respiration 
can  be  easily  calculated  from  these  data.  At  the  beginning  of  the  experiment 
the  amount  of  water  contained  in  the  seeds  and  in  the  whole  system  is  equal 
to  A  —  S  —  U  —  m,  which  may  be  designated  as  X.  At  the  end  of  the  experi- 
ment the  amount  of  water  in  the  system,  aside  from  the  absorption  tubes,  is 
equal  to  B  —  S  —  U  —  n,  which  may  be  called  Y.  The  amount  of  water  re- 
tained in  the  absorption  tubes  (0)  is  to  be  added  to  F,  to  give  the 
total  amount  present  at  the  end  of  the  experiment.  The  difference 
between  the  amount  present  at  the  beginning  and  that  at  the  end, 
is  of  course  the  amount  produced  by  respiration.  If  this  difference 
is  represented  by  Z,  then  we  have: 

Z  =  Y  +  O  -  X  =  B  -  n  +  0  -  A  +  m. 

The  results  obtained  by  Liaskovskii  may  be  summarized  as  follows: 
i .  In  the  early  stages  of  germination  very  little  water,  or  none 
at  all,  is  produced. 

2.  With  higher  temperatures  the  production  of  water  is  rela- 
tively less  than  with  lower  temperatures. 

3.  There  is  no  constant  relation  between  the  amount  of  carbon 
dioxide  and  that  of  hydrogen  given  off. 

The  low  rate  of  water  formation  in  the  early  stages  of  germina- 
tion may  be  due  to  the  fact  that  various  hydrolytic  processes  are 
very  active  at  this  time.     How  great  may  be  the  amount  of  water 
{After  Reg-  fixecj  by  hydrolytic  changes  will  be  brought  out  by  the  experiments 

11  CI  'ill.) 

of  Bonnier,  to  be  described  in  the  next  following  section. 
§7.  Liberation  of  Heat  During  Respiration. — The  internal  temperature  of 
the  plant  body  is  generally  about  the  same  as  that  of  the  surrounding  air,  and  it 
is  only  by  very  careful  experimentation  that  it  is  possible  to  demonstrate  slight 
differences.  The  temperature  of  growing  shoots  usually  exceeds  that  of  the 
surrounding  air  by  not  over  o.3°C.  Only  two  periods  in  the  life  of  the  plant 
exhibit  an  appreciable  production  of  heat,  that  of  seed  germination  and  that 
of  flowering.'  The  temperature  of  germinating  seeds  is  from  7  to  2o°C.  higher 
than  that  of  the  surrounding  air,  and  the  difference  is  still  more  pronounced  in 
the  case  of  opening  flower  buds.1  A  temperature  of  490  has  been  observed 
in  the  flowering  spadix  of  some  of  the  Aroideae,  when  that  of  the  surrounding 
air  was  only  190.  The  rise  of  temperature  is  here  concomitant  with  an 
accelerated  rate  of  oxygen  absorption. 

1  Kraus,  Gregor,  Physiologisches  aus  den  Tropen.  ///.  Uber  Bluthenwarme  bei  Cycadeen,  Palmen 
und  Araceen.  Ann.  Jard.  Bot.  Buitenzorg  13:  217-275.      1896. 

1  Large  leaf  buds  of  deciduous  trees,  as  they  open  in  the  spring,  should  also  be  mentioned 
here.     Expanding  buds  of  the  horse-chestnut  (^Esculus)  furnish  an  example. — Ed. 


Fig.  93. 
Calorimete  r 


FERMENTATION   AND    RESPIRATION  2IQ 

Bonnier1  has  carried  out  extensive  researches  upon  the  production  of  heat 
during  seed  germination,  using  either  a  calorimeter  of  the  Berthelot  type  or 
the  modified  thermo-calorimeter  of  Regnault.  The  latter  apparatus  (Fig.  93) 
consists  essentially  of  a  mercury  thermometer  the  bulb  of  which  is  expanded  to 
form  the  wall  of  a  chamber  (A),  the  latter  being  closed  by  a  stopper  (B).  The 
plants  or  plant  parts  to  be  studied  are  placed  in  this  chamber  and  their  tem- 
perature is  directly  read  on  the  thermometer  scale.  In  some  of  Bonnier's  ex- 
periments analyses  of  the  gas  contained  in  the  chamber  were  also  carried  out. 
Pea  seeds  placed  in  this  calorimeter  and  allowed  to  grow  until  the  cotyledons 
had  disappeared  produced  the  following  amounts  of  heat  per  minute,  per  kilo- 
gram of  seeds,  at  different  stages  of  their  development. 

Heat  Produced 
Stage  of  Development,  Pea  per    Minute, 

gram-calories 

1 .  Soaked  seeds 9 

2.  Seedlings  with  roots  5  mm.  long 125 

3.  Seedlings  with  roots  50-60  mm.  long 75 

4.  Seedlings  with  green  stem  abuut  20  mm.  long 60 

5.  Seedlings  with  cotyledons  withering 22 

6.  Seedlings  from  which  cotyledons  have  fallen 6 

This  experiment  shows  that  the  rate  of  heat  production  varies  with  the  develop- 
ment of  the  plant,  the  maximum  rate  occurring  with  a  very  early  stage  of 
germination. 

If  the  rates  of  heat  liberation  for  the  different  developmental  stages  are  cal- 
culated from  the  rates  of  the  elimination  of  carbon  dioxide  and  of  the  absorption 
of  oxygen,  the  results  do  not  agree  with  the  corresponding  ones  determined 
calorimetrically,  as  is  clear  from  the  following  table,  which  gives  the  rates  of 
heat  production  per  kilogram  of  barley  seeds  per  minute. 


Heat  Produced  per  Minute 

Respiratory 

Stage  of  Development,  Barley 

Calorimetrically 
Determined 

Calculated 

Ratio  Value 

gram-calories 

5 
62 

40 

15 
0 

gram-calories 

3 

45 

3i 

12 

3 

1 .00 

2.  Root  primordia  showing 

3.  Main  root  3  mm.  long 

4    End  of  germination  .            

0.65 
0.80 

°-95 

5    Leafy  stems                        

1 .00 

The  amounts  of  heat  actually  produced  in  germination  markedly  exceed  the 
corresponding  calculated  amounts,  and  it  is  therefore  evident  that  exothermic 
reactions  other  than  that  of  oxidation  occur  during  germination,  especially  in 
the  earlier  stages.     Among  such  reactions  are  to  be  included  starch  inversion 

1  Bonnier,  Gaston,  Recherches  sur  la  chaleur  v6getale.     Ann.  sci.  nat.  Bot.  VII,  18 :  i-35-     1893. 


2  20  PHYSIOLOGY    OF    NUTRITION 

and  other  hydrolytic  processes.     (See  last  paragraph  of  the  next  preceding 
section,  p.  218.) 

More  mature,  growing  stems  are  seen  to  be  different  from  germinating  seeds 
in  this  regard;  while  the  calculation  leads  us  to  expect  a  rate  of  heat  production 
here  of  3  g.-cal.  per  minute,  the  calorimetric  determination  shows  that  no  heat 
is  liberated  at  all.  In  this  case  the  energy  is  not  set  free  as  heat  but  must  be  con- 
sidered as  taking  the  form  of  work,  the  accomplishment  of  which  is  a  necessitv 
in  every  active  cell.  Work  and  heat  are  merely  different  modifications  of  the 
same  thing,  energy — just  as  the  yellow  and  red  varieties  of  phosphorus,  or  the 
diamond  and  amorphous  carbon,  are  simply  different  forms  of  matter.1 

Some  thermo-chemical  considerations  are  of  interest  in  this  connection. 
The  heat  of  formation  of  carbon  dioxide  is  97,600  g.-cal.  per  gram-molecule, 
and  that  of  the  C02  used  for  a  gram-molecule  of  carbohydrate  (employing  the 
empirical  formula  for  starch,  C6H10O5)  is  97,600  X  6,  or  585, 600 g.-cal.'  Experi- 
ment shows  that  the  heat  of  formation  of  a  gram-molecule  of  carbohydrate 
to  be  actually  667,000  g.-cal.,  however,  and  the  excess  (81,400  g.-cal.,  the  so- 
called  heat  effect)  is  the  amount  of  heat  corresponding  to  the  formation  of  a 
gram-molecule  of  starch  from  C  and  H20.  The  heat  of  combustion  of  starch  is 
thus  made  up  of  the  heat  of  formation  of  6  molecules  of  carbon  dioxide  and  that 
of  the  combination  of  5  molecules  of  water  with  these.  When  carbohydrates 
are  completely  oxidized  in  the  animal  body  there  is  the  same  excess  of  heat 
(81,400  g.-cal.)  above  that  of  the  oxidation  of  the  carbon  in  the  carbohydrate 
molecule.  This  explains  the  fact — not  otherwise  to  be  understood — that  the 
animal  body  produces  an  apparent  excess  of  heat  above  that  which  is  calculated 
from  the  amount  of  carbon  dioxide  eliminated,2  or  from  the  quantity  of  oxygen 
absorbed,  this  calculation  being  based  simply  on  the  oxidation  of  carbon  to 
carbon  dioxide.  In  the  concrete  case  just  considered,  the  calculated  heat  of 
combustion  of  starch  (585,600)  is  about  six-sevenths  of  the  value  obtained  by 
direct  observation  (667,000).  The  differences  encountered  in  Bonnier's  experi- 
ments are  so  great,  however  (see  the  table  given  above),  that  they  are  not  to  be 
referred  simply  to  the  heat  effect.  It  is  strongly  suggested  that  reactions  occur 
in  seed  germination  whereby  heat  is  liberated  without  the  occurrence  of  oxidation . 

The  experiment  of  Bonnier,  above  described,  shows  that  the  highest  rate  of 

CO 

heat  production  occurs  when  the  respiratory  ratio,  —=.    ,  assumes  a  minimum 

U2 

value  and  the  rate  of  oxygen  absorption  is  much  accelerated. 

§8.  Anaerobic,  or  Intramolecular,  Respiration. — When  plants  that  usually 
require  oxygen  are  placed  in  an  oxygen-free  atmosphere  they  do  not  die  at  once 

1  Ostwald,  Wilhelm,  Theoretische  Chemie.     Moscow,  1891.     P.  73.* 

2  Ostwald,  Wilhelm,  1801.*     [See  reference  just  given.] 

1  This  number  corresponds  to  the  formation  of  6  gram-molecules  of  carbon  dioxide  from 
carbon  and  oxygen,  the  hydrogen  and  oxygen  of  the  starch  molecule  being  considered  simply 
as  5  molecules  of  water.  In  other  words,  C6Hio05  is  considered  as  though  it  were  6C  +  5H0O. 
The  hydrogen  and  oxygen  of  starch  are  not  combined  to  form  water,  however,  and,  as  is  brought 
out  in  the  next  sentence  of  the  text,  the  heat  of  formation  of  C6Hi0O5  from  6C  +  5H0O  is  the 
excess  there  referred  to.  The  German  edition  agrees  with  the  7th  Russian  edition  in  stating 
this  excess  as  82,300,  instead  of  81,400  g.-cal. — Ed. 


FERMENTATION    AND    RESPIRATION  221 

but  remain  alive  for  a  time,  and  the  evolution  of  carbon  dioxide  continues.1 
Ethyl  alcohol  is  usually  formed  also.2  This  anaerobic,  or  intramolecular,  res- 
piration is  mainly  the  same  as  alcoholic  fermentation. 

Sometimes  the  amount  of  carbon  dioxide  produced  with  access  of  oxygen 
is  the  same  as  in  the  absence  of  oxygen,  but  such  cases  are  rare;  usually  carbon 
dioxide  production  is  considerably  less  when  oxygen  is  not  available.3  The 
value  of  the  ratio  of  the  amount  of  carbon  dioxide  eliminated  anaerobically  to 
the  amount  given  off  in  the  same  time  in  the  presence  of  oxygen  is  given  below 
for  several  plants. 

Young  seedlings  of  Vicia  faba  (Windsor  bean) i  •  197 

Young  seedlings  of  Tritkum  vulgare  (wheat) 0.490 

Young  twigs  of  Abies  excelsa  (fir) 0.077 

Young  twigs  of  Ligustrum  vulgare  (privet) 0.816 

The  amount  of  carbon  dioxide  formed  in  anaerobic  respiration  is  primarily 
dependent  upon  the  carbohydrate  content  of  the  plant  in  question.4  Etiolated 
bean  leaves  produce  but  very  little  carbon  dioxide  in  the  absence  of  oxygen,  and 
die  within  two  days.  If  they  are  previously  kept  with  their  petioles  in  sugar 
solution  for  some  time,  being  then  placed  under  anaerobic  conditions,  they  pro- 
duce much  carbon  dioxide  and  live  much  longer  than  when  they  are  employed 
without  the  preliminary  sugar  treatment.  After  two  days  they  are  still  alive 
and  they  afterwards  become  green  if  illuminated. 

In  anaerobic  respiration,  alcohol  is  formed  only  from  carbohydrates.  Sev- 
enty-one etiolated  leaves  of  Vicia  faba,  which  had  been  previously  supplied 
with  sugar  as  above,  formed,  without  oxygen,  782.4  mg.  of  carbon  dioxide  and 
724.6  mg.  of  alcohol,  in  twenty-five  hours.  The  same  number  of  similar  leaves, 
not  previously  supplied  with  carbohydrate,  but  otherwise  treated  in  the  same 
way,  gave  off  256.8  mg.  of  carbon  dioxide  and  68.3  mg.  of  alcohol,  in  thirty 
hours.  In  the  first  case  the  ratio  of  the  amount  of  carbon  dioxide  to  that  of 
alcohol  produced  is  100:  92.6,  and  in  the  second  case  the  corresponding  ratio 
is  100:  26.5.  It  should  be  added  here  that  alcohol  elimination  in  the  second 
instance  was  confined  to  the  first  few  hours  of  the  experiment,  before  the  limited 
amount  of  plastic  carbohydrates  that  was  present  had  been  exhausted.5 

1  Lechartier,  G.,  and  Bellamy,  F.,  Etude  sur  les  gaz  produits  par  les  fruits.  Compt.  rend.  Pans 
69:356-360.  1869.  Idem,  De  la  fermentation  des  fruits.  Ibid.  69 :  466-469.  1869.  Idem,  same  title. 
Ibid.  75:  1203-1206.  1872.  Pasteur,  Louis,  Paits  nouveaux  pour  servir  k  la  connaissance  de  la  theorie 
des  fermentations  proprement  dites.     Ibid.  75:  784-791.      1872. 

-  Godlewski,  E.,  and  Polzeniusz,  F.,  Ueber  Alkoholbildung  bei  der  intramolecularen  Athmung  hoherer 
Pflanzen.  (Vorlaufige  Mittheilung.)  [Title  also  in  Russian,  text  in  German.]  Bull.  Int.  Acad.  Sci. 
Cracovie  1897:  267-271.  1897.  Idem,  Ueber  die  intramoleculare  Athmung  von  in  Wasser  gebrachten 
Samen  und  liber  die  dabei  stattfindende  Alkoholbildung.  [Title  also  in  Russian  and  French,  text  in  Ger- 
man.] Ibid.  1901:  227-276.  1901.  Nabokich,  A.  J.,  Ueber  die  intramolekulare  Atmung  der  hoheren 
Pflanzen.  Ber.  Deutsch.  Bot.  Ges.  ax:  467-476.  1903.  Palladin,  W.,  and  Kostytschew,  S.,  Anaerobe 
Atmung,  Alkoholgarung  und  Acetonbildung  bei  den  Samenpflanzen.  Zciisch.  physiol.  Chem.  48:  214- 
239.  1906.  Idem,  Ueber  anaerobe  Atmung  der  Samenpflanzen  ohne  Alkoholbildung.  Ber.  Deutsch.  Bot. 
Ges.  25:  51-56.  1907.  Stoklasa,  Julius,  Ernest,  Adolf,  and  Chocensky,  Karl,  Ueber  die  glykolytischen 
Enzyme  im  Pflanzenorganismus.     Zeitsch.  physiol.  Chem.  50:  303-360.     1906-1907- 

sPfeffer,  W.,    Ueber  intramolekulare  Athmung.     Untersuch.     Bot.  Inst  Tubingen  1 :  636-685.      1881- 

1885. 

*  Palladin,  W.,  Sur  le  role  des  hydrates  de  carbone  dans  la  resistance  a  l'asphyxie  chez  les  plantes  supen- 
eures.     Rev.  g6n.  bot.  6:  201-209.      1894. 

5  Palladin  and  Kostytschew,  1906,  1907.     [See  note  3,  p.  215.] 


222  PHYSIOLOGY    OF    NUTRITITION 

According  to  Kostychev's1  experiments,  Psalliota  (Agaricus,  the  ordinary 
cultivated  mushroom)  forms  considerable  amounts  of  carbon  dioxide  but  no  trace 
of  alcohol,  when  grown  under  anaerobic  conditions.  This  mushroom  was  found 
to  contain  no  sugar  at  all.2  The  same  writer  found  that  Aspergillus  niger,s  grown 
anaerobically  in  a  medium  without  carbohydrates,  produces  much  carbon  dioxide. 
Whatever  may  be  the  decomposition  products  arising  in  this  case,  it  is  clear  that 
anaerobic  respiration  is  not  always  the  same  thing  as  alcoholic  fermentation. 
Although  it  was  long  supposed4  that  plants  containing  mannite  eliminate  not 
only  carbon  dioxide  but  also  molecular  hydrogen,  when  deprived  of  oxygen, 
Kostychev5  was  unable  to  detect  any  production  of  hydrogen  by  such  plants. 

When  plants  are  transferred  to  aerobic  conditions  after  a  prolonged  period 
without  oxygen,  an  accelerated  production  of  carbon  dioxide  is  sometimes  ob- 
served.6 This  may  be  explained  by  supposing  that  unoxidized  decomposition 
products  of  anaerobic  respiration  are  oxidized  as  soon  as  oxygen  becomes  again 
available. 

Both  lower  and  higher  plants  consume  more  nutritive  materials  during 
anaerobic  than  during  aerobic  respiration.  The  processes  of  oxidation  (respira- 
tion) are  thus  more  efficient  from  the  standpoint  of  the  organism  than  are  those 
of  reduction  (fermentation).7  Anaerobic  respiration,  like  aerobic,  is  influenced 
by  many  kinds  of  conditions,  some  of  which  accelerate  while  others  retard  the 
production  of  the  carbon  dioxide.8 

§9.  Respiration  Chromogens/ — Very  widespread  in  plants  are  a  group  of 
substances  called  by  Palladin9  respiration  chromogens.     To  obtain  them,  an 

1  Kostytschew,  S.,  Ueber  anaerobe  Athmung  ohne  Alkoholbildung.  Ber.  Deutsch.  Bot.  Ges.  25  :  188-191. 
1908.  Idem,  Zweite  Mitteilung  iiber  anaerobe  Atmung  ohne  Alkoholbildung.  Ibid.  26a  :  167-177. 
1908. 

2  Kostytschew,  S.,  Ein  eigentumlicher  Typus  der  Pflanzenatmung.  Zeitsch.  physiol.  Chem.  65:  350- 
382.     1910. 

3  Kostychev,  S.,  Untersuchungen  uber  die  anaerobe  Athmung  der  Pflanzen.  [Abstract  in  German, 
P-  155-162.     Text  in  Russian.]     Scripta  Botanica  Hort.  Univ.  Imp.  St.  Petersburg  25  :  1-162.      1907. 

*  Miintz,  A.,  Recherches  sur  les  fonctions  des  champignons.  Ann.  chim.  et  phys.  V,  3:  56-92.  1876. 
Luca,  Sebastiano  de,  Recherches  chimiques  tendant  a.  dfimonstrer  la  production  de  l'alcool  dans  les  feuilles, 
les  fleurs  et  les  fruits  de  certaines  plantes.     Ann.  sci.  nat.  Bot.  VI,  6:  286-302.      1878. 

6  Kostytschew,  S,.  Zur  Frage  iiber  die  Wasserstoffausscheidung  bei  der  Atmung  der  Samenpflanzen. 
Ber.  Deutsch.  Bot.  Ges.  24:  436-441.  1906.  Idem,  Zur  Frage  der  Wasserstoffbildung  bei  der  Atmung 
der  Pilze.     Ibid.  25:  178-188.     1907. 

•  Palladin,  W.,  Ueber  normale  und  intramolekulare  Atmung  der  einzelligen  Alge  Chlorothecium  sac- 
charophilum.     Centralbl.  Bakt.  //,  11:  146-153.     1904. 

'  Palladin,  V.  I.  [W.],  [Title  and  text  in  Russian.]  Bull.  Soc.  Imp.  Nat.  Moscow  62":  44-126.  1886. 
Palladin,  W.,  Bedeutung  des  Sauerstoffs  fur  die  Pflanzen.  (Extract  from  the  Russian  paper  just  cited.) 
Ibid.  627/:  127-133.     1886. 

8  Smirnoff,  1903-  [See  note  6,  p.  213.].  Kostytschew,  1902.  [See  note  3,  p.  87.]  Morkowin.  N., 
Ueber  den  Einfluss  der  Reizwirkungen  auf  die  intramolekulare  Atmung  der  Pflanzen.  Ber.  Deutsch. 
Bot.  Ges.  21:  72-80.     1903. 

»  Palladin,  V.  I.  [W.],  Sur  la  repartition  et  la  formation  des  chromogenes  respiratoires  dans  les  plantes. 
Russian.]  Bull.  Acad.  Imp.  Sci.  St. -Petersbourg  VI,  2  :  977-990.  1908.  [This  work  is  also  reported  in  the 
next  two  references.]  Palladin,  W.,  Die  Verbreitung  der  Atmungschromogene  bei  den  Pflanzen.  Ber. 
Deutsch.  Bot.  Ges.  26a:  378-389-  1908.  Idem,  Ueber  die  Bildung  der  Atmungschromogene  in  den 
Pflanzen.  Ibid.  26a:  389-394-  1908.  Palladin,  V.  I.  [W.],  Sur  le  prochromogenes  des  chromogenes 
respiratoires  des  plantes.  [Russian.]  Bull.  Acad.  Imp.  Sci.  St. -Petersbourg  VI,  3:  371-376.  1909. 
[This  is  also  reported  in  the  next  reference.]  Palladin,  W.,  Ueber  Prochromogene  der  Pflanzlichen  At- 
mungschromogene. Ber.  Deutsch.  Bot.  Ges.  27:  101-106.  1909.  Palladin,  V.  I.  [W.],  Contributions  a. 
la  physiologie  des  lipoides.  [Russian.]  Bull.  Acad.  Imp.  Sci.  St. -Petersbourg  VI,  4:  785-795.  1910. 
Palladin,  W.,  Synergin,  das  Prochromogen  des  Atmungsfermente  der  Weizenkeime.  Biochem.  Zeitsch. 
27:  442-449.      1910. 

*  Sections  0  and  10  are  translated  from  the  7th  Russian  edition;  they  differ  from  the  corre- 
sponding sections  (10  and  9)  of  the  German  edition.  —  Ed. 


FERMENTATION   AND   RESPIRATION  223 

extract  of  the  plant  tissue  is  prepared  with  boiling  water  and  filtered.  The 
addition  of  peroxidase  arid  hydrogen  peroxide  to  the  filtrate  thus  obtained 
produces  a  red  (rarely  lilac  or  violet)  color,  due  to  the  respiration  pigment  formed 
by  oxidation  of  the  chromogen,  and  this  rapidly  changes  with  further  oxidation, 
to  a  dark  violet  or  black. 

Respiration  chromogens  appear  to  exist  in  plant  tissues  mainly  in  the  form 
of  pro-chromogens,  which  may  be  glucosides.  To  obtain  the  pro-chromogen  of 
wheat  embryos,  the  material  is  first  extracted  with  alcohol  and  the  pro-chromo- 
gen is  precipitated  from  the  extract,  by  acetone.  It  is  soluble  in  water  and  is 
decomposed  by  emulsin,  with  the  production  of  the  chromogen.  The  latter  is 
oxidized  by  peroxidase,  without  hydrogen  peroxide,  into  the  red  respiration 
pigment.  The  experiments  of  Combes1  showed  that  the  transformation  of  the 
chromogen  into  the  pigment  is  accompanied  by  increased  respiratory  activity. 
An  alkaline  solution  of  chromogen  absorbs  oxygen  very  actively.2  Some  of 
the  natural  plant  dyes  are  obtained  by  the  complete  oxidation  of  chromogens.3 

The  chromogens  appear  to  belong  in  the  same  class  with  ortho-dioxy- 
benzene.4  Urushiol,  the  chromogen  of  Japanese  lacquer  (from  Rhus  vernicifera, 
etc.),  has  the  formula  C20H30O2  and  its  structure  is  that  of  o-dioxy-benzene  with 
a  large,  unsaturated  side-chain. 

By  forming  water,  the  respiration  chromogens  remove  the  hydrogen  pro- 
duced by  the  respiration  process.  If  the  pigment  be  represented  by  the  letter 
R,  this  reaction  is  shown  by  the  equation:  R  (pigment)  +  H2  (hydrogen)  = 
R-H2  (chromogen).  By  the  action  of  oxidase,  the  chromogen,  as  it  is  pro- 
duced, absorbs  oxygen  from  the  air  and  forms  water  and  the  pigment,  as  accord- 
ing to  the  equation:  R-H2  (chromogen)  +  O  (oxygen)  =  H20  (water)  + 
R  (pigment).  Thus  the  respiration  pigments  may  be  regarded  as  acceptors  of 
hydrogen  (see  page  207.) 

§10.  Respiratory  Enzymes.5 — Recent  studies  agree  in  indicating  that  plant 
respiration  is  the  summation  of  a  number  of  fermentation  or  enzymatic  proc- 
esses. If  plants  are  killed  without  destroying  their  enzymes,  the  production 
of  carbon  dioxide  and  the  absorption  of  oxygen  still  continue,  but  in  such  cases 
only  the  primary,  anaerobic  phase  of  the  process  (corresponding  to  alcoholic 
fermentation)  is  present.  In  some  kinds  of  plants  thus  killed,  in  spite  of  the 
fact  that  they  are  plentifully  supplied  with  peroxidase,  the  secondary,  direct- 

1  Combes,  Raoul,  Les  ^changes  gazeux  des  feuilles  pendant  la  formation  et  la  destruction  des  pigments 
anthocyaniques.  Rev.  g£n.  bot.  22:  177—212.      1010. 

2  Rupe,  Hans,  Die  Chemie  der  natiirlichen  Farbstoffe,  Braunschweig,  1900,  1909.  2  v.  [This  state- 
ment and  citation  are  omitted  in  the  7th  Russian  Edition. — Ed.] 

3  Palladin,  V.  I.  [W.],  and  Tolstaia,  Z.  N.,  Sur  l'absorption  de  l'oxygtae  par  les  chromogenes  respira- 
toires  des  plantes.  [Russian.]  Bull.  Acad.  Imp.  Sci.  St. -P6tersbourg  VI,  7:  93-108.  1913.  [Also  reported 
in  the  following  reference.]  Palladin,  W.,  and  Tolstaja,  Z.,  Ueber  die  Sauerstoffabsorption  durch  die 
Atmungschromogene  der  Pflanzen.     Biochem.  Zeitsch.  49:  381-397.      1913. 

*  Majima,  R.,  and  S.  Cho,  Ueber  einen  Hauptbestandteil  des  japanischen  Lackes.  (Vorlaufige  Mitteil- 
lung.)  Ber.  Deutsch.  Chem.  Ges.  407^:  4390-4393.  1907.  Majima,  Riko,  Ueber  den  Hauptbestandteil 
des  Japanlacks.  (I.  Mitteilung.)  Ueber  Urushiol  und  Urushiol-dimethylather.  Ibid.  42*:  1418-1423. 
1909.  Idem,  Ueber  den  Hauptbestandteil  des  Japanlacks.  (II.  Mitteilung.)  Die  Oxydation  des  Urushiol- 
dimethylathers  mit  Ozon.  (I.  Mitteilung.)  Ibid.  42m:  3664-3673.  1909.  Idem,  Ueber  den  Haupt- 
bestandteil des  Japanlacks.  (III.  Mitteilung.)  Die  katalytische  Reduktion  von  Urushiol.  Ibid.  457/: 
2727-2730.     1912. 

5  Palladin,  1909.     [See  note  3,  p.  204.] 


2  24  PHYSIOLOGY    OF    NUTRITION 

oxidation  phase  is  entirely  absent;  in  other  kinds  of  plants  direct  oxidation 
occurs,  but  quite  differently  from  its  occurrence  in  the  living  organism. 

In  an  atmosphere  free  from  oxygen  the  anaerobic  phase  of  aespiration,  in 
plants  killed  without  injury  to  the  enzymes,  is  accompanied  by  the  production 
of  both  carbon  dioxide  and  ethyl  alcohol,  but  in  most  plants  the  production  of 
alcohol  is  the  less  vigorous  of  the  two  processes.  Under  such  conditions  the 
formation  of  carbon  dioxide  ceases  after  a  time,  and  if  oxygen  is  then  admitted 
to  the  tissues  this  formation  may  begin  again  or  not,  according  to  the  kind  of 
plant  employed.  In  some  forms  (e.g.,  wheat  embryos)  no  further  production 
of  carbon  dioxide  takes  place.  In  other  forms  the  killed  plants  (with  their 
enzymes  still  intact)  give  off  carbon  dioxide  even  more  vigorously  in  the  presence 
of  oxygen  than  they  did  in  its  absence.  In  this  latter  case,  however,  the  carbon 
dioxide  produced  after  the  admission  of  oxygen  is  not  to  be  considered  as  the 
product  of  direct  oxidation.  For  example,  Palladin  and  Kostychev1  found  that 
germinating  peas,  killed  without  injury  to  the  enzymes,  developed  considerably 
larger  amounts  of  carbon  dioxide  when  air  was  admitted  than  they  had  done  in 
the  absence  of  oxygen.  Alcohol  formation  was  likewise  increased,  however,  so 
that  the  acceleration  of  carbon  dioxide  formation  cannot  be  regarded  as  the 
direct  result  of  oxidation.  In  such  cases  Ivanov2  supposes  that  the  oxygen  is 
supplied  by  the  activity  of  the  enzyme  zymase. 

Another  example  may  be  presented.  Etiolated  bean  leaves  that  had  been 
killed  by  freezing  were  deprived  of  oxygen  until  carbon  dioxide  ceased  to  be 
given  off,  after  which  air  was  admitted,  when  the  elimination  of  carbon  dioxide 
was  resumed  and  the  leaves  became  black,  as  a  result  of  the  oxidation  of  the 
chromogen.  Although  the  renewed  production  of  carbon  dioxide  was  not  here 
accompanied  by  alcohol  formation,  still  we  must  refrain  from  supposing  that  it 
was  the  direct  result  of  oxidation,  as  will  become  clear  from  the  following 
considerations. 

Anaerobic  decomposition  is  accompanied  not  only  by  the  evolution  of  carbon 
dioxide  but  also  by  the  production  of  hydrogen.  In  some  plants  this  hydrogen 
disappears  in  the  reduction  (to  form  alcohol)  of  intermediate  products  of  the 
decomposition,  but  in  most  plants  little  alcohol  is  formed.  In  the  latter  case 
the  hydrogen  must  unite  either  with  the  respiration  pigment  or  with  some  other 
hydrogen  acceptor,  and  when  all  acceptors  of  hydrogen  become  satisfied  (having 
taken  up  all  the  hydrogen  they  can)  there  should  be  no  further  decomposition 
(and,  consequently,  no  more  evolution  of  carbon  dioxide).  When  the  cells  are 
exposed  to  the  air  the  acceptors  of  hydrogen  oxidize  their  hydrogen  to  water, 
however,  and  thus  become  able  to  absorb  still  more  hydrogen.  Therefore, 
exposure  to  air  results  first  in  the  regeneration  of  the  hydrogen  acceptors,  which 
is  accompanied  by  a  renewal  of  hydrogen  absorption  and  a  consequent  renewal 
of  anaerobic  decomposition,  the  latter  being,  of  course,  accompanied  by  the 
giving-off  of  carbon  dioxide,  just  as  occurred  at  first.     It  is  thus  seen  how  this 

1  Palladin  and  Kostytschew,  1906.     [See  note  3,  p.  215.] 

-  Iwanoff,  Leonid,  Ueber  die  Sogenannte  Atmung  der  zerriebenen  Samen.  Ber.  Deutsch.  Bot.  Ges. 
29:  563-570.     191 1. 


FERMENTATION    AND    RESPIRATION  22$ 

carbon  dioxide  is  the  result  of  anaerobic  respiration  rather  than  of  oxidation 
by  free  oxygen  (compare  page  221).  When  oxygen  is  first  admitted  to  tissues 
in  which  the  hydrogen  acceptors  have  already  been  satisfied,  the  renewed 
evolution  of  carbon  dioxide  is  very  vigorous. 

As  has  been  stated  (pages  200,  208),  in  the  presence  of  methylene  blue 
and  a  catalyzer,  formic  acid  decomposes  into  carbon  dioxide  and  hydrogen,  so 
long  as  absence  of  oxygen  prevents  the  regeneration  of  the  methylene  blue  from 
the  leuco-compound  formed  from  the  dye  by  union  with  hydrogen;  HCOOH  + 
M  =  COo  +  M-H2,  where  M  represents  methylene  blue  and  M-H2  rep- 
resents the  leuco-compound.  Access  of  oxygen  allows  the  removal  of  the 
extra  hydrogen  from  the  leuco-compound  and  regenerates  the  methylene  blue 
(M-H2  +  O  =  M  +  H20),  thus  rendering  it  again  able  to  absorb  hydrogen. 
Consequently,  the  evolution  of  carbon  dioxide  begins  anew  and  it  appears, 
superficially,  as  though  this  were  the  result  of  the  oxidation  of  the  carbon  of  the 
formic  acid  by  atmospheric  oxygen.  Here  the  methylene  blue  behaves  as  an 
acceptor  of  hydrogen,  as  such  acceptors  are  supposed  to  act  in  plant  respiration. 

Bach  and  Batelli,1  and  also  Palladin,2  regard  all  the  carbon  dioxide  eliminated 
in  respiration  as  the  product  of  anaerobic  fermentation.  Palladin  thinks  water 
enters  into  this  decomposition  reaction;  thus,  C6Hi206  (glucose)  +  6  H20  = 
6  C02  +12  H2.  Since  much  hydrogen  should  result  from  this  sort  of  reaction 
and  since  hydrogen  is  never  actually  given  off  by  higher  plants,  it  follows  that 
the  differing  capacities  of  different  kinds  of  plants  for  the  anaerobic  evolution 
of  carbon  dioxide  depend  upon  the  various  powers  of  the  plants  to  carry  out 
reductions  that  result  in  alcohol,  and  upon  the  differing  amounts  of  hydrogen 
acceptors  present. 

In  living  plants,  the  hydrogen  produced  by  anaerobic  decompositions  is 
taken  up  by  the  respiration  pigments,  forming  the  corresponding  chromogens. 
From  these  it  is  subsequently  removed  and  oxidized  to  form  water,  through  the 
action  of  oxidase.  The  reactions  are  shown  by  the  two  following  equations, 
where  R  represents  the  pigment  and  R-H2  the  chromogen.  (1)  12  H2  + 
12  R  =  12  R-H2.  (2)  12  R-H2 +602=  12  H20+ 12  R.  It  thus  appears  that 
the  respiration  enzymes  are  water-producing  enzymes,  carrying  out  the  same 
reactions  in  the  living  plant  as  they  do  in  vitro.  Thus  oxidase  (or  peroxidase 
together  with  hydrogen  peroxide)  oxidizes  colorless  hydroquinone  (chromogen) 
to  form  red  quinone  (pigment)  and  water,  according  to  the  equation: 

Hydroquinone  Quinone 

C6H602  +  O  =  C6H402  +  H20. 

In  plants  that  have  been  killed  without  destroying  their  enzymes  the  con- 
trols that  govern  the  various  activities  during  life  are  greatly  disturbed,  and  the 
respiration  pigments  in  such  tissues  remove  not  only  the  hydrogen  that  thev 
normally  take  up  (this  being  then  oxidized  to  form  water),  but  also  the  hydrogen 
simultaneously  being  produced  by,  and  taking  part  in,  the  anaerobic  processes. 
Consequently,  such  killed  tissues  that  are  rich  in  chromogens  give  off  more 

1  Bach,  A.,  and  Battelli,  F.,  Degradation  des  hydrates  de  carbone  dans  l'organisme  animal.      Compt. 
rend.     Paris  136:  1351-1353.     1903. 

-  Palladin,  1912  (i,  2  ).     [See  note  3,  p.  207.] 
15 


2  26  PHYSIOLOGY    OF    NUTRITION 

carbon  dioxide  in  the  air  when  they  have  been  previously  kept  for  a  time  in 
an  atmosphere  free  from  oxygen.  This  fact  has  been  mentioned  before,  but  the 
following  example  will  make  it  clearer. 

Of  two  portions  of  frozen,  etiolated  bean  leaves,  one  portion  was  exposed 
to  the  air  for  sixty-three  hours  and  the  other  was  first  exposed  for  twenty-three 
hours  to  an  atmosphere  of  hydrogen,  and  then  to  the  air  for  forty  hours.  The 
first  portion  (in  air  for  sixty-three  hours)  gave  off  286  mg.  of  carbon  dioxide. 
The  second  portion  gave  off  183  mg.  of  carbon  dioxide  during  its  twenty-three 
hours  in  hydrogen  and  245  mg.  during  the  succeeding  forty  hours  in  air,  or  428 
mg.  during  the  entire  sixty-three  hours.  During  the  whole  period  the  second 
portion  gave  off  50  per  cent,  more  carbon  dioxide  than  did  the  other.  In  the 
first  portion  (in  air  all  the  time)  the  respiration  pigments  removed  a  part  of  the 
active  hydrogen  produced  by  the  first  stage  of  anaerobic  respiration,  and  there- 
fore exerted  the  same  retarding  influence  upon  the  process  as  was  evident  in 
the  experiments  of  Palladin  and  Lvov  (see  page  207),  in  which  the  chromogen 
of  the  beet  or  methylene  blue  retarded  alcoholic  fermentation.  In  considering 
plant  respiration  it  is  thus  necessary  to  distinguish  between  the  hydrogen  that 
is  normally  taken  up  by  the  hydrogen  acceptor  and  is  then  oxidized  to  form 
water,  and  the  other,  more  active,  hydrogen  that  is  simultaneously  being  pro- 
duced by  the  anaerobic  reactions  under  the  influence  of  reductase,  as  in  the 
formation  of  alcohol  by  reduction.  This  latter  hydrogen  is  necessary  for  the 
continuation  of  the  anaerobic  process. 

As  has  been  stated  previously  (pages  213),  the  respiration  process  is  accel- 
erated by  wounding.  Krasnosselskaia1  has  shown  that  this  acceleration  is  con- 
comitant with  an  increase  in  the  amount  of  anaerobic  enzymes  (such  as  zymase, 
perhaps)  and  also  with  an  increase  in  the  amount  of  peroxidase  present  in  the 
tissues.  Four  equal  portions  of  leek  bulbs  that  had  been  wounded  and  allowed 
to  remain  alive  for  one,  four,  seven  and  fifteen  days,  respectively,  were  finally 
frozen  and  treated  with  pyrogallol  and  hydrogen  peroxide.  The  four  portions 
produced  25.2,  74.8,  149.6,  and  200.4  mg-  or  carbon  dioxide,  respectively,  which 
indicates  the  progressive  increase  in  the  amount  of  respiration  enzymes  in  the 
wounded  bulbs. 

Poisons  also  accelerate  plant  respiration  (see  page  213),  but  without  increas- 
ing the  respiration  enzymes.2  Two  similar  lots  of  etiolated  stems  of  Viciafaba 
were  kept  in  darkness  for  some  time,  with  their  cut  ends  in  sugar  solution.  One 
lot  was  then  treated  with  quinin,  and  produced  21.4  mg.  of  carbon  dioxide  in 
two  hours,  while  the  lot  without  the  alkaloid  formed  only  n  3  mg.  Both  lots 
were  then  killed  by  freezing.  After  thawing,  the  one  with  quinin  produced  37.2 
mg.  of  cabon  dioxide  in  twenty-five  hours,  while  the  other  formed  37.6  mg.  A 
very'marked  acceleration  in  the  evolution  of  carbon  dioxide  is  seen  to  have  been 

1  Krasnosselsky,  T.,  BiHung  der  Atmungsenzyme  in  verletzten  Pflanzen.  Ber.  Deutsch.  Bot.  Ges. 
23:142-155.  1905.  Idem,  Bildung  der  Atmungsenzyme  in  verletzten  Zwiebeln  von  Allium  cepa.  Ibid. 
24:  134-141.      1906. 

-  Palladin,  V.  I.  [W.],  Respiration  des  plantes  comme  somme  des  proces  de  fermentation.  [Russian. 
Mem.  Acad.  Imp.  Sci.  St.-Petersbourg  VIII,  205:  1-64.  1907.  Idem,  sur  Taction  des  poisons  sur  la  respira- 
tion des  plantes.  [Russian.]  Bull.  Acad.  Imp.  Sci.  St.-Petersbourg  VI,  4:  401-421-  tgio.  [This  is  also 
reported  in  the  reference  given  in  note  3.  p.  213.] 


FERMENTATION   AND    RESPIRATION  2  27 

produced  by  quinin  treatment  when  the  tissues  were  still  alive,  but  the  alkaloid 
exerted  no  accelerating  influence  in  the  case  of  the  frozen  and  thawed  tissues, 
which  were  dead  but  still  contained  their  enzymes. 

Respiration  in  living  plants  is  thus  accelerated,  not  only  by  certain  sub- 
stances that  are  necessary  for  life  (such  as  co-enzymes),  but  also  by  unnecessary 
and  generally  injurious  substances  (poisons,  in  the  usual  sense).  Both  kinds  of 
substances  produce  the  same  result,  namely  an  acceleration  of  respiratory  acti- 
vity, but  the  chemical  responses  within  the  cells  are  quite  different  in  the  two 
cases.  In  one  case  we  have  to  do  with  phenomena  of  nutrition  and  in  the  other 
case  with  those  of  poisoning.  In  living  plants  this  difference  is  not  apparent, 
but  Ivanov1  has  clearly  demonstrated  it  with  plants  that  were  killed  without 
destroying  their  enzymes.  Phosphates,  which  belong  to  the  class  of  necessary 
accelerators,  produce  a  marked  influence,  both  upon  living  plants  and  upon  those 
that  have  been  killed  but  that  still  retain  their  enzymes. 

§11.  Materials  Consumed  in  Respiration.— Notwithstanding  the  fact  that 
respiration  in  plants  is  accompanied  by  a  decrease  in  carbohydrates  and  fats, 
which  are  non-nitrogenous,  it  was  generally  supposed  until  quite  recently  that 
such  nitrogen-free  compounds  were  not  directly  consumed  in  this  process  and 
that  atmospheric  oxygen  acted  directly  to  oxidize  only  proteins.  The  nitro- 
genous residues  left  as  products  of  protein  decomposition  were  supposed  to 
combine  with  carbohydrates,  .thus  regenerating  the  proteins.  According  to 
this  conception,  as  long  as  the  supply  of  reserve  carbohydrates  is  not  exhausted 
the  amount  of  protein  material  in  the  organism  remains  unchanged,  while,  the 
non-nitrogenous  reserve  gradually  diminishes;  but  as  soon  as  the  reserve  of 
carbohydrates  has  been  exhausted  then  decomposition  of  proteins  becomes 
apparent  and  the  nitrogenous  products  of  this  decomposition  begin  to  accumu- 
late. Evidence  in  favor  of  the  idea  that  protein  is  directly  oxidized  in  respira- 
tion was  found  in  the  fact  that  the  respiration  process  is  especially  active  in 
young,  growing  tissues,  rich  in  protein.  This  conception  has  proved  to  be  un- 
tenable, however. 

The  protein  of  the  organism  does  not  remain  constant  in  amount  as  long  as 
carbohydrates  are  available;  in  the  germination  of  seeds,  for  example,  the  de- 
composition of  proteins  proceeds  most  rapidly  in  the  earliest  stages  of  germina- 
tion, when  the  seeds  are  still  very  rich  in  carbohydrates.  With  decreasing  car- 
bohydrate content  protein  decomposition  becomes  less  vigorous  and  finally 
may  even  cease  altogether.  To  give  an  illustration  of  this,  100  g.  of  wheat  seeds 
contained  0.0668  g.  of  protein  nitrogen,  and  etiolated  seedlings  six  days  old,  from 
a  similar  lot  of  seeds,  contained  only  0.0554  g.,  so  that  0.0114  g.  of  protein  nitro- 
gen had  been  lost  during  germination.  When  the  seedlings  were  fourteen  days 
old  their  content  in  protein  nitrogen  was  0.0549  g.,  so  that  only  0.0005  g-  had 
been  lost  during  the  last  eight  days.  The  progress  of  protein  decomposition 
in  dark-grown  wheat  seedlings  has  been  graphically  shown  in  Fig.  88. 

Carbohydrates  are  necessary  for  aerobic  respiration,  even  in  the  presence  of 

1  Ivanov  N.  N.,  Action  des  agents  stimulants  utiles  et  nuisibles  sur  la  respiration  des  plantes.     [Russian 
Bull.  Acad.  Imp.  Sc.  St.-Petersbourg    VI,  4:  571-581.      .oro.     This  is  also  reported  in  the  second  refer^ 
ence  given  in  note  1,  p.  214.] 


228  PHYSIOLOGY    OF    NUTRITION 

an  excess  of  proteins.  Etiolated  bean  leaves,  which  are  rich  in  protein  but  con- 
tain only  a  little  carbohydrate,  produce  carbon  dioxide  at  an  exceedingly  low  rate ; 
Palladin1  found  that  ioo  g.  of  such  leaves,  at  room  temperature,  gave  off  carbon 
dioxide  for  three  successive  hours  at  the  rates  of  102.8,  95.9,  and  70.2  mg., 
respectively,  with  an  average  rate  of  89.6  mg.  per  hour.  The  same  leaves  were 
floated  upon  cane-sugar  solution  in  darkness  for  two  days,  by  which  treatment 
their  carbohydrate  content  was  markedly  increased  without  serious  alteration 
of  their  protein  content,  and  they  then  gave  off  carbon  dioxide  for  four  succes- 
sive hours  at  the  rates  of  152.6,  147.5,  146.8,  and  144.5  mg->  respectively,  with 
an  average  rate  of  147.8  mg.  per  hour. 

If  etiolated  bean  leaves  are  kept  upon  cane-sugar  solution  longer  than  two 
days  their  carbohydrate  content  continues  to  increase,  but  this  further  increase 
in  carbohydrates  is  without  influence  upon  the  rate  of  elimination  of  carbon 
dioxide.  After  forty  hours  upon  cane-sugar  solution  100  g.  of  these  leaves  pro- 
duced 144.5  mg-  0I  carbon  dioxide  in  one  hour.  After  forty-two  hours  longer 
upon  the  sugar  solution  they  gave  off  144. 1  mg.  of  carbon  dioxide  in  an  hour. 
The  longer  period  upon  sugar  solution,  although  resulting  in  higher  carbohy- 
drate content,  did  not  produce  any  alteration  in  the  respiration  rate;  the 
protein  content  of  the  leaves  remained  unchanged  and  the  supply  of  carbohy- 
drates was  adequate  in  both  cases.  This  experiment  shows  that  there  exists 
no  constant  relation  between  the  rate  of  evolution  of  carbon  dioxide  and  the 
supply  of  carbohydrates.  During  the  shorter  period  upon  sugar  solution 
these  leaves  had  absorbed  enough  sugar  so  that  the  sugar  content  of  the  tissues 
was  adequate  for  the  maximum  respiration  rate  with  the  given  amount  of 
proteins,  and  still  further  addition  of  sugar  was  without  influence  upon  the 
rate  of  elimination  of  carbon  dioxide. 

An  excess  of  carbohydrates  is  to  the  living  cell  what  a  coal  supply  is  to  a 
manufacturing  establishment;  as  long  as  there  is  sufficient  coal  on  hand  to  oper- 
ate the  machinery  at  maximum  speed,  the  amount  of  the  coal  supply  determines 
only  how  long  the  factory  can  be  kept  in  operation,  and  is  without  influence  upon 
the  daily  rate  of  production.  The  daily  output  from  such  an  establishment,  so 
long  as  enough  coal  is  available  to  operate  the  machines  at  their  maximum  speed, 
is  dependent  only  upon  the  capacity  of  the  machines  themselves.  Similarly, 
only  the  duration  of  the  respiration  process  in  a  cell  is  dependent  upon  the  supply 
of  carbohydrates  present,  providing  only  that  the  supply  is  adequate  for  the 
maximum  rate,  and  this  maximum  rate  depends  upon  the  capacity  of  the  living 
protoplasm  to  carry  on  the  respiratory  process.  Other  conditions  remaining 
the  same,  this  capacity  depends  upon  the  amount  of  protoplasm  present  in  the 
cell.  Regarding  the  cell  as  a  factory,  carbohydrates  are  the  coal  and  the  proto- 
plasm is  the  machinery.  Only  upon  the  amount  of  protoplasm  present  does  the 
rate  of  the  life-processes  thus  depend,  assuming  the  supply  of  carbohydrates, 
water,  etc.,  to  be  adequate  and  the  temperature,  etc.,  to  be  optimum. 

Carbohydrates  are  not  directly  acted  upon  by  the  protoplasm,  but  their  de- 

1  Palladin,  W.,  Recherches  sur  la  respiration  des  feuilles  vertes  et  des  feuilles  6tiolees.     Rev.  gen.  bot. 
5:  449-473.      1893- 


FERMENTATION    AND    RESPIRATION  229 

composition  is  brought  about  by  the  action  of  specific  enzymes,  the  amount  of 
which  depends  upon  the  amount  of  protoplasm  present.  As  has  been  noted 
(page  157),  not  all  proteins  are  to  be  regarded  as  constituents  of  the  living  pro- 
toplasm; the  plant  cell  contains  larger  or  smaller  amounts  of  non-protoplasmic 
proteins,  and  the  question  arises  whether  the  respiration  rate  is  a  function  of  the 
total  protein  content  or  of  the  protoplasmic  proteins  only.  During  germination 
in  darkness  the  total  protein  content  is  lowered  while  the  rate  of  carbon  dioxide 
production  gradually  rises  (see  pages  180,  227),  so  that  seedlings  with  little 
protein,  in  the  later  stages  of  germination,  respire  more  vigorously  than  do  seed- 
lings with  more  protein,  in  earlier  stages.  During  this  process  of  germination  in 
darkness,  however,  it  is  only  the  non-protoplasmic  or  reserve  proteins  that  de- 
crease; the  proteins  that  are  indigestible  in  gastric  juice,  which  are  just  the 
ones  that  are  to  be  considered  as  part  of  the  protoplasm,  increase  during  germ- 
ination (see  Fig.  88,  p.  181).  Palladin1  carried  out  parallel  series  of  deter- 
minations of  the  amounts  of  carbon  dioxide  given  off  by,  and  of  indigestible 
proteins'  present  in,  wheat  seedlings  during  germination  in  darkness.  These 
determinations  showed  that,  in  the  intermediate  stages  of  germination,  with 
adequate  supply  of  carbohydrates,  the  rate  of  elimination  of  carbon  dioxide 
is  proportional  to  the  amount  of  indigestible  protein  present  in  the  plantlet.2 
In  later  stages  of  germination,  as  has  been  said,  the  respiration  rate  decreases, 
on  account  of  the  diminishing  supply  of  carbohydrates,  but  the  indigestible 
proteins  still  continue  to  increase  in  amount. 

With  the  same  temperature  and  with  adequate  carbohydrate  supply,  equal 
amounts  of  carbon  dioxide  are  produced  per  unit  of  time,  for  a  given  amount  of 
indigestible  proteins.  In  the  case  of  wheat  germinating  at  a  temperature  of 
from  20  to  2i°C,  the  ratio  of  the  hourly  rate  of  carbon  dioxide  production  to  the 

amount  of  nitrogen  in  the  indigestible  proteins  of  the  seedling  (       "I  had  the 

following  values,  at  successive  stages  of  germination;  seedlings  four  days  old, 
1.06;  six  days  old,  10.5;  seven  days  old,  1.18;  nine  days  old,  1.15.  It  thus  ap- 
pears that,  with  a  plentiful  supply  of  carbohydrates,  the  respiratory  rate  depends 
upon  the  amount  of  nuclein  materials  (taken  to  be  proportional  to  the  amount  of 
proteins  indigestible  in  gastric  juice)  that  are  present  in  the  seedling. 

This  conclusion  is  also  supported  by  the  observation  of  Burlakov,3  that  em- 
bryos respire  much  more  actively  in  proportion  to  their  weight  than  do  entire 
seeds.  One  hundred  grams  of  wheat  seeds,  after  soaking  in  water  forty-eight 
hours,  gave  off  carbon  dioxide  at  the  rate  of  15.2  mg.  per  hour,  at  a  temperature 
of  from  20  to  2  2°C.  The  same  weight  of  separate  embryos,  after  soaking 
twenty-four  hours,  produced  241.8  mg.  per  hour.     The  respiration  of  the  em- 

1  Palladin,  1896.     [See  note  6,  p.  180.] 

:  Although  the  amount  of  living  protoplasm  in  the  plant  may  thus  be  approximated  in  terms  of  the 
amount  of  indigestible  protein,  the  method  is  confessedly  not  precise,  as  more  recent  studies  show.  It 
was  the  best  available  for  these  experiments,  however. 

3  Burlakov,  G.  G.,  Sur  la  question  de  la  respiration  du  germe  de  froment.  [Russian.]  Trav.  Soc.  Imp. 
Nat.  Univ.  Kharkov  31:    V-XV.     1897.     [Pagination  in  Roman  numerals.] 

'  The  term  indigestible,  as  used  in  the  text,  refers  to  those  proteins  that  are  found  to  be 
undigested  by  gastric  juice. — Ed. 


230  PHYSIOLOGY   OF   NUTRITION 

bryos,  which  were  much  richer  in  nuclein  substances,  was  thus  seventeen  times 
as  vigorous  as  that  of  the  entire  seeds. 

Respiration  in  seed-plants  occurs,  in  general,  by  the  destruction  of  carbohy- 
drates. Its  dependence  upon  proteins  is  due  (1)  to  the  fact  that  carbohydrates 
may  be  formed,  under  certain  conditions,  from  proteins,  and  (2)  to  the  fact  that 
respiratory  enzymes  are  formed  by  the  protoplasm;  on  the  amount  of  protoplasm 
depends  the  amount  of  these  enzymes,  and,  consequently,  the  rate  of  respiratory 
activity. 

§12.  Special  Cases  of  Respiration  in  Lower  Plants. — In  many  lower  forms 
of  plant  life  carbohydrates  are  not  the  substances  that  are  decomposed  in  respira- 
tion. Among  these  forms  occur  not  only  various  types  of  fermentation,  as  has 
been  pointed  out,  but  also  various  types  of  aerobic  respiration.  The  respiration 
process  in  acetic-acid  bacteria,  for  example,  is  just  an  oxidation  of  ethyl  alcohol 
to  acetic  acid,  according  to  the  following  equation: 

Ethyl   Alcohol  Oxygen  Acetic   Acid  Water 

CH3CH2OH  +  02  =  CHaCOOH  +  H20. 
This  process  is  really  not  a  fermentation  at  all,  in  the  restricted  sense  of  this 
term;  it  is  to  be  regarded  as  a  special  kind  of  aerobic  respiration.  The  true  fer- 
mentations (anaerobic  respiration)  are  characterized  by  the  decomposition  of 
complex  compounds  into  simpler  ones,  while  oxidations  are  characteristic  of 
aerobic  respiration.  As  long  as  alcohol  is  present,  the  end  product  of  the  respira- 
tion of  these  organisms  is  acetic  acid,  but  as  soon  as  the  supply  of  alcohol  has 
been  completely  consumed  they  begin  to  oxidize  acetic  acid  into  carbon  dioxide 
and  water. 

Pasteur  was  the  first  to  recognize  acetic  acid  fermentation  as  a  vital  process, 
and  he  thought  that  the  bacteria  controlling  it  were  of  the  single  species,  My- 
coderma  aceti.  Hansen1  showed  later  that  the  bacterial  membranes  (mother) 
arising  during  this  process  consist  mainly  of  three  different  species  of  bacteria, 
Bacterium  aceti,  Bacterium  pasteurianum  and  Bacterium  kuetzingianum.  These 
three  forms  are  briefly  described  below. 

Bacterium  aceti,  when  grown  on  beer  at  room  temperature,  forms  (in  twenty- 
four  hours)  a  smooth  slimy  skin,  which  consists  of  chains  of  rod-like  cells  (Fig.  94) . 
These  cells  are  colored  yellow  by  iodine.  With  a  temperature  of  from  40  to 
45°C.  the  rod-like  cells  form  long,  thin  filaments. 

Bacterium  pasteurianum,  grown  on  beer,  forms  a  dry  superficial  skin,  which 
is  usually  wrinkled.  This  consists  also  of  chains  of  rod-like  cells  (Fig.  95) ,  but  the 
latter  are  larger  than  in  the  form  just  described.  The  slimy  layer  surrounding 
the  cells  of  a  newly-formed  skin  is  colored  blue  by  iodine. 

Bacterium  kuetzingianum  forms,  on  beer  at  34°C,  a  dry  surface  skin  which 
grows  upward  at  the  edges,  on  the  walls  of  the  culture-vessel.  The  skin  con- 
sists of  rod-like  cells  but  these  do  not  occur  in  rows  or  chains  but  are  generally 
single  or  joined  in  pairs.  The  slime  about  the  cells  is  colored  blue  by  iodine,  as 
in  the  last  form. 

1  Hansen,  Emil  Christian,  Rechcrches  sur  les  bacteries  acetifiantes.      Compt.  rend.  trav.  Lab.  Carlsberg, 
Kjobenhavn  3'":  182-216.      1894.     (Rev.  by  Fr.  Lahar  in  Bot.  Zeitg.  52":  337-342.      1894-! 


FERMENTATION    AND    RESPIRATION 


23T 


Besides  the  three  bacteria  just  described  other  bacteria  are  also  employed  in 
the  manufacture  of  vinegar.     Bacterium  xylinum  is  commonly  used  in  England. 

The  oxidation  of  alcohol  to  acetic  acid  is  carried  on  in  the  cells  of  these 
bacteria  by  a  specific  intracellular  enzyme.  Buchner  and  Gaunt1  obtained 
acetone  preparations  of  acetic  acid  bacteria,  which,  like  Buchner's  "zymin" 
(see  page  167),  possessed  keeping  qualities,  and  had  the  power  causing  the  oxi- 
dation of  alcohol  to  acetic  acid. 

Another  special  kind  of  aerobic  respiration,  similar  to  that  of  the  acetic  acid 
bacteria  just  considered,  is  that  of  the  sorbose  bacteria,2  which  merely  oxidize 
sorbite  to  sorbose.     The  following  equation  represents  the  reaction: 

Sorbite  Oxygen  Sorbose  Water 

2  CeHuOe    +      02      =  2  C6H1206  +  2  H20. 

Still  other  alcohols  are  oxidized  by  microorganisms,  producing  the  correspond- 
ing aldehydes  and  ketones.     Such  a  physiological  oxidation  process  furnishes 


0>*Q*>, 


Fig.  94. — Bacterium  accti,  skin 
formed  at  the  surface  of  beer. 
(Highly  magnified.) 


Fig.  95. — Bacterium  pasleurianum,  cells 
from  skin  formed  at  the  surface  of  beer. 
(Highly  magnified.) 


the  best  method  for  obtaining  dihydroxyacetone  from  glycerine,  the  reaction 
being  as  represented  below. 


Glycerine 


Oxygen 


Dihydroxyacetone 


Water 


2  CH0OH-CHOH-CH0OH  +  02  =  2  CH2OH-CO-CH2OH  +  2  H20. 

The  nutrition  of  bacteria  by  mineral  substances,  which  has  been  previously- 
considered  (see  page  47),  also  really  represents  special  cases  of  aerobic  respira- 
tion. One  form  of  bacteria  oxidizes  hydrogen  sulphide,  another  oxidizes  am- 
monia, a  third  oxidizes  hydrogen,  etc.  The  cosmic  importance  of  these  special 
tvpes  of  physiological  oxidation  is  very  great,  for  it  is  through  these  processes 
that  the  natural  circulation  of  sulphur,  nitrogen,  and  hydrogen  is  largely  brought 
about.  The  total  amounts  of  the  various  chemical  elements  available  for  life- 
processes  upon  our  planet  remain  practically  constant,  but  the  various  com- 
pounds are  always  decomposing  and  being  reformed,  so  that  the  elements  are 
forever  in  a  state  of  circulation,  and  bacteria  play  a  very  important  role  in  this 
great  process. 

1  Buchner,  Eduard,  and  Gaunt,  Rufus,  Ueber  die  Essiggahrung.  Liebig's  Ann.  Chem.  u.  Pharm. 
349:  140-184.      1906. 

-  Bertrand,  G.,  Etude  biochimique  de  la  bacterie  du  sorbose.  Ann.  chim.  et  phys.  VIII,  3:  181-288. 
1904. 


232  PHYSIOLOGY    OF    NUTRITION 

§13.  Circulation  of  Energy  in  Nature. — The  circulation  of  energy  is  quite 
different  from  that  of  matter.  The  available  supply  of  energy  upon  the  earth 
is  inadequate  for  a  long  continuation  of  plant  and  animal  life,  which  would  soon 
cease  were  it  not  for  the  continuous  influx  of  energy  from  the  sun.  From  the  law 
of  the  conservation  of  energy  it  is  clear  that  the  solar  energy  stored  up  in  poten- 
tial form  by  the  photosynthetic  process  in  green  plants  must  be  completely 
liberated  by  the  reverse  process  (the  formation  of  carbon  dioxide  and  water), 
as  this  occurs  in  combustion  or  in  plant  and  animal  respiration.  The  carbon 
dioxide  thus  produced  can,  of  course,  enter  again  into  organic  compounds, 
but  that  portion  of  the  energy  liberated  by  respiration  and  fermentation  that 
takes  the  form  of  heat  is  almost  entirely  lost  from  the  organism  and  does  not 
again  become  available  for  organic  synthesis;  it  becomes  dissipated  into  space 
and  is  gone  forever  from  the  earth.  Thus  vital  activity  upon  our  planet  is 
directly  dependent  upon  the  sun,  from  which  new  supplies  of  energy  must 
continually  come  if  life  is  to  be  long  continued. 

This  process  of  energy  dissipation  may  be  illustrated  somewhat  as  follows. 
If  a  small  beaker  of  hot  water  is  poured  into  a  large  tank  of  cold  water,  the  cold 
water  is  warmed  but  little;  supposing  the  original  temperatures  to  be  950  and  50, 
respectively,  the  temperature  of  the  tank  may  perhaps  rise  to  6°  when  the  hot 
water  is  added.  At  first  the  heat  energy  is  concentrated,  or  intensive,  in  the 
beaker;  later  it  is  dissipated,  or  extensive,  in  the  tank.  The  coefficient  of 
energy  dissipation,  that  fraction  of  the  original  energy  that  can  no  more  be  con- 
verted into  mechanical  work,  is  termed  entropy,  and  entropy  always  tends 
toward  a  maximum.  In  this  process  of  the  dissipation  of  the  intensive  energy 
of  our  solar  system,  plants  play  a  direct  role. 

Summary 

1.  General  Discussion  of  Fermentation  and  Respiration. — All  changes  and  move- 
ments of  materials  involve  changes  with  respect  to  energy,  and  the  material  trans- 
formations and  movements  that  occur  within  the  living  plant  are  not  exceptions  to  this 
principle.  Some  of  the  processes  of  living  tissues  result  in  the  setting  free  of  energy, 
while  others  of  these  processes  result  in  energy  fixation  or  accumulation.  The 
photosynthesis  of  carbohydrates  from  carbon  dioxide  and  water,  in  chlorophyll-bearing 
tissue,  results  in  the  transformation  of  radiant  energy  (sunlight)  into  the  stored  potential 
energy  of  the  combustible  compounds  that  are  formed;  this  is  therefore  an  energy- 
fixation  process,  and  the  fixed  energy  remains  in  the  plant.  Transpiration  is  a 
process  by  which  kinetic  energy  (light,  heat)  is  transformed  into  the  potential  form,  as 
the  latent  heat  of  water  vapor;  it  is  an  energy-fixation  process,  but  the  fixed  energy 
leaves  the  plant.  Whenever  a  carbohydrate  is  oxidized  in  the  living  tissue,  energy  is 
set  free,  just  as  when  wood  is  burned.  Some  of  the  energy  resulting  from  this  oxida- 
tion escapes  from  the  plant,  but  much  of  it  is  consumed  in  other  chemical  processes 
and  is  retained  for  a  longer  or  shorter  period.  Most  of  the  chemical  transformations 
that  occur  in  the  living  protoplasm  take  place  because  of,  and  at  the  expense  of,  energy 
that  is  set  free  by  oxidations.  The  processes  that  set  energy  free  in  this  way,  in  the 
living  organism,  are  grouped  together  as  the  process  of  respiration. 

It  appears  that  the  oxygen  consumed  in  the  primary  steps  of  respiration  is  generally 
not  free  oxygen  (02) ;  it  is  derived  from  compounds  that  contain  other  elements  (especi- 


FERMENTATION   AND    RESPIRATION  233 

ally  carbon  and  hydrogen)  as  well  as  oxygen.  The  oxygen  of  one  part  of  a  complex 
molecule  may  oxidize  even  another  part  of  the  same  molecule.  These  primary  steps 
of  respiration  are  called  intramolecular  respiration,  anaerobic  respiration,  or  fermenta- 
tion. They  proceed  under  the  influence  of  fermentation  enzymes  and  they  result  in 
incomplete  oxidation,  some  or  all  of  the  new  substances  produced  being  only  partially 
oxidized;  but  considerable  amounts  of  energy  are  set  free  by  these  fermentation 
processes.  The  partially  oxidized  substances  thus  formed  may  accumulate  in,  and 
escape  from,  the  organism  without  further  alteration,  or  their  oxidation  may  be 
completed  by  the  action  of  oxidizing  enzymes  in  the  presence  of  an  adequate  supply  of 
free  oxygen,  the  ultimate  products  being  then  all  completely  oxidized.  In  the  pres- 
ence of  free  oxygen,  the  products  of  the  primary  fermentation  processes  may  be 
different,  or  complete  oxidation  may  occur  before  they  are  formed.  The  final  steps  of 
the  respiration  process  are  called  normal  respiration  or  aerobic  respiration.  In  aerobic 
respiration,  free  oxygen  is  absorbed,  and  completely  oxidized  substances  are  produced, 
with  the  setting  free  of  much  more  energy  than  was  previously  made  available  by  the 
anaerobic  processes.  Intramolecular  or  anaerobic  respiration,  or  fermentation,  occurs 
in  every  living  cell;  but  there  are  many  kinds  of  cells  in  which  aerobic  respiration  does 
not  occur,  either  because  the  cells  lack  the  necessary  oxidizing  enzymes  or  else  because 
free  oxygen  is  not  supplied.  Some  microorganisms  are  unable  to  live  at  all  in  the 
presence  of  free  oxygen  (obligate  anaerobes),  and  their  respiration  is  consequently 
limited  to  the  primary  fermentation  processes;  these  forms  give  off  products,  some  or 
all  of  which  are  incompletely  oxidized.  Organisms  that  thrive  in  the  presence  of  free 
oxygen  may  give  off  some  incompletely  oxidized  substances  even  with  a  good  supply  of 
oxygen — as  if  these  substances  diffused  out  of  the  cells  before  the  completion  of 
oxidation.  With  an  inadequate  supply  of  oxygen,  fermentation  products  generally 
become  conspicuous,  as  in  the  roots  of  ordinary  plants  in  poorly  aerated  soil  (see 
Chapter  V,  Section  5). 

The  chemistry  of  respiration  may  be  pictured  superficially  by  means  of  the  follow- 
ing equations,  which  are  to  be  considered  simply  as  illustrations  of  the  kinds  of  proc- 
esses that  are  apparently  involved. 
I.  Fermentation  or  anaerobic  processes: — 

1.  Oxygen  from  the  same  molecule. 

Glucose  Sugar  Ethyl  Alcohol  Carbon  Dioxide 

C6H1206      =     2  C2H5OH  +  2  CO>  . 

(oxidation  (oxidation 

incomplete)  complete) 

2.  Oxygen  from  another  compound. 

Glucose  Sugar  Water  Hydrogen  Carbon  Dioxide 

C6Hi:;Oe       -f-6H20=      12  H2      +  6  CO2 

(oxidation  (oxidation 

incomplete)  complete) 

II.  Aerobic  processes  (with  free  oxygen): — ■ 

Glucose  Sugar  Oxygen  Water  Carbon  Dioxide 

i.  C6H1206      +     6O2    =  6H20  +         6CO2 

Ethyl  Alcohol  Oxygen  Water         Carbon  Dioxide 

2.  C2H5OH      +     3O2    =3H20+  2C02 

Hydrogen  Oxygen         Water 

3.  2H2       +      02      =  2H20 

When  a  certain  amount  of  any  substance  is  transformed  by  fermentation,  the 
quantity  of  energy  set  free  is  much  less  than  when  aerobic  respiration  occurs  and 


234  PHYSIOLOGY    OF    NUTRITION 

oxidation  is  complete.  The  fermentation  of  a  gram-molecule  of  glucose  (forming  2 
g. -molecules  of  ethyl  alcohol  and  2  g. -molecules  of  carbon  dioxide)  should  give  57 
kg.-cal.  of  heat,  while  the  complete  oxidation  (to  water  and  carbon  dioxide)  of  the 
alcohol  thus  produced  (2  g. -molecules)  should  give  652  kg.-cal.  in  addition.  The 
complete  oxidation  of  a  g. -molecule  of  glucose  should  consequently  give  57  + 
652,  or  700,  kg.-cal.  To  set  free  a  given  amount  of  free  energy,  more  than  twelve 
times  as  much  glucose  must  be  used  in  fermentation  as  would  be  required  in  aerobic 
respiration. 

2.  Alcoholic  Fermentation  by  Yeast. — The  Saccharomycetes  absorb  sugar  from  the 
medium  and  derive  free  energy  from  the  decomposition  of  this  sugar  by  means  of  the 
respiration  enzyme  zymase.  The  main  products  of  this  alcoholic  fermentation  are  ethyl 
alcohol  and  carbon  dioxide,  which  diffuse  from  the  cells  into  the  medium.  Some 
nitrogenous  material  and  mineral  salts,  as  well  as  sugar,  are  necessary  for  the  growth  of 
yeasts,  just  as  for  that  of  other  plant  forms. 

It  appears  that  this  fermentation  process  proceeds  by  two  stages,  employing  an 
inorganic  phosphate  (such  as  K2HPO4)  as  a  co-enzyme,  along  with  zymase.  In  the 
first  stage  carbon  dioxide,  ethyl  alcohol,  water,  and  a  hexose  phosphate  are  produced. 
In  the  second  stage  the  hexose  phosphate  is  decomposed,  giving  more  water  and  repro- 
ducing the  mineral  phosphate  and  some  of  the  original  sugar. 

Yeast  develops  best  in  the  presence  of  a  plentiful  supply  of  oxygen,  although  the 
process  of  alcoholic  fermentation  is  not  directly  influenced  by  the  oxygen  supply.  It 
appears  that  the  reasons  why  ethyl  alcohol  is  set  free  without  being  further  oxidized  in 
this  case  (even  in  the  presence  of  plenty  of  oxygen)  are  (1)  that  yeast  is  but  poorly 
supplied  with  oxidase  and  (2)  that  the  alcohol  diffuses  out  of  the  cells  about  as  rapidly 
as  it  is  formed.  As  the  concentration  of  alcohol  increases  in  the  medium,  the  yeast  cells 
ultimately  become  poisoned  by  the  alcohol,  and  the  fermentation  process  ceases 
altogether  when  the  alcohol  concentration  reaches  a  magnitude  of  about  16  per  cent. 

Different  kinds  of  yeast  act  somewhat  differently.  They  may  be  separated  and 
identified  by  several  methods,  as  by  the  time  required  for  the  production  of  ascospores, 
by  the  forms  of  their  giant  colonies,  etc.  Many  bacteria  and  moulds,  as  well  as  yeasts, 
produce  alcoholic  fermentation. 

In  the  metabolism  of  yeasts  and  other  alcoholic-fermentation  organisms,  the  more 
complex  carbohydrates  are  generally  first  hydrolyzed  (as  when  cane  sugar  is  acted  on 
by  the  enzyme  invertase)  to  form  glucose  sugar,  and  the  latter  is  then  fermented  by 
zymase.  Other  substances,  simpler  than  glucose,  some  of  which  may  occur  as  inter- 
mediate products  in  the  breaking  down  of  the  latter,  may  be  fermented  in  a  similar 
manner.  Thus,  pyrotartaric  acid  (CH3COCOOH)  forms  carbon  dioxide  and  acetic 
aldehyde  (CH3COH)  under  the  influence  of  carboxylase,  the  aldehyde  being  subse- 
quently reduced  to  ethyl  alcohol  (CH3CH,OH)  by  the  action  of  reductase.  The 
reductase  enzymes  act  by  transmitting  hydrogen  from  one  substance  to  another.  The 
substance  that  supplies  the  hydrogen  is  a  reducing  agent,  while  the  substance  that 
receives  the  hydrogen  is  an  oxidizing  agent.  The  latter  is  called  the  acceptor  of  hydro- 
gen. Reductase  action  may  be  illustrated  by  the  fermentation  of  lactic  acid,  which 
may  be  pictured  by  means  of  the  following  equations,  in  which  M  represents  a  respira- 
tion pigment  acting  as  hydrogen  acceptor. 

Lactic  Acid  Pyrotartaric  Acid 

i.   CH3-CHOH-COOH  +  M  =  CH3-CO-COOH  +  MH, 

Pyrotartaric  Acid  Acetic  Aldehyde 

2.  CH3-CO-COOH  =  CO,  +         CH3-COH 

Acetic  Aldehyde  Ethyl  Alcohol 

3.  CH3-COH  +  MH,  =  CH3-CH,OH  +  M 


FERMENTATION    AND    RESPIRATION  235 

The  hydrogen  taken  from  the  lactic  acid  is  shown  as  finally  added  to  the  acetic  aldehyde, 
the  latter  being  reduced  to  ethyl  alcohol.  The  hydrogen  acceptor  is  not  used  up  in  the 
process.     Reductase  can  not  act  unless  both  an  oxidizer  and  a  reducer  are  present. 

3.  Other  Kinds  of  Fermentation. — Lactic  acid  fermentation  (the  ordinary  souring  of 
milk)  is  caused  by  the  lactic  acid  bacillus,  which  grows  in  the  presence  of  oxygen,  and 
the  same  process  is  carried  on  by  many  other  forms.  It  results  in  the  hydrolytic 
splitting  of  lactose  (Ci2H>20ii)  into  four  times  as  many  molecules  of  lactic  acid 
(C3H603),  one  molecule  of  water  being  consumed  for  each  molecule  of  lactose  decom- 
posed. Other  sugars  (such  as  saccharose  and  maltose)  are  similarly  decomposed  with 
the  formation  of  lactic  acid,  by  other  microorganisms. 

Butyric  acid  fermentation  occurs  in  the  absence  of  oxygen  and  results  in  the  forma- 
tion of  carbon  dioxide  and  hydrogen,  as  well  as  of  butyric  acid.  It  is  caused  by  certain 
forms  of  bacteria,  especially  species  of  Clostridium.  Either  glucose  (CcHi206)  or 
lactic  acid  (C3H603)  may  be  fermented  in  this  way. 

Very  many  other  fermentation  processes  are  known,  due  to  numerous  different 
forms  of  bacteria,  etc.,  each  organism  being  limited  to  certain  kinds  of  fermentation. 

4.  Conditions  Influencing  Aerobic  Respiration  in  Plants. — Ingen-Housz  (1779) 
discovered  that  ordinary  green  plants  respire  like  animals,  taking  in  oxygen  and  giving 
off  carbon  dioxide,  and  DeSaussure  made  the  first  quantitative  study  of  this  process. 
The  rate  of  gaseous  exchange  is  greater  for  higher  temperatures,  up  to  about  40°C, 
above  which  the  rate  remains  about  the  same  until  death  occurs.  Any  change  of 
temperature  accelerates  respiratory  activity  for  a  time.  The  value  of  the  respiratory 
ratio  (the  amount  of  carbon  dioxide  given  off  divided  by  the  amount  of  oxygen  ab- 
sorbed, in  a  given  time  period)  is  low  (about  .35  to  .40)  for  temperatures  about  io°  or 
i5°C,  and  is  progressively  higher  for  either  progressively  higher  or  progressively  lower 
temperatures.     For  temperatures  about  35°C.  this  value  was  found  to  be  .95. 

Aerobic  respiration  in  chlorophyll-bearing  cells  is  apparently  related  to  carbo- 
hydrate photosynthesis  (which  may  be  considered  as  the  reverse  of  respiration), 
especially  on  account  of  the  dependence  of  respiration  on  water-soluble  carbohydrates. 
Of  course  th.e  carbon  dioxide  produced  by  respiration  in  green  leaves  in  sunlight  is 
regularly  fixed  by  the  photosynthetic  process.  During  periods  of  sunlight  (other 
conditions  being  suitable)  no  carbon  dioxide  passes  from  green  leaves  to  the  surround- 
ing air  and  no  free  oxygen  enters  the  leaves;  photosynthesis  is  then  more  active  than 
respiration,  and  the  net  result  of  both  processes  is  absorption  of  carbon  dioxide  and 
elimination  of  oxygen.  The  direct  influence  of  light  on  the  respiration  rate  may  be 
readily  studied  in  organisms  and  tissues  without  chlorophyll. 

The  partial  pressure  of  oxygen  in  the  surroundings  influences  the  rate  of  respiration. 
since  this  pressure  affects  the  rate  of  oxygen  supply  to  the  respiring  cells.  The  supply 
of  water  and  the  o'smotic  value  of  the  cell  sap  and  of  the  environmental  solutions, 
influence  the  respiration  rate,  as  do  also  the  rates  of  supply  or  partial  concentrations 
of  many  other  substances.  Here  may  be  mentioned  phosphates,  and  many  alkaloids, 
ethers,  alcohols,  aldehydes,  etc.  Respiration  is  accelerated  by  the  presence  of  poisons 
(such  as  alcohols,  ether)  if  these  substances  are  supplied  in  the  right  concentration, 
which  must  be  very  weak.     Wounding  accelerates  aerobic  respiration. 

The  aerobic  respiration  rate  in  ordinary  plants  is  closely  related  to  the  rate  of  en- 
largement; as  the  latter  rate  increases  and  then  decreases,  during  the  grand  period  of 
growth,  the  respiration  rate  alters  in  a  similar  manner.  Actively  enlarging  tissues 
generally  absorb  somewhat  more  oxygen  than  they  give  off  in  the  carbon  dioxide 

eliminated;  the  value  of  their  respiration  ratio  (    „     )  is  less  than  unity. 


236  PHYSIOLOGY   OF    NUTRITION 

The  nature  of  the  material  consumed  in  respiration  largely  determines  the  value  of 
the  respiration  ratio.  For  germinating  starchy  seeds  this  value  is  about  unity,  but  for 
germinating  fatty  seeds  it  is  much  lower.  The  following  equations,  for  the  complete 
oxidation  of  starch  [(CeHioOs)*]  and  for  that  of  triolein  (glycerine  trioleate,  the  main 
fat  in  cotton  seed,  for  instance),  serve  to  show  why  oxygen  accumulates  in  germinating 
fatty  seeds  and  does  not  do  so  in  germinating  starchy  seeds.  Starch  contains  much 
more  oxygen,  in  proportion  to  its  carbon  content,  than  does  fat. 

Carbon 
Starch  Oxygen  Dioxide  Water 

i.  C6H]0O5  +  6  02   =    6  CO,  +  5H20.      In  this  case    ~  =  \  =  1.00 

U2  0 

Carbon 
Triolein  Oxygen        Dioxide  Water 

2.    C3H503(C18H330)3+So  02  =  57  COo  +  52  H20.     In  this  case  ~  =  |7-  =  71 

Ripening  fruits  in  which  fat  is  being  formed  from  carbohydrates  exhibit  a  respiration- 
ratio  value  much  greater  than  unity. 

5.  The  Measurement  of  Aerobic  Respiration. — The  rate  of  aerobic  respiration  may 
be  measured  in  terms  of  the  rate  of  oxygen  absorption  or  in  terms  of  the  rate  of  carbon- 
dioxide  elimination.  The  value  of  the  respiration  ratio  is  derived  from  the  magnitudes 
of  these  two  rates. 

6.  Respiration  Water. — Water  is  produced  by  aerobic  respiration,  as  has  been  said, 
but  the  rate  of  water  formation  is  very  difficult  to  measure  and  but  few  studies  on 
respiration  water  have  been  reported.  It  will  be  remembered  that  hydrolytic  processes 
(controlled  by  hydrolytic  enzymes;  see  Chapter  VII,  Section  3)  consume  water  and  that 
the  reverse  processes  liberate  this  substance.  For  example,  saccharose  combines  with 
water  and  forms  dextrose  (glucose)  and  levulose;  but  if  a  molecule  of  dextrose  and  one 
of  levulose  unite  to  form  a  molecule  of  saccharose,  a  molecule  of  water  is  produced. 

Saccharose  Water  Glucose 

Ci2H220n    +  H20  *±  2  C6H120G 

The  formation  of  carbohydrates  by  photosynthesis  consumes  large  amounts  of  water, 
one  molecule  of  water  for  each  atom  of  carbon  fixed  in  the  process.  These,  as  well  as 
other  water-consuming  or  water-producing  processes  that  occur  in  the  plant,  tend  to 
hide  the  production  of  water  by  respiration. 

7.  Liberation  of  Heat  During  Aerobic  Respiration. — The  temperature  of  the  plant 
body  is  generally  very  nearly  the  same  as  that  of  the  surroundings,  simply  because  the 
periphery  conducts  and  radiates  heat  with  so  little  resistance  that  no  considerable 
temperature  gradient  between  the  environment  and  the  tissues  is  generally  maintained. 
The  processes  of  respiration,  including  the  final  oxidations,  liberate  considerable 
amounts  of  energy  within  the  active  tissues,  and  much  of  this  takes  the  form  of  heat, 
which  tends  to  raise  the  tissue  temperature.  But  this  excess  of  heat  is  generally 
conducted  to  the  surroundings  about  as  rapidly  as  it  is  formed;  consequently  the 
internal  temperature  is  usually  only  slightly,  if  at  all,  higher  than  the  external.  As  has 
been  noted,  the  absorption  of  solar  radiation  tends  to  raise  the  temperature  of  plant 
parts  that  are  exposed  to  sunlight,  during  the  periods  of  such  exposure,  and  this  is 
another  source  of  increased  heat  within  these  parts.     But  this  heat  also  is  usually  lost 


FERMENTATION   AND    RESPIRATION  237 

about  as  rapidly  as  it  is  developed.  Besides  outward  conduction  (and  some  outward 
radiation)  of  heat,  a  very  large  part  of  the  heat  developed  in  the  aerially  exposed  parts 
of  plants  disappears  in  the  process  of  transpiration;  it  passes  to  the  surrounding  air 
without  raising  the  temperature  of  the  latter,  for  it  becomes  potential  energy  (the 
latent  heat  of  water  vapor).  Rapidly  transpiring  leaves  are  generally  a  little  cooler 
than  the  surrounding  air,  even  in  direct  sunlight. 

When  there  are  large  numbers  of  very  active  cells  crowded  into  a  small  space,  with 
not  too  ready  heat  conduction  to  the  surroundings,  the  heat  developed  by  respiration 
becomes  evident,  and  the  temperature  of  the  tissue  may  be  much  higher  than  that  of 
the  surroundings.  The  internal  temperature  of  an  Arum  spadix  with  opening  flowers 
may  be  more  than  2  5°C.  higher  than  that  of  the  surrounding  air.  A  mass  of  germina- 
ting seeds  or  of  opening  leaf-buds  may  develop  very  high  temperatures  (70  to  20°C. 
higher  than  those  of  the  surrounding  air),  especially  if  outward  heat  transfer  is  arti- 
ficially hindered,  as  by  enclosing  the  seeds  in  a  Dewar  flask.  In  germinating  seeds  the 
maximum  rate  of  heat  production  occurs  very  early,  just  after  germination  begins,  and 
this  rate  becomes  lower  as  the  seedlings  develop.  The  highest  rates  of  heat  production 
appear  to  occur  with  the  lowest  values  of  the  respiration  ratio. 

The  heat  produced  by  respiration  is  generally  in  excess  of  the  amount  calculated 
from  the  carbon  dioxide  given  off  or  from  the  amount  of  oxygen  absorbed,  considering 
that  carbon  and  oxygen  simply  unite  to  form  carbon  dioxide.  A  part  of  the  difference 
is  accounted  for  by  considering  the  process  as  starting  with  carbohydrate  and  oxygen, 
instead  of  with  carbon  and  oxygen.  Not  all  the  energy  set  free  by  respiration  appears 
as  heat;  some  of  it  disappears  in  the  performance  of  the  various  kinds  of  work  accom- 
plished in  the  organism. 

8.  Anaerobic,  or  Intramolecular,  Respiration. — In  active  plant  tissues  that  usually 
require  oxygen,  anaerobic  respiration  continues  for  a  time  after  the  supply  of  oxygen 
has  been  cut  off.  As  has  been  said,  this  part  of  the  respiration  process  gives  rise  to 
incompletely  oxidized  carbon  compounds,  such  as  alcohols,  acids,  etc.,  as  well  as  to 
some  carbon  dioxide  or  water,  or  both.  If  kept  too  long  without  oxygen  supply, 
tissues  finally  die,  being  perhaps  poisoned  by  the  accumulation  of  incompletely  oxidized 
products. 

9.  Respiration  Chromogens  and  Pigments. — Pro-chromogens  appear  to  be  common 
in  plant  tissues.  These  are  substances  apparently  of  the  nature  of  glucosides.  They 
are  decomposed  by  the  glucoside  enzyme  emulsin,  with  the  formation  of  correspond- 
ing chromogens.  The  latter  seem  to  play  an  important  role  in  aerobic  respiration;  they 
apparently  unite  readily  with  free  oxygen  under  the  influence  of  oxidizing  enzymes, 
producing  water  and  corresponding  respiration  pigments.  These  pigments  then  act  as 
acceptors  of  hydrogen,  uniting  with  the  hydrogen  produced  by  the  anaerobic  phase  of 
respiration,  and  thus  produce  the  corresponding  chromogens  once  more.  The  pig- 
ments act  as  carriers  of  hydrogen,  taking  it  up  as  it  is  produced  (thereby  becoming 
chromogens)  and  then  delivering  it  to  free  oxygen,  with  the  formation  of  water  (and 
the  re-formation  of  the  pigments) :  pigment  +  hydrogen  =  chromogen ;  chromogen 
-f-  oxygen  =  water  +  pigment. 

10.  Respiration  Enzymes. — Plant  tissues  may  be  killed  without  destroying  their 
enzymes,  and  they  may  then  continue  to  give  off  carbon  dioxide  and  to  absorb  oxygen, 
but  in  a  somewhat  different  way  from  that  exhibited  by  the  living  tissues.  From 
studies  on  the  respiration  of  such  tissues,  Palladin  and  others  suggest  that  the  carbon 
dioxide  given  off  in  aerobic  respiration  all  arises  from  the  anaerobic  phase,  while  the 
water  formed  is  a  product  of  the  union  of  free  oxygen  with  respiration  chromogens,  in 


238  PHYSIOLOGY   OF    NUTRITION 

the  aerobic  phase.  It  is  supposed  that  sugar  and  water  unite  and  form  carbon  dioxide 
and  hydrogen,  that  the  hydrogen  unites  with  respiration  pigments  and  thus  forms  chro- 
mogens,  and  that  the  chromogens  are  directly  oxidized  by  free  oxygen,  forming  water 
and  the  pigments.  According  to  this  hypothesis,  as  long  as  an  unsatisfied  acceptor  of 
hydrogen  is  present,  alcohol  and  similar  substances  are  not  formed,  and  the  acceptor 
(pigment)  is  kept  unsatisfied  through  the  oxidation  of  the  chromogen  as  long  as  free 
oxygen  is  adequately  supplied.  On  the  other  hand,  in  the  absence  of  free  oxygen  the 
pigment  soon  becomes  satisfied  and  ceases  to  be  able  to  absorb  hydrogen,  after  which 
alcohol,  etc.,  arise  from  the  original  decomposition  of  sugar,  along  with  carbon  dioxide. 

11.  Materials  Consumed  in  Respiration. — In  ordinary  plants  it  is  generally  true 
that  carbohydrates  are  the  substances  consumed  by  respiration.  The  respiration 
processes  are 'controlled  by  enzymes,  and  these,  in  turn,  are  formed  in  the  protoplasm. 
On  the  amount  of  protoplasm  in  a  tissue  depends  the  amount  of  enzymes  present,  and 
the  latter  determine  the  rate  of  respiration  as  long  as  the  supply  of  carbohydrates  is 
adequate.  With  inadequate  supply  of  carbohydrates  the  respiration  rate  is  low, 
even  with  plenty  of  protoplasm  and  enzymes;  on  the  other  hand,  an  excess  of  carbo- 
hydrates exerts  no  influence  on  the  respiration  rate.  With  plenty  of  carbohydrates 
it  appears  that  the  respiration  rate  varies  with  the  amount  of  nucleins  in  the  respiring 
tissue,  the  amount  of  nucleins  being  considered  as  proportional  to  the  amount  of  com- 
plex proteins,  insoluble  in  gastric  juice.  It  may  be  supposed  that  the  amount  of 
complex  proteins  present  is  proportional  to  the  amount  of  respiration  enzymes,  and  this 
supposition  may  explain  the  apparent  relation  between  the  respiration  rate  and  the 
supply  of  complex  proteins.  Neither  simple  nor  complex  proteins  are  generally  used 
in  respiration;  carbohydrates  may  sometimes  result  from  protein  decomposition, 
however,  and  these  may  be  used. 

12.  Special  Cases  of  Respiration  in  Lower  Plants. — In  many  lower  forms,  sub- 
stances other  than  carbohydrates  are  decomposed  in  respiration.  In  acetic-acid 
bacteria,  for  example,  respiration  is  the  simple  oxidation  of  ethyl  alcohol  (by  means  of 
free  oxygen),  with  the  formation  of  acetic  acid  and  water.  When  the  supply  of 
alcohol  has  been  consumed,  however,  these  bacteria  oxidize  acetic  acid  and  thus  form 
carbon  dioxide  and  water.  Many  other  alcohols  are  similarly  oxidized  by  micro- 
organisms. 

As  already  mentioned  (Chapter  II,  Section  3),  many  bacteria  obtain  energy  from 
inorganic  substances,  and  it  should  be  remarked  that  the  decompositions  thus  brought 
about  are  respiration  processes.  Hydrogen  sulphide,  ammonia,  hydrogen,  etc.,  are 
thus  oxidized. 

13.  Circulation  of  Energy  in  Nature. — While  the  amount  of  matter  in  and  on  the 
earth  remains  always  practically  the  same,  almost  no  material  being  now  given  off  to, 
or  received  from,  the  rest  of  the  universe,  the  energy  exchange  between  the  earth  and 
its  surroundings  is  very  rapid  and  exceedingly  important.  Energy  is  continually  and 
rapidly  radiated  from  the  earth's  surface  into  sidereal  space,  and  the  supply  available 
to  organisms  would  soon  be  practically  exhausted  if  it  were  not  for  the  fact  that  new 
radiant  energy  is  continuously  being  supplied  from  the  sun.  A  very  small  part  of  the 
radiant  energy  emanating  from  the  sun  is  intercepted  by  the  earth,  and  a  small  portion 
of  what  is  intercepted  is  rendered  potential  by  the  photosynthetic  formation  of 
carbohydrates  in  chlorophyll-bearing  plant  tissues.  The  potential  energy  of  the 
carbohydrates  thus  formed  becomes  again  kinetic  through  the  processes  of  respira- 
tion, oxidation,  and  combustion.  Most  of  this  energy  from  carbohydrates  is  quickly 
radiated  from  the  earth  into  the  surrounding  universe,  and  the  remainder  goes  the 


FERMENTATION    AND    RESPIRATION  2$$ 

same  way  after  it  has  taken  part  in  the  physical,  chemical,  and  physiological  processes 
that  occur  in  organisms,  and  otherwise,  on  the  earth's  surface.  The  dissipation  of 
solar  energy  is  merely  somewhat  delayed  by  carbohydrate  formation  in  chlorophyll- 
bearing  tissues  and  by  other  processes  of  energy  fixation  that  occur  in  plants. 


PART  II 

PHYSIOLOGY  OF  GROWTH 
AND  CONFIGURATION 


CHAPTER  I 

GENERAL  DISCUSSION  OF  GROWTH 

§i.  Anatomical  Relations  of  Cell  Growth. — Microscopical  observation  of 
the  development  of  plant  cells  shows  that  three  different  stages  of  growth  may 
be  distinguished.  The  growth  of  the  cell  begins  with  its  formation  by  division, 
this  is  the  first  stage  of  growth.  The  cell  then  begins  to  increase  in  size,  thus 
passing  into  the  period  of  enlargement,  which  is  the  second 
stage.  Enlargement  finally  ceases,  to  be  followed  by 
thickening  of  the  cell  wall  through  the  deposition  of  new 
layers  of  cellulose,  and  this  constitutes  the  third  stage  of 
growth.  The  last  two  stages  are  not  entirely  distinct  but 
merge  gradually  into  each  other,  for  deposition  of  new 
layers  of  cellulose  occurs  simultaneously  with  the  enlarge- 
ment of  the  cell.  Fig.  96,  a  cross-section  through  the 
cambium  region  of  the  stem  of  the  Scotch  pine,  shows  all 
three  stages  in  the  development  of  tracheides  from 
cambium  cells.  If  all  the  cells  of  a  tissue  are  in  the  first 
or  in  the  third  stage  of  growth,  the  growth  changes  charac- 
teristic of  these  stages  are  without  effect  upon  the  size  of 
the  tissue  mass.  In  considering  a  tissue,  these  two  stages 
may  therefore  be  designated  as  stages  of  internal  growth,  as 
distinct  from  the  second  growth  stage,  that  of  enlargement, 
of  which  increase  in  the  dimensions  of  the  tissue  or  organ 
is  the  most  characteristic  feature." 

0  Not  only  is  a  sharp  distinction  between  the  second  and  third 
stages  of  growth  impossible,  as  the  author  states,  but  the  same  is  also 
true  regarding  the  first  and  second  stages;  a  certain  amount  of  en- 
largement usually  precedes  each  cell  division  in  tissues  that  are  ac- 
counted as  in  the  first  stage.  The  three  stages  furnish  a  convenient  mode  of  reference,  how- 
ever, to  the  corresponding  portions  of  the  continuous  march  of  the  growth  process.  The  first 
stage  (called  also  the  embryonic  or  formative  phase)  is  mainly  characterized  by  cell  division, 
the  second  (called  the  phase  of  enlargement)  is  mainly  characterized  by  cell  enlargement, 
and  the  third  (called  the  phase  of  maturation)  is  mainly  characterized  by  thickening  and  other 
alterations  in  the  cell  walls,  frequently  also  by  changes  of  other  sorts. — Ed. 
16  241 


Fig.  96. — Cambium 
cells  of  Scotch  pine, 
showing  transforma- 
tion into  tracheides. 
The  Roman  numbers 
denote  the  three  stages 
of  growth. 


242 


PHYSIOLOGY    OF    GROWTH    AND    CONFIGURATION 


Physiological  studies  of  the  rate  of  growth  of  a  plant  are  generally  carried 
out  by  measuring  the  part  in  question,  either  with  a  simple  millimeter  rule  or 
with  special  measuring  apparatus.  In  experiments  of  this  kind  only  the  external 
growth,  or  the  enlargement  of  the  plant,  is  measured,  and  the  rate  of  enlargement 
is  determined  for  a  definite  time  period  and  under  a  certain  set  of  conditions. 
Internal  growth  cannot  be  studied  with  a  rule,  it  can  be  measured  only  by  means 
of  the  microscope,  or  by  qualitative  and  quantitative  analyses  of  the  materials 
found  in  the  plant  at  different  periods  of  its  development. 

§2.  Conditions  Favorable  to  Growth. — Growth  of  the  cell  is  a  result  of  the 
activity  of  protoplasm,  and  a  large  number  of  conditions  must  be  fulfilled  in 
order  that  it  may  take  place.  If  a  single  one  of  the  necessary  external  conditions 
be  absent,  then  growth  ceases,  and  if  the  internal  conditions  necessary  for 
growth  are  not  all  fulfilled  growth  fails  to  occur  in  this  case  also,  even  though 
all  other  conditions  are  favorable. 

\V- A 


N- 


12  34 

Fig.  97. — Different  stages  in  plasmolysis  of  a  cell.     N,  nucleus;  V,  vacuole.      {After  de  Vries.} 

Turgidily  is  one  of  the  internal  conditions  necessary  for  cell  enlargement. 
If  a  growing  cell  is  placed  in  a  10  per  cent,  solution  of  sodium  chloride,  potassium 
nitrate  or  sugar,  it  immediately  begins  to  decrease  in  size  (Fig.  97).  At  first 
the  cell  wall  and  the  protoplasmic  membrane  contract  equally,  but  later,  when 
the  cell  wall  can  contract  no  more,  the  protoplasm  still  continues  to  move 
inward,  thus  retreating  from  the  cell  wall.  Finally,  the  entire  contents  of  the 
cell  collect  into  a  ball-like  mass  in  the  center  of  the  cell, with  the  outer  proto- 
plasmic membrane  on  the  outside.  This  process  is  known  as  plasmolysis,  as 
has  been  pointed  out  (page  114).  If  a  plasmolyzed  cell  is  placed  in  pure  water 
it  enlarges  and  finally  regains  its  original  size  and  form.  The  external  condi- 
tions that  produce  these  changes  in  cells  are  likewise  effective  in  causing  the 
shrinkage  of  an  animal  bladder  filled  with  weak  salt  solution,  when  this  is 
placed  in  a  strong  salt  solution.  The  cell  sap  of  plant  cells  is  a  solution  of 
various  substances,  which  have  an  attraction  for  water.  The  osmotic  pressure 
produced  in  the  cell  when  plenty  of  water  is  supplied  results  in  the  turgidity  of 
the  cell. 

The  enlargement  of  each  cell  begins  with  the  stretching  of  the  cell  wall  by 


GENERAL    DISCUSSION    OF    GROWTH 


243 


turgor,  and  the  effect  of  this  stretching  becomes  subsequently  established  by 
the  deposition  of  new  layers  of  cellulose.  Traube's  artificial  cell  is  closely 
analogous  to  the  living  cell  in  some  respects.  If  a  drop  of  gelatine  is  introduced 
into  a  tannin  solution,  a  precipitation  membrane  of  gelatine  tannate  is  formed 
at  the  surface  of  the  deop,  and  the  cell  thus  artificially  produced  begins  to 


Pig.  98. — Horizontal  microscope. 


enlarge.  This  enlargement  can  be  explained  only  by  supposing  that  the  gelatine 
extracts  water  from  the  tannin  solution;  the  outward  pressure  thus  produced 
causes  a  stretching  of  the  membrane,  which  becomes  ruptured  at  many  places. 
Through  the  small  openings  thus  formed  the  gelatine  once  more  comes  into 
contact  with  the  tannin  and  the  precipitation  membrane  is  reformed,  when 
the  process  is  repeated. 


244 


PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 


Experiments  with  plasmolysis  were  at  first  conducted  only  with  single 
cells,  but  de  Vries1  plasmolyzed  entire  plant  organs  during  the  period  of  en- 
largement. He  showed  that  when  pieces  of  the  growing  region,  of  stems,  roots 
or  flower-stalks,  were  placed  in  concentrated  salt  solution  a  considerable  shorten- 
ing was  evident.  This  shortening  is  due  to  plasmolysis  of  the  cells,  and  the 
plasmolyzed  pieces  were  always  wilted  and  flaccid,  but  when  they  were  returned 
to  pure  water  they  regained  their  former  length  and  rigidity.  Mature  organs, 
however,  whose  enlarging  periods  were  over,  showed  no  shrinkage  when  placed 
in  strong  salt  solutions;  the  stretching  caused  by  turgor  had  by  this  time 
become  fixed  through  further  deposition  of  cellulose  on  or  in  the  walls. 


Fig.  99. — Auxanometer.      (After  Pfeffer.) 


Turgor  can  thus  produce  enlargement  of  cells  only  when  the  walls  are  capable 
of  being  stretched  by  the  pressure  that  is  developed.  Experiments  carried  out 
by  Wortmann2  showed  that  the  cell  walls  of  young  cells  possess  this  quality  of 
extensibility  in  a  much  higher  degree  than  do  older  ones,  extensibility  decreas- 
ing gradually  with  advancing  age.     The  ultimate  loss  of  this  quality  of  the 

1  Vries,  Hugo  de,  1877,  1-  2,     [See  note  1,  p.  121.] 

-  Wortmann,  J.,  Beitrage  zur  Physiologie  des  Wachsthums.  Bot.  Zeitg.  47:  220-239.  245-253.  261-272, 
277-288,  293-304.  1889.  Schwendener,  S.,  and  Krabbe,  G.,  Ueber  die  Beziehung  zwischen  dem  Maass 
der  Turgordehnung  und  der  Geschwindigkeit  der  Langenzunahme  Wachsender  Organe.  Jahrb.  wiss.  Bot. 
25:  323-369-      1893- 


GENERAL    DISCUSSION    OF    GROWTH 


245 


walls  results  in  the  termination  of  cell  enlargement,  even  though  turgor  may 
not  have  decreased.  Extensibility  of  the  wall  is  therefore  the  second  condition 
necessary  for  cell  enlargement.  Various  external  conditions  are  also  necessary 
for  growth,  such  as  favorable  temperature  conditions,  the  presence  of  oxygen 
in  the  surrounding  air,  and  an  adequate  supply  of  water. 

§3.  Apparatus  for  the  Study  of  Growth. — The  simplest  equipment  for  the 
study  of  plant  enlargement  is  a  millimeter  rule.  A  horizontal  microscope  (Fig. 
98)  or  a  cathetometer  may  be  used  for  finer  and  more  accurate  measurements. 
The  auxanometer,  a  self-registering  apparatus  for  growth  measurement,  may 
also  be  used  (Fig.  99).  A  waxed  thread  is  fastened  to  the  top  of  the  stem  to  be 
studied  and  is  passed  vertically 
upward  and  over  a  pulley,  and  a 
weight  is  attached  to  the  free  end. 
The  pulley  turns  as  the  plant 
elongates  and  the  weight  descends. 
The  growth  increments  are  magni- 
fied by  introducing  a  larger  pulley, 
mounted  on  the  same  axis  as  the 
first,  over  which  is  passed  a  second 
thread  with  a  weight  at  either  end. 
A  pointer  is  fastened  to  one  end 
of  the  second  thread,  its  tip  rest- 
ing lightly  upon  a  vertically  placed 
drum  revolved  by  clockwork  and 
covered  with  smoked  paper.  As 
the  drum  revolves  and  as  the 
pulley  turns  with  the  elongation 
of  the  plant,  a  curve  is  traced  on 
the  paper,  the  slope  of  which  rep- 
resents the  time  rate  of  this 
elongation  during  the  period  of 
operation. 

If  it  is  required  to  determine 
whether  all  parts  of  an  organ  grow 
with  equal  rapidity,  the  organ  may 

be  marked  into  millimeter  or  centimeter  spaces   or  zones,  by  means  of  India 
ink.     After  some  time  the  spaces  are  remeasured. 

The  apparatus  shown  in  Fig.  100  may  also  be  employed  to  study  growth. 
One  end  of  a  waxed  thread  is  attached  to  the  tip  of  the  plant  and  passes  vertically 
upward,  ending  by  being  wound  about  a  small  pulley  on  a  horizontal  axis.  To 
this  pulley  is  attached  a  long,  counterbalanced  pointer,  the  free  end  of  which 
moves  upward  or  downward  in  front  of  a  large  graduated  arc,  as  the  pulley  is 
turned.  As  the  plant  elongates  the  thread  is  released  and  the  magnified  growth 
increments  are  read  directly  in  degrees  of  arc. 


Fig.  100. — Apparatus  for  the  study  of  growth. 


246  PHYSIOLOGY    OF    GROWTH   AND    CONFIGURATION 

Summary 

1.  Anatomical  Relations  of  Cell  Growth. — The  first  stage,  or  phase,  of  cell  growth 
is  that  of  cell  division — this  being  also  called  the  formative,  meristematic,  or  embryonic 
phase.  After  its  formation  by  division  each  cell  enters  the  second  phase,  that  of 
enlargement,  in  which  it  attains  its  mature  size.     After  enlargement  ceases  various 

•changes  occur  leading  to  the  condition  of  maturity,  such  as  the  thickening  of  walls, 
etc.,  and  these  changes  characterize  the  third  phase,  that  of  maturation.  The  three 
growth  phases  cannot  be  sharply  distinguished,  however. 

Measurements  of  growth  rates  frequently  refer  only  to  the  seco'nd  phase,  that  of 
enlargement,  since  this  is  the  most  easily  studied  by  means  of  a  millimeter  rule,  etc. 
Microscopic  methods  are  resorted  to  in  studies  of  all  three  phases,  growth  in  general  is 
frequently  measured  in  terms  of  increase  in  weight,  and  chemical  determinations  of  the 
various  substances  formed  are  often  employed,  especially  for  studies  of  the  third 

phase. 

2.  Conditions  Favorable  to  Growth.— Growth  is  a  complex  physiological  process, 
being  the  resultant  of  many  component  processes,  and — like  all  other  processes— it 
cannot  occur. unless  all  the  essential  conditions  are  fulfilled.  Some  of  the  essential 
conditions  are  internal  (within  the  plant  body),  while  others  are  external  (in  the 
environment).  One  of  the  primary  internal  conditions  necessary  for  cell  enlargement 
is  turgidity,  which  is  produced  by  osmotic  pressure  or  imbibition  pressure  within  the 
cell.  By  this  pressure  the  protoplasm  is  held  against  the  cell  wall  and  the  latter  is 
more  or  less  stretched.  Cell  enlargement  is  primarily  due  to  osmotic  and  imbibition 
pressures  developed  through  the  absorption  of  water,  and  to  the  resultant  stretching 
of  the  cell  wall.  New  cellulose  is  deposited  in  the  stretched  wall  and  more  stretching 
occurs,  with  still  further  addition  of  cellulose,  until  the  second  phase  of  growth  is 
completed.  In  the  third  phase  of  growth  the  cell  wall  often  thickens  on  account  of 
deposition  of  cellulose  without  further  stretching. 

The  importance  of  turgidity  is  shown  experimentally  by  plasmolysis  and  the 
recovery  therefrom.  Artificial  osmotic  cells,  especially  Traube's  artificial  cell  (a  drop 
of  gelatine  solution  in  a  solution  of  tannin),  illustrate  some  of  the  phenomena  of  turgor 
and  plasmolysis.  When  enlarging  plant  organs  or  tissues  are  placed  in  properly 
concentrated  salt  or  sugar  solutions  a  pronounced  contraction  results,  due  to  the 
removal  of  the  turgor  pressure  within  the  cells.  The  wilted  tissue  returns  to  its 
original  turgid  and  stretched  condition  after  the  concentrated  solution  has  been 
replaced  by  water  or  by  a  very  weak  solution.  After  the  second  phase  of  growth  has 
been  completed  plasmolysis  of  the  cells  results  in  little  or  no  contraction  of  the  tissue; 
in  the  third  phase  of  growth  the  cell  walls  are  stretched  but  little  or  not  at  all.  Exten- 
sibility of  the  cell  wall,  under  the  influence  of  the  pressure  of  turgor  that  occurs  in  the 
cell,  is  therefore  another  internal  condition  necessary  for  cell  enlargement. 

Many  external  conditions  are  also  necessary  for  growth,  such  as  temperatures 
within  certain  limits,  proper  oxygen  supply,  water  supply,  etc. 

3.  Apparatus  for  Studying  Plant  Enlargement. — The  enlargement  of  an  organ  or 
plant  may  be  measured  by  various  devices,  from  the  simple  metric  scale  to  very 
precise  auxanometers,  auxographs,  etc.  Equally  spaced  marks  may  be  made  upon 
the  surface  of  an  enlarging  organ  and  subsequent  determination  of  the  distances 
between  the  marks  indicates  the  relative  rates  of  enlargement  of  the  various  regions  of 
the  organ. 


CHAPTER  II 

GROWTH  PHENOMENA  THAT  ARE  CONTROLLED  BY  INTERNAL 

CONDITIONS 

§i.  The  Grand  Period  of  Growths — Plants  and  their  component  organs  and 
tissues  do  not  enlarge  at  the  same  rate  throughout  the  period  of  their  develop- 
ment. Enlargement  begins  at  a  slow  rate,  which  gradually  increases  until  a 
maximum  is  reached,  after  which  the  rate  progressively  decreases  until  enlarge- 
ment ceases  altogether.  The  time  period  corresponding  to  this  march  of  rate 
of  enlargement  was  designated  by  Sachs1  as  the  grand  period  of  growth,  and  the 
same  author  called  the  graph  representing  this  march,  the  grand  curve  of  growth. 
This  peculiar  march  of  the  growth  rate  is  due  to  the  fact  that  each  individual 
cell  of  the  plant  body  passes  through  a  similar  grand  period  of  development. 
External  conditions  can  lengthen  or  shorten  the  period  of  growth,  but  the  general 
character  of  the  curve  is  not  altered.  Thus,  in  one  experiment,  the  daily  incre- 
ments of  elongation  of  the  terminal  internode  (3.5  mm.  in  length)  of  a  seedling 
of  Phaseolus  multiflorus,  with  a  temperature  of  12.8  to  i3.8°C,  had  the  values 
shown  below. 

Increment  of 
Number  of  Elongation 

Day  mm. 

1         1.2 

2         1.5 

3         2-5 

4         5-5 

5         7-0 

6         9.0 

7         '40 

8         10. o 

9         70 

10         2.0 

§2.  Growth  of  Root,  Stem  and  Leaf. — While  it  is  generally  true  that  the 
three  most  important  organs  of  the  plant  (roots,  stems  and  leaves)  all  pass 
through  a  grand  period  of  growth,  nevertheless  there  are  individual  peciilarities 
to  be  observed  in  each  case. 

In  roots,2  the  elongating  region  is  restricted  to  a  portion  near  the  tip,  usually 
not  more  than  10  mm.  when  the  roots  are  surrounded  by  soil.  Aerial  roots  are 
an  exception  to  this;  the  elongating  regions  of  the  aerial  roots  of  Monster  a 

1  Sachs.  J.,  Ueber  den  Einfluss  der  Lufttemperatur  und  des  Tageslichts  auf  die  stundlichen  und  taglichen 
Aenderungen  des  Langenwachsthums  (Streckung)  der  Internodien.  Arbeit.  Bot.  Inst.  Wurzburg  i :  99- 
192.      1874. 

Sachs,  J.,  Ueber  das  Wachsthum  der  Haupt-  und  Xebenwurzeln.  Arbeit.  Bot.  Inst.  Wurzburg  1 : 
385-474.  584-634.      1874. 

247 


248 


PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 


deliciosa  are  about  30  to  70  mm.  in  length,  while  those  of  Vitis  velutina  may 
exceed  100  mm.  The  individual  parts  of  the  region  of  elongation  in  the  root 
show  unequal  rates  of  growth.  The  most  rapidly  elongating  portion  lies  in  the 
center  of  the  region,  while  the  parts  above  and  below  grow  more  slowly.  An 
experiment  in  which  young  roots  of  Viciafaba  seedlings  were  divided  (by  India 
ink  lines)  into  ten  zones  each  a  millimeter  long,  the  zones  being  measured  after 
twenty-four  hours,  gave  the  following  values  for  the  increments  of  elongation  of 
the  respective  zones.  The  temperature  was  2o.5°C.  and  the  zones  were  num- 
bered from  the  tip  upward. 


Number  of 
Zone 

X 

Increment    of 

Elongation 

m  m. 

O.I 

IX 

....                  0.2 

VIII 

0.3 

VII 

0.5 

VI 

1.3 

v 

1.6 

IV 

3.5 

III 

8.2 

II 

5-8 

Fig.  ioi. — Three  stages  in  the  elongation  of  a  root  of  Vicia  faba. 


In  Fig.  101  are  shown  three  stages  in  the  elongation  of  the  primary  root  of 
a  Viciafaba  seedling.  A  shows  the  root  divided  into  millimeter  zones,  at  the 
beginning  of  the  experiment,  and  B  and  C  show  the  same  seedling  after  six  hours 
and  after  one  day,  respectively. 


GROWTH    PHENOMENA    CONTROLLED   BY   INTERNAL    CONDITIONS       249 

Each  zone  of  the  elongating  region  of  the  root  likewise  passes  through  a 
grand  period  of  growth.  In  an  experiment  in  which  the  primary  root  of  a  seed- 
ling of  Viciafaba  was  marked  into  millimeter  zones,  each  zone  being  measured 
after  one,  two,  three,  etc.,  days  (the  temperature  being  from  180  to  2i.5°C), 
the  following  daily  increments  of  elongation  of  the  youngest  zone  were  observed. 


Number  of 
Day 

Increment  of 

Elongation 

mm. 

1.8 

7 

x                                                                                                                      17 

s 

17 

5 

17 

0 

14 

7 

0 

....                  0 

0 

Fig.  102. — I,  Croats  longiflorus. 


Z,  contracting  roots.      Half  natural  size. 


Neither  does  the  stem1  enlarge  throughout  its  entire  length  at  the  same  time, 
but  the  elongating  regions  are  here  much  longer  than  in  the  root.  The  stem  of 
Galium  molligo  has  a  terminal  region  of  elongation  from  2  to  4  cm.  long,  embrac- 
ing from  8  to  10  internodes;  this  region  in  Aristolochia  sipho  is  from  40  to  50  cm. 
long  and  embraces  from  8  to  10  internodes;  in  Elodea  canadensis  it  is  from  2  to  3 
cm.  long,  with  from  43  to  50  internodes;  and  in  Hippuris  vulgaris  it  is  from  20 
to  30  cm.  long.  The  single  individual  zones  of  the  stem,  as  is  true  also  of  the 
root,  elongate  unequally,  and  each  passes  through  a  grand  period  of  growth. 

Leaf  enlargement2  is  mainly  basipetal,  the  enlarging  region  being  situated  in 
the  lower  portion  of  the  organ,  near  the  stem.     In  the  table  below  are  given  the 

1  Askenasy,  E..  Ueber  eine  neue  Methode,  urn  die  Vertheilung  der  Wachsthumsintensitat  in  wach- 
senden  Theilen  zu  bestimmen.     Verhandl.  Xaturhist.-Med.  Ver.     Heidelberg  2  :  70-153.      1880. 

:  Stebler,  F.  G.,  Untersuchungen  liber  das  Biattwachsthum.     Jahrb.  wiss.   Bot.   11:   47-123-     1878. 


2  5° 


PHYSIOLOGY    OF    GROWTH    AND    CONFIGURATION 


daily  increments  of  elongation  in  a  leaf  of  Allium  cepa  (onion),  at  different  stages 
of  its  development,  with  a  temperature  of  from  19  to  2i°C.  The  leaf  was 
divided  into  2.5-mm.  zones,  and  these  zones  are  here  numbered  I  to  IX,  begin- 
ning with  the  basal  one.  The  experiment  began  on  March  8,  and  the  increment 
of  each  zone  was  determined  after  one  day.  The  average  daily  increments  were 
again  determined  for  the  period  from  March  16  to  18,  and  finally  for  the  period 
from  March  22  to  23. 


Average 

Daily  Increment 

Total  Incre- 

Number of 

of 

Elongation 

ment  of  Elon- 

2.5-MM. 
Zone 

gation, 

March 
3-q 

March 
16-18 

March 
22-23 

March 
8-23 

mm. 

mm. 

mm. 

mm. 

Leaf  sheath . . 

I 
II 

0. 1 
0.  i 

0.0 

2.9 

0.0 
0.0 

7-9 

26.4 

• 

III 

0. 1 

2.9 

0.  2 

25- 1 

IV 

0.4 

5-i 

0. 1 

48.1 

Leaf    blade 

V 
VI 

0.4 
0.2 

3-° 

2 . 1 

0.0 
0.0 

3°-i 

19. 1 

VII 

0.  2 

1.6 

0.0 

16.7 

VIII 

0.  2 

0.7 

0.0 

10.4 

IX 

O.I 

0.8 

0.0 

i-4 

Total  for  entire  leaf 

1.8 

18.3 

0.3 

185. 1 

It  is  evident  from  these  data  that  elongation  soon  ceased  in  the  upper  part  of 
the  leaf  (zone  IX),  and  that  the  greatest  elongation  occurred  in  the  lower 
and  younger  part. 

Growth  may  sometimes  result  in  a  shortening,  instead  of  an  elongation.1 
This  may  arise  from  active  growth  of  the  parenchymatous  cells  of  the  cortex, 
in  a  radial  direction,  in  which  case  the  vascular  bundles  assume  an  undulating 
form.  Shortening  is  sometimes  pronounced,  and  it  frequently  has  great  biolog- 
ical significance  where  it  occurs.  Many  roots  shorten  or  contract  longitudinally 
and  thus  draw  the  buds,  located  above,  down  into  the  soil,  so  that  the  latter  are 
protected  from  wounding  and  shielded  from  injurious  atmospheric  conditions. 
In  the  case  of  Arum  maculatum,  the  little  tubers  formed  at  a  depth  of  2  cm.  are 
subsequently  drawn  into  the  soil  to  a  depth  of  10  cm.  If  the  tubers  are 
planted  less  deeply,  strongly  contractile  roots  are  soon  formed,  which  draw 
them  deeper  into  the  soil.  In  the  case  of  Crocus  longiflorus  (Fig.  102),  only 
slender  roots  are  formed  in  the  spring.  Thick  lateral  roots  with  great  con- 
tracting power  are  formed  later,  and  these  drag  the  corm  downward  to  a 
considerable  depth,  and  then  wither  away. 

1  Vries,  Hugo  de,  Ueber  die  Kontraktion  der  Wurzeln.  Landw.  Jahrb.  9 :  37-80.      1880. 


GROWTH    PHENOMENA    CONTROLLED   BY    INTERNAL    CONDITIONS       25 1 

§3.  Tissue  Strains." — Each  plant  organ  consists  of  many  kinds  of  tissues, 
and  the  different  sorts  of  cells  do  not  divide  and  enlarge  at  a  uniform  rate.  It 
thus  follows  that  opposing  forces,  or  stresses,  develop  between  the  tissues,  one 
tissue  pressing  against  another  while  the  latter,  in  its  turn,  also  tends  to  enlarge 
and  press  against  the  former.  Thus  result  what  are  called  tissue  strains, 
which  increase  the  rigidity  of  plant  organs.  In  every  plant  some  organs  are  in 
a  state  of  strain  by  traction  (/.  e.,  they  are  stretched),  while  others  are  under 
pressure  (i.e.,  they  are  compressed).  Strains  may  occur  either  longitudinally 
or  transversely.  Longitudinal  strains  may  be  easily  demonstrated.  Two 
longitudinal  cuts  are  made,  perpendicular  to  each  other,  through  the  center  of 
a  dicotyledonous  stem  or  the  flower  stalk  of  one  of  the  Liliacese  or  of  Taraxacum 
(dandelion),  which  is  still  elongating.  The  four  strips  of  stem  thus  formed  bend 
outward,  the  originally  outer  surface  becoming  concave.  From  this  it  follows 
that  the  epidermis  and  cortex  are  stretched  in  the  uncut  stem,  while  the  pith  is 
compressed.  Splitting  the  stem  allows  the  pith  to  expand  and  the  cortex  to 
contract.  Each  concentric  layer  of  tissue  in  an  internode  that  is  elongating 
is  stretched  with  respect  to  the  next  layer  within  and  compressed  with  respect 
to  the  next  external  layer.  If  the  strips  just  mentioned  are  placed  in  water  the 
bending  becomes  more  pronounced,  and  frequently  results  in  coiling. 

Transverse  strains  may  be  seen  best  in  old  stems  of  dicotyledonous  plants. 
These  strains  are  produced  by  the  occurrence  of  more  rapid  enlargement  in  the 
wood  than  in  the  bark,  so  that  the  latter  is  stretched  and  the  former  compressed. 
If  a  girdling  band  of  bark  is  removed  from  such  a  stem  (willow,  for  example), 
and  if  it  is  then  returned  to  its  original  position,  the  two  ends  fail  to  meet,  be- 
cause of  the  fact  that  the  band  contracted  as  it  was  removed. 


Summary 

1.  The  Grand  Period  of  Growth. — The  enlargement  of  a  plant,  organ,  or  tissue 
begins  at  a  slow  rate,  and  the  rate  gradually  increases  to  a  maximum,  after  which  it 
progressively  decreases  until  enlargement  ceases  altogether.  The  time  period  corre- 
sponding to  this  march  of  the  elongation  rate  is  called  the  grand  period  of  enlargement. 
Each  cell  has  its  grand  period.  The  influence  of  external  conditions  may  lengthen 
or  shorten  the  grand  period  or  may  alter  the  maximum  rate  of  enlargement,  but  the 
general  march  of  the  rate  is  essentially  controlled  by  internal  conditions.  For  ex- 
ample, the  terminal  internode  of  a  seedling  bean  elongated  1.2  mm.  on  the  first  day,  14 
mm.  on  the  seventh  day,  and  2  mm.  on  the  tenth  day. 

a  The  word  strain  is  here  used  in  its  mechanical  sense,  meaning  any  sort  of  deformation, 
whether  of  tension  (enlargement),  of  co mpression  or  of  shearing  (changes  of  shapes  without  any 
change  of  volume).  Many  writers  of  English  still  use  tension  where  strain  is  here  employed, 
being  thus  led  to  the  awkward  teutonicism  by  which  compression  is  called  negative  tension.  It 
may  be  remarked  that  the  force  that  tends  to  produce  any  kind  of  strain  (whether  actual  defor- 
mation occurs  or  not)  is  to  be  called  a  stress,  so  that  there  are  three  kinds  of  stress  correspond- 
ing to  the  three  kinds  of  strain  above  mentioned.  In  this  connection,  see  Ewart's  remarks  in 
v.  2,  p.  62,  footnote  1,  of:  Pfeflfer,  W.,  The  physiology  of  plants.  Translated  by  A.  J.  Ewart, 
Oxford,  1903. — Ed. 


252  PHYSIOLOGY    OF    GROWTH   AND    CONFIGURATION 

2.  Enlargement  of  Roots,  Stems,  and  Leaves. — Elongation  in  roots  is  confined  to  a 
region  near  the  tip.  Different  parts  of  the  elongating  region  exhibit  different  rates  of 
enlargement;  the  most  rapidly  elongating  portion  is  near  the  middle  of  the  region,  while 
the  parts  above  and  below  enlarge  more  slowly.  The  tip  millimeter  of  a  root  of 
Windsor  bean  elongated  but  1.5  mm.  in  24  hours,  while  the  third  millimeter  from  the 
tip  elongated  8.2  mm.,  and  the  tenth  elongated  only  0.1  mm.  The  tip  millimeter  of 
another  root  of  the  same  kind  elongated  1.8  mm.  during  the  first  day,  17.5  mm.  during 
the  fourth  day,  7  mm.  during  the  seventh  day,  and  not  at  all  during  the  eighth  day. 

In  stems,  elongation  is  generally  confined  to  a  few  internodes  near  the  tip,  and  each 
elongating  internode  exhibits  different  rates  of  enlargement  for  its  different  regions. 
In  onion  leaves  growth  is  confined  to  the  basal  portion  in  all  but  very  young  specimens. 

Growth  may  sometimes  result  in  the  contraction  of  an  organ,  as  in  the  contractile 
roots  by  which  Crocus  corms  are  pulled  downward  in  the  soil. 

3.  Tissue  Strains. — Since  all  parts  of  a  plant  organ  do  not  enlarge  at  exactly  cor- 
responding rates,  and  since  the  various  parts  are  all  rather  firmly  joined,  some  tissues 
become  stretched  and  others  compressed,  by  adjacent  tissues.  Strains  may  thus 
be  developed,  in  any  direction,  and  they  result  in  increased  rigidity  of  the  organ- 
Each  concentric  layer  of  tissue  in  an  elongating  internode  is  stretched  with  respect 
to  the  next  layer  within  and  compressed  with  respect  to  the  next  layer  outside.  The 
bark  of  an  enlarging  willow  shoot  shows  transverse  stretching,  while  the  inner  part  of 
the  shoot  is  compressed. 


CHAPTER  III 

INFLUENCE  OF  EXTERNAL  CONDITIONS  ON  GROWTH 

AND  CONFIGURATION1 

§*.  Dependence    of    Growth    and    Configuration    upon    Temperature- 
Medium  temperatures2  are  most  favorable  for  growth,  which  ceases  with  very 
high  and  with  very  low  temperatures.     The  following  table  shows  the  incre- 
ments  of  elongation  of  three  plants  for  a  forty-eight  hour  period,  at  various 
temperatures. 


Temperature 

Lupixus  Albus 

Pisum  Sativum 

Triticum  Vulgare 

(Lupine) 

(Pea) 

( Wheat) 

deg.  C. 

mm. 

mm. 

mm. 

14-4 

9.1 

50 

4-5 

17.0 

11 .0 

5 

3 

6.9 

21.4 

25.0 

25 

5 

41.8 

24  S 

31  0 

3° 

0 

59-i 

25-1 

40.0 

27 

8 

59-2 

26.6 

54- 1 

53 

9 

86.0 

28.5 

50.1 

40 

4 

73-4 

30.2 

43-8 

38 

5 

104.9 

311 

43-3 

38 

9 

91. 1 

33-6 

12.9 

8 

0 

40-3 

36.5 

12  .6 

8 

7 

5-4 

The   minimum,  optimum  and  maximum  temperatures  for  the  growth  of 
several  different  plants  are  shown  in  the  next  table.     This  table  shows  clearly 


Horde um  vulgare  (barley) 

Sinapis  alba  (white  mustard) 

Lepidhun  sativum  (garden  cress) 

Phaseolus  mu'tijlorus  (scarlet-runner  bean) . 

Zea  mays  (maize) 

Cucurbiia  pepo  (gourd,  squash) 


Minimum 

Optimum 

Maximum 

deg.C. 

deg.  C. 

dcg.C. 

5-o 

28.7 

37-7 

0.0 

21.0 

.      28.0 

1.8 

21 .0 

28.0 

9-5 

33-7 

46.  2 

9-5 

33-7 

46.  2 

13-7 

33-7 

46.2 

1  [On  plant  movements  in  general,  see:  Pringsheim,  Ernst  G.,  Die  Reizbewegungen  der  Pflanzen.  326  p. 
Berlin,  1912.] 

2Koppen,  W.,  Warme  und  Pflanzenwachsthum.  Bull.  Soc.  Imp.  Xat.  Moscou  43":  41-110.  1870. 
Sachs,  J.,  Physiologische  Untersuchungen  uber  die  Abhangigkeit  der  Keimung  von  der  Temperatur. 
Jahrb.  wiss.  Bot.  2:  338-377.  i860.  [Lehenbauer,  P.  A.,  Growth  of  maize  seedlings  in  relation  to 
temperature.  Physiol,  res.  1:247-288,  1014.  Also  see:  Fawcett,  H.  S.,  The  temperature  relations 
of  growth  in  certain  parasitic  fungi.      Univ.  Calif.  Pub.  Agric.  Sci.  4:   183-232.  1921.I 

253 


254  PHYSIOLOGY    OF    GROWTH    AND    CONFIGURATION 

that  the  minima,  optima  and  maxima  of  temperature  are  not  the  same  for  differ- 
ent plants.  The  differences  between  the  various  minima  are  especially  strik- 
ing. Whereas  growth  of  some  plants  is  terminated  at  from  io°  to  i5°C,  other 
plants  are  still  able  to  develop  at  o°;  thus  Soldanella  (an  alpine  plant  of  the 
primrose  family)  begins  to  develop  in  the  spring  when  the  plants  must  break 
through  the  snow  before  the  shoots  reach  the  air. 

Still  more  striking  variations  in  minimum  and  maximum  temperatures  may 
be  observed  in  microorganisms.  Bacteria  are  known,  for  instance,  that  not 
only  live,  but  multiply  vigorously,  at  o°C.  In  sea  water  at  o°  have  been  found 
as  many  as  150  bacteria  per  cubic  centimeter.  If  such  water  is  allowed  to  stand 
without  change  of  temperature,  this  number  increases  to  1750  in  four  days, 
which  shows  that  bacteria  continue  to  reproduce  at  the  temperature  of  the 
freezing  point  of  water. 

Bacillus  thermophilus  is  very  different  from  the  bacteria  just  mentioned, 
being  able  to  reproduce  actively  at  7o°C.  While  the  optimum  temperature 
for  most  bacteria  lies  between  10  and  150,  Bacillus  thermophilus  ceases  to 
reproduce  at  temperatures  below  420. 

Bacterial  spores  can  endure  great  extremes  of  temperature,  some  being  able 
to  withstand  a  short  period  of  exposure  in  liquid  oxygen  at-2i3°C.  The  spores 
of  some  soil  bacteria  can  bear  very  high  temperatures,  but  the  higher  the  tem- 
perature is,  the  shorter  is  the  time  required  to  kill  the  spores.  The  time  periods 
required  to  kill  such  spores  in  steam  at  various  high  temperatures  are  given 
below. 

Temperature  of  Time  Required  to 

Steam,  Kill, 
deg.C.  hours 

100 16 

105-110 2-4 

115 0.5-1.0 

125-130 0.08 

135 0.02-0.08 

140 : 0.02 

Temperature  affects  the  configuration  as  well  as  the  rate  of  enlargement  of 
plants.  In  polar  regions  and  on  high  mountain-tops,  where  the  temperatures 
are  low,  it  is  usual  to  find  plants  very  short  and  lying  very  close  to  the  soil.  It 
has  been  observed  that  the  soil  of  high  mountains  is  relatively  much  warmer 
than  the  air,  and  plants  that  remain  close  to  the  soil  are  thus  in  a  warmer  en- 
vironment than  would  be  the  case  if  their  stems  extended  up  into  the  air. 
Moreover,  these  low  forms  are  covered  in  winter  with  a  deep  layer  of  snow, 
which  protects  them  from  freezing.  The  stems  and  branches  of  Pinus  humilis 
do  not  grow  vertically  into  the  air  but  occupy  a  horizontal  position.  Even 
trunks  as  much  as  20  cm.  in  diameter,  which  might  quite  well  support  a  broad 
top  if  they  had  a  vertical  position,  lie  almost  horizontal  upon  the  soil  surface. 
So  much  for  the  observed  facts,  but  experiments  are  needed  for  more  definite 
knowledge.     Recently,  it  has  been  possible  to  show  that  changes  in   tempera- 


INFLUENCE    OF   EXTERNAL    CONDITIONS    ON    GROWTH 


255 


ture  alone,  other  conditions  being  equal,  are  sufficient  to  produce  differences  in 
the  external  appearance  of  certain  plants.  Thus,  for  example,  the  stem  of 
Mimuliis  tilingii  grows  vertically  upward  at  ordinary  temperatures,  while  it 
bends  or  even  assumes  a  horizontal  position  at  lower  temperatures. 

It  is  well  known  that  the  climate  of  high  mountains  is  characterized  by  great 
fluctuations  in  temperature,  and  the  question  arises  whether  this  environmental 
feature  does  not  also  play  a  part  in  producing  the  peculiar  aspect  of  alpine  plants. 
To  answer  this  question  by  experiment,  plants  from  low  altitudes  were  grown 
from  the  seed  in  vessels  that  were  surrounded  with  ice  at  night  and  were 
exposed  to  the  usual  lowland  conditions  during  the  day,  thus  simulating  the 
daily  temperature  fluctuation  observed  on  high  mountains.  Plants  thus 
grown  possessed  the  special  peculiarities  of  the  forms  occurring  in  alpine  floras 
(limited  enlargement,  short  internodes,  small,  tough  leaves,  and  early  flowering 
periods). 

A  striking  example  of  the  influence  of 
temperature  upon  plant  configuration  is 
found  in  the  case  of  a  species  of  acetic 
acid  bacterium  (Bacterium  pasteurianum) . 


>/ 


—Bacterium  pasteurianum, 
grown  at  34°C. 


Fig.    104. — Bacterium    pasteurianum, 
grown  at  40°C. 


Cultivated  at  medium  temperatures,  this  organism  assumes  the  form  of  short 
rods,  usually  joined  together  in  rows  or  chains  (Fig.  103).  If  a  part  of  such 
a  culture  is  transferred  to  fresh  nutrient  solution  and  subjected  to  a  tem- 
perature of  4o°C,  the  cells  elongate,  after  a  few  hours,  into  slender  filaments 
(Fig.  104).  These  filaments  are  sometimes  as  much  as  150  times  as  long  as  are 
the  original  rod-shaped  forms.  When  such  a  filamentous  culture  is  returned  to 
a  temperature  of  340,  the  rod  form  is  once  more  produced;  the  filaments  first 
develop  local  swellings  and  then  the  portions  between  these  thickened  regions 
divide  into  the  short  cells  of  the  other  form.  The  thickened  portions  remain 
unchanged,  and  finally  die. 

The  dependence  of  development  upon  temperature  can  be  established  by 
phenological  observations.  To  find  out  the  temperature  requirements  of  any 
annual  plant,  the  average  or  maximum  temperature,  above  zero,  is  recorded  for 
every  day  from  the  time  of  planting  until  the  complete  ripening  of  the  fruit. 
The  sum  of  these  daily  temperatures  is  taken  to  represent  the  amount  of  heat 
necessary  for  the  complete  development  of  the  plants  in  question. 


256 


PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 


It  is  self-evident  that  such  methods  of  observation  can  give  but  inaccurate 
and  merely  approximate  results. a  Plant  growth  is  not  proportional  to  tem- 
perature. On  a  certain  day,  for  example,  a  temperature  of  350  may  occur,  while 
the  best  temperature  for  the  growth  of  the  plant  in  question  may  be  250.  The 
additional  io°  may  not  only  be  useless  in  promoting  growth  but  it  may  even  be 
injurious  to  the  plant.  Because  a  plant  has  developed  under  conditions  giving 
a  certain  sum  of  daily  temperatures,  it  is  not  safe  to  conclude  that  the  same 
plant  might  not  have  developed  equally  well  under  conditions  giving  a  smaller 
temperature  summation.  The  birch  grows  near  Kiev  at  a  higher  temperature 
than  it  experiences  in  the  neighborhood  of  Petrograd.  The  following  table,  by 
which  the  course  of  development  of  the  vegetation  at  Brussels  and  at  Petrograd 
are  compared,  substantiates  this  conclusion.  Six  groups  of  plants  are  considered, 
the  first  group  consisting  of  the  earliest-flowering  plants  (Anemone,  Corylus) 
and  the  other  groups  being  composed  of  progressively  later-flowering  forms. 
The  temperature  measurements  were  begun  in  Brussels  on  Jan.  16,  and  in 
Petrograd  on  Apr.  8.  The  date  of  flowering  for  Brussels  is  given  for  each  group 
of  plants  and  also  tjie  number  of  days  between  this  date  and  the  .corresponding 
date  for  Petrograd.  The  temperature  summations,  above  o°C,  are  also  given 
for  each  group  at  the  two  stations,  up  to  the  time  of  flowering  in  each  case. 


Group  No. 

Date  of 

Flowering 

at  Brussels' 

Difference  between 
Dates  of  Flower- 
ing at  Brussels 
and  at  Petrograd 

Summation  of  Daily  Tempera- 
tures Above  o°C. 

At  Brussels 

At  Petrograd 

1 
2 

3 

4 

5 
6 

Mar.  16 
Apr.     7 
Apr.  29 
May  19 
June    4 
June  30 

days 

5i 
44 
39 
33 
22 
11 

deg.    C. 
184 
334 

583 

791 
1017 
1466 

deg.    C. 

93 
216 
421 
617 
698 
937 

These  observations  show  that  the  plants  at  Petrograd  came  to  flowering  with 
a  smaller  temperature  summation  than  did  those  at  Brussels.  It  is  also  note- 
worthy that  the  date  of  flowering  at  the  northern  station  is  very  markedly  later 
than  that  at  the  southern  only  in  case  of  the  early-flowering  forms,  and  that  the 

0  On  the  general  problem  of  integrating  temperature  values  to  obtain  a  measure  of  the 
effectiveness  of  temperature  conditions  for  plant  growth  and  development,  see:  Livingston,  B. 
E.,  Physiological  temperature  indices  for  the  study  of  plant  growth  in  relation  to  climatic  con- 
ditions. Physiol,  res.  1:  399-420.  1916-  Other  references  are  there  given.  Also  see: 
McLean,  F.  T.,  A  preliminary  study  of  climatic  conditions  in  Maryland,  as  related  to  plant 
growth.  Ibid.  2  :  1 29-208.  1917-  Hildebrandt,  F.  M.,  A  physiological  study  of  the  climatic 
conditions  of  Maryland  as  measured  by  plant  growth.  Ibid.  2  :  341-405-  1921-  It  must  be 
remembered  that  many  environmental  conditions  besides  temperature  are  influential  in 
determining  plant  behavior,  and  that  these  also  vary  from  day  to  day  and  from  place  to 
place.  Blackman's  discussion  of  limiting  conditions  for  plant  processes  has  a  bearing  on  this 
general  problem.  See :  Blackman,  1905,  1908.  (See  note  w,  p.  35-)  See  also :  Livingston,  B.  E., 
and  Shreve,  Forrest,  The  distribution  of  vegetation  in  the  United  States,  as  related  to 
climatic  conditions.  16  +  590  p.     Carnegie  Inst.,  Washington,  Publ.  284.     1921—  Ed. 


INFLUENCE    OF   EXTERNAL   CONDITIONS    ON    GROWTH  257 

difference  between  the  two  dates  decreases  as  the  date  for  Brussels  becomes 
later;  the  difference  is  only  eleven  days  in  the  case  of  the  latest-flowering  forms 
here  considered,  the  linden  being  one  of  this  group.     This  last  observation  may 
be  explained  by  pointing  out  that  the  period  with  temperatures   below   the 
freezing  point  of  water  is  also  important  in  the  development  of  perennials.     This 
is  a  period  of  low  activity,  but  not  one  of  complete  inactivity,  and   various 
chemical  transformations  are  completed  during  the  cold  winter,  which  prepare 
the  plant  for  the  active  growth  of  spring.     These  transformations  are  accelerated 
only  very  slightly  by  higher  temperatures,  as  may  be  seen  in  the  case  of  the 
sixth  group  considered  above.     The  linden  began  to  flower  at  Brussels  only 
eleven  days  earlier  than  at  Petrograd,  although  the  temperature  at  the  southern 
station  was  already  above  zero  by  the  middle  of  January,  and  zero  was  not 
passed  as  Petrograd  until  early  April.     Direct  experiment  shows  that  higher 
temperature  alone  is  not  sufficient  to  bring  plants  out  of  the  resting  condition 
into  active  growth.     In  an  experiment  in  this  connection  twigs  were  removed 
from  a  cherry  tree  at  intervals  throughout  the  winter  and  placed  in  a  green- 
house with  a  temperature  of  from  20  to  25°C.     Twigs  cut  in  the  autumn  failed  to 
produce  leaves  or  flowers  and  finally  died,  while  those  cut  during  the  winter  and 
early  spring  flowered  after  they  had  been  exposed  to  the  greenhouse  temperature 
for  a  certain  time,  this  period  becoming  shorter  with  the  advance  of  the  season. 
The  number  of  days  of  greenhouse  conditions  required  to  produce  flowers  on 
these  twigs  is  shown  below,  for  twigs  cut  at  various  dates.     In  spite  of  the 
favorable  temperature  of  the  greenhouse,  the  earlier  the  twigs  were  cut,  the 
longer  was  the  period  before  flowering. 

Period  Required  to 
Date  of  Cutting  and  Placing  in  Greenhouse  Produce  Flowers 

days 

Dec.  14 

,  27 

Jan.    10 ig 

Feb.     2 

Mar.    2 I7 

,,  12 

Mar.  23 o 

Apr-  ^ .::::::::::::::::::::::::         s 

This  experiment  shows  that,  in  making  an  estimate  of  the  amount  of  heat 
necessary  for  development  of  the  plant,  it  is  necessary  to  consider  the  resting 
period  which  may  continue,  or  even  begin,  in  spite  of  temperature  conditions 
generally  favorable  to  active  growth.  Certain  trees  and  shrubs,  when  trans- 
ferred from  temperate  to  warm  climates  and  thus  removed  from  the  conditions 
of  their  winter  resting  period,  although  adequately  supplied  with  moisture  and 
heat  (so  that  vital  activity  need  not  be  directly  retarded),  still  retain  their 
earlier  habit  for  a  long  time,  losing  their  leaves  and  passing  over  into  the  resting 
condition  for  a  part  of  the  year.  The  life  of  the  plant  is  thus  not  governed 
entirely  by  the  amount  of  heat  received;  the  internal  conditions  of  the  plant 
must  also  be  considered.6 

"In  this  connection,  see : Klebs,  G.,  Ueber  das  Treiben  der  einheimischen Baume speziell der 
Buche.     Abhandl.  (math.-naturw.,  Kl.,)  Heidelberg.     Akad.  Wiss.  3:  1-116      1014      This 
author  has  succeeded  in  overcoming  the  tendency  to  become  dormant,  by  the  control  of  culture 
conditions. — Ed. 
17 


258 


PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 


As  Molisch1  has  shown,  even  though  the  resting  period  may  not  be  ter- 
minated by  subjecting  the  plant  to  medium  temperatures,  it  can  be  brought  to  a 
close  by  application  of  high  temperature,  especially  if  the  branches  to  be  forced 
are  immersed  for  from  ten  to  twelve  hours  in  water  at  300  to  35°C.  or  above. 
Fig.  105  shows  a  hazel  branch  the  right  side  of  which  was  subjected  to  Molisch's 
warm-bath  treatment,  while  the  left  side  was  untreated.  Nine  days  after  the 
treatment  the  right  side  was  already  in  full  bloom,  while  the  buds  on  the  left 
side  were  still  in  the  resting  condition. 

§2.  Dependence  of  Growth  and  Configuration  upon  the  Oxygen  Content  of 

the  Surroundings. — Higher  plants  usually  grow  only 
when  they  may  absorb  oxygen;  when  the  oxygen  sup- 
ply is  cut  off  growth  is  immediately  stopped.  Noba- 
kikh2  has  shown,  however,  that  when  certain  con- 
ditions are  fulfilled  seed-plants  may  be  made  to  grow 
in  an  atmosphere  free  from  oxygen.  He  placed  the 
plants  in  a  solution  of  glucose.  A  double  object  was 
thus  attained:  the  plants  were  furnished  with  nutri- 
ent material  and,  at  the  same  time,  the  products  of 
fermentation  harmful  to  growth  were  allowed  to 
pass  into  the  solution.  These  results  were  later  sub- 
stantiated by  other  authors.  As  has  been  pointed 
out  above  (page  214),  the  amount  of  oxygen  ab- 
sorbed by  germinating  seedlings  increases  as  the 
growth  rate  becomes  more  rapid.  The  march  of  the 
respiration  rate  in  germinating  seeds  may  be  expressed 
by  a  grand  curve  of  respiration  which  agrees,  in 
general,  with  the  grand  curve  of  growth  (see  page  241 ) . 

resting  "udThf  wa^i^atTrl         The  amount  of  oxygen  contained  in  the  surround- 
the  right  side  of  the  branch  ing  atmosphere  exerts  a  marked  influence  upon  the 

rate  of  growth.  An  excess  of  this  gas,  as  well  as  a 
deficiency,  decreases  the  growth  rate  and  may  even  cause  growth  to  cease 
entirely.  On  the  other  hand,  if  the  pressure  of  the  air  does  not  vary  too  far 
from  the  normal,  in  either  direction,  then  such  a  change  produces  an  accelera- 
tion of  growth.  This  brings  out  the  very  noteworthy  fact  that  growth  under 
normal  atmospheric  pressure  is  less  rapid  than  when  the  pressure  is  somewhat 
higher  or  somewhat  lower  than  normal.3 

It  appears  that  oxygen  is  one  of  the  most  important  factors  in  the  life  of 
microorganisms.  For  some  organisms  oxygen  is  essential,  others  can  exist  a 
long  time  without  it,  and  still  others  can  reproduce  only  under  conditions  where 
it  is  entirely  absent  (see  Part  I,  Chapter  VIII).  Microorganisms  may  thus  be 
separated  into  aerobes  and  anaerobes,  according  to  their  oxygen  requirement. 

1  Molisch,  H.,  Das  Warmbad  als  Mittel  zum  Treiben  der  Pflanzen.     Jena,  1909. 

2  Nabokikh,  A.  I.,  Temporary  anaerobiosis  of  higher  plants.  'Russian.]  Dissert.  New  Russia  Univ., 
St.  Petersburg,  1904.  Nabokich,  A.  J.,  [Idem],  Temporare  Anaerobiose  hohere  Pflanzen.  Landw.  Jahrb. 
38:  51-194      1909- 

3  Jaccard,  Paul,  Influence  de  la  pression  des  gaz  sur  le  developpement  des  vegetaux.  Rev.  gen.  bot. 
5:  289-302,  348-354.  382-388.      1893- 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH 


259 


Aerobes  require  oxygen  for  their  development,  while  anaerobes  can  develop 
in  the  complete  absence  of  this  gas.  Anaerobes  are  either  obligate  or  facultative. 
Obligate  anaerobes  reproduce  only  when  oxygen  is  entirely  absent;  it  acts  upon 
them  as  a  poison.  Facultative  anaerobes  are  not  seriously  injured  by  oxygen 
and  they  also  thrive  in  its  absence.  Acetic  acid  bacteria  may  be  mentioned  as 
an  illustration  of  aerobes;  yeasts,  of  facultative  anaerobes;  and  the  bacteria  of 
butyric  acid  fermentation  are  obligate  anaerobes. 

Motile  bacteria  may  be  used  as  an  indicator  of  the  relative  amounts  of 
oxygen  present  in  different  regions  of  a  mass  of  nutrient  medium.  In  Fig.  106, 
respiration  figures  for  three  different  kinds  of  bacteria  are  shown.  In  each  case  a 
drop  of  the  culture  was  placed  upon  a  slide  and  covered,  the  circular  cover  glass 
being  raised  at  one  edge  by  a  bit  of  platinum  wire.  The  drop  of  liquid  thus  came 
to  lie  under  the  half  of  the  cover  that  was  nearest  to  the  slide.  The  first  figure 
(I)  shows  the  behavior  of  typhus  bacteria,  which  are  aerobes.  The  moving 
cells  are  most  numerous  in  the  region  of  the  drop  that  contains  the  most  oxygen. 
Those  in  the  zone  r  have  ceased  moving  because  of  deficiency  of  oxygen,  while 


an 


I  n 

Fig.  106. — Respiration  figures  of  motile  bacteria. 


m 

{After  Beijerinck.) 


the  zone/  is  free  from  bacteria.  The  next  figure  (II)  represents  the  distribution 
of  spirillum,  bacteria,  which  require  a  small  amount  of  oxygen.  The  cells  have, 
collected  in  the  zone  sp,  a  certain  distance  from  the  free  surface  of  the  liquid. 
The  third  figure  represents  the  activity  of  anaerobes  in  this  sort  of  mounting. 
All  the  cells  have  collected  in  the  central  zone  of  the  drop,  an,  where  oxygen 
is  least  plentiful. 

In  the  culture  of  anaerobes  it  is  essential  that  precautions  be  taken  to  pre- 
vent the  access  of  oxygen  to  the  nutrient  medium.  For  this  purpose  Pasteur 
employed  a  layer  of  oil  over  the  nutrient  solution/  The  air  may  also  be 
pumped  out  of  the  vessels  in  which  the  cultures  are  grown,  or  the  oxygen  may 
be  absorbed  from  the  air  of  the  culture  vessels  by  means  of  a  solution  of  pyro- 
gallol  and  potassium  hydroxide.  The  test-tube  containing  the  culture  is  placed 
within  another  larger  test-tube,  which  is  partially  filled  with  alkaline  pyrogallol 
(P,  Fig.  107).     The  larger  tube  is  tightly  closed  with  a  rubber  stopper,  the 

c  The  effect  of  an  oil  layer  in  lowering  the  rate  of  oxygen  supply  to  the  liquid  below  depends 
upon  the  kind  of  oil  used  as  well  as  upon  the  thickness  of  the  layer.  It  must  not  be  assumed 
that  such  an  oil  layer  cuts  off  the  supply  of  oxygen  entirely.  Of  course  the  contents  may  be 
placed  in  a  chamber  of  nitrogen  or  hydrogen,  etc. — Ed. 


260 


PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 


oxygen  is  absorbed  by  the  alkaline  pyrogallol,  and  the  bacteria  of  the  inner  tube 
are  thus  exposed  to  an  atmosphere  without  oxygen. 

The  form  of  the  plant  may  also  be  controlled  by  the  oxygen  content  of  the 
surroundings.  Thus  Mucor,  a  very  common  mould,  develops  a  much-branched 
mycelium  in  the  presence  of  oxygen,  and  produces  vertical  sporangiophores  that 
grow  up  from  the  mycelium,  sometimes  attaining  a  length  as  great  as  10  cm. 
(Fig.  108).  If,  however,  the  mycelium  is  grown  in  the  bottom  of  a  flask  filled 
with  beer-wort,  where  the  supply  of  oxygen  is  inadequate  for  the  usual  growth, 
then  alcoholic  fermentation  begins  and  the  mycelium  divides  into  single  cells, 
which  become  separated  and  resemble  those  of  ordinary  yeasts.     Thus  arises 


// 


^y 


Fig.     107. — Culture 
of  anaerobes. 


Fig.  108. — Mucor  mucedo,  showing  mycelium  and  sporangiophores. 


the  so-called  mucor  yeast  (Fig.  109).     This  example  represents  an  extreme  case 
of  the  influence  of  the  medium  upon  the  form  of  organisms. 

§3.  Influence  of  Other  Gases  on  Growth  and  Configuration. — Plants 
orow  normally  only  when  the  air  about  them  has  its  usual  composition.  The 
carbon  dioxide  content  of  the  atmosphere  is  about  0.03  to  0.04  per  cent.  The 
investigations  of  Brown  and  Escombe1  and  those  of  Chapin2  showed,  in  a 
quite  unexpected  way,  that  an  increased  carbon  dioxide  content  of  the  atmos- 
phere was  not  only  not  favorable  to  the  growth  of  certain  plants  but  might  even 
be  injurious.  An  increase  in  the  carbon  dioxide  content,  so  that  this  became 
0.2  per  cent.,  resulted  in  unhealthy  plants,  which  were  often  very  poorly  sup- 
plied with  leaves  (Fig.  no).  [But  improved  growth  has  been  secured  in 
many  cases  by  slightly  increasing  the  carbon-dioxide  content  of  the 
atmosphere.] 

1  Brown,  Horace  T.,  and  Escombe,  F.,  The  influence  of  varying  amounts  of  carbon  dioxide  in  the  air  on 
the  photosynthetic  process  of  leaves  and  on  the  mode  of  growth  of  plants.  Proc.  Roy.  Soc.  London  70: 
397-413.     1902. 

2  Chapin,  Paul,  Einfluss  der  Kohlensaure  auf  das  Wachsthum.     Flora  91 :    348-379-     1902. 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH 


26l 


Neliubov1  has  shown  that  the  form  of  plants  is  influenced  by  the  presence  of 
very  small  amounts  of  illuminating  gas  in  the  air  about  them,  but  especially  by 


Fig.  109. — Formation  of  mucor-yeast  in  an  oxygen-free  medium. 


A  B 

Fig.  iio. — Impatiens  platypetala;  A,  in  normal  atmosphere;  B,  in  atmosphere  rich  in  carbon 

dioxide. 


1  Neljubow,  D.,  Ueber  die  horizontale  Xutation  der  Stengel  von  Pisum  sativum  und  einiger  anderen 
Pflanzen.  Beih.  Bot.  Centralbl.  10:  128-138.  1901.  Idem,  Geotropismus  in  der  Laboratoriumsluft. 
Ber.  Deutsch  Bot.  Gcs.  29:  97-112.     1911. 


262 


PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 


ethylene  and  acetylene,  which  are  present  in  illuminating  gas.  The  shoots 
grow  erect  in  an  atmosphere  without  illuminating  gas,  but  when  even  very  min- 
ute traces  of  this  gas  are  present  they  bend  and  assume  a  horizontal  position 
Fig.  in).  Many  different  kinds  of  gases  and  vapors  are  thus  injurious  to  the 
growth  of  plants.1 


pIG    ITI pea  seedlings  grown  in  darkness;  /  and  III  in  laboratory  air  containing  illumin- 
ating gas,  II  in  the  same  air  with  the  poison  gas  removed.      (After  Neliubov.) 


1 

A  B 

Fig.  112. — Effect  of  ether  upon  the  flowering  of  lilac.  All  shoots  excepting  the  fifth 
from  the  left  (as  seen  in  A)  were  treated.  The  untreated  shoot  is  seen  unaltered  in  B,  where 
the  others  are  all  in  full  leaf  and  flower. 

1  Haselhoff,  Emil,  and  Lindau,  G.,  Die  Beschadigung  der  Vegetation  durch  Rauch;  Handbuch  zur 
Erkennung  und  Beurteilung  von  Rauchschaden.  Leipsig,  1903.  [In  this  connection,  see:  Crocker.  W., 
and  Knight,  L.  I.,  Effect  of  illuminating  gas  and  its  constituents  on  flowering  carnations.  Plant  world 
12:  83-88.  1909.  Idem,  Toxicity  of  smoke.  Bot.  gaz.  55:  337-371-  1913.  Crocker,  W.,  Knight, 
L.  I.,  and  Rose,  R.  C,  A  new  method  of  detecting  traces  of  illuminating  gas.     Science,  n.s.  31 :  636.     1910.] 


INFLUENCE    OF   EXTERNAL    CONDITIONS    ON    GROWTH 


263 


On  the  other  hand,  some  gases  have  a  stimulating  effect  upon  growth.  In 
Johannsen's1  experiments,  bulbs  sprouted  much  more  rapidly  in  an  atmosphere 
containing  ethyl  ether  than  in  one  lacking  it.  Johannsen  recommended  treat- 
ment with  ether  as  a  method  for  forcing  plants.  In  Fig.  112,  A,  is  shown  a 
branch  of  Syringa  (lilac)  in  November,  eight  days  after  treatment  with  ether 
vapor;  the  fifth  twig  from  the  left  was  protected  from  contact  with  the  gas. 
In  Fig.  112,  B,  the  same  branch  is  shown  three  weeks  after  treatment,  and  is  in 
full  bloom  excepting  that  the  twig  originally  untreated  (here  also  on  the  right) 
still  remains  leafless. 

§4.  Influence  of  Moisture  on  Growth  and  Configuration. — The  condition  of 
the  soil  and  that  of  the  air,  with  respect  to  water,  determine  the  amount  of 
water  absorbed  and  also  its  rate  of  movement  through  the  plant.  When  the 
atmosphere  is  saturated  with  water  vapor,  transpiration  from  the  leaves  is 
materially  lessened  and,  consequently,  the  further  absorption  of  water  by  the 
roots  is  similarly  decreased.  Dry  air,  on  the 
other  hand,  accelerates  both  transpiration 
and  water  absorption. 

Plants   grow    luxuriantly    only    with    a 
plentiful  supply  of  water.     Tropical  vegeta- 
tion   is    exceptionally    luxuriant    since    an 
abundance  of  water  is  here  combined  with 
favorable    temperature     conditions.      The 
virgin  forests  of  the  tropics  are  frequently 
impenetrable  jungles,  where  plants  grow  not 
only  on  the  soil  but  even  on  each   other 
(epiphytes).     It  is  quite  different  with  arid 
regions;  the  plant  world  here  maintains  only 
a  scanty  existence.     Parallel  with  the  de- 
creased number  of  plants  occurring  in  arid 
regions,    the    individual    plant    also  is  smaller    in    such   regions.     Plants  of 
moist  regions  have  well-developed  foliage,  often  with  very  large  leaves  that  have 
a  high  water  content.     Plants  in  dry  climates  have  relatively  small  leaf  surfaces, 
so  that  the  loss  of  water  is  not  so  great.     Thus  the  leaves  of  Rubus  squarrosa 
(Fig.  113),  which  is  closely  related  to  the  European  raspberry  {Rubus  idaus) 
are  very  small.     Many  xerophytes,  such  as  the  cacti,  have  no  leaves  at  all,  or 
they  lose  them  very  soon  after  they  are  formed.     In  this  case  the  activities 
that  are  usual  for  leaves  occur  on  the  stem.     Such  plants  are  furnished  with 
many  arrangements  that  hinder  the  loss  of  water.     The  epidermis  is  very  tough, 
frequently  possesses  hairs,  and  is  often  covered  by  wax  and  other  incrustations. 
Thus  Rochea  falcata,  a  South  African  plant,  is  armed  with  a  siliceous  coat  of 
mail.     A  cross-section  of  the  leaf  shows  that  the  small  cells  of  the  epidermis 
are  overlaid  with  a  continuous  layer  of  large,  bladder-like  cells  (Fig.  114),  the 
walls  of  which  are  richly  impregnated  with  silica.     These  siliceous  cells  are  filled 
with  water,  which  is  replaced  by  air  only  when  they  become  old.     As  long  as 

1  Johannsen,  Wilhelm  L.,  Das  Aetherverfahren  beitn  Fruhtreiben.      2te  Aufl.  Jena,  1906. 


Fig.  113. — A  branch  of  Rubus  squarrosa 
{Y<L  natural  size).      (After  Wiesner.) 


264 


PHYSIOLOGY    OF    GROWTH    AND    CONFIGURATION 


these  cells  contain  water  they  behave  like  reservoirs  from  which  the  deeper- 
lying  cells  of  the  leaf  draw  their  supply. 

The  leaves  of  Stipa  capillata  (Fig.  115)  furnish  an  example  of  characteristic 
arrangements  that  prevent  excessive  transpiration.     Fig.  115,  A'  shows  a  cross- 


Fig.  114. — Section  through  leaf  of  Rochea  falcata,  showing  siliceous  cells  of  upper  epidermis. 


section  of  a  leaf  of  this  plant  under  normal  conditions.  When  drought  begins, 
however,  the  stomata  not  only  close  but  the  leaf  also  rolls  and  forms  a  tube 
(Fig.  115,  A),  so  that  only  one  of  its  surfaces — and  indeed  the  surface  that 
possesses  thick  cuticle  and  is  quite  devoid  of  stomata — is  exposed  to  the  outer 


Fig.  115. — Cross-sections  through  leaves  of  Stipa  capillata  (A,  A')  and  of  Festuca  alpestris  (B). 


air.     All  the  stomata  are  then  on  the  inner  surface  of  the  leaf.     Fig.  115,  B, 
represents  a  cross-section  of  a  similarly  rolled  leaf  of  Festuca  alpestris. 

Other  arrangements  are  exhibited  by  Dischidea  rafflesiana,  a  climbing  plant 
with  two  kinds  of  leaves;  some  of  the  leaves  have  the  usual  form,  but  others  are 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH 


2°5 


like  bags  or  pouches,  with  an  opening  above.  A  vigorous  aerial  root  arises 
from  the  stem  at  the  place  of  attachment  of  the  bag  and  grows  down  into  the 
cavity  of  the  latter.  Water  collects  in  the  bag  when  it  rains,  and  this  stored 
water  is  absorbed  by  the  root  and  thus  transferred  to  the  rest  of  the  plant  (Fig. 
116). 


Fig.    116. — Diichidia  raffiesiana,    showing  sack-like  leaves   with   aerial  roots  in   the  cavity. 


Aquatics  are  likewise  distinguished  by  special  structures.  Their  weak  stems 
are  permeated  with  numerous  air. passages.  The  submerged  leaves  usually 
have  deeply  cleft  lamina,  with  filamentous  lobes.  When  such  plants  develop 
on  land,  however,  the  form  of  the  leaf  often  becomes  remarkedly  altered.  Ra>i- 
unculns  fluitans,  for  instance,  is  such  an  aquatic  with  filamentous  leaves  (Fig. 
117,  1).  When  growing  on  land  the  aerial  leaf  has  the  typical  broad  lamina 
(Fig.  117,  2).     Several  kinds  of  leaves  are  frequently  found  on  the  same  stem. 


266 


PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 


The  flowering  specimen  of  Bidens  beckii  shown  in  Fig.  118  bears  three  kinds  of 
leaves.  The  lower,  submerged  part  of  the  stem  bears  the  deeply  cleft  leaves 
typical  of  many  aquatics.  The  upper  part  of  the  stem,  however,  which 
formed  above  the  surface  of  the  water,  has  simple,  nearly  entire  leaves.  In  the 
intermediate  region  of  the  stem  are  found  leaves  that  are  intermediate  in  char- 
acter/ The  ordinary  arrow-head  {Sagittaria  sagittifolia) ,  which  grows  in  stag- 
nant or  slowly-flowing  water,  has  arrow-shaped  leaves  with  long  petioles.  If 
the  plants  are  grown  entirely  under  water,  then  only  linear  leaves  are  formed, 
but  if  the  water  level  is  not  very  high  (Fig.  119),  only  the  completely  sub- 


Fig.  117. — Ranunculus  fluilans.     i,  water  form;  2,  land  form. 


merged  leaves  remain  narrow,  while  the  rest  assume  the  usual  arrow-shaped 
form.     There  are  numerous  transition  stages  between  these  two  forms. 

These  observations  lead  to  the  conclusion  that  the  form  of  the  plant  is 
greatly  influenced  by  the  amount  of  available  water.  This  conclusion  is  sub- 
stantiated by  direct  experiment.  If  one  specimen  of  an  herbaceous  annual  is 
grown  with  rather  dry  soil  and  atmospheric  conditions,  and  if  another  is  grown 
in  very  moist  soil  and  in  a  nearly  saturated  atmosphere,  plants  of  very  different 
structure  are  developed.  The  experiment  with  dry  conditions  may  be  conducted 

d  For  a  discussion  of  the  conditional  determination  of  leaf-form  in  aquatic  plants,  see: 
McCallum,  W.  B.,  On  the  nature  of  the  stimulus  causing  the  change  of  form  and  structure  in 
Proserpinaca  palustris.  Bot.  gaz.  34:  93-108.  1902.  MacDougal,  D.  T.,  The  determina- 
tive action  of  environic  factors  upon  Neobeckia  aquatica  Greene  [Nasturtium  lacustre  A. 
Gray].     Flora  106:  264-280.     1914- — Ed. 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH 


267 


by  placing  the  plant  under  a  bell-jar,  with  a  vessel  of  calcium  chloride  or  concen- 
trated sulphuric  acid  to  reduce  the  vapor  pressure  of  water.  To  obtain  moist 
conditions,  a  sponge  saturated  with,  water  may  be  introduced  into  the  bell-jar  and 
the  walls  of  the  latter  may  be  moistened.  The  plant  develops  long  internodes 
and  broad  leaf-blades  in  a  moist  atmosphere,  but  short  internodes  and  much 
smaller  leaf-blades  prevail  under  dry  conditions.  The  anatomical  characters  of 
the  two  plants  are  likewise  quite  different.     Plants  that  have  been  cultivated 


Fig.  118. — Bidens  beckii.  The  Fig.  119. — Sagittaria  sagiuifolia.  Lower,  linear  leaves 
lower  leaves  have  formed  under  formed  under  water;  upper,  arrow-shaped  leaves  formed 
water  and  the  upper  ones  in  air.  in  air. 


with  dry  soil  and  dry  air  have  a  thick  cuticle,  well-developed  collenchyma,  and 
both  bast  and  wood  fibers.  Plants  grown  under  moist  conditions  have  thin 
cuticle  and  poorly  developed  woody  tissue,  and  collenchyma  and  bast  fibers  are 
often  not  formed  at  all.  An  experiment  with  Tropceohim  majus1  may  serve 
as  an  example  here.  The  plants  were  cultivated  under  four  different  sets  of 
conditions,  as  shown  in  the  table  below,  which  also  presents  the  results  of 
the  experiment. 

1  Kohl,  1886.     [See  note  3,  p.  I35-I 


268 


PHYSIOLOGY    OF    GROWTH   AND    CONFIGURATION 


Cul- 

External 
Conditions 

Relative 
Size  of 
Leaf- 
blade 

Kind 

OF 

Cuticle 

Anatomical  Characters 

ture 

Epidermis 

No. 

Soil 

A» 

Collenchyma 

i         Moist 

i 

2  Moist 

3  Dry 

4  Dry 

Moist 

Dry 

Moist 
Dry 

5 

4 

3 
i 

Thin 

Thick 

Thin 
Thick 

Cells  tangentially 
elongated,  thin 
outer  walls 

Cells  radially  elon- 
gated, thick  outer 
walls 

Cells   almost   cubical 

Cells  very  much  elon- 
gated radially 

None 

Two    adjacent    layers 
well  developed 

Poorly  developed 
Less    developed    than 
in  2 

M 


DOOOOC 


13I3QQ> 


XX3GC 


The  leaves  formed  by  Tropaeolum  plants  growing  in  moist  air  and  moist 
soil  were  thus  five  times  as  large  as  those  formed  in  the  driest  cultures.     In 

Fig.  120,  D,  is  shown  a  cross-section  through  the 
epidermis  of  a  leaf  of  Lupinus  mutabilis  from  a  culture 
in  dry  air,  a  corresponding  section  of  a  leaf  grown 
in  moist  air,  being  shown  in  Fig.  120,  M.  The  dif- 
ferences in  the  thickness  of  cell  wall  and  of  cuticle 
are  very  great.  A  leaf  of  the  dandelion  (Taraxacum 
officinale)  grown  in  a  nearly  saturated  atmosphere  is 
shown  in  Fig.  1 2 1 ,  A ,  similar  ones  grown  under  usual 
conditions  being  shown  in  Fig.  121,  B  and  B' . 
Fig.  120.— Sections  of  leaf  Plants  growing  in  dry  regions  often  possess 
epidermis  of  Lu pinn. s  mniabiiis  thorns,  and  if  such  plants  are  grown  in  a  very  moist 

D,  grown  in  drv;  M,  in  moist      .  ,  ,-,        ,,  ,,  ,  ,    , 

air<  atmosphere   the   thorns  are  generally  replaced  by 

short,  leafy  branches.  Two  branches  of  broom 
(Genista  anglica)  are  shown  in  Fig.  122,  one  (C)  grown  under  normal  conditions, 
the  other  (B)  grown  in  moist  air.  The  difference  is  so  great  that  they  might 
be  taken  to  be  distinct  species. 

Wiesner1  has  demonstrated  that  there  may  be  a  descending  as  well  as  an 
ascending  water  stream  in  plants.  The  presence  of  the  former  may  be  clear- 
ly demonstrated  in  the  following  way.  A  cut  branch  of  grapevine  or  similar 
leafy  shoot  is  placed  with  the  youngest,  terminal  portion  of  the  stem  in  water, 
while  the  rest  projects  into  the  air.  After  some  time  the  part  of  the  stem 
under  water  wilts,  which  is  explained  by  the  fact  that  the  actively  trans- 
piring leaves  remove  more  water  from  the  terminal  portion  than  it  can  absorb, 
in  spite  of  the  fact  that  it  is  surrounded  by  water. 

Many  structural  peculiarities  of  plants  may  be  explained  as  due  to  the 
descending  water  current.  For  instance,  in  many  plants  a  withering  of  the 
'terminal  bud  occurs,  with  the  consequent  formation  of  a  sympodium.     The 

1  Wiesner,  J.,   Der  absteigende  Wasserstrom  und  dessen  physiologische  Bedeutung.     Bot.  Zeitg.  47  : 
1-9,  24-29.      1889. 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH 


269 


B 


Fig.    122. — Two   branches   of   broom,    Genista   anglica.     C, 
grown  in  dry  air;  B,  in  moist  air. 


I 


<*k 


E  I  M 

Fig.    121. — Leaves  of  Tarax-    Fig.  123. — Sempervivum.     I,  normal;  II,  grown  in  moist 
acum.     A,  grown  in  very  moist  air;  III,  grown  in  darkness, 

atmosphere  (actual  length  about 
60  cm.).  B  and  £',  grown  under 
usual  conditions  (actual  lengths 
about  15  and  12  cm.,  respectively). 


270  PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 

leaves  develop  very  early  in  such  plants,  so  that  active  leaves  are  formed  imme- 
diately beneath  the  terminal  growing-point.  These  leaves  withdraw  water, 
by  transpiration,  from  the  terminal  bud  and  thus  cause  its  destruction.  If  such 
plants  are  cultivated  in  an  atmosphere  nearly  saturated  with  water  vapor,  the 
terminal  bud  is  protected  from  destruction  and  the  stem  develops  with  mono- 
podial  branching.  Various  plants  that  usually  have  short  internodes,  such,  for 
instance,  as  Bellis  perennis,  Capsella  burs  a- pastor  is,  and  Sempervivum  when  culti- 
vated in  a  saturated  atmosphere,  develop  a  stem  with  leaves  arranged  spirally 
(Fig.  123).  In  these  cases  the  reduction  of  the  primary  stem  occurring  under 
usual  conditions  is  due  to  a  deficiency  of  water;  the  rosette  of  leaves  forms 
rapidly  and  transpires  very  actively,  thus  depriving  the  terminal  bud  of  adequate 
water  supply. 

All  these  observations  and  experiments  show  that  the  same  species  may  be 
very  definitely  modified,  in  external  form  as  well  as  in  internal  structure,  by 
variations  in  the  moisture  condition  of  soil  and  air,  and  that  the  changes  thus 
produced  are  very  striking.  The  question  now  arises:  Why  does  the  amount 
of  water  absorbed  by  the  plant  have  so  great  an  influence  upon  its  formal 
development? 

Turgidity,  as  is  well  known,  is  a  condition  essential  to  growth.  The  more 
water  is  contained  in  the  plant,  the  more  its  cells  can  be  stretched  from  within. 
Enlargement  is  terminated  when  water  ceases  to  enter  the  cell.  Wortmann 
found,  in  experiments  with  Lepidium  sativum,  that  root-hairs  are  very  long  and 
thin  when  grown  in  water,  while  they  remain  short  and  their  cell  walls  are 
much  thickened  when  they  are  grown  in  sugar  solutions.  The  cellulose  that 
produced  the  increased  expanse  of  cell  wall  in  the  first  case,  produced  thickening 
in  the  second  case.  The  same  thing  occurs  when  the  water  supply  is  not  suffi- 
cient for  the  usual  growth  of  the  plant,  small  cells  with  thick  cell  walls  being 
formed  in  this  case  also. 

Substances  dissolved  in  water  influence  the  entrance  of  the  solvent  into  the 
cells,  not  only  by  their  osmotic  activity,  but  also  by  changes  that  they  may  pro- 
duce in  the  protoplasmic  membrane,  as  was  shown  by  the  investigations  of 
Ritter.1  This  author  found  that  both  organic  and  inorganic  acids  produce 
striking  structural  changes  in  the  hyphae  of  some  of  the  lower  fungi,  especially 
the  Mucorinae.  Giant  cells  are  formed  which  may  be  thirty  or  forty  times  as 
large  as  are  the  ordinary  hyphal  cells.  The  giant  cells  of  Mucor  spinosus  are 
typical  of  these;  they  are  formed  when  the  spores  are  allowed  to  germinate 
in  a  nutrient  medium  containing  citric,  tartaric,  or  malic  acid. 

This  phenomenon  is  due,  at  any  rate,  to  a  change  in  the  osmotic  properties 
of  the  plasma  membrane  under  the  influence  of  acids.  Such  a  conclusion  is 
supported  by  the  later  work  of  Czapek,2  who  has  furnished  direct  evidence  favor- 
ing the  hypothesis  that  acids  may  greatly  increase  the  permeability  of  the  plasma 
membrane,  thus  facilitating  the  outward  diffusion  of  substances  dissolved  in  the 
cell  sap. 

1  Ritter,   G.,   Ueber  Kugelhefe  und   Riesenzellen  bei  einigen   Mucoraceen.     Ber.    Deutsch.   Bot.   Ges. 
25:253-266.      1907. 

2  Czapek,  F.,  Vcrsuche   iiber   Exosmose  aus    Pflanzenzellen.     Ber.   Deutsch.   Bot.   Ges.   28:    150-169. 
1910. 


INFLUENCE    OF   EXTERNAL   CONDITIONS    ON   GROWTH  27 1 

Further  examples  of  the  effect  of  dissolved  substances  upon  the  permeability 
of  protoplasm  may  be  found  in  the  work  of  Demoore  and  Sztics.  Demoore1 
found  that  the  addition  of  peptone  to  a  very  weak  solution  of  sodium  chloride, 
which  itself  had  no  injurious  effect  upon  the  cell,  greatly  increased  the  perme- 
ability of  the  protoplasm.  Sodium  citrate  neutralized  this  action  of  the  peptone. 
Sziics2  showed  that  the  addition  of  an  electrolyte  retards  the  entrance  of  basic 
aniline  dyes  into  the  cell. 

Alterations  in  the  turgidity  of  the  cell,  due  to  changes  in  the  amounts  of  water 
and  of  dissolved  substances  in  the  surrounding  medium,  are  among  the  causes 
that  bring  about  changes  of  form  in  plants.  The  amount  of  water  vapor  in 
the  surrounding  air  influences  the  rate  of  plant  transpiration,  and  the  more  water 
is  lost  by  transpiration,  the  more  is  absorbed  from  the  soil,  if  the  supply  is  ade- 
quate. But  plants  absorb,  along  with  water,  the  essential  ash-constituents  and 
upon  the  latter  depend,  in  turn,  the  formation  and  migration  of  various  organic 
substances.  That  the  amount  of  water  absorbed  determines  not  only  the  ex- 
ternal form  and  the  internal  structure  of  the  plant  but  also  its  chemical  compo- 
sition, maybe  seen  from  the  experiments  of  Schlosing.3  He  cultivated  tobacco 
plants  under  glass  bell-jars  and  also  in  the  open  air.  The  dry  weight  produced 
in  the  moist  atmosphere  in  four  weeks  was  40  g.,  while  that  produced  in  ordinary 
air  in  six  weeks  was  only  29.4  g.  The  leaves  of  the  moist  culture  formed 
and  accumulated  more  non-aqueous  material.  But  this  material  of  the  moist 
culture  contained  less  ash;  the  ash  content,  in  percentage  of  the  total  dry  weight, 
was  13  per  cent,  for  the  moist  culture  and  21.8  per  cent,  for  the  culture  in  ordi- 
nary air. 

These  analyses  also  show  that  the  leaves  of  the  moist  culture  of  this  experi- 
ment differed  in  other  ways  from  those  grown  under  usual  conditions.  The 
modified  rate  of  transpiration  affected  also  the  formation  of  various  organic 
compounds.  The  following  table  shows  the  amounts  of  various  substances 
found  by  Schlosing  in  the  leaves  of  his  plants  grown  under  the  two  sets  of  condi- 
tions, the  numbers  representing  percentages,  on  the  basis  of  the  dry  weight  of  the 
leaves. 

Moist  Usual 

Conditions        Conditions 

Urea 4-°°  S-°2 

Nicotin 1.32  2.14 

Other  nitrogenous  compounds 17 .40  18.00 

Oxalic  acid o .  24  6 .  66 

Citric  acid 1  ■  91  2 .  79 

Malic  acid 4-68  9 .  48 

Pectic  acid 1 . 7°  4-36 

Cellulose 536"  8.67 

Starch 19 .30  1.00 

1  Demoore,  J.,  Influence  du  citrate  de  soude  sur  les  ^changes  cellulaires.  Bull.  Soc.  Roy.  Sci.  M6d. 
et  Nat.  Bruxelles,  No.  4,  p.  70-81.     1909.     [Rev.  by  Micheels  in  :   Bot.  Centralbl.  116:  166.      1911.] 

8  Sztics,  Josef,  Studien  iiber  Protoplasmapermeabilitat.  Ueber  die  Aufnahme  der  Anilinfarben  durch 
die  lebende  Zelle  und  ihre  Hemmung  durch  Elektrolyte.  Sitzungsber.  (math,  naturw.  Kl.)  K.  Akad.  Wiss. 
Wien.  ug1:  737-773.     1910. 

3  Schlosing,  1869.  [See  note  1.  p.  147.]  [But  for  another  study  on  tobacco,  giving  quite  the  opposite 
conclusion,  see:  Hasselbring,  1914.      (See  note  w,  p.  148.) — Ed.] 


272  PHYSIOLOGY   OF    GROWTH   AND   CONFIGURATION 

The  very  large  amount  of  starch  found  in  the  leaves  grown  in  moist  air  is  spe- 
cially noteworthy,  as  is  also  the  observation  that  this  high  starch  content  is  con- 
comitant with  relatively  low  amounts  of  the  other  substances  here  considered. 
It  is  supposed  that  the  carbohydrates  formed  in  the  leaves  are  combined,  in 
other  regions  of  the  plant,  with  elements  derived  from  the  soil  solution;  in  this 
case  there  was  a  deficiency  of  these  elements  in  the  plants  grown  in  moist  air, 
owing  to  their  low  transpiration  rate,  so  that  much  of  the  starch  was  retained  in 
the  leaves.  This  great  accumulation  of  starch  is  probably  one  of  the  causes  for 
the  relatively  large  size  of  leaves  grown  in  a  moist  atmosphere.  Differences  in 
inorganic  salt  content  therefore  constitute  a  second  cause  for  the  differences 
in  plant  form  produced  by  differences  in  the  water  conditions  of  the  external 
environment. 

Plant  growth  and  development  are  markedly  influenced  by  the  concen- 
tration of  dissolved  mineral  salts  in  the  surrounding  medium,  as  has  been  known 
for  a  long  time,  from  studies  of  plant  cultures  in  solutions  of  different  concen- 
trations. Plants  grown  in  weak  solutions  resemble  those  of  moist  regions  while 
those  grown  in  very  strong  solutions  have  a  markedly  xerophytic  appearance.1 
It  is  immaterial,  therefore,  whether  the  plant  receives  excessive  amounts  of 
the  minerals  through  high  rates  of  transpiration  or  through  culture  in  concen- 
trated solutions,  the  result  being  the  same  in  both  cases:  namely,  the  forma- 
tion of  short  internodes,  thick  cell  walls,  etc.,  with  generally  marked  tissue 
differentiation.6 

Many  strand  plants  have  xerophytic  characteristics  in  spite  of  the  moist 
surroundings  in  which  they  grow.  Schimper2  noted  this  fact  and  "explained "  it 
teleologically  by  supposing  that  these  plants,  growing  in  sand  that  is  frequently 
saturated  with  a  concentrated  salt  solution — from  the  ebb  and  flow  of  the  tide 


1  Nobbe,  F.,  and  Siegert,  T.,  Beitrage  zur  Pflanzencultur  in  wasserigen  Nahrstofflosungen.  I.  Ueber  die 
Concentration  der  Nahrstofflosungen.  Landw.  Versuchsst.  6:  19-45.  1864.  [For  a  thorough  review  of 
the  literature  of  water-cultures,  see:  Tottingham,  1014.      (See  note  d,  p.  84.)] 

2  Schimper,  A.  F.  W.,  Ueber  Schutzmittel  des  Laubes  gegen  Transpiration,  besonders  in  der  Flora  Java's. 
Sitzungsber.  K.  Preuss.  Akad.  Wiss.  Berlin  1890:  1045-1062.     1890. 

e  Whether  these  responses  have  any  relation  to  the  supply  of  mineral  salts  is  at  least  ques- 
tionable. The  phenomena  here  dealt  with  in  a  very  cursory  way  are  exceedingly  complex 
and  cannot  be  generally  and  satisfactorily  explained  along  the  lines  followed  by  the  author. 
The  water  content  of  the  tissues  appears,  in  itself,  to  act  as  the  main  control  in  such  cases  as 
are  here  brought  forward.  It  ought  to  be  remarked  that  this  water  content  of  the  plant,  or  of 
any  tissue,  is  a  function  of  the  relation  that  has  previously  obtained  between  the  rates  of 
water  entrance  and  of  water  exit.  Concentrated  solutions  about  the  roots  retard  water 
entrance  in  much  the  same  way  as  does  a  soil  of  low  moisture  content.  The  last  sentence 
in  the  text  might  be  reasonably  replaced  by  the  following  one:  It  is  immaterial,  therefore, 
whether  the  water  content  of  the  plant  becomes  low  through  high  rates  of  water  loss  or  through 
low  rates  of  water  intake. — For  discussions  of  some  of  the  considerations  that  are  not  clearly 
set  forth  in  the  text  but  are  quite  necessary  in  dealing  with  this  general  subject  of  plant  water 
relations,  see:  Livingston,  B.  E.,  and  Hawkins,  Lon  A.,  The  water-relation  between  plant 
and  soil.  Carnegie  Inst.  Wash.  Pub.  204:  3-48.  191 5.  Pulling,  H.  E.,  and  Livingston, 
B.  E.,  The  water-supplying  power  of  the  soil  as  indicated  by  osmometers.  Ibid.  204 :  40-84. 
1 9 1 5.     These  papers  furnish  numerous  other  references  to  the  literature. — Ed. 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH  273 

— develop  a  number  of  structural  adaptions  in  order  to  retard  transpiration  and 
so  prevent  too  great  an  accumulation  of  mineral  salts/ 

Plants  of  the  far  north  frequently  have  xerophytic  characters  also,  even 
though  they  grow  in  very  wet  soil.  Under  these  conditions  they  may  suffer 
from  a  deficiency  of  water,1  for  the  entrance  of  water  into  the  roots  is  dependent 
upon  certain  temperature  conditions;  water  absorption  is  slow  when  the  soil  is 
cold,  and  if,  at  the  same  time,  the  atmospheric  conditions  produce  high  rates  of 
transpiration,  then  wilting  may  very  easily  occur,  even  though  the  roots  are 
surrounded  with  water.  A  heavy  cuticle  prevents  the  external  conditions  from 
raising  the  rate  of  transpiration  as  much  as  they  would  if  the  cuticle  were 
thinner. e 

1  Kihlmann,  A.  Osw.,  Pflanzenbiologische  Studien  aus  Russisch-Lappland.  Ein  Beitrag  zur  Kenntnis 
der  regionalen  Gliederung  an  der  polaren  Waldgrenze.     Helsingfors,  1890. 

f  Of  course  this  is  not  an  explanation,  and  it  has  no  bearing  on  the  problem  in  hand.  Plants 
do  not  produce  peculiar  structures  "in  order  to  retard  transpiration"  or  for  any  other  purpose; 
the  peculiar  structures  result  from  the  interaction  of  preexisting  conditions,  and  the  effect  of 
the  presence  of  these  structures,  after  they  are  produced,  is  to  retard  water  loss.  For  a  work- 
ing hypothesis,  it  may  be  supposed  that  the  high  salt  content  of  the  soil  retards  water  intake  in 
the  case  of  these  strand  plants  (either  osmotically  or  by  a  chemical  influence  upon  the  root 
protoplasm,  such  as  rendering  this  only  slowly  permeable  to  water),  and  that  the  open  exposure 
of  such  plants  makes  the  rate  of  water  loss  (transpiration)  relatively  high,  so  that  the  water 
content  of  the  tissues  is  maintained  comparatively  low. — Ed. 

g  The  heavy  cuticle  of  such  plants  may  result  from  low  water  content  of  the  tissues  (see 
note  /,  just  preceding). — It  appears  that  one  main  reason  for  the  dominance  of  plants  with 
foliar  structures  that  retard  transpiration,  in  bogs,  and  perhaps  generally  in  the  far  north, 
is  the  presence  of  toxic  materials  in  the  soil.     (See  note  k,  p.  101 .) 

This  whole  discussion,  as  given  in  the  text,  is  rendered  unsatisfactory  by  the  confusion  of 
two  entirely  distinct  problems,  one  physiological  and  the  other  in  the  realm  of  distributional 
ecology.  From  the  standpoint  of  physiology,  we  should  seek  the  conditions  (internal  and 
external)  that  make  one  plant  produce  xerophilous  structures,  etc.,  while  another  does  not. 
This  involves  experimental  problems  like  that  dealt  with  by  Schlosing  and  by  Hasselbring 
(page  271),  and  like  that  considered  by  the  author  in  reference  to  the  experiments  of  Nobbe 
and  Siegert  'page  272).  Without  adequate  measurement  of  the  effective  conditions  that 
obtain,  a  knowledge  of  these  relations  cannot  be  achieved  by  ordinary  field  observations, 
no  matter  how  thoroughly  such  observations  may  be  subjected  to  subsequent  attempts  at 
interpretation. 

From  the  standpoint  of  distributional  ecology,  on  the  other  hand,  we  desire  to  know,  first, 
what  physiological  types  of  plants  occur,  and  are  dominant,  in  different  habitats  and  geograph- 
ical regions.  As  an  example  of  this  sort  of  knowledge  we  have  the  observed  fact  that  thick 
foliar  cuticle  is  of  dominant  occurrence  on  the  plants  of  bogs  and  of  the  far  north.  The 
ecological  interpretation  of  this  observation  does  not  have  anything  at  all  to  do  with  the 
physiological  question  as  to  what  may  be  the  necessary  conditions  for  the  production  of  thick 
cuticle,  but  it  does  deal  with  the  question  as  to  what  kinds  of  environmental  complexes  may 
prevent  the  development  of  plant  forms  that  do  not  produce  such  cuticle,  at  the  same  time 
allowing  forms  that  do  produce  thick  cuticle  to  dominate.  Given  a  number  of  plants,  some 
with  and  some  without  xerophilous  foliar  structures  (no  matter  by  what  sets  of  conditions  these 
structures  may  have  been  produced  or  inhibited  in  the  different  cases),  we  observe  that  bog 
habitats  are  characterized  by  the  dominance  of  plants  of  the  first  class,  and  we  suppose  that 
plants  of  the  second  class  (without  xerophilous  foliar  structures)  are  generally  unable  to  thrive 
in  such  habitats.  The  question  then  emerges,  as  to  what  are  the  peculiar  environmental  con- 
ditions that  so  generally  prevent  the  growth  of  the  non-xerophilous  forms.  The  generalized 
18 


274 


PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 


Unequal  amounts  of  moisture  on  the  two  opposite  sides  of  a  plant  organ  also 
exert  an  influence  upon  growth.  If  seeds  germinate  in  a  sieve  filled  with  saw- 
dust and  suspended  so  that  its  bottom  is  at  an  angle  of  45  degrees  from  the 
horizontal  (Fig.  124),  the  primary  roots  soon  penetrate  through  the  openings 
in  the  bottom,  but  they  grow  no  farther  in  the  vertical  direction.  They  bend 
laterally  toward  the  bottom  of  the  sieve  and  grow  downward  along  its  outer 
surface,  to  which  they  become  closely  appressed.  This  bending  of  plant  organs 
toward  water,  or  away  from  the  drier  side,  is  called  positive  hydrotropism. 

§5.  Dependence  of  Growth  and  Configuration  upon  Light.1— Light  exerts  a 
marked  influence  upon  the  rate  of  plant  growth  as  well  as  upon  the  formation 


Fig.  124. — Experiment  showing  positive  hydrotropism  of  roots. 

answer  to  this  question  seems  to  be,  soil  conditions  that  hinder  water  absorption.  Toxic  sub- 
stances appear  to  do  this  by  poisoning  the  roots,  so  that  these  organs  possess  but  a  limited 
power  to  take  up  water,  in  spite  of  the  presence  of  a  plentiful  supply  of  water  in  the  soil.  Low 
soil  temperature  (as  in  subarctic  regions)  may  hinder  water  absorption  from  wet  soils  in  some- 
what the  same  way.  These  considerations  may  furnish  at  least  a  partial  explanation  of  the 
fact  (if  it  be  a  fact)  that  plant  forms  without  special  foliar  structures  that  retard  water  loss  are 
generally  unable  to  thrive  in  bogs  and  in  the  far  north. 

The  ecological  question  just  touched  upon  is  one  with  which  physiology,  as  such,  need  not 
be  concerned,  and  distributional  and  physiological  problems  ought  not  to  be  so  commonly 
confused  as  is  now  the  case  in  botanical  literature.  Physiology  enquires  how  the  plant  comes 
to  be  what  it  is,  and  how  it  operates  as  a  machine.  Its  explanations  have  to  deal  with  migra- 
tions and  transformations  of  matter  and  energy.  Distributional  ecology,  on  the  other  hand, 
enquires  what  are  the  characteristics  of  any  plant  form  and  of  any  given  set  of  environmental 
conditions,  by  virtue  of  which  the  given  habitat  can  or  cannot  support  the  plant  form  con- 
sidered, or  by  virtue  of  which  the  plant  form  can  or  cannot  thrive  in  the  given  habitat.  How 
the  conditions  of  the  habitat  came  to  be  what  they  are,  involves  questions  of  climatology, 
physiography,  soil  science,  etc.;  why  the  plant  has  the  internal  characteristics  that  it  has, 
involves  questions  of  physiology. — Ed. 

1  Wiesner,  J.,  Der.  Lichtgenuss  der  Pflanzen.  Leipzig,  1907  Idem,  same  title.  Verhandl.  Ges. 
Deutsch.  Naturforscher  u.  Aerzte  81 :  66—86.     1909. 


INFLUENCE    OF  EXTERNAL   CONDITIONS    ON    GROWTH 


275 


of  individual  organs.  The  most  common  phenomenon  to  be  noted  in  this  con- 
nection is  the  daily  periodicity  of  growth.  Plants  grow  more  slowly  by  day 
than  by  night,  so  that  it  appears  that  light  exerts  a  retarding  influence  upon 
growth.1  The  growth  maximum  occurs  in  the  early  morning  hours  and  the 
minimum  occurs  in  the  evening.  The  curve  3s  of  Fig.  125  shows  the  diurnal 
march  of  the  rate  of  plant  growth,  which  is  seen  to  increase  gradually  from  about 
6  p.m.  to  about  6  a.m.,  after  which  it  gradually  decreases,  from  morning  until 
evening.  The  accelerated  growth  of  the  night  hours  occurs  in  spite  of  the  lower 
night  temperature,  as  may  be  seen  from  the  figure  just  mentioned,  where  the 
curve  t°  represents  the  diurnal  march  of  temperature  corresponding  to  that  of 
growth.  This  periodicity  is  mainly  dependent  upon  light,  although  it  continues 
to  be  manifest — but  with  less  regularity — when  the  plant  is  kept  continuously 


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corresponding  graph  of  temperature.     (After  Sachs.) 

in  darkness.  The  latter  fact  has  been  explained  as  an  induced  rhythm;  the 
ancestors  of  the  present  plants  have  been  exposed  for  countless  generations  to 
the  diurnal  alteration  of  light  and  darkness,  and  the  periodicity  of  growth  ap- 
pears to  have  become  a  habit  (due  to  internal  conditions),  which  is  more  or  less 
markedly  inherited. 

One-sided  illumination  brings  about  a  bending  of  plant  organs,  this  response 
being  termed  phototropism  or  heliotropism.'1  When  an  organ  bends  toward  the 
more  brightly  lighted  side  it  is  said  to  be  positively  phototropic;  when  it  bends 
away  from  the  more  intense  light  it  is  negatively  phototropic.  Positive  photo- 
tropism is  very  common  among  plants  and  is  usually  observed  when  growing 
stems  are  subjected  to  one-sided  illumination. 

1  Baranetzky,  J.,  Die  tagliche  Periodizitat  im  Langenwachstum  der  Stengel.  (M6m.  Acad.  Imp.  Sci. 
St.-Petersbourg,  VII,  2T-  ■  1-91.      1897.     Godlewski,  Emil,  Studyja  nad  wzrostem  roslin.     Krakau,  1891.* 

2  Wiesner,  Juluis,  Die  heliotropischen  Erscheinungen  im  Pflanzenreiche.  Eine  physiologische  Mono- 
graphic I  Theil.  Denksch.  K.  Akad.  Wiss.  Wien  30^:  143-209.  1879.  Idem,  same  title.  II  Theil. 
Ibid.  437:  1-92.     1882.     Idem,  Das  Bewegungsvermogen  der  Pflanzen.     Wien,  1881.     P.  37-84. 


276 


PHYSIOLOGY    OF    GROWTH   AND    CONFIGURATION 


Among  plants  that  are  especially  sensitive  to  these  differences  in  light  in- 
tensity, on  the  two  opposite  sides,  may  be  mentioned  Vicia  saliva.  If  etiolated 
seedlings  of  this  plant  are  placed  between  two  sources  of  light  differing  so  slightly 
that  the  difference  cannot  be  detected  by  ordinary  photometric  methods,  the 
seedlings  always  bend  promptly  toward  the  source  of  the  more  intense  light. 
Phototropic  bending  is  often  difficult  to  observe  in  plants  growing  in  sunny 
places  in  the  open,  such  as  dehor  ium  intybus,  Verbena  officinalis,  Sisymbrium 
strictissimum,  Achillea  millefolium  (yarrow).  If  such  plants  are  grown  in 
weaker  light,  however,  the  light  reaction  becomes  apparent.  The  stems  of 
Dipsacus  (teasel)  and  Equisetum  are  but  slightly  phototropic  and  those  of 


Fig.  126. — Leaf-mosaic 


oston  ivy.      (From  Gager.) 


Verbascum  thapsns  (mullein)  and  V.  phlomoides  do  not  exhibit  phototropism 

at  all. 

Phototropic  responses  occur  very  commonly  in  leaves,  these  organs  tending 
to  assume  such  positions  that  they  do  not  shade  one  another.  Observed  from 
above,  such  an  arrangement  of  leaves  appears  like  a  mosaic,  as  in  the  case  of  the 
ivy  leaves  shown  in  Fig.  126.  In  this  case,  the  lobes  of  one  leaf  approxi- 
mately fill  the  indentations  of  others,  so  that  a  closely  fitting  arrangement 
results. 

Many  leaves  bend  so  as  to  place  the  blades  at  right  angles  to  the  direction 
of  strongest  illumination  (Fig.  127).  Shortly  after  sunrise  the  upper  surfaces 
of  these  leaves  are  inclined  toward  the  east,  at  midday  the  blades  take  a  nearly 
horizontal  position,  and  in  the  evening  they  are  turned  toward  the  west.     In 


INFLUENCE    OF   EXTERNAL    CONDITIONS    ON    GROWTH 


277 


all  these  cases  the  upper  surface  of  the  leaf-blade  becomes  so  oriented  that  it  is 
perpendicular  to  the  direction  of  the  impinging  rays.     Even  if  such  a  plant  is  in- 


«+ 


Fig.  127. — Diagrams  showing  phototropic  movements  of  leaves,  with  reference  to  the  direc- 
tion of  impinging  light,  this  direction  shown  by  the  arrows. 


Fig.  128. — Inverted  Phaseolus  plant.  Two  petioles  are  fastened  with  wire  so  as  to  hold 
them  in  their  normal  position.  Leaf-blade  b  is  represented  as  in  its  normal  position,  while 
a  has  become  re-oriented  after  the  plant  was  inverted.  Leaf  c  has  responded  by  a  torsion 
of  the  petiole  as  well  by  a  bending.     (After  Pfeffer.) 

verted  (Fig.  128)  the  leaves  bend  in  such  a  way  as  to  direct  their  normally 
upper  surfaces  toward  the  source  of  strongest  illumination,1  the  movement  being 

iVochting,  Hermann,  Ueber  die  Lichtstellung  der  Laubblatter.  Bot.  Zeitg.  46:  501-514,  517-527, 
533-54L  540-560.     1888. 


278 


PHYSIOLOGY    OF    GROWTH   AND    CONFIGURATION 


brought  about  by  either  a  bending  or  a  twisting  of  the  petiole,  frequently  by 
both  of  these  processes  together.  If  the  plant  is  inverted  and  lighted  only  from 
below,  then  the  leaves  react  so  as  to  maintain  their  normally  upper  surfaces 
directed  downward,  toward  the  source  of  illumination. 

What  has  been  stated  above  con- 
cerning the  phototropism  of  leaves 
holds  for  most  plants,  but  there  are 
a  few  exceptions.  The  leaves  of 
some  plants  growing  in  hot  regions 
do  not  find  their  position  of  pho- 
totropic  equilibrium  when  the  leaf- 
blade  is  perpendicular  to  the  direc- 
tion of  the  impinging  light,  but  they 
bend  so  as  to  make  the  blade  assum  e 
an  acute  angle  to  the  line  of  the  light 
rays.  Finally,  there  are  so-called 
compass-plants,1  which  more  or  less 
regularly  bring  their  leaves  into  a 
position  so  that  the  two  faces  of  the 
blade  face  east  and  west,  the  leaf- 
tips  pointing  obliquely  upward  and 
alternately  north  and  south  (Fig. 
129).  This  arrangement  results  in 
the  so-called  profile  position  of  the 
leaves  at  midday,  at  which  time  the 
leaf  surfaces  are  parallel  to  the  direc- 
tion of  the  direct  rays  of  sunlight, 
an  orientation  that  tends  to  render 
them  less  liable  to  excessive  heat- 
ing. Such  reactions  to  light  are 
more  or  less  perfectly  exhibited 
in  Sylphium  lacineatum,  Lactuca 
scar  tola  (wild  lettuce),  and  others. 
Many  flowers  also  exhibit  the 
phototropic  response.  Several 
species  of  Tragopogon  furnish  ex- 
amples of  flower-heads  that  bend 
toward  the  sun.  Before  sunrise 
the  flower-heads  all  bend  toward 
the  east,  though  they  are  still  closed.  They  open  as  soon  as  the  sun  rises. 
In  the  morning  a  meadow  of  blossoming  Tragopogon  appears  all  bright  with 
flowers  when  viewed  from  the  east,  but  looks  uniformly  green  when  seen  from 
the  west;  in  the  latter  case  only  the  green  involucres  of  the  flower-heads  are 
seen.     During  the  day  the  flowers  change  their  position  as  the  sun  advances 

1  Stahl,  E.,  Ueber  sogenannte  Compasspflanzen.     Jenaische  Zeitsch.  Naturwiss.    15:  381-389.  1881. 


Fig.  129. — Compass-plant,  Sylphium  laciniatum 
as  seen  from  the  east  or  west  (left),  and  as  seen 
from  the  north  or  south  (right).      (After  Stahl.) 


INFLUENCE    OF   EXTERNAL    CONDITIONS    ON    GROWTH 


279 


across  the  sky,  and  in  the  evening  they  all  face  the  west.  They  close  about 
sunset  and  then  become  erect  on  their  stalks,  remaining  so  until  morning,  when 
movement  begins  anew.  This  movement  can  be  stopped  by  very  intense  light. 
In  Fig.  130  are  shown  closed  and  open  flower-heads  of  Hieracium,  a  plant 
closely  related  to  Tragopogon  and  showing  the  same  responses. 

Phototropic  bending  occurs  also  in  non-green  plants — in  moulds,  for  example. 
If  fresh  horse  dung  is  placed  in  a  closed  chamber  with  a  small  glass  window,  a 
dense  growth  of  Pilobolus  soon  develops  and  the  sporangiophores  all  bend  to- 
ward the  window.  The  sporangia,  containing  the  ripe  spores,  are  thrown  with 
considerable  force,  well-aimed  at  the  glass  window,  to  which  they  adhere  (Fig. 

i3i)-x 

Negative    photropism    is    not  0 

very    common,    but   occurs   with  1 

many   tendrils   and   aerial   roots. 

Weisner2  studied  the  aerial  roots 


1\ 


Fig.  130.  Fig.  131. 

Fig.  130. — Flower  of  Hieracium  pilosella.     A,  open,  as  by  day;  B,  closed,  as  by  night. 

Fig.  131. — Diagram  showing  phototropic  response  of  Pilobolus.  The  culture  is  in  a 
chamber  and  receives  light  only  through  small  window  at  left.  Spore-masses  are  discharged 
toward  the  window. 

of  sixty-one  different  plant  forms  and  found  that  the  negative  phototropic  re- 
sponse was  very  marked  in  twenty-seven  species  and  was  not  so  marked  in 
twenty-four  species,  while  six  species  showed  but  little  sensitiveness  to'light 
and  the  remaining  four  were  not  sensitive  at  all.  This  phenomenon  does  not 
occur  commonly  in  ordinary  subterranean  roots,  but  if  mustard  seedlings 
(Sinapis  alba)  are  grown  in  water-culture  it  is  easy  to  demonstrate  both  posi- 
tive phototropism  of  the  shoots  and  negative  phototropism  of  the  roots. 

Phototropic  bending  results  from  unequal  growth  on  the  two  sides  of  the 
organ  in  which  this  bending  occurs,  and  the  response  takes  place  only  in  the 
enlarging  region.  The  degree  of  bending,  or  its  rate,  depends  upon  light 
intensity.  Light  of  medium  intensity  produces  the  most  pronounced  bending, 
and  the  response  is  less  marked  both  with  higher  and  with  lower  intensities.  The 
phototropic  response  is  slight  when  the  light  intensity  is  low,  increases  to  a 
maximum  with  medium  light  intensities,  and  becomes  less  when  the  light  in- 

1  For   an   excellent   study  of   the   light   reaction   of   Pilobolus,    see:   Parr,    Rosalie,    The   response   of 
Pilobolus  to  light.     Ann.  bot.  32:  177-205.   1018. 
-  [Wiesner,  1879,  1882.     [See  note  2,  p.  275.] 


2  8o 


PHYSIOLOGY    OF    GROWTH    AND    CONFIGURATION 


tensity  is  still  further  increased.  It  is  due  to  unequal  illumination  of  the  two 
sides  of  the  sensitive  region  of  the  bending  organ,  and  the  difference  in  illumina- 
tion between  the  two  sides  is  of  course  generally  greatest  with  medium  intensities 
of  the  light  impinging  on  them.  When  the  light  upon  one  side  of  an  organ  is 
very  strong  the  tissues  are  penetrated  and  the  cells  on  the  opposite  side  receive 
nearly  as  much  illumination  as  do  those  on  the  directly  illuminated  side.  It  is 
for  this  reason  that  phototropic  bending  is  not  frequent  in  plants  growing  in 
intense  sunshine,  and  this  explains  the  retardation  of  the  phototropic 
movement  in  Tragopogon  when  exposed  to  intense  light. h 

The  various  wave-lengths  of  sunlight  do  not  all  have  the  same  phototropic 
influence  upon  plants,  as  is  shown  by  the  graphs  of  Fig.  132.  In  this  figure  the 
letters  at  the  base  represent  the  positions  of  the  Fraunhofer  lines  in  the  solar 
spectrum,  A,  B,  C,  etc.     The  curve  XY  represents  the  comparative  growth 


Fig.    132. — Graphs  representing  rates  of  growth  and  phototropic   sensitiveness  of  plants  in 

various  wave-lengths  of  sunlight. 

rates  of  sunflower  seedlings  in  the  different  regions  of  the  spectrum,  this  rate  being 
highest  at  X  and  lowest  at  F.  Curve  I  represents  the  phototropic  sensitiveness 
of  vetch  seedlings,  curve  II  that  of  cress  seedlings,  and  curve  III  that  of  etiolated 
willow  shoots. 

In  yellow  light,  about  the  D-line,  no  phototropic  response  is  apparent. 
With  longer  or  shorter  wave-lengths  phototropism  becomes  evident,  and  the 
sensitiveness  of  the  plants  becomes  greater  as  the  wave-length  increases  or  di- 
minishes. The  rays  of  the  shorter  wave-lengths,  in  the  right  half  of  the  spec- 
trum, are  the  most  effective  to  produce  bending  in  all  three  cases,  and  etiolated 
willow  shoots  fail  to  show  any  response  to  the  long  wave-lengths  of  the  red 
region.  Thus,  of  the  visible  spectrum,  violet  light  is  most  effective  to  produce 
phototropic  bending. 

Light  retards  plant  elongation,  as  is  clear  from  the  daily  periodicity  of 
growth,  but  this  retardation  differs  in  amount  with  different  wave-lengths. 

h  Also,  with  strong  illumination  the  light  received  by  reflection  from  the  sky,  from  sur- 
rounding objects,  etc.,  is  comparatively  intense. — Ed. 


INFLUENCE    OF   EXTERNAL    CONDITIONS    ON    GROWTH  28 1 

The  curve  XY  of  Fig.  132  shows  that  the  greatest  retardation  occurs  with  violet 
and  ultra-violet  light,  this  effect  decreasing  with  longer  wave-lengths  until  it  is 
minimal  in  the  yellow  region,  about  the  D-line.  Beyond  this  region,  with  still 
longer  wave-lengths,  the  retarding  effect  again  increases.  These  facts  furnish 
an  explanation  of  the  differences  between  the  phototropic  responses  brought 
about  by  different  qualities  of  light.  The  greater  is  the  growth-retarding 
effect  of  any  given  quality  of  light,  the  stronger  is  its  phototropic  influence. 
Other  conditions  remaining  unchanged,  the  most  pronounced  phototropic 
influence  is  exerted  by  light  that  impinges  perpendicularly  to  the  surface  of 
the  sensitive  plant  organ. 

Phototropism  is  of  great  ecological  significance.  Positive  phototropic 
responses  bring  the  plant  and  its  parts  into  the  most  favorable  conditions  of 
illumination,  and  the  negative  responses  of  tendrils  and  aerial  roots  take  these 
organs  out  of  the  sunshine  into  the  vicinity  of  surfaces  to  which  they  can 
become  attached,  such  as  the  surfaces  of  fences,  walls,  tree-trunks,  etc. 

It  has  recently  been  shown  that  many  plants  possess  special  structures  that 
are  supposed  to  act  as  organs  of  light-perception.1  For  example,  the  epidermal 
cells  of  the  leaves  of  Campanula  persicifolia  are  characterized  by  condensing 
lenses  in  their  outer  walls,  these  thickenings  being  impregnated  with  silicic  acid. 
These  lens-like  structures  are  somewhat  similar  to  the  lenses  of  animal  eyes. 

It  has  been  seen  that  temporary  absence  of  light  (as  during  the  night  hours) 
and  one-sided  illumination,  which  brings  about  phototropic  responses,  are  both 
markedly  effective  in  determining  the  rate  of  growth  and  the  formal  develop- 
ment of  plants,  and  it  is  now  to  be  added  that  prolonged  absence  of  light  exerts 
an  even  more  pronounced  influence.  Plants  grown  in  darkness  are  very  differ- 
ent from  those  exposed  to  the  ordinary  succession  of  day  and  night.  Such 
plants  are  said  to  be  etiolated;  they  differ  greatly  in  form  but  are  primarily  char- 
acterized by  having  yellow  leaves  and  white  stems.2 

In  plants  that  do  not  produce  stems  in  darkness  (such  as  wheat),  the  dark- 
grown  leaves  are  longer  and  narrower  than  are  leaves  grown  in  light.  In  such 
plants  the  leaf  surface  is  generally  greater  when  they  are  etiolated  than  when 
they  are  grown  in  light.  In  plants  that  form  stems  in  darkness,  the  internodes 
are  much  longer  in  darkness  than  in  light  and  the  leaves  remain  rudimentary 
in  darkness.  In  this  class  belong  the  pea  (Pisutn  sativum),  the  Windsor  bean 
(Viciafaba),  millet  (Panicum  miliaceum),  the  potato  {Solatium  tuberosum),  etc. 
The  scarlet-runner  bean  {Phaseolus  multiflorus)  is  also  one  of  this  class;  it  is 

1  Haberlandt :  G.,  Die  Lichtsinnesorgane  der  Laubblatter.     Leipzig,  190S. 

-  In  this  connection,  see:  Sachs,  Julius,  Ueber  den  Einfluss  des  Tageslichts  auf  Neubildung  und  Entfal- 
tung  verschiedener  Pflanzenorgane.  Bot.  Zeitg.  21 :  (Beilage;  separately  paged, 1-30).  1863.  Batalin,  A., 
On  the  influence  of  light  upon  the  structural  development  of  plants.  [Russian.]  Dissertation.  St.  Peters- 
burg, 1872.  [Latest  German  paper  located  is  the  following:  Batalin,  A.,  Ueber  die  Wirkung  des  Lichtes 
auf  die  Entwicklung  der  Blatter.  Bot.  Zeitg.  29:  660-686.  1871.  For  an  account  of  a  large  amount  of 
experimentation  upon  the  morphogenic  influence  of  light  see:  MacDougal,  D.  T.,  The  influence  of  light  and 
darkness  upon  growth  and  development.  Mem.  New  York  Bot.  Garden,  v.  2.  XIII  +  319  p.  New  York, 
1903.  On  the  influence  of  different  lengths  of  alternating  periods  of  light  and  darkness,  see:  Garner,  W. 
W.,  and  Allard,  H.  A.  Effect  of  the  relative  length  of  day  and  night  and  other  factors  of  the  environment 
on  growth  and  reproduction  in  plants.     Jour.  Agric.  Res.  18:  553~6o6.      1920. 


282 


PHYSIOLOGY    OF    GROWTH    AND    CONFIGURATION 


shown  in  the  etiolated  and  in  the  usual  condition  in  Fig.  133.*  Most  etiolated 
stems  fail  to  develop  lateral  branches,  but  the  etiolated  potato  sprout  is  an 
exception  to  this  rule.  It  has  much-elongated  internodes  and  rudimentary 
leaves,  but  it  bears  small  lateral  branches  (Fig.  134). 

Many  plants  that  develop  only  very  short  stems  in  light,  with  leaves  in 
rosettes,  like  Bellis  perennis  and  Sempervivum  (Fig.  123,  page  269),  form 
elongated  stems  in  darkness,  with  spirally  arranged  leaves. 

Another  group  of  plants  that  do  not  produce  longer  internodes  in  darkness 
than  in  light  includes  those  in  which,  under  normal  conditions,  the  leaves  are 
much  retarded  in  their  development  and  the  young  internodes  quickly  become 
greatly  elongated.     Such  forms,  among  which  belong  the  hop  {Humulus  lupulus) 


Fig.  133. — Seedlings  of  scarlet-runner  bean.     A,  grown  in  darkness;  B,  grown  in  light. 


and  Polygonum  dumetorum,  when  grown  with  the  alternating  light  and  darkness 
of  day  and  night,  develop  full-grown  leaves  only  on  the  older  internodes,  which 
have  ceased  to  elongate.  Thus,  the  younger,  elongating  portion  of  the  plant 
appears  very  much  as  if  it  were  etiolated,  and  no  marked  difference  in  the 

'  In  such  twining  plants  as  the  scarlet-runner  bean  the  manner  of  growth  of  the  younger 
portion  of  the  shoot  changes  as  they  become  older  and  the  long  internodes  and  small  leaves  of 
etiolated  plants  are  produced,  even  in  the  presence  of  light.  Thus,  if  the  plant  shown  in  Fig. 
133,  B,  continued  to  grow  in  light  it  would  soon  become  terminated  by  a  long,  slender  shoot 
such  as  is  shown  in  A  of  this  figure.  This  kind  of  etiolation,  generally  shown  by  the  younger 
portions  of  the  stems  of  twiners,  occurs  in  light,  but  it  is  similar  to  the  etiolation  of  other  plants 
(or  of  the  same  plant  in  its  early  stages  of  development)  that  is  brought  about  by  absence  of 
light.  As  the  light-grown  shoot  becomes  older  its  leaves  finally  expand,  however.  This 
matter  receives  attention  in  the  text,  just  below,  where  Humulus  and  Polygonum  dumetorum 
serve  as  examples.     See  also  page  311.—  Ed. 


INFLUENCE    OF   EXTERNAL    CONDITIONS    ON    GROWTH 


283 


2-\] 


■■ 


form  of  this  region  is  brought  about  when  these  plants  are  grown  in  continuous 
darkness. 

Phyllocactus,  which  produces  fiat,  leaf-like  stems  and  branches  under  usual 
conditions,  forms  slender,  cylindrical  internodes  in  continuous  darkness.1 

When  darkness  produces  etiolation  the  anatomical  structure  of  etiolated 
plants  is  also  different  from  that  of  .~ 

the  same  forms  grown  in  light;  the 
dark-grown  individuals  are  charac- 
terized by  exceptionally  well-de- 
veloped thin-walled  parenchyma,  by 
exceptionally  thin  cuticle,  by  small 
size  and  number  of  the  vascular 
bundles,  and  by  a  pronounced  retard- 
ation in  the  formation  of  mechanical 
tissue. 

Experiments  with  colored  light- 
screens  show  that  plants  assume 
their  usual  forms  only  when  they 
receive  blue  and  violet  light.  When 
grown  in  light  of  other  colors  [that 
is,  with  the  intensity  of  the  blue  and 
violet  rays  very  greatly  diminished 
as  compared  to  their  intensity 'n 
sunlight],  etiolation  becomes  mani- 
fest.2 The  curve  IF,  Fig.  132, 
shows'  how  greatly  growth  is  re- 
tarded by  blue  and  violet  light. 

The  fact  that  photosynthesis  can- 
not occur  in  darkness  was  formerly 
supposed  to  explain  the  phenomena 
of  etiolation,  but  the  experiments 
with  colored  lights  just  mentioned 
show  clearly  that  the  photosynthetic 
process  has  practically  no  direct  in- 
fluence upon  plant  form.  In  the 
green-violet  portion  of  the  spectrum, 
where  photosynthesis  is  least  pronounced,  plants  grow  as  usual,  while  in  the 
red-orange  portion,  where  photosynthesis  is  most  active,  they  become  etiolated. 
Furthermore,  Godlewski3  obtained  normal  plants  in  the  presence  of  light  but  in 

1  Vochting,  Hermann,  Ueber  die  Bedeutung  des  Lichtes  fur  die  Gestaltung  blattformiger  Cacteen.  Zur 
Theorie  der  Blattstellungen.  Jahrb.  wiss.  Bot.  26:  438-494-  1894-  [The  same  phenomenon  is  exhibited 
by  some  of  the  platyopuntias  of  southern  Arizona. — Ed.] 

-  Wiesner,  J.,  Photometrische  Untersuchungen  auf  pflanzenphysiologischem  Gebiete.  I  Abt.  Orien- 
tirende  Versuche  uber  den  Einfluss  der  sogenannten  chemischen  Lichtintensitat  auf  den  Gestaltungsprocess 
der  Pflanzenorgane.     Sitsungsber.  (math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien  102^  =291-350.     1893- 

3  Godlewski,  Emil,  Zur  Kenntniss  der  Ursachen  der  Formanderung  etiolirter  Pfianzen.  Bot.  Zeitg. 
37:  81-92,97-107.  113-125.  137-141-     1879. 


B  A 

Fig.  134. — Potato  sprouts  grown  in  light  (A) 
and  in  darkness  (B).     (After  Pfeffer.) 


284  PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 

the  absence  of  carbon  dioxide.  Thus,  light  of  the  shorter  wave-lengths,  and  not 
the  possibility  of  photosynthesis,  is  the  requisite  condition  for  normal  form. 
This  conclusion  is  also  supported  by  the  experiments  of  Vines,1  who  grew  plants 
in  light  but  in  a  soil  without  iron.  Chlorotic  plants  were  thus  obtained,  but 
their  form  was  quite  similar  to  that  of  normal  plants,  even  though  they  were 
without  chlorophyll  and,  consequently,  could  not  assimilate  carbon  dioxide. 

Only  in  certain  plants  is  the  shape  of  the  leaves  determined  by  the  occurrence 
or  non-occurrence  of  photosynthesis.  Some  etiolated  leaves,  such  as  those  of 
wheat,  contain  little  protein  material  and  relatively  large  amounts  of  [dissolved 
or  digestible]  carbohydrates,  while  some  other  leaves,  such  as  those  of  bean 
and  lupine,  are  rich  in  protein  material  and  contain  almost  no  [dissolved  or 
digestible]  carbohydrates  at  all,  excepting  only  a  very  little  starch  in  the 
stomatal  guard  cells.  The  relative  amounts  of  proteins  in  wheat  and 
bean  leaves,  in  the  etiolated  and  normal  condition,  are  given  below,  in 
percentage  of  total  green  weight.     It  thus  appears  that  etiolated  bean  leaves 

Green  Etiolated 

Wheat  leaves 1.99  1 .  28 

Bean  leaves 4 .  95  8.38 

contain  more  protein  than  do  normal  leaves,  but  they  nevertheless  remain  small 
and  undeveloped.  As  has  been  stated  (page  228),  the  respiratory  activity  of 
etiolated  bean  leaves  is  very  low,  but  respiration  is  greatly  increased  when  sugar 
is  supplied.  Carbohydrates  are  necessary  for  the  growth  of  all  leaves,  but  in 
those  of  the  bean  and  similar  plants,  where  carbohydrates  [aside  from  the 
celluloses  of  the  cell  walls]  do  not  accumulate,  these  substances  must,  under 
normal  conditions,  be  derived  directly  from  photosynthesis.  Thus  bean  leaves 
kept  in  darkness  are  deficient  in  carbohydrates  and  so  cannot  grow.  Leaves 
of  the  other  group  of  plants  (such  as  wheat)  are  not  dependent  for  their  supply 
of  carbohydrates  at  any  particular  time  upon  the  rate  of  photosynthesis,  for 
these  substances  accumulate  in  such  leaves  and  the  latter  always  contain  much 
starch.  Therefore  wheat  leaves,  as  has  been  seen,  attain  their  usual  size  in 
darkness,  or  even  become  larger  than  in  light. 

The  necessity  of  carbohydrates  for  normal  leaf  development  is  also  shown  by 
the  experiments  of  Jost,2  who  obtained  etiolated  leaves  of  almost  normal  size 
in  darkness,  by  supplying  the  needed  nutrient  materials.  These  etiolated  leaves 
lived  a  long  time  in  spite  of  the  absence  of  light.  When  green  leaves  were  placed 
in  darkness,  however,  they  degenerated  rapidly,  in  spite  of  the  fact  that  nutrient 
materials  were  supplied  as  in  the  other  case.  Jost  suggests  that  perhaps  the 
chlorophyll  (or  the  whole  photosynthetic  apparatus)  is  subject  to  decomposition 
in  darkness,  thus  giving  rise  to  products  that  may  be  injurious  to  the  cells  in 
other  ways. 

Etiolated  plants  in  darkness  give  off  water  at  a  lower  rate  than  do  green 
plants  in  light  and,  as  has  been  mentioned,  the  decrease  in  transpiration  rate 
brought  about  when  plants  are  kept  in  a  nearly  water-saturated  chamber  exerts 

1  Vines,  Sydney  Howard,  The  influence  of  light  upon  the  growth  of  leaves.     Arbeit.  Bot.  Inst.  Wurzburg 
2  :  1 14-132.     1882. 

2  Jost,    Ludwig,  Ueber  die  Abhangigkeit  des  Laubblattes  von  seiner  Assimilationsthatigkeit.     Jahrb. 
wiss.  Bot.  27:  403-480.      1895. 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH  285 

a  marked  influence  upon  form  and  structure  even  in  light.  It  therefore  appears 
that  Palladin1  is  justified  in  supposing  that  etiolation  in  darkness  is  at  least 
largely  caused  by  diminished  transpiration.  The  anatomical  characters  of 
etiolated  plants  are  quite  like  those  of  plants  grown  in  light  but  with  water- 
saturated  air,  and  all  of  the  formal  responses  of  etiolation  appear  to  be  explain- 
able as  resulting  partly  from  alterations  in  the  conditions  controlling  the  rate 
of  water  loss  and  partly  from  the  consequent  alterations  in  the  internal  influences 
of  the  different  organs  upon  one  another.  Thus,  Bellis  perennis,  which  forms  a 
stem  with  spirally  arranged  leaves  when  grown  in  darkness,  also  shows  the  same 
response  when  grown  in  light  with  a  water-saturated  atmosphere. 

Plants  in  which  the  leaves  are  slow  to  develop,  such  as  the  hop,  form  almost 
as  long  internodes  in  light  as  in  darkness.  In  such  cases  stem  growth  is  not 
influenced  by  leaf  formation  either  in  light  or  in  darkness,  so  that  the  inter- 
nodes can  elongate  freely. 

Finally,  Weber's2  studies  show  that  etiolated  plants  are  poorer  in  ash,  espe- 
cially in  calcium,  than  are  green  plants.  Some  results  of  Weber's  analyses  of 
etiolated  and  green  pea  leaves  are  given  in  the  following  table,  which  shows 
the  total  ash  content  and  that  of  seven  constituent  elements  (the  latter  reckoned 
as  oxides),  in  percentage,  on  the  basis  of  total  dry  weight  in  each  case.  In  the 
same  table  are  given  similar  results  for  bean  leaves  as  obtained  by  Palladin. 


Ash-constituents 
Material         Condi-  Iotal 

Analyzed  tiox  Ash 

K20     Na20     CaO     MgO    Fe203     P205      SO3       SiO, 


Pea  leaves 
Bean  leaves 


[Green  4.85      o.n      3.21       1.02      0.09      1.67      1.64       ....       1: 


4.85 

o.n 

3-21 

1 .02 

0.09 

4-49 

0.14 

1.24 

0.67 

0.21 

4.49 

.... 

i-33 

0.66 

o.n 

3-42 

.... 

0.  26 

0.40 

0.03 

/  / 
10. II 


[Etiolated     !  4.49      0.14      1.24      0.67      0.21      2.05      1.31 

[Green  4.49      1.33      0.66      0.11      2.19      0.83      0.56      10.30 

{Etiolated       3.42       0.26      0.40      0.03      3.25      0.12      006        7.54 


Similar  results  were  obtained  by  Schlosing  from  plants  that  had  been  grown 
with  light  but  in  a  chamber  with  very  moist  air. 

Among  the  conditions  causing  the  structural  peculiarities  of  etiolated  plants 
are  therefore  to  be  considered:  reduced  rates  of  transpiration,  the  conse- 
quent modification  in  the  distribution  of  water  and  dissolved  mineral  substances 
in  the  plant  body,  the  non-occurrence  of  the  photosynthetic  process  and  (to 
some  extent)  light  as  such. 

Some  of  the  chemical  reactions  that  are  necessary  for  normal  growth  occur 
only  in  the  presence  of  the  blue-violet  light  rays.  In  the  general  influence  of 
light  upon  plant  growth  and  structure,  many  different  kinds  of  reactions  have 

1  Palladin,  W.,  Transpiration  als  Ursache  der  Formanderung  etiolirter  Pflansen.  Ber.  Deutsch  B  ot. 
Ges.  8:  364-371.  1890.  Idem,  Ergrunen  und  Wachsthum  der  ctiolirten  Blatter.  Ibid.  9:  220-232. 
1891.  Idem,  Eiweissgehalt  der  Griinen  und  ctiolirten  Blatter.  Ibid.  9:  194-198.  Idem,  Aschenge- 
halt  der  etiolirten  Blatter.     Ibid.  10:  179-183-      189-'-     Idem,  1893-     [See  note  1,  p.  228.] 

-  Weber,  Rudolph,  Ueber  den  Einfhiss  farbigen  Lichtes  auf  die  Assimilation  und  die  damit  zusammen- 
hangende  Vermehrung  der  Aschenbestandtheile  in  Erbsen-Keimlingen.  Landw.  Versuchsst.  18:  18-48. 
1875. 


286  PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 

been  found  to  take  part,  such  as  oxidation,  polymerization,  decomposition,  and 
even  synthesis — the  last  in  the  presence  of  hydrocyanic  acid,  which  is  widely 
distributed  in  plants.1  These  processes  are  very  rapid  in  the  presence  of  inor- 
ganic salts.2  They  have  not  yet  been  studied  in  plants  excepting  in  con- 
nection with  the  activity  of  chlorophyll,  but  there  is  no  doubt  that  they  must 
be  important.  Neuberg  was  right  when  he  wrote:  "These  rapid  chemical  re- 
actions caused  by  light  may  furnish  a  clue  to  the  chemical  processes  that  under- 
lie phototropic  responses,  and  even  to  the  chemical  nature  of  sunlight  effects, 
in  general  upon  both  plants  and  animals"  (Neuberg,  cited  just  above). 

It  is  well  known  that  the  seeds  of  certain  plants  germinate  only  in  darkness,3 
while  seeds  of  other  plants,  and  certain  spores,  germinate  only  in  light.  In  the 
latter  case,  as  in  growth  phenomena  generally,  light  acts  not  only  as  a  stimulus 
that  releases  a  reaction  but  also  supplies  energy  that  is  necessary  for  the  process 
in  question.  This  statement  seems  to  elucidate  the  fact,  among  others,  that 
the  light  requirement  of  many  seeds  depends  upon  internal  conditions,  such  as 
the  stage  of  maturity  of  the  seeds;  light  is  especially  requisite  for  the  germina- 
tion of  seeds  that  have  not  been  allowed  to  reach  complete  maturity.  Many 
spores  that  ordinarily  show  a  low  percentage  of  germination  in  darkness  germi- 
nate very  well  when  iron  salts  of  organic  acids  are  supplied.4  Finally,  Wiesner's 
observations  [see  note  i,  page  274]  on  the  optimal  light  conditions  (Lichtgenuss) 
for  various  plants  have  shown  that  the  light  requirement  increases  as  the  tem- 
perature of  the  surroundings  falls.  The  various  characteristic  forms  and  struc- 
tures resulting  from  etiolation  are  thus  to  be  regarded  as  correlations  between 
the  different  parts  and  organs  of  the  plant,  these  being  due  partly  to  a  deficiency 
in  organic  assimilation  products,  partly  to  a  cessation  of  those  photo-chemical 
processes  that  are  independent  of  chlorophyll,  and  partly  to  a  modified  distribu- 
tion, in  the  plant  body,  of  water  and  dissolved  mineral  substances,  which  results 
from  reduced  transpiration.  All  these  conditions  must  also  influence  the  com- 
position of  the  cell  sap,  which  in  turn  controls  turgor  and  the  properties  of  the 
protoplasmic  membranes. 

Not  only  a  complete  lack  but  also  an  inadequate  supply  of  light  produces 
modifications  in  plant  form  and  structure.  If  plants  of  the  same  species  are 
grown,  some  in  bright  sunlight  and  some  in  diffuse  light,  the  two  groups  exhibit 
very  different  structures,  this  difference  being  especially  pronounced  in  the 
leaves.5    Leaves  grown  in  diffuse  light  are  always  thinner  than  those  grown  in 

1  Ciamician,  G.,  La  chimica  organica  negli  organismi.     99  p.     Bologna,  1908.     Idem,  1908.     [See  note 

3.  P-  34-1 

2  Neuberg,  1908.     [See  note  4,  p.  34] 

3  Kinzel,  Wilhelm,  Ueber  den  Einfluss  des  Lichtes  auf  die  Keimung.  ["Lichtharte  "  Samen.  (Vorlaufige 
Mitteilung.)  Ber.  Deutsch.  Bot.  Ges.  25:  269-276.  1907.  Idem,  Die  Wirkung  des  Lichtes  auf  die 
Kiemung.  (Vorlaufige  Mitteilung.)  Ibid.,  26:  105-115-  1908.  Idem,  Lichtkeimung.  Einige  besta- 
tigende  und  erganzende  Bemerkungen  zu  den  vorlaufigen  Mitteilungen  von  1907  und  1908.  Ibid.  26: 
631-645.  1908.  Idem,  Lichtkeimung.  Weitere  bestatigende  und  erganzende  Bemerkungen  zu  den  vor- 
laufigen Mitteilungen  von  1907  und  1908.     Ibid.  26  :  654-665.      1908. 

4Laage,  A.,  Bedingungen  der  Keimung  von  Farn-  und  Moossporen.  Beih.  Bot.  Centralbl.  21  :  76-115. 
1907. 

6  Dufour,  Leon,  Influence  de  la  lumiere  sur  la  forme  et  la  structure  des  fueilles.  Ann.  sci.  nat.  Bot.  VII, 
5:  311-413-     1887. 


INFLUENCE    OF   EXTERNAL   CONDITIONS   ON   GROWTH 


287 


direct  sunlight,  the  palisade  parenchyma  being  weakly  or  not  at  all  developed 
in  the  former,  while  it  is  strongly  developed  in  the  latter  (Fig.  135).  Sunshine 
leaves  have  smaller  epidermal  cells  with  smooth  lateral  walls,  while  shade  leaves 
have  larger  epidermal  cells  with  wrinkled  or  wavy  walls.  These  differences  in 
the  epidermal  cells,  between  leaves  grown  in  sunshine  and  those  grown  in 
shade,  are  so  great  that  the  two  kinds  of  leaves  might  easily  be  regarded  as 
belonging  to  entirely  different  species  (Fig.  136). 

In  some  cases  very  differently  shaped  leaves  may  be  produced  on  the  same 
individual  plant  by  allowing  some  leaves  to 
develop  in  sunshine  and  others  in  shade. 
Campanula  rotundifolia  may  serve  to  illus- 
trate this  (Fig.  137).  This  plant  usually 
produces  two  kinds  of  leaves :  those  near  the 
base  (which  develop  in  spring,  in  the  shade 
of  surrounding  plants)  are  rounded,  kidney- 
shaped  and  borne  on  long  petioles,  while 
those  on  the  upper  part  of  the  stem  (which 
develop  later,  in  strong  light)   are  linear, 

pointed  at  base  and  apex,  and  without  long  petioles.  If  a  plant  bearing  both 
sorts  of  leaves  is  kept  for  a  time  in  very  weak  light  the  lateral  buds  on  the 
upper  part  of  the  stem  develop  reniform,  long-petioled  leaves,  like  those  nor- 
mally occurring  exclusively  near  the  ground. 

Although  light  is  necessary  for  the  normal  development  of  green  plants,  they 
do  not  necessarily  develop  normally  with  continuous  illumination;  an  alteration 
of  periods  of  light  and  darkness  seems  necessary  to  produce  structures  such  as 
occur  in  nature.     Continuous  illumination  was  obtained  in  the  experiments  of 


Fig.  135. — Cross-sections  through 
leaves  of  Fragaria  vesca,  grown  in  direct 
sunlight  (L).  and  in  shade  (5).  (After 
Dufour.) 


Fig.  136.— Surface  view  of  upper  leaf  epidermis  of  Tussilago  farfara,  grown  in  direct  sunlight 

(L),  and  in  shade  (S).     (After  Dufour.) 

Bonnier1  by  means  of  electric  arcs,  the  plants  receiving  no  light  but  electric  light 
through  the  entire  six  or  seven  months  of  their  development.  Some  of  these 
plants  were  lighted  continuously,  day  and  night,  and  others  were  darkened 
by  means  of  opaque  covers,  for  a  period  each  day  from  6  p.m.  to  6  a.m.  The 
injurious  effect  of  ultra-violet  light  (which  is  relatively  more  intense  in  the 
light  of  the  electric  arc  than  in  sunlight)  was  avoided  by  the  use  of  clear 
glass  screens,  which  of  course  absorbed  the  ultra-violet  rays. 

In  these  experiments,  the  plants  that  were  darkened  at  night  developed  in 
the  normal  way  and  possessed  normally  differentiated  tissues,  but  the  con- 

'  Bonnier,  Gaston,  Influence  de  la  lumiere  electrique  continue  sur  la  forme  et  la  structure  des  plantes. 
Rev.  gen.  bot.  7:  241-257,  280-306,  332-342,  409-419.     189S. 


28S 


PHYSIOLOGY    OF    GROWTH    AND    CONFIGURATION 


tinuously  illuminated  plants,  although  they  contained  more  chlorophyll,  pos- 
sessed a  much  simpler  anatomical  structure  than  the  others,  and  resembled  in 
certain  respects,  plants  grown  in  continuous  darkness.  The  leaves  of  Helle- 
borus  niger,  for  example,  had  normal  structures  when  the  plants  were  darkened 

every  night;  the  mesophyll  com- 
prised the  usual  layer  of  palisade 
parenchyma  above  (containing 
most  of  the  chloroplasts)  with 
loose,  spongy  parenchyma  below, 
the  latter  having  numerous  large 
air  passages  (Fig.  138,  /).  On 
the  other  hand,  the  Helleborus 
leaves  grown  with  continuous  illu- 
mination were  very  different  from 
the  others  in  several  respects. 
Chloroplasts  were  here  much  more 
numerous  than  in  the  other  case 
and  they  occurred  almost  through- 
out the  entire  tissue,  instead  of 
being  mainly  confined  to  the 
palisade.  Instead  of  the  loose, 
spongy  parenchyma  there  was  a 
tissue  more  like  the  fundamental 
parenchyma  of  growing  regions, 
with  almost  no  intercellular  spaces  at  all  (Fig.  138,  F). 

While  photosynthesis  is  mainly  dependent  on  the  less  refrangible  half  of  the 
spectrum,  normal  growth  and  development  require  the  more  refrangible  half 
(Fig.  132,  curve  XY).  These  more  refrangible  rays  (blue  and  violet  light)  are 
strongly  absorbed  by  plants. 
If,  on  a  bright  spring  day,  for 
example,  the  intensity  of  the 
blue-violet  light  is  666  in  the 
open ,  it  is  only  2 1  in  the  shade 
of  a  fir  tree,  all  but  about  one 
thirty-second  of  the  energy  of 
these  rays  having  been  re- 
flected or  absorbed  by  the 
leaves  of  the  tree.  Many 
formal  characteristics  of 
plants  depend  upon  the  intensity  of  the  blue-violet  light  that  reaches  them. 
In  evergreen  plants,  only  the  peripheral  leaf-buds  develop,  since  the  interior 
buds  are  shaded,  but  in  deciduous  trees  leaf-buds  develop  throughout  the 
crown;  in  the  latter  case  the  tree  is  leafless  at  the  time  the  buds  are  opening 
and  all  buds  are  at  first  equally  lighted.1 

Plants  differ  with  respect  to  their  light  requirements  and  they  may  be 

1  Wiesner,  1893.     [See  note  2,  p.  283. 1 


Fig.  137. — Upper  portion  of  plant  of  Campanula 
rotundifolia,  with  reniform  leaves  developed  from  a 
lateral  bud  in  diffuse  light.      (After  Goebel.) 


Fig.  138. — Cross-sections  of  leaves  of  Helleborus  niger, 
grown  in  continuous  light  (F)  and  darkened  during  the 
night  hours  (J).     (After  Bonnier.) 


INFLUENCE    OF   EXTERNAL   CONDITIONS    ON   GROWTH  289 

classified  by  this  criterion,  into  shade  plants  and  non-shade  plants.  In  this 
connection  the  work  of  Wiesner  has  brought  his  term  Lichtgenuss  of  plants 
into  considerable  prominence. ; 

By  relative  Lichtgenuss,  Wiesner  means  the  light  income  of  the  plant  in 
question,  expressed  as  a  fractional  part  of  the  total  sunlight  intensity  that  might 
reach  it  if  it  were  not  shaded  at  all  in  its  habitat.  It  is  clear  that  the  light 
income  of  different  parts  of  the  same  individual,  and  of  different  individuals 
in  the  same  natural  habitat,  is  not  a  constant,  but  ranges  between  certain  limits; 
either  the  maximum  or  minimum  requirement  of  light  intensity  may  be  of  inter- 
est (the  limits  of  the  range  of  light  incomes  under  which  a  given  species  may 
thrive),  or  the  average  light  income  of  an  individual  or  group  may  be  studied. 
The  range  of  light  intensities  that  a  plant  can  bear,  with  which  the  work  of  Wies- 
ner was  most  concerned,  is  a  quantitative  expression  of  the  degree  of  the  plant's 
adaptation  for  growing  under  various  light  conditions;  it  tells  something  of  the 
internal  conditions  or  properties  of  the  plant  as  far  as  its  light  requirement  is 
concerned.  If  the  relative  light  genuss  (relative  photolepsy)  of  a  plant  is  said 
to  be  0.25,  it  is  to  be  understood  that  that  particular  plant  is  growing  in  a  shaded 
place  where  its  light  income  is  approximately  0.25  of  what  that  income  would  be 
if  all  the  shade  were  removed.  Wiesner  also  employed  what  he  terms  the  abso- 
lute genuss  (absolute  photolepsy,  absolute  light  income,  etc.),  which  is 
expressed  in  photometric  units;  he  used  the  Bunsen-Roscoe  unit.1 

The  ranges  of  the  relative  light  incomes  of  several  plants  growing  in  their 
natural  habitats  at  Vienna  are  shown  below: 

Buxus  sempervirens  (box) : 1-H00  (0.010) 

Fagus  sylvatica  (beech) i-^io    (0.013) 

Betula  verrucosa  (birch) i-^i      (o .  111) 

Larix  decidua  (larch) i~}i      (o .  200) 

1  Wiesner,  1909.     [See  note  1,  p.  274.] 

>  Although  Wiesner  expresses  the  hope  that  the  term  Lichtgenuss  may  eventually  come  to 
be  an  international  technical  word,  it  seems  hardly  probable  that  this  hope  will  be  realized. 
As  an  alternative  he  has  suggested  photolepsy.  [Wiesner,  J.,  Sur  l'adaptation  de  la  plante 
a  l'intensite  de  la  lumiere.  Compt.  rend  Paris  138:  1346-1340.  1904.  Idem,  1907,  p.  5 
(see  note  1,  p.  274).]  Whatever  may  be  the  pros  and  cons  with  reference  to  these  two  words, 
it  is  clear  that  neither  one  of  them  can  ever  have  quite  the  same  suggestiveness  that  Licht- 
genuss has  in  German.  In  that  language  the  word  itself  is  familiar  to  every  one  and  the  tech- 
nical meaning  given  it  by  Wiesner  is  derived  from  the  ordinary  meaning.  To  the  non-techni- 
cal German,  Lichtgenuss  carries  a  meaning  very  similar  to  that  employed  by  Wiesner,  while 
neither  Lichtgenuss  nor  Photolepsy  has  any  meaning  at  all  to  such  a  reader  in  most  other 
languages.  It  therefore  seems  desirable  to  employ  a  simple  and  straightforward  English 
word  or  phrase  for  non-technical  purposes.  Light  income  and  optimal  light  intensity  may  be 
used.  Neither  of  these  has  as  much  teleological  implication  as  has  the  word  Lichtgenuss  in 
German.  Light  income  means  simply  the  amount  of  light  actually  impinging  upon  the  plant 
in  question.  The  optimal  light  intensity  denotes  the  amount  of  light  that  must  impinge  upon 
the  plant  in  order  that  it  grow  best,  or  most  rapidly,  etc.  The  light  requirement  of  a  given 
species  is  the  range  of  light  intensity  within  which  that  species  can  thrive,  etc.,  being  limited 
by  a  maximum  and  a  minimum  requirement.  Measurements  of  light  intensity  should  be 
recorded  in  absolute  terms,  not  as  percentages  of  the  intensity  of  unobstructed  sunshine 
at  the  given  time  and  place,  which  itself  varies  greatly  and  rapidly  at  any  locality  and  is 
often  not  at  all  the  same  for  different  places  at  the  same  time.  Of  the  light  actually  reach- 
ing the  plant  surface  only  a  partis  absorbed,  of  course;  much  is  directly  reflected  at  the 
periphery  and  some  usually  passes  through  or  is  reflected  from  internal  surfaces. — Ed. 
19 


290  PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 

These  numbers  may  be  regarded  as  the  maxima  and  minima  of  relative  light 
requirement  for  these  plants.  The  relative  minimum  increases  with  the  geo- 
graphical latitude.  Acer  platanoides,  for  example,  has  a  relative  minimum 
light  requirement  of  }{$  (0.018)  at  Vienna,  %S  (°-°3°)  at  Hamar,  Norway,  and 
H  (0.200)  at  Tromso,  Norway.  Of  course  the  light  intensity  in  the  open 
decreases  with  latitude,  which  suggests  an  explanation  of  this  decrease  in  the 
relative  minimum  light  requirement.  Also,  with  lower  temperatures  the  mini- 
mum light  requirement  is  higher. 

There  is  also  a  relation  between  the  light  income  of  plants  and  mycorhiza, 
the  development  of  which  occurs  only  in  connection  with  plants  that  are  con- 
fined to  shady  situations.  Finally,  the  amount  of  chlorophyll  in  plants  and 
the  color  of  their  leaves  is  related  to  the  light  income. 

In  one  of  his  later  papers  Wiesner1  expresses  the  two  following  conclusions: 
(1)  Plants  that  are  especially  well  adapted  for  growing  in  diffuse  light  are  char- 
acterized by  having  their  green  parts  (especially  their  leaves,  which  are  strongly 
absorptive  of  light)  so  arranged  as  to  receive  light  very  freely;  in  many  cases, 
indeed,  the  leaves  are  so  placed  as  to  receive  the  maximum  intensity  of  diffuse 
light  that  the  habitat  affords.  (2)  Plants  that  are  especially  well  adapted  for 
growing  in  direct  sunshine,  on  the  other  hand,  are  characterized  by  leaves  and 
other  green  parts  so  placed  as  not  to  receive  the  light  at  its  highest  intensities, 
but  to  receive  only  the  lower  intensities.* 

1  Wiesner,  J.,  Ueber  die  Anpassung  der  Pflanze  an  das  diffuse  Tages-  und  das  directe  Sonnenlicht.  Ann. 
Jard.  Bot.  Buitenzorg.  Supplement  3':  48-60.      1910. 

k  In  connection  with  the  interpretation  of  all  this  work  of  Wiesner's  it  must  be  borne  in 
mind  that  his  measurements  were  made  in  terms  of  the  effect  produced,  by  the  radiation  stud- 
ied, upon  photographic  paper.  This  paper  is  especially  sensitive  to  light  radiation  of  the  shorter 
wave-lengths  (blue-violet  and  ultra-violet),  it  is  less  sensitive  to  the  medium  wave-lengths  of 
light  (green,  yellow)  and  is  almost  wholly  unaffected  by  the  long  wave-lengths  of  light 
radiation  (orange,  red  and  infra-red).  It  is  thus  seen  that  the  Weisner  method  automatically 
applies  a  relative  weighting  to  the  effect  produced  by  each  one  of  the  different  wave-lengths 
that  constitute  the  radiant  energy  impinging  upon  the  instrument,  and  the  value  obtained  from 
any  test  is  the  integration  of  these  weighted  partial  values.  The  relative  sensitivities  of  the 
paper  used  might  be  experimentally  determined  for  a  variety  of  different  short  ranges  of  wave- 
lengths, and  weighting  coefficients  might  thus  be  determined  for  each  range,  by  the  use  of  which 
it  might  be  possible  to  calculate  from  any  given  reading  an  approximate  relative  value  for  the 
actual  radiation  intensity  as  a  whole,  providing  all  the  tests  dealt  with  radiation  made  up  of 
intensities  of  the  various  wave-lengths  in  a  constant  set  of  proportions.  But  the  radiation  to  be 
studied  varies  from  place  to  place  and  from  time  to  time,  not  only  in  total  energy  content,  but 
also  in  the  relative  proportions  of  the  intensities  of  the  various  component  wave-lengths;  that 
is,  in  quality.  From  these  considerations  it  becomes  evident  that  the  Wiesner  method,  for 
measuring  and  comparing  the  amounts  of  radiation  received  by  plants  in  different  places  and 
at  different  times,  must  be  regarded  as  crude  and  unsatisfactory,  at  its  very  best. 

Besides  this  very  serious  physical  objection  to  the  method  employing  photographic  paper, 
there  must  be  considered  another  objection  that  is  just  as  serious,  based  on  physiological  rela- 
tions. For  the  purposes  of  ecology  and  physiology  it  is  necessary,  not  only  that  the  quality 
and  intensity  of  the  radiation  received  by  plants  in  different  places,  etc.,  be  measured  and  com- 
pared as  such,  but  that  the  physical  values  obtained  by  such  measurement  be  subjected  to  a 
physiological  weighting,  so  as  to  give  an  index  of  the  radiation  received  in  each  of  the  different 
habitats  as  it  may  affect  plants  growing  therein.     It  is  unnecessary  to  add  that  the  sensitive- 


INFLUENCE    OF   EXTERNAL   CONDITIONS    ON    GROWTH  29 1 

There  are  many  plants  whose  flowers  open  normally  in  darkness,  so  long  as 
the  rest  of  the  plant  is  exposed  to  light.  In  some  cases  the  form  of  the  flowers 
produced  is  dependent  upon  light  conditions.  Thus,  Vochting1  found  that  the 
formation  of  cleistogamous  flowers  (which  are  self-pollinated  and  never  open)  is 
markedly  influenced  by  external  conditions,  especially  by  light.  The  plants  of 
Vochting's  experiment  were  placed  on  the  inner  side  of,  and  at  various  dis- 
tances from,  a  northeast  window,  so  that  they  received  light  of  various  inten- 
sities. With  some  plants  the  effect  of  being  placed  farther  from  the  source  of 
light  produced  only  a  decrease  in  the  number  and  size  of  the  flowers,  but  the 
flowers  opened  in  all  cases.  In  the  case  of  plants  with  a  tendency  toward 
cleistogamy,  however,  the  number  of  cleistogamous  flowers  produced  increased 
as  the  plants  were  farther  from  the  window.  With  such  plants  it  is  possible  to 
obtain  either  ordinary  or  cleistogamous  flowers  at  will,  by  controlling  the  light 
intensity  during  the  flowering  period. 

The  flowers  of  many  plants  are  open  only  by  day  and  are  closed  at  night2 
(see  Fig.  130,  p.  279),  while  those  of  some  other  plants  are  open  only  at  night 
and  are  closed  by  day.  These  periodic  movements  of  petals  and  sepals  are 
frequently  dependent  upon  light  variation,  and,  as  is  shown  by  measurements, 
they  are  directly  due  to  unequal  growth  on  the  two  sides  of  the  organ.  When 
growth  of  the  outer  or  lower  regions  of  the  petals  is  more  rapid,  the  flower 
closes,  and  opening  occurs  when  growth  is  more  rapid  on  the  inner  or  upper 
side.  Such  movements  of  floral  parts  may  also  be  brought  about  by  tempera- 
ture changes,  to  which  many  flowers  are  especially  sensitive  in  this  way;  thus, 
a  temperature  change  of  5°C.  is  sufficient  to  produce  complete  closing  or 
opening  of  Crocus  flowers. 

Light  also  exerts  an  influence  upon  the  development  of  lower  plants,  such 
as  fungi.3  Pilobolus,  for  example,  develops  normally  in. weak  light  but  pro- 
duces very  long  sporangiophores  in  darkness,  where,  also,  the  spores  fail  to  ma- 
ture. Light  is  injurious  to  colorless  bacteria,  which  are  killed  by  direct  sunlight 
and  hindered  in  their  growth  by  diffuse  light.  This  is  shown  very  beautifullv 
by  H.  Buchner's  experiment.  He  pasted  black  paper  letters  on  the  bottom  of  a. 
Petri  dish  containing  a  freshly  prepared  plate  culture  of  typhus  bacteria  iru 
nutrient  agar,  and  then  exposed  the  dish,  bottom  upward,  to  direct  sunshine 
for  one  and  a  half  hours.  The  dish  was  then  placed  in  darkness  for  twenty-four 
hours,  after  which,  when  the  black  paper  was  removed,  the  forms  of  the  letters 
could  be  plainly  seen  in  the  agar  plate,  because  of  the  numerous  white  colonies 
that  had  developed,  exclusively  where  the  bacteria  had  been  protected  from  the 

ness  of  photographic  paper  does  not  vary  in  the  same  way,  with  the  wave-length  of  impinging 
radiation,  as  does  the  effectiveness  of  the  radiation  to  favor  plant  growth  and  development. 
The  problem  is  an  exceedingly  complex  one,  for  which  none  but  very  general  methods  may 
even  be  suggested  at  present,  but  progress  may  be  best  furthered  by  a  frank  appreciation  of  the 
logical  requirements. — Ed. 

1  Vochting,  Hermann,  Ueber  den  Einfluss  des  Lichtes  auf  die  Gestaltung  und  Anlage  der  Bltithen. 
Jahrb.  wiss.  Bot.  25:  149-208.      1893. 

-  Pfeffer,  W.,  Physiologische  Untersuchungen.     Leipzig,  1873. 

3  Brefeld,  [O.],  Ueber  die  Bedeutung  des  Lichtes  fur  die  Entwickelung  der  Pilze.     Bot.  Zeitg.  35:  386 
401-408.     1877. 


292 


PHYSIOLOGY   OF    GROWTH    AND    CONFIGURATION 


sunlight  by  the  black  letters.     The  portions  of  the  plate  not  thus   protected 
were  entirely  free  from  living  bacteria. 

When  bacteria  are  exposed  to  sunlight  the  majority  of  them  are  killed  in  the 
first  few  minutes  of  exposure.  This  was  shown  with  twelve  similar  plate  cul- 
tures of  Bacillus  anthracis,  one  of  which  was  kept  in  darkness  throughout  the 
experiment,  the  other  eleven  being  first  exposed  to  sunlight  for  ten,  twenty, 
thirty,  etc.,  minutes,  respectively,  and  then  exposed  to  darkness  for  the  rest  of 
the  culture  period.  When  sufficient  time  had  elapsed  for  the  colonies  to 
develop,  these  were  counted  in  each  of  the  plates.  The  following  table  shows 
the  results  of  these  counts. 


Period  of  Exposure 
to  Sunlight 


Number  of  Colonies 
Developed 


Period  of  Exposure 
to  Sunlight 


minutes 

Not  illuminated 

10 

20 

3° 


2520 
360 

!3° 

4 


minutes 
40 
50 
60 
70 


Number  of  Colonies 
Developed 


3 

4 

5 
o 


It  is  thus  evident  that  light  possesses  very  great  disinfecting  power,1  and  the 
Italian  proverb,  "Where  sunshine  enters  not,  there  enters  the  physician,"  has 
a  foundation  in  bacteriological  science.  Light  is  a  potent  factor  in  the  auto- 
matic purification  of  polluted  rivers.  As  they  issue  from  cities,  streams  contain 
innumerable  bacteria  of  many  kinds,  but  before  they  have  flowed  far  their 
waters  become  practically  free  from  these  organisms,  through  the  action  of 
sunlight.  Water  containing  a  hundred  thousand  cells  of  Bacterium  coli  com- 
mune per  cubic  centimeter  was  found  to  be  entirely  free  of  living  bacteria  after 
exposure  to  sunshine  for  a  single  hour.  The  ultra-violet  rays  {rayons  abiotiques, 
of  Dastre2)  are  especially  injurious  to  colorless  bacteria. 

The  colored  bacteria  are  not  affected  by  light  as  are  the  colorless  ones.  The 
purple  bacteria  studied  by  Engelmann  are  attracted  toward  brightly  lighted 
portions  of  the  medium  in  which  they  are  growing,  and  they  develop  best  in 
the  presence  of  bright  light. 

§6.  Influence  of  Gravitation  on  Growth  and  Configuration.3 — That  stems 

1  E.  W.  Schmidt  has  attempted  to  utilize  the  sensitizing  action  of  fluorescent  substances  upon  micro- 
organisms, enzymes,  etc.,  as  a  means  of  disinfection.  In  this  connection  see:  Tappeiner,  Hermann,  von,  and 
Jodlbauer,  A.,  Die  sensibilisierende  Wirkung  fluorescierender  Substanzen.  Leipzig.  1907,  Schmidt, 
Ernst  W.,  Enzymologische  Mitteilungen.     Zeitschr.  physiol.  Chem.  67:  314-323.     1010. 

2  Cernovodeanu,  P.,  and  Henri,  Victor,  Etude  de  Taction  des  rayons  ultraviolets  sur  les  microbes. 
Compt.  rend.  Paris  ISO  :  52-54.  1910.  Idem,  Comparison  des  actions  photochemiques  et  abiotiques 
des  rayons  ultraviolets.  Zft/d.  150:  540-551.  1910.  Urbain,  Ed.,  Seal,  CI.,  and  Feige,  A.,  Sur  la  steriliza- 
tion de  l'eau  par  1'ultraviolet.     Ibid.  150:  548-549.     1910. 

'  Wiesner,  1881.  P.  85-130.  [See  note  2,  p.  275.]  Idem,  Untersuchungen  uber  die  Wachsthumsbe- 
wegungen  der  Wurzeln.  (Darwin'sche  und  geotropische  Wurzelkrummung.)  Sitzungber.  (math-naturw. 
Kl.)  K.  Akad.  Wiss.  Wien.  80' :  223-302.  1884.  Fitting,  Hans,  Untersuchungen  uber  den  geotropischen 
Reizvorgang.  Teil.  I.  Die  geotropische  Empfindlichkeit  der  Pflanzen.  Jahrb.  wiss.  Bot.  41:  221-330. 
1905.  Idem,  same  title.  Teil  II.  Weitere  Erfolge  mit  der  intermittierenden  Reizung.  Ibid.  41 :  331-396. 
1905.  Bach,  H.,  Ueber  die  Abhangigkeit  der  geotropischen  Presentations-  und  Reaktionszeit  von  verschied- 
enen  Aussenbedingungen.  Ibid.  44:  57-123-  1907.  Nordhausen,  M.,  Ueber  Richtung  und  Wachs- 
tum  der  Seitenwurzeln  unter  dem  Einfluss  ausserer  und  innerer  Faktoren.     Ibid.  44:  557-634.      1907. 


INFLUENCE    OF   EXTERNAL   CONDITIONS    ON   GROWTH  293 

grow  upward  and  that  roots  grow  downward  are  such  obvious  facts  that  they 
remained  uninvestigated  for  a  long  time.  The  first  author  to  give  this  difference 
serious  attention  was  Dodart,1  and  much  work  has  been  published  in  this  con- 
nection since  his  time,  but  no  real  insight  into  these  phenomena  has  even  yet 
been  obtained. 

If  a  growing  plant  is  changed  from  the  vertical  to  the  horizontal  position, 
the  root-tip  soon  bends  downward  and  the  tip  of  the  stem  upward.  Knight2 
showed  that  this  bending  of  growing  plant  organs  is  due  to  the  influence  of  the 
force  of  gravitation.  Seeds  were  allowed  to  germinate  while  attached  to  a  rapidly 
rotating  wheel.  The  axes  of  the  seedlings  assumed  positions  in  the  radii  of 
the  rotating  disk,  all  of  the  main  roots  directing  their  tips  outward  while  the 
tips  of  the  main  stems  were  directed  inward.  Here  the  force  of  gravitation  was 
not  allowed  to  act  continuously  upon  the  seedlings  in  any  particular  direction 
(since  the  axis  of  the  wheel  was  horizontal),  and  in  place  of  this  force  as  it 
usually  acts  on  plants  was  substituted  the  centrifugal  force  generated  by  rota- 
tion. The  primary  roots,  which  usually  elongate  in  the  direction  of  the  pull  of 
gravitation,  now  grew  in  the  direction  of  the  centrifugal  pull;  that  is,  toward  the 
circumference  of  rotation.  The  primary  stems,  which  usually  direct  their  tips 
away  from  the  center  of  the  earth,  grew  in  the  direction  opposite  to  that  of  the 
centrifugal  pull;  that  is,  toward  the  center  of  rotation. 

The  phenomenon  of  bending  in  response  to  the  force  of  gravitation  is  termed 
geotropism.  When  the  organ  bends  so  as  to  direct  its  tip  toward  the  center  of 
the  earth  its  geotropism  is  said  to  be  positive,  and  when  the  bending  occurs  in 
the  opposite  direction  it  is  said  to  be  negative.  Primary  stems  are  generally 
negatively  geotropic  and  primary  roots  are  generally  positively  so. 

The  geotropism  of  lateral  branches  of  both  shoots  and  roots  is  less  pro- 
nounced; these  organs  generally  do  not  assume  the  vertical  position,  but  take 
an  oblique  direction,  more  or  less  nearly  approaching  the  horizontal.  [They 
are  said  to  be  apo geotropic  or  plagiotropic] 

For  the  removal  of  the  one-sided  geotropic  stimulus  in  experiments,  various 
forms  of  clinostat  are  used,  as  well  as  the  centrifuge  already  mentioned.  The 
Pfeffer  clinostat  (Fig.  139)  consists  essentially  of  a  metal  axis  (c)  rotated  by  a 
clock-movement  (a)  and  bearing  at  its  free  end  the  objects  of  the  experiment. 
The  axis  may  be  arranged  so  as  to  have  any  desired  position,  horizontal,  ver- 
tical, etc.,  the  clock  being  correspondingly  tilted  and  fastened  by  the  screw  n. 

If  a  cork  disk  (/,  Fig.  139,  B)  bearing  germinating  seeds  is  attached  to  the 
horizontal  axis  of  a  clinostat,  with  its  plane  surfaces  perpendicular  to  the  axis, 
and  slowly  rotated,  the  seedlings  do  not  bend,  but  continue  to  grow  in  whatever 
direction  they  may  have  had  when  attached.  The  force  of  gravitation  is  of 
course  not  prevented  from  acting  upon  the  plants  in  such  a  case,  but  the  direc- 
tion of  this  force  is  continually  varied,  so  that  during  each  revolution  the  gravity 

1  [Dodart,  [  .],  Sur  l'affectation  de  la  perpendiculaire  remarquable  dans  toutes  les  tiges,  dans  plusieurs 
racines,  et  autant  qu'il  est  possible  dans  toutes  les  branches  des  plantes.  Hist.  Acad.  Roy.  Sci.  1700 
(2nd  ed.)  :  47-63-     Paris,  1741-] 

2  [Knight,  Thomas  Andrew,  On  the  direction  of  the  radical  and  germen  during  the  vegetation  of  seeds. 
Phil,  trans.  Roy.  Soc.  London  1805  tPart  I)  [96]:  99-108.  1806.] 


294 


PHYSIOLOGY    OF    GROWTH   AND    CONFIGURATION 


pull  is  applied  as  much  to  one  side  of  the  plant  as  to  any  other.  Thus,  if  a 
certain  region  of  the  rotated  plant  lies  underneath  for  a  short  time,  this  region 
soon  comes  to  lie  above  for  the  same  period,  so  that  gravitation  acts  successively 
in  opposite  directions  upon  each  portion  of  the  plant,  and  a  tendency  to 
bend  toward  one  side  is  offset  by  an  equal  tendency  to  bend  toward  the 
opposite  side.  Thus  no  geotropic  bending  occurs  in  such  an  experiment. 
Geotropic  bendings  are  due  to  unequal  growth  on  the  two  sides  of  the  bend- 
ing organ,  and  they  occur  only  in  the  growing  regions  of  stems  and  roots;  after 
the  tissues  have  become  mature  and  have  ceased  to  grow  these  bendings  are  no 
longer  possible.  Also,  the  more  rapidly  an  organ  is  growing  the  more  quickly 
it  bends  in  response  to  gravitation,  and  all  conditions  that  retard  growth  also 
retard  the  geotropic  response. 


Fig.  139- — Pfeffer's  clinostat.     A,  arranged  for  rotation  of  potted  plant  on  horizontal  axis1 
B,  glass  moist  chamber,  for  rotating  germinating  seeds,  etc. 

The  effect  of  gravitation  upon  the  geotropically  stimulated  plant  is  to  release 
certain  chemical  and  physical  reactions,  and  these,  in  their  turn,  lead  to  the  bend- 
ing itself,  but  only  after  a  certain  time  has  elapsed.  The  time  period  extending 
from  the  beginning  of  the  application  of  the  stimulus  to  the  beginning  of  the 
visible  response  is  termed  the  reaction  time,  and  its  length  varies  with  different 
organs  and  plants,  from  about  forty  minutes  to  several  hours.  It  is  not  neces- 
sary, however,  that  the  stimulus  be  continued  throughout  all  of  this  reaction 
period.  If  a  plant  is  stimulated  for  a  period  shorter  than  its  reaction  time,  as 
by  lying  quietly  on  its  side,  and  is  then  rotated  on  the  clinostat  so  as  to  equalize 
the  lateral  pull  of  gravity,  geotropic  bending  finally  occurs,  providing  the  original 
period  of  stimulation  was  of  adequate  length.  The  shortest  possible  time  of 
stimulation  that  is  sufficient  to  bring  about  the  later  response  is  called  the 
minimum  presentation  time  of  the  geotropic  stimulus.     Generally  this  is  only 


INFLUENCE    OF   EXTERNAL    CONDITIONS    ON    GROWTH 


295 


from  two  to  four  minutes,  rarely  longer,  and  the  fact  that  this  period  is  so  short 
is  evidence  in  favor  of  the  conclusion  that  the  first  effect  of  the  stimulus  is  that 
of  a  release.  By  intermittent  stimulation  (by  means  of  a  specially  constructed 
clinostat1)  the  presentation  time  may  be  made  still  shorter. 

The  angle  assumed  by  leaves  with  reference  to  the  stem  is  influenced  by 
gravitation  as  well  as  by  light.  In  Fig.  140,  B,  is  shown  a  Coleus  plant  that  has 
been  rotated  on  a  horizontal  shaft  parallel  with  its  own  axis  for  twenty-four 
hours.  The  leaves  are  seen  to  be  bent  backward  toward  the  stem  in  a  charac- 
teristic way.  In  the  plant  that  has  stood  upright  (Fig.  140,  .4)  the  leaves  are 
nearly  perpendicular  to  the  stem. 


Fig.  140. — Coleus  plants,  in  usual  position  (A)  and  after  rotating  for  24  hours  (B),  showing 

difference  in  leaf  position.      (After  Pfeffer.) 

Gravitation  also  frequently  controls  the  position  of  floral  parts,2  as  for  in- 
stance the  stamens  and  pistil  of  Amaryllis  formosissima.  When  the  flower  bud 
opens  under  usual  conditions  these  organs  are  directed  downward  (Fig.  141, 
at  the  left),  but  if  the  bud  is  allowed  to  open  in  an  inverted  position  (Fig.  141, 
at  the  right),  the  stamens  and  pistil  assume  the  same  position  with  reference  to 
the  earth,  but  the  opposite  direction  with  reference  to  the  remaining  floral  parts. 

Plants  that  normally  bear  zygomorphic  flowers  may  be  made  to  produce 
actinomorphic  ones  if  they  are  rotated  in  the  proper  manner  during  the  de- 
velopment of  the  flowers.     A  zygomorphic  flower  is  capable  of  being  divided 


1  Fitting,  1905.     [See  note  3.  P-  292.] 

:  Vbchting,  Hermann,  Ueber  Zygomorphie  und  deren  Ursachen. 


Jahrb.  wiss.  Bot.  17:  297-343.     1886. 


296 


PHYSIOLOGY   OF    GROWTH  AND    CONFIGURATION 


into  two  symmetrical  halves  by  but  a  single  plane.  Actinomorphic  flowers, 
on  the  other  hand,  are  symmetrical  with  reference  to  any  plane  passing  through 
the  floral  axis,  being  really  symmetrical  about  that  axis.  The  flowers  of  Epi- 
lobrium  angustifolium  are  zygomorphic  when  they  develop  normally  (Fig.  142, 
at  the  left).  If,  however,  a  flowering  shoot  with  young  buds  is  slowly  rotated 
about  a  horizontal  axis,  its  own  axis  being  parallel  to  that  of  the  clinostat,  then 
the  flowers  that  open  under  these  conditions  are  actinomorphic  (Fig.  142,  at 
the  right). 

The  reasons  why  gravitation  generally  produces  such  different  effects  upon 
root  and  shoot,  leading  to  positive  geo tropic  bending  in  the  one  and  to  negative 
geotropic  bending  in  the  other,  are  to  be  sought  in  the  organs  themselves;  these 


Fig.  141. — Flower  of  Amaryllis  formosissima  that  has  developed  under  normal  conditions 
(at  the  left),  and  another  that  has  developed  from  the  bud  in  the  inverted  position  (at  the 
right);  stamens  and  pistil  are  directed  downward  in  both  cases.     {After  Vochting.) 


organs  are  internally  different  and  their  various  tissues  are  correlated  in  specific 
ways  in  each  case.  Similarly,  the  various  responses  of  leaves  grown  in  dark- 
ness are  not  due  to  the  external  light  conditions  alone,  but  must  be  related  to 
special  correlations  between  leaves  and  stem. 

As  has  already  been  remarked,  no  insight  into  the  fundamental  nature  of 
geotropic  phenomena  has  yet  been  obtained.  The  suggestion  of  certain  zoolo- 
gists that  the  otocysts  of  lower  animals  serve,  not  as  organs  of  hearing,  but  as 
organs  of  equilibration,  has  led  some  botanists1  to  seek  such  bodies  in  plants. 

1  Haberlandt,  G.,  Ueber  die  Perception  des  geotropischen  Reizes.     Ber.  Deutsch.  Bot.  Ges.  18 :  261-272. 
1900. 


INFLUENCE    OF   EXTERNAL   CONDITIONS    ON   GROWTH 


297 


Nemec1  has  advanced  the  idea  that  starch  grains  act  as  such  "statoliths"  in 
plant  cells.  The  force  of  gravitation  is  thus  supposed  to  act  upon  the  starch 
grains,  which  are  of  higher  specific  gravity  than  the  liquid  about  them,  so  that 
they  always  lie  in  that  part  of  the  cell  nearest  to  the  center  of  the  earth  (Fig. 
143).  The  pressure  exerted  by  these  grains,  upon  the  protoplasm  of  the  cell, 
is  supposed  to  inaugurate  the  series  of  protoplasmic  changes  which  finally  result 
in  visible  bending. 

To  this  attempt  at  a  physical  interpretation,  Czapek2  has  opposed  a  chemical 
one.*  This  writer  was  able  to  demonstrate  certain  chemical  changes  in 
tissues  affected  by  geotropic  as  well  as  in  those  affected  by  phototropic  stimuli. 
In  this  connection  the  observations  of  0.  Richter3  may  be  important,  to  the 
effect  that  negative  geotropism  disappears  in  plants  under  the  influence  of  the 
more  or  less  poisonous  air  of  the  laboratory  (see  also  page  261). 

Chemical  investigation  of  growth  phenomena  is  the  only  method  of  ap- 
proach that  promises  to  furnish  a  fundamental  explanation  of  geotropic  and 


Fig.  142. — Normal  flower  of  Epilobrium  an  gusli  folium 
(at  the  left),  and  actimorphic  flower  (at  the  right),  the  latter 
produced  by  rotation  of  the  plant  about  a  horizontal  axis. 
(After  Vochling.) 


Fig.  143. — Tip  of  cotyledon 
of  Panicum  mileaceum,  showing 
starch  grains  lying  on  the  phys- 
ically lower  side  of  each  cell. 
(After  Nemec.) 


phototropic  reactions.  For  the  present  it  can  be  said  simply  that  under  the 
influence  of  gravitation  the  primary  shoot  grows  upward  and  the  primary  root 
downward. 

1  Nemec,  B.,  Die  Perception  des  Schwerkraftreizes  bei  den  Pflanzen.  Ber.  Deutsch.  Bot.  Ges.  20: 
339-354-     1902. 

2  Czapek,  F.,  Stoffwechselprocesse  in  der  geotropisch  gereizten  Wurzelspitze  und  in  phototropische 
sensiblen  Organen.  Ber.  Deutsch.  Bot.  Ges.  20:  464-470.  1902.  Czapek,  F.,  and  Rudolf,  Bertel, 
Oxydative  Stoffwechselvorgange  bei  pflanzlichen  Reizreaktionen.  (I.  Abhandlung.)  Jahrb.  wiss.  Bot.  43 : 
361-467.  1906.  Grafe,  V.,  and  Linsbauer,  K.,  Zur  Kenntnis  der  Stoffwechselvorgange  bei  geotropischer 
Reizung.     Sitzungsber.  (math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien.  no/:  827-852.     1910. 

3  Richter,  Oswald,  Die  horizontale  Nutation.  Sitzungsber  (math.-naturw.  Kl.)  K.  Akad.  wiss.  Wien 
119':  1051-1084.     1910. 

'To  the  editor  there  seems  to  be  no  opposition  between  these  two  views.      The  suggestions 

of   Nemec   and    Haberlandt   attempt  to  explain  only  how  the  attraction  of  gravitation  may 

become  converted  into  a  pressure  of  some  cell-components  upon  others,  and  it  is  self-evident 

that  this  can  represent  only  the  first  link  in  the  chain  of  cause  and  effect  that  finally  terminates 

in  an  alteration  of  growth  rate  in  certain  cells  of  the  bending  region  of  the  plant.     Between  the 

pressure  postulated  by  the  physical  theory  and  the  bending  itself,  there  must  occur,  as  the 

author  has  already  suggested,  an  unknown  series  of  chemical  and  physical   reactions,  and 

Czapek's  studies  seem  to  deal  with  some  of  these. — Ed. 


298 


PHYSIOLOGY   OF    GROWTH   AND    CONFIGURATION 


The  following  experiments  show  that  gravitation  acts  only  as  a  release,  the 
conditions  that  control  the  phenomena  of  geotropic  response  residing  in  the 
plant  itself.  As  has  been  mentioned,  lateral  roots  do  not  exhibit  positive  geotro- 
pism,  but  are  diageotropic,  taking  a  position  nearly  horizontal  when  the  axis  of 
the  plant  is  vertical.     Bruck1  has  shown,  however,  that  when  the  terminal  2  mm. 

of  the  primary  root  is  cut  away,  thus 

putting  an  end  to  the  elongation  of  this 

organ,  then  the  laterals  just  above  the 

wound  become  positively  geotropic  and 

bend  vertically  downward  (Fig.  144). 

The  same  sort  of  response  is  observed 

in   stems.     In   Fig   145   is    shown  the 

upper    portion    of    a    fir-tree     (Abies 

pectinata)  from  which  the  tip  has  been 

broken  away  for  some  time.     One  of 

the  lateral  branches  is  seen  to  have 

become    negatively    geotropic   and    to 

have  bent  upward,  just  as  if  it  were 

trying  to  replace  the  lost  tip. 

Errera2  proposed  to  explain  such  phenomena  as  those  just  mentioned  by 

postulating  "internal  secretions;"  that  is,  special  hormones  that  might  regulate 

growth.     In  those  cases  where  lateral  roots  or  shoots  take  the  place  of  primary 

ones,  the  apparent  purposefulness  of  the  response  impresses  itself  upon  some 


Fig.  144. — Root  system  from  which  the 
tip  of  the  primary  root  has  been  cut  away. 
The  laterals  nearest  to  the  cut  have  become 
positively  geotropic.      {After  Bruck.) 


Fig.  145. — Upper  portion  of  tree  of  Abies  pectinata.     Removal  of  the  tip  of  the  main  stem  has 
made  one  of  the  branches  negatively  geotropic.     {After  Errera.) 

minds  so  strongly  that  it  is  not  easy  for  them  to  think  of  the  chemical  basis  of 
the  phenomena  in  question.  There  are  other  cases,  however,  where  similar 
responses  occur  without  the  complication  of  what  may  seem  like  purposeful- 

»  Bruck,  Werner,  F.  Untersuchungen  uber  den  Einfluss  von  Aussenbedingungen  auf  die  Orientierung 
der  Seitenwurzeln.     Zeitsch.  Physiol.  3:  486-518.     1904. 

2  Errera,  L.,  Conflits,  de  preseance  et  excitations  inhibitoires  chez  les  vegetaux.  Bull.  Soc.  Roy.  Bot. 
Belgique  42:  27-43.      1904-1905. 


INFLUENCE    OF   EXTERNAL    CONDITIONS    OX    GROWTH 


2Q9 


ness.  Thus,  Bassler1  showed  that,  in  plants  that  bear  no  lateral  branches,  de- 
capitation of  the  main  stem  produces,  within  twenty-four  hours,  an  upward 
bending  of  the  leaves  nearest  the  cut.  The  leaves  may  thus  move  through 
arcs  of  from  5  to  30  degrees,  and  even  more  in  some  plants.  The  reaction  is 
more  pronounced  the  nearer  the  leaves  are  to  the  wound.  The  wounding  of 
the  stem  by  a  longitudinal  incision  fails  to  produce  the  response  of  leaf  move- 
ment. Vochting  observed  a  still  more  remarkable  case  than  those  just  men- 
tioned. The  removal  of  the  inflorescence  from  a  plant  of  Brassica  rapa  var. 
oleifera  produced  such  a  marked  upward  bending  of  the  uppermost  leaf  that  the 
latter  became  quite  vertical.2 

Plants  can  withstand  a  very  rapid  rotation  upon  the  centrifuge,  so  that  aleu- 
rone  grains,  starch  grains  and  nuclei  may  be  displaced  in  the  cells;  nucleoli  may 


Fig.  146. — Mycelium  of  Mucor  racemosus, 
grown  in  sugar  solution  (.4),  and  in  peptone  solu- 
tion (B).     (After  Klebs.) 


Fig.  147. — Diagrammatic  representa- 
tions of  various  forms  of  Bacillus  sub- 
tilis;  for  description  see  text,  preceding 
page.      (After  H   Buchner.) 


be  thrown  out  of  the  nuclei  and  raphides  may  be  made  to  penetrate  through 
the  cell  walls.3 

§7.  Influence  of  Nutrition  on  Growth  and  Configuration. — If  ordinary  green 
plants  are  grown  in  mineral  nutrient  solutions,  the  nature  and  concentration 
of  the  solution  determine  not  only  the  rate  of  growth,  but  also  the  configuration 
and  the  internal  anatomy  of  the  plant.  This  relation  of  developmental  phe- 
nomena to  the  conditions  of  nutrition  is  still  more  clearly  evident  in  the  case  of 
lower  plant  forms  that  are  nourished  by  absorbed  organic  substances.  Mucor 
racemostiSjiov  example,  produces  thick  hyphse  with  blunt  branches  in  sugar  solu- 

1  Bassler,  Friedrich,  Ueber  den  Einfluss  des  Dekapitierens  auf  die  Richtung  der  Blatter  an  orthotropen 
Sprossen.     Bot.  Zeitg.  67':  67-91.     1909. 

-  Vochting,  Hermann,  Untersuchungen  zur  experimentellen  Anatomie  und  Pathologie  des  Pflanzen- 
korpers.     Tubingen,  1908.     See  Taf.  18,  Fig.  2;  Taf.  19,  Fig.  9. 

3  Andrews,  Frank  Marion,  Die  Wirkung  der  Centrifugalkraft  auf  Pnanzen.  Jahrb.  wiss.  Bot.  28:1-40. 
1903. 


3°° 


PHYSIOLOGY   OF   GROWTH   AND   CONFIGURATION 


tion  (Fig.  146,  A),  but  forms  thin  hyphse  with  pointed  branches  in  peptone 
solution  (Fig.  146,  B).1 

The  hay  bacillus  (Bacillus  subtilis)  shows  pronounced  polymorphism,  ac- 
cording to  the  medium  in  which  it  grows.2  In  a  slightly  alkaline,  5-per  cent, 
solution  of  beef-extract  the  cells  are  rod-shaped,  6-10  /j,  long  and  0.5  n  in  diam- 
eter (Fig.  147,  1,  a).  In  neutral,  5-per  cent,  sugar  solution,  containing  also  0.1 
per  cent,  of  beef-extract,  the  cells  are  shorter  and  thicker,  4-6  /x  long  and  0.8  /x 
in  diameter  (Fig.  147,  2,  a).  Very  large  cells  are  produced  in  hay  infusion,  12  jx 
long  and  1.0  /jl  in  diameter  (Fig.  147,  3,  a).  In  all  of  these  media  cell  division 
proceeds  very  rapidly,  but  the  newly-formed  cross-walls  are  so  thin  and  so 

little  refractive  toward  light  that  they  cannot 
be  seen  at  all  excepting  in  stained  preparations. 
When  the  rods  above  described  are  stained 
with  iodine,  each  one  is  seen  to  be  composed  of 
a  chain  of  much  shorter  cells  (Fig.  147,  1,  b;  2, 
b;3,b).* 

§8.  Influence  of  Wounding,  Traction  and 
Pressure  on  Growth  and  Configuration. — 
Wounding  of  all  sorts  exerts  a  pronounced  in- 
fluence upon  the  rate  of  growth  of  plant 
organs;  a  wound  may  simply  retard  growth  or 
may  cause  it  to  cease  altogether.  Wounding 
is  frequently  followed,  also,  by  various  kinds 
of  bendings  in  growing  organs.  Especially 
noteworthy  is  the  Darwinian  response  of  roots, 
so  called  by  Wiesner,  in  honor  of  Charles 
Darwin,4  who  first  described  this  reaction.  If 
a  root-tip  is  laterally  wounded  (as  by  cutting, 
burning,  etc.),  the  root  bends,  after  a  time,  in 
the  direction  toward  the  uninjured  side. 
Frequently  this  bending  is  so  pronounced  that 
the  root-tip  is  carried  upward  and  then 
downward  again,  thus  forming  a  loop  in  the  growing  region.  This  response 
has  sometimes  been  regarded  as  purposeful,  since  its  effect  is  to  remove 
the  root-tip  from  a  dangerous  neighborhood.  Wiesner5  has  shown,  in  later 
studies,  that  the  Darwinian  response  is  really  a  double  one,  being  composed  of 
two  consecutive  bendings  in  opposite  directions.  From  twenty-five  to  forty- 
five  minutes  after  the  occurrence  of  the  wounding  a  very  slight  bending  takes 
place  in  the  upper  portion  of  the  region  of  growth,  the  direction  of  this  bending 
being  such  as  to  move  the  root-tip  toward  the  position  occupied,  at  the  time  of 


Fig.  148. — Lupine  seedling  with 
bent  primary  root,  showing  the 
formation  of  laterals  exclusively  on 
the  convex  side  of  each  bend. 


1  Klebs,  Georg,  Die  Bedingungen  der  Fortpflanzung  bei  einigen  Algen  und  Pilzen.     Jena,  1896. 
2Buchner,  Hans,  Beitrage  zur  Morphologie  der  Spaltpilze.     Nageli's  Untersuchungen  fiber  niederen. 
Pilze  aus  dem  Pflanzen.     Miinchen  and  Leipzig,  1882.     P.  205-224. 

3  Also,  compare  the  experiments  of  Ritter,  1907.     [See  note  1,  p.  270. | 
1  [Darwin  and  Darwin,  1880.     [See  note  1,  p.  314.] 
»  Wiesner,  1884.     [See  note  3,  p.  292.] 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH 


3OI 


wounding,  by  the  object  that  caused  the  wound.  This  first  response  is  so 
slight  that  it  is  to  be  demonstrated  only  by  very  precise  observation.  From 
forty-five  to  one  hundred  thirty-five  minutes  after  the  occurrence  of  the  wound- 
ing, the  second  response  begins,  a  bending  in  the  lower  portion  of  the  growing 
region.  This  second  bending  of  the  root  is  in  the  direction  opposite  to  that  of 
the  first,  thus  moving  the  root-tip  as  if  to  withdraw  it  from  the  wounding 
object.  The  second  bending  is  more  pronounced  than  the  first  and  is  of  course 
the  one  studied  by  Darwin.  The  detailed  mechanics  of  these  bendings  is  still 
not  understood."1 


Fig.   149. — Witches'  broom  on  leaf  of  Pteris  quadriaurila,  caused  by  the  fungus  Taphrina 

laurentia.     {After  Goebel.) 

Under  usual  conditions  the  laterals  are  distributed  evenly  over  the  surface 
of  the  primary  root,  but  when  bends  occur  in  the  primary  roots  the  secondary 
ones  develop  in  each  bent  region  only  on  the  convex  side  (Fig.  148). l 

Parasitic  fungi  often  cause  striking  changes  in  plant  form  and  structure. 
Sempervivum  hirtum  normally  bears  obovate  leaves,  about  twice  as  long  as 
broad.  When  infected  with  the  fungus  Endophyllum  sempervivi,  however,  this 
plant  produces  leaves  that  are  as  much  as  seven  times  as  long  as  broad.  On 
various  trees  and  shrubs  frequently  occur  peculiar  structures  known  as  "witches' 

1  Noll,  F.,  Ueber  den  bestimmenden  Einfluss  von  Wurzelkrummungen  auf  Entstehung  und  Anordnung 
der  Seitenwurzeln.     Landw.  Jahrb.  20:  361-426.     1900. 

m  In  connection  with  these  traumatropic  responses  (or  wound  reactions),  see:  Spalding, 
VolneyM.,  The  traumatic  curvature  of  roots.     Ann.  bot.  8:  423-451.     1894. — Ed. 


302 


PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 


brooms,"  strikingly  modified  branch  systems,  which  are  caused  by  parasitic 
fungi.     A  very  interesting  witches'  broom  is  produced  by  the  fungus  Taphrina 

laurentia  upon  the  fern  Pieris  quadriaurita,  as 
is  shown  in  Fig.  149.  These  curious  outgrowths 
are  always  formed  on  the  upper  side  of  the  leaf, 
and  they  grow  upward  in  such  manner  as  to 
suggest  that  another  leafy  plant  has  established 
•itself  upon  the  fern.  They  resemble  similar 
lateral  outgrowths  found  on  the  leaves  of  fossil 
ferns. 

From  the  point  of  view  of  plant  phylogeny,n 
it  is  sometimes  possible  to  throw  light  on  genetic 
relationships  by  the  study  of  pathological  phe- 
nomena that  may  include  the  formation  of  atavis- 
tic structures.  These  latter  may  be  apparently 
quite  new  for  the  plant  in  question ,  but  may  be  ac- 
tually like  structures  that  were  usual  in  its  remote 
ancestors.1  Thus,  the  compound  flower-heads 
of  Crepis  biennis,  when  infected  with  the  mite 
Eriophyes,  are  very  different  from  the  uninfected 
heads,  and  the  modification  appears  to  be  an 
atavistic  one,  reverting  to  an  ancestral  type 
(see  Fig.  150).  Also,  the  dioecious  plant  Meland- 
ryum  album  bears  perfect  ("bisexual")  flowers 
when  infected  with  the  parasitic  fungus  Ustilago 
anther  arum  (see  Fig.  151). 
As  has  been  stated  (page  251),  some  tissues  in  ordinary  plants  are  subjected 
to  traction,  while  others  are  subjected  to  pressure.  An  artificial  pull  may  be 
applied  to  a  plant,  to  determine  the  effect  of  traction  upon  growth.     Hegler's2 


Fig.  150. — Flower-heads 
Crepis  biennis;  two  unmodified, 
and  two  modified  by  the  presence 
of  the  mite  Eriophyes. 


Fig.  151. — Flowers  of  Melandryum  album,  in  vertical  section.  The  normal  staminate  and 
pistillate  flowers  are  shown  at  left  and  right,  respectively,  and  the  middle  diagram  represents  a 
perfect  flower  (with  both  stamens  and  pistils),  this  modification  being  produced  by  the  pres- 
ence of  the  fungus  Ustilago  antherarum. 

1  Potonie,  H.,  Grundlinien  der  Pflanzen-Morphologie  im  Licht  der  Paleontologie.     Jena,  1912. 

-  Hegler,  Robert,  Ueber  den  Einfluss  des  mechanischen  Zugs  auf  das  Wachsthum  der  Pflanze.     Cohn's 
Beitrage  zur  Biol.  d.  Pflanzen.  6:  383-432.     1893.     [Newcombe,  Frederick  C,  The  regulatory  formation  of 
mechanical  tissue.     Bot.  gaz.  20:  441-448.     1895-     Pieters,  Adrian  J.,  The  influence  of  fruit-bearing  on 
the  development  of  mechanical  tissue  in  some  fruit-trees.     Ann.  bot.  10:  511-529.      1896.] 
"  This  paragraph  appears  for  the  first  time  in  the  7th  Russian  Edition. — Ed. 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH 


3°3 


experiments  may  be  mentioned  as  examples  of  this  sort  of  study.  A  thread  was 
attached  to  the  tip  of  the  shoot  to  be  experimented  upon,  was  passed  over  a 
pulley  above,  and  bore  a  weight  on  its  free  end,  the  downward  pull  of  the  latter 
being  transmitted  so  as  to  produce  an  upward  pull  upon  the  end  of  the  shoot. 
The  following  table  presents  the  results  of  some  of  Hegler's  measurements  of 
the  daily  rates  of  elongation  of  various  plants  with  and  without  traction  and 
with  different  amounts  of  traction. 


Amount 

OF 

Traction 
Applied 

1ST 

Day 

2D 

Day 

3D 

Day 

4TH 

Day 

Plant 

Rate 
of 
Elonga- 
tion 

Alter- 
ation in 

Rate 
Due  to 
Traction 

Rate  of 
Elonga- 
tion 

Alter- 
ation in 
Rate, 
Due  to 
Traction 

Rate  of 
Elonga- 
tion 

Alter- 
ation in 
Rate, 

Due  to  1 
Traction 

Rate  of 
Elonga- 
tion 

Alter- 
ation in 

Rate, 

Due  to 

Traction 

Sunflower 
seedling 

Hemp  seed- 
ling 

Dahlia 
shoot 

grams 

00 

SO 

00 
20 

00 

50 

100 

mm. 

IS- 2 

8.2 

10.2 

4.0 

21  .1 

16.2 

per  cent. 

mm. 
10.7 
11 .2 

7-9 
3-9 

IS- 5 
17. 1 

per  cent. 

mm. 
6.4 
6.9 

S.6 

6.1 

9-3 

per  cent. 
+  7.8 

mm. 

3-5 

4.2 

per  cent. 

-46.0 

+  4-7 

+  20.0 

—  60.7 

-50.6 

+   8.9 

1 

5-7 

—  23.2 

+  10.0 

7-9 

-ISO 

6.8 

+  193 

The  first  effect  of  applying  an  upward  pull  to  the  plant  is  seen  to  be  a  pro- 
nounced retardation  of  growth,  but  the  rate  of  elongation  afterwards  increases,  if 
the  same  traction  is  continually  applied,  so  as  to  equal  and  finally  even  to  exceed 
the  rate  of  the  control  plant  without  traction.  Frequently,  as  with  the  sun- 
flower seedlings  and  Dahlia  shoots  of  the  above  table,  the  period  of  growth 
retardation  lasts  only  about  one  day,  but  in  some  cases,  as  with  the  hemp  seed- 
lings, it  lasts  longer.  If  the  traction  is  increased  after  the  growth  rate  begins  to 
surpass  that  of  the  control,  a  second  period  of  retardation  ensues,  as  is  seen  in  the 
case  of  the  Dahlia  shoots,where  the  weight  was  increased  at  the  beginning  of  the 
third  day,  from  50  g.  to  100  g. 

Traction  is  effective  to  modify  the  anatomical  structure  of  plants  as  well 
as  to  produce  alterations  in  the  rate  of  enlargement. 

Our  knowledge  of  the  effect  of  pressure  upon  plant  growth  has  been  much 
advanced  by  the  work  of  Pfeffer,1  who  embedded  growing  plant  parts  in  plaster 
of  Paris  or  gelatine,  and  studied  the  pressures  developed  by  growth,  and  their 
effects  upon  the  tissues.  According  to  the  problem  in  hand,  either  the  entire 
plant  or  just  the  growing  region  was  embedded.  Plaster  of  Paris  proved  very 
satisfactory  in  these  experiments,  since  it  furnishes  a  rigid  material  when  it 
hardens  and  at  the  same  time  allows  free  access  of  both  air  and  water  to  the 


!  Pfeffer,  W.,  Druck-  und  Arbeitsleistung  durch  wachsende  Pflanzen.     Leipzig,  1893. 


3°4 


PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 


embedded  organ.  The  pressures  developed  by  growing  plant  tissues  are  con- 
siderable; the  primary  root  of  a  bean  seedling  must  be  enclosed  in  a  plaster 
cylinder  from  i.o  to  1.5  cm.  in  diameter,  if  the  bursting  of  the  cast  is  to  be 
avoided. 

With  the  retardation  of  enlargement  that  occurs  in  organs  confined  in  plaster 
casts,  there  occurs  an  acceleration  in  the  development  of  the  internal  tissues  and 
structural  elements.  In  a  bean  root  that  has  been  thus  embedded  for  from  fif- 
teen to  twenty-seven  days,  fully  developed  spiral  and  pitted  tracheae  are  found 
at  a  distance  above  the  root  tip  of  only  1.6  mm.,  while  in  a  similar  root  growing 
normally  these  vessels  do  not  extend  farther  than  to  within  from  25  to  35  mm.  of 
the  tip.  In  general,  a  transverse  section  from  near  the  tip  of  such  a  confined 
root  has  the  same  appearance  as  a  similar  section  taken  from  30  to  50  mm. 
above  the  tip  of  a  normal  root. 

When  enlargement  is  not  completely  checked  but  is  merely  retarded,  then 
the  region  of  elongation  is  found  to  be  shorter  than  in  normally  growing  roots,  in 

proportion  to  the  growth-retardation  to 
which  the  root  has  been  subjected.  The 
normal  bean  root  has  a  region  of  elonga- 
tion about  10  mm.  long,  while  this  region 
may  frequently  be  only  5  or  6  mm.,  or  even 
no  more  than  3  mm.,  long  in  roots  in  which 
growth  has  been  artificially  retarded  by 
pressure. 

The  experiments  just  described  show 
that  growing  plant  organs  may  develop  rel- 
atively very  great  pressures  as  they  react 
against  obstacles  to  their  growth.  Pfeffer 
carried  out  a  series  of  experiments  to  de- 
termine the  magnitudes  of  the  forces  thus 
brought  into  play.     Cubes  of  plastic  clay 

■===  were  prepared,  with  small,  shallow  open- 

Fig.     152. — Pfeffer's     apparatus     for   .  ,  .  ,     ,,  r 

measuring  the  downward  pressures  de-  inSs>  into  whlch  the  ^PS  ©f  growing  roots 
veioped  by  growing  roots.    (After  Pfeffer .)  were    placed.     The    roots    continued    to 

elongate,  in  spite  of  the  resistance  offered 

by  the  clay,  and  penetrated  into  the  cubes.     Then  iron  replicas  of  the  roots 

were  forced  into  the  same  cubes  into  which  the  roots  had  penetrated,  and  the 

amount  of  pressure  thus  required  was  determined.     From  many  tests  Pfeffer 

concluded  that  this  pressure  was  as  great  as  from  100  to  140  g.  for  the  Windsor 

bean.     More  precise  measurements  were  made  with  a  spring-dynamometer 

(Fig.  152).     To  keep  the  root  from  bending  as  the  pressure  developed,  its  upper 

portion  was  embedded  in  a  fixed  plaster  of  Paris  block  (Fig.  152,  c).     The  tip 

was  set  in  a  movable  plaster  block  (d)  which  was  pressed  downward  as  growth 

of  the  root  occurred,  thus  transmitting  the  pressure  of  the  growing  organ  to  the 

spring  (I)  of  the  dynamometer.     The  following  table  presents  the  results  of  a 

number  of  experiments  of  this  kind.     In  each  case  are  given:  the  duration  of  the 


INFLUENCE    OF    EXTERNAL    CONDITIONS    ON    GROWTH 


305 


experiment,  the  diameter  and  cross-sectional  area  of  the  root,  the  total  pres- 
sure developed,  and  the  pressure  per  square  millimeter  of  cross-sectional  area, 
the  last  both  in  terms  of  grams  and  in  atmospheres.  The  total  pressure  divided 
by  the  cross-sectional  area  of  the  root  is  of  course  the  pressure  per  square 
millimeter.  The  last  value  is  then  divided  by  10.33  (tne  weight,  in  grams,  of 
a  mercury  column  760  mm.  high  and  with  a  cross-section  of  1  sq.  mm.),  to  give 
the  pressure  in  atmospheres. 


Experiment 
No. 


Duration 

of 
Experiment 


Root 

Diameter 


Cross- 
sectional 
Area  of 
Root 


Total 

Pressure 
Developed 


Pressure  per 
sq.  mm. 


hours 

I 

70 

2 

72 

3 

36 

4 

192 

5 

120 

6 

94 

7 

94 

8 

58 

9 

58 

mm. 

sq.  mm. 

grams 

grams 

atm. 

2.1 

3  4° 

257-5 

72.8 

7.04 

2  .2 

3-7° 

294-3 

79-5 

7.70 

2  .0 

3.20 

352-7 

no. 2 

10.67 

1.8 

2  .60 

260.6 

100.  2 

9.70 

2.0 

3.10 

272  .0 

87.7 

8.49 

1 . 2 

1   13 

226.0 

200.0 

19.36 

1.6 

2.01 

226.0 

107.9 

10.44 

2.4 

3  46 

250.0 

72  .2 

6.98 

3° 

4-7i 

250.0 

53- 1 

5-i6 

From  these  data  it  appears  that  the  root  of  the  Windsor  bean  (Viciafaba) 
may  develop  a  downward  pressure  of  from  226  to  352  g.,  or  that  it  may  exert  a 
pressure  of  from  5  to  19  atmospheres. 


Summary 

1.  Influence  of  Temperature  on  Growth  and  Configuration. — Other  conditions 
being  suitable  for  growth,  each  plant  form  grows  most  rapidly  with  a  certain  tempera- 
ture (called  its  optimum  temperature  for  growth).  With  lower  or  higher  temperatures 
growth  is  less  rapid,  until  the  minimum  or  maximum  temperature  is  reached,  beyond 
which  this  process  fails  to  occur  at  all.  The  minima,  optima,  and  maxima  differ  for 
different  plants.  Considering  plants  in  general,  the  minimum  temperature  for  growth 
may  be  as  low  as  o°C,  or  even  a  little  lower,  and  the  maximum  may  be  far  above  5o°C. 
(algae  of  thermal  springs) .  The  optimum  temperature  for  the  growth  of  ordinary  plants 
generally  lies  between  200  and  35°C.  When  plants  are  in  an  inactive  condition 
(as  in  the  case  of  dry  seeds  or  spores),  they  can  retain  vitality  through  prolonged  expo- 
sures to  temperatures  that  are  far  above  the  maximum,  or  far  below  the  minimum,  for 
growth. 

Within  the  limits  of  the  range  between  the  minimum  and  the  maximum  for  growth, 
the  kind  of  growth  is  greatly  influenced  by  temperature,  which  is  thus  markedly 
effective  in  determining  the  configuration  of  the  plant  body.  Temperature  fluctua- 
tion is  especially  influential.  One  of  the  acetic  acid  bacteria  forms  short  rods  when 
grown  with  a  temperature  of  34°C,  while  filaments  are  produced  in  cultures  grown  with 
20 


306  PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

a  temperature  of  4-o°C.  Alpine  forms  of  ordinary  plants  that  grow  also  at  lower 
altitudes  are  markedly  different  from  the  lowland  forms,  and  this  is  partly  due  to  the 
different  temperature  conditions  of  the  two  environments.  The  date  of  flowering  is 
generally  much  later  for  plants  grown  in  a  cold  region  than  it  is  for  other  individuals  of 
the  same  form  grown  in  a  warm  region,  and  this  difference  is  related  to  differences 
between  the  two  regions  with  respect  to  the  temperatures  of  the  preceding  autumn 
and  winter,  as  well  as  of  the  spring.  Molisch  introduced  the  warm-bath  method  for 
breaking  the  dormant  period  and  forcing  the  early  formation  of  flowers,  in  shrubs, 
etc.  Shoots  bearing  dormant  winter  buds  are  submerged  in  warm  water  for  half  a 
day,  after  which  treatment  the  buds  immediately  proceed  to  develop  flowers  under 
greenhouse  conditions,  while  untreated  shoots  do  not  respond  to  the  same  conditions 
until  the  season  is  much  farther  advanced. 

2.  Influence  of  the  Oxygen  Content  of  the  Surroundings  on  Growth  and  Confi- 
guration.— It  appears  that  ordinary  plants  may  be  influenced,  as  to  their  rates  of 
growth,  by  alterations  in  the  oxygen  content  of  the  surrounding  air.  For  microorgan- 
isms the  oxygen  supply  is  of  the  utmost  importance.  Aerobes  (such  as  acetic  acid 
bacteria)  require  oxygen  for  their  development,  while  anaerobes  can  develop  without 
it.  Obligate  anaerobes  (such  as  butyric  acid  bacteria)  are  poisoned  by  oxygen,  but 
facultative  anaerobes  (such  as  yeasts)  thrive  either  with  or  without  a  supply  of  this 
element.  Some  aerobes  require  less  oxygen  than  others.  The  mould  Mucor  develops 
the  usual  hyphal  weft  and  sporangiophores  when  growing  on  the  surface  of  a  suitable 
medium,  with  plentiful  air  supply,  but  its  growth  is  similar  to  that  of  yeasts  when  it 
grows  at  the  bottom  of  a  mass  of  liquid  medium;  this  difference  in  configuration  may  be 
due  to  the  difference  in  oxygen  supply. 

3.  Influence  of  Other  Gases  on  Growth  and  Configuration. — The  carbon  dioxide 
supply  influences  the  growth  of  ordinary  plants;  it  may  be  either  too  low  or  too  high  for 
healthy  development.  Some  seedlings  are  very  sensitive  to  small  traces  of  ethylene 
and  of  other  toxic  gases  in  the  air  about  them,  and  plants  are  generally  injured  by 
considerable  amounts  of  illuminating  gas  in  the  soil  surrounding  their  roots.  If  the 
supply  is  very  low,  some  poisonous  gases  accelerate  the  growth  of  ordinary  plants. 
Johannsen  introduced  the  ether  treatment  for  breaking  the  dormant  period  and 
forcing  the  early  formation  of  flowers,  in  shrubs,  etc.  Shoots  bearing  dormant 
winter  buds  are  enclosed  for  a  number  of  hours  in  a  chamber  containing  ether  vapor, 
after  which  treatment  the  buds  immediately  proceed  to  develop  leaves  and  flowers 
under  greenhouse  conditions,  while  untreated  shoots  do  not  respond  to  the  same  condi- 
tions until  the  season  is  much  farther  advanced. 

4.  Influence  of  Moisture  on  Growth  and  Configuration. — The  rate  of  water  supply 
to  plant  or  organ  must  generally  be  somewhat  greater  than  the  rate  of  water  loss, 
since  growth  is  usually  accompanied  by  the  accumulation  of  water  in  the  enlarging 
tissues.  As  already  pointed  out,  the  water  supply  for  ordinary  plants  is  from  the  soil, 
while  transpiration  represents  the  main  form  of  water  loss.  Consequently,  the  mois- 
ture condition  of  a  plant  may  be  altered  (1)  by  a  change  in  the  power  of  the  soil  to 
supply  water  to  the  roots,  (2)  by  a  change  in  the  power  of  the  roots  to  absorb  water 
that  is  in  contact  with  their  external  surfaces,  (3)  by  a  change  in  the  power  of  the  air 
(including  the  sunlight  effect)  to  remove  water  vapor  from  the  foliage,  etc.,  (4)  by  a 
change  in  the  ability  of  the  aerially  exposed  surfaces  to  hinder  the  evaporation  of  water 
{i.  e.,  to  retard  transpiration),  or  (5)  by  any  two  or  more  of  these  changes  operating  at 
the  same  time.  If  the  environmental  conditions  are  such  that  the  mean  value  of  the 
ratio  of  intake  to  outgo  is  less  than  unity,  then  the  plant  is  unable  to  develop  under 


INFLUENCE    OF    EXTERNAL   CONDITIONS    ON    GROWTH  307 

those  conditions.  Although  the  internal  conditions  that  influence  the  value  of  this 
moisture  ratio  (2  and  4,  above)  are  capable  of  great  internal  adjustment,  yet  this  adjust- 
ment is  limited  for  each  plant  form;  consequently  some  forms  require  a  moist  climate, 
others  a  dry  one,  etc.  Plants  that  thrive  in  dry  periods  are  characterized  by  structures 
that  facilitate  water  absorption  and  hinder  transpiration.  Within  the  limits  of  its 
capacity  for  internal  adjustment,  the  same  plant  form  may  develop  under  widely 
different  moisture  conditions.  With  relatively  humid  conditions,  the  internodes  are 
generally  long  and  the  leaf  blades  are  extensive,  the  cuticle  is  thin,  and  there  is  not 
much  woody  tissue,  etc.  With  relatively  arid  conditions,  the  internodes  are  generally 
shorter  and  the  leaves  are  smaller,  the  cuticle  is  thicker,  and  there  is  a  greater  develop- 
ment of  woody  tissue.  Arid  conditions  often  promote  the  formation  of  thorns  and 
spines — also  the  development  of  succulence  (as  is  usual  for  cacti).  In  some  plants  the 
morphological  characters  are  so  much  influenced  by  the  moisture  conditions  of  the 
surroundings  that  two  individuals,  one  grown  in  an  arid  and  the  other  in  a  humid 
climate,  often  appear  to  be  quite  different  species.  Some  plants  that  develop  partly 
under  water  and  then  extend  into  the  air  produce  very  different  structures  in  the  two 
environments,  and  this  difference  seems  to  be  largely  related  to  moisture  conditions. 
As  to  the  manner  in  which  external  moisture  conditions  influence  plant  growth  and 
development,  a  few  considerations  may  be  mentioned.  Growth  by  enlargment  can 
not  occur  in  cells  that  are  not  turgid,  and  the  rate  and  kind  of  growth  that  occur  depend 
upon  the  degree  of  turgidity  present.  The  turgidity  of  every  cell  is  inversely  propor- 
tional (other  conditions  being  constant)  to  the  resistance  offered  to  water  absorption  or 
to  the  forces  tending  to  remove  water  from  the  cell.  The  relation  of  the  rate  of  water 
supply  to  that  of  water  loss  determines  whether  turgidity  shall  increase,  decrease,  or 
be  maintained. 

If  the  environmental  moisture  conditions  remain  constant,  on  the  other  hand,  the 
turgidity  (and  growth)  of  any  cell  may  be  altered  by  internal  changes,  such  as  alter- 
ations in  the  permeability  of  wall  or  protoplasm  to  water,  or  alterations  in  the  osmotic 
and  imbibitional  attraction  for  water,  exerted  by  the  cell  contents.  Such  internal 
changes  are  promoted  by  alterations  in  the  amounts  of  various  dissolved  substances 
within  the  cell,  such  as  acids,  salts,  etc. 

The  transpiration  rate  largely  determines  the  rate  of  entrance  and  transport  of 
dissolved  materials  from  the  soil  (when  the  soil  moisture  supply  is  adequate  and  the 
cell  membranes  are  permeable  to  these  solutions) ;  the  chemical  content  of  any  tissue 
is  therefore  partially  controlled  by  the  water  conditions  of  the  surroundings,  and  the 
chemical  content  of  a  cell  markedly  influences  its  growth.  The  kinds  and  amounts 
of  substances  dissolved  in  the  soil  water  exert  potent  influences  on  the  growth  of 
ordinary  plants. 

The  roots  of  many  plants  are  hydrotropic.  When  exposed  to  unlike  moisture 
conditions  on  opposite  sides,  the  root  elongates  more  rapidly  on  the  drier  side,  thus 
producing  a  bending  of  the  root  away  from  the  drier  environment.  This  response  to 
one-sided  moisture  conditions  is  due  to  hydrotropism. 

5.  Influence  of  Light  on  Growth  and  Configuration. — Light  conditions  are  very 
important  in  determining  not  only  the  rate  but  also  the  kind  and  extent  of  growth  in 
ordinary  plants.  Stems  generally  elongate  less  rapidly  by  day  than  by  night,  and  this 
seems  to  indicate  that  ordinary  daylight  retards  stem  elongation.  Plant  stems  in 
continuous  darkness  elongate  more  rapidly  and  produce  longer  internodes  than  do 
those  in  light  or  with  the  natural  day-night  fluctuation,  but  leaves  generally  remain 
very  small  in  maintained  darkness  and  expand  to  their  regular  size  only  when  light  is 


308  PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

present  at  least  part  of  the  time,  as  in  nature.  Stem  elongation  appears  to  be  differ- 
ently retarded  by  different  ranges  of  light  wave-lengths;  for  wave-lengths  about  like 
those  of  sodium  light  (yellow)  the  retardation  is  least,  notwithstanding  the  fact  that 
the  greatest  intensity  of  sunlight  generaUy  occurs  in  this  region  of  the  spectrum. 
Retardation  is  greater  with  wave-lengths  corresponding  to  red  and  green  light,  and  it 
is  greatest  with  wave-lengths  corresponding  to  violet  light. 

Prolonged  absence  of  light  induces  etiolation  in  ordinary  plants.  Etiolated  plants 
have  yellow  leaves.  If  they  produce  stems,  these  are  white  or  yellowish  and  have  un- 
usually long,  slender  internodes,  with  only  rudimentary  leaves.  The  potato  sprout 
grown  in  darkness  is  an  example  of  this  kind  of  etiolation.  Such  plants  as  Bellis  and 
Sempervivum,  which  form  rosettes  under  ordinary  light  conditions,  produce  long 
stems  in  darkness,  with  spirally  arranged,  rudimentary  leaves.  The  youngest  inter- 
nodes of  twining  plants,  when  subjected  to  natural  light  fluctuation,  are  usually  in  a 
condition  that  closely  resembles  etiolation;  they  are  therefore  not  greatly  different 
when  grown  in  maintained  darkness.  Under  ordinary  conditions  these  shoots  subse- 
quently become  green,  and  the  leaves  develop  and  become  green  in  the  usual  way; 
they  are  thus  "normally  etiolated"  only  when  young. 

The  etiolation  of  ordinary  plants  is  prevented  by  an  adequate  supply  of  light  that 
has  wave-lengths  corresponding  to  blue  and  violet  light.  But  etiolation  generally 
occurs  if  the  plants  are  grown  in  red-yellow-orange  light — that  is,  in  sunlight  from  which 
the  shorter  wave-lengths  have  been  removed  or  very  much  weakened.  This  relation 
of  etiolation  to  light  wave-lengths  is  not  directly  connected  with  carbohydrate 
photosynthesis.  In  some  cases,  however,  the  behavior  of  etiolated  leaves  seems  to  be 
related  to  the  supply  of  soluble  carbohydrates. 

It  appears  that  etiolation  is  brought  about  through  the  operation  of  several  condi- 
tions, among  which  are  to  be  mentioned:  low  transpiration  rates  and  resultant  modi- 
fications in  the  absorption  and  distribution  of  water  and  salts,  low  carbohydrate 
supply  (especially  to  leaves),  and  absence  of  the  direct  effects  of  light,  as  such.  It 
seems  certain  that  many  essential  photochemical  processes  occur  in  illuminated  plants, 
besides  the  one  by  which  carbohydrates  are  formed,  which  alone  has  been  much  studied. 

Plants  subjected  to  the  natural  alternation  of  day  and  night  develop  very  differ- 
ently according  to  the  intensity  of  the  light  they  receive  in  the  daytime,  as  well  as 
according  to  the  relative  lengths  of  the  day  and  night  periods.  Leaves  that  receive 
only  diffuse  light  during  the  daytime  are  generally  thinner,  with  less  palisade  tissue, 
than  leaves  of  the  same  plant  form  receiving  direct  sunlight  during  their  periods  of 
illumination.  Shade-grown  plants  exhibit  other  characteristic  differences  from  sun- 
grown  plants,  and  shade-grown  leaves  or  branches  are  in  many  cases  markedly  differ- 
ent from  sun-grown  leaves  or  branches  of  the  same  individual.  •  Plant  forms  differ 
with  respect  to  their  light  requirements  and  with  respect  to  the  intensity  of  light 
they  are  able  to  bear;  they  may  be  classified  roughly  into  shade  plants  and  non-shade 
plants. 

Lower  forms  of  plants,  such  as  fungi  and  bacteria,  are  influenced  by  light.  Pilo- 
bolus  grows  healthily  only  when  exposed  to  diffuse  light  during  the  daytime.  The 
colorless  bacteria  (e.  g.,  the  typhoid  bacillus)  are  killed  by  a  brief  exposure  to  direct 
sunlight.  Sunlight  (especially  the  ultra-violet  rays)  is  a  potent  influence  in  the  puri- 
fication of  the  water  of  rivers  polluted  by  sewage. 

Ability  to  respond  to  one-sided  illumination,  the  response  being  more  rapid  enlarge- 
ment on  one  side  of  the  responding  organ  than  on  the  other,  is  called  pholotropism,  or 
heliolropism.     With  positive  pholotropism  the  organ  bends  toward  the  more  strongly 


INFLUENCE    OF    EXTERNAL    CONDITIONS    OX    GROWTH  309 

illuminated  side;  with  negative  phototropism  it  bends  toward  the  more  weakly  illumin- 
ated side.  Positive  phototropism  is  common  in  stems  (including  flower  scapes)  and 
frequent  in  leaves.  It  is  pronounced  in  the  sporangiophores  of  the  fungus  Pilobolus. 
Negative  phototropism  occurs  in  many  tendrils  and  in  some  roots,  especially  aerial 
ones.  In  many  leaves  the  phototropic  response  is  such  as  to  bend  or  twist  the  petiole 
so  as  to  place  the  upper  surface  of  the  blade  perpendicular  to  the  axis  of  strongest 
illumination.  Leaf  mosaics  arise  from  phototropic  bendings.  Some  leaves  (of  "com- 
pass" plants)  respond  to  strong,  direct  sunlight  by  bendings  and  twistings  of  the 
petioles  or  leaf  bases  in  such  manner  that  the  surface  of  the  leaf-blade  comes  to  lie 
parallel  to  the  direction  of  the  direct  solar  rays. 

Since  phototropic  bending  results  from  unequal  enlargement  on  the  two  opposite 
sides  of  the  organ,  the  response  occurs  only  in  the  region  of  enlargement,  where  the 
tissues  are  in  the  second  phase  of  growth.  The  sensitive  region,  in  which  the  one-sided 
illumination  sets  up  the  primary  protoplasmic  disturbance  that  leads  to  the  response, 
is  usually  distinct  and  separated  by  a  considerable  distance  from  the  bending  region. 

Phototropic  bending,  like  the  retardation  of  enlargement  by  light,[is  most  markedly 
promoted  by  light  of  short  wave-lengths  (violet  region  of  the  sunlight  spectrum). 
Wave  lengths  corresponding  to  yellow  light  are  without  phototropic  effect,  but  the 
longest  wave-lengths  (red  region  of  the  spectrum)  are  somewhat  effective. 

6.  Influence  of  Gravitation  on  Growth  and  Configuration. — Gravitation  influences 
the  form  of  plants  especially  through  geotropic  bendings.  Like  other  bendings  due  to 
tropisms,  these  are  produced  by  more  rapid  enlargement  on  one  side  of  the  bending 
organ.  Not  only  roots  and  stems,  but  also  leaves,  flowers,  and  floral  parts,  are  influ- 
enced in  their  positions  and  forms  by  gravitation. 

Gravitation  acts  continuously  on  all  objects,  and  the  pull  is  always  toward  the 
center  of  the  earth,  but  a  plant  organ  may  have  any  direction  as  related  to  the  axis 
and  direction  of  gravitation.  Different  organs  that  exhibit  geotropism  differ  with 
respect  to  their  equilibrium  positions — that  is,  the  positions  in  which  they  continue 
to  grow  equally  on  all  sides  in  spite  of  the  one-sided  pull  of  gravitation.  Positively 
geotropic  organs  (like  primary  roots)  bend  in  such  a  way  as  to  direct  the  tips 
toward  the  center  of  the  earth,  while  negatively  geotropic  organs  (like  the  primary  shoots 
of  many  plants)  bend  so  as  to  direct  the  tips  away  from  the  center  of  the  earth.  Primary 
branches  of  roots  and  shoots  are  generally  in  the  equilibrium  position  with  respect  to 
gravitation  when  the  tips  point  in  a  direction  forming  an  angle  with  the  axis  of  gravi- 
tation; these  are  said  to  be  apogeotropic  or  plagiolropic.  Root  branches  usually  bend 
so  as  to  direct  the  tips  outward  from  the  main  root  and  downwar d,  while  shoot  branches 
usually  bend  so  as  to  direct  the  tips  outward  from  the  main  shoot  and  upward.  The 
effect  of  gravitation  may  be  avoided  with  organs  that  are  not  in  their  equilibrium  posi- 
tions (and  bending  may  thus  be  prevented)  if  the  plant  is  slowly  rotated  upon  a  clin- 
ostat  with  horizontal  axis.  The  clinostat  may  be  rotated  rapidly,  so  as  to  act  as  a 
centrifuge,  in  which  case  the  effect  of  gravitation  is  removed  and  the  effect  of  centri- 
fugal force  is  made  manifest.  Knight's  experiment  demonstrates  that  centrifugal 
force  acts  like  gravitation  in  its  influence  on  plant  bending.  When  thus  treated, 
positively  geotropic  organs  bend  so  as  to  direct  the  tips  toward  the  circumference 
of  rotation,  with  the  centrifugal  force,  while  negatively  geotropic  organs  bend  so  as 
to  direct  the  tips  toward  the  center  of  rotation,  against  the  centrifugal  force. 

In  order  that  geotropic  bending  may  occur,  the  organ  in  question  must  exhibit 
geotropism,  its  sensitive  region  (tip  of  root  or  stem)  must  be  in  a  position  other  than 
that  of  its  geotropic  equilibrium,  this  region  must  remain  in  that  position  for  a  certain 


310  PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

time  (presentation  time),  and  the  bending  region  (situated  a  considerable  distance 
back  from  the  tip)  must  be  enlarging.  After  a  period  considerably  longer  than  the 
presentation  time  (reaction  time)  bending  occurs  in  the  bending  region.  In  clinostat 
experiments  the  primary  protoplasmic  disturbance  of  stimulation  may  be  started  by 
stationary  exposure  for  a  period  somewhat  longer  than  the  presentation  time,  and 
then  slow  rotation  may  begin  and  continue.  In  such  experiments  bending  occurs 
after  the  lapse  of  the  reaction  time;  the  period  from  the  end  of  the  presentation  time 
to  the  end  of  the  reaction  time  is  called  the  latent  period. 

The  hypothesis  has  been  advanced  that  when  the  sensitive  region  first  comes  to  be  out 
of  its  equilibrium  position  some  heavier  cell  components  (e.  g.,  starch  grains)  begin  to 
settle  through  the  somewhat  viscous  cell  contents,  finally  (at  the  end  of  the  presenta- 
tion time)  coming  to  be  on  the  physically  lower  side  of  each  cell.  This  shifting  of 
starch  grains,  etc.,  is  supposed  to  release  some  form  of  process,  which  may  be  the  first 
of  a  series  or  chain  of  chemical  and  physical  disturbances,  the  final  one  of  which  acts 
directly  on  the  cells  of  the  distant  enlarging  (bending)  region  and  produces  unequal 
enlargement  on  the  opposite  sides.  The  latent  period  is  here  supposed  to  be  the  time 
necessary  for  the  protoplasmic  disturbance  to  be  transmitted  from  the  sensitive  to  the 
bending  region.  The  differences  in  direction  between  the  bendings  produced  by  the 
same  gravitational  pull  (between  positive  and  negative  geotropic  bendings,  etc.)  must 
be  due  to  internal  differences  in  the  bending  organs  themselves. 

7.  Influence  of  Nutrition  on  Growth  and  Configuration. — The  nutrition  supply, 
both  of  organic  substances  and  of  salts,  exerts  great  influence  on  the  rate  and  kind  of 
growth.  Especially  in  lower  forms,  such  as  moulds  and  bacteria,  different  nutrient 
media  may  produce  pronounced  morphological  differences. 

8.  Influence  of  Wounding,  Traction,  and  Pressure  on  Growth  and  Configuration.— 
Wounding  of  an  enlarging  tissue  may  retard  or  check  enlargement,  and  therefore 
result  in  bending.  The  Darwinian  (traumatropic)  response  of  roots  is  a  bending 
away  from  an  object  that  wounds  the  tip,  the  bending  itself  occurring  in  the  region  of 
elongation  above  the  tip.  Some  of  the  tissue  strains  in  a  bending  primary  root  appear 
to  favor  the  production  of  branches;  the  latter  more  often  arise  on  the  convex  than  on 
the  concave  side  of  a  bend,  or  than  on  unbent  portions  of  the  primary  root.  Para- 
sitic insects  or  fungi  often  cause  striking  structural  peculiarities  in  the  host  plant  (e.  g., 
"witches'  brooms")-  Some  dioecious  plants  bear  perfect  flowers  when  infected  with 
the  right  fungus.  Traction  (as  by  thread,  pulley  and  weight)  may  greatly  modify  the 
rate  and  kind  of  growth  in  ordinary  plants.  External  pressure  that  hinders  or  checks 
enlargement  (as  when  a  growing  root  is  enclosed  in  a  rigid  plaster  cast)  has  marked 
influence  on  the  maturation  of  the  tissues. 

Pfeffer's  experiments  showed  that  the  downward  pressures  exerted  by  enlarging 
roots  may  be  very  great,  as  great  as  350  grams  in  a  root  of  Windsor  bean,  or  200  grams 
(over  iq  atmospheres)  per  square  millimeter  of  the  cross  section  of  the  root. 


CHAPTER  IV 

TWINERS  AND  OTHER  CLIMBING  PLANTS 

§i.  Twiners.1 — The  stems  of  many  plants  are  so  slender  and  so  weak 
mechanically  that  they  cannot  grow  upright  unless  they  climb  upon  supporting 
objects.  Without  such  mechanical  support  these  plants  always  creep  upon  the 
ground.  Climbing  plants  grow  up  into  the  air  by  twining  about,  or  attaching 
themselves  to,  other  plants  or  any  available  support,  and  they  are  thus  able  to 
attain  the  best  illumination. 

Twiners  have  long,  slender  stems,  the  growing  tips  of  which  twine  about 
suitable  objects  that  happen  to  be  near.  Familiar  examples  of  twiners  are 
the  hop  {Humulus  lupulus),  the  scarlet-runner  bean  {Phaseolus  multiflorus), 
various  species  of  Convolvulus  (morning  glory),  and  also  some  Polygonum 
species,  as  P.  dumetorum  and  P.  convolvulus  (bind- weed).  The  terminal  por- 
tion of  a  twining  stem  of  Humulus  lupulus  is  shown  in  Fig.  153.  In  all  twin- 
ing plants  the  growing  tip  moves  about  the  axis  of  the  older  part,  describing  a 
more  or  less  circular  path;  the  direction  of  this  movement  is  clockwise  in  some 
plants,  and  counter-clockwise  in  others  (Fig.  154).  In  most  plants  the  moving 
portion  consists  of  the  last  two  or  three  internodes.  The  time  required  for  a 
complete  revolution  varies  with  the  plant  as  well  as  with  the  environmental 
conditions.  In  one  experiment  this  time  period  was  found  to  be  one  hour 
and  seventeen  minutes  for  Scyphanthus  elegans,  one  hour  and  forty-two  min- 
utes for  Convolvulus  septum,  one  hour  and  fifty-seven  minutes  for  Phaseolus 
vulgaris,  and  nine  hours  and  forty-five  minutes  for  Lonicera  brachypoda.  The 
circular  movement  of  the  terminal  region  continues  until  some  solid  object,  such 
as  the  stem  of  another  plant,  is  encountered  and  then  the  twiner  begins  to 
wind  itself  about  the  support,  providing  this  is  of  suitable  shape  and  size. 

The  turns  of  the  resulting  spiral  are  not  closely  applied  to  the  support  at 
first,  especially  if  the  support  is  very  slender;  later,  however,  the  spiral 
elongates  and  becomes  narrower,  and  the  stem  thus  becomes  firmly  bound  about 
the  supporting  object.  A  firmer  hold  is  effected  by  the  stiff  hairs  that  are 
frequently  present  on  the  stems  of  twiners. 

Twining  plants  are  able  to  wind  about  very  slender  objects,  but  the  diameter 
of  the  support  must  not  be  too  great,  or  twining  is  prevented.  The  maximum 
diameter  of  the  support  varies  with  different  plants;  Phaseolus  multiflorus 
twines  about  a  support  from  7  to  10  cm.  in  thickness,  but  twining  fails  to  occur 
if  the  diameter  of  the  support  is  as  great  as  23  cm.  Many  tropical  twiners 
can  twine  about  thick  supports. 

1  Darwin,  Charles  R.,  Movements  and  habits  of  climbing  plants.  2nd  ed.,  revised.  London,  1875.  Bara- 
netzki,  J.,  Die  kreisformige  Nutation  und  das  Winden  der  Stengel.  Mem.  Acad.  Imp.  Sci.  St.-Peters- 
bourg  VII,  3iv///:  1-73.  1883.  Pfeffer,  W.,  Zur  Kenntnis  der  Kontaktreize.  Untersuch.  Bot.  Inst. 
Tubingen  1:  483-535.  1881-1885.  Voss,  Wilhelm,  Xeue  Versuche  iiber  das  Winden  des  Pflanzensteng- 
els.  Bot.  Zeitg.  6o7:  231-252.  1902.  [MacDougal,  D.  T.,  Practical  text-book  of  plant  physiology, 
XIV  +  352  p.      New  York.  1901.     Pringsheim,  i<ji2.      (See  note  1,  p.  253.)] 

311 


312 


PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 


If  a  twining  plant  is  placed  upon  a  clinostat  and  slowly  rotated  about  a 
horizontal  axis,  the  twining  movement  ceases  and  growth  proceeds  in  a  direc- 
tion parallel  to  the  axis  of  rotation,  while  the  younger  turns  of  the  previously- 
formed  spiral  become  straightened  out.  Such  experiments  indicate  that  a 
geotropic  response  is  necessary  for  twining. 

§2.  Non-twining  Climbers.1 — The  long  stems  of  non-twining  climbers  are 


Fig.  153.- — Twining  stem  of  Humnlus  lupulus,  in 
successive  stages  of  movement.     (After  Pfeffer.) 


B 


Fig.  154. — A.  Pharbitis,  shoot 
showing  counter-clockwise  twining. 
B.  Myrsiphyllum  asparagoides,  shoot 
showing  clockwise  twining.  (After 
Bonnier.) 


unable  to  twine,  but  they  climb  by  means  of  hairs,  thorns,  aerial  roots,  tendrils, 
etc.  Tendrils  are  the  most  frequent  of  these  special  structures.  These  are 
morphologically  different  in  different  plants;  in  some  forms  (Vitis,  Ampelopsis, 
the  Cucurbitacese)  they  correspond  to  twigs,  while  in  others  they  are  leaves; 
thus  the  upper  part  of  the  pea  leaf  is  a  tendril  while  the  pinnately  arranged  leaf- 
ets  of  the  lower  part  are  quite  like  those  of  ordinary  leaves. 

1  Darwin,  Charles,  1875.  [See  note  1,  p.  311.]  Vries,  Hugo  de,  Langenwachsthum  der  Ober-und  Un- 
terseite  sich  krummender  Ranken.  Arbeit.  Bot.  Inst.  Wtirzburg,  1:  302-316.  1874.  Schenck,  Heinrich, 
Beitrage  zur  Biologie  und  Anatomie  der  Lianen  im  besonderen  der  in  Brasilien  einheimischen  Arten.  2  v. 
Jena,  1892-1893.  [Lengerkin,  August  von,  Die  Bildung  der  Haftballen  an  den  Ranken  einiger  Arten  der 
Gattung  Ampelopsis.  Bot.  Zeitg.  43 :  337-34°.  353-361,  360-379,  385-393,  401-411.  1885.  MacDougal, 
D.  T.,  Mechanism  of  the  curvature  of  tendrils.  Ann.  bot.  10:  373-402.  1896.  Idem,  1901.  (See  note 
1,  p.  311.)     Pringsheim,  1912.      (See  note  I,  p.  253.)] 


TWINERS    AND    OTHER    CLIMBING    PLANTS 


313 


Young,  actively  growing  tendrils  nutate,  so  as  to  become  hook-shaped. 
When  the  tendril  comes  into  contact  with  a  solid  object  coiling  begins  near  the 
tip,  so  that  it  wraps  itself  about  the  support,  if  this  is  of  suitable  size  and  shape. 
This  coiling  movement  results  from  unequal  growth  on  the  two  opposite  sides, 
brought  about  as  a  response  to  the  stimulus  of  contact.  The  portion  of  the 
tendril  that  lies  between  the  point  of  attachment  and  the  base  does  not  remain 
permanently  straight  but  subsequently  also  becomes 
coiled,  in  the  form  of  a  spiral  spring,  so  that  the 
plant  is  drawn  nearer  to  the  support.  The  stem 
is  thus  not  supported  by  a  straight  and  inelastic 
suspension,  which  might  be  easily  broken,  but  it 
hangs  upon  a  coiled  spring,  which  stretches  a  little 
when  the  plant  is  moved  by  the  wind,  thus  largely 
avoiding  the  possibility  of  breaking.  The  tendril 
can  become  attached  to  a  support  only  while  still 
growing,  and  those  that  have  not  come  into  con- 
tact with  a  suitable  support  during  the  growing 
period  generally  wither  and  fall  away.  Fig.  155 
represents  a  portion  of  the  stem  of  Bryonia  dioica, 
with  a  tendril  attached  to  a  twig  of  another  plant. 
The  middle  portion  of  the  tendril  forms  the  spiral 
spring  mentioned  above. 

The  tendrils  of  Ampelopsis  behave  in  a  peculiar 
manner  when  they  happen  to  come  into  contact 
with  an  object  about  which  they  cannot  twine,  as  in 
growing  along  a  wall,  for  example.  Some  of  the 
tendrils,  which  are  appressed  against  the  wall  by  a 
negative  phototropic  response  and  which  continually 
nutate,  happen  to  reach  into  crevices  in  the  support. 
Such  a  tendril  becomes  thickened  at  the  end  within 
the  crevice,  so  that  it  cannot  be  readily  withdrawn, 
thus  supporting  the  plant.  [These  tendrils  also 
form  adhering  disks  at  their  tips,  by  which  they 
become  attached  to  nearly  smooth  surfaces, 
(Fig.  156.)] 

Investigations  of  the  anatomy  of  tendrils  show  that  these  possess  special 
arrangements  that  facilitate  the  reception  of  stimuli.  The  otherwise  thick 
external  walls  of  the  epidermis  of  pumpkin  (Cucurbita)  tendrils,  for  example,  are 
characterized  by  minute  pits  that  extend  the  cell  cavity  outward,  nearly  to  the 
outer  surface  of  the  wall,  which  is  very  thin  at  these  points  (Fig.  157,  A). 
These  pits  are  filled  with  protoplasm  which  is  continuous  with  the  protoplasm 
of  the  cell  cavity  itself,  and  these  protoplasmic  projections  frequently  contain 
small  crystals  of  calcium  oxalate,  which  have  been  thought  to  play  a  part  in 
the  propagation  of  the  contact  disturbance.  These  structures  have  been  called 
contact  papilla.     Such  papillae,  of  the  external  walls  of  the  epidermis  of  a  pump- 


Fig.    155.- 


Tendril   of   Bryonia 
dioica. 


3i4 


PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 


kin  tendril,  are  shown  in  Fig.  157,  B,  where  the  shaded  portion  represents  pro- 
toplasm. A  crystal  of  calcium  oxalate  is  shown  embedded  in  the  protoplasm 
of  each  papilla. 

§3.  Circumnutation.1 — Darwin  showed  that  all  growing  plants,  although 
they  seem  to  be  elongating  in  a  definite  direction,  are  actually  swinging  about 
in  more  or  less  circular  paths,  but  that  these  movements  are  so  slow  or  so  slight 
that  they  are  usually  quite  unnoticed,  without  the  employment  of  special 
methods  of  observation.     Darwin  thought  that  this  sort  of  movement  (which 


Fig.  156. — Tendrils  of  Ampelopsis  heterifolia.  At  the  right  a  young  tendril,  with  swollen 
tips;  at  the  left,  an  old  one  with  adhering  disks,  caused  by  contact  with  the  wall,  and  coiled 
basal  part.      (After  Pringsheim.) 


A  B 

Fig.  157. — A,  Epidermal  cells  from  tendril  of  Cucumis  sativus,  showing  protoplasm- 
filled  pits  in  outer  walls  (contact  papillae).  (After  Pfeffer.)  B,  Contact  papillee  of  the  outer 
walls  of  tendril  epidermis  of  Cucurbita  pepo  (pumpkin).      (After  Haberlandt.) 


he  called  circumnutation)  is  the  fundamental,  phylogenetically  simple  move- 
ment from  which  other  plant  movements  due  to  unequal  growth  have  evolved. 
Wiesner  has  maintained,  however,  that  this  hypothesis  is  not  tenable;  in  many 

1  Darwin,  Charles  R.,  and  Darwin,  Francis,  Power  of  movement  in  plants.     London,    1880.      Wiesner, 
1881.     [See  note  2,  p.  275.] 


TWINERS    AND    OTHER    CLIMBING    PLANTS  315 

growing  organs,  he  failed  to  find  any  circumnutation.a  Where  it  occurs  it  is 
caused  merely  by  inequalities  in  the  rate  of  elongation  on  different  sides  of  the 
axis. 

Summary 

1.  Twiners.— Climbing  plants  gain  support  by  twining  about  objects  or  by  forming 
mechanical  attachments  in  other  ways.  Twiners  have  very  slender  stems,  with  long 
internodes.  After  the  seedling  stage  of  development  is  past,  each  new  internode 
elongates  very  rapidly  at  first  and  the  leaves  of  the  youngest  two  or  three  nodes  are 
retarded  in  their  enlargement.  Also,  the  youngest  two  or  three  internodes  and  the 
retarded  leaf  buds  are  pale  in  color.  Consequently,  this  youngest  region  of  the  twining 
plant  appears  much  as  if  it  were  etiolated,  as  has  been  said,  although  grown  under 
natural  day-night  conditions  of  light.  The  rapidly  elongating,  younger  portion 
enlarges  in  such  a  way  that  the  tip  is  made  to  swing  in  a  more  or  less  circular  path  about 
the  vertical  axis,  clockwise  in  some  species  and  counter-clockwise  in  others.  The  time 
required  for  a  revolution  is,  in  general,  between  one  and  ten  hours.  If  a  suitable 
support  is  encountered  (this  must  be  nearly  vertical  and  must  not  be  of  too  great 
diameter),  the  elongating  stem  twines  about  it,  each  turn  of  the  stem  being  higher  than 
the  preceding  one.  As  elongation  is  about  to  cease,  each  internode  straightens  as 
much  as  possible,  thus  tightening  the  spiral  on  the  support.  At  about  this  time  the 
leaves  expand,  and  the  stem  becomes  green.  Twining  results  from  more  rapid  elonga- 
tion on  one  side  of  the  stem  than  on  the  opposite  side,  the  lateral  region  of  most  rapid 
elongation  migrating  regularly  around  the  stem.  The  regularity  of  this  change  is  in- 
ternally controlled,  but  twining  ceases  when  the  pull  of  gravitation  is  equalized  about 
the  plant  axis  by  clinostat  rotation. 

2.  Non-twining  Climbers. — The  stems  of  non-twining  climbers  behave  much  like 
those  of  twiners,  except  that  they  do  not  twine.  They  bear  tendrils,  aerial 
roots,  etc.,  by  which  they  become  attached  to  any  suitable  support  with  which  they 
happen  to  come  into  contact.  In  some  forms  tendrils  correspond  to  leaves  (pea),  in 
other  forms  they  correspond  to  branches  (grape).  Tendrils  are  sensitive  to  contact. 
They  may  grow  around  a  suitable  support  by  thigmotropic  response,  or  they  form 
adhering  disks  at  their  tips  when  stimulated  by  contact.  After  the  tip  is  attached 
the  main  part  of  the  tendril  elongates  very  much  throughout  a  narrow  lateral  region, 
thus  producing  a  double  spiral,  which  acts  like  a  spiral  wire  spring.  Many  tendrils 
have  contact  papilla,  thin  spots  in  the  epidermal  walls  of  the  contact-sensitive  region. 

3.  Circumnutation.— Charles  Darwin  showed  that  the  tips  of  all  vertically  elonga- 
ting stems  swing  slightly  away  from  the  vertical  and  around  it,  as  elongation  proceeds. 
He  called  this  swinging  circumnutation.  To  a  very  slight  and  frequently  almost 
imperceptible  degree,  and  in  a  very  irregular  manner,  ordinary  plant  tips  therefore  act 
somewhat  like  the  tips  of  twiners.  Circumnutation  is  caused  by  an  irregular  and 
spasmodic  migration,  about  the  elongating  portion  of  the  shoot,  of  a  lateral  region  of 
more  rapid  enlargement. 

0  Circumnutation  is  often  very  difficult  to  demonstrate,  but  it  is  doubtful  if  any  shoot 
ever  elongates  with  its  own  axis  exactly  vertical  for  more  than  momentary  periods  of  time. 
It  seems  safe  to  regard  circumnutation  as  universal  in  elongating  stems.  It  is  very  irregular  in 
many  cases,  and  frequently  very  slight  indeed. — Ed. 


CHAPTER  V 

MOVEMENTS  OF  VARIATION" 

§i.  General  Survey  of  Plant  Movements. — All  characteristic  plant  move- 
ments may  be  classified  into  two  groups:  the  first  includes  growth  movements,  of 
growing  organs,  including  nutation  movements  and  tropisms,  while  the  second 
embraces  movements  of  mature  organs,  movements  of  variation.  Only  growth 
movements  (the  first  group)  have  thus  far  been  considered;  as  has  been  seen, 
they  occur  in  growing  organs  and  cease  when  growth  is  completed.  Growth 
movements  may,  in  their  turn,  be  separated  into  two  groups:  in  one  are  included 
movements  that  are  produced  by  external  conditions,  such  as  movements  due 
to  phototropism  and  geotropism,  which  are  called  par  atonic  or  receptive  growth 
movements;  in  the  other  group  are  included  autonomic  or  spontaneous  growth 
movements,  which  are  dependent  upon  the  internal  organization  of  the  plant, 
such  as  the  circular  movements  of  twiners;  and  those  due  to  epinasty,  hypo- 
nasty,  etc.  Epinasty  is  the  phenomenon  of  increased  growth  on  the  upper 
side  of  a  leaf  or  stem,  as  compared  to  the  lower  side,  and  it  results  in  the 
downward  bending  of  the  organ.  Hyponasty  denotes  the  opposite  condition, 
where  growth  is  more  rapid  on  the  under  side  of  an  organ.  Both  phenomena 
depend  upon  the  internal  organization  of  the  organs  in  question,  rather  than 
upon  specific  stimuli  from  the  surroundings.  Movements  of  variation  are 
also  divided  into  paratonic  and  autonomic  movements. 

§2.  Autonomic  Movements  of  Variation. — Among  the  somewhat  limited 
number  of  cases  of  autonomic  movements  of  variation  that  are  now  known,  the 
most  striking  example  is  found  in  the  lateral  leaflets  of  Desmodium  gyrans,1 
the  free  ends  of  which  move  through  an  elliptical  path.  The  rate  of  movement 
depends  upon  the  temperature;  with  high  summer  temperature  a  complete 
circuit  is  completed  in  about  three  minutes.  Similar,  but  much  slower,  move- 
ments may  be  observed  in  other  plants;  thus,  the  terminal  leaflet  of  red  clover 
(Trifolium  pratense)  completes  its  upward  and  downward  movement  in  from 
one  to  four  hours  at  summer  temperatures. 

§3.  Paratonic  Movements  of  Variation.2 — The  leaves  of  Mimosa  pudica, 
(sensitive  plant)  which  droop  at  a  slight  touch,  furnish  the  best  example  of 
paratonic  movements  of  variation.     The  leaf  consists  of  a  long  petiole  to  which 

1  Hofmeister,  Wihelm  F.  B.,  Die  Lehre  von  der  Pflanzenzelle.     Leipzig,  1867. 

2  Briicke,  Ernst,  Ueber  die  Bewegungen  der  Mimosa  pudica.     Muller's  Arch.  Anat.  Physiol,  u.  wiss. 
Med.  1848:  434-455.     1848.     Pfeffer,  1873.     [See  note  2,  p.  291.]     Haberlandt,  G.,  Reizleitendes  Gewebe- 
system  der  Sinnpflanze.     Leipzig,  1890.      [MacDougal,  D.  T.,  The  mechanism  of  movement  and  trans- 
mission of  impulses  in  Mimosa  and  other  "sensitive"  plants;  a  review  with  some  additional  experiments. 
Bot.  gaz.  22:  293-300.      1896.] 

0  In  general,  see:  MacDougal,  1 901.     [See  note  1,  p.  311.]     Pringsheim,  1912.     [Seenotei, 
p.  253].— Ed. 

316 


MOVEMENTS    OF   VARIATION 


317 


four  pinnate  leaflets  are  palmately  attached;  each  of  these  leaflets  consists,  in 
turn,  of  a  secondary  petiole  and  rachis,  which  bears  a  large  number  of  small 
leaflets  of  the  third  order  (Fig.  158).  The  main  petiole  bears  at  its  base  a  well- 
developed  cushion  or  pulvinus,  and  organs  of  this  kind  occur  also  at  the  bases  of 
the  petioles  of  the  leaflets  of  the  second  and  third  orders.  A  very  slight  touch 
upon  the  largest  pulvinus  is  enought  to  cause  the  primary  petiole  to  fall,  and  the 
leaflets  of  the  third  order  to  become  erect  with  the  upper  surfaces  of  each  pair  of 


Fig.    158. — Leaves  of  Mimosa  pudica. 


A,  normal  position;  B,  after  stimulation. 
Pfeffer.) 


{After 


opposite  leaflets  against  each  other  (Fig.  158,  B).  If  the  stimulus  is  strong 
enough  it  is  propagated  through  the  stem  to  the  other  leaves  of  the  plant,  both 
above  and  below,  and  these  also  fall  and  fold  together.  After  a  time  the  leaves 
gradually  re-expand  and  regain  their  earlier  positions.  These  phenomena  occur 
in  completely  mature  leaves,  and  they  are  entirely  independent  of  growth. 

Observations  relating  to  details  of  the  response  here  considered  have  shown 
that  the  movements  of  the  leaf  are  caused  by  changes  in  the  form  of  the  pulvinus. 


318  PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

The  main  body  of  this  organ1  consists  of  parenchymatous  tissue  containing 
many  intercellular  spaces.  The  cell  walls  are  markedly  thinner  in  the  lower 
half  than  in  the  upper  half  of  the  pulvinus.  A  vascular  bundle  transverses  the 
central  part.  It  can  be  shown  that  a  very  great  tissue  strain  normally  exists 
in  the  pulvinus,  the  exterior  portion  being  under  strong  pressure  while  the  inner 
part  is  stretched.  This  may  be  observed  easily  if  the  pulvinus  or  some  part  of  it 
is  cut  out  and  placed  in  water,  when  the  outer  part  expands,  while  the  inner  part 
contracts.  The  direct  inference  may  be  drawn  from  these  facts,  that  the  falling 
of  the  stimulated  leaf  is  the  result  of  a  change  in  turgidity  in  the  cells  of  the 
upper  or  lower  half  of  the  pulvinus. 

If  the  lower  half  of  the  pulvinus  is  cut  away  as  far  as  the  vascular  bundle, 
the  petiole  falls  and  remains  in  this  position  without  again  rising.  If  the  upper 
half  of  the  pulvinus  is  similarly  removed,  the  petiole  also  falls  subsequently, 
but  it  afterward  erects  itself  and  assumes  a  higher  position  than  before.  It 
therefore  follows  that  the  falling  of  the  leaf  is  produced  by  a  decrease  in  turgidity 
of  the  cells  in  the  under  half  of  the  pulvinus,  while  the  opposite  movement  is  the 
result  of  a  return  of  turgidity  in  these  cells.  That  the  leaf  finally  takes  a  higher 
position  when  the  upper  half  of  the  pulvinus  is  removed  is  due  to  the  fact  that 
the  cells  of  the  lower  half  are  now  able  to  expand  to  a  much  greater  degree  than 
before  the  operation,  since  they  encounter  no  resistance  from  the  turgidity  of  the 
opposite  portion.  If  a  stimulus  is  applied  to  an  inverted  Mimosa  plant,  the 
leaves  do  not  sink  but  begin  to  rise  instead;  that  is,  they  move  in  the  same  direc- 
tion, with  reference  to  the  stem  and  roots,  as  they  did  when  the  plant  was  up- 
right. This  rise  is  a  result  of  the  removal  of  resistance  on  the  usually  lower 
(now  upper)  side. 

The  decrease  in  turgidity  of  the  cells  of  the  normally  lower  half  of  the  pul- 
vinus is  accompanied  by  a  decrease  in  their  circumference,  a  part  of  the  water 
contained  in  these  cells  therefore  migrates  elsewhere.  This  water  does  not 
escape  to  the  outside,  for  the  surface  of  the  cushion  is  dry  after  the  response. 
It  may  be  observed,  however,  that  the  pulvinus  is  dark-colored  after  the  leaf 
falls,  appearing  as  though  injected  with  water.  Brticke  concluded  that  the 
water  escaping  from  the  cells  passes  into  the  intercellular  spaces,  displacing  the 
air;  when  the  stimulus  is  removed  this  water  soon  re-enters  the  cells  and  the  inter- 
cellular spaces  become  refilled  with  air,  thus  rendering  the  pulvinus  again  light- 
colored. 

The  cause  of  the  temporary  extrusion  of  water  by  the  cells  of  the  lower  half 
of  the  pulvinus  is  naturally  to  be  attributed  to  changes  in  the  properties  of 
their  protoplasmic  membranes,  brought  about  as  a  result  of  the  stimulus.  The 
exact  nature  of  these  changes  is  still  unknown.  The  response  of  the  Mimosa 
leaf,  which  is  one  of  the  indications  that  the  plant  is  alive,  occurs  only  under 
conditions  that  are  favorable  to  the  life-processes  in  general;  there  must  be  the 
proper  kind  and  intensity  of  the  temperature  and  moisture  conditions,  and 
oxygen  must  be  supplied  from  the  surrounding  atmosphere.     Chloroform  anes- 

1  The  pulvinus  of  the  primary  petiole  is  best  for  this  kind  of  investigation  and  all  the  experiments  here 
described  have  reference  to  this  organ. 


MOVEMENTS    OF  VARIATION 


119 


thetizes  Mimosa  and  causes  the  plant  to  lose  its  power  of  reaction  for  some 
time. 

The  leaves  of  many  other  legumes,  as  well  as  those  of  some  species  of  Oxalis, 
also  respond  to  stimuli  much  as  does  Mimosa,  but  their  sensitiveness  is  not 
nearly  so  pronounced. 


Fig.  159. — Epidermal  cell  of  staminal  filament  of  Opuntia  vulgaris,  showing  a  contact  papilla. 

(After  Haberlandt.) 

Filaments  of  the  Cynareae  (Centaurea  jacea,  for  example)  and  some  other 
groups  of  plants  also  respond  to  contact  stimuli.  They  contract  when  weak 
pressure  is  applied,  the  shortening  being  accompanied,  as  in  the  Mimosa  pul- 


Fig.  160. — Two  branches  of  Destnodium  gyrans.     A,  in  day  position;  B,  in  night  position. 

(After  Darwin.) 

vinus,  by  an  extrusion  of  water  into  the  intercellular  spaces.  The  epidermal 
cells  of  the  filaments  have  specially  sensitive  papillae  with  very  thin  cell  walls, 
into  which  the  protoplasm  extends  (Fig.  159).  These  papillae  are  the  sensi- 
tive organs  that  receive  the  stimuli. 

The  fully  mature  leaves  of  many  plants  take  a  different  position  during  the 
day  from  that  assumed  at  night.     Their  leaflets  approach  each  other  at  night 


320  PHYSIOLOGY   OF   GROWTH  AND  CONFIGURATION 

and  the  petiole  frequently  falls.  This  phenomenon  is  called  nyctitropism  or 
night  movement  of  the  leaves.6  The  falling  of  mechanically  stimulated  leaflets 
of  Mimosa  is  caused  by  decreased  turgidity  in  the  lower  half  of  the  pulvinus,  but 
the  night  movement  of  Mimosa  leaves  is  the  result  of  increased  turgidity  in  the 
upper  half  of  the  pulvinus.  Artificial  shading  also  causes  nycti tropic  move- 
ments in  leaves.  In  Fig.  160  two  branches  of  Desmodium  gyrans  are  shown, 
the  leaves  of  one  in  the  day  position  and  those  of  the  other  in  the  night  position. 
The  approach  of  night  causes  the  leaves  to  fall  and  lie  against  one  another. 

Summary 

i.  General  Survey  of  Plant  Movements. — B endings  of  ordinary  plants  (move- 
ments of  one  part  of  the  plant  body  with  reference  to  the  rest)  may  be  classified  in 
two  groups,  growth  movements  and  variation  or  turgor  movements.  Each  group  has  two 
classes,  autonomic  and  par  atonic  movements.  Autonomic  movements,  whether  of 
growth  or  of  variation,  are  specifically  controlled  by  internal  conditions;  that  is,  they 
are  automatic  or  spontaneous,  not  being  occasioned  by  changes  or  one-sided  influences 
in  the  surroundings.  Paratonic  movements,  of  both  primary  groups,  are  always 
occasioned  by  some  special  change  or  asymmetry  in  the  surroundings.  For  autonomic 
movements  the  development  of  the  plant  first  prepares  the  mechanism  for  movement 
and  then  supplies  the  st  mulus  that  sets  the  mechanism  in  operation.  For  paratonic 
movements  the  deve  opmental  processes  prepare  the  mechanism,  but  they  do  not 
furnish  the  stimulus  that  sets  the  mechanism  in  operation;  the  stimulus  must  come 
from  the  environment. 

Growth  movements  are  due  to  unequal  enlargement  on  the  opposite  sides  of  the 
bending  part.  Here  belong  the  bendings  due  to  the  tropisms.  They  are  always 
confined  to  parts  that  are  still  in  the  second  phase  of  growth,  the  phase  of  enlargement. 
Variation  movements  occur  in  mature  or  maturing  parts  (that  have  ceased  to  enlarge). 
They  are  due  to  rapid  changes  in  the  turgidity  of  certain  portions  or  regions  of  the 
bending  organ,  which  set  up  new  kinds  of  tissue  strains  and  thus  produce  bending. 

Some  of  the  main  paratonic  growth  movements  have  been  considered  (Chapter  III, 
Sections  5  and  6),  those  due  to  phototropism  and  geotropism.  The  autonomic  growth 
movements  include  nutation,  circumnutation,  the  circular  movements  of  twiners,  and 
the  nastic  bendings.  Epinasty  is  more  rapid  enlargement  on  the  upper  side  of  a  leaf, 
resulting  in  a  downward  bending  (as  in  dandelion  leaves).  Hyponasty  is  more  rapid 
enlargement  on  the  lower  side  of  the  organ,  resulting  in  an  upward  bending. 

The  following  scheme  will  help  to  make  the  classification  of  plant  movements  more 
easily  understood. 

I.  Growth  movements  (confined  to  enlarging  parts  or  organs). 
1.  Autonomic  growth  movements  (due  to  internal  stimuli). 

(a)  Nutation  (as  of  bean  epicotyls). 

(b)  Circumnutation  (as  of  most  vertically  elongating  shoots). 

(c)  Twining  movements  (as  of  the  terminal  internodes  of  hop,  etc.). 

(d)  Nastic  bendings  (epinasty  and  hyponasty). 

b  These  movements  are  not  properly  to  be  considered  as  tropisms,  for  the  latter  are  all  growth 
bendings.  Perhaps  the  best  term  for  the  day-night  movements  in  question  (which  are 
paratonic  movements  of  variation)  is  photeolic  movements,  due  to  alterations  in  light 
intensitv. — Ed. 


MOVEMENTS     OF    VARIATION  32 1 

2.  Paratonic  growth  movements  (the  tropisms,  due  to  external  stimuli). 

(a)  Phototropic  bendings. 

(b)  Geotropic  bendings. 

(c)  Bendings  due  to  other  tropisms  (hydrotropism,  chemotropism,  trauma- 

tropism,  thigmotropism,  etc.). 
II.  Movements  of  variation,  or  turgidity  movements  (in  mature  or  maturing  organs) . 

1.  Autonomic  movements  of  variation  (due  to  internal  stimuli). 

Movements  of  the  lateral  leaflets  of  the  telegraph  plant,  Desmodium  gyrans. 

2.  Paratonic  movements  of  variation  (due  to  external  stimuli). 

(a)  Stomatal  movements,  opening  and  closing  of  the  stomatal  pores  (due  to 

changes  in  light  intensity). 

(b)  Photeolic  movements  of  leaves  of  legumes,  Oxalis,  and  some  Euphorbias 

(often  called  "sleep"  movements;  due  to  changes  in  light  intensity). 

(c)  Contact,  etc.,  movements  of  sensitive  plants  (as  Mimosa  piidica). 

2.  Autonomic  Movements  of  Variation. — The  most  striking  example  of  autonomic 
movements  of  variation  is  found  in  the  movements  of  the  lateral  leaflets  of  the  telegraph 
plant,  which  move  in  such  a  way  that  the  tip  of  each  leaflet  transcribes  an  ellipse.  The 
movement  is  very  rapid  and  quite  noticeable  with  high  summer  temperatures.  The 
terminal  leaflet  of  red  clover  moves  in  somewhat  the  same  way,  but  much  more  slowly. 

3.  Paratonic  Movements  of  Variation. — The  contact  movements  of  the  leaves  of 
the  sensitive  plant  are  paratonic  movements  of  variation,  as  also  are  stomatal  move- 
ments and  the  night-day  movements  of  leaves  of  the  legumes,  etc.  In  the  contact 
movements  and  night-day  movements,  bending  is  not  dependent  on  enlargement  but 
is  due  to  a  rapid  change  in  the  turgidity  of  cells  of  the  leaf  pulvini,  which  are  special 
bending  organs.  Upon  being  stimulated,  the  protoplasm  of  the  active  cells  quickly 
increases  its  permeability  toward  the  osmotic  substances  dissolved  in  the  vacuoles, 
some  of  the  cell  sap  moves  into  the  intercellular  spaces,  and  the  tissue  becomes  flaccid. 
After  a  time  the  sap  is  absorbed  again  and  turgidity  is  regained.  Some  other  plants 
exhibit  movements  similar  to  those  of  the  sensitive  plant,  but  to  a  less  marked  degree. 
The  staminal  filaments  of  some  flowers  show  pronounced  contact  responses  of  a  similar 
nature. 

The  night-day  (photeolic)  movements  of  the  leaves  of  many  plant  forms  (leguminous 
plants,  Oxalis,  some  Euphorbias)  are  brought  about  by  pulvinus  reactions  much  like 
those  described  above,  but  in  these  cases  the  stimulus  is  not  mechanical  contact,  but 
a  decrease  or  increase  in  light  intensity. 


21 


CHAPTER  VI 

DEVELOPMENT  AND  REPRODUCTION 

§i.  Influence  of  External  and  Internal  Conditions  on  Development. — The 

form  and  the  arrangement  of  the  parts  of  plants  are  dependent  upon  external 
conditions  to  a  very  marked  degree.  According  to  the  conditions  under  which 
they  develop,  plants  vary  in  their  external  form  as  well  as  in  their  internal 
structure,  and  many  peculiarities  in  configuration  that  appear  to  be 
brought  about  solely  by  internal  conditions  are  mainly  the  result  of  the  ex- 
ternal conditions  that  prevailed  during  the  period  of  development.  It  has  al- 
ready been  seen  (Part  II,  Chapter  III)  that  each  external  condition — such  as 
heat,  light,  atmospheric  pressure,  humidity,  gravitation,  and  the  supply  of 
nutrient  material — exerts  an  influence  upon  plant  growth,  and  consequently 
upon  both  external  form  and  internal  structure.  This  influence  is  of  course 
more  pronounced  when  a  number  of  different  environmental  conditions  affect 
the  plant  simultaneously,  as  is  the  case  in  nature. a     For  example,  the  climato- 


Fig.  161. — Achyrophorus  quitensis,  an  alpine  plant.      (%  natural  size.) 

logical  conditions  of  high  mountains  are  very  different  from  those  of  lowlands, 
and  alpine  plants  differ  in  a  corresponding  way,  in  form  as  well  as  in  structure, 
from  those  growing  at  lower  levels.1     The  predominating  plants  of  high  moun- 

1  Wagner,  A.,  Zur  Kenntnis  des  Blattbaues  der  Alpenpflanzen  und  dessen  biologischen  Bedeutung. 
Sitzungsber.  (math.-naturw.  Kl.)  K.  Akad.  Wiss.  Wien  ioi7:  487-548.     1892. 

0  The  relations  of  external  and  internal  conditions  to  growth  and  development  are  far  too 
complex  to  be  treated  satisfactorily  in  the  space  devoted  by  the  author  to  this  aspect  of 
physiology.  In  this  chapter,  as  well  as  in  the  preceding  ones  devoted  to  growth,  the  author  has 
frequently  secured  brevity  of  treatment  by  slighting  fundamental  principles  and  letting  the 
presentation  be  largely  a  series  of  superficial,  or  at  least  incompletely  analyzed,  examples 
or  illustrations  from  observations.  Although  it  seems  to  the  editor  that  this  part  of  physiology 
really  merits  just  as  thorough  analysis  and  just  as  careful  thought  as  does  respiration,  for 
instance,  still  no  attempt  has  been  made  to  improve  the  analysis  or  to  better  the  presentation  in 
this  chapter.  A  somewhat  more  analytical  point  of  view  is  taken  in  the  editor's  very  brief 
treatment  presented  in  the  summary.  A  more  thorough  attempt  to  bring  out  the  fundamental 
principles  of  these  ecologico-physiological  considerations  is  to  be  found  in  Part  II  of  Livingston 
and  Shreve's  book  on  climate  and  plant  distribution,  especially  pages  97-148.  (See  note  a, 
p.  256.) 

322 


DEVELOPMENT  AND  REPRODUCTION 


32S 


tains  have  more  or  less  reduced  stems,  relatively  large,  rigid  leaves,  and  large, 
brightly  colored  flowers.  Fig.  161  represents  a  specimen  of  Achyrophorus 
quitensis,  a  plant  with  well-developed  alpine  characteristics,  found  at  altitudes 
of  from  3000  to  4000  m.  in  the  Andes,  from  Colombia  to  Peru. 


Fig.  162.- 


-Two  plants  of  Betonica  officinalis,  one  grown  in  the  lowland  (P)  and  the    other  in 
the  mountains  (M).     (Afler  Bonnier.) 


The  experiments  of  Bonnier1  have  shown  that  many  of  the  peculiarities  of 
alpine  plants  are  due  to  the  environmental  conditions  under  which  they  grow. 
This  author  raised  plants  from  the  same  lowland-grown  seed  in  three  different 

1  Bonnier,  Gaston,  Cultures  expeVimentales  dans  les  Alpes  et  les  Pyrenees.  Rev.  gen.  bot.  2:  Si 3-546, 
1890.  Weinzierl,  Theodor,  Ritter  von,  Der  alpine  Versuchsgarten  auf  der  Vorder-Sandlingalpe  bei  Aussoe. 
und  die  daselbst  im  Jahre  1890  begonnenen  Samenkultur-  und  Futterbauversuche.  Landw.  Versuchsst. 
43:  27-126.     1894. 


3-M 


PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 


localities,  near  Paris,  in  the  Alps  and  in  the  Pyrenees.  Those  grown  near  Paris 
had  the  usual  appearance  of  their  lowland  parents,  while  those  grown  in  the 
mountains  had  many  of  the  characteristics  of  alpine  forms.  For  example,  of  the 
two  specimens  of  Betonica  officinalis  shown  in  Fig.  162,  one  (M)  grew  in  the 


Fig.  163. — Two  plants  of  Helianthus  tuberosus  (Jerusalem  artichoke),  one  grown  in  the 
lowland  (P),  the  other  in  the  mountains  (M) ;  at  the  right  the  latter  is  enlarged  (M').     (.After 

K/MMHi'l'         I 


Bonnier.) 


Fig.  164. — Picea  (spruce)  seedlings,  three  years  old,  grown  under  like  conditions  but  from 
different  stocks.  I,  seed  from  the  Achental  (in  the  Austrian  Tyrol)  at  an  altitude  of  1600 
m.;  2,  seed  from  the  same  region  but  at  an  altitude  of  800  m.;  3,  seed  from  Finland. 


mountains  and  the  other  (P)  in  the  lowland.     In  the  mountain  form  the  whole 
plant  was  smaller  and  the  leaves  were  more  crowded  and  nearer  the  base  of  the 


DEVELOPMENT  AND  REPRODUCTION 


325 


stem.  The  difference  between  plants  of  Jerusalem  artichoke  {Helianthus 
tuberosus)  grown  under  these  two  sets  of  conditions  was  very  striking  (Fig.  163). 
In  this  case  the  lowland  form  was  tall,  with  spirally  arranged  leaves,  and  the 
whole  plant  was  very  similar  to  the  common  sunflower  {Helianthus  annuus),  but 
the  alpine  plant,  grown  at  an  altitude  of  2300  m.,  was  quite  different  in  appear- 
ance, being  very  much  smaller,  with  almost  no  stem  and  with  the  leaves  in  a 
rosette  close  to  the  ground.  This  species  is  thus  so  strongly  influenced  by  the 
climatological  conditions  of  high  altitudes  that  it  assumes  the  typical  form  of 
an  alpine  plant  even  in  the  first  generation  under  these  conditions. 

These  examples  show  how  readily  the  forms  of  many  plants  become  altered 
by  changed  external  conditions.  Even  in 
the  first  generation  this  influence  of  the 
surroundings  may  be  very  marked,  and 
when  the  new  set  of  conditions  is  effective 
throughout  a  number  of  generations  the 
resulting  changes  may  be  inherited.  Such 
inherited  characteristics  may  then  be 
retained  throughout  a  number  of  genera- 
tions, notwithstanding  further  environ- 
mental changes.1  Fig.  164  represents 
spruce  seedlings  three  years  old,  all  grown 
under  identical  conditions,  but  from  seed 
that  came  from  different  regions.  Seed 
from  trees  growing  under  favorable  con- 
ditions, at  relatively  low  altitude  (800 
m.),  produced  very  large  plants  (Fig. 
164,  2),  but  seed  from  trees  growing  in 
the  same  geographic  region  but  at  higher 
altitude  (1600  m.)  produced  much  smaller 
plants  (Fig.  164,  1).  The  plants  obtained 
from  seed  that  grew  in  Finland  (Fig.  164, 3) 
were  much  smaller  than  any  of  the  others. 

Practical  as  well  as  theoretical  impor- 
tance is  attached  to  the  principle  of 
heredity  just  illustrated,  for  to  obtain  a 
good  agricultural  crop  not  only  must  the 
soil  be  well  cultivated  and  fertilized  but 
seed  of  a    good  stock  or  strain  must  be  used  also. 

Scientists  have  not  been  satisfied  with  studying  the  influence  of  external 
conditions  in  the  control  of  form  and  structure  of  plants,  but  they  have 
also  been  interested  in  discovering  the  genetic  relationships  that  exist  between 
plant  organs.  Until  very  recently  problems  of  this  sort  have  been  attacked 
exclusively  by  the  method  of  simple  observation.  From  such  morphological  ob- 
servations, the  plant  body  (in  the  case  of  vascular  plants)  is  considered  as  made  up 

1  Demoore,  J.,  La  mSmoire  organique.     Bull.  Soc.  Roy.  Sci.  M6d.  et  Xat.  Bruxelles  65:  28-40 


potato 

tubers  above  the  soil,  on  darkened  por- 
tion of  the  stem.     {After  Vochting.) 


1907. 


326 


PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 


of  three  primary  parts  or  organs — roots,  stems  and  leaves;  all  other  organs  not  at 
first  recognizable  as  roots,  stems  or  leaves  are  regarded  as  modifications  of  one  of 
these  three  types.  Thus  floral  parts  are  considered  as  modified  leaves.  Potato 
tubers  area  special  kind  of  short,  thick,  underground  stems,  since  they  are  formed 
on  subterranean  stem-branches  and  not  on  the  roots.  The  so-called  potato- 
eyes  are  dormant  buds  with  embryonic  leaves,  which  furnish  additional 
evidence  that  the  tuber  is  really  a  kind  of  stem.  This  conception  arose  as 
the  result  of  simple  observation  and  comparison,  but  experimental  support 
therefor  was  furnished  by  Vochting,1  who  found  that  potato  tubers  may  be 
made  to  develop  above  ground,  on  branches  that  arise  when  the  lower  portion  of 
the  plant  is  deprived  of  light  (Fig.  165). 

Absence  of  light  may  therefore  be  considered  as  a  condition  favoring  the  for- 
mation of  tubers,  but  it  is  not  an  essential  condition  for  this,  for  aerial  tubers 
may  be  obtained  in  light  also.  A  leafy  shoot  is  cut  from  the  potato  plant  and  all 
buds  are  carefully  removed  from  the  basal  portion,  after  which  the  shoot  is  so 
planted  in  soil  that  there  are  no  underground  buds.  Roots  develop  and  a  new 
plant  is  formed  but  no  underground  branches  can  develop,  and  consequently  no 
underground  tubers,  on  account  of  the  absence  of  buds  from  the  subterranean 
part  of  the  stem.     As  the  plant  grows  the  starch  that  is  formed  in  the  leaves 


Fig.  166. — Formation  of  aerial  tubers  from  ordinary  buds  of  the  potato  plant.      (After  Vochting.) 

accumulates  in  the  ordinary  buds,  above  the  soil  surface,  and  these  develop 
into  aerial  tubers  (Fig.  166).  These  are  very  similar  to  underground  tubers, 
except  that  they  are  bright  cherry  red  in  color  and  have  large  eyes  that  bear 
green  leaves.  Under  such  conditions  the  tubers  are  always  formed  at  the  base 
of  the  stem,  but  they  may  be  produced  near  the  tip  by  placing  this  portion  in  a 

'Vochting,  Hermann,  Ueber  die  Bildung  der  Knollen.     Bibliotheca  botanica  I4:  11-53.      1887. 


DEVELOPMENT  AND  REPRODUCTION 


327 


dark  chamber  (Fig.  167).  In  the  latter  experiment  the  direction  of  the  move- 
ment of  organic  materials  through  the  stem  occurs  mainly  in  the  direction  oppo- 
site to  that  in  which  it  usually  occurs;  these  substances  here  move  from  the 
leaves  below  to  the  tubers  above. 

Vochting1  showed  that  tuber-formation  in  the  potato  is  dependent  also  upon 
many  other  external  conditions,  besides  those  here  mentioned.  Aerial  tubers 
may  be  similarly  produced  on  other  plants  that  usually  bear  subterranean  tubers. 
Because  of  their  position  in  the  soil,  rhizomes  or  root-stocks,  which  are  of 
frequent  occurrence  in  plants,  are  often  thought  to  be  roots,  but  they  are  really 
subterranean  stems,  for  they  possess  dormant  buds  that  may  develop  later 
into  aerial  branches.  Vochting2  has  shown  experimentally  that  this  is  true  for 
Stachys  tuberifera  and  Stachys  palustris,  both  of  which  have  underground  rhi- 
zomes. Aerial  rhizomes  may  be  obtained  with  these  plants  by  the  same  treat- 
ment as  was  employed  to  bring  about  the 
development  of  aerial  tubers  in  the  potato. 
If  all  the  buds  are  removed  from  the  basal 
portion  of  a  cut  leafy  branch  and  this  por- 
tion of  the  stem  is  then  placed  in  soil, 
roots  develop  but  no  under-ground  rhi- 
zomes are  formed,  there  being  no  buds  on 
the  underground  portion  of  the  stem,  from 
which  rhizomes  might  arise.  Under  these 
conditions  rhizomes  do  develop,  however, 
from  axillary  buds  on  the  upper  portion 
of   the   stem,   thus   replacing   the   usual 


Fig.     167. — Development    of    terminal  Fig.  168. — Transformation  of  a  leafy  branch 

buds  into  aerial  tubers  as  a  result  of  darken-  of    Stachys    tuberifera    into    aerial    rhizomes, 

ing,  by  surrounding  the  upper  part  of  the  {After  Vochting.) 
stem  with  an  opaque  box.      {After  Vochting.) 

lateral  branches  (Fig.  168).  Aerial  rhizomes  may  be  obtained  in  another  way, 
in  the  plants  employed  by  Vochting  (especially  in  Stachys  palustris) .  If  normally 
developed  plants,   with   subterranean   rhizomes,  are  brought  indoors  in  late 

1  Vochting,   Hermann,   Ueber   die    Keimung   der    Kartoffelknollen.     Experimentelle   Untersuchungen. 
Bot.  Zeitg.  6o7:  87-114.      1902. 

2  Vochting,  Hermann,  Ueber  eine  abnorme  Rhizom-Bildung.     Bot.  Zeitg.  47:  501-507.     2889. 


328 


PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 


autumn,  when  they  are  full-grown  and  are  about  to  die,  growth  is  resumed  after 
a  time  and  aerial  rhizomes  are  produced.  These  experiments  prove  definitely 
that  tubers  and  rhizomes  are  really  modified  stems,  in  the  sense  of  the  plant 
morphologists. 

In  the  examples  described  above,  of  the  experimental  production  of  aerial 
tubers  and  rhizomes,  the  nutrient  materials,  being  unable  to  accumulate  in 
the  usual  subterranean  storage  organs,  proceed  to  accumulate  in  the  aerial 
stems  and  so  transform  these  into  storage  organs.  It  is  possible,  however,  to 
bring  about  the  accumulation  of  food  material  in  an  entirely  different  kind  of 
organ  from  that  in  which  it  usually  occurs.  For  example,  in  Boiissingaultia 
baselloides,  which  forms  tubers  under  usual  conditions,  the  accumulation  of 
starch,  etc.,  may  be  made  to  occur  ,■ 

in  the  root.  To  accomplish  this, 
the  petiole  of  a  cut  leaf  is  buried 
in  soil.  Roots  develop  at  the 
cut  end  of  the  petiole,  and  there 
results  a  simple  kind  of  plant  con- 
sisting of  a  leaf  and  roots,  with- 
out any  stem.  The  organic 
materials  produced  in   the  leaf 


Fig.  169. — Swollen,  tuber-like 
root,  developed  at  the  cut  end  of  the 
petiole  of  a  leaf  of  Boiissingaultia 
baselloides. 


Fig.  170. — Two  segments  of  a  willow  twig,  one 
suspended  in  the  normal  (^4)  and  the  other  in  the  in- 
verted position  (B).  S,  stem-pole;  W,  root-pole. 
(After  Vochting.) 


accumulate  in  one  of  the  roots  in  this  case,  which  becomes  greatly  thickened 
and  forms  a  tuber-like  storage  root  (Fig.  169). 


DEVELOPMENT  AND  REPRODUCTION 


329 


§2.  Influence  of  Internal  Conditions  on  Development.— Tn  the  phys- 
iological study  of  plant  development  and  of  the  conditions  con- 
trolling this  process,  internal  as  well  as  external  conditions  must  of  course  be 
considered.  The  existence  of  a  polarity  in  stems,  for  example,  was  demonstrated 
by  Vochting1  in  the  following  manner.  Cut  pieces  of  a  willow  shoot  are  sus- 
pended vertically  in  a  moist  chamber,  some  of  them  being  inverted,  so  that  the 
end  that  was  originally  toward  the  root  (the  root-pole)  is  now  uppermost.  The 
upright  pieces  form  roots  at  the  lower  end  and  leafy  shoots  at  the  upper,  while 
the  inverted  pieces  develop  only  roots  at  the  upper  end — where  these  organs 
seem  to  be  teleogically  useless — and  only  branches  at  the  lower  end  (Fig.  170). 
It  thus  appears  that  each  piece  of  willow  stem  possesses  two  poles,  a  root-pole 
and  a  shoot-pole,  and  the  tissues -near  each  pole  always  produce  the  kind  of 
organ  characteristic  of  that  particular  pole,  without  reference  to  external  con- 
ditions, such  as  gravitation,  light,  etc. 

The  mutual  influence  of  various  organs  and  their  peculiar  and  seemingly 
purposeful  activities  in  the  developmental  process— in  fact,  all  that  is  implied 
in  the  term  consensus  partium — have  long  constituted  an  enigma  in  physiological 
science.  In  animals,  the  regulating  activities  by  which  the  correlation  between 
different  organs  and  tissues  are  brought  about  have  been,  until  recently,  ascribed 
to  the  nervous  system,  but  it  is  now  known  that  there  are  special  substances 
that  control  the  activities  of  the  different  organs  and  even  bring  about  the 
development  of  new  organs.  Each  of  these  substances  is  formed  in  some 
special  part  of  the  organism  and  is  then  transferred  to  other  parts,  which  may 
be  at  a  great  distance,  and  it  may  there  induce  various  kinds  of  chemical  reactions. 
Starling8  has  introduced  the  term  hormone  for  this  kind  of  substance,  which 
acts,  as  it  were,  like  a  chemical  messenger.  The  effect  of  the  development  of  one 
organ  upon  that  of  another  was  emphasized,  for  the  animal  organism,  by  Brown- 
Sequard,  who  showed  that  there  is  a  chemical  substance  in  the  testes  of  the  male 
that  affects  the  whole  condition  and  even  the  mentality  of  the  organism.  His 
conclusions  concerning  the  influence  of  these  substances  are  embodied  in  the 
following  quotations.  "  Je  crois  encore  qu'il  est  parf aitement  possible  de  reparer 
des  ans  les  outrages  reparables."3  "Les  testicules  donnent  a  l'homme  ses  plus 
nobles  et  ses  plus  utiles  attribute  "     (Brown-Sequard,  1889,  page  652.) 

Substances  are  produced  in  the  testes  by  internal  secretion,  and  these, 
being  distributed  through  the  body,  occasion  many  of  the  pronounced  differ- 
ences between  male  and  female  animals.  There  are  many  illustrations  of 
hormone  action  in  animal  physiology,  of  which  a  single  instance  may  be  referred 
to  in  detail  here,  the  relation  between  pregnancy  and  the  development  of  the 
lactiferous  glands.     Ribbert4  grafted  a  mammary  gland  from  one  animal  on  to 

>  Vochting,  Hermann,  Ueber  Organbildung  im  Pflanzenreich.     I  and  2  Th.  Bonn.  1878  and  1884. 

■  Starling,  E.  H.,  The  Croonian  Lectures  on  the  chemical  correlation  of  the  functions  of  the  body. 
Lancet  169:  330-341.  423-425.  501-503,  579-583.  1905.  Bayliss  and  Starling,  1906.  [See  note  2,  p. 
170.] 

»  Brown-Sequard,  C  E.,  Experience  demonstrant  la  puissance  dynamogenique  chez  l'homme  d'un  liquide 
extrait  de  testicules  d'animaux.     Arch,  physiol.  1:  651-658.     1889. 

«  Ribbert,  Hugo,  Ueber  Transplantation  von  Ovarium,  Hoden  und  Mamma.  Arch.  Entwickelungs- 
mech.  der  Organismen  7:  688-708.     1898. 


330  PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

another  female,  near  the  ear,  and  the  grafted  gland  enlarged  during  the  preg- 
nancy of  the  animal  on  which  it  was  grafted,  and  even  yielded  milk  at  the  end  of 
pregnancy.  Starling's  experiments  and  those  of  Lane-Claypon1  have  shown 
that  a  special  hormone,  developed  in  the  embryo  and  distributed  through- 
out the  body  of  the  mother,  is  involved  in  the  case  just  described.  These 
workers  succeeded  in  inducing  the  development  of  lactiferous  glands  in  virgin 
females  of  the  rabbit  by  injecting  an  extract  of  the  foetus  from  a  pregnant 
female.  The  artificially  produced  gland  was  about  as  large  as  in  the  case 
of  a  normal  pregnant  female  at  about  the  ninth  or  tenth  day  of  pregnancy. 

The  following  quotation  from  Biedl2  gives  an  idea  of  some  modern  concep- 
tions concerning  hormone  action.  "Today  we  find  that  the  theory  of  internal 
secretion  plays  an  important  part  in  nearly  all  the  problems  of  physiology  and 
pathology  and  that  it  is  very  important  in  connection  with  general  biological 
problems.  Nothing  is  more  characteristic  of  the  recent  change  in  our  attitude 
toward  the  role  of  specific  internal  secretions  than  is  Schiefferdecker's  hypothesis 
concerning  the  role  of  specific  internal  secretions  in  the  control  of  the  nervous 
system.  This  hypothesis  supposes  that  the  influence  upon  other  cells,  exerted 
by  the  metabolic  products  emanating  from  nerve  cells  during  their  ordinary 
nutritive  processes,  is  tropistic  in  nature,  while  the  irifluence  exerted  by  sub- 
stances arising  in  nerve  cells  during  their  special  activity  is  to  be  considered  as  a 
stimulating  one.  These  conceptions  of  the  nature  of  nervous  control  are  now 
indeed,  generally  accepted,  but  they  show  very  clearly  how  our  attitude  toward 
nerve  activity  has  changed  in  recent  times.  All  correlations  in  activity  between 
organs  used  to  be  regarded  as  nervous  phenomena,  now  nervous  control  is 
regarded  as  of  a  chemical  nature." 

Hormones  probably  occur  also  in  plants,  as  well  as  in  animals.3  Even  as 
early  a  writer  as  Duhamel  gave  vague  expression  to  the  idea  that  various  phe- 
nomena of  plant  growth  and  development  are  not  to  be  explained  by  reference 
to  external  conditions  alone,  and  Sachs  elaborated  this  idea  and  expressed  the 
opinion  that  an  explanation  of  many  such  phenomena  must  be  sought  inside  the 
plant  itself.  In  a  paper  on  the  relation  of  material  to  the  form  and  structure 
of  plant  organs4  this  author  expressed  himself  very  definitely,  stating  that 
"with  a  diversity  in  the  form  of  organs  goes  a  corresponding  diversity  in  the 
materials  of  which  they  are  composed."  Before  Brown-Sequard  and  other 
authors  entered  this  field  in  animal  physiology  Sachs  had  written  of  organ- 
forming  materials  ("Organbildende  Stoffe"),  and  in  his  work  concerning  the 
influence  of  ultra-violet  rays  upon  the  formation  of  flowers  he  wrote:  "These 
flower-forming  substances  act,  like  ferments,  upon  large  masses  of  plastic 
material,  although  they  themselves  are  present  in  exceedingly  small  amounts."5 

1  Lane-Claypon,  (Miss)  J.  E.,  and  Starling,  E.  H.,  An  experimental  enquiry  into  the  factors  which 
determine  the  growth  and  activity  of  the  mammary  glands.     Proc.  Roy.  Soc.  London  B  77 :  505-522.      1906. 

2  Biedl,  Arthur,  Innere  Sekretion.  Ihre  physiologische  Grundlagen  fur  die  Bedeutung  ftir  die  Patho- 
logic    Berlin,  1910.     P.  23. 

3  Massart,  Jean,  Essai  de  classification  des  reflexes  non  nerveux.  Ann.  Inst.  Pasteur  15  :  635-672. 
1901     [Idem,  same  title.     Receuil  Inst.  Bot.  Bruxelles  5:  299-345.     1901.] 

*  Sachs,  J.,  von,  Stoff  und  Form  der  Pflanzenorgane.  Arbeit  Bot.  Inst.  Wiirzburg  2:452-488,  689-718. 
1882. 

6  Sachs,  Julius,  Ueber  die  Wirkung  der  ultravioletten  Strahlen  auf  die  Bluthenbildung.  Arbeit.  Bot. 
Inst.  Wiirzburg  3:  372-388.  1887.  Idem,  Gesammelte  Abhandlungen  iiber  Pflanzenphysiologie  1:  307- 
309.     Leipzig,  1892.* 


DEVELOPMENT  AND  REPRODUCTION  33 1 

If  the  word  hormones  is  substituted  ior  ferments  in  this  sentence  the  statement 
becomes  quite  modern.  Many  phenomena  of  growth  and  of  the  developmental 
configuration  of  plants  will  surely  be  found  to  be  dependent  upon  various  hor- 
mones, and  one  of  the  main  problems  of  future  investigators  will  doubtless  deal 
with  these  internal  secretions  of  plants. 

In  recent  years  proof  of  the  unity  of  all  living  organisms  and  their  common 
genetic  origin  has  repeatedly  been  adduced  from  physiological  studies.  Related 
organisms  generally  contain  characteristic  substances  that  are  chemically 
related.  Studies  on  animals  have  given  important  results  in  this  connection. 
For  instance,  repeated  injection  of  foreign  blood  into  living  rabbits  leads  to  the 
formation  of  a  special  precipitin  or  antiserum  in  the  rabbits'  blood,  and  this 
precipitin  produces  coagulation  in  blood  of  the  kind  injected.1  When  rabbits' 
serum,  taken  from  an  animal  thus  treated,  is  added  to  the  blood  of  other  animals , 
the  latter  blood  is  coagulated  only  when  these  animals  are  of  the  same  species  as 
the  animal  from  which  the  foreign  blood  originally  came,  or  when  they  are  closely 
related  to  that  animal.  Blood  of  species  not  thus  closely  related  to  the  animal 
furnishing  the  injected  blood,  is  not  affected.  The  antiserum  obtained  by 
injecting  human  blood  into  an  animal  precipitates  only  the  blood  of  man  and  of 
the  closely  related  anthropoid  apes  (the  gibbon,  orang-outang,  chimpanzee  and 
gorilla)  while  blood  of  the  apes  of  the  new  world  is  not  thus  coagulated.  '  The 
antiserum  produced  by  the  blood  of  a  member  of  the  genus  Canis(dog)  coagulates 
blood  of  other  species  of  this  genus  but  not  that  of  the  less  closely  related  beasts 
of  prey.  Similar  results  have  been  obtained  also  in  plants.  Rabbit  serum 
from  an  animal  that  has  been  injected  with  yeast  extract,  precipitates  extract 
of  yeast  and  that  of  truffles,  but  not  that  of  ordinary  mushrooms.  It  therefore 
follows  that  yeasts  and  truffles  are  members  of  the  same  group  of  fungi  (Asco- 
mycetes).  Experiments  of  this  kind  with  seed-plants  show  that  injection,  into 
an  animal,  of  extracts  of  different  parts  or  regions  of  the  same  plant,  causes  the 
formation  of  the  same  antiserum. 

§3.  Reproduction. — The  physiology  of  plant  reproduction  has  been  very 
little  studied,  but  it  is  clear  that  this  process  is  dependent  upon  both  external 
and  internal  conditions.  The  alga  Vaucheria,  for  example,  consists  of  a  long, 
unicellular  filament  that  reproduces  both  sexually  and  asexually.  In  asexual, 
or  vegetative,  reproduction  the  terminal  portion  is  separated  from  the  remainder 
of  the  filament  by  a  dividing  wall.  The  cell  thus  cut  off  is  the  zoosporangium, 
from  which  the  zoospore  escapes  as  a  many-ciliated,  motile  cell.  After  a 
period  of  free  movement,  this  cell  enlarges  and  grows  into  a  filament  like  its 
parent,  thus  forming  a  new  individual.  The  process  of  zoospore  formation  is 
markedly  influenced  by  external  conditions,  as  has  been  shown  by  Klebs.2 
Vaucheria  may  be  grown  indefinitely  without  forming  zoospores,  or  zoospores 
may  be  produced  at  any  time,  according  to  the  desire  of  the  experimenter. 
Zoospores  never  develop  when  the  cultures  are  kept  in  moist  air,  but  the  filaments 

1  Seber,  M.,  Moderne  Blutforschung  und  Abstammungslehre.  Frankfurt  a.  M.,  1909.*  Ballner,  Franz, 
Ueber  die  Differenzierung  von  Pflanzlichem  Eiweiss  mittels  der  Komplementbindungsreaktion.  Sitzungsber. 
(math.-naturw.  Kl.)  K.  Akad.     Wiss.  Wien  nglrl:  17-58.      1910. 

-  Klebs,  1896.     [See  note  1,  p.  300.] 


332  PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

need  only  to  be  transferred  to  water  to  bring  about  the  formation  of  these  special 
cells.  They  continue  to  be  produced  for  some  time  under  these  conditions,  but 
finally  the  process  ceases  even  in  water.  If  the  water  culture  is  then  removed 
from  light  to  darkness,  zoospore  formation  begins  again,  and  by  transferring 
such  a  culture  back  and  forth,  between  darkness  and  light,  it  is  possible  to  call 
forth  this  reproductive  response  or  to  check  it,  at  will.  If  the  plant  is  grown  in 
water  without  the  requisite  mineral  salts,  the  power  to  form  zoospores  is  lost 
and  does  not  reappear,  even  if  the  culture  is  transferred  to  darkness,  unless  the 
essential  nutrient  salts  are  re-supplied. 

In  sexual  reproduction  each  Vaucheria  filament  usually  develops  two  lateral 
outgrowths,  one  of  which  forms  the  antheridium  while  the  other  becomes  the 
oogonium.  The  egg  cell  of  the  mature  oogonium  is  fertilized  by  one  of  the 
numerous  sperms  liberated  from  an  antheridium,  and  the  oospore  formed  by 
this  union  develops  into  a  new  individual,  the  whole  process  constituting  sexual 
reproduction. 

Sexual  reproduction  in  Vaucheria  is  dependent  upon  external  conditions. 
Adequate  light  conditions  and  the  presence  of  carbon  dioxide  in  the  solution  or 
in  the  air  about  the  cells,  are  necessary  for  the  production  of  sex  organs,  for  the 
ordinary  processes  of  nutrition  must  continue  during  the  formation  of  these 
organs.  No  sexual  organs  are  formed  in  light  when  carbon  dioxide  is  lacking, 
unless,  indeed,  the  lack  of  the  latter  is  supplied  by  sugar  in  the  solution. 
Absence  of  light  cannot  be  thus  counteracted  by  the  presence  of  sugar,  how- 
ever. When  the  culture  medium  contains  sugar  and  the  atmosphere  is  with- 
out carbon  dioxide,  antheridia  and  oogonia  are  formed  in  light  and  not  in 
darkness.  Vaucheria  filaments  may  be  so  treated  that  they  are  unable  to 
reproduce  sexually,  even  when  illuminated.  If  the  culture  is  grown  for  a 
comparatively  long  time  in  a  sugar  solution,  in  weak  light  or  in  darkness,  the 
cells  become  gorged  with  oil  and  lose  the  power  to  reproduce. 

Finally,  the  quantitative  relation  between  the  number  of  oogonia  and  the 
number  of  antheridia  may  be  modified  by  altering  the  external  conditions. 
There  is  generally  one  oogonium  for  each  antheridium  in  Vaucheria  repens,  for 
example,  though  less  frequently  there  may  be  one  antheridium  for  each  two 
oogonia.  The  number  of  oogonia  formed  may  be  reduced,  while  the  number  of 
antheridia  may  be  greatly  increased,  by  subjecting  the  plants  to  high  tempera- 
ture or  to  much  reduced  atmospheric  pressure.  As  many  as  five  antheridia  in 
a  group,  without  any  oogonia  at  all,  may  sometimes  be  formed  with  this 
treatment. 

In  connection  with  the  study  of  sexual  reproduction  the  question  arises  as 
to  what  may  be  the  conditions  determining  the  entrance  of  the  sperms  into 
archegonia  or  oogonia.  To  attack  this  problem  experimentally,  very  fine 
capillary  glass  tubes  filled  with  various  solutions  are  laid  in  a  drop  of  water 
containing  the  sperms  to  be  studied.  According  to  the  nature  of  the  solutions 
diffusing  from  the  open  ends  of  the  tubes  and  according  to  the  kind  of  sperms 
present,  the  latter  are  either  attracted  in  large  numbers  and  swim  into  the  tubes, 
or  they  are  not  affected  at  all.     It  appears  that  each  species  of  sperm  is  attracted 


DEVELOPMENT  AND  REPRODUCTION 


333 


more  by  certain  substances  than  by  others;  fern  sperms  are  strongly  attracted 
by  malic  acid  and  still  more  attracted  by  the  common  soluble  salts  of  this  acid, 
while  moss  sperms  are  most  attracted  by  cane  sugar.  There  appears  to  be  no 
doubt  that  the  maturing  moss  archegonia  secrete  a  special  substance  that 
attracts  sperms  of  the  same  species.  Upon  the  sperms  of  other  plants  this 
substance  appears  to  have  no  effect. 

The  reproduction  of  fungi  is  also  influenced  by  a  large  number  of  external 
conditions.1  It  is  generally  true  that  reproduction  does  not  occur  in  algae 
and  fungi  under  conditions  favorable  to  vegetative  growth,  while  conditions 
favoring  reproducton  usually  retard  vegetative  growth.2 

Sexual  consanguinity6  is  necessary  for  the  union  of  the  sexual  cells  of  seed- 


Fig.  171. — Germinating  pollen-grains  of  Vallota  purpurea,  their  tubes  directed  toward  a  mass 

of  diastase.      (After  Lidforss.) 

plants  as  well  as  of  spore-plants.  The  chemotaxis  of  sperms  (as  of  ferns)  is 
paralleled  by  the  chemotropism  of  the  pollen-tubes  of  flowering  plants.  Just  as 
the  sperms  swim  toward  the  source  of  diffusion  of  the  attracting  substance  (such 
as  malic  acid),  so  do  the  pollen-tubes  bend  and  elongate  toward  this  source. 
Fig.  171  shows  a  culture  of  pollen-tubes  of  Vallota  purpurea  growing  in  a  30-per 

1  Klebs,    Georg,   Zur   Physiologie   der   Fortpflanzung   einiger   Pilze.     III.    Allgemeine   Betrachtungen. 
Jahrb.  wiss.  Bot.  35:  80-203.      iooo. 

2  Also,  see:  Jickeli,  Karl,  F.,  Die  Unvollkommenheit  des  Stoffwechsels  als  Veranlassung  fur  Vermehrung, 
Wachsthum,  Differenzierung,  Ruckbildung  und  Tod  der  Lebewesen  im  Kampf  urns  Dasein.     Berlin.  1902. 

b  This  and  the  next  following  paragraph  are  added  from  the  7th  Russian  edition. — Ed. 


334  PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

cent,  solution  of  sugar  with  gelatine  enough  to  form  a  jelly.  The  dark  area  in  the 
center  represents  a  mass  of  diastase,  toward  which  the  growing  filaments  are 
attracted.1 

It  appears  that  there  are  substances  in  the  flowers  of  some  plants  that  pre- 
vent fertilization  by  pollen  from  the  same  individual,  thus  resulting  in  self-ster- 
ility. If  the  pollen  is  applied  to  the  stigmas  of  another  individual  of  the  same 
species,  however,  fertilization  is  not  thus  prevented.2  In  such  cases  the  pollen, 
to  be  effective,  must  be  applied  to  an  individual  of  different  sexual  origin  from 
the  one  that  bore  it. 

Parthenogenesis  is  also  controlled  by  external  conditions.  Nathansohn,3  for 
instance,  succeeded  in  obtaining  parthenogenetic  reproduction  in  several  species 
of  the  genus  Marsilia  by  subjecting  the  spores  to  high  temperatures. 

Higher  plants  may  propagate  themselves  vegetatively,  by  means  of  tubers, 
bulbs,  etc.  An  organ,  or  even  a  portion  of  an  organ,  removed  from  the  plant, 
may  generate  a  new  individual.4  For  instance,  if  a  Begonia  leaf  is  cut  off  and 
laid  upon  moist  sand,  adventitious  roots  are  formed  and  a  new  leafy  branch 
develops.  If  the  leaf  is  taken  from  a  plant  that  is  in  bloom,  the  branch  that 
develops  bears  flowers  instead  of  being  leafy.  Fig.  172  shows  a  leaf  of 
Achimenes  haageana  that  was  taken  from  a  plant  just  about  to  bloom;  flowers 
have  been  developed  instead  of  leaves.5  Leafy  branches  or  flowers  may  be 
obtained  at  will,  by  cutting  the  leaves  for  propagation  from  plants  in  the  proper 
stage  of  development.  It  thus  appears  that  the  leaves  of  a  plant  about  to 
bloom  contain  different  chemical  substances  from  those  found  in  the  leaves  of 
earlier  developmental  stages.6 

The  ancient  Greeks  were  already  aware  that  if  a  bud  is  taken  from  one  plant 
and  grafted  upon  another  a  new  branch  is  produced  by  the  development  of  the 
bud,  and  that  this  branch  retains  the  special  character  of  the  plant  from  which 
the  bud  originally  came.  The  operation  of  grafting,  known  to  gardeners  for  so 
long  a  time,  furnishes  the  physiologist  with  a  valuable  means  for  studying  the 
processes  of  growth  and  metabolism.     Vochting7  has  collected  the  scattered 

1  Lidforss,  Bengt,  Untersuchungen  uber  die  Reizbewegungen  der  Pollenschlauche.  Zeitsch.  Bot.  I : 
443-496.     1909. 

2  Correns,  C,  Selbststerilitat  und  Individualstoffe.  Festschr.  (84  Versamml.)  Deutsch.  Naturf.  u. 
Aerzte,  med.-naturwiss.  Ges.     P.  186—217.      Munster  i.  Westf.,  1912. 

3  Nathansohn,  Alexander,  Ueber  Parthenegenesis  bei  Marsilia  und  ihre  Abhangigkeit  von  der  Tem- 
peratur.     Ber.  Deutsch.  Bot.  Ges.  18:  99-100.     1900. 

*  Goebel,  K.,  Ueber  Regeneration  im  Pflanzenreich.  Biol.  Centralbl.  22:  385-397,  417-438,  481-505. 
1902.  [In  this  connection  see  also;  Loeb,  Jacques,  Rules  and  mechanism  of  inhibition  and  correlation  in 
the  regeneration  of  Bryophyllum  calycinum.  Botgaz.  60:  249-276.  1915.  Idem,  Further  experiments  on 
correlation  and  growth  in  Bryophyllum  calycinum.  Ibid.  62:  293-302.  1916.  Idem,  On  the  association 
and  possible  identity  of  root-forming  and  geotropic  substances  or  hormones  in  Bryophyllum  calycinum. 
Science,  n.  s.  44 :  210-211.  1916.  Idem,  Influence  of  the  leaf  upon  root  formation  and  geotropic  curvature 
in  the  stem  of  Bryophyllum  calycinum,  and  the  possibility  of  a  hormone  theory  of  these  processes.  Bot. 
gaz.  63 :  25-50.  1917.  Idem,  A  quantitative  method  of  ascertaining  the  mechanism  of  growth  and  of  in- 
hibition of  growth  in  dormant  buds.  Science,  n.  s.  45:  436-439.  1917.  Idem,  The  chemical  basis  of  re- 
generation and  geotropism.  Ibid.  46:  115-118.  1917.  Idem,  The  organism  as  a  whole.  X  +  153  p. 
New  York,  1916.] 

6  Goebel,  Karl  E.,  Organographie  der  Pflanzen,  inbesondere  der  Archegoniaten  und  Samenpflanzen. 
Jena,  1898-1901.  Part  I,  p.  41.  [Idem,  Organography  of  plants  especially  of  Archegoniatae  and  Sper- 
maphyta.     Translated  by  Isaac  Bayley  Balfour.     2v.     Oxford,  1900-1905.] 

6  Klebs,  Georg,  Ueber  die  Nachkommen  kiinstlich  veranderter  Bluthen  von  Sempervivum.  Sitzungsber 
(math.-naturw.  Kl.)  Heidelberg.  Akad.  Wiss.     19096:  1-32.     1909. 

7  Vochting,  Hermann,  Ueber  Transplantation  am  Pflanzenkorper.     Tubingen,  1892. 


DEVELOPMENT  AND  REPRODUCTION 


335 


literature  of  this  subject  and  has  employed  the  surgical  term  transplantation  to 
designate  all  kinds  of  coalescences  between  plant  parts. 

Experiments  have  shown  that  widely  different  portions  of  plants  may  be 
brought  together  and  made  to  coalesce.  Even  the  transplantation  of  a  leaf 
directly  on  to  a  root  may  be  accomplished,  as  in  the  case  of  the  beet.  The 
whole  upper  portion  of  a  beet  plant  is  cut  away,  leaving  nothing  but  the  fleshy 
root,  in  the  lower  portion  of  which  an  incision  is  made.  Into  this  incision  is 
inserted  the  cut  end  of  a  leaf  petiole  and  the  two  parts  are  bound  together. 
The  tissues  coalesce  and  the  leaf  remains  alive  and  grows.1  Even  portions  of 
different  varieties  of  fruit  may  be  made  to  coalesce  in  this  way.  For  example 
(Fig.  173),  a  gourd  fruit  of  the  variety  poire  verte  was  grafted  by  its  stem  upon 
one  of  the  variety  a  fruits  jaunes;  then  the  lower  part  of  the  former  was  cut 
away  and  a  similar  portion  of  a  fruit  of  a  third  variety,  a  fruits  blancs,  was  trans- 


Fig.   172. — Leaf  of  Achimenes  haageana,  from  which  roots  and  flowers  have  been  formed. 

(After  Goebel.) 

planted  to  the  cut  surface  thus  left.     The  whole  system  of  three  different  kinds 
of  fruit  continued -to  grow  after  the  operation. 

One  of  Vochting's  experiments2  illustrates  how  this  sort  of  operation  may 

1  Daniel,  Lucien,  Recherches  morphologiques  et  physiologiques  sur  la  greffe.  Rev.  gdn.  bot.  6:  5-21, 
6©-75.  1894.  Idem,  Sur  quelques  applications  pratiques  de  la  greffe  herbacde.  Ibid.  6:  356-369.  1894- 
Idem,  Un  noveau  precede'  de  greffage.  Ibid.  q:  213-219.  1897.  Idem,  Les  conditions  de  reussite  des 
greffes.  Ibid.  12:355-368,405-415.447-455.511-529-  1900.  Dorofejew,  N.,  Ueber  Transplantations- 
versuche  an  etilierten  Pflanzen.     (Vorlaufige  Mitteilung.)      Ber.  Deutsch.  Bot.  Ges.  22:  53-61.      1904. 

2  Vochting,  H.,  Ueber  die  durch  Pfropfen  herbeigefuhrte  Symbiose  des  Helianthus  tuberosus  und  Heli- 
anthus  annuus.     Sitzungsber.     K.  Preuss.  Akad.  Wiss.  Berlin.  1894:  705-721.     1894. 


33&  PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

furnish  evidence  concerning  the  chemical  processes  in  plants.  In  this  case  the 
leafy  stem  of  a  young  sunflower  plant  {Eelianthus  annuus)  was  cut  off  a  short 
distance  above  the  soil  and  to  the  cut  surface  of  the  stump  was  grafted  a  leafy 
branch  of  the  Jerusalem  artichoke  {Eelianthus  tuberosus).  Union  of  the  two 
parts  soon  occurred  and  a  new  plant  was  formed.  Examination  of  the  sap 
showed  that  the  upper  portion,  down  as  far  as  the  plane  of  the  graft,  contained 
inulin  in  abundance,  while  the  part  below  the  plane  of  the  graft  contained  starch 
but  no  inulin.  In  this  case  the  simple  organic  substances  in  the  sap  of  both 
portions  were  produced  in  the  artichoke  leaves  above.  In  the  reverse  experi- 
ment, where  the  upper  part  was  sunflower  and  the  lower  Jerusalem  artichoke, 
a  similar  result  was  obtained;  namely,  that  starch  but  no  inulin  was  present  in 
the  sunflower  portion  while  the  artichoke  portion,  which  here  received  its  simple 
organic  substances  from  the  sunflower  leaves,  contained  an  abundance  of  inulin 


Fig.  173— Three  varieties  of  gourd  grafted  upon  one  another;  a,  &  fruits  jaunes;  b,  poire  verte; 

c,  a  fruits  blancs. 

and  even  bore  tubers,  in  which  inulin  accumulated  in  the  same  way  as  if  the 
whole  plant  had  been  of  the  artichoke  species.  Inulin  clearly  acts  only  as  a 
reserve  carbohydrate.  In  both  experiments  the  products  of  photosynthesis 
were  present  in  both  stem  and  roots  as  glucose,  but  within  the  limits  of  the  sun- 
flower portion  they  accumulated  as  starch,  while  within  the  limits  of  the  arti- 
choke portion  they  accumulated  as  inulin. 

The  operation  of  transplantation  is  successful  only  when  closely  related 
species  are  involved,  as  may  be  understood  from  the  foregoing  discussion  (page 
329)  of  hormones  and  of  the  chemical  differences  between  the  metabolic  sub- 
stances of  forms  not  closely  related. 


DEVELOPMENT  AND  REPRODUCTION  337 

Summary 

i.  Influence  of  External  Conditions  on  Development. — The  development  of  a 
plant  is  of  course  made  up  of  all  of  its  growth  activities  considered  together.  The  exter- 
nal or  internal  conditions  that  influence  growth  also  influence  development.  As  the 
plant  develops,  its  internal  conditions  (its  physiological  characteristics)  are  continually 
changing,  the  conditions  of  the  natural  surroundings  are  also  always  in  a  state  of 
fluctuation,  and  consequently  the  relations  between  internal  and  external  conditions  are 
likewise  continually  varying.  It  is  these  relations  that  really  determine  the  develop- 
mental processes.  With  a  given  kind  of  internal  complex,  a  certain  set  of  environ- 
mental conditions  would  produce  a  certain  kind  of  growth.  If  either  the  internal  or 
external  conditions  were  markedly  different,  the  kind  of  growth  would  be  corres- 
pondingly different.  Thus,  different  species  in  the  same  environment  develop  differ- 
ently, and  different  individuals  of  the  same  species,  but  in  different  environments,  also 
develop  differently.  Finally,  present  internal  conditions,  or  characteristics,  are  the 
results  of  past  internal  and  the  past  environmental  conditions,  acting  together.  These 
relations  are  somewhat  complex,  but  it  is  clear  that  we  may  not  say  that  any  plant 
response,  or  any  form  of  development,  etc.,  is  exclusively  brought  about  by  either  the 
internal  or  the  external  conditions.  Both  sets  of  conditions  are  of  course  necessary 
for  growth,  and  the  two  sets  always  act  simultaneously. 

Environmental  complexes  that  are  favorable  to  the  development  of  one  kind  of 
plant  are  not  favorable  to  that  of  another,  sufficiently  different,  kind.  Environ- 
mental complexes  may  therefore  be  said  to  be  adapted  to  the  development  of  those 
plants  that  can  thrive  under  their  respective  influences.  Thus,  American  desert 
conditions  are  very  delicately  and  nicely  adapted  to  the  growth  and  reproduction  of 
certain  kinds  of  cacti  and  other  spiny  shrubs,  but  they  are  not  at  all  suited  to  the 
development  of  the  spiny  roses  found  growing  plentifully  in  the  more  humid  regions  of 
North  America.  The  conditions  of  the  humid  regions,  on  the  other  hand,  are  well 
adapted  to  the  development  of  these  roses,  but  are  not  adapted  to  the  development  of 
the  desert  cacti.  The  present  conditions  of  desert  and  humid  regions  have  been 
brought  about  by  a  long  evolutionary  series  of  climatic  and  physiographic  changes, 
leading  directly  to  the  present  characteristics  of  these  regions,  a  series  of  changes  that 
began  long  before  there  were  any  plants. 

In  a  similar  way,  plants  that  thrive  with  one  set  of  environmental  conditions  do  not 
thrive  at  all  under  another,  sufficiently  different,  set.  It  follows  that  plant  forms  may 
be  said  to  be  adapted  to  the  particular  environmental  complexes  under  which  they 
thrive.  The  internal  conditions  characteristic  of  existing  plant  species  have  been 
brought  about  by  a  long  series  of  evolutionary  steps,  leading  directly  to  the  present 
species,  a  series  of  steps  that  began  with  the  inception  of  terrestrial  life,  long  after  the 
corresponding  climatic  and  physiographic  series  of  evolutionary  changes  had  been 
started  on  its  predetermined  way. 

It  should  be  added  that  physiographic  and  climatic  evolution  has,  in  some  cases, 
been  greatly  influenced  by  organisms,  and  that  plant  evolution  has  always  been  influ- 
enced by  physiographic  and  climatic  evolution;  the  two  lines  of  evolution  are  inter- 
woven, and  they  have  operated  together  to  bring  about  present  environments  and 
existing  plants. 

While  each  species  or  form  of  plants  requires  for  its  development  climatic  and  soil 
conditions  that  lie  within  certain  definite  limits,  each  can  thrive  under  any  one  of  a 
number  of  rather  different  environmental  complexes,  so  long  as  all  of  these  lie  within 
22 


338  PHYSIOLOGY  OF  GROWTH  AND  CONFIGURATION 

the  fixed  limits  for  that  form.  When  two  environmental  complexes  are  different  to  a 
considerable  degree  but  both  are  suitable  for  the  development  of  a  given  species, 
development  with  one  complex  may  be  very  different  from  that  with  the  other. 
Thus,  Bonnier's  experiments  showed  that  the  same  plant  (Jerusalem  artichoke, 
for  example)  developed  very  differently  in  lowlands  and  in  alpine  regions. 
Also,  seed  of  the  same  kind  of  plant,  each  lot  grown  under  a  different  set  of  climatic 
conditions,  may  produce  very  different  plants  when  all  lots  are  germinated  together 
and  the  seedlings  are  reared  side  by  side.  This  point  is  of  agricultural  importance. 
Potato  tubers  are  branch  stems  that  develop  underground.  In  darkness,  tubers 
may  be  caused  to  develop  above  the  soil  surface.  Vochting  was  able  to  arrange  condi- 
tions so  that  tubers  were  produced  above  the  soil  and  in  light,  even  at  the  tip  of  the 
shoot,  in  which  case  the  carbohydrates  formed  in  the  leaves  must  have  moved  upward 
through  the  stem  to  the  tubers.  The  same  author  accomplished  similar  results  with 
rhizome-bearing  forms,  as  well  as  with  tuberiferous  plants.  If  the  organs  in  which 
starch  usually  accumulates  are  removed,  this  substance  may  be  made  to  accumulate  in 
organs  not  usually  serving  as  places  of  accumulation.  If  it  usually  accumulates  in  a  sub- 
terranean tuber,  it  may  be  made  to  accumulate  in  aerially  formed  tubers,  or  in  roots, 
etc. 

2.  Influence  of  Internal  Conditions  on  Development. — Each  part  of  the  plant  body 
influences  the  development  of  other  parts,  and  these  internal  influences  (called  correla- 
tions) are  in  many  cases  so  marked  that  they  cannot  be  readily  overcome,  if  that  is 
possible  at  all,  by  altering  the  external  conditions.  Correlations  appear  to  be  due  to 
small  amounts  of  specific  substances  produced  in  the  cells  and  influencing  the  growth 
and  development  of  other  cells  that  are  often  situated  at  a  great  distance.  Such 
growth-controlling  internal  secretions  are  well  known  to  occur  in  animals  and  they  have 
been  called  hormones,  or  chemical  messengers.  It  seems  probable  that  similar  sub- 
stances occur  in  plants. 

3.  Reproduction. — Reproduction  is  a  special  kind  of  growth.  In  sexual  reproduc- 
tion, among  the  various  organs  appearing  in  a  mature  individual  are  the  reproductive 
organs,  in  which  are  produced  the  reproductive  cells  (eggs  and  sperms).  The  forma- 
tion of  these  organs,  like  that  of  other  organs,  is  controlled  by  internal  and  external 
conditions  acting  together.  Thus,  Klebs  was  able  to  secure  oogonia  or  antheridia, 
or  both,  by  proper  treatment  of  the  right  form  of  Vaucheria.  With  the  right  treat- 
ment, this  alga  could  also  be  made  to  live  indefinitely,  reproducing  by  zoospores  and 
by  branching,  without  the  formation  of  sexual  organs  at  all.  Sperms  of  algae,  mosses, 
and  ferns,  are  attracted  to  the  archegonia  or  oogonia  of  the  same  or  of  a  similar  species 
by  certain  substances  that  diffuse  (dissolved  in  water)  from  these  organs.  The 
sperms  are  said  to  be  positively  chemotropic  toward  these  substances.  Pollen  tubes  of 
higher  plants  are  similarly  attracted  by  substances  formed  in  the  stigma,  etc.;  in  this 
case  the  tubes  bend  because  of  chemotropism,  this  being  a  growth  bending,  due  to  un- 
equal elongation  on  the  opposite  sides  of  the  organ. 

In  some  cases  egg  cells  develop  into  new  individuals  without  fertilization,  this 
phenomenon  being  parthenogenesis.  By  proper  treatment  of  the  unfertilized  eggs, 
parthenogenesis  may  be  artificially  induced  in  some  forms  in  which  it  does  not  usually 
occur. 

It  is  common  in  plants  for  parts  of  the  body  to  separate  from  the  rest  and  develop 
into  new  individuals,  without  any  fusion  of  cells.  This  is  asexual  reproduction.  In 
Vaucheria,  for  a  simple  example,  the  terminal  portion  of  the  protoplasm  of  a  filament 
becomes  a  zoospore,  which,  after  moving  about  for  a  time,  simply  grows  into  a  new 


DEVELOPMENT  AND  REPRODUCTION  339 

plant.  By  proper  treatment  Klebs  was  able  to  produce  zoospores  in  this  alga  at  will, 
or  to  grow  the  plant  without  their  being  formed. — Higher  plants  reproduce  asexually 
by  means  of  outgrowths  of  various  kinds,  such  as  tubers,  bulbs,  etc.  A  branch,  a 
leaf,  or  a  piece  of  root,  may  thus  act  as  a  reproductive  organ.  Many  cultivated  plants 
are  propagated  by  cuttings;  advantage  is  taken  of  asexual  reproduction  in  order  to 
maintain  valuable  varieties,  which  would  be  lost  in  many  cases  if  propagated  by  seeds. 
Related  to  propagation  by  cuttings  is  propagation  by  grafting  or  transplantation. 
A  bud  or  branch  (scion)  cut  from  one  plant  and  inserted  on  another  (stock)  develops  on 
the  new  stem  or  root,  retaining  all  the  characters  of  the  plant  from  which  the  bud  or 
branch  was  taken.  Widely  different  parts  of  plants  may  be  joined  by  transplantation. 
In  general,  transplantation  is  possible  only  when  closely  similar  species  or  forms  are 
involved. 


INDEX 


Note. — This  list  includes  most  of  the  more  important  topics  considered  in  the  book,  embracing  physio- 
logical terms,  names  of  substances  (even  when  used  only  as  reagents),  and  genetic  names  of  plants.  Some 
analysis  is  attempted  for  a  few  topics;  spatial  limitations  preclude  more  complete  analyses.  Authors' 
names  are  also  included,  with  brief  characterizations  of  the  subject  considered.  Plant  names  are  in  Italics. 
authors'  names  in  black-face  type.  Page  numbers  are  in  black-face  type,  (i)  when  the  topics  are  chapter 
or  section  headings,  and  (2)  when  they  refer  to  full  citations;  where  authors  are  mentioned  without  complete 
citations,  page  numbers  are  in  ordinary  type.  A  dash  indicates  all  intervening  pages  between  the  number 
preceding  and  that  following. — Ed. 


Abbott  and  Fowle,  on  pyrheliometer  and  solar 
constant,  22 

Abderhalden,  Lehrbuch  der  physiol.  Chemie,  155, 
158;  Handbuch  der  biochem.  Arbeitsmetho- 
den,  155,  163,  177;  Biochem.  Handlexikon, 
158;  on  proteins,  159,  161.  (See  also  Fischer 
and  A.) 

Abel,  Bacteriology,  56 

Abies  (see  also  fir),  27,  221,  298 

Absorption,  of  materials,  in  general,  Pt.  I,  Chap. 
V,  104-130;  of  ash  constituents,  Pt.  I,  Chap. 
IV,  82-101;  of  dissolved  substances,  101,  119- 
125;  of  gases,  105-109;  of  water,  135,  136,  263, 
271,  273,  274;  of  light,  288,  289 

Acacia,  9 

Acceptors,  of  hydrogen,  207,  208,  223 

Acer,  290 

Acetic  aldehyde,  206,  207 

Acetic  acid  bacteria,  230,  231,  255 

Acetone,  11,  12,  163,  167,  170,  184,  223 

Acetylene,  262 

Achental,  325 

Achillea,  276 

Achimenes,  334 

Achyrophcrus,  323 

Acid,  97,  149,  159.  183,  184,  188,  192,  199,  206,  286; 
amino,  159,  161,  173.  175,  177,  189,  191;  acetic, 
6,  79,  135.  156,  164,  209,  230;  arsenic,  164; 
aspartic,  160,  161,  172,  177;  boric,  58;  butyric, 
79,  125,  209,  210;  carbolic,  58;  citric,  117,  120, 
125.  164,  270,  271;  formic,  31,  125,  166,  199, 
208,  225;  glutamic,  160,  161;  glycoxylic,  156, 
IS9;  hydrochloric,  11,  12,  125,  156,  164,  177, 
179.  185,  186;  hydrocyanic,  164,  165,  179, 
187,  286;  hydrofluoric,  58;  lactic,  125,  207,  209, 
210;  levulinic,  162;  malic,  124,  125,  142,  270, 
271.  333",  mucic,  196;  myronic,  166;  nitric, 
43,  47,  48,  SO,  Si.  66,  67,  68,  71,  72,  73.  9i,  98. 
125.  142,  156;  nitrous,  43,  156;  nucleic,  154, 
162,  175;  oxalic,  31,  117.  125,  166,  173,  188, 
216,  291;  pectic,  271;  phosphoric,  72,  83,  93, 
94,  95,  125,  162,  173,  185;  propionic,  125;  pyro- 
tartaric,  206,  207;  rosolic,  120;  saccharic,  186; 
silicic,  49,  89,  88,  93,  281;  succinic,  125,  201; 
sulphuric,  19,  50,  51,  53,  64,  91,  125,  136,  156, 
157.  163,  185.  209.  267;  sulphurous,  58;  tartaric, 
46,  125,  205.  270;  organic  acids,  188 


Acidity,  of  solutions,  189;  of  soils,  96;  of  bog  water, 

101 
Ackermann,  on  apporhegmas,  176;  A.  and  Kutscher 

on  apporhegmas,  176 
Actinic  rays,  22 
Actinomorphic  flowers,  302 
Activators,  170,  188 
Adamkiewicz's  reaction,  156,  157 
Adaptation,  243;  chromatic,  26 
Adenin,  162,  173,  175,  176 
Adonite,  38 
Adsorption,  66,  184 
Aerobic  respiration,  etc.,   182,  201,  222,  227,    230, 

231,  258,  259 
ALlhalium,  154 
Agar,  43,   124 
Agaricus,  186,  222 
Agulhon,  on  boron  in  plants,  87 
Air,  germs  in,  53-55;  in  plants,   132,   144;  nitrogen 

of,  64-65 
Alanin,  159,  161 

Albert,  Buchner  and  Rapp,  on  acetone  yeast,  167 
Albumin,  124,  154,  156,  157,  158 
Albuminates,  158 
Albumoses,  156,  158 
Alcohol,  xxviii,  6,  8,  9,  20,  21,  28,  36,  44,  no,  in, 

157.  158,  164-168,  177,  183,  184,  200-202,  204, 

207,  213,  221-226,  230 
Alcoholic    fermentation,    167,    168,    170,    201-208, 

214,  221,  222,  223,  226,  260 
Aldehydes,  30,  31,  199,  231 
Aleurone  grains,  154,  157,  299 
Alfalfa,  157 

Alga,  14,  17,  20,  21,  26,  28,  29,  38,  126,  331,  332 
Alisma,  108 
Alkaloids,  1S2,  213;  alkaloids,  toxins  and  antitoxins, 

181-183 
Allard,  see  Garner  and  Allard. 
Allium  (see  also  onion),  250,  251 
Allyl  isothiocyanate,  166 
Almond,  165,  187 

Alpine  plants,  etc.,  255,  323,  324,  325 
Altmann,  on  nucleic  acid,  162 
Alum,  87 

Aluminium,  82,  87,  92;  phosphate,  125;  sulphate,  87 
A  maryllis,  295 
Amides,  177 
Ammonia  xxviii,  42,  43,  47,  48,  49,  50,  6s,  66,  68- 

72,  90,  91.  IS6,  157.  173.  177.  231;  ammonium 


341 


342 


INDEX 


carbonate,  65;  chloride,  84,  117,  158,  159,  210; 
citrate,  93,  94;  chromate,  113;  -magnesium 
phosphate,  90,  91;  molybdate,  91;  nitrate,  46; 
phosphate,  46;  phospho-molybdate,  91;  sul- 
phate, 46,  48,  89,  96,  I57-IS9;  tartrate,  43; 
ammoniacal  copper  oxide,  15,  23,  25;  ammo- 
nium salts  in  general,  65,  67,  71,  72,  79,  96,  98 

Ampelopsis,  312,  313,  314 

Amygdalin,  165,  187,  188 

Amylase,  165 

Anaerobic  cultures,  etc.,  79,  168,  182,  199,  208,  214, 
222-226,  230,  258,  259;  anaerobic  respiration, 
220-222 

Anesthesia,  204,  319 

Anatomical  relations,  of  cell  growth,  241-242 

Andes,  323 

Andre",  see  Berthelot  and  A. 

Andrews,  on  centrifuged  cells,  299 

Andromeda,  97 

Anemone,  256 

Aniline  dyes,  120,  271 

Anions,  189 

Antheridium,  332 

Anthocyanins,  21 

Anthrax,  182 

Anti-enzymes,  170 

Antiseptics,  57,  58 

Antiserum,  331 

Antitoxins,  alkaloids,  and  toxins,  181-183 

Antoni,  see  Buchner  and  A. 

Apogeotropism,  293 

Apparatus  for  the  study  of  growth,  245 

Appert,  on  preserves,  53 

Appleman,  on  oxidase  and  catalase,  168 

Apporhegmas,  176 

Aquatics,  265 

Arabinose,  186 

Arbutin,  187 

Archegonium,  332 

Areca,  125 

Arginin,  160-162,  175,  177 

Arislolochia,  249 

Armstrong,  Carbohydrates  and  glucosides,  186 

Arnaud,  on  carotin,  etc.,  and  on  cholesterin,  19 

Aroidece,  140,  218 

Arrhenius,  on  electrolytic  dissociation,  118 

Arrow-head,  266 

Arsenic,  82 

Artari,  on  chlorophyll  formation,  17;  on  physiology 
of  green  algae,  14 

Artichoke,  88 

Arum,  250 

Ascending  water  current,  133.  146 

Ascomycetes,  331 

Ascospores,  44,  205 

Ash,  of  plants,  etc.,  82,  89,  142,  148,  190,  271;  ash- 
analysis,  88-90;  microchemical,  90-91;  ash- 
constituents,  absorption  of,  Pt.  I,  Chap.  IV, 
82-101;  essential,  importance  of,  84-85; 
non-essential,  importance  of,  85-88 

Askenasy,  on  ascent  of  sap,  143.  146;  on  growth, 
249 

Aso,  on  lime  in  plants,  85 

Asparagin,  xxviii,  69,  166,  170,  172,  I75-I77,  185 
191,  192,  215 

Aspergillus,  79,  87,  121,  123,  173.  211-213,  222 

Aspirator,  136,  215,  216 


Assimilation,  33,  34,  65,  75,  190;  of  more  carbon  and 
solar  energy,  by  green  plants,  Pt.  I,  Chap.  I, 
1-39;  of  carbon,  by  green  plants,  importance 
of,  1-2;  of  carbon  and  of  energy,  by  plants 
without  chlorophyll,  Pt.  I,  Chap.  II,  42-61; 
of  energy,  from  organic  compounds,  by  plants 
without  chlorophyll,  42-47;  of  energy,  from 
inorganic  substances,  by  plants  without  chloro- 
phyll, 47-51;  of  nitrogen,  Pt.  I,  Chap.  Ill,  64- 
79;  of  nitrogen  compounds,  by  lower  plants, 
79;  of  atmospheric  nitrogen,  by  bacteria,  77~79 

Atavistic  structures,  302 

Atkins,  on  osmotic  relations,  124,  167.  (See  also 
Dixon  and  A.) 

Atmometer,   137 

Atmospheric  moisture,  137,  263,  272;  pressure,  35, 
146,  258;  internal  atmosphere,  109;  atmos- 
pheric gases,  influence  of,  on  growth  and  con- 
figuration, 260-263 

Alriplex,  141 

Atwater,  on  ammonia  assimilation,  65 

Autoclave,  57 

Auto-digestion,  166,  187,  188;  auto-fermentation, 
202;  auto-oxidation,  183 

Autolysis,  see  auto-digestion. 

Autonomic  movements  of  variation,  316 

Autumn  colors,  of  leaves,  16 

Avena  (see  also  oat),  159 

Avogadro's  principle,  1,  117 

Auxanometer,  245 


B 


Babcock,  on  metabolic  water,  189,  217 

Bach,  A.,  on  photosynthesis,  31;  on  oxidases,  167; 
on  reduction  enzymes,  168;  B.  and  Batelli  on 
decomposition  of  carbohydrates  in  animals, 
225;  B.  and  Chodat,  on  oxidases,  etc.,  167 
(See  also  Chodat  and  B.) 

Bach,  H.,  on  geotropism,  292 

Bacillus  anthracis,  58,  182,  292;  lactici  acidi,  209; 
oligocarbophilus,  50;  pantolrophus,  50;  ramosus, 
70;  subtilis,  299,  300;  tetani,  182;  thermophilus, 

254 

Bacteria,  42,  43,  50,'  121,  169,  170,  182,  208,  231; 
acetic^acid,  259;  butyric  acid,  259;  hydrogen, 
50,  51;  methane,  231;  sulphur,  50;  colored,  not 
killed  by  light,  292;  colorless,  killed  by  light, 
291;  as  oxygen  indicator,  23;  nitrifying,  47,  48. 
50,  51;  purple,  292;  of  soil,  67-69,  78,  79.  98; 
of  root  tubercles,  77;  temperature  limits  of, 
254;  assimilation  of  free  nitrogen  by,  78,  79! 
bacterial  membranes,  230 

Bacterioids,  of  root  tubercles,  75,  76,  77 

Bacterium  aceti,  230;  coli  commune,  209,  292;  kuet- 
zingianum,  250;  pasteurianum,  230,  255;  radi- 
cola,  76,  77;  xylinum,  231;  various  species,  209 

Baeyer,  on  photosynthesis,  29,  30 

Baker,  on  effects  of  formaldehyde,  30 

Bakke,  on  transpiring  power,  137 

Balanopkorce,  47 

Ballner,  on  complementary  reactions  of  plant 
proteins,  331 

Bamboo,  32,  179 

Bang,  on  lipoids,  183,  184 

Bangia,  38 

Baranetsky,  see  Baranetskii. 


INDEX 


343 


130 


299 


Baranetskii,  on  osmosis,  in;  on  artificial  cellulose 
membranes,  112;  on  transpiration,  138;  on 
bleeding,  141;  on  starch-splitting  enzymes, 
164;  on  periodicity  of  stem  elongation,  275; 
on  twining,  311 

Baranetzki,  see  Baranetskii. 

Baranetzky,  see  Baranetskii. 

Barium,  82;  carbonate,  216;  chloride,  215;  hydrox- 
ide, 6,  215 

Barley,  15,  17.  158,  150.  164.  173,  219,  253 

Barnes,  on  "photosyntax,"  3 

Barthelemy,  on  gas  exchange, 

Bartlett,  see  True  and  B. 

Bary,  de,  on  guttation,  140 

Baryta  water,  215 

Basipetal  growth,  249 

Bassler,  on  correlations,  etc. 

Bast,  267 

Batalin,  on  chlorophyll,  16;  on  light  and  develop- 
ment, 281 

Batelli,  see  Bach  and  B. 

Bayliss  and  Starling,  on  hormone  action,  170,  329 

Bean  (see  also  Phaseolus),  17,  101,  181,  211,  212, 
213,  224,  226,  228,  253,  281,  282,  284,  285,  304. 

311 
Becquerel,  on  assimilation  of  light,  33,  34 
Bedford  and  Pickering,  on  toxins  in  soil,  99 
Beech,  88,  89,  97.  137,  289;  copper,  21 

Beer,  209,  230;  diseases  of,  205;  beer-wort,  43,  44, 

59,  60,  20s,  260 
Beeswax,  36,  106 
Beet  (see  also  Beta),  21,  159,  175.  207,  226,  335 

Beggialoa,  49,  Si 

Begonia,  115,  144.  334 

Beijerinck,  on  bacteria  assimilating  carbon  dioxide 
in  darkness,  49,  52;  on  bacteria  of  legume 
nodules,  75,  76;  on  nitrifying  bacteria.  78,  79 

Bellamy,  see  Lechartier  and  B. 

Bellis,  270,  282,  285 

Bell-jar,  double- walled,   IS 

Benz,  see  Willstatter  and  B. 

Benzaldehyde,  165,  187 

Benzene,  184 

Benzine,  9,  19,  184 

Berkeley  and  Hartley,  on  osmotic  pressure,  112 

Bernthsen,  Organic  chemistry,  187 

Berthelot  calorimeter,  219 

Berthelot,  D.,  on  electric  discharge  and  nitrogen 
combination,  72;  B.  and  Gaudichon,  on  arti- 
ficial photosynthesis,  31 

Berthelot,  M.,  on  nitrogen  fixation  in  soil,  78; 
Chemie  vegetale,  84;  on  catalytic  formation 
of  formic  acid,  etc.,  199;  B.  and  Andre,  on  car- 
bonates, nitrates  and  oxalates  in  plants,  178 

Bertholetia,  158 

Bertrand,  on  sorbose  bacteria,  231 

Berzelius,  on  catalysis,  xxviii 

Beta  (see  also  beet),  123 

Betonica,  323,  324 

Betula  (see  also  birch),  27,  289 

Bicollateral  bundles,  148 

Bidens,  266 

Biedl,  on  hormones,  etc.,  330 

Bilirubin,  12 

Bindweed,  311 

Biochemical  tests,  156 

Birch  (see  also  Betula),  106,  142 


Bismarck  brown,  120 

Blackman,  on  gas  exchange,  4,  105,  108;  on  limiting 
factors,  35,  256;  on  photosynthesis  and  respi- 
ration, 36,   105;  B.  and   Matthaei,  on  photo- 
synthesis and  temperature,  35 
Bladder  membrane,  104,  in 
Bleeding,  140-142 
Blood,  166 
Boehm,  see  Bohm. 
Bog  soil,  70,  92,  101;  bog  water,  101 
Bohm,  on  starch  formation,  28,  38,  187;  on  ascent 

of  sap,  143,  146 
Boletus,  186 

Bondi  and  Eissler,  on  lipoproteins,  184 
Bonnier,  on  heat  of  respiration,  218,  219,  220;  on 
configuration    and    maintained    electric    light, 
287,  288;  on  alpine  cultures,  322,  323-325;  B. 
and    Mangin,    on   photosynthesis,    4,    31;     on 
respiration,   etc.,   of  mushrooms,   210,   212;  on 
respiration  of  tissues  without  chlorophyll,  212, 
214;  on  respiration,  216,  217 
Borodin,  on  crystallized  chlorophyll,  9;  on  pigments 
with  chlorophyll,   19;  on  asparagin,   171,   175, 
177;  on  leucin,   172,   I73>   175;  on  respiration, 
211,  214 
Boron,  82,  87 

Bossard,  see  Schulze,  Steiger  and  B. 
Botrytis,  186 

Bottom  fermentation,  205 
Bouillon,  61,  70 

Boussingault,  Agronomie,  2,  64,  170,  190;  on  gas 
exchange,  2,  3;  on  assimilation  of  nitrogen,  64, 
6s,  72,  75;  on  organic  nitrogen  sources,  66;  on 
asparagin,  170,  171 
Boussingaullia,  328 

Brasch,  on  physical  chemistry  in  physiology,  119 
Brassica  (see  also  cabbage,  turnip),  299 
Breal,  on  nitrogen  nutrition,  72 
Bredeman,  on  nitrifying  bacteria,  78 
Bredig,  on  catalysis,  xxx,  164;  B.  and  Sommer,   on 

catalysis,  200,  208 
Brefeld,  on  light  and  fungus  growth,  291 
Briggs  and  Shantz,  on  water  requirement,  137,  139 
Briosi,  on  oil  stored  instead  of  starch,  29' 
Britten,  see  Livingston,  B.  and  Reid. 
Bromine,  13,  58,  82 
Bronner,  on  absorption  by  soil,  66 
Broom,  268,  269 

Brown,  H.  T.,  on  assimilation  of  light,  34i  105.  108, 
138;  B.  and  Escombe,  on  carbon-dioxide  pres- 
sure, photosynthesis  and  growth,  260;  on  pho- 
tosynthesis and  diffusion,  34i  10S.  108;  B.  and 
Morris,  on  physiology  of  leaves,  28,  163,  165, 
186 
Brown,  W.  H.,  see  Livingston  and  B. 
Brown-Sequard,  on  hormone  action,  329,  330 
Bruck,  on  geotropism  of  lateral  rootlets,  298 
Briicke,  on  the  cell,  in,  IS4',  on  Mimosa,  316,  318 
Brtihl,  on  plant  alkaloids,  181 
Brussels,  256,  257 
Bryonia,  313 

Buchner,  E.,  on  zymase,  163;  Buchner,  E.,  Buchner, 
H.,  and  Hahn,  on  zymase,  etc.,  167,  201;  B. 
and  Antoni,  on  zymase,  etc.,  204;  B.  and  Gaunt, 
on  acetone-treated  acetic  acid  bacteria.  231; 
B.  and  Meisenheimer,  on  alcoholic  fermenta- 
tion, 167.      (See  also  Albert,  B.  and  Rapp.) 


344 


INDEX 


Buchner,  H.,  on  sterilizing  effect  of  light,  291;  on 
polymorphism  of  bacteria,  300.  (See  also 
Buchner,  E.  B.  and  Hahn.) 

Buckland,  in  anecdote,  33 

Buckwheat,  84,  86 

Budrin,  on  nitrogen  fertilizers,  87 

Buds,  218,  325-327 

Biuret  reaction,  156,  159,  162 

Bunsen,  on  gas  analysis,  4 

Burgerstein,  on  transpiration,  etc.,  134,  140 

Burlakov,  on  respiration,  299 

Butkewitsch,  see  Butkevich. 

Butkevich,  on  proteolytic  enzymes,  166;  on  pro- 
teins in  lower  plants,  173;  on  decomposition 
of  nitrogenous  substances,  174,  177 

Butlerow,  on  synthesis  of  sugar-like  substances 
from  oxymethylene,  29,  30 

Butomus,  49 

Butyric  acid  fermentation,  209,  259 


Cabbage  (see  also  Brassiea),  21 

Cacti,  263 

Caffein,  38,  176 

Calamin  violet,  87 

Calcium  (see  also  lime),  70,  71,  82,  85,  89-93,  104, 
183,  28s;  carbide,  73;  carbonate,  49,  72,  94,  101 
125,  173,  209;  chloride,  91,  125,  218,  267; 
cyanamide,  see  lime-nitrogen;  cyanide,  73; 
hypochlorite,  58;  lactate,  168,  209;  nitrate,  82 
oxalate,  188,  313;  phosphate,  94;  sulphate, 
49,  91;  calcium  plants,  88 

Calla,  36 

Calorie,  xxviii;  calorimeter,  219 

Caltha,  36 

Cambium,  241 

Cameron,  Soil  solution,  92.  (See  also  Whitney  and 
C.) 

Campanula,  281,  287,  288 

Candolle,  de,  on  toxins  in  soil,  99 

Cane  sugar  (see  also  saccharose),  116,  118,  122,  186, 
187,  189,  202,  204,  212,  213,  215,  228,  332 

Cannabis  (see  also  hemp),  158,  159,  184 

Capsella,  220 

Capus,  on  water  transport,  144 

Carbon,  xxii,  175,  176;  bisulphide,  15,  19,  20;  diox- 
ide, 1-4,  14,  18,  24,  31,  32,  48,  104-109,  167-170, 
185,  186,  198,  199,  201,  202,  204,  206-216,  218- 
226,  228-230,  232,  260,  284,  331-333;  monox- 
ide, 31;  carbon  black,  101.  Carbon,  assimila- 
tion of,  by  green  plants,  Pt.  I,  Chap.  I,  1-39; 
importance  of,  1—2;  by  plants  without  chloro- 
phyll, Pt.  I,  Chap   II,  42-61 

Carbonic  acid,  light  and  decomposition  of,  21-28 

Carbohydrates,  17,  18,  85,  86,  87,  149,  154,  171,  178, 
179.  181,  183,  185,  i87,-i89,  211,  215,  221, 
227-230,  272,  284 

Carboxylase,  206 

Carlsberg  Laboratory,  44 

Carotin,  6,  8,  16,  19-21 

Carrot,  19 

Caryophylacece,  175 

Casease,  168 

Casein,  209 

Castor  bean  (see  also  Ricinus),  183 

Catalase,  168 


Catalpa,     108 

Catalysis  (see  also  fermentation,    enzymes),  xxviii, 
xxix,  163 

Cavendish,  on  electric  combination  of  nitrogen  and 
oxygen,  72 

Caventou,  see  Pelletier  and  C. 

Cell,  as  physiological  unit,  154 

Cell  sap,   123,  242;  walls,   105-107,   119,   126,    144, 
146,  185,  186,  245,  270,  318 

Cellulose,  107,  112,  185,  186,  189-192,  215,  271 

Centaur ea,  319 

Centrifuge,  293,  299 

Ceramium,  38 

Cernovodeanu,  and  Henri,  on  microorganisms  and 
ultra-violet  light,  292 

Chamcecyparis,  16 

Chamberland  filter,  58,  183 

Chapin,  on  carbon  dioxide  and  growth,  260 

Chara,  88 

Charcoal,  82 

Chemotaxis,  332,  333 

Chemotropism,  333 

Cherry  laurel,  32,  257 

Chicle,  135 

Chitin,  186 

Chlorides,  82,  90,  91 

Chlorine,  58.  82,  86,  87;  chlorinated  lime,  58 

Chloroform,  19,  68,  98,  150,  184,  187,  202 

Chlorophyll,  2,  5-19.  21,  27,  31.  35.  85,   187,   284, 
286,  290 

Chlorophyllan,  11 

Chloroplasts,  154,  156,  288 

Chlorosis,  16,  85,  178,  284 

Cho,  see  Majina  and  C. 

Chocensky,  see  Stoklasa,  Ernest  and  C. 

Chodat  and  Bach,  on  oxidases,  etc.,  167.      (See  also 
Bach  and  C.) 

Cholera,  of  chickens,  182 

Cholesterin,  19,  154,  183 

Chouchak,  see  Pouget  and  C. 

Christensen,  on  nitrifying  bacteria,  78 

Chromogens,  respiration,  188,  222-223 

Ciaccio,  on  lecithin,  184 

Ciamician,  on  photosynthesis,  34,  286;  on  hydro- 
cyanic   acid    in    plants,    286;    C.    and    Silber, 
on  chemical  action  of  light,  199,  200 
Cichorium,  276 
Circumnutation,  314 

Clautriau,  on  Nepenthes,  37;  on  alkaloids,  182 
Claypon  and  Starling,  on  hormone  action,  330 
Cleistogamous  flowers,  291 
Climate,  256,  263,  274,  322 

Climbing  plants,  Pt.  II,  Chap.   IV,   311-314;   non- 
twining,  312-314 
Clinostat,  293,  312 
Clostridium,  79,  209 
Clover,  316 
Coal,  33,  228 
Coalescence,  335 
Coagulation,  of  proteins,  158 
Cobalt,  82,  cobalt-chloride  paper,  136 
Cocoa  butter,  36 
C  odium,  121 
Co-enzymes,  202 
Cohesion,  of  water,  146 
Cohnheim,  on  chemistry  of  proteins,  155 
Coiling,  of  tendrils,  313 


INDEX 


345 


Coleus,  295 

Collenchyma,  267,  268 

Collodion,  in,  112 

Colloids,  in,  113.  114,  189;  colloidal  chlorophyll,  11 

Colombia,  323 

Combes,  on  respiration  chromogens,  223 

Combustion  (see  also  oxidation,  respiration), 
xxviii,  xxx,  198,  200 

Compass  plants,  278 

Complementary  chromatic  adaptation,  26;  com- 
plementary pigments,  26 

Concentration,  of  medium,  113,  272 

Configuration  and  growth,  influence  of  external 
conditions  on.     Pt.  II,  Chap.  Ill,  253-305 

Conglutin,  158,  159 

Congo  red,  126 

Conifers,  14,  175 

Consanguinity,  333 

Consensus  partium,  329 

Conservation,  of  energy,  xxix,  xxx;  of  mass,  xxvii 

Contact  papilla?,  313,  319 

Contractile  roots,  250 

Convallaria,  188 

Convolvulus,  311 

Copper.  82;  ferrocyanide,  112,  113;  hydroxide,  157; 
oxide,  ammoniacal,  15.  23.  25;  sulphate,  15, 
112,  120,  156 

Correlations,  169,  296,  298,  329 

Correns,  on  self-sterility,  334 

Cortex,  132,  133,  148,  150 

Corylus,  256,  258 

Cotyledons,  149,  190 

Crepis,  302 

Cress,  253 

Crocker  and  Knight,  on  gas  poisoning,  262;  C,  K. 
and  Rose,  on  gas  poisoning,  262 

Crocus,  249,  250,  291 

Crystalloids,  ill,  113,   114 

Cucumis,  314 

Cucurbita  (see  also  gourd),  175.  191,  253,  313,  314 

Cucurbitacem,  18,  312 

Cultures,  pure,  58-61;  in  artificial  media,  82-84 

Cuprous  oxide,  199 

Curcuma.  115,  116 

Curtius  and  Franzen,  on  aldehydes  in  green  plants, 
30;  C.  and  Reinke,  on  aldehyde-like  substances 
in  green  plants,  30 

Cuscuta,  47 

Cuticle,  107,  267,  268,  273,  283 

Cyanin,  120 

Cyanophycece,  21,  26 

Cynarece,  319 

Cyssus,  138 

Cystin,  160,  161 

Cystoseira.  38 

Cytisus,  77 

Cytoplasm,  154 

Czapek,  on  root  excretions,  125;  on  transfer  of 
organic  materials,  150;  Biochemie,  155;  on 
respiration,  210,  on  outward  diffusion  from 
cells,  270;  on  geotropic  and  phototropic  per- 
ception, 297;  C.  and  Rudolf,  on  perception,  297 


Dachnowski,  on  bog  soil,  100,  101 
Dahlia,  9,  144,  165,  303 


Dakin,  on  "chlorazene,"  58 

Dandelion  (see  also  Taraxacum),  251,  268 

Daniel,  on  grafts,  335 

Darwin,  Chas.,  on  evolution,  13;  on  traumatropism, 
300;  Insectivorous  plants,  37;  Climbing  plants, 
311,  312;  D.  and  Darwin,  F.,  Movement  in 
plants,  300,  301,  314 

Darwin,  Francis,  on  transpiration,  139.  (See  also 
Darwin,  Chas.,  and  D.) 

Darwinian  bending,  of  roots,  300 

Dastre,  on  sterilizing  action  of  light,  292;  Physique 
biologique,  109 

Daubeny,  on  light  and  photosynthesis,  22 

Death,  without  injury  to  enzymes,  168,  169,  173, 
223-227 

De  Bary,  see  Bary,  de. 

De  Candolle,  see  Candolle,  de. 

Deciduous  trees,  288 

Demoore,  on  protoplasmic  permeability,  271; 
Memoire  organique,  325 

Dephlogisticated  air,  2 

Descending  current,  of  organic  substances,  133;  of 
water,  268 

Desmodium,  316,  319,  320 

Detmer,  on  seed  germination,  192 

Devaux,  on  gas  exchange  of  aquatics,  109 

Development,  influence  of  external  and  internal 
conditions  on,  322-331;  development  and  re- 
production, Pt.  II,  Chap.  VI,  322-339 

DeVries,  see  Vries,  de. 

Dextrin,  38,  210 

Dextrose,  167,  186 

Diageotropism,  298 

Dialysis,  104,  ill,  159 

Dianlhus,  9 

Diastase,  164,  165,  333,  334 

Dicotyledons,  148,  251 

Diels,  on  alga?  penetrating  stone,  126 

Dietz,  on  reversible  enzyme  action,  168 

Diffusion,  104,  105,  107,  124,  125;  differential, 
130,  131;  in  sieve  tubes,  etc.,  148;  through 
membranes,  106,  107,  114,  121,  122,  123; 
through  pores,  108,  109;  outward  from  cells, 
121;  of  gases,  104-105;  of  dissolved  substances, 
109-119 

Digitalis,  141 

Dihydroxyacetone,  167,  168,  231 

Dioncea,  37 

Dipsacus,  276 

Diphtheria,  182,  183 

Dischidia,  264,  265 

Diseases,  infectious,  182 

Disinfectants,  58;  light  as  disinfecting  agent,  291, 
292 

Dissociation,  electrolytic,  118 

Dissolved  substances,  absorption  of,  1 19-126; 
diffusion  of,  109-119;  and  water,  movement  of, 

133-134 

Distilled  water,  as  culture  medium,  64 
Dixon,  on  ascent  of  sap,  145,  146;  on  transpiration, 
147;  D.  and  Atkins,  on  osmotic  pressures  in 
cells,   124;  D.  and  Mason,  on  photosynthesis, 
186 
Dodart,  on  geotropism,  293 
Dodder,  47 

Dorofejew,  on  transplantation,  335 
Doyere,  on  respiration  and  gas  analysis,  4 


346 


INDEX 


Draper,  on  light  and  photosynthesis,  22 

Drosera,  37 

Drying  oven,  56 

Duclaux,  Microbiologic  163,  20 r 

Dufour,  on  light  and  leaf  form,  286 

Duhamel,  on  correlation,  330 

Dumas,  on  carbon  assimilation,  3 

Dutrochet,  on  osmosis  and  on  osmotic  pressure,  no 

Dynamometer,  304,  30s 


E 


Eberdt,  on  transpiration,  138 

Ecology,  273,  274 

Edestin,  158,  159 

Ehrlich,  on  oxygen  requirement,  168 

Eissler,  see  Bondi  and  E. 

Elder,  122 

Electric  discharge,  31,  72;  light,  287,  288 

Electrolytes  and  dissociation,  118,  242 

Elfert,  on  digestion  of  cell  walls,  186 

Elodea,  5,  249 

Elongation,  in  growth,  253,  280,  281,  303 

Emich,  on  microchemistry,  90 

Emulsin,  165,  187,  223 

Endophyllum,  301 

Endosperm,  150,  165,  190 

Energy  (see  also  light),  in  general,  xxix,  xxx,  51, 
232;  in  plant,  23,  24,  33,  52,  198;  assimila- 
tion of,  and  carbon  assimilation,  by  green 
plants,  Pt.  I,  Chap.  I,  i~39»  32-341  and  carbon 
assimilation,  by  plants  without  chlorophyll, 
Pt.  I,  Chap.  II,  42-61;  assimilation  of,  from 
organic  compounds,  by  plants  without  chloro- 
phyll, 42-47;  from  inorganic  compounds,  by 
plants  without  chlorophyll,  47 

Engeland  and  Kutscher,  on  apporhegmas,  176 

Engelmann,  on  bright  leaf  colors,  21;  on  oxygen 
evolution  from  cells,  23;  on  complementary 
pigments,  26;  on  purple  bacteria,  26,  292;  bac- 
terial method  for  studying  photosynthesis, 
23.  24 

Engler  and  Weissberg,  on  auto-oxidation,  167 

Enlargement,  in  growth,  241,  242,  247,  270 

Entropy,  232 

Environment,  267 

Enzymes  (see  also  catalysis,  fermentation,  hydroly- 
sis), 163-170,  xxviii,  xxx,  158,  164,  166,  168, 
170,  173,  176,  184,  185,  187,  201,  204,  206,  208, 
224-226,  229,  231;  respiratory,  223-227 

Eosin,  7 

Epidermis,  263,  268,  287 

Epilobium,  296 

Epinasty,  316 

Epiphytes,  263 

Equilibration,  296 

Equiselum,  276 

Eriophyes,  302 

Ernest,  see  Stoklasa  and  E.,  also  Stoklasa,  E.  and 
Chocensky. 

Errera,  on  myriotonie,  119;  on  transpiration,  144; 
on  hormones,  298 

Escher,  on  carotin  and  lycopin,  19.  (See  also  Will- 
statter  and  E.) 

Escombe,  see  Brown  and  E. 

Ether,  6,  19,  21,  98,  150,  156,  166,  180,  183,  184, 
213;  in  forcing,  262,  263 


Ethyl  chlorophyllide,  8,  9;  phsophorbide,  13 

Ethylene,  262 

Etiolated  leaves,  etc.,  14,  17-19,  86,  141,  170,  174, 

181,  188,  210,  212,  213,  221,  224,  226,  228,  276, 

281-286 
Etiophyllin,  8 
Euler,  Pflanzenchemie,   154,  155.  163;  Chemistry  of 

enzymes,  163 
Evaporation,  134.  137,  138,  146,  147 
Ewart,  on  photosynthesis,  3;  on  tissue  strains,  251 
Excelsin,  158 
Excretion,  of  liquid,  139;  of  salts,  83;  from  bacteria, 

183;  from  roots,  99-126 
Exothermic  reactions,  219 
Exudation,  140-142 


Faber,  on  leaf  nodules,  77,  78 

Fagus  (see  also  beech),  88,  89,  289 

Famintsin,  see  Famintzyn. 

Famintzyn,  on  light  and  chlorophyll  formation,  14; 
on  starch  formation  in  alga?,  28;  on  transpira- 
tion, 138 

Fats,  149,  154,  166,  183,  184,  189,  191,  192,  215,  227 

Fatty  seeds,  190,  215 

Faust,  on  animal  toxins,  181 

Favorskii,  on  oxidation  by  water,  199 

Feige,  see  Urbain,  Seal  and  F. 

Ferments,  see  enzymes,  catalysis. 

Fermentation  (see  also  catalysis,  enzymes),  44-46, 
54,  79,  199,  201-207,  230,  232,  258;  and  respira- 
tion, Pt.  I,  Chap.  VIII,  198-232;  alcoholic, 
167,  168,  170,  200,  201-208;  non-alcoholic, 
209-210;  at  sea-bottom,  50;  in  human  intes- 
tine, 56;  in  soil,  198 

Ferns,  14,  175,  333 

Ferric  chloride,  112,  120,  179;  hydrate,  199;  phos- 
phate, 82;  sulphate,  46 

Ferrous  carbonate,  198;  sulphate,  179,  199 

Fertilizers,  70,  71,  73.  93,  95.  96;  artificial,  73 

Festuca,  264 

Fibrin,  166 

Filaments,  staminal,  319 

Findlay,  Osmotic  pressure,  109,  112 

Finland,  325 

Fir  (see  also  Abies),  221,  288,  298 

Fischer,  E.,  on  sugar  synthesis,  30;  on  proteins, 
161;  F.  and  Abderhalden,  on  proteins,  161 

Fitting,  on  osmotic  pressure  in  cells,  123;  on  geo- 
tropism,  292,  295 

Flowers,  cleistogamous,  291;  color  and  salt  nutri- 
tion, 87;  geotropism  in,  29s;  and  light,  291; 
flower-heads  and  parasites,  302 

Flowering,  218,  256,  257 

Fluorescence,  6,  7,  9 

Fluorine,  82 

Fcetus,  extract  of,  330 

Forcing,  in  greenhouse  culture,  257,  258 

Formaldehyde,  18,  29-31,  213 

Fowle,  see  Abbott  and  F. 

Fragaria,  287 

Frank,  on  lime-nitrogen,  73;  on  mycorrhiza,  97 

Frankfurt,  on  chemistry  of  seeds,  etc.,  186,  191. 
(See  also  Schulze  and  F.) 

Franzen,  see  Curtius  and  F. 

Fraunhofer  lines,  9,  138 


INDEX 


347 


Freezing,  of  tissues,  163,  211.  224;  freezing-point, 
of  bog  water,  101;  of  plant  juices,  etc.,  124 

Fremy,  on  chlorophyll,  6 

Freudenreich  flask,  59!  on  nitrifying  bacteria,   78 

Friedel  on  photosynthesis,  35 

Fructose,  17.  38.  202,  209 

Fruits,  respiration  of,  215 

Fuchsin,  120 

Fungi,  19,  42,  46,  86,  97.  126,  186,  211,  212,  222, 
291.  301,  302,  333 

Furfurol  reaction,  156 


Gaidukov,  on  chromatic  adaptation,  26 
Galactans,  186 
Galactose,  186 
Galeopsis,  9 
Galium,  249 

Ganong,  Laboratory  plant  physiology,  28 
Gardiner,  on  nectaries,  etc.,  140 
Garner  and  Allard,  on  light  duration  and  develop- 
ment, 251 
Gases,  104;  exchange  of,  2-5,  108,  109,  130;  diffu- 
sion of,  104-105,  106;  absorption  of,  105-109; 
movement  of,   130-133;   stimulation  by,   263; 
given  off  by  differential  diffusion,  131,  132 
Gastric  juice,  154,  162,  173,  180 
Gaudichon,  see  Berthelot  and  G. 
Gaunt,  see  Buchmer  and  G. 
Gauthier,  on  toxins,  181 
Gelatine,  43,  60,  61,  77,  113,  114.  i24.  126,  143,  206, 

243,  303;  filter,  202;  tannate,  243 
Genista,  268,  269 
Geotropism,  293-290;  of  leaves,  etc.,  295,  299;  of 

twiners,  312 
Gerlach,  on  lime-nitrogen,  73 
Germs,  in  air,  54,  55 

Germination,  of  seeds,  149,  155.  166,  171,  173.  174. 

179,  180,  189-192,  203,  214,  215,  207-220,  224, 

227,  229,  258,  286 

Giant  cells,  of  Mucor,  270;  colonies,  of  yeast,  205 

Gies,  and  Kantor,  on  biuret  test,   156.      (See  also 

Rosenbloom  and  G.) 
Gilbert,  see  Lawes  and  Gilbert. 
Gingko,  16 

Girdling,  133,  143,  148,  149 
Gladiolus,  213 

Glands,  143;  of  animals,  143,  320-330 
Glaucophyllin,  13 
Gliadin,  158 
Glikin,  on  lecithin,  183 
Globulin,  158,  159 
Globulose,  158 

Glucosamin  chlorhydrate,  186 

Glucose,  xxviii,  38,  69,  117,  121,  124,  164-166,  168, 
185-191,  202,  209,  225,  258;  as  analdehyde,  30; 
heat  of  combustion  of,  200;  hydrolysis  of,  167 
Glucosides,  179,  181,  187-188,  213,  223 
Glutamin,  175,  177,  192 
Glutelin,  158 
Gluten,  158 
Glycerine,  17,  21,  38,  117.  121,  123,  163,  165.  166, 

191,  20i,  231 
Glycocoll,  159 
Glycin,  161 
Godlewski,  on  starch  formation  and  carbon-dioxide 


concentration,  28;  on  photosynthesis,  oil  and 
starch,  29;  on  nitrification  by  bacteria,  69;  on 
water  transfer,  143;  in  intramolecular  respira- 
tion, asparagin,  etc.,  173;  on  respiration,  215; 
on  light  retarding  growth,  275;  on  etiolation, 
283;  G.  and  Polzeniusz,  on  anaerobic  respira- 
tion, 221 

Goebel,  on  ventilation  roots,  132;  Organography, 
334;  on  regeneration,  334 

Gourd  (see  also  Cucurbita) ,  253,  335 

Grafe,  on  photosynthesis,  30;  on  absorption  of  or- 
ganic substances,  39;  on  salt  nutrition,  83,  155; 
G.  and  Linsbauer,  on  geotropic  perception,  297 

Grafting,  334 

Graminem,  86,  190 

Gram-molecules,  113,  115 

Grand  curve,  of  growth,  214,  247,  249;  of  respira- 
tion, 214,  258 

Grandeau,  on  nitrogen  assimilation,  64 

Grape,  140,  268;  grape  juice,  43,  201;  grape  sugar, 

79 

Gravitation,  influence  of,  on  growth  and  configura- 
tion, 292-299 

Green,  Vegetable  physiology,  xxii;  on  proteins  in 
latex,  158;  soluble  ferments,  163.  (See  also 
Vines  and  G.) 

Greening  (see  also  chlorophyll),  14-17 

Griessmayer,  on  proteins,  155 

Grigoriew,  see  Gromow  and  G. 

Gris,  on  chlorosis,  16 

Gromow  and  Grigoriew,  on  protein  decomposition, 
174,  on  zymin,  204 

Growth,  general  discussion  of,  Pt.  II,  Chap.  I,  241- 
245;  of  cell,  anatomical  relations  of,  241-242; 
conditions  favorable  to,  242-245;  apparatus  for 
the  study  of,  245;  grand  period  of,  214,  247, 
249;  phenomena  of,  that  are  controlled  by 
internal  conditions,  Pt.  II,  Chap.  II,  247-251; 
of  root  stem  and  leaf,  247-251;  three  stages  of, 
241;  regions  of,  156,  248-250;  periodicity  of, 
275;  and  circumnutation,  314;  and  coiling 
of  tendrils,  313;  and  climate,  263;  and  geotro- 
pism, 294;  and  movement  of  floral  parts,  291; 
and  respiration,  214;  and  temperature,  254, 
255,  257;  and  strains,  302-304;  movements  due 
to,  316;  resulting  in  shortening,  250;  diurnal 
march  of,  275 

Growth  and  configuration,  influence  of  external 
conditions  on,  253-305;  dependence  of,  upon 
temperature,  253-258;  upon  oxygen  content  of 
the  air,  258-260;  upon  light,  274-292;  influence 
of  gravitation  upon,  292-299;  influence  of 
nutrition  on,  299-300;  influence  of  atmospheric 
gases  upon,  260-263;  influence  of  moisture  on, 
263-274;  influence  of  wounding,  traction  and 
pressure  on,  300-305 

Griiss,  on  respiration  of  yeast,  207 

Guanin,  162,  173.  175-177 

Gum  arabic,  113,  114 

Gum  guaiac,  166 

Gunnera,  123 

Guttation,  140 


H 


Haar,  van  der,  on  oxidases,  etc.,  167 
Haarst,  van,  see  Pitsch  and  van  H. 


348 


INDEX 


Haas  and  Hill,  Chemistry  of  plant  products,  6,  19, 

21.  30,  155,   157.   187 
Haberlandt,  on  water  secretion,  140;  on  light  per- 
ception, 281;  on  geotropic  perception,  296,  297; 
on  Mimosa,  316 
Habit,  275 

Hahn,  see  Buchner,  Buchner  and  H. 
Hales,  Staticks,  135,  140,  141 
Hall,  Rothamsted  experiments,  73 
Halliburton,  Chemical  physiology,  155 
Halophytes,  17,  36 
Hamar,  290 

Hamburger,  on  osmotic  pressure,  etc.,  119 

Hammarsten,  Physiological  chemistry,  155 

Hansen,  on  acetic  acid  bacteria,  230;  on  yeast  cul- 
ture, etc.,  44-46,  59,  201,  205 

Hanson,  on  phycoerythrin,  21 

Hansteen,  on  protein  formation,  180 

Hanstein,  on  transfer  of  organic  substances,  148 

Harden  and  Nonis,  on  reducing  enzymes,  208;  H. 
and  Young,  on  alcoholic  fermentation,  202 

Harrington,  see  Hibbard  and  H. 

Harris  and  Lawrence,   on   osmotic  values  of  ex- 
pressed juices,  124 

Hartig,  on  transpiration,  137;  on  ascent  of  sap,  143; 
on  asparagin  and  seed  germination,  170 

Hartley,  see  Berkeley  and  H. 

Haselhoff  and  Lindau,  on  smoke  injury,  262 

Hasselbring,  on  salt  absorption  and  transpiration, 
148,  271,  273 

Hatchek,  on  colloids,  m 

Haushofer,  on  microchemical  analysis,  90 

Hawkins,  see  Livingston  and  H. 

Hay  bacillus  and  hay  infusion,  300 

Hazel,  256,  258 

Heat,  xxviii,  15,  50,  200,  219,  220;  liberated  in  res- 
piration, 218-220 

Hedera,  276 

Hegler,  on  strains  as  stimuli,  302,  303 

Heine,  on  starch  sheath,  149 

Helianthus  (see  also  sunflower),  34,   141,  165,  184, 
191,  324,  325,  336 

Heliophilous  and  heliophobous  plants,  27 

Heliotropism   (see  also  phototropism),  275 

Helleborus,  288 

Hellriegel  and  Wilfarth,  on  nitrogen  assimilation,  75 

Helmont,  van,  on  sources  of  plant  material,  xxvii ;  on 
spontaneous   generation,    52 

Hematoporphyrin,  11- 13 

Hemicelluloses,  185,  186,  192 

Hemin,  12 

Hemoglobin,  7,  11,  12 

Hemopyrrol,  12 

Hemp,  158,  159,  184.  303 

Henius,  see  Wahl  and  H. 

Henri,  see  Cernovodeanu  and  H. 

Heracleum,  124 

Heredity,  xxxi 

Herlitzka,  on  colloidal  chlorophyll,  11 

Hettlinger,   on   protein   formation   and   wounding, 
180 

Hexose.  31 

Hibbard    and    Harrington,    on    freezing-points    of 
triturated  tissues,  124 

Hseracium,  279 

Hiestand,  on  phosphatides,  183.      (See  also  Winter- 
stein  and  H.) 


Hilgard,  Soils,  92 

Hill,  A.  C,  on  reversible  zymohydrolysis,  168 

Hill,  T.  G.,  see  Haas  and  H. 

Hiltner,  see  Nobbe  and  H.;  Nobbe,  Schmid,  H.  and 
Hotter. 

Hinze,  on  sulphur  bacteria,  51 

Hippuris,  249 

Histidin,  160,  161,  175 

Histones,  162 

Hober,  Physikalische  Chemie  der  Zelle,  119,  154 

Hocheder,  see  Willstatter  and  H. 

Hoff,  Van't,  Theoretical  chemistry,  35;  on  osmotic 
pressure,  117,  118 

Hoffman,  on  calamin  violet,  87 

Hofmeister,  on  ascent  of  sap  and  bleeding,  141;  on 
the  cell,  154.  155.  316 

Hohnel,  on  gas  in  stems,  132,  144 

Holle,  on  oil  in  Strelitzia,  29;  on  wilting,  etc.,  145 

Hop,  46,  282,  285,  311 

Hoppe-Seyler,  on  fermentation  in  soils,  etc.,  198 

Hordein,  158 

Hordeum  (see  also  barley),  159,  164,  253 

Hormones,  170,  188,  298,  329,  330-331.  336 

Horn,  see  Morse  and  H. 

Horowitz,  on  pigments,  7 

Horse-chestnut,  19 

Hotter,  see  Nobbe,  Schmid,  Hiltner  and  H. 

Hoyer,  on  lipolytic  enzymes,  166 

Hubbenet,  see  Kostychev  and  H. 

Hug,  see  Willstatter  and  H. 

Humidity,  of  air,  and  transpiration,  139,  263 

Hamulus  (see  also  hop),  282,  311 

Humus,  93,  98 

Hungerbuhler,  on  starch  formation  and  proteins 

in  unripe  potato  tubers,  185 
Huni,  see  Willstatter  and  H. 
Hydathodes,  139 
Hydnora,  47 
Hydrangea,  36,  87 
Hydrocharis,  165 
Hydrogel,  189 

Hydrogen,    xxviii,    14,    49,    50,    51,    79,    105,    163, 
189-191,    199,    200,    207-210,    223-226,    231; 
acceptors  of,  224-226;  peroxide,  58,  164,  167, 
168,  223,  226;  sulphide,  42,  48-49,  164,  177,  198, 
231 
Hydrogenase,  168 
Hydrogenomonas,  51 
Hydrolysis  (see  also  enzymes),  159,  164,  166,  172, 

189,  191,  218,  220 
Hydroquinone,  187,  225 
Hydrosol,  189 
Hydrotropism,  274 
Hydroxyl,  189 
Hydroxy-prolin,  160 
Hyponasty,  316 
Hypoxanthin,  162,  173,  175,  176,  177 


Illumination,  one-sided,  275 

Imbibition,  in  cell  walls,  144,  146,  147;  in  bladder 

membrane,  11 1 
Imidazol,  160,  163 
Immunization,  182 
Impatiens,  140,  261 
Indican,    187 


INDEX 


349 


Indigo,  124,  187;  indigo  carmine,  5 

Indigotin,  187 

Indol,  160 

Indoxyl,  187 

Infection,  182 

Infusorial  earth,  167 

Ingen-Housz,  on  "purification"  of  air  by  green 
plants,  2;  on  respiration,  210 

Inghilleri,  on  photosynthesis  of  sorbose,  31 

Injection,  of  vessels,  with  mercury,  133 

Inoculation,  of  cultures,  61;  of  legumes,  with  tuber- 
cle bacteria,  77 

Insectivorous  plants,  37 

Integration,  of  temperature,  256 

Intercellular  connections,  124;  spaces,  in  Mimosa 
pulvinus,  318 

Intermittent  stimulation,  in  geotropism,  295 

Internal    atmosphere,    130;    secretions,    298,    329, 

330-331 

Intestinal   microorganisms,    56 

Intramolecular  respiration,  220-222 

Inula,  165 

Inulase,  16s 

Inulin,  165,  336 

Invertase,  16s 

Iodine,  15,  28,  36,  58,  82,  112,  164,  230,  300 

Ions,  in  solutions,  118,  119 

Iraklionoff,  see  Iraklionov. 

Iraklionov,  see  Palladin  and  I. 

Iron,  7,  16,  82,  85,  90-92,  104,  183,  285,  286; 
tannate,  120;  iron  bacteria,  52 

Isachenko,  on  chlorophyll  formation,  18 

Isatchenko,  see  Isachenko. 

Isler,  see  Willstatter  and  I. 

Isobutyl  alcohol,  213 

Isolation,  of  bacteria,  43 

Isoleucin,  160 

Isoprene,  8 

Isosmotic  coefficients,  114-119 

Ivanov,  L.,  on  proteins  and  phosphorus,  174,  181; 
on  respiration  and  phosphates,  214;  on  zymase 
and  respiration  in  ground  seeds,  224 

Ivanov,  N.,  on  acceleration  of  respiration,  214,  227 

Ivanovskii,  on  colloidal  chlorophyll,  n;  on  chloro- 
phyll action,  25;  on  alcoholic  fermentation, 
203,  204 

Iwanoff,  see  Ivanov. 

Iwanow,  see  Ivanov. 

Iwanowski,  see  Ivanovskii. 


Jaccard,  on  gas  pressure  and  development,  258 

Jensen,  on  respiration.  167 

Jerusalem  artichoke  (see  also  Helianthus),  324,  325, 

336 
Jickeli,  on  relation  of  vegetative  and  reproductive 

processes.  333 
Jodlbauer,  see  Tappeiner  and  J. 
Johannsen,  on  ether-forcing,   263 
Jorgensen,  A.  P.  C,  on  fermentation  industry,  44 
Jdrgensen,  I.,  and  Stiles,  on  photosynthesis,  4 
Jost,  on  photosynthesis,  4;  on  ventilation  organs, 

132;  on  etiolation,  leaf  growth,  etc.,  284 


K 

Kalkstickstoff,  73 
Kamienski,  on  mycorhiza,  97 


Kantor,  see  Gies  and  K. 

Karapetoff,  see  Karapetova. 

Karapetova  and  Sabashnikova,  on  protein  decom- 
position, 173 

Karczag,  see  Neuberg  and  K. 

Kaserer,  on  hydrogen  absorbing  bacteria,  50,  51 

Kations,  189 

Keil,  on  sulphur  bacteria,  51 

Kerb,  see  Neuberg  and  K. 

Ketones,  231 

Kieselguhr,  167 

Kiev,  256 

Kihlmann,  on  soil  aridity  in  far  north,  273 

Kinases,  170 

Kinzel,  on  light  and  seed  germination,  286 

Kjeldahl's  method  for  nitrogen  determination,  157 

Klebs,  on  forcing  beech,  257;  on  reproduction  in 
alga?  and  fungi,  300,  331;  on  reproduction  in 
fungi,  333;  on  control  of  floral  structure 
in  Sempervivum,  334 

Klement  and  Renard  on  microchemical  analysis,  90 

Knees,  of  cypress,  131 

Kniep  and  Minder,  on  photosynthesis  and  wave- 
length of  light,  25 

Knight,  L.  I.,  see  Crocker  and  K.;  Crocker,  K. 
and  Rose. 

Knight,  T.  A.,  on  geotropism,  293 

Knop,  on  ash  of  plants  and  salt  nutrition,  82;  on 
buckwheat  without  chlorine,  86;  K's  solution, 
82,  83;  K.  and  Nobbe,  on  water-cultures,  82 

Kny,  on  photosynthesis,  5 

Koch,  on  lodging  of  grain,  86 

Kohl,  on  photosynthesis  and  light,  5,  25;  on  carotin, 
19;  on  water  absorption,  transpiration,  etc., 
135.  138,  267;  on  calcium  salts  and  silica  in 
plants,  188 

Kolkunoff,  see  Kolkunov. 

Kolkunov,  on  photosynthesis  and  stomata,  36 

Kolkwitz,  Pflanzenphysiologie,  5 

Komleff,  see  Palladin  and  K. 

Kooper,  see  Otto  and  K. 

Koppen,  on  temperature  and  growth,  253 

Korsakoff,  seeKorsakova. 

Korsakova,  on  respiration  of  killed  yeast,  170;  on 
cell  lipoids,  185 

Korsakowa,  see  Korsakova. 

Kosinski,  on  respiration  of  Aspergillus,  212 

Kossel,  on  protamines,  163;  on  chemistry  of  cell, 
184 

Kossovich,  on  ammonium  salts  as  nitrogen  source, 
72;  on  nitrogen  fixation  by  legumes,  77 

Kossowitsch,  see  Kossovich. 

Kostychev,  on  soil  microorganisms,  67;  on  anaerobic 
respiration  of  moulds,  87,  208,  222;  on  alcoholic 
fermentation,  206;  on  respiration,  222;  K.  and 
Hubbenet,  on  yeast  fermentation,  226.  (See 
also  Palladin  and  K.) 

Kostytschew,  see  Kostychev. 

Kovchoff ,  see  Kovshov. 

Kovshov,  on  protein  decomposition,  174;  on  wound- 
ing and  protein  formation,  180;  on  nucleopro- 
teins,  181 

Krabbe,  see  Schwendener  and  K. 

Krascheninnikoff,  see  Krasheninnikov. 

Krasheninnikov,  on  photosynthesis  and  dry-weight 
increase,  32,  33;  on  non-assimilation  of  carbon 
monoxide.  36 


35° 


INDEX 


Krasnosselskaia,     on     respiration     enzymes     and 

wounding,  226 
Krasnosselsky,  see  Krasnosselskaia;  also  Walther 

et  al. 
Kraus,  G.,  on  chlorophyll,  6;  on  starch  formation 

in  algae,  28;  on  water  distribution  in  plants, 

189;  on  heat  of  respiration,  218 
Kreusler,   on   photosynthesis  and  respiration,   26; 

on  photosynthesis  and  temperature,  35 
Kiihne's  dialyzer,  159 

Kuijper,  on  temperature  and  respiration,  210 
Kiister,  on  culture  of  microorganisms,  56 
Kutscher,  see  Ackermann  and  K.;  Engeland  and  K. 


Laage,  on  light  and  leaf  form,  286 

Laccase,  143 

Laccol,  166 

Lacquer,  223 

Lactic  acid  bacteria  and  fermentation,  59,  209 

Lactose,  38,  202,  209 

Lactuca,  278 

Lafar,  Technical  mycology,  201 

Lane-Claypon,  on  correlation  and  hormones,  330 

Langley,  on  light  and  vision,  22 

Langstein,  on  formation  of  carbohydrate  from 
protein,  185 

Larix,  27,  289 

Laskovski,  see  Liaskovskii. 

Latex,  166 

Liaskovskii,  on  chemistry  of  seed  germination, 
191,  217 

Lathyrus,  9,  165 

Latitude,  and  light   requirement,    175 

Laurent,  on  denitrifying  microorganisms,  79 

Lauterborn,  on  sulphur  bacteria,  51 

Lavoisier,  on  mass  conservation,  xxvii 

Lawes  and  Gilbert,  on  nitrogen  fertilizer  problems, 
73 

Lawrence,  see  Harris  and  L. 

Lead,  82;  acetate,  177 

Leaves,  metabolism  of,  16,  21,  33,  77,  89,  108,  130, 
132,  137,  138,  143.  165.  178,  181,  265,  271; 
form  of,  260,  265,  284,  286,  301,  302,  313;  re- 
sponses of,  249,  276-278,  290,  29s,  299,  316, 
317,  320;  leaf-mould,  67 

Lebedeflf,  see  Lebedev. 

Lebedev,  on  hydrogen  bacteria,  50;  of  zymase, 
167;  L's  dried  yeast,  208.  See  also  Nabokikh 
and  L. 

Lebedew,  see  Lebedev. 

Lechartier  and  Bellamy,  on  respiration  of  fruits,  221 

Lecithin,  174,  177,  184 

Leek,  179,  180,  226 

Leeuwenhoek,  inventor  of  microscope,  52 

Leguminosa,  73-77,  191 

Legumelin,  158 

Legumes,  75,  171,  175 

Legumin,  158,  159 

Lengerkin,  on  tendrils,  312 

Lenticels,  105,  106,  130 

Lepidium  (see  also  cress),  98,  253,  270 

Leptome,  149 

Lesage,  on  chlorophyll  formation, 


Leucin,  160,  161, 
Leucophyll,  17 


17 
166,  171-173.  175.  176 


Leucoplasts,  154,  185 

Leucosin,  158 

Levshin  on  light  and  respiration  in  fungi.  212 

Liaskovskii,  on  respiration  and  water,  191,  217,  218 

Lichtgenuss,  286,  287 

Lidforss,  on  chemotropism  of  pollen  tubes,  334 

Liebermann's  reaction,  156 

Lieffrauenberg,  65 

Liebig,  on  ash  analyses,  88 

Lieske,  on  iron  bacteria,  52 

Light  (see  also  energy,  spectrum),  15,  23,  26,  27, 
186,  290;  and  metabolism,  14,  is,  19,  22,  23, 
25-27,  29,  31,  33,  34,  38,  83,  86,  138,  171,  178, 
179,  181,  188-190,  210-212,  284-286,  288,  291, 
292;  responses  to,  275-277,  279,  281-284,  286, 
289,  291,  330-332;  light  requirement,  27,  289, 
290;  decomposition  of  carbon  dioxide  influ- 
enced by  light,  21-28;  growth  and  configura- 
tion influenced  by  light,  274-292 

Ligustrum,  36,  221 

Likiernik,  see  Schulze  and  L. 

Lilac,  165,  262,  263 

Liliacea,  251 

Lime  (see  also  calcium),  71,  98,  101 

Lime-nitrogen,  72 

Lind,  on  penetration  of  fungi  into  stone,  etc.,  126 

Lindau,  see  Haselhoff  and  L. 

Linden  (see  also  Tilia),  32,  257 

Lindner,  on  yeast  and  fermentation,  44,  205 

Linsbauer,  see  Grafe  and  L. 

Lipase,  166,  168 

Lipins,  183 

Lipoids,  184,  185;  lipoids  and  phosphatides,  183- 
185;  lipoid-proteins,  184 

Liquids,  104 

Liro,  on  chlorophyll  formation,  14,  18 

Lister,  on  lactic  fermentation,  etc.,  59 

Lithium,  82 

Lithospermum,  86 

Liubimenko,  on  light  and  seed  development,  14;  on 
ombrophilous,  etc.,  plants,  26;  on  dry  weight, 
chlorophyll  production  and  light  intensity.  26; 
on  photosynthesis  and  amount  of  chlorophyll, 
26,  34,  35;  on  light  and  assimilation  of  organic 
substances,  38.      (See  also  Monteverde  and  L.) 

Livingston,  on  physiological  action  of  distilled 
water,  93;  on  toxins  in  soil,  83,  99;  on  bog 
water,  101;  diffusion  and  osmotic  pressure,  109; 
on  osmotic  pressures  of  cells,  123;  on  foliar 
resistance  to  transpiration,  136,  137;  on  at- 
mometry,  137;  on  integration  of  temperature 
values,  256;  L.,  Britten  and  Reid,  on  toxins  in 
soils  99;  L.  and  Brown,  on  foliar  water-con- 
tent, 138;  L.  and  Hawkins,  on  water  relations, 
272;  L.  and  E.  B.  Shrere,  on  cobalt-chloride 
method,  137;  L.  and  Forrest  Shreve,  on  climate 
and  plant  distribution,  256  (See  also  Pulling 
and  L.) 

Lloyd,  on  foliar  water  content,  138 

Lob,  supporting  Baeyer's  hypothesis  of  photosyn- 
thesis, 30,  31 

Lochinovskaia,  see  Palladin,  Sabanin  and  L. 

Lodging,  of  grain,  86 

Loeb,  Dynamics  of  living  matter,  168;  organism  as 
a  whole,  334;  on  regeneration,  etc.,  in  Bryophyl- 
lum,  334 

Loew,  on  liming  soils,  85;  on  catalytic  oxidation,  199 


INDEX 


351 


Loewschin,  see  Levshin. 

Lohnis,  on  nitrifying  bacteria,   78;  on  toxins  from 

soil  bacteria,  101 
Lonicera,  311 
Lowschin,  see  Levshin. 
Lubimenko,  see  Liubimenko. 

Luca,  de,  on  alcohol  production  in  leaves,  etc.,  222 
Ludwig,  on  imbibition,  etc.,  m 
Luff  a,  18 
Lupinus,  17.  158,  159.  i"5.  176,  180,  184,  191,  253. 

268,  284 
Lusk,  Nutrition,  170 
L'vov,  see  Lvov. 
Lvov,  see  Palladin  and  L. 
Lycopin,  20 
Lysin,  160,  161,  175 


M 


Macallum,  on  microscopical  tests  for  chlorides,  etc., 

90 

MacDougal,  on  photosynthesis,  3;  on  influence  of 
environment  on  form,  266;  on  light  and  devel- 
opment, 281;  Plant  physiology,  311,  312,  316; 
on  tendrils,  312;  on  movements  in  Mimosa, 
3i6 

MacMillan,  on  photosynthesis,  3 

Magnesium,  7,  13.  82.  85,  91,  92,  104,  288-289; 
carbonate,  46,  48,  69;  chloride,  117;  sulphate. 
92,   117,  158 

Maize,  137.  138,  ISO.  158,  159.  184.  190,  253 

Majima,  on  urushiol,  223;  M.  and  Cho,  on  urushiol, 
223 

Maksimov,  on  light  and  respiration  of  fungi,  212. 
(See  also  Walther  et  al.) 

Malfiewsky,  see  Malchevskii. 

Malchevskii,  see  Walther  el  al. 

Malpighi,  on  girdling,  143,  148;  on  water  transfer, 
133 

Malt,  164 

Maltase,  165,  168 

Maltose,  17,  165,  168,  202,  209 

Manganese,  87 

Mangin,  on  r61e  of  stomata,  35,  36.  (See  also 
Bonnier  and  M.) 

Mannite,  38,  222 

Mannose,  186 

Manometer,  217 

Marble,  125 

Marchlewski,  see  Nentskii  and  M.;  Schunck  and  M. 

Marl,  71 

Marsilia,  334 

Martin,  on  papain,  158 

Mason,  see  Dixon  and  M. 

Massart,  on  hormone  action,  330 

Material  transformations,  in  the  plant,  Pt.  I,  Chap. 
VII,  154-192 

Materials,  absorption  of,  in  general,  Pt.  I,  Chap.  V, 
104-130;  absorbed  by  plants,  104;  movement 
of,  in  the  plant,  Pt.  I,  Chap.  VI,  130-150 

Mathews,  Physiological  chemistry,  159 

Mathewson,  on  biochemical  tests,  156 

Matruchot  and  Molliard,  on  chlorophyll  formation, 

17 

Matthaei,  on  photosynthesis  and   respiration,  35. 

(See  also  Blackman  and  M.) 
Maturity,  of  seeds,  stages  of,  286 


Maximow,  see  Maksimov. 

Maximum,  temperature,  253,  254;  light  require- 
ment, 288-289 

Maxwell,  see  Schulze,  Steiger  and  M. 

Mayer,  Adolf,  on  ammonia  assimilation  by  leaves, 
65;  on  grand  curve  of  respiration,  214.  (See 
also  Wolkoff  and  M.) 

Mayer,  A.  E.,  Agrikulturchemie,  33,  84 

Mayer,  E.  W.,  see  Willstatter,  M.  and  Huni. 

Mayer,  J.  R.,  on  energy  conservation,  xxix;  on  role 
of  green  plants,  32 

McCallum,  on  determination  of  leaf  form,  etc.,  266 

McLean,  on  climatic  conditions,  256 

Measurement,  of  growth,  245 

Measuring  apparatus,  242,  245 

Media,  artificial,  cultures  in,  82-84 

Meisenheimer,  see  Buchner  and  M. 

Melanpyrite,  38 

Melandryum,  302 

Melanins,  13 

Membranes,  osmotic,  104,  no,  112 

Mercuric  chloride,  58;  nitrate,  156,  177;  sulphide, 
156,  177 

Mercury,  82,  106,  132,  156,  203,  216 

Merlis,  on  seeds  and  etiolated  seedlings,  176 

Merrill,  on  distilled  water  and  toxic  solutions,  83 

Mesophyll,  288 

Mesoporphyrin,  12 

Metabolism,  13 

Metaproteins,  158 

Methane,  51,  198 

Methyl,  in  chlorophyll  molecule,  8;  methyl  green, 
orange,  violet,  120 

Methylene  blue,  120,  168,  225,  226;  as  hydrogen 
acceptor  and  respiration  pigment,  207,  208 

Mettais,  6s 

Meunier,  on  asparagin,  171 

Mica-schist  soil,  92 

Michaelis,  on  cell  acidity,  etc.,  189 

Microchemical  tests,  90 

Micrococcus,  209 

Microorganisms,  distribution  of,  in  nature,  52-56; 
physiological  characters  of,  42,  43;  in  air.  54, 
55;  in  bog  soil,  98,  99.  101;  in  milk,  56;  in  rain- 
water, 52;  in  human  intestine,  56 

Microscope,  invention  of,  52;  horizontal,  243,  245 

Mieg,  see  Willstatter  and  M. 

Milk  microorganisms  of,  56;  souring  of,  209 

Millet,  86,  94,  281 

Millon  reaction,  156,  162 

Mimosa,  xxiv,  316,  318-320 

Mimulus,  255 

Minder,  see  Kniep  and  M. 

Minimum,    light    requirement,    289;    temperature, 

253. 254 

Minsk,  95 

Mites,  302 

Mitscherlich,  Bodenkunde,  92 

Miyoshi,  on  penetration  of  fungi  through  mem- 
branes, 126 

Moisture,  influence  of,  on  growth  and  configuration, 
263-274 

Molar  movement,  and  diffusion,  106,  107 

Molecular  solutions,  113,  115 

Molisch,  on  relation  of  plants  to  iron,  16,  85;  on 
phycocyanin.  phycoerythrin  and  phycopha?in, 
21 ;  on  purple  bacteria,  26;  on  sulphur  bacteria, 


352 


INDEX 


5 1 ;  on  iron  bacteria ,  52 ;  on  soil  and  flower  color, 
87;   Mikrochemie,  90,    178;   on  bleeding,   143; 
on  furfurol  reaction,    156;   on  warm-bath  for 
forcing,  258.     (See  also  Wiesner  and  M.) 
Moll,  on  excretion  of  liquid  water,  139 
Molliard,  see  Matruchot  and  M. 
Monobutyrin,  168 
Monocotyledons,  148 
Monopodial  branching,  270 
Mono-potassium  phosphate,  82 
Mono-sodium  phosphate,  94,  95 
Monstera,  247 
Montanari,  on  lycopin,  20 

Monteverde,  on- protochlorophyll,  etc.,  9,   18;  on 
protochlorophyll    and    chlorophyll    formation, 
18;    on    nitrates   in   plants,    178;    on    calcium 
oxalate,  etc.,   in  plants,    188;   M.   and  Liubi- 
menko,  on  chlorophyll  formation,  17,  18 
Monteverdi,  see  Monteverde. 
Montsourie,  Park  of,  55 
Morse  and  Horn,  on  osmotic  membranes,  112;  M. 

et  al.,  on  osmotic  pressure,  113 
Morchella,  186 

Moritz  and  Morris,  Brewing,  164,  201 
Morkovin,  on  respiration,  alkaloids  and  anesthetics, 
213;  on  stimulation  of  intramolecular  respira- 
tion, 222 
Morkowin,  see  Morkovin. 
Moor  soils,  92 

Morris,  see  Brown  and  M.;  Moritz  and  M. 
Mosaic,  of  leaves,  276 
Moscow,  95 

Mother,  of  vinegar,  230 
Moulds,  46,  79,  85,  121,  123,  208 
Movement  of  materials,  general  occurrence  of,  130; 
of  materials  in  the  plant,  Pt.  I,  Chap.  VI,  130- 
150;  of  gases.  130-133;  of  water  and  dissolved 
substances,    133-134;    of    organic    substances, 
148-150;  of  variation.  Pt.  II,   Chap.  V,  316- 
320;  autonomic  movements  of  variation,  316 
paratonic  movements  of  variation,  316-332 
Mucor,  79,  260,  270,  299 imucor  yeasts,  208,  260,  261 
Mucoracece,  206 
Mullein.  276 
Miintz,   on   physiology  of  mushrooms,   222.      (See 

also  Schldsing  and  M.) 
Musa,  29 

Mustard,  166,  253,  279 
Mutation,  316 
Mycobacterium,  77 
Mycoderma,  230 
Mycorhiza,  38,  97,  98,-290 
Mycotrophic  plants,  97,  98 
Myriotonie,  119 
My  rosin,  166 
Myrsiphyllum  ,312 


X 


Nabokich,  see  Xabokikh. 

Nabokikh,  on  anaerobic  respiration,  221;  on  anaero- 

biosis  of  seed  plants,  258;  N.  and  Ledebev,  on 

hydrogen  bacteria,  50 
Nadson,  on  starch  formation.  38;  on  penetration  of 

alga  into  stone,  etc.,  126 
Nagamatsz,  on  photosynthesis,  36.      (See  also  Sachs 

and  X.) 


Nancy,  65 
Naphtha,  6,  156 

Nathansohn,  on  sulphite  bacteria,  49,  52;  Stoffaus- 

tausch,   121;  on  artificial  parthenogenesis,  334 

Negative  pressure,  of  gases  in  plant,  106,  132,  133, 

144 
Neliubov,  on  gas  poisoning  and  nutation,  261 
Neljubow,  see  Xeliubov. 
Nelumbium,  130,  131 
Nemec,  on  geotropic  perception,  297 
Nencki,  see  Xentskii. 

Nentskii,  on  chlorophyll,  13;  N.  and  Marchlewski, 
on  hemopyrrol,  12;  N.  and  Silber,  on  hemato- 
porphyrin,  11,  12;  N.  and  Zaliesskii,  on  meso- 
porphyrin  and  hemin,  12 
Nepenthes,  37 
Nereunt,  107 

Nettle  (see  also  Urtica),  19,  47 

Neuberg,  on  fermentation  of  pyrotartaric  acid,  206; 
on  photochemical  processes,  34,  286;  N.  and 
Karczag,    on   carboxylase,    etc.,    206;    N.   and 
Kerb,  on  yeast  without  sugar,  206 
Neumeister,  on  isolation  of  peptones,  159;  on  pro- 
teolytic enzymes,  166 
Newcombe,  on  tissue  strains  and  development,  302 
Nickel,  82 

Nicloux,  on  enzymes,  166 
Nicolas,  on  respiration,  210 
Nicotin,  101,  271 
XTictitropic  movements,  320 
Nigrosin,  5 

Niklevskii,  on  hydrogen  bacteria,  51 
Niklewski,  see  Xiklevskii. 
Nile  silt,  92 

Nitrates,  65-69,  70-73,  79,  98,  178 
Nitrification,  in  soil,  67-72 
Nitrifying  bacteria,  48-51,  68,  69,  79 
Xrtrite  bacteria,  69 
Nitrites,  65,  70 
Nitrobacler,  69,  70 

Xitrogen,  assimilation  of,  Pt.  I,  Chap.  Ill,  64-79; 
circulation   of  in  nature,   72—73,   211;  atmos- 
pheric, 64-68;  assimilation  of,  by  bacteria,  78- 
79;  fixation  of,  by  Leguminosce,  etc.,  73-77;  of 
soil,   65-67,   75;  nitrogen   compounds,  assimi- 
lated by  lower  plants,  79;  in  nutrition,  82,  104, 
157,  172,  176,  180,  181,  185,  190,  202,  227;  oxi- 
dation of,  by  calcium  carbide,  73 
Nitrosobacter,  69 
Nitrosococcus,  69 
Nitrosomonas,  43,  69,  70 

Nobbe,  on  buckwheat  without  chlorine,  86;  N.  and 
Hiltner,   on  nitrogen  fixation,  77;  N.,  Schmid, 
Hiltner  and  Hotter,  on  nitrogen  fixation,  77;  N. 
and  Siegert,  on  water-cultures,  272 
Noll,  on  root  bending  and  laterals,  301 
Nordhausen,  on  lateral  roots,  292 
Normal  respiration,  201,'  203 
Norris,  see  Harden  and  N. 
Xucleins,  85,  162,  180,  192,  229,  23c 
Nucleo-proteins,  162,  173,  175,  180 
Xucleoli,  299 
Xucleus,  154 
Nutation,     of    tendrils,     313;    and    poison    gases. 

262 
Xutrient  media,  47,  48,  59-61,  202,  300;  salts  and 
reproduction,  332 


INDEX 


353 


Nutrition,  of  fungi,  79.  1731  compared  to  poisoning, 

227 
Nutting,  Applied  optics.  22 


O 


Oak,  leaf-mould  from  leaves  of,  67 

Oat  (see  also  Avena),  73,  74.  88,  94.  96,  13".  T59. 
161,  172 

Ohno,  on  gas  excretion  in  Xclumbium,  130 

Oil,  29,  150,  166,  332;  to  exclude  oxygen,  etc.,  13s. 
259;  linseed,  xxviii;  mustard.  166 

Omelianski,  see  Omelianskii. 

Omelianskii,  on  sulphur  bacteria,  49;  on  nitrifying 
organisms  of  soil,  49,  69;  on  nitrifying  organ- 
isms, 69;  on  bacteriological-chemical  methods, 
210.     (See  also  Vinogradskii  and  O.) 

Omeliansky,  see  Omelianskii 

Onion  (see  also  Allium),  180 

Oogonium,  332 

Oppenheimer,  Fermente,  163,  201 

Optimum  temperature,  253,  254 

Opuntia,  319 

Organic  acids,  188;  compounds,  xxvii,  xxviii;  forma- 
tion of,  and  in  soil,  67 ;  nutrition  of  green  plants 
by,  36-39;  assimilation  of  energy  from,  by 
plants  without  chlorophyll,  42-47;  transfer  of, 
148-150 

Orlov,  92 

Ortho-dioxy-benzene,  223 

Osborne,  on  plant  proteins,  155,  157,  158 

Osmometers,  ill,  112,  243 

Osmosis,  104,  109 

Osmotic  membranes,  104,  no,  113,  114,  119, 
122;  pressure,  no,  in,  113;  117.  118, 119,  123, 
185;  of  cells,  114,  123;  values,  116,  117;  of  bog 
water,  101;  of  cell  sap.  123 

Ostwald,  Willi.,  General  chemistry,  115;  Theoret- 
ische  Chemie,  220;  on  enzymes,  xxviii,  xxx 

Ostwald,  Wolfg.,  on  colloids,  ill 

Otocysts,  256 

Otto  and  Kooper,  on  poisons  in  soil,  101 

Overton,  E.,  on  absorption  of  dyes,  120;  on  lipoids 
and  narcosis,  183 

Overton,  J.  B.,  on  ascent  of  sap  and  transpiration, 
145,  147 

Oxalis,  249,  319 

Oxidases,  xxix,  166-168,  223,  225 

Oxidation  (see  also  combustion  and  respiration), 
xxviii,  xxix,  43,  48,  104,  189,  198,  199,  201, 
208,  219,  220,  224,  230 

Oxidizers,  207 

Oxidizing  enzymes,  166 

Oxygen,  xxviii,  1-5,  16,  18,  49,  67,  101-105,  107, 
150,  168,  172,  173,  182,  185,  190,  191,  198,  199, 
203,  204,  208,  209,  212,  214,  216,  218-220,  254, 
258;  influence  of  oxygen  content  of  air  on 
growth,  etc.,  258-260 

Oxygenases,  144,  168 

Oxymethylene,  29.  30 

Ozone,  58 


Palisade  parenchyma,  287,  288 

Palladin,   on   etiolated   leaves  and   on  chlorophyll 
formation  and  solution  concentration,   17;  on 


plant  proteins,  158;  on  respiration  enzymes, 
163;  on  reductase,  168,  207;  on  enzyme  action 
in  killed  plants,  169;  an  anaerobic  protein  de- 
composition, 172;  on  respiration'andinitrogen- 
ous  substances,  180,  229;  on  light,  protein 
formation  and  respiration,  181;  on  carbohy- 
drates from  protein,  185;  on  respiration,  204, 
223;  on  respiration  pigments  and  water  in 
respiration,  207,  225;  on  temperature  and 
respiration,  210,  211;  on  respiration  and  poi- 
soning, 213,  226;  on  respiration  and  growth, 
214;  on  carbohydrates  and  asphyxiation,  221; 
on  respiration  in  Chlorothecium,  222;  on  oxygen 
and  respiration,  222;  on  respiration  chromo- 
gens,  222;  on  respiration  as  fermentation,  225, 
226;  on  respiration  of  green  and  etiolated 
leaves,  228,  229,  285;  of  growth  and  ash  of 
etiolated  leaves,  285;  on  transpiration  and 
configuration,  285;  P.  and  Iraklionov,  on  oxi- 
dases, etc.,  167;  P.  and  Komleff,  on  respiration 
and  solution  concentration,  212;  P.  and 
Kostychev,  on  methods  for  studying  gas  ex- 
change, 4,  215;  on  anaerobic  respiration,  221, 
224;  P.  and  Lvov,  on  respiration  chromogens 
and  alcoholic  fermentation,  207,  226;  P.  and 
Sabanin,  on  fermentation  of  lactic  acid,  207; 
P.,  S.  and  Lochinovskaia,  on  respiration.  207; 
P.  and  Stanevich,  on  respiration  and  lipoids, 
184;  P.  and  Tolstaia,  on  respiration  chromo- 
gens, 223 

Palladine,  see  Palladin. 

Palladium  black,  199 

Pancreatic  juice,  13 

Panicum,  281,  297 

Pantanelli,  on  conditions  affecting  photosynthesis. 
26 

Papaver  (see  also  poppy),  159 

Papilionacem,  94 

Papillae,  contact,  of  tendrils,  313 

Papin's  digester,  57 

Paragalactan,  185 

Paraldehyde,  213 

Parasites,  47,  86,  301;  parasitic  fungi,  126,  301,  302 

Paratonic  movements,  of  variation,  316-320 

Parchment  paper,  112,  121,  159 

Parenchyma,  142,  287,  288,  318 

Paris,  324 

Parthenogenesis,  334 

Pasteur,  life  and  work  of,  xxix;  on  bacteria  cultures 
and  fermentation,  43,  200,  201,  221;  on  sterili- 
zation, 53,  54;  on  anthrax,  182;  on  yeast  with- 
out oxygen,  203 ;  on  purification  of  yeast  cul- 
tures, 205;  on  acetic  acid  fermentation,  230; 
on  oxygen-free  cultures,  259;  Pasteur  flask,  54, 
60 

Pathogenic  bacteria,  182,  183 

Pavetta,  78 

Pea,  73.  74.  76,  88,  94.  137.  158,  159.  165.  184, 
219,  224,  253,  262,  281,  285,  312 

Peach,  187 

Pelargonium,  211 

Pelletier  and  Caventou,  on  chlorophyll,  6 

Penetration,  of  cells  and  stone  by  fungi,  etc.,  126 

Penicillium,  79,  123,  168,  173 

Pentoses,  162 

Peptones,  43,  69.  156,  158,  159,  161,  173.  271, 
300 


354 


INDEX 


Perception,   of   contact   stimuli,   313,    319;   of  geo- 
tropic  stimuli,  297;  of  phototropic  stimuli,  281 
Periderm,  of  potato  tuber,  106 
Periodic  movements,  of  floral  parts,  291 
Periodicity,  in  transfer  of  carbohydrates,   150;   in 

transpiration,  138;  in  growth,  27s 
Permeability,  of  protoplasm,  119,  120,  270,  271,  318 
Peroxidases,  167,  223,  225,  226 
Peroxides,  167 
Peru,  323 

Pettenkoffer  tubes,  215,  216 
Petri  dish,  61 
Petrograd,  256,  257 
Petrolatum,  107 

Petruschewsky,  see  Petrushevskaia. 
Petrushevskaia,  on  temperature  and  enzyme  action, 

169 
Pfannenstiel,  see  Willstatter  and  P. 
Pfeffer,  Osmotische  Untersuchungen,  112,  113;  on 
absorption  of  aniline   dyes,   119;   on  selective 
absorption,    121;    on   proteins   and   asparagin, 
171;   on   respiration,   201;   on   respiration  and 
wounding,  213;    on  intramolecular  respiration, 
221;    plant   physiology,    4,    250;    on   day   and 
night  movements  of  floral  parts,  291,  316;  on 
pressures  exerted  by  growth,  303,  304,  305;  on 
contact  sensibility,  311;  Pfeffer  clinostat,  293; 
osmotic  cell,  112 
Pfingstberg,  55 
Pfliiger,  on  respiration,  201 
Phaeophytin,  13 
Pharbilis,  312 
Phaseolus  (see  also  bean),  148,  188,  247,  263,  277, 

281,  311 
Phenol,  58.  205 

Phenol-phthalein,  101  , 

Phenological  observations,  255,  256 
Phenyl-alanin.  160,  161 
Phloem,  149,  150 
Phosphates,  91,  202,  214,  227 
Phosphatides,  85;  and  lipoids,  183-185 
Phosphorite,  94-96 
Phosphorus,  3,  67,  82,  8s,  89,  90,  93.  104.  154.  162, 

174.  181,  183,  285 
Photographic  paper,  290 
Photolepsy  (see  also  Lichtgenuss),  289 
Photometric  sensitiveness,  276 

Photosynthesis,  3,  4;  r61e  of  chlorophyll  in,  18,  19; 
role  of  carotin  in,  19;  products  of,  28-32;  in- 
fluence of  conditions  on,  34-36;  and  light,  21, 
28,  32-36,  212;  and  asparagin,  171;  and  cane 
sugar,  186;  and  energy  circulation,  232;  and 
etiolation,  283-285;  and  development,  284, 
288 
Phototropism,  275,  276,  279,  280,  297;  of  flowers, 
278;  of  leaves,  277,  278;  of  moulds,  279;  of 
roots,  279;  of  tendrils,  313 
Phycocyanin,    21;   phycoerythrin,    20,    21;   phyco- 

phaein,  21 
Phyllocadus,  283 
Phyllocyanin,  11 
Phyllophyllin,  13 
Phylloporphyrin,  11-13 
Phylloxanthin,  1 1 

Phylogeny,  of  plants,  302;  of  twining  habit,  314 
Physiography,  274 
Physiological  dryness,  of  soil,  101 


Physiology,  xxvii,  274;  the  cell  as  physiological  unit, 

154 

Phytin,  185 

Phytoalbumins,  158 

Phytoglobulins,  158,  159 

Phytyl,  in  chlorophyll  molecule,  8,  9,  13 

Picea,  324,  325 

Pickering,  on  toxins  in  soil,  99,  10 1 

Pieters,  on  tissue  strains  as  stimuli,  302 

Pigments  (see  also  respiration  pigments),  21,  119, 
120;  accompanying  chlorophyll,  19-21;  comple- 
mentary, 26 
Pilobolus,  279,  291 

Pine,  27,  241,  254 

Pisum  (see  also  pea),  165,  184,  253,  281 

Pith,  150 

Pitsch,  on  nitrate  fertilizers,  72;  P.  and  van  Haarst, 
on  nitrate  fertilizers,  72 

Plagiotropism,  293 

Plant  lice,  86 

Plasmodium,  154 

Plasmolysis,  114-116,  121,  242,  244 

Plaster,  of  Paris,  44,  125,  146,  303,  304 

Plastic  materials,  149;  transfer  of,  133 

Plastiline,  135 

Plastin,  192 

Platinic  chloride,  xxix,  90,  163 

Plimmer,  on  proteins,  155,  162;  P.  and  Scott,  on 
phosphoproteins,  162 

Podsol,  95,  96 

Poisoning,  compared  to  nutrition,  227 

Poisons,  182,  213;  and  geotropism,  297;  and  nuta- 
tion, 261,  262;  and  respiration,  226,  227;  and 
starch  formation,  38;  for  enzymes,  170 

Polarity,  329 

Pollacci,  on  aldehyde  in  plants,  30 

Pollen,  334;  chemotropism  of  pollen  tubes,  333 

Polovtsov,  on  respiration  of  fatty  seeds,  215 

Polygonum,  187,  282,  311 

Polymerization,  286 

Polymorphysm,  of  hay  bacillus,  300 

Polypeptides,  161,  176 

Polyporus,  186 

Polzeniusz,  see  Godlewski  and  P. 

Poppy,  159,  I9i,  215 

Pores,  diffusion  through,  108,  109 

Posternak,  on  formation  of  oxymethyl-phosphoric 
acid  in  leaves,  31 

Potassium,  73,  82,  88-90,  92,  104,  285;  carbonate, 
46;  chloride,  84,  85;  chloroplatinate,  90;  citrate, 
117;  dichromate,  15,  23,  25;  ferrocyanide,  91, 
112;  hydroxide,  4,  6,  28,  53,  156,  179,  216. 
259;  iodide-iodine  solution,  28;  myronate,  166; 
nitrate,  82,  84,  113-117,  118,  122,  123,  208,  242; 
permanganate,  25,  58;  phosphate,  48;  silicate, 
46;  sulphate,  87,  117,  118,  166 

Potato,  87,  ior,  142,  157,  182,  185,  214,  28r,  283, 
325,  326 

Potonie,  on  morphology  and  paleontology,  302 

Pouget  and  Chouchak,  on  "soil  sickness,"  101 

Prantl,  on  guttation,  140 

Prazmovskii,  on  bacteria  of  root  tubercles,  76 

Prazmowski,  sec  Prazmovskii. 

Precipitation  membranes,  112,  119,  243 

Precipitin,  in  rabbit,  331 

Presentation  time,  in  geotropic  response,  294 

Preserves,  and  sterilization,  53 


INDEX 


355 


Pressure  (see  also  negative  pressure),  in  tissues,  145. 
251;  as  stimulus,  303,  304;  developed  in  grow- 
ing roots,  304,  305;  negative,  in  stems,  106; 
pressure,  wounding  and  traction,  influence  of, 
on  growth  and  configuration,  300-305 

Prianischnikow,  see  Prianishnikov. 

Prianishnikov,  on  fertilizers,  94,  95,  96;  P.  and 
Shulov,  on  asparagin  formation,  177 

Priestley,  on  gas  exchange,  2,  3;  on  photosynthesis, 
210 

Pringsheim,  E.,  Reizbewegungen,  253,  311,  312, 
316 

Privet,  36,  221 

Pro-chromogen,  223 

Profile  position,  of  leaves,  278 

Prolin,  160 

Propagation,  vegetative,  334 

Protamins,  162 

Proteinaceous  seeds,  190 

Proteins,  155-163;  determination  of,  156,  157;  struc- 
ture of,  150-163;  synthesis  of,  31,  38,  85,  170, 
171,  178-181,  189;  transformations  of,  173; 
transfer  of,  149;  hydrolysis  and  decomposition 
of,  159-161,  166,  169,  170-174,  175-179,  185; 
191,  200,  227;  nitrogenous  products  of,  175- 
178;  in  leaves,  284;  in  Plasmodium,  154;  in 
sap,  142;  in  seeds  and  seedlings,  184,  191,  192; 
in  soil,  67;  in  root  tubercles,  75,  76;  with 
magnesium,  85;  in  respiration,  227—229 

Proteolytic  enzymes,  166,  176,  185 

Proteose,  158 

Protochlorophyll,  18 

Protonema,  luminous,  27 

Protophyllin,  13,  14 

Protoplasm,  alkalinity  of,  189 

Protoplasmic  membranes,  106,  119 

Prunus,  35 

Prussian  blue,  179 

Psalliota,  222 

Pteris,  302 

Pulling  and  Livingston,  on  water  relations,  272 

Pulvinus,  of  Mimosa,  317,  318 

Pumice,  82 

Pumpkin,  217,  313 

Pure  cultures,  43,  56;  of  root-tubercle  bacteria,  76; 
of  yeast,  59 

Purievich,  on  photosynthesis,  25;  on  transfer  of 
organic  materials,  150;  on  decomposition  of 
organic  acids  in  plants,  188,  210;  on  respiration 
ratio,  210;  on  respiration,  213 

Puriewitsch,  see  Purievich. 

Purin,  162,  163;  bases,  175 

Pyrenees,  324 

Pyrimidin,  162,  163 

Pyrogallol,  4,  31,  226,  259 

Pyrrol,  12,  160 

Pyrrophyllin,  13 


Quartz,  82,  167 
Quinin,  38,  226 
Quinone,  199,  225 


R 

Rachis,  317 

Radiant  energy,  14-17,  138, 


190 


Radium,  169 

Raffinose,  17 

Rajlesiacew,  47 

Ranunculus,  265 

Raphides,  299 

Rapp,  see  Albert,  Buchner  and  R. 

Raulin,  on  nutrient  media,  46,  87 

Reaction  time,  294 

Receptive  movements,  316 

Reducer.  207 

Reductase,  168,  207,  208,  226 

Reduction,  168,  207,  208,  225 

Reductor,  207 

Reed,  on  transpiration  and  chemicals,  139.     (See 

also  Schreiner,  R.  and  Skinner.) 
Regnault,  calorimeter,  219;  on  carbon  assimilation, 

3 

Regulation,  of  enzyme  action,  170 

Reid,  see  Livingston,  Britten  and  R. 

Reinhardt,  and  Sushkov,  on  starch  formation,  38. 

(See  also  Zaliesskii  and  R.) 
Reinitzer,  on  respiration,   210.      (See  also   Curtius 
and  R.) 

Reinke,    on    chlorophyll    decomposition,    greening,  ' 
photosynthesis   and   light,    23;    on    photosyn- 
thesis, 30,  154;  Theoretische  Biologie,  154 

Renard,  see  K16ment  and  R. 

Renner,  on  osmotic  solutions,  113;  on  transpira- 
tion, etc.,  1,  5,  138,  145,  147 

Reproduction,  331-336;  and  development,  322-336 

Reserve  materials,  157,  158,  162,  185,  190,  229 

Resin,  106 

Respiration  (see  also  combustion,  oxidation),  xxviii, 
38,  104,  168,  169,  171,  182,  184,  197,  198,  203, 
210-215,  258,  259,  284;  apparatus  for  measur- 
ing, 215-217;  anaerobic,  220-222;  and  fer- 
mentation, Pt.  I,  Chap.  VIII,  198-232;  forma- 
tion of  water  by,  217-218;  liberation  of  heat 
by,  218-220;  materials  consumed  in,  227-230; 
special  cases  of,  230-232;  chromogens,  188, 
222-223,  224,  226;  enzymes,  222-223,  225,  226, 
229,  230;  pigments,  207,  233-226;, ratio,  204, 
210,  212-214,  219,  220 

Resting  cells,  155;  period,  257 

Reversibility  of  enzyme  action,  168 

Rhone  river,  55 

Rhizomes,  327 

Rhodophyllin,  13 

Rhus,  166,  223 

Rhythm,  275 

Ribbert,  on  transplantation  and  hormones,  329 

Ricinus,  183,  191 

Richter,  A.,  see  Rikhter. 

Richter,  O.,  on  microchemical  analysis,  90;  on 
poison  gases  and  geotropism,  297 

ki. -smaller,  on  ash  analyses,  89,  90 

Rigg,  on  bog  water,  101 

Rigidity,  and  tissue  strains,  251 

Rijn,  van,  on  glucosides,  181,  187 

Rikhter,  A.,  on  photosynthesis  and  light,  25;  on 
death  by  freezing,  211;  on  zinc  and  copper  in 
Aspergillus  nutrition,  87 

Ripening,  of  potato  tubers,  185 

Rischavi,  on  respiration,  214 

Ritter,  on  denitrifying  organisms,  79;  on  giant 
cells  of  Mucor,  270,  300 

Robinia,  27,  77 


356 


INDEX 


Rochea,  124,  263,  264 

Roots,  38,  76,  89,  97.  121,  125,  130,  132,  244,  249, 
250,  274.  279,  298,  300,  301,  304,  305;  root  ex- 
cretions, 83,  99,  125,  126;  hairs,  270;  pressure, 
140,  141,  146,  147;  pole,  329;  tubercles,  75 

Rootstocks,  327 

Rose,  see  Crocker,  Knight  and  R. 

Rosenbloom,  on  lipins,  183;  R.  and  Gies,  on  lipins, 
183 

Rubber  membrane,  in 

Rubiacece,  77 

Rubidium,  82,  87 

Rubus,  263 

Rudolf,  see  Czapek,  and  R. 

Rumex,  36,  101 

Rupe,  on  respiration  chromogens,  223 

Russell,  on  soils,  etc.,  73,  84,  92,  99 

Rust,  of  grains,  86 

Rye,  88,  96,  173 

Rysselberghe,  van,  on  protoplasmic  permeability, 
122 


Sabashnikova,  see  Karapetova  and  S. 

Sabanin,  on  silica  in  seeds,  86.  (See  also  Palladin 
and  S.;  Palladin,  S.  and  Lochinovskaia.) 

Sabachnikoff,  see  Sabashnikova. 

Sabinin,  see  Sabinin. 

Saccharase,  16s 

Saccharomyces  (see  also  yeast),  44-46,  201,  202,  205 

Saccharose  (see  also  cane  sugar),  17,  38,  46,  113, 
114,  165,  168,  181,  186,  202 

Sachs,  on  leucophyll,  17;  on  light  and  photosyn- 
thesis, 23;  on  products  of  photosynthesis,  28; 
on  ammonia  assimilation,  65;  on  water  trans- 
fer, 143;  on  transfer  of  organic  substances,  149; 
on  elongation,  temperature  and  light,  247;  on 
grand  period  of  growth,  247;  on  temperature 
and  germination,  253;  on  light  and  develop- 
ment, 281;  on  correlations,  "Stoff  und  Form," 
etc.,  330;  Abhandlungen,  331  ;  S.  and  Naga- 
matsz,  on  starch  formation  and  wilting,  36 

Sachsse,  Agrikulturchemie,  137;  on  asparagin,  177 

Safranin,  120 

Sagittaria,  266 

Salts,  absorbed,  104 

Sambucus,  122 

Sap,  analyses  of,  141,  142;  ascent  of,  145,  extrusion 
of,  140;  sap  pressure,  140 

Saponification,  166 

Saposchnikoff,  see  Sapozhnikov. 

Sapozhnikov,  on  photosynthesis  and  proteins,  31, 
38;  on  starch  formation  from  sugar,  and  trans- 
fer of  organic  substances,  38,  149,  150 

Saprophytes,  47 

Saratov,  92 

Saturation  deficit,  of  plants,  138 

Saussiire,  de,  on  gas  exchange.  2,  3;  on  respiration, 
210 

Sawdust,  12 

Seal,  see  Urbain,  S.  and  Feige. 

Schenck,  on  lianas,  312 

Schiefferdecker,  on  hormone  hypothesis,  330 

Schiff's  reagent,  30 

Schimper,  on  chlorophyll  formation,  17;  on  pnoto- 
synthesis    and    sodium    chloride,    36;    on  salt 


assimilation,  90;  on  cypress  knees,  131;  Plant 
geography,  101,  131;  on  calcium  oxalate  in 
leaves,  178;  on  strand  plants  and  transpiration, 
272 

.Schisoslega,  27 

Schloesing,  see  Schlosing. 

Schlosing,  on  ammonia  assimilation  by  leaves,  65, 
72;  on  ammonia  absorption  by  soil,  66;  on 
nitrification  in  soil,  67;  on  transpiration  and 
salt  content,  147,  271,  273;  on  ash  of  leaves, 
285;  S.  and  Miintz,  on  nitrification  in  soil,  68 

Schmid,  see  Nobbe,  S.,  Hiltner  and  Hotter. 

Schmidt,  on  light  as  disinfectant,  292 

Schbnbein,  on  formation  of  ammonium  nitrite,  72 

Schreiner,  Reed  and  Skinner,  on  toxins  in  soil,  99; 
S.  and  Shorey,  on  toxins,  etc.,  in  soil,  67,  99; 
S.  and  Skinner,  on  nitrogenous  substances  of 
soil,  67 

Schroder,  on  bleeding,  142 

Schroeder,  see  Schroder. 

Schryver,  on  photosynthesis  and  formaldehyde,  18 

Schulow,  see  Shulov. 

Schulze,  E.,  on  protein  decomposition,  172,  175; 
on  glutamin,  175;  on  physiology  of  seedlings, 
176;  on  phosphatides,  184;  on  chemistry  of 
cell  walls,  185;  on  identification  of  cane  sugar, 
186;  S.  and  Frankfurt,  on  lecithin  in  plants, 
184;  on  cane  sugar  in  plants,  186:  S.  and 
Likiernik,,  on  lecithin  in  seeds,  184;  S.  and 
Steiger,  on  lecithin  in  plants,  184;  S.,  Steiger 
and  Bossard,  on  nitrogenous  substances  in 
plants,  172;  S.,  Steiger  and  Maxwell,  on  chem- 
istry of  cell  walls,  185;  S.  and  Umlauft,  on 
chemistry  of  germination,  191;  S.  and  Winter- 
stein,  on  protein  decomposition,  175;  on  phos- 
phatides, 184;  on  lecithin  in  plants,  184 

Schulze,  F.,  on  infection  from  air,  53 

Schunck  and  Marchlewski,  on  chlorophyll,  n,  12, 
13 

Schiitzenberger's  reagent,  5 

Schiitt,  on  phycophaein,  21 

Schwendener,  on  ascent  of  sap,  143,  S.  and  Krabbe, 
on  turgidity  and  elongation,  244 

Scott,  see  Plimmer  and  S. 

Scyphanthus,  311 

Sea-water,  49,  50,  254 

Seber,  on  blood  and  descent,  331 

Sedum,  211 

Seedlings,  190,  219,  220,  229 

Seeds,  metabolism  of,  166,  190,  229,  286;  germina- 
tion of,  189-192 

Selective  culture,  43 

Selenium,  82,  168 

Self-sterility,  334 

Seliwanoff,  on  chemistry  of  potato  sprouts,  186 

Sempervivum,  188,  269,  270,  282,  301 

Senebier,  Physiologie  vegetale,  2;  on  carbon-dioxide 
absorption,  2 

Sensitiveness,  phototropic,  280 

Sensitive  plant  (see  also  Mimosa),  xxx,  316 

Sensitizer  action  of  chlorophyll,  19 

Septa,  osmotic  (see  also  osmotic  membranes).  104 

Serin,  159,  161 

Serumtherapy,  183 

Shade  plants,  289,  290,  leaves,  287 

Shantz,  see  Briggs  and  S. 

Shears,  double,  144 


INDEX 


357 


Shive,  salt  nutrition,  water  culture,  etc.,  83,  84,  139 

Shoot-pole,  329 

Shorey,  see  Schreiner  and  S. 

Shortening,  in  growth,  250 

Shreve,  Edith  B.,  on  saturation  deficit,  etc.,  138. 
(See  also  Livingston  and  S.) 

Shulov,  see  Prianishnikov  and  S. 

Sieber,  see  Xentskii  and  S. 

Siegert,  see  Nobbe  and  S. 

Sieve,  tubes,  148 

Silber,  see  Ciamician  and  S. 

Silicon,  82,  8s,  88,  89,  92,  285;  and  lodging  of  grain, 
86;  in  Rochea,  263 

Silver,  82;  salts  of,  decomposed  by  red  light  in 
presence  of  chlorophyll,  19 

Sinapis  (see  also  mustard),  253,  279 

Sinigrin,  166 

Sisymbrium,  276 

Skinner,  see  Schreiner,  and  S.;  Schreiner,  Reed  and 
S. 

Smirnoff,  on  respiration  and  wounding,  213,  222 

Smolenski,  on  phosphatides,  183.  (See  also  Win- 
terstein  and  S.) 

Soda  lime,  126 

Sodium,  82,  28s;  chloride,  ill,  118,  121,  124,  158, 
242,  271;  citrate,  271;  hydroxide,  108,  109, 
162;  nitrate,  96,  121;  phosphate,  91;  selenite, 
168,  170;  sulphate,  111;  sulphite,  5,  58 

Sonngen,  on  methane  bacteria,  51 

Soil,  92-101;  nitrogen,  65-67;  nitrification  in, 
67-72;  acidity  of,  96;  bacteria,  etc.,  of,  43,  55, 
69,  79,  98,  99,  101,  183,  202;  action  of  root  ex- 
cretions on,  125,  126;  organic  matter,  67;  oxy- 
gen of,  198;  physiological  dryness  of,  10 1 ;  salts 
in,  93,  273;  of  moors,  198;  sterilized,  72-75,  98; 
soil  science,  10 1 ;  soil  sickness,  99,  274;  tempera- 
ture, 254,  274;  toxins,  99,  273;  moisture  and 
growth,  263 

Solanin,  182 

Solatium,  20,  123,  281 

Soldanella,  253 

Solids,  104 

Solute,  no 

Solution,  no,  115,  118,  119,  123;  soil,  75,  92,  101, 
125,  126 

Solvent,  no 

Sommer,  see  Bredig  and  S. 

Sorby,  on  chlorophyll,  etc.,  7 

Sorbose,  31 

Sorbus,  123 

Sbrensen,  on  cell  acidity,  etc.,  189 

Spalding,  on  traumatropism,  301 

Spallanzani,  on  spontaneous  generation,  52;  on 
sterilization.  53 

Spectrum  (see  also  light),  and  metabolism,  9,  10, 
14,  21,  24,  29,  138;  and  growth,  280,  281,  288 

Sperms,  162,  332 

Spharocoaits,  209 

Spirillum,  259 

Splenic  fever,  182 

Spoehr,  on  photosynthesis,  31;  on  respiration,  etc., 
212 

Spontaneous  generation,  S2-S4I  movements,  3r6 

Sporangia,  bursting  of,  no 

Sporangiophores,  260,  279 

Spree  river,  55 

Spruce,  325,  326 


Squash,  253 

Stab  cultures,  61 

Slachys,  327 

Stahl,    on    leaf    pigments,    16;    on    bright-colored 

leaves,  21;  on  stomata,  photosynthesis,  starch 

formation  and  excess  of  salts,  36;  on  mycorhiza, 

97;  on  injurious  effects  of  microorganisms,  98; 

on  cobalt -chloride  paper,  etc.,  136;  on  compass 

plants,  278 
Stanevich,  see  Palladin  and  S. 
Stanewitsch,  see  Stanevich. 
Starch,  xxii,  28,  36,  38,  87,  149,  150,  164,  165,  185, 

187,  189,  190,  210,  211,  271,  272.  284,  33s,  336; 

heat  of  combustion  of,  50,  220;  hydrolysis  of, 

164,  219;  in  root  tubercles,  76;  starch  grains, 

297,  299;  starch  sheath,  149 
Starchy  seeds,  190 
Starling,  on  hormone  action,  329.      (See  also  Bayliss 

and  S.,  Claypon  and  S.) 
Statoliths,  297 
Stebler,  on  leaf  growth,  249 
Stefan,  on  diffusion  in  solution,  124 
Stegmann,  see  Winterstein  and  S. 
Steiger,  see  Schulzeand  S.;  Schulze,  S.  and  Bossard; 

Schulze,  S.  and  Maxwell. 
Stems,    metabolism,    etc.,    of,    89,    132,    143,    147; 

growth,  etc.,  of,  244,  249,  311,  312 
Stephenson,  in  anecdote,  32,  33 
Sterilization,   52-54,   56—58,   291;  and  disinfection, 

56-58 
Sterilizer,  dry  air,  56;  steam,  57 
Stich,  on  reproduction  and  wounding,  213 
Stiles,  see  Jorgensen  and  S. 
Slipa,  264 

Stokes,  on  chlorophyll,  7 
Stoklasa,  on  lecithins,  etc.,  184;  S.  and  Ernest,  on 

root  excretions,  126;  S.,  Ernest  and  Chocensky, 

on  glycolytic  enzymes,  221;  S.  and  Zdobnicky, 

on  photosynthesis  without  chlorophyll,  31 
Stoll,  see  Willstatter  and  S. 
Stomata,  35,  36,  105,  107,  108,  109,  130,  136,  264, 

284 
Storage  organs,  327,  328 

Strains  (see  also  traction),  in  tissues,  251,  302,  318 
Strasburger,  on  water  transfer,  143 
Streak  culture,  61 
Streaming,  and  diffusion,  105,  107 
Slrelilizia,  29 
Streptococcus,  209 
Stress  (see  also  strains,  traction;,  in  tissues.   251; 

in  water  columns,  146 
Strontium,  82;  nitrate  and  sulphate,  91 
Stutzer,  on  proteins,  157 
Suberization,  107 
Sugar,  31,  38,  142,  149,  179.  192,  221,  222,  226,  242, 

270,  284,  299,  300,  330 
Sugar-cane,  32,  88 

Sulphite  bacteria,  52;  sulphur  bacteria,  49-51 
Sulphur,  85,  91,  93,  104,  204,  285;  circulation  of,  in 

nature,  231;  oxidation  of,  by  bacteria,  49 
Sundew,  37 
Sunflower  (see  also  Helianlhus),  138,  165,  184,  191, 

303,  335.  336 
Sunlight,  32,  232,  287,  289 
Surface  tension,  of  gas  bubbles  in  vessels,  144 
Suschkoff,  see  Sushkov. 
Sushkov,  see  Reinhard  and  S. 


358 


INDEX 


Swamp  water,  101 

Sylphium.  278 

Symbiosis,  in  root  tubercles,  75 

Sympodium,  268 

Synthesis,  of  proteins,  170,  171,  178,  179,  181 

Syntonins,  158 

Syringa,  165,  262,  263 

Szucs,  on  protoplasmic  permeability,  etc.,  27 r 


Tannin,  120,  149,  165,  143 

Taphrina,  302 

Tappeiner,  on  fluorescence,  19;  T.  and  Jodlbauer, 

on  fluorescence,  292 
Taraxacum,  251,  268,  269 
Taxodium,  9,  1 1 
Taxus,  27 
Teasel,  276 

Temperature,  and  metabolism,  xxviii,  15.  18.  34,  35. 
38,  44,  113,  122,  123,  160,  167,  169,  188,  200, 
210,  218,  253,  255,  256,  274;  and  growth,  etc., 
182,  253-258,  275,  286,  316,  332 
Tendrils,  279,  312,  313 
Tetanus,    182,    183 
Tetrose,  21 

Thallium,  82;  chloride,  91;  sulphate,  91 
Theobromin,  176 
Thermochemistry,  219,  220 
Thermostat,  210 

Thoday,  on  photosynthesis  and  respiration.  33 
Thomas  slag,  93.  94 
Thorns,  268 

Thudicum,  on  phosphatides,  183 
Thunderstorms,  72 
Thuya,  16 
Thymol,  156,  166 
Tieghem,  van,  culture  cell,  59 
Tilia  (see  also  linden),  27 
Timiriazeff,  see  Timiriazev. 

Timiriazev,  anecdote   concerning  Boussingault ,   3; 
on  chlorophyll,  6;  on  photosynthesis,  14,  23,  24, 
26,  29,  34;  on  protophyllin,  14 
Tin,  82 

Tissue  strains,  302 
Titanium,  82 
Tobacco,  32,  88,  101,  271 
Tolstaia,  see  Palladin  and  T. 
Tolstaja,  see  Tolstaia. 
Toluol,  184 
Tomato,  20 
Tonie,  119 

Top-fermentation,  205 
Tottingham,  on  salt  nutrition,  water-calture.  etc., 

84,  139,  272 
Toxins,  alkaloids  and  antitoxins,   181-183;  toxins, 

'  99,  101,  182,  183,  273.  274 
Tracheae,  304 
Tracheides,  241 

Traction  (see  also  strains,  stress),  251,  302,  303; 
traction,  wounding  and  pressure,  influence  of, 
on  growth,  300-305 
Tradescantia,  115 
Tragopogon,  278,  279 
Transeau,  on  bog  water,  101 

Transfer,  of  organic  substances,   130,   148-15";  of 
water,  143 


Transformations,  material,  Pt.  I,  Chap,  VII,  I54~ 

192 
Transpiration  stream,  134-148;  transpiration,  133, 
134,  136-139.  ML  147,  148.  263,  271.  273.  274. 
285;  and  growth,  263,  270,  272,  273 
Transpiring  power,  136 
Transplantation.  329.  334-336 
Traube's  artificial  cell,  243 
Traumatropism,  300,  301 
Treboux,  on  starch  formation.  38 
Treub,  on  hydrocyanic  acid  in  plants,  179 

Trier,  see  Winterstein  and  T. 

Tri folium,  316 

Triolein,  215 

Tripsin,  154 

Triticum  (see  also  wheat),  159,  221,  253 

Trommsdorff,  on  yeast  killed   without  injuring  en- 
zymes, 169 

Tromso,  290 

Tropasolin,  120 

Tropaolum,  267,  268 

Tropisms,  316 

True,  on  distilled  water,   83;  T.  and  Bartlett,  on 
salt  excretion,  etc.,  83 

Truffles,  331 

Trusov,  on  organic  matter  of  soil,  67 

Tryptophan,  13.  156,  160,  161 

Tswett,  on    chlorophyll,    T,    on    chlorophylline,    7; 
on  brown  alga  pigments,  21 

Tubercles,  root,  75 

Tubers,  325,  326 

Turgidity,  242,  244,  270,  271,  318,  320 

Turnip  (see  also  Brassica),  70 

Turpentine,  184 

Tussilago,  287 

Twiners,  and  other  climbers,  Pt.  II,  Chap,  IV,  311- 
315;  twiners,  282 

Tyndall's  solution,   15 

Typhus  bacteria,  291 

Tyrol,  325 

Tyrosin,  156,  160,  161,  166,  171-173.  !"5.  177 


U 


Ulbricht,  on  bleeding,  142 

Ultra-violet  light,  15,  3L  287,  292.  330 

Viva,  38 

Umlauft,  see  Schulze  and  U. 

Urbain,  Seal  and  Feige,  on  light  as  disinfectant,  292 

Urea,  xxviii,  122,  171,  271 

Urobilin,  12 

Ursprung,  on  cohesion  of  water,  146 

Urtica  (see  also  netrle),  141 

Urushiol,  223 

I'stilago,  302 


V 


Vaccination.  182 

Vacuole,  115 

Valin,  160,  175 

Vallery-Radot,  Life  of  Pasteur,  xxix 

Yallola,  333 

Van  Rysselberghe,  see  Rysselberghe,  van. 

Van  Tieghem,  see  Tieghem,  van. 

Van't  Hoff,  see  Hoff,  van't. 


INDEX 


359 


Variation,  movements  of,  Pt.  II,  Chap.  V,  316-320; 
autonomic  movements  of,  316;  paratonic  move- 
ments of,  316-320 

Variegated  leaves,  178 

Vaucheria,  331,  332 

Yerbastiim,  276 

Verbena,  276 

Verworn,  on  conditional  control,  xxxi;  General 
Physiology,  154 

Vesque,    on    absorption     and     transpiration,     136 

Vessels,  gas  in,  144;  movement  of  sap  in,  146; 
transmission  of  pressure  in,  145;  negative  pres- 
sure in,  106,  132,  133.  144 

Vetch  (see  also  Vicia),  19.  157.  159,  280 

Vicia  (see  also  Vetch),  lor,  159,  162,  174,  225,  226, 
248,  249,  276,  281 

Vienna,  289,  290 

Ville,  on  chlorophyll  formation  and  soil  fertility,  16 

Vinegar,  231 

Vines,  on  enzymes  of  Nepenthes,  37;  on  light  and 
leaf  growth,  284;  V.  and  Green,  on  proteins 
of  Asparagus,  158 

Vinogradskii,  on  nitrifying  organisms,  48,  68;  on 
selective  culture,  43;  on  sulphur  bacteria,  49; 
on  iron  bacteria,  52;  on  nitrifying  organisms  of 
soil,  68;  on  nitrogen  fixation  by  microorgan- 
isms, 78;  V.  and  Omelianskii,  on  nitrobacteria. 

69 

Viola,  87 

Virulence,  of  bacteria,  182 

Vitis,  248,  312 

Vochting,  on  light  and  leaf  position,  277;  on  light 
and  development  of  cacti,  283;  on  light  and 
floral  development,  291;  on  zygomorphy,  29s  ; 
on  correlations,  299;  on  formation  of  tubers, 
326;  on  sprouting  of  potato  tubers,  327;  on  in- 
duced rhizome  formation,  327;  Organbildung, 
329;  Transplantation,  334,  33s;  on  symbiosis 
of  Helianlhus  annuus  and  //.  tuberosus,  335 

Volatile  oils,  136 

Volkens,  on  guttation,  140 

Vorbrodt,  on  phosphorus  compounds  and  phytin, 

174.  185 

Voronezh,  95 

Voss,  on  twining,  311 

Votchal,  on  water  transfer,  143,  145,  146;  on  solanin 
in  plants,  182 

Votchall,  see  Votchal. 

Vries,  de,  on  turgidity,  isosmotic  coefficients,  etc., 
114,  us,  116,  119;  on  osmotic  values  of  cell 
sap,  123;  on  plasmolysis,  etc.,  121,  244;  on 
protoplasmic  streaming,  123;  on  root  contrac- 
tion, 250;  on  tendrils,  312 


W 


Wagner,  A.,  on  leaves  of  alpine  plants.  322 
Wagner,  P.,  fertilizer  experiments,  70,  73,  94 
Wahl  and  Henius,  Book  of  brewing,  etc.,  201 
Walden,  on  osmotic  membranes,  113 
Walther,  Krasnosselskii,  Maksimov  and  Malchev- 

skii,  on  hydrocyanic  acid  in  bamboo,  179 
Washburn,  on  osmotic  pressure,  etc.,  109,  1  to,  1  i_\ 

119 
Wasps,  distributors  of  yeast,  201 
Water,  absorption  of,  273,  274;  importance  of,  188- 

189;  in  metabolism,  18,  79,  82,  189,  198,  207, 


208,  217,  218,  223,  225;  in  respiration,  217-218; 
transfer  of,   107,   133-134.   143.   145.   146;  and 
configuration,  266,  270;  purification  of,  by  sun- 
shine, 292 
Water-plants,  38 
Water-pouches,  264,  265 
Water-requirement,  137 
Wax,  263 

Weather,  and  gas  in  vessels,  144 
Weber,  on  ash  of  etiolated  leaves,  285 
Weevers,  on  potassium  in  plants,  90;  on  caffcin  and 

theobromin,  176 
Wehmer,  on  ash  analyses,  89;  on  Mucor  fermenta- 
tion, 208;  on  oxalic  acid  in  fungi,  188 
Weighting  of  light  values,  290 
Weimarn,  on  colloids,  in,  112 
Weinzierl,  on  alpine  cultures,  323 
Weissberg,  see  Engler  and  W. 

West,  on  chlorophyll,   6;   on  non-chlorophyll  pig- 
ments, 21 
Weyl,  on  proteins,  158 

Wheat  (see  also  Triticum),  17,  158,  159.  161,  172, 
184,  188,  190,  221,  223,  227,  229,  281,  284,  331 
Wheat  rust,  86 

Whitney  and  Cameron,  on  soil  fertility,  99,  101 
Wieland,  on  oxidation  processes,  199,  208 
Wieler,  on  bleeding,  140 
Wiener,  on  iron  in  plants,  90 

Wiesner,    on    chlorophyll    formation,    14,    15;    on 
transpiration,    135,    137,    138;    on    descending 
water  stream,  268;  on  diffusion  in  plants,  107; 
on  light  relations,  27,  274,  283,  2S6,  288,  289, 
290;  on  geotropism,  292,  300;  on  circummuta- 
tion,  314;  on  phototropism,  275,  279,  292,314; 
W.  and  Molisch,  on  gas  movement  in  plants,  I06 
Wilfarth,  see  Hellriegel  and  W. 
Wille,  see  Ville. 
Willow,  250,  251,  280,  329 

Willstatter,   on   chlorophyll,   6,   7,   8,    13;   W.   and 
Asahina,   on   chlorophyll   derivatives,    12;    W. 
and  Benz,  on  chlorophyll,  7,  9;  W.  and  Escher, 
on  lycopin,  20;  W.  and  Fritsche,  on  chlorophyll 
derivatives,    n,    13;    W.    and    Hocheder,    on 
chlorophyll  derivatives,  8,  13;  W.  and  Hug,  on 
chlorophyll,  6;  W.  and  Isler,  on  chlorophylls 
of  different  plants,  13;  W.,  Mayer  and  Huni,  on 
phytol,  8;  W.  and  Mieg,  on  yellow  pigments, 
19;  W.  and  Pfannenstiel,  on  rhodophyllin,  13; 
W.  and  Stoll,  on  chlorophyll,  6,  11,  13,  20;  on 
chlorophyllase,  8 
Wilting,  36,  145,  273 
Winkler,  on  gas  analysis,  4 
Winogradsky,  see  Vinogradskii. 
Winterstein,    on    fungus   cellulose,    186;    on    phos- 
phatides,   183;    W.    and    Hiestand,    on    phos- 
phatides, 183;  W.  and  Smolenski,  on  phospha- 
tides, 183;  W.  and  Stegmann,  on  phosphatiili is, 
183;  W.  and  Trier,  on  alkaloids,  181.      (See  also 
Schulze  and  W.) 
Witches  broorns,  301,  302 
Woburn  Experimental  Farm,  99 
Wohler,  on  synthesis  of  urea,  xxvii 
Wolff,  on  ash  analyses,  88 
Wolkoff  and  Mayer,  on  respiration,  210,  216 
Wollny,  on  evaporation  from  soil,  etc.,  137 
"Wood,  air  of,  132;  strains  in,  251;  water  movement 
in,  133 


360 


INDEX 


Work,  of  plants,  198,  220 

Wortmann,  on  respiration,  201;  on  growth,  244;  in 

root  hairs,  270;  on  yeast  in  grape  juice,  201,  202 
Wottschal,  see  Votchal. 
Wounding,     traction     and     pressure     influencing 

growth,   300-305;  wounding  and  metabolism, 

143,  180,  182,  213,  226;  and  responses,  298,  299, 

300 
Wulfert,  on  determination  of  nitrates,  178 


X 


Yegunov,  on  sulphur  bacteria, 
Young,  see  Harden  and  Y. 


49 


Xanthin,  162,  173.  I75-I77 
Xanthophyll,  6,  20 
Xanthoproteic  reaction,  156 
Xerophytes,  263 
Xylem,  142,  143,  150 
Xylose,  186 


Yarrow  (see  also  Achillea),  276 

Yeast  (see  also  Saccharomyces),  42,  43,  46,  79,  162, 

165,   167,   169,   170,   201,   20s,  208,  259,  331; 

Mucor  yeast,  260,  261 
Yegounow,  see  Yegunov. 


Zaleski,  see  Zaliesskii. 

Zaliesskii,  on  phosphoproteins,  162;  on  respiration, 
168;  on  nucleo-proteins,  173;  on  protein  forma- 
tion, 178,  180,  181;  in  seeds,  174;  on  protein  de- 
composition, 174;  on  phosphorus  compounds  in 
seeds,  and  on  phosphoproteins,  174;  on  sprout- 
ing of  onion  bulbs,  179;  on  ether  and  transfer  of 
substances,  180;  on  ammonia  formation,  174, 
180,  181;  on  nucleic  acid  in  germinating  seeds, 
181;  on  carboxylase,  206;  on  stimulation  of  re- 
spiration, 213;  Z.  and  Reinhardt,  on  respiration 
and  salts,  214.      (See  also  Nentskii  and  Z.) 

Zdobnicky,  see  Stoklasa  and  Z. 

Zea  (see  also  maize),  159,  184,  253 

Zein,  158 

Zimmermann,  on  microtechnic,  90 

Zinc,  82,  87,  121,  163;  chloride,  112,  sulphate,  46.  121 

Zoospores,  331,  332 

Zygnema,  120 

Zygomorphic  flowers,  295 

Zymase,  163,  167,  169.  202,  224,  226 

Zymin,  167,  169,  204