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GRAY’S BOTANICAL TEXT-BOOK.

VoLuUME II.

PHYSIOLOGICAL BOTANY.

GRAY’S BOTANICAL TEXT-BOOK

CONSISTS OF

Vou. I. Srructrurat Borany. By Asa Gray.
TI. Puystotocicat Botany. By Grorcre L. GoopaLe.

III. Inrropuction to Cryprogamic Botany, BOTH
“SrructurAL AND Systematic. By Witiiam G.

Fartow. (Jn preparation.)

IV. Sxkercn or tHe Natura Orpers oF PHANOGAMOUS
Piants; their Special Morphology, Useful Pro-
ducts, &c. (Jn preparation.)

GRAY’S BOTANICAL TEXT-BOOK.

(SIXTH EDITION.)

Vou. I.

PHYSIOLOGICAL BOTANY.

I.

OUTLINES OF THE HISTOLOGY OF
PHANOGAMOUS PLANTS.

II.
VEGETABLE PHYSIOLOGY.

BY

GEORGE LINCOLN GOODALE, A. M., M.D.,

PROFESSOR OF BOTANY IN HARVARD UNIVERSITY.

NEW YORK -:+ CINCINNATI -:- CHICAGO
AMERICAN BOOK COMPANY

@
OKAS
Got

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ee Oe ra

Copyright, 1885,

By Grorek LINcoLN GooDALE.

Printed by
William vison
Wew Work, U.S, A.

PREFACE TO THE SERIES.

THE first edition of the Botanical Text-Book was pub-
lished in the year 1842, the fifth in 1857. Each edition
has been in good part rewritten, —the present one entirely
so, — and the compass of the work is now extended. More
elementary works than this, such as the writer’s Lessons
in Botany (which contains all that is necessary to the prac-
tical study of systematic Phenogamous Botany by means
of Manuals and local Floras), are best adapted to the
needs of the young beginner, and of those who do not
intend to study Botany comprehensively and thoroughly.
The present treatise is intended to serve as a text-book
for the higher and completer instruction. To secure the
requisite fulness of treatment of the whole range of sub-
jects, it has been decided to divide the work into distinct
volumes, each a treatise by itself, which may be indepen-
dently used, while the whole will compose a comprehen-
sive botanical course. The volume on the Structural and
Morphological Botany of Phenogamous Plants properly
comes first. It should thoroughly equip a botanist for the
scientific prosecution of Systematic Botany, and furnish
needful preparation to those who proceed to the study of
Vegetable Physiology and Anatomy, and to the wide and
varied department of Cryptogamic Botany.

vi PREFACE.

The volume upon Physiological Botany (Vegetable His-
tology and Physiology) has been prepared by the writer's
colleague, Professor GOODALE.

The Introduction to Cryptogamous Botany, both struc-
tural and systematic, is assigned to the writer’s colleague,
Professor FARLOW.

A fourth volume, a sketch of the Natural Orders of
Phenogamous Plants, and of their special Morphology,
Classification, Distribution, Products, etc., will be needed
to complete the series: this the writer may rather hope
than expect himself to draw up.

ASA GRAY

HERBARIUM OF HarvarD UNIVERSITY,
CaMBRIDGE.

PREFACE TO VOLUME IL.

THE present volume is devoted to a consideration of
the microscopic structure, the development, and the func-
tions of flowering plants; that is, to their Vegetable His-
tology, Organogeny, and Physiology. In the first volume
of the Botanical Text-Book these topics were treated only
incidentally, or in an elementary manner, as an introduc-
tion to Morphology.

Cryptogams, or flowerless plants, are treated in this
volume only so far as their study may throw light on
certain features of the anatomy and physiology of Pheeno-
gams. The simple structure of many of the flowerless
plants, especially of those of the lower grades, makes them
suitable objects in which to investigate numerous phe-
nomena of vegetable nutrition, growth, and reproduction,
and they have been extensively employed as convenient
material for this purpose. Reference must therefore be
made in the present treatise to some of the more important
results.

Vegetable Histology treats of the minute anatomy of
plants. A knowledge of its leading facts is indispensable
to a clear understanding of Vegetable Physiology, and
their presentation must needs precede any satisfactory
examination of the latter. The technique of Vegetable
Histology requires special treatment, and therefore con-

viii PREFACE.

siderable space has been devoted to its appliances and
methods. ‘This special treatment has been supplemented
by a series of practical exercises which the student is
urged to perform in the order designated. It will be
seen that in some cases several examples are suggested :
the beginner is advised to examine thoroughly at least
one of the examples under each head.

Organogeny, the study of nascent organs, occupies much
of the middle ground between Histology, Morphology, and
Physiology. The means by which it is investigated are
those of Histology, but its answers are given to Mor-
phology. For convenience, the study of the development
of each organ of the plant is made to precede the examina-
tion of its mature state.

Vegetable Physiology concerns itself with the life of
plants. The appliances of which it makes use are taken
chiefly from Physics and Chemistry, and facility in their
employment demands some practical acquaintance with
those departments. To one who has worked systemati-
cally in a physical and chemical laboratory, experimental
vegetable physiology presents little difficulty. To aid the
work of students whose opportunities for experimenting
in Physics and Chemistry have been slight, a series of
practical exercises in Experimental Physiology has been
added. The appliances selected for these examples are
not complicated or expensive, and it is hoped that teachers
and students alike may find their employment practica-
ble. The Praxis embodies in compendious and conven-
ient form the directions which have been employed by
the author in his classes.

The illustrations of tissues and of apparatus have been
taken from many sources. They have been selected with

PREFACE. ix

reference to the special needs of those students to whom
the larger works and the current journals are not easily
accessible. The same rule has been largely followed in
the treatment of citations from authorities, Where it has
been possible to do so without too great sacrifice of
space, the phraseology of the original reference has been
given.

In the preparation of this volume the author has had at
many steps the wise counsel of his teacher and associate,
Professor ASA GRay, to whom he wishes to make his
grateful acknowledgments.

In the proof-reading, verification of references, and In-
dex, Mr. W. W. Noten, Assistant in Biology, has rendered
aid of great value. His painstaking and good judgment
have lightened in every way a formidable and burdensome
task.

GEORGE LINCOLN GOODALE.

Boranic GARDEN oF Harvarp UNIVERSITY,
CaMBRIDGE, Mass., August, 1885.

CONTENTS.

PART I.

INTRODUCTION.
HISTOLOGICAL APPLIANCES. PAGi
Microscopes .. . ee ab UR Set Nata Goran eeh toca, EN Cay aa) ay aca) MB 1

Dissecting Tnietronnents eS ee ee ee ee ae eR 2
Media and Reagents . . . . 1. 1 1 ee ee te we ew te ee 4
Staining Agents. . . Sa Sia eh RS ae a a a MIS ahnge Stok es oa?
Mounting-media . . eee ae ae ee «« « 20

CHAPTER I.

THE VEGETABLE CELL IN GENERAL: ITS STRUCTURE,
COMPOSITION, AND PRINCIPAL CONTENTS.

Protoplaam . . . + 0 ee ee we et ee es tena 726
The Cell-wall. . . 2. 2. 2. ee ee Bes RG ees uel RL Se 229)
Cellulose .. ty ats tie ait ae ee AS OE leads et Get Gas kot. veo

Modifications of ihe Cell: wall Be ae, Gl a oe we ee BA
Plastids: «i: a: 6. ai is. (4 a oe we ee a ee ewe OO
Protein Granules . . 1 1 6 1 ee ee ee we ew we we ew 4
Starch . . . 1 sw oo @ 6 os WY Aw Re Rw ee ee Oe
Inulin «4 4 % 8 ew eH SS we Se RH we Re ie & Se 60
Cellsap . 2 6 0 et ee eee te he et we we ee ee CSI
Crystals s, 6 6 8 we ee ee Rw Se ee ee ee BD

CHAPTER II.

CELLS IN THEIR MODIFICATIONS AND KINDS, AND THE
TISSUES THEY COMPOSE.

Typical and Transformed Cella . . . 2 1. se es we eee . 656
PARENCHYMA, se Go @ a wR ee ee te ee 80
Parenchyma proper» . . 6 + + e+ + + et © ee ew ew ew + 660
Epidermis . . So Mal Gabwcat-san aS SNS Sa. wernt ie oo) ete tee ae HOE
Epidermal Cells Botan ry Ga eee Aah Seem aoe es Ga ee oy OD
Trichomes «3 4 4 6 @ ee Hw we ee ee we we we GB
Stomata: <<. «(te se oe Hine ek a) Gee ele ew Se ONO
Cork . «2 2 ee we es we te we Bi TL SOARS We Ge WY Ge sep

xu CONTENTS.

PROSENCHYME 2 @ uw dw wow ea a Se Boe wwe ewe FE
Prosenchyma proper . «eee ee ee ee ee ee ee OT
Woody: Fibrés-. 4 ee 6 4g Bowe gy we ee ww we a was. 2 BO
Tracheids . . Boy sake dee ee dD og. GR AD ASE ste Ca OLS are Gk olten LOZ
Trachee,or Ducts 2. 6 6 6 6 ee ee ee ee ee ee
Teibereibrese se! ek ode oe Bie ake cee, ar ae BR ee a ee we,

CRIBROSHOBTUS 6. a. ck ee a ge a OR Sw ee ee OT

LATEX-CELLS . . . Bee ge ee as ee ER Se: Re OE:

Receptacles for Seemstians ese ide ih eG oe se eee wow ee OT

Intercellular Spaces. 6 6 ee ee et we te ee ee eee 8D

CHAPTER III.

MINUTE STRUCTURE AND DEVELOPMENT OF THE ROOT,
STEM, AND LEAF OF PHANOGAMOUS PLANTS.

The Systems of Tissues . . . Oe PS a ee ee egy 02
Structure of a Fibro-vascular Brndle seek ee Sw esq AOS
THE Roor. . . bop es ae we Selah Ste He eo @ ce we Be S106
Primary Sieudines tet Sore Sa, BrAg. Seley aoa: Be e106
The Root-cap . . a eee ee ee ee 107
The Piliferous ae: eet. Guin ae ee A ees ee aoe ae ae LO
The Central Cylinder . . 2 6 2 2 ee ee ew we es «621210
Secondary Structure . 2. 6. 2 6 ee 6 ee ee ew we we ee 112
Tue Stem . 3 aC RL OR Oe ey a: A ee gh 8
Primary Saianwe 3 a BO a SOR es A we ee a we ee DD
The Epidermis . . 6. 6 1 6 6 0 @ ee we ee ww - 119
Primary Cortex .. . ef eh eh a I a ee we ws TD
Primary Bundles . . 2 6 6 8 4 6 wo © © © © oe 2 ws 120
Pith 3 2% See an aa a se Gp ee ee St oo ge ge
Medullary nae a ee ee a 2
Course of the Bundles . . . «ee ee ee ee ee we 185
Secondary Structure . . 2. 6 6 6 ee ew ew ee - « 185
Of Monocotyledons . 2. 1 6 6 6 we ew ew ee ew we 185
Of Dicotyledotis: «.-%. @ & w@ @ aoe wo wow Be ww Se 186
Changes by Growth . «6 1 6 ee ww ew ew wet ew we 187
Anomalous Stems. . . eR oe AS eee ew ee 8B
Spring and Autumn Wood. {8 ewe ew 6 ww ew 188
Annual Layers: « 2 ss @ # #0 @ «oe % * « «© « « @ “189
Color of Wood. BS dh, RR Ney rot igs ok da I Se . 141

Preservation of Wood... . 1... ees & & « » 142
DOHSItY <0 ao A eR ea a a we ee ee
Bark... eae Nae ie tae Setewlen ey GAs ie cle a ee AT
Secondary Lifer Se ay Gols iby oy Gch eae sie Ga a & « & » 147
Cork ee BR Ba A RR ee ees Ae, AS

Injuries of the stan eS eS Se Ae ae we ee -D
Lenticels . 6 6 6 ee es ee ee ee eee ee DBI
GHaLt be! a a 6! ene Ae RAP aig ee ee oe) - . 162

CONTENTS. Xiii

Pack

Rudimentary and Transformed Branches . . . . .... . . 158
Stems of Vascular Cryptogams . .. ..... +... 154
Stems of Mosses. . . . 1 1 1 eee ee ee we ew we 1S
"DY GBA 4.) os ee ta eR ew ae a se a er

Development: .. #6 % Se ee Be A ee we ee ee ee DO
Bundles: <0. it > seve aie fad te a tee ae 8 i a ge tee eee Sh ee, Gg a BD
Parenchyma;. 2 e604 % % 8 @ we 8 ee ee ee me ae ew ASB

TS pid@ BMS)» er i8 coe coor tie cee ee te Ey ay a ee a AE
Fallof the Leaf... 6.0. 6 2 4 ee ee Sw ew wee ew 1E2
Leaves of Cryptogams. . . . . 1. 6. 6 ee we eo ee es 164

CHAPTER IV.

MINUTE STRUCTURE AND DEVELOPMENT OF THE FLOWER,
FRUIT, AND SEED.

Ture FLrowrr. . . » . . 166
Preparation of Materiat for he Senay a its Develggiiieats, +. . 166
Stages in its Formation . . Ss Ae Mh aiss, Bay NAS EOP icky HL So. EOS
Tissue Systems of the Flower . ; or oe cdr oar a) oer eh CO
Development of the Stamens . . ete hon ARG “ae cat Ser sae “oe tale
Style, Stigma, and Ovary. . . eS Sen aa: LAD,
Distribution of Fibro-vascular Bundlewis in Simple Pistils . sce 7 TS
Distribution of Fibro-vascular Bundles in Compound Pistils . . . 1738
Formation of the Ovule . . . 2 ee oe ay i we

Tue Fruir .... Pb Re oe eS ee we Se mo wee OWS
Tie Strwctnre: 3 6 sx: a aoa de Ge SS ee Ra we ie 6
Tis: Coloring-matters.. 5 2 ss 6 «© @ © & & © R ee wo o w AIT

Tue SEED. . . Kee ee ee wo WS
Structure of the Gad eat a its Appendages de ey de Gt ae TS:
Nucleus of the Seed .... ti el Se Se ST

Food Materials and Protein Gravales’ in ‘Beeds dpa Niho May Gh Sale tan tees BR

CHAPTER V.
PHYSIOLOGICAL CLASSIFICATION OF TISSUES.

Division or LaBpor IN THE PLANT . ...... ee ee (185

Work of the Plant Organism. A ge ew eg BS
Organs and their Classification . os Se ee ew ee we a 186
Haberlandt’s Classification of Organs . . . . 1. + + « « . 187
MecHanics OF TISSUES. ba as Bit BEB pte RMN ae iy od ian ee ins SOO

Strength of Tissues. . . © 2 6 ee ce ee ew ew ww es 190
Stereom and Mestom ....... det ab Se.- pt “at - so aps te GOD

xiv CONTENTS.

PART IL.

CHAPTER VI.
PROTOPLASM AND ITS RELATIONS TO

Occurrence of Protoplasm
Chemical and Physical Phonettiee of Fistopleem
Protoplasmic Movements . so
Relations of Protoplasm to Heat . . .

To Light . ech wap ey Mine a eto fe

To Electricity .

To Mechanical tritadion :

To Gravitation . Se a ee Bo eS

To Moisture ee et fee ee i Ue

To Various Gases . . Pa ee ee
Structure of Protoplasm . . . . . . se
Continuity of Protoplamm .. . Eile Ss
Relations of the Cell-wall to Proteplaan, o Jew

Historical Note regarding Protoplasm

CHAPTER VII.

ITS

DIFFUSION, OSMOSIS, AND ABSORPTION

DIFFUSION AND OsMoSsIS . ....
Diffusion of Liquids. . . . ....
Rate of Diffusion. . . 2... 2...
Osmosis oy aa oe
Precipitation- -petieanel @ vas ee: ee ae

Traube’s Cell . . ‘

Pfeffer’s Apparatus for eee :
ABSORPTION OF Liquips THROUGH Roots .

Root-hairs

Extent of Root- autcne

Adhesion of Soil to Roots . a

Do Roots go in Search of Food? . .

CHAPTER VIII.

SURROUNDINGS.
PAGE

6g oie 198

& aosice ADE
ee owe 4 OD:
ie at a 201
ioe ee » 206
«4 ae ow 207
oe ee we ae 208
ace ae we ae 208)
«6 oe oe 209

i a ee ew NO
owl ae oe a EE
jg ee ar ae RTA,
Be Ag dy clan doo er 8
Say GES ae Ge ee 1)

OF LIQUIDS.

oe B20
ao iar ee ee 22
aa ee 1222

224

226
226
230
231
232
3.3)
eee 285

SOILS, ASH CONSTITUENTS, AND WATER-CULTURE

Amount of Water and of Ash in Plants
SOs. % 2 « + « x
Formation of Soils . . . . 6. . 2 we

236

ee we ew es 287

CONTENTS. XV

PAGE
Classification of Suils . . . . a) le le ere Fas, Bw BB
Absorption and Retention of Motsute by Soils . . 2... . . . 289
Chemical Absorption by Soils . . . . . . - BY Katana! 28 243,

Condensation of Gases by Soils. . . . . 1 2 2 e we we 244
Root-absorption of Saline Matters from Soils . . .... . =. 244
‘Temperature of Soils ie : cae
Effects of Roots upon Soils . . . . Bi yd Pee
AsH CONSTITUENTS OF PLANTS . . . ee 4 ee ee ee
Amount and Distribution. . . 6. 6 6 2 6 we we ee ee 246

Composition Ce ee ee eee ee ae Se 247
WATER-CULTURE feo RE lg eo ea a) fee Ge ee ee ee ee AS
Apparatus . fhe eae SO AS ee ee BD
Nutrient Solutions . Be Ge oe Al Re ty Oe Se ee wee a 280
Method of Practice . . Oh Ba ai ao) os Oa a te
OrFicE OF THE DIFFERENT ‘Katy Conanunnenns: Bote Me Re ee eee 220"
Potassium . . . PSs Sh teh Feist a ae. Reh et cranes THO
Calcium and NMacneetiven go see ae ig i el ce ave «Soho eh gis OD

Plissplorise: s: = 6 4 wt a) @ oo ace Ve ae A Ae bee 208
TVODs Ger 4 Rt en Be SE ae des a tay ae do es SOE
Chlorine... ys aig oe i ee et ee a Ge ce ae ce DE
Sulplive yous. 6 eo ww Bk a Be eae ig ape es BBB
Sodium a 4 oes fee abr. “Se cen $8 VAR) ay fas a GE ZOD
Rarer Gonstitents Se hb, ae Me ee eee eae ee AOD

CHAPTER IX.
TRANSFER OF WATER THROUGH THE PLANT.

Tur Revations or WaTER TO TIssuES .... +++ + ++ 207
Transfer of Water in Woody Plants. . . . ee we oe a 208)
Determination of the Path and Rate of Transter. ees Ms She wr Sarge oe!

Rate of Ascent of Water in Stems. . . 261
Effect, upon Transfer of Water, of Bposing a Cut Siefine i the sie 263
Pressure and Bleeding . . se aoe ee oe 2h

Exudation of Water from ainijmeed Parts ‘of Plants ee Oa ee ae OT
TRANSPIRATION © 6 5 ee ee ee eee ee ee ee ee 268

Stomata . Se Bi A Mae Sl OAL Sa Ge tee ee SR Heh elles ced eae 2208
Mechanism . . . eed ae eel dal Ane va Bee 209
Relations to Hieternal Tifluenees og agg hk a’ de he ay TO

Amount of Water given off in Transpiration. . . . - - + © + 271

Transpiration compared with Evaporation proper . . - + + + + 275
Effect of Moisture in the Air upon Transpiration . . . . . - + 275
Effect of the Soil upon Transpiration. . . . . 2. +. + + + + 276
Relations of Temperature to Transpiration . . . . . - + + + 277
Effect upon Transpiration of Light . . - . 6 se ee es 277

Of different Rays of the Spectrum. . . . . - + e+ + + + 278

Of Mechanical Shock . . . . Skee age a pee Se eS
Relation of Age of Leaves to ataspiation peas oboe) es eee: Ha 279

Xvi CONTENTS.

Relation of Transpiration to Absorption . . . +. +.
Adaptations of Plants to Dry Climates .
Chief Effects of Transpiration upon the Plant

Influence of Transpiration upon Amount of Moisture in ties Air ‘

Effect of Transpiration upon the Soil
Do Leaves absorb Aqueous Vapor? . . . » . + -

CHAPTER X.
ASSIMILATION.

APPROPRIATION OF CARBON, OR ASSIMILATION PROPER .
Conditions of Assimilation Sy dy hu Ba wees
Assimilating System of the Plant. . . ....

Chilorophiyll’s. ee. wa Bea ao ee Ee
Origin of the Granules . . . ......
Occurrence of the Granules . . . .

Structure of the Granules . . . ie ee
The Chlorophyll Pigment, and its Btchetion .
Spectrum of Chlorophyll . 2... 2... wee
Fluorescence of Chlorophyll. . ......-..
Plants devoid of Chlorophyll. . . . ......
“Colored” Plants. . 2. 2. 6 6 6 et we
Htiolation: 2 2 0h ewe eww Re
Chlorosis. . . . . . he ee I WE GS Gh
Autumnal Changes of Caler ico. seam os .
Chlorophyll in Evergreen Leaves . . 2. . .

The Raw Materials required for Assimilation, and their
by the Assimilating Organs
Absorption of Carbonic Acid by Water Plans
Absorption of Carbonic Acid by Land Plants .
Diffusion of Gases . 6
Passage of Gases through Hipidenhits free ions Stemi «
Passage of Gases through Stomata
Composition of the Atmosphere
Practical Study of Assimilation ae Mee hin Nes Gen Ge
Energy ost
Classification of the fava of tlie Spesecumn,.
The Depth to which Light can penetrate Green ‘Taswen.
Quality of Light which penetrates the Tissues of a Leaf
Effect of Colored Light upon Assimilation . ee
Measurement of the Amount of Assimilation .
Engelmann’s Method
Effect of Artificial Light upon Asstoslaiien
Relations of Temperature to Assimilation

Reception

Effect upon Assimilation of Variations in the Aina of Carbonle

Acid furnished the Plant . ......

PAGE
279
280
281
281
283
283

285
285
285
286
287
288
259
2v0
292
204
294
294
295
297
297
298

299
299
300
301
302
303
303
305
307
308
3809
309
310
312
314
316
316

318

CONTENTS.

Ratio of the Oxygen evolved by Plants to that of the Carbonic Acid
decomposed . . : bo
What are the Products of Azsiunilation proper? :
First Visible Product of Assimilation
Formic Aldehyde Hypothesis
Pringsheim’s Views in regard to the First Product of Asshafilatton
Early History of Assimilation
APPROPRIATION OF NITROGEN
Amount of Nitrogen in Plants .
Sources of Nitrogen furnished to Plants
Nitrogen Compounds in the Atmosphere
Nitrogen Compounds in Rain-water .
Office of the Atmosphere in the Formation atl Disttibation of ‘Nitro-
gen Compounds . : ,
Products of the Decomposition of ‘Asia iad Veuirbite “Matter i
Natural and Artificial Fertilizers
Synthesis of Albuminous Matters in the Plant
APPROPRIATION OF SULPHUR . 5
APPROPRIATION OF OrGaNIC MATTERS .
Humus-plants, or Saprophytes .
Parasites . . Be ies ofan. ew a ye wea a
Insectivorous or Gacnivonsis Plants .
Drosera rotundifolia. . 2. . 1. 6. 2 ew eee
Dionea muscipula . ........ lee Ge
Aldrovanda 2 a 8). 9 s84al GG Gt ete) Cech SA he Ged BE cs
Drosophyllm 4. a ew ee
ROn@U as ches: Ko Ge ie ee Se eee te oe SES
BBLS ol) Gar Se Sie ap iGO Se a es
Pinguicula . a) A RS
Utricularia
Genlisea .
Sarracenia
Darlingtonla =: je ee ROR eS
Nepenthes :
Dipsacus, or Teasel .
Epiphytes, or Air-plants .

CHAPTER XI.
CHANGES OF ORGANIC MATTER IN THE PLANT.

TRANSMUTATION, OR METASTASIS
Utilization of Food .
For Supply of Energy for Work
For Repair of Waste . :
For Construction of New Parts .
Assimilation proper compared with Teenieation
Course of Transfer of the Assimilated Matters in the Plant.

xvii

PAGE

319
320
321
822
822
823
825
325
327
331
331

332
333
33d
335
336
337
387
338
338
339
342
844
345
845
345
345
346
346
347
349
349
350
362

854
354
355
855
355
356
356

Xvili

CONTENTS.

Classification of the Principal Organic Products. . . . .. . . 887

Products free from Nitrogen .

Carbohydrates
Vegetable Acids.
Fats, or Glycerides
Certain Astringents
Glucosides
Ethereal Oils.
Resins and Balsams

Albumin-like Matters
Asparagin
Alkaloids . r
Unorganized Reements
RESPIRATION . ,
Measurement of Heapination ‘

oie : 360

- . < ee ‘ 360

eo oie 1as Ae 8 361

a oe es 362

° Cae ok 362

ae . ee « se 868
Products containing Nitrogen . . 2. 1 6 6 ew we ee + (868
G28 363

ee 364

‘ . 365

7 365
367

So ee Bs soe + + 867

‘i 368

Plants in Dwelling-houses .

Relations of the Carbonic Acid. given off in ic Regpinatian 16 tha Oxy-

gen absorbed. ao 368
Influence of Temperature and Light sia ic Rewpicaian, ee ee 069
Resting State : ie eS 369
Respiration accompanied iy s an Hyolution of Heat. . .... 370
Intramolecular Respiration ek ce 370

CHAPTER XII.
VEGETABLE GROWTH.

Nature of Growth
Cell-division

In the Development nl Gtomata. Do em eS eS Be SS ew ce BIG

In Cambium .

In the Development of Pollen. -grains. ©. 1. 1 www we ee 8D

In Plant-hairs . : 380
Directions in which che: new Cell- wail, ‘cay he laid deer. eet 380
Growth of the Cell-wall 8) Ge ee a a) ak OBR
Measurement of Growth . . 383
Conditions necessary for Growth . . a Nt 8 384
Relations of Growth to Temperature . . . . 2. 6 ew ee. 885
To Light . P ae . 387

To Supply of Giepaen

Periodical Changes in the Rate of Growth, <e & s * e ww 4 389
Properties of New Cellsand Tissues . . . . 2... ee ss 889

Tensions in the Cell-wall .
Tension of Tissues .
Geotropism .

Heliotropism eit
Hydrotropism. . . .. .

ei 390

. ete 2 é 390
sew ee 392

oe fe . : 892

ee oe ae - + 9898

CONTENTS.

Thermotropism . . . ism fea
Assumption of Definite Horm during ‘Geaathe
Amount of Force exerted during Growth .

CHAPTER XIII.
MOVEMENTS.

Locomotion 7
Movements of Chlorophyll Gunite! in Leaves z
Hygroscopic Movements . : gos 2
Movements due to Changes in Siradpute dniine ‘Hipentiie of Fruits
Revolving Movements, or Circumnutation .
Methods of Observation ee
In Seedlings . . ee
Of the Young Parts of Native Plants . s
In Twining Plants
Modified Circumnutation .
Nvetitropic or Sleep Movements .

Of Cotyledons. . . . eC. tS Soni edocs iy Be
Of Floral Organs. . . Bd Ah ee Coe te. dh “ee oe
Times of Opening and Closing of Riawane : Sj teh dee Sbo ers
Spontaneous or Autonomic Movements a So tee Ae Sat ae Se
Telegraph Plant . . ‘i o [ne chet sees 8S
Cause of Autonomic Movements a0 fully lcneaen be Ta Se
Sensitiveness . . - ss te toh ee eee te ee
Of Roots. . ig 3G TO Utah vere aun a), Yar rset ee is
Of Stems and Beanehes bog te ele wep He Gio Scien a Es
Of Tendrils. . . 2. 6 + 8 ee eo # © he tH ew ee
OfPetioles . . . 6 2 se ee ee ee ee He ee
OfLeaf-blades. . 2. 2 6 2 © © © © fe HH et
Of Sensitive Plant . . 2. 2. 6 + # es ee ee eee
Of Stamens. . . oe oe we ee ee a
Effects of Anustivetaes pon Sensitiveness. . - - - + e 6 +

CHAPTER XIV.

REPRODUCTION.
Individuality in Plants . . Be Me datee ay eo ay ae eS
Methods of Reproduction. . - . + e+ © ee ee ee
FERTILIZATION IN ANGIOSPERMS . - + s+ + e © + 6
The Pistil . . . - Be Maye ak: Re BORE LE net Oa
The Stigmatic Secnetibi So Sa ROS ok oe
The Pollen-grain. . - 2 6 6 ee ee eh ee th et
Structure. 2... 6 8 8 oe ee eee

Contents . . 6 1 6 6 ee ew ee te ee

397
398
399
400
400
401
403
405
405
407
409
411
412
412
418
413
414
414
415
417
417
419
419
420
423
424

xx CONTENTS.

Emission of the Pollen-tube . . . . eo SG we ew ee “AD
Time required for tlhe Descent of the Pollen« tube . .... . 481

The Ovule. . . . sR as eh DS ee ae Se a 482
Structure and Heseinpment Dats tee Laden eta ai a Mee Mat doe
Changes following Fertilization. . . 2...» «ee ee « 485

FurTILIZATION IN GYMNOSPERMS . . . 2. 1 + 5 + ew ee es 487

The: Pollen-grain: sa a se eA we we 437

The Ovule . . . eA oa m ee xem jae Go) Sn 482

Contact of the Pollen _— the Ove : b> Ais sae “alee 438

Contrast between the Results of Sexuai and Renseeaal ‘Reprodnetion. 443
Bud-propagation. . 0. 1. we ee ee eee tw ww ee 4G

Apogamy . . HR. Bieta ch Bd. GE OP Be rie GUS ae Se AE
Parthenogenesis . . xt SR. Gh See “ee ae a ey Gee “Gaps nay Qs can, ee "AG
Polyembryony .. . . Sg eee ae a ay sie Ae ser AED
Close and Cross Fertilization . . . ie ee SA aa TAT
Nectar... . “ ao a me OS . 451

Secreting sland ‘ 4 BOs oo ee ea Xe wee SEE

Specific Gravity . 4 Be ED-OB OS: Re okie Se aS Le 452

Period of most Copious Skoration « 6 ee ewe ee a we » 462
Colors of Flowers . 2... 1 eee ss eee FEN ts 452
Odors of Flowers . ........ Bie ch iseh vas VEN 454
Ay DTIGIZatiOMys ee OK os ea RR ah ge 455

CHAPTER XV.
THE SEED AND ITS GERMINATION.

Nature of the Life of the Embryo . . . ........ . 459
Ripening of Fruitsand Seeds . . . . . 2... sw. we se . 460
Dissemination of Seeds Ce ee aaa eae ee ee we 460
Vitality of Seeds . 1. 1... ita? Se. 1g: Oe Ge oe Se, A AOL
GERMINATION. . gh as ae Gal ay ele 8 a: ee Cy ep RD
Conditions of Goininaion Se 4 we ee ee we ew ew we w SE
Moisture... joe ee See Se) ee Gwe ee we 402
Access of Free on eribiole, UB A, Se ap ike ap a a Sage ie AB
Temperature . .. Sy Mo ae Me Gl aes ish, fae eaehouat bape 464
Phenomena of Garwiuation ray ae ae ee eae he 466
Fire=weedsi:s. sca. seers a Sa a a a Ga Gh ee, se HOD

CHAPTER XVi.
RESISTANCE OF PLANTS TO UNTOWARD INFLUENCES.

Extremes of Heat and Cold. . . gS wf Gol ke ok we a aa ad a TO

Winterkilling . a ep ao Mees fe» ae Sees Ge “see sae ie ey ae a TAD
Triterise Light. se ae ee he a ew a RS ww we AS
Improper Food Goi Benes Beh ee See Se he aoa! oo 8

CONTENTS, XKu

PAGE

Poisons) eee ig we Gy we ew 478
Noxious Gases: . 2 « &} S 8 @ «6 @ © Rw eB ws 4 473
Liquids and Solids . . Sim ae Ge, iy EOD. Gah ae > od eas oe 476
Mechanical Injuries . . «©. 2 ee ee ee ee ee 476

tNDEX +e & Si We ER a Se SR eS 479

PHYSIOLOGICAL BOTANY.

INTRODUCTION.

HISTOLOGICAL APPLIANCES.

Tue instruments and other appliances used in the exami-
nation of minute vegetable structure are, with the exception of
a few special ones to be considered later, the following : —

1. Simple microscope. For the preliminary preparation ot
many objects, a simple stage-microscope is indispensable. It
should be furnished with only the best lenses, preferably doub-
lets or triplets, magnifying from ten to at least twenty diameters.
The glass portion of the stage should be not less than an inch
and a half in diameter; supports at the sides of the stage, on
which the wrists may rest during dissections, are of considerable
use. If the compound microscope described below is provided
also with an inverting eye-piece and with an objective of long
focus, it can be made to serve for most dissections ; otherwise a
simple microscope should always be at hand.

2. Compound microscope. When reduced to its simplest terms,
this consists of a stage, or flat support for the object to he ex-
amined, an adjustable tube carrying two combinations of lenses,
the objective and the eye-piece, and finally some means of illu-
minating the object. The desiderata to be borne in mind in the
selection of a compound microscope for use in Vegetable His-
tology, are: excellence in the optical parts, ease and steadiness
in their adjustment, and simplicity of construction. Other things
being equal, a microscope with a short tube and with a low
stand will be most convenient, on account of the large number
of cases in which reagents must be employed, their application

requiring a horizontal stage.
4

D) INTRODUCTION.

3. Three objectives and two eye-pieces, from combinations of
which inagnifying powers of forty to eight hundred diameters
can be obtained, will suffice for nearly all the histological work
described in this volume. Two objectives and a single eye-
piece furnishing powers of sixty to five hundred diameters are
enough for all ordinary investigations of minute structure. Ade-
quate and convenient illumination is secured by a plane and a
concave mirror under the stage. If this is supplemented by an
achromatic condenser, so much the better. The stage, prefer-
ably thin, should be provided with a perforated revolving disc,
or other suitable system of diaphragms, by which its central
aperture can be made larger or smaller.

4. The student ought, at the outset of his work, to make
himself familiar with the principal effects which are produced
in the appearance of the object in the ficld of the microscope,
by changes in the amount and direction of the light thrown by
the mirror. Details can sometimes be brought out clearly by
oblique illumination, which are only faintly, if at all, seen in
direct light.

5. In general, low magnifying powers are to be preferred to
higher ones; and combinations of high objectives with low eye-
pieces, securing a given magnifying power, are always better
than those in which low objectives and high eye-pieces are used
to obtain the same enlargement.

6. The slips of glass, or ‘‘ slides,” upon which microscopic
objects are commonly prepared and preserved, are three inches
(76 mm.) long by one inch (25 mm.) wide. This is for most
cases a more convenient size than that frequently employed in
Germany ; namely, 48 x 28 millimeters. The glass should be
free from color and from imperfections. The preparation to be
examined under the microscope should be covered with a disc
of thin glass before it is brought under the objective. Perfect
cleanliness of slide and cover-glass is absolutely necessary in all
examinations, and must be secured by the exercise of scrupulous
care.?

ia

7. Dissecting instruments. Sharp delicate needles, by which

1 For cleaning glass perfectly, the following preparation may be used :—

A strong solution of potassie bichromate to which about half as much con-
centrated sulphuric acid is cautiously added. To this mixture add an equal
volume of water. The glass slips, or covers, are to be kept in this solution for
a short time, and then thoroughly rinsed in pure water, after which they may
be dried with cloth or wash-leather. For ordinary use alcohol of usual strength
answers the purpose very well.

INTRODUCTION, 3

the parts can be separated by teasing, are often hetter than
any cutting instruments. They are indispensable in the ex-
amination of very young flower-buds, and of great use in the
isolation of tissues under the dissecting microscope.

8. Sufficiently thin sections of soft parts may be made by any
keen-edged knife. A razor of good quality is generally to be
preferred to the ordinary dissecting scalpel, since its wide and
stiff blade can be held with greater steadiness, and its steel
admits of as sharp an edge. As a rule, the razor should be
dipped in water before using, as this permits the steel to pass
more easily through tissues.1_ If the parts from which sections
are to be made are too small to be held in the fingers, they can
be firmly seized between slices of pith. It is often convenient
to imbed the object in paraffin or in an alcoholic solution of
soap.” These melt below the temperature of boiling water, but
are solid at ordinary temperatures, and the latter, if properly
made, is transparent. <A little of the melted imbedding sub-
stance is poured into a small cone of glazed paper, and when it
begins to cool, the object is placed in the middle of the mass.
Upon complete cooling it is firmly held therein.

Before putting the object into paraffin it should first be satu-
rated with alcohol, and this replaced by benzol or oil of cloves,
in order to enable the paraffin to hold the specimen firmly. The
paraffin may be dissolved away from the sections by application
of benzol, oil of cloves, or turpentine (see also 110).

9. Thin sections are best removed from the knife by a
camel’s-hair pencil, and are to be placed at once in water or
some other liquid. Except in certain cases, water may be used
as a medium for the preliminary examination of sections.

10. Microtome. Any of the simpler microtomes, or section-
cutters, will be convenient in much histological work, and of
great use in the preparation of a series of sections from any
very minute object, since this permits them all to be of exactly
the same thickness.

11. Measurements. Microscopic objects are measured hy
micrometers. The eye-piece micrometer can be more rapidly
used than one on the stage of the instrument; and if its value

1 Advantage is frequently gained by moistening the edge of the knife with
dilute potassic hydrate before dipping it in water, thus removing traces of
oil which may have adhered to it during sharpening. But potassic hydrate
should not be used in this way if reagents are to be subsequently employed.

2 Made by dissolving enough of any good transparent soap in hot alcohol,
to form, upon cooling, a firm, clear mass, J te

4 INTRODUCTION.

for the different objectives and for the length of tube has been
determined accurately, it is usually preferable.

The values of the spaces in the cye-piece micrometer are
ascertained by comparison with known values of the spaces on
a standard stage micrometer; for example, if one space in the
eye-piece micrometer corresponds to five spaces of the stage
micrometer, and the latter has a value of one thousandth of a
millimeter, each space of the former equals five thousandths of a
millimeter.

The unit of microscopic measurement is the ‘* micro-miili-
meter,”* one thousandth of a millimeter. It is expressed by
the Greek yp.

12. Drawing. An image of the object under the microscope
may be cast by reflection upon paper at the side of the micro-
scope, by means of a Camera lucida. Several forms of the
Camera lucida are adapted to use with the tube of the micro-
scope in a vertical position, and are more convenient for the
majority of cases coming within the scope of the present work.
Oberhiuser’s, Milne Edwards’s, and Abbe’s are of this kind.

13. Polarizing apparatus. ‘This is of great use in the exami-
nation of certain contents of cells. It consists of two Nicol
prisms, one below the stage of the microscope and receiving
the light which is refiected from the mirror, the other in the
eye-piece. Upon turning one of the prisms, distinctive op-
tical characters, not otherwise seen, are presented by grains of
starch, ete.

14. Media and reagents. The fluid in which a microscopic
specimen is submitted to examination is technically known as its
medium. Chemical agents subsequently added for the purpose
of producing changes by which the chemical character of the
objects may be recognized, are termed reagents. Some of the
media, however, in common use produce characteristic changes
in certain cases, and might be as truly referred to the latter
class as several of the reagents themselves. The substances in

1 For convenience of reference, the following table of comparative measure-
ments is given : —

Be INCHES. Bh INCHES. IncHEs. be

1 -000039 6 ... 1... .000236 1. 9.5399
D vesevs 000079 apc .000276 pee .
8 ........, 000118 Briard ees -000315 dos = 25.3997
Core - 000157 D asvis coe OO0854

5. .000197 10 ......... .0003894 tho = 253.9972

One meter = 39.870432 inches.

INTRODUCTION. 5

which microscopic specimens are preserved are termed mounting-
media. 7

15. Mepra. In all ordinary cases pure water is the best
medium in which to place the object for examination. If dis-
tilled water cannot be procured, filtered rain-water or melted ice
will answer perfectly. In some instances water produces an
immediate change either in the cell-wall or in the contents of
the cells. For instance, the superficial cells of the coats of
many seeds swell up at once when they are placed in water, and
lose their former shape; on the other hand, important contents
in the seeds of many plants are dissolved immediately when the
sections are moistened. Hence, other media must be sometimes
substituted for water. Absolute alcohol (see 40) is the most
useful for meeting the cases above referred to. Thus, if 4 sec-
tion of a seed-coat be first examined in absolute alcohol, and the
alcohol be gradually replaced by water as directed in 17, the
changes due to water will take place slowly, and can be watched
throughout. For the cases in which the cell contents are sus-
pected of undergoing change from water, castor-oil is a useful
medium. If thought best, this can be removed subsequently
from the specimen by alcohol or ether, and the latter in turn
may be made to give place to water, and the changes can be
followed with certainty.

16. Glycerin (see 60), either concentrated or somewhat
diluted with water, is a highly useful medium, imparting a good
degree of transparency to most specimens. It withdraws a part
of the water of the cell-sap, and in the case of thin-walled cells
this is followed by some change of form. The remarkable effects
produced upon some of the contents of cells by the action of
glycerin and similar agents will be referred to under Protoplasm.

17. One medium may be replaced by another by the careful
use of bibulous paper. Good filtering paper is the best for this
purpose. If a little of the liquid which it is desired to place
under the cover-glass be put at the edge of the cover, and the
opposite edge be then touched lightly with the paper, the liquid
will be at once drawn through. By successive applications of
the same liquid, the specimen can be thoroughly washed without
removal of the cover-glass.

18. Reacents. Four reagents are in very common use in
nearly all histological examinations ; namely, caustic potash, a
solution of iodine, an acid, and a staining agent. Even in ordi-
nary cases, however, it is desirable to have a somewhat wider
choice than this, and therefore the following brief hints are

6 INTRODUCTION.

given as to the preparation and employment of some of the
most useful reagents. More detailed directions must be sought
in special treatises upon micro-chemistry.1 The list and the
general rules here given will serve for most investigations.

19. It is best to try first a very small amount of the reagent,
and carefully note its effect before adding more. If it is neces-
sary to increase the amount, draw a little through by means of
bibulous paper, as previously directed. Many reagents are slow
in producing their effects. Hence some tiie must be allowed to
elapse before one reagent is replaced by another, and it is well
in some cases to apply slight heat to accelerate or increase the
action ; but this must be very cautiously done.

20. If one reagent is to be followed by another, attention
must be given to the effects which the reagents have upon each
other, or upon the medium, as well as upon the specimen. For
instance, small dark crystals of iodine separate from an alcoholic
solution when this is brought into contact with water. Removal
of the cover-glass is advised in all cases where one reagent is to
be washed out before the application of a second, or where one
is to be immediately followed by another, provided the specimen
is not so delicate as to be disturbed by it. Some parts of the
specimen are apt to escape action, if the washing or the intro-
duction of several reagents in these operations is conducted
without lifting the cover; but by the exercise of great care
both these operations may be carried on successfully by the use
of bibulous paper without removing the cover-glass.

21. Owing to their importance, potash and iodine are de-
scribed first. The other reagents are given in alphabetical
order, for convenience of reference.

22. Potash, Potassic hydrate, Caustic potassa, are names
interchangeably given to white solid potassa and to its solutions.
This substance absorbs carbonic acid so eagerly from the air,
that it must be kept in glass-stoppered bottles. To prevent the
stoppers from becoming fastened by the action of the alkali on
the glass, it is well to smear them with vaseline or paraffin.

23. Solutions of two strengths are used. J. Concentrated.
Solid potassa is dissolved in the smallest amount of water (not
far from half its own weight) by which it will become liquid.
This dense syrupy liquid is too strong for ordinary use. II. A
common solution made with one part of solid potassa in three,

1 Consult the following: Botanical Micro-Chemistry, by Poulsen, translated
by Trelease (Cassino, Boston), 1884. Hilfsbuch by Behrens (Schwetschke,
Braunschweig), 1884.

INTRODUCTION. 7

five, or ten parts of water, depending upon the particular case
in which it is to be used.

24, For use as a macerating agent in separating cells, a strong
solution is preferable, and is more efficient when it is slightly
warmed. For dissolving or rendering transparent most of the
contents of cells, more dilute solutions are better. Owing to the
prompt effect produced on the cell-wall, and upon the contents
of cells, especially of young ones, a moderately strong solution
of potassa is the most useful clearing agent that we have. After
amass of tissue, for instance an embryo, has been acted on by
a solution of potassa until it has become translucent, it is to be
cautiously subjected to the action of an acid, preferably acetic
or hydrochloric, and then washed. <A second treatment, or even
a third, may be necessary to wake the object sufficiently clear.
Sometimes, however, the potassa renders the tissues too nearly
transparent, in which case they may be slightly clouded by a
little alum-water. This process of clearing tissues was first
used by Hanstein in the examination of the tissues at points of
growth, and it is of very wide applicability.

25. Some structures are darkened at first by the use of
potassa, but cautious treatment afterwards with a dilute acid
and a second application of potassa will generally produce a
good degree of transparency.

26. Potassa is a solvent for many of the substances which
inecrust the cell-wall, but in most cases the solutions must be
used warm; in a few instances heated even to boiling. The
cell-wall, washed after such treatment, will give the cellulose
reactions (see 145). Suberin can thus be removed from the
cell-walls of cork, forming with the potassa yellowish drops.

27. As the aqueous solution of potassa causes considerable
swelling of the cell-wall, it is desirable to have also at hand
an alcoholic solution. This is best made by mixing 95 per
cent alcohol with a strong aqueous solution of potassa until a
cloudiness appears. The mixture is then to be shaken fre-
quently, and, after a day or so, the clear liquid above is to be
carefully poured off. This solution may be diluted with alcohol
if necessary.?

28. Solutions of caustic soda can replace potassa in most
of the foregoing reactions. The special cases in which these
aikalies are employed for the identification of certain contents
o£ sells will be described later.

1 Russow’s Potash-alcohol.

8 INTRODUCTION.

29, Iodine. This clement is only very slightly soluble in
pure water. Upon exposure to strong light, however, a some-
what larger amount of iodine passes into solution after a while,
owing probably to formation of hydriodic acid. If it is neces-
sary to examine the effect of iodine alone, as in certain parts of
Lichens, a fresh solution should be used. In fact, it is recom-
mended that in such cases a minute fragment of solid iodine be
placed in pure water under the cover-glass at the moment of
examination.

30. But for all ordinary examinations, a solution of iodine in
water which contains iodide of potassium is used. The propor-
tions employed vary widely. A convenient strength is obtained
by dissolving one gram of iodine and five grams of potassic
iodide in enough water to make one hundred cubic centimeters.
Even this solution is too strong for some purposes. In a few
cases a different solution is advised, made by dissolving five
centigrams of iodine and twenty centigrams of potassic iodide in
fifteen grams of water.1 But, in general, dilute solutions are
preferable.

31. A solution of iodine and iodide of potassium in glyce-
rin is employed by some. An alcoholic solution is sometimes
useful.

32. Iodine is a characteristic test for starch, to which it
imparts a blue color, depending for its depth chiefly upon the
strength of the solution. Iodine in absolute alcohol gives with
dry starch a brownish color; if the alcohol is not absolute, that
is, anhydrous, a blue color is given as with ordinary aqueous
solutions.

33. In most cases cellulose is colored pale yellow to deep
brown by iodine. If the specimen is acted on by concentrated
sulphuric acid, either just before or just after the application
of the iodine, a blue color appears. This reaction for cellulose
is disguised by various incrusting matters, which can be removed
by strong acids or alkalies; after their removal the washed
specimen will give the characteristic cellulose reaction (see also
143).

84. Iodine and a metallic iodide in a strong solution of chlo-
ride of zine form a very useful reagent for cellulose, to which a
blue color is given. The reagent is easily made by dissolving
pure zine in concentrated hydrochloric acid until there is no
further action of the acid. The solution, with a little metallic

1 Poulsen,

INTRODUCTION. 9

zinc still undissolved, is to be evaporated to a syrupy consist-
ence, saturated with potassic iodide, and lastly enough pure
iodine added to render the whole a deep red or brown. Cell-
walls that have incrusting matters, for instance, cork-cells and
most wood-cells, are turned yellow by this reagent. It is known
as Schulze’s reagent. Behrens advises the preparation of modi-
fications of this important reagent, all depending on the relative
amount of iodine and the degree of dilution. A little practice
in their use will suggest the cases to which each is specially
applicable. Solutions of iodine color protoplasm, and other
albuminoid bodies, yellow to deep brown.

35. Owing to the tendency of iodine solutions to form hydri-
odic acid, it is reeommended by many authors that they be kept
out of the light; but this precaution is not necessary unless the
investigation calls for pure iodine alone; in such a case it is
better to use only freshly prepared solutions.

The following reagents are arranged in alphabetical order.

36. Acetic acid. Glacial acetic acid diluted by two or four
parts of water, or the ordinary concentrated acid of the shops, is
used (1) to neutralize the alkali in Hanstcin’s method (see 24) ;
(2) to discriminate between oxalates and carbonates, the latter
dissolving with effervescence in it, the former remaining un-
changed in it, but dissolving quietly in hydrochloric acid; (8) in
the study of the nucleus.

37. Alcohol. Common strong alcohol, or the so-called ‘* 95
per cent,” is widely employed for the preservation of micro-
scopic material. In it soft tissues become hardened. This is a
great advantage in the case of specimens which are too yielding
to be cleanly cut when fresh. If it is desirable to again soften
tissues which have been hardened by the action of alcohol, it is
merely necessary to soak them for a short time in water, when
they will assume nearly the consistence they had when fresh.
This reagent produces certain marked changes in the contents of
vegetable cells: the protoplasmic matters become more or less
shrunken, many oils and fats are dissolved, and certain sub-
stances in solution in the cell-sap are separated out (see 183).

38. The air which occurs in intercellular spaces and in all
dry specimens is generally removed with ease by the action of
alcohol, especially if a little heat is applied.

89. Alcohol is of use also in the preparation of some of the
staining agents.

40. Absolute alcohol contains only the merest trace of water.
Hence it must be used instead of ordinary alcohol whenever the

10 INTRODUCTION.

specimen is affected by water, as is the case with mucilagi- /
nous tissues, crystalloids, etc. Asa reagent for use under the
cover-glass it is more satisfactory than common alcohol, but
in keeping it the greatest care must be exercised to exclude |
moisture.

41. Alum. Either potash- or ammonia-alum may be used to
diminish the transparency of cells which have been acted on by
potassa (see 24). Alum is a mordant in some of the processes
for staining (see 98).

42. Ammonia. Aqueous ammonia may replace the fixed
alkalies, potassa and soda, but possesses no advantage over
them except in its somewhat slower and less violent action.
For its use in the examination of albuminoids, see 125. Its
principal use in microscopy is in the preparation of certain
staining agents (see 77) and cuprammonia.

43. Anilin chloride. Dissolved in alcohol, this reagent im-
parts a pale yellow color to lignified cell-walls. Upon addition
of hydrochloric acid, the color is much deepened. This is Héhnel’s
test for lignin.

44. Anilin sulphate. This substance in aqueous or alcoholic
solution gives to lignified cell-walls a pale yellow color, which is
much deeper when the reagent is followed by sulphuric acid, —
Wiesner’s test for lignin.

45. Argentic nitrate, or nitrate of silver, in extremely dilute
alkaline solution freshly made, has been recommended for dis-
criminating between living and dead protoplasm, the former
turning dark, the latter remaining unchanged (see details in
Part II.).

46. Asparagin. A concentrated solution of asparagin is
suggested by Borodin for the recognition of asparagin itself
when its crystals have been formed in tissues blanched by dark
ness.

47. Aurie chloride, long used for staining preparations in
animal histology, has been somewhat employed for coloring the
cells of certain lower plants, and in the same manner as argentic
nitrate, for detecting the condition of protoplasm.

48. Benzol is a powerful solvent for various vegetable fats
and resins. It is also used for the preparation of benzol-balsam
(see 112), and in dissolving paraffin (see 8).

49. Calctie chloride. Treub employs this for clearing tis-
sues. The fresh section, after having been moistened by a
little water, is covered with dry powdered chloride, warmed
until it is about dry, and afterwards placed in a little water.

INTRODUCTION. 11

From this it is to be transferred to glycerin, where it soon
wecomes clear.?

50. Culcie hypochlorite in aqueous solution bleaches many
tissues without the use of an acid, but, in general, specimens
which have been subjected to its action are more thoroughly de-
colorized if they are subsequently placed in dilute hydrochloric
acid, washed in pure water, and finally transferred to glycerin.
Preparations which have been bleached by this method are easily
colored by some of the staining agents described on page 10.
Sodic hypochlorite may replace it in all cases.

51. Carbon disulphide is used as a solvent for fats.

52. Carbolic acid, or phenol, dissolved in the least quantity
of concentrated hydrochloric acid which will take it up, gives
a green color with lignified cells. It is better to add to a few
drops of the strongest hydrochloric acid a small quantity of
crystallized phenol, warm the mixture slightly, and upon its
cooling add enough acid to remove any cloudiness.

58. Chloral hydrate in aqueous solution is recommended by
Arthur Meyer? as a clearing agent. Two parts of water are
added to five parts of chloral, and used somewhat above the
temperature of 15° C.

54. Chromic acid. The pure acid, in strong solution, acts
promptly on cell-walls, dissolving all except those which are
silicified and those which are cutinized. Even the latter yield
to prolonged action. If the solution is more dilute, the action
goes on only so far as to cause swelling of the cell-wall, bring-
ing out, in special cases, a very distinct stratification. Solutions
which are so dilute as to be merely pale yellow cause hardening
of soft tissues, and this acid therefore forms an excellent adju-
vant to alcohol for this purpose (see Part II.).

55. Cuprammonia. To a solution of cupric sulphate add
enough soda (or potassa) to produce a precipitate. After
removal of the excess of liquid by filtration, place the precipitate
in a flask, wash once with water which las been freed from air by
boiling, and then dissolve the mass in the least quantity of con-
centrated ammonia which will take it up. The freshly prepared
solution should act promptly on delicate fibres of cellulose,
cotton for example, causing them to swell and apparently pass
into solution. Lignified and cutinized cell-walls are not acted

1 Plahault: Accroissement terminal de la racine. Ann. des Sc. nat., 1875,
vi. p. 24.
2 Das Chlorophyllkorn, Leipziy, 1883.

12 INTRODUCTION.

upen until the foreign matter has been removed by the agents
previously spoken of (see 26).

This reagent, known as Schweizer’s,! possesses its chief in-
terest from the fact that it is the only liquid known in which
cellulose appears to dissolve without essential change of compo-
sition. It has a limited application in the discrimination of
fibres used in the arts.

56. Cupric acetate in aqueous solution is used as a preparatory
liquid for the examination of resins. The part to be examined
is kept in a concentrated solution for some days, and sections
are then made from it. If certain resins are present, they will
appear of a green color. The above is Franchimont’s test based
on a reaction discovered by Unverdorben.?

57. Cupric sulphate in saturated aqueous solution is used
for the detection of certain carbohydrates (see 184) and albumi-
noidal matters (see 124). Commercial blue vitriol, recrystallized
two or three times, will answer for all ordinary cases.

58. ther is used as a solvent for fats, ete.

59. Ferric chloridz in aqueous solution was formerly recom-
roended as a test for the tannins ;® the tannin of oak-bark be-
coming bluish-black ; that in the leaves of the sumach, greenish-
black. But the distinctions are not constant. Ferric acetate
and sulphate are now more generally used than the chloride as
a test, and are better.

60. Glycerin. Only the purest glycerin should ever be em-
ployed in microscopic examinations. The following are among
the most important of its many applications: 1. In clearing
specimens. It is used not only as an adjuvant in the Hanstein
and other methods of clearing, but, in many cases, it serves well
without any other reagent. 2. To cause withdrawal of water
from fresh cells, the degree of effect depending on the strength
of the glycerin. 8. In the examination of protein granules
(see 175). 4. As a test for inulin; this substance separates
sooner or later in the form of spherocrystals. 5. As a solvent
for iodine (see 31).

61. LZydrochloric acid. Pure concentrated acid is one of the
racat satisfactory agents for the maceration of woody tissues.
When dilute, it serves for the discrimination between carbonates
and oxalates, the former dissolving with effervescence, the latter

* Schweizer: Vierteljahrsschrift natur. Ges., Zuneh, 1857.
° Behrens: Hilfsbuch, p. 877.
* Watts’s edition of Fownes’s Chem., p. 672.

INTRODUCTION. 13

without. It must be remembered that acetic acid dissolves
carbonates, but not oxalates (see 36).

This acid has been used by Pringsheim! in the study of
chlorophyll grains; fresh sections of tissues containing chloro-
phyll being exposed to the action of the acid for some hours.
From the grains, minute spheres of a brownish color become
nearly detached, and these afterwards appear as clusters of
acicular crystals (see Part II.). Hydrochloric acid is also of
use in the examination of some protcin matters (see 124).

62, Indol (Niggl’s test? for lignin) is used in an aqueous so-
lution. The specimen, subjected to the action of the solution for
a few minutes, is transferred to sulphuric acid of specific gravity
1.2 (made by adding one part of concentrated acid to four parts
of water). Lignified structures become red.

63. MMercuric chloride, or corrosive sublimate, dissolved in
fifty parts of absolute alcohol renders protein grains insoluble
in water. Pfeffer? recommends that the specimen should remain
in this reagent at least twelve hours. Dippel* uses a dilute
aqueous solution (1 in 500) to render visible the currents in the
most delicate threads of protoplasm (and for the demonstration
of the nucleus without affecting the other contents of the cell).

64. MMillon’s reagent, commonly called acid nitrate of mercury,
is best prepared, according to its discoverer, by pouring upon
pure mercury its own weiglt of concentrated nitric acid. For
a short time the action is violent; when it subsides a little,
gently warm the liquid until the metal is completely dissolved.
The solution is immediately diluted by twice its volume of pure
water. After a few hours the liquid is to be decanted from the
crystalline mass which has formed, and it is then ready for use.®

This reagent is more efficient when freshly made.

Albuminoid substances are colored red by this reagent even
in the cold, but much more readily upon the application of heat.
According to Millon, the reaction is due to the presence in the
liquid of both mercuric nitrate and nitrite.

This reagent has been employed for the demonstration of the
stratification and spiral striation of certain cell-walls.

65. Mitric ucid gives to protein matters a yellow color,
which is intensified upon the subsequent use of ammonia. The

1 Pringsheim’s Jahrbiicher, Bd. xii, p. 294, et seq.
2 Flora, 1881, p. 545, et seq.

3 Pringsheim’s Jahrbiicher, viii. p. 441,

* Dippel: Das Mikroskop, i. p. 281.

5 Quoted from Behrens: Hilfsb. p. 247.

14 INTRODUCTION.

same treatment, especially if the slide is slightly warmed, colors
the so-called intercellular substance ycllow. ‘The acid is also
used as a test for suberin (see 158).

66. Osmic acid (perosmic acid) is very volatile, and there-
fore is best preserved in sealed glass tubes until wanted for use,
when the tube can be broken under water. Even from the aque-
ous solution the irritating acid escapes in small amount, render-
ing it a disagreeable reagent to work with. The solutions are
usually of one per cent strength.

Oils are colored brown by the reduction of the acid to me-
tallic osmium on the surface of the drops. Living protoplasm
is killed at once by even dilute solutions of this acid, and there
is usually more or less discoloration of the different parts.
Hence it is a useful agent for arresting the processes of cell-
division and growth at any desired stage. Advantage is some-
times gained, according to Poulsen,! by the combination with it
of chromic acid.

67. Phenol (see carbolic acid, 52).

68. Phloroglucin, used by Wiesner as a test for lignin.?
The specimen is first acted on by hydrochloric acid, and then
moistened by a solution of phloroglucin in water or alcohol. If
the cell-walls are lignified, they will at once assume a red color.
Hihnel® suggests the employment of a strong decoction of cherry
wood instead of the phloroglucin. Used in the same way, it im-
parts a violet color to lignified cells. This test is hardly so
satisfactory as the other.

69. Potassic bichromate in aqueous solution is used to harden
tissues, and is about as good as chromic acid. It has been also
employed by Sanio* for the detection of tannin.

70. Potassic chlorate, used with nitric acid, is the most con-
venient macerating agent. If a few small crystals of this salt
are added to a little concentrated nitric acid in a test-tube con-
taining a fragment of wood, and the liquid is carefully warmed,
violent action begins somewhat below the point of boiling, and
the wood is speedily disintegrated. By selecting acid of the
right strength, and by careful regulation of the heat applied, the
action of the liquid can be kept well under control, so that
almost any degree of action can be obtained. It is not safe to
use this reagent in the room where delicate apparatus is kept,

1 Mikrochemie, p. 19.

2 Sitzungsber. Akad. Wien, 1878, p. 60.
3 Tb. 1877, p. 685.

# Bot. Zeitung, 1863, p. 17.

INTRODUCTION. 15

since the gases evolved act upon metals. This is Schulze’s
macerating process.

71. Potassic nitrate) used in the examination of proto-
plasm (see Part II.).

72. Rosolic acid, or corallin, dissolved in water containing a
trace of sodic carbonate, forms a purple fluid which colors vege-
table mucus red. It is used also to demonstrate the structure of
cribrose-tissue.?

73. Schwetzer’s reagent (see cuprammonia).

74. Sodie chloride (common salt), used in aqueous solution
in the examination of protoplasm (see 120).

75. Sugar. Cane sugar dissolved in water to form a thick
syrup is allowed to act for some time on tissues containing pro-
toplasm: a drop of concentrated sulphuric acid is then placed
on the object, when the protoplasm will take on a faint rose-red
color. The reaction is uncertain.

76. Sulphuric acid. Pure concentrated acid is used as an
adjuvant in many tests, é g., with iodine solutions in the identi-
fication of cellulose, but it is also of great use by itself in break-
ing down cellulose. By it, a cellulose wall can be destroyed
without destruction of the protoplasm within (see 141).

77. Staining agents. A few of the chemicals in the foregoing
list impart to certain tissues, and certain contents of cells, colors
which have a good degree of permanence when the specimens
are preserved in a suitable medium. But the colors produced
by most reagents are fugitive, and serve only a temporary pur-
pose. When, therefore, it is desirable to stain or tinge a given
part of a specimen permanently, recourse must be had to dyes
which do not readily fade.

78. Some of these have been long in use in Vegetable His-
tology for the purpose of preparing attractive specimens for the
demonstration of tissues, but it is only within a recent period that
they have been successfully employed in the study of cell-divi-
sion. In the examination of the changes which take place in
the interior of cells during division, they are indispensable: in
the examination of the tissues themselves, their use is far from
satisfactory. As will be specially shown later, the chemical
differences between the cell-walls of certain tissues which it is
desirable to distinguish from each other under the microscope
are not very great, and they often behave alike as respects

1 Treub: Naturk. Verh. d. koningl. Akad. vol. xix., 1878, p. 9.
2 Behrens: Hilfsbuch, p. 313.

16 INTRODUCTION.

staining agents. Hence it is impossible to lay down rules
which will apply to all cases in which tissues are to be stained:
the staining of the nucleus, however, can be readily secured by
following the explicit directions given in the chapter on ‘ Cell-
growth.”

79. Of the whole class of staining agents, it may be said that
exposure to strong light diminishes the brilliancy of the coloring
they produce in the specimen, and in many cases completely
destroys it. In general, the staining obtained by allowing the
specimen to remain for a long time in a dilute solution of a
dye is more satisfactory than when a stronger dye is used with
haste.

80. Carin. Two grades are readily procurable in this coun-
try; namely, (1) ‘* No. 40,” (2) ‘* Orient.” The former is the
cheaper, and will answer for all cases described in this treatise ;
but attention must be called to the fact that it is sometimes
adulterated, and hence it may be found necessary to change the
proportions given in the following formulas. A good carmin,
even of the grade first mentioned, should leave only little residue
when placed in strong ammonia. If more than a trace of resi-
due is found, the amount of carmin in the formula must be
proportionately increased.

81. Ammonia-carmin. Pure powdered carmin is rubbed
up with a little water to form a thin paste, enough strong am-
monia to dissolve it is cautiously added, and the whole is then
filtered. The filtrate is to be evaporated slowly over a water-
bath. The dried mass dissolves readily in water, forming a
clear liquid which keeps well; but it is better to preserve the
mass in a tightly-stoppered bottle, dissolving it only as required
(Hartig’s carmin).!

82. A modification of this carmin is made as follows: .2 to
4 gram of carmin is shaken up with 30 ¢.c. of water, and a
few drops of ammonia added. A part of the carmin dissolves,
and is to be filtered. If the filtrate smells strongly of ammo-
nia, it is allowed to stand for half a day under a bell-jar. A
drop of ammonia will re-dissolve any slight trace of carmin
which may separate. This fluid is to be added to water, drop
by drop, until the right color is obtained (Gerlach’s ammonia-
carmin).?

83. If, to the filtrate last mentioned, 30 grams of glycerin

1 Dippel: Das Mikroskop, i. p, 284.
2 Behrens: Hilfsbuch, p. 257.

INTRODUCTION. 17

and 10 grams of strong alcohol are added, a liquid is obtained
which is known as Frey’s glycerin-carmin.

84. Beale’s carmin is nearly the same. Ten grains of carmin
are placed in a test-tube, and half a drachm of strong ammonia
added; the mixture is shaken, and gently heated over a spirit-
lamp. The solution is to be boiled for a few seconds and then
allowed to cool. In an hour two ounces of glycerin and two
ounces of water are to be added, together with half an ounce of
alcohol; the Jiquid is then filtered.?

85. Thiersch’s borax-carmin.? 2 grams of borax are dis-
solved in 28 ¢.c. of distilled water, and .5 gram of carmin
added. The solution is next mixed with 60 c.c. of absolute
alcohol, and filtered.

86. Thiersch’s oxalic-acid carmin.? 1 gram of carmin is
dissolved in 1 ¢.c. of ammonia and 3 ¢.c. of water. Another
solution is prepared by dissolving 8 grams of crystallized oxalic
acid in 175 c.c. of water. The two solutions are then mixed,
16 e.c. of absolute alcohol added, and the whole filtered. This
liquid is violet when ammonia is in excess; orange, if too much
oxalic acid is present.

87. Grenacher’s alum-curmin.* Carmin is dissolved in a
solution of potash-alum or ammonia-alum until the required
color is obtained. This has been modified by Tang] as follows :
To a saturated solution of alum, enough carmin is added to give
a deep color (1 grm. in 100 ¢.¢. of solution), the whole boiled
for ten minutes, and filtered upon cooling.

88. Woodward’s carmin. ‘* Pulverized carmin 7} grains,
water of ammonia 20 drops, absolute alcohol half an ounce,
glycerin 1 ounce, distilled water 1 ounce. Put the pulverized
carmin in a test-tube and add the ammonia. Boil slowly for a
few seconds, and set aside uncorked for a day, to get rid of the
excess of ammonia. Add the mixed water and glycerin, and
next the alcohol, and filter.”

89. Curmin with picric acid. This agent, known as Ran-
vier's picrocarmin, is made by cautiously adding to a concentrated
solution of picric acid enough ammonia-carmin solution (81)
to saturate it, and then evaporating to one-fifth the volume.

1 Beale: How to Work with the Microscope, p. 125.
% Behrens: Hilfsbuch, p. 258.
3 Behrens: Hilfsbuch, p. 257. In Dippel(Das Mikroskop), p. 285, the pro-
portions are somewhat different.
4 Archiv. fiir Mikyosk. Anat., 1879, p. 465. Tangl, in Pringsh. Jahrb.,
Bd. xii., 1880, p. 170.
2

18 INTRODUCTION;

Upon cooling, a slight sediment is deposited. After filtration
from this sediment the liquid is evaporated to dryness, and
afterwards dissolved in water in the proportion of 1: 100.
Another formula is: 1 gram of carmin and 4 ¢.c. of concen-
trated ammonia are mixed with 200 ¢.c. of water, and 5 grams
of picric acid then added. After nearly complete solution the
clear liquid is poured off, and exposed to the air for some weeks.
The red powder left after this slow evaporation is to be dis-
solved when requirecdl in water in the proportion of 2:100, and
the solution filtered through two thicknesses of filter-paper.
Cochineal, the substance from which carmin is prepared, may
be used in aqueous extract, or with alum. ‘The formula for the
preparation with alum is given as follows: Rub to a fine powder
one gram of cochineal with one gram of burnt alum; mix with
100 ¢.c. of water, and boil down to 60. c.c. When cold, filter the
solution several times, and add a few drops of carbolic acid.
90. Hematoxylin (a dye obtained from logwood) is used dis-
solved in alcohol, or alum-water, according to circumstances.
Frey gives the formula: 1 gram of haematoxylin is dissolved
in absolute alcohol. This solution is added, drop by drop, to a
three per cent aqueous solution of alum, until it becomes deep
violet in color. After exposure to the air for a few days, it is
to be filtered, and is then ready for use; but a fresh filtration
will be found necessary after a time. Poulsen advises that a
few drops of a ten per cent solution of alum be added to an
aqueous solution of hematoxylin (.85 gram in 10 ¢.c. water).
Aqueous extracts of several other dye-woods can replace
hematoxylin in some cases, but they have no advantage over it.
91. Picrie acid (trinitrophenic acid) in aqueous solution is
valuable for staining and hardening protoplasm. It may be
used alone, combined with carmin (see 89), or with nigrosin.
92. Alkanet-root (alkanna) in alcoholic solution tinges resin-
ous globules and serves to prepare for cutting specimens which
contain them. The method of use is described under ‘+ Resins.”
93. The coul-tar colors. Under this name are comprised the
anilin derivatives and a few others of a slightly different origin.
The following table will indicate to some extent the changes of
color which may be expected when these dyes are used with
tissues which have a marked acid or alkaline reaction. But it
should be observed that the names of several of the dyes are
loosely applied, and that the dyes made by different manufac-
turers are not always of the same character or strength. All of
the dyes mentioned below are soluble in water and alcohol.

INTRODUCTION,

19

Name.

Effect of dilute TI Cl.

| Ieffect of dilute Ammonia.

Magenta.
Safranin.

Re] anilin.
Acid azo-rubin.
Kosin

Ponceau.

Solid yellow.
Orange ** R.”
Gold orange.

Meth) l-green.

Brilliant green.
Emerald green.

Cotton-blue ‘* B ”
Methy!-violet ** BBBBBB.”’
Nigrosin.

Led dyes.

Color fades to brown or light
purple.

Color changes to purple, and
a brown precipitate occurs,

Deep orange-brown color,

Slight change of tint.

Orange precipitate.

No change of color

Yellow and Orange dyes.

Purple precipitate.
Unchanged.
Little change.

Green dyes.

The bluish tint becomes deep
green.

Fades somewhat.

Fades out.

Blue and Violet dyes.
Unchang'd.

Greenish precipitate,
Little change.

Fades completely.
Little change.

Reddish precipitate,
Little change.

No marked change.
No change.

Unchanged.

Little change.
| Color deepens to red.

Whitish precipitate.

Fades out.
| Whitish precipitate.

Purple precipitate.

| Fades somewhat.
Little change.

94. A solution of any of the above dyes consisting of one

gram with enough water to make one hundred cubic centimeters,
although too strong for most cases, is very convenient, since it
can easily be diluted at will. From even very dilute solutions
parts of a specimen, for instance, a cross-section of a stem, will
take up some of the color with more or less change. If the
staining is too deep, a part of the color can be removed by
careful washing in alcohol, or in a very dilute acid or alkali
(see above table for each case).

95. Double-stuining. It is sometimes possible to color dif-
ferent parts of a specimen with more than one dye ; for instance,
staining the fibres of the bark green, and the wood of the same
specimen red. The best results are obtained by the use of an
aleoholic solution of one of the dyes and an aqueous solution of
the other. The following method proposed by Rothrock! gives
excellent results, ‘The dyes are Woodward’s carmin (see 88)
and anilin green (or ‘iodine green”). The specimen (whether
bleached by sodic hypochlorite or left unbleached) is first
thoroughly saturated by alcohol, which hardens it, and causes
contraction of the contents; it is then kept for a day in a dilute

! Botanical Gazette, September, 1879.

20 INTRODUCTION.

alcoholic solution of anilin green. In a row of watch-crystals
the following liquids are placed: (1) water, (2) Woodward’s
carmin, (3, 4, 5) alcohol, (6) absolute alcohol, (7) oil of cloves.
The specimen, taken from the green, is dipped for a moment in
water, then for about a minute in the carmin, then successively
through the alcohols, in each of which it remains ten to twenty
minutes, except in the first, where it remains only long enough
to have the unfixed carmin washed away. From the last alcohol
it goes into oil of cloves (or benzol), where it should remain
long enough to become perfectly transparent. It is then to be
mounted in balsam.

96. Double-staining can also be effected by the successive use
of hematoxylin and an anilin color. By the use of two or more
anilin dyes different parts of a specimen may be colored differ-
ently; but asa rule all these effects are uncertain, and cannot be
relied upon for the positive identification of tissues. In general,
however, long bast fibres take characteristic colors.

97. The following combinations for double-staining are rec-
ommended by Dr. Stirling, and though originally designed only
for animal tissues, serve well with sections of plauts:—

1. Osmic acid and picrocarmin. 2. Picric acid and picro-
carmin, 8. Picrocarmin and logwood (hematoxylin). 4. Pi-
crocarmin and an anilin dye. 5. Logwood and iodine green.
6. Eosin and iodine green. 7. Eosin and logwood. 8. Gold
chloride and an anilin dye.

98. In the cases which require special treatment, for instance,
the staining of the nucleus, the precautions laid down must
be attended to in order to insure success. But in the ordinary
instances where it is desirable to stain a specimen merely to
bring some part into prominence for purposes of demonstration,
the widest choice in dyes and their use is advised. A few mor-
dants have been tried in order to fix the colors, but with little
success. The best are tannin in solution, and aqueous solutions
of any of the alums. A little practice will show which mordant
is best for each case.

99. Specimens stained by nearly all of the above dyes can
be mounted securely in balsam, as directed in section 110; but
glycerin and glycerin-jelly mounts are apt to become faded or
discolored after a time.

100. Mounting-media. Pollen and other dry specimens are
preserved in shallow cells formed by a thin ring of asphalt-

1 Journ, Anat. and Phys., 1881, p. 349,

INTRODUCTION. 21

cement, varnish, or whitc lead, allowed to dry nearly to hardness,
upon which a cover-glass fits firmly, and is retained by a second
ring of the same cement. If the precaution is taken to have the
cover-glass fit evenly to the first layer of cement, there is little
danger that the subsequent layer, which is to hold the cover in
place, will creep under it and into the cell.

101. Glycerin, pure water, calcic chloride solution, potassic
acetate, and like liquids may be used as mounting-media in cells
prepared in the manner just mentioned, but made of greater
thickness. Care must be observed to avoid touching the upper
edge of the cement ring with the liquid; and yet the cell must
be completely filled, in order to exclude air.

102. If a specimen has been prepared in glycerin, and it is
not considered well to disturb the cover-glass, a cement ring or
square can be built up around the cover at a little distance from
it, provided the glass slide is thoroughly cleaned at the place
where the cement is to be put. After the requisite number of
layers have hardened sufficiently, a ring of the same or, better,
of a more quickly drying cement may be placed across from the
edge of the cell to the cover-glass, to hold it in place. As this,
in drying, will contract somewhat, it is a good plan to place two
or three fragments of thin glass under the cover, that these
may receive the pressure and prevent crushing the specimen.

103. Of the mounting-media, one of the best is glycerin and
acetic acid in equal parts, boiled and filtered. It serves well for
thin-walled specimens (especially in the lower plants).

104. Specimens of fresh cells or of juicy tissues which are to
be mounted in glycerin are best treated in the manner recom-
mended by Beale.! ‘* The specimen is first immersed in weak
glycerin, and the density of the fluid is gradually increased,
either by adding from time to time a few drops of strong gly-
cerin, until it bears the strongest, or by allowing the original
weak solution to become gradually concentrated by slow evapo-
ration. In this way, in the course of two or three days the
softest and most delicate tissues may be made to swell out
almost to their original volume in the densest glycerin or syrup.
They become more transparent, but no chemical alteration is
produced, and the addition of water will at any time cause the
specimen to assume its ordinary characters.”

105. It is plain that mounts in any liquid must be liable to
injury from displacement of the cover-glass; but this can be

1 How to Work with the Microscope, p. 360.

22 INTRODUCTION.

partially guarded against by fastening to the upper surface of
the slide, near its two ends, square pieces of pasteboard a little
thicker than the cell itself.

106. Glycerin-jelly, a mixture of glycerin with pure gelatin, is
liquid at the temperature of boiling water, and solidifies again
on cooling. Any specimen which is not injured by being slightly
heated can be mounted satisfactorily in the jelly, provided it
is first thoroughly saturated with glycerin. But this precaution
is by no means necessary in all cases.

107. A drop of the melted jelly, free from air-bubbles, is
placed on the slide (a fragment of the solid jelly can be melted
on the slide if preferred), the specimen placed therein, and the
cover-glass, previously moistened slightly on the under side with
glycerin, is carefully laid on, and the preparation now allowed
to cool. When the jelly is again hard, a varnish or cement ring
may be placed around the edge of the cover to hold it in place.
Asphalt-cement is apt to impart to the jclly a dark tinge, which
may sooner or later spoil the mount, and hence the colorless
varnishes are better.

108. The edge of the jelly may be lightly touched with a
strong solution of a chromate, for instance, bichromate of potas-
sium, and exposed for a while to light. This renders the jelly
insoluble, and firmly sets it.

109. The following are among the best formulas for making
this useful mounting-medium : —

One part of pure gelatin, three parts of water, and four of
glycerin (Schacht, quoted by Dippel). Nordstedt uses the same
proportions, and advises the addition of a small piece of cam-
phor or a drop of carbolic acid, to prevent moulding.

One part of gelatin is soaked in six parts of water for two
hours, seven parts of glycerin are added, and one per cent of
carbolie acid is added to the whole. The mass is heated for
fifteen minutes, with constant stirring, and then filtered through
glass-wool. All the ingredients must be absolutely pure (Kaiser,
Bot. Centrbl., 1880, p. 24).

The proportions employed in the second formula, but without
the addition of the carbolic acid, give a clearer jelly ; and it has
not been apt to mould, especially if the cork of the bottle con-
taining it be wrapped in a thin picce of linen, which has been
dipped in dilute carbolic acid.

110. Canada balsam. This is used either (1) alone, or (2) in
solution. In either case the specimen must be free from water,
and permeated by some liquid easily miscible with the balsam.

INTRODUCTION. 23,

This is easily effected by first saturating the object with alcohol
(beginning preferably with dilute, and then using stronger), in
order to expel all water; next placing the alcoholic specimen
in oil of cloves, turpentine, or benzol, until the alcohol is in
turn expelled. The specimen thus permeated is transferred to
balsam which has been previously placed on the slide. Care
must always be taken to have the balsam perfectly free from
air-bubbles.

111. When used alone, the balsam on the slide may be
heated, to drive off a part of its more volatile constituents, and
the specimen can then be placed in the warm liquid. But this
method is not applicable when the specimen is affected by slight
heating; it is best adapted to hard tissues, like woods and fibres.
Balsam which has thus been heated hardens on cooling to a good
degree of firmness. This firmness is secured with balsam used
without heat only after a longer lapse of time, during which the
more volatile matters have escaped.

112. If pure balsam is cautiously beated in a capsule until it
no longer gives off vapors, the melted mass will cool into a pale
amber-colored solid. This solid dissolved in a small quantity of
benzol forms a liquid of the consistence of syrup, which is useful
for all mounting where heat is injurious. ‘The specimens must
be treated successively with alcohol and benzol, and they are
then ready to be immersed in the benzol-balsam on the slide.
An equally serviceable solution is made by dissolving the mass
in chloroform. Chloroform-balsam requires the specimen to be
saturated with chloroform before immersion.

113. In all the above cases two precautions will save disap-
pointment: 1st. the slides and cover-glasses should be heated
slightly, to drive off any moisture on the surfaces which are to
come in contact with the mounting-medium; 2d. the covers
should be held in place by means of a slight weight, or by the
pressure of a spring clip, until the balsam or its solution has
become tolerably firm. <A little experience will show that speci-
mens mounted in balsam may require a somewhat different
management of the mirror under the stage from those which are
mounted in a medium with a different refractive power. Damar
may replace balsam when the latter, which is the better, is not
to be had.

114. Hoyer’s mounting-media are mghly recommended by
Strasburger.!. The one which is preferred for anilin preparations

1 Das botan. Practicum, 1884, p. 40.

24 INTRODUCTION,

is made by adding colorless pieces of gum-arabic to a solution
of potassic acetate or ammonic acetate, until the liquid becomes
of the density of thick syrup, while in that intended for carmin
preparations the gum is dissolved in a five to ten per cent
aqueous solution of chloral hydrate, and about ten per cent of
glycerin added. Either of these media, or a plain solution of
pure gum-arabic, will be found to answer admirably for all prepa-
rations of woods which are to be photographed.

115. The edges of the cover-glass are usually painted with
some varnish of good quality. Those in best repute are : —

1. Asphalt-varnish, to be thinned with turpentine when too
thick.

2. Maskenlack, a German preparation, thinned with alcohol.

3. Mikroskopirlack, also thinned with absolute alcohol.

4. Shell-lac in alcohol, tinged with some anilin color. If a
few drops of castor-oil are added to the solution, it dries into
a less brittle finish.

5. Gold-size.

6. White lead (with oil).

It is a good plan to revarnish slides whenever the varnish
first shows any indication of breaking away.

A few works in regard to microscopic manipulation and
micro-chemistry which may be advantageously consulted by the
student are the following : —

BEALE. How to Work with the Microscope (London). This is a large
octavo volume, with very minute descriptions of microscopical appliances and
manipulation. Several editions have been printed.

CARPENTER. The Microscope (London). A small octavo of about 900 pp.
This work deals at some length with the structure of animals and plants.

Benrens. Hilfsbuch zur Ausfiihrung Mikroskopischer Untersuchungen
im Botanischen Laboratorium (Braunschweig, 1883). This is specially de-
voted to microscopic manipulation and micro-chemistry. An English trans-
lation has appeared.

Poutsen. Botanical Micro-Chemistry. Translated and enlarged by Pro-
fessor Wm. Trelease (Boston, 1884). An excellent account of the chemicals
used in the examination of vegetable structures, together with some directions
for their employment.

Srraspurcer. Das botanische Practicum. See ar account of this work
on page 165.

Bower anb Vines. A Course of Practical Instruction in Botany (London,
1885). A most useful and couvenient guide to the study of the histology of
flowering plants, ferns, and their allies.

PAR! 1

CHAPTER I.

THE VEGETABLE CELL IN GENERAL: ITS STUCTURE, COM-
POSITION, AND PRINCIPAL CONTENTS.

116. The unit in Vegetable Anatomy, the fundamental compo-
nent of which the fabric of plants is constructed, and from which
all the diverse histological elements are derived, is the cell.
Even the elements which are the least cellular in appearance,
and which have names of their own (as fibres, ducts, etc.), are
only transformed cells, or simple combinations of them; so that
the cell is the type as well as the unit of vegetable structure,
as indeed it is of animal structure also. The name celd is one
which would not be given to it if the nomenclature were to be
founded upon our present knowledge. Cells were originally
taken to be only closed cavities in a vegetable mass.1. We now

1 The earliest recognition of cellular structure in plants appears in Robert
Hooke’s Micrographia (1665), p. 113. ‘‘Our microscope informs us that
the substance of cork is altogether fill’d with air, and that that air is perfectly
enclosed in little boxes or cells distinct from one another.”

Nehemiah Grew, of London (The Anatomy of Plants, book i. p. 4), under
date of 1671, says of the mass through which the framework of a young
plant is distributed, ‘‘It is a Body very curiously organiz'd, consisting of an
infinite number of extreme small bladders,” etc.

Malpighi, of Bologna, in a work presented to the Royal Society in the same
year, uses nearly the same language: ‘‘ Exterior etenim cuticula utriculis, seu
sacculis horizontali ordine locatis, ita ut annulus efformetur, componitur, ete.”
(Anatomes Plantarum Idea, p. 2).

Asa preliminary study, w beginner should prepare and examine a few sec-
tions like the following :—

(1) From the tip of the root of a bean (which has germinated on wet sponge
or paper) cut a thin section lengthwise, and carefully examine it under a
power of 200-400 diameters. If the section is thin enough, the contents of the
cells can be made out, and will be seen to consist of a colorless lining (proto-
plasm), in which one part (the nucleus) appears denser than the rest. Next,
treat the section with a solution of iodine, and notice what parts are colored, —
the protoplasm and nucleus are yellow and brown, but the cells on the looser
part of the tip contain bluish granules (starch). This starch can best be shown
by first dissolving out the protoplasm with dilute potash.

26 THE VEGETABLE CELL IN GENERAL.

know them to be organs and even organisms. Histology there:
fore begins with the cell in its independent condition.

117. A complete and living vegetable cell consists of a cell-
wall enclosing certain essential contents.

118. In their earliest state some of the lower plants exist as
amass of motile living matter, not bounded by any envelope.
But in all plants of the higher grades the living matter of the
cell is from the very first protected by a cell-wall.

119. That which is essential to the vital activity of a cell is an
apparently half-solid substance, — protoplasm. With the prop-
erties of protoplasm as a living thing, Physiology and not His-
tology is immediately concerned. But it is necessary throughout
the study of Histology to make a distinction between the cells
which are vitally active and those which serve chiefly or wholly
some mechanical end; and hence attention must be called at the
outset to the means by which the living matter of the cell can be
identified.

120. Protoplasm exists in all young cells — for instance, in
the soft cone of tissue in buds, in root-tips, and other points of
growth —as a nearly transparent or finely granular substance.?
It completely fills the interior of very young cells, but with
increase of the cells in size there arise cavities (vacuoles) con-
taining sap, and these by their enlargement and confluence may
appear to occupy the entire space within the cell. If, however,
such a cell be acted upon by anything which causes contraction

(2) Make a thin section through the petiole of a begonia or some common
house-plant, and observe the granules imbedded in the protoplasm (ch/orophyll-
granules); notice also crystals, either in masses or single.

(3) Examine a thin section through dry pine wood, test with iodine, and
observe the absence of protoplasmic matters. Examine in the same way any
hard wood.

(4) Make a section through any starchy seed, for instance a common bean,
and treat it with a solution of iodine ; notice the distribution of protoplasmic
matters in the form of thin irregular films throughout the cells. Examine a
similar section in oil, and see what differences, if any, can be detected. Prob-
ably the presence of protein granules will be made out.

From these preliminary examinations a beginner will have demonstrated
the protoplasmic matter in its active, resting, and reserve states ; he will have
seen chlorophyll, the nucleus, and starch, the chief form in which food is
stored in plants. He will also have seen a few of the more common crystals.

After such a study the student is urged to examine practically the charac-
teristics of the cell-wall and the cell-contents as they are presented in this
chapter.

1 By the use of staining agents, especially hematoxylin, protoplasm can in
many cases be shown to possess a complicated mesh of very delicate fibres,

PROTOPLASM. QT

of the protoplasm,! as, for instance, a solution of common salt,
the protoplasm separates from the cell-wall, and by its con-
traction shows clearly that it is a
closed sac. Ata later stage
in some cells even this thin
protoplasmic sac wholly dis-
appears.

121. Protoplasm itself must
be regarded as essentially
transparent and colorless, but
it is seldom found without
some admixture of other mat-
ters, which give it a granular
appearance. The granules
are generally very small, and
as a rule are not found at the
periphery of the mass. The
limiting surface of the proto-
plasmic mass is further dis-
tinguished by being somewhat denser and firmer than the sub-
stance it encloses; and although it cannot be separated from
the latter by mechanical means, it is often spoken of as a film ;?

which take up the coloring matter readily, leaving the remainder of the mass
unstained. It is believed by Schmitz that the unstained mass is a homoge-
neous liquid filling the meshes (Sitzungsber. der niederrhein. Gesellschaft in
Bonn, 1880).

1 Such substances are termed plasmolytic agents.

2 Of the appearance of protoplasm, the following remarks by Mohl, who first
gave it the name in 1846, are of interest. ‘‘If a tissue composed of young cells
be left some time in alcohol, or treated with nitric or muriatic acid, a very
thin, finely granular membrane becomes detached from the inside of the wall
of the cell in the form of a closed vesicle, which becomes more or less con-
tracted, and consequently removes all the contents of the cell, which are
enclosed in this vesicle, from the wall of the cell. Reasons hereafter to be
discussed have led me to call this inner cell the primordial utricle. . .. In
the centre of the young cell, with rare exceptions, lies the so-called nucleus
cellule of Robert Brown. . . . The remainder of the cell is more or less
densely filled with an opaque, viscid fluid of a white colour, having granules
intermingled in it, which fluid I call protoplasm” (Mohl: The Vegetable Cell,
Henfrey’s Translation, 1852, pp. 36, 37).

Fig. 1, From developing anther of Orchis maculata, showing young cells com-
pletely filled with protoplasm. Observe also the nucleus with its nucleolus, in each
cell. (Guignard.)

Fic. 2. A hair from the stamen of Tradescantia pilosa, showing the protoplasm in
the form of granular threads running from side to side of the cell-cavity. The white

spaces between these threads are vacuoles. The nucleus can also be seen in each of the
four cells. (Jacobs.)

28 THE VEGETABLE CELL IN GENERAL.

and where there is any break in the continuity of the mass, for
instance in the case of sap-cavities, a similar limiting film may
be supposed to exist.

122. The consistence of protoplasm depends on the amount
of water which it contains. Thus in dry seeds it is nearly as
tough as horn, while in the same seeds during germination it
becomes like softened gelatin. It absorbs water readily and be-
comes permeated by it, thereby increasing its apparent fluidity,
but it never becomes a true fluid. Moreover, there is a limit
to the amount of water which it takes up.

123. Chemically considered, protoplasm is a very complex
substance. It belongs to a group of bodies of which the albumin
of egg may be conveniently taken as the type. They undergo
many slight but sometimes remarkable changes, and have been
collectively termed proteids. The terms albuminoids and pro-
teids may be used interchangeably (see 857).

124. The albuminoids, or proteids, which form with water the
bulk of protoplasm proper, are of course associated with the
matters which this living substance makes, uses, and discards.
But these matters exist in the protoplasm in very different pro-
portions at different times, though never in such amount as to
obscure the peculiar reactions of the albuminoids. These are
the following: 1. The yellow or brownish color imparted by
solutions of iodine. 2. The purple color produced when the
specimen first saturated with a solution of cupric sulphate is
acted on by potassic hydrate. 3. The rose color, often faint,
which follows the successive action of a solution of sugar
and strong sulphuric acid. 4. The red color given by Millon’s
reagent. This test generally requires the cautious application of
heat. 5. The yellow or orange color following the application,
in succession, of strong nitric acid and ammonic hydrate.

125. Dilute solutions of the caustic alkalies dissolve proto-
plasm; concentrated solutions do not. Ifa young cell is acted
on by concentrated potash, its protoplasm is not essentially
affected ; but if water is now added, the protoplasm dissolves
at once.

126. The spherical or ellipsoidal mass found in the protoplasm
of active cells, and differing from the rest of the protoplasm in
its greater density, is the mwcleus. The sharply defined point
often seen in the nucleus is the nucleolus.

127. The nucleus undergoes remarkable changes during the
earliest stages of the cell, which will be described in the chapter
on ‘*Growth.” The relations which exist between the proto-

THE CELL-WALL. 29

plasm in one cell with that in contiguous cells will be considered
in Chapter VI.

128. The cell-wall. The cell-wall is produced from materials
contained in protoplasm,! and is laid down in intimate contact
with it, as an even homogeneous film which exhibits at first no
obvious structure, but with increase in size generally becomes
modified in appearance, consistence, and composition.

129. Its evenness of surface is in most cases early lost by
addition of new matter, giving rise to protuberances or markings
of different sorts. Though at first possessing no evident struc-
ture, it may become clearly differentiated into layers, and thus
become stratified, or striations may appear. Its consistence, at
the outset that of the most delicate bleached linen fibre, may
soon become changed, on the one hand to that of soft gelatin,
or on the other to that of the densest wood. Moreover, although
devoid of color when first produced, it may acquire distinct color-
ation; and, lastly, its chemical character may undergo such im-
portant changes that its normal reactions are no longer given.

130. The markings of the cell-wall. Uniform thickening of
the whole cell-wall is extremely rare; even in the examples
which are commonly given to illustrate it, pores or channels,
more or less distinctly visible, interrupt
its continuity.

1381. The thickenings may possess
great irregularity, or they may be so
strictly localized and regular as to form
characteristic features of the widest use
in diagnosis. They may project out-
wardly, forming ridges, spines, and
other sculpturings ; or, as is most com-
monly the case, inwardly, giving rise
to rings, spirals, etc.

132. If the wall is thickened through-
out, except at well-defined points, de-
pressions or pits are produced, varying
considerably in outline, but occurring
generally as simple dots or lines. In
some cases it is not difficult to see that these dots or lines are
true pores or fissures running from one cell to the next.

! According to Schmitz, the cell-wall is produced by the conversion of the
limiting film of protoplasm into cellulose. That the cell-wall is formed a¢ the
limiting film admits of no question.

Fia. 3. Pitted duct; from stem of Cichorium Intybus. (Jacobs.)

30 THE VEGETABLE CELL IN GENERAL.

133. Bordered pits are a very common modification of the
last. A comparatively large spot remains unthickened, but
becomes covered by a low dome which has at its top a small
aperture; at a corresponding point of the wall of the neighbor-
ing cell another thickening produces a similar dome, so that the
two domes constitute a double convex body which appears as
a disc with a central perforation. These bodies are known as
discoid markings.

134. Sometimes the spot covered by the arched projection or
dome is elliptical instead of round. When this kind of marking
becomes linear, or nearly so, it is termed scalariform.

135. When annular and spiral thickenings occur the cell-wall
lying between them remains so thin that a slight strain suf-
fices to break it, releasing the rings
and coils. The number, the direc-
tion, and the steepness of the spi-
rals furnish in some cases diagnostic
features.

136. Besides spirals and rings,
there are intermediate forms, which
pass easily over into netted or reticu-
lated thickenings. It happens some-
times that the reticulated markings
are so regular that their interspaces
appear as regular polygons.

137. The external seulpturing of
the cell-wall can be seen in many
pollen-grains, and in the hairs of
many plants, though in the latter
case the projections may be partly

4 due to irregularities in the form of
the cell.

188. Stratification and striation. The cell-wall, even at an
early stage, frequently exhibits a distinctly stratified structure.
In some cases, at least, removal of all the water which forms a
constituent of the wall obliterates every trace of stratification,
and this fact supports the hypothesis that the appearance of
lamination is caused by differences in the amount of water con-
tained in alternating layers of the wall. The less strongly
refractive layers are supposed to contain more water than those
which are highly refractive. But there are cases of stratification

D

Uh

Ma

\

Or

W KALLA
ee Se

Fig. 4, Annular and spiral markings; vertical section through stem of Tradescantia
pilosa, (Jacobs.)

CELLULOSE. 81

which cannot be satisfactorily explained by this hypothesis.
There are, besides, numerous instances in which the stratified
appearance is not clearly shown until the cell has been acted
on by an acid or an alkali; a good example of this is afforded
by the firm cells of the albumen of the vegetable ivory (Phy-
telephas) .?

139. An appearance of spiral striation,? ascribed also to the
unequal distribution of water, is often seen, especially in the
cells of the liber of Apocynaceze and allied orders, and in many
wood-cells. The striations are not constant as regards the
steepness of the spiral; in fact, in a few instances rings instead
of spirals are present. <A striated appearance is sometimes pre-
sented in walls which have been deprived of all their water.

140. Chemically considered, the young cell-wall consists essen-
tially of cellulose, a substance which has the same percentage
composition as starch, namely, C,H,,0,. Even in its purest
state it is associated with a trace of mineral matters which
remain behind as ash when it is burned, and in the living cell it
is always permeated by water.

141. Cellulose is not soluble in any of the following liquids
commonly used in microscopic manipulations, — water, alcohol,
glycerin, dilute alkalies, and dilute acids. It is, however, more
or less strongly acted on by hot concentrated alkalies, without
passing into true solution, and it 1s apparently dissolved by
strong sulphuric acid. Whether cellulose becomes truly dis-
solved by concentrated sulphuric acid, or merely forms some
other carbohydrate under its action, is of little consequence, so
far as the destruction of cell-walls is concerned. In nearly all
cases its action is so energetic that the wall of a cell can be

1 As shown by Mohl, the action of a mineral acid of proper degree of con-
centration causes the wall to swell up, and the lamellar structure becomes
very distinct. ‘By this means the lamellar structure may be demonstrated
even in those cases in which the unaltered membrane appeared completely
homogeneous” (Moll: Vegetable Cell, p. 10).

2 ««The stratification is visible on the transverse and longitudinal sections
of the cell-wall, the striation on the surface as well; it is usually most evident
there, but is in general less easily seen than the stratification ; it depends on
the presence of alternately more or less dense layers in the cell-wall, meeting
its surface at an angle. Generally two such systems of layers may be recog-
nized mutually intersecting one another. There are thus all together three
systems of layers present in cell-wall : one concentric with the surface, and two
vertical or oblique to it mutually intersecting, like the cleavage planes of a
crystal splitting in three directions (Nigeli) ; and just as this cleavage is some-
times more evident in one direction, sometimes in another, so it is also with
the stratification and striation”’ (Sachs: Text-book, 2d Eng. ed., p. 20).

82 TH VEGETABLE CELL IN GENERAL.

wholly removed by this acid, even without destroying the proto-
plasmic contents; and this fact has been extensively employed
in the examination of the continuity of the protoplasm in con-
tiguous cells.t

142. The only known solvent from which cellulose can be re-
covered without change of composition is Schweizer’s reagent,
ammoniacal solution of cupric oxide. In this liquid, cellu-
lose swells considerably, and slowly disappears. It is thought
by some chemists that it does not truly dissolve. From its
apparent solution, it can be precipitated in the form of a floccu-
lent mass by acids, salts of many kinds, and even by the addi-
tion of a large amount of water (see 55).

148. Freshly prepared aqueous and alcoholic solutions of
iodine do not color pure cellulose beyond giving a faint yellow-
ish tint; but if the reagents have been kept for some time, par-
ticularly in the light, they may impart a blue color.? The latter

1 Unsized, well-bleached linen paper is nearly pure cellulose. If it is dipped
in a cold mixture of one volume of water and two volumes of strong sulphuric
acid, withdrawn after ten to twenty seconds, and washed thoroughly in water,
and finally in dilute ammoniacal water, it becomes much like parchment. This
“vegetable parchment” is a suitable membrane for certain experiments in
absorption. The acid in this experiment is supposed to convert at least a
portion of the cellulose into a substance which closely resembles starch in its
chemical reactions, termed amyloid. Parchinent paper can be made also by
concentrated zinc chloride, and by a few other agents.

2 Mohl (The Vegetable Cell, p. 24, Eng. Trans.) says: ‘‘ When imbued
with iodine, it becomes indigo-blue if wetted with water.” In a note on
pages 28 and 29, he further says: ‘‘ My researches shewed me that the in-
fluence of sulphuric acid was by no means necessary for the production of the
blue colour in membranes which are not strongly incrusted, as in the paren-
chymatous cells of succulent organs, but that iodine and water alone are suffi-
cieut; while in full-grown and hardened cells sometimes the primary membrane
alone, sometimes even a greater or sinaller portion of the secondary layers had
through the deposition of foreign substances, altogether lost the property of
becoming blue on the application of sulphuric acid and iodine, although they
were still composed of cellulose, and iodine alone would very readily produce
a blue colour in all their membranes after the infiltrated matters had been
removed. The means I employed to remove the infiltrated substances were
caustic potash and nitric acid. . . . After this treatment, the whole of the
layers of all elementary organs are coloured a beautiful blue by iodine even
when they offer so great a resistance to the action of sulphuric acid before the
treatment with nitric, as is the case in the outer membrane of wood-cells and
of vessels, and in the brown cells at the circumference of the vascular bundles
in Ferns.”

It is plain that, in the latter cases, the cell-wall had been very powerfully
acted on before the application of the iodine, and to this severe preliminary
treatment may be ascribed the efficiency of the latter in producing the blue
color.

REACTIONS OF CELLULOSE. 23

color, however, is given even by fresh solutions of iodine to
cellulose which has been previously treated with certain chemi-
cal agents, for instance, strong sulphuric acid. A convenient
method of employing this reaction as a test for cellulose is to
thoroughly moisten the object with a dilute solution of iodine,
and then to apply strong sulphuric acid, upon which the cellulose
immediately turns bright blue. It is sometimes advantageous
to dilute the sulphuric acid employed, either with water or with
glycerin; but for most cases the concentrated acid is the best.

Schulze’s solution of iodine, better known as chloroiodide of
zinc, used alone, gives with pure cellulose a blue color inclining
to purple. This reaction, though not always so prompt as the
other, is generally more manageable, and, on the whole, more
satisfactory.

In a few instances the cell-membrane becomes yellowish-
brown throughout, upon the application of an iodine solution,
a reaction which might be easily mistaken for that which albu-
minoids give; that the color, however, is not here due to their
presence, appears on subjecting the tissue to the action of
Millon’s reagent. Vertical sections of the stem of Begonia, as
noticed by Nageli, afford an instructive example of this.?

1 That the yellow color imparted by iodine has been otherwise interpresea,
will appear from the following : —

Harting (Ann. des Se. nat., sér. 3, tome v. p. 328) states, that ‘all lignified
cells have Protein matters in their walls.”

Mohl (The Vegetable Cell, p. 25) says: ‘‘Nitrogenous compounds do nct
occur in the membranes of cells which are just at the commencement of their
development, for these are not coloured yellow by tincture of iodine, yet hardly
a full-grown cell is met with in which this is not the case.”

It is held by Nageli that vegetable cell-membranes consist, in some in-
stances, of two isomeric substances, unequally soluble, which are intimately
commingled. One of these is soluble in cold water, more easily in hot water,
and sometimes needs for its complete extraction a dilute acid. From the solu-
tion iodine throws down a blue or bluish-green precipitate.

A synoptical table, based on differences in solubility of cellulose and its
modifications, and in their behavior towards iodine, has been constructed by
Nigeli. The part of the table which is given below affords excellent practice
for the beginner.

I. DiFFERENCES IN SOLUBILITY.

(1) In cold water, becoming swollen ; in hot water, disappearing, vegetable
mucilage ; ¢.g., in the outer layer of the cells forming the testa of quince secds
and those of flax.

(2) Soluble in concentrated sulphuric acid, and in cuprammonia; e. g., cotton-
hairs, bast-fibres, etc.

3

34 THE VEGETABLE CELL IN GENERAL.

144. The principal modifications of the cell-wall are the fol-
iowing : —

(1) Partial or complete conversion into mucilage (Gelatina-
tion); (2) Lignification; (3) Cutinization (or Suberification) ;
(4) Mineralization. g

145. All of these, except the first, change the chemical char-
acter of the cell-wall only by what may be regarded as infiltra-
tion; upon removal of the infiltrated matter by means of proper
agents, the cellulose basis of the wall is left behind with very
little if any change.

146. It sometimes happens that one part of the membrane of
a cell, or even one of its layers, may be modified in one way, and
another in another; it is also possible for the same membrane to
undergo two of the changes above mentioned; namely, Lignifi-
cation and Mineralization.

147. The mucilaginous modification. Commonly the cell-wall is
not much changed by immersion in water. It may become more
nearly transparent, but its size and density are not essentially

(3) Soluble in sulphuric acid, insoluble in cuprammonia (unless previously
acted on by acids or alkalies) ; c. g., the pith, and medullary rays of woods.

(4) Solubie in concentrated sulphuric acid ; insoluble in cuprammonia, but
becoming soluble in this upon previous treatment with Schulze’s macerating
liquid ; ¢. g., wood-cells of pine, oak, yew, ete.

45) Insoluble in concentrated sulphuric acid and euprammonia, but soluble
in boiling concentrated potassic hydrate; e. g., cuticle, and the outer layer of
the membrane of older ducts.

II, Iopinz Reactions.

(1) With iodine and water, a blue color : lichen-filaments, etc.

(2) With iodine and water, no color ; but giving a blue tint with iodine and
a metallic iodide ; or when iodine is followed by sulphuric acid : —

A. Thin-walled Parenchyma (which will often turn blue when a pure iodine
solution acts with repeated drying), o/der Purenchyma, the inner part of thick-
ened wood-celis of Pinus and Abies, and the bast-fibres of hemp.

B. Only when the reagents have been preceded by the application of nitric
acid: al membranes in the interior of the plant, e. g., the outer part of wood-
cells and ducts, the brown cells which surround the vascular bundles in
ferns, etc.

C. Only when the reagents have been preceded by the use of boiling potassic
hydrate: cork, etc.

According to Frémy and Urbain, the substances which form the skeleton of
plants are principally pectose and derivatives from it, cellulose and its isomers,

vesculose, and cutose. These four groups are thus distinguished from one
another.

Pectose acted on by alkaline carbonates is changed into pectic acid, and

we,

THE MUCILAGINOUS MODIFICATION. 385

affected. It sometimes happens, however, that the cell-wall
acquires wholly new relations to water, and becomes capable of
absorbing a large amount of it with great increase of volume and
translucency. A cell-wall whjch has undergone this mucilagi-
nous modification takes on, when placed in water, the consist-
ence of soft gelatin, and if the mass is then warmed it appears
to dissolve, forming a thick mucilage. Upon drying, the muci-
lage hardens into a translucent gum, in which the cellulose char-
acter is nearly or wholly lost.

148. Generally the changes produced in such a wall by water
are so rapid that it is desirable to place the specimen at first in
alcohol, and then to replace this medium cautiously by water or
by dilute glycerin, when the variations in shape, size, and con-
sistence can be easily followed. The addition of alcohol will of
course arrest the changes at any stage desired.

149. These changes can be easily traced in the outer cells of
the integument of a flax-seed. The mucilage appears as an
obscurely stratified: mass nearly filling the cells, except at their
centre, where there is a low-arched cavity. On the cautious

pectates are formed. These are readily decomposed by hydrochloric acid, and
insoluble gelatinous pectic acid is thrown down.

Cellulose and its isomers agree in being soluble in concentrated sulphuric
acid, but they differ in the following points: Cellulose dissolves at once in
cupramimonia ; paracellulose, only after the action of acids ; metacellulose, not
even then.

Vasculose is not easily soluble in concentrated sulphuric acid, but after the
action of oxidizing agents gives rise to resinous acids, which are separable by
alkalies from associated cellulose.

Cutose, the transparent film covering the aerial organs of plants, is dissolved
neither by concentrated sulphuric acid nor by cuprammonia, but dissolves
without change in alkaline liquids. The following results of analyses by Frémy
and Urbain (Ann. Se. nat. bot., 1882) show approximately the amount of
these substances in different parts of certain plants.

Root of Paulownia. — (1) Substances soluble in water and in dilute alkalies:
cork 45, soft bast 56, body of root 47. (2) Vasculose: cork 44, soft bast 34,
body of root 17. (8) Paracellulose : cork 4, soft bast 4, body of root 30.

Stems. — Vasculose increases in amount with the density of the wood. The
pith contains: of cellulose 37, paracellulose 38, vasculose 25 per cent. Cork
contains: matters soluble in acids and alkalies 5, cutose 43, vasculose 29,
cellulose and paracellulose 12 per cent (cutose and vasculose forming together
the subérine of Chevreul).

Leaves of Ivy. — Water and substances soluble in neutral solvents 707.7,
parenchyma (formed of cellulose and pectose) 240, fibres and vessels (of vascu-
lose and paracellulose) 17.8, epidermis (cutose and paracellulose) 35 parts.

Petals of Dahlia. — Water and soluble matters 961.30, parenchyma (of cel-
lulose and pectose) 31.63, vasculose 1.20, paracellulose 2.27, cutose 3.60 parts.

36 THE VEGETABLE CELL IN GENERAL.*

addition of water, this cavity becomes more clearly defined, the
whole mass of the cell swells, and the mucilage can then be
made out as a distinctly
stratified structure belong-
ing apparently as much to
the outer ‘as to the inner
face of the cell-wall. But.
if the action of water is
prolonged, the stratified ap-
pearance vanishes, and the
wall becomes optically ho-
mogeneous, with the excep-
tion of its middle portion,
the so-called primary mem-
brane, which remains un-
changed. On the addition
of iodine and sulphuric
acid, the primary membrane, but not the mucilage, becomes blue.
Furthermore, the lateral walls of the cells are not converted
into mucilage.

150. The mucilaginous modification can be examined to ad-
vantage in the seeds of some Polemoniacee (especially Collomia)
and a few Acanthacee, e. g., Ruellia. These seed-coats are
covered with hairs which break open when wet, and allow not
only the mucilage but also slender coiled threads to escape.
The achenes of some Composite of the Senecio group and the
nutlets of a few Labiate (the Salvia tribe) exhibit nearly the
same phenomenon.

151. Lignification. Induration of the cell-wall is caused
most commonly by the presence of an incrusting substance
known as lignin. Owing to the difficulty of separating it from
the cellulose, with which it is associated, its chemical composi-
tion must be regarded as uncertain. Although generally spoken
of as a single substance, it is probable that the lignin, or in-
crusting matter, is made up of several different substances,?

Seaton Gee

fs

era

1 Payen (Mém. des savants étrangers, ix., 1846, pp. 68, 5) distinguished
four such incrustiug matters, differing in their composition and in their be-
havior to solvents. Lignose: insoluble in water, alcohol, ether, and ammo-
nia; scluble in solutions of potassa and soda. Lignone: insoluble in water,
alcohol, and ether; soluble in ammonia, potassa, and soda. Lignin: in-
soluble in water and ether; soluble in alcohol, ammonia, potassa, and soda.

Fic. 5. Section of the albumen of Ceratonia siliqua, showing mucilaginous modifica-
tion, (Saclis.)

LIGNIFICATION. 387

which occur in different proportions in different plants and in
different parts of the same plant.

152. Lignin dissolves readily in Schulze’s macerating liquid
and in potassic hydrate, but not in cuprammonia, the well-
known solvent for cellulose.

153. By the use of Schulze’s macerating liquid a lignified cell-
wall can be wholly freed from its incrusting substance, and pure
cellulose will be left behind. For control, it is well to employ
the tests for lignin given below, both with ordinary wood and with
siinilar specimens which have been treated with this solvent.

154. Lests for lignin. 1. Salts of anilin. If a lignified
cell-wall is subjected to the action of a strong solution of anilin
sulphate acidulated with sulphuric acid, or to that of a solution
of anilin chloride acidulated with hydrochloric acid, it will at
once turn yellow. The depth of the color depends somewhat
upon the strength of the solution. The color is destroyed by
alkalies, but is restored by acids. Wiesner, who first applied the
foregoing reagents to the detection of lignin, has suggested an-
other which is for many cases even more satisfactory ; namely,
2. Phloroglucin. In an alcoholic or aqueous solution of this
substance (.01 per cent) a lignified cell-wall does not change
color ; but if the specimen is slightly acidulated with hydrochloric
acid, it becomes violet or purple. 3. Carbolie acid (phenol)
and hydrochloric acid. The solution described on page 11 im-
parts to lignified cell-walls, when exposed to a strong light, a
green color which is very fugitive. Specimens under examination’
should therefore be watched from the moment that the reagent
reaches them. 4. Indol. An aqueous solution is to be replaced
under the cover-glass, after it has moistened the specimen thor-
oughly, by a little dilute sulphuric acid; lignified cells will be-
come red or reddish-violet. This reagent does not appear to have

Ligniréose : soluble in all the solvents mentioned above, but only to a slight
extent in water.
CHEMICAL COMPOSITION.

Carbon. | Hydrogen.| Oxygen.
U6 (40 (0): a ee a ee 46 10 6.09 47.81
Mignone: a he 50.10 5.82 4408
AQUA 55 sep se ee a we 62 25 5 93 31.82
MG WERSS: ne ge Se a Se OO Dw 67.91 6.89 25.20
Cellulose (of cotton) . . 2... 2. wee 44.35 6.14 49,51

According to Franz Schulze, the probable composition of lignin is : Carbon,
55.55; Hydrogen, 5.83; Oxygen, 38.62.

38 THE VEGETABLE CELL IN GENERAL.

any marked advantage over that which gives nearly the salse
color, namely, phloroglucin.

155. By the employment of these reagents many cell-walls
have been shown to be distinctly lignified when the older re-
agent — iodine in solution — failed to detect the change |

156. Cutinization. Ordinary and lignified cell-walls, aid those
which have undergone the mucilaginous m » absorb

water freely. On the other hand, the walls of
chiefly on the exterior of organs are repellent:
which imparts the repellent character to the ce
as cutin; when restricted to cork it is called sub ‘3

157. Cutin and suberin have been described aP differen t sub-
stances ; but although the former is more generally/associated Witline -
waxy matters, its reactions are essentially the same as’ chose of
suberin. The water-proofing of the cell-wall may be superficial,
as in most young epidermal cells, or it may affect the whole
structure of the wall, as in the case of cork. If a distinction is
made between the two states, the first may be termed cutiniza-
tion, the second, suberification.

158. Cutin can be removed from the walls with which it is
associated, by the use of Schulze’s macerating liquid, subsequent
treatment with potassa, and careful washing. It is sometimes
necessary to heat the section in potassa before the cellulose can
be completely freed from the other matters.

159. Hébnel? has shown that the wall of a cork-cell, with
the exception of the young cork-cells in Coniferse, is composed of
five plates: (1) a middle plate, common to the two contiguous
cells; (2) two plates, one on each side of the latter, consisting
of cellulose which is both cutinized and lignified ; (8) two plates
of cellulose forming the inner lining of the respective cells. The
latter plates may be more or less lignified. Differences in the
relative proportions of these constituent plates give rise to dif-
ferences in the character of different kinds of cork.

160. As in the case of lignin, the difficulty of extracting cutin
renders its chemical composition doubtful. It is usually given
as follows : —

Carbon i a Ste a se S74 Den pent
Hydrogen . . »~ «. . «. «. . 10
Oxygn ........ . 16 «

But there is also a trace of nitrogenous matter demonstrable ;
this probably belongs to residual protein matters which are in

1 Sitzungsber. d. k. Akad. Wien, Bd. Ixxvi. 1 Abth.

MINERALIZATION. 389

the cell-cavity, and not in the cell-wall. Sulphuric acid and
chromic acid, even when concentrated, produce little effect on
cutinized membranes, beyond removing traces of cellulose pres-
ent in the cell-wall. The latter acid, however, increases the
transparency of cutinized membranes, especially after prolonged
action.

161. Potassic hydrate softens such membranes and colors
them yellow; when heated it breaks them into a granular mass
which may be removed by careful washing. Cautiously heated
with Schulze’s macerating liquid, they disintegrate into granules
of ceric acid, —a substance which dissolves in alcohol, ether, and
benzol. Several of the coal-tar colors stain the cutinized por-
tions of cell-walls very deeply ; if the specimen thus colored is
placed in absolute alcohol, the cutinized parts alone remain
colored.1. Two points relative to the cutinization of epidermal
cells may be noted: (1) the cutin may take on the form of lay-
ers, often numerous and conspicuous; (2) there may be a con-
siderable irregularity in the outline of the deposits, sometimes
as folds, hooks, and the like, which do not strictly conform to
the cellulose wall on which they arise.

162. Mineralization of the cell-wall. Although all cell-walls,
even the most delicate, can be shown to contain traces of inor-
ganic matter, it is only in a few special cases that such substances
appear in a form to be noticed under the microscope. Minerali-
zation of the wall may be general or local, may depend upon
the presence of crystals or of amorphous deposits, and these may
consist of silicic acid or of calcium salts.

163. General mineralization of the wall depends most fre-
quently on silicic acid, and may be best demonstrated by first
boiling the specimen in nitric acid, drying, heating to redness on
platinum-foil, and, lastly, treating again with nitric acid. The
silicie acid remains behind as a delicate skeleton which copies in
all particulars the contour of the wall of which it formed a part.
Fine examples are afforded by the harder grasses.?

Calcium salts may exist in crystalline or amorphous form, and
may be distinguished by the tests to be given for them under
the section on ‘‘ Crystals.” That in some cases they constitute
an integrant part of the wall itself admits of no question.

164. In the cells of many plants, especially Urticaces, pedi-
cellated concretions occur, which, on superficial examination,

1 Olivier: Bull. Soc. bot. de Fr., 1880, p. 234.
2 Tabasheer consists of the siliceous substances which occur in the joints
of bamboo in large quantities.

40 THE VEGETABLE CELL IN GENERAL.

appear to be much like the sphere-crystals described in 186. But
if they are carefully treated with dilute hydrochloric acid, the
chief part of the concretion disappears, leaving behind a delicate
trace of cellulose which was intermingled
with it. That this cellulose was an in-
trusive growth into the cell from the
wall, is shown by a study of its develop-
ment. In most cases such concretions
(Cystoliths) are plainly stalked, but in
some instances they are only obscurely
stalked, and are with difficulty distin-
guished from the ordinary cell concre-
tions. In the leaf of Ficus elastica (see
Fig. 6) they are more completely devel-
oped than in any other common plant.

165. Other changes, chiefly those of
degradation, may take place in the cell-
wall, giving rise to products variously
known as gums, resins, &c.; but in all these cases there is such
a commingling of the cellulose derivatives with those formed
from the contents of the cell, that they cannot be readily dis-
tinguished.

166. Protoplasm, as was shown in the previous sections, gives
rise upon its exterior to the cell-wall. Inside the cell, likewise,
it produces, either directly or indirectly, various substances. In
the present chapter these substances are to be considered only so
far as relates to their detection and identification. Most of them
are to be examined later, with reference to their office in the life
of plants.

167. Plastids. In the protoplasm of active cells certain gran-
ules having substantially the same chemical and, with the excep-
tion of their color, the same physical properties as protoplasm,
are clearly differentiated. They are imbedded in the general
protoplasmic mass, and are not separable from it by mechanical
means.

168. Such granules may be conveniently referred to three
types,? depending upon the color: (1) those which are green, —

1 Recent investigations render it probable that these three kinds of granules
are derived from a common source, and although hardly distinguishable from

Fic. 6. Cystolith from the upper part of a leaf of Ficus elastica. e, epidermis;
h, hypoderma; ce, cystolith; ch, ch, cells containing chlorophyll. It will be observed
that the pedicel of the cystolith appears to be attached to the lower wall of the upper
epidermal cells.

CHLOROPHYLL GRANULES. 41

Chloroplastids, or chlorophyll granules, also called chloroleu-
cites; (2) those which have some color other than green, —
Chromoplastids, or chromoleucites ; (8) those which are devoid
of color, — Leucoplastids, or leucites.

169. Chlorophyll Granules,
or Chloroplastids, are met with (
in the green parts of all plants ;
in fact, to them the green color
is due. But they are some-
times masked by the presence
of color in the cell-sap. Their
shape is spherical or spheroidal,
and somewhat flattened. They
have an average diameter of 2 to
5 p, but many granules are con-
siderably larger than this. It
frequently happens that they be-
come of great size, owing to the
presence of solid contents, — for
instance, starch, — which may
accumulate in large amount.

170. If the granules are sub-
jected to the action of alcohol,
their coloring matter is wholly
removed ; but they retain their
former volume and shape, ap-
pearing faintly outlined in the
protoplasmic mass in which
they are imbedded. Hence it
is proper to distinguish be-
tween the chlorophyll body of
the chloroplastid and the chloro-
phyll pigment which imparts to 7
it its characteristic color.

The chlorophyll body may be shown, by the process described
in 61, to be somewhat spongy in structure, and to have on its

each other at the outset, become chloroplastids, chromoplastids, or leucoplas-
tids, according to the part which each is to play. Moreover, one kind of
granule can, under certain conditions, perform work which properly belongs to
another, and hence it is not always easy to identify the different kinds. In
most cases, however, their discrimination is very simple.

They are also called, collectively, Chromatophores.

Fiae,7. Chlorophyll granules in the leaf of Vallisneria spiralis. #99. (Weiss.)

42 THE VEGETABLE CELL IN GENERAL.

exterior a delicate film. Meyer believes that the coloring matter
takes the form of grains of extreme minuteness which are inter-
spersed through the whole substance, while Tschirch holds that
the pigment, dissolved in a liquid similar to the ethereal oils, is
diffused through the mass.
; 171. If starch is present in large amount in chloroplastids,
iodine causes at once a deep bluish-brown color; but if the starch
1s not very abundant, the characteristic blue reaction is concealed
by the yellow produced by the protein reaction of the protoplasm.
Hence it is well, after having removed the chlorophyll pigment
by alcohol and subsequent washing with water, to treat the speci-
men with moderately strong potassic hydrate in order to dissolve
the protein matters. If this has been well done, and the speci-
men carefully freed from the potash, the protoplasmic mass and
its imbedded granules will seem to have completely disappeared ;
but the skilful use of oblique illumination will show that an un-
dissolved trace of something having the former contours remains
behind. Application of iodine brings out minute blue points
where the granules were.

Chloral hydrate of the strength recommended in 53 may
replace potassic hydrate in this examination.

172. The starch in chlorophyll granules is sometimes wholly
within the granule; but it is occa-
sionally — especially in the case of
flattened granules — found on their
extcrior, forming a noticeable pro-
tuberance.

173. When a plant containing
chlorophyll granules is kept for a
time in darkness, the production of
starch is arrested; and if other forms of activity continue, even
that starch which has already accumulated in the granules soon
disappears. Furtbermore, the
color of the granules is changed
from green to ycllow ; and if the
change is not arrested at this
point by bringing the plant
again into the light, all the
granules will break up and be-
come apparently merged in the

Fra. 8. Chlorophyll granules with protruding starch-grains. From the cortex of

Philodendron grandifolium. °%°. (Schimper. )
¥ic. 9a. From the epidermis of Philodendron grandifolium. Young cell with amylo-

genic bodies newly formed. °§*. (Schimper. )

LEUCOPLASTIDS. 43

general protoplasmic mass of the cells, being no longer recog-
nizable. Those, however, which have been changed no further

than by loss of color, closely resemble another kind of granule ;
namely, leucoplastids. (For exceptions see Chapter X).

174. ZLeucoplastids. These are found in parts which are
normally devoid of chlorophyll, such as tubers, rhizomes, ete.

They may be wholly colorless, or faintly tinged with yellow, and
hence are apt to escape detection. They may he considered as
the points around which starch accumulates when stored for the
future needs of the plant. Schimper,! who first accurately de-
scribed them in all their relations, terms them ‘‘ starch genera-
tors;” they are also known as amylogenie bodies, which of
course means the same thing. They are seen to the best advan-

1 Schimper: Bot. Zeit., 1880, 1881, 1883.

Fia 9b. Same, more advanced: a, the amylogenic bodies are covered with starch-
grains; 6, two nuclei on a cell-wall, each surrounded by amylogenic bodies covered by
starch. °2°, (Schimpevr.)

Fic. 10. a, Young amylogenic bodies surrounding the nucleus of a cell in the root of
Phajus grandifoliug; 6, same, with starch-grains developing; c, same, more advanced.
839, (Schimper.)

44 THE VEGETABLE CELL IN GENERAL.

tage in thin sections of many starchy tissues, by the use of dilute
tincture of iodine, which colors them more or less deeply yellow.
Millon’s reagent colors them red.

Owing to the minuteness of the leucoplastids, the following
explicit directions by Strasburger will aid in their detection:
Make thin longitudinal sections through the upper part of a
young pseudobulb of Phajus grandifolius, taking care that the
cut extends to its green surface. Immediately place the sections
in an alcoholic solution of iodine diluted with one half its volume
of water. (Picric acid may be advantageously used instead of
the iodine solution.) In good preparations the leucoplastids will
be seen in the inner part of the section as small staff-shaped
bodies which, at the first glance, appear to be homogeneous, but
are afterwards recognized as somewhat granular in structure.
The section is next to be examined nearer its outer part, and it
will then be seen that the bodies there possess a green color,
are larger, and lenticular in form. They are also plainly porous,
their increase in size being apparently associated with a spongi-
ness of their substance. Their size diminishes towards the outer
cellular layers, they become somewhat rounded, and finally take
the familiar form of chloropliyll granules. Prismatic colorless
protein crystals are frequently associated with these bodies.
In sections which are placed in water, the leucoplastids disap-
pear almost instantaneously, and even the chlorophyll granules
soon begin to disorganize, while the swollen protein crystals then
appear as colorless parts of the latter.

In the rhizome of Iris Germanica the sections for examination
must be taken parallel to the surface. In uninjured cells the
leucoplastids appear as collections of protoplasm at the end of
each starch-granule. If the section is in water, the leucoplastids
become granular and finally break up into minute granules which
show the Brownian or molecular movement.

Chromoplastids, or the color-granules which occur abundantly
in flowers and fruits, will be specially treated later.

175. Protein granules. The protein matters in plants have
been divided into two classes: (1) the active, such as active
protoplasm, the nucleus, ete. ; (2) the reserve, which can change
their dormant condition and become active when occasion de-
mands. Inactive, amorphous protoplasm, as it sometimes exists
in certain cells, where it is simply a tough shapeless mass, does
not need further consideration at present; the reserve matters

1 Strasburger: Das botan. Practicum, 1884, pp. 67, 68.

PROTEIN GRANULES. 45

now to be examined being those which take the form of more or
less regular grains. These which are known as

176. Protein granules may be either independent, or asso-
ciated with other substances. In
nearly all cases they are more or
less soluble in water, and hence
require special treatment for their
satisfactory examination. Cells
supposed to contain them may be
placed for examination in any fixed
oil, and the granules will remain
unchanged. A more practicable
method of treatment is suggested
by Pfeffer; namely, to subject the
granules to the action of an alco-
holic solution of mercuric chloride, _
by which they are rendered insoluble (see 63). The solution
is made by dissolving one part of mercuric chloride (corrosive
sublimate) in fifty parts of absolute alcohol; in this solution
the thin sections of seeds, etc., suspected of containing pro-
tein granules, must be kept for at least twelve hours. Upon
removal to water, after this period, they remain substantially
unchanged. The precaution must be taken not to touch with
any metal the sections after they have been placed in the
mercuric chloride solution.
They must be removed by a
camel’s-hair brush.

177. The protein matter
of which protein granules
consist may be wholly with-
out definite shape, or a por-
tion may assume somewhat
the form of crystals. The
latter have been called pro-
tein crystals or crystalloids, and they are generally associated,
in the granules of which they form a part, with inorganic matters
either amorphous or crystalline. Hence in some protein gran-
ules we have to distinguish between the inorganic contents, the

Fie. 11. Cells from cotyledons of Vicia sativa, showing protein matters in a finely
divided state, intermingled with starch-granules. (Schmidt.)

Fic. 12. Protein granules from the endosperm of Ricinus communis. The specimen
isin oil. 49°. (Pfetfer.)

Fic. 13. Protein granules from the endosperm of Ricinus communis. The specimen,
first treated with mercuric chloride in absolute alcohol, is now in water. 49°. (Pfefter.)

46 THE VEGETABLE CELL IN GENERAL.

protein crystal-like bodies, and the protein basis or stroma in
which all of these are held.

The protein basis sometimes, if not always, appears to consist

of two substances, differing in their solubility in water, and com-

mingled as granulose and

cellulose are in starch-

granules. While the pro-

PERE REESE foieniabenes tein basis is generally very
c soluble in water (not per
a 6 se, but owing to the pres-

ence of potassic phos-
phate), the protein crystals are insoluble, or only slightly affected
by it, usually becoming more or less swollen. After solution of
the protein basis has taken place, a delicate membrane is left
behind, and through this transparent film the protein crystals
are clearly seen. The relative amounts of protein basis and
protein crystals vary widely ; in some cases the former appears
to be wanting, the latter wholly filling the interior of the mem-
brane. Such crystals appear in potato-tubers in the form of

small cubes. Protein crystals of great beauty are easily dem-
onstrated in the endosperm of the common Brazil-nut (Ber-
tholletia). Very instructive phenomena are presented when
different sections of the seed are subjected to the following
reagents; (1) osmic acid (one per cent solution) ; (2) heematoxylin

Fic. 14. Single protein granules treated as in Fig. 12, ®92. (Pfeffer.)

Fig. 15. Protein granules from Silybum marianum, In the cell on the left they have
crystalline contents; in that on the right, globoids This section was taken from the
cotyledons of a dormant seed, and after treatment with mercuric chloride in alcohol was
placed in water. 5¢°. (Pfeffer.)

Fic. 16. The mesh of the ground mass of the cell has been cleared by dilute potassic
hydrate and hydrochloric acid. n=nnueleus. °9°. (Pfeffer.)

Fie 17. Cells from the cotyledons of a germinating seed which has just ruptured the
seed-coat. The protein granules have disappeared, but their contents are recognizable.
699, (Pfeffer.)

Fic. 18. Silybum marianum, Cell from the cotyledon of a nearly ripe seed in which
the formation of protein granules has just begun. °{°. (Pfeffer.)

STARCH. 47

in concentrated glycerin ; (3) concentrated potassic hydrate,
water being added afterwards. Permanent preparations of pro-
tein crystals can be made by first acting on the section with
mercuric chloride for a day or more, washing in water, staining
with eosin, and finally mounting in potassic acetate (101).

The inorganic matters associated with the protein crystals
in protein granules are either
(1) amorphous or globular con-
cretions of a double phosphate of
calcium and magnesium, known
as globoids, or (2) crystalline
clusters of calcic oxalate.

“The protein granules, espe-
cially those which are most com-
plex in their composition, are also known as Alewrone grains.
The protein crystals are generally termed crystalloids.1 For an
analytical classification of protein granules in seeds, see pages
182 and 183.

178. Starch, the principal form in which the elaborated food
of plants is held in reserve, occurs as minute spheroidal or
polyhedral granules. Under a suf-
ficiently high power, and with
proper management of the mirror
of the microscope, the single gran-
ules exhibit an appearance of
{ stratification which is sometimes
PH very distinct, but more commonly
eS obscure ; in the latter case dilute
tees chromic acid can be used to ren-
der the stratification plainer. The
layers of stratification are ar-
ranged around a point, — often very eccentrically, as in potato

22

1 The fact that protein crystals have, as a rule, less constancy in their angles
than inorganic crystals, taken together with the fact of their swelling when
immersed in water, has led authors to speak of them as erystalloids rather than
as crystals. But Famintzin has recently shown that certain crystalline forms
artificially produced obscure these distinctions, since they agree more closely in
some of their physical characters with organic structures than with ordinary
inorganic crystals (Ber. der deutsch. bot. Gesellsch., 1884, p. 32).

Fie. 19. A cell from nutmeg lying in ofl. In the ground mass are very numerous
crystals of fat. Some of the granules are compound starch-granules, but others are
protein granules with crystalloids. The rhombic granule has hardly any envelope.
590, (Pfeffer.)

Fig. 20, Globoids of Vitis vinifera. 599. (Pfeffer.)

Fig. 21. Large protein granules from Vitis vinifera. 52°. (Pfeffer.)

Fig. 22 Whceat-grain, showing cells containing starch-granules. (Schmidt.)

48 THE VEGETABLE’ CELL IN GENERAL.

starch, or with great regular-
ity, asin wheat. This point is
known as the nucleus, or hilum.
1f two or more nuclei are dis-
cernible, the granule is said to
be compound.
23 Occasionally many small sin-
gle granules cohere slightly to
form an aggregate which can be easily broken. According to
Wiesner, there may be as many
as 30,000 granules in a single
aggregate of this kind.

Both simple and compound
granules may occur in the same
cell, but some plants have only
simple, and others only com-
pound granules. Canna and
Curcuma may be cited as exam-
ples of the former; Jatropha, of
the latter.

Since starch occurs in every
plant in all stages of development, the size of the granules must

be extremely variable. Nevertheless, a
le statement of the more common limits may
g (4}) aid in their identification.
SF Wiesner gives the following limits of size
& for some of the more cormomon sorts of starch,
& first grouping them into small, medium, and
8 & large granules.

Small granules (from 0.002 to 0.015 mm.) :
as the simple granules of rice, oats, buck-
wheat; also the smaller granules of wheat, rye, barley, etc.

Medium granules (from 0.02 to 0.05 nm.) : as the compound
granules of rice and oats, the larger ones of wheat, rye, and
barley, the simple granules of Indian corn, and of the common
leguminous plants.

Large granules (distinguishable as granules to the naked eye) :
as the simple granules of Curcuma leucorrhiza, Canna edulis,
potato, ete.

25

Fia. 23. Starch-granules from the bulb of Phajus grandifolius, showing the nu-
cleus at the upper part and the starch generator or amylogenic body below. ®§°
(Schimper. )

Fie. 24. Cells from potato-tuber, showing starch-granules (Schmidt )

Fic. 25, Starch-granules from sarsaparilla, (Berg and Schmidt.)

STARCH. 49

Starch is insoluble in cold water, but forms with boiling
water a paste in which all traces of structure are lost. If a

specimen of starch be gently heated with water upon a glass
slide, the granules will be seen to swell at a temperature of

G)

40°-50° C., and the appearance of stratification will often be-
come plainer. The alkalies and mineral acids generally hasten the

Fig. 26. Starch-granules of wheat. Fig, 29. Starch-granules of oats.
Fic. 27. Starch-granules of Indian corn. Fie. 30. Starch-granules of rice.
Fig. 28. Starch-granules of barley. Fig. 31. Starch-granules of potato.

Fig. 32 Starch-granules of Maranta (arrow-root)
Fie. 33. Starch-granules of Bomaria (Chili arrow-root).
Fig. 34. Starch-granules of Vicia sativa, var. leucosperma. All the figures of
starch are from Berg and Schmidt.
4

50 THE VEGETABLE CELL IN GENERAL.

formation of starch-paste, and bring about some other changes,
such as its conversion into soluble matters.

179. Starch is usually said to have the following composition,
C,H,,0,;, and these proportions are doubtless correctly stated ;
but it is probable that the molecular constitution is more com-
plex than this formula would indicate.?

180. When starch is acted on by saliva or pepsin, it is slowly
separated into two substances, one of which passes into solution,
while the other remains as a skeleton, and with little change of
form. This delicate framework, which remains after the soluble
matter is removed, is closely related to cellulose, as shown hy
its behavior with reagents. and has received the name of starch
cellulose. The substance which is removed by the action of saliva
is termed granulose.

181. When starch is not associated with too large a propor-
tion of protein matters, it can always be detected by the blue
color which it takes with iodine in solution; but if protein suh-
stances are present in considerable amount, they may obscure
the reaction by the yellowish or brown color which iodine im-
parts to them. Iodine does not, however, always produce a blue
color with starch; the shade may vary towards red, forming a
purple which may be almost black. Furthermore, as the tran-
sient color given by this reagent fades, it may pass through
various tints of orange and yellow.

Protein matters which mask the starch reaction may be re-
moved by careful treatment of the specimen with potassic hy-
drate (not too concentrated), and subsequent washing with pure
water. After such treatment it sometimes happens that the
starch appears as a diffused mass instead of in minute dots.

182. When starch-granules are seen in polarized light they
generally exhibit two crossed lines which appear to turn as the
Nicol prism is revolved. Many kinds of starch give under the
polarizer characteristic figures, many of them of great beauty.

183. Inulin, although occurring in solution in cells, is never-
theless thrown down in characteristic forms by means of the
preservative media alcohol and glycerin, aud can be examined as
a solid. If the root of Dahlia, Helianthus, or any of the com-
mon Conipositee which store up their food in fleshy underground
parts, be subjected to the action of alcohol for a few days, thin
sections will exhibit in the cells peculiar masses of a spheroidal

’ W. Nageli, however, gives the formula for starch as follows : CggHg 0g}.
Beitr, z. naéheren Kenntniss der Starkegruppe, 1874.

INULIN. 51

form which are distinctly radiating in structure. Occasionally
these masses have large rifts which run across the surface of the
sphere.

In composition, inulin closely resembles starch, but does not
give any color with iodine. To de-
tect it when in solution, a thin sec-
tion of the plant containing it is
moistened on the glass slide with
absolute alcohol, when a cloudy pre-
cipitate will at once appear; in a
short time (the supply of alcohol
having been replenished as it evap-
orates) the specimen grows clearer,
and small spheerocrystals of inulin
are seen. If now the specimen is
carefully washed with water, the
smaller granules disappear and the
well-defined remain.

184. The carbohydrates dissolved
in the cell-sap may be grouped in two
classes: (1) those which are isomers
of cellulose (7. e., have tie same per-
centage composition, C,H,,0,), and (2) the sugars.

1. The isomers of cellulose are mucilage, gums, and dextrin,
all of which are probably derivatives of starch. Various sub-
stances intermediate between them have been described, but the
above are all that need now be taken into account. (a) Mucilage,
when not plainly resulting from the breaking up of the cell-
wall, is colored red by rosolic acid, and the color is not readily
removed by alcohol. (6) The gums, of which cherry gum
may be taken as an example, are not tinged by rosolic acid.
(c) Dextrin can be detected by Trommer’s test, which Sachs ap-
plies as follows: a section which is at least a few cells in thick-
ness is placed in a porcelain capsule with a strong solution of
cupric sulphate, and the liquid is heated to boiling ; the specimen
is then washed in water, and dipped at once in hot potassa.
If the cells contain either dextrin or grape-sugar, there will
immediately appear a reddish precipitate. ‘To discriminate be-
tween dextrin and grape-sugar, it is merely necessary to keep
portions of the plant to be examined in 90 or 95 per cent alcohol,
which will dissolve out the sugar and leave the destrin, if any

Fia. 35. Spherocrystals of inulin from root of Cichory treated with alcohol. 4§%.
(Jacobs. )

52 THE VEGETABLE CELL IN GENERAL.

is present. Usually all the grape-sugar is extracted in a day
or two.

2. The sugars. Grape-sugar has been just referred to as
giving the same reaction as dextrin with Trommer’s test. Its
formula is C,H,,O,. Cane-sugar, which has the formula C,,H,,0,,,
gives no red precipitate with the same test, but the liquid in the
cells becomes bright blue, and quickly diffuses into the potassa.?

185. Crystals are of such general occurrence in widely differ-
ent orders of the higher plants, that there are perhaps none
in which they may not be detected. They have been found in
nearly all parts of the vegetable structure, more commonly in
the interior of parenchyma cells, sometimes in specialized crys-
tal-receptacles, occasionally in the very substance of the cell-
wall. They occur either singly or in groups; either separate or
barely coherent, or in various degrees of combination.

When solitary and simple they are usually octahedra or
prisms, and their aggregations are combinations of these. Good
octahedral crystals are afforded by the petioles of Begonia ;
examples of the prismatic form are found in the outer scales of
onions, in-orange leaves, in the inner bark of maples and apple-
trees, and in most of the tissues of Lris and its allies.

When the prisms are very long and slender their angles and
faces are seldom well defined.2 Indeed, the most attenuated
forms are usually terete, or slightly flattened, and taper gradually
to a point at both ends. To these De Candolle long ago gave
the name Ltaphides, — that is, needles.? These are generally
massed in a compact bundle, like a wheat-sheaf, occupying a
large part of the interior of the containing cell.

Raphides are by no means of such general occurrence as
are ordinary crystals, but (as Gulliver has pointed out) are
seemingly restricted to certain orders.* They are universal in
Aracee and Onagracez. In the common Arums and Callas,
raphides-bearing cells may readily be found in the parenchyma

1 Pringsheim’s Jahrb., iii. p. 187. In the Sitzungsber. d. k. Akad, Wien,
for 1859, Sachs has given colored figures illustrative of these reactions.

2 When the longer prisms are clearly defined, they are referable to the mono-
clinic system. Measurements of angles are given by Holzner, in Flora, 1864,
p. 292. A paper by Bailey (Am. Journ. of Sc. and Arts, vol. xlviii., 1845,
p. 17) also contains determinations.

8 Organographie, 1827, p. 125.

4 Gulliver has examined representative plants of all the more important
orders of the British Flora, with respect to the occurrence of diagnostic crys-
tals (Annals and Magazine of Natural History, 1863 to 1867).

CRYSTALS. 53

of the leaves, and detached entire; on becoming turgid when
wetted, they will usually discharge their raphides one by one
from one or both ends of the cell until the bundle is almost
exhausted.!

186. When the ordinary octahedral or prismatic crystals
are aggregated or
combined, they
generally compose
a spherical mass.
Such aggrega-
tions are of two
principal types :
(1) those made
up of many small
crystals irregular-
ly grouped, and
usually presenting
sharp points over
the surface, as
in Fig. 36a, (2)
those with a distinctly radiated structure (Fig. 367). Good
examples of the former are abundant in the foliage of Chenopo-
diaceze and the stems of Cactacee. Clusters belonging to the
latter, or stellate, type are not uncommon in Malvaceze. Both
forms have been termed Spheraphides? and Sphere-crystals.
The term cystolith, sometimes improperly applied to them,
should be wholly restricted to the peculiar bodies described on
page 40.

187. Owing to the mechanical difficulty of isolating plant-

1 Turpin (Annales des Se. nat., sér. 2, tome v., 1836) described the raphides-
bearing cells of Caladium, in which this discharge takes place, under the name
of biforines.

2 «They are most irregularly scattered through the tissues of the plant.

. . I have never failed to find them in a single species of the order Caryo-
phyllacee, Geraniacee, Lythracer, Saxifragacer, and Urticacer, and believe
that few if any orders could be named in which spheraphides do not exist as
part and parcel of the healthy and growing structure of the plant’”’ (Gulliver,
in Annals and Magazine of Natural History, vol. xii., 1863, p. 227).

Fig, 36. The more important forms of crystals of calcic oxalate: a, three cells from
the petiole of Begonia manicata; b, from the leaf of T'radescantia discolor; ¢ and
d, from the leaf of Allium Cepa; e, from the inner bark of Asculus Hippocastanum;
J, from the leaf of Cycas revoluta; g, a cell containing raphides, from the frond of
Lemna trisulca; h.a single crystal from the same, more highly magnified; , sphzero-
crystal from Phallas eaninus, (Kny.)

54 THE VEGETABLE CELL IN GENERAL.

erystals for examination, their chemical composition has not yet .
been determined with certainty in all cases. ‘That a protoplas- .
mic film usually envelops both solitary and aggregated crystals,
can be shown by the method pointed out by Payen;! namely,
by dissolving the crystal slowly in very dilute nitric acid, and
testing with iodine, when the film will become yellowish-brown.
It has also been made out beyond question that some crystals
have a considerable admixture of cellulosic matter, and that a
few others are covered by a membrane of cellulose.? But these
two substances do not obscure the chemical reactions in ordinary
cases, by which it has been shown that the larger number of crys-
tals consist of calcic oxalate, after which, in frequency of occur-
rence, comes the carbonate of the same metal. These two salts
can be easily distinguished from each other by the following
simple tests : —

Reagent. Calcic Oxalate. Calcic Carbonate.
‘ : issolves with effer-
Acetic acid. No effect. Di
vescence.
Hydrochloric acid Dissolves without ef- Dissolves with effer-
One” : fervescence. vescence.

Since these two salts may occur in the same specimen, it is best
to use acetic acid first; by this agent all traces of the carbonate
are removed, and hydrochloric acid can then be applied in order
to detect the presence of oxalates. Sanio® and Holzner have
shown conclusively that many crystals which have been supposed
to be calcic carbonate consist merely of the oxalate.

Crystals of calcic sulphate have beeu reported as occurring
in certain Musacez,* in the bark of the willow, in the roots of
aconite, bryony, and rhubarb; and also in the root of a young
bean.® Calcic phosphate is said to have been detected in the

1 Payen : Mém. des savants étrangers, ix., 1846, p. 91.

2 Rosanoff (Bot. Zeit., 1865, 1867), Crystals in pith of Ricinus and Kerria.
Pfitzer (Flora, 1872), crystals in the leaves of orange and the bark of many
trees. i

Hilgers has investigated the occurrence of crystals at different periods of
growth of different organs. From his results it appears, (1) that in the very
youngest parts no crystals are to be found; (2) they appear, however, very
early in most parts, and (3) speedily attain their maximum size, after which
they undergo no change (Pringsheim’s Jahrb., vi., 1867, p. 285).

8 Sanio: Monatsber. Berliner Akad., 1857.

* Van Tieghem: Traité de Botanique, p. 526.

5 Sitzungsberichte der Wiener Akad., xxxvii., 1859, p. 106.

CRYSTALS. 55

wood of Tectona grandis (Indian Teak).! Holznei* uses the
following reaction to detect calcic sulphate: a solution of baric
chloride (not too concentrated) is brought into contact with
the crystal under examination; calcic sulphate soon becomes
covered with a whitish deposit of baric sulphate. This test
failed to show the presence of calcic sulphate in the plant-
crystals hitherto referred to this salt; they all gave, however,
the reaction for the oxalate.

188. Crystals closely resembling in most respects those which
are found in cells can be produced by Vesque’s method.’ Three
test-tubes are placed side by side: in the first is a moderately
strong solution of calcic chloride; in the middle one, a five per
cent solution of sugar; and in the third, a solution of potassic
oxalate. From the liquid in the first to that in the second a
short strip of filtering-paper runs, and a similar strip passes
from the second to the third test-tube; and thus the liquids in
the three tubes are brought into indirect contact. Crystals will
be formed in the middle tube, their character depending upon
the nature of the liquid there. In a solution of sugar, raphides
are produced; in pure water, prisms of small size, but with
sharply defined faces and angles.

189. According to Souchay and Lenssen,* monoclinic (“ Clino-
rhombic”) crystals of calcic oxalate containing two equivalents
of water are produced upon quick precipitation, while by very
slow action right octahedra with six equivalents of water are
formed.

A few works of reference are the following : —

Mout. Principles of the Anatomy and Physiology of the Vegetable Cell.
Translated by Henfrey (London, 1852). An octavo of 158 pages, This is an
excellent translation of a classical work.

HormeisTer. Die Lehre von der Pflanzenzelle (Leipzig, 1867). An octavo
of 397 pages. The volume treats very fully of the physical properties of pro-
toplasm,

EBERMAYER. Physiologische Chemie der Pflanzen (Berlin, 1882). This is
the first volume of an expensive work which deals with the relations of plants
to soil and climate.

HuseMANnn und Hiteer. Die Pflanzenstoffe (Berlin, 1882). Two large
volumes. It has very extensive references to the literature of the subject, and
most of its abstracts are excellent.

1 Ples: Naturkundig Tijdschrift voor Nedrlandsch-Indié, 1858, p. 345.
Quoted from Holzner.

2 Flora, 1864, p. 283. This communication contains a good abstract of the
literature of plant-crystals up to 1862.

3 Ann. des Sc. nat., sér. 5, tome xix., 1874, p. 300.

* Annalen der Chemie und Pharmacie, c., 1856, p. 311.

CHAPTER II.

CELLS IN THEIR MODIFICATIONS AND KINDS, AND THE
TISSUES THEY COMPOSE.

190. Wuitz cryptogamous plants of the lower grade may
consist of single cells, or of a series or stratum of simple and
undifferentiated cells, phanogamous plants, although equally
simple and homogeneous at the initiation of each individual,
develop into a more complex organization, at an early period
differentiate some of their cells into peculiar kinds, multiply the
kinds into tissues or fabric, and of these build up the organs
and parts which are familiar in ordinary vegetation.

191. The microscropical study of the parts even of a single
herb or tree, and much more that of a variety of plants, reveals
numerous forms or kinds of cells, and also (as might be expected
from their common origin) brings to view series of gradations
between the kinds, sometimes even between those which are,
upon the whole, widely differentiated from each other. While,
therefore, a general classification of the cells of any ordinary
plant into kinds is easy, any classification which shall satis-
factorily exhibit our present knowledge of the histological ele-
ments, and discriminate their varieties, is very difficult, if not
at this time practically impossible. At least, it must be said that
the most recent classifications are based upon considerations
of a character too recondite and special to be mastered at the
beginning by an ordinary student.

192. The most general and obvious division of the histological
components of a stem, root, or leaf would be into, (1) funda-
mental or typical cells, and (2) transformed cells. The first are
those in which the normal cellular character persists without pro-
found, if any, alteration or disguise ; as in the pulp of leaves, the
pith of stems, and in a portion of the bark. The second are those
which assume or affect lengthened or fibrous forms and a longi-
tudinal development (at least in all axes, and commonly in leaves
and other expanded organs), and, combined into threads, fasci-
cles, bundles, or more massive structures, constitute the frame-
work, which imparts solidity and strength throughout. Some

TYPICAL CELLS. 57

of these cells are so long in proportion to their breadth, and of
such diminished calibre, that they have naturally been called
fibres, although all gradations between them and typical cells
may be demonstrated. All these cells are interchangeably
called woody fibres or wood-cells, and one kind of them takes
the name of bast-cells.

193. Others are of larger calibre, are peculiarly marked by
thickenings on certain lines or in certain patterns, incline to be
developed end to end in a chain or row, and to become confluent
at the junctions, so as to form conduits of considerable length ;
these are called vessels, or ducts. Vessels and fibres are
associated in the plant; almost every separate thread of frame-
work consists of both, and so is called a fibro-vascular bundle or
fascicle. Morcover, the known gradations between the two are
such as to render a complete distinction between them nearly im-
practicable; so that they form the fibro-vascular, or, when a
single word is used, the vascular system. To this system, also,
pertain specially differentiated cells, such as cribrose-cells, in the
bark, etc.

194. All these are developed in or among the fundamental
or untransformed cells, and originate from the differentiation of
some of them.

195. The fundamental or typical cells may therefore be said
to constitute the fundamental system; which may also be con-
veniently called the cellular system, in contradistinction to the
vascular.

196. In an ordinary leaf it forms all but the framework of
ribs and veins; in the stem of a dicotyledon, the outer bark, the
pith, and the rays which traverse the wood; in that of a mono-
cotyledon, which generally has a looser texture than the last, it
is the common mass through which the definite bundles of the
vascular system are distributed. Of the fundamental system,
the most typical or unmodified cells are such as the chlorophyll-
bearing cells of leaves and of the green bark of stems, as well as
those with uncolored contents forming the pith, ete. Borrowing
a word from the old anatomists, the carly investigators of vege-
table structure called tissues composed of such cells Parenchy-
ma, perhaps taking the idea of the name from leaves in which
the veins are distributed through the softer parts as blood-vessels
through the parenchyma of the glands.

197. Parenchyma, therefore,.is the name of cellular tissue
in contradistinction to fibro-vascular tissue. In its primary
sense, only comparatively soft and thin-walled cellular tissue

58 MORPHOLOGY OF THE CELL.

took this name, and this is indeed typical parenchyma; but the
name rightly includes, as species or varieties, thicker-walled and
even solidified tissues composed of cells similar in other respects
to the type, as those in the hard endosperm of seeds.

198. A counterpart name, Prosenchyma, was employed to
designate tissues formed of elongated cells, such especially as
wood-cells and bast-cells. These being usually thick-walled,
and those of typical parenchyma thin-walled, this character was
brought into the definition; that is, cells of prosenchyma were
said to be thick-walled as well as long and narrow, those of
parenchyma thin-walled as well as isodiametric. But this dis-
tinction does not hold out well. All fibro-vascular tissues are
thin-walled at first, and some remain so; while portions of pure
parenchyma may become thick-walled, firm and hard, or take on
every intermediate condition. So that prosenchyma may be best
held to denote tissue of the fibro-vascular system, and typically
that formed of wood-cells.?

199. An explanation of the mode of production, multiplica-.
tion, and transformation of cells is deferred to a later stage.
Suffice it here to advert to the fact that every phanogamous
plant, orivinating in the seed, begins as an isolated cell, which
develops into a globular cluster of parenchyma cells, and grows
into the embryo or rudimentary plantlet, taking on the shape and
degree of development characteristic of its kind. In embryos
which are considerably developed in the seed, the axis and be-
ginnings of the leaves are already outlined or rudimentarily
indicated there ; in others the indication takes place in the early
stages of germination.

200. From this if not from an earlier period development
is no longer homogeneous. <A superficial layer of the common
parenchyma becomes distinguishable as the epidermis; while in
an inner zone, or at special points, certain cells develop into ducts
and wood-cells (prosenchyma), and thus are initially delineated
the outlines of the systems or regions which are to characterize
the whole growth; namely, — taking a dicotyledonous embryo
for the type, —an epidermal layer, a cortical layer, a fibro-vascu-
lar zone, and a medullary portion. As stem and root develop,
these primordial tissues complete themselves and have only to
go on growing, each after its kind; but at the developing points
(apex of the stem and of the root), as also in special portions or

1 “Zu dem Prosenchym im weitern Sinne kénnen wir auch die Gefasse
zihlen” (Nageli : Beitriige, i. p. 2).

CLASSIFICATION OF CELLS. 59

zones, initial differentiation continues. Here the nascent tissue,
consisting of parenchyma cells, multiplying by successive divi-
sions, and also the nascent prosenchyma as it forms and while
still capable of further division, has been named Meristem.

201. Meristem, therefore, is not a kind of tissue, but the
nascent state or early condition of any tissue. It is developing
parenchyma, either multiplying as such, or differentiating into
elongated forms, as for instance, in cambium.

Leaving the processes of cell-development to be considered
under the head of “Growth,” and the disposition of cells and
tissues in the fabric to be described under the several organs
(root, stem, leaf, ete.) which they compose, the kinds of cells
are here to be indicated, without particular reference to their
arrangement in the plant. In all classifications of objects which
are understood to have been developed from one type, interme-
diate forms of almost every gradation are to be expected. It is
specially so with plant-cells ; and of them it should be said, once
for all, that the kinds which have reccived distinct names, with
or without sufficient reason, are only types, or leading modifica-
tions, —some of a very marked, some of a quite subordinate
character.?

202. Plant-cells are to be described in this chapter under the
following classification : —

I. Cells of the fundamental system, or parenchyma cells, —
permanent typical cells.

1. Parenchyma cells, strictly so called, including as modi-
fications collenchyma cells and sclerotic parenchyma
cells, or grit-cells, such as the lignified cells of seed-
coats and drupes, ete.

2. Epidermal cells, and their modifications; e. g., Tri-
chomes.

3. Cork-cells, forming suberous parenchyma, or cork.

II. Cells and modified cells of the fibro-vascular system, — pros-
enchyma in the widest sense.

1. Cells of prosenchyma proper.

a. Typical wood-cells and woody fibres, including libri-
form cells (Sanio), and the secondary wood-cells
(De Bary).

8. Vasiform wood-cells, or Tracheids.

1 Sometimes a single cell in a uniform tissue may develop unlike its neigh-
bors-as regards one or more of the following characters : form, size, nature of
cell-wall or cell-contents. Such cells are termed by Sachs, idioblasts.

60 MORPHOLOGY OF THE CELL.

2. Vessels, or ducts.
a. Dotted.
6. Spirally marked.
ec. Annular.
d. Reticulated.
e. Trabecular.
3. Bast-cells, Bast-fibres, or Liber-fibres.
III. Sieve-cells, or Cribrose-cells.
IV. Latex-cells.

Intercellular spaces and canals are neither cells nor tissues,
but they require consideration in connection with them.

I, Cells of the Fundamental System,— Parenchyma in the widest
sense, including Modifications for Protective Surfaces.

PARENCHYMA.

203. This term is applied at present to all typical cellular
tissue except that which belongs to the epidermal system. It
therefore constitutes
the mass which sur-
rounds fibro-vascu-
lar bundles, forming
pith, medullary rays,
the pulp of leaves
and fruits, ete. It
occurs in nearly all
parts of all plants.
The elements of
parenchyma are sim-
ple cells more or less
separable from each
other, in some cases
by slight pressure,
and in others by the
ST cautious use of a
macerating solution.
The cells vary greatly in form, but usually are polyhedral or
spheroidal. Extended classifications of the cells themselves,
based upon form, have been made, but they are of no utility
and of small historical interest. Yet three principal shapes may
well be distinguished ; namely, short or isodiametric, elongated,
and flattened.

Fic. 37. Parenchyma from stem of Marrubium. 44°, (Jacobs.)

PARENCHYMA. 61

204. In the youngest state of organs short parenchyma cells
form the whole mass; here they are relatively small, filled with
protoplasm, and have
no intercellular spaces.
Later they are changed
in shape and size, may
have conspicuous in-
tercellular spaces, and
the protoplasm may be
replaced, at least in
part, by other matters.

205. If the cells are
loosely aggregated and
have conspicuous in-
tercellular spaces, the
tissue is called spongy
parenchyma. The cells meant
in such cases are apt
to be more or less
branched, and in some plants assume regular stellate forms.

206. Elongated parenchyma cells are generally more com-
pactly combined than the short ones. They are well seen in the
upper part of most leaves, where
they have received the significant
name palisade-cells.

207. Flattened parenchyma
eells are the common form in the
vertical plates (medullary rays)
which radiate from the pith to
the bark in woody plants.

208. The walls of typical pa-
renchyma cells are thin, and may
be variously marked with pits,
especially at the points of con-
tact with other cells. Thicken-
ing threads forming reticulations
and spirals are not uncommon ;
the latter occur in the aerial
roots of Orchidaces. A crum-
pling or folding-in of the wall is seen in some of the cells of pine
leaves.

Fic. 38, Forms of parenchyma in leaf of Pyrus communis, (Jacobs.)
Fig. 39. From pith of Sambucus nigra, showing pitted walls. (Gris.)

62 MORPHOLOGY OF THE CELL.

209. Thin-walled parenchyma cells play an important part in
assimilating and storing, and special names are given to cells
which have these offices, such as chlorophyll parenchyma, starch
parenchyma, ete. In the tissues of most succulents, and in the
leaves of a few plants, some of the parenchyma cells are filled
with clear sap and more or less mucilaginous matter, and con-
stitute the so-called water tissue.

210. The walls of typical parenchyma cells consist of ordinary

cellulose ; but even slight deviations from the type furnish good
illustrations of lignified and of cutinized membranes.

211. Lignification may increase the thickness of the cell-wall,
greatly reducing the cell-cavity, or it may merely harden the
membrane without much thickening. The parenchyma cells
found associated with other elements in .woody tissues have
walls of the latter character; the grit-cells in pears and many
other fruits show good examples of the former. Such hardened
cells are called sclerotic parenchyma cells.

Fig. 40. Sclerotic parenchyma cells from fruit of the pear. ( Weiss.)

ENDODERMIS. 63

In many cases it can be shown that canals run through these
thickened walls, as shown in
Fig. 41.!

212. Certain modified pa-
renchyma cellsare often united
to form sheaths around fibro-
vascular bundles. These cells
are prismatic, and in close
apposition. Their walls are
thin, except at their faces of
mutual contact, where they are
conspicuously thickened, and
often plicate, and nearly all
parts of the membrane are
more or less cutinized.

213. These cells con-
stitute the endodermis.
They generally contain a
large amount of starch.

214. Parenchymacells
may undergo the mu-
cilaginous modification
(see 147), as in the con-
ductive tissue of the
style of many flowers
and the albumen of many
seeds. This change is
comnion also in the lower
plants.

215. An appearance
closely resembling in
some points that pro-
duced by the mucilagi-
nous modification is pre-

1 A second kind of sclerotic parenchyma sometimes accompanies the longer
sclerotic cells in a few ferns and some monocotyledons. Its cells appear as if
segments of a jointed fibre, somewhat flattened on the side next the long cells,
and decidedly convex on the other. Such flattened cells are unequally thick-
ened on the two sides, and the walls are somewhat silicified. But the most
striking feature in many cases is the deposition within the cavity of the cell
of a mass of silicic acid; this is well seen in the hard cells which accompany
the fibro-vascular threads in the leaves of some palins.

Fie. 41. A sclerotic cell from the nutshell of Juglans regia. (Reinke.)

Fig. 42. Section through the central cylinder of a binary root of a vascular crypto-
gam (Cyathea medullaris). p, 7,7 = endodermis. (Van Tieghem.)

64 MORPHOLOGY OF THE CELL.

sented by the parenchyma cells just under the epidermis, or
outer layers of cells, in many plants. The cell-wall is thickened

very considerably at the angles, and upon the application of
dilute acids swells greatly, but without becoming clearly muci-
laginous. When moist,
such cells have a bluish-
white color and a marked
lustre. They are known
as

216. Collenchyma cells.
They are generally some-
what elongated, and so
united as to form threads
which possess great
strength, and are believed
to serve an important me-
chanical office in the plant.
Good examples of these
are afforded by the stems
4 of many Umbellifere.

EPIDERMIS.

217. This is the outermost layer of cells covering the sur-
face of the plant. In some of the higher plants it persists with
little change throughout the life of the organism ; in others it is

Fic. 43. Parenchyma with walls which have undergone the gelatinous modification:
a, from the centre of the style of Salvia scabiosefolia; b, from the stigma of Gesneria
elongata. (Capus.)

Fia. 44, ‘Transverse section of root-stock of Smilacina bifolia, showing collenchyma
cells just under the epidermis, ep. Note also the ordinary parenchyma at pc, and the
endodermis at ap. (Van Tieghem.)

EPIDERMIS. 65

sooner or later thrown off, and replaced by a subjacent protective
tissue, — cork.

218. Except at peculiar openings (stomata, ete.), the epider-
mal cells are in close apposition. Upon their exposed surface
they are cutinized, and thus a continuous hyaline film is formed,
known as the Cuticle.

219. Sometimes the epidermis may be torn off without much
disturbing the underlying tissues.

220. Besides the cells which compose the proper tissue of the
epidermis, there are certain ap-
pendages or accessory structures,
mainly hairs or analogous pro-
ductions (together called tri-
chomes), and peculiar cells which
constitute the stomata.

221. Epidermal cells proper are
in uninterrupted contact. They
are usually of a tabular or pris-
matic form. The lines which
mark their outlines as viewed
from above are sometimes
straight, but oftener sinuous, at least on the longer sides of the
cell, which here as elsewhere correspond with the direction of
growth. Near stomata and trichomes the cells frequently assume
very irregular forms.

222. Their upper or free surface is generally slightly convex,
and often has minute outgrowths, for instance, in velvety petals ;
when these are larger and longer, they constitute the simplest
form of plant hairs.

223. Delicate epidermis possesses thin walls; but in a large
number of fleshy and tough plants the walls have considerable
thickening, yet not always on the same part. Thus in the leaves
of Cycads the upper wall is the thicker; in many Bromeliaceze,
the lower and side walls. In a few cases the cell-cavity is nearly
filled by the thickening material. Stratification, striation, and
pitting of the cell-wall may also occur, great diversity existing
in all these respects.

224. When the epidermis is very delicate, the demonstration
of the thin film of cuticle requires great care in the employment

1 By De Candolle the term cuticle was applied to the layers of epidermal
cells, anid not restricted to the cutinized film (Physiologie, 1832, p. 109).

Fria. 45. Stoma of Sambucus nigra surrounded by epidermis.
5

66 MORPHOLOGY OF THE CELL.

of the reagents. According to de Bary,! the cuticle merely
covers the pure soft cellulose membrane of the epidermal cells
when these are thin-walled; but when the walls are thicker,
especially in epidermis which is long-lived, that part of the cell-
wall which borders on the cuticle becomes infiltrated with cutin,
and thus there arise one or more layers of modified cellulose,
each of which exhibits the reac-
tions of cutin. When such cells are
treated with warm potassic hydrate
(a ten per cent solution is, on the
whole, strong enough), the eutin is
slowly removed, and the cellulose
wall remains, although with con-
siderable loss of substance. Walls
which are thus impregnated with
cutin in strata form cuticularized
layers? The management of a
warm solution of potassic hydrate,
in order to obtain satisfactory re-
sults in the demonstration of the
fine stratification, demands much
care. It is advisable to apply very
gradual increments of heat to the
glass slide in the case of the more
delicate specimens.

225. Waxy and resinous matters
are frequently associated with the
cuticle. In some cases the amount
of such substances is large, and assumes commercial importance.
The young leaves of the wax palm (Ceroxylon andicola) are said

1 Vergleichende Anatomie, p. 80.

2 This division into apparent lamelle can be easily demonstrated in some
cases by the application of chloroiodide of zinc, which imparts a yellowish
color to the thick film, except at its outer surface. Mohl explained the struc-
ture of the exposed cell-wall in Viscum album, where the film is very thick,
as follows: ‘‘The epidermis cells consist here of two or three generations
enclosed one within another, of which all the thickened walls on the outer
side have become blended together into a membrane composing the cuticle.
These layers are to be called the cuticular layers of the epidermis, to dis-
tinguish them from the mass secreted on the outside of the cells, the true

Fia. 46. Transverse section of the leaf of Aloe verrucosa: @, section in water, — the’
non-cuticularized parts of the membranes shaded; above these are the cuticular
layers covered by the cuticle proper; 6, section heated in potassic hydrate; the culicle
proper has been raised from the cuticularized layers; c. section boiled in potassic hy-
drate; cuticle proper removed, epidermal cells separated, cuticular layers distinguished
by finer stratification,

EPIDERMIS. 67

to yield twenty-five pounds of wax to each tree. Bayberry wax
is 8 more familiar example.

226. To such waxy coatings is due the glaucous appearance
of the leaves and fruits of many plants. The coatings are chiefly
of the following kinds (de Bary’) : —

1. Coherent layers or incrustations upon the epidefmis. 2.
Crowded vertical rods of considerable length, as, for instance,
those on the internodes of Saccharum officinarum, from ten to
fifteen hundredths of a millimeter in height. 38. Very short
rods or rounded grains. ‘These, on the leaves of Tropzolum,
are not very near together, but on those of the cabbage, tulip,
etc., are more crowded. 4. When the grains are more minute,
and have the shape of needles irregularly massed together, they
constitute the peculiar bloom of the leaves of Eucalyptus,
Ricinus, ete.

227. Between the above kinds there are many intermediate
ones, Agave Americana, for instance, furnishing forms between
the two last named.

228. Epidermal cells proper have a delicate lining of proto-
plasm and a distinct nucleus. The cell-sap is generally colorless
and transparent, allowing light to pass with very little obstruc-
tion to the layers beneath the epidermis; but in some cases
it is so colored as to impart a conspicuous hue to the plant.
In many water-plants there is no well-marked distinction be-
tween epidermis and the subjacent tissue, even the cells of
the upper layer containing chlorophyll, but epidermal cells are
mostly free from either chlorophyll or starch. Brongniart has
shown that some amphibious plants have chlorophyll in the
epidermal cells of the aquatic but not of the terrestrial form.
That the rule is not universal is shown by Callitriche, which,
according to Hegelmaier, has epidermis without chlorophyll in
both forms.

229. Epidermis usually consists of only one stratum of cells,
but it may be made up of two, three, or even more layers.
Division of the original epidermal cells by one or more partitions
parallel to the surface of the leaf gives rise to superposed cells ;
and thus multiple epidermis results, as in the upper surface of

cuticle, which is soluble in caustic potash, and in most cases forms but a very

thin coating over the epidermal cells” (Veg. Cell, Henfrey’s trans., p. 35).

Good examples for study of the different kinds of cuticular infiltrations are

afforded by the following, — leaves of Dianthus caryophyllus, Galanthus nivalis,

Ilex, Pinus, Hoya, Sassafras, and Taxus, and twigs of Viscum and of Oleander.
1 Botanische Zeitung, 1871.

68 MORPHOLOGY OF THE CELL.

the leaves of many species of Peperomia, Ficus, and Begonia.
Multiple epidermis is not always of even thickness throughout ;
sometimes a portion may be only one or two cells thick, while
adjacent portions are composed of many layers. Such differ-
ences are generally associated with the occurrence of stomata,
hairs, ete. The subjacent cells in some forms of multiple epi-
dermis are smaller than those above them, and in these cases
the arrangement of the cells in the successive layers presents
striking inequalities.

230. Trichomes. Under
this term are included the
multifarious forms of hairs,
scales, bristles, and prickles.

Hairs are sometimes of
diverse forms on the same
plant, and even on the same
part, but sometimes so pecu-
liar and uniform throughout
large genera, or even orders,
that they aid in their iden-
tification; as, for instance,
in Malpighiaceze, Loasaceze,
and Eleagnacer.

231. Simple hairs, whether
branched or unbranched, are
formed by the prolongation
of a single epidermal cell,
either slight, forming a
mere papilla, or to a great
length, as in the so-called
fibres of cotton. Simple
hairs are abundant upon the
rootlets of most plants at a
little distance behind the ad-
vancing tip, where they play an important part.

232. Compound hairs are of all degrees of com-
plexity. They may start from a single cell, or from
a group of cells, and may have the derivative cells
47a ~—s arranged in many ways. The cells at or near the

Fi. 47a. Upper portion of a glandular hair of Martynia proboscidea, 19. (Martinet.)

Fic. 47 b. View from above, of the upper portion of the same. 999, (Martinet )

Fic. 48. Cynoglossum officinale. Longitudinal section through a young angular
bristle at the beginning of the thickening. 249. (Strasburger.)

TRICHOMES, 69

foot of the hair may differ somewhat in shape, size, and arrange-
ment from the other epidermal cells. They may form an emi-
nence upon which the foot rests, or they may be somewhat
sunken so that the body of the hair
hardly reaches the general surface of
the epidermis; but usually the hair
projects for a considerable distance
above the border of the depression.

Both simple and compound hairs
may be variously curved and
branched, giving rise to stellate and
many other forms.

233. Scales are trichomes which
are mostly compound, and consist
of discs borne by their edges or cen-
tres, either with or without a short
foot or stalk. If the disc is com-
posed of radiating cells, the scale
becomes stellate, a form which re-
sembles or passes into the stellate
and tufted hairs common in Mal-
vacere, etc. Well-marked stellate
scales are met with in Oleacex and
Eleagnaceze.

234. Brisiles, prickles and epidermal spines are firmer or
stouter outgrowths. When such outgrowths are truly epidermal,
they come off with the epidermis.

Hairs, scales, and prickles differ very greatly as to their per-
sistence, some being exceedingly short-lived, as, for instance,
the hairs which occur on roots; while others, for instance the
prickles on the rose, last for long periods.

235. In certain outgrowths from the edges of leaves or else-
where the structure is complicated by the presence of a portion
of the underlying framework. This is notably the case in the
fringe upon the leaves of Droseraceze. There are all degrees of
variation between such trichomatous outgrowths and spinulose
teeth, or lobes.

236. The consistence of the cell-wall in trichomes varies
widely, from extreme tenuity to the density of a silicified wall.
The more delicate hairs are transparent, so that the contents

Fia. 49. Branching unicellular hairs: a, from Humulus (the hop); 4, stellate hair
of Deutzia. (Van Tieghem.)

70 MORPHOLOGY OF THE CELL.

can be plainly seen, thus affording opportunity for examining
the-movements of protoplasm, and for the study of the cffects
of reagents upon the contents of cells.

Young hairs contain much protoplasmic matter; at a later
stage they have a large proportion of cell-sap; still later many
are filled only with air.

237. At first the epidermis is always completely continu-
ous, the cells being in close contact with each other; but
soon there appear, especially in leaves, guarded openings
through which the interior of the plant is brought into com-
munication with the surrounding atmosphere. These apertures
are of two principal kinds, the most important and widely dis-
tributed being

238. Stomata. These are combinations of epidermal cells of
a peculiar character, between
which a narrow slit extends
directly throughtheepidermis — ,
to an intercellular space be-
low. The cells bordering the
slit are well termed guardian
cells, on account of their
opening and closing under
certain circumstances. The
neighboring epidermal cells
are frequently arranged in a
definite order; and the po- BL
sition of the stoma has in
many cases a plain relation to the underlying framework.

Stomata belong especially to green organs exposed to the air ,
but they have been detected on all superficial parts of the plant,
with the exception of roots.?

239. Viewed from above, stomata appear generally as elliptical
bodies through which runs a narrow slit in the direction of the
longer diameter. Each guardian cell is therefore half the ellipse.
The cleft varies in width according to certain external condi-

1 The following cases are cited by de Bary (Vergl. Anat., p. 49) : On rhizo-
mata and tubers (young potatoes), on the perianth, the anther (in Lilium
bulbiferum), on the pistil, on the seed-coat (Canna). Plants destitute of chloro-
phyll may also be destitute of stomata, as in Monotropa Hypopitys ; or have
them only on the pistil, as in Lathrea,

Fig. 50. Adult stoma of Hyacinthus orientalis, seen from above. (Strasburger.)
Fic. 61. The same, seen from below.

STOMATA. 71

tions hereafter to be described, the stoma being in fact a deli-
cately balanced valve. A vertical section shows that the outer
part of the opening is wider than the narrow passage farther
down, and that the space below this widens somewhat towards
the intercellular cavity.

1 The following table, compiled from figures given by Weiss, gives the num-
ber of stomata on the upper and under sides of the leaves of various plants
for the most part readily procurable by students. To show the wide differences
in size, the longer and shorter diameters have been added, and, finally, the frac-
tion of a square millimeter covered by a single stoma.

F The space ina
coe . , 2 mm covered
sae 4 € || by astoma.
Name of plant. 2 3
So 53 g a Bo Bg
meg sg al AQ arg ts
52 | 5% Be | 52
Abies balsamea . . . «4 6 s 9 228 0.047 0.031 0 0.2660
Abies nigra. > 2 31 82 0.042 0.027 0.0276 | 0.073L
Acer Pseudoplatanus, ib. ch te 0 400 0.024 0 017 0 0.1280
Amarantus caudatus,L . . 171 193 Roce ieee | 0.0195 | 0.0672
Anemone nemorosa, L. . . « 0 67 0045 | 0040 || 0 0.0947
Asclepias incarnata, L. . . . 67 191 0.026 0018 | 00247 | 0 0702
Avena sativa, L. 48 27 { 9.054 | 40.035 11 9 o7og | 0.0554
rtp Ore cg 0.060 0.050 * ;
Berberis vulgaris, L. - . . . 0 229 0.033 0.022 0 0.1305,
Betulaalba,L. . . . ew e 0 237 0.029 0.018 0 0.0972
Brassica oleracea, ) Oe 219 301 0.1137
Buxus sempervirens . . . . 0 208 0 032 0.031 0 0.0942
Caltha palustris, L. ae ee ond 43 0 042 0,034 0 0.0482
Euphorbia Cyparissias, L.. 0 259 0.027 | 0.018 0 0.0989
Ficus elastica. . . . 2. 1 0 145 0.028 0 019 0 0.1187
Galanthus nivalis, Ths i x 30 55 0.034 | 0.022 || 0.0176 | 0.0323
Geranium Robertianum. . . _ 297 0 045 0.032 0.3356
Helianthus annuus, L. . . 175 325 0.034 0.023 |; 0.1074 | 0.1995
Hydrangea quercifolia, Bertr. 0 330 0.020 0.019 0 0.1015
Ilex Cassine . . . 2. 1. 2 e 0 212 0.029 0.025 0 0.1206
Juglans nigra, L. . . . 0 461 0.024 0 018 0 0.1563
Lilium bulbiferum, L. aan 0 62 0.071 0,050 0 0.1751
Maclura aurantiaca, Nutt. . 0 251 oe 0.016 0 0.0695
017 0.009
Mimosa pudica,L. . ... | 138 | 302 { o026 | {oor {| 00164 | 0.0927
0.018 | { 0.008 =
Morusalba,L. . 2...) 0 480 { 0008 { anes 0 | 0.0537
Nympheaalba,L.. .... 460 0 0.026 | 0.022 || 0 2070
Pinus Strobus,L. . . 2... 142 0 0.05 0.032 0.1945
Pinus sylvestris, L. wn Se 50 7 0.034 0.023 0.0307 | 0.0436
Pisum sativum, L. . Perot 101 216 0.024 0.017 0.0323 | 0.0691
Pittosporum Tobira, Ait. as 0 382 0 OBL 0.027 0 0.2494
= %
Populus dilatata, Ait. . . . | 65 | 270 |) {033 | {Ojon | 0.0368 | 0.1471
Ribes aureum, Pursh. . . . 0 145 0.036 | 0 025 0 0.1025
Secale cereale, L. _ 25 0.051 0 029 0 0 0269
Sequoia gigantea (young plants) 0 82 0.053 | 0.033 0 0.1434
Sileneinflata,Sm..... . valu 166 0.033 | 0.02L || 0.0386 | 0 0905
Solanum Duleamara . . . . 60 263 0.021 0.014 |: 0.0139 | 0.0607
Stellaria media, Sm. 5 ees 128 — 0029 | 0.026 || 0.0758
Syringa vulgaris, Lew ae 0 330 0.028 0 016 0 0.1162
Vinca minor, L. . 0 417 0.029 0.018 0 0.1961
Vinca minor var. variegata é 0 405 0.024 0.016 0 0.1223
Zea Mais, L. Ser tee de: 94 158 0.037 | 0.029 |} 0.0792 | 0.1332

72 MORPHOLOGY OF THE CELL.

240. Asappears from
the following figures, the
first stage in the devel-
opment of an ordinary
stoma is the separation
of a part of an epider-
mal cell by means of a
vertical partition, thus
forming the mother-cell
of the stoma. This
next divides by a verti-
cal plane which soon
exhibits a narrow chink.

Yhe cells thus slightly separated at their common wall may

by subsequent growth
bring about changes
in the relations of the
neighboring cells.

In Sedum, as shown
by Strasburger, there
are preparatory divi-
sions in different di-
rections, while in
some monocotyledons
there are simultaneous
divisions in contigu-
ous epidermal cells.

241. Stomata are
not present, at least

in a perfect form, in any submerged plant. In aquatics with

Fic. 52. Vertical section of stoma of Hyacinthus orientalis. (Strasburger.)
Fic. 53a, b,c. Three stages in the development of the stomata of Sedum spurium.
Fig. 63c shows the narrow slit made by the neighboring epidermal cells, (Strasburger.)

STOMATA. 13

floating leaves they are confined to the upper surface of the
leaf. The leaves of certain plants, as those of monocotyledons
and those which take a vertical po-
sition, have them in nearly equal
numbers on the two sides; but in
most cases the number on the under
exceeds that on the upper surface,
as will be seen from the table on
page 71. As regards the approxi-
mate number on leaves of average
size in some of our common plants,
the following figures may be of
interest : —

Nymphea. . . . . . «+ + ~~ 7,650,000
Brassica oleracea. . . we) + «11,540,000
Helianthus annuus. . . . . . . 13,000,000

242. Water-pores. Directly over the extremities of the fibres
of the framework of many green leaves are found apertures in

the epidermis which have no true guardian cells,’ but which
closely resemble ordinary stomata in most other respects. *Owing

1 That is, the bordering cells do not close under external influences.

Fria. 54. Vertical section of stoma of Sedum spurium. (Strasburger.)

Fic. 55. Water-pores in leaf of Rochea coccinea. The left-hand figure shows both
an ordinary stoma (the lower one) and a water-pore (the upper), as seen on upper surface
of leaf. The right-hand figure slows the structure displayed by a vertical section. (Van
Tieghim.)

74 MORPHOLOGY OF THE CELL.

to the fact that their cavity answering to the intercellular space
of a stoma is often filled with water instead of air, these have
been called water-pores. At certain times liquid water passes
through these pores, collecting at the opening and sometimes
leaving there, upon evaporation, slight incrustations of calcic
carbonate. Water-pores assume different forms and vary much
in size. Good examples are afforded by many Aroidea, by the
teeth of the leaves in some species of Fuchsia, the leaf-margins
in Tropzolum, etc.?

Small rifts of nearly the same shape can be found in certain
grasses ; but in these the aperture comes from a mechanical rup-
ture,’ and the underlying structure is very simple.*

CORK.

243, This protective tissue is formed beneath and replaces
epidermis in the older superficial parts of plants; it also con-
stitutes the films by which wounds are healed. Only the inner
layers of cork-tissue possess cellular activity, tlose which lie
outside of them having perished: the former contain protoplasm
and ‘are capable of cell-division; the latter contain air, and
occasionally small clusters of crystals. The inner, active, and
growing layers are known as cork meristem, cork cambium, or
Phellogen ; the outer, produced from this and no longer living,
make up the bulk of the outer bark, and are ordinarily called
cork. Although the older cork-tissues must be further described
in Chapter ILI., under ‘‘ Bark,” their elements may be conven-
iently treated of now in connection with the cells which produce
them.

244. Origin. Cork may arise from several different sources,
the principal of which are the following: (1) from division of
cells in the epidermis (e. g., specics of Pyrus, Salix, Viburnum,
etc.) ; (2) more commonly from underlying parenchyma, in a few
cases even from that which occurs in the inner bark (the bast
parenchyma), asin Vitis and Spirea; (3) from parenchyma at
injured surfaces, as in the healing of wounds.

245. It is normally produced upon the stems and roots of
flowerihg plants, especially dicotyledons. Its cells are generally

1 For a full account of water-pores, see de Bary’s Anatomie, p. 54, and
Jahrb. konig]. botan. Garten, Berlin, 1883.

2 De Bary : Anatomie, p. 57.

8 Gardiner: Proceedings Camb. Phil. Soc., 1883.

CORK. vis)

formed by the division of the mother-cell into two tabular cells, by
a partition parallel to the surface of the organ. In most cases
the outer cell becomes
cork, while the inner re-
tains its power of division
and in turn produces new
cells. But with the first
appearance of the cork-
layer a change takes place
in all layers lying to the
outside of it: they are cut
off from nutritive supplies
and soon die. The con-
tinuous layers of cork are
called, collectively, Peri-
derm, a name restricted
by Mohl to tough cork in
distinction from soft cork,
but now employed with a
wider signification.

246. Cork meristem
gives rise to successive
layers of cork-cells: if the
new layers differ much
from the preceding in the
shape and size of their cells, an appearance of stratification
naturally results. Cork meristem may, in exceptional instances,
produce on its inner side permanent parenchyma, the cells of
which contain chlorophyll; these green layers are called Phel-
loderm, and are observed well in the beech, willow, etc. (see
Chapter IIL.).

247. Cork-cells are tabular, or sometimes cubical, and with
few exceptions have no intercellular spaces. In the case of very
flat cells which cohere more firmly laterally than in the line of
the radius, the cork-tissue may be readily separated in films or
sheets.

248. The walls of older cork-cells are cutinized or suberized
throughout. The demonstration of cellulose in cork-cells is not
possible unless the cells have been first acted on by solvents,

Fic. 56 Formation of cork in a branch of Ribes nigrum, one year old; part of trans-
verse section: hk, hair; e, epidermis; pr, cortical parenchyma, somewhat distorted;
K, the total product of the phellogen c; k, cork-cells; pd, phelloderm; J, bast-cells.
(Sachs. )

76 MORPHOLOGY OF THE CELL.

such as caustic potash, and the like. But sometimes the cell-
wall seems to be completely changed into cork-substance.

249. Cork-substance behaves towards reagents in nearly all
respects as culin does (see 157).

A

250. Cells which hare been completely suberized can be sepa-
rated from each other by the gradual action of Schulze’s macer-
ating solution.?

251. The color of cork-cells is not dependent upon the amount
of the change of the wall into cork-substance. The walls of the
cells in some species of willow are colorless, while those in other
species are distinctly yellow; and yet the former have been as
thoroughly changed into cork-substance as the latter.

II. Cells of the Fibro-vascular System,— Prosenchyma in the
widest sense.

252. The cells and modified cells of this system constitute
the framework of a plant. In a few of the higher and in many
of the lower plants it is barely if at all developed, the entire
structure consisting, in such cases, of a mass of parenchyma
covered by epidermis. But in most plants it exists as a skeleton

1 This fact has led to the belief that there exists in such cases an interme-
diate plate which differs in its character from the rest of the cell-wall ; but
prolonged action of the same reagent, especially with warming, causes the cells
to break down and ultimately form a disorganized mass.

Fia. 57. Formation of cork and secondary cortex in Betulaverrucosa. A, B, C, D,
successive stages; 1, first layer of secondary cortex; 2, layer which divides in B, to give
outside the first layer of cork (shown in C), and a layer, 3, within, which again divides
in D, (Sanio.)

>

WOOD-PARENCHYMA. 77

bringing all parts into closer relations, and strengthening the
whole.

253. The cells are normally of considerable length in pro-
portion to the transverse diameter, and are generally more or
less sharply pointed (prosenchyma proper). The most impor-
tant of the modified cells belonging to this system unite to form
long rows in which the terminal partitions are nearly or quite
obliterated, throwing the cavities into one, and thus forming a
cylinder, termed a duct. Between proper prosenchyma cells
and ducts there are numerous connecting forms which render
impossible any attempt at classifying them exactly.’

Associated with these cells, but differing in some important
particulars, are cribrose and latex cells, which for convenience
are here to receive separate treatment.

254. Before developing the provisional classification given
on page 59, attention must first be directed to the peculiar
transitional forms constantly met with, which belong as much
to parenchyma as to prosenchyma, but are more conveniently
examined in connection with the associated wood-elements.

Chief among these intermediate forms must be mentioned
those of which Fig. 58, No. 9, may be taken as a represen-
tative. Here the whole structural element is isolated as an
elongated combination of three cells, one of which has flattened
ends, while the other two, attached to these ends, have their
free extremities pointed. In spite of their form, such cells are
usually described as wood-parenchyma cells. When their walls
are thicker, they are not easily distinguishable from septate
libriform cells (see 263).

255. The forms shown in Fig. 59, No. 19, are common in
the wood of many plants, notably the oaks. They are rela-
tively small, have rather blunt extremities and thin walls. They
occur with these characters especially in the autumnal wood of
the oaks (see 395), while in the spring wood they are apt to

1 For the satisfactory study of the relations of the elements of prosenchyma,
very thin sections are necessary; but for the examination of the elements them-
selves, recourse to some process of maceration, by which they can be isolated,
is always desirable. In general, there is nothing preferable to Schulze’s solu-
tion in any strength adapted to the special case; it must be remembered that
the slow action of a dilute solution gives hetter results than the more rapid
action of a concentrated one. If the section to be examined is first subjected to
the action of the macerating solution of proper strength and then thoroughly
washed, it can be dissected at pleasure under a high power of a simple lens.
This method is always to be preferred to the ordinary one of disintegrating the
whole specimen and obtaining a confused mass of separated cells.

78 MORPHOLOGY OF THE CELL.

pass over into the variety shown in Fig. 59, No. 18. The latter
are known as ‘‘ conjugate cells.”

PROSENCHYMA PROPER.

256. Typical wood-cells. ‘These are best illustrated by elon-
gated, often pointed cells, of which good examples are found in
the cambium layer (that is, the layer of merismatic or formative

ae

“PYM U MYM

aes ine
5 6

Fra 58. Drawings of wood-elements. 1-7. Avicennia sp. 1. Wood-parenchyma
cells united with each other; tangential section. 2, 3,4. Conjugate wood-parenchyma
cells isolated by Schulze’s solution. 5, 6. Portions of spirally striated libriform fibres
isolated by Schulze’s sclution. 7. The septum of a duct. 8-12, Tectona grandis; the
elements separated by maceration. 8. Conjugate wood-parenchyma cells, 9, Ordinary
wood-parenchyma fibre 10. Substitute fibre. 11. Simple libriform fibre. 12. Sep-
tate libriform fibre. 15. Porlieria hygrometrica; conjugate substitute fibres seen in
radial section. The wood-cells are omitted in order not to confuse the diagram.
37. Radial section through the wood of Jatropha Manihot. 38, Tangential section
through a libriform fibre and two cells from a medullary ray. of the same plant.
39-42, Bast-cells of Cytisnas Laburnum, 39. Cross-section through a part of a young:
bast-bundle acted on by chloroiodide of zinc. 40. 41,42 Cross-sections through young
bast-cells, acted on by chlorviodile of zinc. (Sanio.)

WOOD-ELEMENTS. 79

tissue just under the bark of dicotyledonous plants). Their
walls are thin, and at first nearly or quite free from pits or
other markings.

They grade into three constantly recurring forms; namely,
(1) parenchyma (see 254) ; (2) attenuated forms, often so slen-

909%
a)

o|
26
Zo
3
Be
Be
Be,
cr
2 8
O38
3
23

3
Hos &
HS 9;
HS °:
So’
So!
ss
USO

59

der as to deserve the name of fibres; (3) forms with peculiar
markings at most points of contact, and thus much resembling
ducts or vessels.

Fic. 59. Drawings of wood-elements. 13. Tracheid from Tectona grandis. 14-18.
Porlieria hygrometrica. 14. Conjugate substitute fibres seen in transverse section.
16. Ordinary substitute fibre after maceration. 17, 18. Conjugate substitute fibres
after maceration. 19-22. Cytisus Laburnum; the elements separated by maceration.
19. Wvod-parenchyma fibre. 20. Substitute fibre. 21. Simple libriform fibre. 22. Tra-
cheid. 23. Cross-section through the cambium and youngest wood of Cytisus Labur-
num, 24-23. Ducts from Mahonia Aqnifolium. 24. After maceration. 25. Longitudinal
section. 26-31. Ducts from Hieracium, separated by maceration; showing the ex-
tremity only. 32-34. Ducts from Onorpordon acanthium, separa‘ed by maceration.
35. Spirally marked duct from Vitis vinifera, after maceration. 36. Libriform fibre
from Jatropha Manihot. (Sanio.)

80 MORPHOLOGY OF THE CELL.

257. The drawings of wood-elements represented in Figs. 58
and 59 are from Sanio’s work, and are given with his nomen-
clature. The cells figured in Nos. 10 and 16, termed by Sanio
substitute fibres (German, Ersatzfasern), answer well to the type
of prosenchyma. When these cells are much reduced in calibre,
they are known as libriform fibres.

258. Ordinary prosenchyma vells usually have simple pits, but
no true spirals. ‘The pits may be round, and of the same size as
those on the ducts with which they may be in contact, but some-
times they are elongated slits, and run obliquely, as shown in
Fig. 59. If two of these cells are in contact, processes may
extend from one cell to corresponding protrusions in the other,
and thus one cell is united with the next. By careful macera-
tion such cells can be separated, and then each appears to have
one or more rows of square teeth or short tubes. It sometimes
happens that the wall at the end of these intrusive tubes is
broken down, thus allowing free communication between the
cells.

Good examples of substitution cells are to be found in the
wood of Magnolia, Liriodendron, many Leguminose, etc. They
are not so common, however, as conjugate parenchyma cells (see
Fig. 58).

259. Woody fibres are of two chief classes: (1) those in
which the narrowed cavity is continuous throughout the whole
length, and (2) those which have partitions dividing it (sep-
tate fibres).

The first class has been again divided into two groups depend-
ing upon the presence of starch, but the division is not wholly
satisfactory. The first group comprises all those fibres which
have a trace of protoplasm, while those of the second have also
more or less starch, and generally some tannin.

All of these woody fibres resemble the bast-fibres of the inner
bark of dicotyledons so closely that they have been well called
libriform. They are described by Sanio, from whose paper on
the subject most of these names are taken, as being always
spindle or fibre-form, relatively strongly thickened, and occa-
sionally furnished with bordered pits which somewhat resemble
those of vasiform elements (264), but are smaller and less
clearly defined. They never have true spiral markings, and
very seldom any spiral striation. They contain during the
periods of rest of vegetation in winter more or less starch,
and perhaps some chlorophyll and tannin, but at other times
only air.

LIBRIFORM CELLS. 81

260. The unseptate fibres, the true libriform cells, are only
sparingly pitted, except in a few species like Oleander, where
they are pitted on both the radial and tangential walls. The
pits are generally elongated and oblique, and according to Sanio
always running from left to right.

261. The cell-wall of these fibres is always lignified, and pre-
sents three layers; and in some instances there is also a layer
which is plainly gelatinous, ¢. g., in Betula and Alnus. These
gelatinized fibres are not found in all of the annual rings, nor
in all parts of even one ring.

262. Libriform cells are variable in length in different plants ;
some of the shortest occurring in Daphne Mezereum, .14 mm.,
and the longer in Avicennia,2 mm. In all cases they are the
longest elements in the mass of wood. They are generally sim-
ple, but occasionally branched cells are met with, as in Tilia and
Cladrastis. They are sometimes irregularly grouped together,
sometimes radially arranged. Species of Magnolia exhibit the
latter, Ulmus the former, mode of arrangement.

263. Septate libriform cells have sometimes been confounded
with wood-parenchyma; but Sanio points out the following
distinctive characters: (1) they are always thicker walled;
(2) they have oblique slits, while wood-parenchyma has only
roundish pits; (3) they become septate only after the thicken-
ing has progressed to some extent, while in wood-parenchyma
the divisions begin before the cambium cells‘ from which it is
derived have begun to thicken.

Septate libriform cells are less common than any other woody
element; examples, however, are not rare in Vitis, [Hedera,
and Rubus.

264. Vasiform clements. Neither of the two forms already
considered — namely, typical wood-cells and woody fibres — has
distinctive spiral markings or true bordered pits (that is, dis-
coid markings) ; but another important class of wood-elements,
of which mention must next be made, is characterized by such
thickenings.

265. To this class of elements it is difficult to give any
satisfactory name. They have been collectively termed vascu-
lar, but a large part of them are comparatively short and closed,
and cannot be properly known as ducts or vessels; the name
Tracheal (or Tracheary), more widely employed, is open to

1 The immediate derivatives from the cambium, which are partly formed
woody fibres, have been termed cambium fibres (Sanio : Bot. Zeit., 1863).
6

82 MORPHOLOGY OF THE CELL.

the objection that while it is a significant term when applied to
trachea-like bodies (ducts) it is a misnomer when applied to an
elongated cell wholly free from annular or spiral markings.

266. Tracheal cells are of two chief kinds: (1) those which
are closed throughout, — at least until a very late stage of devel-
opment; (2) those formed by rows of cells which lose their
intervening partitions, and hence are thrown into a long canal,
or vessel. The former are known as Tracheids,! the latter as
Trachee ; for which terms may be substituted the following,
applicable in nearly all cases, — Wood-cell and Duct.

The distinctive markings of tracheids and trachee are bordered
pits, or discoid markings, and various thickenings of which the
spiral may be taken as an example.

Tracheids and trachese further agree in the following point:
when complete, the protoplasmic mass disappears, leaving gen-
erally no trace. The cavity is filled in a few cases with watery
fluid, in some with water and air, but in most with air alone.
Occasionally other matters may be found in the trachere, for in-
stance, latex ; but these are so exceptional as to need no further
mention at this point.

267. Vasiform wood-cells, or tracheids, are elongated and taper-
ing cells, more or less lignified, and having peculiar markings,
the principal kinds of which, although previously referred to in
133, require a more extended treatment here.

268. Bordered pits, called also areolated dots and discoid mark-
ings, are very common, especially in wood of gymnosperms,
where they form a characteristic feature both in fossil and

1 But the term ¢racheid, as usually understood, is applied to wood-cells with
peculiar markings, next to be described.

The following measurements by Sanio show the difference between the length
of some tracheids and the libriform celis in the same plant : —

Trachevds. Libriform cells.
Rhamuus eatharticus. . . . . . 628 mm. -52 mm.
Asculus Hippocastanum. . . . . . 26 * 430“
Daphne Mezereum . . ..... 15 * 221. *
Ribesrubrum . . . . ww ee 4D 47

Where, however, the tracheids alone are present, they are sometimes much
longer ; for instance, in Staphylea pinnata, 1 mm., and in Philadelphus coro-
narius, .85 mm.

According to Sanio, the bordered pits of ducts are the same as those of the
tracheids, as regards size, form, and usually as regards frequency.

Occasionally tracheids are found which are plainly septate. It thus appears
that the tracheids form a gradation between true ducts and libriform cells with
bordered pits.

BORDERED PITS, 83

recent plants. When the wood ina pine stem is cut radially,
the flattened sides of the wood-cells exhibit the dotted appear-
ance seen in Fig. 60. The number and mode of distribution of
the markings in the wood-
cells or tracheids of Co- a
niferze are so nearly con-
stant, that they may be
used with considerable
certainty in the discrimi-
nation of a few genera.
269. In a transverse
section of the mature tra-
cheids the discoid mark-
ings are plainly seen to
be pits having an arched
border or incomplete
dome, and it is also e

seen that the thin spot
or pit is common to VINE?
two contiguous cells. Se

Hence the two domes,

being on opposite sides of a partition-wall, have a lens shape,
and the central perforations are nearly or exactly opposite each
other (Fig. 62). Even in the same speci-
men the bordered pits vary within com-
paratively narrow limits both as regards
the size of the disc and that of the central
aperture.

The two domes making up a single dis-
coid marking are at first separated by a
delicate plate of unequal thickness; but
later this middle lamella may be broken
down, and then a free passage extends
from one cell to the other.

The character of the domes and the mid-
dle plate can be understood from the ac-
companying figures of sections of the stem of Pinus sylvestris
(Figs. 62 and 63). According to Sanio, the sections should be

boiled in acetic acid, in order to remove all cell-contents.

Fie. 60. Areolated or disciform markings of the wood-cells (tracheids) of Pinus
Laricio: a, aspect of radial walls; 6, a transverse section; c, development of the

markings in Pinus sylvestris. (Sanio.)
Fics. 61 and 62. Pinus sylvestris, ‘Transverse sections of nearly perfect and perfect

discoid markings. (Strasburger.)

8t MORPHOLOGY OF THE CELL.

The cambium-cells and the youngest tracheids have uniform
and smooth walls, but in those next older there appear thin
spots, which are well defined above
and below, but not on the sides, for
here they grade off into the thicker
part of the wall. In the cells which
are still older the thin places take the
shape of discoid markings, and are
clearly seen in any radial view. Com-
parison of radial with transverse sec-
tions shows that at the margins of the
thin places a portion of the wall ex-
tends as a slight projection upwards,
and partly over the spot. In the more
mature form the thin place is still re-
tained as a delicate plate separating
the two cells, but easily broken down
perhaps in further growth.

270. Scalariform markings (see
134) are especially abundant in ferns.
The bordered pits are much elongated,
and appear as clefts with only narrow
portions of the wall between them
(Fig. 647). They often follow each
other with as much regularity as the
‘“‘rounds” of a ladder, whence the name (from scalaria,—~a
flight of steps). They are more commonly found in

DUCTS.

271. Ducts, or Trachee, are variously marked by pits, and
by the thickenings described in Chapter I. Some of the more
common forms of dots are shown in Fig. 64.

Spiral, annular, and reticulated markings are all formed by
the thickening of parts of the wall by which narrow lines or
bands are produced on the inner surface. In these cases the
portions of the wall which are not thickened are often of extreme
tenuity, and break upon slight pressure or strain, permitting the
spiral to uncoil or the rings to separate (Fig. 64, s s').

272. Spiral markings. The number of threads or narrow
bands varies from one to fifteen or even twenty, the latter in the
petioles of Musa.!| They wind, as a rule, from right to left;

’ De Bary: Vergleichende Anatomie, 1877, p. 163.

Fic. 63. Pinus sylvestris. Cross-section through the cambium and young wood-cells.
(Strasburger. )

MARKINGS OF DUCTS. 85

but, according to Moll, from left to right in a few plants. Thus
in the wood of Vitis vinifera, Berberis vulgaris, and some others,
they run from left to right in the ducts first formed, but in the
reverse direction in those which are produced later. And by
interruption of the spiral it may have two directions in the
same duct, as in those of Cucurbita.1 The steepness of the

——S=

spiral depends in part on the age of the cell, or vessel, — at least
in some cases. According to Mohl, ‘if the vessel is developed
in an organ which has already completed its longitudinal growth,
the turns of the spiral lie close together ; but if the organ under-
goes elongation after the completion of the development of the
vessel, the turns of the fibre are drawn far apart by the stretch-
ing which the vessel suffers; consequently very loosely wound
spiral vessels are usually found in the posterior first-formed por-
tion of the vascular bundle nearest to the pith, while those lying
nearest the bark have close convolutions.”?

273. Annular and reticulated markings have been regarded as
mechanical modifications of spirals, and it is true that inter-
mediate forms exist between these types. For instance, tightly
wound spirals are nearly annular, and in some cases there are
threads which run either vertically or obliquely from one part of
a spiral to the contiguous thread. But even in the youngest
states of some ducts the markings appear as rings or as a net-

1 Mohl: Vermischte Schriften, 1845, pp. 287, 321, Ueber den Bau der
Ringgefisse.

2 Mohl: Vegetable Cell, Eng. Trans., 1852, p. 19.

Fic. 64, Vertical radial section of hypocotyl of Ricinus communis, illustrating differ-
ent markings of ducts; ¢’ ¢, pitted; /, scalariform; s’ s, spiral, the spirals beginning to
uncoil. (Sachs.)

86 MORPHOLOGY OF THE CELL.

work. While, therefore, they may and probably do have a
common origin with spirals, it is not necessary to assume, nor is
it probable, that they have resulted from mechanical displace-
ments of them. The relative positions of the separate rings
may be explained in the same way as the steepness of the
spirals.?

274. Cases are met with, in which projections from the wall
may extend nearly or quite across the cell-cavity, somewhat after
the manner of beams. Such cross-beam cells or ducts are called
trabecular. A good example can be found in some of the tracheids
of the leaf of Juniperus communis.?

1 “The notion was extensively held that the spiral fibre could not follow
the expansion which the vessel underwent during its growth, and tore up into
fragments which were again united into rings, and thus brought about the
formation of annular vessels. Completely as this idea, which was a contradic-
tion to all observation, had been refuted by Moldenhawer, it remained a stand-
ing article in all phytotomical writings up to Meyen’s Physiologie” (Mohl:
Vegetable Cell, p. 21).

2 De Bary: Vergleichende Anatomie, p. 171.

The following measurements of wood-cells and ducts are given by Wies-
ner (Die Rohstoffe des Pflanzenreiches, 1873, p. 525) :—

Average diameter of wood-cells.
Rhus-Gotinus. 2 « . «© @ «eo ee eo ee HOM

Lonicera Xylosteon . 2 1. ee eee ee we 8B
Salix Caprea. 2 6 1 ee ww ee ee we «611
Viburnum Lantana. . . . . 7 ee ew «22.0
Alnus glutinosa Oa lela we Le eek er Re a BOLO
Fraxinus excelsior . . . 1 1 1 1 se ee ee 28.0“

Average diameter of ducts.

Hematoxylon Campechianum. . . . . + + + + 12m,
CesalpiniaSappan . ee ee ee ee et 120 *

Ochroma Lagopus. . . - Gx Sw ee) ee La TOE
Fraxinus excelsior. 2 2 2 + 2 + + ee ew «140
Ulmus campestris. 2 6 6 6 6 ee ee ee 158“
Tectona grandis... + + ee ew ee eee 160%
Juglans regia 2. 6 ee ee ee ee ee 2208
Caryavalba. a. 2 4% we Be Fs ee ae 248
Quercus sp... 6. ee ee ee ee + 200 to 300 *

The ducts in the foregoing examples are so large that in cross-section
they can easily be seen by the naked eye. The following are considerably
smaller : —

Tiliasp.. 6 6 ee ee ee we we ewe OM
Acer Sfins ao Ge ow we 2 ew ee ew ew | TE
AlNNS Spe @ aa Oe Se ae a ee TE
Rhus Cotinus . . 6 6 6 6 6 ew we ww ee BO
Betula.sp: « 5 & s # S$ 6 we Se we ~ eo

BAST-FIBRES. 87

275. Tyloses. If a cell still growing is in contact with a duct
at one or more of its perforations, the cell may intrude into the
cavity of the duct, and to a considerable extent. Such intrusive
growths are known as Tyloses (German, Thyllen).

If the intrusive portion of the tylosis further multiplies, pro-
ducing new cells, the cavity of the duct may contain a confused
mass of irregular cells of various shapes and sizes. Such masses
are often found in the ducts of Quercus alba, Q. castanea, Q. ma-
crocarpa, Q. tinctoria, Q. virens, Castanea vesca, Carya alba,
C. oliveformis, C. amara, Juglans nigra, Sassafras officinalis,
Morus rubra, Maclura aurantiaca, and Robinia Pseudacacia. In
the latter they are especially striking.?

BAST-FIBRES (LIBER-FIBRES).

(Sclerenchyma of many recent German authors.)

276. The name bast was originally given to the inner bark of
the linden (bass-wood), and hence originated its use as a prefix
in ** bast-matting,” etc.; the name liber was applied in a more
general way, namely, to any smooth inner bark (upon which one
could write). That which imparts strength to inner bark, mak-
ing it of use in the arts, consists of long and tough cells with
very much reduced calibre; but these are not confined by any
means to inner bark. Owing to this fact, some have thought best
to abandon the terms bast and liber for such cells, and adopt,
on account of their firmness, a term formerly given to grit-cells,
namely, sclerenchyma; the older terms, however, are not likely
to lead to confusion, whereas the other might. It is in the bark
of dicotyledons that liber-cells or liber-fibres occur most abun-
dantly.

Their prevailing shape is that of a slender spindle, which may
taper simply, or may be somewhat forked at the extremity.

The following can be seen only under a lens : —

Euonymus Europeus. . . . . . 2. 2. ee) 20m,
Fagus Spi. ae Bow Xo we a we ee Oe a ae OO
Crategussp: 4 ace GB Ria Ao ww ae we “BOR
Ligustrum sp... eta SL aah ge. BES
Pyruscommunis . . . . . ae ime a 40%

1 Mr. P. H. Dudley, who communicates some of the names in this list, adds
in his note: ‘‘So far I have never found any tyloses in ducts with scalariform
markings.”

88 MORPHOLOGY OF THE CELL.

Occasionally fibres which are very much branched are met th,
notably in the leaves of Camellia, for instance common tea; see
Fig. 68. Generally the walls are thickened unevenly, even form-
ing conspicuous projections into the cavity of the cell; while
some fibres have regular and characteristic markings, a few

\

65

of which are shown in Fig. 65. Septate forms are occasionally
found. The change in the character of the cell-wall which ac-
companies the thickening is essentially lignifivation, like that
observed in wood-cells and ducts. It is generally said that the
walls of liber-cells are less brittle than those of the elements
of wood, and this is commonly so; but there are some flexible
wood-elements, and there are, on the other hand, some very
brittle fibres of sclerenchyma. ‘The thickening of the wall in
liber-cells takes place not only in different degrees, but with va-
riations in the amount of infiltration of foreign matters, which
give rise to differences in the behavior of the fibres with reagents.
In a few cases the inner part of the wall is somewhat gelatinous

Fig. 65. Fragments of some of the more common bast-fibres used in the arts. 749,

a, Flax. Linum usitatissimum. (Wiesner )
b, Hemp, Cannabis sativa. (Schacht.)

e, Jute, Corchorns capsularis. (Wiesner.)
d, China-grass, Boehmeria nivea.

BAST-FIBRES. 89

and possesses the power of swelling in water and in dilute acids
(compare Collenchyma) ; in some others the outer part of the wall
is gelatinous, while the inner is hard. Morus alba, Gleditschia
triavanthos, and Robinia Pseudacacia are examples of the first,
Astragalus falcatus of the second, condition (Sanio).

277. One of the most striking characters of the bast-fibres of
many plants is the abundance of crystals found therein. Ex-
cellent examples are afforded by the inner bark of some of our
ligneous plants (294).

or)

(Pe )aoaoe

6) B92 (o
ore
0,2 20
30%

5
9

te 0
San

Oo

iP oLho8
Y2os

a\/o

& io O

> (aa
S ;

(x
a8

~

i—
e620
<@!
nde,
cS
Ses

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i
&

i
66 67 68
278. The firm attachment of fibres to those above and those
below them has given rise to erroneous ideas relative to the
length of single fibres, as the table on the following page shows.'
By careful management it is possible to isolate a connected
thread of fibres of great length; the value of fibres for textile
purposes depends largely upon this fact.

1 The table on page 90 has been compiled from data given by Wiesner and
also by Vetillart, which are here rearranged for greater convenience of refer-
ence.

Fic. 66. Fibre of Agave Americana: a and b, $9; c, 24°. Only the upper part of
each fibre is shown in the left-hand figures. The right-hand figure shows a cross section
of a group of cells.

Fig. 67. Fibre of Coir (Cocos nucifera): a and c, §°; b, 28°. a@ shows three separate
and complete fibres, b, the upper part of a single one, c, a cross-section of a group of
cells.

Fic. 68. Transverse section through leaf of Camellia (Thea) viridis, showing:
a, epidermis, 6, branched liber-cell; d, oil-drop; ¢, crystals, (Mirbel.)

MORPHOLOGY OF THE CELL.

90

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CRIBROSE-CELLS. 91

III. Cribrose-cells, Sieve-cells, or Sieve-tubes.

279. In the inner bark of stems of dicotyledons with normal
structure certain long cells of peculiar character are found as-
sociated with bast-fibres. They
are of tubular or prismatic form,
and are characterized by the pres-
ence of circumscribed panels in
the walls, in which are numerous
fine perforations permitting com-
munication between contiguous
cells. The panels are known as
sieve-plates ;_ the perforations, as
sieve-pores. These cells consti-
tute an essential, though by no
means always a conspicuous, element of fibro-vascular bundles.
Taken collectively,
they may be known
as cribriform tissue.
By their union end to
end they appear like
long tubes with the
continuity interrupted
here and there by cross
partitions. These par-
titions which separate
the individual cells
are sometimes nearly
horizontal, but more
generally oblique, as
shown in the annexed
figures where they
mostly cut the lateral
wall of the cell at a
sharp angle.

280. The walls of
cribrose-cells are
never lignified ; on
the contrary, they are

69 70

Fic. 69. Pinus sylvestris. Face view of radial wall containing two cribrose-plates
wuolly deprived of callus. “5, (Janczewski.)

’ Fig. 70. Pinus sylvestris. Radial wall of a young tube, face view. The future cri-
prose-plates are composed of callus-cylinders, filling the meshes of a cellulose network,
1195, (Janczewski.)

Fic 71. Cribrose-cells in Vitis vinifera: 4, transverse anastomosis of two cribrose-

92 MORPHOLOGY OF THE CELL.

very soft and colorless. Owing to their yielding character, it is
not easy to make satisfactory sections for their demonstration,
from fresh material ; it is better
to keep the material in alcohol
for a while, or to dry it care-
fully, as Russow advises. All
sections, to show the sieve-cells,

72 73

must be very thin. The following measurements of single large
cells given by de Bary serve to indicate their wide range in size:

Length, mm. Transverse diameter, mm.
Cucurbita Pepo. . . . .870-.450 . - 045
Calamus Rotang. . . . 2.000 oe 6 6030 -.050
Potamogeton natans . . .275 see 6025

Vitis vinifera. . . . . .6

281. The sieve-plates occur at the points of contact of sieve-
cells. They are always found at the ends of the cells, and may

cells isolated by maceration; the septa are in their winter state. B, branching of
cribrose-cell isolated by maceration. (, tangential section across a medullary ray, show-
ing the transverse anastomosis of cribrose-cells; the callus at the septa is in its winter
state. (Wilhelm.)

Fig. 72. Cribrose-cells in Vitis vinifera. Longitudinal tangential section (beginning
of July) through the bast of a stem 1 cm. thick, vq, cribrose-cells, the oblique as well as
one horizontal perforated septum cut longitudinally. The face of one septum, however,
is shown at the upper part of the figure: rm, medullary rays. (De Bary.)

Fic. 73. Cucurbita Pepo Longitudinal section showing terminal sieve-plates at
q, 7, and a lateral one at si; ps, contracted protoplasm, (Sachs.)

SIEVE-PLATES. 93

likewise appear upon the lateral walls. When the terminal par-
titions are horizontal, or nearly so, they are cross-plates, the
whole partition forming one plate; but on very oblique ends the
plates may be separated and lie in one or more rows. The plates on
the walls are smaller and irregularly distributed. On parts of the
wall contiguous to cells of any other kind there
may be dots; there is yet some doubt as to
whether they are perforations.

The diameter of the sieve-pores is given by
Mohl as not far from 2»; but although some
are even 5 » in diameter, the former figure is
too high for the average.

282. That which
is characteristic
of sieve-plates, in
distinction from
groups of perfo-
rations elsewhere
found, is a thick-
ening mass, of
bluish lustre and
apparently homo-
geneous struc-
ture, known tech-
nically as the
callus. It is best
shown at the ter-
minal plates, es-
pecially after the
application of a
solution of iodine
which turns it
yellow, and makes
it more sharply defined. In concentrated sulphuric acid and in
the strong alkalies this mass swells up so as to be several times
its original size; and in the former it soon dissolves, leaving
only slender threads in its place. The character of the callus

74 KG)

Fic. 74. Pinus sylvestris, Transverse section across four entirely passive tubes,
which are somewhat compressed laterally. 2485. (Janczewski.)

Fig. 75. Pinus sylycstris. Terminal partition. A tube inserted upon the radial
wall. The pores of the terminal partition are filled with warty callus, in the midst of
which the cellulose network may always be seen; in the pore of the radial wall the
callus is completely smooth and round, Tangential section. 2485, (Janczewski.)

94 MORPHOLOGY OF THE CELL.

varies with the age of the cell and with the time of year, as
shown in the figures.

283. <Anilin blue is the best pigment for bringing ont the
form of the callus clearly. If, as Russow? recommends, its use
be supplemented by that of Schulze’s iodide, the callus may be
seen to be made up of at least two portions, distinguished by
the depth of color. In young and active cribrose-cells the callus
usually appears to be a gelatinous layer on each side of the sieve-
plate ; in most old cells it is no longer seen.

284. Contents of the cells. In the younger and active state
just referred to, the cells contain a watery liquid which holds
more or less granular matter, and the walls are lined by a delicate
film of protoplasmic substance. ‘That the callus is also of a pro-
toplasmic nature is not clear, although some of its reactions
suggest this. It frequently contains minute granules of starch,
which sometimes give a bluish-brown color with iodine, like
starch which has been acted on by diastase. Russow thinks that
a ferment is present in the cells in their active state. When
old, most cells lose not only the callus but also the greater part
of their other contents. In active cells there are frequently
found very small but brilliant globules which are albuminoidal.
All the contents above mentioned vary within certain limits at
different periods of the year.

285. The sieve-cells of the higher cryptogams have been
shown by Janczewski? to be nearly if not quite imperforate at
all seasons. In gymnosperms, they pass through two periods:
the first, or the evolutive, in which the plates produce the callus,
the cells themselves containing parietal protoplasm ; the second,
or passive, stage, in which the protoplasm disappears entirely,
and communication between the contiguous cells oceurs. In
monocotyledons and dicotyledons the cells have four periods;
namely, the evolutive, the active, the transitory, and the passive.

IV. lLatex-cells, Latex-tubes.

286. Certain plants when wounded exude a milky juice known
as latex. They belong to widely separated orders; for instance,
to Papaveracee, Campanulacese, Asclepiadacese, Urticacer, ete.

The cells in which latex occurs are characterized by a soft-
ness of cell-wall which renders them easily compressible ; hence,

1 Annales des Sc. nat. bot., sér. 6, tome xiv., p. 167.
2 Annales des Se. nat. bot., sér. 6, tome xiv., p. 50.

LATEX-CELLS. 95

bounded by turgescent
tissues, their contents
readily escape through
any incision.

Latex-cells are not
restricted to any one
organ of the plant, but
may, and generally do,
occur in all parts, and
may be associated with
more than one tissue-
system. They are, how-
ever, usually found in
parenchyma, and run in
the same general direc-
tion as the fibro-vascular
bundles near which they
lie. For convenience, they may be divided into the simple and

a b the complex.

287. The simple
forms are _ single
cells, which may be
much and yariously
branched, Subse-
quent to the devel-
opment of one of
these cells in a plant,
and when it has ex-
tended its ramifica-
tions throughout the
different organs, a
new cell may inde-
pendently give rise to
new branchings, and
to a new system, some
of the branches of
the two cells perhaps
becoming confluent.
Good examples of the
simple forms are af-

Fig. 76. Longitudinal section through a sepal of Chelidonium majus, showing latex-

tubes. (Weiss.) ; j
Fic. 77. Latex-tubes composed of confluent cells: a, in the root; b, in the stem of

Chelidonium majus. (De Bary.)

96 MORPHOLOGY OF THE CELL.

forded by the following orders, — Asclepiadacee, Apocynacee,
and Euphorbiaceze.

The complex forms consist of rows of cells which coalesce to
form a latex-system. ‘The individual cells may Have their parti-
tion-walls broken down very carly, a mere vestige of them remain-
ing; or the partitions may be simply perforated, so as to allow a
free communication between contiguous cells. Moreover, the
confluent cells may be conjoined laterally, thus constituting a
complicated network which runs through the plant.

288. Occasionally roundish groups of perforations resembling
in a few particulars those of sieve-plates are found in the latex-
cells of Papaver and some Cichoraceze ; but they are coarser and
more irregular, and are devoid of the peculiar sieve-plate struc-
ture. Moreover, no true intermediate forms have been proved
to exist between the two kinds.!

289. The wall of a latex-cell is often very thin, and free from
any markings; but with even slight increase of thickness, stria-
tions and stratification make their appearance, projections may
extend into the cavity of the cell, or even spirals may be present.
In character, the cell-wall possesses many of the peculiarities of
collenchyina, especially in its behavior with iodine.

290. That the cells contain a protoplasmic lining is highly
probable, but this has not yet been satisfactorily demonstrated.
The liquid in the cells consists of granular matters suspended in
a watery fluid, and imparting to it a milky appearance. Often
the color of the liquid is yellow, as in Argemone, or orange, as in
Chelidoninm. The watery fluid contains in solution sugar, gums,
resins, traces of albuminoid matters, and various principles, for
instance, alkaloids (like morphia), and organic acids.

The suspended matters are of minute size, with the excep-
tion of peculiar forms of starch-granules. When perforation
is made in the latex-system of a turgescent stem, these granules
can be seen to move towards the point of injury. The same
movement can be observed when the pressure on one part of
the stem is materially increased ; and hence arose the erroneous
belief that there is a circulation of latex.?

291. Upon exposure to the air latex coagulates, and forms
upon drying a sticky, elastic mass, which in some plants is suffi-
ciently abundant to furnish the india-rubber of commerce.

1D. H. Seott: On the development of articulated Jaticiferous vessels.
Journ. Mic. Science, 1882, p. 144. An interesting account is also given by
de Bary, from notes by Sehmalhausen, Vergleichende Anatomie, p. 205.

2 Schultz : Die Cyklose des Lebenssaftes in den Pflanzen, 1841, p. 282.

IDIOBLASTS. 97

RECEPTACLES FOR SECRETIONS.

292. Individual cells (idioblasts) may differ greatly from their
neighbors as respects their contents. Such cells may be well
named after their characteristic contents ; as crystal-cells, resin-
cells, mucilage-cells, tannin-cells, ete.

293. ‘They vary much in shape and size. Frequently they are
not readily distinguishable from their immediate neighbors by
anything except their contents. In other cases, however, they
may assume forms widely different from those of the cells around
them, and may also be distinguished by their size. They are
often so associated together as to form ‘+ glands.”

294. Crystal-cells. ‘These sometimes, as de Bary points out,
curiously resemble the shape of the crystal or groups of crystals

which they contain. Thus globular clusters are generally con-
tained in spherical cells, elongated prisms in elongated cells
(as in Quillaja). ‘¢In many trees each cambium-cell (as it
develops into a bast-fibre) may be divided by diagonal partitions
into numerous (20 to 30) chambers, the height of which is about
the same as the width, and each is filled by a crystal or a small
cluster. In this case the general outline of the original cambium-
cell remains unaltered, and the whole row of compartments may
be isolated as a chambered fibre.”1 The bast-cells containing
crystals have been already noticed.

295. Sesin-cells. In a large number of plants soft viscid
substances are present, which exude when the tissues are
wounded. They may be roughly classed into (1) Balsams, in
which resinous matter is mixed with a considerable proportion of

1 De Bary : Vergleichende Anatomie, p. 145.

Fic. 78, Crystal-cells: a, from the petiole of Begonia manicata; b, a cell with raph-
ides, from Lemna trisulca; c, from Phallus caninus, (Kny.)

=

/

98 MORPHOLOGY OF THE CELL.

one or more essential oils, forming a thickish liquid; (2) Resins,
which have comparatively little essential oil commingled, and are
of various grades of hardness; (3) Gum-resins, or resins hay-
ing more or less mucilaginous or gummy matters. To the latter
class are sometimes referred
the products lett by the drying

Cc

TT
i ae
ANS

SEES

of many milky juices (latex); of such, caoutchouc is an ex-
ample. All the foregoing substances may be found in single
cells, which are of very diverse forms.

296. Roundish cells of this character are found in the Mag-
noliacesw and some Composite, ete. Long cells are to be de-
tected in some Liliaceze, etc., and they are connected by many
intermediate forms with resin-ducts arising from the confluence
of several cells. On the other hand, they pass by various gra-
dations into structures which are generally referred to the latex-

Fig. 79. Transverse section through the leaf of Psoralea hirta; the epidermis con-
sisting of one layer with some of the tissue shown on both sides of the gland: A, very
young state in which the secretion is not yet present; B, somewhat older, secretion
commencing; C mature state. (De Bary.)

Fig. 80. A “gland” in Dictamnus Fraxinella: A, B, early stages; C, mature state;
P.p,c, mother-cells of tle gland-tissue; (, the covering layer forming a continuation of
the epidermis; 0, a large drop of vil. (Rauter.)

INTERCELLULAR SPACES. 99

system. To this system should perhaps be referred also numer-
ous case of pigment-cells, like those in the roots of madder and
rhubarb; also the peculiar bodies seen in the periphery of the
pith of Sambucus, and the milk-sacs of some species of Acer.

297. Mucilage-cells are larger than the surrounding cells, and
sometinies closely resemble iutercellular spaces filled with muci-
laginous matter. In some instances the mucilage is distinctly
referable to changes in the coutents of the cell, in others to a
disorganization of a portion of the wall, while in still others
both scarces may be recognized.!

298. Cells containing tannin in very large amount are fre-
quently met with, but they do not call for special remark.

299. Resins and the like are found not only in single cells
but also in spaces formed by the breaking down of the interven-
ing walls of cell-clusters of various shapes; hence various forms
of receotacles for these substances may be looked for.

INTERCELLULAR SPACES.

300. The walls of cells still capable of division are generally in
unbroken contact; but as differentiation goes on they may be-
come separated more or
less by unequal growth
or by a breaking down
of intermediate cells.?
The intercellular spaces
thus formed may be mere
chinks, or they may be-
come chambers of large
size. They may con-
tain merely air, or air
and watery sap, or most
of the matters described
in the previous sections.

Air-spaces in the
looser tissues of plants
are generally so con-

1 The details of this subject can be found in Prings. Jahrb., vy. 161 (Frank),
and Annales des Sc. nat., sév. 6, tome i. p. 176 (Prillieux).

2 The first mode of development of intercellular spaces has been termed
schizogenic, the latter Lysigenic ; moreover, a distinction may be made between
those intercellular spaces which are formed when the tissues begin to differen-
tiate, — protoyenic, — and those formed in older tissues, — hysterogenic.

Fig. 81. Transverse section through the stem of Elatine Alsinastrum, showing large
intercellular spaces, /, containing air, (Reinke.) :

100 MORPHOLOGY OF THE CELL.

nected throughout the plant, and communicate so directly with
the stomata, that they constitute an apparatus for bringing the
interior of the structure into close relations with the outer air.
Sometimes the aggregate volume of the air-spaces is very large
in proportion to the volume occupied by the cells themselves.?

In composition, the air within the plant usually differs from
that of the atmosphere in containing a larger proportion of
nitrogen. If the air-spaces are much smaller than the cells
which surround them, they are termed tvterstices; if about as
large as the cells, Zacune ,; if conspicuously larger, air-passages
or air-chambers. Two chief forms of lacunee are distinguished
by de Bary; namely, cavities surrounded by cells which are
more or less branched, and those surrounded by plates of cells.
Good examples of the former are afforded by many water-plants,
rushes and the like; of the latter, by the stems of many Aracee,
for instance, Acorus Calamus.

301. The continuity of the larger air-passages may be inter-
rupted by plates crossing at an angle (generally slightly oblique).
Such dividing plates, termed diaphragms, are frequently com-
plicated in their structure.

302. Hairs, sometimes much branched, are found in the larger
air-passages of many plants. These form the stellate structures
in the Nympheaces, and the ‘* H-like” cells in some Araceze.

303. Intercellular spaces, usually those of small size, may
contain water together with air. This is the case in the cavities
under the water-pores of Fuchsia, etc.

804. When intercellular spaces contain resins, oils, and the
like, they constitute, together with the simple cells described in
295, the structures loosely called internal glands. Often these
are merely irregular spaces left by the breaking down of one or

1 The following measurements are taken from Unger (Sitzungsb. d. Wiener
Akad., xii. 373).

i Na of pats.
= ‘ y volume of air
Name of plant. Parts examined. in 1000 parts
of the plant.
Paspalum setaceum. Four leaves with their sheaths. 68
Musa sapientum. Piece of the leaf-stalk. 480
Nicotiana Tabacum, Leaf with leaf-stalk, 256
Brassica Rapa, Leaf with leaf-stalk. 175
Begonia manicata, Onc leaf with its stalk. 66
Camellia Japonica, Two leaves with their stalks. 224
Prunus Laurocerasus, One leaf with its stalk. 219
Aucuba Japonica, One leaf with its stalk. 273
Ardisia crenulata, Four leaves with short stalks. 220

RESIN-PASSAGES. 101

more cells, but they sometimes have a remarkable regularity of
form and clearness of outline.

It has been observed that these spaces filled with resinous and
other matters are not, as a rule, met with in the plants which are
provided with the simpler receptacles, consisting of single cells
or small groups. De Bary classifies these resin-passages and

spaces as follows: (1) those passages which contain mucilage
and gums, as those in the Cycads, species of Canna, Opuntia,
and some Araliacee ; (2) resin-canals and cavities containing
resins, ethereal oils, emulsions of resinous gums, etc., variable in
quality in different cases; a, passages or canals, as those in
Conifers, Alismaces, Aroides, the tubuli-flowered Composite,
Umbelliferze, Araliacese, Anacardiaceee ; b, short cavities, as in
species of Hypericum and the true Rutacez, many species of
Oxalis and Myrtacew, and some species of Lysimachia. The
cells which surround the more complete cavities are so different
from the neighboring parenchyma that they have been termed,
collectively, the epithelium of the spaces.

It is not fully known in what way the various resinous and
wmucilaginous matters are produced in the cavities. In some
instances, at least, the matters appear at a very early stage of
the development of the cells which are afterwards broken down
to form the cavity. The special cases, like those of the Myrta-
cee, in which the cavities contain oil, are best for purposes of
study, because they are so frequently to be found in the thinnest
leaves, and at an early stage of development.

Fic. 82. Transverse scction of part of leaf of Pinus Laricio, showing a resin-passage,
HC. (Kny.)

CHAPTER Iif.

MINUTE STRUCTURE AND DEVELOPMENT OF THE ROOT,
STEM, AND LEAF OF PHANOGAMOUS PLANTS.

GENERAL CONSIDERATIONS.

305. ‘THE tissue elements, described in the preceding chapter,
are arranged in various ways to form and connect the organs of
the plant. If elements of the same kind are united, they consti-
tute a tissue, to which is given the name of those clements; thus
parenchyma cells form parenchyma tissue or simply parenchyma ;
cork-cells form cork, ete. A tissue can therefore be defined as
a fabric of united cells which have had a common origin and
have obeyed a common law of growth.

Tissues are united to form systems; systems, to form organs.

306. In nearly all plants with which the present treatise deals
there is some kind of framework consisting mainly of the more
elongated cells and ducts. This framework runs throughout
the entire organism. It is surrounded by parenchyma, in which
other tissue elements may also occur; the epidermis in some of
its modifications covers the whole.

307. The three chief systems found in plants are, therefore,
the fascicular, the cellular, and the epidermal; and these corre-
spond in a general way to three classes of functions. In the
cellular system are found the active cells by which assimilation,
the proper work of the plant, is effected ; the fascicular system is
largely conductive, and serves also important mechanical ends ;
the epidermal system brings the assimilative apparatus of the
plant into safe relations with the surroundings.

No discussion of the cellular and epidermal systems, intro-
ductory to a special consideration of them as they occur in the
different organs, is needed ; but some general statements relative
to the fascicular system will obviate repetitions later.

308. The fascicular system, in its most complete development,
comprises the following tissue elements, which occur in very
different proportions in different cases, —prosenchyma in the
widest sense, including wood-cells of all kinds, ducts, fibres, and
cribrose-cells; together with some commingled parenchyma. With

FIBRO-VASCULAR BUNDLES. 103

the exception of the parenchyma, all these elements are elongated
and are arranged in various sorts of fascicles or bundles, whence
the name, the fasctewlar system. Since fibres and vessels play.
such an important part in the composition of this system, it has
been also called the fibro-vascular system, and the bundles, fibro-
vascular bundles.

309. When reduced to its lowest terms, a fibro-vascular bun-
dle consists of two tissue elements, namely, cribrose-cells and
tracheal cells, the latter being sometimes replaced either wholly
or in part by ducts.

310. The two elements are usually associated with some
parenchyma and with a considerable proportion of long bast-

if k i Keo lh R
as) es nf

leh
cel

poe ae g ipa Macey ae 0

5

fibres ; but, while preserving a general uniformity of structure
throughout, a bundle may become considerably changed in com-
position during its course. This is well shown by comparing
sections taken at some distance from each other; for instance,

Fig. 83. Longitudinal radial section of a collateral fibro-vascular bundle, from the
stem of a dicotyledon: b—i, wood; i—n, liber; the wood comprises, 0, 7 narrow annular
duct, c, wider spiral duct, 7, a duct with septum, e, woody parenchyma, J, woody fibre,
g, wide duct with areolated pits, 2, septate woody fibres ; the liber comprises, , liber-
fibres, m, short parenchyma, 1, cribrose-cells, i, cambium, /, long parenchyma or cam-
biform. (Kny.)

104 MINUTE STRUCTURE OF ORGANS.

one made in the middle of the course of a bundle with one near
its extremity.

811. The cribrose part of the bundle may also be termed its
liber-portion or bast-portion ; the tracheal, its woody portion.
These terms are not liable to be confounded with any others,
since it is with the cribrose portion that the well-known bast-
fibres or liber-fibres are associated, while it is in the tracheal
portion that all the constituents of wood are found.

312. For the first term (bast-portion), Nigeli has introduced
the word Phloém ; for the second (wood-portion), Xylem. In
this treatise these terms will be used interchangeably with the
others. But the woody portion of a bundle is sometimes very
far from being conspicuously lignified, and the bast-portion may
be much reduced.

318. The three principal ways in which the elements of bun-
dles are arranged are: 1, A single strand of liber has one side
in contact with a single strand of wood, the’ two running side by
side, — the collateral bundle. This mode of arrangement is com-
mon in the stems of phanogams. <A variety of the collateral
bundle has a strand of liber on each side of the wood, or, con-
versely, a strand of wood on each side of the liber, — the bicollat-
eral bundle. 2. The strands of liber and wood are in different
radii, — the radial bundle. This is the most common mode of
arrangement in roots. 3. A strand of one element is wholly en-
veloped by the other element, —the concentric bundle. These
modes of arrangement will be further discussed under ‘‘ Roots ”
and ‘* Stems.”

314. The bundles are surrounded by parenchyma; but this is
very frequently limited at the periphery of the bundle by a cylin-
der formed of closely united parenchyma cells, which contain
considerable starch. The endodermis is a special case of this
structure, in which the cells are more or less distinctly cutinized.
When this enveloping cylinder is well defined, it is known as the
bundle-sheath.?

315. At first, each bundle consists of similar cells (procam-
bium), some of which differentiate into fibres, vessels, etc.
Bundles in which all the procambium cells become permanent
cells are closed ; those which retain an inner portion (cambium)
capable of further differentiation are open.

1 In a great number of instances it is convenient to refer to the same struc-
ture the long and firm bast-cells which are found at one side of the bundle ;
but the subject, when examined from the point of view of development, espe-
cially when the vaseular cryptogams are taken into account, presents so many
difficulties that it may be here left without further treatment.

MERISTEM. 105

316. As regards the course of the bundics through the plant,
it is sufficient to note here that they are variously coinbined in the
different organs, sometimes forming compact masses of tissues,
and at others running as slender and delicate isolated threads.

317. It bas been seen in 201 that meristem is the nascent
state of any tissue, and that it may multiply as such, or first
become differentiated
into elongated forms
(cambium). For con-
venience of reference,
the meristem at the
growing-points of the
axis of the plant is
given special names:
Dermatogen, the
layer of nascent epi-
dermis ; Periblem,
the layer of nascent cortex just beneath the epidermis ; Plerom,
the cylinder or shaft of nascent fascicles. The cells from which
these primordial layers or masses of nascent tissues arise are
known as tnitial cells)

The initial cells produce primordial layers or masses of tissues ;
by their further development the primordial layers or masses
give rise to the early distinctive tissues of an organ. The tis-
sues thus early formed constitute the primary structure of the
plant.

318. In the further growth of an organ, especially in plants
which are to live more than a single year, or which have a well-
defined period of rest, remarkable changes may take place in its
structure, especially by the introduction of new elements. Such
changes are known as secondary, and give rise to the secondary
structure of the organ. From the nature of the case, it is im-
possible to draw a sharp line between the primary and secondary
structure ; but the division is nevertheless useful in the exami-
nation of the minute anatomy of the plant.

1 Hanstein: Die Scheitelzellgruppe im Vegetationspunkt der Phanerogamen,
1868 ; also in Botanische Abhandlungen, 1871, p. 3.

The distinction between meristem proper and cambium is insisted on by
Nigeli in his Beitrige (1858).

Fic. 84. Longitudinal section through the middle of the root-tip of the embryo of
Pontederia cordata. The lower initial cells produce the cap. c; the middle. the nascent
cortex, ec; the upper, the nascent central cylinder, cc. The nascent epidermis, ep, of
the stem is continued down to the cap; s, the point to which the suspensor wag attached.
In other terms, cc is the plerom, ec, periblem, ep, dermatoger. (Flahault.)

106 MINUTE STRUCTURE OF THE ROOT.

THE ROOT.
Primary STRUCTURE.

319. It was stated in Vol.
I., p. 27, that the root, or
descending axis, ‘‘ normally
begins in germination at the
root-end of the caulicle, or
so-called radicle; but that
roots soon proceed, or may
proceed, from other parts of
the stem, when this is favor-
ably situated for their pro-
duction.”

320. A longitudinal sec-
tion through the tip of a
germinating radicle exhibits

BD: only parenchyma cells. Slight
differences exist between these
cells, both as regards shape
and size; at the very end of the
radicle they are relatively large,
and form a sort of cap-like cov-
ering (root-cap) for the smaller
cells lying directly back (the
growing-point). If the section
is thin enough, it will be seen
that at the growing-point numer-
ous rows of cells appear to con-
verge, the fact being that all the
cells of such rows are derived by
multiplication from those at the
growing-point.

821. Certain differences in the
arrangement of these rows can
be seen upon comparing the radi-
cles of plants of different classes.

Fic. 85. Longitudinal section through the middle of the root-tip of Fagopyrum escu-
Jentum. The lower initial cclls give rise to the cape, and the epidermis e’p; the middle
produce the cortex e’e; pe, peripheral layer of the central cylinder cc, which comes
from the upper initial cells. (Janezewski.) 7

Fig. 86. Longitudinal section through the middle of a lateral root of Pontederia
erassipes: cc, nasvent central cylinder (plerom); e’c, nascent cortex (periblem); e'p,
nascent epidermis (dermatogen); c, root-cap. (Flahault,)

THE ROOT-CAP. 107

Thus in most cases the group composing the point of growth
consists of three kinds of superposed cells, so arranged in layers
that cach gives rise to a determinate portion of the forming
root: (1) the outer or lower layer, to the root-cap and the rest of
the epidermis; (2) the middle, to the cells which are immediately
under the epidermis, — the cortex ; (3) the inner or upper layer,
to the central cylinder. But in some plants? there are more
than three layers of initial cells (e. g., Sparganium, Raphanus,
etc.), while in others there are less than three (¢. g., only one in
Cucurbitaceze, two in Triticum).

322. The Root-cap. The growing-points of nascent roots origi-
nate just below the surface of the organ whence they proceed ;
hence roots are said to be formed endogenously. In emerging,
they rupture the layer of tissue by which they had been covered,
but are from the first protected at the end by a thicker or thinner
mass of parenchyina, — the root-cap.?

323. It does not always have the same origin, as will be seen
by the notes,’ nor has it the same shape and size in all plants.

1 Janczewski (Aun. des Se. nat., sér. 5, tome xx., 1874) describes six types
of development of the tissues of the root : —

1. Four distinct layers of meristem ; namely, Plerom, Periblem, Dermato-
gen, and Calyptrogen ; ¢. g., Lfydrocharis.

2. A distinct Plerom and Calyptrogeu, but the Periblem and Dermatogen.
have initial cells in common ; ce. g., Graminece.

3. A distinct Plerom; the Periblem, Dermatogen, and Calyptrogen have
common initial cells ; ¢. g., Iridacee.

4, A distinct Plerom and Periblem ; the Dermatogen and Calyptrogen have
comnion initial cells; ¢. g., Helianthus annuus.

5. All four layers have common initial cells; ¢. y., Phascolus and Pisum.

6. Only a distinct Plerom and Periblem ; therefore there is neither true
epidermis nor root-cap, since these are formed simply by outer layers of the
Periblem ; ¢. 9., Gymnosperince.

Treub (1876) and Eriksson (1878) distinguish seven types.

2 According to Olivier, a part of the tissue thus broken through by the
advancing radicle of grasses remains at its base, as the coleorhiza, while the
rest becomes the root-cap (Ann. des Se. nat., sév 6, tome xi., 1881, p. 19).

8 According to Flahault (Recherches sur l'accroissement terminal de la racine
chez les Phanérogames, Ann. des Sc. nat., sér. 6, tome vi., 1878), who bases his
opinion on an exaniination of three hundred and fifty species of Phenogams,
the terminal growth of the root may be referred to two structural types which
are characteristic of monocotyledons and dicotyledons.

{n monocotyledons the epidermis is generally formed by the initial cells of
the cortex. The epidermis never gives rise to a root-cap ; the rvot-cap once
formed is continually renewed by the activity of its internal layers. In dicoty-
ledons, on the other hand, the epidermis is almost always independent of the
cortex ; the root-cap is continually renewed by the activity of the cortex and
epidermis.

108 MINUTE STRUCTURE OF THE ROOT.

Roots which grow in the earth seldom have it much developed ;
but in many aquatics it becomes of large size, though it is always
thin. In some species of Pontederia the cap envelops the root
for the length of half a centimeter; but it is free
at its upper part, and is in contact with the root
only at its very tip. The roots of Typhacez
and Lemnaces exhibit nearly the same struc-
ture. The cap consists in these cases of only
one or two layers of thin-walled cells.

The aerial roots of some plants have large
root-caps composed of firm-walled cells. This
is well shown in Pandanus, where the cap con-
sists of many layers of cutinized cells. The
cap in all cases exfoliates on its exterior, and
is as constantly renewed by the cells within.
Nearly all of its cells contain starch-granules
in abundance.

324. The peripheral tissue in the rootlet does
not always have the same origin; it may in some
cases be regarded as true epidermis, in others as
the outermost portion of the cortical parenchyma. In the vast
majority of cases this youug superficial tissue is furnished with
root-hairs ; it is therefore designated the piliferous layer.?

325. The piliferous layer has no intercellular spaces (a few
cases of aerial roots of Orchids excepted). ‘The hairs are con-
fined to a narrow zone a short distance behind the tip, although
in Triglochin they have been found on the edges of the cap,
and in Philodendron very near its edge. When first formed
they have delicate transparent walls, and are filled with pro-
toplasm. By the advance of the growing-point and with the
formation of new hairs, the older become less active, their walls
thicken and turn brown, their contents disappear, and they fall
off, generally leaving a nearly glabrous surface.

3826. The hairs are generally simple, but in the adventitious
roots of some Bromeliacez * compound hairs are also found.

Branched hairs are seen on the roots of Saxifraga sarmentosa,
Brassica Napus, ete.

87 88

1 Olivier (Ann. des Se. nat., sér. 6, tome xi, 1881, p. 19), according to whom
it is never homologous with the epidermis of tue stem (p. 28).

2 Jorgensen, Butanisk Tidsskrift, 1878, p. 144.

Fig. 87. Seedling of Sinapis alba, showing root-hairs.

Fic. 88. Seedling of same, showing the manner in which fine particles of earth cling
to the root-hairs. (Sachs. )

ROOT-HAIRS. 109

327. Root-hairs are best obtained for study by cultivating
seedlings on mouist glass, or with the rootlets in water. It is well
to compare the forms thus obtained with those found on roots of
the same plant grown in loam, sand, fine clay, etc. Masters has
shown that the develop-
ment of the hairs is fa-
vored by many conditions,
such as porosity of the
soil, moisture, etc.; and
this fact should be borne
in mind in the examina-
tion of the root-hairs of
any plant.

828. The walls of root-
hairs are only slightly cu-
tinized, but there is a great
difference in this respect
in different plants.

329. The cells of the
superficial layer of the
rootlet, other than those
with hairs, are more or
less cutinized, the degree
of infiltration depending
upon their age. In some
cases (€ g-5 “Asphodelus) the thickening is very considerable.

330. On a few plants? no root-hairs have been detected, as
Crocus sativus, Cicuta virosa, Abies pectinata and many other
gymnosperms.

331. Roots of orchids. The newer parts of the aerial roots
of Orchids have an epidermis consisting of nearly spherical
tracheids, which, except sometimes in the outermost layers, co-
here without intercellular spaces. The walls of these cells are
colorless, though in mass they may have a silvery lustre, and
when immersed in water they soon become sufficiently trans-
parent to permit the subjacent green tissue to be seen.?

1 Duchartre (EJéments de Botanique, 1867, p. 214) cites other plants.

See also a valuable paper by Schwarz in Untersuchungen aus dem bot.
Inst., Tibingen, 1882.

2 According to Leitgeb, the old roots of Vanda furva are green because their
tracheids contain minute Algae (De Bary, Vergl. Anat., p. 238).

Fic. 89. Root-hairs distorted by contact with the soil. Four in the right-hand upper
corner, Selaginella; three in lower corner, Trifolium ; the others, Avena, The dark
points indicate the attached particle of soil. a@,a,a, minute prolongations of the cell-
wall. (Saclis.)

110 MINUTE STRUCTURE OF THE ROOT.

332. Sometimes there are papillar outgrowths from these tra-
cheids, which are to be regarded as root-hairs. They occur
chiefly on younger parts of the roots which are in contact with
a moist support, or which are kept wet. They cling tenaciously
to moist surfaces, and may become much widened and flattened.?

333. The cortex of different plants varies greatly in thickness
and compactness, and in the thickness of the cell-walls. In

a few cases remarkable lacunz are to be seen (e. g., Meny-
anthes).

334. The cells bounding the inner layer of the cortex have the
general characters described under ‘‘ Endodermis ;” their radial
walls are generally more or less plicate, and there are no inter-
cellular spaces.

335. In the primary cortex of roots all the various kinds
of secreting cells and receptacles for exudations described on
p. 97 may be looked for; but as a rule they are less developed
than in the stem. Collenchyma occurs sometimes in roots;
é. g., Raphidophora.

336. The central cylinder has, at first, a peripheral layer of

1 Leitgeb : Die Luftwurzeln der Orchideen, Wien Akad. Denkschr., xxiv.,
1865, p. 179.

Fic. 90. Transverse section of the central cylinder of a root of a vascular cryptogam
(Marattia levis): e, internal layer of the proper cortex; p, endodermis; m, peripheral
layer of the cylinder; /, liber fascicles; », woody fascicles; c, conjunctive parenchyma
(pith and medullary rays). (Wan Tieghem.)

THE CENTRAL CYLINDER. 111.

thin-walled cells
in close union
with the endoder-
mis; at certain
points on this lay-
er the woody and
the liber fasci-
cles appear, the
latter alternating
with the former
throughout — the
circle, and the
spaces hetween
them being filled
with parenchyma.

837. The num-
ber of fibro-vas-
cular bundles in
the central cylin-

der varies accord-
ing to the class of
plants, and in the
same plant accord-
ing to the age and
size ot the root.
There are generally
two in Crucifere,
often three in Er-
vum Lens, four in
Ricinus, five in Vicia
Faba, six in Alnus,
and eight in Fagus ;
but these numbers
are by no means
constant.

338. The woody
part of the bundle
may become re-

Fia.91. Transverse scction of the central cylinder of a root of a monocotyledon (Colo-
casia antiqnorum) : e, internal layer of the proper cortex; p, cndodermis; m, peripheral
layer of the cylinder; 7, liber fascicles; v, woody fascicles; c, conjunctive parenchyma
(pith and medullary rays). (Van Tieghem.)

Fig. 92. Transverse section of the central cylinder of a root of a dicotyledon (Artanthe
elongata): e, internal layer of the proper cortex; py, endodermis; m, peripheral layer
of the cylinder; /, liber fascicles; 7, woody fascicle; c, conjunctive parenchyma (pith
and medullary rays). (Van Tieghem.)

112 MINUTE STRUCTURE OF THE ROOT.

duced to a single duct, as in some Carices, or there may be a
large duct surrounded by smaller ones with or without inter-
vening cells, or many large and small ducts variously conjoined.
Moreover, there are all degrees of compactness in the union of
the different bundles of woody tissue with each other.

339. The cribrose part of the bundle may be reduced to a
single cribrose tube (¢. g., Anacharis), or two or three (é. g., Pon-
tederia) ; but usually there are many, which may be variously
disposed.

340. Bast-fibres may be associated with the cribrose-eells in
the primary structure of the root, and they may be scattered (and
occasionally with some sclerotic parenchyma) in the cortex. In
Philodendron these scattered groups of bast-fibres frequently
contain oleo-resin canals.

SEconpARY STRUCTURE.

341. The older parts of roots, even the recently formed por-
tions lying just back of the root-hairs, may undergo changes
either by the alteration
of their existing tissue
elements or by the in-
troduction of new ele-
ments. Some roots,
however, do not. suffer
much change from first
to last. Their cells may
become more strongly
cutinized or lignified
as the case may be,
but no new elements
are brought in. This
is true of the roots of
many monocotyledons,
but in dicotyledons the
secondary changes are
generally very marked.
The changes may af-
fect either the cortex or
the central cylinder; in some cases the former more than the
latter.

93

Fic. 93. Section through the central cylinder of a binary root of a vascular cryptogam
(Cyathea medullaris): ¢, internal layer of the proper cortex; p, endodermis; m, pe-
ripheral layer of the cylinder; /, liber fascicles; v, woody fascicle; c, conjunctive paren-
chyma (pith and medullary rays). (Van Tieghem.)

THE CENTRAL CYLINDER. 113

342. In the cortex, according to Olivier,’ the secondary tissues
are either parenchymatous or suberous (corky). The secondary
parenchyma of the integument proceeds from the peripheral
layer of the central cylinder. The suberous tissue in gym-
nosperms and in dicotyledons with caducous primary cortex is
derived froin the pericambial layer; it is composed of tabular
cells with very short radial walls, and begins to form outside
of the primary liber. In the case of woody dicotyledons with
late-formed secondary vessels, and in monocotyledons, it is pro-
duced in the external zone of the cortical parenchyma, and is
composed of cubical cells.

345. In a given species the level of the root where cork ap-
pears depends on the transverse diameter of the root, and also
on the surroundings; in roots of the same size the cork gen-
erally appears earlier, and is more abundant in aerial than in
earth roots.

The cortical parenchyma is renewed by layers of cells just out-
side of the sheath of the central cylinder, and its development is
wholly centrifugal.

344. The central cylinder undergoes its most remarkable
changes as the root grows older, in the group of dicotyledons.
There is very little change, if any, in monocotyledons, but in a
few of the latter some of the secondary changes now to be de-
scribed can be observed (e. g., Draceena).

845. In dicotyledons, including gymnosperms, the thin-walled
cells of the central cylinder are in contact with the inner face of
the endodermis, and are known collectively as the pericambium.
Touching this pericambium like the two ends of a bow, there
runs a mass of delicate cells behind each liber bundle. At the
point where these bows touch the inner face of the liber bundle
a group of cells divides tangentially, forming a cambium layer,
which soon gives rise within to new woody elements (often
coalescent with those of the primary woody bundles), and on the
outside to new liber elements. These new productions are
called secondary wood and liber.

3846. In some cases — for instance Pinus — the cells of the
pericambium outside of the primary woody bundles produce new
wood and new liber. The wood is in contact with the primary
wood, while the liber may serve to connect the bundles of
primary liber, thus bringing abont a union more or less com-
plete between similar elements. From these secondary pro-

1 Annales des Se, nat., sér 6, tome xi., 1881, p. 129.
8

114 MINUTE STRUCTURE OF THE ROOT.

ductions come, of course, the apparently unbroken rings of liber

and the solid masses of wood in old roots.

If this development
of new wood and
liber in a perennial
dicotyledonous
plant proceeds
uninterruptedly,
there will exist at
the end of the first
year secondary ele--
ments in large
amount. After a
period of rest, a
perennial root re-
sumes growth at
the points where it
was suspended, and
the formation of
new cork, cortex,

liber, and wood goes on as before, until it receives further
checks. Owing to conditions to be explained later, the charac-

ter of the woody elements is
not the same at the begin-
ning and end of an active
period ; hence there is gen-
erally a clearly defined out-
line bounding the product of
growth of successive years.
347. More or less of the
parenchyma of the original
cylinder may remain in the
form of radial lines or of
bands (medullary rays),
some of the same sort of
tissue may be subsequently
produced from new points of

95
activity, and hence long and short radii will be met with.

Fic. 94. Section through the central cylinder of a binary root of a dicotyledon (Beta
vulgaris): e, internal layer of the proper cortex; p, endodermis; m, peripheral layer of
.the cylinder; J, liber fascicles; v, woody fascicle; c, conjunctive parenchyma (pith and

medullary rays.) (Van Tieghem.)

Fig. 95. Section through the central cylinder of a binary root of a monocotyledon
(Allium Cepa): ¢, internal layer of the proper cortex; »,endodermis; m, peripheral layer
of the cylinder; /, liber fascicles; v, woody fascicle; c, conjunctive parenchyma (pith

and medullary rays). (Van Tieghem.)

TERTIARY FORMATIONS IN THE ROOT, 115

848. The distinction of texture marking the periods of rest
is not clear in the liber, though even here it may sometimes be
detected. The cork of the root frequently exhibits such dis-
tinction, but never so clearly as does the cork of stems.

349. Itis a familiar fact, that the fleshy roots of many plants —
beets, and the like —enhibit in the first year from seed concentric
rings, which resemble those found in perennials. This appear-
ance is due, according to de Bary,’ to the fact that at an carly
stage of development (when the root is only about half a milli-
meter thick) a new cambium zone is formed in the parenchyma
on the outer part of the central cylinder, and this divides tan-
gentially, extending therefore in a radial direction, producing
woody and liber clements, and at the same time divides laterally,
so that the whole constitutes a zone hardly broken by the rays.
Soon a second zone is produced in like manner, and afterwards
others. In all these cases the elements are usually not much
lignified, but the whole mass remains succulent.

It happens sometimes that tertiary formations are produced in
the root, bearing somewhat the same relation to the secondary
as these do to the primary. Even formations of higher order
are sometimes met with. But the elements of all of these are
easily identified, and their mutual relations can generally be so
clearly understood that they do not need special description.
The following enumeration embraces the most important of these
formations: tertiary cork and cortex ; fibro-vascular bundles in
secondary cortex; tertiary liber and wood in secondary wood.
Such anomalies are more frequent in the stem.

850. Roots branch by the development of certain cells at the
peripheral layer of the central cylinder, and just in front of the
woody fascicles.”

The root branches only laterally in flowering plants; in the
Lycopodiacee there appears to be terminal bifurcation, and here
each branch shares with its fellow the tissue elements of the root
from which they both come.

1 Vergleichende Anatomie, p. 616.

2 Three types of branching are described by Janczewski: 1. The mother-
cells of this layer (the so-called Rhizogenic cells) most frequently give rise
to all the tissues of the rootlet. 2. They produce only the central cylinder
and cortex, but not the root-cap and piliferous layer, these being furnished by
the endodermis of the root. 3. They produce only the central cylinder, the
other tissues coming from the endodermis or from the layers immediately out-
side of it. The subsequent growth of the rootlet both in length and thickness
is like that of the root.

116 MINUTE STRUCTURE OF THE ROOT,

351. Parasitic roots,’ or those which fasten themselves for
nourishment on other plants, are so much modified by the pecul-
jar conditions under which they live, that they require special
mention. Their structure can be best understood by a section
through the root of Cuscuta.

Here there is no central cylinder, properly so called, nor is
there anything answering to the root-cap. The cortex is regarded
as reduced
to a pilifer-
ous layer,
since some
of its cells
are pro-
longed to
form a fasci-
cle of long
hairs in inti-
mate contact
with the tis-
sues of the
host upon
which it has
fastened. In
the centre of
this fascicle of hairs some of the elements are tracheid-like
cells, which are in contact with ducts.

352. The roots of many plants have distinctive colors: in
some the color belongs to the wood (see 402); in others it is
due to the cell-sap ; in others, for instance, the common carrot,
to orange-colored crystalline bodies. The crystalline forms
found in the parenchyma of the roots of the carrot are minute
rhombs, or sometimes rectangular plates to which starch-gran-
ules are attached. They are associated with small quantities
of protoplasmic matter. (See Chapter IV., for an account of
somewhat similar bodies occurring in flowers and fruits.)

853. The roots of the higher Cryptogams (such as Ferns and

1 An exhaustive paper on this subject will be found in Pringsheim’s Jahrb.,
1867 : Ueber den Bau und die Entwicklung der Ernahrungsorgane parasitischer
Phanerogamen, von Hermann Grafen zu Solms-Laubach. Koch’s paper is in
Hanstein’s botan. Abhandlungen, vol. ii., 1875.

Fia. 96. Vertical section of an haustorinm of Cuscuta perforating the host-plant.
9, 9. absorbing hairs; the central cells are thickened at the base, where they are in contact
with the ducts. (Koch.)

ROOTS OF CRYPTOGAMS. 117

their allies) do not differ essentially from those of Pheenogams ;
in most cases, however, the terminal growth, except in the order
Lycopodiacez, is from a single apical cell instead of a group of
cells. The apical cell produces not only the tissue of the body
of the root as it extends in length, but gives rise also to the
superficial cells at the extremity which constitute the root-cap.
Lateral roots start from the interior layer of the cortical paren-
chyma, and not from the pericambium (sce 345).

354. The fibro-vascular bundles are concentric (see 313), as
indeed they are in the
stems of most of these
plants; that is, the bast
part surrounds the wood
part, as if with a sheath,
even where the latter part
is rudimentary. There is
a tendency in the root, less
marked than in the stem,
to the production of scle-
rotic cells of a dark color.

The roots of the higher
eryptogams do not materi-
ally increase in thickness
after they are first formed.

355. Proper roots are
not found in Muscinese (the
mosses and hepatics) ; the
absorbing organs here are
more strictly root-hairs.
These arise as papillee from.
the outer cells, and speedily
develop into tubular and
frequently complex bodies.
They often become
branched in a remarkable
manner, twisting and coil-
ing around one another like the fibres in a thread. They, as
well as the somewhat simpler organs of the same nature, found
in the Thallophytes (such as Algve, and the like), are termed
Rhizoids.

oT

Fig. 97. Seedling of Cucurbita Pepo, showing the main root, side roots, and root-
hairs. (Sachs. )

118 MINUTE STRUCTURE OF THE STEM.

Neither in Muscinez nor Thallophytes are fibro-vascular bun-
dles found, although in the former the arrangement of elongated
cells sometimes resembles that of the constituents of a simple
fascicle. The root-like bodies by which large sea-weeds cling
to their supports are hold-fasts, rather than true roots; the
whole surface of the plant being bathed in water, all parts can
probably absorb equally well.

THE STEM.

356. That part of the axis of the embryo which is below
the cotyledons is known as the radicle. It is more properly
termed caulicle (that is, stemlet), for its mode of growth is
not like that of the root, but like that of the stem above the
cotyledons. The name radicle should be restricted to that
which is the beginning of the root, namely, the free end of the
caulicle. The caulicle is termed also the hypocotyledonary stem,
or hypocotyl; while for the axis which is developed above the
cotyledons, that is, from the plumule, the name epicotyledonary
stem may be used. A large hypocotyl, which has begun to
germinate, displays the structure of the stem to good advantage ;
but the initial cells and the nascent tissues of the stem must be
sought at an earlier stage, for instance, in the plumule of a well-
formed embryo, as that of Phaseolus or Faba. A vertical section
through the plumule, made transparent by a clearing agent (see
24), shows that the cells have much the same arrangement as in
the root-tip, except that no protective cap is present.

357. The onter layer has divisions only at right angles to the
surface; it is continuous with the epidermis further back, and
is easily recognizable as nascent epidermis (Dermatogen). En-
closed by this are layers which form an arch, the nascent cortex
(Periblem). This encloses a mass of tissue from which the fas-
cicular system is derived (Plerom). These tissues are essen-
tially the same in character and development as the corresponding
nascent tissues of the root.

358. As the tissue elements develop from these nascent. tis-
sues, the stem is produced; its structure is, however, generally
complicated by the early formation of lateral appendages, — leaves
in some of their modifications. Moreover, the tissues of the
stem are continuous with the tissues of the leaves, and it is there-
fore necessary to take into account the mutual relations of these
two organs. The problem becomes still further complicated, in
a large number of cases, by the production of branches of some

EPIDERMIS AND CORTEX. 119

kind, the tissues of which are of course intimately united with
those of the main axis from which they are given off.!

Primary STRUCTURE.

359. In the stem, or ascending axis, the distribution of tissue
elements is similar to that in the descending axis, — the root.
There is a more or less transient epidermis, a cortical substra-
tum, and a central cylinder of some kind.

360. The epidermis of stems presents few peculiarities of
structure beyond those already described in Chapter IL. In
most herbaceous plants it persists with little change, except in
the matter of trichomes, throughout the life of the plant; but
in most ligneous plants it is replaced, often early, by other pro-
tective tissues. Persistent epidermis is found in many woody
and half-woody plants; for instance, Russelia juncvea, Leyces-
teria formosa, and Ptclea trifoliata.

In Palms? ‘‘ the epidermis exists in old age only in the cane-
like and calamoid stems; in the rest it is more or less destroved
by the action of the weather. In Calamus it consists of a simple
layer of minute cclls elongated in the direction from without
inward, and forms a stony, brittle, shining layer.”

361. The primary cortex® consists essentially of parenchyma
in which isolated cells of a peculiar character may often be found,
such, for instance, as crystal cells, laticiferous cells, tannin cells,
and the like (see 292); and its intercellular spaces sometimes
serve as receptacles for the various exudations. The paren-
chyma cells generally contain more or less chlorophyll, and some
starch.

362. Immediately beneath the epidermis, and not easily dis-
tinguished from multiple epidermis, is a portion of the cortex
known as Hypoderma.* It is rarely sclerotic parenchyma, more

1 Jn the plumule and other buds all these parts exist potentially ; and the
sequence of their development can be successfully followed out by the employ-
ment of seeds in different stages of germination, or buds collected on succes-
sive days in spring and preserved at once in alcohol. In all cases care must
be taken to have the date of collection of each specimen revorded in such a
manner that no confusion can afterwards arise.

2 Mohl: Ray Society, Reports and Papers in Botany. The Palm-stem,
Henfrey’s Translation, 1849, p. 14.

3 Vesque (in Ann. des Se. nat., sér. 6, tome ii., 1875, p. 82) gives a very full
treatment of the subject.

4 The word Hypoderma was introduced by Kraus (Pringsheim’s Jahrb.,
1865-66, p. 321), to designate the layer of colorless cells under the epidermis
of leaves, ‘‘das Analogon des Rindencollenchyms.” It has since been ex-
tended to apply to the external cortex just under the epidermis of stems.

120 MINUTE STRUCTURE OF THE STEM.

frequently it is collenchyma. Excellent illustrations of the
latter kind of hypoderma are furnished by most Malvacee and
Labiate.

363. Schieiden? distinguished four types of external cortical
layers in dicotyledonous stems: 1. That existing as a perfectly
closed layer (penetrated in some cases only by small canals
opening into stomata) ; as in most of the Cactace, Rosa, Begonia,
etc. 2. That divided into many bundles, so that the green cor-
tical parenchyma reaches the epidermis ; ¢. g., in Malvacez, Sola-
nace, etc. 3. That which may be quite distinctly recognized
as a special layer, but still grading into parenchyma at the
borders; ¢. g., in Pyrus Malus, Hedera, Ficus, ete. 4. That
more completely merging into cortical parenchyma, and therefore
less distinct; ¢. g., in Populus, Salix, Sambucus, etc. There are
some plants in which it is not distinguishable; ¢. g., in Cheiran-
thus, Mesembryanthemum, etc.

In Papaver and species of Thalictram the cells of the cortex
next to the epidermis have thin walls, while the zone next to the
central cylinder may be sclerotic.

The inner boundary of the cortex of the stem is, as in the
root, the endodermis. The thin-walled cells just within it form
the peripheral layer of the central cylinder, or shaft.

364. Variations in the cortex consist chiefly in one of the
following modifications: 1. Increase of its layers, sometimes
to an extraordinary extent, and often accompanied, especially
in water-plants, by the formation of large air-bearing intercellular
spaces. ‘The student should examine the peculiar structure of
the cortex at the nodes, in these cases of spongy cortex. 2. It
has been previously shown (215) that collenchyma is a common
modification of cortical parenchyma. A variation in structure
reaching the same end as collenchyma, namely, strengthening
the stem, is found in a great number of plants; the cortical
parenchyma, especially at the outer part, becoming conspicuously
sclerotic, and the tissue very compact. 3. Fibres may occur in
the cortex, either isolated or in small fascicles.

365. The primary fibro-vascular bundles of the stem are de-
veloped at definite points in the peripheral Jayer of the central
cylinder. Their structural elements, wood and liber, vary as
regards their relative amount, even in the same plant. A given
bundle may and generally does change much during its course,
interlacing here and there with other bundles, and giving off
branches at different points.

1 Principles of Scientific Botany, p. 240.

COLLATERAL BUNDLES. 121

When corresponding bundles of plants of different groups are
compared together, some cliversities as regards the arrangement
of the wood and liber elements are exhibited; but most of the
cases can be referred without difficulty to the class of

366. Collaterul bundles (see 313) of the ordinary type ;
namely, those having liber on the external aspect and wood on
the internal aspect. In some cases, however, this order may be
exactly reversed ; ¢.g., in the cortical fascicles of Calycanthacee.
The wood-clements in collateral bundles are generally arranged
in radial series; the inner ducts or their equivalents (tracheids)
being more slender and having more closely coiled spiral mark-
ings than those nearer the periphery of the bundle. The radial
series may be in close contact, separated by very thin plates
of parenchyma, ‘or
may have a large
amount of this tis-
sue between them. ow OM
In dicotyledons, as
a rule, the ducts - Bru)
at any given dis- g
tance from the cen- :
tre of the stem have e
a noticeable uni-
formity, so that a
cross-section of 2
the primary tissue
shows a number of =~
concentric circles of S Z
ducts of the same
size. Sometimes,
however, the ducts Fd
in a radial series / é
may be reduced to 98
one. In stems of monocotyledons there is less regularity in the
arrangement of the wood-elements, but there is a substantial
likeness in their structure in any group. They are generally in
the form of a blunt wedge, the apex towards the centre of the
stem, the space between the inclined sides of the wedge being
mostly occupied by small ducts, wood-cells, and fibres.

a

(< }

Se ane

Fig. 98. Transverse section of a collateral fibro-vascular bund'e of the stem of Indian
corn: p, p, conjunctive parenchyma; a, outer face; i, inner face of the closed fibro-vas-
eular bundle, which consists of a xylem portion (g,g, two large pitted ducts; s, spirally
thickened duct; 7, isolated ring of an annnlar duct; /, aeriferous lacuna, caused by
splitting resulting from growth) and a phloém portion, 2, v. The whole bundle is sur-
reunded by a bundle-sheath of thick-walled cells. (Sachs.)

122 MINUTE STRUCTURE OF THE STEM.

867. The cribrose portion of a collateral bundle often has, in
addition to true cribrose-cells, prismatic, thin-walled cells, known
as cumbiform cells.}

368. According to Véchting? the cambiform and cribrose cells
appear in some cases to have a common mother-cell, which di-
vides obliquely in the direction of its length. The cambiform

cells may divide by transverse partitions, and if the cells are
moderately large the last divisions may be parenchymatous. In
most monocotyledons and dicotyledons the cribrose-cells are much
larger than the cambiform ones, and their cross-sections are distin-
guished by being less sharply quadrangular. In many succulents
there are also very small cells resembling undeveloped cribrose-
cells.

369. The cribrose and woody parts of a collateral bundle are
generally distinguishab!e from each other by the lignified char-

1 De Bary reserves for these cells the term Cambiform, which was used by
Nageli in a wider sense.

2 Beitriige zur Morphologie und Anatomie der Rhipsalideen, Pringsheim's
Jahrb., 1874, p. 327.

Fig. 99. Transverse section of a part of the central cylinder of the mature hypocoty-
Jedonary portion of the stem of Ricinus communis: r, parenchyma of the primary
cortex; m.of the pith; between rand 0 is the simple endodermis containing starch-
grains; the fibro-vasenlar bundle is made up of the phloém 8, y, the xylem g, ¢, and the
cambium c, c; cb, interfascicular cambium. In the phloém are the bast-fibres b, b, the
soft bast y, y (partly parenchyma and partly cribrose-tubes); in the xylem, small pitted
ducts ¢,/, wider pitted ducts y, g, and between them woou-tibres. (Sachs.)

BUNDLES OF THE STEM. 123

acter of the latter and the softer texture of the former. As has
been before noticed (see 345), in dicotyledons and gymnosperms
in which there is annual increase in diameter there is a layer
of peculiar merismatic tissue (cambium) between the two parts.
It is generally easy to identity the cells of this cambium layer, on
account of their elongated form and intimate contact with each

NTN
inane)
UN,

WU

Jad stot
YOOOH
\ ML
AUTEN

other. Their development gives rise (1) to new cells like them-
selves, (2) to cribrose and (3) to woody elements; all of which
are to be examined later, under ‘‘ Secondary Structure.”

370. The sheaths of collateral bundles may have the character
of typical endodermis and envelop the single bundles, or may
consist of strands of long fibres (hard bast), which are on one
side of the cribrose portion, and accompany the bundle through
its whole course in the stem. The strands of fibres frequently
encroach upon the cribrose part of the bundle so much as to be
more or less commingled with it (see 311).

371. The stem may sometimes have dicollaterul bundles cither
(1) with the woody part on the interior as well as on the exterior
aspect (é. g., Cucurbitaceze), or (2) with an envelope of wood
surrounding the liber; this envelope is seen at the extremities of
the bundle, while the rest of it has the ordinary character (Iris).

372. The bundles of the stem may be concentric (see 313) ; 2

Fig. 100. Longitudinal section of a fibro-vascular bundle of Ricinus (the cross-section
being shown in Fig. 99): 7, cortical parenchyma; gs, bundle-sheath; 6, bast-fibres;
Pp, pliloém-parenchyma; c, cambium (the row of cells between c and p develops after-
wards into a cribrose-tube); in the xylem portion of the bundle the elements are devel-
oped successively from s to ¢’; s, the first slender and long spiral duct; s’, wide spiral
duct, the spiral band uncoiling; 2, duct, thickened partly in a scalariform, partly in
a reticulate manner; h, h’, hk’, h'’, wood-cells; t, pitted duct: g, absorbed septum;
t’, pitted duct, still young; in /, t, and ¢’ the boundary lines of the adjoining cells which
have been removed are shown in the wall of the ducts; m, parenchyma of the pith.
(Sachs.)

124 MINUTE STRUCTURE OF THE STEM.

ring of liber may surround the whole of the woody portion, or
the wood may surround the liber. The former of these arrange-
ments is common in the vascular cryptogams (see 354).

373. The pith of the stem consists of parenchyma frequently
intermingled with other structural elements in small amount,
especially long fibres, woody prosenchyma, and latex-cells.

The parenchyma cells of pith have been classified in the
following manner: (1) active cells, having the office of storing
starch and other assimilated
products for a time; (2) crys-
tal-cells, in which crystals are
formed ; (8) inactive cells,
which, having lost the power
of receiving starch or other
products, remain empty.

These apparently unimpor-
tant distinctions have been
shown by Gris? to be valuable
in the identification of consid-
erable groups of plants. Pith
composed of active or inactive
cells alone is termed by him
homogeneous ; that which con-
tains more or less of both kinds of cells, heterogeneous. The
arrangement of the elements in heterogeneous pith is so nearly
constant as to have much interest for the systematist.

374. The medullary rays comprise the conjunctive parenchy-
ma, which lies between the bundles in the stems -of normal
dicotyledons. The cells are for the most part much flattened
radially, always so in those cases where the bundles are closely
approximated (see also 207).

375. The stem develops from the bud by extension of its
internodes. When these have attained a certain length, different

1 The peculiar structures found occasionally in the periphery of the pith of
Sambucus, and sometimes in the bark, have been mistaken for fungi, but have
been shown hy Oudemans and by Dippel to be receptacles for a very heteroge-
neous mixture of tannin and other matters (Verh. d. Nat. Vereins d. Preussens,
Rheinlande und Westphalens, 1866, p. 1).

2 A detailed account of the orders of plants examined by Gris will be found
in Nouvelles archives du Muséum, t. vi. fasc. 8, 4, p. 201 (9 plates), An extract
from the same is given in Ann. des Se. nat., sér 5, tome xiv., 1872, p. 34.

Fig. 101. Clethra alnifolia. Longitudinal section through the reticulated pith of a

young branch; each active cell contains a nucleus and chlorophyll grains, December.
(Gris.)

COURSE OF THE BUNDLES IN THRE STEM. 125

for different stems, and depending often on some external con-
ditions, they do not further elongate; but those tissues of the
internodes by which growth in length has taken place become
gradually firmer, and constitute permanent tissue. It sometimes
happens that the nodes and internodes of the stem are not plainly
distinguishable from each other. This is the case in most palms,
where the growth takes place from the terminal bud alone.

376. Even a cursory examination of the structure of a stem
which has thus unfolded from a bud shows that the number and
the distribution of the bundles have much to do with the number
and the arrangement of the leaves. Comparative investigations!
of large orders of vascular plants have shown that the number
of the bundles of the stem always bears some relation to that of
the leaves at a given portion of the axis, and to the arrange-
ment of the leaves. ‘‘The more bundles in a given leaf, and
the greater the number of leaves in a cycle or whorl, the more
numerous will be the bundles in the stem at that level. In
monocotyledons with a large crown of leaves these two condi-
tions are met with, and in these stems are found the greatest
number of bundles.” ?

377. Course and distribution of the bundles in the stem. In
the internodes, the bundles mostly run parallel to the axis, or in
curves of very long radius; at the nodes, they may interlace
transversely. If a bundle is followed through its course from
below upwards, it will be found to branch at some of the nodes ;
the branch of the bundle going directly into the leaf at that
point, or else passing upwards through other nodes until it
reaches a leaf, the number of nodes traversed varying according
to the kind of plant and the region of the stem.® More than
one branch of the bundle may, however, go to a single leaf.

878. If, now, the course of the bundle be examined from
above downwards, it can be seen that each leaf contributes its
simple or compound fascicle to the larger bundle with which that
from the leaf sooner or later becomes confluent. The fascicle
from the leaf can frequently be followed down for several inter-
nodes as a separate thread, the so-called foliar trace. If such
foliar traces are nearly isolated in their course, a cross-section
of the stem will give a ground-plan of the leaf-arrangement.
Usually, however, there is much complexity in the distribution

1 Nigeli : Beitrége zur wissensch. Botanik, 1858, and Hanstein: Prings-
heim’s Jahrb., 1858.

2 Van Tieghem: Traité de Botanique, 1884, p. 746.

8 Van Tieghem: Traité de Botanique, 1884, p. 733.

126 MINUTE STRUCTURE OF THE STEM.

of the fascicles, and they
curve considerably in their
course, so that it is often dif-
ficult to follow the foliar trace
for more than a short dis-
tance. Ifthe stem has alter-
nate leaves, the direction of
the foliar traces will of course
be different from that in a
stem with opposite or verti-
cillate arrangement of the
leaves. The following figures
exhibit the course and dis-
tribution in a few cases : —

In the leafy shoot of Clem-
atis, Fig. 102, the leaves are
opposite and decussate. From
each leaf there descend three
fibro-vascular bundles ; for
instance, at the lower node
cv there are a, 6, c,and e, f, d.
The leaves at the node next
g above decussate with those
3\\ fe below ; each of them has
] three fibro-vascular bundles,
respectively, 7, g, 4,
and k, h, m, which
become somewhat
smaller as they de-
scend to the next
node, where they be-
come blended with
the bundles there.
An examination of
the third node shows
that the two leaves
there contribute bun-
dles to the axial cyl-
inder; there is again
a blending of the bundles at the node helow.

Fic. 102. Diagrammatic view of a leafy stem of Clematis, showing the arrangement of
the fibro-vascular bundles: a, b, c, — e, /, d, the fascicles from the lower pair of leaves;
i, g, |, —k, h, m, the fascicles from the second pair of leaves; qg, 7, s,—p, n, v, the

DISTKIBUTION OF THE BUNDLES IN THE STEM. 127

Both lateral strands of a leaf in such a case as this run down
through one internode, bend outwards at the node below, and
attach themselves to the lateral strands belonging there.

Suppose, now, that a cross-section of the stem of Clematis is
made at the lowest node represented in Fig. 102; all the fibro-
vascular bundles at that point will be seen in their relative posi-
tions, some of them cut squarely off,
others obliquely, according to curves
which they make. A cross-section in
the internode above would show slen-
derer bundles, but all arranged in much
the same manner as in the thicker inter-
node below; that is, in a circle.?

The circle is made up of fibro-vas-
cular bundles which have an inner por-
tion of wood ; within the circle is paren-
chyma (the pith), and outside of it more
parenchyma (the cortex), which can be
stripped off with the bast-portion of the
central cylinder as bark.

Compare Fig. 102 with Fig. 103. In
the latter, the stem does not exhibit in
cross-section the fibro-vascular bundles
arranged in a circle: they are more or
less scattered ; there is no clearly de-
fined central portion nor well-marked
outer portion free from them. Hence it
cannot be said that such a stem has any
distinction of pith, wood, and bark.

A further distinction may be here
noted; namely, that the bundles in Fig.
102 have the power of increasing in
thickness, adding new wood and new bast to the primary struc-

1 Another feature must be attentively studied ; namely, the relation of the
forming bundles to the young leaves at the upper part of the stem. One may
say the bundles descend from the leaf to the stem, or ascend from the stem to
the leaf. But since the development of the leaf part and the stem part of a
bundle goes on together, these terms, ascend and descend, should be under-
stood to refer to our method of tracing the bundles out, and not to the method
of their development.
fascicles from the third pair of leaves; 2, ¢, fascicles of the fourth pair of leaves; 8, a, —
y, 6, pairs of undeveloped leaves not as yet having fascicles. The diagram illustrates
both Clematis Viticella and C. Vitalba. (Nigeli.)

Fie. 103. Longitudinal section through the stem of Aspidistra elatior, showing the
curved course of the fibro-vascular bundles in the simplest palm-type. (Falkenberg.)

128 MINUTE STRUCTURE OF THE STEM.

ture (see 390) ; but in Fig. 103 the bundles are closed (see 315),
and incapable of
further increase in

, thickness. Hence

any further growth

in thickness of the
stem shown in

Fig. 103 must be

by the intercala-

tion of new bun-
dles.

879. It was held
by Desfontaines ?
that the new vas-
cular bundles in
Palms originate in

w z

1 Quoted by Mohl,
in The Structure of
the Palm-Stem (The
Ray Society, Reports
and Papers on Bot-
any; London, 1849).

| Another illustration
of the arrangement of
fibro-vascular bundles

is here given : —
The stem of the Vi-
a tis vinifera is usually

: \ ‘ 3 | clr i\ regarded as sympo-

dial; that is, it is com-
posed of internodes
belonging to different
axes (see vol. i. pp. 54
and 154). In this
species of grapevine
two leaves in succes-
sion have a tendril on
the opposite side, then
follows a leaf without
any tendril, next the
sequence of two with

104

Fia. 104. Diagrammatic projection, showing the disposition of the fibro-vascular bun-
dles in a leafy shoot of Vitis vinifera, Tach leaf has five fascicles, which are unsymme-
trically arranged: a,b, ¢,d,¢; 4, G4, 1, my a. py gy 7, 85% ear, or, ys a, By yy, 8,65 mS
6,4, «, Kach tendril has three fibro-vascular bundles passing in from the stem, g, t, @:
the axillary buds have also three, fand »,. (Niageli.)

STEMS OF MONOCOTYLEDONS AND DIGOTYLEDONS. 129

the centre of the stem, and that the hard and thick vascular
bundles, situated at the periphery of the stem, are older than
the softer ones occupying the centre. For stems like those of
Palms he used the term endogenous, giving the name exogenous
to the other class, in which new layers are added to the outside
of the wood. The terms endogenous and exogenous were
adopted by De Candolle, and have played an important part
in Systematic Botany. Comparative researches have shown that
the term endogenous as applied to the growth of stems like
those of Palms is not appropriate, and hence the correlative
words have been generally

abandoned as names of the a y

two great groups of plants. — Ne
They are now generally re-

placed by the words monocoty- rl |g 17

ledonous and dicotyledonous
(see Vol. I. p. 69).

Moreover, it is now gener- ey 1-2 Pel Imi | g
ally admitted that, although
the distinctions pointed out in
366 — namely, those relating YY :

to the arrangement and course a of |e
of the bundles — are valid for
most plants of the two great
groups, monocotyledons and
dicotyledons, they do not hold

a

for all. is
380. Instead of describing

the numerous exceptions to f
both of these groups as ex- te f Pee Pen
ceptions, many authors have
endeavored to construct some
new classification which shall 105

embrace most of the anoma-

lies in one or more co-ordinate divisions. Of these attempted

tendrils is resumed. Every leaf has five fibro-vascular bundles, which are
arranged unsymmetrically, as shown in the figure. The long distance through
which some bundles can run before uniting with any others, and the differences
in structure at the successive nodes, are clearly exhibited in the diagram.

Fig. 105. Diagrammatic projection of the disposition of the fibro-vascular bundles in
Phaseolus vulgaris. This diagram, like Fig. 104, superposes two longitudinal sections,
both seen from the axis: «, b,c,d; A.g, h, i: /,m,n,o; q,7, 8, t; u,v,w, x; the succes-
sive leaf-traces, each with four fascicles. Of the upper leaf-trace, the first two fascicles,
Y, % are visible. e, k, k, p, fascicles for the three leaves below. (Nageli.)

9

180 MINUTE STRUCTURE OF THE STEM.

classifications only one will be given here, and that only in part
and somewhat rearranged ; namely, de Bary’s : —

I. The palm-type. A cross-sec-
tion of most monocotyledons shows
that the bundles are not arranged
in a simple ring, but that they are
irregularly scattered or more or
less crowded to form a shaft, which

may be hollow as in most grasses, or filled in the centre with
parenchyma through which scattered bundles run. The periphery
of this cylinder or shaft is not a true bark, nor is the middle a
true pith. In the simple palm-type, all the bundles are leaf-
strands.

II. The dicotyledonous type, in which all the primary bundles
are leaf-trace threads. The bundles are arranged in a simple
circle within which is pith, outside of which is cortex ; medullary

Fig. 106. Transverse section through the outer part of the stem of Kunthia mon-
tana, a Palm. (Mohl.)

Fic. 107. Transverse section through the middle part of the stem of Corypha
cerifera, a Palm. (Mobl.)

STRUCTURE OF PALM-STEMS. 131

rays run between the parenchyma of the pith and that of the
cortex. To this type belong most dicotyledons, Conifer, and
Gnetaces (with the exception of Welwitschia').

III. Anomalous dicotyledons, differing from the last in not
having all their primary bundles arranged in a simple circle.
The extra bundles may either be in the cortex, as in some Mela-
stomaceze and Rhipsalidese, or they may lie in the pith either
seattered or arranged in rings, as in Cucurbitacez, the herba-
ceous Berberidacez, species of Papaver, Thalictrum, Amaran-
tus, and Phytolacca, many Nymphzacez, some Begoniacez, and
a few species of Aralia. 3

De Bary’s other classes comprise anomalous monocotyledons
and certain higher cryptogams.

381. To make clearer the somewhat complicated structure of
palm-stems which have unfortunately been selected in many text-
books to illustrate the histology of monocotyledons, a few general
statements are now given as introductory to the special treatment
in the note.2— That portion of a palm-stem which lies above the
lowest active leaves (better called fronds) is of a conical shape,
is often much elongated, and carries all the new and forming

1 For a description of this interesting plant, and an account of its peculiari-
ties of structure, consult J. D. Hooker on Welwitschia.

2 The exposition by de Bary of the structure of the simpler forms of Palms is
given nearly in full in the translation which follows :—

‘* Since the appearance of Mohl’s Palmenanatomie, the following main char-
acters have been recognized as belonging to the simple palm-type.

‘¢ All the bundles in the cylinder (with some doubtful and certainly extremely
insignificant exceptions which will be mentioned later) are leaf-traces. The
base of the leaf includes the whole circumference of the stem, or at any rate
the greater part of it. The leaf-trace is always several threaded: generally it
consists of many threads, in stout stems even of a couple of hundred; its width
is nearly the whole of the circumference of the stalk. From the base of the leaf
the threads curve down into the cylinder, within which they descend, some in
its outer surface and nearly radial and perpendicular, others radial and oblique,
first pressing inward toward the long axis of the cylinder in a curve which is
convex towards the upper and inner side of the stem, then curving outward,
and gradually passing towards the outer surface of the cylinder, and in propor-
tion as they approach this, approximating towards « perpendicular position.
All threads descend through many internodes, and unite at last in the outer
portions of the cylinder with others which enter it further down, attaching
themselves to these in a direction which is sometimes tangential, sometimes
yadial, and sometimes oblique. Until this attachment of their lower ends, the
bundles run independently. The union of the lower ends of bundles with
others that enter the cylinder lowcr down generally takes place in such a way
that the whole number of the bundles in successive internodes of equal cir-
cumference remains about the same. As the successive internodes and leaves

132 MINUTE STRUCTURE OF THE STEM.

leaves. It is known as the Phyllophore. The newest leaves are
formed nearest the apex of this cone ; and here, as before shown,
all the fibro-vascular bundles common to the leaves and stem origi-
nate. In most cases there is absolutely no increase in thickness
of the stem below the base of this cone; but as the apex of the
cone is developed and extends further upwards, thus elongating
the stem, there is also a growth in thickness of the part of the
cone just above its base. Thus a uniform size of the cylindrical
stem is kept. But such increase in thickness cannot continue
below the point at which there are active leaves.

increase in size, the number of bundles grows larger, and conversely. The
number of internodes through which a bundle passes cannot be fixed with
exactness.

“Those bundles in a leaf-trace which curve like a bow towards the middle of
acylinder do not penetrate to equal depths ; as a general thing, the median
bundle of a series lies deepest, and the others lie less deep in proportion to their
distance from this ; the marginal ones descend nearly perpendicularly in the
outer surface of the cylinder. Where there are several series of bundles, those
in the inner series generally penetrate more deeply than those in the outer
ones which lie at an equal distance from the median thread.

“The necessary consequences of the course described are : first, that in the
cross-section of an internode the bundles stand closer together in proportion as

they are nearer to the outer

hawt surface of the cylinder, —
a phenomenon which is
especially noticeable when
the bundles are distributed
over the whole surface of
the cross-section of the
cylinder ; second, the suc-
cessive traces dwindle, and
their curving threads cross
each other. Mohl’s cele-
>» |} brated plan, which is here
reproduced in Fig. 108, ex-
hibits this latter relation
in a radial longitudinal
section, being based on
~~ |—| the untenable assumption
that all the threads of a
trace are nearly equally
curved, and are placed in
a tangentially perpendicu-
| | lar direction, so that they
108 109 form in the outer surface
an open curving cone. Ifit

Fig. 108. Mohl’s diagram of the course of the fibro-vascular bundles.
Fre. 109. Diagram of the course of fibro-vascular bundles in a palm-stem with dis-
tichous leaves. (De Bary.)

STEMS OF MONOCUOTYLEDONS. 1388

382. Branner? has shown that the bundles in Palms do not
end blindly at their lower extremities upon the surface of the
stem. but that they are connected in sections or divisions from
base to summit one with another, and one on top of another.
He has further shown that each bundle lies in a spiral curve
within which it grows; and whether it returns to the surface
upon the side in which it originated or upon the opposite side, it
is always in this curve.

383. The structure and development of monocotyledons have
received much attention during the last few years, and the
results obtained have caused some modification of previously
existing classifications. Two of the proposed methods of re-
arrangement are herewith given : —

384. Falkenberg recognizes the three following types of stems
of monocotyledons.

I. The tissue of the central cylinder is not plainly separable
even in its mature state into conjunctive parenchyma and fibro-
vascular bundles. (To this type belong the water-plants,
Zostera, Potamogeton, and probably all submerged monocoty-
ledons. )

II. The bundles and the fundamental tissue are plainly differ-
entiated; the former extending almost horizontally from the
leaves to the middle of the cylinder, then curving downwards,
running outwards, and finally terminating in the superficial

is assumed that the leaves alternate with precisely one half divergence, and in-
clude the stem, and that the threads stand tangentially perpendicular, then the
actual course in the stem will be shown in the plan of a radial section through
the median thread of a leaf given in Fig. 109. But the assumption of a radi-
ally perpendicular course is valid only for those bundles which are also tangen-
tially perpendicular. As was first observed by Meneghini, admitted afterwards
by Mohl (Verm. Schriften, p. 160), and more minutely shown by Nageli, each
radially curving thread runs also in a tangentially oblique direction, and
in spiral curves which are proportionate to the radial curving. Nageli found
the median thread of a leaf of Chamedorea elatior, Mart., for example, making
14 revolutions in six internodes ; in the sixth, it had not, in its outward course,
quite reached the middle point between the centre of the stem and the inner
surface of the bark. In stems with very short internodes and closely crowded
bundles the spiral curves are at once perceptible in the cross-section, being
plainest in the bundles of the stem of Xanthorrhoea, which press almost hori-
zoutally towards the centre of the stem, this peculiarity giving to its cross-
section the strange appearance which has been frequently mentioned.

‘* Finally, many variations from that course of a thread which has here been
described as typical may occur; there may be curvings alternately toward
the outside and the inside, etc., which are not constant.”

1 Proceedings of American Philosophical Society, 1884, p. 459.

1384 MINUTE STRUCTURE OF THE STEM.

layers of the central cylinder. (The Mohl-Mirbel Palm-Type,
illustrated by Asparagus, Iris, Canna, Aspidistra (see Fig. 103),
Acorus, Scirpus, Zea, etc., the
underground parts of Lilium,
Tulipa, ete.).

I. The bundles and the
fundamental tissue are plainly
differentiated ; the bundles run-
ning downwards, and gradually
converging at a point in the
middle of the central cylinder,
here blending with the leaf-
traces of older leaves, without
again curving outwards. (Ex-
amples are afforded by Trades-
cantia, the parts above ground
of Lilium, Tulipa, etc.).

385. Guillard? describes six
types of structure in the stems of

110 monocotyledons which depend
chiefly upon the relations of a central zone (called ‘ interme-
diate”) to the fibro-vascular bundles in the remaining portions of
the stem. The classification has no substantial advantage over
that of Falkenberg.

1 These types will be better understood after some peculiarities in the ter-
minology are explained. By ‘‘ pith,” in monocotyledons, Guillard means the
centrai region of parenchyma; by ‘‘ intermediate zone,” the active zone imme-
diately surrounding the central region ; by ‘‘cortical zone,” the zone outside
the external circle of bundles and the products of the intermediate zone. The
six types are the following : —

1st Type. No intermediate zone between the pith and cortical zone ;

é. g., Polygonatum vulgare.

2d Type. An intermediate zone represented by different tissues : —

1. Consisting of cauline bundles ; ¢. g., Iris florentina.

2. Consisting of meristemiform tissue (that is, tissue which produced
from secondary meristem retains the shape but not the activity of
meristem) ; ¢. g., Chamedorea elatior.

3. Consisting of a fascicular sheath ; ¢. g., Epipactis palustris.

4. Consisting of the three foregoing ; ¢. g., Acorus Calamus.

3d Type. A single external zone of bundles, with a potential intermediate

zone; é. g., Luzula campestris.

4th Type. Common bundles in two groups: one at the centre of the stem,

the other forming the ordinary circle, separated from the first by a poten-

tial intermediate zone ; e. g., Tradescantia Virginica.

Fie. 110, Distribution of the fibro-vascular bundles in the leaf-shaped branch ot
Ruscus hypoglossum. (Ettingshausen.)

SECONDARY STRUCTURE. 138

SECONDARY STRUCTURE.

386. It has been noticed that the fibro-vascular bundles of
monocotyledons differ from those of dicotyledons chiefly in the
possession by the latter of a layer of merismatic tissue (cambium)
between the cribrose and woody portions. ‘The stems of peren-
nial dicotyledons increase in thickness from year to year chiefly
by the annual production of a new mass of wood upon the in-
side of this layer, and of liber

in spite of numerous anomalies,
to consider the secondary struc-
ture of the stem under these two
heads.

387. Secondary structure of
monocotyledonous stems. As has
been already observed, the pri-
mary bundles in palms run from
the leaves in curves of long ra-
dius until they again approach
the surface of the stem, and their
fullest development is found in
the middle part of their course.
While a cross-section exhibits
these bundles as scattered without
much order in a mass of paren-
chyma, a vertical section shows
that they have entered the stem
at different heights (since the
leaves with which they were developed were at different points
on the stem). A vertical section can display only parts of most
of these curved bundles. At the stem of a palm just below the
crown of leaves there are as many bundles seen in a cross-sec-

\ J

upon the outside; but the stems

of most monocotyledons have no off}
provision for annual increase in el
diameter. Hence it is convenient, : Ne :

===

5th Type. A central mass of secondary tissue, formed from central meris-
tem. Intermediate zone well developed ; ¢. g., Triglochin maritimum.

6th Type. Bundles having several distinct liber elements; ¢. g., Tamus
communis. (Anatomie de la tige des Monocotylédones, Ann. des Se.
nat., sér. 6, tome v., 1878, p. 1.)

Fie. 111, A diamond-shaped mesh of primary fascicles intermingled with secondary
fascicles in the stem of an Opuntia. (Reinke.)

136 MINUTE STRUCTURE OF THE STEM.

tion as have been derived from the leaves at that point; and
since taese bundles do not possess a cambium layer, they have
no power of increasing in size. The only changes therefore to
be looked for in the stem of a palm from year to year are those
in the ragged exterior from which the leaves fall, and the pos-
sible increase in firmness of the individual elements of the older
bundles. The stems of most palms are as thick when they begin
to ascend from the ground as they will afterwards be, their bun-
dles early becoming permanent tissue throughout.

388. The presence of obscure nodes in the stem may com-
plicate its structure somewhat by the introduction of horizontal
interlacing bundles ; but there is in these cases, as in the former,
no provision for increase in thickness.

389. In some monocotyledonous stems new bundles can arise
in a merismatic layer just within the cortex, and therefore cause
an increase in the diameter of the stem.

A similar mode of increase in thickness is met with in the
stems of many dicotyledons; as those of Nyctaginaceee, many
Chenopodiaceze and Amarantacez, etc. Secondary bundles are
formed in a merismatic layer outside the primary bundles, and
in contact with their liber.

390. The secondary structure of normal dicotyledonous stems
(see 369) is easily understood when it is remembered that the
cambium of their primary bundles possesses the power of form-
ing the following kinds of tissue: @, new wood on the outside
of that which was last produced ; 0, a layer of new liber; ¢, fresh
cambium for subsequent activity; and d@, continuations of the
medullary rays.

The cambium layer in the stems of most dicotyledons is com-
posed of extremely delicate, thin-walled cells, which are filled
with protoplasm and building materials. In the spring, when
the hark is readily stripped from the wood, this layer appears as
a thin film of mucilaginous matter, showing, to the naked eye, no
cellular structure. In the case of such plants as the maple,
birch, and pine, this juicy mass possesses a very sweet taste,
owing to the large amount of organizable nutrient matter which
it contains.

391. The cambium layer exposed by removal of the bark soon
dies, and of course all further increase in diameter is impossible
unless the wound is healed in some way (see 421).

392. The growth in size of the stems of normal dicotyledons
depends therefore upon the existence and activity of cambium
cells between the wood and bark. The juxtaposition of the

INCREASE IN SIZE OF STEMS. 137

primary bundles brings the cambium into the form of a circle,
sometimes broken, but frequently uninterrupted. If the cam-
biumn circle is substantially unbroken, a new compact ring of wood
is laid upon the wood

of the primary bun- B A

dle, and a new ring fa
of liber forms within
the older liber. This
action may be indefi-
nitely repeated; and
in a climate where
there are notable dif-
ferences either in tem- C
perature or moisture
between the seasons,
the concentric circles
are records of the
years.

If the primary bun-
dles are not in con-
tact, the new wood
added year by year
simply increases the
size of the wedges at
their outer part.

393. New bundles
may be intercalated
directly between those
already present, and
grow in much the
same manner as the
primary ones ; or they
may arise at new points of activity and produce great changes
of form. In the same way tertiary changes and those of a
higher order may follow the secondary ones, giving rise to stems
which have a very complicated structure. The most puzzling

Fig. i112. Diagrams showing the secondary increase in thickness of a normal dicoty-
ledonous stem: /?, cortex; p, phloem with three fascicles of hard-bast fibres; x, xylem;
M, pith. A shows only primary structure; B exhibits formation of the ring of cam-
bium; fe, fascicular cambium; /c, inter-fascicular cambium; 3, b,d, fascicles of hard
bast; C,at the end of the year, after the formation of the secondary fibro-vascular ring;
p, liber; fh, secondary wood of the bundle; ifp, inter-fascicular liber; ifh, inter-fas-
cicular secondary wood; the entire ring is subdivided by medullary rays of different
lengths. (Sachs.)

1388 MINUTE STRUCTURE OF THE STEM.

cases can generally be referred to eccentric growth of some one
or more parts, as in flattened stems, or explained by the intro-
duction and more vigorous growth of supernumerary bundles.

394. Extraordinary anomalies are afforded by the lianes of
tropical countries, woody climbers with distorted stems. They
belong chiefly to a few orders; namely, Bignoniacez, Mal-
pighiacee, Menispermacez, and Aristolochiacese. A few inter-
esting cases are shown in the accompanying figures, and are
sulliciently explained in the descriptive letter-press.

395. Spring wood and autumn wood. The secondary wood an-
nually produced in a temperate climate like ours exhibits certain
differences between the inner and the outer portion of the year’s

Fig. 113, Transverse section of the stem of a liane belonging to the order Malpighi-
aces: m, pith; b, the central portion of the wood, arranged in concentric layers around
the pith. (Duchartre.) a

Fie. 114. Transverse section of the stem of a liane belonging to the order Malpighi-
aces: m,the pith. The bark follows all the irregularities of the wood. (Duchartre.) f

Fig. 115. Transverse section of a liane belonging to the order Sapindaces: }, pri-
mary woody body having its own pith m, and bark e’c; b’, b’, b’, three secondary woody
bodies without pith, but having as thick a bark as the primary body. (Duchartre.)

Fic. 116. Transverse section of the stem of aliane belonging to the order Sapindacez:
b, the primary or central woody body having its own pith m; 0’, b’, b', b', a circle of un-
equal secondary woody bodies; b’’, tertiary woody bodies. (Duchartre.)

ANNUAL RINGS. 139

ring. That which is produced earliest (spring wood) has some-
what larger ducts and wood-cells than that which is formed later
(autumn wood). The difference is not very striking when the
wood of a single year is examined, for the diminution in size
is gradual from within outwards; but if the autumn wood of one
year is compared with the spring wood in the next ring, the dif
ference is very marked. The cause of the difference in character
between the early and later wood formed during a single season
is supposed to be the greater pressure exerted by the tense bark
in autumn. The experimental evidence in favor of this view
will be presented in the chapter on ‘‘ Growth.”

396. In climates where there is no marked arrest of vegetative
activity during the whole year, for instance, in that of the equa-
torial zone, the secondary wood seldom presents any clearly
defined annual rings. In the wood of warm, temperate zones,
however, well-marked annual rings are not uncommon.

397. It has long been known that in temperate climates a tree
may exceptionally form a double ring in a single year. The
cause of this in cases which have been carefully examined ap-
pears to be: (1) a partial cessation of activity owing to injury,
followed by (2) a renewal of activity in the same season. Thus
an elm may be stripped of its leaves in early summer and suffer
a temporary check; but the buds already formed for another
year develop into full leaf in a short time, the assimilative activ-
ity is resumed, and two rings are formed as a result of this ces-
sation and renewal. Kny1has found this to be the case with
several trees which had been deprived of their foliage at the end
of June. Wilhelm has found by experiment that a tolerably
well-defined double ring was formed in Quercus sessiliflora, from
which he removed all the leaves on the 7th of June; while in a
second case, where the foliage was removed later (July 10th),
the duplication of the ring was not apparent.

398. From this statement it would appear that even in tem-
perate climates, where there is a prolonged period of complete
inactivity due to the cold, the number of rings shown in the
cross-section of a stem may not exactly coincide with the num-
ber of years through which the tree has lived. But, as matter
of fact, the lines of limitation in the intercalated rings are so
much less distinct than those on either side, that the two lesser
rings would be counted as one, and therefore be credited to the
growth of one year instead of two.

1 Verhandl. d. botan. Vereins der Prov., Brandenburg, 1880,
2 Child: Popular Science Monthly, December, 1883.

140 MINUTE STRUCTURE OF THE STEM.

The largest number of rings yet reported in any case appears
to be that given for the great trees of California ; namely,
“2,100, with a probability that others considerably exceed this.” !
Other higher numbers of rings or estimates of age are, however,
given in some works.?

399, That it is unsafe to base any calculation of the age of a
tree upon its diameter follows from the fact that its growth dur-
ing one year differs from that during another (see 400). Even the
use of De Candolle’s modification of Otto’s rule,® which is per-
haps the best yet given, leads to erroneous results. The method
assumes that the number of rings averages nearly the same to
any given unit of thickness in the outer as in the inner part of
the stem. Having determined the number of rings in an inch
just under the bark, this number is multiplied by the radius in
order to obtain the whole. For example: Extract from opposite
sides of a tree two pieces having a depth of two inches each.
Suppose the number of rings in the two-inch piece on one side
to be 20, while in the other there are 32, the average per inch
will be 13. Deduct twice the thickness of the bark from the
whole diameter of the tree, to obtain the diameter of the wood
in inches, and multiply one half of the diameter by 13.

400. The woody rings annually formed in a stem differ con-
siderably in size; a narrow ring being the growth of a cold

1 §. Watson, in Addendum to Botany of California.

2 The following estimates cited by De Candolle (Physiologie Végétale,
p- 1007) are believed to range altogether too high : —

The Linden of Neustadt, in Wiirtemberg, 1147 years.

The Oak of Bordza (on the Baltic), 710 distinct rings counted and 300 in-
distinct rings estimated = 1010 years. (By Otto's rule this would be 1080
years. )

The Yew of Crow-Hurst (Surrey), measured by Evelyn in 1660, 1458 years.

The Yew of Braburn (Kent), measured by Evelyn in 1660, and said by him
to be superannuated, 2880 years.

The estimate given by De Candolle, of the age of trees of Adansonia (Bao
bab); namely, 6,000 years, has been shown by Dr. Gray (North American
Review, 1844) to be wholly erroneous.

3 Otto’s rule is thus given by De Candolle : Ascertain the diameter at the
height of about five feet, and make a notch at the same point on the circular
surface, to count a certain number of annual layers which we measure. We
then tind the annual growth of those trees which have left off growing in height

by the formula ae ® ¥ and of those which continue to grow in height by

the formula Pap 2 asy, D being the diameter of tree ; 7, volume of same ;
d, thickness of annual layers which have been counted ; , the number of these
layers (Physiologie Vigétale, p. 981 .

SAP-WOOD AND HEART—Woop. 141

season, a broad ving of a warmer one. Their width varies also
in the same species in different localities: thas, in Pinus sylves-
tris, grown between 50° and 60° north latitude, in Europe (the
space occupied by the British Isles), the annual layers are very
seldom less than 4 of a millimeter in thickness; while in the
same tree, grown far north, the thickness is not yy of a milli-
meter.1_ The width varies also in different parts of the same
ring. For instance, in the case of Pinus sylvestris, Bravais and
Martins found the two opposite radii in a stem to have the ratio
of 9 to 19, the side having the greatest thickness being that
which had its foliage best exposed to air and light. The eccen-
tric growth of the wood of branches has been often noted; the
longer radii are those on the lower side.

401. Sap-wood (Alburnum). The new and soft wood con-
tains a larger proportion of soluble organic matters, of nitro-
genous substances, and, when fresh, of water, than the older,
harder wood lying just within. The ‘‘ sap” of the tree is found
in largest amount in the newer wood. The name alburnum was
given to the sap-wood by the early histologists on account of its
white or pale color. Contrasted with it, but not always very
sharply, is the harder substance, Heart-wood, or Duramen.? The
latter was given its name because of its greater hardness, or
durability. Generally there is some distinction in color between
the sap-wood and heart-wood, owing to the presence of peculiar
coloring-matters lodged in the texture of the latter.’

402. Color of wood. The deep colors which characterize many
kinds of wood are contained chiefly in the walls of the ceils and
ducts. In Hematoxylon Campechianum the coloring-matter
sometimes occurs also in crystals inside the cells themselves or
in clefts of the wood. The wood of Pterocarpus santalinus (Red
Sanders-wood) consists of libriform cells intermingled with small
groups of very large ducts, both of which contain the ruby color-
ing-matters in large amount. Many Berberidaceee, Cladrastis
tinctoria, Cercis, etc., have yellow coloring-matters in the wood ;
in Guaiacum the color is greenish; in black walnut, brown; in
ebony, nearly black.

1 Bravais and Martins: Ann. des Se. nat., sér, 2 tome xix., 1843, p. 129.

* The word Duramen is used by some writers to denote merely that heart-
wood which has become very dense by peculiar infiltrations (Saunersdorfer, in
Sitzungsber. d. k. Akad. Wien., 1882).

3 The following figures, giving the proportion of sap-wood to the entire vol-
ume of the trunk, are from Tredgold (Principles of Carpentry, Section X., cited
by Rankine) : Chestnut, 0.1; Oak, 0.294; Scotch Fir, 0.418.

142 MINUTE STRUCTURE OF THE STEM.

403. It may be here mentioned that many woods have charac-
teristic odors ; for instance, sandal-wood, violet-wood, and many
of the coniferous woods.

404. The presence of resinous matters in wood, particularly
when these are evenly although sparingly distributed through the
mass, exerts a marked effect in retarding decay. The durability
of the wood of Southern Cypress, even when exposed to the joint
action of the warmth and moisture of a greenhouse, is usually
attributed to their presence. But there are some cases of great
resistance to the influences producing decay, which cannot be
referred to the same mode of protection; for instance, those of
Robinia Pseudacacia (or common ‘ Locust”) and Catalpa.

405. Various processes have been tried for destroying the
putrescible matters in cells, or so modifying the character of
the cell-wall that the wood can be protected against decay.

406. The oldest known method of preserving wood is car-
bonizing, or charring, by which those constituents of the wood
specially liable to decay are so changed as to be no longer liable
to putrefaction. The wood-preserving processes known as Bur-
nettizing and Kyanizing have for their object the coagulation of
protein matters in wood-cells, thus retarding if not preventing
putrefaction.

407. In Kyanizing, a solution of mercuric chloride is forced
into the texture of the wood; but the cost of this substance
is so great, that it has led to a general abandonment of the
process.

408. In Burnettizing, the wood is impregnated with a solution
of zine chloride containing about fifty-five per cent of the dry
chloride. This is forced into the wood under pressure.

409. Another process — creosoting — depends upon the intro-
duction into the wood of a solution of impure creosote, a pressure
of about one hundred and fifty pounds to the square inch being
maintained until the wood has absorbed a sufficient amount of
the antiseptic liquid. Some of the antiseptic matters obtained
by a rough distillation of coal-tar are also used for preserving
wood.

It is an interesting fact that even wood which in the air
is specially liable to decay can be preserved for a long time if
deeply submerged in water.

410. There is an appreciable difference, especially in length,
between the wood-cells of the carlicr annual rings and those
which succeed them; and Sanio has shown that an increase of
length of the cells occurs up to a certain period of growth, when

SIZE OF WOOD-CELLS. 143

an average appears to be established. This fact is illustrated
by the following table, based on measurements of tracheids of
Pinus sylvestris.4

Number of the annual Medium length of the Medium width of the

ring. tracheids. tracheids.
il er a a gh .95 mm. -017 mm,

7 bose Boe oy Dede

HO: ae aye » « 813%

31 oe 9 3.69 *

37 .—(t«w me _ 8.87

38 et -# » 3.91 %

39°. 5% 4.00 <‘S

$0 we . 404 °

43 = 4 . 4.09 **

45 ee . 421 “

46 eG - 4.21 *¢

72 4g 4 a Aso .032 mm.

From this table it is seen that the increase can be traced up to
the forty-fifth year, but that from that time on, the tracheids in
one ring have the same length as those in the next. Those in
the forty-fifth annual ring have an average length of about five
times that of those in the first. In the wood of oak, the libri-
form cells exhibited the greatest difference in length. Thus
Sanio found that in a stem of Quercus pedunculata, with 130
rings, the medium length of these elements in the ring of the
first year was .42 mm., and in the three outer rings 1.22 mm.
Tracheids in the same rings measured, however, only .39 mm.
and .72 mm. respectively. With this increment in the length of
wood elements in successive rings, Haberlandt associates a fact
noticed by Alexander Braun ;? namely, that the wood elements
in some stems and branches stand not parallel with the axis, but

1 Ueber die Grdsse der Holzzellen bei der gemeinen Kiefer, Prings. Jahrb.,
viii. 409.

2 Ueber den schiefen Verlauf der Holzfiser, und die dadurch bedingte
Drehung der Baume, Berlin, 1854.

It is proper to refer at this point to an instructive paper by Abromeit
upon the histology of the oaks, in which the most marked characters of the
North American species are fully treated (Pringsheim’s Jahrb., 1884, p. 209).
According to Abromeit, the oaks can be plainly classified as follows : —

I. With wide well-marked medullary rays.

A, The annual rings distinctly defined by the concentric circles of the
larger ducts of the spring wood, and seen by the naked eye. The
smaller ducts are arranged in radial rows in the autumn wood.

w. With thin-walled ducts.
a. The radial rows of small ducts touch each other tangentially :
Quercus lyrata, alba, Durandii, stellata, macrocarpa, Wislizeni
Prinus, Garryana, bicolor (var. Michauxii).

144 MINUTE STRUCTURE OF THE STEM.

semewhat oblique thereto. The degree of obliquity is generally
from 4° to 5°, but it is sometimes much higher than this; for
instance, 10° to 20° in horse-chestnut, 30° in Syringa vulgaris
(Lilac), 40° in Sorbus aucuparia, and 45° in Punica Granatum.

411. Density of wood. Owing to its greater firmness and
smaller amount of putrescible substances, heart-wood is economi-
cally of far greater value than sap-wood; and hence nearly al!
determinations of density, strength, etc., are made upon it,

B. The radial rows of the smaller ducts are relatively narrow and
for the most part isolated tangentially : Quercus bicolor, ses-
siliflora, Iberica, grosseserrata, castaneifolia, pedunculata,
Thomasii, undulata (var. grisea), Mongolica, macranthera,
heterophylla.

y. The radial rows of the smaller ducts are very narrow, and the
ducts differ somewhat in width. The large ducts are in groups
in the concentric circles : Quercus lobata.

b. With thick-walled duets.

u. The large ducts in the concentric circles are indistinctly grouped,
while the small ducts are crowded in narrow radial rows :
Quercus rubra and the var.? Texana. Quercus tinctoria.

8. Large ducts, as in the previous group. The radial lines of the
smaller ducts wide, and the ducts themselves visible to the
naked eye : Quercus imbricaria, hypoleuca, laurifolia, Kelloggii,
palustris, falcata, Catesbei, aquatica, nigra.

y. With distinct radial grouping in the circles of the larger ducts of
the spring wood. The radial rows of smaller ducts narrow and
straight. The small ducts visible to the naked eye: Quercus
Cerris, serrata, Phellos, coccinea.

B. Having thiek-walled ducts of one kind, and these arranged in radial
rows or groups. The annual rings are not distinct to the naked eye,
and are defined chiefly by the thick-walled wood-cells of the outer
layers of the autumn wood. They are easily made out under the
microscope.

a. The radial rows of ducts are for the most part wide: Quercus
virens, oblongifolia, chrysolepis, rugosa, Ilex, coccifera, Calli-
prinos, lanuginosa, paucilammellosa, glabra, Burgeri, gilva,
thalassica.

8. Radial rows of ducts mostly narrow: Quercus Suber, agrifolia,
glauca.

II. The wide medullary rays appear under the microscope to be somewhat
interrupted by wood-cells, so as to appear like groups of narrower
rays: Quercus dilatata.

The principal kinds of wood-cells in oaks, according to the nomenclature of
Abromeit, are: first, the ‘* pointed,” of which there are two varieties, the septate
and the unseptate ; and, second, the ‘‘ blunt,” which are of comparatively wide
caliber, and have thin walls. The length of the pointed cells in an average of
171 measurements was found to be 1.224 mm. ; that of the blunt cells only
-lmm._ Besides these two chief kinds, there are transitional forms of every
sort.

DENSITY OF WOOD. 145

rather than upon the latter. The lightest wood is probably the
so-called ‘* cork-wood” of the West Indies (Ochroma Lagopus),
with a specific gravity of .25; the heaviest is Condalia ferrea,
specific gravity 1.3021 The specific gravity of pure cellulose ig
given by authors variously as 1.25 to 1.52;? hence the figures
noted above for the extremes of wood-density show indirectly the
degree of buoyancy imparted by the air entangled in the tissues?

412. Wood-fibre used for paper-pulp. The longer wood-cells
of many common ligneous plants can be profitably separated

1 Tenth Census of the United States, vol. ix., p. 272.

2 Ebermayer : Chemie der Pflanzen, 1882, p. 164. Husemann and Hilger:
Die Pilanzenstoffe, 1882, p. 108.

3 The following determinations were made under the direction of Professor
C. 8. Sargent, for the Tenth United States Census.

pi | 3B
Botanical name. Common name. Region. ds, ree
a Cen
es
Sequoia gigantea. Big Tree. California. 0.2882 | 18.20
Pinus Strobus. White Pine. North Atlantic. 0.3854 | 24.02
Tsuga Canadensis. Hemlock. North Atlantic. 0.429 | 26 42
ones ‘Tulipi- | Whitewood. Atlantic. 0.4230 | 26.36
era.
Taxodium distichum. | Cypress. South Atlantic. 0.4543 | 27.65
Castanea vulgaris, var. | Chestnut. Atlantic. 0.4504 | 28 07
Americana,
Abies nigra. Black Spruce. North Atlantic. 0.4584 | 28 57
Populus grandidentata] Poplar. North Atlantic. 0.4632 | 28.87
Pinus resinosa. Norway Pine. North Atlantic, 0.4854 | 30.25
Pinus rigida. Pitch Pine. Atlantic Coast. 0.5151 | 82.10
Acer dasycarpum. Silver Maple. Atlantic. 0.5269 | 32.44
Pyrus Americana Mountain-Ash. Atlantic, 0.5451 | 33 97
Betula nigra. Red Birch. Atlantic. 0.5762 | 35 91
Platanus occidentalis. | Sycamore, Buttonwood! Atlantic. 0.5678 | 35.38
Juglans nigra. Black Walnut. Atlantic. 0.6115 | 38.11
Larix Americana. Larch. North Atlantic. 0.6236 | 38.46
Ulmus Americana. White Elm. Atlantic. 0.6506 | 40 54
Fraxinus Americana | White Ash. Atlantic. 0.6548 | 40 77
Quercus rubra. Red Oak. Atlantic. 0.6540 | 40 75
Acer saecharinum., Sugar Maple. Atlantic. 0.6912 | 43.08
Fagus ferruginea. Beech. Atlantic. 0.6883 | 42 89
Quercus alba. White Oak. Atlantic. 0.7470 | 46 35
Betula lenta. Cherry-Birch. Atlantic. 0.7617 | 47.47
Quercus virens. Live Oak. South Atlantic. 0.9501 | 59.21
Guaiacum sanctum. Lignum Vite. Semi-tropical Florida. | 1.1482 | 71.24

The specimens used in the above determinations hy Mr. 8. P. Sharples were
dried at a temperature of 100° C. until they ceased to lose weight, when the
specific gravities were obtained by measurement with micrometer calipers and
calculation from the weights of the specimens.

For the purpose of utilizing histological features in the identification of
woods, classificatory tables have been prepared by many anthors. One of the
most useful of these is given in Schacht’s work, Die Ptlanzeuzelle, in which
the different wood-cells of Coniferw are described, in order to aid in the recog-
vition of the genera. Another is de Bary’s (Vergleichende Anatomie. p. 509,

10

.

146 MINUTE STRUCTURE OF THE STEM.

from each other by mechanical or chemical means for use in the
manufacture of paper-pulp. The woods which appear to have

translated in Sachs’s Text-book, 2d Eng. ed., p. 651), in which the structural
characters of many kinds of wood are given. The table will be found con-
venient for reference.
1. Wood consisting only of tracheids with bordered pits : —

Wintereie (Drimys Winteri, Tasmannia aromatica ; also Trochodendron

aralioides) : (Conifers).
2. Wood consisting of vessels, tracheids, parenchyma, and intermediate cells ;
that is, substitute or replacing cells or fibres (ersatzfasern) : —

a. With no intermediate cells ; Hex aquifolium, Staphylea pinnata, Rosa
canina, Crategus monogyna, Pyrus communis, Spiraea opulifolia,
Camellia, ete.

b. With no parenchyma ; Porlieria.

c. With both parenchyma and intermediate cells; Jasminum revolutum,
Kerria, Potentilla fruticosa, Casuarina equisetifolia and torulosa,
Aristolochia Sipho, etc.

8. Wood consisting of vessels, trachieids, fibres, parenchyma, and intermediate
cells : —

a, With no intermediate cells ; fibres unseptate ; ¢. g., Sambueus nigra
and racemosa, Acer platanoides, Pseudoplatanus, aud campestris.

b. With both parenchyma and intermediate cells ; fibres unseptate ; Ber-
beris vulgaris, Mahonia ; (Ephedra).

c. With no intermediate cells; fibres septate and unseptate; Punica,
Euonymus latifolius and Europeus, Celastrus scandens, Vitis vini-
fera, Fuchsia globosa, Centradenia grandifolia, Hedera Helix, ete.

d. With all four kinds of cells ; Miihlenbeckia complexa, Ficus.

4. Wood consisting of vessels, tracheids, fibres, parenchyma, and intermediate
cells. This isthe most common, and may be taken as the typical structure:

a. With no intermediate cells ; Sparmannia Africana, Calycanthus, Rham-
nus catharticus, Ribes rubrum, Quercus, Castanea, Carpinus sp.,
Amygdalew, Melaleuca, Callistemon sp., etc.

6. With no parenchyma ; Caragana arborescens.

c. With both kinds of cells; most foliage-trees and shrubs; ¢. g., Salix,
Populus sp., Liriodendron, Magnolia acuminata, Alnus glutinosa,
Betula alba, Juglans regia, Nerium, Tilia, Hakea suaveolens, Ailan-
thus, Robinia, Gleditschia sp., Ulex Europeus, etc.

5. Wood consisting of vessels, fibres, parenchyma, and intermediate cells : —

«. With no parenchyma; Viscum album.

b, With no intermediate cells ; Avivennia.

ce. With both kinds of cells; Fraxinus excelsior, Ornus, Citrus medica,
Platanus, ete.

6. Wood consisting of vessels, fibres, and parenchyma : —
Cheiranthus Cheiri, Begonia. Also many Crassulaces and Caryophyl-
lacece.
7. Wood consisting of vessels, fibres, parenchyma, and true woody-fibres : —
Colens Macraei, Eugenia australis, Hydrangea hortensis.
8. Wood consisting of vessels, tracheids, woody fibres, septate fibres, paren-
chyma, and intermediate cells : —
Ceratonia siliqua, Bignonia capreolata ; it is, however, still doubtful if
true woody-fibres are present.

SECONDARY LIBER. 147

been most extensively employed up to the present time are some
of the species of Abies, Betula, Populus, Tilia, and Liriodendron
Tulipifera (in the United States sometimes called ‘+ Poplar”).
The chemical processes depend (1) upon the solvent power of
caustic soda under pressure, and with heat, upon the so-cailed
intercellular substance which unites the cells, or (2) upon the
similar power of a sulphite, preferably magnesic, also under
pressure and with heat.

413. Bark. A, Secondary liber. Each yearly addition to the
inner surface of the bark is seldom plainly distinguishable from
those which have preceded it, and hence we cannot determine
positively the age of an old tree by the layers of its inner bark.
The bast-fibres of a single year often cling together in a strik-
ing manner, forming bands or strips of considerable strength,
and in a few cases, notably that of Daphne Lagetta, there are
fine meshes between the fibres, so that the inner bark seems to
he composed of layers of delicate lace.

A piece of thick bark of linden macerated for a while in water
becomes so softened that the younger portion of the inner bark
can-be easily separated into the annual layers. Strips of the
coherent fibres form the Russia matting of commerce. The
strips often measure 2—3 meters in length, 2-5 cm. in width,
and .04—.08 mm. in thickness. Scattered among the individual
hard-bast fibres there are many parenchyma cells, some of which
plainly belong to the medullary rays, and others to the fibro-
vascular bundles.

414. The bast-fibres, in a few instances, instead of being re-
tained upon the stem for an indefinite period, are separated early,
leaving the newer bast exposed. This is the case with some of
our species of Vitis, in which the bast becomes detached in the
form of long, loose shreds after the first year.

415. The crystals found in bast are very abundant. They
are chiefly monoclinic, and occur both singly — arranged in
rows — and in clusters.!

416. The appearance and distribution of the fibres of bast

1 De Bary gives the following list, taken chiefly from Sanio : —

Clusters of crystals in bast of Juglans regia, Rhus typhina, Viburnum Oxy-
coccus, V. Lantana, Prunus Padus, Punica Granatum, Ptelea trifoliata, Ribes
nigrum, Lonicera Tatarica.

Single monoclinic crystals in bast of species of Acer, and the Pomacee,
Robinia, Cladrastis, Ulmus campestris, Berberis, etc.

Single monoclinic crystals and clusters in bast of Quercus, Celtis, Asculus
Hippocastanum, Hamamelis Virginica, Morus, Salix, Fagus, Populus, Car-
pinus, Betula, Tilia, ete.

148 MINUTE STRUCTURE OF THE STEM.

are so characteristic in certain kinds of bark that they may be
used for identification. An example is given below.’

417. B, Cork, which has already been described in part in
Chapter Il , plays a very important part in the structure of older
bark. Its relations to the cells which produce it, and to the
epidermis which it displaces at an early period of its growth, will
be plain from an examination of Fig. 117. In its production
there are periodic arrests of activity just as in the case of wood,
and hence in cork-tissue of firm: texture it is possible to detect
the lines of annual demarcation. When the cork of the cork-
oak has reached a merchantable thickness (usually in ten to fifteen
years), it is removed down to the phellogen, or cork cambium,
and from this tissue new growths begin.?

1 “The liber is traversed by medullary rays, which in cinchona are mostly
very obvious, and project more or less distinctly into the middle cortical tissue.
The liber is separated by the medullary rays into wedges, which are constituted
of a parenchymatous part, and of yellow or orange fibres. The number, color,
shape, and size, but chiefly the arrangement of these fibres, confer a certain
character common to all the barks of the group under consideration.

“The liber-tibres are elongated and bluntly pointed at their ends, but never
branched, mostly spindle-shaped, straight, or slightly curved, and not exceed-
ing in length 3mm. They are consequently of a simpler structure than the
analogous cells of most other officinal barks. They are about 4 to 4 mm.
thick, their transverse section exhibiting a quadrangular rather than a circu-
lar outline. Their walls are strongly thickened by numerous secondary depos-
its, the cavity being reduced to a narrow cleft, a structure which explains
the brittleness of the fibres. The liber-fibres are either irregularly scattered
in the liber-rays, or they form radial lines transversely intersected by narrow
strips of parenchyma, or they are densely packed in short bundles. It is a
peculiarity of cinchona barks that these bundles consist always of a few fibres
(three to five or seven), whereas in many other barks (as cinnamon) analogous
bundles are made up of a large number of fibres. Barks provided with long
bundles of the latter kind acquire therefrom a very fibrous fracture, whilst
cinchona barks, from their short and simple fibres, exhibit a short fracture.
It is rather granular in Calisaya bark, in which the fibres are almost isolated
by parenchymatous tissue. In the bark of C. scrobiculata a somewhat short
fibrous fracture is due to the arrangement of the fibres in radial rows. In
C. pubescens the fibres are in short bundles, and produce a rather woody frac-
ture” (Fliickiger and Hanbury, Pharmacographia, p. 317).

2 As noticed in 246, the inner layer of cork-meristem may give rise to paren-
chyma cells containing chlorophyll. Of these cells Sanio says: ‘‘They never
become cork-cells, but are truly parenchymatous ; they are filled with chloro-
phyll, starch, and sometimes with crystals. They never become lignified, but
the wall remains as unchanged cellulose, and, in short, they are true cortical
cells. Since, then, they owe their origin to the activity of the cork-meristem,
but behave throughout their whole subsequent development precisely like the
cells of the cortex, they may be called cork-cortex cells. When they form a
distinctly defined layer, the term Phelloderm is appropriate” (Pringsheim’s
Jahrb., 1860, p. 47).

i BARK. 149

418. In some plants, notably the birch, papery layers exfo-
liate from time to time, while in some other plants, ¢. g., the
shag-bark hickory, large strips of irregular form and thickness
are detached. Owing to the mode of their formation, such sepa-
rated pieces may contain very heterogeneous elements. Of them
Sachs says:' ‘¢ Not un-
frequently the formation
of cork penetrates much
deeper [than the peri-
derm]: lamelle of cork
arise deep within the stem
as it increases in thick-
ness; parts of the funda-
mental tissue and of the
fibro-vascular bundles, or
of the tissue which after-
wards proceeds from them,
become, as it were, cut
out by lamelle of cork.
Since everything which
lies outside such a struc-
ture dies and dries up, a
peripheral layer of dried
tissue collects, which is
very various in its form
and origin. This struc-
ture, abundant in Conif-
ere and in many dicoty-
ledonous trees, is the dark, the most complicated epidermal
structure in the vegetable kingdom.”

419. Injuries of the stem. The stem, especially in the case
of plants living many years, is particularly liable to injuries, the
most frequent of which are of course the wounds left by the fall-
ing of the lower limbs. It is proper to treat here of the natural
repair of such injuries.

420. When any part of a plant suffers serious mechanical
injury by which the deeper tissues are exposed, the surface of

1 Text-book, 2d Eng. ed., 1882, p. 95.

Fig. 117, Formation of cork in a branch of Ribes nigrum, one year old; part of a
transverse section; ¢, epidermis; h, hair; b, bast-cells; pr, cortical parenchyma, dis-
torted by the increase in the thickness of the branch ; X, total product of the phellogen c;
k, the cork-cells radially in rows, formed from c in centrifugal order; pd, phelloderm
(parenchyma containing chlorophyll formed centripetally from c), (Sachs.)

150 MINUTE STRUCTURE OF THE STEM.

the wound exhales moisture very rapidly, and under ordinary
circumstances, except i in spring, soon becomes dry. As Hartig!
has shown, the drying of the exposed tissues is fatal to their
component cells, and the organic contents speedily undergo
chemical decomposition. The products of this decomposition
have been further shown by him to be fatal to neighboring cells,
and under certain conditions the mischief may progress to an
irreparable extent. But usually there is an arrest of the de-
structive action either from lack of the free oxygen necessary for
the putrefactive process, or by the protection afforded by tissues
for repair. Wounds in resinous trees are measurably hindered
from effecting much damage, owing to the exudation of liquid
resins which exclude air.

421. The smaller wounds of a plant are generally healed by
cork or by callus. 1. By cork. The superficial layer of cells at
the surface of the wound is destroyed by the injury, and dries
at once. In soft tissues the layer just below this immediately
becomes merismatic, and behaves precisely like normal cork-
meristem, covering the entire wound with a grayish or brownish
film, which is in unbroken connection with the edges of the
wound. Extreme dryness of the air, or, on the other hand, ex-
treme humidity, hinders repair by cork. 2. By callus. This is
best studied in leaves and in ‘‘ cuttings.” When a young, juicy
leaf is wounded by an incision, some of the cells at the exposed
surface may give rise to elongated sac-like bodies, which fill up
the greater part of the injured cavity, and, according to Frank,”
serve asa new epidermis: Or small cells in close apposition
may be at once formed, and completely protect the tissue below.
In ‘‘ cuttings” the callus immediately forms a swelling near the
wound. A portion of the callus may by continued cell-division
extend over the cut end, everywhere bounded on its exposed
surface by a cork layer. Activity of the cells in the callus and
around the fibro-vascular bundles soon gives rise to new parts,
for instance, roots.

422. It often happens under favorable conditions that a large
mass* of tissue is gradually formed around, and finally over, a
large injured surface.

1 Zersetzungserscheinungen des Holzes, Berlin, 1878. (Quoted by Frank.)

2 Die PAanzonieranlehetten, 1879.

8 Usually when a branch dies it remains attached for a while to the stem ;
and no wound is in fact caused until the slow desiccation of the deeper tissues
has gone on to a considerable extent, aud without exposure to atmospheric
air or outside moisture. When the branch at last falls off, the tissues around

LENTICELS. 161

423. Lenticels are peculiar breaks in the continuity of the
periderm of dicotyledons. In some cases they can be detected
under minute elevations of the epidermis of the first year, which
split open either at the end of that season or during the next,
forming a rift running lengthwise of the stem. Through this cleft

\\

ay

118

underlying tissues appear, protruding in an irregular manner,
the whole structure constituting a lenticel. According to Stabl,}
there are two types of lenticels: 1. Those with loose cells in the
rift, alternating with denser lines of cells. This is the most
common type, good examples being afforded by Alnus, Prunus,
ZEsculus, ete. 2. Those with closely united cells and with no
alternating denser lines. Illustrations can be found in Sam-
bucus (see Fig. 118), Salix, Cornus, etc. The same authority
states that in winter both of these kinds form an impervious
periderm-like layer. It appears from Stahl’s examination that
in their complete and open state they aid in the exchange of
gases between the interior and exterior of the stem. Klebahn?

its base are in a healthy condition, while the internal shaft of wood is dry, and
not liable to undergo rapid decay. The formation of a separative mass over
the wood can therefore go on to completion.

1 Bot. Zeit., 1873. Compare Haberlandt: Sitz. d. k. Akad. Wien, Band
lxxii. Abth. i., 1875.

2 Berichte der deutschen botanischen Gesellschaft, 1883, p. 119.

Fie. 118. Section through a lenticel in the periderm of Sambucus nigra: /, peri-
derm; 7, primary cortex; v, meristem, above which are the cells therefrom produced;
b, liber. (Stabl.)

152 MINUTE STRUCTURE OF THE STEM.

has lately shown that even in stems with the periderm free from
lenticels, provision for exchange of gases is secured by certain
intercellular spaces at or near the points where the medullary
rays come to the periphery of the stem.

424. Grafting. If the cambium tissue of a young shoot is
retained for a time in close apposition with that of a nearly
related plant, union of the two parts may take, place, and the
wound may heal by the natural process before described. Suc-
cess in this operation depends upon selection of suitable stock
and scion, choice of the proper season, freshness of the cut sur-
faces, and, generally, exclusion of air from the wound. The
methods of bringing the surfaces of the stock and scion together
in this operation of grafting are innumerable, but for the pres-
ent purpose may be referred to two principal types: (1) that in
which the scion, wholly separated from the plant on which it
grew as a branch, is placed in some sort of a cleft of the plant
which is thenceforth to furnish it with nourishment; (2) that in
which the scion is still retained in its connection with the parent
plant, but is bent over and a freshly cut surface kept in contact
with a cut surface of another plant, until the scion has fairly
become attached by organic union. When this is accomplished,
it is cut off from the parent plant. This type of grafting, in its
many varieties, is known as ‘approach grafting.” It takes place
in nature, as shown in the following paragraph. —

425. Two branches of one plant may become united when,
after removal of a section of bark from each, the two denuded
surfaces are kept in apposition for a time. Such unions of axial
organs are not rare. Occasionally they may take place between
two shoots at a point near the root, so that the trunk will ulti-
mately consist of a single deeply grooved stem. The union may
be between two plants of the same species, or even between
plants of different species. The attrition of two branches which
have grown against one another may suffice to wear off the bark
on both down to the cambium, and then, if their exposed surfaces
are held together for a while, union will follow. Such natural
grafts are met with frequently at the borders of forests.

426. In the kindred operation of budding, a bud with a little
of the tissue behind it is placed in a cleft in the bark of the
stock, so that the cambinm layer of the two may come into close
contact.

427. The stem may be invaded by parasitic roots at any part,
and its subsequent development seriously affected thereby. Such
invasions often give rise to swellings, distortions, etc., by which

RUDIMENTARY AND TRANSFORMED BRANCHES. 153

the structure of the stem becomes much disguised. In the case
of parasites like Phoradendron, which live for several years, a
vertical section through the stem of the host-plant shows how
complete the union is between the host and parasite. The junc-
tion has been well compared to that which takes place between
a scion and its stock, since the newer-formed tissues of both
plants become perfectly united, and their subsequent growth
goes on together.

428. The relations of the root to the stem are not complicated,
except as regards the bundles at the ‘‘ crown” of the root, or the
point where it meets the stem. When the primary structure of
dicotyledons in which the liber of the root is arranged in one
way and that of the stem in another, as shown in Figs. 92 and
112, pages 111 and 187, is followed by the formation of a true
cambium ring, the subsequent growth of root and stem is alike.
Yearly additions are made in the root in the same way as in the
stem; but owing to the unequal resistance exerted by the soil,
such increments are often very irregular.

Roots may be produced at any part of a stem where adequate
moisture and warmth are furnished; but they strike off chiefly
at nodes, and, in the case of cuttings, also at the seat of injury
where the callus is formed. Such secondary roots form on stems
in much the same manner as root-branches do upon roots.

429. Rudimentary and transformed branches present few ana-
tomical difficulties. In the structure of a branch tendril, or
runner, it is generally easy to recognize the degree of reduction
which the normal fibro-vascular system has undergone. In the
case of underground stems and branches there are often puzzling
anomalies, but they can mostly be explained by the following
facts brought out by Costantin,! who has made a special study
of a large number of rhizomes: 1. The epidermis, if present,
is modified by becoming cutinized first on its outer walls, where
it may acquire considerable thickness, and later on its lateral and
internal walls. 2. The cortex increases either by enlargement
of its cells or by their multiplication, the collenchyma diminish-
ing or completely disappearing. 3. A cork-layer is sometimes
produced at an early period, from different points in the epi-
dermis, in the cortical parenchyma, in the endodermis, in the
peripheral layer of the bundles, or, lastly, in the liber. This
replaces to a great extent the fibrous layer which is so com-
mon in aerial, but never much developed in underground stems.

1 Ann. des Se, nat., sér 6, tome xvi., 1883, p- 164.

154 MINUTE STRUCTURE OF THE STEM.

4. The cortex is developed largely at the expense of the pith.
d. There is only slight lignification of the elements. 6. There is
a great accumulation of reserve materials.

430. The relations of a branch to the main axis of the stem
seldom present any histological difficulties, the tissues of the
former being continuous with those of the latter. When a
branch breaks off close to the stem, and the portion remaining
becomes buried by stem-tissues which are subsequently produced,
a knot is formed.

431. Stems of vascular cryptogams.!| The following outline
indicates the principal points of difference between the stems of
Phnogams and those of Ferns, Equisetacez, and their allies.

I. In vascular cryptogams the fibro-vascular bundles are
closed and as a rule are concentric. 1. In Equisetum they are
slender and are arranged in a circle. From the median line of
each tooth of the ‘‘ sheath” (see Gray’s Manual) a fascicle de-
scends perpendicularly through one internode and divides at the
one below into two branches, which unite with the lateral ones
next to them. 2. In Osmundacez the arrangement of the con-
stituent parts of the central cylinder is not unlike that in certain
Conifere. 8. Lycopodiacese have the bundles largely dependent
upon the arrangement of the leaves, but the axial cylinder is
essentially cauline. 4. Ferns proper may have (@) an axial cylin-
der, or (2) several concentrically curved bundles. In either case
there may also be isolated and rather slender bundles. In both
cases above mentioned the bundles coalesce to form a very com-
plicated network, which apparently is not dependent for its char-
acter upon the distribution of the leaves upon the stem.

II. In vascular eryptogams the parenchyma in certain places
may become largely sclerotic, forming dense and often brown
masses, the constituent cells of which are sometimes considerably
elongated.

III. The epidermis in Equisetacee is strongly silicified. The
stomata in these plants are in the grooves; their development is
peculiar in that from one epidermal cell four guardian cells are
formed in one plane; but soon the two outer cells grow more
rapidly and crowd down the two inner ones, so that the latter
afterwards become distinctly below them. The epidermal cells
of Ferns frequently contain chlorophyll granules.

432. Stems of mosses. Here no true fibro-vascular bundles
are met with, but elongated cells fill their place, forming what

1 De Bary : Vergleichende Anatomie, p. 289 et seq.

DEVELOPMENT OF THE LEAF. 155

has been termed a fascicle. Comparison of these threads — if
such they can indeed be called — with the rudimentary fibro-
vascular bundles of some water-plants suggests that the former
are bundles of the simplest possible kind.

The parenchyma cells are bounded in true mosses by smaller,
‘thicker-walled cells, which do not contain chlorophyll.

THE LEAF.

433. It was shown in 322 that roots are formed under the
superficial tissues of the stem, and have these outer layers, or
derivatives from them, as coverings during at least a portion
of their growth. But leaves are never thus covered by layers of
stem-tissue ; hence they are termed exogenous productions,
while the term endogenous is applied to the manner in which
roots are formed.

434. Development. In the earliest stage of its development
the leaf is a mere papilla consisting of nascent cortex (periblem)
and nascent epidermis (dermatogen). As soon as the papilla
elongates, or becomes flattened, some of its interior cells, making
up procambium tissue (see 315), differentiate into fibro-vascular
bundles. But the procambium of the nascent leaf and that of
the cone of soft tissue constituting the growing-point of the
stem are in unbroken connection with each other; in like man-
ner the bundles which are derived therefrom are continuous, and
it is not possible to detect any line of demarcation between them.
In fact, the newly formed bundles in a young leaf appear as if
they are merely the slender prolongations and terminations of
those in the young stem.’

435. With the transverse and longitudinal enlargement of the
nascent leaf there is generally more or less curvature, so that
the outer, lower, and earlier leaves infold the upper leaves and
the growing-point of the cone. In most cases, some of the
lower leaves which thus envelop the growing-point become modi-
fied to form protecting scales; such is the ordinary structure of
buds (see ‘* Structural Botany,” page 42, fig. 83).

1 It should be remembered, however, that some of the bundles in the stem
(see 865) may be derived from procambiuin peculiar to the stem, and which
does not extend into the leaf. -Hence it is necessary to distinguish between
stem-bundles, common bundles, and leaf-traces. The former belong to the
stem alone; the common bundles are common to stem and leaf; the leaf-traces
are leaf-bundles which are in the stem and which at some point unite with
other bundles of the same kind to form common bundles.

156 MINUTE STRUCTURE OF THE LEAF.

436. The growth of the young leaf is plainly terminal at first,
— that is, new cells are added just in front of the older ones; but
it soon becomes intercalary as well, new cells being introduced
between those previously existing. According to the seat of
activity, this growth may be basipetal (the zoue of growth being
near the base of the leaf-blade) or basifugal (the zone nearer
the apex of the leaf). In most cases the base of the leaf-blade
and the stipules early attain a good degree of development, after
which the petiole appears.

For the purpose of noting the peculiar mode in which the leaf-
blade expands, the simple device suggested by Hales‘ is perhaps
as good as any. Through a piece of stiff pasteboard sharp pins
are thrust, and fastened at equal distances from each other ; for
instance, so as to form little squares of } inch side. By this sim-
ple instrument a young leaf is pierced through with holes at equal
distances; then if the leaf elon-
gates more than it widens in the
space thus covered, the holes will
separate in the direction of the
length of the leaf more than in that
of its width. The injury done to
the leaf by these small perforations
does not appear to check or other-
wise much modify its growth.

437. Fibro-vascular bundles.
The distribution of fibro-vascular
bundles in leaves has been con-
sidered in Vol. I., under ‘* Vena-
tion.” The two principal types of
distribution of the bundles, there
spoken of as ‘‘ veins ” or ‘‘nerves,”
were shown to be (1) parallel,
(2) reticulated. Parallel venation
(see Fig. 119) is characterized by
having large ‘‘ veins” or ‘‘ nerves ”
running free through the leaf (that
is, not connecting with each other),
or without any obvious anastomo-
sis; while in rediculated venation
the veins form a more or less com-
plicated network.

1 Statical Essays, vol. i., 1781, p. 344.
Fig. 119. Venation of the leaf of Convallaria latifolia. (Ettingshausen.)}

VENATION OF LEAVES. 157

120

438. Parallel venation is of two
principal kinds: (1) that in which
large nerves run in long curves
from the base to the apex of the
leaf; (2) that in which smaller
nerves run generally at right an-
gles from a main nerve (or midrib)
to the edges of the leaf. In both
these kinds of parallel venation
the veins are more or less con-
nected by means of inconspicuous
cross-veinlets and by the anasto-
mosing extremities, but some of
the veins may be free.

439. Reticulated venation is
likewise of two principal kinds:
(1) palmate (Fig. 120), in which
relatively large veins diverge from
each other at the base of the leaf;
(2) pinnate (Fig. 121), in which

121

Fic. 120. Venation of the leaf of Asarum Europeum. (Ettingshausen.)

Fic. 121. Venation of the leaf of Salix grandifolia.

(Ettingshausen.)

158 MINUTE STRUCTURE OF THE LEAF.

side veins strike off through the whole length of a strong midrib.
In both these cases the veins divide and subdivide and have
numerous cross-connections both large and small, until the ulti-
mate ramifications are in great part free.

440. Thus it appears that in both types there is abundant
communication between the veins of leaves; but in some cases,
especially in rudimentary and submerged leaves, in the leaves of
Coniferz, etc., the veins are very generally free, and few if any
cross-veinlets are met with.

441. The fibro-vascular bundles of lcaves are essentially like
those of stems (see 3865), and need no special description here.
Their extremities are for the most part tracheids, often arranged
in double rows, but their diversities of structure and arrange-
ment are innumerable. One of the more striking special cases of
these has been already shown in the illustration of a water-pore
(v, Fig. 55) ; others will be considered later (see ‘+ Insectivorous
Plants’). The tracheids which terminate the final ramifications
of the veins in leaves are in close contact with parenchyma cells.

442. According to Casimir De Candolle, the leaf may be re-
garded histologically as a branch with its upper, that is its
posterior, side atrophied:

443. The stipules have the saine arrangement of elements in
their fibro-vascular bundles as the blade, — that is, liber below
(outside), wood above (inside). But in ligules (organs which are
formed by radial deduplication) the arrangement is just the
reverse of this, —the liber is above, the wood below.

444, Parenchyma. The forms of the parenchyma cells which
constitute the pulp of leaves are: (1) spherical or nearly so;
(2) ellipsoidal, sometimes much elongated; (3) branched, some-
times stellate. Examples of these three are often met with in
the structure of a single leaf; the upper layers generally being
composed of ellipsoidal cells, the lower layers of more nearly
spherical ones, intermingled with some which are branched.

445. The arrangement of the parenchyma of the leaf-blade
is referred by de Bary? to two chief types: (1) the centric, in
which the chlorophyll parenchyma is uniformly disposed through-
out the whole organ; (2) the difacial, in which there is a de-
cided difference between the compact tissue of the upper and the
spongy tissue of the lower side of the leaf.

) Archives des sciences de Ja Bibliothéque universelle, 1868, tome xxXxil.
p- 82, ‘un rameau A face posterieure atrophide.”
2 Vergleichende Anatomie, p. 423.

PARENCHYMA OF THE LEAF-BLADE. 159

446. The centric arrangement has two modifications: (1) that
in which the whole pulp is composed of chlorophyll parenchyma,
but towards its mid-
dle plane has larger
cells with less chlo-
rophyll, and some-
times has conspicu-
ous lacune (many
grasses, Yucca fila-
mentosa, Crassula,
etc.); (2) that in
which it is composed
of layers which are
uniformly — distrib-
uted above and be-
low a middle layer
of colorless cells free
from chlorophyll, but, in succulents, very rich in sap (Aloe,

Mesembryanthemum,

| SESS SSSESSSSSESSS, ete.). In both the
FOQVOORG Oe ; SOaoagae foregoing modifica-
tions the upper layer
of the parenchyma
may be composed of
somewhat longer cells
than those below, and
to them can be applied
the term more gener-
ally given to those in
the next type, namely,
palisade-cells.

447. The bifacial
arrangement has the
denser tissue in that
part of the leaf which
is exposed to the
light. This usually consists of several layers of palisade paren-

125

Fig. 122, Leaf of Pinus Laricio. Cross-section of a part of the leaf, showing the
stomata, hypoderma, and parenchyma. The folded walls of the parenchvma-cells (see
208) are plainly shown in the cells below the resin-passage (/7C), where they have been
emptied of their contents. (Kny.)

Fic. 123. Transverse section of a leaf of Ilex Aquifolium, showing arrangement of
the parenchyma: pp, palisade parenchyma; pe, spongy parenchyma; h, hypoderma;
la, fibro-vascular bundle. Stomata are found only upon the lower surface of the leaf.
(Areschoug. )

160 MINUTE STRUCTURE OF THE LEAF.

chyma; but the aggregate thickness of these may not be so
great as that of the spongy parenchyma on the other side of
the leaf (sce 205).

448. In some plants the palisade parenchyma is found almost
as abundantly in the under as in the upper portions of the
leaves. Bessey! has shown that this is the case in the leaf of the
Compass plant (Silphium laciniatum) : ‘+ Its chlorophyll-bearing
parenchyma is almost entirely arranged as palisade tissue, so
that the upper and lower portions are almost exactly identical
in structure.” Another plant possessing substantially the same
leaf-structure is Lactuca Scariola. When its leaves are grown in
the light, they take a vertical position (and generally stand north
and south); but if grown in the shade, they are horizontal.
The leaves which are developed in the light have palisade paren-
chyma on both the upper and under portions ;* but those which
are developed in the shade have ordinary parenchyma above
and more or less stellate parenchyma below.

449. According to Stahl,® exposure of a leaf to light or shade
during development has very much to do—in the plants thus
far examined —with the form and arrangement of its paren-
chyma. ‘The leaves of the common beech afford good: material
for the study of the subject. In some cases, at least, those
which are grown in the deep shade of a grove are different in
texture from those which are formed in bright sunlight.

450. The parenchyma of the petiole is generally much like
that of the stem to which it is attached; layers or lines of thin-
walled collenchyma sometimes extending without interruption
from the stem into the petiole. In the petioles of Cycads scle-
rotic elements like those of the stem are often abundant, and are
continuous with them.*

451. In some leaves which have the power of movement the
petiole is much enlarged at its base, forming what is known as
the pulvinus. The parenchyma of this structure is sometimes
peculiar in being thick-walled on the upper side of the petiole
and thin-walled on the under. Other peculiarities will be de-
scribed under ‘‘ Movements.”

1 See also American Naturalist, 1877.

2 Pick: Botanisches Centralblatt, 1882, vol. xi. p. 441.

3 Stahl: Ueber den Einfluss des sonnigen oder schattigen Standortes auf
die Ausbildung der Laubblatter, Jena, 1883.

Haberlandt, on the other hand, does not think the effect of light in con-
trolling the character of leaf-structure is well marked.

4 Kraus: Pringsheim’s Jahrb., 1865, vol. iv. p. 305.

EPIDERMIS OF THE LEAF. 161

452. The epidermis of the leaf is continuous with that of the
stem. Its principal features have been described in Chapter IL.,
and only the following need now be recalled. 1. It may be
simple, that is, composed of one layer of cells; or multiple, —
of more than one. 2. Immediately below it may be found in
some cases one or more layers of
cells known as the hypoderma.
3. The epidermal cells are in un-

broken contact with each other ana ;

except at (1) rifts, (2) water-pores, 4 -¢4 ase eg. 2
(3) stomata. 4. Their surfaces ap mes
may exhibit nearly.every form of 4 )
trichome. dtd a

453. Glands secreting nectar
are found on different portions of
the leaves of various plants; for
example, at the junction of the
petiole with the blade (Poplar),
at the base of the petiole (Cassia
occidentalis), on the lower side of
the midrib of the leaf (cotton-
plant), or scattered over the lamina
(turban squash). Such glands are :
particularly noticeable in insec- 104
tivorous plants, as Sarracenia and
Nepenthes (see Part II.). On making a section of one of the
nectar-glands found on a young poplar leaf, the epidermis will
be seen to be transformed into a double layer of thin-walled,
elongated cells forming the secreting surface, which is charged,
together with the parenchyma lying below it, with a syrup de-
rived from the transformation of starch. At times the secretion
from a gland is so abundant that drops of considerable size
collect upon the surface of the leat, and if rapid evaporation
takes place, crystals of sugar are deposited at the gland.?

454. The leaves of submerged phenogams, for example those
of Potamogeton and Myriophyllum, possess no true epidermis ;
the parenchyma is therefore in direct contact with the surround-

1 Trelease : Nectar and its Uses, in Report on Cotton Insects (United States
Department of Agriculture, 1879), and Nectar-Glands of Populus, Botanical
Gazette, vol. vi. p. 284.

Fia. 124. Transverse section through leaf of Camellia (Thea) viridis, showing: a

epidermis; 6, branched liber-cell ; d, oil-drop; e, crystals. (Mirbel.)
il

162 MINUTE STRUCTURE OF THE LEAF.

ing water. On the external surface its thin-walled cells are in
close contact (there being nothing answering to stomata); but
in the interior of the leaf there are often lacune filled with air.
These were thought by Brongniart to be essentially the same as
those cavities found in the parenchyma of many marsh plants.

The veins of submerged leaves have no true ducts; the elon-
gated fascicles generally consisting merely of rows of elongated
cells.?

455. Roots may be produced from leaves in much the same
way as they are from stems; that is, some of the cells at the
liber may divide in such a manner as to form a protuberance
which pushes before it a part of the endodermis. As the root
thus formed emerges, the tissues are speedily produced, the wood
being continuous with the wood of the leaf, the liber with its
liber. Roots may arise naturally in some leaves by simply plac-
ing them in contact with moist earth, or they may be produced
artificially by mutilation of the petiole or lamina. Bryophyllum
calycinum affords a good example of the former; Begonia,
Peperomia, ete., of the latter mode of origin.

456. Buds may form spontaneously on the margin of leaves,
especially those in contact with a moist surface, or they may
grow from the cells under the scar where a mutilated leaf has
healed.

457. In some of these cases only the epidermal cells take
part in producing the meristem from which the bud is developed :
in others the parenchyma just below the epidermis also divides,
or the cells under the scar may produce all the axial tissue ele-
ments. Begonia is an example of the first method of production.
Bryophyllum of the second, Peperomia of the third.

It is interesting to observe that in all these cases the bud forms
without the intervention of the fibro-vascular bundles of the leaf.
The newly formed axis has fibro-vascular bundles, which may
anastomose with those pre-existent in the leaf, but usually they
are entirely distinct. The axis is, however, provided with its
own root-system, and after a time it becomes severed by a plane
of cork from the leaf which produced it.

458. Fall of the leaf. In deciduous plants the leaf separates
from the stem or twig by the formation of a plane of cells?”
cutting sharply through the petiole at or very near its base.
The dividing plane may be partially formed early in the growing

1 Brongniart : Ann. des Sc. nat., tome xxi., 1880, p. 442.
2 Called by Mohl the separative layer (Botanische Zeitung, 1860, p. 1).

FALL OF THE LEAF. 163

season, but generally it is not far advanced in development until
near the end of summer. The leaflets of the larger compound
leaves — for instance, those of Ailanthus, Gymnocladuas, Ju-
glans, etc. — afford excellent material for examining the process
of defoliation. Strong leaves of uny of the plants mentioned
are to be kept between damp (not wet) paper in a warm place
for a number of hours, when the formation of the dividing plane
can be observed. The plane is so far completed by the end of
the second or third day that the leaflets fall with the slightest
touch.

459. The strong leaves of horse-chestnut are employed by
Strasburger as material for demonstrating the process of defolia-
tion. He says that alcoholic material answers very well for the
purpose, but that it happens occasionally that the distinctive
brown color of the cells adjoining the cutting plane is nearly or
quite lost. The petiole is to be cut through in its median line,
and then several very thin longitudinal sections parallel to this
are to be carefully made and placed at once in water. In a good
preparation the cells making up the cutting plane should be
clearly seen extending from the epidermis of the petiole to the
fibro-vascular bundles. If the leaf was taken at just the right
time, the preparation should show also that the cutting plane
has invaded even the tissue of the fibro-vascular bundles. The
plane consists of one to several layers of cells, some of which
are plainly cutinized ; thus, as a rule, the place of separation is a
scar healed before the leaf falls.

It happens frequently that changes take place at the middle
portion of the cutting plane, by which its layers near the leaf
are forcibly separated from those nearer the stem ; in such cases
the leaf falls because it is forced off.?

460. The excision of the leaf usually takes place at the base
of the petiole, so that the surface of the scar is even with the

1 «The provision for the separation being once complete, it requires little
to effect it ; a desiccation of one side of the leaf-stalk, by causing an effort of
torsion, will readily break through the small remains of the fibro-vascular bun-
dles ; or the increased size of the coming leaf-bud will snap them ; or, if these
causes are not in operation, a gust of wind, a heavy shower, or even the
simple weight of the lamina, will be enough to disrupt the small connections
and send the suicidal member to its grave. Such is the history of the fall of
the leaf. We have found that it is not an accidental occurrence, arising simply
from the vicissitudes of temperature and the like, but a regular and vital pro-
cess, which commences with the first formation of the organ, and is completed
only when that is no longer useful” (Dr. Inman, in Henfrey’s Botanical
Gazette, vol. i. p. 61).

164 MINUTE STRUCTURE OF THE LEAF.

surface of the stem; but it may occur a little higher up, so that
some of the petiole remains attached to the stem’ (Rubus,
Oxalis, ete.).

461. Evergreen leaves are those which remain upon the stem
without much apparent change during at least one period of
suspension of vegetation. The leaves of some evergreens per-
sist through only one year, falling off as soon as those of the
succeeding year have fully expanded. It is not unusual in warm
temperate climates to have trees and shrubs which are normally
deciduous in colder regions retain their leaves until new ones
are produced.

Pines and spruces lose some of their oldest leaves every year,
but new ones are as regularly formed. Their branches are never
completely defoliated, but may bear at one time the leaves which
have been formed during several years.

462. The colors assumed by leaves before they fall can be
better examined after the subject of the pigment of chlorophyll-
granules has been treated in Part II.

463. The fronds of ferns and the leaves of their allies present
few peculiarities, and do not need to be here examined. The
formation in ferns of the sori, or spore-dots, the sporangia, or
spore-cases, and the spores themselves falls properly within the
province of Volume III.

464. The leaves of mosses are characterized by great sim-
plicity of structure. For their study any of the species of Poly-
trichum, or Hair-cap Moss, will answer. In these there is no
true fibro-vascular bundle; a series of somewhat elongated and
rather firm cells, known as the conducting thread, takes its place.
Upon this conducting thread the parenchyma cells are distributed
more or less regularly, on one side forming slender elevations
four or five cells in height. The cells contain chlorophyll, and
generally much starch.*

465. In the thallophytes there is no clear distinction of leaf
and axis; the tissue consists throughout of parenchyma more or
less modified. In some algze there is often a lateral parting of
the frond into segments resembling leaves; but as they are not
leaves morphologically, they need no further consideration here.

1 For full and interesting accounts of the changes which cause the fall of
the leaf, see Mohl’s paper in Botan. Zeitung, 1860, p. 1, and also Van Tieghem
and Guignard in Bull. Soc. bot. de France, 1882.

2 Tn Strasburger’s Botanische Practicum, p. 304, the student will find a
full and interesting account of the structure of the leaves of Polytrichum and
Mnium.

WORKS OF REFERENCE. 165

In the examination of the tissues of the organs of vegetation
the student is referred to the following works : —

De Bary. Vergleichende Anatomie (Leipzig, 1877). An octavo volume
of about 660 pages, of which an excellent English translation is newly pub-
lished under the title, ‘Comparative Anatomy of the Vegetative Organs of
Phanerogams and Ferns,” by A. De Bary. Translated by F. O. Bower and
D. H. Scott, 1884. This exhaustive treatise gives all needful references to
the literature of the subject up to 1876.

Moun. Vermischte Schriften. This is a collection of Hugo von Mohl’s
most important works, which have appeared from time to time in various
journals.

Straspurcer. Das botanische Practicum (Jena, 1884). This work, of
which an English translation is promised, is of very great use both to beginners
and advanced students of Histology. The directions for procuring, preserving,
and using material are explicit, and for the most part are conveniently ar-
ranged. The volume, of more than 600 pages, is divided into separate studies,
such as the structure of the bast and wood of the pine, the anatomy of a few
common leaves, etc.

Ourver. Bibliography of the Stems of Dicotyledons (Natural History Re-
view, 1862 and 1863). A citation of the more important works on the stems
of different dicotyledons, arranged according to the natural fainilies.

For a treatment of the anatomy of the organs of aquatics and parasites, the
fully illustrated work of Chatin may be consulted.

Those curious to examine the diverse and now mostly abandoned views
regarding the growth and structure of the stem, will find much of interest in
the works of Du Petit Thouars and of Gaudichaud. An account of these and
other views will be found in Schleiden’s ‘‘ Principles of Botany” (1849).

CHAPTER IV.

MINUTE STRUCTURE AND DEVELOPMENT OF THE
FLOWER, FRUIT, AND SEED,

THE FLOWER.

466. In Volume I. Chapter VI., it has been shown that a
flower is to be regarded as a modified branch with very short
internodes and with the foliar expansions assuming forms unlike
those of ordinary leaves. Jn the outer circle — the calyx — the
parts have frequently the texture and color of foliage ; but in all
the other circles of the flower they are notably metamorphosed.
Notwithstanding their disguises, the parts of the flower are iden-
tifiable as leafy structures arranged upon an axis. ‘On the care-
ful examination of flower-buds the homology between all their
parts and those of a leaf-bud becomes evident. In fact, in their
earliest state it is impossible to discriminate between these two
kinds of buds. Each has a rounded or cone-like: extremity,
upon which are disposed at definite points the papillze which are
to develop into foliar organs. In one, these papillae become
green leaves; in the other, the parts of a flower.

467. Two features in the development of flowers require
special attention ; namely, the sequence in which the organs are
produced, and the order in which the histological elements make
their appearance. But it is not well in any given case to under-
take the examination of the development either of the organs or
of the tissues which compose them, until the student has made
himself familiar with the characters of the full-grown flower.

468. Undeveloped racemes afford the best material for the
study of the developing organs of the flower, and it is generally
possible to find in a single young cluster flowers in all the earlier
stages of development. There are two good methods of pre-
paring the material for the compound microscope: (1) the whole
raceme, first decolorized by absolute alcohol and then softened
by glycerin, is to be dissected under a simple lens, and the sepa-
rate flowers are to be bleached with sodic hypochlorite; or (2) the

DEVELOPMENT OF TIT FLOWER. 167

very tip of the raceme is to be cut squarely across and placed
with a drop of water under a cover-glass, when some of the young-
est flowers can be seen cither standing vertically or slightly in-
clined. The aircan bedrawn
out from the specimen by
placing the slide for a min-
ute under the air-pump ; the
outlines of the floral organs
will then be distinct.

469. Astill better method
is to make tolerably thick
vertical sections of separate
flowers, one of which in
each flower must be through
the median line; and then,
arranging the sections! in
their proper sequence, clear them for examination either by the
use of potassic hydrate (as directed in 24), or by the following
method, recommended by Stras-
burger as applicable to many cases
of thick masses of soft tissues :
Treat the part first with absolute
alcohol for a day or two, and then
place it in concentrated carbolic
acid, after which it becomes clear.
For the carbolic acid either of the

126 following may be substituted, —

(1) three parts of oil of turpen-

tine and one part of creosote, or (2) equal parts of alcohol and
creosote.

By any one of these methods it is generally possible to obtain
preparations of sufficient clearness to exhibit in optical section
all the internal tissues.

1 Pfeffer advises that the young flowers should first be tinged with anilin
blue, and then imbedded in a strong solution of gum-arabic (to which a little
glycerin has been added to prevent brittleness of the mass on drying). Then,
when the gum is dry, sections can be easily cut in any direction.

Fig. 125. Lysimachia quadrifolia. Flower seen from the side, and somewhat ob-
liquely, the calyx being removed. At this period the parts of the corolla have not
coalesced: sp, place where the excised sepals were; p, petal; st, stamen. (Pfeffer.)

Fic. 126. Lysimachia quadrifolia. Thin longitudinal section through the median
line of a flower, in which the organs are beginning to form. Before the sinuses of the
calyx, as well as before its lobes, cell-division has taken place on all sides; for instance,
at st,n, and w. (Pfeffer.)

.

168 MINUTE STRUCTURE OF THE FLOWER.

470. The fully grown flower of Lysimachia quadrifolia is thus
characterized: Calyx hypogynous, deeply 5-parted, the lobes
valvate or very slightly imbricated in the bud: corolla hypogy-
nous, wheel-shaped, and deeply 5-parted with hardly any tube,
its lobes convolute in the bud; no teeth between the lobes of the
corolla; lobes of the corolla longer than the narrow lanceolate
lobes of the calyx; stamens of unequal length, plainly united at
the base, inserted opposite the lobes of the corolla, glandular ;
anthers barely oblong; ovary one-celled, surmounted by an un-
divided style and stigma, and containing 10-15 ovules on a
central placenta.

st

Ny
ASTANA
SAAN iv

a Unaseise
SO

127

Fig. 126 shows the appearance of a very young flower of this
species ; on the rounded
or somewhat flattened
apex of the axis minute
elevations are seen, the
outer being the nascent
sepals. Fig. 127 shows
the flower in a more ad-
vanced stage. Fig. 128
represents a portion only,
the right, in a still more
advanced condition.
Fig. 129 exhibits all the
organs of the flower, so
far as they can be shown

Fie. 127. Lysimachia quadrifolia. A longitudinal section through a flower some-
what more advanced than in Fig. 126; the letters are the same as in Fig. 128. (Pfeffer.)

Fig. 128. Lysimachia quadrifolia. Longitudinal section through an elevation which
is considerably advanced before the appearance of the petals: st, stamen; 7, cells
where the petals will appear. (Pfeffer.)

Fig. 129. Lysimachia quadrifolia. A longitudinal section through a flower in which
all the organs are well developed, and even the parts of the ring by which the corolla-
lobes are to coalesce have begun to grow: s7,sepal; p, petal, or corolla-lobe ; s¢, stamen ;
g, ovary; c, placenta; sp. u, and p. u, the tissue uniting the parts of the calyx and corolla
respectively. (Pfeffer.)

ORDER OF APPEARANCE OF FLORAL ORGANS. 169

in a single longitudinal section. Comparison of these figures
gives a clear idea of the sequence in which the organs make
their appearance; namely, in acropetal succession, — that is,
the younger or newer are always nearest the extremity.

471. According to Payer, the sepals always precede the petals,
the petals the stamens, and the stamens the pistils, in time of
appearance. But in a few cases, of which Lysimachia is one,
it may happen that a given circle of organs is somewhat de-
layed in forming; for instance, in the figures the stamens are
seen as considerable protuberances before the petals are clearly
outlined. This fact has been considered by some to indicate
that the corolla in such cases consists of an intercalated whorl
between two other whorls already somewhat developed. Buta
careful examination of Lysimachia and most other cases shows

130

rather that the petals or the corolla-lobes are laid down in their
proper sequence, but that they are temporarily outstripped by
the sepals and the stamens.

The appearance of the forming flower when seen in vertical
section is shown in Fig. 180, and a perspective view is given
in Fig. 125, exhibiting the late-appearing petals and the much
larger stamens.

472. Since the several organs of the flower are modified
leaves symmetrically arranged on an axis, the histological con-
stituents of a leafy branch will be found in the flower, albeit
much modified in some of their characters. These constituents
are, (1) a framework of fibro-vascular tissue, upon which is
extended (2) parenchyma, covered by (3) epidermis.

Fig. 130. Lysimachia quadrifolia. Longitudinal section through a flower in which
the corolla is just appearing. The elevation on the right has been cut through exactly
in the median line, while that on the left has been cut on itsedge. Letters the same as
in Fig. 129. (Pfetfer.)

170 MINUTE STRUCCURE OF THE FLOWER.

473. The fibro-vascular bundles of the flower are essentially
the same as the collateral bundles found in ordinary green
leaves, except that their clements are usually more delicate in
texture, and in the inner whorls of organs very much reduced.

474. The parenchyma calls for no special remark beyond aliu-
sion to the fact that some one of the different kinds of internal
glands is frequently associated with it.

475. The epidermis has stomata, — which are generally rudi-
mentary, —and most of the forms of trichomes. One of the most
interesting peculiarities of structure presented by the parts of
the flower is found in the papillar outgrowths alluded to in 222.
These are of course minute and short hairs, which, owing to
their abundance, impart a velvety appearance to the part on
which they occur. This appearance is well shown by the petals
of a very large number of the flowers most common in cultiva-
tion.

476. The cuticle of the epidermal cells of the more delicate
petals is sometimes very distinctly striated in an irregular man-
ner. The walls of the cells generally have a sinuous outline.

477. The colors of petals and other colored parts of the
flower are dependent either on the presence of corpuscles
(the colored plastids) or of matters dissolved in the cell-sap.
The following account of the coloring-matters in the very com-
mon Viola tricolor is condensed from Strasburger.

A vertical section through a petal exhibits the epidermis of the
upper side as consisting of elongated papillz, while that of the
lower side has only slightly rounded ones. Just below the epi-
dermis of the upper side there is a layer of compact cells, under
which are several rows of smaller cells with conspicuous inter-
cellular spaces. The cells of the epidermis of both sides contain
violet sap and yellow granules; the layer of compact cells under
the epidermis of the upper side contains only yellow granules.
The striking diversities in color presented by different parts of a
given petal depend wholly upon combinations of these two ele-
ments of color; namely, violet sap and yellow granules. In
some places which are devoid of either of these elements there
are white spots; at these places the light is refracted and re-
flected by the intercellular spaces which contain air. If the air
is removed by pressure, the spots will become transparent.

478. The cell-sap in the parts of the flower may have almost
any color, especially shades of red and blue; from this sap the
coloring-matter sometimes crystallizes in the forin of short and
slender needles ; for instance, in Delphinium Consolida.

DEVELOPMENT OF STAMENS. 171

479. Development of the stamens. The following outline may
serve as an introduction to the study of
the development of the stamens. At
first, the stamen exists as a mass of
homogeneous parenchyma; later, a del-
icate fascicle, continuous with one in the
filament, becomes differentiated in one
part of the stamen, the connective. Four
longitudinal ridges appear on the an-
ther, which coincide with four lines of
large cells within. These cells give rise
to the mother-cells of the pollen and to
the very delicate pollen-sac.!

480. The mother-cells of the pollen
have at first thin walls, but later these
become irregularly thickened. In a
large number of cases — many mono-
cotyledons, and most if not all dicoty-
ledons — the nucleus of a mother-cell divides into two nuclei,
which themselves divide
at right angles to the
plane of the first division,
thus producing four nuclei
forming a_ tetrahedron.
Cell-walls are next formed,
and four cells are pro-
duced, which are called
the tetrad. After the
mother-cells of the pollen
have been changed into
tetrads, the mass of pro-
toplasm in each of the
cells of a tetrad becomes
covered, as Strasburger
has shown, with a new

1 The cells which make up the layer forming the pollen-saec are known,
collectively, as the Archesportum. The epithelium which lines the pollen-sae
has been termed the Tapetwm.

Fig. 131. Orchis maculata. A pollen-mass in process of enlargement, with the anther-
wall on the outside: ep, epidermis; 1, layer of cells under the epidermis remaining un-
divided ; 2’ and 3’, layers arising from division; 3’, the endothecium. The little mass
cm, formed by the mother-cells, is surrounded by a thickened wall. 4°. (Guignard )

Fira. 132. 4, transverse section of a young anther of Mentha aquatica; B, a fourth
of this magnified; C,section through a young anther of Symphytum orientale; D, a
fourth of this magnified. The dotted lines in 4 and C show the part. taken for exami-
nation. £, section of a young anther of Leucanthemum vulgare (Warming.)

172 MINUTE STRUCTURE OF THE FLOWER.

cell-wall, the proper cell-wall of the pollen-grains. This wall
may be variously marked, sculptured, and cuticularized, giving
rise to the characteristic forms and features of the grains as
they are met with in the mature flower. In gymnosperms, the
development of pollen-grains differs from that described in some
particulars which are interesting chiefly from their resemblance
to what occurs in the higher cryptogams.

481. The stigma is a surface formed of peculiar cells which
secrete a viscid, saccharine matter, slightly acid in reaction. In
some cases the walls of the stigmatic cells undergo the mucilagi-
nous modification (Solanum, etc.). The wide differences which
exist in the character of the cells of the stigma are illustrated by
the following examples: (1) cells with no marked papille, as in
Umbellifere ; (2) papillose, as in Salvia, Convolvulus, Spirzea ;
(3) hairy, as in Hypericum, Geranium ; (4) with compound hairs,
as in Reseda. In some of the above the cells are rather loosely
aggregated. while in others they are much more compactly com-
bined. Below the stigma the style often has collecting hairs, as
in Composite, Campanulacee, etc. (see Volume I. page 222).

482. The style is a prolongation of the ovary, and shares with
it its fascicular system. In the interior there is a slender thread
of loose tissue made up of thin-walled cells containing consider-
able food-material, starch or oil, etc. The cell-walls often pass
into the mucilaginous condition. The style is sometimes tubular,
and lined with the tissue just described.

483. The simple ovary is a modified leaf-blade provided with
epidermis, parenchyma, and a fascicular system. The epidermis
of the outside of the ovary, and that which lines its cavity, may
have all the characters of ordinary epidermis ; stomata and hairs
may be present, the latter often being mere papillse, which upon
the ripening of the ovary into the fruit become long hairs.

484. In the interior of the ovary there is frequently a pecul-
iar modification, either of the epidermis itself or of the sub-
jacent parenchyma as well. In such cases very loose tissue,
sometimes appearing as if composed of felted hairs. lines the
cavity of the ovary (or is found at some one portion of it). The
walls of this tissue may undergo the mucilaginous modification
either in whole or in part. Its cells contain a considerable
amount of food-materials (oil and starch). This loose tissue,
together with that of the same character found in the style, is
known as conductive tissue, and serves as a path of least resist-
ance for the penetrating pollen-tuhe (see Part IT.).

485. The distribution of the fibro-vascular bundles in ovaries

FIBRO-VASCULAR BUNDLES OF THE OVARY. 173

is of much interest, and can best be examined under the two
heads of ‘* Simple Pistils”? and ‘* Compound Pistils.”

486. Simple Pistils. ‘he tibro-vascular bundle consists of
wood and liber running through the median line of the carpellary
leaf, — that is, through the dorsal suture. Two branches are
given off by this bundle not far from the base of the leaf, near
its two united margins, — that is, at the ventral suture.

487. he folded carpellary leaf has incurved margins ; so that
whatever the arrangement of the wood and liber may be in the
median line of the leaf, the reverse will be found at the margins.
Thus in each of the three carpels shown in Fig. 133 a, the fibro-

vascular bundle running through the dorsal suture has liber on its
outside (the unshaded portion) and wood on its inside (the dark
portion). But in each of its branches at or near the ventral
suture liber occurs on the inside (that is, nearest the centre of
the flower) and wood on the outside.

488. Compound Pistils. If several carpels unite to form a
compound ovary, the same inversion of the order of the parts of
the bundles (as shown in Fig. 133 @) will be seen when the
bundles at the centre of such an ovary are compared with those
at its periphery (see diagrams 6 to /, Fig. 133).

Fra. 133. Transverse section of superior ovaries, showing the arrangement of the
fibro-vascular bundles of carpels: @, Eranthis hyemalis; b, Hyacinthus orientalis;
c, Tulipa Gesneriana ; d, Impatiens tricornis; e, Anagallis arvensis; /, Lychnis dioica,
(Van Tieghem.)

174 MINUTE STRUCTURE OF THE FLOWER.

489. But if the ovaries, instead of being superior, as those in
Fig. 133, are inferior, as those in Fig. 134, further complications
are caused. The fibro-vascular bundles of the several floral
whorls united with the pistil are distributed in circles in the
parenchyma tissue of the ovary. Thus in Fig. 134 a, we find
five such circles, corresponding to the calyx, corolla, stamens,
and dorsal and ventral sutures of the carpel. The bundles in
Fig. 184 @ are arranged in radial lines from the centre outwards ;
the six bundles nearest the centre of the ovary are those of the
ventral sutures, and have wood outside and liber inside; in the
next circle the three with reverse arrangement of elements are
those of the dorsal sutures from which the bundles just spoken
of branched. In Fig. 134 6, all the fibro-vascular bundles save
those of the carpels
are united to form a
single circle, thus giv-
ing rise to the three
circles of bundles
seen in the cross-
section, and at the
base of the ovary
even these did not
exist separate. In
Fig. 134 c, the bun-
dles of all the floral
whorls are blended
for a considerable
height in the ovary ;
finally, the bundles
of the ventral sutures
become separated
from the rest, which
continue united
throughout, forming
the large bundles seen on the periphery of the ovary in Fig.
134¢. The arrangement of the bundles in this figure should be
compared with that in Fig. 133.

490. The structure of the peduncle and the pedicels is sub-
stantially the same as that of the stem, and the structure of

Fic. 134 Transverse section of the inferior ovary, showing the arrangement of fibro-
vascular bundles both in the carpels and the external parts of the flower: a, Alstroe-
meria versicolor, the fascicles of the whorls independent; 6, Galanthus nivalis, the
fascicles no longer so distinctly radial; c, Campanula Medium, the fascicles of the
whorls blended. (Van Tieghem.)

DEVELOPMENT OF THE OVULE. 175

the bracts is much like that of the leaf; therefore these need not
be specially considered here.

491. Ovules are normally formed at definite points or lines
upon the ovarian wall, which answer to the edges of the carpel-
lary leaves. The funiculus arises as a slight elevation produced
by the multiplication of a cell or a group of cells under the
epidermis ; in the centre of this elevation, and also under the
epidermis, further development produces a spheroidal or cone-
like mass, —the nucleus. Then, a little later, cells at the base
of the nucleus begin to produce a cylinder (the inner integu-
ment), and shortly after, a second one is formed below and
outside this (the outer integument). Subsequent development
carries the outer integument quite up and around the inner one,
and the nucleus; leaving a small opening (the foramen).. For
peculiarities in the morphology of the ovule, and for cases in
which one or both integuments may be wanting, see Volume I.
page 278.

492. The funiculus has a collateral fibro-vascular bundle,
having its median plane coincident with that of the ovule. The

y,
<a

bundle is surrounded by parenchyma and epidermis. It is fre-
quently prolonged into the integuments, being there more or less
branched.

Fic. 135. Development of the ovule of Aristolochia Clematitis. 4, young ovule in
vertical section; B, same, more advanced; ti, internal integument forming; C, a later
stage of same; ¢i, internal integument; fe, external integument forming; D and £,
later stages of nucleus, to be described in Part II. (Warming.)

176 MINUTE STRUCTURE OF THE FRUIT.

THE FRUIT.

493. The fruit is the ripened pistil. But, as shown in Vol-
ume L, “itis a loose and multifarious term, applicable alike to
a matured ovary, to a cluster of such ovaries, at least when
somewhat coherent, to a ripened ovary with calyx and other.
floral parts adnate to it, and even to a ripened inflorescence when
the parts are consolidated or compacted.”

494. Histologically considered, fruits present few difficulties,
although the changes in form which a pistil undergoes as it ripens
are not greater than the changes which it may suffer in minute
structure. These histological changes are referable to a few
simple kinds: (1) a great development of sclerotic elements, seen
in the harder dry-fruits and in the putamen of all stone-fruits ;
(2) a large increase in the amount of soft-walled parenchyma,
containing sap, as in the pulp of all fleshy fruits ; (3) a consid-
erable development of color, especially in the superficial parts.

495. Sections to exhibit the structure of the very hard parts
of fruits are made most easily by carefully grinding the parts
on a fine oil-stone. First, a fragment of the hard shell of a nut
or of the putamen of a drupe is obtained by means of any strong
cutting instrument, and a flat surface parallel to the plane of
the section desired made by a clean file. On a glass slide a
drop of Canada balsam is placed, and heated until the more
volatile portion is expelled (see 111). Then the flat side of the
object just prepared is held upon this balsam until the latter
becomes cool and hard; and when thus securely fastened, the
specimen is rubbed down on an oil-stone to any required de-
gree of thinness. It is removable from the slide by oil of
turpentine, and can afterwards be mounted in a fresh portion of
balsam or of benzol-balsam (see 112).

496. The contents of the parenchyma cells of fruits depend
very largely on the degree of maturity of the fruit. Changes in
the contents go on from the formation of the fruit until it is fully
ripe. In some of the more common cases these consist largely
in the production of various sugars, especially that which is
known as fruit-sugar; and organic acids, for instance, citric,
tartaric, and malic acids. A consideration of these changes
belongs to Part IT.

497. The coloring-matters in fruits, like those in flowers, are
either color-corpuscles (chromoplastids), or substances dissolved
in the cell-sap. In a few cases the walls of the cells them-
selves have more or less color,

COLORING-MATTERS OF FRUITS. 177

498. The berries of a common house-plant, Solanum Pseudo-
capsicum, furnish excellent material for the examination of the
coloring-matters of fruits. The following account, condensed
from Kraus,! will show the essential characters of the color-
granules in this case, and it should be compared with what has
been already said about the structure of chlorophyll granules
and leucoplastids (168 e¢ seg.), as well as with the account of
the chromoplastids in the parts of flowers (477).

A section through the ripe pericarp shows that it consists of
twenty to thirty or more layers of cells, in most of which color-
granules occur. In the outermost cells the granules closely
resemble both in form and structure ordinary granules of chloro-
phyll. In some of the granules the coloring-matter is evenly
diffused through the whole mass, while in others it is confined
to some one part, the rest of the granule remaining without color
of any kind. In these cases the colored and the uncolored parts
are not very sharply divided from each other.

499. Other granules less like chlorophyll-granules occur, in
which there is a sharp demarcation between the colored and
uncolored parts; such have been shown to be vacuolar, the
vacuoles assuming widely different shapes. These are abundant
in the cells which lie five to eight layers, or rather more, from
the outside.

In some of these the colored portion appears spindle-form or
sickle-form, in others curved twice, like the letter S. It fre-
quently happens that several of these long granules are placed
end to end, forming an irregular chain.

500. In the part of the berry which envelops the seeds the
color-granules are extremely slender, and needle-shaped.2 All
of the granules lie in the protoplasm; usually in greatest
number in that lining the walls, and immediately around the
nucleus,

501. Occasionally in the larger pericarp-cells roundish col-
ored objects are met with, which close examination shows are
nothing but vacuoles in the protoplasm of the cell filled with
colored sap; sometimes these have been mistaken for the
granules themselves, but they can usually be distinguished from
them without difficulty, on account of the distortion which they
undergo upon slight pressure.

1 Kraus: Pringsheim’s Jahrb., 1872, p. 181.
2 Trécul: Ann. des Se. nat., sér. 4, tome x, 1858, p. 154. Weiss: Sitz. d. k
Akad. Wien, 1864 (Band 1.), and 1866 (Band liv.).
12

178 MINUTE STRUCLURE OF THE SEED,

THE SEED.

502. The ripened ovule is the seed. In ripening, the ovule
undergoes changes in the structure both of the integuments and
the nucleus. The integuments of the seed answer morphologi-
cally to the primine and secundine of the ovule; the outer being
the testa, or seed-shell, — also called spermoderm or episperm,
—the inner the tegmen, or endopleura. The nucleus of the
seed also answers to the nucleus of the ovule. The morpho-
logical relations of the different parts of the seed have been
sufficiently treated in the first volume, ‘+ Structural Botany,” and
therefore only the histological features will now be presented.

503. Considered as a whole, the testa varies greatly in con-
sistenee; it is in some cases as dense as any sclerotic tissue.
while in others it is pulpy, and in others still, membranaceous.
But it is usually divisible under the microscope into two or more
layers, which are not constant in their characters.

504. The ordinary layers met with in the seeds of most
agricultural plants have been described hy Nobbe * in the follow-
ing terms: 1. The hard layer, composed generally of palisade
or staff-like cells of considerable firmness. In Leguminosee it
is the external layer, and its exposed surface is cuticularized.
In flax and species of Brassica, it is the second, in cabbage
and mustard, the third layer. In a few cases the cells of this
layer are tabular instead of staff-shaped. 2. The mucilaginous
layer, not present in all the common agricultural seeds, is com-
posed of cells whose walls have the power of swelling greatly
when they are placed in water. This layer is sometimes found
in the outer part of the testa, sometimes in the inher. 3. The
pigment layer, which imparts characteristic colors to the coats of
the seeds of many plants, is not constant in the form of the cells.
The color may reside in the cell-wall, or in the dried contents of
the cell. Sometimes a few pigment-cells are scattered among
others of a neutral tint, and even among those which cannot be
said to have any proper color at all. In some cases one of the
other layers may contain more or less color. In a few other
instances the color is not dependent on a pigment layer; for, as
Frank ? has shown, in the steel-blue seeds of species of Preonia
the color is purely a result of reflected light, and is in no wise
due to the presence of any true coloring-matter. The dried
seeds are dark red or dark brown; but when thoroughly moist-

1 Handbuch dev Samenkunde, p. 73. ? Botanische Zeitung, 1867.

HAIRS. 179

ened with water (or better still in a fresh state), they are dis-
tinctly blue. 4. The protein layer, the cells of which contain
granular albuminoid matters.

The layers just described are different in different seeds, and
sometimes different in
different parts of the
same seed-coat, so that
the division bas really
little utility.

505. The external in-
tegument or testa may
have well-developed hairs,
as has been shown in Vol-
ume I. p. 306. Only one
of these cases of hairs
can be here described;
namely, those which form
the felted covering of cot-
ton-seeds, and which are
the ‘‘ cotton” of commerce. These are slender cells with col-
lapsed walls. As they ap-
proach maturity, the cells
become more or less twisted ;
the resulting spiral is that
which imparts to cotton its
value as a material for spin-
ning. Some other seeds,
notably those of species of
Asclepias, have long and
strong hairs, but none of
these have any spiral twist
which fits them for textile
purposes.

Regarding the size of cot-
ton ‘‘fibres” (hairs of the
seed), the following meas-
urements by Ordway are of interest: Maximum length in the
‘‘sea-island” variety, about two inches (five centimeters) ; in

Fig. 136. Cross-sections of cotton-fibres. A A, unmature fibres; BB, half-mature
fibres; CC, fully mature fibres; D, section of fibre, showing laminated cell-walls.
(Bowman.)

Fie 137. A, Glassy, structureless fibre; B, thin, pellucid, immature fibre; C, half
mature fibre, with thin cell-wall; D and £, fully mature fibre, with full twist and well-
Gefined cell-wall. (Bowman.)

180 MINUTE STRUCTURE OF THE SEED.

upland or ‘‘ short-staple” cotton, a little over one inch and a
half (three and three-fourths centimeters). The greatest width
of fibre was found to be .0013 inch. A single fibre sustained
without breaking a weight of 150 grains.?

506. It has been shown in Volume I. that the seed-coats of
many Polemoniacez, etc., are furnished with microscopic hairs,
‘*which come usefully into play in arresting farther dispersion at
a propitious time or place. . . . The testa is coated with short
hairs, which when wetted burst, or otherwise open and discharge
along with mucilage one or more very attenuated long threads
(spiricles) which were coiled within. These protruding in all
directions, and in immense numbers, form a limbus of considera-
ble size around the seed, and evidently must serve a useful end
in fixing these small and light seeds to the soil in time of rain,
or to moist ground, favorable to germination, to which they may
be carried by the wind.” The best example of this structure is
afforded by the genus Collomia; in this the spiricles are long
and very numerous.

507. The nervation of the seed-coats furnishes in many
cases excellent diagnostic characters, but they need no special
remark histologically. The forms of branching of the fibro-
vascular bundle of the funiculus indicate that the ovule and
seed are of the nature of leaflets on the margin of the carpellary
leaf?

1 The above measurements are approximate; those which follow are the
exact determinations as they are given by Professor Ordway in the Tenth
Census of the United States.

Length of fibre. Maximum length found in the ‘‘sea-island” variety of
South Carolina, where it was 1.996 inches. The maximum length of the
upland or “short-staple” cotton was 1.669 inches. The minimum of length
(0.695 inch) was found in North Carolina cotton, grown on a light, sandy
loam soil.

Width of fibre. The widest (rii¥¥so inch wide) was quite short (0.945 inch).
By far the largest number of wide fibres come from uplands. The ‘‘sea-island”
variety had a width of 7583850 inch.

Strength of fibre. The strongest specimen examined had a breaking weight
of 149.4 grains. Professor Ordway mentions some instances which lead him to
think that the strength of the fibre may hold some relation to the amount of
phosphoric acid in the soil where it is grown.

Weight of seeds and lint. (Maximum weight for five seeds with lint at-
tached, 22.14 grains.) Light-weight seeds appear to come from sandy soils,
heavy-weight seeds from heavy and productive soils.

2 The reader is referred to a memoir by Le Monnier, in Ann. des Se.
nat., sér, 5, tome xvi., 1872, p. 233, and one by Van Tieghem in same Jonrnal,
1872.

ce

ALBUMINOUS AND EXALBUMINOUS SEEDS. 181

508. The so-called ‘‘grains” of the ccreals are fruits instead of
seeds ; the accompanying figures exhibit, therefore, not only the

CI
wee

structure of the integuments of the seeds, but also of the ripened
ovarian wall.

509. As shown in the ‘ Structural Botany,” page 309, the

nucleus of the seed consists of the embryo and its supply of

abe food. If the store of food is wholly

; within the tissues of the embryo, the

Ayu
Bey

sco

we= arose
ir}
Bogor

seed is said to be exalbuminous ; if partly outside of the embryo,
as, for instance, in the cereals here figured, it is said to be
albuminous. The albumen is the supply of food in the nucleus
of the seed which is not stored i1 the embryo itself.

Fic. 138. Cross-section from the periphery of the fruit of Zea Mais, highly magni-
fied: a, fruit-capsule; b, seed-coat; c, adherent cellular layer; d, starch containing
albumen of seed. (Berg and Schmidt.)

Fig. 139. A cross-section from the periphery of the fruit of Avena sativa, highly
magnified: a, chaff; b, fruit-capsule with the seed-coat; c, adherent cellular layer ;
d, starch containing albuminoid parenchyma. (Berg and Schmidt.)

Fic. 140. Cross-section from the periphery of the fruit of Oryza sativa, highly mag-
nified: a, chaff; ), fruit-capsule with seed-coat; c, adherent cellular layer; d, starch
containing albuminoid parenchyma, (Berg and Schmidt.)

Fic. 141. Cross-section from the periphery of the fruit of Hordeum vulgare, highly
magnified: a, chaff; b, fruit-capsule with the seed-coat; c, adherent cellular layer;
d, starch containing albuminoid parenchyma (Berg and Schmidt.)

182 MINUTE STRUCTURE OF THE SEED.

510. The embryo may exist as a cluster of parenchyma cells
without any clear distinction of parts, or it may possess a defi-
nitely formed axis and leaves (see “ Structural Botany,” p. 311).

The microscopic structure of the nucleus has been illustrated
in put by the figures of the grains of cereals (see also Fig. 22,
on page 47), aud it has been considered also to some extent in
the descriptions of the nascent root and the nascent stem in the
embryo. The study of the development of the embryo within
the seed helongs to a special subject, which will be treated in
Part Il. under ‘+ Reproduction.” It therefore will suffice here to
state that the parenchyma cells of which the nucleus is composed
contain food materials and protein matters in large amount.

511. The proper food materials in seeds are chiefly oils and
starches. ‘The seeds of a large number of plants have been ex-
amined by Nigeli? with reference to the occurrence of starch, and
the following facts are taken from his extensive treatise : —

Gymno- ;Monocoty-| Dicotyle- Total
fuer, | dete | ie | Pamilc
Phenogams containing | eS | e HUE NIERS
(Inallspecies ~ 3 20 190 213
oh } In a majority F 10 10
No starch in the seed 49), pat : ; eee ; 10 10
Inasmall number a i 1 2 3
Starch in the albumen, jan nllispecles : uw 1 a
notin the embryo In halfe ss ' a te 3 3
Starch in the embryo, aus

not in the albumen { Ayal species: 7 7
In all species 4 1 15

Starch in the albumi- [In a majority 1 1
nous embryo Inhalf. . . . 5 5
(Inasmallnuniber} . . 13 13
Starch in the embryo 4 In all species 1 1 2
and albumen a ao ajcrity ‘ at ps

{ In all species 2 3 5
Starch in the seed j In a majority 1 3 4
throughout In half. ie 8 8
( In asnall number 13 13

512. The protein granules in seeds are classified by Vines * as
follows : —

1 Die Starkekérner, 1858, p. 387.

2 Proceedings of the Royal Society, vols. xxviii., xxx., and xxxi, On
page 62 of the volume last mentioned the following table of seeds and their
aleurone grains is given : —

J. Soluble in water ; P:onia officinalis (type), Ranunculus acris, Aconitum
Napellus, Nigella damascena, Helleborus foetidus, Amygdalus com-
munis, Prunus cerasus, Pyrus malus, Leontodon Taraxacum, Dipsa-
cus Fullonum, Ipomeea purpurea, Phlox Drummondi, Vitis vinifera.

II. Completely, and more or less readily, soluble in ten per cent NaCl
solution.

PROTEIN GRANULES IN SEEDS. 183

I. Soluble in water; ¢. g., Peonia officinalis.
If. Completely, and more or less readily, soluble in ten per
cent NaCl (sodic chloride) solution.
a. Grains without crystalloids.

(a.) Soluble in saturated NaCl solution after treatment
with alcohol or ether; e. g., Pisum sativum.

(@.) Soluble in saturated NaCl solution after treatment
with alcohol, but not after ether; e. g., Helianthus
annuus.

6. Grains with crystalloids.

(a.) Crystalloids soluble in saturated NaCl solution after
treatment with alcohol or ether; ¢. g., Bertholletia
excelsa.

(8.) Crystalloids soluble in saturated NaCl solution after
alcohol but not after ether; ¢. g., Ricinus communis.

a. Grains without crystalloids.

(a.) Soluble in saturated NaCl solution after treatment with alcohol or
ether : Lupinus hirsutus (type), Vicia Faba, Pisum sativum, Phase-
olus multiflorus, Allium Cepa, Iris pumila (var. atroccerulea), Colchi-
cum autumnale, Berberis vulgaris, Althea rosea, Tropzeolum majus,
Mercurialis annua, Empetrum nigrum, Primula officinalis.

(8.) Solable in saturated NaCl solution after alcohol, but not after
ether : Helianthus annuus (type), Platyeodon (Walhlenbergia) grandi-
flora, Sabal Adansoni, Delphinium cardiopetalum, Trollius Europeus,
Actea spicata, Caltha palustris, Aquilegia vulgaris, Dianthus Caryo-
phyllus, Brassica rapa, Lepidium sativum, Medicago sativa, Larix
europea, Cynoglossum officinale, Spinacia oleracea.

b. Grains with crystalloids.

(a.) Crystalloids soluble in saturated NaCl solution after treatment
with alcohol or ether : Bertholletia excelsa (type), Adonis autumna-
lis, Aithusa Cynapium, Digitalis purpurea, Cucurbita Pepo.

(8.) Crystalloids soluble in saturated NaCl solution after aleohol, but
not after ether: Ricinus communis (type), Datura Stramonium,
Atropa Belladonna, Klais Guineensis, Salvia officinalis, Taxus bac-
cata, Pinus Pinea, Cannabis sativa, Linum usitatissimum, Viola
elatior, Ruta graveolens, Juglaus regia.

III. Partially soluble in ten per cent NaCl solution.

«. Entirely soluble in one per cent sodic carbonate solution : Pulmonaria
mollis, Omphalodes longiflora, Borago cancasica, Myosotis palustris,
Clarkia pulchella.

b. Entirely soluble in dilute potassic hydrate.

(a.) Grains without crystalloids : Anchusa officinalis, Lithospermum
officinale, Echium vulgare, Heliotropium Peruvianum, Lythrum
Salicaria.

(B.) Grains without crystalloids: Cupressus Lawsoniana, Juniperus
eommunis, Euphorbia Lathyris.

by which a

184 MINUTE STRUCTURE OF THE SEED.

III. Partially soluble in ten per cent sodie chloride solution.
a. Entirely soluble in one per cent sodic carbonate solu-
tion; e. g., Clarkia pulchella.
6. Entirely soluble in dilute potassic hydrate.
(a.) Grains without crystalloids ; e. g., Lythrum Salicaria.
(8.) Grains with crystalloids; e. g., Juniperus communis.

513. The appendages of the seed known as the strophiole (at
the base of the seed), the caruncle (at the micropyle or orifice),
and the membranaceous and pulpy forms of arillus (see Vol-
ume I. pages 308, 309) do not call for further remark.

‘The separation of the fruit at maturity, and the separation of
the ripened seed as well, are due to changes analogous to those
described in 458, under the ‘ Fall of the Leaf.” Some of the
special forms of mechanisms by which the detachment occurs
may be examined in Part II., under ‘‘ Dissemination.”

CHAPTER V.

PHYSIOLOGICAL CLASSIFICATION OF TISSUES.

DIVISION OF LABOR IN THE PLANT.

514. Tue simplest plant, a green cell living in water, pos-
sesses all the appliances needful for the work of vegetation ;
namely, a protoplasmic body containing chlorophyll, and a cell-
wall protecting it. It finds in the water in which it floats, and in
the sunlight to which it is exposed, everything requisite for its
full activity.

515. Its work is twofold: First, that which it does not share
with the animal, and which may therefore be called the proper
office of the plant, — the production of organic matter out of
inorganic materials, under the agency of light. This work is
dependent upon the presence of chlorophyll in the cell, and is
known as Assimilation. Second, that which the animal like-
wise can perform, — the conversion into various forms of ac-
tivity of the energy stored up in food. This takes place in the
protoplasm, whether chlorophyll be present or absent.

516. In a spherical cell isolated from others and leading an
independent existence, floating free in the water, and therefore
presenting no one part exclusively to the light, there is very
slight if indeed any division of labor. One part of its cellulose,
protoplasm, or chlorophyll has the same work to perform and is
substantially under the same conditions as any other part. But
if the cell becomes one of many aggregated to form a mass of
tissue, its relations to its surroundings are not the same as be-
tore, for its exterior is no longer equally exposed either to water
or to light. The cells in the interior of such a mass must derive
their supply of material from without through the agency of the
neighboring cells; hence division of labor begins. Inspection
of the mass shows that some of its cells have the office of ab-
sorption, others that of assimilation, others that of treasuring
up the products of manufacture, ete. With this incipient divi-
sion of labor there are also notable changes in the form of cells,
by which a more complete adaptation to a particular kind of

OF

186 PHYSIOLOGICAL CLASSIFICATION OF TISSUES.

work is secured. These adaptations are as marked in the inter-
nal anatomy as in the external configuration.

517. ‘The parts of a living being which have definite kinds of
work to do are known as organs? (cf. éoyov, work). Since they

1 The organs of the higher plants are reducible to three members ; that. is,
three types of structure, which bear to each other definite relations of position
and sequence of appearance. Tlese members are the root, stem, and leaf, — to
which some add also the plant-hair. In Sachs’s Vorlesungen, the number of
members is given as two; namely, root and shoot.

In their very youngest state all the modified leaves upon a given plant are
indistinguishable from each other; the leaves which are to become petals,
stamens, leaf-traps, or tendriis, are like those which are to be ordinary foliage.
The same is true of modified stems and modified roots ; however diverse in
shape and function the modified stems or branches of a plant may finally be,
they are at their very beginning precisely alike.

In the determination of the rank of an organ, that is, its reference to one of
the three plant-members already enumerated, the following criteria are em-
ployed: (1) its position with respect to other parts; (2) its nascent condi-
tion ; (3) its presence or absence in organisms obviously allied to the one in
which it occurs, its rank in these not being obscure.

So far as the organs seen by the naked eye are concerned, it is seldom that
any serious difficulty exists in the application of at least one of these criteria
to the determination of their rank, and it is generally possible to use more
than one. But it is different in the case of the histological organs, for (1) the
position can be made out only in sections of the given part ; (2) their early
nascent condition is the simple cell, common to all tissues ; (8) it is not easy
to determine whether an organ exists in a rudimentary form in allied organisms
or is wholly absent from them.

It is so difficnlt to apply these criteria to the study of tissues, and the
results obtained are so contradictory, that there is no complete agreement
among botanists as to what constitutes a histological member except the sim-
ple cell itself. In fact, as stated in 191, it is doubtful whether with the
material now at hand it would be possible to construct a satisfactory system
of tissue elements or histological organs upon a purely morphological basis,
Even in the systems which most nearly approach this there are some physio-
logical notions which have affected a few of the minor divisions.

A classification of tissues upon the basis of physiology alone is open to
serious objections ; one kind of work in the plant can be performed by diverse
tissues, and on the other hand one kind of tissue can perform more than one
kind of work. This is illustrated by the structural elements through which
mechanical ends are reached ; the long bast-fibres, woody fibres, collenchyma,
and short sclerotic parenchyma, — very diverse elements, but accomplishing the
same result. Yet one of these, namely, the woody fibres, is among the most
important of the elements by which crude liquids are carried through the
plant.

Moreover, in the examination of the minute structure of a part it is not
easy to discriminate between the different offices which one of its given ele-
ments may fill, because the element is associated with so many others in the
formation of a complex organ.

DIVISION OF LABOR IN THE PLANT. 187

are parts of a whole, — the organism, — they must have definite
relations to each other as regards position and office.

518. The relations of origin and position, so far as the organs
of the plant are concerned, are discussed in the first volume ;
the relations of origin and position of the component parts of
their structure have occupied the earlier portion of the present
volume. From a review of the facts there presented, it appears
that any given part may subserve different ends; for instance, a
leaf may carry on its proper work, namely, that of assimilation,
and at the same time may aid as a tendril, and, in the case of
Nepenthes, as a stomach for digestion. On the other hand, it
is equally clear that the same kind of work may frequently be
performed by different parts. For instance, the proper work of
the leaf can be carried on by any green tissue; not merely in
proper leaves, but in the cortex of young stems, and even in the
outer tissues of young roots of certain aerial plants. It is there-
fore sometimes advantageous in Vegetable Physiology to distin-
guish between systems of tissues having different offices, rather
than between organs which are often masses of heterogeneous
tissues.

519. Among the systems of classifications of tissues chiefly
upon a physiological basis is that of Haberlandt, which is as
follows : —

A. The Protective System.
1. Of the surface (Epidermis, cork, and bark).
2. Of the skeleton (Bast-fibres, libriform cells, collenchyma,
and sclerotic parenchyma).
B. The Nutritive System.
1. Absorbing system (Epithelium of roots and the root-
hairs ; absorbing tissue of haustoria, etc.).
2. Assimilating system (Chlorophyll parenchyma, both pali-
sade and spongy).
3. Conducting system (Conducting parenchyma, vascular
bundles, latex cells and tubes).
4. Storing system (Reserve-tissues of seeds, bulbs, and
tubers; water-tissue, etc.).
5. Aerating system (Aeriferous intercellular spaces, together
with their external openings, stomata and lenticels).
6. Receptacles for secretions-and excretions (Glands, oil,
resin, and mucus canals, crystal-sacs, etc.).

To these might be added the groups of tissues concerned in
reproduction.

188 PHYSIOLOGICAL CLASSIFICATION OF TISSUES.

MECHANICS OF TISSUES.

520. In Haberlandt’s classification * the tissues having a me-
chanical office to fill are brought into one group, which is then
subdivided into (1) those tissues which protect the softer tissues
of the interior from the harm which would result from exposure,
and (2) those which hold the soft tissues in place. An exami-
nation of the work performed by tissues may accompany an in-
vestigation of the work by organs themselves; in the examina-
tion of the work of organs in Part IT. the necessary facts relative
to their structure will be presented.

521. Those tissues which serve simply to impart strength to
the plant belong almost as much to lifeless as to living parts, and
can best be examined before the subjects of physiology are taken
up. The present division has for its object the consideration of
that which in Haberlandt’s classification is called the skeleton,
and which is known to serve chiefly mechanical ends.

522. In the case of a water-plant, for instance an alga, which
has about the same specific gravity as the water in which it is
borne, no special mechanical support is demanded. Its own
buoyancy suffices to keep the structure as a whole in place;
while the different parts of the simple organism have a degree of
stability which enables them to resist the action of the waves.
As might be expected, such an organism can attain a very great
size; for instance, Macrocystis pyrifera of the Southern Pacific
Ocean has been known to measure nearly one thousand feet, and
less trustworthy measurements have been recorded which far
exceed this. In this and other water-plants the medium which
buoys the plant up takes the place practically of any internal
framework.

523. A land-plant, existing in a far lighter medium than the
water-plant, must have a definite mechanical support. Those
species of Calamus which furnish the ‘‘ rattan” of commerce pos-
sess a terminal shoot from which are unfolded in rapid succession
strong leaves armed with recurved hooks. Having reached the
thickly clustering tops of a tropical forest, the terminal bud de-
velops its leaves, and these cling with tenacity to the branches
upon which they rest, so that the mechanical support is afforded
in this case by the vegetation beneath. Thus supported, the ex-
tension of the shoot is indefinite, so that examples of Calamus

1 Physiologische Pflanzenanatomie (Leipzig, 1884).

MECHANICAL ELEMENTS OF PLANTS. 189

with a length of 300 feet are not uncommon, aud some figures
much higher than this are noted.

524. In both the above cases the extraordinary size has been
attained with very little expenditure of material for mere me-
chanical support. The same is true, although in a less striking
because a more familiar manner, in our ordinary twining and
climbing plants; other plants or outside supports of some kind
being necessary to bring their stems and leaves into the best
relations to their surroundings. But what tissues serve to keep
erect or in position the larger plants which are not water-plants
or climbers? What tissues serve mainly mechanical ends?

525. The subject was extensively investigated, so far as
monocotyledonous plants are concerned, by Schwendener,? in
1874, since which time some important additions have been
made. According to Schwendener, the mechanical elements
in the plant are (1) bast-fibres, (2) libriform cells and fibres,
(3) collenchyma cells. That these are the chief elements of
strength, especially in monocotyledonous plants, appears from
his instructive experiments, which have been repeated by others.
Strips, 150 to 400 mm. in length and about 2 to 5 mm. wide, were
carefully taken from stems or leaves and immediately fastened
in a vise at one end, the other end being firmly grasped by strong
pincers to which weights could be attached at will. Behind a
strip, vertically suspended from the vise, a measuring-bar was ,
placed, so that any elongation of the strip under tension could be
accurately measured. After the apparatus was properly adjusted,
a small weight was attached to the pincers, the elongation of
the strip observed, and the weight then removed in order to see
whether the strip recovered its original length. Up to a certain
point the recovery was found to be complete ; beyond this point
the elasticity was lost, and not again regained.

526. Strips from the middle part of the leaf of Phormium
tenax, 890 mm. long and 1.5 to 2 mm. wide, were placed in the
apparatus and subjected to the action of a weight of 10 kilograms.
They became 5 mm. longer, but on removal of the weight were
found to recover their original length; in other words, they re-
mained perfectly elastic under this weight. A weight of 15
kilograms broke the strips into two parts. These strips con-
tained only five fibro-vascular bundles, with an amount of bast
which was believed to be about half a square millimeter in cross-

1 Das mechanische Princip im anatomischen Bau der Monocotylen (Leipzig,

1874).

190 PHYSIOLOGICAL CLASSIFICATION OF TISSUES.

section. From this experiment Schwendener places the strength
of the bast of Phormium tenax at 20 kilograms per square milli-
meter.’

527. The tables in the notes show that good bast equals good
iron in its tensile strength within the limits of elasticity, while in
its breaking-weight it is greatly exceeded by the latter. Schwen-
dener well remarks that Nature has given her whole care to pro-
viding that these mechanical elements should be strong within
the limits of elasticity, and with good reason; for beyond those
limits the plant gains nothing by greater strength. Attention is
called also to the great difference between bast and the metals
with regard to their elongation under weight.

1 The results of experiments made with the bast of various plants in the
manner described are given below. Most of the cases cited are from Schwen-
dener ; others are from Haberlandt (Physiologische Pflanzenanatomie, p. 105).
The determinations for metals are from Weisbach.

; ; | Breaking-
Tensile strength in| ~ i
Elongation | kilograms per sq. weight in
Name. in 1000 parts.| mim, (within limits eae
of elasticity). mnie
Phormium tenax A g 2 13. 20. 25.
6s ee ae eee ae % 14. 16,
Fritillaria imperialis « 12. ‘
Lilium auratum 7.6 19,
Juba spectabilis. . . . ; 12.6 20.
Dasylirion longifolium f 13.3 . 17.8 21.6
Dracena indivisa . . . é 17. 17. 21.8
Hyacinthus orientalis q i car 12.3 16.3
Alliam Porrum . - ices 14.7 17.6
Polytrichum juniperinum (stem) . sae eyo sae 7.5
(seta) Bed bit oa 115
Papyrus antiquorum Sanita 15.2 20. -
Molinia coerulea . . . ... 11. 22.
Pincenectia recurvata A 14.5 25.
Dianthus capitatus . 75 143
Secale cereale . . ‘ ° 4.4 15 to 20

These should be compared with the results of determinations made with
other materials : —

Name Elongation in|Tensile strength) Breaking-weight
: 1000 parts. per sq. mm. in kilograms
Malleabie i iron in rods 67 13,13 40.9
in wire 8 1.90 21.9

i “ in plate . F .80 14.6
Hammered German steel 1.20 24.6 82.
Brass. . os 15 4.85
Brass wire. . 135 13.3
Cast zine. é; 3 24 2.3
Copper wire . . Tray ae a 1.00 12.1
Silver. a ia i Re deo 11. 29

SitBREOM AND MESTOM. 191

528. The strength of other tissues besides bast has been meas-
ured ; thus Ambronn assigns to colleuchyma a breaking-weight of
12 kilograms per square millimeter, and these cells become per-
manently elongated under a weight of from 1.5 to 2 kilograms.

Haberlandt found that the breaking-weight of the internal
‘* thread” of the common graybeard lichen, Usnea barbata, is
1.7 kilograms per square millimeter, but that this thread could be
stretched to double its length before breaking. The breaking-
weight of cotton fibre is calculated to be between 18 and 20
kilograms per square millimeter, and that of the seed-hair of
Asclepias Syriaca not far from 40 kilograms.

529. Examination of any of the figures of fibro-vascular
bundles given in Part I. shows how well their elements are dis-
tributed in order to secure the greatest strength with economy of
material. To the elements which impart strength to a bundle
Schwendener has given the name stereom ; to the other parts of
the bundle, mestom ,; thus the fibres are stereom elements, the
ducts are mestom elements.

530. The striking adaptations! of the fibro-vascular bundles
to serve as light and very strong building materials in the plant

1 The following table from Schwendener, with a few illustrative examples,
is given to serve as a guide to the student in tracing out a few of these adapta-
tions : —

DisrripuTioN OF MECHANICAL ELEMENTS IN MoNocoryLEDons.

I. In cylindrical organs.

1. System of subepidermal nerves of bast. Simple fascicles of bast lie

under the epidermis.
First type. Arum, Arisaema.
Second type. Petioles of Colocasia and Alocasia.

2. System of compound peripheral girders. Subepidermal fascicles of bast
unite with those which lie more deeply to form girders in which
the ‘‘web” or binding-tissue is partly mestom, partly parenchyma.

Third type. Stems of Scirpus cspitosus and Eriophorum alpinum.
Fourth type. Stems (above ground) of Cyperus alternifolius.

Fifth type. Stems of Schcenus nigricans.

Sixth type. Stems of Juncus effusus.

Seventh type. Carex lupulina.

Eighth type. Scirpus lacustris.

Ninth type. Isolepis pauciflora.

Tenth type. Cladium Mariscus.

3. System characterized by a nerved hollow cylinder, the nerves of
which are united with those at the epidermis.

Eleventh type. Many grasses ; ¢. y., Alopecurus pratensis.
Twelfth type. Panicum Crus-galli.

4, System of peripheral bast-fascicles strengthened by mestom.
Thirteenth type. Zea Mais.

192 PHYSIOLOGICAL CLASSIFICATION OF TISSUES.

are seen plainly when the distribution of the bundles in the stems
of monocot) ledons is examined in cross-section. In many cases
the shape of the section of the bundle is nearly that of the
well-known ** 1” or “*H” beain or girder. Jn the most clearly
marked instances the stereom portion is well developed on
both sides of the mestom, and thus forms the ‘ flanges” or
‘* plates,’’ while the mestom is the ‘‘ web;” the stereom has
therefore to bear either compression or tension, according to
the bending of the part. It will further be observed that in all
cases the bean is placed with respect to the rest of the stem, so
as to insure the greatest efficiency of the stereom portion.

Bat it is only upon a careful examination of the many methods
of arrangement of the stereom and mestom in the bundles
of diverse forms of dicotyledonous stems, together with an ex-
amination of the arrangement of the bundles themselves with
respect to the surrounding tissues, that the adaptations of the
various elements to strength can be fully appreciated.

The modes of distribution of the stereom and mestom met
with in monocotyledons are so numerous that they cannot be
reduced to a few types; their diversity is so great that they can
only with difficulty be brought into any system of classification.

5. System of subcortical fibro-vascular bundles with strongly marked
bast development.
Fourteenth type. Bambusa species.
Fifteenth type. Palms.
Sixteenth type. Yucca.
Seventeenth type. Musa.
Eighteenth type. Maranta.
6. System of subcortical fibro-vascular bundles united tangentially.
Nineteenth type. Juncus Gerardi.
7. System characterized by a simple hollow cylinder with imbedded or
attached fascicles of Mestom.
Twentieth type. Commelynaces.
II. In bilateral organs.
1, System of subepidermal girders.
First type. Leaves of Cyperus.
Second type. Middle part of leaves of Zea.
Third type. Leaves of Musa.
Fourth type. Leaves of Tradescantia.
Fifth type. Leaves of Pardanthus.
2. System of internal girders.
Sixth type. Leaves of Cypripedium.
Seventh type. Petiole of Aspidistra.
3. System of complex girders: subepidermal nerves of bast combined
with interior girders.
Eighth type. Petioles of many palms.

PHYSIOLOGICAL CLASSIFICATION OF FigsuES. 193

631. The distribution of material in the skeleton of a ligneous
dicotyledonous plant is somewhat different from that in a mono-
cotyledon.! More of the mechanical work falls on the proper
wood, but even here in some cases the bast serves an important
purpose.

032. The data for calculating the strength of the woody stem
and branches of a dicotyledonous plant are to be found in vari-
ous works on mechanical engineering ; but it is to be borne in
mind that the figures given for timber are usually based on ex-
periments with dry heart-wood.

033. The trunk is to be regarded as a column bearing the
weight of the whole crown of branches, each of these being a
tapering beam supported at one extremity. The crushing-weight
the crown exerts upon this column is far within the limits of
safety, even when the liability of the trunk to be much bent and
twisted by high winds is taken into account. The branches at
their point of union with the trunk form different angles in
different plants,” and this angle must be taken into consideration

1 DIstRIBUTION OF MrcHANIvAL ELEMENTS IN DIcOTyLEDONs.

1. With bast in the bark.

First group. Axial organs when young have an unbroken ring of bast ;
in much older stems this is interrupted or cast off. Aristolochia.

Second group. Axial organs with a layer of bast-bundles which is
thrown off later. The bast-bundles form the first mechanical system,
which is soon replaced by the ring of wood. Nerium Oleander.

Third group. With simple ring of bast-bundles in first year, later with
isolated bast-fibres. Ausculus Hippocastanum.

Fourth group. With strong bast, even when far atlvanced. Tilia.

Fifth group. With subepidermal bast-nerves. Russelia.

2. With transition to an intra-cambium ring of libriform cells.

Sixth group. The cambium of the bundles lies partly outside, partly
inside the mechanical ring, or is imbedded therein. Gaillardia.
Seventh group. Isolated vascular bundles. Silphiuin perfoliatum.

3. Intra-cambinm libriform ring without medullary rays.

Eighth group. Without bast on the outer side of the cambium or cam-
biform layer. Impatiens Nolitangere.

Ninth group. With larger or smaller amounts of bast on the outer side
of the cambriform. Urtica dioica.

Tenth group. In the libriform elements all shades of transitions to
ducts. Mirabilis Jalapa.

4. Intra-cambium libriform ring with parenchyma rays.

Eleventh group. Rays formed of elongated cells. Vinca major.
Twelfth group. Typical dicotyledons with medullary rays.

2 McCosh has given the angles in a large number of plants, a few of which
are here cited: Ash, 60°; horse-chestnut, 50°-55°; alder, 50°; elm, 50°; oak,
large branches, 50°, small branches, 65°- 70° ; beech, 45°; linden, 40°. He calls
attention to the fact that in these and many other cases the angle at which the

13

194 PHYSIOLOGICAL CLASSIFICATION OF TISSUES.

in determining the actual force exerted upon the fibres at the
base of the branch.?

584. The part which sclerotic parenchyma and thickened
epidermal and hypodermal cells play in affording strength to
plants need only be alluded to (see 211). In a few cases,
especially in some succulents, a considerable share of the me-
chanical support of the plant is afforded by the more superficial
parts.”

535. The veining of leaves and the structure of leaf-margins
present some interesting problems. Comparative investigations ®
have shown that strength at the edge of the leaf is obtained in
very different ways, even in closely allied plants. The resist-
ance to tearing which is exhibited by some of the larger leaves
of dicotyledons is remarkable.

The distribution of the strong ribs in the leaves of the greater
water lilies (for instance, Victoria regia), and to a less striking
extent that in the smaller water lilies of cold climates, secures
great strength with the utmost economy of material.

The trunks of many tropical trees are provided with lateral pro-
jections (buttresses) which strengthen the stem very materially.‘

veinlets come off from the midrib is the same as that formed by the branch and
the trunk. The angles in the above cases are those formed above the points
where the branches arise (British Assoc. Report, 1852, part ii. p. 68).

1 Very instructive illustrations of the different capacity of different trees to
resist the action of high winds are given in the Reports of the Signal Service.

2 Full and interesting accounts of the adaptations of the framework to the
external conditions of plants are to be found in the works of Schwendener and
Haberlandt. -

3 Westermaier: Monatsber. der k. Akad. d. Wissenschaften Berlin, 1881.

4 «All are tall and upright columns, but they differ from each other more
than do the columns of Gothic, Greek, and Egyptian temples. Some are
almost cylindrical, rising up out of the ground as if their bases were concealed
by accumulations of the soil; others get much thicker near the ground like
our spreading oaks ; others again, and these are very characteristic, send out
towards the base flat and wing-like projections. These projections are thin
slabs radiating from the main trunk, from which they stand out like the but-
tresses of a Gothic cathedral. They rise to various heights on the tree, from
five or six to twenty or thirty feet; they often divide as they approach the
ground, and sometimes twist and curve along the surface for a considerable
distance, forming elevated and greatly compressed roots. These buttresses are
sometimes so large that the spaces between them if roofed over would form
huts capable of containing several persons. Their use is evidently to give the
tree an extended base, and so assist the subterranean roots in maintaining in
an erect position so lofty a column, crowned by a broad and massive head of
branches and foliage” (Wallace: Tropical Nature, 1878, p. 30).

PART IL.

CHAPTER VI.
PROTOPLASM AND ITS RELATIONS TO ITS SURROUNDINGS.

536. Upon the framework which imparts strength to the
plant the active, living cells are distributed. In old ligneous
dicotyledonous plants the living parts are relatively so super-
ficial that they have been said to form a mere film of living
tissue held in place by a dead skeleton.! -

537. The living cells are those which contain protoplasm.
Each of these cells has definite relations to the neighboring cells,
most of which relations have been presented in Part I. But each
of these cells has also definite relations to the external world,
which it is the province of Physiology to investigate. Such an
investigation naturally begins with a consideration of the char-
acter of protoplasm.

1 ‘The living parts of a tree or shrub, of the exogenous kind, are obviously
only these: Ist, The summit of the stem and branches, with the buds which
continue them upwards, and annually develop the foliage. 2d, The fresh
roots and rootlets annually developed at the opposite extremity. 38d, The
newest strata of wood and bark, and especially the interposed cambium-layer,
which, annually renewed, maintain a living communication between the root-
lets on the one hand and the buds and foliage on the other, however distant
they at length may be. These are all that are concerned in the life and growth
of the tree ; and these are annually renewed. . . . The plant is a composite
being, or community, lasting, in the case of a tree, through an indefinite and
often immense number of generations. These are successively produced, en-
joy a term of existence, and perish in their turn. Life passes onward con-
tinually from the older to the newer parts, and death follows, with equal step,
at a narrow interval. No portion of the tree is now living that was alive a
few years ago ; the leaves die annually and are cast off, while the internodes or
joints of the stem that bore them, as to their wood at least, buried deep in the
trunk under the wood of succeeding generations, are converted into lifeless
heart-wood, or perchance decayed, and the bark that belonged to them is
thrown off from the surface. It is the aggregate, the blended mass alone, that
long survives” (Gray's Structural Botany, pp. 83, 84.)-

196 PROTOPLASM.

538. Protoplasm, the living matter of the plant, can be ex-
amined to advantage, either as it exists without a cell-wall in
some of the lower organisms (Myxomycetes), or confined within
a transparent cell-wall, as in young plant-hairs.

539. The Myxomycetes live in the interstices of moist porous
substances ; for instance, decaying leaves and stems, spent tan,
etc. Passing over all details regarding their fructification, —a
subject to be looked for in the volume on ‘* Cryptogamic Botany,”
— their present examination can begin with the period when the
germinating spores of these plants rupture their walls, and
become confluent as masses of naked protoplasm known as
plasmodia.

540. The plasmodium of /&thalium septicum is not difficult
to procure, as it occurs in summer upon heaps of moist tan in
the open air, and even during the winter in moist places in
greenhouses where tan is used as a stratuin for flower-pots. It
is a soft, gelatinous mass of yellowish color, sometimes measur-
ing several inches in diameter. Removal of any portion of this
mass to a glass slide is apt to break up the plasmodium so much
as to render it useless for observation ; therefore the following
explicit directions given by Strasburger for obtaining small por-
tions to examine will be found useful. A tumbler is to be filled
with water up to the brim, and from the brim a strip of moist
filtering-paper, somewhat less than an inch in width and one or
two inches in length, is to be stretched to the top of a glass slide
placed in a vertical position (or, better, leaning a little out-
wards) ; the lower end of the slide being placed in sand to catch
the water which will soon begin to flow slowly over its surface.
Next, a piece of bark with the plasmodium upon it is to be
placed at the foot of the slide, the whole covered with a bell-jar
and a dark cover of pasteboard, and from time to time the
water in the tumbler replenished. In the course of ten or twelve
hours some of the protoplasmic mass will climb up the slide in
the form of delicate threads, which branch more or less and con-
stitute a sort of network. The slide is then transferred to the
stage of the microscope, care being taken (1) to use only a
little light, and (2) to avoid any pressure by the cover-glass.
The latter may be prevented by fragments of glass placed under
the corners of the cover-glass; or, better still, the cover-glass
may be fastened on the slide by means of four minute drops
of cement, leaving its side exposed, and then the slide, thus
furnished with a cover, placed in the nearly vertical position al-
ready advised, when the plasmodium will creep under the cover,

CHEMICAL AND PHYSICAL PROPERTIES. 197

and be all ready for examination, with no disturbance whatever.
If the plasmodium is allowed to creep over the face of a slide
placed horizontally, it is apt to be too thick for a demonstration
of some of the points which are now to be referred to.

541. Chemical and physical properties of protoplasm. When
the plasmodia of AXthalium septicum collect in large masses on
the surface of spent tan, they afford good material for the exam-
ination of some of the chemical and physical characters of pro-
toplasm; but there is, of course, the serious objection that it
is impossible to obtain the protoplasm in a state of absolute
purity. Upon such material, however, Reinke and Rodewald +
have conducted some instructive experiments, the principal re-
sults of which are detailed in the following paragraphs.

542. The organic substance of the protoplasm of Athalium
proved to have the following elementary composition :? —

Per cent, air-dried Per cent, dry
substance. substauce.

i C. 38.56 40.52
Reis \# 5.82 6.10
aia mana 5.63 5.91
Second - ea ee

analysis. : oe :
N. 5.39 5.65

In oth mars ee oxygen is a fourth constituent.

1 Studien iiber das Protoplasma, Berlin, 1881.
2 The composition of the air-dried substance is approximately as follows :—

TWiaGOTe) dah ue ser ar See, Pa cic tbe> lee Se eae Teo ESO
Pepsinand Myosin. . . . .. . ss ~ 1.00
VAteMIA ew ee ee Goce oy Mae a Gee ee ay ae ve, OHO
Plastini os: ee en ee ae Be ee Se RR er AD
Guanin

Xanthin} e solr ate » » OL
Sarkin

Ammonic carbonate. . . 2. 2. es ss © 10
Asparagin and otheramides . . . . . . . 1.00
Pepton and pace foe ae ae we a 00
Lecithin . .. Sbcé. ee ev eos gh aa ee 20
Glycogen, aio jee. sas re ae ere pe A
Aithalium sugar . .. » . . 8,00
Calcic eomiounds of lishee fatty acids . + « 5,88
Calcic formate 42
Calcic acetate . Do ee eres & UPR ays
Calcic carbonate . . 2. 1. ee ew ee © 27.70
Sodic chloride . . Res eo ald
Hydropotassic phosthate (PO,KH) ae ee ee ee |

Tron phosphate (PO,Fe?). . . a aap cate es ON

198 PROTOPLASM.

548. One hundred and seventy-nine grams of fresh proto-
plasm of a soft consistence were placed in closely woven linen
cloth and subjected to pressure by the hand; 58 grams of a
turbid fluid were expressed; the mass was then placed under
a pressure of 4,000 kilograms, by which 62 grams more were
forced out, leaving a dry cake behind. Thus 66.7 per cent
of the mass was pressed out. The fluid thus expressed has a
specific gravity of 1.209. That this fluid is intimately incorpo-
rated with the more solid portion of the protoplasm, appears from
the fact that it cannot be forced from the protoplasm by cen-
trifugal force alone. To it the name enchylema has been given ;
to the solid matter, the name stroma is applicable. The amount
of water contained in fresh protoplasm of AMthalium septicum
is approximately 71.6 per cent.

The reaction of protoplasm is alkaline.

544. In young cells the protoplasm exhibits essentially the
same characteristics as those presented by the naked protoplasm
of the Myxomycetes already alluded to. The phenomena in cells
can be most satisfactorily seen in thin-walled plant-hairs. These
should be transferred to a glass slide with as little injury as pos-
sible, covered immediately with pure water, and examined under
a cover-glass which is prevented by bits of wax or thin glass
from pressing on the delicate object. The stamen-hairs of Trad-
escantia Virginica, pilosa, or zebrina are the best, for in these
the cells are sufficiently large to be managed without difficulty,
and the walls are perfectly transparent. The cells in the thin
leaves of many water-plants answer very well, but they generally
contain so much chlorophyll that the protoplasm is obscured.
The hairs of the flowers and of the young leaves of plants of
the Gourd family and those of the nettle’ are also excellent
objects for the study of protoplasm; and in general it may be
said that almost any plant-hair, if it is young enough and has a
thin wall, will serve very well (see Fig. 175).

545. Protoplasm in cells exists as a nearly colorless mass
a Z

Ammonio-magnesic phosphate . . . . . . 1.44
Tricalcic phosphate . 6 2 ee ee ee ee OL
Caleicoxalate . 2 1 6 1 ee ww ew ew ee 210
Chlolesterin . . Sone te ow hoot Ded
Fatty acids extmated by athar fy Se AS a 00
Resinous matter... foe ecco ey B00
Glycerin, coloring-matter, ae ee rec)
Undetermined siathats i ae oe » 5.00

1 Huxley: Protoplasm (Half Hours with Modern ore 1871).

MOVEMENTS. 199

lining the walls and extending irregularly from side to side in
slender threads. At some one part the mass appears a little
denser than at others, and if the outline of this firmer mass is
at all well defined it is easily recognized as the nucleus (see
Fig. 2).

546. Circulation of protoplasm in cells. Under a power of
300 diameters the delicate threads of protoplasm can be clearly
seen to have imbedded in them minute granules which are slowly
moving. It happens sometimes that a slight warming is re-
quired before any motion is apparent. When the current is fully
established, its different changes can be watched for a long time
without other disturbance of the specimen than that resulting
from the addition of water to replace that lost by evaporation.

Two features of the motion require special notice: (1) the
granules do not pass from one cell to the contiguous one, but
remain confined in one; (2) the threads in which the granules
move gradually change their shape and direction, growing wider
in one place and becoming narrower in another, while at the
points of contact with the lining of the wall the threads seem to
slip or glide very slowly, and accumulations of the protoplasm
here and there take place. The movement of the granules from
place to place in a steady current is called the circulation of
protoplasm ; the sluggish changes of the threads as they alter-
nately increase and diminish in size resemble the amcboid
movements (see 555 and Fig. 175).

547. In some examinations it is instructive to add a very

little glycerin or sugar to the water on the slide, in order to
cause a slight contraction of the protoplasm; its whole mass
then appears as a shrunken sac, in the interior of which the
circulation can be detected.
_ 548. In a good specimen of the stamen-hair of Tradescantia
the protoplasmic currents are seen to course in slender threads
with a considerable degree of regularity. In some of the
threads or bands the currents go in one direction, in others in
another ; and it occasionally happens, as Hofmeister has pointed
out, that two opposite currents may pass in a single narrow
channel.

549. There is more or less accumulation of protoplasmic
matter in the immediate vicinity of the nucleus, and there are
generally some slight projections into the interior of the cell.
The rate of circulation appears to be greater at the middle of
the threads than at the sides or ends of the cell.

550. If these movements in a cell are compared with the

200 PROTOPLASM.

movements exhibited by naked protoplasm, no substantial dif:
ference can be seen beyond that which depends upon the con-
finement of the mass in one case within practically rigid walls.
The naked protoplasm moves slowly from place to place, by
thrusting out an irregular projection which soon enlarges, and
in its turn gives out new projections, while the mass behind is
slowly moving up. This movement is identical with that observed
in the amoeba. In the substance of a mass of naked proto-
plasm granules can be seen to move in varying channels; and
this corresponds strictly to the movement known as the circu-
lation. Moreover, in the naked protoplasm larger or smaller
vacuoles (see 120) are observed to increase and diminish in size,
their limiting walls answering essentially to the threads before
described.

551. Rotation of protoplasm in cells. The film of protoplasm
in contact with the cell-wall does not generally share in the
movement of the softer part which it encloses, but usually re-
mains entirely stationary, or else very slowly shifts its posi-
tion on the wall. In some cases, however, the whole mass
of protoplasm slowly revolves on its own axis, carrying with
it all imbedded matters. This movement should be called
rotation ; but the term is often employed interchangeably with
circulation.

552. Rate of protoplasmic movements. In the cells of the
shaft of any Chara which has transparent walls — for instance,
Nitella—the rapid movement can be very clearly seen to be
confined to the interior of the protoplasm, the outer part in which
chlorophyll-granules are imbedded not moving to any great ex-
tent, if indeed at all. At its interior the protoplasm moves with
what seems under the microscope to be a very rapid rate; it is,
however, absolutely very slow; being only about one and a half
millimeters per minute, at a temperature of 15° C.

553. The rate differs considerably in different plants; for
instance, according to several observers, the distance traversed
in one minute at a temperature of 15° C. is as follows: —

Name of plant. mm. Observer.
Potamogeton crispus, leaf-cell . . . .009 . . . Hofmeister.

Ceratophyllum demersum, Jeaf-cell . .094 . . . Mohl.
Tradescantia Virginica, stamen-hair . .137

Sagittaria sagitteefolia . 2. . . . 4174 . Mohl.
Vallisneda spiralis Ee F "228-1, 086 - Mohl.
Hydrocharis Morsus-rane, root- hae 543

Nitella flexilis, cells of the shaft . . 1.500-1.600 . Niigeli.

AMCEBOID MOVEMENT. 20L

In the naked protoplasm of Myxomycetes the rates of move-
ment of the currents are much greater, as Hofmeister shows by

the following examples : —
mm. per minute.

Didymium Serpula . . 2. 2. wee 10
Physarum species. . . . 2 2 ee ee OB

554. The above rates are not constant even in the same speci-
men; after having been uniform for a few minutes, the rate
may slowly diminish for a time, the temperature and other con-
ditions remaining apparently unchanged, and then as slowly
increase until the maximum is again reached. Again, the rate
is subject to sudden changes. In general, however, it is nearly
the same for the same part of a given plant.

555. The ameboid movement in naked protoplasm is rather
more sluggish than the circulation, as the following figures from

Hofmeister show :—
mm. per minute,

Didymium Serpula . . . 2. 2 ew ew ee 04
Physarum sp. . 2... 1 ee ee eee (029
Stemonitis fusca. Sp Netchiee ae Wes car tats “at Kan 2 O8LD.

The far more rapid movement of ciliated protoplasmic bodies
will be described under ‘‘ Movements.”

556. The effects upon protoplasm of various agents — for in-
stance, heat, light, electricity, ete. —can be studied in the same
cells in which the movements are observed ; in fact, their effects
upon the movements themselves are among the most striking
phenomena noticed. It must be remembered, however, that in
experimenting upon the protoplasm in cells which are furnished
with a cell-wall and provided with cell-sap, other factors are
present than those which must be taken into account in deal-
ing with the naked protoplasm of plasmodia. And hence it is
proper in most cases, in interpreting the results obtained in
experiments upon the protoplasm of cells, to speak of the effects
of the agents upon the cells themselves.

557. Relations of protoplasm to heat. In experimenting upon
the effect of heat on protoplasm, the apparatus generally em-
ployed is the so-called warm chamber. In its simplest form this
consists of a hollow-walled box, having a slit in which a slide
can be placed, and at the centre of the upper and lower walls
holes of the same size as the largest diaphragm of the micro-
scope, so as to allow light to pass from the mirror directly
through the slide and thence to the objective. Connected with
the box are two tubes to which pieces of rubber tubing may

202 PROTOPLASM.

be attached ; these pieces run toa small réservoir of water which
can be heated at pleasure by means of a spirit-lamp, as shown
in the figure. Suppose a slide to have upon it a good specimen
of a stamen-hair of ‘Tradescantia, furnished with sufficient water
and properly covered. It is placed in the aperture f of the
hollow box, and the rest of the apparatus
is then arranged as shown in the cut. The
rate of circulation of the protoplasm is now
carefully observed, and the temperature
shown by the thermometer ¢ is also noted.
With increments of heat from the upward
current of water through the tube and

Se =
in ae
=i

through the box the rate of the protoplasmic circulation is in-
creased. The amount of heat applied can be easily regulated
by the height of the reservoir. If it is desirable to observe the
effects of cold, the reservoir can be placed in a vessel of ice and
raised above the stage of the microscope, so that a current of
cold water can flow down through the box.

558. Experiments upon the effect of heat can also be con-
veniently conducted by means of a less expensive apparatus
which consists of a double-walled box of zinc placed on firm
supports at the height of a few inches above the table, and large

RELATIONS OF PROTOPLASM TO HEAT. 203

enough to receive the body of the microscope. Through a hole
in the top of the box the tube of the microscope projects for a
short distance, and the front of the box is furnished with a glass
window, which affords enough light for the mirror. The space
between the walls of the box having been filled with water, and
the object placed on the stage of the microscope, a lamp under
the box is lighted, and the effects of the increase of temperature
noted. It is best in this case to have the thermometer in the
closest proximity to the slide. It is essential in the use of both
these instruments to note the temperature at short intervals,
and it is only by the greatest care in the use of the thermometer
that any trustworthy results can be obtained (see Fig. 170).

559. As might be expected from the nature of heat as a mode
of molecular motion, the rate of protoplasmic movement is
accelerated by increase of temperature up to a given point (the
optimum) ; with increase beyond this point the movement may
continue, but with diminished rapidity, until an upper limit of
temperature (the maximum) is reached, above which no move-
ment is observable. At or very near this limit structural changes
take place, and death of the protoplasm speedily ensues.

560. The optimum temperature for protoplasmic movement
is different for different plants, but is not far from 37°.5 C.

Name of plant. Optimum temperature. Observer.
Nitellasyncarpa . . . . . 879 . « . « . «. Nigelit
Chara fetida. . . . . . . 88°1 . . . . . . Velten.?
Vallisneria spiralis . . . . . 88°.75 . a a nae:

ef ee “« 4 & ee 40? ~ 2 « « + » Sachs.
Anacharis Canadensis . . . 86°.25 Bide -% « Velten.?

561. The maximum temperature beyond which no movement
is seen, is also different for different plants, but may be given as
not higher than 50° C.

Name of plant. Maximum. Observer.
Chara fetida. . . . . . . 42°81. =... =. . Velten.?
Vallisneria spiralis . 2. . . . 45° 2. 2 ww we 038

s€ es ‘ 50° « « « « « » Sachs?

Sachs‘ states that when the hairs of Cucurbita Pepo are im-
mersed in water of 46° or 47° C. the protoplasmic movements
are arrested within two minutes; but that the hairs can bear

1 Beitrige z. wiss. Botanik, 1860, ii. p. 77.
2 Flora, 1876, p. 177 et seq.

8 Flora, 1864, p. 5 e¢ seq.

4 Lehrbuch der Botanik, 1874, p. 700.

204 PROTOPLASM.

exposure for ten minutes to a temperature of 49°-50° in the air
before arrest of movement takes place. In Tradescantia hairs
the current stops within three minutes upon exposure in air of
a temperature of 49°, beginning again when the temperature
falls.

562. The lower limit (minimum) of temperature at which
motion takes place may be stated at 0° C., although —2° has
been observed ! in a single plant, — Nitella syncarpa.

Until a temperature of at least 15° C. is attained, the move-
ment is sluggish.

563. Suclden changes of temperature have been said by some
writers to cause a temporary arrest of the protoplasmic move-
ment. Thus de Vries* observed that in the root-hairs of Hydro-
charis Morsus-ranz the protoplasmic current at 21°.7 C. was so
rapid that it passed through one millimeter in 205 seconds; but
upon sudden elevation of temperature to 33° C., 240 seconds
were required for it to traverse the same distance. And Hof-
meister? found that the rapid movement in Nitella flexilis was
arrested in two minutes when the specimen was taken from a
room at 18°.5 to one at 5°. But, on the other hand, Velten*’
failed to detect such an effect.

564. Ator near the maximum temperature remarkable changes.
take place in the form of the protoplasmic threads and films.
They become more or less rounded, although very irregularly,
and may be completely disintegrated. Such changes have been
noted by Max Schultze® at a temperature of about 40° C. in
the hairs of Urtica, the stamen-hairs of Tradescantia, and the
leaf-cells of Vallisneria. According to Kiihne,® such changes
take place within two minutes in the plasmodium of Atthalium
septicum (see 540) at a temperature of 39° C.; the plasmodium
of Didymium serpula was affected in the same way at a con-
siderably lower point, namely, 30° C.

565. When subjected to a temperature lower than the mini-
mum for movement, the protoplasmic mass may become disin-
tegrated, the solid part separating from a watery portion, which
latter may freeze.” If, now, very gradual increments of heat

1 Botan. Zeitung, 1871, p. 723 (Cohn).

2 Archiv. Néerlandaises, v., 1870, p. 385.

* Die Lehre von der Pflanzenzelle, 1867, p. 53.

4 Flora, 1876, p. 213.

5 Das Protoplasma d. Rhizopoden und Pflanzenzellen, 1863, p. 48.
* Untersuchungen iiber das Protoplasma, 1864, p. 87.

7 Untersuchungen iiber das Protoplasma, 1864, p. 101.

RELATIONS OF PROTOPLASM TO HEAT. 205

are applicd, the disorganized parts may become reunited, and
after a while the movement may begin again. No such recovery,
however, is possible when the protoplasmic mass has become
disintegrated by a high temperature; the change thus produced
is practically coagulation.?

566. The temperature of certain hot springs in which living
alge have been found shows that protoplasm can bear without
injury a greater degree of heat than is indicated by the figures
in 561. Thus alg have been seen in the following thermal
waters : —

Temperature. Observer.
Carlsbad. 2 ww. 58°7C. ©. . Cohn?
Lip Islands. . . . 58% . « . « Hoppe-Seyler.8
Dax 2. Gx te cen ak ve VDSS . . . « Serres.#
California Geysers. . 98° . . . « Brewer.8

Hoppe-Seyler found algz growing on the edge of a fumarole
where they were subjected to a temperature (from the escaping
vapor) of 60°.®

567. That the protoplasm of many kinds of seeds and spores
can preserve its vitality during exposure to dry air at a tem-
perature above that of boiling water has been shown by many
experimenters ;7 but unless the precaution is taken to remove
all water from the seeds by very careful and slow drying, any
temperature above 100° C. is injurious. Seeds thus cautiously
freed from moisture have been heated to 110°, and even for a
short time to 120°, without losing their power of germination
(see also “ Germination”). Nor does there seem to be any es-
sential difference between the seeds which contain oils and those
which contain starch in their capacity to endure high tempera-
tures. Hoffinann® and Pasteur® have shown that the vitality of
perfectly dry seeds and spores may in some cases be retained
until a temperature of 130° C. is reached.

1 Pfeffer : Pflanzenphysiologie, 1881, ii. p. 386. 2 Flora, 1862, p. 538.

8 Phliiger’s Archiv., 1875, p. 118. * Botan. Centralblatt, 1880. p. 257.

6 Am. Journ. Se. and Arts, 2d series, xli. 391.

6 Pfliiger’s Archiv., 1875, p. 118.

A much higher temperature is noted by Humboldt ; namely, 85° C. for the
hot spring of Trinchera, Caraccas, in which he found the roots of certain plants
growing.

7 Milne Edwards and Colin: Ann. des Se. nat., sér. 2, tome i., 1834, p. 264;
Sachs’s Handbuch der Experimental-Physiologie, 1865, p. 65 e¢ seg. ; Just, in
Cohn’s Beitriage zur Biologie der Pflanzen, 1877, p. 311.

8 Pringsheim’s Jahrb., 1860, p. 324.

® Ann. d. Chimie et de Physique, 1862, p. 90.

206 PROTOPLASM.

568. On the other hand, the protoplasm of dry seeds can be

subjected to extremely low temperatures without suffering any
injury (see ‘‘ Germination”’).
_ 569. The relations of protoplasm to light are best examined in
the plasmodia of the myxomycetes and the hairs of Tradescantia,
for here they are not complicated by the presence of chlorophyll
(which, as will be seen later, exerts a marked influence). Ac-
cording to Hofmeister, plasmodia thrust forth longer and more
numerous processes in darkness than in light. In A¢thalium sep-
ticum the processes developed in light are short and compressed,
while those grown in darkness are long, slender, and thin.?
This is especially noticeable when the light falls only on one
side of the mass. In some of Baranetzky’s experiments,’ in
which the incident rays of light were parallel to the substratum
(wet filtering-paper) on which the plasmodium was placed, the
change of form resulting from diminished extension on the
lighted side and increased extension on the other was very
marked after fifteen minutes’ exposure to bright sunlight, while
in diffused light half an hour was required for a similar change.
These results should be compared with those obtained by
Schleicher,? who observed that young plasmodia move towards
light of low intensity, and that older plasmodia may move even
towards strong light. The movement into bright light appears
to just precede the formation of the spores.

570. The more refrangible rays of light — that is, the violet
and indigo— appear to be more efficient in influencing move-
ment than are the less refrangible, — the red and yellow.

571. The ‘ circulation” of protoplasm in plant-hairs goes on
not only in darkness, but even when the hairs are developed on
plants blanched by absence of light.* No marked effect upon
the rate of such movement appears to be caused by presence or
absence of light, except so far as the concomitant action of heat
comes into play. Hofmeister states that he saw the protoplasmic

1 Die Lehre von der Pflanzenzelle, 1867, p. 21.

2 Mémoires de la soc. des sciences nat. de Cherbourg, 1875, p. 340. It is,
however, well known that plasmodia often emerge slowly from their sub-
stratum ; for instance, tan, if the surface is only very faintly lighted.

3 Jenaische Zeitschrift, 1878, p. 620.

4 Sachs: Botan. Zeit., 1863, Supplement. Reinke: ibid., 1871, p. 797.
Kraus : ibid., 1876, p. 504. Few observations have been recorded upon the
effect upon protoplasmic movements of sudden changes of illumination. In
the case of an amceba (Pelomyxa palustris) Engelmann found that light,
and not its sudden withdrawal, appeared to exert a stimulant effect (Pfeffer :
Pflanzenphysiologie, ii. p. 387).

RELATIONS OF PROTOPLASM TO ELECTRICITY. 207

Movement as distinctly in hairs which had been developed in
darkness, and had remained without light for thirty hours, as in
any which had grown in the open daylight. According to Du-
trochet, it requires a withdrawal of the light for about twenty
days to cause an entire cessation of the movement in Chara.

The effect of very intense light, and the influence exerted by
it upon protoplasm containing chlorophyll, will be examined
under ‘* Assimilation.”

572. Relations of protoplasm to electricity. Chemical changes
within the plant result in the production of electrical currents in
protoplasm ; at this point it is proper to examine briefly the
effect produced upon protoplasm by continued and induced
currents.

When the plasmodium of a myxomycete is placed between
platinum electrodes on a glass slide under the microscope, and
a current sent through the mass from one small Grove element,
very little if any effect is observable; but if the current from a
few clements is employed, there is at once more or less rounding
of the branched mass, and there may also be a reversal of the
course of the circulation. When more elements are used, the
protoplasm may be killed. If the protoplasm in cells be experi-
mented upon, nearly similar phenomena are noticed. Protoplasm
is not a good conductor of electricity. Jiirgensen made some
experiments on the action of a current from small Grove cle-
ments upon the leaf-cells of Vallisneria spiralis. A continued
eurrent from one element did not cause any appreciable change
in the protoplasmic movement; but when two, three, or four
were employed, the current retarded the movement, and after
a while completely arrested it. In those cases where the move-
ment had been simply checked, it was re-established in full in-
tensity shortly after cutting off the current of electricity ; but in
those where it had been entirely stopped, it did not begin again.

573. The effect of an interrupted current of clectricity is
essentially the same as that produced by mechanical shock.
The protoplasm generally contracts at certain points forming
small roundish masses in the lines of the slender threads, and
the movements are arrested.

574. Hofmeister states that a constant current is practically
without any influence upon the circulatory movement in the cells
of Chara, but that the interruption of the current produces
nearly the same effect as a sudden mechanical shock or a sharp
change of temperature. He observed essentially the same phe-
nomena in the hairs of the nettle, although in these there was

208 PROTOPLASM.

also more or less of the aggregation into rounded masses alluded
to in 564.

575. The effect of mechanical irritation upon protoplasm in
plants can be easily examined in cells or in plasmodia. When
a cell of Niteila which exhibits rapid circulation of protoplasm
is held somewhat firmly by pressure on the cover-glass, the
movement is arrested instantly, but after a short time it is
resumed. Even in those cases where the pressure has been
sufficient to disturb the arrangement of the chlorophyll granules,
the arrested motions are soon to be seen again. For experi-
ments upon the effect of pressure and shock, the stamen-hairs of
Tradescantia are even better than cells of Nitella or Chara,
for pressure brings about an apparent disintegration of the
threads, and all motion is suspended for several minutes; but if
the injury has not been too severe, it soon begins again. How
far such injuries can be carried without affecting the vitality of
the protoplasm, may be seen from the following observations.

According to Gozzi,! if a cell of Chara is ligated firmly, the
circulation is checked for a short time, and then begins in each
half of the cell. It is stated by Hofineister that when a root-
hair of Hydrocharis Morsus-rane is severed, the protoplasm in
the cell remains motionless for a short time, during which the
cut surface of the cell is being closed by a portion of the proto-
plasmic mass. When the surface is completely closed, the cir-
culation begins again within the healed cell.

576. Rosanoff’s observation,? which has been repeated many
times, is of much interest in connection with this subject.
When a cell from the endosperm of Ceratophyllum demersum,
having rapid circulation of protoplasm, is placed under the mi-
croscope, and a slight pressure is exerted on the cover-glass
for a moment, the circulation stops at once, the thick axile
threads of protoplasm begin to round at one or more places, and
from the aggregations slight processes, somewhat like tenta-
cles, appear. After a while these are retracted, and the normal
circulation is resumed. But sometimes it happens that these
tentacles become separated from the threads to which they be-
long, for a time lie without movement near them, and then
become again confluent with them.

Mechanical shock * causes the active plasmodia of the myxo-

1 Quoted by Hofmeister in Die Lehre von der Pflanzenzelle, 1867, p. 50.
2 Die Lehre von der Pflanzenzelle, p. 51.
3 Hofmeister : Pflanzenzelle, p. 26.

RELATIONS OF PROTOPLASM TO GRAVITATION. 209

mycetes to become rounded into the form of somewhat flattened
drops, from which slender branches protrude after a short time.
If pressure is now made upon those portions of the branched
plasmodium in which circulation is to be seen, the movement
stops at once, and is not resumed for two or three miautes ;
but after that period of rest it goes on as before. When a
plasmodium is cut in halves, the circulation is to be seen after
a while in the separated portions.!

577. Relations of protoplasm to gravitation. Concerning the
influence of gravitation on the form assumed by protoplasm, it
need only be said here that the less dense plasmodia appear some-
times to yield to this force. But Pfeffer? found that in a saturated
atmosphere the plasmodium of Asthalium moved in the dark with
equal freedom whether the moist bibulous paper on which it rested
was held horizontally or vertically ; Strasburger? also has noted
the same fact. If one part of the paper is more moist than an-
other, it is to the very wet spot that the plasmodium wanders.

578. Relations of protoplasm to moisture. The relations of
water to the activity of protoplasm are not yet thoroughly under-
stood. It has been seen (577) that there is a tendency of plas-
modia to move to the points where there is the most moisture ;
and in general it may be said that a large amount of water is
favorable to all protoplasmic movements. ‘Thus Delinecke *
found that the protoplasm in the cells of the collenchyma of
Balsamina exhibited no circulation until the section had been
placed in water; and the same phenomena can be shown in
sections of many active plants.

On the other hand, Velten has shown that in some eases the
protoplasmic movement stops when a plant-hair is placed or kept
for a time in water, but is resumed if it is transferred to a dilute
solution of gum-arabic, although the protoplasm was furnished
with a greater supply of water in the former than in the latter
case.

579. Some harmless plasmolytic agents (see p. 27), for in-
stance a dilute solution of sugar, added to the water in which the

1 Pfeffer: Pflanzenphysiologie, ii. 390.

2 Pfeffer: Pflanzenphysiologie, ii. 388.

8 Wirkung des Lichtes auf Schwarmsporen, 1878, p. 71. Dehnecke (Ueber
nicht assimilirende Chlorophyllkorper, 1880) has shown that the various
bodies which occur in protoplasm of cells — for instance, chlorophyll granules,
starch-grains, and the like — have a marked tendency to sink to that part of
the cellulose wall which is lowest. The change of position takes place some-
times in a few minutes, sometimes only after several hours.

4 Flora, 1881, p. 8.
14

210 PROTOPLASM.

protoplasm of the cells of Tradescantia stamen-hairs is exhibit-
ing rapid circulation, cause an increase in the rate of movement.
This fact has been considered to show, in connection with the
cases mentioned, that for the most rapid circulation of proto-
plasm there must be a definite amount of water, —the optimum.

580. When any of these plasmolytic agents are used in too
concentrated a solution they may exert a much more marked
effect upon the protoplasmic contents of a cell; not only does
all movement cease, but the mass shrinks into small bulk, and
does not afterwards recover its former shape and size. Asa
result of their action, two other phenomena are presented : (1) the
protoplasm of one cell can be seen in some cases to be connected
through the cell-wall with the protoplasm in the adjoining cell;
(2) a change takes place in the firmness or turgor of the cell-
wall. Both of these phenomena must receive attention at a later
stage. When a cell containing living protoplasm is placed in a
harmless and dilute solution of any coloring-matter, for instance
logwood, its wall becomes more or less tinged by the dye, but
the protoplasm retains for a while at least its power of move-
ment, and does not take up any of the dye. If, however, the
protoplasmic mass is injured or dead, it absorbs the coloring-
matter with great avidity.

581. Relations of protoplasm to various gases. Experiments
upon the effects of gases on the behavior of protoplasm can
be best conducted by means of the simple gas-chamber shown
in Fig. 195. A current of the gas employed is drawn through
the tube @ by means of any simple aspirator; and in a few
seconds the specimen previously placed upon the glass at 8,
and protected by a cover-glass, is thoroughly surrounded by
it. By the use of this apparatus it has been found that the
presence of free oxygen is essential to protoplasmic movements.
Hofmeister and Kihne have shown that when this gas is no
longer supplied to the protoplasmic mass or to the cells in
which the protoplasm is contained, all movements cease. Thus
IJofmeister! found that the circulation of Nitella was completely
arrested in thirteen minutes after the air was wholly removed.
Kiihne? replaced by hydrogen the air in which the hairs of
Tradescantia had shown rapid movement, and after several
hours all motion was arrested.

582. Corti,’ the discoverer of the circulation in Nitella, placed

1 Die Lehre von der Pflanzenzelle, p. 49.
‘2 Untersuchungen iiber das Protoplasma, 1864, p. 107.
8 Meyen : Pflanzenphysiologie, ii. 224.

STRUCTURE OF PROTOPLASM. 211

cells in which the movements were plainly seen, in olive-oil, in
order to exclude the air. A short time after this was done the
movement stopped. In Hofmeister’s? repetition of Corti’s ex-
periment the arrest of the protoplasmic movement occurred in
five minutes in olive-oil; after the oil had been carefully poured
off, the movements recommenced in thirty minutes.

583. Kiihne experimented algo upon the replacement of the
oxygen needful for protoplasmic movements by carbonic acid,
and found this gas much better than oil for excluding air.
Upon removal of the plant-hairs from oil, it is difficult to take
away the last trace of adherent oil.

584. The ordinary anesthetics, chloroform and ether, arrest
the movements of protoplasm.?

585. The structure of protoplasm. Having thus briefly ex-
amined some of the more striking phenomena of protoplasmic
movement, the question must now be asked, What is the struc-
ture of a substance which exhibits these phenomena?

By the highest power of the microscope it appears as a homo-
geneous hyaline mass holding in its substance, but apparently
as foreign bodies, very minute granules. But when the proto-
plasmic matter is stained by the skilful use of pigments, its
homogeneous character disappears.

586. Schmitz has confirmed and extended the observations
of Frommann, which show that in some cases at least the pro-
toplasmic body is a reticulated framework of extremely delicate
fibrils, between the meshes of which is a homogeneous liquid.
There is unobstructed communication between the different
meshes, so that the whole of the liquid may be regarded as
practically one mass. The network of fibrils does not possess
any rigidity, but is constantly mobile under favorable condi-
tions, and undergoes manifold changes of form. The reticulated
structure is most clearly seen in the parietal protoplasm, and the
larger bands of cells which contain relatively considerable sap.

When, after hardening, protoplasm is carefully stained with
hematoxylin, the whole mass appears to be equally and evenly
colored ; but it is in reality only the network which takes up the
color, the liquid in the meshes remaining uncolored.

Imbedded in the protoplasm, especially in the inner portions,
there are generally minute granules which have a high degree
of refringency, and which stain very deeply with the dye; these
are the microsomata of Hanstein.

1 Die Lehre von der Pflanzenzelle, p. 49.
2 Claude Bernard : Legons sur les Phénoménes de la Vie, 1879.

212 PROTOPLASM.

587. Up to the present time the microscope has not revealed
more than these facts respecting the intimate structure of proto-
plasm, and from these alone no clear conception can be formed
of the mechanics! of protoplasmic movements.

588. It is just at this stage of the inquiry respecting the
structure of protoplasm that many have sought to apply an
hypothesis known as Nigeli’s; namely, that all organized
bodies consist of structural particles (termed micelle), each of
which is individually enveloped by a film of water holding vari-
ous substances in solution. According to Nigeli’s view, as origi-
nally given, the micelle are never spherical, but possess a true
crystalline character, as shown by the relations of organized
bodies to polarized light.2 These micellze are believed to obey

1 Hofmeister regarded protoplasmic movements as directly dependent upon
changes in the capacity of living protoplasm for absorbing water, shown by
pulsating vacuoles (see 120). In the mass of a plasmodium, or in the free
spores of some alge, there are generally to be detected easily under the micro-
scope minute spherical cavities filled with watery sap which are constantly
changing in size. Their rhythm of change, or pulsation, as it is called, is differ-
ent for different plants, varying from a few seconds to as many hours. Their
increase in size is usually gradual until the maximum is reached, when sud-
denly the cavity or vacuole contracts even to the point of vanishing, and
then it slowly begins to form again at the same place in the mass. The
rhythm of the pulsations can be made to vary with changes in the surround-
ings ; for instance, with changes of temperature, or by the application of dilute
solutions, or by any agent which modifies the absorptive power of proto-
plasm for water. But these agents are also efficient in controlling the rate
of protoplasmic movement. The spontaneously pulsating vacuoles appear to
indicate that the absorptive power of protoplasm changes spontaneously, and
is different successively in different parts of the mass, thus disturbing the
equilibrium of the soft mass sufficiently to force some portions from place
to place. But Hofmeister gave no explanation of the cause of variations in
the imbibition power of protoplasm.

2 In his earliest work on the subject (Die Stiarkekérner, 1858) Nageli applied
the word molecule (which had not then obtained such general acceptance in
chemistry and physics, with a different signification) to what he now calls the
micella. His hypothesis has undergone sundry changes from time to time,
one of his last important publications (Theorie der Garung, 1879) containing
some modifications.

The terminology now proposed by Nageli applies the word pleon to those
aggregates of molecules which cannot be increased or diminished without
changing their chemical nature ; for instance, crystals which contain water of
crystallization would be called pleons, for the molecule H,O has a definite
numerical relation to the molecules of the salts, and examples of similar pleons
are afforded by such compound salts as the alums.

Compare with this the following statement : —

“It has also been a question among chemists whether molecular combination
was possible ; in other words, whether it is possible for molecules of different

te

NAEGELI’S HYPOTHESIS. 213

the following attractions: (1) that of cohesion, by which each
individual micella is an aggregate of molecules; (2) that which
tends to bring adjacent micelle together; (3) that of ache-
sion, by which the surfaces of the micelle retain their films of
water.

kinds to combine chemically, each preserving its integrity in the compound. ...
Any antecedent improbability on theoretical grounds is far more than out-
weighed by the evidence of a large number of compounds whose constitution
is most simply explained on the hypothesis of molecular combination. For
example, in the crystalline salts it is impossible to doubt that the water
exists as such, not asa part of the salt molecule, but combined with it as a
whole. So also there are a number of double salts whose constitution is most
simply explained on a similar hypothesis” (Cooke’s Chemical Philosophy,
1882, p. 137).

The word micella is applied by Nageli to those aggregates of molecules
which (like crystals) can increase or diminish in size without changing their
chemical nature. The micella is assumed to be much larger than the pleon.
“The internal structure of the micella is crystalline, while the exterior may
assume any shape.” The micelle unite to form micellar aggregates ; of such
the crystalline protein granules afford a good example. Thus, according to
Nageli, five terms must be recognized, — the atom, the molecule, the pleon, the
micella, and the micellar aggregate. Pfeffer applies a general term, Tagma, to
all aggregates of molecules, thus bringing under one head the pleon, micella,
and micellar aggregate ; and he applies the name Syntagma to all bodies made
up of tagmata. The subject will be again referred to under ‘‘ Osmosis.”

To make clearer the conception of a micella, it may be well to examine
briefly two terms in common use ; namely, atom and molecule.

When a solid body, for instance a crystal of sodic chloride (common salt),
is mechanically separated into the smallest possible fragments, each particle
still possesses all the properties of salt. Beyond this mechanical limit of sepa-
ration the process of subdivision may be carried still further by solution :
the minutest fragments of the salt can be broken up and diffused through the
solvent, and yet not lose their essential character as salt; in fact, they can be
again recovered without change from the solution. But it is impossible to go
beyond this latter limit of separation without altering the essential properties
of the substance. In other words, by this subdivision the physical limit has
been reached ; namely, the molecule.

A molecule is understood to be the smallest amount of any substance
which can exist as such in the free state. Hence the molecule is the physical
unit.

If, however, the salt is subdivided by chemical means, — for instance, by the
action of strong sulphuric acid, —its identity is destroyed, and its component
parts enter into new relations, and cannot be restored to their original relations
except by an exceedingly complicated process. In other words, the physical
limit has been overpassed and the chemical limit reached ; namely, the atom.

Atom is generally defined as ‘‘the smallest amount of a given substance
which can exist in combination,” or “the smallest mass of an element that
exists in any molecule.” The atom is the chemical unit.

Atoms are variously combined to form molecules: molecules are variously
aggregated to form masses.

2id PROTOPLASM.

Contiguous micelle in any organized substance, for instance
cell-wall or starch, frequently possess different chemical charac-
ters, as is shown by the fact that from such a substance one por-
tion can be taken without materially disturbing the external form.

589. By means of the changes which go on in the formation
of new micelle, and in their reconstruction, it is sought to account
for the nutrition, growth, and movements of organized substances.
This is essentially the basis on which Engelmann! founds his
explanation of the movements of protoplasm.?

590. Continuity of protoplasm. It was supposed until recently
that the protoplasm in one young cell is completely shut off from
that in contiguous cells by an imperforate cell-wall, and that even
in the cases where the wall is perforate there is no communi-
cation of protoplasm through the pores. There is abundant
evidence to show the incorrectness of this view. In some cases
the protoplasm in one cell is practically continuous with that in

1 Hermann’s Handbuch der Physiologie, i. 1879, p. 374.

_ 2 The application of this hypothesis by Sachs is given somewhat fully in
the following extract (Text-book of Botany, 2d Eng. ed., 1882, p. 666) :
‘*Chemical compounds of the most various kinds meet between the micella
of an organized body, so that they act upon and decompose one another. It
is certain that all growth continues only so long as the growing parts of the
cell are exposed to atmospheric air; the oxygen of the air has an oxidizing
effect on the chemical compounds contained in the organized structure ; with
every act of growth carbon dioxide is produced and evolved. The equilibrium
of the chemical forces is also continually disturbed by the necessary production
of heat ; and this may also be accompanied by electrical action. The moeve-
ments of the atoms and molecules within a growing organized body represent
a definite amount of work, and the equivalent forces are set free by chemical
changes. The essence of organization and life lies in this : — that organized
structures are capable of a constant internal change ; and that, as long as they
are in contact with water and with oxygenated air, only a portion of their forces
remains in equilibrium even in their interior, and determines the form or frame-
work of the whole ; while new forces are constantly being set free by chemical
changes between and in the molecules, which forces in their turn occasion
further changes. This depends essentially on the peculiarity of micellar struc-
ture, which permits dissolved and gaseous (absorbed) substances to penetrate
from without into every point of the interior, and to be again conveyed out-
wards. Neither the chemical nor the molecular forces are ever in equilibrium
in the protoplasm ; the most various elementary substances are present in it in
the most various combinations ; fresh impulses to the disturbance of the internal
equilibrium are constantly being given by the chemical action of the oxygen
of the air ; and energy is continually being set free at the expense of the proto-
plasm itself, which must lead to the most complex actions in a substance of so
complicated a structure. Every impulse from without, even when impercep-
tible, must call forth a complicated play of internal movements, of which we
are able to perceive only the ultimate effect in an external change of form.”

CONTINUITY OF PROTOPLASM IN CELLS. 215

the next, by means of delicate threads which pass through
pores in the intervening cell-wall. Doubtful instances afforded
by the cribrose-cells have been already alluded to (see 279).
The endosperm cells of seeds of Strychnos Nux-vomica afford
a well-marked example of the cases of communication between
cells of seeds. Tangl? advises that very thin sections parallel
to the flat surface of the seed be shaken with dilute tincture
of iodine or with a solution of iodine in iodide of potassium for
about five minutes, and then thoroughly washed with pure water.
The protoplasinic and other contents of the uninjured cells will
then appear as a contracted ball having somewhat the shape of
the cell. From the mass in one cell minute threads run through
pores or canals in the wall to the masses in the adjoining cells,
and there is no break in their continuity. In the endosperm of
the allied species, Strychnos potatorum, Tangl did not detect
canals of the character found in S. Nux-vomica.

Gardiner? has demonstrated the existence of communication
between the protoplasmic masses in contiguous cells of the pul-
vini of the leaves of some plants having the power of motion.
When sections of these leaves are placed in a solution of a salt
which causes contraction of the protoplasm, the shrunken mass
is seen to be connected with the cell-wall by extremely delicate
threads of protoplasm. The threads can be traced to pits in the
wall, and there it can be seen that they are exactly opposite the
threads on the other side of the wall. If the solution of the salt
used is too strong, some of the threads may be ruptured, and
then one free end of each thread will retract to the main mass
while its other part goes to the cell-wall. If fresh sections are
treated with strong picric acid, and then, after washing in alco-
hol, are stained with anilin blue, the continuity of the proto-
plasm in uninjured cells becomes apparent. Mimosa affords
excellent material for this purpose.

Hillhouse? reports similar continuity of protoplasm in the cor tee
of the stem of Laburnum, and in the petiole of several leaves.
The fresh material is to be placed for a few days in absolute
alcohol, and the thin sections made from it are to be treated
with dilute alcohol. The sections are then to be placed in
concentrated sulphuric acid, and after the acid has removed the
cell-wall, its excess is to be withdrawn by means of a pipette,

1 Pringsheim’s Jahrbiicher, 1880, p. 170.
i Philosophical Transactions Royal Society, 1883, clxxiv. 817.
3 Botanisches Centralblatt, 1888, xiv. 89, 121.. ei

216 PROTOPLASM.

and the preparation very carefully washed. The application of
strong glycerin completes the treatment. The specimen must
not be removed from the slide during the whole series of opera-
tions. If the manipulation has been careful throughout, the
minute threads can be seen passing from one mass of protoplasm
to the next.

591. The directions given by Strasburger for demonstrating
the continuity of protoplasm are as follows: From the stem of a
dicotyledonous shrub or tree (the diameter of which should be
at least a centimeter) the periderm is removed by a knife, and
very thin tangential longitudinal sections are then made through
the soft green bark. The parenchyma cells which are inter-
mingled with the liber contain more or less chlorophyll, and may
have pits, the very smallest of which are not bordered (see 268).
If the first sections have shown in any case that these cells are
furnished with pits, others are then prepared and placed at once
in a drop of a solution of iodine (that of iodine in an aqueous
solution of potassic iodide is best). The excess of the solution
is at once removed and the preparation covered with a glass
cover. At the edge of the cover-glass there is placed a drop
of concentrated sulphuric acid, and by the side of this a couple
of drops of dilute sulphuric acid; when these are mingled the
mixture is allowed to flow under the cover-glass, while a bit of
filtering-paper on the other edge of the glass draws it through.
The specimen becomes dark blue. If the color is deep, the cover-
glass is cautiously lifted and the preparation is then thoroughly
but carefully washed in water. After this washing, a drop of
a solution of anilin blue is added, whereby the object- becomes
stained ; then, after washing again, a little glycerin? is added,
and the cover-glass is fastened down with some cement. For
the examination of the specimen the strongest objectives — pref-
erably the so-called ‘‘ homogeneous immersion,” employed with
cedar-oil — are indispensalle.

Under a sufficiently high power the middle lamella of the wall
is seen to be somewhat swollen, while the contents of the cells
are contracted and colored. ‘The periphery of the individual
protoplasmic masses in the cells of the cortical parenchyma is
smooth on that face which was in contact with the cell-wall hav-
ing very small pits; but it has minute protrusions on that face
which was next the bordered pits. Moreover, the protrusions
in contiguous cells are exactly opposite each other. Between

1 Strasburger advises the addition of a little anilin blue to the glycerin.

CONTINUITY OF PROTOPLASM IN CELLS. 217

the protrusions at the bordered pits there extend extremely deli-
cate threads of protoplasm which have a granular character.
The threads are somewhat curved (especially the outer ones),
and are slightly swollen in the middle. In peculiarly good
preparations it has been shown that there is an apparent inter-
ruption at the middle of their course, but that at this break
there are still minute filaments which serve to connect them.
From these and kindred observations Strasburger and some
others have adopted the view that there is such a degree of
continuity between the protoplasmic masses in the cells that
they form throughout the plant an unbroken whole.?

592. That protoplasin may perhaps occur in intercellular spaces
appears from the observations of Russow? and of Berthold? To
‘demonstrate this, one-year-old twigs of Ligustrum vulgare are
hardened for a few days in absolute alcohol, longitudinal sections
of the primary cortex placed in dilute iodine solution (see 30),
the excess of iodine removed, and dilute sulphuric acid added.
The contents of the cells and of the intercellular spaces will then
appear as yellowish-brown masses.

593. That protoplasm can in some cases pass through an im-
perforate cell-wall appears from the observation of Cornu,* that
in the formation of the macroconidia of a certain Nectria all the
protoplasm of the five or six cells of the spore emerges to form
the macroconidium, which arises as an outgrowth of one of the
cells of the spore. The four or five partition-walls through which
the protoplasm must pass are, however, neither dissolved nor
perforated.

It is probable that a striking phenomenon of fertilization in
phenogams, namely, the complete emptying of the pollen-tube
of its protoplasm (see ‘* Fertilization”) without apparent break
in the continuity of the wall, must be referred to the same pene-
trative power of protoplasin.

The withdrawal of the principal part of the protoplasmic
matters from deciduous leaves before the fall of the leaf may be
perhaps explained in the same way.

Strasburger cites as an illustration of this penetrative power
the well-known case of the removal of protoplasmic matters

1 Das botanische Practicum, 1884, p. 617. Strasburger : Bau und Wachs-
thum der Zellhaiite, 1882, p. 246. Frommann : Beobachtungen iiber Structur
des Protoplasma der Pflanzenzellen, 1880.

2 Sitz. der Dorpater Naturforscher-Gesellschaft, 1882, p. 19.

8 Berichte der deutschen botanischen Gesellschaft, ii. 20.

‘ Comptes Rendus, 1877, tome lxxxiv. p, 133.

218 PROTOPLASM.

from the cells around the buds which form on the incised leaves
of Begonia.

594. The relations of the cell-wall to protoplasm are not yet
fully understood; and in regard to some of them there ‘exists
among botanists considerable diversity of opinion. The two
principal views are the following: 1. The cell-wall is formed
by the solidification upon the exterior of a protoplasmic mass,
of matters previously dissolved in it. The pellicle thus pro-
duced is regarded as a sort of excretion (since in most cases it
is not again to be dissolved and employed by the organism) or
as a secretion (because in a few instances it can be dissolved
and utilized a second time by the plant). The substance capa-
ble of thus solidifying upon the surface of protoplasm consists of
cellulose combined with water and a small amount of incombus-
tible matters, but it is not positively known in what condition
these were previously combined in the protoplasm. 2. The
cell-wall may be regarded as directly produced by a conversion
of the outer film of protoplasm into cellulose with which some
other matters are intermingled.”

595. The young cell-wall® is practically a homogeneous film of
cellulose, which speedily undergoes changes both in its chemical
and physical character. In many of the lower plants the wall
differs in some particulars from that found in the higher plants
(see p. 29), but the differences need not enter into the present
description.

596. Two views are held respecting the mode of growth of
the cell-wall. The first may be regarded as based upon the
hypothesis of Nageli spoken of in 588. From some of the mate-
rials held dissolved in the adherent film of water around each
mnicella new micelle of cellulose are supposed to be produced,

1 “That protoplasm can pass through closed cell-walls is beyond doubt”
(Vines, note to second edition of Sachs’s Text-book, p. 946).

2 The view that cellulose is a kind of secretion is stated at great length in
Hofmeister’s Pilanzenzelle, and in several communications by Sachs in Bota-
nische Zeitung. The second view is given by Schmitz, Sitz. der niederrhei-
nischen Gesellschaft fiir Natur- und Heilkunde, Bonn, 1880. He bases his
opinion largely upon the fact that in some cases the cells gradually become
emptied of protoplasm as the amount of cell-wall increases, and upon the phe-
nomena which attend the increase of the cell-wall in thickness.

8 It was believed by some of the earlier phytotomists that the cell-wall was
a close, firm network of extremely fine fibres, while others held it to be com-
posed of minute granules. In these explanations of structure it was confessed
that the ultimate fibres, or ultimate cuuues lie quite beyond the reach of the
highest powers of the microscope. :

GROWTH OF THE CELL-WALL. 219

which are interpolated between the old. This is the intussus-
ception theory. It has gradually displaced an older theory,
namely, that of growth by apposition. As the older theory was
usually held, it presented two modifications,— one that the
growth of a cell-wall in thickness takes place on the exterior of
the wall, so that in a stratified wall all the outermost portions
are the newer; the other, that all the new matter is laid down
upon the interior of the old.

The apposition theory has recently attracted much attention
from the studies of Schmitz, and from its adoption and advocacy
by Strasburger.?- As now held by these authors, the view is this:
stratified and other cell-walls grow in thickness by the deposi-
tion of new particles upon the inner face of the cell, much as a
crystal adds new particles to itself; growth in surface is the result
of a simple stretching of the wall by the pressure of the con-
tents upon it.

Any solution which causes a shrinking of the contents of the
cell, and thus diminishes the pressure on the wall, may cause
a diminution of the size of the cell itself. The bearing of this
upon the turgescence of the cell will be again adverted to under
‘¢ Properties of New Cells and ‘Tissues.”

To the physical characters of cellulose already mentioned
(see 129), may now he added that property which is possessed
also by many other organized substances; namely, that of swell-
ing greatly when placed in water. The wall of a living and active
cell is of course moist, and its increase in size on the addition of
more water is seldom marked; but under certain circumstances
the amount of water in the cell-wall even of an active cell may
fall below its usual amount, and then the application of water
will cause an appreciable change of bulk. Such change in the
amount of water may take place with great rapidity upon
slight external disturbances, such as shock: in these cases, the
amount of water in the protoplasm in contact is correspondingly
modified.

597. Historical note regarding protoplasm. The word proto-
plasm appears first in a memoir by Mohl, in 1846, ‘‘ On the
Movement of Sap in the Interior of Cells,” which deals, however,

1 For an account of the two modifications of the apposition theory, the
student is referred to Harting’s paper, translated in Linnza, 1846, and Mobl’s,
in Botanische Zeitung, 1846. A fair statement of the first modification is
presented in Mulder’s Physiological Chemistry.

2 Strasburger : Bau und Wachsthum der Zellhaiite, 1882.

220 PROTOPLASM.

not,so much with the movement of what would to-day be called
cell-sap, as with the general behavior of all the motile contents
of active vegetable cells. After showing that his predecessors
had not clearly understood the important part played in the life
of the cell by the viscous matter known vaguely up to that time
as schleim, or mucus, Mohl points out the essential identity of
the nucleus, primordial utricle, and the basic substance filling all
but the sap-cavities of the ccll. For the substance which is
essential to the formation of every new cell and to the develop-
ment cf newly formed cells he proposed, upon physiological
grounds, the significant name protoplasma.

For convenience of reference, the paragraph in which the word
is first employed is here given: —

‘‘Da wie schon bemerkt diese zihe Fliissigkeit iiberall, wo. Zellen
entstehen sollen, den ersten, die kiinftigen Zellen andeutenden festen
Bildungen vorausgeht, da wir ferner annehmen miissen, dass dieselbe
das Material fiir die Bildung des Nucleus und des Primordialschlauches
liefert, indem diese nicht nur in der niichsten riumlichen Verbindung
mit derselben stehen, sondern auch auf Jod auf analoge Weise reagiren,
dass also ihre Organisation der Process ist, welcher die Entstehung der
neuen Zelle einleitet, so mag es wohl gerechtfertigt sein, wenn ich zur
Bezeiclnung dieser Substanz eine auf diese physiologische Function
sich beziehende Benennung in dem Worte Protoplasma vorschlage.”’ 1

In 1835 Dujardin described a contractile substance capable of
spontaneous movement in certain of the lower animais, to which
he gave the name Sarcode. The identity of sarcode with that
substance which forms the essential body of animal cells and
with the protoplasm of vegetable cells was suggested by several
investigators and finally demonstrated by Max Schultze in 1861.?

Schwann, even as early as 1839, pointed out various analogies
and homologies between animal and vegetable cells, and enun-
ciated the following proposition: animal cells are completely
analogous to vegetable cells, and are quite as independent in
their mode of growth. The bearing of Schultze’s demonstra-
tion upon the foregoing proposition is obvious. Schwann
instituted also certain comparisons between the mode of forma-
tion of cells and that of crystals (‘‘ Microscopical Researches
into the Accordance in the Structure and Growth of Animals
and Plants.” translated by Henry Smith for the Sydenham
Society, 1847).

1 Botanische Zeitung, 1846, p. 75.
2 Archiv fiir Anatomie, Physiologie, und wiss. Medicin, 1861, pp. 1-27, and
Das Protoplasma der Rhizopoden und der Pflanzenzellen, Leipzig, 1863.

CHAPTER VII.
DIFFUSION, OSMOSIS, AND ABSORPTION OF LIQUIDS.

DIFFUSION AND OSMOSIS.

598. Wuen two liquids which are not miscible — for instance,
oil and water — are shaken together, and then left at rest, they
will separate sooner or later, according to their specific gravity.
But if two miscible liquids are shaken together, they remain as a
homogeneous mixture no matter what their specific gravity may
be. Also when two miscible liquids are left in contact, without
any agitation they become thoroughly commingled, and constitute
a uniform mixture; this uniform commingling of two or more
miscible fluids is termed diffusion.?

599. Furthermore, if two miscible liquids are separated by
a membrane which can be moistened by them, they will diffuse
through it and make a uniform mixture. This latter kind of
diffusion, in which the contact between the two liquids is not
direct, but takes place through a septum of some substance, is
known as osmosis. In the plant and in its surroundings the
two kinds of diffusion play such an important part that they
must receive special attention.

600. Diffusion of liquids. The rate of diffusion varies with
the nature of the liquids and the temperature. The statements in
the following paragraphs are substantially as given by Graham.*

1 Pfaundler applies this term to the commingling whether it is or is not
brought about by agitation (Miiller's Lehrbuch, 1877, i. 162).

2 They are based upon two series of experiments conducted with very sim-
ple apparatus. In the first series a small, wide-mouthed vial containing one
liquid was placed in a jar holding the other liquid, allowed to stand a few
days, withdrawn, and the amount of diffusion noted. In the second series
Graham pursued the plan of placing in a cylindrical glass jar, 152 mm. high
and 87 mm. wide, seven tenths of a liter of pure water, and then carefully car-
rying to the bottom of the jar, by means of a fine pipette, one tenth of a liter
of the liquid to be diffused. The jar was then left at rest in an apartment
where the temperature was nearly constant, and after a certain time its contents
were drawn off carefully in portions of fifty cubic centimeters, each portion
evaporated separately, and the residue remaining after evaporation weighed.

222 DIFFUSION AND OSMOSIS.

601. Different salts in solutions of equal strength diffuse in
unequal times. Thus potassic hydrate diffuses with donble the
rate of potassic sulphate, and the latter with double the rate
of crystallized sugar. But these substances have a compara-
tively high rate of diffusion. A solution of caramel (sugar
heated till it becomes brown) diffuses very slowly ; the sugar in
this case has been so changed in its character that its rate of
diffusion has been reduced from a high to a very low one. Gela-
tin may be taken as the representative of the almost ‘‘ fixed” or
slowly diffusible class of substances ; most crystalline substances,
as representatives of the highly diffusible class. The former are
collectively known as colloids (xéAAa, glue), the latter as crystal-
loids. It must be noted that Graham’s use of this word ‘ crys-
talloid” is different from that in which it has been employed in
speaking of the protein bodies (177).

602. With each salt the rate of diffusion increases at a
slightly higher rate than the temperature of the solution.

603. The members of certain chemical groups are equally dif-
fusible. Thus hydrochloric, hydrobromic, and hydriodic acids;
the chlorides, bromides, and iodides of the alkaline metals, etc.,
have equal rates of diffusion into pure water.

604. The diffusion of a solution of a salt into the dilute solution
of another salt takes place nearly as rapidly as into pure water ;

The difference in the rates of diffusion of ten per cent solutions of different
substances experimented upon in the manner described on the preceding page
is clearly shown by the annexed table.

uber of stratum from above odin
ices downwards, chloride. Sugar. Gum. Tannin.

104 -005 003 003
DE sce sie 1st Sin Bo idee spa ER te, 129 008 -003 -003
(ee a -162 012 -003 004
4 198 .016 .004 .003
BP oat ah ate re ee ae ae Las 267 -030 -003 005
Go sae, oe eo 340 059 004 007
7 429 102 006 017
8 } Sele OSS 535 -180 031 031
De es ee aS eG at ss 654 805 .097 069
10 ee ee Ea eG 766 495 215 145
MDS ee oe aig a vid ar ee te 881 740 407 288
12 eo ay ee a oa eae 991 1.075 134 656
1B) Ue koa Phe Ee eee 1.090 1.435 1.157 1.050
14. me Gap oR eS fel HE 1.187 1.758 1.731 1,719
TD,AG 4. eae es ee 2.266 3.783 5.601 6.097
9.999 10.003 9.999 9.997

The first series of experiments are described in Philosophical Transactions,
1850; the second, in 1861.

RATES OF DIFFUSION. 223

but if the second solution contains some of the salt, ike that in
the first solution, the rate of diffusion is retarded.
605. The rate with which a salt passes from a stronger into
a more dilute solution is nearly proportional to the degree of
concentration. The approximate times required for the diffu-
sion of equal weights of various substances into watey are given
in the following table : —
Hydrochloricacid . . . . . 2... ee. OUD
Sodic chloride. . . . Boe a ae ee ee ee 12338;
Magnesic sulphate . . 2. 2. ee ee ee OT
Cane-sugar . Bi: Re Aoi athe BP. ea aS ee Ee
AMDWAMD: 35 Gao 2 Secs SE Oe ro ce Se ae de AD
Caramel . . . eRe woe Oe ee oe BBS
606. Of the colloids, Graham says:1 ‘* Low diffusibility is
not the only property which the bodies last enumerated possess
incommon. . . . Although often largely soluble in water, they

1 Philosophical Transactions, 1861.

Graham says further: ‘‘ Although chemically inert in the ordinary sense,
colloids possess a compensating activity of their own arising out of their
physical properties. While the rigidity of the crystalline structure shuts out
external impressions, the softness of the gelatinous colloid partakes of fluidity,
and enables the colloid to become a medium for liquid diffusion, like water
itself. The same penetrability appears to take the form of cementation in such
colloids as can exist at a high temperature. Hence a wide sensibility on the
part of colloids to external agents. Another and eminently characteristic qual-
ity of colloids is their mutability. Their existence is a continued metastasis.
A colloid may be compared in this respect to water while existing liquid at a
temperature under its usual freezing point, or to a supersaturated saline solu-
tion. Fluid colloids appear to have always a pectous modification (ryxrés,
curdled), as fibrin, casein, albumin. But certain liquid colloid substances are
capable of forming a jelly, and yet still remain liquefiable by heat and soluble
in water. Such is gelatin itself, which is not pectous in the condition of ani-
mal jelly, but may be so as it exists in the gelatiferous tissues. Colloids
often pass under the slightest influences from the first into the second condi-
tion. The solution of hydrated silicie acid, for instance, is easily obtained in
a state of purity, but it cannot be preserved. It may remain fluid for days or
weeks in a sealed tube, but is sure to gelatinize and become insoluble at last.
Nor does the change of this colloid appear to stop at that point. For the
mineral forms of silicic acid, deposited from water, such as flint, are often
found to have passed during the geological ages of their existence, from the
vitreous or colloidal into the crystalline condition (H. Rose). The colloidal
is, in fact, a dynamical state of matter; the crystalloidal being the statical
condition. The colloid possesses energia. It may be looked upon as the
probable primary source of the force appearing in the phenomena of vitality.
To the gradual manner in which colloidal changes take place (for they always
demand time as an element), may the characteristic protraction of chemico-
organic changes also be referred.”

224 DIFFUSION AND OSMOSIS.

are held in solution by a most feeble force. They appear singu-
larly inert in the capacity of acids and bases, and in all the ordi-
nary chemical relations. But, on the other hand, their peculiar
physical aggregation with the chemical indifference referred to,
appears to be required in substances that can intervene in the
organic processes of life. The plastic elements of the animal
body are found in this class.”

607. Osmose, or Osmosis. Diffusion of liquids through mem-
branes. The interposition of a permeable septum between mis-
cible liquids does not prevent diffusion. Thus if a solution of
sodic chloride is separated from pure water by an intervening
membrane, as one of bladder or of vegetable parchment (see
page 32), diffusion takes place in about the same time as if no
membrane were present.

608. For most experiments in osmosis the simple apparatus
known as an osmometer answers very well. It consists of a
small reservoir furnished with a membrane bottom, and a gradu-
ated tube at its upper part. A very good osmometer can be
prepared from a short-necked bottle from which the bottom has
been carefully removed. After the edges at the bottom have
been made smooth, a piece of wet parchment paper is tightly
fastened on by waxed thread. Great care must be taken to
select parchment or parchment paper which is free from perfora-
tions,! and the tube at the neck must be well fitted to a velvet
cork, so that no escape of liquid can take place in any way. A
film of ordinary unsized paper evenly covered with a solution of
warm gelatin, which cools to form a firm mass upon its surface,
makes a good substitute for parchment in this apparatus. <A
thin film of white of egg coagulated by heat will also serve well
for a covering.

609. The osmometer, filled to a certain point on the tube with
the liquid to be experimented upon, is suspended in pure water so
that the liquid in the apparatus is on exactly the same level as
the water. It will be seen by the experiment that not only does
diffusion take place, but that there is a change in the level of
the liquid in the tube.

610. When any of the more diffusible substances are placed
in a state of solution in the reservoir, a small amount of the
crystalloid passes outwards, while a much larger amount of

1 The existence of actual perforations in good parchment can be demon-
strated by subjecting the apparatus to pressure, or even by repeatedly wiping
the exposed surface of the parchment with filtering-paper.

PRECIPITATION-MEMBRANES. 225

water passes inwards. The change of level caused is of course
accompanied by an immediate change in the hydrostatic pres-
sure, and hence water should be added to or removed from the
outer vessel, to balance inequalities of height as fast as they
occur.

611. The proportional amounts of the substances inter-
changed have been determined by various observers. Jolly,}
by an ingenious modification of the osmometer, obtained the
following results; the figures representing the weight of water
which replaced in osmosis one part by weight of the substance:

Sodic chloride . . 2. 2. 1... ie AB
DU CAL ay Ge om. Me ctke ag Gh sen. ca ale AR. Anat Ot. Sa
Sediesulphate:s <2 22 2 @ . ww % % « IDG
Magnesic sulphate. ©. 2. 2. 2. 2. 1. ww es «6126
Potassic sulphate . 2. 2. 2 1 ew ee ee OD

Potassic hydrate 2. 2 1. 6 1 ee ew ew ew ee 2157

612. These figures are known as the osmotic equivalents of
the respective substances, but they are by no means constant ;
since, as Ludwig’ bas shown, they depend partly on the de-
gree of concentration of the solution used, the duration of the
experiment, and the character of the membrane.

613. If, however, a colloidal body is placed in the reservoir,
very little comparatively passes outwards, and in the case of
some colloids nothing. ‘Indeed, an insoluble colloid, such as
gum-tragacanth, placed in powder within the osmometer, was
found to indicate the rapid entrance of water, to convert the
gum into a bulky gelatinous hydrate. Here, no outward or
double movement is possible.”? This very important fact must
be borne in mind in the application of the phenomena of os-
mose to those of absorption of liquids by the colloids in active
vegetable cells.

614. Precipitation-membranes. Traube* (in 1867) discovered
that when a drop of a solution of copper-sulphate is placed in
a solution of potassic ferrocyanide, there is produced over its
whole surface a coherent membrane (of precipitated cupric ferro-
cyanide), known as a ‘ precipitation-membrane.” This at once
begins to increase in size, but somewhat irregularly, as if breaks
occurred at the upper part through which a portion of the liquid

1 Zeitschrift fiir rationelle Medicin, 1849, vii. p. 83.

® Poggendorff : Annalen der Physik und Chemie, Ixxviii. p. 307.

3 Graham : Journ. Chem. Soc., 1862, p. 269.

* Archiv fiir Anat. u. Physiol. du Bois-Reymond u. Reichert, 1867, p. 87.
15

226 DIFFUSION AND OSMOSIS.

within flowed ont only to meet the exterior liquid, and there
formed instantly a precipitate cohering with the edges of the
rupture. Ifa fragment of chloride of copper is placed in a test-
tube containing a strong solution of potassic ferrocyanide, the
action is more rapid than with copper-sulphate. The fragment
dissolves at once, and forms a green globule at the bottom of
the tube. If it now be carefully watched, it will be seen that a
delicate transparent film (the precipitate of cupric ferrocyanide,
which in a flocculent state is brown) is produced over the glob-
ule, and the sphere begins at once to grow into a cylindrical
body. The liquid in the upper part of the closed cylinder is
almost colorless; that at the bottom is deep green. The inter-
mittent growth in height appears to admit of only one explana-
tion; namely, that the membrane is torn by the great pressure
within, and the solution of copper chloride which flows through
is immediately covered by a newly formed film. By careful
management, such growths of cylindrical form can be produced
several inches long.

Traube also discovered that when a drop of @ gelatin (gelatin
which has been boiled continuously for about three days, there-
by losing its power of coagulation) is placed in a solution of
tannin, a film forms at once, which begins to grow into a spheri-
eal cell, but without the appearance of irregular and intermit-
tent rupture. Such an artificial cell is best prepared by placing
a glass tube having a drop of 8 gelatin on the tip into a solution
of tannin. Its growth is even and uninterrupted, and unless
the apparatus is disturbed. no appearance of rupture is observed.
A further discovery was made by Traube; namely, that a co-
herent film may be formed even by the contact of pure water.
The coagulum produced when gelatin is acted on by tannin (the
so-called tannate of gelatin) is soluble in a concentrated solution
of tannin, but is insoluble in a dilute solution. If a drop of a
solution of tannate of gelatin thus prepared is placed in pure
water, a coherent film forms at the surface which can increase
up to a certain size.?

615. Pfeffer has employed the precipitation-membranes dis-
covered by Traube, in an ingenious apparatus by which the
pressure developed in the so-called artificial cell can be accu-
rately measured. The apparatus consists of a porous porcelain

) At this point should be mentioned the observation of Niageli, that when-
ever cell-contents rich in protein matters come in contact with watery media, u
membranous film is formed over the surface (Pflanzenphysiologische Unter-
suchungen, 1855, pp. 9, 10).

EXPERIMENTS OF PFEFFER. 227

or clay cell, like those which are used in the Bunsen battery,
connected by means of a glass collar with a suitable manometer.
Within the clay cell a precipitation film is formed ;+ the cell is

1 The following account of details essential to success in these experiments
of Prof. Pfeffer has been prepared by one of his students, Dr. W. P. Wilson.

The principal portion of the apparatus is a porous porcelain cell, z, 46 mm.
high and 16 mm. in diameter, with walls 14 mm. in thickness. This cell is
cemented on to a piece of glass tubing, v. A second piece of tubing, ¢, with
lateral tube, is cemented into the first piece. The lateral opening ig for the
manometer m, the one at g is for the convenience of filling and sealing the
cell.

One of the two fluids used in forming the
membrane for experimentation is allowed
to penetrate the porous cell from without.
When this has thoroughly taken place, the
second fluid is poured into the interior. The
contact of the two fluids takes place, there-
fore, on the inner surface of the porous cell,
and here the precipitate is formed which is
termed the pellicle-membrane or precipita-
tion-membrane. Substances which by their
mutual contact give rise to such precipitation-
membranes are termed membranogenic. It
will readily be seen that during any internal
pressure the porous porcelain cell acts as a
support for the membrane. If the exterior
solution is copper-sulphate, the interior solu-
tion potassie ferrocyanide, then the precipi-
tated membrane will be cupric ferrocyanide.
After the membrane has been formed, then
any solution not chemically incompatible
with it may be employed in the cell; namely,
syrup from cane-sugar, a solution of saltpetre,
or a still stronger solution of potassic ferro-
cyanide than was used in the preparation of
the cell.

As the successful working of the apparatus
depends upon the exact carrying out of quite a number of minor details, the
following description of the methods of putting the parts together may be
found useful : —

In order to insure absolute freedom from any foreign substance, the porcelain
cell must be successively washed in dilute solutions of potassic hydrate and
hydrochloric acid, and then thoroughly dried. Warm a piece of sealing-wax
in the spirit-lamp and draw it to a point. Slowly heat the open end of the
cell in the alcoholic flame. When hot enough to very readily melt the wax,
apply the point; and while the cell is continually rotating, cover evenly a space
to the depth of 15 mm. with wax in the interior. It should be about 2 mm.
in thickness. Pick up the short piece of tubing, v, which has been previously
waxed on one end, and rotate it over the flame. When both porcelain cell and
glass tube are as warm as they can be made and yet the wax kept smooth

228 DIFFUSION AND OSMOSIS.

then filled with any diffusible liquid, — for instance, a dilute solu-
tion of sugar, — the manometer is attached, and the whole appa-
ratus is placed in pure water or any aqueous solution.

and even on all sides, place them quickly together, lapping about 15 mm.,
and continue the rotary motion until cool. Take a scalpel with a point bent
at right angles to the blade, heat it, and, inserting it in the glass tube,
cut away the wax at its inner end, thus exposing a shoulder of the thickness
of the glass. Roll out in the form of a pencil about 2 mm. in diameter a piece
of sealing-wax which has been made a little soft by the addition of a drop or
two of turpentine. A piece of this, equal in length to the inner circumference
of the glass tube, in a long coil, should be placed on the point of the scalpel,
carried in to the shoulder and pressed into it. A little heat very cautiously
applied from without, with proper turning of the cell, will easily cause this
softer wax to flow and fill the shoulder with perfect smoothness. The use of
the softer sealing-wax makes a joint which will not crack under strong pres-
sure. Now cement the tube ¢ very firmly into v, with the same precautions
as above. Unless a pressure of more than three atmospheres is desired, the
soft wax need not here be used.

The cell is now ready to be prepared for filling. In order to saturate the
porous porcelain with any given solution, the air must first be wholly removed.
Place the apparatus in a beaker of water which has been freed from air by boil-
ing, and set the whole under the bell-jar of an air-pump. Exhaust and admit
the air into the bell-jar repeatedly until bubbles can no longer be seen to rise
from the porcelain. Transfer the cell to a three per cent solution of copper-
sulphate, and exhaust the air again. Four or five hours will be required for
this solution to thoroughly penetrate the porous cell. At the end of this time
remove it from the copper-sulphate, empty it, and with some long twisted
strips of bibulous paper quickly dry up all moisture from its inner surface. If
at any time the exterior surface of the cell begins to appear dry before the
moisture from within has been wholly removed, dip it at once in the solution
from whence it came. At the moment when the moisture is properly removed,
fill the cell to the second joint with a three per cent solution of potassic ferro-
cyanide and replace it in the copper-sulphate, taking care that the surfaces of
the two fluids are in the same plane. An interim of at least twelve hours must
now elapse in order that the membrane may be properly formed. At the end of
this time the cell is ready to be used, either with the solution which it already
contains or with some other. If some other solution is to be employed, then
carefully empty out the potassic ferrocyanide, and after washing the cell with
a little distilled water, fill it with the fluid to be used.

The cell must be so filled and sealed as to leave absolutely no air within,
otherwise the pressure cannot be accurately measured. Insert a perforated
rubber cork at g. Fill the manometer from the quicksilver to the extremity
of the tube with potassic ferrocyanide, or whatever other solution is to be
used in its place, and push it into position in the cork. Fill the cell com-
pletely full, and press firmly into place the second perforated cork, taking
great care, first, that no bubble of air remains at its base; and second, that
not a particle of potassic ferrocyanide comes in contact with the outside of
the cell.

A bent glass tube, drawn to a capillary point at one end, should now be
filled with potassic ferrocyanide and slowly pushed into the cork. If this is

THE CELL AN OSMOTIC APPARATUS. 229

In certain experiments by Pfeffer, made with a single cell, in
which was a solution of cane-sugar containing a trace of one of
the membranogenic substances, while the water outside contained
a trace of the other, the following pressures were indicated : —

Percentage of sugar in the 7 , i
solution, by weight. Temperature. Mercurial pressure.

1 13°.7 C, 53.8 cm
1 13.6 jas2:
2 14. rs 101.6 **
4 13.8 208.2 *
6 14.7 307.5 **
1 14.6 ie **

With a 3.3 per cent solution of potassic nitrate in the cell,
Pfeffer obtained a mercurial pressure of 436.8 cm.

616. An active vegetable cell is an osmotic apparatus. The
chief agent in its work of absorption is the peripheral film of
the colloidal protoplasmic mass, and this receives mechanical
support from the wall of cellulose in which it is held. It was
formerly believed that in osmosis there is always an exchange
of materials, one current passing inwards (endosmose), the
other outwards (exosmose); and there are numerous cases in
which this is true, and in which the osmotic equivalent can be
calculated (see 612). But Pfeffer’s experiments show how great
a force may be exerted by osmosis in cases in which there is
little or no substance passing out to replace the liquid ab-
sorbed. In the series of experiments in which a solution of
sugar was employed in his osmotic apparatus, no trace of this

properly done, any small quantity of air which may be in the upper part of the
cork will rise during insertion to the capillary point. Gradually and cautiously
warm the tube, beginning close to the cork. This will expand the fluid and’
drive the air wholly out. At the moment when the solution completely fills
the tube, fuse the capillary point in the spirit-lamp. The cell is now entirely
free from air and hermetically sealed. During the time of inserting the ma-
nometer, corking, and sealing, the porcelain part of the cell must not be allowed
to become dry, but must be frequently dipped into the solution from which it
was taken. With unannealed brass wire secure both corks after the fashion
of champagne-bottles.

Now suspend the cell in the solution of copper sulphate so that the porce-
lain shall be wholly submerged but shall not touch the sides of the vessel
containing the solution. Note the position of the mercury in the manometer,
and see that the temperature remains constant in the room. If the cell is
perfect, a certain degree of pressure will be indicated in less than an hour. fi

230 ABSORPTION OF LIQUIDS THROUGH ROOTS.

substance could afterwards be discovered in the water on the
outside. The apparatus lined with its colloidal film, containing
a small amount of saccharine solution, and surrounded by a very
dilute aqueous solution of mineral matters, is an instructive
imitation of a vegetable cell.

ABSORPTION OF LIQUIDS THROUGH ROOTS.

617. Submerged aquatics may absorb with their whole surface.
They are bathed in dilute saline solutions containing the gases
essential to vegetative activity, and the materials for their food
can be taken from the medium surrounding them, perhaps quite
as well by one of their parts as by another. This fact is well illus-
trated by the larger algze, in which the organs popularly called
roots are merely mechanical hold-fasts, and the work of absorp-
tion can proceed at any part of the frond. The simplest differ-
entiation of organs for absorption is met with in the rhizoids or
complex root-hairs of mosses, and in the filaments of fungi which
bury themselves in a nutrient substratum. Above the mosses
the differentiation of organs into roots for absorption, and stems
for the support of the assimilative tissue, is very plain. For our
present purpose it is best to begin an examination of the absorp-
tion of liquids by plants with a study of the structure and the
office of the root.

618. It has been shown in Part I. that the younger parts of
the root are clothed with extremely delicate epidermal cells,
which, with the slender trichomes associated with them, con-
stitute the absorbing apparatus of the plant. (These epicder-
mal cells of the root, taken collectively, have been called the
Epiblema.')

619. The root-tip with its protective cap does not share to
any great extent, if indeed at all, in the work of absorption;
and yet to the soft, spongy, rounded mass of tissue forming the
root-tip was formerly given the name of spongiole, on account
of its spongy nature, and its supposed office of sucking up nu-
trient matters from the soil.*

1 This term, early introduced, was retained by Schleiden: Principles of
Scientific Botany, 1849, pp. 68, 218.

? Thus De Candolle, in his Physiologie Végétale, 1832, p. 41, says: ‘La
succion des racines s’exécute par des points spéciaux qu'on nomme spongioles,
qui sont composés d’un tissu cellulaire trés-fin et tonjours nouveau, puisque les
racines s'alongent sans cesse par leur extrémité. Le liquide de la terre tend
a entrer dans les méats de ce tissu: I. par la force de capillarité; II. par

ROOT-HAIRS. 231

620. Root-hairs. It was shown experimentally by Ohlert! in
1837, that the tip of the root is not the absorbing part. By
careful excision of the tip, and the use of a harmless water-
proof varnish to cover the wound caused, he obtained full absorp-
tion of liquids through the sides, and not the end of a young
root. He further demonstrated the very general occurrence of
delicate hairs upon the sides of young roots, and expressed the
opinion that these were the efficient agents in root absorption.

621. That the abundance of the hairs on new roots is depend-
ent largely on the amount of moisture to which they are ex-
posed, appears from experiments on the roots of some of the
more common cultivated plants, — Allium Cepa, Cucurbita Pepo,
Zea Mais, etc. In all these cases the plant can almost be said
to regulate the amount of its absorbing surface by the amount
of moisture within its reach, and it is thought by some that all
the epidermal cells of a young and developing root have the
power of extending into hairs. The number of hairs to the
square millimeter on a root of Zea Mais grown in a moist place
was found by Schwarz to be 425; and on a root of Pisum
sativum, 232.

622. Root-hairs are, as has been shown in Part I., cylindrical
protuberances from the external wall of the epidermal cells.
They vary in length from .1 mm. to8 mm. The former length
occurs in a few grasses, the latter in some water plants. Schwarz
gives the following measurements of length: root-lairs of Pota-
mogeton, 5 mm.; of Anacharis, 4 mm.; of Brassica Napus in
moist air, 3mm.; of Pisum sativum and Avena sativa, 2.5 mm. ;
of Vicia Faba, 8 mm.

623. When root-hairs are developed in contact with soil, they
become much distorted (see Fig. 89), and generally dwarfed ;
they curve more or less irregularly around the particles of soil,
and frequently are enlarged at the immediate place of contact.
Moreover, the character of the cell-wall is somewhat changed at
the place of contact with the particles; in many instances the
wall undergoes a sort of mucilaginous modification, and becomes
so firmly united to the particles that these cannot be removed

Vhygroscopicité. Ces deux proprictés de tissu peuvent bien expliquer l’énorme

quantité d’eau qui pénétre dans la plante vivante, les variations de cette quan-

tité selon les espéces, les saisons, etc. I] souffit d’admettre que les cellules des

spongioles douées de contractions alternatives, augmenteut et diminuent alter-

nativement les méats intercellulaires, et tendent ainsi & absorber de l'eau en

quantité proportionnée a la force et 4 la rapidité de leurs contractions vitales.”
1 Linnea, 1837.

232 ABSORPTION OF LIQUIDS THROUGH ROOTS.

without laceration of the delicate cells. Notwithstanding the
extreme tenuity of the cell-wall, it is thought by some to play an
important mechanical part in fastening the roots in the soil.*

624. That the hairs upon the root vastly increase its absorb-
ing surface is self-evident. Schwarz has shown that in Indian
corn grown in moist air the surface presented by the velvety
hairs which cover the young roots is 5.5 times greater than that
of the part of the root on which the hairs occur; while the ratio
of these surfaces in the roots of peas is as 12.4 to 1; and in the
aerial roots of Scindapsus pinnatus, as 18.7 to 1. But all these
figures, which are at best only approximate, appear to be very low.

625. Extent of Root-systems. In extending, the root, by
growth at its protected extremity, can insinuate itself between
particles of soil which could not be easily displaced by simple
thrust. The branches from the main root extend exactly as does
the main root itself, — by continual additions just behind the
tip, — and the area covered by a root-system finally becomes
very large. One of the earliest recorded measurements is that by
Hales,’ who estimated that the roots of a sunflower (3 ft. high),
taken together, were no less than 1,448 feet in length. The plant
had ‘‘eight main roots reaching fifteen inches deep, and side-
ways from the stem; it had, besides, a very thick bush of lateral
rovts, which extended every way in a hemisphere about nine
inches from the stem and main roots,”

626. Nobbe has shown that in year-old plants of certain
closely allied gymnosperms the root-systems differ remarkably
in the number of the rootlets and the total length of the
roots.? In three species the determinations of the total length
were as follows : —

1 Haberlandt: Physiologische Pflanzenanatomie, 1884, p. 152.

2 Hales gives as the entire surface of these roots 2,286 square inches, or
15.8 square feet (Vegetable Statics, 1731, p. 6).

3 The plants examined were grown from May to October. Two of Nobbe’s
tables (Die landwirthschaftlichen Versuchs-Stationen, xviii., 1875, p. 279) are
here given :—

a. Number oF Root ets.

Norway Spruce. Silver Fir. Scotch Pine.
Roots of the 1st order. 1 1 1
eee) ee 85 48 404
ty “c 8d “ 162 85 1,955
“ “ 4th “se 5 0 749
“ “ bth “ 0 0 26

EXTENT OF ROOT-SYSTEMS.

Silver Fir
Norway Spruce
Scotch Pine.

233

1 meter.
2 meters.

12 meters.

All the plants upon which these averages are based were grown

under the same conditions.

627. When any plant
is lifted, even with great
care, from the soil in
which it has grown, many
of its more delicate root-
lets are torn off and left
behind. Hence it is
difficult to ascertain the
total amount of roots
belonging to a plant.
Even the best plan yet
devised for cleaning the
root previous to measur-
ing it— that of allow-
ing a stream of water to
wash away all the earth
which it will detach —
usually causes a few of
the finer rootlets to be
carried off. It has been
shown, however, that the
roots of peas, beans, and
the common cereals are
abundantly branched to
a depth of more than a
meter, and that many of

them penetrate considerably further.

144

Schubart states that the
amount, by weight, of roots in peas and wheat, compared with that

b&b. Lenora In MILLIMETERS.

Norway Spruce Silver Fir. Scotch Pine.
Roots of the 1st order. 300 73
ee ee 0 636 4,438
fe te Bdi 2 56 5,491
“ “ 4th « _ 1,143
“ “ 5th “ ees 41

Fig. 144. Roots of seedlings of Triticum vulgare. B, plant four weeks older than 4.

The soil clings in each case to the younger parts,

(Sachs.)

234 ABSORPTION OF LIQUIDS THROUGH ROOTS.

of the whole plant (all being dried), is less than fifty per cent.?
By comparison of the weights and lengths of average pieces of
the roots of barley, it has been found that the whole root-system
in a vigorous plant is not far from thirty-seven meters in length ;
and that all this could be packed in a small volume of fine soil
(about , of a cubic foot).?

628. The nature of the soil, and especially the amount of
moisture and of nutritive matters which it contains, have a
marked influence upon the development of the root-system of
a plant. Other things being equal, fertility: of the soil favors
compact branching, as is shown by experiments by Nobbe.®

Indian corn was grown for a time in several cylinders con-
taining clay soil; then the earth was carefully washed away and
the roots were compared. In the first cylinder the soil had

1 Amounts as given in Chemische Ackersmann, i. p. 193.

Roots of winter wheat (in April). . . . . 40 per cent.
‘« peas (four weeks after planting) . . . 44
“© (at flowering) . 2. 1. 1. . 24

2 Hellriegel : Hoffinaun’s Jahresbericht, 1864.

Nobbe ( Versuchs-Stationen, 1875, p. 279) has given some instructive figures,
showing the ratio of the surface above ground to that below in yearling plants
of some common species of Conifers grown under similar conditions. Some of
his figures are here given.

uw. SURFACE OF ROOTLETS.
Square millimeters,

Silver. Fir 6 ee oe ek aS we Se ee eS ABD
Norway Spruce . . 2. 1 ee ee ee) 4,189,
Scotch Pine . . . s 4 @ = « « = 20,5515.

6. SuRFACE OF THE GREEN PARTS OF THE PLANTS.
Square millimeters.

Silver Bit a bh wr ok a ee a ae DL

Norway Spruce. Sak Ge be Se tee ASO

Scotch Pine. . . 2. «© 2 ee ew ee 4,804,

c. Ratio oF PARTS IN THE PLANTS EXAMINED.
Silver Fir. Norway Spruce. Scotch Pine
Parts above ground . . . 100 : 107 : 297
Parts below ground . . . 100 ; 168 : 837
d. RATIO OF THE PARTS ABOVE GROUND TO THOSE BELOW.
Silver Fir. 6. 2. ee ee eee «100 : 2169
Norway Spruce . . . . . « « « « 100 : 267

Scotch Pine . . . . . . . . . . 100: 477
8 Versuchs-Stationen, iv., 1862, pp. 220, 221.

DEVELOPMENT OF ROOT-SYSTEMS. 235

been uniformly mixed with a fertilizing substance, and in this
soil the roots had developed in a normal manner. In the sec-
ond cylinder a layer of the fertilizing material had been placed
three to four centimeters below the surface, and in the soil at
this plane the roots had branched very abundantly. In the
third cylinder a similar layer of the fertilizing matter had been
placed half-way down the cylinder, and here the root-branches
were far more numerous than elsewhere. In other cases the
fertilizing substance had been placed at the bottom, around the
sides, or in the middle of the cylinder, and in these places respec-
tively the root-branches were most abundant. Substantially the
same thing is observed in earth where the roots of plants meet
with buried bones: the finer root-branches are developed around
and afterwards in the substance of the decomposing animal
matter, often forming dense mats.?

629. In some cases roots extend to very great distances ;
thus those of an elm have been known to fill up drains fifty
yards distant from the tree.? It may be said, in general, that
the roots of the common forest and shade trees reach to and be-
yond the eaves of the roof made by the leafy branches. ‘‘There
is a constant relation between the horizontal extension of the
branches and the lateral spreading of the roots. It is not by
watering a tree close to the trunk that it will be kept in vigor,
but by applying the water on the soil at the part correspond-
ing to the ends of the branches. The rain which falls on a tree
drops from the branches on that part of the soil which is situ-
ated immediately above the absorbing fibrils of the roots.” ®

630. The root-system of a plant, ever extending by its in-
numerable subdivisions into new soil, and clothed near the
extremities of the rootlets with delicate epidermal cells, is a
complex apparatus for osmosis placed under the most favorable
conditions for absorption.

631. The course of the water after it has found its way into
a plant through the epidermal cells of the newer portions of the
roots, and the pressure which at times the watery liquids in roots
exert, can be more conveniently examined at a later stage (see
Chapter IX., ‘‘ Transfer of Water through the Plant’).

1 See also a paper by Detmer : Versuchs-Stationen, 1872, p. 107.

2 Journal Royal Agricultural Society, vol. i. p. 364, contains some interest-
ing cases of great length of roots.

8 Balfour: Class Book of Botany, 1854, pr. 427.

CHAPTER VIII.
SOILS, ASH CONSTITUENTS, AND WATER-CULTURE.

632. WuHen a plant is carefully dried at a temperature slightly
exceeding that of boiling water until it ceases to lose weight,
there remains behind a brittle combustible residue. The dif-
ference between the weight of the plant and that of the resi-
due represents the amount of water previously contained in
the plant. This differs widely, according to the kind of plant
and its age. The following table gives the proportion of water
contained in a few of the most common plants : —

Red Clover, before flowering. . . . . . . 88 per cent.
ee «in full flower 2. 1 7 ww. 78)
Oats, before owering. . . . . . . . . 82
$8 AM TLOWEN 5, oe. le Si ae ae a
Tarnip (root) 2 2 «2 & 2 2 & ee « » SL *
Beech (leaves), in summer . . . . . . . 75 *
#8 es inautumn . . ..... 55 ©
Drygrains, «¢ 2 soe we 2 eo ew © Adtols “
Dry woods: 8 #3 6 «ew we 8 aoe Th

633. If the brittle residue left after complete expulsion of the
water is burned in the open air, there remains behind a smali
amount of gray ash; all the rest is wholly consumed. The
amount of ash also varies widely, according to the kind of plant
and its age. In the following table’ are given the proportions

for a few common plants : —
Per cent of ash in Per cent of ash in

fresh material. dry material.
Red Clover... . 1... 1.5 5.6
Sugar Beet (root) . Se eg 8 4.3
Indian Con. 2. 2. 7 ww 11 5.5
ae “ (grain) . . 2. we 2.1 1.5
Beech (leaves), in summer . . . 1.3 _
“s ss inautumn . . . 3. _

#34. Ina general way it may be said that the combustible
matters are derived chiefly from the atmosphere, while all the

1 The student is referred, for detailed accounts of analyses from which these
figures have been chiefly taken, to Johnson’s ‘‘ How Crops Grow,” 1868.

FORMATION OF SOILS. 237

water and the incombustible ash come from the soil. In the case
of aquatics this general statement would not appear to hold, for
they obtain all their substance from the water in which they live ;
but, as will be seen later, this source is essentially the same.
We have examined in the previous chapter one of the means
by which plants obtain their supply of water and ash materials,
and it will be best to consider now the source from which this
supply comes, before approaching the study of the combustible
substance of plants.

SOILS.

635. Formation of soils. Soils are produced by the disinte-
gration of rocks. This may be mechanical, as that caused by
crushing, attrition, and the action of frost; or it may be and
generally is associated with more or less chemical change. In
soils, some of the products of the decomposition of organic sub-
stances are usually intermingled with purely mineral matters
aggregated in various degrees of fineness. Soils exposed to
atmospheric influences constantly change both in their physical
properties and chemical composition, the changes being brought
about chiefly by the combined action of moisture, carbonic acid,
and oxygen.

636. Water not only wears away solid rocks by its mechanical
action, but after it has insinuated itself into the crevices of
rocks it accomplishes the work of disintegration far more rapidly
by its expansion during freezing.’

When rocks become loosened by running water, or by the
slow movement of glaciers, the crushing and grinding of the
pieces which come into contact are sufficient to pulverize
the hardest of the more common ones.

Water, especially when it holds carbonic acid in solution, is
a very important agent in changing the characters of rocks ;
sometimes it does this hy dissolving out portions of the rocks,
sometimes by bringing about new combinations of their con-
stituents. Moreover, rain-water contains a minute quantity of
other matters besides carbonic acid, and these exert a powerful
effect in disintegrating and dissolving certain rocks.

637. The free oxygen of the atmosphere is also an efficient
agent in the changes by which rocks are broken down to form

1 The amount of expansion is usually given as approximately one fifteenth
of the volume.

238 SOILS.

soils. Many rocks contain ferrous oxide, which readily under-
goes further oxidation ; certain sulphides in rocks are oxidizable
under the ordinary conditions found in a moist atmosphere, and
in such cases the chemical action results in rendering the rocks
brittle.

638. Water can easily transport the finer particles of soil
from where they were formed by disintegration of the rocks to
points at distances from their source, varying with their weight.
For this reason the particles accumulate in different degrees
of fineness at different points along water-courses.

639. It is believed that during the Glacial period, when large
portions of the northern hemisphere were covered deeply with
sheets of moving ice, immense amounts of coarse and fine
soils were carried far from the places where they were formed,
and were heaped up more or less irregularly in the masses which
now form grayelly hills and ridges. The glacial action now
going on in the Alps shows how vast must have been the soil-
making and soil-carrying power of the glaciers which once cov-
ered so much of’ our continent.

640. Soils which have not been carried by water or ice from
the place where they were formed by some of the agencies men-
tioned above are not generally of great depth, and their nature
can usually be made out by examination of the contiguous
rocks.

641. Classification of soils. For our present purpose soils
may be classified as gravelly, sandy, clayey, calcareous, loamy,
and peaty. Gravelly soils differ widely in their chemical char-
acter, since the pebbles which compose them may be either chiefly
quartz and fragments of rocks in which quartz predominates, or
there may be also a good proportion of limestone, or of feld-
spathic rocks. With the coarse pebbles is intermingled a
certain proportion of finer soil. Sandy soils are usually made
up of fine quartz with which some other matters are asso-
ciated, such as some compound of iron, grains of feldspathic
minerals, micaceous particles, cte. In a few cases, however,
the sandy soils differ widely from this composition; for in-
stance, the green sand of New Jersey contains a large proportion
(more than fifty per cent) of green grains of a silicate of iron and
potassium. Clayey soils are generally derived from the dis-
integration of various feldspathic rocks, and are mixtures of
hydrated aluminic silicate with many other matters. Such soils
are generally adhesive, are retentive of water, and dry into
a hard mass; these characters which belong to true clay are

PHYSICAL PROPERTIES OF SOILS. 239

found also in some soils which are not clays, and hence the
term clayey is sometimes loosely applied. Caleareous or lime
soils contain calcic carbonate in large amount. To calcareous
clay, when the ingredients are in a state of rather fine subdi-
vision, the name marl is frequently applicd. Peaty or humus
soils are those which contain a considerable proportion of par-
tially decayed vegetable matter ; when such matter decays under
water it becomes peat, or muck; when it decays without muc
water it is generally known as mould.

642. By mechanical analysis, as by simple washing and sift-
ing, it is possible to separate a soil into its mechanical ingre-
dients, which are: (1) Gravel; (2) coarse sand; (3) fine sand ;
(4) clayey sand; (5) clayey substance, or fine clay.

The mechanical subdivision of soils has an important bearing
upon their physical properties and upon their adaptability to
the growth of roots and the sustenance of plants.

From interesting studies by Darwin,’ it is plain that in some
localities earth-worms have exerted, by their burrowing and
tunnelling, a vast influence in changing the physical character
of the soils in which they thrive.

643. Physical properties of soils. Of these, the most important
to be considered here are those which affect the relations of soils
to liquids, to gases, and to heat; for all of these directly affect
the growth and indirectly the nutrition of plants.

644, Absorption and retention of moisture by soils. It is con-
venient to examine the relations of soils both to liquid water
and to aqueous vapor. Soils can absorb from the atmosphere
and condense upon the surface of their particles, or in their inter-
stices, a certain amount of the vapor of water. This property
of absorption, known as that of hygroscopicity, is different in
different soils, as shown by the following table from Schiibeler.®

Five hundred centigrams of each soil carefully dried were
spread over a surface of thirty-six thousand square millimeters,
and exposed for varying periods to an atmosphere saturated
with watery vapor; the amounts of waters absorbed (in centi-
grams) were as follows : —

1 The reader should examine a paper by J. D. Whitney (Plain, Prairie, and
Forest), in which is discussed the probable influence of the extreme fineness of
prairie soils upon the absence of forests. See American Naturalist, October
and November, 1876.

2 Darwin: The Formation of Vegetable Mould through the Action of
Worms.

3 Knop’s Lehrbuch der Agricultur-Chemie, 1868, vol. ii. pp. 18, 14.

240 SOILS.

12 hours. 24 hours. 48 hours. 72 hours.
Quartz sand. . 0.0 0.0 0.0 0.0
Calcareous sand 1.0 1.5 1.5 Lob
Clayey soils. . 10.5 to 15. 13 to 18. 14 to 20. 14 to 20.5
CHa ys) ices ah oe 18.5 21.0 24.0 24.5
Garden earth . 17.5 22.5 25.0 26.0
Humus ... 40.0 48.5 55.0 60.0

From these figures it appears (1) that the greater part of the
vapor is condensed before the expiration of a single day, (2) that
humus is by far the most hygroscopic, but (3) that clay can ab-
sorb a large quantity of vapor.

Temperature exerts a marked influence upon the capacity of
soils to absorb aqueous vapor, as is shown by Knop’s exami-
nation’ of a sandy and of a rich earth: the amount of vapor
absorbed diminishes with elevation of temperature.

645. The amount of liquid water which soils can absorb and re-
tain is very different for different kinds of earth. In the follow-
ing determinations by Schiibeler dry soils were saturated with
water upon a funnel, and the increase of weight was noted after
all the excess of water had dripped away. The first column gives
the percentage of increase in weight of soil; the second, the num-
ber of volumes of water that one hundred volumes of soil can take
up; the third, the percentage of this water which evaporates from
the soil in four hours when it is spread over a given surface.?

Ty 2; 3.
Quartzsand . .... 25 37.9 88.4
Caleareous sand ie. hg 29 44.1 75.9
Clay soil (60% clay) . . 40 51.4 52
Clay soil (76% clay) . . 50 57.3 _—
Heavy clay (89% clay) . . 61 62.9 34.9
Pureclay . . .... 70 66.2 31.9
Humus® « 6. « ¢ @ « 190 69.2 25.5

646. The degree of fineness exerts also some influence upon
the absorptive power; but while pulverization increases that

1 Versnchs-Stationen, vi., 1864, p. 281, where are found also some interesting
results recorded by Knop, in regard to the absorption of aqueous vapor by
various organic substances.

2 Knop’s Lehrbuch, 1868, vol. ii. p. 26. The third column is cited from
Johnson’s ‘‘ How Crops Feed,” 1870, p. 180.

3 Samples of peat have been known to absorb from 300 to more than 500
per cent of water.

ABSORPTION OF MOISTURE BY SOILS. 241

power in some kinds of soil it diminishes it in others. Thus
Zenger has shown that fine quartz sand absorbs about twice as
much water as that which is coarse; on the other hand, fine
brick-clay is not so absorbent as coarse.

647. Admixture of heterogeneous matters with soil generally
lowers the absorptive and retentive power both of the soil and of
the added substances. Treutler examined certain soil mixtures
in the following manner: fifty grams of the soil were placed in
one hundred cubic centimeters of water for twenty-four hours,
the excess of water was allowed to drip away, and the amount
then retained noted. The following are among his results : —

Soils. Mixtures.

Cubic centime-
ters of water
retained.

Cubic centime-
ters of water
retained.

Fine earth 34.2 || 40 orm. fine earth and 10 grm. caustic lime
Quartz sand | 14. 40 grm. quartz sand and 10 grm. caustic lime
Caustic lime | 61. 40 grm. quartz sand and 10 grm. bone-dust 16.5
Bone-dust 46. 80 grm. quartz sand andl 20 grm. bone-dust 9.

op
Cie as

From Treutler’s tables it appears that the absorptive and
retentive capacity of a mixture of two substances may equal
that of the constituents, but that generally it becomes lower.

648. A soil may be so fine and compact that rain will not
readily penetrate it; or on the other hand it may be so porous
as to allow the water which falls on it to pass rapidly down
through it. A soil of proper texture will receive the rains, and,
as has been shown by the foregoing paragraphs, retain a certain
amount in its pores, the excess draining away.

649. Evaporation of water goes on continually from the sur-
face of moist soil, unless the atmosphere is saturated, and the
amount of evaporation depends largely upon the amount of
moisture present in the state of vapor in the atmosphere at any
given time. But the retentive power spoken of above (which
is plainly opposed to evaporation) is very different in different
soils; for this reason about three times as much water evaporates
from quartz sand as from the same amount of humus equally
exposed for a given time. When by evaporation the soil be-
comes dry at the surface, a draft is made upon the supply of
water retained in it at a greater depth, and this water then rises
by capillarity to the drier layers. It is therefore said that there
is a constant movement of water in the soil.

6

242 SOILS.

650. A distinction may be properly made between (1) that
water which remains as a copious supply beneath the surface of
the ground, existing there plainly as a liquid, (2) that which ad-
heres to the particles of soil imparting to them a moist appear-
ance, (3) that which adheres to the particles of an air-dry soil
and which does not affect at all the appearance of the particles.
The first has been called hydrostatic, the second, capillary, the
third, hygroscopic water. It is from the two latter that the
roots of plants other than aquatics usually obtain their supply
of moisture.?

651. The relations which evaporation and drainage bear to
the total rain-fall upon the soil have been examined during a
series of nineteen years at Rothamsted, in England. The fol-
lowing figures are based on the results during ten years (Sep-
tember, 1870, to August, 1880).

Rain-fall 2 6 1 ww we ew eee ee ee . «(80.68 inches,
Drainage from soil
at 20 inches depth ‘ eee ee ee oe BL
at 40‘ SE eee A a oe oe 13.94 *
at 60 ‘* NE ia ap) te Via aya WE Gea a “ter Eee, Seca 1 DE yp SE
Amount of water retained by soil, or evaporated.
at 20 inches depth . . . be he Re A. AES Uk ee DE ES
at 40‘ a ae a
at 60 ‘* BS a Gp OR OE Aes ah » . 18.51 *
Percentage of rain-fall lost by drainage
at 20 inches depth . fo 3 bd we ce ee asa Ot
at 40“ BEES cot Tm teea ol SUS Wel. CE Sa. E> & 45.4 of
at 60 ‘f GE SS es BS Geli ee TE GES a, SORE. re
Percentage of rain-fall retained by soil, or lost by evaporation
at 20 inches depth . . . . . . . . . ss. . 569 *
at 40 ‘** GO" ea ee oa cae oe aes ee, OAS
at 60 ‘* se SoD Be aioa, Gee a Sw oe OOS: -

652. Soils are not only acted upon by the solvent power of
water, as shown in 636, but many soils possess the remarkable
property of removing saline matters from aqueous solutions.

The interesting fact that impure water can be freed from some
of its foreign matter by being filtered through earth has long
been known, but its significance in the nutrition of plants does
not appear to have received attention until 1819. Gazzeri? at

1 For a full discussion of this subject, which is most important in its bear-
ings upon the cultivation of plants, the student should study Johnson’s ¢ How
Crops Feed,” p. 199,

2 From a note by Orth: Versuchs-Stationen, xvi., 1873, p. 57. The discovery
is generally ascribed to Bronner, 1836. The fullest treatment was by Way :
Journal Royal Agricultural Society, 1850, and later.

CHEMICAL ABSORPTION BY SOILS. 2438

that date says: ‘¢ Earth, especially clay, seizes upon the sol-
uble matters intrusted to it, and holds them back, in order
that it may gradually furnish them to plants according to their
needs.”

653. When dilute solutions of a salt are slowly filtered through
sand which contains a good admixture of clay, the water passes
out for a time without more than a trace of the salt, and in
some cases all the salt is retained by the soil. Even sewage
liquids can by this method be freed from their offensive ingre-
dients. This, phenomenon of filtration is due to adhesion (that
is, the attraction which the surface of one kind of matter has
for another kind of matter). The substances which are removed
by the particles of soil are so fastened to them that even
when the soil is washed in pure water only traces of them are
removed.

654. Chemical absorption by soils. Besides this physical ad-
hesion, there are exhibited by many soils certain chemical phe-
nomena also, which have been collectively termed chemical
absorption. If a solution of potassic nitrate is filtered through
a well-pulverized clay soil containing an adinixture of insoluble
compounds of magnesium and calcium, such as are met with in
almost any ordinary soil, the water which drains off will con-
tain very little if iadeed any potassium; but it will have, in-
stead, magnesium and calcic nitrate in appreciable amount. But
this absorptive power of a soil is soon satisfied; for after
a certain amount of potassium has been removed no more is
taken up.

The strength of the saline solution affects the amount of
absorption, more of the base being absorbed from strong solu-
tions. Different substances are absorbed by the soil in different
amounts; thus in the experiments by Peters the bases were
absorbed in the following order: (1) Potassa, (2) Ammonia,
(3) Soda, (4) Magnesia, (5) Lime. Different soils absorb the
same substance in different amounts, depending upon the physi-
eal condition of the soil, but chiefly, it is believed, upon the
mode in which the substance is combined ; thus, more potassa is
absorbed from the phosphate than from the carbonate, and more
from the latter than from the sulphate.

In general it may be said that the salts of the alkalies and
the alkaline earths are so absorbed by rich soils that the bases
are retained in new combinations, while the acids pass off,
having also, of course, formed new combinations. The phos-
phates and silicates are retained undecomposed. The case of

244 SOILS.

‘the latter compounds may be regarded as the ordinary physi-
cal absorption, that of the former as the so-called chemical
absorption.

655. The matters absorbed by the soil may be released after
a time and pass into solution again, or they may be displaced
from the soil-particles by the filtration of new solutions. When
it is remembered that rain-water exerts a powerful solvent action
upon some portions of the soil, and that, on the other hand,
the soil can remove from aqueous solutions some of the matters
therein dissolved, the complicated nature of the problem which
presents itself is at once apparent. Examination of the waters
which drain through soil, and which may fairly represent the
resultant of the solvent action of the water and the absorptive
power of the soil, shows that from thirteen to fifty parts of solid
matters may remain dissolved in 100,000 parts of water. (The
question of nitrogen compounds in drainage-water will be ex-
amined in a subsequent chapter.)

656. Condensation of gases by soils. Soils have the power of
condensing in their pores certain amounts of different gases.
These condensed gases are released when the soils are subjected
to a high temperature, say 140° C., and their amounts can then
be measured. The figures below give the results of the meas-
urements in several instances, 100 grams of soil being taken
in each case.

Soil. Cubic centimeters of gas yielded,
Peaty day oy ae ee ee ee ke > ei = ED
CLAN ng eR ROB, oa Sp a oe EE GS ae 80
Moist garden soil . . . 2... we ee se 614

It is found that in the soil there is present a smaller amount
of oxygen and a larger amount of nitrogen than in the atmos-
phere. The percentage of carbonic acid in the soil is also some-
what larger than that in the atmosphere; especially in soils
which contain much organic inatter.

657. Root-absorption of saline matters from soils. Having scen
that the soil, the principal medium in which roots extend, pos-
sesses the power of absorbing and retaining water, saline mat-
ters, and gases, attention must next be directed to the conditions
under which the root-hairs can abstract from it the matters
requisite for the plant. These conditions are (1) presence of free
oxygen, (2) a certain temperature, (3) the presence of saline
matters in an available form in the soil.

658. Free oxygen is necessary to all protoplasmic activity,

SOIL TEMPERATURES. 245

and the plant will speedily show when the amount required for
the absorptive activity of its roots is not furnished. Different
plants, however, require different amounts: thus aquatics and
marsh-plants do not need so much oxygen for their roots as
do plants which ordinarily grow in a porous soil. Partial ex-
clusion of oxygen from the roots of the latter by keeping the
soil saturated with water usually injures the plants in a short
time.

It has been shown by Sachs and others that seedlings of many
plants normally growing in dryish soil will develop if treated as
aquatics ; better results are obtained, however, if air is occasion-
ally passed through the water.

659. The temperature needed for the absorptive activity of
roots varies with different plants. It may be said, however,
that for any given plant the absorptive power increases with
increase of temperature.

660. Different soils have very different relations to temper-
ature. Leaving out of account the small amount of warmth
derived from the chemical changes going on in the soil by which
heat is evolved, it may be said that the heat of the soil is derived
from the sun’s rays. The angle at which these rays strike the
soil must have a great influence upon its temperature. Again,
there are various local causes, such as protecting or reflecting
walls, which may considerably modify the temperature in any
given case. The soil itself exerts a marked influence upon the
amount of heat which it can receive and retain. Dark soils ab-
sorb heat most readily; but it has been shown that black soils
are less absorbent of heat-rays than are those which are dark
gray. The radiating power of a soil depends upon the character
of its surface, being much greater in the case of fine mould than
in that of coarse, gravelly soils.

661. It must be noted, however, that the heat-rays which fall
upon a given soil may have different degrees of intensity. Some
bodies (¢. g. lampblack), can absorb and give off by radiation
heat of high as well as that of low intensity ; while other bodies
(é. g- snow), absorb heat of low intensity only. Heat of high
intensity is converted into that of low intensity by the interpo-
sition of a black covering of any kind which can absorb it and
give it out below as heat of low intensity.

662. At the depth of fifty feet the temperature of the soil in
the temperate zone varies within the limits of one degree, and
at a depth somewhat below this it is constant. The stationary
temperature at such a depth is the same as that of the mean

246 ASH CONSTITUENTS OF PLANTS.

annual temperature of the atmosphere in temperate regions.
Moisture exerts a very great effect in equalizing the capacities
of different soils for absorbing and retaining heat.

663. That the saline matters in the soil must be in a form in
which the plant can make use of them, appears from what has
been said about osmosis. It should be specially noticed, how-
ever, that younger roots may exert a solvent action upon soil-
particles.

Root-hairs, as Sachs? has shown, evolve small amounts of
acid, which exert a distinctly corrosive effect upon certain min-
eral matters with which they come in contact. Hence there is a
continual unlocking of the nutritive mineral materials fastened in
the soil; the release being at the very points where the root-hairs
are present to absorb them.

ASH CONSTITUENTS OF PLANTS.

664. These occur in all parts of plants. It has been shown
(p. 39) how frequently cell-walls are impregnated or incrusted
by mineral matters, which after careful calcination may be left
as a distinct skeleton of the tissues of which they formed a part,
But the matters within cells, both the protoplasmic substance and
the cell-sap, also contain a certain amount of incombustible ma-
terial. The total amount of ash constituents varies greatly in
different plants, in different parts of the same plant, aud also

1 Penhallow, Soil Temperatures (Houghton Farm Experiment Department),
1884. See also Knop, Aygricultur-Chemie, i., 1868, p. 469.

2 Moldenhawer (Beytrage), in 1812, expressed the view that roots probably
set free certain matters which can unloose nutritive materials. De Candolle
(Physiologie, 1832) described the corrosive action of lichens on underlying
rocks ; and Liebig, in 1839, studied the action of roots on the color of litmus
solutions.

Sachs’s experiment (1860) is well adapted to class demonstration. A pol-
ished plate of marble is covered with moist saw-dust, and in this a few seeds are
planted. After the seedlings have grown for a time the saw-dust is removed,
when the marks left upon the stone by the corroding rootlets ean be plainly
seen. If the corroded marble is rubbed slightly with a little vermilion, the
traces made by the root-hairs will be very distinct. In the early publication
of Sachs, the secretion by which the corrosion is effected was said to be car-
bonic acid ; but he does notappear to hold this view now. Whether the action
is due to acetic acid, as Oudemann and Rauwenhoff suggest, or to different:
acids varying with plants or times, as intimated by Pfeffer, it is certainly
highly corrosive in some cases. In an experiment by Schulz, the rootlets of
germinating Leguminose and Graminee exhibited a faint alkaline reaction
(Journal fiir Praktische Chemie, Ixxxvii., 1862, p. 135). :

COMPOSITION OF THE ASH. 247

in many cases with the age of the plant. The following table?
indicates the per cent of ash in a few instances : —

Turnip: (fresh): 4 2.6 woe we wwe aw a7
Sugar beet (fresh) . . . 2 6 6 1 we ee 8
Potatoes (fresh). 6 2 2. we ee a)
Red clover (fresh) . . SO e 1.3
Red clover (dry). . 2. 2. 2. 5.6
Birch-wood (dry) i a ae ee ee ee ee 2
Apple-tree wood (dry). . 2 6. ee we 11
Walnut-wood (dry). . 2. . 1. 1 : 2.5
Birch-bark . . . . a a ee a 1.1
Mulberry leaves (fresh) . . 2. 2. 1. ew 11
Horse-chestnut leaves (spring) . . 2.1
Horse-chestnut leaves (autumn) . 3.0
Apples (fresh) 3
Pears (fresh) . a ae ee ee rer
Flax-seed . . . : a) Sat ee . . 8.2
Clover-seel . . . Bet GPG Al oy) ar ae TONS
Hemp-seed 5 3 4 @ es ey @ & « ew = AS
sBeechsnitts: a 6 Be eS wh ee RD - 2.7
' Wheat-grains. .. ; j ‘ 2 ae
Hemp (entire plant). eee ead - 2.8

665. Composition of the ash of plants. Examination of trust-
worthy analyses of the ash of flowering plants shows that certain
elements are always present in it. These are potassium, calcium,
magnesium, and phosphorus. Besides these, which always ap-
pear in appreciable amount, there are others which are nearly
or quite as constant in occurrence, although in some reports of
analyses they are not given, because existing in such-small pro-
portion. They are iron, chlorine, sulphur, and sodium. The
elements mentioned are usually recorded in analyses in the fol-
lowing combinations: potassa, phosphoric acid, lime, magnesia,
sulphuric acid, soda, and ferric oxide. But it is to be observed
that the combinations stated in the tabulation of analyses are by
no means designed to exhibit all those in which the elements
occur in the plant; for instance, the sodium and potassium are
presumably combined with the chlorine. Again, it must be no-
ticed that upon combustion the mineral matters in the plant are
commingled with a larger or smaller amount of carbonates, the

1 £. Wolff, Die Mittlere Zusammensetzung der Asche, 1865, p. 77 e¢ seq.
See also an excellent revised translation of Wolff’s tables in the Appendix of
Johnson’s ‘‘How Crops Grow” (1868). For the percentage of ash in trees
and woody plants, as well as the amounts of phosphoric acid and potash found-
in such ash, see a very valuable table by Storer (Bulletin Bussey Institution,
1874, pp. 207-245).

248 WATER-CULTURE.

amount depending somewhat ‘‘upon the temperature at which
the ash is prepared.” In the following short table a few of the
many analyses collated by Johnson} have been brought together
to exhibit the proportions of the ash constituents.

2 2 a | 2 3 3

@ | 23] $ 8 |u| ¢ | % | 4

Name of plant. 8 05 g &® |S] B g Fe 5

2/2) 4) 2\/E|4)8) 12

cy a | é 5

Root of sugar beet. | 48. [14.4] 6.4] 9.5/4.7] 10.4] 1. 3.8 | 2.3

Potato tubers . . | 60.9/18.38] 2.4] 4.6] 7. 1.7} 9) 1.9] 2.7
Stalks of Indian corn | 36.8] 8.3] 10.8] 5.7 | 5.2| 1.25 | 2.4 | 28.8
Wheat-grain . . | 31.8/46.1] 38.2/12.3 3.2 1.9

666. The foregoing table indicates that wide diversity exists
in the amounts of the ordinary ash constituents of common
plants. But comparison of a large number of analyses shows
that the following general statements may be made: —

1. Plants which closely resemble each other in structural
characters have substantially the same proportions of ash con-
stituents.

2. The proportions of the ash constituents in any part of a
plant may vary within certain limits ; and these limits may differ
at different periods of growth.

3. The proportions may vary widely for different parts of the
same plant.

667. Not only are the elements enumerated in the first list in
665 always present in the ash of flowering plants, but they are
shown by experiment to be indispensable to their full develop-
ment; and there is a reasonable certainty that iron, sulphur,
and probably chlorine, should be placed in the same category of
indispensable elements.

According to Nigeli,? some of the flowerless plants, notahly
the moulds and the schizomycetes, can attain full development
with fewer elements.

WATER-CULTURE.

668. Apparatus. While chemical analysis of the ash of plants
reveals the character of the mineral matters which they absorb
from water and soil, it cannot materially aid the investigator in

1 How Crops Grow, 1868, p. 150.
2 Sitzungsb. d. bayer. Akad., 1879, p. 340,

APPARATUS. 249

learning the office of each constituent. This is more satisfac-
torily accomplished by water-culture, which, reduced to its sim-
plest terms, consists in furnishing to the plant under proper
conditions different mineral matters in aqueous solution, and
noting their effects upon it. It bas been long known that plants
can be grown to a considerable size in ordinary river-water, or
water holding in solution certain imineral salts.1. Bat it was not
until 1858 that the method of water-culture was systematically
applied by Sachs, Knop, and Nobbe to the investigation of the
relative value and the office of the different mineral constituents
in the nutrition of plants. It has since been widely employed in
the examination both of flowering and flowerless plants.

669. The method adopted for ordinary flowering plants is es-
sentially as follows: seeds are made to germinate upon some clean
support, for instance moist sponge or
eotton, horse-hair cloth, or perforated
parchment-paper, and when the root
of the seedling is a few centimeters
long and the plumule is somewhat
developed, the plantlet is secured to
a firm support at the surface of a cy-
lindrical glass vessel, in such a man-
ner as to allow the roots to dip into
the nutrient liquid which it contains,
while the body of the seed is not im-
mersed. One of the simplest sup-
ports for the plantlet is shown in
Fig. 145. A perforated cork is cut
in halves, and the two parts are held
together by a spring. The pressure
exerted by the spring is sufficient to
keep the plantlet in place, and not
enough to injure it in any way. When the plant has attained
the height of a few inches, it is well to provide a firm rod at the
side of the cork, so that the stem can be held in place. Certain
precautions have been found advantageous: (1) the roots in the
liquid should be kept darkened; (2) the solution should be fre-
quently renewed.

When skilfully managed, this method of culture gives very

1 Woodward (Philosophical Transactions, 1699) and Duhamel (Traité des
Arbres, 1765) have given accounts of their cultivation of various plants in
this way.

250 WATER-CULTURE.

satisfactory results; in many cases plants have been carried
safely throughout their whole development from seed to seed.
The principal difficulties arise from the invasion of moulds, and
from the continual changes which the nutrient solution under-
goes.

670. In Tharandt,? where the method has been very success-
fully applied in numerous series of cultures, the following out-
fit suffices: (1) small glass vessels covered with gauze, upon
which the seeds swollen by twelve hours’ immersion in water,
and subsequently sprouted on filtering-paper, are placed for
further development; (2) wide-mouthed vessels of the capacity,
respectively, of one, two, and three liters, each of which is pro-
vided with the spring and cork already described.

671. By the careful use of these simple appliances the réle
which each of the ash constituents plays in the life and growth
of plants has been ascertained. But although there is a sub-
stantial agreement among experimenters as to the more impor-
tant points, there are a few unsettled questions.?

672. Normal nutrient solution. It is plain that an aqueous
solution of the salts necessary for the most active and complete
development of the plant should have these salts in the right
proportion. The solution advised for ordinary use in the above
experiments is generally known as the Tharandt normal-culture
solution. Nobbe? gives the proportions as follows : —

1 Success in water-culture demands the closest attention to all the external
conditions of the plant. The amount of light and heat must be carefully regu-
lated, and the plants must be kept free from any insects and parasitic fungi.
The latter is one of the most difficult and discouraging tasks connected with
the method of experimenting. In order to secure the best surroundings for
the cultivation of plants in water, a heavy table moving with wheels on rails
has been employed at the experiment-station at Tharandt ; upon this the glass
vessels can be carried with the least liability to jarring, from the open air in
the daytime to a suitable protection at night or during wet weather.

2 Moreover it is to be borne in mind that the conditions of water-culture
are very unlike those of ordinary culture in respect to the surroundings of the
roots themselves, and it is believed that to this difference of conditions may be
ascribed some of the unsettled questions. The root-hairs developed in contact
with moist particles of soil are not the same as those grown in water alone.
To avoid this possible source of error, various finely divided substances have
been suggested as a proper support for the roots and rootlets ; for instance,
the charcoal from sugar, powdered quartz, ete. When these are employed, the
roots of the plant are made to grow directly in the artificial soil which is
watered with the experimental solutions.

3 By the use of this solution buckwheat plants can be carried through their
entire development, as is shown by Nobbe, in Versuchs-Stationen, 1868, p. 4.
He arranged nine plants in five vessels, each of three litres capacity, in such

NUTRLENT SOLUTIONS. 251

4 Equivalents of . . + + « « « « Potassic chloride
4 Equivalents of . ied) a -2 Calcic nitrate
1 Equivalent of . . Magnesic sulphate (crystallized)

One part of the mixture of these salts is to be dissolved in
one thousand parts pure water, and then a trace of ferric phos-
phate is to be added, and at times during any culture a trace
also of potassic phosphate. ‘The proportions of the above salts
to a liter of water are given as follows by Bretfeld :}—

Gram.
Potassic chloride © 2 1 1 1 1 ee eee +207
Caleic nitrate . . . Sree hs BEE et, RE co cts 456
Magnesic sulphate. . 2. 2 2 1. ee ee 171

673. Pfeffer recommends the formula suggested by Knop :?—

Calcic nitrate . . . . . . . . . 4 parts by weight
Potassic nitrate . uF . - . 1 part by weight
Magnesic sulphate (crystallized) i 1 part by weight
Potassic phosphate . . . . . . . JI part by weight

These salts are to be thoroughly mixed and the mixture used
in the proportions of so, rooa> sho parts of water. To the
solutions, when ready for use, a drop or two of a solution of
some iron salt, or a decigram of ferric phosphate, must be
added.

674. According to Knop. the first of the solutions mentioned
above (one half pro mille) is as dilute as can be useful; and on
the other hand, a five pro mille solution is as strong as can be
employed with safety. But the stronger solution should be used
as the plant comes into flower. The slight turbidity which is
frequently noticed in these solutions may be disregarded.

If the solutions become alkaline while in contact with the
roots, as they are very apt to do, a trace of dilute nitric acid
may be added with advantage. But it must not be forgotten
that it is best in every case to renew the solutions frequently,
and as a rule to employ them in tolerably large amounts.
Moreover, it is advantageous to pass a current of air occasion-
ally through the solutions in which the roots are placed, for the
purpose of supplying more oxygen to them.?

a manner that 1 and 2 contained one plant each, 3 and 4 two plants each, and
5 three plants.
1 Das Versuchswesen auf dem Gebiete der Pflanzenphysiologie, 1884, p. 120..
2 Lehrbuch der Agricultur-Chemie, i. 1868, p. 605.
3 For solutions for the cultivation of fungi various formulas have been pro-.
posed, only a few of which can be here referred to :.(1) 3 to 8 grams of sugar

252 WATER-CULTURE.

675. The constituents may be taken up by the roots in larger
proportion than the needs of the plant demand. The excess
may (1) remain in solution in the sap of the plant, (2) may es-
cape to a slight extent through superficial parts,’ (3) may form
insoluble incrustations or concretions upon or in the plant.?

676. The office of the different ash constituents. Potassium.
The most conclusive evidence in regard to the importance of this
element is atforded by experiments by Nobbe, Schroeder, and
Erdmann.* Plants of Japanese buckwheat were grown in a
nutrient solution free from any trace of a potassium salt. Ex-
amination after a few weeks showed that all the organs of the
plants were free from starch, and that although the points of
growth remained sound, all growth had practically ceased. Even
in the chlorophyll-granules not more than a trace of starch could
be detected. As soon as a salt of potassium was added to the
water, the plants began to grow again, and thenceforth the de-
velopment was normal. From the same series of experiments it
appeared that the chloride was the best form in which potassium
could be given to these plants, and the nitrate the next best ; while
on the other hand the phosphate and the sulphate appeared to
exert a less favorable effect. After use of a solution of the latter
salt the leaves were fleshy, more or less rolled up, and it was
evident that the starch formed in them was not transferred to
the other organs of the plant. Nobbe’s statement follows:
‘¢The production of starch in the leaves is not dependent upon
the form in which potassium is afforded to the plant, but this

in 100 cubic centimeters of water, to which 3 to 3 pro mille of the above salts
(see 673) may be added, and also a trace of ammonic tartrate (Pfeffer, PAlanzen-
physiologie, i. p. 254); (2) Pasteur (Ann. de Chimie et de Physique, 1862,
p. 106) recominends the addition to 100 c.cin. of water, of 10 grams of cane-
sugar, .5 gram of ammonie tartrate, and .1 gram of the ash of yeast ; (3) Nageli
(Sitzungsb. d. bayer. Akad., 1879) has the following : 100 cm. water, 3 grams
eane-sugar, 1 gram ammonic tartrate, 4 grams phosphoric acid neutralized by
the ash of peas or wheat; (4) Nigeli suggests also, for the cultivation of
Schizomycetes, 100 c.cm. water, .1035 gram hydro-potassic phosphate, .016
gram magnesic sulphate, .018 gram potassic sulphate, .0055 gram calcic
chloride.

1 Sachs (Botanische Zeitung, 1862, p. 264) states that drops of water placed
on the leaves of Tropzolum and Cucurbita are found after a time to be alkaline.
Saussure (Recherches chimiques, 1805, p. 263) asserts that if leaves of fresh
plants are washed with water, the ash which they yield on combustion is found
to be poorer in alkaline salts than that of leaves which have not been so treated.

2 Cystoliths and the like, the incrustations upon certain species of Saxi-
frage, are cited as examples of the latter.

3 Versuchs-Stationen, xiii, 1870, p. 357.

OFFICE OF THE ASH CONSTITUENTS. 258

element must be present in order to have any starch formed.
The transport of the starch from the leaves to other parts is,
however, dependent upon the form in which the potassium is
presented to the plant, and for this purpose the chloride is most
efficient.”

677. Calcium and magnesium. These elements cannot re-
place one another in the plant, though it is not clear what office
they perform. Pfeffer regards it as possible that calcium may
play an important part in the formation of the cell-wall, inas-
much as it can always be detected there. Melnikoff is quoted by
Pfeffer* as stating that in the cell-wall calcium generally exists
as the carbonate. It is suggested by Sachs that this element
muy enter into combination with cellulose, as it does with some
other carbohydrates.

When seedlings are grown in pure water their development
after a short time becomes completely checked, and the addition
of all necessary substances except calcium salts fails to stimulate
a normal growth; but after the addition of a small amount of
any calcium salt the normal processes of the plant recommence
at once.” Regarding the almost universal occurrence of calcic
oxalate in plants, Sachs says: ‘The importance of calcium
must therefore be sought partly in its serving as a vehicle for
sulphuric and phosphoric acid in the absorption of food-material,
and partly in its fixing the oxalic acid, which is poisonous to
the plant, and rendering it harmless.” ®

678. Phosphorus. The principal and perhaps the only com-
bination of this element available for plants is phosphoric acid
(the phosphates). The experiments by Ville upon the absorption
by plants of calcic phosphite and hypophosphite, although not
conclusive, make it appear probable that these salts cannot
replace the phosphate ia absorption.

It is not clear what the office of phosphorus is in the plant,
but in some of its compounds it is so often associated with the
soluble albuminoids that it is believed to assist in the transfer
of these matters. Schumacher holds that the chief work of the
alkaline phosphates is the acceleration of the diffusion of these
difficultly diffusible substances (the albuminoids).* (See 957.)

! Pflanzenphysiologie, i., 1881, p. 259.

2 Boehm: Sitzungsb. d. Wien. Akad. Band Ixxi. Abth. i., 1875, p. 481.

3 Text-book, 2d ed., 1882, p. 699.

4 *Tf these [alkaline phosphates] substances are mixed with a solution of
albumin, or if a solution of them is permitted to diffuse against one of albumin,
a much greater amount of the latter will pass through the membrane than -

254 WATER-CULTURE.

679. Iron.) When a plant is provided with a nutrient solu-
tion containing all essential elements except irun, its chlorophyll-
granules fail to attain complete development. They remain in
an imperfect condition, and do not have the characteristic green
color. Upon the addition of a mere trace of a salt of iron to the
solution a change is observable at once, the granules assuming
their proper shape and color. Plants grown in a solution with-
out iron have a pale and even blanched look, which at once
disappears when iron is added; moreover, a local effect is pro-
duced when a solution of a salt of iron is placed on the surface
of the blanched leaves of such plants, — a green color is given
wherever it touches. But it must not be supposed that the fail-
ure of some leaves to produce chlorophyll at certain points or
spots is always due to absence of iron.

It is not clear that iron, which is so necessary to the produc-
tion of chlorophyll, cnuters into the composition of cither the
granule or the pigment; but according to Pfeffer there is a
strong probability that in the latter it exists in the form of some
organic compound. Iron has been found in the cell-walls of cer-
tain algee* (as an incrustation), and also in the fruit of Trapa
natans, the frond of Lemna trisulca, and sparingly in other
plants, as shown by the analyses collated by Wolff.

680. Chlorine. This eleinent appears, from experiments by
Nobbe? and Beyer,* to be indispensable to the full development
of some plants (é. g., buckwheat), but it is not required for many
others (¢. g., Indian corn).° Nobbe concludes, from his experi-

would otherwise be the case. In the life of the plant this work of the alkaline
phosphates plays a very important réle” (Physik der PAlanze, 1867, p. 129).

1 That iron is indispensable to the full vigor of plants was shown by Eusebe

Gris in 1848, and the subject was further studied by Arthur Gris in 1857.
,Salm-Horstmar (in 1856), Sachs, and others have added much to the knowledge
of the subject, showing that no other element can replace iron in producing
the changes noted above.

2 Cohn: Beitrige zur Biologie der Pflanzen, 1870, p. 119.

8 Versuchs-Stationen, vii., 1865, p. 371; xiii., 1870, p. 394.

* Versuchs-Stationen, xi., 1869, p. 262.

5 Knop: quoted by Pfeffer, Planzenphysio'ogie, i., p. 259.

The conclusions reached by Johnson in 1868 appear to need little modifica-
tion at the present date. ‘1. Chlorine is never totally absent. 2. If indis-
pensable, but a minute amount is requisite in the case of the cereals and clover.
8. Buckwheat, vetches, and perhaps peas, require a not inconsiderable amount
of chlorine for full development. 4. The foliage and succulent parts may
inciude a considerable quantity of chlorine that is not indispensable to the life
ef the plant” (How Crops Grow, p. 182).

OFFICE OF THE ASH CONSTITUENTS. 255

ments, that it is required for the transfer of starch. Associating
this view with what is known regarding the office of potassium,
it is easy to see why potassic chloride should be so useful a
salt.?

681. Sulphur is absorbed by plants in the form of the soluble
sulphates. These are believed to undergo immediate decompo-
sition.in the plant; for example, calcic sulphate is decomposed
at once by oxalic acid, and calcic oxalate is formed. The sul-
phuric acid thus set free is reduced, the sulphur entering into
the constitution of the albuminoids? (see 884).

682. Sodium salts cannot wholly replace potassium salts in
the plant; nevertheless, for a portion of the potassium needed
by the plant an equivalent amount of sodium can in some cases
be substituted. It has been found possible to cultivate success-
fully some maritime plants which normally contain a certain
amount of sodium salts, when potassium has replaced sodium
in the water furnished to the plant.

683. Rarer constituents. Besides the ash constituents always
detected in plants, there are certain elements which are only
occasionally met with in greater or less amount, and these will
be next considered.

684. Silicium. This element is so abundant in the ash of
many grasses, Equisctacee, etc., that it almost claims a place
in the list of indispensable elements; but experiments have
shown abundantly that in grasses at least, the proportion of it
present can be reduced to a very low point without materially
affecting the vigor of the plant or the strength of the culms.
Thus Sachs * showed, in 1862, that the amount of silicic acid in
the ash of Indian corn could be reduced from 18 per cent to .7
per cent. without injurious effect on the plant.

685. Zinc has been detected in many plants grown on soil
containing it in considerable amounts; for instance, that at
Altenberg* (near Aix). Freytag ® found that all plants experi-
mented upon were able to absorb more or less zinc when it

1 Bretfeld : Das Versuchswesen, 1884, p. 184.

2 Holzner: Flora, 1867. Aun interesting paper by Hilgers (Pringsh. Jahrb.,
vi., 1867, p. 285) gives an account of the formation of crystals of calcic oxalate
in various parts of plants, and presents certain speculations as to their origin.

8 Flora, 1862, p. 53. Further experiments are recorded by Knop (Ver-
suchs-Stationen, iv., 1862, p. 176), Rautenberg and. Kiihn (Versuchs-Stationen,
vi., 1864, p. 359), Birner and Lueanus (Versuchs-Stationen, viii., 1866, p. 141).

* Sachs : Handbuch der Experimental-physiologie, 1865, p. 153.

5 Chemisches Central-blatt, 1870, p. 517.

256 WATER-CULTURE.

was offered in large amount; nevertheless, Gorup-Besanez!
could detect none in peas and buckwheat cultivated in a soil
containing a fair amount of zine carbonate. It is sometimes
said that Viola tricolor and Silene inflata grown on zine soil take
up an appreciable amount of this element; and further, that
certain plants are directly affected in shape by the presence of
zinc in the soil; in fact, varieties based upon this supposed
relation have been described. The experiments of Hoffmann,?
however, throw much doubt upon the relation of the zine to a
change of form, except in the single case of Viola lutea.

Aluminium? occurs in traces in many plants, while in species of
Lycopodium (e. g. complanatum) it is present in large amount.

Manganese‘ is abundant in the ash of Trapa natans, Quercus
Robur, and Castanea vesca.

Cesium and Rubidium® have been detected by the spectro-
scope in minute amounts in many plants.

Fluorine® has been found in the ash of Lycopodium clava-
tum, and traces of it in other plants. Iodine and Bromine’ are
found in marine alge, in much smaller proportions in aquatics
growing in estuaries (for example, Zostera), and in minute
amount in some plants grown far from the sea.

Barium, Strontium, and Silver have been found in the ash of
Fucus. Mercury, Lead, Copper, Cobalt, Nickel, Tin, Thallium,
Selenium, Titanium, and Boron have all been found by analysts
in the ash of certain plants, but always in the merest traces.
Arsenic® has also been detected in a few instances.

1 Annalen der Chemie und Pharmacie, cxxvii., 1868, p. 2438. This paper
contains an account of the relations of agr.cultural plants to metallic poisons.

2 Botanische Zeitung, 1875, p. 628.

3 Knop: Lehrbuch, p. 263; Rochleder: Phytochemie, 1854, p. 287.
Wolltf’s Die Mittlere Zusammensetzung der Asche.
Laspeyres : Annalen der Chemie und Pharmacie, cxxxviii., 1866, p. 126.
Salm-Horstmar: Annalen der Physik und Chemie, cxi., 1860, p. 339.

7 Chatin, in Comptes Rendus, Ixxxii., 1876, p. 128.

8 Numerous references to the literature of this subject will be found in
Sachs’s Experimental-physiologie, and in Mayer’s Lehrbuch der Agrikultur-
chemie.

aa e

CHAPTER IX.
TRANSFER OF WATER THROUGH THE PLANT.

686. Water is a constituent of all active cells. The proto-
plasmic body of the cell possesses a marked affinity for it, and
up to a given point can abstract it from the ordinary surround-
ings, but under certain conditions releases it again. If a water-
plant in full activity is removed from water and exposed to the
air, it speedily loses by evaporation a considerable part of its
constituent water, and shows the effect of this loss by a col-
lapsing of its cell-walls and by a withering of all its parts. But
if only a small portion of the plant is lifted above the surface
of the water, the loss which takes place will be partially sup-
plied by transfer through the cells remaining submerged. Two
points are made clear by this simple experiment: (1) evapora-
tion goes on with great rapidity from the exposed surface of the
plant ; (2) only a part of the loss of water can be made good by
transference from submerged portions.

687. Comparison of the structure of a water-plant with that
of an ordinary plant adapted to growth in the air shows that
the surface of the latter is such as to prevent very rapid evapo-
ration, and also that the loss caused by the evaporation can be
made good if the lower part of the plant remains in contact with
water. In other words, the plant (1) has a surface which protects
it against too great loss of water; and (2) is provided with a
system by which the needed supply of water can be replenished.

688. But it is not alone by evaporation from the surface that
water is consumed by the plant. Wherever growth goes on or
work is done, water is consumed, and a fresh supply is required.
The question of the transfer of water is therefore a general one.

SOME OF THE RELATIONS OF WATER TO TISSUES.

689. The cell-wall which separates the cavity of one cell from
that of its neighbor is a permeable membrane. According to
the hypothesis of Nigeli (see 588), it is composed of solid par-
ticles (micelle), each of which is enveloped in an adherent film

17

258 TRANSFER OF WATER THROUGH THE PLANT.

of water, and thus prevented from coming in contact with those
around it. According to this hypothesis, all the water in a cell-
wall is practically continuous, and can flow freely between the
micelle ; therefore, if a cell contains its maximum amount of
water, and the cell-wall is tense, the water is in a state of equi-
librium. Likewise in a tissue containing its maximum amount of
water this is in equilibrium. But the balance can be easily dis-
turbed in a plant by evaporation from the surface, or by other
causes before mentioned. If, however, a sufficient part of the
absorbing surface of the plant is in contact with water, the bal-
ance can be restored, since the water in the cell-walls is practi-:
cally continuous with that in the surroundings. ‘The equilibrium
is restored by the transfer of the water outside the cell-wall to
the cell-wall itself, and thence to the parts within. The tendency
to the restoration of the equilibrium of water in a plant is so
great that root-hairs can abstract even the firmly adherent hygro-
scopic water from particles of soil (see 644). From the roots or
other absorbing organs the water passes sooner or later to the
place of consumption.

690. In most cellular plants and in masses of cellular tissue
all the cell-walls have substantially the same capacity for transfer
of water ; but in all plants which possess a fibro-vascular system
the transfer takes place chiefly by means of the lignified cell-
walls; and even in cellular plants like mosses, it is in those cells
which are elongated and otherwise differentiated to form an im-
perfectly developed framework that the rapid transfer is made.

691. Transfer of water in woody plants. In ligneous plants
the water is transferred most rapidly through the woody tissues. -
This is experimentally proved by ‘‘ girdling” their stems; that
is, removing a ring of bark without injuring the wood. For a
time the leaves remain fresh, and the plants appear to suffer
only slightly, if indeed at all. An early experiment in regard
to the transfer of water is that by Hales (in 1731), who says :?
‘¢T cut off the bark, for one inch length, quite round a like’
branch of the same oak; eighteen days after the leaves were
as green as any on the same tree.” Further experiments have
shown that the rapid transfer is made chiefly in the younger
wood of the stem, and not in the heart-wood; and, also, that
the water is transferred most rapidly in the portions of new wood
having the coarser texture known as spring wood ? (see 395).

1 Statical Essays, i., 1731, p. 130.
2 Sachs: Vorlesungen iiber Pflanzenphysiologie, 1882, p. 275.

PATH AND RATE OF TRANSFER. 259

692. The converse of Hales’s experiment is equally conclu-
sive. If the continuity of the wood of a stem is interrupted by
the removal of a short truncheon without at the same time much
injuring the bark, the leaves wither in a short time. Cotta?
asserts that upon a shoot of willow which still maintains its
connection with the plant through the bark, but has had a sec-
tion of wood removed, the leaves will wither as quickly as they
would upon a shoot wholly severed from the parent plant.

693. That water can be conveyed through the stem in a
direction opposite to its normal course is shown in an experi-
ment by Hales: ‘*I took a large branch of an apple-tree, and
cemented up the transverse cut at the great end, and tied a wet
bladder over it; I then cut off the main top branch where it was
€ inch diameter, and ‘set it thus inverted into a bottle of water.
In three days and two nights it imbibed and perspired four
pounds two ounces and one half of water, and the leaves con-
tinued green; the leaves of a hough cut off the same tree at the
same time with this, and not set in water, had been withered
forty hours before.” ”

694. Determination of path and rate of transfer. ‘Two modes
of experimenting have been employed in order to ascertain ex-
actly the path and the rate by which water is transferred through
ligneous plants. The first of these consists in using a colored
solution, which, when taken into the plant, tinges all the tissues
with which it comes directly in contact. The stem or branch
used in the experiment is cut sharply off and its end is plunged
at once into a colored solution, for instance, of some aniline
dye or some colored vegetable juice. As the liquid ascends the
stem, certain portions of the tissues become more or less deeply
tinged, and its course and rate of ascent cau be traced by sec-
tions made at any given time, at different distances above the cut
end. A similar method has been also employed by plunging in
colored water the uninjured roots of the plant to be examined.®

1 Quoted by Pfeffer: Pfllanzenphysiologie, i. 128.

2 Statical Essays, i., 1731, p. 181.

3 «Quel que soit le liquide employé et les variations de l’expérience, les
résultats généraux ont peu varié, savoir: que l’eau colorée ne pénétre ni par
Vécorce ni par la moelle, mais toujours au travers du corps ligneux, tantot
dans toute son étendue, quelquefois dans sa partie la plus jeune, savoir, l’ex-
térieur du corps ligneux des exogénes, et l’intérieur des endogénes. On obtient
ce méme résultat général, soit qu’on plonge les plantes munies de toutes leurs

. . , z. x ” , : .
racines, soit qu’on emploie des branches coupées” (De Candolle’s Physiologie
yégétale, p. 83).

260 TRANSFER OF WATER THROUGH THE PLANT.

695. The two objections to the first method are: (1) that the
protoplasmic body of the cell resists the entrance of nearly all
coloring-matters, therefore with many dyes it is necessary to
experiinent with cut stems and branches, allowing the dye to
enter at the cut surface; but, as will be shown later, a cut sur-
face which has been exposed to the air, even for an instant,
loses part of its power of absorbing water ; (2) it is by no means
certain that the dye passes through the stem as rapidly as the
water in which it is dissolved. That it does not, seems more
than probable from the simple experiment of stispending one
end of a strip of filter-paper in a solution of any dye; the water
will rise faster than the dye, and form a moist space above that
part of the paper which becomes colored.

696. The second method of experimenting is based upon
the ease with which ccrtain chemical substances foreign to the
plant can be detected in it if once they can be introduced into
and carried through its tissues. Dilute solutions of salts of
lithium, for instance the citrate, serve best for this method, and
Pfitzer suggests that they be applied to the roots of a plant
which has been allowed to wilt somewhat from drought.

697. The two objections which may be urged against the second
method, are: (1) the chemical used may cause more or less dis-
turbance in the plant, and may even excite disordered processes,
and it is plain that no correct conclusions relative to the rapid-
ity of transfer in a healthy plant can be drawn from one which
is in a state of disease; (2) the presence of a diffusible salt, for
instance one of lithium, may change the osmotic relations of the
tissues with which the salt comes in contact. But in spite of
these serious difficulties, these methods are of considerable use
when cautiously employed.

698. The above methods indicate that the most rapid transfer
of water is through the lignified cell-walls of the framework of
the plant. ‘I'he source of supply at the root furnishes the need-
ful amount of water to the ligneous tissues of the fibrils, and
these convey it to the converging bundles which constitute the
framework of the plant. In the leaves the framework divides and
subdivides to form the network of the leaf blade, and here the
ligneous cells and ducts are in intimate contact with the paren-
chyma cells which make up the pulp of the leaf. That water
finds its way by preference through the fibro-vascular bundles
even in the more delicate parts, is shown by placing the cut
peduncle of a white tulip, or other large white flower, in a harm-
less dye, and then again cutting off its end in order to bring a

RATE OF ASCENT IN THE STEM. 261

fresh surface in contact with the solution, when after a short
time the dye will mount through the flower-stalk and tinge the
parts of the perianth according to the course of the bundles.
699. Rate of ascent. The following are some of the discor-
dant results obtained by the methods mentioned in 694 : —

Name of plant Rate of ascent per hour. Observer.
Prunus Laurocerasus . . 42-100cm. . . . . . . McNab.
Salix fragilis . . 2. 8h“ ew ee ee 6) CBS achs:
Vitis vinifera. . . . . PE hs Oe Men 8 @ #g
Nicotiana Tabacum. . . ig 2 3 & © * « oe
Helianthus . .. . 9200 "os . . . Pfitzer.

700. But little is known as to the reason of the high conduct-
ing power of ligneous tissues. That it is not wholly due to
eapillarity (as has been suggested on account of the abundance
of ducts of small calibre in most wood), is shown by the struc-
ture of the wood of coniferous plants in which no ducts are
present. Again, at the very time when the evaporation from
leaves of plants is most rapid, and the transfer of water to sup-
ply the loss must be greatest, the cavities of the ducts are not
wholly filled with liquid, but contain a considerable amount of
air; whereas according to the theory of capillarity they should
contain only liquid. By a very ingenious series of experiments
Sachs has determined the relative amount of space occupied by
the cell-walls, water, and cavities in several fresh woods. In
the case of fresh coniferous wood he found the following ratios
in 100 cubic centimeters of wood : —

Cell-wall, reckoned asdry . . . . i gel ae “ep ABI
Water, in the cell-wall and in the oanttios se Gale eae 5868
Air-spaces 2 6 6 6 1 8 ew ee e » « 36.56

But, as Sachs says, since neither intercellular spaces nor ducts
are present in this wood, the 16.56 per cent of air must be con-
tained in the cavities of the wood-cells; and further, since the
cell-walls can take up only about half their volume of water
(say 12.4 cubic centimeters), the remainder (46.23 ¢.c.) must
exist in the cell-cavities.

701. The method of determining the amount of water held hy
the cell-walls of dry wood is the following : —

A thin cross-section of fresh wood is hung up in dry air until
it ceases to lose weight. During drying a crack appears, run-
ning from the centre to the circumference. After ascertaining
the weight of the dise thoroughly dried (at 100° C.), the wood
is suspended in a saturated atmosphere until enough water is

262 TRANSFER OF WATER THROUGH THE PLANT.

absorbed to cause a swelling of the tissues and a closing of the
crack. In this condition it is safe to assume that the cell-walls
themselves are saturated, but that there is no liquid water in the
cavity of the cells. ‘The difference between the weight of the dry
and that of the saturated disc gives the weight of the water
taken up and held; this, converted into volume, is found to be
approximately one half that of the space occupied by the cell-
wall itself.

702. The water which is taken up in relatively small amount
and held in the micellar interstices of lignified cell-wall is in the
state of equilibrium previously described. When, however, this
equilibrium is disturbed by evaporation at any point, there is an
immediate transfer of the imbibed water to that point, and the
loss from this transfer must be made good at once by the recep-
tion of more water. This interstitial transfer may take place
through any length of woody tissue, provided there is a con-
sumption of the water at one extremity and an adequate supply
at the other. When the consumption of water is only that which
is duc to the opening of growing buds, or to some chemical pro-
cess, a slow transfer of water to the point of consumption! must
take place. When, however, it is due to evaporation from the
leaves, the transfer is exceedingly rapid.

703. Boehm® considers the ascent of water in ligneous tissue ?
to be ‘¢ a phenomenon of filtration caused by differences in pres-

1 A similar transfer can be demonstrated to take place in porous inorganic
matter, for instance powdered hydrated gypsum. Ifa long tube be filled with
this material and well saturated with water, one end being placed in water
and the other exposed to a dry atmosphere, the continual loss by evaporation
above will be made good hy water brought up from below.

Jamin’s apparatus for demonstrating the pressure exerted by the imbibition
of water by a porous substance consists of a cylinder, in the mouth of which
can be placed a tightly fitting plug of wood, through which passes a ma-
nometer tube. The pulverulent substance, for instance zinc oxide, is closely
packed in the interior of the cylinder, around the open end of the manometer,
and the whole apparatus is then placed in water. With zinc oxide the ma-
nometer shows a pressure of five atmospheres; with powdered starch, more
than six atmospheres. If a manometer is similarly placed ir a block of dry
chalk, and the chalk is then submerged, a pressure of three to four atmos-
pheres is indicated (Legous professées devant la Société chimique, Séance du
8 mars, 1861, quoted by Dehérain: Cours de Chimie Agricole, 1873, p. 165).

2 Ann. des Sc. nat., sér. 6, tome vi., 1878, p. 236.

3 As might he expected, woody tissues never conduct water so readily in a
transverse as in a longitudinal direction. Experiments with regard to this have
been conducted by Wiesner (Sitzungsb. d. Wien Akad., Bd. Ixxii. 1 Abth.,
1875) upon cubes of wood. Four sides of these were protected by varnish

RATE OF ASCENT IN THE STEM. 263

sure in contiguous cells. ... In parenchymatous tissues filled with
sap the movement of water caused by evaporation is a function
of the elasticity of the cell-walls and of atmospheric pressure.”

Herbert Spencer has shown that when a cut stem is quickly
bent backwards and forwards there is a marked increase in the
rapidity with which colored fluids ascend through it. ‘+ To
ascertain the amount of this propulsive action, I took from the
same tree, a Laurel, two equal shoots, and, placing them in the
same dye, subjected them to conditions that were alike in all
respects save that of motion: while one remained at rest, the
other was bent backwards and forwards, now by switching and
now by straining with the fingers. After the lapse of an hour
I found that the dye had ascended the oscillating shoot three
times as far as it had ascended the stationary shoot, this re-
sult being an average from several trials. Similar trials brought
out similar effects in other structures.” ?

704. Effect upon transfer of exposing a cut surface to the air.
One of the most interesting characteristics of the woudy tissues
in relation to the transfer of water is the immediate change
which the cut surface of a stem undergoes upon exposure to air,
unfitting it for its full conductive work. De Vries? has shown
that when a shoot of a vigorous plant, for instance a Helianthus,
is bent down under water, care being taken not to break it even
in the slightest degree, a clean sharp cut will give a surface
which will retain the power of absorbing water for a long time ;
while a similar shoot cut in the open air, even if the end is in-
stantly plunged under water, will wither much sooner than the
first. Shoots cut in the manner first described remain turgescent
for several days. If a cut shoot placed in water has begun to

against the entrance and exit of water, and one of the two surfaces remaining
uncovered was placed in water, the other exposed to air, when the transfer of
water through the wood was found to be more rapid in a longitudinal than in
a transverse, and in a radial than in a tangential direction. :

Another method of experimenting was also employed by him: five sides of
a cube of wood were surrounded by separated portions of dry calcic chloride,
and the remaining side was placed in contact with water; the difference in
rate of transfer ascertained by comparing the weights of the portions of calcic
chloride after a fixed time was found to be essentially that given by the other
method. :

Experiments by Sachs (Arbeiten des botan. Instituts in Wiirzburg, 1879,
p- 298), in which water was forced in different directions through the wood of
coniferous stems, showed, however, that under pressure water passes through
wood more readily in a tangential than in a radial direction.

1 Transactions of Linnean Society, xxv., 1866, p. 405.

2 Arbeiten des botan. Inst. in Wiirzburg, i., 1874, p. 292.

264 TRANSFER OF WATER THROUGH THE PLANT.

wilt, cutting off the stem a little higher up will cause it to regain
in part the power of absorption which it lost upon exposure.

705. Although osmosis can have very little to do directly’
with the rapid transfer of water through the stem, branches, and
leaves, it plays, as has been seen, a very important part in the
introduction of water into the plant, and in supplying the requi-
site amount of it to cells which lie, so to speak, away from the
main channel of transfer.

706. Pressure and ‘‘ bleeding.” If, before its leaves unfold,
a grape-vine be cut off near the root, or a little higher up on the
stem, the cut surfaces will bleed copiously. The part connected
with the roots will continue to yield a supply of watery sap for
a considerable time. The flow is plainly regulated to a very
great degree by the surroundings of the plant, being accelerated
by heat and checked by cold. It is not merely passive; the
application of a suitable pressure-gauge shows that the escaping
liquid exerts much force.

One of the early experiments on this subject was made by
Hales,’ who found the pressure in the case of the grape-vine
to be equal to thirty-eight inches (105 cm.) of mercury, or more
than forty-three feet of water. Other experimenters have
reported higher figures; for example, Clark? found in Betula
lenta a pressure of eighty-five feet of water.

707. Pitra® has shown that a certain amount of pressure is
exerted by sap, even in stems which have been severed from
the parent plant, the lower extremity being placed in water.
In some of his experiments he found that it was not exerted
at once, but only after the lapse of a considerable time. He
further shows that a considerable pressure is exerted by the
sap which flows out of a cut stem the leaves and twigs of which
are submerged.

708. There are considerable individual differences in plants
as to the force with which the sap flows from wounds. Wilson
found that while one specimen of Ampelopsis quinquefolia gave

1 Statical Essays, i., 1731, p. 114.

2 The apparatus for demonstrating the pressure can be easily used. Reduced
to its simplest terms, it consists of a mercurial pressure-gauge, which can be
securely attached to the wounded part of the plant. To the stump of the
plant the gauge must be fastened by means of stout rubber tubing, which has
been made to fit tightly around both plant and tube, and then wired firmly
to prevent the escape of any liquid. Dahlia variabilis, Vitis vinifera, and
Helianthus annuus are good plants for purposes of demonstration.

8 Pringsheim’s Jahrb., xi., 1878, p. 437.

PRESSURE OF THE SAP. 265

no pressure for the root-system, another showed a pressure of
twenty centimeters of mercury.

709. Bleeding is not by any means of universal occurrence in
wounded plants. Horvath found none in the following cases:
Humulus Lupulus, Hedera Helix, Syringa vulgaris, and Sam-
bucus nigra. In some cases there appears to be bleeding only
from the cut root, none occurring from the stem.

710. The bleeding from a plant may be greatest immediately
after the wound is made, or it may in a few cases not reach a
maximum for some hours or even days, after which it gradually
declines until it ceases. It may recommence after the wound
is reopened. According to Hartig,! bleeding may continue in
some cases for a month.

711. The amount of sap which escapes during bleeding is
variable even in the same species. The following cases show
that the loss is very large: —

Betula papyracea, 24 hours, 63} lbs. (Clark).
Agave Americana, 24 hours, 375 cubic inches (Humboldt).

712. Hofmeister has given the following example, to show
how large is the relative amount of sap which can flow from cer-
tain plants. From a specimen of Urtica urens (stinging nettle),
whose root-system had a volume of 1,450 cubic centimeters,
there escaped in 24 days 11,260 cubic centimeters of sap.

713. The pressure at the cut surface of a plant varies widely
in any given case, according to the surroundings. The following
details of an experiment by Clark * will indicate the variations
in pressure noted during a comparatively short time.

‘* A gauge was attached to a sugar-maple March 31st, three
days after the maximum flow of sap for this species. . . . The
mercury [in the gauge] was subject to constant and singular
oscillations, standing usually in the morning below [its] zero,
so that there was indicated a powerful suction into the tree,
and rising rapidly with the sun until the force indicated was
sufficient to sustain a column of water many feet in height.
Thus at 6 a. m., April 21st, there was a suction into the tree
sufficient to raise a column of water 25.95 feet. As soon as the
morning sun shone upon the tree the mercury snddenly began
to rise, so that at 8.15 a. m. the pressure outward was enough to

1 Botanische Zeitung, 1862, p. 89.
2 Report of the Secretary of the Massachusetts Board of Agriculture for

1873, p. 187.

266 TRANSFER OF WATER THROUGH THE PLANT.

sustain a column of water 18.47 feet in height, a change repre-
sented by more than 44 feet of water.”

714. The pressure of the sap rises and falls with the tempera-
ture. The greatest pressure in ligneous plants is found when a
cold night is followed by a warm morning. This has been ex-
plained by the expansion of the air contained in the wood-cells
and ducts. Detmer observed the greatest outtlow of sap in the
case of the herbaceous plants Begonia and Cucurbita to be at a
temperature of from 25° to 27° C, and that the outflow ceased
at 32° for Begonia, at 43° for Guoutbiee y

715. Besides the variations both in bleeding and in pressure
of sap due to external influences there are some periodical
changes which are not yet satisfactorily explained. Baranetzky
found that the greatest extravasation of sap from the crown of
the root took place in Ricinus between 8 and 10 o’clock a. M., in
Helianthus annuus between 12 m. and 2 pv. M., and in Helianthus
tuberosus between 4 and 6 p.M., the plants being under essen-
tially the same conditions.

716. The great pressure exerted by sap under certain condi-
tions is thas explained by Sachs. From the root-hairs, into
which the water comes by osmosis, it passes by osmosis into the
parenchymatous cells of the cortex. ‘+ But a difficulty occurs in
answering the question why the turgescent cortical cells of the
root expel their water only inwards into the woody tissues, and
not also through their outer walls. We may, however, here
be helped by the supposition that the micellar structure of the
cell-walls is different on the outer and inner sides of the cells,
and that those facing the exterior of the root are best adapted
for permitting filtration under high endosmotic pressure.” ?

Among the reeorded experiments which show a great root-
pressure is one by Clark, described by him thus: ‘+ A gauge was
attached to the root of a black birch-tree as follows. The trec
stood in moist ground at the foot of a south slope of a ravine,
in such a situation that the earth around it was shaded by the

1 A full and satisfactory treatment of this subject in detail will be found in
the following works : —

Schroder: Beitrag zur Kenntniss der Friiljahrsperiode des Ahorn (Pringsh.
Jahrb., vii., 1869). In this, the spring phenomena of the maple are clearly
given.

Baranetzky : Untersuchungen iiber die Periodicitit des Blutens (Abhandl.
des naturforschende Gesellschaft zu Halle, 1873). In this memoir the
experiments cover a wide range.

2 Text-book of Botany, 2il English edition, 1882, p. 688.

EXUDATION OF WATER FROM UNINJURED PARTS. 267

overhanging bank from the sun. The root was then followed
from the trunk to the distance of ten feet, where it was carefully
cut off one foot below the surface, and a piece removed from
between the cut and the tree. The end of the root was en-
tirely detached from the tree and lying in an horizontal position
at the depth of one foot in the cold, damp earth, unreached by
the sunshine, and for the most part unaffected by the temper-
ature of the atmosphere, measured about one inch in diameter.
To this was carefully adjusted a mercurial gauge April 26th.
The pressure at ouce became evident, and rose constantly with
very slight fluctuations, until at noon on the 30th of April it had
attained the unequalled height of 85.80 feet of water.” ?

717. Pfeffer* attributes the tendency of water to pass only
inwards into the woody tissues wholly to the fact that upon that
side of the cells which faces the interior of the root the osmotic
capacity is greater. Within the plant the cell-walls are never
saturated with pure water; but the imbibed liquid is different on
different sides, and hence the plasma meibrane in contact with
the sides must have different capacities for osmosis.

718. In midwinter or in earliest spring some of the tissues
of ligneous plants are stored to a large extent with starch and
other solid products manufactured during the previous season.
At the coming of warmer weather chemical changes take place,
largely following the absorption of water, by which these solid
substances are transformed into a liquid state, occupy a greater
space than before, and of course exert much greater pressure.
The saccharine sap of the maple represents that which dur-
ing the early winter existed in the tissues as starchy matter.
This conversion of material will be further discussed under
‘: Metastasis.”

719. Exudation of water from uninjured parts of plants. Un-
der certain circumstances water can exude in a liquid form from
uninjured parts; for instance, through chinks or rifts in the leaf-
tips of many monocotyledonous plants, and through water-pores
of dicotyledons, especially when these are young. Musset?
reports eighty-five drops of liquid falling in one minute from
the tip of a leaf of Colocasia esculenta. Duchartre* gives the
following figures: Twenty-five drops fell in one minute from

1 Report of the Secretary of the Mass. Board of Agriculture for 1873, p. 189.
2 Pflanzenphysiologie, i., 1881, p. 170.

8 Comptes Rendus, Ixi., 1865, p. 683.

4 Ann. des Se. nat. bot., sér. 4, tome xii., pp. 247, 250.

268 TRANSFER OF WATER THROUGH THE PLANT,

the tip of a leaf of Colocasia antiquorum, and 22.6 grams of
liquid were collected in one night. From the young leaves of
certain Aroids water is sometimes ejected in a fine jet to a
distance of a few inches.’ In these and the previous cases the
liquid escapes through rifts.

TRANSPIRATION.

720. The evaporation of water from the surface of the younger
parts of plants exposed to the air makes, as has now been seen,
a continual draught upon the sources of water-supply. But
while evaporation from the free surface of water or from any
dead membrane ceases in an atmosphere saturated with moisture,
there is some experimental evidence to show that, under certain
conditions of radiation, evaporation from the living plant may
continue to take place even when the atmosphere is completely
saturated. ‘This difference between evaporation from a free sur-
face and that froma plant, although not fully established, ren-
ders it advisabie to employ for the latter phenomenon the term
transpiration. This term is sometimes employed in Physics
with another signification ; but its prior use in Vegetable Physi-
ology should prevent any confusion.

721. Stomata. Neither through the cutinized cell-walls of
the. epidermis, nor through the suberized cell-walls of cork,
can transpiration take place to any extent; ? but at myriads
of points in the epidermis of leaves and young stems there are
minute orifices which permit the air outside the plant to come
into communication with the air within. It has been shown in
Part I. that these openings, the stomata, possess definite rela-
tions as regards position to the intercellular spaces below them,

1 Musset : Comptes Rendus, 1865.

Muntingh (1672), accorling to a reference in Flora (1837, p. 717), noted the
projection of a small jet of water from the leaf of an Aroid, as from a fountain.

2 «Tt is of the highest significance that those plants which are submerged,
or those parts of plants which grow in the ground and therefore cannot lose
water by transpiration, possess a cuticle which permits water and dissolved
matters to pass through with comparative facility; while the parts growing
in the air have a cuticle of a different quality, through which water passes only
with difficulty, and thus they are protected from too great a loss of water”
(Pfeffer : Ptlanzenphysiologie, i., 1881, p. 139).

The amount of aqueous vapor which can escape through cuticle is very
small. According to Boussingault, .005 gram of water may evaporate in one
hour from one square centimeter of the rind of an apple, while from the surface
of a peeled apple fifty-five times as much is lost (Agronomie, vi-, 1878, p. 349).

MECHANISM OF STOMATA. 269

so that they may be fairly regarded as a part of the system for
aerating the plant.

722. By reference to the structure of the more common kinds
of leaves (see Chapter III.), it will be seen that the terminations
of the delicate fibrils of the framework approach very closely
to the aeriferous spaces, and thus by the uninterrupted com-
munication between the minute fibrils in the root-system, the
stem-system, and the leaf-system of the plant, water which has
been absorbed by the roots is brought finally to the parenchyma
cells which surround the spaces under the stomata. If it
evaporates from the outer side of the wall of these cells into
the intercellular spaces, the water may make its escape through
the stomata.

723. Stomata are not mere epidermal rifts having an aper-
ture of unvarying width. ‘The guardian cells of a stoma are so
arranged with respect to each other and the proper epidermal
cells contiguous to them, that the width of the opening between
them can be increased or diminished upon certain changes in
the surrounding conditions.

724. Mechanism of Stomata. In examining the mechanism of
stomata it is necessary to distinguish hetween their three parts
which are shown in a vertical section; namely, (1) the anterior
groove, (2) the cleft, and (3) the posterior groove, which is
usually continuous with an intercellular space. It is plain that a
stoma is most widely open when the edges of the cleft are farthest
apart and the rim of the cup not closed. Hence an inspection
of the anterior face of a stoma is not suflicient to show whether
the stoma is most widely open; the width of the cleft itself must
be ascertained.

725. In distinction from proper epiderinal cells, the guardian
cells contain chlorophyll, and hence under the influence of light
can produce carbohydrates (see ‘‘ Assimilation’). As might be
expected, the osmotic tension is different in these two groups
of cells.

726. The following account, condensed from Strasburger,
shows the relations which the guardian cells sustain to those
around the stoma as regards the thickness of the walls. The
guardian cells are strongly thickened on the upper and under
angles of the walls of their opposed faces, while elsewhere their
walls are relatively thin. At the cleft there are opposing
projections forming its edges. The opening and closing of a
stoma depend upon the difference in the thickness of the parts
of the walls. When the turgescence of the guardian cells

270 TRANSFER OF WATER THROUGH THE PLANT,

increases, they curve more strongly, and the cleft widens; but
when their turgescence diminishes, the cleft becomes straighter
and narrower, it being clear that with increasing turgescence
the guardian cells must become more convex on the side of
least resistance, and more concave upon the side of greatest
resistance.

727. Relations of stomata to external influences. In a classical
series of expeviments upon the relations of stomata to their sur-
roundings, Mohl? has shown that when the uninjured leaves of
certain orchids, lilies, etc., are wet with water, the clefts of the
stomata open; but these plants form exceptions to the general
rule, for it was found that in the greater number of cases studied
the cleft closes when the stoma is brought in contact with water.
In Amaryllis and the grasses, this closing takes place with great
rapidity. °

728. When a thin film of epidermis with its stomata is de-
tached, and examined under the microscope, the belavior is the
reverse of that above. In a detached film the guardian cells of
the stoma are partially freed from the action of the contiguous
proper epidermal cells, and as a result the cleft widens when
water is applied, the turgescence being increased ; but if a solu-
tion of sugar in water is employed, the cleft grows narrower,
since the turgescence of the cells is at once diminished by
osmosis.

According to Mohl, in a wilted leaf the clefts of the stomata
are partially or wholly closed, but the application of water causes
them.to open. If kept wet, they soon close again.

729. The cleft of a stoma opens more widely in the light
than in darkness; thus leaves of Lilium which have been kept
in the dark in a saturated atmosphere for some days have the
stomata closed, and when wet the cleft opens only slightly.
Upon exposure to sunlight, the cleft gradually opens.

730. According to Van Tiegheim,? stomata are always open
in sunlight and closed in darkness. In order to cause open
stomata to close, it is merely necessary to suddenly change the
amount of light. ‘This closing of the stomata takes place in half
an hour when a bright light is replaced by diffused light.

It has been found that heat has no marked effect upon the
opening and closing of stomata; thus when a plant is kept in
darkness at a temperature of from 15° to 17° C., they are closed,

1 Botanische Zeitung, 1856.
2 Traité de Botanique, 1884, p. 636.

AMOUNT OF TRANSPIRATION. 271

and will not open when the plant, still kept in darkness, is
subjected to a higher temperature, say from 27° to 30° C.

731. From the foregoing, it appears (1) that stomata are
delicately balanced valves, which are exceedingly sensitive to
external influences; (2) that in wilted leaves they are partially
closed; (3) that in most cases, on the application of liquid
water, stomata which are open close ; (4) that strong light causes
stomata to open widely ; (5) that a sudden shock causes them to
close.

732. Amount of water given off in transpiration.! This is
determined chiefly by the balance.

In the oft-cited experiment of Hales,? in 1724, the amount

1 The earliest experiments upon this subject appear to have been those by
Woodward in 1699 (Philosophical Transactions). They were made from July
to October, and gave the following results (here reduced for convenience to
grams) :—

Name of plant and kind of First weight of | Final weight of | Total amount of
water furnished. the plant. the plant. water evaporated.

Mint in rain water . < 1.79 2.88 192.3

Mint in spring water .. 172 268 163.6

Mintin Thames water. 1.79 3.45 159.5

Pea in spring water . R 6.27 6.46 160.

Woodward’s most interesting observations relate to the ratio of growth to
evaporation when plants are cultivated in different kinds of water. Thus
when mint was grown in water mixed with garden earth, the ratio of growth
to evaporation was 1:52; but when it was grown in distilled water, 1:214.

2 «July 3, 1724, in order to find out the quantity imbibed and perspired
by the Sun-Flower, I took a garden-pot with a large Sun-Flower, 3 feet + $
high, which was purposely planted in it when young; it was of the large
annual kind.

“T covered the pot with a plate of thin milled lead, and cemented all the
joints fast, so as no vapour could pass, but only air, thro’ a small glass tube
nine inches long, which was fixed purposely near the stem of the plant, to
make a free communication with the outward air, and that under the leaden
plate.

*¥ cemented also another short glass tube into the plate, two inches long
and one inch in diameter. Thro’ this tuhe I watered the plant, and then
stopped it up with a cork ; I stopped up also the holes at the bottom of the
pot with corks.

“‘T weighed this pot and plant morning and evening, for fifteen several days,
from July 3, to Aug. 8, after which I cut off the plant close to the leaden
plate, and then covered the stump well with cement; and upon weighing
found there perspired thro’ the unglazed porous pot two ounces every twelve

272 TRANSFER OF WATER THROUGH THE PLANT.

transpired from a vigorous sunflower, three feet and a half high,
during twelve hours of a very warm day, was one pound four-
teen ounces, and, on an average, one pound four ounces was
transpired every twelve hours. Any evaporation from the sur-
face of the soil in the flower-pot in which the plant was growing
was prevented by a lead cover.

A still simpler method of preventing evaporation is to en-
velop the flower-pot with a thin rubber membrane, and tie this
tightly around the stem of the plant. A fresh supply of water
can be given to the plant at any time by means of a tube close
to the stem. In experiments upon transpiration the plant should
be weighed frequently, care being taken to note all the external
conditions, such as light, moisture of the atmosphere, etc. For
weighing, an open balance with large pans should be used. The
form known as the box scale will answer all ordinary purposes ;
but for delicate weighings one of special construction, having a
long beam, is preferable.

hours day, which being allowed in the daily weighing of the plant and pot, I
found the greatest perspiration of twelve hours in a very warm dry day, to be
one pound fourteen ounces; the middle rate of perspiration one pound four
ounces. The perspiration of a dry warm night, without any sensible dew, was
about three ounces; but when any sensible, tho’ small dew, then the per-
spiration was nothing ; and when a large dew, or some little rain in the night,
the plant and pot was increased in weight two or three ounces. N. B. The
weights I made use of were Avoirdupoise weights.

T eut off all the leaves of this plant, and laid them in five several parcels,
according to their several sizes, and then measured the surface of a leaf of each:
parcel, by laying over it a large lattice made with threads, in which the little
squares were } of an inch each ; by numbering of which | had the surface of
the leaves in square inches, which multiplied by the number of the leaves in
the corresponding parcels, gave me the area of all the leaves ; by which means
I found the surface of the whole plant, above ground, to be equal to 5616
square inches, or 39 square feet.

“‘I dug up another Sun-Flower, nearly of the same size, which had eight
main roots, reaching fifteen inches deep and sideways from the stem: It had
besides a very thick bush of lateral roots, from the eight main roots, which ex-
tended every way in a Hemisphere, about nine inches from the stem and main
roots.

“Tn order to get an estimate of the length of wll the roots, I took one of the
main roots, with its laterals, and measured and weighed them, and then
weighed the other seven roots, with their laterals, hy which means I found the
sum of the length of all the roots to be no less than 1448 feet.

‘And supposing the periphery of these roots at a medium, to be }§ of an
inch, then their surface will be 2286 square inches, or 15.8 square feet ; that
is, equal to 2 of the surface of the plant above ground” (Vegetable Staticks,
2d ed., 1731, vol. i. p. 4).

KRUTIZKY S APPARATUS. 273

733. Vesque has devised an automatie apparatus! by which
the disturbance of the equilibrium of the balance as the water
evaporates can be recorded upon a revolving drum. In this
apparatus, as soon as the needle records the moment of descent
of the beam, an electrical current releases a valve so as to per-
mit the passage of a sufficient quantity of mercury to the losing
side of the balance to restore the equilibrium.

731. The registering apparatus of Krutizky* is simple, but
unfortunately can be used ouly with
cut stems or branches. It consists
of a U-tube filled with water, in one
end of which a leaf or stem (cut off
under water) is inserted, through a
tightly fitting cork. Through a cork
in the other end extends the short
leg of a siphon. In a jar of water
there floats a tube balanced to keep
it erect. This is somewhat like an
hydrometer (but open at the top),
and contains a certain amount of
water into which comes the long leg
of the siphon. When by evapora-
tion from the plant water is drawn
up through the siphon out of the
floating tube, the tube (called a
‘*swimmer”) of course becomes
lighter and rises in the jar. Ifan
index is attached to the swimmer, as in the figure, it can be used
to record upon a revolving drum the rise of the swimmer as the
plant transpires. To prevent evaporation from the water in the
jar and in the swimmer, its surface is covered by a film of oil.?

735. When a transpiring plant is placed under a bell-jar, a
certain amount of the transpired water will collect upon the
inside of the jar, — often a sufficient quantity to appear as large

1 For a full account of its construction see Annales des Sc. nat., sér. 6,
tome vi., 1878, p. 186.

2 Botanische Zeitung, 1878, p. 161.

3 A simpler piece of apparatus arranged by Pfeffer answers well for class
demonstration. It is easily understood from Fig. 147. The fall of water in
the small lateral tube is very marked, but attention should be called to the
varying pressure caused by the constantly changing level of the water in the
tube.

Fic. 146. Krutizky’s apparatus.
18

274 TRANSFER OF WATER THROUGH THE PLANT,

drops. This method of demonstrating transpiration has been
used, when somewhat modified, by many investigators, notably
Dehérain.. It is well adapted to class experiments, since very

simple appliances? can be used: for instance,
a leafy stem can be inserted in a piece of
pasteboard, and the cut end of the stem
placed in a tumbler of water; another tum-
bler, inverted over the stem, rests on the
pasteboard. The water in the lower tumbler
is prevented from evaporating into the upper
one. The amount of water which collects on
the inside of the upper tumbler comes wholly
from the transpiration of the plant, and will be
found to vary according to the surroundings
(see page 275 et seq).

736. If a weighed
amount of calcic chlo-
ride is placed with a
transpiring plant in a
confined atmosphere, the
salt will readily take up
the aqueous vapor, and
its increase in

weight gives yl
the amountof “ANG

—\\\
LUKE
SSNS

water exhaled by the plant. This
method of measuring the amount
of transpiration has been em-
ployed by several experimenters,
who have obtained results sub-
stantially in accord. It must be
noted, however, that in this
method the air to which the
plant is exposed is rendered ab-
normally dry by the presence of
the salt, and the plant is there-

148

fore subjected to an unusual draft upon its water-supply.
737. Garreau’s method of comparing the relative amounts of
transpiration on opposite sides of a leaf is based on that last

1 Cours de Chimie Agricole, 1873, p. 180 et seq.
2 Henslow. See Oliver’s Botany (1864), p. 15.

Fig. 147. Apparatus for demonstration of transpiration.
Fic. 148. Garreau’s apparatus.

TRANSPIRATION AND EVAPORATION COMPARED. 27)

mentioned, and is of easy application. Two tubulated bell-jars,
each furnished with a mercury trap (7 and m/), are secured firmly
with soft wax to opposite sides of any large leaf. In each bell-
jar is a small capsule (¢ and ce’) containing dry calcic chloride of
known weight. After a given time the salt placed in each bell-
jar is weighed, and the excess over its original weight shows the
amount of water transpired. The following are some of Gar-
reau’s results : —

(1) The quantity of water exhaled by the upper face of a
leaf is to that exhaled by the lower as 1:1, 1:3, or some-
times as 1:5.

(2) There are marked but not exact relations between the
quantity of water exhaled and the number of stomata.?

738. Transpiration compared with evaporation proper. The
evaporation from a given surface of water is between three and
six times as great as that from an equal surface of green leaves
similarly exposed. Unger? foundethat leaves of Digitalis pur-
purea with a surface of five thousand square millimeters tran-
spired from 3.232 to 1.232 grams in a given time; while from an
equal surface of water from 4.532 to 8.459 grams evaporated.
Sachs® found that from a surface of sunflower stem and leaf meas-
uring 4,920 centimeters enough water transpired to form a layer
2.23 mm. thick over the same surface; while from an equal sur-
face of water enough evaporated to lower the level 5.8 mm.

Sachs also found that the evaporation from an animal mem-
brane is greater than that from an equal surface of free water.
When a surface of water is covered by a moist layer of vegetable
parchment, evaporation is somewhat retarded ;* but even then it
is greater than that from an equal surface of leaves.

But the area of a leaf does not express its evaporating sur-
face, since the latter consists of intercellular spaces which have
been estimated to bear the ratio of ten to one to the cuticularized
exterior. In the intercellular spaces the air is saturated with
moisture, hence the slowness of the rate of transpiration.®

739. Effect of moisture in the air upon transpiration. All ex-
periments show that with increase in the amount of aqueous
vapor contained in the air the amount of water transpired from

1 Ann. des. Sc. nat., sér. 3, tome xiii, 1849, p. 321. Bonnet’s early ex-
periments are interesting.

2 Sitzungsb. d. Wiener Akad., Bd. xliv., Abth. 2, 1861, p. 206.

8 Handbuch der Experimental-physiologie, 1865, p. 231.

4 Baranetzky: Botanische Zeitung, 1872, p. 65.

5 American Naturalist, 1881, p. 385.

276 TRANSFER OF WATER THROUGH THE PLANT,

a plant exposed to it diminishes.1 When the air is completely
saturated, a slight amount of transpiration can take place,?
which, as Sachs has pointed out,? is probably due to the fact
that the temperature of the plant is higher than that of the
surrounding air.

740. Instructive experiments upon the exhalation of moisture
by some of the more common desert plants in the dry air of the
Western plains have been made by Sereno Watson,‘ from which
it appears that in about four hours young shoots furnished with
about fifty per cent of leaves lost, when severed from the stem,
water amounting to nearly half their weight.

741. Effect of the soil upon transpiration. The physical prop-
erties of the soil have an influence upon transpiration. Sachs®
cultivated plants of tobacco in clay and in sandy soil, and ob-
served the amount of water transpired by them under like con-
ditions. Although his experiments are not conclusive, they
indicate that transpiration is more uniform from the foliage
of the plants grown in clay-than from the plants grown in
sand; the former soil is much more retentive of moisture, and
thus the supply of hygroscopic water is given up more gradually
to the roots of the plant.

The chemical properties of soils affect transpiration to a cer-
tain extent. Senebier, in 1800, stated that acids increase the
rate of transpiration, and he ascribed the same effect also to.

1 The relations between humidity of the air and transpiration are shown
by the results obtained by Unger with two plants of Ricinus, one of which
was in the open air, the other under a bell-jar. (The leaf surface of one plant
was 190, and that of the other 160 square centimeters ; but in the table a cor-
rection has been made so that equal surfaces are compared).

a r Loss of water Loss of water Temperature of
Duration of the Experiment. open air. : bell-jar. : the air in C°.
July 19to2, , . 2. 11.60 ce. 1.60 ce. 16.
“ 20to21. . Benet 17.05 ‘ 1.14 * 13.6
1 QOD. ws me ag 16.77 “ 1.55 * 15.4
Total. . . ‘ 45.42 cc. 4,35 cc.

The total losses bear a ratio of 10.44 : 1.

2 Handbuch der Experimental-physiologie, 1865, p. 227. Dehérain in
Comptes Rendus, lxix. p. 381.

3 Sitzungsber. d. Wiener Akad., Bd. xxvi., 1857, p. 326.

* Report of the Geological Exploration of the Fortieth Parallel, Botany
(1871), p. 1.

5 Versuchs-Stationen, 1859, p. 232.

EFFECT OF HEAT UPON TRANSPIRATION. 217

alkalies. But as Sachs? showed in 1859, even a very little free
acid in water hastens, while an alkali retards, transpiration.

Burgerstein? in a long series of experiments showed that
while a single salt added to water in less amount than .5 per
cent hastens transpiration, any per cent above this produces a
marked retardation. When a solution of nutrient salts is used,
even if its concentration is as low as .05 of’ solid inatter, there
is a retardation, and this is greater when the solution is more
concentrated.

In the experiments, the results of which are given below,
four plants of Indian corn were employed. The temperature
varied between 16.7°, and 18° C., and the observations con-
tinued through one hundred and three hours. The amounts
transpired are given in percentages of the weight of the fresh
plants.

Nutrient solution. . 2. 2. 2. 2 1 we ee 24704
Distilled water 2. 1 1. ww oe (26407
Potassi¢ nitrate . jg Bok ee Bos . 283.2
Ammonie nitrate oe, Se a feo a . . 884.2

742. Temperature and transpiration. Rise of temperature in-
creases the rate of transpiration not only by affecting evaporation
in general, but indirectly also by augmenting the absorption of
water and heightening the turgescence of the cells. Burger-
stein shows that leafy twigs of yew can transpire even at a
temperature of —10.7° C., while the leafless shoots of horse-
chestnut are said by Wiesner to transpire at —13°C.%

Sudden changes of temperature greatly influence transpiration,
since the ‘atmosphere and the plant cannot follow the course
of temperature with equal rapidity, and a rarefication of the
air saturated with moisture within the plant must favor its
release.” *

743. Effect of light upon transpiration. Transpiration goes on
more rapidly in light than in darkness, even when the tempera-
ture in darkness is somewhat higher. But differences in the
intensity of diffused light do not produce very marked differences
in the amount of transpiration. When, however, diffused light

1 Versuchs-Stationen, i., 1859, p. 223.

Sachs met with some anomalies in his experiments, in one case finding a
noticeable retardation of transpiration upon the addition of an acid.

2 Sitzungsb. d. Wiener Akad., 1876 and 1878.

5 Quoted by Pfeffer: PAanzenphysiologie, i., 1881, p. 148.

* Pfeffer: Pfanzenphysiologie, i., 1881, p. 148.

278 TRANSFER OF WATER THROUGH THE PLANT,

is replaced by direct sunlight, the increase in transpiration is
striking.?

744. Effects of different rays upon transpiration. Wiesner’s
conclusions,” based on a study of transpiration in different rays
of the spectrum, are as follows: (1) the presence of chlorophyll
appreciably increases the action of light upon transpiration ;
(2) it is the rays corresponding to the absorption-bands of
chlorophyll, and not the most luminous rays, which cause trans-
piration; (8) rays which have passed through a solution of
chlorophyll have only a feeble effect upon the process; (4) the
non-luminous heat-rays act as do the luminous rays, but in a
less marked manner, the ultra-violet chemical rays have sub-
stantially no effect; (5) whatever the rays are, they always act
by elevating the temperature of the tissues.

745. Effect of shock upon transpiration. According to Bara-
netzky,* shaking a plant for a short time increases transpiration

1 As shown by the following experiments by Wiesner : —

giana iffused day- :
Name of piznt. Ty darkness. | ™ ante ay In sunlight.
Zea Mais, etiolated . 106 me 112 mg. 290 mg.
Zea Mais, green. 97“ 114 “ 785 “
Spartinm jinceum (flowers) 64 “ 69 “¢ 174 “
Malva arborea (flowers) . 23 6 28 “* 70 “

The amounts of water are caleulated-for a surface of 100 square centimeters,
But it is not perfectly clear to what the special action of

and for one hour.
light can be due.

account for all cases,

the transpirati
2 Annale

note wien the same subject by Dehérain.
"3 See also Herbert Spencer's Experiments, on page 263.
4 Botanische Zeitung, 1872, p. 89.
The following example will show the results of Baranetzky’s experiment
upon a leafy stem of Inula Helenium. ,

The lgawtl size of the cleft of stomata under light cannot
ses Tor according to Wiesner young maize plants, in which
“is large, have their stomata closed.

des Sc, nat., sér 6, tome iv., 1877, in which may be found alse a

Time (morning) | State of plant. Tan ees iets e°, gp as
7.40 quiet. _ _ =
8.10 fe .50 22.1 76 per cent.
8.40 shaken. .52 22.2° 7m
9.10 quiet. 68 22.4 76 ie
9.40 es AT 22.5 76

10.10 bs 5B 22.7 7 a
10.40 ee 54 22.9 76 a
11.10 shaken. 59 231 m6 *
11.40 quiet. 45 23.3 om *
12.10 ee 52 23.4 16 ss

RELATION OF TRANSPIRATION TO ABSORPTION. 279

appreciably ; if the plant is then kept at rest, the rate falls be-
low that previous to the shaking, after which it gradually rises
to its normal point. Even a sharp single shock is enough to
produce some effect upon transpiration, but the shaking must
continue at least a second in order to change the rate very much.

df, however, the shaking is long continued, or short shakings
are often repeated, there is a noticeable diminution in the rate.
Baranetzky attributes the heightening of the rate by a sudden
shock to the correspondingly sudden compression of the inter-
cellular spaces and the consequent renewal of the air therein
contained; while the diminished rate which follows continued
shaking is due to a partial closing of the stomata (see also
731). :

746. Relation of age of leaves to transpiration. According to
Dehérain* and Hobnel,? young leaves exhale more water than
older leaves. Experiments were made by the former upon the
upper, middle, and lower leaves of rye. From the newly devel-
oped leaves more water was exhaled than from the middle, and
more from the latter than from those farther down the stem.
Sachs? states that young leaves exhale less than those which
are fully developed, but that there is some diminution in the
case of old leaves.

747. Under external conditions which are as nearly uniform as
can be secured there are variations in the rate of transpiration
not yet understood ; these are generally referred to variations in
the tension of tissues (see 1025).

748. Relation of transpiration to absorption. It is plain that
transpiration from leaves is the chief cause of absorption by
the roots; but it has been shown by Vesque?* that these two
functions are not necessarily proportional. According to him
it is only when a plant is subjected to uniform conditions of
diffused light, and a moderate amount of moisture in the air,
that they are about equal. In a very dry air, transpiration in
the case of most plants far exceeds absorption until wilting
comes on. When, on the other hand, a plant is withdrawn from
a moderately moist air and placed in an atmosphere saturated
with moisture, absorption goes on for a time more rapidly than
transpiration, but both become soon arrested.

The dependence of the rate of absorption upon temperature

1 Cours de Chimie Agricole, 1873, p. 178.

2 Forschungen auf d. Geb, d. Agrikulturphysik, 1878.

3 Handbuch der Experimental-physiologie, 1865, p. 226.
4 Annales des Sc. nat., sér. 6, tome vi., 1878, p. 222.

280 TRANSFER OF WATER THROUGH THE PLANT.

has been shown by many investigators, notably by Sachs,’ who
found that well-rooted and full-leaved plants of gourd and
tobacco wilted when the temperature of the air and soil ranged
from 3.7° to 5° C., although the ground was plentifully supplied
with water. When the temperature of the soil became higher,
the leaves became again turgescent.

Another cause which may disturb the relation between absorp-
tion and transpiration is found in the diminished conductivity of
woody tissue at low temperatures.?

749. Cheeks upon transpiration. Among the more obvious adap-
tations of plants to dry climates are: (1) reduction of foliage to
a minimum, as in the case of condensed stems (see Vol. I. p. 64) ;
(2) a coriaceous or even denser texture of leaves or of branches
resembling leaves, such as phyllocladia (Vol. I. p. 65); (8) ver-
tically placed leaves or their analogues, phyllodia, in many if
not most of which the structure of the parenchyma and of the
epidermis with its stomata is the same on’ both sides; hence
the sides have substantially the same exposure to air, and, in
the compass leaves, to light as well (see 448). Another adap-
tation has been pointed out by Pfitzer® and by Westermaier ;*
namely, the possession of an epidermal or subepidermal “ water
tissue,” or ‘+ water-storing tissue ” (see 209).

Leaves provided with water-storing tissue show the effect of
drought first in the partial collapse of these cells, their radial
walls becoming somewhat undulate, while the assimilating cells
remain full and unchanged in form. These water-storing cells
lose comparatively little water by transpiration ; the water which
they contain is given up as required to the assimilating paren-
chyma. When a fresh supply of water is afforded to the
collapsed water-storing tissue, the recovery of turgescence is
immediate. Examples are found in the following among many
other plants: Peperomia, Tradescantia discolor, Ficus elastica.

In numerous succulents the vacuoles of the assimilating cells
frequently contain a thin mucus, from which water evaporates
only slowly, and this is believed to play an important part in
the storage of water.®

1 Botanische Zeitung, 1860, p. 124.

2 Beitriige zur Theorie des Wurzeldruckes, 1877, p. 88, quoted by Pfeffer,
Pflanzenphysiologie.

8 Ueber die mehrschichtige Epidermis, Pringsheim’s Jahrb., viii., 1872, p. 16.

4 Ueber Bau und Function des pflanzlichen Hautgewebesystems, ibid., xiv.

5 Plants which are peculiarly adapted to dry climates are termed by
De Candolle Xerophiious. Among them are found many Composit, notable

EFFECTS OF TRANSPIRATION, 281

730. The chief effects of transpiration upon the plant are:
(1) the transfer of dilute solutions of mineral matters to the
cells where assimilation, or the production of organic matter,
takes place; (2) the concentration of these dilute solutions by
evaporation. The extent to which such concentration must
take place can be easily inferred from the large amounts of
water which are exhaled from some common plants under ordi-
nary conditions of culture. According to Haberlandt,’ the total
amount of water exhaled from a plant of Indian corn during
173 days of growth was 14 kilograms; of hemp during 140 days,
27 kilograms; and of sunflower during the same period, 66 kilo-
grams. Hdéhnel? estimates the amount of aqueous vapor given
off between June 1st and December Ist, by a hectar of beech
forest (the trees averaging rather more than one hundred years
in age), to be between 2,400,000 and 3,500,000 kilograms.
That the leaves in autumn contain more ash constituents than
in spring, appears from numerous analyses, of which a few
are here given from Storer’s compilation.

Name of Plant. | Time. en pes icone Analyst.
Oak. . . . . | May | Fresh. 1.30 | Saussure.
fo ee se | Sept. |e 2.40 “
Mulbeny . . | April ee 2.15 | Pupils of Fresenius.
oe ‘ F Aug. ce 4.90 “ce “ce
Beech . . . . | May | Dried at 100°C. | 4.67 | Rissmiiller.
fe a a oe [SNov. ee es 11.42 fe

751. Influence of transpiration upon the air. Ebermeyer? has
shown that in the course of the year the absolute humidity in the

proportions of Labiate, Liliacee, Palmacese, Myrtacex, and Euphorbiacez ; but
the most characteristic orders are Zygophyllacee, Cactacee, Mesembryanthe-
mace, Cycadacee, and Proteacce (Constitution dans le régne végétal de
groupes physiologiques, Arch. Bibliotheque universelle, ]., 1874).

1 Wissensch.-prakt. Untersuchungen, 1877, Bd. ii., p. 158.

2 Ueber die Transpirationsgrosse d. forst]. Holzgewichse, 1879, p. 42. Both
this and the preceding citation are from Pfeffer’s Pflanzenphysiologie, i. p. 153.

“Some of Haberlandt’s figures for crops are obviously too high, probably
from overlooking the diminution in the rate of transpiration which attends
crowding plants together. Thus he makes the total amount of water exhaled
froin an hectar of oats during the period of vegetation to be 2,277,760 kg. ; of
barley, 1,236,710 kg.”

8 Die physikalischen Einwirkungen des Waldes auf Luft und Boden, 1873,
p- 148.

282 TRANSFER OF WATER THROUGH THE PLANT,

air of a forest is scarcely greater than that in air over open
ground. But the relative humidity in the former case is about
six per cent greater than that in the latter.

782. It has been held by many that forests have a direct effect
in increasing the amount of rain-fall, presumably by bringing,
through transpiration, the amount of moisture in the atmosphere
of a wooded place nearer the point of precipitation. But the
weight of evidence now available is against this view.?

753. On account of the shelter which they afford, the trees of
a forest play an important part in the storage of a water-supply.
Under their branches small plants can thrive, and by their hold
upon the ground impart to even very porous soil a good degree
of stability.

Soil covered with mosses and other humble plants which live
in the shade not only holds back a large part of any given rain,
so that the water drains off more slowly, but it is not likely to
be itself washed down to lower levels. Upon a treeless slope,
however, the rains which fall sweep down at once.

754. There is, furthermore, less evaporation from a_ soil
covered by a growth of trees than from open ground. Obser-
vations during the summer months recorded by Ebermeyer?
show that the evaporation of water from the soil of a forest,
when the surface is not covered by grass, is only sixty-two per
cent of that which takes place from open ground. But if the soil
under the shade of a forest is covered with grass, the evaporation
is eighty-five per cent of that in the open ground.

Von Mathieu found that the evaporation from open ground
from April to October was about five times as much as from
wooded soil; but he does not state whether the soil in the latter
case had grass upon it or not.

1 “* Forests increase the annual relative moisture of the air, but this in-
fiuence is much more noticeable at high elevations than at low elevations.
The precipitation of moisture (dew, cloud, rain, snow) takes place more readily
on this account in wooded than in treeless regions, and the frequency and
intensity of these precipitations increase with elevation above the surface of
the sea. Moisture descends more readily and frequently upon a wooded than
upon a treeless mountain of the same height. Forests affect rain-fall only so
far as they increase the relative amount of water held in the air, and thus
bring the relative amount nearer the point of saturation ; thus with the fall of
temperature in the forest, a part of the moisture is easily precipitated. .. .
Forests make the climate of a country moister, and especially so in summer”
(Ebermeyer: Die physikalischen Einwirkungen des Waldes auf Luft und
Boden, 1873, p. 151).

2 Die physikalischen Einwirkungen des Waldes, p. 175.

EFFECTS OF TRANSPIRATION. 283

755. Effect of transpiration upon the soil. The amount of
water taken from the soil by the trees of a forest and passed into
the air by transpiration is not as large as that accumulated in the
soil by the diminished evaporation under the branches. Hence
there is an accumulation of water in the shade of forests which
is released slowly hy drainage. But if the trees are so scattered
as not materially to reduce evaporation from the ground, the
effect of transpiration in diminishing the moisture of the soil is
readily shown. It is noted especially in case of large plants
having a great extent of exhaling surface, such, for instance,
as the common sunflower. Among the plants which have been
successfully employed in the drainage of marshy soil by transpi-
ration probably the species of Eucalyptus? (notably E. globulus)
are most efficient.

756. Do leaves absorb aqueous vapor? It is everywhere known
that leaves which wilt during the daytime from slight dryness
of the soil may recover their turgescence during the night, for
then transpiration is reduced to a minimum, and the demand for
water is very slight, so that there is a speedy readjustment of
the equilibrium which was disturbed during the day. It is still
a disputed point whether wilted leaves can absorb any appre-
ciable amount of water from the dew which falls upon them.
Experiments by Duchartre? indicate that the amount must be
very small, if indeed any at all. That leafy branches detached
from the plant can absorb water through the leaves is well
known, and has been already alluded to.

1 See a very interesting account by Mueller in Eucalyptographia, 1881.
Also an article by H. N. Draper in Chambers’s Journal, lviii. 193, reprinted
in Littell’s Living Age, cxlix. 376.

2 Ann, des Se. nat., sér. 4, tome xv., 1861, p. 109.

CHAPTER X.

ASSIMILATION IN ITS WIDEST SENSE, APPROPRIATION OF
CARBON, NITROGEN, SULPHUR, AND ORGANIC MATTERS.

757. Tue term assimilation, as generally understood in Vege-
table Physiology, means the conversion by the plant, through
the agency of chlorophyll, of certain inorganic matters into
organic substance.

Some authors, however, give to the word assimilation a wider
signification, namely, the conversion into utilizable substance
of all matters whatsoever brought into the organism. Such?
regard chlorophyll assimilation as only a special case under a
general class which comprises the appropriation of (1) carbon,
(2) nitrogen, (8) sulphur, so far as this is a constituent of
protoplasm, (4) certain organic matters.

758. It will presently be seen that with the appropriation of
carbon by the plant, there is always associated the appropriation
of the elements of water, namely, hydrogen and oxygen ; but the
mere entrance, transfer, and exit of water, which is known to.
undergo no chemical change jn the organism, have already been
examined in Chapters VII. and IX., and do not strictly belong to
the process of assimilation. There are sundry mineral matters
which, though absolutely essential to the well-being of the plant,
are conveniently examined without special reference to assimi-
lation, even in its widest sense. Some of them, like the salts of
potassium, are indispensable to the process of assimilation ; but
they do not become at any period an indispensable part of the
substance of the plant. In the case of sulphur, however, a small
amount of the element is appropriated by the plant and consti-
tutes a component part of its protoplasmic matter. The matters
which by their temporary presence in the plant contribute to
its activities, have been likened to the absolutely necessary lu-
bricants without which machinery cannot run easily or perhaps
at all.

1 See Pfeffer’s Planzenphysiologie, i. 186.

ASSIMILATING SYSTEM OF THE PLANT. 285

APPROPRIATION OF CARBON, OR ASSIMILATION
PROPER.

759. The appropriation of carbon, and its combination with
the elements of water, is by far the most striking of the kinds of
assimilation ; and since it underlies to a certain extent the forma-
tion of the matter with which nitrogen and sulphur are incorpo-
rated to constitute the living substance, it may well lay claim to
be considered assimilation proper. It was employed in this sense
by Asa Gray in 1850, in. the second edition of the Text-book.

For brevity, therefore, the term assimilation in the present
section will be made to refer to the appropriation of carbon.

760. With some exceptions, to be mentioned later, the follow-
ing statement holds good for all plants: assimilation is essen-
tially a process of reduction in which the inorganic matters are
(1) water taken trom the soil, and (2) carbonic acid} taken from
the air; and the organic substance produced from these is some
carbohydrate which contains less oxygen than the two together.
Hence in assimilation there is, with the evolution of oxygen,
a partial reduction of the inorganic matters employed in the
process.

761. Assimilation takes place only under the following condi-
tions: (1) The assimilating organ must contain living chlorophyll
or its equivalent ; (2) water and carbonic acid must be furnished
in proper amount ; (3) rays of light of a certain character must act
upon the organ; (4) it must be kept at a certain temperature,
there being a minimum degree of heat below which, and a maxi-
mum degree above which, no assimilation can occur ; (5) a minute
amount of certain inorganic matters other than those named,
notably some compound of potassium, must be within reach.

762. The assimilating system of the plant. All cells which con-
tain chlorophyll or its equivalent, and which admit of exposure
to the sun’s rays, constitute the assimilating system of the plant ;
but it must not be understood that they perform only assimilative
work. In the simplest vegetable organisms (unicellular or fila-
mentous algz) and even in some water plants of the higher
grade (Anacharis) these cells are at one and the same time
members of an absorbing, a storing, and an assimilative sys-
tem. In land plants, and in some water plants, however, certain
cells have the office of assimilation as their special and dominant

1 In general throughout this work, the term carbonic acid will be employed,
instead of carbon dioxide, to denote COg.

286 ASSIMILATION,

function. These cells are found chiefly in expansions upon or of
the axis; of course, most commonly in ordinary leaves. But in
many cases the primary axis itself and the secondary and other
axes (branches) may have a considerable share of the proper
assimilating tissue of the plant. In some instances, for exam-
ple, in solid-stemmed and fleshy plants (as Cactacea), the whole
assimilative apparatus is to be found on the surface of axial
instead of foliar organs; and the same is true of certain ligneous
plants specially adapted to desert conditions (e. g., Colletia).

763. The development of the assimilative system in land
plants appears to have been controlled by two opposed factors ;
namely, (1) the advantage to be derived from exposure to air and
light, and (2) the disadvantage consequent upon too great loss
of moisture by evaporation. Even the most superficial examina-
tion of the tropical plants cultivated in our hot-houses reveals
the striking manner in which a balance has been struck between
these conflicting influences: the plants of warm jungles (e. g.,
Scitamineee) having broad and long leaves suited to a humid
atmosphere, while the plants of parched sands (Cactacee and
the like) are characterized by some protection against excessive
evaporation. In both these extreme cases the provision for a
certain amount of evaporation is, on the whole, seen to be
tributary to the essential work of all green tissue, namely,
assimilation.

764. Proper exposure of the assimilating apparatus of a plant
to light is secured (1) by the shape and position of the assimilat-
ing organ, whether it be axis or leaf, and (2) by the arrangement
in the organs of the cells themselves. Concerning the first, see
Volume I.; in regard to the second, see this volume, page 159.

765. Chlorophyll! (yAwpds, green, and piAdor, leqf). The term
chlorophyll, originally applied to the pigment rather than to the
substance which contains it, is now used indifferently to denote
the coloring-matter and the portions of protoplasmic mass which
are tinged by it. It is better, however, to designate the former
chlorophyll pigment, the latter, chlorophyll granules, or grains.

766. In regard to the genesis of the chlorophyll granules
which are the essential constituent of the assimilative cells, the

1 “Nous n’avons aucun droit pour nommer une substance connue depuis
longtemps, et & l'histoire de laquelle nous n’avons ajouté que quelques faits ;
cependant nous proposerons, sans y mettre aucune importance, le nom de
chlorophyle, de chloros, couleur, et Pvddov, feuille; ce nom indiquerait le role
quelle joue dans la nature” (Pelletier and Caventou: Journ. de Pharmacie,
iii, 1817, 490).

ORIGIN OF CHLOROPHYLL GRANULES. 287

following view? appears to be most in consonance with recent
investigations. Imbedded in the protoplasm at every growing
point there are peculiar bodies (plastids) which have substan-
tially the same characters and structure as the protoplasm, and
are more or less clearly differentiated from it even at an early
period. As the cells which develop from the growing point
assume the different characters which fit them for special ser-
vice, for example, those in certain tubers and roots for store-
houses, those in leaves for assimilation, and those in some
flowers and fruits for color, their plastids may likewise assume
special characters. Those which are destined for the store-
houses become leucoplastids, or starch-formers ; those in green
tissue, chloroplastids or chlorophyll granules; and those in col-
ored flowers and fruits, chromoplastids. As might be expected
from their common origin, the plastids which under one set of
conditions might become leucoplastids, may, under another set,
become chloroplastids, etc.

767. The recognition of this view regarding the origin of
chlorophyll grains, ete., although it is as yet partly hypotheti-
eal, will enable the student to explain some of the extraordli-
nary intermediate forms met with; for instance, those where the

1 Meyer (Das Chlorophyllkorn, 1883, and Botanisches Centralblatt, 1882) has
reached substantially the same results as those obtained by Schimper, which in
the account above given have been presented with Schimper’s nomenclature.
Meyer employs, however, the somewhat different terminology given below.

Older Nomenclature. Schimper. Meyer. Van Tieghem.
General Plastid. Trophoplast. | Leucite.
term. | cotoriess protoplasmic
Special granule. Leucoplastid. Anaplast. Leucite proper.
terms, | Chlorophyll granule, | Chloroplastid. | Autoplast. Chloroleucite.

Color-granule. Chromoplastid. | Chromoplast. | Chromoleucite

For a fuller account of the views of Meyer and Schimper, the student must
consult the original memoirs in Botanische Zeitung, 1883, or an excellent
abstract by Bower (Quarterly Journal of Microscopical Science, 1884).

Schmitz (Die Chromatophoren der Algen, 1882) has described at great
length certain structures analogous to chlorophyll, occurring in some of the
lower plants. These granular bodies, called chromatophores, possess consider-
able diversity of form, but all agree in consisting of a matrix or basis permeated
by coloring-matter. In most green alge there are also found one or more
minute, rounded, granular, colorless bodies embedded in the chromatophore,
known as pyrenoids. These are frequently associated with granules of starch.
Chromatophores are believed by Schmitz to increase only by the process of
division, but the pyrenoids either by division or by fresh formation,

288 ASSIMILATION,

plastids of one sort can for a time undertake the office of the
plastids of another sort. It explains, partially at least, the in-
trusion of chlorophyll grains into parts of the plant where they
do not seem to properly belong, and accounts for some of the
apparent changes which they may subsequently undergo.

768. According to the early investigations of the subject, the
chlorophyll granules were regarded as differentiations, at an
early stage in the embryo and seedling, from a mass of homo-
geneous protoplasm: according to the present view they are
derivatives by division from pre-existing plastids.1| When devel-
oped in darkness, they are pale yellowish, or even devoid of color.
Plants grown in the dark (compare 788) become green upon
exposure to the light, provided they are not at the same time
kept too cold. The minimum temperature at which they turn
green is different for different plants, but may be said to be
in general not far from 6° to 10° C.

Certain Gymnosperms, notably seedlings of Abies and Pinus,
develop a bright green color in the deepest darkness, provided,
as before stated, the temperature is not below a certain point.

769. Occurrence of the chlorophyll granules. The granules are
found only very sparingly in epidermis, being chiefly confined to
the guardian cells of stomata. They oceur principally in paren-
chyma cells, immediately below the epidermis, and seldom out
of reach of the light. But they occur also in a few deep-seated
structures, for instance, in the thick cortex of some ligneous
plants, and in the tissues of not a few embryos.

770. That chlorophyll granules are found in the interior of
some of the lower animals appears reasonably certain, but the
green matter does not always present the same characters. Ac-
cording to recent authorities, it assumes in most cases, for in-
stance in Spongilla and Hydra, the form of minute granules. The
pigment agrees in some of its essential properties with that of
ordinary chlorophyll.? In some cases it must still be considered
an open question whether the granules may not be (or at least
represent) independent organisms dwelling in certain cavities of

1 The views of Gris (Ann. des Sc. nat. bot., 1857) may be summarized as
follows: The granules arise by differentiation of the protoplasm in certain
young cells into two portions; one of these assumes the form of roundish
or lenticular bodies (the proper granules), which under the influence of light
become colored green, while the other remains as a matrix in which they are
embedded.

2 For an interesting treatment of this subject, consult Geddes: Nature, 1882,
and Lankester, Journal of the Royal Microscopical Society, 1882, p. 241.

STRUCTURE OF CHLOROPHYLL GRANULES. 289

these lower animals. These cases of possible symbiosis deserve
and are receiving careful investigation.

771. Many species of plants derive all or a part of the organic
matter required for their growth and proper activities either from
other plants (when they are called parasites), or from decaying
organic matters, such as vegetable mould (when they are called
saprophytes). In the tissues of a few such plants minute traces
of chlorophyll may sometimes be detected.

772. Structure of chlorophyll granules. Under a moderately
high power of the microscope the granules appear as spheroidal }
or polyhedral bodies, apparently homogeneous in structure, hav-
ing neither vacuoles nor granular matter. By the action of cer-
tain solvents it is possible to remove from the granule the pigment
which has imparted
to it its characteristic
color, when the mass_ |
reinains without any
change of form.
Hence it is proper to
distinguish between
‘the chlorophyll pig-
ment and the chloro-
phyll granule, cach
of which will now
be considered. <A

ethod recently dis-
covered makes it pos-
sible to demonstrate
the peculiar structure
of the granules with-
out complete removal
of the pigment. This
method, known as
Pringsheim’s,? depends upon the action of dilute hydrochloric
acid on the green parts of plants. When a thin green tissue,

A

1 In some of the Thallophytes, the whole or nearly the whole of the proto-
plasmic mass seems to he evenly colored, presenting the appearance of colored
spirals, lamelle, stellate forms, ete.; and such colored masses are strictly chloro-
phyll bodies (Die Chromatophoren der Algen. Fr. Schmitz. Bonn, 1882).

2 Pringsheiin’s Jalirb., xii., 1879, p. 289. .

Tie. 149. Hypochlorin. A, a cell of Hdogonium treated with hydrochloric acid for
afew honrs; 3, the sane after some days: C, ), EF, needle-like forms; #, two cells of
Drapernalia kept in hydrochloric acid one month; G, cell of Anacharis in hydrochloric
acid after five months’ treatment. (Pringsheim.) s

19

290 ASSIMILATION.

for instance a leaf of Vallisneria or of Anacharis, is treated
with a solution of one part of concentrated hydrochloric acid
in four parts of water, the first change observed is merely a
fading of the green color of the granules to a yellowish or
brown. After a few hours, however, upon the periphery of each
granule there appears a small rounded mass of a deep brown
color, generally keeping much the shape of the granule from
which it has been extruded. Often more than one of these
masses can be detected, and they sometimes assume needle-like
or staff-like shapes. But, whatever their form may be, they
carry out of the granule all of the coloring-matter, and leave it
as a honey-combed mass of its original shape. Similar extrusion
of a colored mass can be effected by the action of the vapor of
boiling water, or even by immersion in boiling water; but here
the change is produced in a single hour, or even less (in some
cases, in five minutes). When much starch is present in the
chlorophyll granules there is generally considerable change of
outline of the whole mass, and more or less breaking down of
their internal structure. The nature of the vehicle which, under
the action of hydrochloric acid or moist heat, carries out of the
granule all of the coloring-matter, will be referred to later, under
the name given it by Pringsheim, namely, Hypochlorin.

773. The mass of the granule is left by this removal of its
coloring-matter, as a spongy body of about the original shape
of the granule. This spongy stroma, or ‘‘ trabecular mass,” is
plainly different from the granuie which is decolorized by the
action of solvents, for example, alcohol, ether, etc.; for in the
latter case the mass appears to be with an unbroken contour,
and has a solid structure.

774. The chlorophyll pigment can be extracted, although with
various associated waxy and fatty matters, by alcohol and other
solvents. To prepare a solution of the pigment for a study of
its most striking properties, fresh leaves should be bruised, acted
on for a few hours in the dark by warm, strong alcohol, and
then, without exposure to bright light, the liquid should be
carefully decanted. It is not difficult to separate the dark
green solution into two distinct colors by means of the following
methods : —

(1) Fremy’s process. One volume of the alcoholic solution
is shaken with a mixture of two volumes of ether and one of
concentrated hydrochloric acid; after standing for a tiie, its
upper, or ether layer, is yellow (phylloxanthin or xanthophyll),
while its lower, or acid layer, is blue or greenish blue (phylo-

THE CHLOROPHYLL PIGMENT. 291

eyanin). If considerable alcohol is now added, and the mixture
shaken, the liquid again becomes thoroughly mixed and of a
clear green color. Fremy’s later researches have led him to re-
gard the so-called phylocyanin as really an acid (phylocyanic),
which is probably combined with potassium, and the salt thus
formed mixed with phylloxanthin to form the green coloring-
matter of chlorophyll.

(2) Kraus’s process. This method of separating the two
coloring-matters is based on the action of benzol. The alcoholic
solution prepared as directed on page 290, or, much better, with
alcohol of 65 %, is shaken with about twice its volume of benzol,
or, according to R. Sachsse, with benzin (sp. gr. .714). After
a while the turbid liquid separates into a benzol layer above,
having a bluish-green color, and an alcohol layer below, tinged
yellow. The yellowish pigment is called by Kraus, xanthophyll,
the bluish-green, kyanophyll. According to Wiesner, kyanophyll
is nearly pure chlorophyll freed from its associated yellow pig-
ment xanthophyll. It is believed by many that the yellow pig-
ment separated by this process is identical with that found in
plants blanched (etiolated) in darkness, and which has been
called etiolin.

Different methods (some of which are noticed briefly in the
foot-notes!) have been employed for the isolation of the pure

1 (1) Berzelius evaporates the alcoholic extract to dryness, andafter treatment
with hydrochloric acid (sp. gr. 1.14), again dissolves it in alcohol. He then
precipitates with water, redissolves the precipitate after filtration, and lastly,
by acetic acid, precipitates the nearly pure pigment (Annalen der Chemie und
Pharmacie, xxi., 1837, p. 257 ; xxvii., 1838, p. 296.) (2) Fremy throws down
from its alcoholic solution, by use of either aluminic or magnesie hydrate, all
coloring-matter ; and after thoroughly washing the precipitate dissolves it in
alcohol (Comptes Rendus, ]., 1860, p. 405; lxi., 1865, p. 188). (3) Hoppe-Seyler
first extracts all waxy matters from green leaves by repeatedly washing them
with cold ether, and then treats the leaves with boiling absolute alcohol. After
the alcoholic solution has been cooled, again heated, and allowed to stand, red-
dish crystals (erythrophyll) separate from it. These are red in transmitted, but
green or whitish in reflected light. After their separation the residue of the
solution is evaporated to dryness and again dissolved in ether; from the ether

‘solution, upon slow evaporation, granules are thrown down, which are brown
in transmitted and green in reflected light. These granules may be obtained,
by repeated solution and by spontaneous evaporation of the solution, in the
form of crystals of a high degree of purity, which are called by Hoppe-Seyler
chlorophyllan (Zeitschr. phys. Chem., iii. 1879, p. 339). (4) In Gautier’s pro-
cess, bruised leaves are mixed with sodic hydrate and pressed. After this the
residue of the leaves is treated with alcohol at 55° C., again pressed, and then
treated with cold 83 per cent alcohol, all waxy matters being left by the pro-
cess undissolved. ‘he alcoholic solution is mixed with animal charcoal and

299 ASSIMILATION.

coloring-matters of leaves: crystalline substances have been ob-
tained, one of which, marked by its blue or bluish-green color,
contains about five per cent of nitrogen.?

775. Spectrum of chlorophyll. When a ray of white light
which has passed through a coloring-matter, for instance, a solu-
tion of one of the coal-tar dyes, red wine, or a solution of chlo-
rophyll, is examined by means of a spectroscope, certain dark
bands, known as the absorption-bands, are observed at definite
places in its spectrum.

776. For convenience in examining the spectra of small
amounts of coloring-matters, a direct-vision spectroscope attached
to the tube of a microscope is employed, and the coloring-matter
in question is placed in a flat-walled bottle or a glass cell on the
stage of the microscope. The ray of light which is reflected
from the mirror under the stage passes first through the colored
matter, next through the objective, and lastly through the prisms
which compose the microspectroscopic attachment to the tube.

777. In order to compare the spectra of different substances,
a second prism or set of prisms is often used, by which the spec-
trum of a second liquid can be projected by the side of that of

allowed to stand for five days ; all the chlorophyll pigment is thus removed by
the charcoal. Alcohol of 65 per cent strength extracts from the coal a yellow
crystallizable substance, while ether or benzine dissolves out matter which,
upon evaporation of the solution, yields pure chlorophyll pigment (Comptes
Rendus, Ixxxix., 1879, p. 861). By the action of sodium on a benzine solution
of the coloring-matter of Primula or of Allium, R. Sachsse has obtained two
colored masses. One of these is green, solid at ordinary temperatures, in-
soluble in pure water, soluble in a dilute alkali, and also in alcohol and ether;
the other, yellow, brittle, crumbling into an orange mass, soluble in the same
liquids as the first. Besides these two coloring substances he found also a
glucoside (that is, a body which under certain conditions can be split into
some one of the sugars and another substance which is capable of ‘further
changes). Both of the colored masses can he readily broken up into several
different coloring-matters. The matters obtained by this process from the
green mass differ from those obtained from the yellow, in containing about
three to five per cent of nitrogen, while those from the yellow contain none
at all.

1 The green crystals obtained by the evaporation of a purified solution of
chlorophyll in alcohol are called chlorophyllan by Hoppe-Seyler, and chloro-
phyll by Gautier. Their analysis reveals the following composition: —

Hoppe-Seyler, Gautier.
C. TOBER ga me 4 ge ye BROT
H. O26 4 ane 9.80
oO. 9.525 “i 10.33
N. 5.685 5 4.15

Ash i mo ie ASS : soe e175

SPECTRUM OF CHLOROPHYLL. 293

the first. The spectra of chlorophyll solutions from two different
sources can thus be at once compared. One of the combinations
can also be employed to project the solar spectrum (unchanged
by passing through any color whatever), and its constant lines
(Fraunhofer’s lines) can be used for the determination of posi-
tion of the bands seen in the spectrum of the liquid by its side.

778. The spectra of many substances, among which chloro-
phyll occupies a prominent place, have absorption-bands of such
constancy in position and appearance that they are justly regarded
as characteristic.

779. The spectrum of an alcoholic solution of chlorophyll has
been shown to be essentially the saine as that of the chlorophyll
granule itself. In order, however, to obtain all the absorption-
bands characteristic of chlorophyll, it is necessary to examine
successively solutions of different degrees of strength, some of
the bands appearing only in dilute and others only in strong
solutions. For comparison, absorption spectra obtained from
different sources are here given.

Fig. 150. Spectra of chlorophyll. The upper figure shows the spectrum of an alco-
holie solution of medium concentration, while the middle figure gives all the absorption-
bands of chlorophyll; those on the right as shown only in dilute solutions. The lowest
figure exhibits the spectrum of a living leaf of Deutzia scabra. (Kraus.)

994 ASSIMILATION.

780. The fluorescence of chlorophyll pigment is best shown by
allowing rays of light, made convergent by passing through a
double convex lens, to fall upon the surface or side of a strong
alcoholic solution of chlorophyll. The color at the focus of the
lens will then appear blood-red, but by transmitted light the same
solution will appear dark green. By fluorescence is meant the
property possessed by certain substances of diminishing the re-
frangibility of some rays of light; in the case of chlorophyll all
the rays towards the violet end of the spectrum are made to
conform in refrangibility to those near the red. A bright solar
spectrum + cast upon the side of a flat vessel containing a solu-
tion of chlorophyll appears much like a stripe of dull red: in
this red stripe are bands corresponding in their position to the
absorption-bands of chlorophyll. If the blood-red color produced
by a strong light falling on the surface of a concentrated solu-
tion of chlorophyll is examined through a spectroscope, only
red rays having the same degree of refrangibility as those of
the deep absorption-band of the chlorophyll spectrum come to
the eye.

781. Plants without chlorophyll. If whole plants (certain
parasites and saprophytes, for example, Monotropa) are either
white or slightly tawny throughout, it is owing to a complete or
partial absence of chlorophyll; but in some instances such plants
may impart to alcohol, in which they are immersed, a decided
tinge, frequently blue.

782. ‘*Colored” plants. When leaves or stems have some
color other than green, they are said to be colored; if two or
more different colors are intermingled the parts are variegated.

783. In the case of healthy leaves exposed to light, white
spots, streaks, etc., are generally, if not always, characterized
by an absence of chlorophyll. Such spots have relations to their
surroundings which are different from those of the contiguous
green parts; they do not have the power of assimilating in-
organic matters. , ;

784. In plants, the paleness of colors verging upon green or
blue (for example, those in many kinds of cabbage) sometimes
depends wholly on the existence upon the surface of the part, of a
great amount of the waxy matters known collectively as bloom
(see 226). The tissues beneath the surface may be vivid green.

785. Red and yellow colors of healthy and vigorous leaves are
usually due to the presence in the cells (often merely those of

1 Hagenbach: Annalen der Physik und Chemie, cxli., 1870, p. 245.

ETIOLATION, 295

the epidermis) of colored cell-sap. This is sometimes in such
large amount as to mask completely the green granules which
are contained in the same cells.

786. In the Floridese (rose-red marine algze) the chlorophyll
is masked by the presence of a reddish coloring-matter which is
easily extracted by pure water. This reddish pigment is called
phycoérythrine. In solution it is carmine-red by transmitted,
and orange by reflected light. Analogous pigments extracted
by water from alge of colors other than red have received
the following names, — phycopheine (brownish), phycocyanine
(bluish), phycoxanthine (yellowish-brown).

When these coloring-matters have been extracted by cold
water, the chlorophyll is left unchanged in the plant, and it
then imparts to the thallus its characteristic green color. Owing
to the nearly complete insolubility of these reddish pigments in
alcohol, and the complete solubility of the chlorophyll pigment
in that liquid, a green color is given at once to alcohol when an
alga is immersed therein.

787. Colored bodies, not readily, if indeed at all, distinguish-
able from ordinary crystalloids (see 177), are found in many
alge. In some cases these colored granules of crystalline form
occur normally in the living plant; in others they arise from
changes produced by the action of reagents upon the matters of
the cells. The name rhodospermin, given by Cramer to the
granules having the latter origin, has been adopted by Klein in
an extended memoir.

788. Etiolation. Green plants placed in darkness soon turn
pale and become blanched or etiolated. The chlorophyll gran-
ules change their color, and finally appear to become merged,
with more or less change of form, in the protoplasmic mass,
from which they are then no longer easily distinguishable. Etio-
lated plauts when exposed to light recover their color only when
the temperature is above a certain point. The action of light in
restoring color is, moreover, local, being confined to the part of
the plant which is exposed to its influence. It may be here
noted that some plants are not etiolated until after long expos-
ure to darkness; thus the older parts of Cactus speciosus, kept
in the dark, remained green for three months, but the new shoots
were etiolated. Selaginella remained green from four to five
months.!

1 Sachs: Handbuch der Experimental-physiologie, 1865; also Botanische
Zeitung, 1864, and Flora, 1863.

296 ASSIMILATION.

The instructive similarity between the spectrum of the yellow
coloring-matter of chlorophyll and that of the so-called etiolin,
or yellow coloring-matter which can be extracted from blanched
leaves, is shown in the two figures here given.

BC D Ed
= “1200 © 300 | |wo 50D 1000

volt’ isadlaatna li vebawdlis titres 4

N
$

1, 2 g
151

789. An alcoholic solution of chlorophyll undergoes very little
if any change when kept in the dark; but even a short exposure
to strong light destroys its green color, and leaves the liquid
pale brown, or nearly colorless. When, however, strong sun-
light passes through a solution of chlorophyll before it reaches a
second receptacle filled with the same liquid, the first solution
protects the second for a considerable time; and only after the
first has lost a portion of its green color can the second be also
acted upon.

790. Sachs! has pointed out the interesting fact that green
leaves, especially those of delicate texture, become paler when
exposed to a very bright light, and resume their deep green
color when again subjected to a less intense light. If one leaf
is partially shaded by another, the shaded leaf preserves its nor-
mal deep green color, while the leaf exposed to the light grows
distinctly paler. This effect, due probably to a change of posi-
tion of the chlorophyll grains, can be shown experimentally
in the following manner: Fasten closely to a green leaf, still

1 Ber. iiber die Verhandlungen (Math. Phys. Classe) der Siichsischen Ge-
sellsch. xi., 1859, 226 ; and also in Experimental-physiologie, 1865.
Fie. 151. The upper spectrum is that of the yellow constituent of chlorophyll from

Deutzia scabra; the lower, that of the coloring-matter of etiolated barley, in dilute
solution. (Kraus.)

COLORS OF AUTUMN LEAVES. 297

connected to its plant, a narrow strip of flexible lead or tin foil,
and expose the leaf to bright sunlight. After a quarter or half an
hour remove the strip, and the spot which has been kept shaded
by it will be seen to be distinctly deeper in color than the part
which has been exposed to the sun’s rays.

791. Chlorosis, or blanching of plants from lack of iron.
Although iron has not been detected as a constant component
of the pure pigment of chlorophyll, this element has been shown
in many ways, especially by water-culture, to be essential to
the green color and even to the normal formation of the
granules. When a seedling of Indian corn is grown with
its roots abundantly supplied with a nutrient solution from
which all salts of iron are absent, and it has all other condi-
tions favorable to rapid and healthy development, the leaves
are pale yellow, or even whitish, and the whole plant sooner
or later appears sickly and ill-nourished. When, however, a
salt of iron is supplied to the nutrient liquid, a normal green -
color is at once imparted to the leaves and the plant becomes
healthy and vigorous. The effect of the local application of a
salt of iron is thus described: When a weak solution of ferric
chloride, ferric nitrate, or ferrous sulphate is applied to a leaf
blanched by want of iron, the part moistened assumes a nor-
mal green color in a few days, and sometimes in a much shorter
period. Neither cobalt nor nickel salts have similar relations
to chlorophyll.?

792. Autumnal changes in color. The leaves of many decidu-
ous plants undergo changes of color at some period before they
fall. In not a few instances these changes occur early in the
season after full development of the leaf; for example, during
the first days of summer it is not unusual to find on the swamp
maple bright red and yellow leaves. The colors, however, he-
come most striking in temperate climates at the approach of
autumn.

The change of color in autumn leaves is due to changes which
take place in the chlorophyll pigment. This breaks up into
various matters of unknown composition, but classed in a gen-
eral way with the erythrophyll (the reddish coloring-matter) and
xanthophyll (the yeilowish), obtainable artificially from chloro-
phyll. Comparison of the spectra of these substances exhibits
certain very striking features of similarity.

1 Eustbe Gris, 1844, and Arthur Gris, in Ann, des Sc. nat., sér 4,
tome vii., 1857, p. 179.

298 ASSIMILATION.

793. These autumnal changes have been compared, not in-
aptly, to those belonging to the ripening process in colored fruits ;
but this general statement of similarity must not disguise the
fact that in the ripening of fruits special chromoplastids play the
chief part, whereas in the leaf before its fall there is a breaking
up of the protoplasmic basis of the granules of chlorophyll, pre-
paratory to the withdrawal from the leaves into the plant of the
useful products of disintegration.

The changes during disintegration may involve (1) both color
and form of the granules at one and the same time, or (2) the
change in color may precede that in form, or (3) the latter may
occur first.

794. In general, the reddish coloring-matters are found in the
celi-sap of the colored leaves, the yellow in the substance of the
disintegrating grain, and, finally, the brown in the modified
character of the cell-wall itself.

795. That frost is not essential to the production of the leaf-
colors of autumn is plain from the widely known fact that many
leaves undergo precisely these changes of color long before any
frosts appear. It is generally believed, however, that freezing
may somewhat hasten the process of chlorophyll disintegration
which underlies all the changes.

The fact is generally recognized that the autumnal colors,
crimson and scarlet, are more brilliant in the cooler portions of
America than those which characterize the foliage in Europe,
and it has even been remarked that the leaves of American
trees cultivated in Europe do not undergo such marked changes
of color as individuals of the same species do in their native
habitat. This has been accounted for on the ground that there
is less humidity in the atmosphere of eastern America; but this
explanation is not satisfactory, and exact observations regarding
the relative brilliancy of color are wholly wanting.

796. Chlorophyll in evergreen leaves. At the approach of
cold weather the leaves of evergreens undergo, according to
Mohl,’ certain changes of color. Kraus* recognizes two types
of change: (1) the leaves become greenish brown, as in most
Conifers, or (2) they take on a red color on the upper side, as
in Mahonia and some species of Sedum. According tu him, in
leaves of the first type the chlorophyll granules become disinte-

1 Sachs: ' Die Entleerung der Blatter im Herbst, Flora, 1863, p. 200.
2 Vermischte Schriften, 1845.
3 Sitzungsb. der phys.-med. Societit zu Erlangen, 1871, 1872,

AUTUMNAL CHANGES IN LEAVES OF EVERGREENS. 299

grated and impart a brown color to the protoplasmic mass of the
cells; but in the leaves of the second type the color is due to
a highly refractive reddish or yellow mass (supposed to be tan.
nin), concealing from a surface view the clustered chlorophyll
granules within, which retain their vivid hue. In all cases of
evergreen leaves the granules of chlorophyll, at the beginning
of the cold season, pass from the walls to the centre of the cells,
and are there aggregated in compact clusters. Their normal
condition is restored in the warm days of early spring.

797. Kraus has examined the changes in autumn in the chloro-
phyll of Ruscus aculeatus. He finds that in this plant some of the
more superficial cells under the epidermis contain minute granular
masses of a brownish color, but no chlorophyll granules are to
be distinctly seen, and that the subjacent cells have more or less
broken-down granules which are yellowish or brownish green.
In the cells making up the more spongy tissues there are a few
chlorophyll granules quite intact, but there are indications that
some others have been completely destroyed and their coloring-
matter taken up by the surrounding protoplasm, apparently in a
state of solution.

798. It was thought by Kraus that the winter change in the
character of the chlorophyll was due to the lower temperature.
He based his views largely upon experiments with a branch of
Buxus (Box) ; but it has been shown by Batalin? and Askenasy ?
that light has a more important influence upon the chlorophyll
than changes of temperature.

799. The raw materials required for assimilation, and their
reception by the assimilating organs. These are (1) water and
(2) carbonic acid. In earlier chapters it has been shown in
what manner and to what extent water and small traces ef min-
eral matters are brought from the soil into the plant. It is
now necessary to ascertain in what way carbonic acid enters
the organism and is appropriated by it.

800. Absorption of carbonic acid by water plants. These can
absorb carbonic acid substantially as they absorb mineral salts,
directly from the water in which they live. The amount of car-
bonic acid found in rain and other waters is variable, ranging,
according to the best authorities, from about one per cent to
considerably less than one tenth of one per cent. The amount
existing in the free state in natural waters in which plants thrive

1 Botanische Zeitung, 1874.
2 Botanische Zeitung, 1875.

300 ASSIMILATION.

is shown in the following table (taken from the comprehensive
synopsis in Watts’s dictionary) : —
Cubic centimeters
in each liter of water.

Loch Katrine (Scotland) .

Bala Lake (Wales). Be idk en OSE Re a 11
Rhine at Strasburg ie ee soe. 7.6
Rhone at Geneva . . 8 ay oe 8.4
Thames at Kew ‘ : 50.3

All the free carbonic acid dissolved in water can be expelled
by boiling.?

801. Absorption of carbonic acid by land plants. These, with
their foliage exposed to the air, obtain from that source all their
supply of carbonic acid. No carbonic acid is taken up by their
roots: * the supply enters the plant through the younger epider-
mal tissues, chiefly, of course, that of the leaves. By the process
of respiration within the plant (see Chapter XI.) a small but ap-
preciable amount of carbonic acid is produced, and a. part of this
is doubtless appropriated directly by the plant for the process
of assimilation.

802. Carbonic acid and other gases found in the atmosphere
sustain to vegetable membranes certain relations which must

V According to Bunsen (Jahresb. der Chemie, 1853, p. 317), one volume of
water absorbs at 760 mm. barometric pressure, and at the temperatures noted,
the following amounts of various gases : —

8° 2C. 19°.6C,
Nitrogen . . . . .02189 vol. =. © . .01515 vol.
Oxygen . . . . .04553 “ «1. 08258
Carbonic acid . . 1.5184 “ 2... 8545

According to the same authority, these gases occur in rain-water in the fol-
lowing relative proportions : —

0° Cc. 10°C. 20°C,
Nitrogen . . . 63.20 . . . 683.49 . . . 63.69
Oxygen. . . . 383.88 . . 8405 . . . 84.17
Carbonicacid. . 2.92 . . . 246 . . . 2.14

2 This appears to be settled by the results of experiments made by Moll:
(1) when carbonic acid is afforded, even in excess, to shoots, whose leaves are kept
in an atmosphere free from carbonic acid, no formation of starch takes place ;
(2) if such leaves are in the open air, the formation of starch is not increased
above its normal rate; (3) when carbonic acid is supplied to roots of plants
whose leaves and shoots are kept in an atmosphere free from carbonic acid, no
formation of starch takes place. If the leaves and shoots of such plants
are in the open air, there is no increase of starch above the normal amount
(Arbeiten des bot. Inst. in Wiirzburg, 1878, p. 113).

DIFFUSION OF GASES. 301

now be presented in a general manner; and some introductory
reference must be here made to the well-known physical proper-
ties of gases.+

803. Diffusion of gases. When two or more gases are brought
into contact, spontaneous intermixture takes place. This pro-
cess of diffusion, as it is called, goes on even when the gases
are very different in specific gravity, and when they are kept
externally at perfect rest. Thus if a jar of carbonic acid be
placed in connection with a jar of oxygen, the two gases, after
a while, will become uniformly commingled.

Similar commingling of gases also takes place through per-
meable substances, such as thin plates of unglazed porcelain,
graphite, films of membrane, ete.

804. Different gases diffuse through a given membrane in
different times. The rates of diffusion of different gases at the
same temperature and barometric pressure have been shown by
Graham to differ nearly in the inverse ratio of the square roots
of their densities, thus : —

Rate of diffusion it
Name of gas. (air being taken as unity). ¥ Density.
Hydrogen . » . 883 . . . . . 38.78 nearly
Carbonic oxide . . . Ll.0lnearly . . . LOl ‘“
Nitrogen . 2. . . . LOL “wl
Oxygen . be ee SOS oe ee oe “OSL.
Carbonic acid. . . . 81 * : « «8f #8

1 Graham, who made a careful study of the laws which govern gaseous dif-
fusion, has given the following clear account of the physical hypothesis, which
is now generally received : ‘‘ A gas is represented as consisting of solid and
perfectly elastic spherical particles which move in all directions, and are ani-
mated with different degrees of velovity in different gases. Confined in a
vessel, the moving particles are constantly impinging against its sides and oc-
easionally against each other, and this contact takes place without any loss of
motion owing to the perfect elasticity of the particles. If the containing
vessel be porous, then gas is projected through the open channels, by the
motion described, and escapes. Simultaneously the external air is carried
inwards in the same manner and takes the place of the gas which leaves the
vessel. To this molecular movement is due the elastic force, with the power
to resist compression, possessed by gases. The molecular movement is acceler-
ated by heat and retarded by cold, the tension of the gas being increased in the
first instance and diminished in the second. Even when the same gas is
present both without and within the vessel, or is in contact with both sides
of our porous plate, the movement is snstained without abatement — molecules
continuing to enter and leave the vessel in equal number, although nothing
of the kind is indicated by change of volume or otherwise. If the gases in
communication be different, but possess sensibly the same specific gravity
and molecular velocity as nitrogen and carbonic oxide do, an interchange of

302 ASSIMILATION.

805. The movements of gases within the plant are of two
kinds, (1) molecular (see note on the previous page), and (2)
‘the movement of the whole mass depending exclusively on
expansive force.” These are generally conjoined in the passage
of gases through the plant.

806. Passage of gases through epidermis free from stomata.
The assimilating apparatus in ordinary land plants consists of
parenchyma cells frequently so loosely conjoined as to have very
conspicuous intercellular passages, which communicate with sto-
mata either directly or indirectly. All of these parenchyma cells.
have walls of cellulose generally without any impregnation of
foreign matter. But the peripheral cells which bound the whole
as epidermis proper are cutinized on their external aspect, and
must possess relations to gases different from those presented by
common parenchyma with uninfiltrated walls.

807. Through ordinary cell-walls, that is, those which are com-
posed of nearly pure cellulose, water passes and gases diffuse
with facility. But as cutinized cell-walls, like those of the epi-
dermis of leaves, are nearly impervious to water and to aqueous
vapor, it would at first sight appear unlikely that gases could
make their way through them; such, however, is not the case.
Experiments upon epidermal tissues free from stomata show
that under ordinary circumstances gases can diffuse through
cutinized walls.

Thus N. J. C. Miller? used the epidermis of the leaves of
Heemanthus puniceus in three series of experiments upon the
diffusion of different gases. The membrane employed was, in
the first series, two films of epidermis with a layer of water be-
tween them; in the second, two moist films without any layer
of water; in the third, two films joined together and then care-
fully dried in an exsiccator at 40° C. The method used by
Miiller is open in some of its details to criticism, but in a general
way the results are instructive. The following are the mean
ratios indicating the rate of diffusion obtained : —

Series I. Series II. Series UI. |
Hydrogen na ah 100 100 100
Oxygen. 2. 2. . ee. 502 55 37
Nitrogen . . 1. es. 471 73 30
Carbonic acid. . . . . 687 48 45

molecules also takes place without any change in volume. With gases opposed
of unequal density and molecular velocity, the permeation ceases, of course, to
be equal in both directions ” (Philosophical Transactions, 1863).

1 Pringsheim’s Jahrb., 1869, p. 169.

PASSAGE OF GASES THROUGH STOMATA. 303

808. Experiments by a wholly different method were con-
ducted by Boussingault,! upon leaves of Oleander. By a leaf
having an upper surface of 37.2 square centimeters free from
stomata, and completely closed on the under side by tallow,
17.5 cubic centimeters of carbonic acid were absorbed in a given
time.

In another series of experiments Boussingault fastened the
under surfaces of two leaves closely together by means of paste,
so that only the upper surfaces (free from stomata) were exposed
to the air; with these leaves nearly the same results were ob-
tained as in the first series.

809. Passage of gases through stomata. Stomata (see Figs.
52 and 54) are practically minute apertures in thin plates, and
under ordinary circumstances there is no obstruction to the
ready passage of gases through them from the surroundings into
the interior of the plant. The changing pressure caused by agi-
tation of the foliage exerts, as it does in aqueous transpiration,
an important influence in facilitating this passage.

810. Merget? holds that it is chiefly through stomata that
the interchange of gases with the outer air takes place in the
plant; but, on the other hand, it is claimed by Barthelemy ® that
they play only a very subordinate part. There can be little
doubt that the earlier view advanced and illustrated by Du-
trochet,* and further by Garreau,’ is substantially correct ; namely,
that gases enter and escape from the plant freely both by diffu-
sion through the cuticularized cell-walls of the epidermis and
by passage through the stomata.

811. Atmospheric air is chiefly a mixture of two gases, oxygen
and nitrogen. The proportions in which these substances and
others, occurring in much smaller amounts, are found in dry air
are usually stated as follows : —

Proportions by volume. Proportions by weight.

Nitrogen. . 2... « 79.01984 76.8399
Oxygen . . soe ee « 20.94000 23.1000
Carbonicacid . . 1... -04000 .0600
Ammonia a ae ee -00016 .0001
100. 100.

1 Agronomie, iv., 1868, p. 374.
2 Comptes Rendus, Ixxxiv., 1877, p. 376.
Aun. des Se. nat. bot., sér. 5, tome xix., 1874, p. 181.
* Ann. des Sc, nat., tome xxv., 1832, p. 242.
5 Ann. des Sc. nat. bot., sér. 8, tomes xv., xvi.

304 ASSIMILATION.

The first two substances occur in very nearly the same pro-
portions in free atmospheric air wherever found,’ but the amounts
of the last two vary within narrow limits.

Besides the foregoing substances, the following are also men-
tioned as having been found in dry air in minute traces: Nitric
acid, nitrous acid, ozone, marsh gas, carbonic oxide, sulphurous,
sulphydric, and hydrochloric acids, and hydrogen.

812. Under ordinary circumstances the proportion of car-
bonic acid in the atmosphere does not increase much beyond the
amount stated above, namely, four one-hundredths, or one twenty-
fifth of one per cent.? Pettenkofer assigns one twentieth of one
per cent as the amount in the air of Munich (1,690 feet above
the level of the sea).

In contined spaces, however, the accumulation of carbonic
acid (once known by the significant term fixed utr) may be-
come so great as to render the air irrespirable. It was the con-
sideration of the question how such air could be again rendered
fit for respiration that led to the first successful® investigation of
the action of plants upon the atmosphere.

813. The amount of carbonic acid found in ordinary water
which has been exposed for a time to the air is sufficient for the
supply of this gas to water plants. The percentage of the gas
in the atmosphere under ordinary conditions is ample for all the
needs of land plants. The consideration of the effect of supply-
ing a larger amount than usual of this gas to water and land
plants, in order thereby to influence the activity of the assimila-
tive process, must be deferred until all the conditions essential
to assimilation have been considered; but it may be said, in
passing, that any large excess of carbonic acid over the supply
furnished to plants in nature diminishes assimilative activity.

1 For a very instructive summary of results of the examination of the air
in different localities, the reader should consult “‘ Air and Rain, the Begin-
nings of a Chemical Climatology,” by R. Angus Smith (London, 1872).

2 Angus Smith gives the following results of his examination in 1864 of the

air of Manchester, England :—
Per cent of CO, in atmosphere.

In the streets, usual weather... s+» 4 « » » 9408
During fogs . 4 ‘ Me, osha « «0679
Whee. the fields bests oe eR Z .0369
In close buildings . . . se se we & & & ile
Minimum amount found in atiuas Ewen, 5 » « 0291

See also Ann. de Chimie et de Physique, 1883, for reports or the amount of
CO, in the atmosphere of different localities.
8 See the historical sketch, pp. 323, 324.

PRACTICAL STUDY. 305

814. Practical study of assimilation. Before examining the
remaining conditions of assimilation, a simple experiment is here
described by which the reader can study in their proper relations
all the essential conditions of the process, and thus obtain a
clearer idea of the means by which the activity of assimilation
is measured and the indispensable character of the conditions
established.

Fill a five-inch test-tube, provided with a foot, with fresh drink-
ing water. In this place a sprig of one of the following water
plants, — Anacharis Canadensis, Myriophyllum spicatum, M.
verticillatum, or any leafy Myriophyllum (in fact, any small-
leaved water plant with rather crowded foliage). This sprig
should be prepared as follows: Cut the stem squarely off, four
inches or so from the tip, dry the cut surface quickly with
blotting-paper, then cover the end of the stem with a quickly
drying varnish, for instance asphalt-varnish (see 115), and let
it dry perfectly, keeping the rest of the stem if possible moist by
means of a wet cloth. When the varnish is dry, puncture it by
a needle, and immerse the stem in the water in the test-tube,
keeping the varnished larger end uppermost. If the submerged
plant be now exposed to the strong rays of the sun, bubbles of
oxygen gas will begin to pass off at an even and rapid rate, but
not too fast to be easily counted. If the simple apparatus has
begun to give off a regular succession of small bubbles, the fol-
lowing experiments can be at once conducted.

(1) Substitute for the fresh water some which has been boiled
a few minutes before, and then allowed to completely cool: by
the boiling, all the carbonic acid has been expelled. If the plant
is immersed in this water and exposed to the sun’s rays, no bub-
bles will be evolved; there is no carbonic acid within reach of
the plant for the assimilative process. But,

(2) If breath from the lungs be passed by means of a slender
glass tube through the water, a part of the carbonic acid exhaled
from the lungs will be dissolved in it, and with this supply of
the gas the plant begins the work of assimilation immediately.

(3) If the light be shut off, the evolution of bubbles will pres-
ently cease, being resumed soon after light again has access to
the plant.

(4) If glass of different colors be interposed in the path of the
sun’s rays, it will be shortly seen that orange light differs from
violet light in its effects upon the rate of the evolution of the
bubbles.

(5) Place around the base of the test-tube a few fragments of

20

306 ASSIMILATION.

ice, in order to appreciably lower the temperature of the water.
At a certain point it will be observed that no bubbles are given
off, and their evolution does not begin again until the water be-
comes warm.

(6) Examine, at the close of the series of simple experiments,
some of the leaves with iodine solution, for the detection of
starch. Even with no precaution the chlorophyll granules will
reveal the presence of a considerable amount of the first visible
product of assimilation, namely, starch. Lastly, keep a second
uninjured spray of the same plant in the light for a time, and
then in darkness for a day or two, after which examine it for
starch ; probably after this lapse of time no starch can be de-
tected, for although it has been made in the light, in darkness it
has been consumed in the various activities of the plant.

815. According to the accepted theory, light consists of waves
which are set in motion in a tenuous elastic medium termed the
ether. The existence of this medium is made known to us only
by the phenomena which light itself presents; but, having as-
sumed its existence, the phenomena of light can be explained.
The tennity of this medium, which fills all space, far exceeds
that of any known gas, and its elasticity is far higher than that
of any known elastic solid. In it a luminous body sets in mo-
tion undulations which produce upon the retina the sensation of
light; upon differences in the amplitude and the duration! of
these undulations depend differences in the intensity and the
color of the light which reaches the eye.”

1 The terms just employed, namely, amplitude and duration, seem hardly
applicable to waves of such incredible minuteness and velocity as those named
in the following table : —

Color of Number of waves of light in one Length of each wave.
light. second of tirae.
Red . 477 millions of millions. 650 millionths of a millimeter.
Orange . . . 506 et ” ie 609 be = =
Yellow . » 5385 ee ee ee 576 “ ce an
Green... 577 “ “ “ 536 “ “ “
Blue. . » 622 * * e 498 us as
Indigo . 630 “cc 6 6c 470 66 ‘6 “
Violet » . 699 ae be a 442 as ee =

2 «The intensity of the luminous impression must depend upon the force
of the atomic blows which are transmitted to the optic nerves, and it is also
evident that this force must be proportional to the square of the velocity of
the oscillating atoms, or, what amounts to the same thing, to the square of the
amplitude of the oscillation ; assuming, of course, that the oscillations are
isochronous. The connection of color with the time of oscillation is not so

TYPES OF ENERGY. 307

816. Light and assimilation proper. Energy has been defined
as the power of doing work. Of this there are two types: the
energy of actual motion (sometimes termed Ainetic), and the
energy of position (known as potential). The illustration of
their difference is usually given as follows: A ball thrown up-
wards has the power of overcoming the force of gravity tending
to pull it down, and possesses energy of motion; suppose the
ball at the end of its course is lodged upon some projecting
shelf, then its energy of motion disappears, and it now pos-
sesses energy of position. Whenever it is dislodged, it will fall
with the same power which was required for its ascent. From
this and similar examples it is plain that one form of energy
can be changed into another; when one seems to disappear,
it has in fact merely been converted into some other.

817. These types of energy are to be found in molecules as
well as in masses of matter. It is held that all molecules of all
matter are in a state of motion, invisible, but none the less real.
One form of such invisible kinetic energy is heat, and another
is radiant light, where the energy of motion is embodied in the
vibrations or undulations of the ethereal medium. A third form
is that of electrical separation; and still another, with which
Physiology deals especially, is known as chemical separation, of
which a familiar illustration may be given: An atom of oxygen
has so strong an attraction for one of carbon, that if the two
are united, it is difficult to separate them, the force required
to do this being comparable to that demanded to raise a weight
to a certain height. As in the latter case the weight held in
its raised position represents by that position the force which
was employed to raise it, so the separated atoms represent
energy of position ready to be again converted into energy of
motion.?

obvious ; and why it is that the waves of ether beating with greater or less rapid-
ity on the retina should produce such sensations as those of violet, blue, yellow,
or red, the physiologist is wholly unable to explain. We have, however, an
analogous phenomenon in sound, for musical notes are simply the effects of
waves of air beating in a similar way on the auditory nerves ; and, as is well
known, the greater the frequency of the beats, or, in other words, the more
rapid the oscillations of the aerial molecules, the higher is the pitch of the note.
Red color corresponds to low, and violet to high notes of music, and the gra-
dations of color between these extremes, passing through various shades of
yellow, green, blue, and indigo, correspond to the well-known gradations of
musical pitch ” (Cooke: Chemical Philosophy, 1882, p. 189).

1 It is seldom that one of these forms of molecular energy when exhibited in
the phenomena of living beings is not associated with some other form, Thus

308 ASSIMILATION.

818. The conversion of the energy of the motion of the ethe-
real medium (in radiant light) into chemical separation of oxy-
gen from the carbon of carbonic acid, and the production of
this treasured energy under other forms, is the chief office of the
plant.

819. Attention has already been called (see page 306) to the
well-known fact that a beam of sunlight is composed of rays or
lines of undulations differing both in respect to their amplitude
and velocity. Hence it is to be expected that in their action on
the plant these rays, which are in fact vehicles of kinetic energy,
must have diverse effects.

820. Classification of the rays of the spectrum. When a beam
of sunlight is transmitted through a triangular prism, it is broken
up into its constituent rays, which, falling upon a screen, form
what is Known as a spectrum. The colors of the spectrum
grade from red at one end, through orange, yellow, green,
blue, and indigo, to violet. The violet rays are bent further
from their course by the prism than any of the others above
spoken of, and hence are termed the most refrangible ; experi-
ment has also shown that these highly refrangible rays are most
efficient in producing the chemical changes long known to be
attributable to light: for this reason they have been denomi-
nated chemical (or sometimes actinic) rays. The red rays are
bent far less from their course than any of the others above men-
tioned, and hence they are termed the least refrangible. It is
at the red end of the visible spectrum that the greatest amount
of heat is found. The rays which constitute yellow and orange
light are of medium refrangibility ; they are the most distinctly
luminous. It is proper, therefore, for convenience, to distin-
guish rays of the solar spectrum as chemical, luminous, and
heat rays, according to the dominant effect which they produce.
But it should be stated that each of these three groups may
share some of the work specially belonging to the others; and
further, that beyond the visible spectrum are rays which are
efficient in accomplishing certain kinds of work. These latter
are known respectively as the ultra-violet and the ultra-red
rays.

Before examining the action of these different rays of light
upon the assimilative activity of chlorophyll granules, inquiry
must be made as to

absorption, which is essentially a process of molecular adhesion, is accompanied,
as is capillary attraction, by electrical disturbances. In no case is energy lost .
one form disappears only to reappear in some other,

PASSAGE OF LIGHT THROUGH LEAVES. 309

821. The depth to which light can penetrate green tissues. This
can be ascertained approximately by a simple apparatus sug-
gested by Sachs. A pasteboard tube, a foot or so in length
and about an inch in diameter, is cut at one end so as to fit
around the eye very closely and allow no rays to enter except
through the other end of the tube. If a thin leaf be placed
over the distal end of the tube, and it be held towards a bright
light, a large portion of the light will be received by the eye.
If leaf after leaf be placed over the first, the green color soon
gives way to a dull red, and finally is excluded altogether.
The same apparatus shows to what depth light can penetrate
superposed layers of green cells taken from a stem or from thick
leaves.”

822. The quality of the light which penetrates a leaf, or which
has passed through’ one layer of cells containing chlorophyll, is
shown by means of the spectroscope. From what has been
shown (p. 296), it is clear that the light which acts on the cells
below the first layer exposed to the sun’s rays must be different
from the incident rays themselves. The light which reaches
the deeper tissues of a leaf has passed through more than one
film of green tissue.

823. The degree of intensity of white (that is, uncolored) light
most favorable to assimilation has not been determined with
certainty. The lowest limit at which any assimilation has been
observed is considerably above that at which etiolated chloro-
phyll turns green.®

824. It has been shown‘ that very intense white light, even
after it has been deprived of nearly all of its heat rays, can
destroy the vitality of vegetable cells. Considerably before the
death of the cells from this cause, the chlorophyll granules in
them lose all their coloring-matter, even when they preserve
their general form, and having once lost their green color, do
not afterwards regain it.

1 Handbuch der Experimental-physiologie, 1865, p. 5.

2 But it has been shown by Hankel that the angle at which a beam of light
strikes a plate of glass makes a noticeable difference in the amount of the chemi-
cal rays which can pass through it; thus while at a vertical angle 81 per cent
of the rays are transmitted, the rest being absorbed, at an angle of 60° the
amount transmitted is reduced to 71 per cent, and at 80° to 33 per cent. The
subject as relating to plants has not received the attention it deserves (Berichte
iiber die Verhandlungen der Siichsischen Gesellschaft der Wissenschaften).

3 Sachs : Experimental-physiologie, 1865, p. 8.

4 Pringsheim : Monatsberichte der Berlin Akademie, 1879,

310 ASSIMILATION.

825. Colored light and assimilation. Daubeny, in 1835, was
the first! to experiment systematically upon this subject. His
method ? of investigation was as follows: ‘‘A certain number
of fresh leaves, which presented in each case an extent of surface
as nearly as possible equal, and had been previously ascertained
to give out equal quantities of oxygen, were introduced severally
into jars filled with water impregnated with carbonic acid gas,
placed on the surface of a pneumatic trough, and exposed for
a certain time to the influence of the solar rays. The jars in
which the leaves thus selected stood, were severally covered
over by a wooden screen which intercepted all light from the in-
cluded jar,” excepting in front, where a frame was fitted, into which
(1) colored glass or (2) flat bottles filled with differently colored
liquids could be fastened, so that the light reaching the leaves
could be variously modified. The amount and character of ‘the
gas escaping into the upper part of each jar were carefully
determined. The leaves used were those of Brassica oleracea,
Salicornia, Fucus, Tussilago, Cochlearia Armoracia, and Mentha
viridis. Besides plain glass, the following colored varieties were
employed: orange, red, blue, purple, green; while the liquids
used were, for blue, ammonio-sulphate of copper, and for red,
port wine.

In all cases Daubeny determined the amount of gas given off
by the leaves, and afterwards analyzed it in order to ascertain
the percentage of oxygen. He concluded from his experi-
ments,® ‘‘ that the effect of light upon plants corresponds with
its illuminating rather than with its chemical, or its calorific
influence.”

826. J. W. Draper, in 1844, published an account of his ex-
periments upon the relations of green plants to light, as regards
the amount of assimilative activity indicated by the oxygen given

1 Senebier and others had already conducted some inconclusive experiments
in nearly the same field.

2 On the Action of Light upon Plants, and of Plants upon the Atmosphere
(Philosophical Transactions, 1836, p. 149).

The activity of assimilation proper, as will be seen later, can be measured
with a very close approximation to accuracy, by the amount of oxygen gas
which is set free from the assimilating tissues, or, what amounts to substan-
tially the same thing, by the amount of carbonic acid decomposed by them.
For the sake of uniformity, the word assimilation is to be used in the follow-
irg paragraphs, even where the authorities cited refer to the process under
tre terms decomposition of carbonic acid, evolution of oxygen, etc. The term
7 isimilation, in its restricted sense, was adopted by Sachs (1863).

8 Philosophical Transactions, 1836, p. 151.

DRAPER’S EXPERIMENTS, 311

off during exposure to different rays of the solar spectrum. From
his results it appears that ‘‘the rays which cause the decomposi-
tion of carbonic acid gas have the same place in the spectrum as
the orange, the yellow, and the green ; the extreme red, the blue,
the indigo, and the violet exerting no perceptible effect.” ?

Draper lays great stress upon the interesting fact previously
noticed by Daubeny, that the chemical rays appear to have no
effect upon the work of assimilation. He does not, however,
offer any explanation of the curious fact that the chemical activ-
ity of the plant is dependent upon other rays than the chemical
for its excitation.

827. The principal results obtained with submerged water
plants by Cloéz and Gratiolet,? who exposed Potamogeton and

1 A Treatise on the Forces which produce the Organization of Plants, 1844,
p. 177. The method of experimenting is detailed by Draper as follows:
“Having, by long boiling and subsequent cooling, obtained water free from
dissolved air, I saturated it with carbonic acid gas. Some grass leaves, the
surfaces of which were carefully freed from any adherent bubbles or films
of air by having been kept beneath carbonated water for three or four days,
were provided. Seven glass tubes, each half an inch in diameter and six
inches long, were filled with carbonated water, and into the upper part of each
the same number of blades of grass were placed, care being taken to have all
as near as could be alike. The tubes were inserted side by side in a small
pneumatic trough of porcelain. It is to be particularly remarked that the
blades were of a pure green aspect, as seen in the water; no glistening air-
film, such as is always on freshly gathered leaves, nor any air bubbles, were
attached to them. Great care was taken to secure this perfect freedom from
air at the outset of the experiments.

“The little trough was now placed in such a position that a solar spectrum,
kept motionless by a heliostat and dispersed by a flint-glass prism in a hori-
zontal direction, fell upon the tubes. By bringing the trough nearer to the
prism or moving it farther off, the different colored spaces could be made to
fall at pleasure on the inverted tubes. The beam of light was about three
fourths of an inch in diameter. In a few minutes after the commencement
of the experiment the tubes on which the orange, yellow, and green light fell
commenced giving off minute gas bubbles ; and in about an hour and a half
a quantity was collected sufficient for accurate measurement.

“The gas thus collected in each tube having been transferred to another
vessel and its quantity determined, the little trough, with all its tubes, was
freely exposed to the sunshine. All the tubes now commenced actively evolv-
ing gas, which, when collected and measured, served to show the capacity of
each tube for carrying on the process. If the leaves in one were more sluggish,
or exposed a smaller surface than the others, the quantity of gas evolved in
that tube was correspondingly less. As may be readily supposed, I never
could get tubes so arranged as to act precisely alike ; but after a little practice
I brought them sufficiently near to equality. And in no instance was this
testing-process of the power of each tube for evolving gas omitted after the
experiment in the spectrum was over.”

2 Annales de Chimie et de Physique, sér. 3, tome xxxii., 1851, p. 67.

812 ASSIMILATION.

Myriophyllum to the action of light colored by passing through
elass, may be stated as follows: The activity of the plant in
decomposing carbonic acid diminishes with glasses used in the
order given: (1) uncolored ‘‘ ground” glass, (2) yellow, (8) un-
colored transparent glass, (4) red, (5) green, (6) blue. By all
the experimenters now referred to, the evolved gas was collected
and examined.

828. Measurement of the amount of assimilation. Sachs, in
1864, appears to have been the first to employ the now well-
known method of measuring the activity of the assimilative
process by counting the bubbles of gas which are given off
by a submerged water plant (see 814). Since the gas given
off by the plant is not pure oxygen, but is variable in compo-
sition,) the method cannot be regarded as sufticiently precise
for very accurate experiment; but as it admits of such rapid
change in all external conditions, it answers for all practical
purposes.

829. The effect of colored light upon the assimilative activity
of plants not submerged, as in the above experiments, but in
the air, was first examined by Cailletet,? in 1867. He placed
the plant under bell-jars containing air with eighteen, twenty-

1 For remarks upon the possible errors which may attend the use of this
method, consult Miiller (Pringsheim’s Jahrb. vi., 1868, p. 478).

2 L. Cailletet placed leaves in jars filled with air containing from 18 to 30
per cent of carbonic acid, and then exposed these to light which had passed
through colored glass. In‘one case the light was transmitted through a solu-
tion of iodine in carbon bisulphide. After an exposure of from eight to ten
hours, the amount of carbonic acid remaining undecomposed by the action of
the leaves was found to be as follows : —

Per cent of carbonic acid
r in the air. Remarks as to chemical activity
Medium. ight.
18p.c. | 21p.c. | 30p.c.
Todine in CS, 18 2h 30 Photographic paper not blackened.
Green glass 20 30 37 Argentic chloride slowly discolored.
Violet glass 18 19 28 Sensitive paper blackened rapidly.
Blue glass 17 16.50 27 “ & “
Red giass 7 5.50 23, No blackening of argentic chloride
or sensitized paper.
Yellow glass 5 1 18 Paper not blackened.
Ground glass 0 0 2 Paper discolored rapidly.

Two points must be specially noticed : (1) the striking effect of the large
amount of carbonic acid in the third scries ; (2) the anomaly presented by the
green glass, which is quite unexplained. It is to be regretted that no fuller
account of the character of the glasses used is given (Comptes Rendus, Ixv.,
1867, p. 822).

TIMIRIAZEFE’S RESEARCHES, 318

one, or thirty per cent of carbonic acid, and made of red, yellow,
green, blue, violet, and colorless glass. [lis results agree in
general with those obtained by the other methods.

830. In 1870 further investigations in the saine subject were
made by Pfeffer. The following is a résumé of the results of
his experiments with the leaves of five different plants exposed
to colored light: Only the visible rays of the spectrum cause
decomposition of carbonic acid ; and in this process the brightest,
that is, the yellow rays, are as efficient as all the others taken to-
gether, while the most refrangible rays, those which act most en-
ergeticully upon chloride of silver, have only very slight influence
upon the work of assimilation.

Every color of the spectrum may be said to possess a specific
quantitative influence upon assimilation. This influence remains
unchanged whether the color is isolated, combined with one, or
with all the other colors of the spectrum when it acts upon a
part of a plant containing chlorophyll.

831. Examination of the spectruin of chlorophyll (779) shows
that the part of the spectrum which absorbs most of the rays is
that which is pre-eminently its chemical end; but by all the ob-
servers whose results have been cited in the text, it is held that
the chemical end is that which is least efficient in assimilation.
With the exception of the narrow though strong absorption-band
in the red, all the deep absorption-bands of chlorophyll and its
solutions belong at the violet or chemical end of the spectrum.
Miiller and Timiriazeff, cited in the notes, have endeavored to
investigate this anomaly.

832. Timiriazeff,? in a series ol researches in 1877, experi-
mented upon the slender leaves of Bamboo, which he placed
in tubes of sinall calibre containing air of known composition,

1 Arbeiten des botan. Inst. in Wiirzburg, 1871, p. 1.

The following works may also be cited : —

A. von Wolkoff, Einige Untersuchungen iiber die Wirkung des Lichtes von
verschiedener Intensitiét auf die Ausscheidung der Gase durch Wasserpflanzen.
Pringsh. Jahrb., v., 1866, p. 1.

Adolf Mayer, Production von organischer Pflanzen-Substanz bei Ausschluss
der chemischen Lichtstrahlen, Versuchs-Stationen, ix., 1867, p. 396.

N.J. C. Miiller, Untersuchungen iiber die Diffusion der atmospharischen
Gase in der Pflanze und die Gasausscheidung unter verschiedenen Beleucht-
ungsbedingungen, Pringsh. Jahrb., vi., 1867, 478 ; and vii., 1869, 145.

Timiriazeff, Botanische Zeitung, 1869, p. 169.

Prillieux, Ann. des Sc. nat., sér. 5, tome x., 1869, p. 305.

Baranetzky, Botanische Zeitung, 1871, p. 193.

2 Annales de Chimie et de Physique, sér. 5, tome xii., 1877, p. 355.

814 ASSIMILATION.

and exposed to different parts of a large spectrum formed by a
hollow prism filled with carbon bisulphide. By employing a nar-
rower slit for the light than that used by previous experimenters,
he obtained an exposure of the leaves to a very limited portion
of the spectrum: and to this difference in his apparatus he chiefly
attributes his results, which are at variance with those of his
predecessors. Assuming that the results of his analysis of the
evolved gas are accurate, they indicate that the amount of car-
bonie acid decomposed by leaves is proportional to the distri-
bution of effective calorific energy in the spectrum.

Timiriazeff? in his earlier paper did not himself attempt to apply
his results to an explanation of the peculiar relations of the rays
of the spectrum to assimilation; but Van Tieghem, who sub-
stantially adopts the results of Timiriazeff, gives the following
application of them to the associated phenomena. He calls atten-
tion to the fact that the maximum of decomposition of carbonic
acid. under the conditions of Timiriazeff’s experiments, takes
place at the deep absorption-band of chlorophyll, between B
and C; and therefore concludes that the decomposition of car-
bonic acid by leaves exposed to solar radiation depends on two
elements: (1) the elective absorption of the chlorophyll, and
(2) the calorific energy of the absorbed radiations. According
to this view, the most efficient radiations must be those which,
being best absorbed by the chlorophyll, possess at the same time
the greatest calorific energy. Hence, (1) the extreme red and
the dark heat-rays, in spite of their extraordinary calorific energy,
have no effect, because they pass through chlorophyll without
visible absorption ; and (2) the blue rays, which are very strongly
absorbed, exert scarcely any effect, owing to their feeble calorific
energy.”

833. Timiriazeff’s results should be compared with those of
Engelmann, who finds that for green cells the absolute maximum
of assiiilative activity lies in the red, between the lines B and C,
at the point of the first and most pronounced absorption-band of
chlorophyll, and that there is also more or less activity in the
blue at F. If the cells are not of a green color, the maximum of
activity is in some other point; thus in the case of bluish-green
cells it is in the yellow, and in that of red cells in the green.

Engelmann’s method is based upon the extraordinary sensi-

1 Ann. de Chimie et de Physiyue, sér. 5, tome xii., 1877, p. 394, and Ann.
des Sc. nat., sér. 7, tome ii., p. 99.
2 Traité de Botanique, 1884, p. 149.

ENGELMANN’S RESEARCHES. 3815

tiveness of certain bacteria to the presence of free oxygen. By
an ingenious device, simple in its application, it is possible to
determine the parts of the spectrum in which an assimilating cell
or filament gives off oxygen most copiously. Under the stage
of the microscope is placed a microspectroscope, which throws
a clear spectrum upon any object on the glass slide in its place
on the stage, for instance a filament of an alga. The alga is
placed upon the slide in water which contains numbers of the
common Bacterium (B. Termo), easily procured from putrescent
matters. If it is kept from the light, or is exposed to only very
faint light, all assimilative activity is suspended, and the bacteria
after a time are quiescent. But when light in sufficient amount
is permitted to pass through the specimen, assimilative activity is
at once manifested, and the evolution of oxygen from the filament
brings the bacteria into rapid movement. If, instead of white
light, the rays from the spectroscope are passed through the
specimen, the activity of the bacteria is equally manifest, but it
is confined to a comparatively small part of the spectrum; the
bacteria collecting chiefly at the points which are known to coin-
cide with the absorption-bands of chlorophyll? When a some-
what thick cell is employed, there is a noticeable difference
between the amount of activity on its upper and under side.
The figures show the ratio of activity of assimilation between
the under side first exposed, and the upper side which receives
light that has first passed through a green film.

B-C. D. DIE. E-b. F. FIG.
Lower . . . . 100. 48.5 aT 24. 86.5 10.
Upper. . . «386.5 94. 100. §2. 22. 12.

It is to be noted that Engelmann did not in any case find any
assimilation in uncolored chlorophyll, even when the light was
tempered by the interposition of a colored medium (compare 850).
He has proved that assimilation proper takes place only in

1 According to Engelmann, the sensitiveness of bacteria is so great that by
their reaction the trillionth part of a milligram of oxygen can be detected
(Botanische Zeitung, 1888, p. 4). Clerk Maxwell's estimate of the weight of
a molecule of oxygen was one thirteen trillionth of a milligram (Philosophical
Magazine, 1878, p. 453).

2 It is interesting to compare these determinations of the point of greatest
assimilative efficiency in the spectrum with the results of Langley’s researches
upon the distribution of energy in the spectrum (American Journal of Science,
xxv., 1883, p. 169).

3 Botanische Zeitung, 1882, p. 419; 1883, p. 17.

316 ASSIMILATION.

protoplasm which contains coloring-mater, as for instance the
chlorophyll granules, the colored granules in alow, ete.

834. Artificial light and assimilation. De Candolle* exposed
the submerged leaves of several species of plants to the light
emitted by six Argand lamps, and failed to obtain thereby any
evolution of gas. He estimated that the lamps had about five
sixths of the intensity of sunlight. In this experiment the
light, though insufficient to cause the evolution of gas, restored
etiolated plants to their original green color.

835. When, however, a submerged water plant is exposed to
the rays from a calcium light? (as that of an ordinary projecting
lantern), there is a copious evolution of gas from its leaves. The
light from burning magnesium wire is also sufficient to cause the
decomposition of carbonic acid and the evolution of oxygen.®

836. The influence of the electric light upon assimilation has
been investigated by numerous observers. Dehérain, who ex-
perimented in the Palais de l’Industrie, in Paris, found that the
total assimilation produced in the leaves of Anacharis Canaden-
sis, during an exposure for five days, was not equal to that which
followed exposure to sunlight for a single hour.* Siemens has
shown that (1) many plants do not require any period of rest
during the day, but thrive under continued illumination by elec-
tric light and sun-light; (2) electric light, properly regulated,
accelerates growth, and produces upon plants effects comparable
to those produced by sun-light.®

837. Temperature and assimilation proper. In certain cases
the minimum temperature at which assimilation can take place is
only slightly above the freezing-point of water. Boussingault®
found that the leaves of the larch decompose carbonic acid at
a temperature of from 0°.5-2°.5 C.; while Kraus’ gives the

1 Mem. prés. par divers Savans, & l'Institut des Sciences, tome i., 1806,
p. 333, and Physiologie végétale, 1832, p. 181.

Biot, in 1840 (Froriep'’s Notizen, xiii. 10), when measuring, in Spain, the
length of a degree of latitude, found that the light from the powerful signal-
ling apparatus used was not sufficient to cause any cvolution of gas from sub-
merged plants of Agave Americana.

2 Prillieux : Comptes Rendus, Ixix., 1869, p. 408.

8 Heinrich: Versuchs-Stationen, xiii., 1871, p. 153.

4 Annales Agronomiques, tome vii., 1881, p. 385.

5 Proceedings of the Royal Society, xxx., pp. 210, 295, and Report of the
British Association for the Advancement of Science, 1881, p. 474.

® Ann. des Sc, nat., sér. 5, tome x., 1868, p. 336.

7 Kraus (Pringsh. Jalirb., vii., p. 522) placed seedlings of Lepidium sativum
in the dim light of the back of a room, where after six days the cotyledons

ASSIMILATION AND TEMPERATURE. 317

minimum temperature for assimilation by Anacharis, Lepidium,
and Betula as 3°-5° C.; and Heinrich? gives it as 2°.5-4°.5 C.
for Hottonia.

The maximum temperature at which assimilation can occur
in Anacharis ? is between 45° and 50° C.; in Hottonia,? just be-
low 56° C.

The optimum? temperature for Hottonia appears to be not
far from 31° C.

showed no trace of starch. The plants were then distributed in three rooms
of the temperatures mentioned in the annexed table, and with the results there
detailed :—

After 12°.8-13°.7 C, 5°.9-6°.5 C. 0°.3-0°.5 C.

2 hours. | The first starch granules appear | No starch. No starch
in the chlorophyll cells on the
margin of the leaves.

3 hours. | Starch in the whole tip, margins, | Some traces of starch at ss
and petiole. margins of the leaves.
5 hours. | Starch in the whole upper half of | ‘Tip and narrow edge with
the leaf. starch.
13 hours. | ‘he whole leaf contained starch. | Margin with much, sur- Ks

face with little starch.

1 Versuchs-Stationen, xiii., 1871, p. 136.

2 Schutzenberger and Quinquaud : Comptes Rendus, Ixxvii., 1873, p. 272.

8 Heinrich: Versuchs-Stationen, xiii., 1871, p. 136.

* Heinrich’s figures are so instructive that they are here presented in the
following table, which gives the number of bubbles of gas passing off from the
cut surface of single leaves of Hottonia during the space of five minutes : —

Temp. C.° No. of bubbles.

tT OR OOS Be a oe we caer ce STASICO)
W232 2 ee ee a 2 ee % » T80ET90
Bos es Ge ay al a a Mo ee ae, “DTS
Oho A a ee soe ww 6 245-255
Wie 2 ee ee ee oe OR ee WBTRLOGT
Beis ce. ow ae je SD ee Ue oe SBBBEBED)
DO i GE OR ee RE RO ae owe BEDS
D0 oe ee eee ee e & « 8902450
Blo eo wie Boe oe eo ew ewe BETS580
SS oP ae Ok GS) Aw ee oe BOORDLYT
4B ke ee wR . « 225-255
De ces haye os ae eo tes at ig ig! cat age ig DOH 280
Orie: AE SB See Pe ae a ae gS a a oes 0

The student must be reminded that the amount of gas which comes off
in this experiment with submerged plants is not an exact measure of the
assimilation.

318 ASSIMILATION.

838. The amount of carbonic acid unfavorable to assimilation.
Experiments made by Saussure? at the beginning of this cen-
tury proved beyond question that plants are not tolerant of an
atmosphere containing a large proyortion of carbonic acid. In
carbonic acid alone, or even in an atmosphere containing 66
per cent of this gas, vegetation was speedily destroyed. It was
shown, however, that if the plants were exposed to full light,
they could sustain 8 per cent of carbonic acid without injury.
Saussure thought that the presence of free oxygen is necessary
to the assimilative work of the leaf.

839. In 1849, Daubeny ? carried on an extensive serics of re-
searches, chiefly upon plants allied to the dominant vegetation
of the Carboniferous period, namely, ferns and their allies, from
which it appeared that even for these plants an amount of car-
bonic acid above 10 per cent is injurious. Five species were
placed in a receptacle containing about 46 liters of air, and to
this air was added one per cent of carbonic acid, and also one
per cent daily thereafter, until the amount present reached 20
per cent. This proportion was kept for twenty days, small
amounts being added, as occasion required, to make up for loss
by leakage. On the thirteenth day a sensible impairment of
the plants was noticed; and at the end of thirty days all of
them had been more or less damaged, most having lost their
fronds.

840. Boussingault,? in 1864, conducted a series of experi-
ments in order to ascertain whether the presence of free oxygen
in an ‘atmosphere containing carbonic acid is necessary to the
work of assimilation. The results of his researches are given
as follows : —

(1) Leaves exposed to sunlight, in pure carbonic acid, do not
decompose this gas, or if at all, very slowly.

(2) Leaves exposed to sunlight in an atmosphere containing
a mixture of common air and carbonic acid decompose the
latter yas rapidly ; but the oxygen of the air has no part in this
operation, since,

(3) Leaves exposed to sunlight rapidly decompose carbonic
acid gas when this gas is mixed with nitrogen, hydrogen, car-
bonie oxide, or carburetted, hydrogen.

1 Saussure: Recherches chimiques sur la végétation (Paris, 1804), p. 29.
An earlier experiment was made by Percival.

2 Report of British Association, 1849, p. 56; and 1850, p. 15S.

% Agronomie, iv., 1868, p. 301.

RELATIONS OF CARBONIC ACID TO ASSIMILATION. 3819

841. The amount of carbonic acid most favorable to assimilation.
The results of the most exhaustive study of the amount of car-
bonie acid most favorable to assimilation have been given by
their recorder as follows : —

(1) Increase in the amount of carbonic acid in the air, up to
a certain limit (the optimum), favors the evolution of oxygen
by plants ; beyond this it is more or less injurious.

(2) The optimum of carbonic acid is different for different
plants: for Glyceria spectabilis on clear days it is between 8
and 10 per cent; for Typha latifolia, between 5 and 7 per cent;
for Oleander, somewhat less.

(3) Any given increase in the amount of carbonic acid below
the optimum favors the evolution of oxygen far more than a
similar increase above the optimum hinders it.

(4) The stronger the intensity of the light the more the evolu-
tion of oxygen is favored hy increase in the amount of carbonic
acid up to the optimum; and when this limit is passed the
evolution is checked so much the less.

(5) From (+) it follows that the influence of the intensity of
the light on the evolution of oxygen is greater in proportion to
the amount of carbonic acid in the air.

842. Ratio of the oxygen evolved by plants to the carbonic acid
decomposed. The volume of oxygen evolved by plants during
assimilation proper is very nearly that of the carbonic acid
decomposed.

Numerous experiments by Boussingault exhibit this relation
in a very striking manner. In forty-one experiments the volume
of carbonic acid was to that of the oxygen set free as 100: 98.7.

1 Saussure (Recherches chimiques sur la végétation, 1804, pp. 40, 59) is
regarded as the first to indicate this. He arrived at this conclusion by experi-
menting upon a number of plants under different conditions. His first recorded
experiment consisted in surrounding seven plants of Vinca (Periwinkle) with
an atmosphere containing a known quantity of carbonic acid gas. The plants
were exposed to sunlight from five to eleven o’clock in the morning for six
days, after which the air in the bell-jar was examined.

Air in the jar Air in the jar

before the experiment. after the experiment.
Nitrogen . . . . . 4199 cubic cent. . . 4338 cubic cent.
Oxygen . . a: ot “LLEG < - . 1408 sé
Carbonie acid. . 481 “e a te 0 es
Total volume - 5746 ss . . 5746 £¢

Saussure’s conclusion is that plants, in decomposing carbonic acid, assimi-
late a part of the oxygen gas therein contained, and, further, that the amount
of carbon retained by the plant bears a definite relation to the amount of CO,
taken up by it.

3820 ASSIMILATION.

The following table by Boussingault? is very instructive, as it
shows the relation of volume between the amount of carbonic
acid consumed and the oxygen evolved in assimilation; and
also the decomposing power of various kinds of plants under
different conditions.?

; 1 | Time of | Surface | CO, decomposed | Constitu-
Plants. CO, disap- eles éxpusare . of per Ealiate deci tion of at-
pearing. | ing. to light.) leaves, | meter each hour.| mosphere.
c.c. c. ¢. hb. m. cm. sq. cc.
Cherry laurel 52 5.9 40 134 8 co, 1
se 23.2 22.9 40 124 4.7 CO, + air.
“ 4. 45 | 40 90 10 CO,
“ 19.6 199 40 90 5.5 CO, + air.
Pine 13.0 13.0 70 204 9 CO,
“ 18.1 17.8 70 204 1.3 CO, + air.
Oak 4.9 4.0 40 224 5 co,
“ 25, 24.7 | 40 204 2.8 CO, + air.
Holly 5.1 4.9 5 30 52 1.8 ae
Mistletoe 9.9 99 5 0 100 2. ee

843. The gas emitted during the process of assimilation proper
is not pure oxygen. Both Daubeny ® and Draper‘ found varia-
ble amounts of nitrogen in all the cases examined by them.

844. What are the products of assimilation proper? It has
now been shown under what conditions the green tissues of a
plant decompose carbonic acid and evolve oxygen. As the
chief result of this decomposition and its associated processes,
there is formed within the cells which contain chlorophyll a carbo-
hydrate of some kind. This carbohydrate contains the same
eleinents as the carbonic acid and the water from which it was
produced, but it contains less oxygen than the total amount
found in those substances taken together. Hence the process
of assiinilation is essentially one of reduction. ‘There is, how-
ever, no substantial agreement as to the nature or constitution
of the primary carbohydrate formed by it.

The difficulty which attends the investigation of assimilation

1 Agronomie, iv., 1868, p. 286.

2 A well-known relation of volume between oxygen and carbonic acid may
here be pointed out ; namely, that ‘free oxygen occupies the same bulk as the
carbonie acid produced by uniting it with carvon.”

3 Philosophical Transactions, 1836.

* “Tn every instance which I have examined, the gas evolved from leaves
is not pure oxygen, but a variable mixture of oxygen and nitrogen. This result
is of uniform occurrence” (Chemistry of Plants, 1844, p. 182).

5 For an account of the transient evolution of oxygen under exceptional
circumstances where carbonic acid is not present, see Miiller’s Handbuch der
Botanik, 1880.

THE FIRST VISIBLE PRODUCT. 821

is apparent at a glance. The raw materials, the apparatus,
and the ultimate products of manufacture are known; but the
intermediate processes by which chlorophyll granules under the
influence of certain rays of light can cause the dissociation of
carbon from the oxygen with which it is combined in carbonic
acid, and bring about the synthesis of an organic substance from
materials wholly inorganic, are not at present known.

845. The wide field which the synthesis of organic from inor-
ganic matter opens to conjecture has not been left unoccupied.
It is generally admitted that in assimilation there is first formed
some ternary substance, namely, one which contains the three
elements, carbon, hydrogen, and oxygen; and further, that
this contains less oxygen than the two inorganic matters, car-
bonic acid and water, from which it is produced, taken to-
gether. Exactly what the ternary substance is, or low the
dissociation or reduction is carried on in the chlorophyll granule,
is still left in doubt.

846. Starch (C,H,,0,) is the first visible product of assimila-
tion, as was first pointed out by Sachs in 1862.1 Although
Sachs appears to have held at one time that it is the first pro-
duct, his later expressions are more guarded, and simply state
the fact universally admitted, namely, that starch is the first
product which the microscope can detect. When a seedling has
been kept for a time in a dimly lighted room, its cotyledons and
other leaves grow pale or etiolated, and if they are examined
for starch, no trace of it will be found. But upon a very short
exposure of the plant to the direct rays of the sun, provided the
other conditions are favorable, a certain amount of starch will
appear in the chlorophyll granules of the cells at the margin of
the leaves. If the plant is again withdrawn from the light, its
scanty store of starch is speedily consumed, but on renewed in-
solation the loss is made good; this process can be repeated
many times. From the constant appearance of starch in the
chlorophyll granules under the above circumstances it has been
generally recognized as the first visible product of assimilation
proper. But it has obviously such a complex molecular struc-
ture that chemists are unwilling to believe that its formation in
the plant is not preceded by the production of some simpler
substance. Furthermore, there are a few cases in which oil
replaces starch as the first visible product, thus indicating that
there may be some earlier product possibly common to both.

1 Botanische Zeitung, 1862 ; Flora, 1862.
21

822 ASSIMILATION.

847. Glucose. It is held by some that this product is glucose
(C,H,,0,) or some substance having the same atomic propor-
tions of these elements. Early and not well-defined views in
regard to glucose may be replaced by the following statement of
a theory widely taught.

848. Formic aldehyde hypothesis. According to Gautier,
chlorophyll exists in two conditions, white chlorophyll, rich in
hydrogen, and green chlorophyll, poorer in this element. By his
hypothesis the yellow ray absorbed by the assimilating tissues
furnishes a certain amount of energy which is partially con-
verted into heat, and promotes evaporation of water (transpira-
tion) ; and at the same time it permits the chlorophyll granule to
decompose the water with which the protoplasmic mass is satu-
rated. In the presence of CO, and H,O the reducing process
‘gives rise to formic acid (CH,O,), which in its turn is reduced to
formic (or methylic) aldehyde, CH,O. The latter has the same
atomic proportions as glucose (C,H,,0,).

849. Whether, in assimilation, the ternary substance be for-
mic aldehyde, or glucose, or starch, it is certainly a substance
capable of undergoing further oxidation, and hence, chemically
speaking, an unsaturated compound. When this unsaturated
compound is osxidized,? a definite amount of energy of motion
is set free, and this is manifested to us under one of its many
phases, namely: (1) movements of the whole plant, as in some
of the lowest organisms; (2) movements of liquids within the
plant, as in the transfer of matter to points of consumption ;
(3) heat; (4) electrical disturbances, and all the proper vital
activities correlated with these. The energy of motion in solar
radiance is treasured for a time in the ternary and derivative
products, thence to be released as occasion requires.

850. It is proper to refer at this point to a novel view in
regard to the product of assimilation which has received much
adverse criticism ; namely, that of Pringsheim.? Attention has
already been called to the interesting observations by this bota-
nist on the constitution of chlorophyll granules. In prosecuting
his investigations he became convinced that the peculiar colored
substance which is extruded from the granules under the influ-
ence of certain agents is a product of assimilation. To this
product he gave the name hypochlorin. According to him, when

1 La Chimie des Plantes. Revue Scientifique, Feb. 10, 1877, p. 767.
2 Compare Claude Bernard, Lecons sur les Phénoménes de la Vie, 1878.
3 Jahrb., xii., 1879-1881, p. 288.

EARLY HISTORY. 3823

any active cells containing chlorophyll granules are subjected
to conditions favorable to assimilation, hypochlorin is formed
in considerable amount; but when the conditions for assimi-
lation are not present, only traces of it are produced. Prings-
heim used an entirely novel method of experimenting ; namely,
that of subjecting the chlorophyll granules to the action of
intense light from which the heat rays had been extracted as
perfectly as possible; and under these conditions he failed to
detect any hypochlorin, but observed a marked increase in the
amount of CO, given off as in ordinary respiration (see Chapter
XI.). Hence he arrived at the conclusion that assimilation
proper is the characteristic office of chlorophyll granules solely
on account of their pigment, which tempers the light reaching
them. According to him, the pigment, by its absorption of the
so-called chemical rays, serves as a regulatory screen gov-
erning the amount of light, and so controlling the amount of
respiration and assimilation proper.

851. Outline of the early history of assimilation. The follow-
ing extracts from the works of early experimenters upon the
relations of green leaves to the atinosphere show the manner in
which the problem of assimilation was first attacked.

852. Priestley! discovered in 1771% that air in which candles
can no longer burn, and which is irrespirable, can be restored to
its original condition by the presence in it, for a time, of vig-
orous plants. The account below is given in, his own words:

‘¢ Finding that candles would burn very well in air in which plants
had grown a long time, and having had some reason to think, that
there was something attending vegetation which restored air that had
been injured by respiration, I thought it was possible that the same

1 Experiments and Observations on Different Kinds of Air (3d edition,
1781), p. 51.

2 In 1754 Bonnet published his observations upon the behavior of leaves
in water. It is well known that when green leaves are immersed in water and
exposed to sunlight for a time, bubbles of air appear on their surface. Bonnet
believed that the leaves drew common air from the water and this swelled into
conspicuous bubbles under the heat of the sun. He was confirmed in this
belief upon ascertaining that bubbles did not appear on green leaves ex-
posed in water which has been boiled to expel the air (Recherches sur l’usage
des Feuilles dans les Plantes, p. 26). If we consider the state of chemical
science at the time of Bonnet’s researches, his error is in no wise surprising.
It is now known that the bubbles which Bonnet took to be air are nearly
pure oxygen which escapes as a by-product of assimilation. Bnt from water
which has been boiled, all the carbonic acid essential to assimilation has been

expelled.

324 ASSIMILATION.

process might also restore the air that had been injured by the burning
of candles. ‘

‘* Accordingly on the 17th of August, 1771, I put a sprig of mint into
a quantity of air, in which a wax candle had burned out, and found
that, on the 27th of the same month, another candle burned perfectly
well in it. This experiment I repeated, without the least variation in
the event, not less than eight or teu times in the remainder of the
summer.

‘« Several times I divided the quantity of air in which the candle
had burned out, into two parts, aud putting the plant into one of them,
left the other in the same exposure, contained also in a glass vessel
immersed in water, but without any plant; and never failed to find
that a candle would burn in the former, but not in the latter. I gen-
erally found that five or six days were sufficient to restore this air, when
the plant was in its vigour; whereas I have kept this kind of air in glass
vessels immersed in water many months without being able to perceive
that the least alteration had been made in it.”

853. Ingenhousz in 1779 showed that light is necessary to
assimilation. He proved experimentally that the purification
of air does not go on in darkness, but that light is essential.
His statements are here given : —

‘ Plants not only have a faculty to correct bad air in six or ten days,
by growing in it, as the experiments of Dr. Priestley indicate, but they
perform this important office in a complete manner in a few hours.
This wonderful operation is by no means owing to the vegetation of
the plant, but to the influence of the light of the sun upon the plant.
. . « This operation of plants diminishes towards the close of the day,
and ceases entirely at sunset, except in a few plants which continue
this duty somewhat longer than others. This office is not performed
by the whole plant, but only by the leaves and the green stalks that
support them. Acrid, ill-scented, and even the most poisonous plants
perform this office in common with the mildest and the most salutary.” 2

1 Priestley thought that this effect upon the air is due to the growth of the
plant, an idea which will be shown in Chapter XII. to be wholly erroneous. On
pages 50 and 52 of the volume quoted above are the following statements :
“One might have imagined that since common air is necessary to vegetable, as
well as to animal life, both plants and animals had affected it in the same man-
ner; and I own | had that expectation when I first put a sprig of mint into a
glass jar standing inverted in a vessel of water: but when it had continued
growing there for some months I found that the air would neither extinguish a
candle nor was it at all inconvenient to a mouse which I put into it... . This
restoration of the air, I found, depended upon the vegetating state of the plant ;
for though I kept a great number of the fresh leaves of mint in a small quan-
tity of air in which candles had burned out, and changed them frequently, for
a long space of time, I could perceive no melioration in the state of the air.”

2 Experiments upon Vegetables, discovering their great Power of purifying
the Comiwon Air in the Sun-shine, 1779, p. xxxiii.

APPROPRIATION OF NITROGEN. 825

854. Senebier! first demonstrated that plants obtain all their
carbon from carbonic acid gas.

855. That definite quantitative relations exist between the
amounts of carbonic acid decomposed, carbon retained, and oxy-
gen evolved by the plant, was first pointed out by Saussure.?

APPROPRIATION OF NITROGEN.

856. It has been shown that all Jand and many water plants
contain a variable amount of air in their tissues, chiefly in the
intercellular spaces and older modified cells (tracheids, trachee,
etc.). When there is an active interchange of gases by any
plant, a portion of the nitrogen contained in its included air is
very likely to be eliminated. A trace of nitrogen is so generally
found with the oxygen evolved during assimilation proper, that
this has been regarded by some as a constant accompaniment
of the assimilative process.

857. Amount of nitrogen in the plant. Besides the free nitro-
gen which constitutes a part of the included air of the plant,
there is a certain amount of combined nitrogen always present
in active cells as an essential component of their living matter.
The protoplasmic matters in plants contain about 15 per cent of
nitrogen in combination. For all practical purposes they may
be regarded as having chemically a common albuminous? basis
(roughly comparable to the white of egg), with which (as has

1 Mémoires Physico-chymiques, 1782.

Many of Senebier’s observations are almost identical with those of Ingen-
housz (as given in his ‘‘ Nutrition of Plants’’), and it has been thought by
some that the priority of the above discovery belongs rightfully to the latter.
It is to be remembered that at the date at which both of these experimenters
were working, chemists were just beginning to acquire, through the studies
of Lavoisier, clear notions in regard to the important part which oxygen
plays, and that in the early part of this transition period an obscure nomen-
clature renders it difficult to apportion to each of these observers his proper
share of credit.

2 Recherches chimiques sur la végétation, 1804.

Some of the relations of light to the process of decomposition of carbonic
acid by green parts of plants were first indicated by Daubeny, and further ex-
amined by Draper. The subsequent history of assimilation, to which Sachs,
Pfeffer, Engelmann, and many others have contributed, has been referred to
in the text snd in citations in the notes.

8 Attention may again be called to the vatious expressions employed to
designate the compounds in the plant which resemble albumin, and which
have been collectively termed albuminoids. Authors have made a distinction

326 ASSIMILATION,

been seen on page 197) there is always intermingled an incon-
stant amount of carbohydrates, or proper food-materials, ete.
At different stages in the life of a cell its protoplasmic matters
may pass through considerable changes of form and structure,
as indicated in an examination of a ripening seed; but under all
these varying conditions nitrogen in combination is never absent
from the living substance of the plant.

858. For the formation of new protoplasmic matters in the
plant, supplies of nitrogen in an available form must be fur-
nished ; for healthful growth, these supplies must be adequate
in amount.

859. Dissolved albuminous matters of various kinds are met
with in the sap of some cells. This in many cases appears to
be, as will be shown later, a form in which their transport from
one part of the plant to another is secured. A small number of
these albuminous substances have been shown to be ferments,
which play a very important part in the nutrition of the plant.

860. Although by far the greater part of the combined nitro-
gen of the plant exists in one or more of the combinations men-
tioned in Chapter XI., there is often to be detected a small and
variable amount as a nitrate’ (generally potassic), and even as
a salt of ammonia.

between certain groups of these bodies as they are represented in the animal
kingdom, dividing them into (1) albuminons matters and (2) their derivatives
or albuminoids (see Gorup-Besanez, Lehrbuch der Chemie, iii., 1874, p. 115).
Although the latter term, without the restriction here noted, is in common
use in vegetable physiology to designate these bodies, an objection can justly
be urged against its employment, on account of the more common use in
botany of the word a/bumen with an entirely different signification (see Volume
I. p. 14).

CF 1838 Mulder published the theory that all these bodies are practically
derivatives from one substance, termed by him proteine (from mpwredw, to be
first) ; but it was soon shown that this theory was erroneous, and it has been
generally abandoned. The term introduced by Mulder to designate the hypo-
thetical compound common to all these bodies has, however, been since em-
ployed to conveniently denote the whole class. In using the convenient term
protein bodies, or proteids, to designate the members of this group, it must not
be understood that the abandoned theory of Mulder is taken into account at all.

1 For the detection of nitrates the following test may be employed: Toa
drop of the sap under examination add a drop of a solution of brucine, mix,
and then add a few drops of concentrated sulphuric acid, when, if a nitrate is
present, a red color will appear. Sprengel’s reaction may also be used : One
part of phenol is dissolved in four parts of concentrated sulphuric acid, and two
parts of water are added. Ifa drop of this solution is added to a solid nitrate,
a reddish color is produced. On adding strong ammonia, the color turns green
and afterwards yellow.

SOURCES OF NITROGEN FOR THE PLANT. 327

861. There can be found in a large number of plants a small
amount of certain matters termed alkaloids, which contain a defi-
nite percentage of nitrogen. Such are morphia in the poppy,
guinia in Peruvian bark, caffeine in coffee, etc. (see 961).

862. In most analyses the combined nitrogen of the plant is
usually rendered as ‘‘albuminoid.” The percentages in a few
cases are here given :'—

Red clover, full blossom. . . 2. 1... 7 3.7
Sugar beets i Ge He SL AS ee we ek eSHtoe20
Carrot root Paar er ie ies Je) eer ke dN ae Se 1.5
Carrot leaves: Qo ove sn ee te Sp Gh ee a 3.2
Cabbage. . . ce Se a We 1.5
Winter-wheat 2. 5 4 @ © © © ee ww 13.0
Beats (eld) ge ee me OK 25.5
Apples . . . 63s el eS » 22 to .52

Of these amounts about 16 per cent may be roughly estimated
as the content of nitrogen. ‘Therefore in such a case as the
carrot root above mentioned, the total amount of nitrogen is
really very small (0.24 per cent) ; but the presence of this small
percentage is absolutely essential to the life as well as to the
health of the plant.

863. Reserving for a later chapter all consideration of the
numerous chemical transformations which nitrogenous matters
may undergo in the plant, it is necessary to ask now, (1) whence
can the plant obtain adequate supplies of available nitrogen, and
(2) how can the plant appropriate, or, to use an equivalent term,
assimilate them.

864. Sources of nitrogen for the plant. It must first be shown
whence nitrogen is zo¢ supplied. The free nitrogen of the at-
mosphere does not appear to be directly available for plants.
Although most of the higher plants possess an aerating system
(see p. 300), through which atmospheric air can easily enter and
traverse the plant and be brought intu contact with the tissues,
the nitrogen which forms so large a part of the atmosphere is
not utilized. This is the interpretation of experiments in cul-
ture in which every kind of combined nitrogen is carefully ex-
cluded from the plants while they have, at the same time the
free nitrogen of the atmosphere in an unlimited supply.

865. The earliest? systematic investigations relative to the

1 For other cases the student should consult the tables in the Appendix to
Johnson’s ‘‘ How Crops Grow,” 1868, pp. 385-392.

2 The following citations refer to earlier observations, none of which, how-
ever, can be considered as having fixed any important points relative to the use
of atmospheric nitrogen by plants ; —

328 ASSIMILATION.

above subject were made by Boussingault in 1837,’ who em-
ployed the following method: In calcined soil, supplied with dis-
tilled water, and having free access of air, clover was cultivated
for two and for three months, and at the end of that time it was
found that there was a very slight gain in nitrogen over the
amount which had been present in the seed sown. In two
parallel experiments with wheat no gain was observed. One
year later, peas, clover, and oats were experimented on; both
the peas and clover gained a little nitrogen, but there was no
gain whatever in the case of the oats. Boussingault’s conclu-
sions from this series have heen stated as follows: Under several
conditions certain plants seemed adapted to take up the nitrogen
in the atmosphere, but it is still a question under what circum-
stances and in what state the nitrogen is fixed in the plants.

866. It was not, however, until 1851 that the subject received
any further attention from Boussingault. In that and the two
subsequent years his experiments were conducted with certain
precautions, by which the plants were confined in limited vol-
umes of air; and in no case was an unequivocal gain in nitrogen
to be detected. In 1854 he placed plants in a suitable recep-
tacle where they could be supplied with a current of air washed
to free it from all traces of combined nitrogen. The atmosphere
within the receptacle was furnished with from two to three
per cent of carbonic acid. In all of the experiments, part of
which were upon leguminous plants, there was a slight loss of
nitrogen.

867. During the progress of the experiments now alluded to
others were conducted in the following manner: Plants were
placed in a case from which nearly all dust could be excluded,
but which would allow of a free circulation of the external air;
aud under these circumstances there was the very slight gain in
nitrogen equal to about one twelfth of that contained in the seed
sown. Boussingault attributed this almost inappreciable gain

Priestley : Experiments and Observations on Different Kinds of Airs, iii.,
1772.

Saussure : Recherches chimiques sur la végétation, 1804, p. 205. In this
will be found a short account of the results of the previous observers and also
of Saussure’s own conclusions, which are, — that plants do not appropriate any
appreciable amount of nitrogen furnished to them as it exists in the atmosphere
in the free state.

1 For a short but excellent abstract in English of Boussingault’s researches,
referred to in the text, the student may consult Philosophical Transactions of
the Royal Society for 1861, p. 447. The original communications are in
Annales de Chimie et de Physique, sér. 2, tomes lxvii. and Ixix., 1838.

VILLE’S EXPERIMENTS. 829

to the aamonia in the atmosphere, and also to organic matters
in small amount which may have entered the case in the form of
very fine dust; but, taking into consideration all the conditions
of the experiment, he was not inclined to the belief that any
nitrogen had been received by the plants from the free nitrogen
of the atmosphere.

868. In 1855 and 1858 the same chemist experimented upon
certain plants which were supplied with a known amount of com-
bined nitrogen in some available form. The results of his ex-
periments have been formulated as follows: (1) There was no
appropriation of free nitrogen; (2) Theré was a slight loss of
the nitrogen which had been supplied to the plant; (8) The
amount of assimilation of carbon bore a close relation to the
amount of nitrogen taken up by the plant.

869. From 1849 to 1854 Georges Ville, of Paris, conducted
experiments which were interpreted as showing that plants can
take from the nitrogen of the atmosphere a certain part of that
which they require. In the autumn of 1854 he carried on a
series of researches at the Jardin des Plantes, under the super-
vision of a committee appointed by the French Academy. To-
wards the close of the work an element of error crept into it
which could not then be eliminated; but as to the result of
the investigation the committee reported,!— that the experi-
ment made at the Museum d’Histoire Naturelle by M. Ville
is consistent with the conclusions which he has drawn from
his previous labors.

870. In 1861 Lawes, Gilbert, and Pugh,? of England, pub-

1 The report by Chevreul will be found in Comptes Rendus, xli. p. 757.
Results so directly in conflict as those of the two experimenters referred to in
the text led others to investigate this subject, and in 1857-1859 an exhaustive
series of investigations was carried on at Rothamsted, England, by Lawes,
Gilbert, and Pugh.

Méne, in 1851, concluded from his experiments that plants do not appro-
priate the tree nitrogen of the air.

Roy interpreted the results of his own experiments as showing that free
nitrogen dissolved in water can be taken up by plants.

Luva (1856) suggested that the air surrounding plants may be ozonized, and
thus the nitrogen in it converted into nitric acid and made available for the
plants.

Harting (1855) concluded that the free nitrogen of the air is not proved to
serve directly for the nutrition of the plant.

? Philosophical Transactions, 1861, p. 481. For an excellent description
and drawing of the complicated apparatus employed in this capital investiga-
tion the student may consult Johnson’s ‘‘ How Crops Feed,” p. 30.

330 ASSIMILATION.

lished the results of a series of experiments upon the subject of
the appropriation of nitrogen by plants. These experiments were
designed to settle the disputed question. Every conceivable pre-
caution was taken to avoid any error, and the plants were grown
under conditions as little unlike their ordinary surroundings as
possible. Under these conditions to insure healthy growth, they
were deprived of all access to nitrogen except as it existed in
the free state in the atmosphere or dissolved in the water sup-
plied to them. It was found that no plants appeared to make
use of the free nitrogen of the atmosphere or of the nitrogen
dissolved in water supplied to their roots. But in certain cases,
especially of leguminous plants cultivated in the open air, there
is an apparent gain in the amount of nitrogenous products in
the plant over and above that which is directly attributable to
the combined nitrogen furnished to it.

1 The following extracts from the paper by Lawes, Gilbert, and Pugh will
convey a clear idea of the cautious manner in which their important results
are reported : —

“The results obtained with Graminacee in 1858 . . . point without excep-
tion to the fact that under the circumstances of growth to which the plants were
subjected, no assimilation of free uitrogen has taken place. The regular pro-
cess of evll-formation has gone on ; carbonic acid has been decomposed, and
carbon and the elements of water have been transformed into cellulose ; the
plants have drawn the nitrogenous compounds from the older cells to perform
the mysterious office of the formation of new cells ; those parts have been de-
veloped which required the smallest amount of nitrogen, and all the stages of
growth have been passed through to the formation of glumes, pales, and awns
for the seed. In fact, the plants have performed all the functions that it is
possible for a plant to perform when deprived of a sufficient supply of com-
bined nitrogen. They have gone on thus increasing their organic constituents
with one constant amount of combined nitrogen until the percentage of that
element in the vegetable matter is far below the ordinary amount of it, — that
is, until the composition indicates that further development had ceased for
want of a supply of available nitrogen. Throughout all these phases, water
saturated with free nitrogen has been passing through the plant ; nitrogen dis-
solved in the fluid of the cells has constantly been in the most intimate contact
with the contents of the cells and with the cell-walls” (p. 528).

Of leguminous plants the investigators say, ‘‘In those cases in which we
have succeeded in getting leguminous plants to grow pretty healthily for a
considerable length of time, the results, so far as they go, confirm those ob-
tained with Graminacee, not showing in their case, any more than with the
latter, an assimilation of free nitrogen” (p. 526).

Further, they say, ‘‘ From the results of various investigations, as well as
from other considerations, we think it may be concluded that under the cir-
cumstances of our experiments, on the question of the assimilation of free
nitrogen by plants, there would not be any supply to them of an unaccounted
quantity of combined nitrogen due either to the formation of oxygen com-

NITROGEN COMPOUNDS IN RAIN-WATER. 331

871. Nitrogen compounds in the atmosphere. The atmosphere
contains minute amounts! of combined nitrogen in the form of
ammonia, nitric acid, and nitrous acid. ‘The ammonia is be-
lieved to exist (except where from local causes there is an escape
of free ammonia from some source) combined with either carbonic
or nitric acid.

872. Nitrogen in rain-water. The nitrogen compounds are
more or less perfectly removable from the air by rain, and in
solution can be made available to plants through the soil. It
is now necessary to examine the results of analyses of rain-
water in order to ascertain the amount of nitrogen contained
in it.

The following data are taken from the careful experiments
at Rothamsted, under the direction of Lawes, Gilbert, and War-
ington. The nitrogen existing as nitric acid and ammonia in
the rainfall of one year is not far from 3.3 pounds per acre. The
proportion of this calculated as ammonia is between 2.3 and 2.6
pounds per acre, the residue being given as nitric acid. Be-
sides the foregoing substances, there is also a small amount of
nitrogenous organic matter in the air which appears in the
analyses of rain-water, and amounts, according to Frankland, to
-19 parts per million parts of water. Taking a somewhat lower
estimate than this, Lawes, Gilbert, and Warington give the
quantity of nitrogen in the form of organic matter annually

pounds of it under the influence of ozone, or to that of ammonia under the
influence of nascent hydrogen” (p. 540).

But, as shown by Lawes, Gilbert, and Pugh, as well as by many other ex-
perimenters, leguminous crops appropriate from some source considerably more
nitrogen than do grasses; for instance, under apparently similar circumstances
of supply of combined nitrogen.

For an excellent treatment of the whole matter of appropriation of nitrogen,
the student should consult memoirs by Atwater, ‘On the Acquisition of Atmos-
pheric Nitrogen by Plants” (American Chem. Journ., vol. vi., 1885, no. 6).

1 The following figures serve simply to indicate the wide range in results
obtained by different observers who have investigated the amount of ammonia
in the atmosphere. The data are from Proceedings of Am. Assoc. for Ad-
vancement of Science, 1857, p. 152.

Amount of ammonia in one million
cubic meters atmosphere.

Fresenius . Wiesbaden (during the day) ee a ow T2727 or

Observer. Station.

es é s (atnight). . . . . . . 219.47 *
Kemp . . Ireland . . . . 1... 1. . 4423.00 *
Ville . . Paris . . BS ey Gav Ge av see, SRFESOL MS

Horsford . Boston (in July) 2 We woe ew ae OL0570°8

332 ASSIMILATION.

contributed in the rain as 1.08 pounds per acre. ‘‘ We may
probably take 4.5 pounds per acre as the best estimate we can
at present give of the total combined nitrogen annually supplied
in the Rothamsted rainfall. This is only about two thirds as
much as the earlier results indicated as due to ammonia and
nitric acid alone. . . . In addition to the combined nitrogen
carried down from the atmosphere in rain, we have to consider
any gain to the soil or to the crop by direct absorption of am-
monia or nitric acid from the air. As far as any gain from the
atmosphere to the plant itself is concerned, there is very little
direct experimental evidence on the point, but such as is ayail-
able would lead to the conclusion that its amount is practically
immaterial. As to the amount of gain by absorption by the
soil, there is unfortunately no direct or satisfactory evidence
at command. From such evidence as does exist, we are
disposed to conclude that with some soils the amount will
probably be greater and with others less than that supplied by
the rainfall.” ?

873. Direct absorption of ammonia by leaves. Under certain
circumstances ammonia can be absorbed directly by leaves. This
will be further adverted to under ‘‘ Appropriation of Organic
Matters.”

874. How the nitrogen compounds of the atmosphere are formed.
It is a familiar fact that under certain circumstances the free nitro-
gen of the atmosphere can be made to unite with oxygen for the
production of nitric acid ; for instance, by the passage of a spark
of electricity through a confined atmosphere a small amount of
combined nitric acid may be formed. The bearing of this fact
upen the existence of nitrogen compounds in the atmosphere is
very obvious. Schilcesing,? in an interesting study of the nitro-
gen compounds of the air and soil, attributes to the atmosphere
a very important office in forming and distributing nitrogen com-
pounds. According to him, the nitric acid contained in rain-
waters on escaping from the soil, where it is only lightly held,
finds its way to the sea, where under various agencies (notably
that of vegetable organisms of the lowest grade) it becomes,
sooner or later, changed into ammonia. This readily escapes
into the air, and is carried in the atmospheric currents to all
parts of the world, becoming thereby available to land plants.

1 Journal Royal Agricultural Society, vol. xix., part 2, 1883.

2 Comptes Rendus, tome ]xxxi., 1875. he same idea has been more or less
treated by others.

AVAILABLE NITROGEN IN THE SOIL. 833

875. Available nitrogen in the soil. When animal matters rich
in nitrogen undergo rapid putrefaction,! they give rise to numer-
ous compounds, prominent among which are those of ammonia.
Under certain conditions, notably the presence (1) of free oxy-
gen in large amount, or (2) of an alkali, or an alkaline carbonate,
such animal matters are also slowly broken up, and nitrates are
formed. ‘The process by which various compounds of nitrogen
are converted into nitrates is termed nitrification.”

876. Vegetable matters which contain nitrogenous substance
in the usual amount may likewise undergo decomposition ; but
owing to the presence in such matters of a large proportion of
carbohydrates, for instance the cellulose of the cell-walls, the
process of decomposition is more complex than in animal matters
and its products more diverse. Some of the products are proba-
bly identical with those formed trom the decomposition of albu-
minous matters of animal origin; namely, ammonia,’ or ammonia
compounds, and nitrates; but the larger number of them are
compounds which are nearly or quite insoluble and bave been
thought to be inert. But experiments have shown that under
certain conditions these less available compounds of nitrogen

1 For a discussion of the various phases and conditions of decomposition the
student is referred to the third volume of this series, in which the different
forms of fermentation and putrefaction are to be treated. It is enough now to
note that these processes are essentially due to the presence and activity of
minute organisms, — the lowest fungi.

2 The student will find in Johnson’s ‘‘ How Crops Feed,” p. 289, an ex-
cellent account of this most important topie. He is referred also to Boussin-
gault’s ‘‘ Agronomie,” 1860, and various articles in Versuchs-Stationen.

8 The following data indicate the amounts of nitrogen in certain soils, as
determined by Boussingault (Agronomie, ii., 1861, pp. 14, 18). The reduc-
tions to pounds per acre are from Johnson’s “‘ How Crops Feed,” p. 276.

Nitrogen in organic

Ammonia. combination.

Source of the Soil.

per cent. | lbs per acre. | per cent. | lbs. per acre.

Liebfrauenberg (light garden soil) | 0.0020 100 259 12,970
Bechelbronn (wheat-field clay) 0.0009 45 .139 6,985
Argentan (rich pasture) 0.0060 300 513 25,650
Rio Cupari,S. A. (rich leaf-mould)| 0 0525 2,875 685 34,250

4 Experiments by Boussingault (Agronomie, i. 1860) can hardly be in-
terpreted in any other way. One reason for his results has been sought in the
fact that he employed only very small amounts of vegetable matter in his ad-
mixtures of soil; but all of his experiments are regarded as models of accuracy

3834 ASSIMILATION.

in the soil can be turned to a very important account by the
plant.

877. Nitrogen used by wild and cultivated plants. From the
sources described, wild plants obtain a sufficient supply of
available nitrogen. In some localities, notably in portions of
the tropics and along the rich alluvial deposits of rivers, the
stores of available nitrogen are so abundant that all vegetation
flourishes with great vigor, and even cultivated plants, which ap-
pear to be more exacting than wild plants in their demands for
nitrogen, can obtain an adequate supply. Further, it has been
abundantly shown by the long-continued experiments at Rotham-
sted, that the same soil, unenriched by additions of manures, can
yield even after twenty-five years eflough nitrogen for the needs
of fair or moderate crops.

878. In the ordinary cultivation of plants it is profitable
to augment in some way the supply of nitrogen in most soils.
Under some circumstances this augmentation can be accom-
plished to a certain extent by mere tillage or by the exposure
of fresh portions of soil to the action of the atmosphere. But
it is usually effected by the employment of natural or artificial
manures. The former consist of the excrementitious matters
of animals or of the waste products from plants. These ex-
crementitious matters represent a large part of what the ani-
mals have consumed, and must have come either directly
or indirectly from the vegetable kingdom; hence they only re-
store to the soil that which plants had at some time removed
therefrom.

In the preparation of artificial fertilizers an effort is made to.
provide for the plant the mineral and nitrogenous matters which
it requires. A large proportion of these fertilizers are composed

throughout, and can leave no doubt that, under the conditions of his trials,
there was practically no utilization of the soil nitrogen by the plants.

On the other hand, experiments by Wolff (Chemisch.-Pharmaceut. Central-
Blatt, 1852, p. 657), Johnson (Peat and its Uses, 1866, p. 79), and Storer
show that under certain conditions the plant can avail itself of the nitrogen
organically combined in the soil. The works of the above authors, which are
only a few of those bearing on this important matter, will place the student in
possession of the methods of experimenting.

Storer’s interesting commutication in the Bulletin of the Bussey Institu-
tion (vol. i,, 1874, p. 252), ‘‘ On the Importance as Plant-food of the Nitrogen
in Vegetable Mould,” gives not only an account of his experiments but also
a forcible presentation of the principal arguments in favor of the belief that
the “‘soil-nitrogen” (that is, the nitrogen in vegetable mould) is by no means
inert.

SYNTHESIS OF ALBUMINOUS MATTERS 835

of a certain amount of available calcic phosphate together with
a salt of potassa and some available nitrogenous matter.!

It has been shown (p. 248) that some plants require more of
one kind of food than others; and hence the attempt has been
often made to prepare exactly the special fertilizer which a given
crop may require.

879. Nitric acid and the nitrates. Experiments with water-
culture have shown that plants can derive all the combined nitro-
gen needed for their growth from nitric acid and the nitrates.
But it has also been clearly shown that there are striking differ-
ences in the capacity which plants possess for appropriating
nitrogen from these compounds. Even in the common agricul-
tural plants there are some differences in this respect.

880. A large number of nitrogen compounds, such as as-
paragin, urea, albumin, etc., have been employed in experiments
upon plants, but most of the results possess little interest. It
may be said, in general, that the so-called alkaloids (which con-
tain nitrogen) cannot be utilized even by the very plants from
which they were made.?

881. Synthesis of albuminous matters in the plant. <A distinc-
tion is made between the newly formed or first-formed albumi-
nous substances in the plant and those which have undergone
chemical changes in the organism, as for instance the changes
in germination. ‘Two views have been held respecting the place
where the formation of the new protein matters occurs in the

1 The following analyses, taken from the Report of the Connecticut Agri-
cultural Experiment Station for 1883, indicate the composition of a few such
substances : —

° cs of 2

gS | s2 | s3 Phosphoric acid. a

ws CL hed a

Oo os oo Pd

Ba Bo | 28 a

7 5 soluble. reverted.

Tobacco manure (No. 972). 1.20 | 2.90 1.21 7.52 2.08 4.35
“© (No. 965). 10 4.15 60 3.41 1 52 903
Forage crop “ (No. 976). 21 lt 2.91 6.48 aT. 4.06
Potato “Wo. 905). 2.59 .67 6.87 67 9.76

For an account of the commercial prices of the available nitrogen com-
pounds for 1883-1884, see Report of Connecticut Agricultural Experiment
Station, 1885.

2 For a short account of the bibliography of this subject the student should
consult Pfeffer’s Pllanzenphysiologie, i., 1881, p. 242.

336 ASSIMILATION.

higher plants; namely, (1) that in favor of the chlorophyll cells,
(2) that in favor of the conductive tissues of the petiole and
stem. So far as analogy drawn from the lower plants is con-
cerned, one of these views is as tenable as the other; for while
in a simple alga all the formation of new protein matters must
go on in a cell where there is chlorophyll or its equivalent, in
the case of a fungus, nourished as in the experiments of Pasteur
upon a simple ternary body and a nitrate, the process must of
necessity take place in cells where no chlorophyll is present.

882. Exact observations upon the subject of the formation of
albuminous matters in the plant are not abundant. Reference will
be made here chiefly to those by Emmerling, who carried on an
extended series of investigations with Vicia Faba. He examined
all parts of the plant with respect to the inorganic nitrogen com-
pounds furnished, and then sought for the protein compounds
resulting therefrom. Ilis results are interpreted as showing that
the nitric acid which is absorbed from the soil, and can be detected
in all parts of the roots and steins, disappears very rapidly in
the leaves and all parts which are actively growing, so that there
is found only a mere trace in them. According to him, it is in
green leaves that the transformation of nitrogenous matters takes
place. The first product of this transformation is not at present
certainly known ; but there is good reason to regard it as a mem-
ber of the group of carbamides.!_ Those parts of the plant which
are rapidly growing are much richer in amides than the older
and more fully developed portions. This fact is shown by
Kellner? to be true of pasture grass, in which the amides are
more abundant in the young than in the old parts.

APPROPRIATION OF SULPHUR.

883. The amount of sulphur which exists as an essential part
of the albuminous matters of the plant is quite small, being not
far from one per cent.®

884. As ulready shown (681), sulphur is taken into the
plant in the form of sulphates, chiefly calcic. The calcic sul-
phate * is probably decomposed by the oxalic acid produced by
the plant, and thus an insoluble calcic oxalate is formed; then

7 Versuchs-Stationen, xxiv., 1880, p. 113.

2 Centralbl. f. Agric.-Chem., 1879, p. 271.

3 Ranging, according to Ebermayer, from .4 to 1.8 per cent (Physiologische
Chemie der Pflanzen, 1882, p. 616).

4 Holzner: Flora, 1867. :

APPROPRIATION OF ORGANIC MATTERS. 3387

by a process of reduction the sulphur is set free to unite with the
albuminous matters already described.

The abundant occurrence, in conducting tissues of stems and
petioles, of calcic oxalate resulting from the changes described has
been held to indicate the probable seat of albuminous synthesis.!

885. The general statements which have now been made re-
specting the appropriation of carbon, nitrogen, and sulphur hold
good for all ordinary land and water plants. ‘There are a few
plants, however, concerning which they must be somewhat modi-
fied, and these are here for convenience treated of together;
as humus-plants, parasites, insectivorous plants, and epiphytes.
It inust be remembered that in all these apparently exceptional
cases the mechanism of nutrition is not radically different from
that which other plants possess at some period of their lives
or in some slight degree.

APPROPRIATION OF ORGANIC MATTERS.

886. Humus-plants,’ or Saprophytes. Among the higher plants
there are some (for example, Epipogium *) which derive all their

1 Sachs : Text-book, 2d Eng. ed., 1882, p. 711.

2 As a matter chiefly of historical interest, the ‘‘ humus theory ” must be
referred to. As stated in the words of Liebig, its author, it is briefly as
follows : —

‘‘ Woody fibre in a state of decay is the substance called humus... .
Humus acts in the same manner in a soil permeable to air as the air itself; it
is a continued source of carbonic acid, which it emits very slowly. An atmos-
phere of carbonic acid, formed at the expense of the oxygen of the air, sur-
rounds every particle of decaying humus. The cultivation of land by tilling
and loosening the soil, causes a free and unobstructed access of air. An atmos-
phere of carbonic acid is therefore contained in every fertile soil, and is the
first and most important food for the young plants which grow init... . The
roots perform the functions of the leaves from the first moment of their forma-
tion : they extract from the soil their proper nutriment, namely, the carbonic
acid generated by the humus. . . . When a plant is quite matured, and when
the organs, by which it obtains food from the atmosphere, are formed, the car-
bonic acid of the soil is no further required. . . . Humus does not nourish
plants by being assimilated in its unaltered state, but by presenting a slow
and lasting source of carbonic acid, which is absorbed by the roots” (Chem-
istry in its Application to Agriculture, American edition, 1842, pp. 65 et seq).

Tt has been shown by the investigations referred to in the text that plants
can be grown with vigor and carried to complete maturity without the supply
of carbonic acid to the roots, and hence the ‘‘ humus theory ” is emptied of all
its value; but, as will be shown later, the decaying vegetable matter in soils
has important functions.

3 Pfeffer’s Pflanzenphysiologie, i., 1881, p. 226.

22

338 ASSIMILATION.

nutriment from the decaying or decayed remains of other plants ;
while others, like Monotropa uniflora and the Orobanchacez, ob-
tain part of their food from living plants. ‘True parasites obtain
their nourishment from living organisms, whereas humus-plants,
or saprophytes, live upon the structures of dead ones. From the
decaying vegetable mould they procure all the ternary substances
needed for their own fabric, and also the nitrogenous substances
needed for their own protoplasmic matters. It is not known
exactly how saprophytes turn to account the comparatively inert
nitrogenous matters of vegetable mould, but the process is thought
to depend upon the action of a solvent, unorganized ferment,
somewhat similar to that which effects changes in the food within
reach of the embryo of the seed.

887. Parasites obtain a large part of their food from living
organisms. In some cases they
appear to be able thus to procure
all the food they require; but most
of them can be shown to elaborate,
by means of the small amount of
chlorophyll which they possess, a
small part of their food. The
haustoria, by means of which they
abstract from other plants the as-
similated matters, have been de-
scribed in 351. After the parasite
has fairly fastened itself upon the
host-plant, it acts with respect to
the tissues of the latter much as if
it were an offshoot of the host. It
appropriates the assimilated mnatters
as they are needed, and consumes
them in substantially the same way
that an embryo consumes the food stored in the endosperm.’

888. Insectivorous or carnivorous plants, as already explained
in Volume I. page 110, e¢ seg., are those which are provided with
some specialized apparatus for the utilization of animal matters.

1 For an interesting account of the more striking effects produced upon the
host-plant, the reader should consult Frank : Die Pflanzenkrankheiten, 1879.

The relations which exist between the ash-constituents of the parasite and
its host have been examined by Reinsch.

Fia. 152. Cuscuta, a parasite. The coiled embryo and seedling are shown in the

right-hand sketches; in the other sketch, the adult plant, with its flower-clusters, at-
tached to the living stem of another plant.

DROSERA ROTUNDIFOLIA. 3839

The structure and office of the prehensile and digestive appara-
tus are now to be illustrated by the following examples : —

889. Drosera rotundifolia, or round-leaved sundew, grows
abundantly in northern peat-bogs and in sand mixed with vege-
table mould, beth in the Old World and the New. The plant
has a few (4 to 12) leaves, arranged in a flat tuft at the base of
the flower-stalk, and narrowed at their bases into hairy petioles.
The most striking character of the leaves is the thick clothing
of peculiar hairs, otherwise known as tentacles or glunds, from
the tip of each of which exudes a drop of a clear viscid
liquid. These hairs are complicated
in structure. They contain all the
histological elements proper to the
leaf itself; for this reason it has been
thought by some that they should be
regarded as processes from the leaf
rather than as hairs. The marginal
tentacles are long, have purple stalks,
and are terminated by elongated pur-
ple glands ; those towards the middle
of the leaf are shorter, have greenish
stalks and ovoid glands. Each gland
consists of a double layer of polygo-
nal cells which surround a central
body composed of elongated cells
and a few tracheids. The proto-
plasmic lining of all the cells is transparent and thin, and the
cavity is filled with an homogeneous purple fluid. The tra-
cheids pass by insensible gradations into minute spiral ducts.

890. The mode of action in Drosera is as follows: When
a small object is placed on the middle glands, a sluggish move-
ment is soon detected in the marginal tentacles. If the object
is a fragment of animal matter, the motor impulse is commu-
nicated rapidly, and the marginal tentacles curve sharply over
upon the fragment, bringing the glands in contact with it. The
blade of the leaf also sometimes becomes curved, forming a shal-
low cup. Inorganic and such organic matters as are not acted
on by the secretion from the glans act more slowly in causing
movement of the tentacles than do soluble organic substances,
and no movement follows unless the object rests upon the
glands themselves, not merely on the secretion which covers

Fia. 153. Droseza rotundifolia. View of leaf from above. (Darwin.)

340 ASSIMILATION.

them. Darwin found that movement was caused by the contact
of a particle weighing only .0008 milligram (7420 of a grain).

When a tentacle has been excited by
contact with a solid particle, there is seen,
after some hours, a remarkable change in
its cells near the gland. ‘‘ Instead of be-
ing filled with homogeneous purple fluid,
they now contain variously shaped masses
of purple matter suspended in a colorless or
almost colorless fluid.”? ‘Tentacles which
have been thus acted on by contact of par-
ticles have a mottled appearance, and can
be picked out with ease from all the others.
The change of contents is termed by Darwin
aggregation. ‘The little masses of aggre-
gated matter are of the most diversified
shapes, often spherical or oval, sometimes much elongated, or
quite irregular with thread or necklace-like or club-formed pro-
jections. They consist of thick, apparently viscid matter, which
in the exterior tentacles is of a purplish, and in the sbort discal
tentacles of a greenish, color. These little masses incessantly
change their forms and positions, being never at rest. . . .

‘«Shortly after the purple fluid within the cells has become
ageregated, the little masses float about in a colorless or almost
colorless fluid; and the layer of white granular protoplasm which
flows along the walls can now be seen much more distinctly.
The stream flows at an irregular rate, up one wall and down the
opposite one, generally at a slower rate across the narrow ends
of the elongated cells, and so round and round. But the current
sometimes ceases. The movement is often in waves, and their
crests sometimes stretch almost across the whole width of the
cell and then sink down again. Small spheres of protoplasm,
apparently quite free, are often driven by the current round the
cells; and filaments attached to the central masses are swayed
to and fro, as if struggling to escape. Altogether, one of these
cells, with the ever-changing central masses and with the layer
of protoplasm flowing round the walls, presents a wonderful
scene of vital activity.” ?

1 Darwin: Insectivorous Plants, 1875, p. 39.
2 Darwin: Insectivorous Plants, pp. 40, 42.

Fria. 154. Drosera rotundifolia. Leaf with the tentacles on one side inflected over a
bit of meat placed on the disc. (Darwin.)

DROSERA ROTUNDIFOLIA. 841

The aggregation is caused by various nitrogenous organic
fluids and salts of ammonia; the most efficient agent for its pro-
duction being ammonic carbonate, .000482 milligram (qz7y55 of
a grain) being enough to cause aggregation in all the cells of a
tentacle. These figures show the extreme sensitiveness of the
tentacles and glands to slight external impressions.

891. ‘If the glands are excited either by the absorption of
nitrogenous matter or by mechanical irritation, their secretion
increases in quantity and becomes acid.” That it contains an
unorganized ferment admits of no question. The secretion after
excitation possesses the power of dissolving the albuminoids sub-
stantially as the gastric juice of animals does. When an insect
alights upon the leaf of Drosera, its violent struggles to escape
only wind more closely about it the threads of viscid matter
from the glands. Soon the tentacles close around it, and the
increased secretion of the digestive fluid brings about a true
digestion of the nitrogenous matter.

892. That the digested matters can be absorbed. appears from
numerous experiments. In these, after the disappearance of
albuminous matters impregnated with a salt of lithium, it was
possible with the spectroscope to detect the salt in the plant.
Parts of the leaves remote from the seat of digestion, being
dried, calcined, moistened with hydrochloric acid, and placed in
the colorless flame of a Bunsen burner, gave the characteristic
lithium line.

893. Does the plant gain any advantage by this absorption
of organic matter? Francis Darwin’s! experiments upon this
subject may be briefly stated as follows: —

Two sets of thrifty plants of Drosera were cultivated under
the same conditions, with the single exception of a provision of
animal food to the leaves of one set. At the conclusion of an
experiment extending through three months, the ratios between
the unfed and the fed plants were as follows : —

Unfed. Fed.
Weight of plants, exclusive of flower-stems . . . . 100 . 121.5
Number of flower-stems . . . . 2. - © « « + 100: 164.9
Total weight of flower-stems . . ie gy ee OO Fr BBO
Total number of capsules . . . . «ee eee 100 «1944
Average weight perseed . . wos ae « 100-2 15753
Total elendated number of seeds piisdlinesdd » « « » 100 2 241.5
Total calculated weight of seeds. . . . . « «© . 100 : 379.7

1 Journal of the Linnean Society, xvii., 1880, p. 17.
“‘Two hundred plants of Drosera rotundifolia were transplanted in June and
cultivated in soup:plates filled: with moss during the-rest of the summer.- Each

342 ASSIMILATION.

894. Dionwa muscipula, or Venus’s fly-trap, grows sparingly
in sandy soil near Wilmington, North Carolina, and in one or
two other localities along the Carolina coast. Its leaf’ consists of
two rather distinct parts, — the two-valved trap at the extremity,

and a petiole-like support. It is probable that the support is not
a true petiole, but a leaf-blade, while the trap is a special ap-
pendage developed upon the tip of the leaf-blade.

895. The spring-trap is made up of two symmetrical halves
meeting at a median hinge. The outer border of each half is

plate was divided into halves by a low wooden partition, one side being des-
tined to be fed with meat, while the plants in the opposite half were to be
starved. The plates were placed altogether under a gauze case, so that the
‘starved’ plants might be prevented from obtaining food by the capture of
insects. The method of feeding consisted in supplying each leaf (on the fed
sides of the six plates) with one or two small bits of roast meat, each weighing
about one-fiftieth of a grain. This operation was repeated every few days from
the beginning of July to the first days of September, when the final comparison
of the two sets of plants was made” (Nature, xvii., 1878, p. 223).
Fig. 155. A plant of Dionza muscipula, reduced in size.

Fia. 156. Three of the leaves of almost the natural size; one of them open, the
others closed. Probubly a fly is never caught by the teeth as here represented.

DIONZA MUSCIPULA. 845

fringed with stiff bristles so placed as to interlock when the trap
is shut. The upper face of cach half is somewhat convex when
the trap is open, and upon it there are three delicate hairs which
are exceedingly sensitive. Supposing the plant to be in health
and under favorable conditions, the lightest touch upon one of
the hairs upon the face of the trap will cause the valves to close
instantly, bringing their edges in apposition. A light touch in
the median line, that is, at the hinge, will produce the same
effect. The sensitive hairs each consist of several rows of elon-
gated cells so arranged as to form a conical filament resting on
a constricted base and attached by an articulation to a rounded
group of cells. ‘This structure enables the hairs to bend when
the trap is shut.

896. The digestive apparatus consists of minute reddish
short-stalked glands made up of a few polyhedral cells. These
do not secrete any fluid unless excited by the presence of food-
materials, when they secrete copiously a colorless, glairy, acid
liquid, containing an unorganized ferment similar to that produced
by the stomach of animals, if not identical with it. Scattered
among the secretory glands are numerous compound hairs formed
of eight divergent cells, which are generally orange or brown
in color. -

897. From experiments by Darwin and others it is clear that
dry albuminous solids do not excite the action of the glands, but
if moistened very slightly, they call the glands into activity.
Moreover, if the bit of meat or other albuminous matter be
placed on the valves in such a way as not to spring the trap, the
valves will soon slowly close without further touch. Agerega-
tion takes place in the cells of the glands in much the same way
as in Drosera.

898. When a small insect is caught by the springing of the
trap, it can escape after a time through the spaces left between
the bristles at the border; but if the insect is of moderate size,
its escape is impossible: the valves shut down more and more
tightly upon it, and digestion soon begins.

899. The opening of the valves after digestion takes place in
different times according to the vigor of the plant and nature
of the prey. After a mere touch by which the trap is sprung
without anything in it, the valves will again open of themselves
in a day or even less. When the trap is closed by a bit of meat,
the valves open in from three or four days to rather more than
a week; when it closes over a large insect, they remain shut for
a much longer time, even for a month.

344 ASSIMILATION.

900. Canby? states that he has known ‘‘ vigorous leaves to
devour their prey several times; but ordinarily twice, or quite
often once, was enough to render them unserviceable.” Mrs.
Treat ! observes that *‘ several leaves caught successively three
insects each, but most of them were not able to digest the third
fly, but died in the attempt. Five leaves, however, digested
each three flies and closed over the fourth, but died soon after
the fourth capture. Many leaves did not digest even one large
insect.”

901. The following experiments by Darwin illustrate the flow
of the secretion: ‘‘ A bit of albumin ,; of an inch square but
only 35 in thickness, and a piece of gelatin } inch long and 5
broad, were placed on a leaf which eight days afterwards was
cut open. The surface was bathed with slightly adhesive acid
secretion, and the glands were all in an aggregated condition.
Not a vestige of the albumin or gelatin was left. Similarly
sized pieces were placed, at the same time, on wet moss in the
same pot, so as to be subjected to nearly similar conditions ;
after eight days these were brown, decayed, and matted with
fibres of mould, but had not disappeared.” ?

902. That the digested matters are absorbed by the leaf has
been shown by the spectroscope, as in the case of Drosera; but
no experiments are yet on record as to the effect of this nutritive
matter on the plant.

The character of the movement by which the trap is sprung is
spoken of in the chapter on ‘*‘ Movements.” ®

903. Other insect-catching Droseracee. Drosera and Dionza
are members of the order Droseraces. Its four remaining
genera have also the power of capturing insects.

Aldrovanda bas been well called a miniature Dionea. Its
bilobed leaves float in water (the plant being destitute of roots).
Each leat’ is two-valved, something after the fashion of Dionsea,
but each valve is made up of two parts. One, near the hinge
in the median line, is provided with colorless glands; the
other, a sort of thin film outside, has no true glands. On
the inner part there are some extremely delicate hairs which

1 Cited by Darwin: Insectivorous Plants, 1875, p. 311.

2 Insectivorous Plants, p. 302.

3 Burdon Sanderson has investigated the electrical disturbance which takes
place when the trap of Dionea is sprung. For details and conclusions see the
following papers : Proceedings of the Royal Society, vol. xxi. p. 495, and Na-
ture, a., 1874, pp. 105, 127. But similar electrical disturbances are exhibited
when any fresh vegetable structure is sharply bent.

PINGUICULA. 345

have been shown to he sensitive, and on touching them the
valves close. By this plant minute water-insects and crusta-
ceans are captured (see Fig. 190).

Drosophyllum, a rare plant found in Portugal, catches insects
by a viscid secretion from minute mushroom-shaped glands.
The tentacles do not have the power of movement possessed
by those of Drosera. That its glands can secrete a digestive
fluid appears from Mr. Darwin’s experiments.

Roridula, found at the Cape of Good Hope, and Byblis, of
western Australia, closely resemble the viscid-haired Droseraceze,
which have been examined in a fresh state, and they have been
added to the list of the insect-catching plants of the order.

904. Pinguicula is so called from the greasy appearance pre-
sented by the upper surface of its leaf, due to the existence of
great numbers of disc-like glandular hairs with short stalks.
The glandular character of the hairs is shown by the secretion
which exudes from them even when they are not irritated.

905. The secretion which flows when the leaves of Pinguicula
are not excited by the presence of albuminous matter is neutral ;
but upon excitation of the leaf it becomes acid, far more copious
in amount, and has the power of digesting nitrogenous organic
substances. At that time the clear contents of the cells of the
glands also become aggregated, much as in the case of the cells
in Drosera; and this fact is adduced by Darwin as proof that the
digested matters are absorbed.

906. In about three hours after an insect
alights upon a leaf of Pinguicula the margin
begins to roll over it and envelop it, in the
manner shown by the accompanying figure. \
The following experiment by Darwin shows -
what takes place in this incurving: ‘‘A young
and almost upright leaf was selected with its
two lateral edges equally and very slightly in- x
curved. A row of small flies was placed along
one margin. When looked at next day, after \
fifteen hours, this margin but not the other was \
found folded inwards, like the helix of the human
ear, to the breadth of one tenth of an inch, so 157
as to lie partly over the row of flies. The
glands on which the flies rested, as well as those on the over-

So

Fic. 157. Pinguicula vulgaris. Outline of leaf with its left margin inflected over a
row of small flies. (Darwin.)

346 ASSIMILATION.

lapping margin which had been brought into contact with the
flies, were all secreting copiously.” }

The incurvation lasts for only a day or two, after which the
leaf assumes its former position: fragments of glass keep the mar-
gins incurved for a shorter time than do nitrogenous bodies.”

907. Darwin suggests the two following advantages which
the plant can derive from even this transient inrolling: (1)
the captured food and the secretion are protected from rain,
and (2) the food is brought into contact with a larger number
of glands than if the leaf remained flat.

908. It appears probable that the leaves of Pinguicula derive
some nourishment from the seeds, ete., which may fall upon them.
‘*We may therefore conclude that Pinguicula vulgaris, with its
small roots, is not only supported to a large extent by the extraor-
dinary number of insects which it habitually captures, but like-
wise draws some nourishment from the pollen, leaves, and seeds
of other plants which often adhere to its leaves. It is therefore
partly a vegetable as well as an animal feeder.” ?

909. Utricularia, a genus named from the utriculi or little
bladders found on the dissected leaves of some of its species,
belongs to the same natural order as Pinguicula. Its members
capture minute aquatic animals by means of peculiar traps.
Each bladder has at its mouth a few diverging hairs, while just
within the orifice there is a sort of trap-door, which can be lifted
by a slight touch and then falls by its own weight, covering the
mouth and preventing egress. Ifa small aquatic animal passes
through the entrance and pushes by the funnel-shaped trap-door,
it is securely imprisoned. The interior of the bladders is lined
wore or less thickly with peculiar glandular hairs not very unlike
those intermingled with the glands of Drosera, and found also on
the valves of Dionza. These are either bifid or quadrifid.

910. According to Darwin these hairs have the power of ab-
sorbing dissolved matters in a state of decay, but there is in
them no true digestive capacity. If the plants can utilize ani-
mal matter at all, it is only after it has become dissolved during
the process of decay.

911. Genlisea. The plants belonging to the genus Genlisea
—a genus allied to Utricularia — have two kinds of leaves, ordi-
nary and bladder-bearing, and the bladders have something of
the same arrangement at the orifice as has already been alluded
to under Utricularia.

1 Insectivorous Plants, p. 371. 3 Insectivorous Plants, p. 390.
2 Insectivorous Plants, p. 377.

SARRACENIA. 347

912. Sarracenia. All of the eight species of this genus have
hollowed phyllodia, which form slender pitchers or urns. In the
best-known species, S. purpurea,’ the
urn is generally so held that rain can
fall directly into it ; in fact, the upright
foliar expansion would seem to insure
that none be lost. InS. flava, Drum-
mondii, and rubra, the pitchers are
more neatly vertical, and the lid at the
mouth of the tube so disposed when
the leaf is young as to
shed for the most part
rain that falls thereon ;
but in the older leaves
the lid becomes some-
what erect. Even in
the latter position a por-
tion of the rain that falls
upon the leaves is car- iJ
ried off. In the re-
maining species, S. variolaris and psittacina, the
lid is a roof which keeps
the rain from entering the
tube. In all the cases there
is usually considerable water
in the pitchers; in the last
two species it probably all
comes from within as a se-
cretion.

913. Sarracenia variolaris
has been long known to at-
tract insects to the leaves.
Passing over the earlier no-
tices referred to in the Bib-
liography, page 351, the
following quotation from
MacBride,? written in 1815, will indicate sufficiently the char- -
acter of the attraction : —

1 Schimper: Botanische Zeitung, 1882, p. 225.

2 Transactions of the Linnean Society, xii., 1818, p. 48.
Fic. 158. Pitcher-leaves of Sarracenia purpurea; one has the upper part cut away.
Fic. 159. Pitcher of Sarracenia variolaris.
Fig. 160. Pitcher of Sarracenia psittacina,

848 ASSIMILATION,

‘¢ The cause which attracts flies is evidently a viscid substance,
resembling honey, secreted by or exuding from the interna) sur-
face of the tube. From the margin where it commences, it does
not extend lower than one fourth of an inch. The falling of the
insect as soon as it enters the tube is wholly attributable to the
downward or inverted position of the hairs of the internal surface
of the leaf. At the bottom of the tube, split open, the hairs are
plainly discernible, pointing downwards; as the eye ranges up-
ward they gradually become shorter and attenuated, till at or
just below the surface covered with the bait, they are no longer
perceptible to the naked eye nor to the most delicate touch. It
is here that the fly cannot take a hold sufficiently strong to sup-
port itself, but falls.’’

914. The tissues of the internal surfaces of the pitchers have
been classified by Hooker in the following manner : —

‘©(1) An attractive surface, occupying the inner surface of
the lid, which possesses stomata, and (in common with the
mouth of the pitcher) minute honey-secreting glands; it is,
further, often more highly colored than any other part of the
pitcher, in order to attract insects to the honey.

(2) A conducting surface, which is opaque, formed of
glassy cells, which are produced into deflexed, short, conical
processes. These processes, overlapping like the tiles of a
house, form a surface down which an insect slips, and affords
no foothold to one attempting to crawl up again.

‘*(3) A glandular surface (seen in S. purpurea), which occu-
pies a considerable portion of the cavity of the pitcher below the
conducting surface. It is formed of a layer of epidermis with
sinuous ceils, and is studded with glands. Being smooth and
polished, this, too, affords no foothold for escaping insects.

‘*(4) A detentive surfuce, which occupies the lower part of the
pitcher, in some cases for nearly its whole length. It possesses
no cuticle, and is studded with deflexed, rigid, glass-like, needle-
formed hairs, which further converge towards the axis of the
diminishing cavity ; so that an insect, if once amongst then, is
effectually detained, and its struggles have no other result than
to wedge it lower and more firmly in the pitcher.”

915. Mellichamp describes a line of saccharine liquid which
leads up from the base of the leaf to its brim. This secretion
comes from glands at the mouth of the pitcher; but it is found
only at certain periods. Led by this lure, insects are drawn
towards the brim of the pitcher, and sooner or later they are
caught in considerable numbers in the pitchers themselves.

NEPENTHES. 849

916. The exact nature of the liquid in the pitchers is not fully
understood. _Mellichamp’s observations seem to indicate that
it has the power of accelerating the decomposition of animal
matter. Nothing is yet known positively as to the manner in
Which the products of decomposition are utilized by the plant,
if, indeed, they are at all servicealle to it.?

917. Darlingtonia has been examined
by Canby, who finds strong indications
that it allures insects mach as the Sarra-
cenias do.

918. Nepenthes. This striking plant has
long been a favor-
ite in the green-
house on account
of its peculiar
leaves, which often combine
a blade, a tendril, and a well-
formed urn. The species of
Nepenthes (about thirty in
number) produce pitchers at
the extremity of their tendril-
like leaves. When the plants
are young these pitchers are
less elongated and are apt to
rest on the ground, and in
such plants their whole inte-
rior is clothed with secreting glands.
When the plant is older, the pitchers
become more distinctly tubular, and do
not possess such conspicuous wings as those found in the form
just mentioned. All of them have lids; in one case the lid is

161

1 Jt is interesting to observe some of the early conjectures as to the probable
use of these pitchers. ‘‘ Morrison speaks of the lid, which in all the species is
tolerably rigidly fixed, as being furnished by Providence with a hinge. This
idea was adopted by Linneus, and somewhat amplified by succeeding writers,
who declared that in dry weather the lid closed over the mouth and checked
the loss of water by evaporation. Catesby, in his fine work on the ‘Natural
History of Carolina,’ supposed that these water-receptacles might ‘serve as an
asylum or secure retreat for numerous inscets, from frogs and other animals
which feed on them ;’ and others followed Linneus in regarding the pitchers
as reservoirs for birds and other animals, more especially in times of drought”
(Hooker’s Address before British Association, 1874). But Burnett regarded
the tubes as closely analogous to the stomachs of animals.

Fic. 161. Pitcher of Darlingtonia Californica.
Fic. 162, Leaf of Nepenthes; leaf, tendril, and pitcher combined.

850 ASSIMILATION.

thrown back, but in the others its overarching is a conspicuous
feature. The mouth of the pitcher is strengthened by a thick
rim, near which are very numerous glands secreting a sweet
liquid. In the interior of the pitcher there is a conductive sur-
face, somewhat like that seen in Sarracenia. This extends for
some distance down from the mouth, and is frequently crowned
by a sort of funnel-like appendage of the rim. Below the con-
ductive surface there is a secreting surface dotted with iunu-
merable glands. According to looker, from whose notice many
of the facts here given are taken, there are three thousand of
these glands in a square inch.

The fluid which collects in the pitchers bas been shown hy
Gorup-Besanez and Will to be neutral, or only very slightly acid
in reaction, unless animal matter has been introduced. If, how-
ever, any animal matter has been placed in the pitchers, the
glands give forth an acid secretion, which contains an active
ferment that resembles pepsin and has the power of digesting
albuminous substances. It is‘an interesting fact that the neutral
secretion, although it has not the power of digesting albuminous
matters, becomes efficient at once upon the addition of a small
amount of acid (formic). During digestion the glands exhibit
the same phenomena of aggregation as observed in Drosera.

The absorption of animal matter by Nepenthes has been
proved by the Lithium method.

919. By the viscid or glandular hairs of a large number of
plants insects are sometimes caught, but to what extent these
hairs serve in digestion and absorption is not yet clear. From
experiments by Darwin, it appears that in some cases at least
they may aid the plant in absorbing ammonia compounds found
in rain and in the atmosphere, and that the glands may also
‘‘obtain animal matter from the insects which are occasionally
entangled by the viscid secretion.”* One case merits particular
attention; namely, that of

920. Dipsacus, or Teasel. Francis Darwin has called atten-
tion to the extraordinary character of some of the hairs of this
plant. The following abstract gives only the briefest outline
of his interesting paper.

The glandular hairs are multicellular and pear-shaped, being
supported by the small end on a cylindrical stalk, which rests on
an epidermal cell. At the summit of the gland where several of

1 Darwin: Insectivorous Plants, p. 855. The catchfly (Silene) should be
examined with reference to this point.

DIPSACUS. 861

the radiating cells meet, threads of gelatinous matter can be seen
to protrude under certain circumstances. No apertures, how-
ever, can be seen through which the filaments come, therefore
it is thought that they extend directly through the cell-walls.
They have been shown to consist of protoplasmic matter with
which a certain amount of resinous substance is combined, and
at times they contract violently, become thicker, and at last
form a small ball on the summit of the gland. The contraction
can be produced by many chemical and physical agents, e. g.,
ammonic carbonate. If a filament under the microscope is
treated with a drop of a 2 per cent solution of the carbonate, the
following changes occur: The filament contracts, but almost
instantly recovers itself, and is once more protruded; it does
not, however, regain its original form or appearance ; instead of
consisting of thin elongated ropes of a highly refracting sub-
stance, it is converted into necklace-like masses which strongly
resemble the aggregations found in the true insectivorous plants.

Beal has described somewhat similar hairs on some thistles.

It is not the province of this volume to discuss the singular
relationships which are presented by these groups of insec-
tivorous plants. Attention must be directed, however, to the fact
that Dionza and Drosera, with their widely different mechan-
ising for the capture of insects, belong to the same natural family ;
and that Pinguicula and Utricularia, with methods equally di-
verse, are very nearly allied plants. Such facts can be explained
in part by the theory presented in Volume I. page 328, — the
‘¢Theory of Descent.” ?

1 The following list will introduce the student to some of the principal
works upon insectivorous plants. As the list is chronologically arranged, it may
serve as a brief history of the subject.

1768. John Ellis: ‘‘ De Dionga muscipula.” A letter to Sir Charles Lin-
nxus descriptive of the method by which this fly-trap captures insects.

1782. Roth: “ Von der Reizharkeit des sogenannten Sonnenthaues, Drosera
rotundifolia und longifolia” (Beitrige zur Botanik, Bremen, Th. 1, no. iv, pp.
60-76). An account of observations begun in 1779 on the irritahility of the
glands of sun-dew leaves, showing that they respond to contact with in-
sects, but not to a pin or bit of straw. Roth suggests that the plant may
possibly receive some nourishment from the insects. (In Darwin’s Botanic
Garden, 1780, p. 24, it is stated that Whately had made in England observa-
tions similar to those of Roth.)

1791. Bartram : ‘‘ Travels through North and South Carolina, ete.” This
book contains a short sketch of the capture of insects by Sarracenia.

1815. Macbride: ‘‘ On the power of Sarracenia adunca to entrap insects”
(Transactions of the Linnzan Society, xii., 1818, 48-52).

1829. Burnett, in the Quarterly Journal of Science, Literature, and Arts,

852 ASSIMILATION.

921. Epiphytes, or air-plants, obtain their food-materials wholly
without contact with the soil. It is supposed that the ash materials

ii. 290, also gives an account of Sarracenia, together with a description of its
digestive powers, and compares its hollow leaf to an animal stomach.

1834. Curtis, in the Journal of the Boston Society of Natural History, i.,
ee gives a description of the irritability of Dionzea, and of its mode of
action.

1848. Benjamin: ‘ Ueber den Bau und die Physiologie der Utricularien ”
(Botanische Zeituug, vi., po. 1,17, e¢ seg.).

1850. Cohn : “Ueber Aldrovanda vesiculosa” (Flora, p- 673).

1855. Greenland: “ Note sur les organes glanduleux des Drosera” (Ann.
des Se. nat. bot., sér. 4, tome iii. p. 297).

1855. Trécnl: “Organization des glandes pédicellées de la fenille du
Drosera rotundifolia” (Ann. des. Sc. nat. bot., sér. 4, tome iil. p. 308).

pis Caspary: “ Aldrovanda vesiculosa” (Botanische Zeitung, xvii.
p- ‘

; seve Nitschke in Botanische Zeitung, xviii. p. 57, and xix., 1861, p. 145,
givetial excellent description of Drosera, and an account of simple but telling
ee the sensitiveness of the leaves,
ee ‘oe arwin began his experiments upon: Drosera, not published until
1862. Botanische Zeitung of thi ; ;
the subject of Aldrovanda by rete ana (P- 1) contains a second article on
1863. Scott: ‘On the Propagation and In
ers’ Chronicle, p. 30). = Bh
1868. Canby published an account of expe : : ;
the Gardener's Monthly, p. 229. ents on feeding Dionea, in
1872. Ziegler: ‘Sur un fait physiclogiqn :
Drosera” (Comptes Rendus, xxiv. p. 1227).
1873. Treat: “ Observations on the Sun¢
p. 705). In this paper Mrs. Treaty: 88
Drosera carried on in 1571. ;
1873. A. W. Bennett : “On the move!,
(British Association Reports, xlii
1873. Stein: ‘‘ Ueber die Y
handlungen des bot. Vereing
1874. Burdon Sandery

ability of Drosera” (Garden-

Ibservé sur des feuilles de

American Naturalist, vii.

heizbarkeit cer Blatter von Aldrovanda” (Ver-
die Prov. Brandenburg).
Venus’s Fly-Trap” (Nature, x. p. 105).
2 Plants” (Nation, xviii. pp. 216, 232).
> observatt ’ PP ,
An account ar Hie * hat daté hunicated by Darwin, and a short résumé
of the subject up to tha
ellichamp : : ; Sidi

she Bosna uae miches on the pitchers of Sarracenia variolaris,
and the way PR caught in them” (Nature, x. p. 258).
ress before t] tetas eee . =
ment of Science, published in full in as ae Association for pe eis
an excellent account of the digestive eport for 1874. This address gives

especially Nepenthes. > powers of various carnivorous plants,
1875. J. W. Clark: ‘On the

: is Tan absorpt;,

loaves of some insectivorous plants,” Eee ad nutrient material by the
ie 10 gives the r Sarit

ghassid oF SDH SRECHTOSSERe. ser ay ioguieuln, seuducead pith

EPIPHYTES. 853

which they incorporate come to them in the form of dust, which
subsequently dissolves and is absorbed. ‘The sources of their
carbon and nitrogen have already been sufficiently explained.

1875. Darwin : ‘ Insectivorous Plants.” A work of 462 pages, more than
half of which is devoted to Drosera. At the close of his exhaustive discussion
of his experiments upon this plant, Mr. Darwin says: ‘I have now given a
brief recapitulation of the chief points observed by me with respect to the
structure, movements, constitution, and habits of Drosera rotundifolia ; and we
see how little has been made out in comparison with what remains unexplained
and unknown.”

1875. Reess and Will . ‘‘ Einige Bemerkungen iiber fleischessende Pflan-
zen” (Botanische Zeitung, p. 718).

1875. Canby: “ Darlingtonia Californica” (Proceedings American Asso-
ciation, p. 64).

1875. Cohn: ‘Ueber die Function der Blasen von Aldrovanda und
Utricularia” (Beitrage zur Biologie der Pflanzen).

1875-6. Morren published in the Bulletin of the Royal Academy of Bel-
gium the results of experiments which may be interpreted as showing that
the plants derive no benefit from their insects.

1875-6. Gorup-Besanez and Will published some observations regarding
a pepton-forming ferment in plants, in Sitzungsberichte der physikalisch-
medicinisches Societét zu Erlangen.

1876. Francis Darwin: ‘‘ The process of aggregation in the tentacles of
Drosera rotundifolia” (Quarterly Journal of Microscopical Science, xvi.
p- 309).

1876. Sydney H. Vines: ‘‘On the digestive ferment of Nepenthes”
(Journal of Anatomy and Physiology, xi. p. 124).

1876. Faivre: ‘‘ Recherches sur la structure, le mode de formation, et
quelques points relatifs aux fonctions des urnes chez le Nepenthes” (Comptes
Rendus, 1xxxiii. p. 1155).

1876. Munk: “ Die elektrischen und Bewegungsercheinungen am Blatter
der Dionzea muscipula.”

1877. Cramer: ‘‘ Ueber die insectenfressenden Pflanzen.”

1877. Aschman: ‘‘ Les plantes insectivores,” Luxemburg.

1877. Pfeffer: ‘ Ueber fleischfressende Pflanzen und iiber die Ernahrung
durch Aufnahme organischer Stoffe iiberhaupt” (Landwirthsch. Jahrb. v.
Nathusius, p. 969). An excellent account of the mechanism and absorptive
properties of carnivorous plants.

1879. Drude: ‘ Die insektenfressenden Pflanzen.” A full and interesting
examination of the subject in Schenk’s Handbuch der Botanik.

1882. Schimper: ‘ Notizen iiber insectenfressenden Pflanzen ” (Botanische
Zeitung, xl. p. 225).

Several jeux d'esprit have been published, in which the remarkable proper-
ties of a few humble plants have been exaggerated into accounts of man-
catching and man-eating trees of large size.

23

CHAPTER Xi.
CHANGES OF ORGANIC MATTER IN THE PLANT.

922. Ir has now been shown that under the influence of sun-
light green plants produce organic matter out of inorganic
materials. This organic matter is conveyed to points where it
is to be used, or to temporary reservoirs where it is stored for
future use. It undergoes manifold changes in the plant, until
in the ordinary course of nature it is resolved at last into the
very materials from which it originally came; namely, carbonic
acid and water.

923. But as the organic matter of the plant represents in its
construction a definite amount of energy of motion derived from
solar radiance transformed into the energy of position, in its
apparent destruction is involved the reconversion of this energy
of position into energy of motion. Between the first and last
terms of these constructive and destructive processes very differ-
ent periods of time may elapse in different cases, according to
the changes which the organic matter undergoes.

924. That portion of the organic matter which is built into
the fabric of the plant in the form of cellulose more or less modi-
fied is not often broken down into its original components while
the organism is living; but, by decay and by combustion, even
this relatively permanent substance is decomposed, and its ele-
ments are finally given back to the air and soil. A certain por-
tion of the organic matter, however, undergoes speedy and
striking changes, and all of these are now to be examined
from another point of view.

TRANSMUTATION, OR METASTASIS.

925. The physiological expression for the substance formed
by chlorophyll in the sunlight is food. This substance is util-
ized by the organism in many ways; but of these only the fol-
lowing need now be noticed: (1) for the supply of energy for
movements and other work ; (2) for the repair of waste; (3) for

TRANSMUTATION. 855

the construction of new parts. The changes by which these
processes are performed take place in the protoplasm which
receives and in some way disposes of the newly formed food.

926. Supply of energy for work. This is furnished by the
process of oxidation. Jt will be remembered that the inorganic
materials concerned in the production of the food of the plant,
namely, carbonic acid and water, are highly oxidized compounds.
By assimilation a part of the oxygen is liberated, and the or-
ganic matter formed is some carbohydrate capable of oxidation.
The reception of oxygen, the oxidation of the oxidizable matter,
and the release of the products of oxidation by the plant are
collectively termed respiration.

927. Repair of waste. The living matter of plants, like the
living matter of animals, being the seat of all the activities
manifested by the organism, is constantly undergoing waste
and demanding repair. The repair of waste is proper nutri-
tion.

928. The construction of new parts. It has been shown (Chap-
ter X.) that by the appropriation of nitrogen by the plant proteids
are formed, and these are in great part utilized in the produc-
tion of new protoplasmic matter. So far as the latter is an
actual increase in substance, and not a mere repair of waste,
it represents true growth. The growth of any root, stem, or
leaf consists in the formation of new cells and the increase
of these in size. In this process the production of new cell-
wall is of course the most conspicuous phenomenon. The per-
manent increase in size of the cell-walls of a plant disposes of a
large part of the organic matter which is prepared hy assimila-
tion. and this phase of growth is apt to divert attention from
that which really underlies it; namely, growth of the protoplasm
itself.

929. For convenience, the varions chemical changes which
go on within the plant may be divided into two groups; namely,
transmutation and complete oxidation. In the former, the or-
ganic matter changes its properties in some way, either by
the addition of new materials or by the reconstruction of its
existing molecules, but, notwithstanding the change, still re-
mains organic matter; while in the latter it is resolved into its
origina] inorganic components. The change of one kind of food
into another, the transformation of starch into cellulose, and the
formation of proteids, are good examples of transmutation: the
consumption of food for the release of energy, an example of
complete oxidation. The first of these groups of changes cor-

856 CHANGES OF ORGANIC MATTER IN THE PLANT.

responds nearly to what has been called metastasis,! the second
to respiration. But it must be remembered that the distinction
between the two groups is not absolute.

930. The contrast between assimilation and respiration is very
marked: one is substantially the opposite of the other. The
following tabular view displays the essential differences between
them.

Assimilation proper Respiration

Takes place only in cells containing Takes place in all active cells.
chlorophyll.

Requires light. Can proceed in darkness.

Carbonic acid absorbed, oxygen set free. Oxygen absorbed, carbonic acid set free.

Carbohydrates formed. Carbohydrates consumed.

Energy of motion becomes energy of Energy of position becomes energy of
position. motion.

The plant gains in dry-weight. The plant loses dry-weight.

Some of the changes which are grouped under transmutation,
or metastasis, present almost as great a contrast to assimilation
proper as that shown in the above table.

931. Course of transfer of assimilated matters. In the present
state of knowledge it is impossible to trace all the chemical
changes which assimilated matters undergo in the plant, or even
the course which such matters take; only a few of the more ob-
vious modifications have been investigated. Before proceeding
to describe the important forms of organic substance in the
plant, the following general considerations should be presented.

The carbohydrates ave believed to be transferred from one
part to another, in the higher plants, through the thin-walled
parenchyma. The reaction of these cells is almost uniformly
acid. The transfer takes place only when the carbohydrates
are in solution.

The albuminotds are probably carried chiefly by means of
the soft bast of the fibro-vascular bundles; the cells of this bast
have a slightly alkaline reaction.

But that these are not the only paths of transfer, appears from
the frequent occurrence of minute starch-grains in the sieve-
cells, and, on the other hand, of dissolved albuminoids in paren-
chyma cells.

1 The German word Stoffwechsel is usually translated metastasis, —a word
long known in medicine with a totally different signification from that above.
Schwann’s term, metabolism, much used in human physiology, expresses its
idea better, but for some reasons the term transmutation appears preferable.

CARBOHYDRATES. 35

The direction of transfer of the above compounds is towards
the point of use, or of storing; there is never any approach to a
true circulation throughout the plant, corresponding, as was four-
merly taught, to the circulation in animals.

932. Classification of the principal organic products. For the
present purpose these may be conveniently grouped into (1)
those which are free from nitrogen, and (2) those which con-
tain nitrogen. Some have been already treated of in earlier
pages of this volume; of the rest, little more than a mere
enumeration can here be given.

933. Products free from nitrogen. I. Carbohydrates. ‘fi general
these are solid bodies many of which are soluble in water. They
are conveniently divided into the cellulose group, having the
empirical formula, C,H,,O,, and the sugars, — grape-sugar, fruit-
sugar, and cane-sugar.

THE CELLULOSE GROUP comprises the following isomeric
bodies : —

934. Cellulose. This substance (see page 31) is regarded as a
product of the direct transformation of starch or its equivalent.
When once separated from the protoplasm as cell-wall, cellulose
is not again dissolved save in the exceptional cases of germi-
nation where it serves as a food. Sachs has shown that in
the germination of the date, the pitted thickening masses of the
cell-walls of the endosperm are dissolved and utilized by the
embryo.

935. Starch (see pages 47-50). The occurrence of this sub-
stance in the chlorophyll granules under certain conditions has
already been described. Its occurrence in reservoirs of food,
and the relation of this to the starch-generators, have been dis-
cussed in 174.

The following table gives some idea of the amount of starch
found in the ordinary commercial sources : —

Source. Amount of starch present.
Grains of wheat . . . . . . . « « 64 percent.
Grainsofcorn . . .. 4... . © 65 Ee EE
Grains ofrice. . . 2. 1... we 78 Res “See
Potato tubers... 6. a we ee ww D5 HOQ HE 8

When starch is to be transferred from the places where it is
held in reserve to the points where it is to be consumed, it is
converted into a form of sugar by some one or more of the
unorganized ferments occurring in plants. Although the sugar
thus formed passes at once into solution, it is a curious fact

358 CHANGES OF ORGANIC MATTER IN THE PLANT.

that at certain points during its course this solution may tran-
siently exhibit more or less fine-grained starch. The tendency
of starch to form in this way is very remarkable in the process
of germination.

936. Inwin. This substance is dissolved in cell-sap (see 183),
but is easily separated from it upon immersion of the plant sec-
tions in alcohol. It replaces starch in the roots and root-like
stems of many perennials belonging to the following orders, —
Ligulifloree (Composite), Campanulaceze, and Lobeliaces.

937. Lichenin is abundant in certain lichens, amounting in
Cetraria Islandica to nore than 40 per cent.

938. Dextrin. Under this name are comprised at least two
substances? which are produced during the transformation of
starch into sugar. Dextrin occurs in the young sprouts of
potato, in most bulbs as they are starting, and in the spring sap
of many trees.

939. The Gums. These are amorphous substances which
either dissolve in water or merely swell in it to form soft masses
or thick viscous liquids. An example is

Arabin (2C,H,,O,-+ H,0), the chief constituent of Gum Arabic,
obtained from a species of Acacia. It is found associated with
arabic acid, which is supposed to be combined with calcium. It
occurs in cherry-tree guin, and to a slight ainount in the gum of
many other plants.

Of those gums which do not truly dissolve, must be mentioned
Cerasin, abounding in cherry-tree gum; Bassorin, or the essen-
tial constituent of gum-tragacanth ; and Vegetable Mucus, which
occurs in the seed-coats of flax, the pseudo-bulbs of many or-
chids, and the leaves of some mallows.

940. The Pectin Bodies. According to Fremy these are
derivatives from pectose, a neutral insoluble substance found
in unripe fruits and in some fleshy roots. Pectose undergoes
various changes not yet understood. Vegetable jelly, obtained
by boiling subacid fruits, is a familiar example of one of the
products of such changes.

941. THE sugar Group. The more common members of this
group are grape-sugar, fruit-sugar, and cane-sugar. The em-
pirical formulas of these substances have simple relations, ex-
hibited in the following table, in which they are compared with
that of starch :—

1 For an account of the allied substances, amylodextrin and achroodextrin,
see W. Niigeli, Beitrige zur niéheren Kenntniss der Stiirkegruppe, 1874.

THE SUGARS. 859

Starch, C,H,,9;
Cane-sugar, C,,H,,0),
Grape-sugar and fruit-sugar, C,H,,0,

Thus,
2C,H,,0; at H,O = C,,H,0),

Starch. Water. Cane-sugar.

C,.H2.0), + H,O = C,H,,0, + C,H,,0,

Cane-sugar. Water. Grape-sugar. Fruit-sugar.

The three following classes of sugars, based upon their rela-
tions to fermentation, have been made: (1) directly fermenta-
ble, (2) indirectly fermentable, (3) non-fermentable sugars. To
the third class belong Arabinose, Sorbit, etc., which need no
further notice here.

The directly fermentable sugars are grape-sugar, fruit-sugar,
and inverted sugar.

942. Grape-sugar, otherwise termed glucose (or, on account
of its turning the plane of polarization to the right, dextrose), is,
as its name indicates, abundant in the grape, where it may form
from 10 to 30 per cent of the juice. Figs contain, on an aver-
age, 12 per cent; sweet cherries, 9 to 10 per cent; apples and
pears, 7 to 10 per cent; plums, 2 to 5 per cent; and peaches
less than 2 per cent of this sugar.

943. Fruit-sugar, sometimes known as levulose, is uncrys-
tallizable. It is associated in most ripe fruits with dextrose.

944. Inverted sugar occurs in some ripe fruits, where, as
Buignet has shown, it is formed from cane-sugar by the action
of a ferment and not of a fruit-acid. It is also found in the
so-called honey-dew of the leaves of the Linden.

945. The indirectly fermentable sugars, of which common
cane-sugar may be taken as the best example, ferment under the
influence of yeast only when they have first undergone a change
by which they are converted into other sugars.

946. Cane-sugar occurs in the cell-sap of many plants, often
in large amount. The following percentages are regarded as
average ones : —

1 According to Boussingault, 120 square metres of linden leaves yield in
a single warm July day between two and three kilograms of honey-dew. As
to whether this substance is a product of an insect, oran exudation from leaves
under peculiar conditions, is not yet settled (Ebermayer : Chemie der Pflanzen,
1882, p. 255).

860 CHANGES OF ORGANIC MATTER IN THE PLANT.

Sugar-cane stem. . . . . . . . « 16-18 per cent.
Sugar-bects. « ow as aoa mw « « a LO-T4 ee
Sorghum: . «= 4 4 » «¢ @ » «» « » LOT ee
Indiancorn . . 2. . . eertay “ae 5-7 ss
Sugar maple Somat Ue eb el Bee 8 oe

947. Products free from nitrogen. II. Vegetable acids. Of
these the most widely distributed are oxalic, tartaric, citric, and
malic acids.

948. Oaalie acid (C,H,O,) occurs in almost every plant, the
amount in some reaching as high as 4 percent. Most of it is
combined with calcium or with potassium, a part remaining un-
combined. According to Miiller,? the fresh leaves of sugar-beet
contain 4 per cent of this acid, of which one third is in solution.

949. Tartarie acid (C,H,O0,) occurs free, and also combined
with potassium in the juice of the grape and many other fruits.

950. Citric acid (C,H,O,) occurs in the amount of 6 to 9
per cent in the juice of lemons and allied fruits, and is asso-
ciated with other acids in most of our subacid fruits, such as
currants, cherries, etc.

951. Malic acid (C,H,O,) occurs free, or combined with cal-
cium, in the juices of many fruits and in the sap of many plants.
It imparts the sour taste to our most common fruits.

952. Products free from nitrogen. III. Fats, or Glycerides.
According to Ebermayer most of the fats which occur in plants
are mixtures (not compounds) of the following three kinds of
fats in different proportions: Tristearin or stearin, tripalmatin
or palmatin, triolein or olein. The oils in most seeds, however,
are free, fatty acids ; namely, stearic, palmitic, and oleic.

The fats are regarded as compound ethers formed from the
triatomic alcohol glycerin, whence they have been sometimes
termed Glycerin ethers. The following formulas exhibit one view
as to their constitution : —

Tristearin . a via Os

Tripalmatin . Ogee O3
IPrigleiw. wr ay se. er ee Ge He Aa, See aa Os
Stearicacid . 2 2 2. 1 ww we CygHygO2
Palmitic acid 2. 2 1 1 1 ew we CygHg202
Oleic acid 2 6 ew ww ww ew) | Cg ag Oe
(Glycerin. 3 = 4s 2 & & . ©3H;(OH)s)

1 Quoted by Ebermayer, Chemie der Pflanzen, p. 320.

TANNIN AND ALLIED SUBSTANCES. 861

The oils form very intimate mixtures with the albuminoids in
many cases, especially in sceds of such plants as Ricinus, ete.
According to Sachs, ‘‘ in the germination of all oily seeds, sugar
and starch are produced in the parenchyma of every growing
part, disappearing from them only when the growth of the masses
of tissue concerned has been completed. Since, in the case of
Ricinus, the endosperm grows also independently, starch and
sugar are, in accordance with the general rule, temporarily pro-
duced in it. The cotyledons apparently absorb the oil as such
out of the endosperm, whence it is distributed into the paren-
chyma of the hypocotyledonary stem and of the root, serving
in the growing tissues as material for the formation of starch and
sugar, which on their part are only precursors in the production
of cellulose. In these processes tannin is also formed, which is
of no further use, but remains in isolated cells, where it collects
apparently unchanged until germination is completed. It can
scarcely be doubted that the material for the formation of this
tannin is also derived from the endosperm, although perhaps only
after a series of metamorphoses. The absorption of oxygen,
which is an essential accompaniment of every process of growth
and especially of germination, has in this case, as in that of all
oily seeds, an additional significance, inasmuch as the formation
of carbohydrates at the expense of the oil involves the appro-
priation of oxygen.”

Vegetable wax is closely allied to the fats.

953. Products free from nitrogen. IV. Certain astringents.
This indefinite group comprises various matters differing slightly
from one another in some particulars, but agreeing in possessing
a faint acid character, in changing color with salts of iron, and
in combining with certain protein matters. Tannin is sometimes
placed in the next category, namely, among the glucosides; but
according to Schiff it is digallic acid. The most important mem-
bers of this group are Zannin (the so-called tannic acid), Gallic
acid, and the astringent principle in Cinchona, Catechu, and
Kino. According to Niigeli, these matters are to be found in
buds, in unripe fruits, and in those petals which become red or
blue, dissolved in the cell-sap and diffusing through cell-walls.
Tannin sometimes exists in little globules of solution, enveloped
by a delicate film of albuminous matter; for example, in the cells
of the pulvinus of Mimosa and in the bark of many ligneous
plants (Birch, Poplar, etc.). The following views are held as to

1 Text-book, 24 English ed., p. 716.

862 CHANGES OF ORGANIC MATTER IN THE PLANT.

the formation of this substance: Many authors regard it as a
product of the retrograde metamorphosis of certain carbohy-
drates; Sachsse thinks that it always attends the formation
of cellulose from starch, and that there is a slight evolution
of carbonic acid; Wiesner regards it as intermediate in the
series which begins with the carbohydrates and ends with the
resins. This last view is also held by Hlasiwetz, who has ob-
tained the same products from tannin as from the resins, when
each was fused with potassic hydrate.

It is a significant fact that all the barks which are rich in tannin
are also rich in starch.

Nothing is positively known as to the function of tannin and
its associated bodies in the plant. By Hartig they have been
looked upon as reserve materials; but Schroeder was not able
to verify Hartig’s observations. By most observers these sub-
stances are regarded as waste products, having no further nutri-
tive function, but possibly playing some part in the formation of
colors. The following table} shows their amount in some of the
barks and other parts used in tanning : —

Galls 2. 2. 1 6 ee we « © « 80-977 per cent.
Catechu 2. 1. 1 6 ew ew wt ew ee 40-50 ee
Divi-DIWi 4 @ oe a ws we we ws a we «68040 ss
Sumech . = o «© 2 w @ % wa « « J2=18 ce
Oak barks 6 a we me ewe ar ces | FOO es
Willow bark . 2. 1. 6 1 ws wo we) 8D =
Hemlock bark . . . . . . . . | «18-16 6e

954. Products free from nitrogen. YV. Most Glucosides. These
are substances which under certain conditions, especially by the
action of unorganized ferments, are broken up into glucose or
some allied sugar, and at the same time some other body capable
of further decomposition. Most of them are soluble in water.
The following are among some of the best known: salicin, coni-
ferin, sesculin, quercitrin. Tannin is often placed among the
Glucosides.

955. Produets free from nitrogen. YI. Ethereal oils. These
are volatile liquids gencrally approaching Terpene (C,,H,,) in
chemical composition. Nothing is certainly known as to their
formation in the plant. They are not again taken up as plastic
matter, but simply serve some function, often that of attraction

1 For other determinations see Ebermayer’s Chemie der Pflanzen, p. 452,
from which most of the above are taken ; also see the excellent table in the
Tenth Census, vol. ix., p. 265.

ALBUMIN-LIKE MATTERS. 363

or of protection. ‘Lo their presence is due the fragrance of many
fruits and flowers, notably those of orange, bergamot, and the
mints. Associated with the ethereal oils, the camphors occupy a
prominent place. They are generally regarded as the products
of the slight oxidation of some ethereal oils. The following is
the best known, C,,H,,O (Laurel-camphor).

956. Products free from nitrogen. VII. Resins and Balsams.
These substances, which differ much in consistence, color, and
other physical properties, contain comparatively little oxygen,
are mostly amorphous, insoluble in water, and sometimes pos-
sess a slight acid reaction.

Balsams are defined as ‘‘ mixtures of resins with volatile oils,
the resins being produced from the oils by oxidation, so that a
balsam may be regarded as an intermediate product between
a volatile oil and a perfect resin.” ?

The Balsams are generally divided into two groups: (1) those
containing much cinnamic acid, as Balsam of Tolu, Peru, ete. ;
and (2) those which are purely oleo-resinous, as Balsam Copaiba,
Fir, etc.”

Certain resins and caoutchouc-like matters are found in large
amount in the latex.

957. Products containing nitrogen. I. The albumin-like mat-
ters. Ritthausen classifies these substances into (1) Albumin of
plants; (2) Casein of plants; (8) Gelatin of plants.

Albumin of plants is the term applied to the protein mat-
ters which readily coagulate from their aqueous solutions upon
the action of heat or acids. The coagula dissolve more or less
readily in potassic hydrate, exhibiting considerable differences
in respect to solubility. They contain from 2.6 to 4.6 per cent
of ash, and have the following elementary composition : —

Carbon. . . . . . « « « . 52.81-54.33 per cent.
Hydrogen; « « © « #* » - 7.13- 7.73 “
Nitrogen . 2. 2. |. ae: 15.49-17.60 “
FS WU 0) <1 a a -76- 1.55 *
Oxyged, 2 s « « + « « =» 20:55-22.98 §

Casein of plants comprises the following substances: legu-
min, gluten-casein, conglutin. Solutions of these are precipi-
tated by dilute acids and by rennet. The precipitates are readily

1 Watts: Dictionary of Chemistry, i., 1863, p. 491.

2 A solution of the coloring-matter of alkanet root in dilute alcohol applied
to a thin section of a plant containing resins colors the resins red after a few
minutes, but does not serve to distinguish one from another.

3864 CHANGES OF ORGANIC MATTER IN THE PLANT.

soluble in a solution of basic potassic phosphate. Their ultimate
composition is nearly the same as that of the group just men-
tioned.

Gelatin of plants. The associated matters are (1) Gliadin,
(2) Mucedin, (3) Gluten-fibrin. These bodies are soluble in
alcohol, and in water containing a small amount of acid or
alkali. In their fresh state they are tough, viscid masses, only
slightly soluble in water.?

958. Weyl does not accept Ritthausen’s classification, but
holds that legumin is a mixture of vegetable vitellin and casein ;
and further, that there is no true casein in seeds, — the sub-
stance called by this name being a product of secondary changes
in the laboratory.

959. Products containing nitrogen. II. Asparagin (C,H,N,O,).
This substance occurs in the shoots of Asparagus officinalis and
many other plants, from which it can be obtained in the form of
transparent crystals of the orthorhombic system. It is merely
necessary to evaporate the juice of the plants to the consist-
ence of a thin syrup, and after allowing it to stand for a time
the crystals will separate, and may be purified by recrystalliza-
tion. Pfeffer describes the following useful method of preparing
them upon the slide of the microscope: A moderately thick sec-
tion of the tissue suspected of containing asparagin is placed on
a slide, covered with a bit of glass, and treated with absolute
alcohol, when the crystals will be thrown down in the cells, or
will form in the alcohol outside of the specimen. The character
of the crystals can be known certainly by their insolubility in a
concentrated aqueous solution of the same substance (see 46).

The amount of asparagin in certain plants has been given as
follows : —

Name of Plant. Per cent of Asparagin. Observer.
Roots of Althea . . . . 2. Plisson and Henry.
Vetch germs . ae 4s 1D: ge 2 Piria.
Radicles of a germinating

plant dried at 1000. . . 105 . . . Beyer.

960. Asparagin possesses its chief interest from the part
which it probably plays in the transfer of nitrogenous matters
through the plant. According to Pfeffer, although it cannot be
detected with certainty in the seeds of the vetch and pea, it
appears in the young parts, especially in the lines of transfer (for

1 Hunt has called attention to a curious relation between the composition
of animal gelatin and that of starch to which ammonia is added.

ASPARAGIN. 365

example, the petioles of the cotyledons). ‘That the source of the
asparagin must be the reserve albuminous matters in the seed,
appears from the following consideration : ‘¢’The absolute amount
of nitrogen remains the same during germination, and the
nitrogen of seeds is all or nearly all contained in their albumi-
nous ingredients.”! Asparagin and the chief proteid of the
seeds in leguminous plants have been thus compared : —

Asparagin. Legumin. | Difference |
Carbon . O giel ie 36.4 64.9 +28.5
Hydrogen. . 2. . 6.1 8.8 42.7
Nitroven 2 « @ «© + 21.2 21.2 0.0
Oxygen. 2. 2... 36.4 30.6 —5.8

‘¢ Asparagin contains less carbon and hydrogen but more
oxygen than legumin and other proteids. Consequently if the
whole of the nitrogen of legumin is used in the formation of
asparagin, a considerable quantity of carbon and hydrogen must
be given off and a certain amount of oxygen absorbed. Exactly
the opposite will take place upon the conversion of asparagin
into proteid.” }

961. Products containing nitrogen. III. The alkaloids. These
substances all possess the power of uniting with acids to form
salts, and they are often described as basic alkaloids. Among
the most important are Morphia, Quinia, and Strychnia.

The number of alkaloids now known is very great, and the
modes in which they are found combined in the plant are very
diverse. They are more abundant in those plants which are
grown under conditions of considerable warmth, and are much
more abundant in some parts of the plant than in others, as is
shown by the case of morphia. Nothing is positively known as
to their origin or proper function in the organism. It should
be mentioned, however, that many of them when applied to
the very plants from which they were prepared prove to be
poisonous ; thus, morphia poisons the poppy.

962. Products containing nitrogen. IV. Unorganized ferments.
Jt has long been known that there must exist in certain parts of

1 Pfeffer, in Sachs’s Text-Book, 1882, p. 719. Fora full account by Pfeffer,
see Pringsheim’s Jahrbiicher, viii., 1872, p. 429 ; and Monatsbericht der Ber-
lin Akademie, 1873, p. 780. See also Husemann and Hilger: Die Pflanzen-
stoffe, i., 1882, p. 264.

866 CHANGES OF ORGANIC MATTER iN THE PLAN’.

plants, notably in seeds, compounds which possess the power of
effecting changes in the character of starch, etc. ; but it was not
until 1873 that a method was given which enables us to isolate
these compounds in a state of comparative purity. This method
is based upon their solubility in glycerin, and their ready pre-
cipitation from glycerin solutions by means of common alcohol.

By the use of this method Gorup-Besanez has been able to
obtain from the seeds of vetch, flax, ete., a ferment which is
soluble in water and glycerin. The substance contains 7.76 per
cent of ash constituents and 4.5 per cent of nitrogen. Its solu-
tions convert starch into sugar very rapidly at the temperature of
20°-30° C.; and in the presence of a dilute acid, for instance
hydrochloric, it has the power of peptonizing proteids. In solu-
tion, it loses its activity at 80° C. ; but if carefully dried, it can
stand a temperature of 120° C. Up to the present time no fer-
ment capable of effecting changes in the fats of plants has been
isolated.?

963. Baranetzky has shown that in the conversion of starch
into sugar there are two phases: (1) the formation of dextrin,
and (2), at a somewhat higher temperature, the formation of
sugar. He observed an acid reaction in the ferment.

964. In the sap of Carica papaya, Wurtz and Bouchut® have
isolated a peptonizing ferment which acts promptly upon albu-
minoids. The juices of several tropical fruits are said to have
the property of softening meats, and this action is regarded as
dependent upon some unorganized ferment.

965. Besides the products already enuinerated, there are some
bitter and extractive matters and some coloring substances which
do not naturally fall into any of the groups described.

966. From the facts which have now been presented, it is
clear that the composition of the sap which escapes from a plant
when it is wounded must be very complex. The juices of a
plant contain ail its dissolved mineral matters, gases in solution,
and numerous members of both of the nitrogenous and non-
nitrogenous groups already mentioned.

1 Hiifner. Journal fiir praktische Chemie, v., 1872, p. 372, and xi., 1875,
p- 43.

2 For a short account of the work of Kosmann (Journal de Pharmacie et de
Chimie, sér. 4, tome xxii. p. 335) and that of Krauch (Versuchs-Stationen,
xxiii. p. 77), see Husemann and Hilger: Die Pflanzenstoffe, i, 1882, p. 238.

3 Comptes Rendus, Ixxxix., 1879, p. 425; xci., 1880, p. 787. Sce also the
following : Duclaux: Comptes Rendus, xci. p. 731, and Hansen: Sitz. der
physikmedicin. Societat zu Erlangen, 1880.

RESPIRATION. 367

RESPIRATION.

967. It has been long known that air is necessary for the
germination of seeds.1. In 1777 Scheele? pointed out that in this
process, as in the breathing of animals, oxygen (called by him
fire air) is consumed and carbonic acid (called by him air-acid)
is given off. Two years later, Ingenhousz? showed that all
plants at night give off fixed air (carbonic acid), and in 1804
Saussure proved that all plants require oxygen for their growth.
In 1838 Meyen * clearly defined the scope of respiration in plants,
since which time it has been carefully examined in most of its
relations.

968. The relations of gases to plants, so far as their absorp-
tion and elimination are concerned, have been sufficiently dis-
cussed in Chapter X. It is merely necessary to state at present
that oxygen is readily absorbed by all parts of plants, and that
the intercellular passages (519) form a means by which it can
traverse the whole plant very rapidly.

969. In its simplest phases respiration consists in the absorp-
tion of oxygen, the oxidation of oxidizable organic matters, and
the evolution of the products
of oxidation ; namely, carbonic
acid and water. Some other
products are often formed in
minute amount, but these may
be here disregarded.

970. Measurement of Res-
piration. Respiration can be
measured very nearly by the
amount of oxygen which dis-
appears or by the amount of
carbonic acid which is given
off. The ordinary apparatus
for examining respiration is
based upon the measurement
of the latter, and consists es-
sentially of some application of potash-bulbs, or wash-bottles (see
Fig. 163), for the interception of all evolved carbonic acid. The

1 See Malpighi : Opera omnia, 1686.

2 Chemische Abhandlung von der Luft, 1777.

3 Experiments upon Vegetables, 1779, p. xxxvi-
4 Pflauzenphysiologie, ii., 1838, p. 162.

368 CHANGES OF ORGANIC MATTER IN THE PLANT.

air supplied to the seeds in the bell-jar, of course first carefully
freed from every trace of carbonic acid, is drawn through by
means of an aspirator, and in the bulbs all the carbonic acid
derived from the germinating seeds is retained.

971. Plants in dwelling-houses. To what extent can house-
plants injure the air of rooms at night? The carbonic acid which
is given off by plants comes from the breaking up of assimilated
matters in the various activities of the organism, such as growth,
movements, ete. But the total amount of work done by any
plant under the conditions to which ordinary house-plants are
subjected is represented by the oxidation of a very small amount
of food. From the most trustworthy data it is safe to say that
in the case of one hundred average house-plants the whole
amount of carbonic acid resulting from such oxidation during
work would not vitiate the atmosphere of a moderate-sized room
to any appreciable extent; in fact, would be excceded by the
amount evolved from a common candle burning for the same
length of time. -

972. Relation of the carbonic acid given off to the oxygen
absorbed. Owing to the fact that part of the carbonic acid
produced during respiration is retained within the plant, and
that water is formed as a product of respiration, it is difficult to
determine the exact relations of volume of the absorbed oxygen
and the evolved carbonic acid. It is known, however, that in
certain cases the amount of carbonic acid evolved is less than
would be expected from the amount of oxygen absorbed. This
is well shown when the germination of oily seeds is compared
with that of seeds containing chiefly starch. When oily seeds
germinate, the amount of carbonic acid is appreciably less than
that given off by starchy seeds. Hellriegel has shown that in
one instance the fixation of oxygen amounted to an increase in
weight of 1.15 per cent.

973. The free oxygen of the atmosphere is ample for the respi-
ratory process. Saussure? has shown that the amount in the
atmosphere can even be reduced one half without materially
interfering with the functions of the plant.

Most observers have found that in pure oxygen there is an
increase in the activity of the respiratory function.

Bert? has conducted interesting experiments upon the effect

1 Quoted by Pfeffer, Pilanzenphysiologie, i. p. 373.
2 For a discussion of this question, particularly with reference to the lower
organisms, consult Bert: La pression barometrique, 1878.

PERIODS OF REST. 369

of pressure on the various functions, by which it appears that in
ordinary air, under a pressure of six atmospheres, Mimosa per-
ished quickly. In an atmosphere under high compression seeds
germinated, if at all, very slowly.

S74. Influence of temperature upon respiration. Respiration
can go on at low temperatures, even near the freezing-point of
water. The rate of respiration increases with rise of tempera-
ture, as will be seen from the following figures for germinating
beans : —?

Amount of carbonic acid

Temperature. given off each hour.
QC se we ee ee Sa ee a we es a 1OREG mgr.
OF ce ay ee Sel chee ie i ~ 2122 *
18? eo ws ee wm BE eo -& » + « S234 *
QO Gi RB ea ie y = =e @ » Be
soe. tw Bo tk oat Ge sein Ry A ce ARB DS OF

975. Influence of light upon respiration. It is not yet known
positively whether light has any effect upon respiration. In
some experiments there has been a slight increase,’ in others a
diminution,’ in the rate, with increased illumination; but it is
not certain whether all other factors were excluded.

If the produced carbonic acid does not escape readily from the
tissues, respiration goes on more slowly.*

976. Periods of rest. Although all plants require oxygen for
the performance of their normal functions, it by no means follows
that when a plant is supplied with oxygen the normal activities
will be necessarily exhibited. In the case of certain bulbs, seeds,
etc., even with the most favorable surroundings, there may be
no signs of respiratory or other activity until after the lapse of

1 Rischawi: Versuchs-Stationen, xix., 1876, p. 338.

2 Wolkoff and Mayer: Landwirthschaftliche Jahrbiicher, 1874, Heft iv. ;
Cahours: Comptes Rendus, lviii., 1864, p. 1206.

8 Dumas: Annales de Chimie et de Physique, sér. 5, tome iii., 1874,
p- 105; Borodin: Just’s Botan. Jahresbericht, iv., 1878, p. 920.

£ For the bearings of this upon alcoholic fermentation, which, according to
Melsens, is not arrested until a pressure of 25 atmospheres of carbonic acid
is reached, see Pasteur: Annales de Chimie et de Physique, sér 3, tome lii.,
1858, p. 415; and Nageli: Die niederen Pilze, 1877, p. 31.

Alcoholic Fermentation. This process is so intimately connected with
that of respiration that it requires a brief description at this point. Reduced
to its simplest terms, it consists of the changes which are produced in a solu-
tion of sugar by the growth of a microscopic organism. This is some one of
the Saccharomycetes (a group of low fungi which are propagated by a process
of budding). By the growth of this fungus the solution of sugar is broken up
into various products, the most noteworthy being alcohol and carbonic acid.

24

3870 CHANGES OF ORGANIC MATTER IN THE PLANT.

a given period of time. There is little doubt that this refusal
of the resting part to start is an inherited trait connected in
some way with the protection of the plant against untoward
influences.

977. Respiration is accompanied by an evolution of heat.
The flowers of the melon and tuberose were examined by Saus-
sure, who found that in the opening of the former there was
an elevation of 4 to 5C.°, in that of the latter, 38°. Caspary
detected a noticeable rise of temperature in the opening flowers
of Victoria regia, and the same has been observed in flowers of
species of Cactus.

978. In those cases where it is possible to examine an organ
in which the process of respiration is rapid, as in a compact
cluster of flowers of Araceze, the difference between the tem-
perature of the air outside and that inside the spathe is very
marked.

979. The following results by Senebier, obtained by two
methods of experimenting, are very instructive, showing the
remarkable and rapid changes of temperature in such cases.
The plant in this instance was Arum maculatum.

Time. Temperature of air. Temperature of spathe.
c.° C.°
3° P.M 15.6 16.1
5 ss 14.7 17.9
5g 15. « 19.8
6} es 15. 21
63 OCS 14.9 21.8
7 ae 14.3. * 21.2
oF tS ibe 2 4 »& » ae
10h ** 14. 15.7

G ASME as Ge Se a et a es ks RL,

Even higher differences have been observed.

980. Light is produced during the growth of certain of the
lower fungi under certain conditions. The phenomenon called
phosphorescence is not known in any of the higher plants.’
According to Fabre, it is associated with the absorption and
consumption of oxygen, and the evolution of carbonic acid.

981. Intramolecular respiration. Under certain circumstances
plants can continue to give off carbonic acid when no free
uxygen is supplied, and when they are kept in an atmosphere

1 For an aceount of supposed cases of luminous flowers see Balfour's Class
Book of Botany, 1854, p. 676,

INTRAMOLECULAR RESPIRATION. 871

of some other gas.1 The following experiment will illustrate
this : —

If a mass of active seedlings be placed in a current of some
neutral gas, for instance nitrogen, the seedlings will continue to
evolve carbonic acid. Since the amount of carbonic acid given
off is greater than can be derived from the oxygen which might
be fairly assumed to have been retained in the plants at the be-
ginning of the experiment, the conclusion has been drawn that
the production of this gas is at the expense of substances within
the tissues containing combined oxygen. In other words, this
process, which is like respiration in some particulars, differs from
it in this respect: in ordinary respiration free oxygen enters into
the plant and there oxidizes certain matters; while in this case
the molecules of certain compounds break up, and the released
oxygen at once forms, with carbon, carbonic acid, which is
evolved. This process is known as intramolecular respiration.

982. Wortmann? has proved that when seedlings of Vicia Faba
are placed for short periods in an atmosphere free from oxygen,
they give off the same amount of carbonic acid as they do when
oxygen is furnished. Hence he was naturally led to believe that
all the carbonic acid produced by plants has its origin in intra-
molecular respiration, and that the free oxygen of the air takes
no direct part in the formation of the carbonic acid evolved.

983. But, on the other hand, Wilson® has shown that most
plants evolve much larger quantities of carbonic acid when free
oxygen is provided, and that Vicia Faba forms a remarkable
exception to this rule. His experiments were made upon seed-
lings, buds, leaves, flowers, fruits, and cryptogamous plants,
and with uniform results. He cites Pfeffer as saying: ‘‘If an
equal amount of carbonic acid were formed in both intramolecu-
lar and normal respiration, this would only prove that the same

1 The same phenomenon has been observed in the case of some of the
lower animals: Pfliiger (Archives fur Physiologie, x., 1875, p. 251) has shown
that when these animals are kept in an atmosphere of nitrogen, they evolve
during the first few hours nearly the same amount of carbonic acid as if they
had been placed in common air. The chemical processes which cause the
production and evolution of carbonic acid in the absence of free oxygen are
grouped by Pfliiger under the term intramolecular respiration.

2 Arbeiten des botanischen Instituts, Wiirzburg, 1880, p. 500.

3 Flora, 1882, and American Journal, xxiii., 1882, p. 423. For an interesting
account of the literature of intramolecular respiration see Pfliiger’s paper, men-
tioned above. Observations upon the subject were made even during the last
century and early in the present century. For Broughton’s and Pfeffer’s work
see Botanische Zeitung, 1870, and Pflanzenphysiologie.

3872 CHANGES OF ORGANIC MATTER IN THE PLANT.

number of carbon affinities for oxygen had been satisfied in
each case, and would in no way indicate from whence the supply
of oxygen came. And in case free oxygen was active in normal
respiration, in intramolecular respiration, when free oxygen was
absent, its full supply might still be obtained through constant
powerful attractive forces which could take oxygen from other
combinations and thus give rise to secondary changes.”

984. Eriksson! has shown that a slight elevation of tempera-
ture occurs during intramolecular respiration, amounting in the
case of a mass of seedlings, flowers, or fruits, 125 cc. in bulk,
to .1°-.3° C. In the experiments which he made with yeast, he
obtained a much larger increase of temperature. Thus, when he
employed 500 ce. of a fluid containing five parts by weight of
water and one part by weight of yeast, together with 10 per cent
of sugar, he obtained an increase of 3°.9 C. He found, further,
that in intramolecular respiration, both in the case of germina-
tion and in that of yeast, the elevation of temperature can be
noticed for one week. After this time, with diminution of the
respiration, the temperature becomes the same as the surround-
ing air; but even then life is not extinct.

985. The curious experiment of introducing the smallest pos-
sible amount of organized ferment into a liquid from which all
air has been expelled, but which is otherwise fitted to undergo
fermentation or putrefaction, has resulted in setting up one or
the other of these processes, and causing the liberation of con-
siderable quantities of carbonic acid. It is believed that in this
case likewise the needed oxygen is supplied by that in the mole-
cules of oxygen-compounds, which are easily broken down.

986. While the non-nitrogenous compounds are those which
play the most important part in furnishing material for oxidation
and the release of energy, the nitrogenous matters share in this
activity. Some physiologists? look upon the latter as the chief
matters concerned in the process of respiration, and would regard
the non-nitrogenous compounds as merely supplying waste. Ac-
cording to this view, asparagin is a waste product somewhat
analogous to urea in animal economy.

987. From what has been said, it is plain that respiration does
not consist merely in the direct absorption of oxygen and the
immediate oxidation of compounds within the organism, but
that it is a complicated process of which the absorption of oxy-
gen and the evolution of carbonic acid are the extreme terms.

1 Untersuchungen aus dem bot. Inst. zu Tiibingen, 1881, p. 105.
2 Borodin : Botanische Zeitung, 1878.

CHAPTER XII.
VEGETABLE GROWTH.

988. As already shown, vegetable growth consists (1) in the
formation of new cells, (2) in the increase in size of previously
existing ones, or, (3) as is commonly the case, in both of these
processes taking place simultaneously. In the production of
new cells and in the augmentation of cells in size there are cer-
tain chemical and physical phenomena which always accompany
the morphological changes.

989. The chemical changes are essentially those which have
been described under Transmutation and Respiration ; available
matters change their character in order to be utilized in the for-
mation and increase in size of cells. The physical phenomena
are chiefly those which accompany oxidation; namely, the evolu-
tion of heat and the production of electrical disturbances.

990. The materials used by the plant for the formation of new
structures are produced by assimilation; and in annuals a large
part of the assimilated matter is consumed in growth as soon
as it is made. But, in perennials, especially in those which
belong to climates where vegetation has periods of rest, a por-
tion of the assimilated matter is stored up for future use. The
rapidity of the growth from buds in the spring is due to the
abundant supply of assimilated matters prepared during the pre-
ceding summer.

991. Hence growth is not necessarily associated with increase
in weight. In fact, in the growth of new parts from a bulb or
tuber, although there is a marked increase of volume, there is, at
first, an actual loss of dry substance through oxidation. More-
over, one part may grow at the expense of another; and we may
have under certain conditions the anomaly of an increase in
volume of new organs, with simultaneous but larger decrease in
size of older parts, so that the result, as regards the whole, is
diminution of weight.

992. Morphological changes in the cells. The two processes
involved in ordinary growth, namely, increase of cells in number
and in size, may go on together. But growing cells belong to

3874 VEGETABLE GROWTH.

one of two classes: either they are capable of producing other
cells, or, incapable of this, they develop into cells for some
special office. To the former class belong all merismatic tissues ;
(see 201) from the latter all the permanent tissues are derived.
Since growing cells have such different destinies, we must ex-
amine them in their earliest stage to find what they have in
common.

993. The simplicity of structure in many of the lower plants is
so great that a living cell can be kept under observation through-
out its various stages, and through its transparent wall all the
changes which go on within it can be noted. But the points of
growth in most plants, especially those of the higher grade, are
hidden by more superficial cells ; and upon removal of these pro-
tecting parts, pathological changes are brought about at once,
from exposure and mechanical injury, and healthy growth is
arrested. In a few instances only, such as plant-hairs and
other epidermal structures, is it possible to observe directly the
progress of cell-division. Growth in deeper parts must be ex-
amined by an indirect method ; that is, like parts must be com-
pared at different stages of development, care being taken to
select those which have been kept under nearly the same ex-
ternal conditions. By judicious selection of material for the
examination of growth, specimens can be found which exhibit
in a single section several different phases of cell-division.

994. When fresh material is employed, the sections are so
much distorted that it is difficult to secure satisfactory results ;
in fact, the discordant views relative to the formation of cells are
largely attributable to this source of error. If, however, the
tissue to be examined is placed for a while in absolute alcohol,
either with or without a little chromic acid, the cell-wall is
rendered so much harder that the sections are not seriously
distorted, and the contents of the cells are more clearly seen.
When the treatment is supplemented by the use of staining
agents adapted to special cases, the course of development ot
new cells can be followed out with comparative certainty.

995. In the protoplasm of nearly all vegetable cells there is a
spheroidal or lenticular body apparently denser than the proto-
plasm itself. It retains the name nucleus, given to it by Robert
Brown, who first called attention to its importance. Under ordi-
nary circumstances it can readily be detected in all active cells
of the higher plants.

When living, it resists, like the protoplasm in which it is
embedded, the entrance of all coloring agents ; but when dead it

STRUCTURE OF THE NUCLEUS. 875

is at once tinged by them. Upon the application of iodine it
becomes deeper brown-yellow than protoplasm, and _ this led
Hofmeister to the belief that it is richer in albuminoidal mat-
ters.1 Its behavior with digestive fluid and other reagents indi-
cates that, like the nucleus in the animal kingdom,” it contains
a substance rich in phosphorus.?

996. The surface of the nucleus generally appears to be
firmer and more highly refringent than the interior mass, and in
these respects is like the superficial layer of protoplasm. Even
with low powers of the microscope and without reagents the
inner mass of the nucleus is often seen to be far from homo-
geneous, generally containing granules, which are sometimes
irregular, sometimes regular in form. When a single large
granule is present, it is known as the nucleolus; when two or
more, the nucleoli. These vary widely in number, size, and
shape. Besides such granules, vacuoles are frequently present.
Upon the application of suitable staining agents, and by the
use of high powers, the nucleus, formerly thought to be nearly
homogeneous, is shown to be a basic substance possessing a
finely reticulated structure. At times the nucleus appears te
be simply dotted throughout with fine points.

997. When the bodies which are associated with its basic sub-
stance are granular, they are distinct from each other; but when
in the shape of rods, fibres, or delicate threads, they are usually
conjoined to form a sort of network, or so connected together
as to make a long thread which is tangled in a complicated man-
ner. The basic substance of the nucleus, less highly colored by
staining agents than the rest, has been called Achromatin ; while
the portions which take color readily are termed Chromatin by
Flemming, nuclein * by Strasburger.

During cell-division these portions of the nucleus undergo
remarkable changes of shape and position, which, with the
changes observable in the nucleus as a whole, can be illustrated
by a few special cases taken from Strasburger’s treatise, and
given in nearly his words.

1 Hofmeister: Die Lehre von der Pflanzenzelle, 1867, pp. 78, 79.

2 Hoppe-Seyler: Physiologische Chemie, i. p. 84, which contains a good
account of the literature of the subject.

3 Zacharias : Botanische Zeitung, 1881, p. 169.

4 The only objection to the term nzclein is its previous application to the
proximate chemical substance rich in phosphorus which, although a part of
the nucleus, is not proved to be identical with the part which receives colors
most deeply.

&76 VEGETABLE GROWTH.

998. Development of stomata. Each of the mother-cells from
which the guardian-cells of stomata are formed contains at first a
large nucleus with one large nucleolus or several small nucleoli
(Fig. 164, No.1). The nucleus grows in size and becomes gran-
ular, but does not lose its identity in the protoplasmic mass (Fig.
164, Nos. 2,3). At this period faint stripes appear which con-
verge towards the poles of the spheroidal nucleus, while there is
developed midway, at what has been well called the equator, a
row of granules lying in one plane and forming a sort of disc
or plate (Fig. 164, No. 4). The granules next pass for the most
part in the meridian lines towards the poles, and there accumu-
late to constitute new nuclei (Fig. 164, No. 5). The polar masses

are connected by faint stripes, and from this stage (Fig. 164,
No. 6) go rapidly to their fuller development. In them rods
appear which, though somewhat curved, generally lie in the
direction of the axis of the spindle, and the contour of the two
masses becomes clearly defined (Fig. 164, No. 7). Next, the
faint stripes thicken somewhat, while at the equator there is
developed a plane of minute granules (Fig. 164, No. 8), which
become confluent and form a coherent film. ‘This soon splits
into halves between which cellulose is secreted. At first the
secretion takes place in spots, but it soon becomes uniform.
The splitting of the film for the formation of the cellulose is
similar to that of the nuclear disc, except that in the former the

Fig. 164, Changes in the nucleus during cell-division in the mother-cell of a stoma
of Iris pumila, The dark parts in all the figures represent the nuclein. In No. 9
the cell-division is complete. (Strasburger. )

CELL-DIVISION. 377

separation is very slight. At the time of the formation of the
cellulose film certain nuclear threads may stretch as far as the
wall of the mother-cell; but often they do not extend to it, and
in this case the gap is filled out by a corresponding plate from
the protoplasm. The cellulose film is produced almost simul-
taneously throughout the whole extent of the mother-cell, which
is cut into two guardian-cells, forming a stoma (Fig. 164, No.
9)." Although the process goes on without interruption, it may
be divided into three phases; namely, (1) the arranging of the
nucleolar bodies to form a disc in the middle plane of the nucleus ;
(2) the splitting of the nuclear disc into two parts which pass
over towards the poles, there becoming new nuclei, leaving faint
meridional lines connecting them; (8) the thickening of these
lines, and the appearance of granules at the equator, so as to
form a plate which divides into halves. The cellulose film
secreted between these halves sooner or later goes across the
cell cavity, making a partition-wall between two new cells.

The mother-cell from which guardian-cells are developed in
the manner just described is itself produced in nearly the
same manner from an epidermal cell. The latter contains a
spherical nucleus having a diameter about two thirds that of
the cell. It is not wholly filled with protoplasm, as is usually
the case with cells capable of division, but has a very thick
lining of protoplasm along the wall, and in this the nucleus
is embedded. The nucleus extends completely across the cell-
cavity, while above it and below it is cell-sap. If, now, the
epidermal cell is to give rise to a new one, the nucleus passes
over to one end of it and there divides into two parts, essentially
as before described, except that the halves remain close together.
Between these new nuclei the cell disc or plate, and the cellulose
plate, are successively produced, cutting the old cell into unequal
parts.

999. The division of cells in cambium was examined by Stras-
burger? in young shoots of Pinus sylvestris, which had completed
their growth in length and had begun to thicken. These were
selected on account of their rapid development. The cambium
cells of this pine have a lining of protoplasm, together with a
nucleus which occupies the middle of the cell and completely
fills the smaller diameter. The nucleus is nearly spherical, or

1 Strasburger: Ueber Zellbildung und Zelltheilung, 1876, p. 110. This
account is somewhat but not essentially different in the edition of 1880.
2 Ueber Zellbildung und Zelltheilung, 1876, p. 116.

378 VEGETABLE GROWTH.

somewhat lengthened in the direction of the long axis of the cell,
and contains several nucleoli. When it begins to grow, these
nucleoli disappear, and the characteristic striation previously de-
scribed appears transverse to the direction of future division and
of the nuclear disc. The latter is not clearly defined, and its
halves do not recede from one another very far, since, in fact,
there is not space for much expansion in any event. The parti-
tion wall at first is confined to the space hetween the halves,
and these are found in close contact with it, but later it extends

completely across. The remarkable thickness of the radial walls
of the cambium is explained by Sanio as due to the non-absorp-
tion of a part of the mother-cell; but Strasburger ascribes it
to the uninterrupted nutrition of the radial wall from the contents
of the cell itself. The newly formed partition-wall is thin, and
cannot be shown by reagents to be double.?

1 The student should consult Strasburger’s work : Ueber den Theilungs-
vorgang der Zellkerne, 1882; also Das botanische Practicum, chap. xxxiv.

Fic. 165. Behavior of nucleus during cell-division in the endosperm of Allium to
illustrate the extraordinary complexity of the stained bodies. The dark lines represent
the chromatin. (Flemming.)

DEVELOPMENT OF POLLEN-GRAINS. 379

1000. Development of pollen-grains. This affords some of the
most instructive examples of cell-division, and owing to the
fucility with which material can be procured and studied, has
received much attention.

(1) Seperficiul phenomena. These, which can be easily
traced without the employment of staining agents, are in brief
as follows: At the period when the loculi of the anthers begin
as minute elevations at the end of the stamen, the external
layer of cells, which is to serve as epidermis, is underlaid by

a group of small cells which give rise to the mother-cells of the
pollen and to the lining of the anther itself. This group is
termed the archesporium; by division of its inner layer, large
mother-cells are produced which divide to form the pollen-
grains. The division of a mother-cell may give rise to two, three,
or four pollen-grains, and in some cases more, according to the

Fie. 166. Fritillaria Persica. Division of the mother-cells of pollen. a, early stage,
in which the threads are confused; b, the segments in course of longitudinal division;
c, the nuclear spindle in profile; d, the same seen from its extremity or pole; e, division
of the nuclear plate; 7, separation of the derivative or daughter-segments; g, formation
of the derivative tangles and the cell-plate; h, the course of the nuclear threads in the
derivative nuclei; 7, longitudinal extension; /,nuclear spindle, on the right, in profile,
on the left, from its extremity; 7, separation of the segments, on the left seen in pro-
file, on the right from the extremity ; m, formation of the cell-plates. (Strasburger.)

380 VEGETABLE GROWTH.

direction of the lines of fission. It is possible to distinguish
differences in the mode of division which are fairly charac-
teristic of Angiosperms and Gymnosperms, of Monocotyledons
and Dicotyledons. Although the morphology of the tissues
involved and the course of development are not yet completely
understood, it may be said that the formation of pollen-grains
suggests throughout the mode in which the male elements are
produced in the higher cryptogams.

(2) Changes in the Nucleus. The following suggestions by
Strasburger for demonstrating the nuclear changes in pollen-
grains can be applied with few modifications to all cases of cell-
division: Place the young part, in this case a very young
anther, in a solution of methyl-green in acetic acid, and subject
it to slight pressure by which the contents of the anther-cells
will be discharged. Those parts susceptible of staining will take
the color readily and the different stages can be followed out sub-
stantially as shown in the figures. For the staining-agent above
mentioned the following may be substituted, — gentian-violet in
acetic acid, or nigrosin with picric acid. Preparations made with
the latter can be preserved in glycerin without losing color.

Another and better method is to place sections of the tissue
which has been kept for a few days in absolute alcohol, in an
alcoholic solution of safranin, and after twelve hours wash with
absolute alcohol; then transfer them to oil of origanum and
thence to a thick solution of Damar in turpentine, for mounting.

By the safranin the delicate threads of the spindle are not
much colored; they take, however, a good color with heematoxy-
lin. Other combinations of coloring agents give good results.+

1001. Cell-division in plant-hairs. The stamen-hairs of Tra-
descantia Virginica afford excellent material for this examina-
tion. The last or upper three cells while still young are capable
of division. Ifthe very young hairs are transferred carefully to
a slide on which is a three per cent solution of cane-sugar, they
will continue the process of cell-division as shown in Fig. 167.
If the specimen is a good one, and has not been much injured
during its removal, it will remain active for several hours.

All the examinations of cell-division require the use of high
powers of the microscope, none being better for the purpose
than the so-called homogeneous immersion lenses.

1002. The direction in which the new cell-wall is laid down at
the point of growth has been exhaustively examined by Sachs.

1 Das botanische Practicum, 1884, p- 598.

DIRECTION OF CELL-DIVISION. 881

According to him, the planes of the walls at a point of growth
may be thus classified : +—

dee

stars

fA

oF

1 “The relatious of the periclinal and anticlinal planes are illustrated by
the following cases :—

(a) If the outline (in longitudinal section) of the growing point is a parab-
ola, the periclinals will constitute a system of confocal parabolas of different
parameter, the focus of the system being at the point of intersection of two
lines, of which one is the direction of the axis and the other of the parameter.
In this case the anticlinals, being the orthogonal trajectories of the periclinals,
constitute a system of confocal parabolas, the axis and focus of which coincide
with those of the periclinals.

(b) If the outline of the growing point is a hyperbola, the periclinals will
be confocal hyperbolas, with the same axis but different parameter ; the anti-
clinals will be confocal ellipses, with the same focus and axis as the periclinals.

(c) If the outline of the growing point is an ellipse, the periclinals will be
confocal ellipses ; the anticlinals will be confocal hyperbolas” (Abstract from

Fic. 167. Tradescantia Virginica. Process of cell-division in the stamen-hairs.
a, with a quiescent nucleus in the lower cell, and in the upper, one which has just fin-
ished its division; 6, nucleus showing a coarse granular structure with a tendency to
linear arrangement of the particles. The drawings from ec to & inclusive exhibit the
different stages of cell-division at the following points of time: c, at 10 o’clock and 10
minutes; d, 1020; ¢, 10.25; 7, 10.30; g, 10.35; h, 10.40; é, 10.50; j, 11.10; &, 11.30.
(Strasburger. )

382 VEGETABLE GROWTH.

1. Periclinal, those which exhibit in longitudinal section
curves in the same direction as the surface.

2. Anticlinal, those which cut the surface and the periclinal
walls at right angles (forming a system of orthogonal trajecto-
ries for the periclinal walls).

3. Radial, those which pass through the axis of growth and
cut the surface at right angles.

4. Transverse, those which cut both the axis of growth and
the surface at right angles.

1003. Growth of the cell-wall. When the new cell is formed
it undergoes changes in size, and often in shape and thickness.
If it increases in size regularly at all points of the surface, it
preserves, of course, its
original shape ; but if its

| growth is irregular at

| different points, great
| modifications of form re-
| | \ sult. Pollen-grains afford
Mi instances of the former
method of growth, while

| the latter is seen in the

f | multicellular organs, for

=>
& ®

| | example stems and leaves,
} CA I, At the growing points of
SY SS = the stem and leaf the
MT cells when first formed are
<< mtd | | ifr nearly alike in appear-
i | | I ance; but wide differ-
|
|
|
i

ences are soon presented.

The growth of a cell
in size may be terminal,
| when it gives rise to
elongated forms; or lo-
calized at a point, line,
or zone, when projections
and swellings of various kinds are produced.?

Arbeiten des botan. Inst. in Wiirzburg, 1878, in appendix to Text-book, 2d
Eng. ed., p. 951).

The student should also read Sachs’s Vorlesungen, 1882, pp. 523-557.

1 These have already been sufficiently considered in the histological part
of this volume, and it is not necessary to again call attention to the adaptations
of the resultant structures to their respective kinds of work in the organism.

Fie. 168. Arc-auxanometer J, thread connecting plant with short arm of lever a 2.
The weight of long arm balanced by movable weight at k. (Pfeffer.)

RECORDING AUXANOMETERS. 383

1004. Measurement of growth. In some cases it is very easy
to make direct measurements of the amount of increase in vol-
une; but in general it is necessary to employ some form of appa-
ratus by which the amount can be more or less exaggerated by
a multiplier.

Several forms of growth-measurers, or auxanometers, have
been devised for attaining this end. The simplest consists of
a fixed are of large radius (see Fig. 168), on which a delicate
arm moves up or down according to the direction in which a
small wheel at the centre, to which the arm is attached, is moved
by the action of a thread fastened to the plant. Care must be
taken to balance the arm as perfectly as possible, in order to
prevent any strain on the plant by the weight of the index.

This form of apparatus is well adapted to demonstration before
a class; and if a rapidly
growing seedling or strong
scape is chosen for experi-
ment, the movement of the
arm through the are in an
hour will be sufficient to be
clearly seen at a considera-
ble distance. A modifica-
tion of the apparatus by
Professor Bessey reduces
its cost to a mere trifle.
Both the arc and its sup-
porting radii are made of
strong manila paper; the
wheel is a common spool,
and the arm may be a slen-
der straight straw.

1005. Recording Auxano-
meters. For the purpose of
registering growth, several
applications of the chrono-
graph have been made. !
One of the most satisfactory 169
of these consists of a slowly
revolving cylinder covered with smoked paper, upon which a
needle, attached to the end of a balanced thread passing over a

Fic. 169. Registering auxanometer. The thread attached to the plant passes over
the small wheel at 2, and is balanced by a weight. The index zg is balanced by the
weight g; the thread betweeu them goes over the wheel 7. The cylinder is carried round
by the clock-work, which is regulated by the pendulum weight at p. (Pfeffer.)

3884 VEGETABLE GROWTH.

wheel, leaves its trace as it ascends or descends. The wheel is
caused to move by means of a second balanced thread which
passes over its axis, and which is fastened at one end to the
growing part of the plant.

1006. Pfeffer’s modification of this apparatus provides that the
cylinder shall turn a short distance at regular intervals of time,
so that the line made by the needle becomes interrupted and thus
exhibits the appearance of steps; in which the height-of the step
represents the total ascent or descent of the needle during a
given time, while the other line of the step merely marks the dis-
tance through which the cylinder moves at the close cf one of its
intervals.

1007. Examples of very rapid growth are afforded by many
fungi; for instance the common puff-ball, which increases enor-
mously in size during a single night.

Shoots of bamboo have been observed at Kew to grow at the
rate of two to three inches in the twenty-four hours ; and in its
native habitat, Bambusa gigantea has been known to grow more
than ten inches a day.

The expansion of the leaves of Victoria regia is extremely
rapid, under favorable conditions reaching a foot in the twenty-
four hours. The scapes of many plants develop at a rapid rate,
and afford excellent material for practice with the auxanometer.

1008. Conditions of growth. Vegetable growth does not take
place unless there is an available supply of assimilated matter,
access of free oxygen, and a sufficiently high temperature. The
assimilated matter may be furnished to the growing parts di-
rectly from green tissues, or from reservoirs where it has been
stored up. In either case it must come in a state of solution to
the growing cells, and hence a certain amount of water is re-
quired for the transfer. That the amount of water demanded is
not necessarily large, is shown by the starting of shoots from
bulbs, tubers, etc., in the spring, even when no water has been
furnished from outside.

1009. Although the process of respiration in green plants may
go on for a time without free oxygen, as has been shown by the
experiments described on page 371, there is no proof that growth
occurs under such circumstances. In an atmosphere of hydrogen,
nitrogen, carbonic acid, or nitrous oxide, — gases which are not
in themselves harmful to plants, — growth does not take place,
as has been proved by experiments upon seeds and seedlings.
Detmer has shown that growth is immediately checked when the
plant is deprived of free oxygen, but death does not ensue until

RELATIONS TO TEMPERATURE. 385
after a considerable time. During the period of inactivity the
plant is ready to respond at once to the influence of oxygen,
growth being then immediately resumed.

1010. If assimilated matters and free oxygen, both essential
to growth, are abundantly supplied to a plant which is kept at
too low a temperature, growth does not occur. ‘The minimum
limit for growth is different for ditferent plants, and is not the
same for all organs.

Again, it must be noted that there is a maximum limit of tem-
perature above which growth does not take place, and this limit
is also different for different plants. Between the lower and
upper limits there is, for the plants which have been thus far
studied with respect to the effect of heat on growth, an optimum
of temperature at which growth is most rapid.

1011. Relations of growth to temperature. Zhe minimum tem-
perature required for growth is generally much higher for plants
of warm regions than for plants of cold
climates, and there are wide differences
even among plants belonging to the same
climate. A few of the earliest spring
plants begin their growth at or very near
the freezing-point of water: it is thought
by some observers that growth may, in
a few cases, take place even below this
point. Kjellmann states that the ma-
rine alge at Spitzbergen continue to de-
velop their thallus during the polar night
of three months, and that most of them
during this time produce their spores,
the temperature of the sea-water being
on the average one degree below zero,
Centigrade.!

But, on the other hand, many of the
tropical plants? cuitivated in hot-houses
cease growing when the temperature falls below 10° or 15° C.

1012. Themaximum temperature for growth is as wide in its
range for different plants as the minimum. Aside from the

1 Comptes Rendus, Ixxx., 1875, p. 474. See also Falkenberg: Die Algen
im weitesten Sinne, in Schenk’s Botanik, 1882.
2 See De Candolle : Physiologie végétale, 1832.

Fig. 170. Double-walled metallic box for keeping microscopic objects at a given
temperature while under observation. (Sachs.)

25

386 VEGETABLE GROWTH.

instances of plants growing in hot springs, it may be said to
lie at or very near 50° C. ‘The figures obtained by Sachs for the
common plants he experimented upon are in general between
36° and 46° C. Itis a curious fact that some tropical plants
are not capable of bearing a higher temperature than a few
plants of cold countries.?

1013. The optimum tenperature for growth lies in most cases
between 20° and 36° C.

1014. The following table, compiled by Pfeffer, exhibits at a
glance the cardinal points of temperature as they have been
determined by four observers : —

1 Pfeffer : Pflanzenphysiologie, ii., 1881, p. 123.

Fig. 171. Apparatus for keeping seedlings in aconstant temperature The drum at
d isan ordinary thermo-regulator by which the flow of illuminating gas can be controlled
within narrow limits ‘To insure still greater control, the more sensitive regulator, 7.
is also employed. The cylindrical vessel, z, has double walls, the space between them
being filled with water. Under this vessel a very small burner is sufficient even for
ontimum temperature. (Pfeffer.)

RELATIONS TO LIGHT. 387

Temperature for Growth.

plamerotyBlonts Minimum.| Optimum. Maximum. Observer:
°C. 2:6, °c
1
Triticum vulgare. . j oe } a 42.8 Ropoen.!
Hordeum vulgare. 5. 28.7 37.7 | Sachs.
Sinapis alba . 0 j 21. 28.0 |; De Candolle.?
27.4 j over a 2 | De Vries.4
Lepidium sativum . 1.8 i 21. De Candolle.
27.4 i below a7 2 De Vries.
Linum usitatissimum 1.8 j 21. ( 28. De Candolle.
27.4 Vover 37.2 | De Vries.-

Trifolium repens . 5.7 21-25. below 28. De Candolle.
Phaseolus multiflorus 9.5 33.7 46.2 | Sachs.
Pisum sativum 6.7 26.6 Koppen.
| Lupinus albus 7.5 28. Koppen.

j 0.5 33.7 46.2 Sachs.
Zea Mais 9.6 32.4 Koppen.

rt 9. 21-28. 35. De Candolle. ;
Cucurbita Pepo 13.7 33.7 46.2 | Sachs.
Sesamum orientale 13. 25-28. below 45. De Candolle.

1015. Relations of growth to light. It is only under the influ-
ence of light that the plant can prepare from inorganic matter

1 Text-book, 2d Eng. ed., p. 830.

2 Warme und Pflanzensachsthum, 1870, p. 43.

3 Bibliothéque universelle d. Geneve, Archives des Sciences physiques,
xxiv., 1865, p. 243.

e Matériaux pour la connaissance de l’influence- ‘de la température sur les
plantes, Archives Néerlandaises, v., 1870, p. 385. ~

Koppen has given an inatractive table which exhibits the relations of
growth to temperature in a few common plants. The figures denote the growth
in forty-eight hours of the whole descending axis of each plantlet.

i perature, upint Pisum <8 a itie

nee °¢, oe sativum Vicia Faba. | Zea Mais. Ro
10.4 5.5 4.6
144 9.1 5.0 4.5
17. 11.0 5.3 6.9
21.4 25.0 255 9.3 3.0 41.8
24.5 310 30.0 10.1 10.8 59.1
25.1 40.0 27.8 11.2 18.5 59.2
26.6 5h1 53.9 21.5 29.6 86.0
28.5 50.1 40.4 153 26.5 13.4
30 2 43.8 38.5 5.6 64.6 1OL9
31.1 43.3 38.9 8.0 49.4 914
33.6 12.9 8.0 50.2 40.3
36.5 12.6 8.7 20.7 5.4
39.6 6.1 11.2

ah

388 VEGETABLE GROWTH.

materials for its growth ; but ifan adequate amount of assimilated
substance has been stored up, growth can go on in the dark until
this store is exhausted. It is, in fact, in the dark that nearly
all vegetable growth takes place. It is well known that all the
points of growth in the ordinary higher plants are more or less
protected from the action of light. Thus, the growing tissues of
buds are concealed beneath external structures; so also is the
cambium by which dicotyledons increase in thickness.

1016. When, however, a shoot develops in darkness it is apt
to become much more attenuated than when it develops in light ;
its leaves are etiolated, and of abnormal shape and diminished
size. Such shoots are said to be ‘‘ drawn.”

1017. There is considerable difference in the degree to which
different parts of plants are affected by the withdrawal of light,
and there are also differences in this respect between different
species. The effect of darkness upon shoots is well shown by
the simple experiment
of conducting a branch
of some strong plant
like Tropzeolum or a
gourd into a dark box,
all its other leaves be-
ing kept in the light.
The effects are more
striking when the shoot
is a flowering one;
the internodes will be-
come much drawn, the
leaves will be small
and blanched, the calyx
will be pale, but the
rest of the flower will
be hardly affected
either in shape or size.
It sometimes happens,
however, that the flow.
ers will be abnormal.

1018. The relations of growth to oxygen. All growth is accom-
panied by the oxidation of assimilated substance, or food. Can
growth be stimulated by furnishing to the plant a larger amount
of oxygen than it would obtain under natural conditions? This

Fia. 172. Growth of gourd in light and darkness, (Sachs.)

CHANGES IN THE RATE OF GROWTH. 389

question is not yet positively answered by any experiments. It
has been shown that some plants grow, for a time at least, more
rapidly when they are subjected to a slight increase of pressure of
the atmosphere by which they are surrounded ; but there are also
a few cases which indicate that some other plants may grow more
rapidly under a diminished pressure.

The ‘‘ resting” state of some plants cannot be shortened by
any increase in the amount of oxygen furnished; it is only after
the normal time of rest has ended that any growth begins.
When periods of rest cannot be disturbed by any ordinary change
in the surroundings, they may be held to be conservative, since
they are generally correlated with the climatic conditions of
peril from cold or from dryness, under which these plants
naturally live.?

1019. Periodical changes in the rate of growth. Even under
external conditions which are as nearly constant as possible
growth is not quite uniform in its rate. Thus, an extending
internode grows in length at first slowly, then with gradually
accelerating rapidity until a maximum of growth is reached,
from which point the rate declines until with maturity of the part
growth ceases. The line of growth, when given graphically, is
a curve known as the great curve of growth; and the period of
rise and decline is the grand period, to distinguish this from the
minor periods of accelerated growth, which appear on the curve
as small fluctuations.

1020. Properties of new cells and tissues. Newly formed cells
are generally characterized by the possession of a certain amount
of turgidity ; the young cell-wall exerting more or less resistance
to the expansive contents within. The contents are therefore
compressed to some degree by the confining wall; the action
and reaction varying, of course, with changes in the surroundings.
If a part of its water be withdrawn from the cell, the com-
pression is materially lessened; while, on the other hand, an
increase in the amount of water must augment it.

1021. These features have been recently re-examined by De
Vries, who has suggested a quantitative method for determining
the amount of turgidity at any given time. The method, when
reduced to its simplest terms, consists in the use of solutions of

1 For a very curious account of experiments upon the influence of electricity
upon growth, the student should see Grandeau : De l’influence de l’électricité
atmosphérique sur la nutrition des végétaux, Annales de Chimie et de Phy-
sique, sér. 5, tome xvi., 1879, p. 145.

390 VEGETABLE GROWTH.

salts of known strength in which the tissues are placed, and
which are then allowed to act upon the contents of the cells.
When the solutions are more dense than the fluids in the cavity
of the cell, an exosmotic action withdraws a certain amount
of the water from the cell, causing thereby a shrinking of its
contents which can be easily observed under the microscope, or
noted by curvature of the whole section. The method permits
the experimenter to ascertain within narrow limits the density
of the contents of a given cell, and to determine the relative
degree of turgidity in different cases. When a cell undergoes
no change of form upon being placed in a solution of a given
strength, that solution is taken as a measure of the density of
its contents.?

1022. Tensions in cell-wall. There may frequently be observed
a tension of different layers of the cell-wall. This can be easily
demonstrated by making thin sections of any succulent tissues
from which cells can be readily detached ; a curvature will be
detected at the moment of cutting.

1023. Young cell-walls are elastic to a certain extent; but
their limit of elasticity is easily exceeded, and tben they remain
in the stretched condition. When an internode is strongly
stretched in the direction of its length, it undergoes permanent
elongation. This elongation may amount in some cases to three
or even five per cent; whereas the temporary extension in the
same instances may range from seven to seventeen per cent.
The extensibility diminishes, while the elasticity increases, with
the age of the internode.

1024. From his experiments Sachs draws the following con-
clusions regarding growing internodes: (1) After flexion they
do not completely recover their straightness; (2) one vigorons
bending, and to astill greater extent repeated ones in opposite
directions, leave the internode flaccid, or deprive it of its rigid-
ity; (8) when growing internodes are sharply struck, there is
a sudden curvature, the concavity of which lies towards the
direction of the blow.?

1025. Tension of tissues. Under the ordinary circumstances
of growth walls of young cells continue to be somewhat elastic

1 Plusmolysis. For a full account of the quantitative action of numerous
plasmolytic agents the student should consult De Vries’s paper in Pringsheim's
Jahrbiicher for 1884, where the effect of potassie nitrate and other substances
upon the protoplasmic film is detailed at length. In the Laboratory at Cam-
bridge, Mr. Puffer has confirmed most of De Vries’s observations.

2 Sachs : Text-book, 2d Eng. ed., 1882, pp. 784-788.

TENSION OF TISSUES. 391

and hence exhibit distinct tensions. If there is a marked dif-
ference in the rate of growth between the internal and the ex-
ternal cells in any organ, as is the case in most young stems,
the more superficial tissues are stretched to some extent by the
internal ones; hence arise tensions of tissues, the organ in
this state being in a balanced condition, in which the equilibrium
can be disturbed by slight external or internal causes. The
following experiment exhibits the phenomenon of tension very
strikingly: From a long and thrifty young internode of grape-
vine cut a piece which shall measure exactly one hundred units.
for instance, millimeters. From this section, which measures
exactly one hundred millimeters, carefully separate the epi-
dermal structures in strips, and place the strips at once under
an inverted glass to prevent drying; next, separate the pith in
a single unbroken piece wholly freed from the ligneous tissue.
Finally, remeasure the isolated portions, and compare with the
original measure of the internode. There will be found an
appreciable shortening of the epidermal tissues and a marked
increase in length of the pith.1_ The young ligneous tissue is
generally shortened by its release, but this result is by no
means constant. The most astonishing feature is the great
difference which exists between the length of the external tis-
sues and that of the internal tissues which up to the period
of isolation they had compressed. The external parts had been
plainly stretched to a certain extent, while the internal had
been as obviously confined by them. The tensions are not only
in the direction of the length, but are also transverse. Similar
tensions are to be found also in foliar organs. But there are

1 The following table exhibits the remarkable differences in tension be-
tween the outer and the inner parts of young shoots of Nicotiana Tabacum.
Each internode is first cut squarely off at both ends, and then carefully sliced
lengthwise so as to separate the bark, wood, and pith from each other. Sup-
posing the length of the whole internode to be one hundred units, the length
of the cortex will fall short of this, while that of the pith will considerably
exceed it.

Length of the Isolated Tissue.
Number of the Internode, biti

counting from the youngest. Cortex. Woody part. Pith.
I-lV.. . . 94.1 98.5 1029
V.-VII. é a 96.9 98.9 103 5
VIIL.-IX. z 96.5 98.5 100.9
X.-XL. ae . 99.5 99.5 102.4

392 VEGETABLE GROWTH.

some parts, as for example most roots near their extremity,
which do not exhibit this phenomenon.

1026. Geotropism. Suppose a young shoot to possess the ten-
sion already described; let this be placed, while growing, in an
horizontal position. In consequence of its position the nutri-
ent fluids will, from the force of gravitation, have a tendency
to collect in greater amount in the cells upon its under side.
Their presence on that side will not only cause an increase
of turgescence there, but will offer to the growing cells a larger
amount of available material for immediate use in growth,

especially for laying down the cell-wall. From one or from
both of these causes there will therefore be an appreciable elon-
gation of the tissues on the under side, and hence a curving up-
wards will occur, which finally results in the assumption of the
erect position by the organ in question.

1027. If, on the other hand, the organ possesses little or no
tension, it is conceivable that the growth would result in a cur-
vature of the extremity towards the ground; this is seen in the
case of roots. The same factors produce an upward curvature
where there is marked tension of tissues, and permit a down-
ward curvature where there is little or no tension. It is a sig-
nificant fact that in the case of certain branches from roots the
direction of growth is oblique.

1028. Organs which turn towards the earth are termed geo-
tropic ; those which turn upwards are apogeotropic ; those which
pursue in their growth oblique directions have been termed
diageotropic.

1029. Heliotropism. It can be shown by exact measurement
that in many cases light, especially the more refrangible part of

Fig. 173 Vicia Faba Descent of root into mercury, (Sachs.)

HELIOTROPISM. 8938

the spectrum, has a retarding effect upon the growth of certain
parts, — for instance, upon that of shoots, — exhibiting itself
in the curvature of the part towards the side of greatest illu-
mination. Such curvatures are said to be heliotropic. It is,
however, well known that the shoots and some other parts of
a few plants turn away from the light; such are termed
aphelivtropic.

1030. Little is known positively as to the nature of the influ-
ence which light exerts upon growth. The studies of Vines
have shown that the influence is largely due to the modification
of the turgescence of growing cells. ‘* The conditions of growing
and of contractile cells are in some respects the same. Turgidity
is essential to the proper fulfilment of the functions of both, and
it has been shown that light has the power of inhibiting, more or
less completely, the activity of both. The must general case of
the action of light upon growing cells has been shown to be a
diminution in the rapidity of their growth. The cell with dimin-
ished or arrested growth may be fairly compared with one of the
cells of a rigid motile organ. In both, the micelle of the pro-
toplasm are in a state of stable equilibrium so that they do not
yield, in the former case to the force which tends to separate
them, namely, the pressure of the cell contents, and in the latter
to the force which tends to bring them nearer together. The
theory that the action of light upon growing cells and upon those
of motile organs is due to such a modification of the relations
existing between the micelle of the protoplasm that the mobility
of the micellae is diminished, thus gives a satisfactory explana-
tion of many phenomena which at first sight seem not to have
much in common.” ?

1031. Hydrotropism. It has been shown by several experi-
menters that rootlets when developing in moist air deviate
towards a moist surface. This phenomenon, which has been
examined in detail by Sachs, is termed Hydrotropism. The

1 In order to examine the effects of the different parts of the spectrum upon |
the growth and movements of plants, the student should cultivate in cases of
glass of different colors two or three seedlings, as many bulbous plants, and
some well-rooted cuttings of hardy house-plants, for instance Pelargonium.
Observe whether the growth is more or less rapid under blue glass, and note
whether all the seedlings cireumnutate in the same manner in the different
cases, It should be borne in mind that the bulbous plant as it starts has a
generous supply of available food, whereas the seedling has a more scanty store,
and the cutting very little.

2 Arbeiten des bot. Inst. in Wiirzburg, 1878, p. 147.

894 VEGETABLE GROWTH.

accompanying figure shows an easy method of demonstrating
this mode of governing the direction of growing roots.

174

1032. Thermotropism. As might be expected from what has
been said regarding the tensions of tissues and the facility with
which their balance is disturbed, the effect of warmth in govern-
ing the direction of a growing organ must be considerable. Cur-
vatures dependent upon temperature are called thermotropic.

1033. Assumption of definite form during growth depends, of
course, chiefly upon inherited tendencies; but there have been
experiments which show that to a slight extent it may be pos-
sible by external influences to induce special shapes of growing
structures. Among the most interesting of these are the experi-
ments by Pfeffer? upon the growth of bilateral organs in some
of the lower plants, especially Marchantia; by De Vries? upon

1 Arbeiten des bot. Inst. in Wiirzburg, 1871, p. 77.
2 Arbeiten des bot. Inst. in Wiirzburg, 1872, p. 223.
Fia. 174 Roots of seedlings affected by moisture during their descent. The ap-

paratus consists of a network frame filled with moist sawdust in which the seedlings
germinate. (Sachs.)

FORCE EXERTED DURING GROWTH. 395

bilateral symmetry; by Vochting? upon the modification of
foliar and axial organs.

1034. The amount of force which is exerted by certain organs
during their growth has been accurately measured for only a few
cases. Thus Darwin? found that the transverse growth of the
radicle of a germinating bean was able to displace a weight of
1,500 grams, or 3 lbs. 4 oz., and in another instance, 8 lbs. 8 oz.
‘« With these facts before us, there seems little difficulty in under-
standing how a radicle penetrates the ground. ‘The apex is
pointed, and is protected by the root-cap; the terminal growing
point is rigid, and increases in length with a force equal, as far
as our observations can be trusted, to the pressure of at least a
quarter of a pound, probably with a much greater force when
prevented from bending to any side by the surrounding earth.
Whilst tlus increasing in length it increases in thickness, push-
ing away the damp earth on all sides, with a force of above
eight pounds in one case, of three pounds in another case.
. . . The growing part does not therefore act like a nail when
hammered into a board, but more like a wedge of wood, which,
whilst slowly driven into a crevice, continually expands at the
same time by the absorption of water; and a wedge thus acting
will split even a mass of rock.”

By means of a framework placed around the fruit of a vigor-
ous squash kept under conditions most favorable to its rapid
development, Clark? estimated the force exerted by growth to
be about 5,000 pounds.

1035. That external pressure can retard growth is well shown
by the experiments of De Vries* upon the formation of autumn
wood (see page 138). By increasing the external pressure ex-
erted by the bark he was able to diminish the calibre of the
wood-cells and ducts ; whereas, by diminishing the pressure (by
making longitudinal incisions into the bark) he was able to

1 Botanische Zeitung, 1880, p. 593.

2 The Power of Movement in Plants, 1881, p. 76.

3 For a full account of this experiment, see Report of the Secretary of the
Massachusetts Board of Agriculture for 1874.

The great force exerted by the increase in size of the stems and roots of
woody plants is sometimes demonstrated in an extraordinary manner by the
development of seedlings in crevices. Thus, at the Marien Cemetery in
Hanover, Germany, the base of a tree has dislodged the heavy stones of a
strongly built tomb. One of the stones, which measures 23 X 28 X 56 inches,
has been lifted upon one side to the height of five inches. The tree measures
just above its base from ten to fourteen inches in diameter.

4 Flora, 1872, p. 241.

396 VEGETABLE GROWTH.

cause a considerable enlargement of the similar elements. Fur-
ther observations led him to the conclusion that the striking
differences between spring and autumn wood, upon which the
annual rings depend, are due to the greater pressure which is
exerted by the bark in the latter part of the summer.

CHAPTER XIII.
MOVEMENTS.

1036. Most of the movements exhibited by plants are asso-
ciated with growth. In the preceding chapter attention has
been called to some of these movements, especially those which
are characterized by a change in the direction of growing
parts (see Geotropism, Heliotropism, etc.). In the present
chapter it is proposed to examine continuous and recurrent
movements, and indicate to what extent these are likewise the
accompaniment of growth.

In the existing state of knowledge no satisfactory classifica-
tion of the movements of plants can be made. The provisional
one now to be followed is adopted only for convenience.

1037. Locomotion, or movement of the whole organism from
place to place, can be observed in some of the lower plants.
One of the most interesting examples is furnished by Acthalium
septicum, which at certain stages of its existence consists of
approximately pure protoplasm in a naked state. Under favor-
able conditions this naked mass (the plasmodium), which fre-
quently attains considerable size, passes in a creeping manner
over a moist surface, thrusting out processes in an apparently
irregular manner, sometimes retracting them, but more often
bringing up to the advanced part the rest of the uneven mass.

The sensitiveness of this mass to the action of external influ-
ences renders it a suitable object for the examination of the
essential properties of protoplasm, and many of the more im-
portant facts relative to its movement have therefore already
been given (see 550). It is important to notice particularly that
there is a rhythmical pulsation of the sap-cavities or vacuoles in
the plasmodium, dependent, it is supposed, upon the irregular
absorption of water with a varying imbibition power. This spon-
taneous pulsation is somewhat affected by external conditions ;
for instance, it is increased in rate by heat and diminished by
eold.

1038. Portions of protoplasmic matter concerned in the repro-
duction of many of the lower plants, especially those which

898 MOVEMENTS.

live wholly in the water, as the alge, have the power of inde-
pendent locomotion. This is exhibited strikingly in the motile
spores, which are provided with cilia, and can thereby propel
theinselves from place to place with considerable rapidity. Sim-
ilar independent motion is shown also by the antherozoids of
many of the lower and even some of the higher cryptogams.

The protoplasmic movement by which such locomotion is
secured is essentially identical with certain ciliary movements
observed in the animal kingdom.

1039. It is a familiar fact that some minute alge, furnished
either with walls of cellulose (Desmids) or cellulose impregnated
with silicic acid (Diatoms), possess the power of motion, but
the cause is not well understood. In the case of the skiff-shaped
diatom the motion is somewhat spasmodic, and the course of
the organism through the water is not in a straight line, but it
is nevertheless enabled to traverse a considerable distance in a
short time. Owing to the absence of any distinct cilia, it is
difficult to conceive the mechanism of propulsion. According to
Max Schultze there is a minute slit on
the under side of the motile diatoms, and
through this slit a delicate film of proto-
plasmic matter projects. By contact of
this motile film with surrounding objects,
the diatom, as it is supported in the
water, is transported from place to place.

These three cases of locomotion, name-
ly, of (1) naked protoplasm, (2) of ciliated
structures, (3) of apparently closed cells,
do not exhaust the list of instances of
motion of vegetable organisms from place
to place; other cases are referred to the
succeeding volume upon the lower plants.

1040. The movement of protoplasm with-
in cell-walls has already been sufficiently
examined (see 546); but attention should
now be called to the fact that chlorophyll
granules (which are always embedded in
the protoplasmic mass) frequently assume

175 at night, or when a portion of the leaf is
darkened, positions different from those
which they have during strong exposure to light. This change

Fie. 175. Circulation of protoplasm in hair of Gourd. (Sachs.)

HYGROSCOPIC MOVEMENTS. 399

of position is well observed in the thin leaves of some mosses, the
grains generally (1) gathering on the side walls under bright light,
but (2) occupying the upper and lower faces of the cells when
the intensity of the light is much diminished. The first mode
of arrangement is termed apostrophe, the second epistrophe.}

1041. Hygroscopic movements are dependent upon the property
possessed by dry vegetable tissues of swelling more or less under
the influence of moisture. They are most strikingly exhibited in
the case of simple parts, like the filamentous appendages of the
spores of Equisetum and the teeth of the peristome of certain
mosses, notably that of Funaria hygrometrica. They are also
seen in the long appendages of
many fruits; for example, in
the awns of some grasses, in
some Geraniacez, etc., where
they serve the useful purpose of
fastening the fruit with its en-
closed seed in favorable soil.
When the fruit falls upon moist
soil, it at first lies flat; later,
the extremity of the appendage
and the tip of the fruit form
fixed points in the ground; and
then, as moisture is absorbed
by the dry tissue, a spiral curva-
ture throughout the whole takes
place. This continues to twist
the tip of the fruit down into
the soil, much after the fashion
of a corkscrew. This kind of movement is most surprisingly
shown in some of the grasses of South America, and in our
native Stipa.

In not a few instances the whole plant becomes relatively dry,
rolling up into a roundish mass which becomes expanded again
upon access of water. Good examples of such action are afforded

1 In some cases the aggregation of the chlorophyll granules differs somewhat
from that described in the text. For a discussion of this subject, consult
Frank (Botanische Zeitung, 1871, and Pringsheim’s Jahrhiicher, viii., 1872),
also Stahl (Botanische Zeitung, 1880). Sachs, Prillieux, and Famintzin have
contributed much to the discussion.

Fia. 176. Cross-section through the leaf of Lemna triscula, showing the position of
the chlorophyll granules: .4, during the day; B, during exposure to strong light; C,
during the night. (Stahl.)

400 MOVEMENTS.

by the so-called Resurrection plant of California (Selaginella lepi-
dophylla) , and by the Oriental plant known as the Rose of Jericho.
The latter plant, when dry and shrunken into small compass,
takes the shape of an irregular ball, becomes detached from the
ground where it has grown, and may be blown about over great
distances; if it has ripe seeds, these are scattered during transit.

1042. Movements due to changes in structure during ripening
of fruits. The fruit of the common Impatiens, or Touch-me-
not, affords a familiar instance of the movements of this class.
As it approaches maturity, the valves of the capsule become
tense, each one, so to speak, holding the others in place; and
when they are disturbed by even a slight touch they separate
violently, and by their spring throw the seeds to considerable
distances. In some cases the mechanism is more elaborate,
notably in the cucumber-like fruit of Momordica Elaterium. In
this the separation of the fruit-stalk permits a sudden shrinking
of the whole pericarp and a violent escape of the seeds with a
viscid liquid through the opening made by the separation. The
seeds are projected considerable distances from the fruit.

Hildebrand?‘ distinguishes between (1) dry explosive fruits
(such as Violet, Witch-Hazel, and Lupinus luteus), and (2)
fleshy explosive fruits (such as Impatiens, Momordica, and
Cardamine hirsuta).

1043. Revolving movements, or Circumnutation. The tips of all
young growing parts of the higher plants, as well as the tips of
many of the lower, revolve through some orbit, either a circle or
some form of the ellipse, the latter sometimes being so narrow
that it becomes practically a straight line. During its revo-
lution a tip bows or nods successively to all points of the
compass; whence the name nutation, or, as termed by Sachs,
revolying nutation. Darwin, who re-examined the whole subject,
has suggested a more general term, namely, circumnutation.

‘¢Circumnutation depends on one side of an organ growing
quickest (probably preceded by increased turgescence), and
then another side, generally almost the opposite one, growing
quickest.” #

1044. Owing to the fact that there are numerous instances in
which the revolving movements are variously modified, that is,
‘¢a movement already in progress is temporarily increased in

1 Pringsheim’s Jahrbiicher, ix., 1873, p. 235, where the whole subject is
discussed in an interesting manner.

2 Darwin : Power of Movement in Plants, 1880, p. 99.

CIRCUMNUTATION. 401

some one direction and temporarily diminished or arrested in
other directions,” it has been found convenient to discriminate
between circumnutation and modified cireumnutation. Darwin
divides the latter into two classes of movements: (1) those
dependent on innate or constitutional causes, and independent
of external conditions, except that the proper ones for growth
must be present; (2) those in which the modification depends
to a large extent on external agencies, such as the daily alter-
nations of light and darkness, light alone, temperature, or the
action of gravity. It is plain that such a division cannot be ab-
solute ; in fact, numerous intermediate cases are known to exist.

1045. Methods of observation of circumnutation. For meas-
uring the rate and determining the exact direction of the move-
ments of circumnutating parts when the parts are small and
the movements slight, the following methods described by Dar-
win’ can be employed in nearly all cases where it is necessary
to magnify the amount of displacement.

1 Power of Movement in Plants, 1880, p. 6.

Fig. 177. Angular movements of a leaflet of Averrhoa bilimbi during its evening
descent, when going to sleep. Temp. 78-819 F. The ordinates represent the angles
which the leaflet made with the vertical at successive instants. A fal! in the curve
represents an actual dropping of the leaf, and the zero Jine represents a vertically
dependent position. Each oscillation consists of a gradual rise followed by a sudden
fall, (Darwin.)

26

402 MOVEMENTS.

A very slender filament of glass, made by drawing out a thin
glass tube until it is no larger than a hair, is to be affixed to the
tip of the root, stem, or leaf under observation ; this is easily
done by means of a quickly drying varnish, for instance shellac
dissolved in alcohol. In order to mark the path made by the
filament it is best to cement to the tip of the slender hair of
glass a very minute bead of black sealing-wax, ‘‘ behind which
a bit of card with a black dot is fixed to a stick driven into the
ground. The bead and the dot on the card are viewed through
the horizontal or vertical glass plate (according tv the position of
the object), and when one exactly covers the other, a dot is made
on the glass plate with a sharply pointed stick dipped in thick In-
dia ink. Other dots
are made at short
jntervals of time,
and these afterwards
joined by straight
lines. The figures
thus traced are an-
gular ; but if the
dots are made every
one or two minutes
the lines are more
curvilinear, as oc-
curs when radicles
are allowed to trace
their own course on
smoked glass plates ”

‘¢ Whenever a
great increase of the
movement is not re-
quired, another and in some respects a better method of obser-
vation is followed. This consists in fixing two minute triangles
of thin paper, about one twentieth of an inch in height, to the
tivo ends of the attached glass filament; and when their tips are
brought into a line so that they cover one another, dots are made
as before on the glass plate.” !

178

1 It is very convenient to employ large bell-jars, or hemispherical glasses,
as glass screens upon which to record the dots indicating the position of the
tip at any given moment. It must be remembered that in all these cases there

Fie. 178. Tracing, showing the conjoint circumnutation of the hypocotyl and cotyle-

dons of Brassica oleracea during 10 hours and 45 minutes. Figure reduced to one half
original scale, (Darwin.)

CIRCUMNUTATION IN SEEDLINGS. 403

1046. Circumnutation in seedlings. That part of the axis which
is below the cotyledons is made up of a rudimentary stem known
as the cuulicle or hypocotyl, and a rudimentary root or radicle
proper. The part of the young stemlet above the cotyledons is
termed the epicotyl. In the cotyledons of the plantlet, when
freed from the seed-coats, and in all parts of the young axis,
slight movements can be observed. In all observations it is
necessary to remove the plantlet as far as possible from disturb-
ing conditions ; thus, all light must be excluded until the moment
of making the observation, when only a faint light should be
employed.

1047. Two facts are easily apparent with regard to the revolv-
ing rudicle: (1) its extreme sensitiveness to contact; (2) its ten-
dency to yield to geotropism (see 1026).

1048. The caudlicle, upon emerging from the seed-coats, is
often more or less arched: but it may become straight after a
short time, when it can be seen to pass through an elliptical orbit
by which the plane of the cotyledons is somewhat inclined suc-
cessively to all points of the compass. Darwin has shown that
even before the liberation of the caulicle from the seed-coats, when
both columns of the arch are held in the soil, the top of the arch
moves with considerable regularity. It is difficult to understand
how the summit of the arch formed by the curved caulicle can
revolve when both of its supporting columns are fixed in the soil.
Darwin has accepted an explanation suggested by Wiesner,
which is briefly as follows: In a given internode (it must be
remembered that the caulicle represents the first internode of
the seedling, as shown in Volume I. page 9) there may be a zone
in which the growth is equal on all sides, and which may be
termed the zone of indifferent growth, while on each side of this
there may be two others in which there is unequal growth at
intervals of time. Then by the faster growth on one side of the
arch the summit would be thrown to one side, and this process

is more or less distortion produced by the best methods of projection, and in
all accurate observations this must be taken into account.

When seedlings are inverted so that the glass filament is held upwards, it
must be noted that the influence of gravitation must come in as a modifying
element. To mark the amount of influence exerted by gravitation, it is well
to vary the length and weight of the filament employed. But it must be ob-
served that the weight of the organ itself is the most important element in the
problem. Moreover, it has been observed that all young growing parts, espe-
cially the extremity of the radicle, are more or less sensitive ; and hence the
course of the filament may be somewhat modified by even slight contact.

404 MOVEMENTS.

would sooner or later be succeeded Ivy its reversal; and thus the
summit would be made to circumnutate.

1049. Darwin’s? illustration of the movements of the parts of
seedlings gives a clear idea of their sequence. ‘‘ A man thrown
down on his hands and knees and at the same time to one side
by a load of hay falling on him, would first endeavor to get his
arched back upright, wriggling at the same time in all directions
to free himself a little from the surrounding pressure; and this
may represent the combined effects of apogeotropism and cir-
cumnutation when a seed is so buried that the arched hypocoty]
or epicoty] protrudes at first in a horizontal or inclined plane.
The man, still wriggling, would then raise his arched back as
high as he could; and this may represent the growth and con-
tinued circumnutation of an arched hypocotyl or epicotyl before
it has reached the surface of the ground. As soon as the man
felt himself at all free, he would raise the upper part of his body,
whilst still on his knees and still wriggling ; and this may repre-
sent the bowing backwards of the basal leg of the arch, which in
most cases aids in the withdrawal of the cotyledons from the
buried and ruptured seed-coats, and the subsequent straight-
ening of the whole hypocotyl or epicotyl, circumnutation still
continuing.”

1050. The cotyledons not only share the movement of the
caulicle, but they have also an independent movement which
is greatly modified hy slight changes in the surroundings. Freed
from their seed-coats, they move upwards and downwards in very
narrow ellipses, and at different rates in different plants. Gen-
erally their movement takes place only once in the course of the
twenty-four hours: in Cassia tora, on an average, once in about
two hours; in Oxalis rosea, once in about three hours; while in
Tpomeea coerulea Darwin observed the change of position to occur
almost hourly. It is noticeable that the cotyledons may change
the direction of their movement slightly at different times of the
day, and may thus have a zigzag course during a part of the day
and a nearly regular orbit during the rest.

1051. In some of the seedlings which have been examined with
especial reference to their movements there is a joint or swelling
to be detected at the base of the petiole. This is the equivalent
of the pulvinus commonly found in Sensitive plants ; changes in
the position of cotyledons provided with such joints depend, as
in the case of sensitive leaves, upon variations in the turgescence

1 Power of Movement in Plants, 1880, p. 106,

TWINING PLANTS. 405

of the cells composing it, while changes in the position of cotyle-
dons devoid of them are due to unequal growth.

1052. Circumnutation of the young parts of mature plants. By
methods similar to those described in 1045, it can be shown that
the growing extremities of stems, branches, leaves, and their
numerous modifications possess the power of movement; in
sume instances exhibiting essentially the same phenomena as
those presented by the parts of the seedling, while in other cases
they show differences at an early stage. The most striking of
these differences is that observed in twining stems. In this case
there is a greatly increased amplitude of the orbit through which
the tip of the stem passes. Although only a special case under
a general class, twining stems may well receive a somewhat
detailed description.

1053. Twiners are distinguished from proper climbers by the
absence of any special organs, other than the stem itself, for
grasping = sup-
ports; climbers
being provided
with some sort
of tendrils, or
other help, by which the plant is held to its sur-
roundings. Taking the simplest cases of twiners,
such as that of the common Morning Glory, it is
to be observed that (1) the revolving movement
begins at the earliest moment; (2) only a few
young internodes are concerned in the revolving ;
(3) the revolving stem cannot twine around a
smooth support (for example, a glass rod), but
requires in the support some degree of rough-
ness; (4) there is a limit of size to the support,
different for different twiners, beyond which it
cannot be grasped by the revolving stem; (5)
the direction of the revolution is not the same for all twiners;
(6) the rate differs with the plant and with the surroundings.

1054. In the early state of a twining plant the movements are
in narrow ellipses; but with even a slight increase in size of the
seedling, the transverse axis of the ellipse becomes greater, and
goon the orbit is practically a circle.

1055. The number of internodes concerned in the twining
movement is usually not more than three or four, and sometimes

179

Fic. 179. Revolving shoot of Morning Glory.

406 MOVEMENTS.

only two are involved. The internodes below the seat of move-
ment are rigid. The revolving is associated with growth, but
the growth alone is probably not the sole cause of the move-
ment.

1056. It is only the young internodes which are capable of
spontaneous movement; but growth itself, unassociated with
changes in the turgescence of the tissues upon the different sides,,
would not be sufficient to account for the movement. It must
be remembered that the young stem possesses remarkable ten-
sions, which are easily disturbed by slight internal as well as
external causes. The increased turgescence of its cells upon one
side, or their diminished turgescence on the other, or the action
of both conjointly, followed as this is by an increased growth of
the turgescent part, would produce sufficient change in the cur-
vature of the stem to bring about the twining movement.

1057. When a twining stem comes in contact with a smooth
support, it generally slides up the support, but fails to grasp it.
The check which is given by a smooth support sometimes brings
about a change of position in the revolving stem, which is thus
described by Darwin: ‘‘ When a tall stick was so placed as to
arrest the lower and rigid internodes of Ceropegia, at the dis-
tance at first of fifteen and then of twenty-one inches from the
centre of revolution, the straight shoot slowly and gradually slid
up the stick, so as to become more and more highly inclined,
but did not pass over the summit. Then after an interval suffi-
cient to have allowed of a semi-revolution, the shoot suddenly
bounded from the stick, and fell over to the opposite side or
point of the compass, and reassumed its previous slight inclina-
tion. It now recommenced revolving in its usual course, so that
after a semi-revolution it again came in contact with the stick,
again slid up it, and again bounded from it and fell over to the
opposite side. This movement of the shoot had a very odd ap-
pearance, as if it were disgusted with its failure, but was resolved
to try again.”?

1058. Many of the common twiners of temperate climates are
able to twine round very slender supports, for instance a small
cord, but are unable to twine round a post or trunk of a tree.
This does not, however, appear to he wholly dependent upon the
amplitude of the revolution. In tropical regions some of the
twiners ascend trunks of immense size, but they are generally
assisted by adventitious roots, etc.

1 Climbing Plants, 1875, p. 21.

MODIFIED CIRCUMNUTATION. 407

1059. Any given twiner generally twines in one direction
only ; for instance, the hop moves in the direction of the hands
of a watch, or to use another expression, follows the sun ; the
Morning Glory moves in an opposite direction. But there are
some cases in which the direction of twining is reversed even
during a comparatively short distance. In the tropics this
reversal is said to be common.!

1060. The time required for the revolution of a twiner varies
in different plants, and is by no means constant for the same
plant at different stages of its development. In the case of the
Morning Glory, the average time required for the revolution of
a thrifty shoot under favorable conditions is about three hours.

1061. Twiners are affected somewhat by the amount of light
received, but the revolving goes on uninterruptedly night and
day. The increase of rate when a revolving shoot is approach-
ing a window may be equal to a tenth, or somewhat more, of the
whole period of the revolution. Such acceleration is very differ-
ent for different plants.

1062. Modified circumnutation. The effect of the influence of
light in increasing the rate of movement in a twiner is a good
example of a large class of modified movements. These move-
ments have already been considered in the chapter on ‘‘ Growth,”
ander the terms Heliotropism, Geotropism, etc., but must be
again referred to in connection with the universal movement,
circumnutation. When it is desirable to free any circumnu-
tating part from the influence of a disturbing factor, for instance
light, great care must be taken to avoid subjecting it to abnor-
mal conditions such as result when a seedling is kept in the
dark in order to free it from the influence of light on its
movements. When so kept it undergoes changes of form with
its blanching, and therefore little security is felt that all its
behavior is normal. In the instance of green plants which
demand light for their healthy activity the removal of disturbing
factors is a task of considerable difficulty.

A part of the difficulty is removed by the use of some instru-
ment by which the plants can be made to revolve slowly in a
given plane, thus exposing the different sides successively to
the action of the force. A simple form of this appliance is

1 Fritz Miiller is quoted by Darwin as saying, that the stem of Davilla
twines indifferently from left to right or from right to left ; and that he once
saw a shoot which had ascended a tree about five inches in diameter reverse
its course.

408 MOVEMENTS.

known as the clinostat. It consists of a clock-work which car-
ries a disc on which can be placed growing plants: by the revo-
lution of this horizontal disc all parts are in turn given the same
_amount of illumination. If the clock-work is so arranged as to
rotate a horizontal shaft to which a growing plant can be affixed,
any one part of the plant will be exposed to the influence of
gravitation in precisely the same manner and to the same extent
as all other parts.

When circumnutation is plainly modified by unequal growth.
striking disturbances are produced which have received much

(— |

180

investigation. Among these cases are the changes of position
which many peduncles undergo during the development of flow-
ers and fruits. Although the extremity of the flower-stalk passes
through its definite orbit, it is in some instances so affected by
the greater growth of the upper side as to curve downwards,
while a similar excessive growth on the under side will produce
an upward curvature. De Vries, who has given much attention
to these phenomena, has coined the adjectives epinastic, denoting
curvature from growth on the upper side, and hyponastic, that
from growth on the under side of an extending organ.

Fic. 180. Disc ofa clinostat covered by a glass case g, and bearing two Windsor
beans with primary and secondary roots.

NYCTITROPIC MOVEMENTS, 409

1063. The ample revolving movement is not confined to stems,
but is observed in some modified branches and leaves, for ex-
ample in certain ten-
drils, etc. A single
instance will serve to
show the remarkable
nature of the move-
ment in the case of
the tendrils of Echi-
nocystis lobata, as de-
seribed by Darwin :1
“These are usually
inclined at about 45° 181
above the horizon, but
they stiffen and straighten themselves so as to stand upright in
a part of their circular course; namely, when they approach and
have to pass over the summit of the shoot from which they arise.
If they had not possessed and exercised this curious power, they
would infallibly have struck against the summit of the shoot and
been arrested in their course. As soon as one of these tendrils
with its three branches be-
gins to stiffen itself and rise
up vertically, the revolving
motion becomes more rapid ;
and as soon as it has passed
over the point of difficulty,
its motion coinciding with
that from its own weight
causes it to fall into its previously inclined position so quickly
that the apex can be seen travelling like the hand of a gigantic
clock.”

1064. Nyctitropic, or sleep, movements. The foliar organs of
many plants assume at nightfall, or just before, positions unlike
those which they have maintained during the day. In many
cases the drooping of the leaves at night is suggestive of rest,
and the name given by Linnzus to this group of phenomena.
namely, “the sleep of plants,” seems appropriate. But in numer-
ous cases the nocturnal position is one of obvious constraint,
and considerable force has to be expended in lifting the leaf to

1 Power of Movement in Plants, 1880, p. 266.

Fie. 181. Leaf of Coronilla rosea at night. (Darwin.)
Fia. 182. Leaf of White Clover. 4, day position; B, night position. (Darwin.)

410 MOVEMENTS.

the new position. The diversity of positions can be only imper-
fectly indicated by the accompanying illustrations.

According to Pfeffer, the sleep-movements of leaves and of
cotyledons depend upon increased growth on one side of the
median line of the
petiole and midrib,
followed after a
certain interval of
time by a corre-
sponding growth
on the opposite
side. Thus in
ordinary —_ leaves
which droop at
night the depres-
sion is produced
by a slightly in-
creased growth on the upper side, and the rise in the morning
by a similar growth on the under side. But in the most striking
cases there is a
distinct appara-
tus at the base
of the leaf-stalk,
which accom-
plishes the same
movement by
simple turges-
cence of the op-
posite sides.

The apparatus
consists of an
enlargement
formed of cellu-
lar tissue in
which there is
often an appre-
ciable difference
between the
character of the
cell-walls on the upper and under side of the swelling. This
swelling, known as the pulvinus, permits the movement to be

183

Fic. 183 Leaflets of Averrhoa bilimbi at night. (Darwin.)
Fic. 184. Leaf of Acacia Farnesiana during the day and at night. (Darwin.)

SLEEP-MOVEMENTS. 411

continued long after the movements in young leaves destitute
of such an apparatus have ceased.

1065. The sleep-movements of cotyledons are extremely diverse,
but in general consist in an elevation of the tips, bringing the
upper faces into proximity, and sometiines into contact. It may
happen also that one or more of the early leaves developed
from the plumule approaches the elevated cotyledons. Dar-
win has noted that in some cases the cotyledons of plants,
with ordinary leaves which exhibit sleep-movements, may not
change their position at night, except as they do in simple
circumnutation.

185

1066. The utility of the sleep-movements of leaves and cotyle-
dons is believed to consist in protection from too great radiation
during the night. Darwin has shown by simple and conclusive
experiments that in the case of some plants this change of the
position of leaves at the approach of a chilly night is a matter
of life and death.

When leaves which naturally assume nyctitropic positions are
pinned or otherwise kept from changing their position, and the
plant is exposed to a temperature a little below freezing, under
a clear sky, into which the radiation of heat must go on rapidly
from the upper surface of the leaves, serious injuries result, the
leaves becoming browned and even killed; whereas, leaves on

Fig 185. Desmodium gyrans. 4, position during the day; B, position at night,

412 MOVEMENTS.

the same plant which are allowed to take the protective position,
escape.

1067. Sleep-movements of floral organs. These are, in general,
dependent, as Pfeffer has clearly shown, upon the alternate
growth of the opposed surfaces. For instance in a crocus, the
greater growth of the inner surface of the parts of the perianth
will bring about an opening of the flower, whereas the greater
growth of the outer surface will effect a closing.

Pfeffer’s method of investigation is capable of application, pro-
vided one has a microscope which admits of being held with its
tube horizontal. A perianth leaf is carefully detached without
too much violence from the flower, and immediately placed in a
small tube containing water, so that the expanded part may be
brought within the field of the microscope. If fine lines are
measured off upon its inner and outer surfaces in India ink,
their gradually increasing distance from each other can be
watched to good advantage. It can then be clearly seen that
when the part curves outward it is owing to an increased growth
upon the inner surface, and vice versa. That there is an ante-
cedent turgescence is very likely, as has been repeatedly pointed
out by De Vries and others. It is probable also that in a few
cases the opening and closing are due to a temporary turges-
cence unaccompanied by much growth.

Changes in illumination and in temperature are sufficient to
effect the alternations of growth and of turgescence in delicately
constituted parts, where there is a balanced tension existing
between the outer and inner tissues.

1068. Times of opening and closing in the open air. Under the
ordinary conditions of an equable climate the times of opening
and closing of the flowers of a given plant do not vary widely.
Hence it is possible to construct a floral clock which shall mark
the hours with tolerable regularity. ‘The dial at Upsala, Sweden,
suggested by Linnzus. and that designed for Paris by De Can-
dolle,? are approximately correct; but in a climate having the
sharp and sudden differences of heat and of moisture which
characterize eastern North America such floral clocks are not
successful.

1 The following list from De Candolle’s Physiologie gives the hours of the
opening of certain flowers in Paris: —

Ipomeea purpurea 2. 1 ew ew ee ww ew 2 OAM
Calvstegia sepium . . . . ew ww ww Bed
Matricaria suaveolens . . . 2 1. wwe 45

THE TELEGRAPH PLANT.

1069. The Telegraph plant.

413

The most surprising instance of

rapid spontaneous movement is that which is exhibited by the

lateral leaflets of Desmodium
gyrans. Each complete leaf
of Desmodium consists of a
large terminal leaflet and two
little lateral leaficts. At
nightfall the terminal leaflets
sink vertically, and the peti-
oles are somewhat raised, so
that the terminal leaflets are
much crowded together upon
the stem (see Fig. 185.) The
cotyledons do not have this
nyctitropic movement, but
the first true leaf sleeps just
as do the older ones.

The lateral leaflets do not
fall at night, but at the tem-
perature of 36 to 38° C., or
even somewhat higher, keep
up, night and day, an irregu-
lar jerking movement, which
has been compared to the
ticking of the second-hand of
a watch (or, formerly, to the
movements of the arms of a
Semaphore Telegraph).

The tip of the moving leaflet passes

Papaver nudicaule and most Cichoriacee. . . 5 A.M.
Convolvulus tricolor 5-6
Convolvulus siculus : ‘ 6 ae
Species of Sonchus and Hicreenin ‘ 6-7
Species of Lactuca . 7 se
Anagallis arvensis . 8 eg
Calendula arvensis . 9 s
Arenaria rubra ‘ 9-10 **
Mesembryanthemum medion * 10-11 re
Ornithogalam umbellatum 11 ee
Pasciflora cerulea 12 M.
Pyrethrum corymbosum 2 PM
Silene noctiflora . 5-6“
Cnothera biennis 6 sf
Mirabilis Jalapa . 6-7“
Lychnis vespertina . 7 ee
7-8 “ce

Cereus grandiflorus .

Fig. 186. Dasthithenn gyrans,

414 MOVEMENTS.

through its elliptical orbit in a period of from half a minute to a
minute or more, the time varying greatly according to the ex-
ternal conditions, but being nearly uniform under uniform high
temperature. The lateral leaflets move independently of one
another, one sometimes passing downwards while the other is
ascending, but there is no distinct relation between them.

At the base of the terminal leaflet, the base of the lateral leaf-
lets, and the base of the main petiole, are pulvini, to changes
in which the several movements are due.

1070. The cause of autonomic movements not fully known. As
to the cause of the periodic changes in turgescence and asso-
ciated growth which give rise to ‘‘ spontaneous ” movements, little
is at present known. The fact that in the naked protoplasm of
the plasmodium of the Myxomycetes the sap cavities exhibit
a rhythmical pulsation which is thought to be dependent upon
variations in the imbibition power of the protoplasm for water,
throws little light upon the ultimate cause which underlies vari-
able turgescence in one case and variable pulsation in the other.
Although variations in turgescence and associated growth are
everywhere observable in young and still parts of plants, in some
instances similar phenomena can be observed, as we have just
seen, in specialized organs which are no longer capable of
growth.

1071. DeVries? calls attention to the fact that organic acids or
their salts, as they are formed in tissues, have a marked effect
upon the turgescence of the cells composing the tissue. If these
compounds were produced first in the cells on one side of a shoot
or other motile organ, and then in the cells next to these, and
so on, the phenomena of circumnutation would be exhibited.
Its cause will probably be found in chemical processes which
cause the osmotic power of the cell-contents to vary.?

1072. Sensitiveness. By this is meant the capacity to react
against an irritation; thus, the root is said to be sensitive to
moisture, some leaves to light, etc. But it is usual to employ
the term in a more restricted signification ; following Darwin’s
cautious definition, ‘‘a part or organ may be called sensitive,
when its irritation excites movement in an adjoining part.” ® The
irritant may be shock, prolonged contact, a light touch, or a
chemical agent.

1 Botanische Zeitung, 1879, pp. 830, 847, and in an independent communi-
cation.

2 Pfeffer : Periodischen Bewegungen (1875).

8 Power of Movement in Plants, 1880, p. 191.

SENSITIVENESS OF ROOTS. 415

1073. It has been shown (1024) that young shoots react,
although somewhat sluggishly, against mechanical shock, their
change of form or direction depending on the character or direc-
tion of the blows received. In certain delicate tissues, especially
those which possess much simplicity of structure, change of form
and of direction may be produced in response to comparatively
slight mechanical or chemical irritation. It is to these that the
term sensitive tissues is properly applied.

1074. Sensitiveness of roots. ‘The tip of the caulicle is gen-
erally sensitive to contact and to caustics. There are, however,
great differences in the degree of sensitiveness; in some cases
slight contact being sufficient to cause reaction, while in others
the contact must be prolonged and accompanied by direct pres-
sure. If the caulicle with its unformed root is placed under
conditions where growth can take place with great rapidity, the
sensitiveness is much impaired and sometimes is wholly lost;
it is partially lost also when the caulicle grows slowly, or is
forced to grow out of season. Under natural conditions and at
a normal rate of growth the tip is sensitive for about one twen-
tieth of an inch. Ifa piece of caustic is applied to the tip (not
more than 1.5 mm. from the very end), the caulicle will curve
away from the irritated side. ‘The reaction is as plainly seen in
those cases where the caulicle does not elongate, but where the
root itself descends.

1075. The length of the portion of these organs which reacts is
about ten millimetres. The time of reaction varies for different
plants, being sometimes in five hours, and, according to Darwin,
almost always within twenty-four hours.

1076. ‘* The curvature often amounts to a rectangle; that is,
the terminal part bends upwards until the tip, which is but little
curved, projects almost horizontally. Occasionally the tip, from
the continued irritation of the attached object, continues to bend
up until it forms a hook with the point directed towards the
zenith, or a loop, or even a spire. After a time the radicle
apparently becomes accustomed to the irritation, as occurs in
the case of tendrils; for it again grows downwards, although
the bit of card or other object may remain attached to the
tip.”?

1077. The tip of the radicle has been shown (1046) to be
constantly circumnutating. By this movement the sensitive tip
is brought into contact with different sides of minute crevices in

1 Power of Movement in Plants, 1886, p. 193.

416 MOVEMENTS.

the soil,! and ‘as it is always endeavoring to bend to all sides,
it will press on all sides, and will thus be able to discriminate
between the harder and softer adjoining surfaces . . . conse-
quently it will tend to bend from the harder soil, and will thus
tollow the lines of least resistance.” ?

1 Darwin : Power of Movement in Plants, p. 197.

2 The two following passages should be carefully studied by the student,
since they embody in a few words Darwin's summary of most of the results of
his experiments upon radicles. Both passages are from the ‘‘ Power of Move-
ment in Plants,” 1880 :—

‘* We see that the course followed by a root through the soil is governed by
extraordinarily complex and diversified agencies, — by geotropism acting in a
different manner on the primary, secondary, and tertiary radicles, — by sensi-
tiveness to contact, different in kind in the apex and in the part immediately
above the apex, and apparently by sensitiveness to the varying dampness of
different parts of the soil. These several stimuli to movement are all more
powerful than geotropism, when this acts obliquely on a radicle which has been
deflected from its perpendicular downward course. The roots, moreover, of
most plants are excited by light to bend either to or from it ; but as roots are
not naturally exposed to the light, it is doubtful whether this sensitiveness,
which is perhaps only the indirect result of the radicles being highly sensitive
to other stimuli, is of any service to the plant. The direction which the apex
takes at each successive period of the growth of a root ultimately .determines
its whole course ; it is therefore highly important that the apex should pursue
from the first the most advantageous direction ; and we can thus understand
why sensitiveness to geotropism, to contact, and to moisture, all reside in the
tip, and why the tip determines the upper growing part to bend either from or
to the exciting canse. A radicle may be compared with a burrowing animal
such as a mole, which wishes to penetrate perpendicularly down into the
ground. By continually moving his head from side to side, or cireumnutating,
he will feel any stone or other obstacle, as well as any difference in the hard-
ness of the soil, and he will turn from that side ; if the earth is damper on one
than on the other side, he will turn thitherward as a better hunting-ground.
Nevertheless, after each interruption, guided by the sense of gravity, he will
be able to recover his downward course and to burrow to a greater depth”
(p. 199).

‘We believe that there is no structure in plants more wonderful, as far as
its functions are concerned, than the tip of the radicle. If the tip be lightly
pressed or burnt or cut, it transmits an influence to the upper adjoining part,
causing it to bend away from the affected side ; and, what is more surprising,
the tip can distinguish between a slightly harder and softer object, by which
it is simultaneously pressed on opposite sides.

“Tf, however, the radicle is pressed by a similar object a little above the
tip, the pressed part does not transmit any influence to the more distant parts,
but bends abruptly towards the object. If the tip perceives the air to be
moister on one side than on the other, it likewise transmits an influence to the
upper adjoining part, which bends towards the source of moisture. When the
tip is excited by light (though in the case of radicles this was ascertained in
only a single instance) the adjoining part bends from the light; but when

CIRCUMNUTATION OF TENDRILS. 417

1078. Sensitiveness of stems and branches. Under ordinary
conditions even twining stems are not sensitive to slight mechani-
cal irritation. The reactions to moisture, light, gravitation, etc.,
have been already noticed, and it is now intended to call atten-
tion to the extraordinary sensitiveness of certain tendrils, some
of which are modified branches, while others are modified leaves
or parts of leaves.

1079. Tendrils circumnutate, and by their revolving movement
reach out for a proper support. Moreover, they are produced
on the young
and circum-
nutating ex-
tremities of
shoots, so that two modes of revolution
are frequently to be observed simulta-
neously. But in this revolving move-
ment the tendrils are prevented from
becoming entangled with the rest of the
shoot. The manner in which this is
done is thus described: ‘‘ When a ten-
dril, sweeping horizontally, comes round
so that its base nears the parent stem
rising above it, it stops short, rises stif-
fly upright, moves on in this position
until it passes by the stem, then rapidly
comes down again to the horizontal po-
sition, and moves on so until it again
approaches and again avoids the im-
i oy pending obstacle.” }

nee 1080. When a light thread is placed
upon a long revolving tendril of Passifiora, Echinocystis, or

excited. by gravitation the same part bends towards the centre of gravity. In
almost every case we can clearly perceive the final purpose or advantage of the
several movements. Two, or perhaps more, of the exciting causes often act
simultaneously on the tip, and one conquers the other, no doubt in accordance
with its importance for the life of the plant. The course pursued by the radi-
cle in penetrating the ground must be determined by the tip ; hence it has
acquired such diverse kinds of sensitiveness. It is hardly an exaggeration to
say that the tip of the radicle thus endowed, and having the power of directing
the movements of the adjoining parts, acts like the brain of one of the lower
animals ; the brain being seated within the anterior end of the body, receiving
impressions from the sense organs, and directing the several movements”
(p. 572)... :
1 Gray : How Plants Behave, 1872, p. 18.
Fic. 187. Shoot of Passiflora, showing tendrils.
27

418 MOVEMENTS,

Sicyos, a curvature soon takes place in the direction of the con-
tact. If the plant is in a vigorous condition and the tendril is
young, a slight touch is generally sufficient to cause immediate
flexion. If a solid object, for instance a staff, is placed in con-
tact with such a tendril, the bending and coiling takes place at
once, and thus the organ is brought into close apposition with
the support.

1081. As soon as the tendril has coiled around its support, a
striking phenomenon is observed in the portion between the shoot
and the support: it begins to twist, throwing the whole thread
into a double coil, a part of which winds one way and the
rest ancther. There can be no doubt that this comes from the
action of the same force which causes the revolution in the ten-
dril before it becomes attached to the support, and the further
exercise of this force must necessarily produce two coils running

in opposite directions. After the tendril has made fast to its
support, its structure begins to change in a remarkable manner,
becoming much firmer and more elastic than before, —a provision
adapting it admirably to resist sudden strains upon the main
shoot from gusts of wind.

1082. But if the tendril in its revolution has failed to come in
contact with any proper support, it is thrown into a single coil,
which runs from the extremity of the tendril, and extends for
a short distance, perhaps half the whole length of the organ.
Sometimes, however, it simply becomes flaccid.

Fia. 188. Ampelopsis quinquefolia, or Virginia creeper.

SENSITIVENESS O/: LEAVES. 419

1083. In some cases tendrils are not sensitive to contact, but
are distinctly apheliotropic, turning away from the light, and in
this way securing for the plant an adequate mechanical support
upon some wall or the like. Grape-vines and Virginia creeper
furnish good examples of such tendrils. The branches of the
tendrils of the grape-vine sometimes clasp around a slender sup-
port, somewhat in the same way as an object would be grasped
by a thumb and finger.

The much-branched tendrils of species of Ampelopsis are also
apheliotropic ; but when the tips of the branches of the tendrils
come in contact with a wall, they become expanded into flat
discs which cling to the surface.

1084. Sensitiveness of petioles.
This can be easily examined in
the common climbing species of
Clematis,in Solanum jasminoides,
etc. The leaves circumuutate
and, in the case of compound
leaves, the separate leaflets also.
When young the sides of the
petioles are sensitive to touch,
bending towards where the pres-
sure or compact is. Shortly after
clasping the support by means of
this bending the petioles increase
in thickness, become stronger
and tougher than before, and
sometimes take on a structure
suggestive of a rigid branch.- In
Gloriosa the sensitiveness is very
marked in the leaf-tips, but only
on the under surface of the pro-
longed thread-iike extremity.

1085. Sensitiveness of leaf-blades. The fly-trap of Dionza
(considered by some an appendage to the proper leaf-blade) is
exquisitely sensitive to any touch upon the hairs which grow on
the faces of the trap. As soon as these are touched the trap
instantly closes, and the same effect follows a slight touch on
the median line. A cross-section through the leaf shows that
the parenchyma is thin-walled. The leaf of the small water-
plant Aldrovanda has likewise been shown to be sensitive.

Fia, 189. Solanum jasminoides.

420 MOVEMENTS,

1086. The leaflets of numerous plants exhibit a peculiar degree
of sensitiveness even to a slight touch. Among these are sey-
eral species of Mimosa and Oxalis.
The plant which has received the
fullest investigation is the easily
cultivated

1087. Mimosa pudica (the Sen-
sitive plant). This has compound
leaves consisting cf four long leaf-
lets, each of which is divided into
numerous minor leaflets arranged
in pairs. At the base of each leaf-
let, and also at the base of the
petiole, there is a pulvinus, com-
posed of peculiar cells. On the
upper half of the pulvinus these
are thicker-walled than on the
lower ; most of them contain round-
ish globules made up of a strong
solution of tannin in water, surrounded by a film of some albu-
minoid matter. These globules are not,
however, of any significance as concerns the
motility, since they are found in the paren-
chyma of the bark of some ligneous plants
(see 953).

1088. When a fully spread leaf is touched
at its extremity the many leaflets succes-
sively close in pairs, the upper surfaces
approaching and the tips falling somewhat
forward; the four
branches of the leaf
then draw near each
other, and the main
petiole inclines
downwards and
finally droops pas-
sively at the joint.
The recovery from
this position of col- 191
lapse takes place in
a few minutes, generally in about a quarter of an hour.

Fig. 190. Aldrovanda vesiculosa; the lower illustration shows the expanded leaf
much enlarged.
Fic. 191. Mimosa pudica.

SENSITIVE PLANT. 421

1089. If an irritant is applied to a single leaflet, the opposite
one may be the only other affected ; or, if the effect is more pro-
nounced, all the leaflets on a single division of the leaf may be
closed without affecting any on the other branches. Butif a still
sharper impulse is given, not only will all the leaflets on a single
leaf close, but other leaves on the plant may be affected. Thus
it is possible by applying a hot needle to a single leaflet to affect
all those on a small plant. A drop of strong sulphuric acid acts
in the same way.?

When a leaf of Mimosa is separated from its plant by a sharp
cut through its pulvinus, and is at once placed in a saturated
atmosphere, it soon recovers its normal expanded condition; if
now it is touched the leaflets will collapse as usual, and at the
moment of closing a drop of water can be seen exuding from the
cut surface. According to Pfeffer it is possible to observe that
the water comes from the parenchyma of the lower half of the
pulvinus.?

1090. According to Bert,’ who made use of a thermo-electric
apparatus, the pulvinus of a leaf of Mimosa in its normal condi-

1 For a study of the transmission of the shock, see Pfeffer, Pringsheim’s
Jahrbiicher, ix., 1878, p. 308.

Some of the effects produced by irritants upon the hairs of certain insectiv-
orous plants have been already described. The phenomena of aggregation
then alluded to must be now treated more in detail. It is described by Pfeffer
in the following words: ‘‘ Suddenly the contents of the cell acted on become
clouded by a separation of minute particles which aggregate to form masses.
These masses consist essentially of alouminous matters, which, from their col-
lecting the coloring substance in the cell-sap, become tinged. The whole
process of aggregation takes place in the cell-sap.”

Pfeffer points out the curious fact that while ammonic carbonate, without
any other irritant, will cause this aggregation, acetic acid will make it
disappear.

Such changes as aggregation and variations in turgescence are connected in
some way, not yet understood, with the imbibition power of protoplasm for
watery fluids. The mechanical or chemical irritants which temporarily dimin-
ish the capacity of protoplasm for retaining within the cell the maximum
quantity of water will produce a distinct effect upon the tension of the cell-
wall, and result in a change of its size or form, or both. The irritation thus
caused can be transmitted to a distant part. The intimate relations which
exist between the young cell-wall and the protoplasmic lining must not be
overlooked in any consideration of the subject of sensitiveness in plants.
Lastly, the continuity of protoplasm in many mobile and sensitive organs must
be borne in mind in the consideration of this subject.

2 Pflanzenphysiologic, ii., 1881, p. 237. See also Pfeffer’s Physiologische
Untersuchungen, 1873, p. 32.

8 Comptes Rendus, lxix., 1869, p. 895.

422

MOVEMENTS,

tion is always slightly cooler than the rest of the petiole, but
upon the movement from irritation it rises in temperature; not

enough, however,
to account for the
raising of so con-
siderable a weight
as that of the leaf.

1091. Some
physiologists have
regarded the sen-
sitiveness of the
pulvinus of the
Sensitive plant
and of other motile
parts as residing
chiefly if not whol-
ly in the cell-wall,
while others have

thought that it resided in the contractile protoplasm. It is now
generally held to be due to some sudden variation in the osmotic

power of the proto-
plasm, particularly in
its peripheral portion
in contact with the
eell-wall, by which the
turgescence of the cell
is suddenly changed.?

1092. If a plant
with motile leaves is
kept in darkness for
a day or so, even if
the temperature is fav-
orable to motion, its
power of movement is
either greatly impaired
or for a time wholly
lost. A diminished

amount of light is sufficient to produce the same effect in the

case of the Sensitive plant.

1 Compare Hofineister: Die Lehre von der Pflanzenzelle, 1867, p. 300 ;
. Briicke : Archiv fiir Anatomie, Physiologie, und wiss. Medicin, 1848, p. 434 ;
Unger : Botanische Zeitung, 1862, p. 118; 1863, p. 349.

Fic. 192 Transverse section of the motile organ of a leafiet of Oxalis carnea. (Sachs.)
Fic. 193. Vertical section through the motile organ of a leaflet of Oxalis carnea.

{Sachs.)

SENSITIVENESS OF STAMENS. 493

Sachs has given the name Phototonus to the normal motile
condition resulting from alternation of day and night. ‘A
plant in this condition, if placed in the dark, will remain for some
time (hours or even days) ina state of phototonus, which then
disappears gradually ; the plant is therefore under normal condi-
tions in a state of phototonus even during the night. In the
same manner a plant which has become rigid in continued dark-
ness retains its rigidity for some time (hours or even days)
after being exposed to light. The two conditions therefore
pass over into one another only slowly.”

1093. Temporary rigidity is produced in the case of the Sensi-
tive plant by an exposure to a temperature of 15°C. The same
effect is produced by a temperature above 50° C., according to
Bert’s observations at about 60° C. It is stated by him that the
sensitiveness of Mimosa is destroyed by exposure to a green
light, while plants placed under bell-jars of the following colors
remained healthy: white, red, yellow, blue, and violet.?

1094. Sensitiveness of stamens. No better illustration of
this is afforded than that given by stamens of the common Bar-
berry. The six stamens lie curved under the arching petals, but
if a filament is lightly touched it is jerked suddenly forward,
bringing the anther into apposition with the pistil.

1095. The filaments of certain Composites are sensitive. The
case of the common Chicory has been thus described: The
anthers are conjoined to form a tube supported upon five dis-
connected filaments which are at first more or less curved out-
wards. If the filaments in this condition are lightly touched
they instantly straighten, carrying the anther-tube up a little
higher, and thus bringing the pollen all along the style which is
enclosed. After a short time they resume their former curved
condition, retracting the anther-tube to the place which it occu-
pied before. It is to be observed that the irritation of a single
filament excites only that one, and thus the tube of anthers may
be pushed over to one side for a few minutes, again recovering
itself after a little while.

1096. Sparmannia Africana has a cluster of beaded filaments
surrounding the pistil and variously intermingled with the sta-
mens. When these are touched lightly they open out from the
centre with considerable rapidity, and remain thus expanded
for a certain period, after which they revert to the closed posi-
tion. Somewhat the same phenomenon is to be observed in

1 Comptes Rendus, Ixx., 1870, p. 339.

424 MOVEMENTS.

species of Portulaca, where the stamens, upon contact, move
outwards.

1097. The gynandrous style of Stylidium is curved down-
wards; when it is lightly touched it suddenly flies to the other
side of the flower, although sometimes it merely straightens
itself.

Sensitive lobes of the style or stigma are possessed by Mimu-
lus and some other Scrophulariacez,? by Martynia, and some
allied plants.

1098. In all the foregoing cases the sensitiveness is greatest
when the plants, or their sensitive parts, are kept at a tolerably
high temperature. Sachs has shown that the most favorable
temperature for Mimosa movements is about 36° or 37° C.

1099. Effects of anesthetics upon sensitiveness in plants. When
a young plant of Mimosa is placed under a bell-jar in which a
sponge wet with chloroform or an equivalent anesthetic has
filled the confined atmosphere with its vapor, some of the leafiets
droop and remain so, while others retain their normal position.
But after a while the leaflets will be found to have lost all power
of reacting to a touch; in short, they have become insensitive.
The same effect is observed iu the case of Barberry stamens.
Its explanation is looked for in the changed relation of the
sensitive cells to water when they are subjected to the influence
of an aneesthetic.

1100. Plants possess no nervous system. That sensitive plants
must have nerves, or their equivalent, for the recognition of im-
pressions and the transmission of their influence to a somewhat
distant point was formerly held by many writers, but this
opinion is not now entertained by any physiologist.?

1 See Heckel’s Memoir, Comptes Rendus, Ixxix., 1874, p. 702.

2 «Finally, it is impossible not to be struck with the resemblance between
the foregoing movements of plants and many of the actions performed uncon-
sciously by the lower animals. With plants an astonishingly small stimulus
suffices ; and even with allied plants one may be highly sensitive to the slight-
est continued pressure, and another highly sensitive to a slight momentary
touch. The habit of moving at certain periods is inherited both by plants and
animals ; and several other points of similitude have been specified. But the
most striking resemblance is the localization of their sensitiveness, and the
transmission of an influence from the excited part to another, which conse-
quently moves. Yet plants do not of course possess nerves or a central ner-
vous system ; and we may infer that with animals such structures serve only
for the more perfect transmission of impressions, and for the more complete
intercommunication of the several parts” (Darwin ; Power of Movement in
Plants, 1880, p. 571). :

Ww

CHAPTER XIV.
REPRODUCTION,

1101. Iw scientific as well as popular language the term indi-
‘vidual is commonly applied to each and every plant; but if by
individual is meant an organism incapable of subdivision with-
out loss of its identity, the term as applied thus to the higher
plants is obviously a misnomer. It has been shown both in Vol-
ume I. of this series,’ and in Part I. of the present volume,’ that
under certain circumstances any of the higher plants may be
separated into parts, each of which may afterwards lead an inde-
pendent existence. ‘Thus buds may be severed from the parent
plant and soon establish themselves as independent organisms,
‘capable of increase in size, and becoming sooner or later dis-
tinguishable in no wise from the stock from which they came.
But there are serious difficulties in the way of regarding these
separable buds as true individuals :® each bud is the promise of
a branch, and consists of parts which, under certain conditions,
may be separated from each other. In fact, the vegetable indi-
vidual is not reached in such mechanical subdivision until we
come to the cells of which all the parts are composed. Nor do
these satisfy completely the definition of an individual, since in
exceptional cases the cell itself may spontaneously divide into
viable parts.*

1102. In plants, individuality is more or less completely merged
in community. Under normal conditions the separable parts,
while still attached to their common stock, co-operate for the
common good. If separated under favorable conditions they
in their turn become stocks in which are combined congeries of
similar separable parts, or, in other words, become individual
plants, in the ordinary acceptation of the term. For instance,
the tuber of the potato, which is the thickened extremity of an
underground branch, possesses a certain number of buds, each

1 Page 316. 2 Pages 152, 162. 3 Volume i. p. 316.
4 Such a phenomenon is seen in the formation of swarm-spores (or zodgo-
nidia) from a terminal cell of Achlya.

426 REPRODUCTION.

of which may, in suitable soil, give rise to a thrifty plant: the
new plants will in their turn produce new tubers likewise with
buds, and these again new plants, and so on in unlimited
succession. Nevertheless, the divisible organisms are for our
present purpose conveniently termed vegetable individuals.

1103. Plants of the higher grade (Phanogamous plants) are
propagated either by buds or by seeds. In the former case, a
portion of the axis with incipient leaves is separated from the
parent; in the latter case, a new structure (the embryo), capa-
ble of independent existence, is formed by means of a special
apparatus, — the flower. In the flower, two sets of sexual or-
gans, the stamens, constituting the andreecinm, and the pistils,
constituting the gyneecium, produce by their conjoint action an
embryo, or undeveloped plant, within the seed.

Reproduction by buds is non-sexual or asexual; that by the
formation of an embryo is sexual.

1104. Non-sexual reproduction (Agamogenesis) can be traced
through all classes of plants, —from the higher, where it takes
place through proper buds, down to the very lowest, where it
takes place by a single cell dividing spontaneously to form two
or more separated individuals.

1105. Sexual reproduction (Gamogenesis) likewise can be
traced through all classes of plants except the very lowest,
where it has not as yet been demonstrated to exist. As the
series is followed from above downwards, the flower gives place
to other structures, and the seed is replaced by simpler bodies,
known as spores.

FERTILIZATION IN ANGIOSPERMS.

1106. Flowering plants are naturally divided into Angio-
sperms and Gymnosperms: the former are distinguished by the
possession of a closed ovary in which the ovules are contained.
The latter have no closed ovary, and hence the ovules are naked.
A part of the reproductive apparatus is simpler in Gymnosperms
than in Angiosperms; but owing to certain practical difficulties
in the treatment of microscopic material, the demonstration of
the reproductive process is less easy in the former than in the
latter. It is proposed, therefore, to begin with an examination
of the reproductive process, or fertilization, of Angiosperms.

1 The view has been held by some that all the derivatives from one seed,
whether united or separated, constitute collectively a single individual.

STRUCTURE OF THE PISTIL. 427

1107. Three subjects must be briefly reviewed before enter-
ing upon the study of the process itself; namely, the pistil, the
ovule, and the pollen-grain. For all details regarding particu-
lars of form and special morphological relations, pages 249-285
of Volume I., and Chapter IV. of the present volume may be
consulted.

1108. The augiospermous pistil (see Fig. 196) consists of a
closed ovary containing the ovules, which is generally prolonged
into a slender organ known as the style. Either some portion of
the style, or, when this is wanting, some portion of the ovary, is
furnished with a peculiar secreting surface Known as the stigma.
The manifold shapes of ovary, style, and stigma have been suf-
ficiently described in Volame I., and the microscopic structure
of each has been examined in a general way in Part I. of the
present volume. From what was there said, it will be remem-
bered that the form and structure of pistil and stamens have
intimate relations to the transfer of pollen and its reception by
the stigma.

1109. The stigmatic secretion. The surface from which this
exudes may exist as an expanse of considerable extent, or it
may have the form of single or double lines, or be reduced
even to a mere point. The extent of the stigmatic surface
bears a fixed relation to the number of ovules in the ovary.

At a certain period in the development of the flower, the
stigma, which up to that time may have been apparently free
from moisture, hecomes covered with a glutinous secretion of
a saccharine nature. At this period, known as that of ma-
turity, the stigma is from its stickiness likely to catch and
retain upon its surface any pollen which may fall thereon.
The secretion is generally slightly acid? in reaction, and is as
variable in the amount of sugar which it contains as ordinary
nectar.

1110. The pollen-grains of angiosperms when set free from
the cells in which they are produced may become completely
isolated (simple grains), or they may remain firmly coherent in
clusters of four (Typha, Rhododendron, etc.), eight, sixteen,
thirty-two, or even, as in some species of Acacia, sixty-four
(‘‘compound grains”). In many Orchidacez the grains are
more or less compactly fastened together into masses by a glu-
tinous matter forming pollinia, and much the same grouping
into masses occurs in Asclepiadacee.

1 Van Tieghem : Traité de Botanique, 1884, p. 850.

428 REPRODUCTION.

1111. Structure of pollen-grains.1_ The grains consist of sin-
gle cells having a firm membrane and heterogeneous contents.
The membrane is rarely single (as in Zostera), being generally
composed of two coats, —an outer, the extine (called exine by
Schacht), and an inner, the dnéine. The extine may be smooth,
but it is frequently beset with protuberances of some kind, points,
prickles, or other sculpturings, which may be characteristic of
genera or even larger groups. It is also provided generally
with oue or more partial or complete perforations, which are of
course fully closed by the intine which is pressed up against
them. ‘The number of these perforations is constant in certain
groups of plants: for instance, one in most monocotyledonous
plants ; two in Ficus, Justicia, Beloperone; three in Onagracee,
Geraniacese, Composite ; four to six in Impatiens, Ulmus, and
Alnus; many in Nyctaginaceze, Convolvulacese, Malvaces, and
some Caryophyllace. Under the action of concentrated sul-
phuric acid the intine is destroyed, while the extine generally
remains unchanged except in color.?

When the pollen of Thunbergia is acted on by strong sulphuric
acid, the destruction of the intine permits the extine to uncoil
as a band. In no case did Schacht detect any perforation of
the intive.

1112. The contents of a pollen-grain are (1) protoplasmic mat-
ter; (2) granular food materials, such as starch, oil, and, ac-
cording to Schacht, inulin; (8) dissolved food matters, sugar
and dextrin. These heterogeneous contents form what was
formerly called the fovilla.

In the granular protoplasmic matter of pollen-grains it is pos-
sible to demonstrate the existence of a nucleus, and in some
cases two nuclei can be made out distinctly. It is considered
well established* that the single nucleus which exists in the
simple grain at the period of its separation from the mother-cell
divides in most cases into two nuclei of unequal size. The larger
of the two fragmental nuclei remains with no change; while the
smaller may become partitioned off from the rest of the cell either
by a true cell-wall or by a peripheral film of protoplasm, and may
later divide and form a group of two or four minute cells.

1 These details are summarized chiefly from Schacht’s exhaustive treatise
on the subject in Pringsheim’s Jahrbiicher, ii., 1860, p. 109.

2 Tn some cases a double membrane can be shown in the extine, for instance
Cnothera, where the extine separates into a true extine and an datextine.
- § Strasburger: Ueber Befruchtung und Zelltheilung, 1878. See also
Quarterly Journal of Microscopical Science, 1880, p. 19.

POLLEN-GRAINS. 429

1118. The pollen-grains of many plants burst when placed in
water, and the fovilla escapes as a slightly coherent mass which
soon becomes more diffused and allows the finer granules to pass
into the water, where they immediately exhibit the Brownian
movement, common to all minute particles suspended in a
liquid. 2

1114. If pollen-grains are placed in a solution of sugar in-
stead of in pure water, they will increase somewhat in size ;
and in a few hours, if the specimen is kept at the right tem-
perature, there will appear at some point of the surface of each

grain a minute tube, which by great care can be cultivated in a
proper medium until it attains a length of several millimeters.?

1115. The pollen-grains of Tulipa Gesneriana emit their tubes
in a 1 to 3 per cent solution of cane-sugar ; the following require
a somewhat stronger syrup: Leucojum estivam and Narcissus
poeticus, 3 to 5 per cent; most orchids, 5 to 10 per cent; Con-
vallaria majalis, 5 to 20 per cent; Iris sibirica, 30 to 40 per
cent.®

1 For an extended account of the speculations once based upon the occur-
rence in water of motion of the particles of the fovilla, the reader should
consult Meyen: Pflanzenphysiologie, iii., 1839, pp. 192 et scg.; and also the
reinarkable treatise by Robert Brown.

2 Schleiden states that pollen-grains which come accidentally in contact
with nectar readily send out tubes ; and that we often find at the base of the
flower a whole mass of confervoid web, which consists of entangled pollen-
tubes emitted in this manner (Principles of Scientific Botany, 1849, p. 408).

8 Strasburger: Das botanische Practicum, 1884, p. 511.

Fie. 194. a, young pollen-grain of Allium fistulosum, before its division; b, after the
division of the nucleus: c, after the division of the protoplasm; d, young pollen-grain of
Monotropa Hypepitys divided ; e, same emitting its tube, into which the two nuclei
pass; f, coalescent grains of the pollen of Platanthera bifolia during their division; g,
formation of the pollen-tube of Orchis mascula, into which the two nuclei pass. (Stras-
burger.)

430 REPRODUCTION.

1116. When a pollen-grain is deposited upon a fitting stigma,"
at the period when the stigmatic secretion is sufficiently abun-
dant, it increases somewhat in size, and soon? a tube,® scmetimes
more than one, is thrust forth and passes immediately into the
loose tissue of the stigmatic surface. The tube consists of a
protrusion of the intine, and its place of emerging is at some
one of the perforations of the extine. In some instances the
wall separating the larger and the smaller fragments of the
original nucleus of the pollen-grain becomes absorbed, and
then the two nuclei make their way into the tube as it is

prolonged. During its descent the pollen-tube is slender, of
about the same calibre throughout, and has extremely thin
walls. It extends through the conducting tissue of the style,
being nourished by the nutrient matter secreted from the cells of
that tissue, until it at last reaches the cavity of the ovary.

1117. According to Capus,* the extent of the stigmatic surface
bears a definite relation to that of the conductive tissue of the
style, one surface being in fact a mere expansion of the other;
and the volume of the conductive tissue of the style is governed
by the number of ovules which are to be fertilized. Thus, in a

1 An interesting account of the artificial fertilization of certain plants of
the Poppy family after removal of the stigmas is given by Hooker in “ The
Gardeners’ Chronicle,” 1847. It is not known that the experiments have yet
been repeated.

2 According to Gartner, the emission of the pollen-tube begins in some
cases in half a minnte after the pollen has been applied to the stigma ; but in
some others, as in Mirabilis Jalapa and in the Malvacer, it takes from 24
to 36 hours.

3 Amici, in 1822, appears to have been the first to detect the pollen-tube.
His earliest observations were made upon Portulaca oleracea.

# Annales des Se. nat., sér. 6, tome vii. p. 204.

Fig. 195, Apparatus for cultivating pollen-grains, etc, The object is placed on tl?

under side of a glass cover over the circle at a. Ifnecessary, air can be drawn througa
the tube. A simpler contrivance may be made from a piece of moist pasteboard,

DESCENT OF THE POLLEN-TUBE. 431

pistil with a large number of ovules the stigmatic surface is
large, as is also the amount of conductive tissue of the style
through which the pollen-tubes are to descend.

1118. The conductive tissue through which the pollen-tube
descends, and by which it is nourished, is formed at the stigma
by a modification of epidermal cells, and below this arises from
modifications in the parenchyma; in the style it may constitute
a solid mass of delicate cells, sometimes with walls which have
undergone the mucilaginous modification, or it may simply line
the hollow tube which is frequently found, as in the pistil of
the violet.

1119. The time required for the descent of the pollen-tube de-
pends upon the length and character of the path the tube is
to traverse, and is very different in
different cases. Hofmeister states
that in Crocus vernus, with a style
which is from one to two inches in
length or sometimes more, the tube
reaches the ovary in from one to
three days. Schleiden? gives the
following times required for descent
of the tube: Cereus grandiflorus,
haying a style nine inches long, a
few hours; Colchicum autumnale,
with a style thirteen inches long,
twelve hours. In some other cases
(certain orchids) it is weeks before
the end of the tube has descended
for even a very short distance.

112¥. A single pollen-grain of
some flowers can emit more than
one pollen-tube : thus Amici has
seen twenty to thirty tubes proceed
from one grain. Pollen-tubes sometimes branch in their course
downward.

1121. The length of time during which pollen-grains can
preserve their vitality has been determined for a few cases: ?

1 Schleiden: Principles of Scientific Botany, 1849, p. 407.
2 Gartner, quoted by Mohl: Vegetable Cell, p. 134.

Fie 196. Diagram of a longitudinal section of an ovary having only one ovule with
basal placentation, designed to exhibit the course of the pollen-tube from the stigma to
the summit of the embryonal sac above the odsphere. The ovule is anatropous, and
is inserted, as is usually the case in Composite. (Luerssen.)

432 REPRODUCTION.

Those of Hibiscus Trionum at least three days after removal
from the anther; those of Cheiranthus Cheiri, fourteen days ;
those of Camellia, Cannabis, Zea, and Phoenix dactylifera (Date),
one year.

1122. Although each ovule requires for its impregnation only
one pollen-tube, the number of pollen-grains in flowers which
open at maturity is far in excess of the number of ovules. The
ratio has been ascertained in a few cases, among which are
the following: Cereus grandiflorus,! 250,000 grains of pollen
to 80,000 ovules; Wistaria sinensis,? about 7,000 grains of
pollen to each ovule; Ilibiscus Tiionum,® 4,863 grains of pol-
len to about 30 ovules. In some other cases, for instance Geum
urbanum,* the excess of pollen over ovules is about 10:1.

1123. The localization of the conductive tissue in the ovary
itself is sometimes very marked; thus in ovaries with parietal
placentation, the ovarian walls in the immediate vicinity of the
ovules are seen to be distinctly conductive, while in those with
axile placentation, the modified tissue is found in the axis.
Capus distinguishes the following yarietics of conductive pla-
centee: (1) with a smooth surface, the micropyle being close
to the placenta, e. g., Solanum; (2) papillar, the papillee either
simple or compound, sometimes serving to guide the pollen-tube
to the micropyle, e. g., some Cucurbitacexz ; (3) hairy, the hairs
sometimes secreting a mucus or even breaking down into a
gelatinous mass through which the pollen-tube may penetrate
with facility, e. g., some Aroids. Special names were formerly
given to peculiar forms of the conductive tissue, but the terms
now possess no utility. For special examples of the forms, the
reader must consult the practical exercises at the end of this
volume.

1124. Structure of the ovule. As shown on page 175, the
ovules arise as minute protuberances at some part of the ova-
rian wall or upon the axis of the ovary. In orchids the pro-
tuberance consists of only a single row of cells; but in most

1 Morren. 2 Gardeners’ Chronicle, 1846, p. 771.

8 K6élreuter: Vorliufige Nachricht (quoted by Balfour: Class Book of
Botany, p. 564).

4 Gartner: Beitrige zur Kenntniss, p. 346 (quoted by Darwin in “ Effects
of Cross and Self Fertilization in the Vegetable Kingdom,” p. 377).

The following are some of Hassall’s determinations of the number of pollen-
grains {Annals of Nat. Hist. viii., 1842, p. 108): Dandelion, 248,600 grains ;
a flower of Peony, with 174 stamens each containing 21,000 pollen-grains,
3,654,000; while in a plant of Rhododendron the number of grains was esti-
mated to be 72,620,000.

STRUCTURE OF THE OVULE. 433

other cases several rows of cells are superposed, forming the
body known in morphology as the nucleus of the ovule. This,
to avoid the possibility of even slight confusion, will be now
spoken of as the nucellus.

That this distinction is necessary,
will appear from the fact that in one
of the large cells of this body there
is a true cell-nucleus which under-
goes remarkable changes, all of which
must be described. It should there-
fore be remembered that in the fol-
lowing discussion the term nucedlus
means exactly that which in Volume
1. page 277 is called nucleus of the
ovule.

1125. Around the nucellus there is developed in most in-
stances a double ring

for

which soon nearly invests it, forming an
inner and an outer coat. Attention
has been called in Volume I. to the
fact that the integuments of the ovule
do not completely invest the nucel-
lus, but that there is at its true apex
an orifice known as the foramen or
micropyle. It has also been shown
that by a peculiar distortion during
its development the ovule may be
so bent round upon its support, the
funiculus, as to have the micropyle
present itself towards the placental
attachment. Hence, when the apex
of the ovule is spoken of, the micro-
pylar extremity is meant.

1126. At the micropylar extremity of the forming ovule, a
single cell, beneath the surface (except in orchids and some
saprophytes) , elongates in the direction of the length of the ovule,
and by one or sometimes many transverse and vertical partitions
becomes divided into segments of unequal size. The lowest
segment continues the elongation and the enlargement of the
structure thus formed within the ovule, known as the embryo

!
aes sl
A Ss

Wepees,
ae eoee

198

Fie. 197. Longitudinal section of the amphitropous ovule of Baptisia australis.
(Van Tieghem.)

Fie. 198, Longitudinal section of the anatropous ovule of Mimosa pudica. (Van
Tieghem).

28

434 REPRODUCTION.

sac. During the subsequent development of the ovule the
embryonal sac continues to increase in size, often irregularly,
and displaces or obliterates by absorp-
tion many of the cells around it.

1127. At an early period in the de-
velopment of the embryonal sac it is
completely filled with protoplasm con-
taining a cell-nucleus. ‘This nucleus di-
vides, and the two new nuclei are soon
found at opposite ends of the sac, where
each divides into four nuclei. Between
the two groups of four nuclei there may
be a vacuole of considerable size.

The next stage is marked by the pas-
sage of a nucleus from each extremity of
the embryonal sac towards its centre,
where they become united to form a sec-
ondary nucleus.

1128. The nuclei at the lower end of
the sac become surrounded with other
protoplasmic matter, and later by cell-walls; they then consti-

tute what have been termed the antipodal cells. At the upper
end of the sac, also, the three nuclei become surrounded by

Fig. 199. Longitudinal section of the orthotropous ovule of Polygonum divaricatum.
fu, funiculus; fe, the two integuments; nw, the nucellus, whose summit is prolonged
towards the micropyle, mi; se, the embryonal sac. (Strasburger.)

Fig. 200. Polygonum divaricatum. Summit of the ovule with the apex of the em-
bryo sac, and the complete embryonal apparatus. e, the odspore; s, one of the syner-
gidae, the other being hidden from view. (Strasburger.)

Fig. 201. Polygonum divaricatum. Summit of the ovule, showing the encroachment
of the embryo sac upon the adjoining cells. (Strasburger.) 5

CHANGES IN THE OOSPHERE. 435

more or less protoplasmic matter, but are not invested by a
true cell-wall; these have been termed the
egg-apparatus. Two of these naked nu-
cleated bodies are somewhat attenuated at
their upper part and rounded below; the
slender portion contains the nucleus, the
rounded a vacuole. The bodies are termed
the synergide. The remaining cell is near
the lower extremity of the two just de-
scribed, and is known as the odsphere.
All of these parts are shown in the fig-
ures.

Such, then, is the structure of the em-
bryonal sac and of the egg-apparatus,
when the extremity of the pollen-tube
emerges into the cavity of the ovary and
comes in contact with the micropyle, or
foramen. It has been shown by Stras-
burger, that when contact takes place be-
tween the pollen-tube and the summit of
the embryonal sac, one of the synergidze
changes its character; its rather clear pro-
toplasm becomes turbid, its vacuole and
nucleus vanish, and with a slight con-
traction the mass becomes finely granu-
lar, after which it inay wholly disappear.
At this time the odsphere also undergoes
the following changes: it clothes itself
with a thin film of cellulose, and in its
protoplasmic mass a well-marked nucleus,
probably derived as such from the pollen-
tube, appears by the side of the nucleus
of the odsphere, sometimes of the same
size, sometimes smaller. The two nuclei
blend, forming a single ovoid body, with
distinct or with confluent nucleoli. Even
if at first distinct the nucleoli may be-
come confluent at a later period. The

Fria. 202. Synergida: prolonged across the membrane of the embryonal sac. a, b,c,
from Gladiolus communis; d, from Bartonia aurea. @, plane perpendicular to the
plane of the symmetry of the ovule; 8, in the plane of symmetry ; ¢, after separation of
the three parts; d. (Strasburger.) =

Fia. 203. Capsella Bursa-pastoris. Two embryos with cotyledons distinctly devel~
oped. B more advanced than 4. (Luerssen.)

436 REPRODUCTION.

other synergide remains unchanged, or
passes through nearly the same changes
as those described. It should be said
that in some instances the pollen-tube
passes down without apparently affect-
ing the synergide to any very marked
extent, but producing its influence di-
rectly upon the odsphere.

1129. These changes now described
in the odsphere are known collectively
as those of fertilization or impregnation ;
the fertilized or impregnated odsphere
is termed an odspore. It passes through
a series of changes by which a second
cell is formed, then others in a linear
serics, or in a more complex chain,
termed the proembryo or suspensor.
In some cases, however, no suspensor
at all is produced.

am

Fig. 204. Capsella Bursa-pastoris. Embryo developed more than in Fig. 203. A
longitudinal section showing cotyledons, kb; v, point of growth; e, suspensor; pl,
plerom ; p and pe, periblem ; d, and ¢?, dermatogen; h!, and h?, root-cap, (Hanstein.)

Fig. 205. Camelina sativa. «a, two-celled embryo, much exceeded in size by tho
long suspensor. Capsella Bursa-pastoris, the figures b, r, showing different stages in the
development of the embryo; b,c, @, aspects of the embryo divided into quadrants}; ¢,7,9,
different views of the embryo at the formation of the dermatogen; 7, longitudinal sec-
tion showing further divisions and the formation of the periblem and plerom; %, same
asi, bnt given in perspective; 7, longitudinal, m, transverse, scction of the same em-
pryo at a later stage; , perspective view of embryo at a little earlier stage than é/ and
m3; 0,p, 7, later stages; g, same embryo seen from below, exhibiting the first divisions
near the suspensor; s, s’, s”, cells nearest the suspensor, (Lucrssen, after Praz-
mowski.) : tlie ara o., :

FERTILIZATION IN GYMNOSPERMS. 437

1130. The terminal cell of the suspensor is followed by the
initial cell or cells of the embryo proper; the different stages of
the development of the embryo can be traced in the ovule of one
of our most common weeds, Capsella (compare Figs. 203-205).

The case above described is a simple one, but may serve as a
type of all normal cases of fertilization in angiosperms, the innu-
merable deviations from which cannot be further alluded to here.?

1131. With the changes in the embryo sac there are concomi-
tant changes in the whole nucellus and its integuments. A
certain amount of food of some kind (see 509) is stored either
in the sac or in the developing tissues around it, constituting
the so-called albumen of the seed. The food within the develop-
ing embryo sac is termed endosperm; if around it, perisperm.
But the changes do not stop with the ovule as it ripens
into a seed; they go on also in the surrounding parts. In
fact, as soon as fertilization has begun, the flower wilts, and
in most cases the external organs fall. The ovary, sometimes
with associated parts such as the calyx, the receptacle, etc.,
passes through changes by which it becomes the fruit.

FERTILIZATION IN GYMNOSPERMS.

1132. The chief differences between the reproduction in these
plants and that in those
just described are in the
preliminary development
of the pollen and the
ovule.

1133. Pollen of gym-
nosperms. The grain
is distinctly divided by
a curved partition into
two portions, and one of
these portions is fre-
quently divided in much
the same way into two
parts. Comparison of
this pollen with that of

+ The student is urged to study with great care the masterly treatise by
Strasburger, Ueber Befruchtung und Zelltheilung, 1878, and the more succinct
account in his Practicum, 1884.

Fic. 206. A, pollen-grains of Biota before their escape from the pollen-sac. J, fresh,
IT and LT swollen by water; the extine e having split off, the protoplasmic contents

areseen. B, pollen-grains of Pinus pinaster before their escape from the pollen-sac; a
side and a dorsal view. (Sachs.)

438 REPRODUCTION.

angiosperms shows that in the latter the nucleus divides, but
that the division stops here, no true dividing-wall being formed.

1134. Ovule of gymnosperms. The
ovule is always orthotropous. It has an
integument which is sometimes prolonged
so as to form a fleshy tube communicating
with the nucellus.

The nucellus, like that of angiosperms,
contains an embryonal sac; at an early
stage this is filled with endosperm, which
it will be remembered is not developed in
angiosperms until after fertilization. Some
of the upper cells of the endosperm are
rather larger than the others, elongated in
the direction of the axis of the ovule, and
each surmounted by a ‘* rosette” of minute
cells which comes between the group and
the summit of the embryo sac. These large
cells, with their rosettes, are termed cor-
puscules. These corpuscules are considered odspheres. Around
them in the embryo sac there ap-
pears to be nothing corresponding
strictly to the synergidee, the an-
tipodal cells, etc., observed in the
angiosperms, although some ho-
mologies have been pointed out.

In some cases, like that figured,
there is a sort of depression at
the summit of the endosperm,
which has been called the pollinic
chamber.

11385. Contact of pollen with
the ovule. As the name indi-
cates, the gymnosperms are naked
seeded; no stigma or style inter-
venes between the pollen and the
ovule. When the divided pollen
of the gymnosperm falls upon the micropyle of the ovule, it

Fig. 207. Pollen-grain of Ceratozamia longifolia. 4, grain with partial partitions ;
B, the same emitting its tube, ps, which has ruptured the outer coat; y, minute
inactive cells. (Juranyi.)

Fic. 208. Longitudinal section of the nucellus of the naked ovule of Juniperus
Virginiana. m, nucellus; se, membrane of the embryonal sac; e, endosperm; c, cor-
puscles ; , a pollen-grain which has protruded its large tube as far as the corpuscles,
(Surasburger.)

FERTILIZATION IN GYMNOSPERMS. 439

finds there a certain amount of moisture by means of which a
tube is formed from one of the large cells. This extends directly
into the tissue of the nucellus, coming sooner or later into con-
tact with the summit of the embryonal sac, and then affecting
the corpuscules below. From the fertilized corpuscule the embryo
is developed.?

4 For the purpose of affording some means of comparison of the methods of
reproduction in flowering plants and in those of a lower grade, the following
brief notes concerning the reproduction in several of the groups of Cryptogams
have been inserted : —

(1) No sexual reproduction has yet been demonstrated in the very lowest
forms of vegetation. Such plants are termed Protophytes. The fungi which
are associated with fermentation and putrefaction, and certain of the simplest
alge, are examples of the group.

In the study of the Protophytes the beginner can examine with profit the
cells of common yeast. Care should be taken to distinguish between the cells
of the plant and the grains of starch with which compressed yeast is generally
associated.

The simple one-celled plants with
chlorophyll which belong to this group
can be found in almost any stagnant
water. They are spherical, and are fre-
quently grouped in twos or fours.

(2) The sexual process in Zygophytes
is characterized by the confluence of the
protoplasmie masses of two very similar
cells by which a new mass is formed
as the starting-point of the new indi-
vidual. In most of these zygophytes
there is no plain distinction of sex.
Some of the lower moulds and many
of the filamentous alge are examples
of the group.

Excellent specimens for study may
be found in stagnant or slow-running
water in spring and through the sum-
mer. By careful search it is possible
to detect cases in which the process of
conjugation has advanced somewhat :
such specimens can be kept under ob-
servation by having the slide sufficiently
warm and constantly supplied with fresh
water, when the different stages of conjugation and of cell-division may be
examined.

209

Fie. 209. Spirogyra, illustrating the mode of fertilization in the Zygophytes.
Approximating cells of two filaments produce extensions which become conjoined ; the
‘protoplasmic masses in these cells become confluent, forming a single mass which after
escaping becomes clothed with a cell-wall and develops into a tilamentous chain of
eclls, In this case there is no appreciable distinction of sex.

440 REPRODUCTION.

1136. It was formerly thought that no clear gradations could
be detected between the flowering plants and .the higher groups

(3) Odphytes. In this group a mass of protoplasm, known as an odsphere,

is fertilized by specialized threads or slender masses of protoplasmic matter
termed antherozoids, coming
from another part of the
same or of another plant.
By contact with these an-
therozoids the odsphere be-
comes an odspore, the start-
ing-point of a newindividual.
In this group, of which
Fucus or rock-weed may be
taken as an example, the
fertilization is direct.

In the examination of this
group the student may em-
ploy the common rock-weed
which carpets the boulders
along the coast. Sections
should be made in the un-
even pustulated part of the
frond, and in a vertical di-
rection. Good preparations
can be obtained from mate-

210 rial which has been dried or
from that which has been
kept in alcohol, and winter specimens will be found especially good.

Some of the species are
diwcious, having the male
elements in the conceptacles
on one plant and the female
elements in those upon an-
other.

(4) Carpophytes. The
simplest plants of this het-
erogeneous group are illus-
trated by Fig. 211. The
odsphere is contained in a
specialized organ (the car-
pogonium), which is fre-
quently prolonged to form
a style-like process (the tri-
chogyne). Theantherozoids 211
are carried by water to this process, and fertilization results; the ‘product of

Fig. 210. Fucus, illustrating the fertilization of an odphyte. a, section through a
conceptacle exhibiting the reproductive organs; b and c, the odspheres in different
stages of development; d, antheridia with a single antherozoid (g); €, an odsphere
surrounded by antherozoids; 7, an odsphere germinating. (‘Thuret )
| Fie. ait, Nemalion. I.-1V.,acarpophyte. I.,a branch showing antheridia, a, and
& carpogonium, 0, with the trichogyne, ¢(e, spermatium). V., Lejolisia exhibiting a, an-
theridium, c, carpogonium, and f, ripe fruit; e,an escaping spore. (Thuret and Bornet.)

REPRODUCTION IN CRYPTOGAMS. 441

of flowerless plants. Comparative investigations have, however,
shown that such gradations do exist, and that the chain of exist-

fertilization is shown in the figure. Of the more complicated cases this is not
the place to speak ; their treatment, as well as that of all the simpler forms,
may be looked for in Volume III.

Specimens for this demonstration of the different stages of reproduction are
to be procured at different seasons. As will be seen from the figure, most of
the features are so nearly superficial as to need no particular sections for their
exhibition. /

(5) True mosses and their allies are characterized by the possession of an
archegonium or flask-shaped body containing a central cell in which is the
odsphere. The odsphere is fertilized by immediate contact, with autherozoids
which are formed in antheridia; as a result of the fertilization, there is
produced a spore-case filled with spores.

In the examination of the fructification of a moss, the plant must be taken
at an early stage, and search must be made for the sexual organs by removal of
the flower-like cluster of leaves
at the summit of the minute
stalk. If the removal is success-
fully performed, and the plant is
in the right condition, a group 1
of threads like those shown in .
the figure will be plainly seen.
Among these are to be found
some flask-like bodies, the arche-
gonia, and either on the same
receptacle or on another plant
of the same species the male
organs, one of which, greatly
magnified, is shown in Fig. 212.
Under a very high power the
escaping antherozoids can be
seen. When fertilization has
taken place, the archegonium
goes on in its development, be-
coming, after many intermediate
steps, the capsule or ‘ fruit” of
the moss, covered by a sort of
hood or cap, and tightly closed
at its mouth by alid. Removal
of the lid discloses the teeth of
the mouth (peristome) and the
spores within. Upon gerimina-
tion, a spore gives rise to sleuder 212
filaments ainong which is pro-
duced the minute moss-plant with the sexual organs figured in the sketch.

Fig. 212. Funaria Sygrometrica, a moss. 1. Longitudinal section through the
upper part of the plant with archegonia, a, and leaves, &. 2. Antheridium bursting
acd alluwing escape of the antherozoids, a. (Thomé.)

442 REPRODUCTION.

ences is practically unbroken, reaching from the lowest to the
highest forms. The character of this evidence will appear in
the succeeding volume of this scries.

(6) True ferns exhibit the following phenomena of fertilization. On the
back of the frond there are formed spores in spore-cases, which are variously
grouped and protected.
The spores on reaching
a fit surface svon give
rise to thin filins (pro-
thalli), on the under
side of which are pro-
duced the sexual or-
gans, all of which are
shown in the figures.
As a result of the pro-
cess of fertilization there
is produced afern-plant,
which at its adult age
bears the spores above
spoken of.

Jn any greenhouse
where ferns are kept it
is easy to procure, by
careful search on the
soil of the flower-pots,
abundance of the pro-
thalliin different stages.
The most minute of
these exhibit the sexual
organs just forming,
while those which are
more advanced give all
the features shown in
the figures. The stu-
dent must observe that
on the surface of the soil
in the flower-pots many
other growths are to be
found, and care must
be taken not to con-
found other flat films
(belonging, forinstance,

213 to Hepatic) with the
prothalli of the ferns.

Sections through the prothallus will exhibit the sexual organs in different
stages of development. The best material is procured by the cultivation of

Fig. 213. Prothallus of a fern, exhibiting the reproductive organs. At the sinus
of the heart-shaped film are to be seen the archegonia, one of which, more highly mag-
nified, is displayed in section in 4. B, an enlarged antheridium with escaping anthero-
zoids, (Luerssen.)

SEXUAL AND NON-SEXUAL REPRODUCTION. 443

1137. Contrast between non-sexual and sexual reproduction as
regards results. In non-sexual reproduction a certain portion
of living matter is separated from the rest of the living matter
of the plant, and, coming under favorable conditions, pursues
an independent existence; in sexual reproduction, two portions
of living matter, from different parts of the organism or from
different organisms, unite to constitute a new individual.

fern-spores. On a piece of unglazed earthenware, for instance a broken flower-
pot, which has been first boiled for a time in water to destroy any injurious
moulds, a few spores are to be lightly
dusted. If the whole is covered by a
bell-jar and kept dark and warm, after
acertain time the delicate films will be
detected and can then be traced through
their development.

(7) Some of the allies of the ferns
produce spores of more than one sort,
differing in size and subsequent devel-
opment. The larger spores, known as
macrospores, give rise to an included
prothallus which subseyuently becomes
exposed at one portion, where there is
developed an archegonium (or sometimes
more than one). Previous to or coin-
cident with this development there is
formed within the spore-walls a peculiar
tissue which has been termed the endo-
sperm, and which is regarded as the
homologue of the endosperm in gymno-
spermous seeds. The smaller spores are
denominated microspores, and pursue a
peculiar course of development. One
of the cells (seldom more than one)
remains essentially unchanged, while
the others give rise to the mother-cells of the antherozoids. It is therefore
thought proper to consider the sterile cell as the homologue of a rudimentary
male prothallus, and the others of rudimentary antheridia. From the mother-
cells are produced, sooner or later, the antherozoids by which the archegonium
is fertilized.

If these allies of the ferns are compared with the angiosperms, wide differ-
ences are found to exist which can be bridged over, in part at least, by the
gymnosperms. Hence, in some systems of classification the gymnosperms are
placed between the angiosperms and cryptogams instead of between the mono-
cotyledons and dicotyledons.

Fig. 214. Selaginella. 4, ¥, microspores in different stages of formation of the
antheridia G, antherozoid; H, axile longitudinal section of a macrospore six weeks
after fertilization, but before germination; v, rudimentary prothallus of the micro-
Spore; p, prothallus of the macrospore with three archegonia ; end, endosperm ; e,
exosporium. (Pfeffer.) ‘

444 REPRODUCTION.

1138. The new individual, for instance a bud, arising from
non-sexual reproduction, generally repeats in itself all the pecu-
liarities of the organism from which it took its origin; the new
individual, the seed or spore, arising from sexual reproduction,
usually differs in some particulars from the organism or organ-
isms by which it was produced.

1139. Hence, in the higher plants individual peculiarities are
perpetuable by bud-reproduction, whereas the seed gives rise to
variations. If the horticulturist wishes to keep the descendants
of a given stock true to all the characters which give them value,
he relies upon some method of multiplying the plant by buds ;
if, on the contrary, he desires to induce or increase some varia-
tion from the stock, he makes use of seeds.

1140. The ordinary horticultural operations by which buds are
severed from the parent stock and suitably placed for further
advantageous development are: (1) layering, — the fastening a
branch in earth, so that while yet connected with its main stem
it nlay form new roots and afterwards live independently of
the stem; (2) the forcing of cuttings or slips, which in con-
genial soil will produce a supply of roots; (3) grafting, or the
transfer of a shoot (a scion) froin the parent plant to some other
plant by which it can be nourished; (4) budding, the transfer of
a single bud to another plant (see 426).

1141. While in most cases buds produce shoots or plants very
closely resembling the parent, it sometimes happens that re-
markable variations arise. These are known as bud-variations,
and are commonly called sports. In general, when once origi-
nated they are perpetuable by any of the processes of: bud-
propagation just described, but are not likely to be reproduced
by seed. From the long list of them given by Darwin only a
few familiar cases are here mentioned: (1) the moss-rose, from
the Provence rose (Rosa centifolia); (2) Pelargonium, giving
rise to numerous varieties; (3) Dianthus, Sweet William, Car-
nations, and Pinks, which vary very widely in cuttings from
a single plant.

1142. Many of the cases of sports, especially those which have
descended from hybrids, are attributable to reversion to an ances-
tral form; a few seem to be dependent on changes in the sur-
roundings; while others have been attributed to the influence
exerted by a graft.

1143. Ordinarily the scion produces no marked effect upon the
stock, and, conversely, the stock exerts no effect upon the shoot
growing from the scion. But when, for instance, some of the

CYTISUS ADAMI. 445

variegated forms of Abutilon have been grafted on green-leaved
stocks, they have been known to affect many of the subsequent
shoots. Such cases are known as graft-hybrids. The most
remarkable example is that of Cytisus Adami, a form midway
between Cytisus laburnum and purpureus. Of this plant Darwin
says: ‘* Throughout Europe, in different soils and under different
climates, branches on this tree have repeatedly and suddenly re-
verted to both parent species in their flowers and leaves. To
behold mingled on the same tree tufts of dingy red, bright yel-
low, and purple flowers, borne on branches having widely differ-
ent leaves and manner of growth, is a surprising sight. The
same raceme sometimes bears two kinds of flowers, and I have
secn a single flower exactly divided in halves, one side being
bright yellow and the other purple; so that one half of the
standard-petal was yellow and of larger size, and the other half
purple and smaller. In another flower the whole corolla was
bright yellow, but exactly half the calyx was purple. In an-
other, one of the dingy-red wing-petals had a bright yellow
narrow stripe on it; and lastly, in another flower one of the
stamens, which had become slightly foliaceous, was half yellow
and half purple; so that the tendency to segregation of char-
acter or reversion affects even single parts and organs. The
most remarkable fact about this tree is that in its intermediate
state, even when growing near both its parent species, it is
quite sterile; but when the flowers become pure yellow or pure
purple they yield seed.” Passing over the views expressed
by many that Cytisus Adami is a hybrid produced by seed, the
account of its origin, quoted by Darwin, is here given. M.
Adam inserted a shield of Cytisus laburnum in the stem of C.
purpureus; the bud lay dormant a year and then produced a
shoot which was rather more vigorous than those of C. purpureus ;
this shoot was propagated and the plants therefrom were sold as a
variety of Cytisus purpureus, before they had come into flower.?

1 The account of the budding was published after they had flowered, but
before this extraordinary tendency to reversion had been manifested. Upon
a review of the testimony Darwin was inclined to accept the foregoing account
of the origin of Cytisus Adami as a gvaft-hybrid as true. Other cases are to
be placed in the same category.

For a full statement of bud-variations and graft-hybrids the student
should read: Darwin, Variation in Animals and Plants under Domestication,
1868, vol. 1, chap. xi. ; also Focke, Die Pflauzen-mischlinge, 1881, p. 519.
In the latter is an interesting account of the mixed oranges (Bizarria). Con-
sult also Braun, On the Phenomenon of Rejuvenescence in Nature (Ray Society,
1853) ; and numerous papers by Caspary.

446 REPRODUCTION.

1144. Apogamy. ‘The prothallus which develops from a fern-
spore bears upon its under side the sexual organs ; from their
interaction a bud is produced which grows into the fern-plant.
Farlow! has shown that in some cases the prothallus can give rise
to a bud without sexual intervention. De Bary * has traced out
the connection between this mode of budding and that which is
found in certain other plants. ‘To the abnormal budding of the
prothallus and homologous structures he has given the name

apogamy.
1145. Parthenogeuesis * is the production of an embryo with-

out the intervention of pollen (or the equivalent of pollen in the
lower plants). Colebogyne ilicifolia, a species belonging to the
order Euphorbiaceze, has been known to produce seeds with more
than one embryo, and without access of pollen. It has been
held by some that the embryos in this case are formed from
odspheres which had not been fertilized, but investigations by
Strasburger indicate that they are adventitious outgrowths from
the cellular tissue of the nucellus, and are outside of, not in, the
embryo-sac.

In some other cases examined, Strasburger regards the forma-
tion of embryos outside the embryo-sac as dependent upon the
fertilization of the odsphere, but in only one case of this kind
did he observe any embryo form also from the fertilized odspore.

1146. Polyembryony, the production of two or more viable
embryos in a seed after the manner just described, is of frequent
occurrence in oranges, onions, and Funkia (Day Lily).

1147. Fertilization in different degrees of consanguinity. Ithas
been shown in Volume J. that ‘‘ no two individuals are exactly
alike ; and offspring of the same stock may differ (or in their
progeny may come to differ) strikingly in some particulars. So
two or more forms which would have been regarded as wholly
distinct are sometimes proved to be of one species by evi-
dence of their common origin, or more commonly are inferred

1 Quart. Journ. Mic. Science, xiv., 1874, p. 266; Proceedings Am. Acad.,
ix. p. 68.

2 Botanische Zeitung, 1878, p. 449 et seq.

3 Braun: Ueber Parthenogenesis bei Pilanzen, 1857; Hanstein: Die Parthe-~
nogenesis der Ceelebogyne ilicifolia, 1877; Hanstein : Botanische Abhand-
lungen, 1877 ; Strasburger: Befruchtung und Zelltheilung, 1878.

Cases of parthenogenesis occur in the lower plants, where they have been
followed out in cultures continued for a considerable time. Their consideration
belongs to the next volume of this series.

For an account of parthenogenesis in animals, see Balfour: Treatise on
Comparative Embryology, 1880 ; also Brooks on Heredity, 1883, p. 56.

CLOSE AND CROSS FERTILIZATION. 447

to be so from the observation of a series of intermediate forms
which bridge over the differences. Only observation can inform
us how much difference is compatible with a common origin.
The general result of observation is that plants and animals
breed true from generation to generation within certain somewhat
indeterminate limits of variation; that those individuals which
resemble each other within such limits interbreed freely, while
those with wider differences do not. Hence, on the one hand,
the naturalist recognizes Varieties or differences within the
species, and on the other, Genera and other superior associations
indicative of remoter relationship of the species themselves.”

‘* Most varieties originate in the seed, and therefore the foun-
dation for them, whatever it may be, is laid in sexual reproduc-
tion. . . . Upon the general principle that progeny inherits or
tends to inherit the whole character of the parent, all varicties
must have a tendency to be reproduced by seed. But the in-
heritance of the new features of the immediate parent will com-
monly be overborne by atavism; that is, the tendency to inherit
from grandparents, great-graudparents, etc. Atavism, acting
through a long line of ancestry, is generally more powerful than
the heredity of a single generation. But when the offspring does
inherit the peculiarities of the immediate parent, or a part of
them, its offspring has a redoubled tendency to do the same, and
the next generation still more; for the tendencies to be like par-
ent, grandparent, and great-grandparent now all conspire to this
result and overpower the influence of a remoter ancestry.” 2

1148. The reproductive elements in a complete flower may
combine to produce an embryo. In this case the pollen and
ovule have originated upon a single shoot, within very narrow
limits of difference as regards the time, place, and conditions of
their development, and the result of their union is what might
be expected, — a close copy of the parent plant. The fecunda-
tion of a flower by its own pollen is termed close-fertilization, or
self-fertilization.

1149. In cross-fertilization the pollen fertilizing the ovule of
a flower comes from another flower of the same species, and here
the reproductive elements have been developed under dissimilar
conditions.

1150. In hybridization the pollen comes from a flower of a
different species; and in this case the conditions, external and

1 Volume I. pp. 318, 319. The student is urged to review carefully
the following sections also in that volume: 619 to 640, and 657 to 662
inclusive.

448 REPRODUCTION.

internal, under which the reproductive elements have been pro-
duced are widely dissimilar.

The mechanism by which close-fertilization is secured in some
instances and absolutely prevented in others has been fully
explained in Volume I. The account of the mechanism is now
to be supplemented by a statement of the results of reproduction
in the different degrees of relationship.

1151. The results of close-fertilization contrasted with those
of cross-fertilization. It has long been known to cultivators of
plants, that in order to keep the desirable varieties which are
under cultivation ‘+ true to seed” they must be close bred ; that
is, all pollen from other varieties of the same species must be
excluded. ‘The whole subject is best illustrated by reference to
the numerous experiments by Darwin; the exhaustive nature of
which is indicated by an account of a single series given nearly
in his own words.

1152. The plants experimented upon in all cases were raised
from carefully ripened seed, and, when ready to flower, were
placed under nets with meshes of one tenth of an inch in diame-
ter, in order that all pollen-carrying insects might be excluded.

A plant of Ipomeea purpurea (Morning Glory), growing in the
greenhouse, was protected in the manner just described, after ten
of its flowers had been fertilized by pollen from their own sta-
mens, and ten others by pollen from a distinct plant of the same
species. The seeds from the first ten flowers may be termed
self-fertilized, those from the other ten, crossed. The two kinds
of seeds were placed on damp sand on opposite sides of a glass
tumbler covered by a glass plate, with a partition between the
seeds, and the glass was put in a warm place. As often as a pair
of seeds germinated they were put on opposite sides of a pot,
with a superficial partition between them, and the same procedure
was followed until five or more seedlings of exactly the same age
were planted on the opposite sides of several pots. The soil in
the pots in which the plants grew was well mixed, and the plants
on the two sides were always watered at the same time; thus the
seedlings were subjected to practically the same conditions from
a very early stage.

In the same manner sclf-fertilized and crossed seeds were
secured during ten generations. ‘The results, so far as these ean
be shown by measurement of the plants, are exhibited in the
following table: *—

” Darwin : Effects of Cross and Self Fertilization, 1876, p. 52.

CLOSE AND CROSS FERTILIZATION CONTRASTED. 449

IPOM@A PURPUREA.

3 SA oh oj 3
° gi ‘38 ca See
Aupiber af the Se am es sen -
eneration. Pr &e 4 zs ares
E FER | ge | eths
A a ee Na
First. 6 86. 6 65.66 100 : 76
Second 6 84.16 6 66.33 100 : 79
Third . 6 77.41 6 52.83 100 : 68
Fourth 7 69.78 7 60.14 100 : 86
Fifth . 6 82.54 6 62.33 100: 75
Sixth . 6 87.50 6 63.16 100: 72
Seventh . 9 83.94 9 68.25 100: 81
Eighth 8 113.25 8 96.65 100 : 85
Ninth 14 81.39 14 64.07 100: 79
Tenth . 5 93.70 5 50.40 100 : 54
All ten generations aie
taken together. 73 85.84 73 66.02 100 :77

~ 1153. The results of close and cross fertilization, as shown by
the weight of the seed-capsules, are given by Darwin thus: ** The
offspring of intercrossed plants of the ninth generation, crossed
by a fresh stock, compared with plants of the same stock inter-
crossed during ten generations, both sets of plants left uncovered
and naturally fertilized, produced capsules by weight as 100
to 61.7

1 The following summary (Darwin: Effects of Cross and Self Fertilization,
p. 56) shows more of the results : —

First generation of crossed and self-fertilized plants growing in competition
with one another. Sixty-five capsules produced from flowers on five crossed
plants fertilized by pollen from a distinct plant, and fifty-five capsules pro-
duced from flowers on five self-fertilized plants, fertilized by their own pollen,
contained seeds in the proportion of . . . . ee «2 « 100to-93;

Fifty-six spontaneously self-fertilized capsules on the above five crossed
plants, and twenty-five spontaneously self-fertilized capsules on the above five
self-fertilized plants, yielded seeds in the proportion of . . . 100 to 99.

Combining the total number of capsules produced by these plants and the
average number of seeds in each, the above crossed and self-fertilized plants
yielded seeds in the proportion of. . . .. » 2 + « 100 to 64,

Other plants of this generation grown sedan mafamonsble conditions and
spontaneously self-fertilized yielded seeds in the proportion of . 100 to 45.

2a

450 REPRODUCTION.

1154. ‘All the self-fertilized plants of the seventh genera-
tion, and I believe of one or two previous generations, produced
flowers of exactly the same tint; namely, of a rich dark pur-
ple. So did all the plants, without any exception, in the three
succeeding generations of self-fertilized plants; and very many
were raised on account of other experiments in progress not
here recorded. . . . The flowers were as uniform in tint as
those of a wild species growing in a state of nature... .
The crossed plants continued to the tenth generation to vary
in the same manner as before, but to a much less degree,
owing probably to their having become more or less closely
inter-related.” +

1155. In the sixth self-fertilized generation there appeared a
plant which was larger than its crossed competitor, and its pow-
ers of growth and fertility were transmitted to its descendants.
Thus it appears that even with the exclusion of foreign pollen
new characters can assert themselves. :

1156. It was not found in these experiments that simply cross-
ing a flower from another flower on the sane plant was produc-
tive of any advantage ; on the contrary, there are some cases
which show that it may result in an actual disadvantage. ‘‘ The
benefits which so generally follow from a cross between two

Third generation of crossed and self-fertilized plants. Crossed capsules com-
pared with self-fertilized capsules yielded seeds in the ratio of . 100 to 94,
An equal number of crossed and self-fertilized plants, both spontaneously
self-fertilized, produced capsules in the ratio of 100 to 38. And these capsules
contained seeds in the ratio of 100 to 94. Combining these data, the produc-
tiveness of the crossed to the self-fertilized plants, both spontaneously self-
fertilized, was as. ww we ee ew ew ww wt . 100 to 85.
Fourth generation of crossed and self-fertilized plants. Capsules from flow-
ers on the crossed plants fertilized by pollen from another plant, and capsules
from flowers on the self-fertilized plants fertilized with their own pollen, con-
tained seeds in the proportion of . soe ee ee we 6100 to 94.
Fifth generation of crossed and self-fertilized plants. The crossed plants
produced spontaneously a vast number more pods (not actually counted) than
the self-fertilized, and these contained seeds in the proportion of 100 to 89.
Ninth generation of crossed and self-fertilized plants. Fourteen crossed
plants spontaneously self-fertilized, and fourteen self-fertilized plants sponta-
neously self-fertilized, yielded capsules (the average number of seeds per capsule
not having been ascertained) in the proportion of . . . . . 100 to 26.
Plants derived from a cross with a fresh stock compared with intercrosscd
plants. The offspring of intercrossed plants of the ninth generation, crossed
by a fresh stock, compared with plants of the same stock intercrossed during
ten generations, both sets of plants left uncovered and naturally fertilized
produced capsules by weightas . . . . . . . » 100 to 51. ;
1 Darwin: Effects of Cross and Self Fertilization, p. 59.

NECTAR. 451

plants apparently depend on the two differing somewhat in con-
stitution or character. . . . The mere act of crossing two distinct
plants which are in some degree inter-related and which have
been subjected to nearly the same conditions does little good
as compared with that from a cross between plants belonging
to different stocks or families and which have been subjected to
somewhat different conditions.” }

1157. In Volume I. the different methods by which cross-
fertilization is effected were sufficiently described, but certain
special questions were then purposely left unanswered; namely,
those in regard to the anatomical and chemical nature and the
distribution of the attractions by which insects are allured to
flowers to insure cross-poliination.

1148. The nectar which certain flowers offer to insects is made
known by color or odor, or both. It is the sweetish liquid com-
monly called the ‘‘ honey” of the flower, secreted by certain
specialized organs known as nectar-glands. Mention has already
been made (453) of the occurrence of these glands on leaves.
In the flower they consist usually of specialized parenchyma not
unlike the secreting surface of the stigma (see 1109). They
are sometimes raised by a stalk, or adenophore, more or less
above the surface of the floral organ on which they are de-
veloped, but often not elevated at all.

1159. Nectar-glands may occur upon any part of the flower,
upon its bracts, or even upon some part of the flower-stalk near
it. The ‘‘ Cow-pea” of the Southern States affords a good
example of nectar-glands on the flower-stalk. Many species of
Euphorbia have them on bracts; the common Passion-flower
and the cotton plant of the South also have them on the same
organs. The most remarkable case of arrangement of the glands
is found in a tropical plant, Marcgravia nepenthoides; this has
been thus described: ‘‘ The flowers are disposed in a circle,
hanging downwards like an inverted candelabrum. From the
centre of the circle of flowers is suspended a numher of pitcher-
like vessels, which, when the flowers expand in February and
March, are filled with a sweetish liquid. This liquid attracts
insects, and the insects numerous insectivorous birds. The flow-
ers are so disposed, with the stamens hanging downwards, that
the birds to get at the pitchers must brush against them, and
thus convey the pollen from one plant to another.” ?

1 Darwin : Effects of Cross and Self Fertilization, p. 61.
2 Belt : Naturalist in Nicaragua, 1874, p. 128.

452 REPRODUCTION.

1160. From the nectar-glands of proper floral organs the secre-
tion of nectar is generally copious and is prone to collect in
minute cavities such as shallow pits, or in conspicuous special
receptacles, the so-called nectaries. The morphology of these
organs has been sufficiently described in Volume I., Chapter VI.

1161. The specific gravity of nectar is very variable. The
following figures are from Unger’s * determinations : —

Agave Americana... ee ee ee ee 105
“© geminiflora .. ay Say ae 8 - + + « 1.09
er litida: ee we ey eRe eee = oe we ZO

If it is assumed that the solid matter in nectar is wholly sugar,
these figures would correspond respectively to the following
amounts of cane-sugar; namely, 10, 18, and 41.66 per cent.”

1162. The period of most copious secretion of the nectar usually
coincides with the maturity of the anthers or of the stigma, but
in some cases the nectar is prepared in considerable quantity
before the flower opens.*

1163. The secretion of nectar can be arrested, as Wilson has
shown, by carefully washing the secreting surface with a jet of
water and then drying it with filter-paper. Nectaries which
have been thus made inactive through removal of the nectar can
be again brought into activity by adding to the surface a little
strong syrup.

1164. The secretion from nectar-glands is not dependent upon
the pressure exerted by contiguous cells. When the flow of the
nectar from a nectar-secreting surface has been arrested in the
manner described above, a pressure of even 40 centimetres of
mercury upon the stem is insufficient to produce any effect; but
the activity of the surface is at once resumed when a little syrup
is placed upon it.

The secretion of nectar can proceed even when the tissues are
not turgescent.*

1165. The colors of flowers depend, as indicated in 477,
upon the existence in the cells of minute granules or of colored
sap. ‘The shades may be modified to some extent by accidents

1 Sitzungsberichte, Berlin Akademie, xxv., 1857, p. 446.

2 Wilson : in Untersuchungen aus dem bot. Inst., Tiibingen, 1881, p. 7.

3 Bonnier: Les nectaires, Ann. des Sc. nat., sér. 6, tome viil., 1879, p. 5.

4 For details see an important memoir by Wilson in Untersuchungen aus
dem bot. Inst., Tiibingen, 1881, i. p. 1; also an excellent paper by Trelease,
‘Nectar and its Uses” (in Report on Cotton Insects, U. S. Dept. of Agricul-
ture, 1879), which contains a comprehensive bibliography.

COLORS OF FLOWERS. 4538

of surface: é. g., in the case of velvety petals the color is often
softened, sometimes to a remarkable extent.

1166. Contrasted colors are often seen in a single flower. In
general these are so disposed in spots or lines as to suggest that
they bear a direct relation to the point where the nectar is se-
creted ; hence such color-marks were called by Sprengel nectar-
spots or nectar-guides. But in some cases flowers have conspicu-
ous spots without being nectariferous; e. g. certain poppies.

1167. Darwin cites the following case as showing that nectar-
marks have been developed in connection with the nectaries:
““The two upper petals of the common Pelargonium are thus
marked near their bases, and I have repeatedly observed that
when the flowers vary so as to become peloric, or regular,
they lose their nectaries and at the same time the dark marks.
When the nectary is only partially aborted, only one of the
upper petals loses its mark. Therefore the nectary and these
marks stand in some sort of close relation to one another, and
the simplest view is that they were developed together for a
special purpose ; the only conceivable one being that the marks
serve as a guide to the nectary.’”’?

1168. The colors of the flowers in certain species change more
or less after opening; thus many Borraginaceee turn from red
to blue even during a short space of time. One of the most
interesting cases of this change of color is presented by Arnebia.
When the flower opens each lobe of the yellow corolla is con-
spicuously marked by a deep purple spot; after a few hours this
begins to fade, and by the next day entirely vanishes.

1169. Of all colors of flowers white, pale yellow, and yellow?
are the most common.

1 Effects of Cross and Self Fertilization, 1876, p. 373.

2 The following table-by Kohler and Schiibeler (cited by Balfour) exhibits
the relative frequency of certain colors in the plants of twenty-seven different
families of plants : —

Color of flower. In 4200 species. Mean of 1000,
WOR em RO a ws 4 1193 284
, Mellow ge * & a ae HS es 951 226
Rede 4 ve ww & 8 Lee ee 923 220
IBIWG: scat so yas See eA 594 141
i: cee ee eee “8 307 73
Greens < % @ @ a © & ws “ 153 36
Orange . . a ome . 50 12
Brown. lot tas Se tea aes Se ct 18 4
Blacks « g = # % % « 3 8 2

454 REPRODUCTION.

1170. The colors of flowers have been variously classified ; thus
De Candolle divides them into a xanthic (yellow) and a cyanic
(blue) series, both of which can pass into red and white. With
few exceptions, these two series are not represented in the same
blossom.

1171. The odors of flowers depend in some cases (¢. g.
orange-blossoms) upon the presence of a volatile oil which can
be extracted by distillation; but in many other instances the
odoriferous principle cannot be separated by chemical or other
means.

1172. White flowers are more generally fragrant than those
of any other color. ‘+The fact of a larger proportion of white
flowers smelling sweetly may depend in part on those which are
fertilized by moths, requiring the double aid of conspicuousness
in the dusk and of odor. So great is the economy of nature that
most flowers which are fertilized by crepuscular or nocturnal
insects emit their odor chiefly or exclusively in the evening.” ?

1 Darwin: The Effects of Cross and Self Fertilization in the Vegetable
Kingdom, 1876, p. 374.

According to Kohler and Schiibeler (cited by Balfour), the distribution of
odor with regard to color is as follows :—

¥ . Odors Odors
Color. Species. Ouoriferous. agreeable. | disagreeable.
White. 4 5 1193 187 175 12
Yellow ....,.. 951 15 61 14
Red. 4 we He ee 923 85 76 9
Blue Oe Rvs Be De 594 31 23 vd
Violet... Sard 807 23 17 6
Green . 6 we eS 153 12 10 2
crange .. . oo 50 3 1 2
Brown ...... 18 1 0 1

The following classification, taken partly froin Trinchinetti, as cited by
Balfour, indicates the diversity which exists in regard to the periods and per-
manence of odors of flowers.

(1) Flowers which are odoriferous at the time of opening and which remain
so throughout ; e. g. most Roses. . ;

(2) Flowers in which the intermission of odor is connected with their
opening and closing ; and in this class there are two subdivisions : —

._ (@) Those which are closed and scentless during the day, and are open and
odoriferous at night ; ¢. g. Mirabilis Jalapa, Cereus grandiflorus ete.

(2) Those which are closed and scentless at night, and are open and odors
iferous during the day; ¢. g. Convolvulus arvensis, Cucurbita Pepo, some
species of Nymphea. ;

HYBRIDS. 455

1173. Nectar is protected in various ways from unwelcome
msects ; that is, from those which cannot aid cross-fertilization.
The chief of these is by the structure of the flower itself or the
parts below. Characteristic odors and certain colors may con-
tribute to this protection. Thus, as Miller has pointed out,
dull yellow flowers are entirely, or almost entirely, avuided by
beetles, while they are visited by Diptera and Hymenoptera
(flies and bees).

1174. Hybrids are the offspring of crossed species. But, as
shown in Volume I. page 320, the limits which separate varie-
ties from species are sometimes not sharply defined; hence it
happens that the term hydrid has been also applied to crosses
between strongly marked varieties of the same species. Such
offspring should, however, be termed either variety-hybrids or
cross-breeds, aud the word hybrid kept to its proper significa-
tion.

1175. Wide differences exist in the degrees of capacity for
producing hybrids. Thus certain closely allied species cannot
be made to cross, while others much more remote in apparent
relationship are crossed without difficulty.

1176. In general the limits of capacity for hybridizing do not
extend beyond the genus; a few cases, however, are known in
which species usually assigned to different genera have been
successfully crossed.1 Hence it cannot be known beforehand
whether the atteinpt to cross two species will be successful.

(3) Flowers which are always open, but which are odoriferous at one time
and scentless at another. Under this class there are also two subdivisions :

(a) Those always open, and only odoriferous during the day; ¢ g.
Cestrum diurnum, Coronilla glauca, ete.

(6) Those always open, and only odoriferous at night; ¢. g. Cestrum
nocturnum, Hesperis tristis, etc.

In certain cases odors are given out by flowers in an intermittent manner.
This is strikingly shown in some of the larger night-flowering species of
Cactacez.

Delpino has given (Ulteriori Osservazioni sulla Dicogamia nel Regno Vege-
tale, 1868-1874) an elaborate classification of odors as they exist in flowers.
He makes forty-five kinds which are readily distinguishable as peculiar, while
between these kinds there are of course innumerable gradations.

1 Focke notes that hybrids between species belonging to different genera
are comparatively common in the following families: Caryophyllacee, Melas-
tomacex, Passiflorace, Cactacee, Gesneriacee, Orchidacee, Aimaryllidacee,
and Graminee; and he cites also the following instances outside of these
families: Brassica X Raphanus, Galium X Asperula, Centropogon X Sipho-
eampylus, Campanula X Phyteuma, Verbascum X Celsia, Philesia X Lapageria,
(Pflanzen-mischlinge, 1881, p. 456).

456 REPRODUCTION.

1177. In reciprocal hybridization the pollen of A is effective
when applied to the stigma of B; and, conversely, the pollen of
B is potent when applied to the stigma of A. But it sometimes
happens that the rule will not work both ways. Thus the pollen
of Mirabilis longiflora was found by Kélreuter to produce hybrids
when applied to the stigma of Mirabilis Jalapa ; but the pollen
of the latter was without effect upon the stigma of the former.
Otber cases are known, but the cause of this extraordinary
preference is not understood.

1178. Hybrids are produced artificially by the transfer of
pollen from one species to the stigma of another species, care
being taken to exclude all pollen of the second species from its
own stigma. The pollen is best transferred by means of a sable
or camel’s hair pencil.! Exclusion of the pollen of the flower
to be fertilized must be secured by removal of the anthers before
the flower opens. This is easily effected by the use of delicate
forceps, an incision being carefully made in the side of the
corolla. After the application of the pollen to the stigma, the
plant or blossom must be covered by some close netting.

1179. Following the application of the pollen, changes take
place in the fertilized flower. But, as Nageli has pointed out,
these changes in many cases fall far short of yielding satisfac-
tory results to the experimenter. Niigeli describes several grades
of partial fertilization: (1) that in which the ovary, and per-
haps the persistent calyx, grows somewhat without appreciably
affecting the ovules; (2) that marked by greater growth of the
ovary, and by slight enlargement of the ovules, which after-
wards shrivel up; (3) that with small imperfect fruits with
empty seeds; (4) that having good fruits with empty seeds;
(5) that with normal fruits with apparently perfect seeds which
have no germs; (6) that producing good fruits with seeds which
have only minute germs incapable of further development.

In successful fertilization there are produced good fruits hold
ing sound seeds.

Some of the cases in which hybrids have been produced between the
species of different genera are given by Nageli (Sitz. d. k. Akad. d. Wiss. z.
Miinchen, 1865 and 1866), as follows: Rhododendron and Azalea, Rhododen-
dron and Rhodora, Rhodora and Azalea, Rhododendron and Kalmia. Of those
above mentioned, Rhododendron, Rhodora, and Azalea are now placed by
Bentham and Hooker in a single genus, —- Rhododendron.

1 It is of great importance that the pollen should be applied at exactly

the proper period for impregnation. This is usually indicated by the moisture
of the stigmatic surface.

ARTIFICIAL HYBRIDIZATION. 457

1180. If to a stigma pollen from two species is applied simul-
taneously, only that will be potent which has the greatest sexual
affinity, and no apparent effect will be produced by the other.

1181. With some remarkable exceptions, hybrids share the
general characters of their parents, and are intermediate between
ihem. It sometimes happens that part of the offspring of a
single union will have certain characters, while the rest,’ raised
from the same seed-pod, will possess others.

1 This and certain other points referred to in the text are well illustrated
by the case of Parkman’s Lily, which is here described nearly in full : —

“My first attempt was to combine the two superb Japanese lilies, L. specio-
sum (lancifolium) and L. auratum. The former was used as the female
parent. Four or five varieties of it, varying from pure white to deep red, were
brought forward in pots under glass. This was necessary, because L. speciosum
does not ripen its seed in the open air in the climate of New England. When
the flowers were on the point of opening, the anthers were carefully removed
from the expanding buds by means of forceps. As the pollen was entirely
unripe, and as pains were-taken to leave not a single auther in any of the
flowers, self-impregnation was impossible. The pollen of L. auratum was
then applied to the pistils as soon as they were in condition to receive it.
Impregnation took place in most eases. The seed-pods swelled, and promised
an ample crop of seed; but the experiment was spoiled by the bad management
of the man in charge of the greenhouse, in conseyuence of which the pods were
attacked by mildew.

‘‘In the next year I repeated the attempt, with the same precautions.
This time the seed was successfully ripened. Being sown immediately, a por-
tion of it germinated in the following spring, and the rest a year later. In
regard to this seed, two points were noticeable: first, it was scanty, the pods
(though looking well) being in great part filled with abortive seed, or mere
chaff ; and, next, such good seed as there was differed in appearance from the
seed of the same lily fertilized by the pollen of its own species. The latter is
smooth, whereas the hybrid seed was rough and wrinkled. About fifty young
seedlings resulted from it; and their appearance was very encouraging, because
the stems of nearly all were mottled in a manver characteristic of L. auratum,
but not of L. speciosum. Here, then, was a plain indication of the influence
of the male parent. The infant bulbs were pricked out into a cold-fraine, and
left there three or four years, when, having reached the size of a pigeon’s egg,
they were planted in a bed for blooming. This was in 1869. Towards mid-
summer, one of the young hybrids showed a large flower-bud much like that
of its male parent, L. auratum. The rest, about fifty in all, showed no buds
until some time after ; and when the buds at length appeared, they were pre-
cisely like those of the female parent, L. speciosum. The first bud opened on
the 7th of August, and proved a magnificent Hower, nine and a half inches in
diameter, resembling L. anratum in fragrance and form, and the most. bril-
liant varieties of L. speciosum in color. In the following year it measured
nearly twelve inches from tip to tip of the extended petals ; and in England it
has since reached fourteen inches. . . . In this one instance the experiment
had been a great success; but of the remaining fifty hybrids, not one produced
a flower in the least distinguishable from that of the pure L. speciosum. The

458 REPRODUCTION.

1182. Focke has shown that hybrids between remotely related
species are generally delicate and difficult of cultivation, but that
those which result from nearly related species are remarkable for
the vigor of their vegetative organs. Niigeli has also pointed
out that the latter have a somewhat longer lease of life than the
parents; thus annuals can become biennials or even perennials.

1183. Hybrids between closely related species usually have
larger or more showy flowers than either of the parents, but their
reproductive organs are much weaker. This diminution of fer-
tility may be complete, but it is usually only partial. The pollen-
grains are generally fewer and often less developed, the ovules
are less likely to afford sound germs. As a rule, the stamens
are more affected than the pistils.

1184. Derivative hybrids are the offspring resulting from a
union of a hybrid with one of the parent forms, or with another
hybrid from a different source. In the former case there is fre-
quently observed a marked tendency towards reversion, which
may be heightened by repeated experiments in the same direc-
tion, until at last it is complete.!

1185. Hybrids and their offspring exhibit a marked tendency
to vary. This fact is utilized by horticulturists in the production
of new varieties. Varieties thus produced must, however, be
perpetuated by other means than by seed.?

influence of the alien pollen was shown, as before noticed, in the markings of
the stem, and also in a diminished power of seed-bearing ; but this was all.

“In the next year, wishing to see if the male parent would not make his
influence appear more distinctly in the second generation, I fertilized several
of these fifty hybrids with the pollen of L. auratum, precisely as their fe-
male parent had been fertilized. The crop of seed was extremely scanty ; but
there was enough to produce eight or ten young bulbs. Of these, when
they bloomed, one bore « Hower combining the features of both parents ;
but, though large, it was far inferior to L. Parkmanni in form and color.
The remaining flowers were not distinguishable from those of the pure
L. speciosum” (Bulletin of the Bussey lustitution, ii., 1878, p- 161).

1 For a full treatment of this subject, the student should examine Nageli’s
treatise in Sitzungsberichte der Konigl.-hayer.-Akad. der Wissenschaften zu
Miinchen, 1865, ii.; and that by Focke, Pflanzen-mischlinge, 1881.

2 For a full account of the variation of hybrids, the student should see
Naudin, Ann. des Se. nat., sér. 4, 1863, tome xix.

For a study of the influence of foreign pollen on the form of the fruit, see
a paper by Maximowicz: St. Pétersb. Acad. Sci. Bull. xvii., 1872, col. 275.

CHAPTER XV.

THE SEED AND ITS GERMINATION,

1186. Tuus far this treatise has dealt chiefly with the phenom-
ena presented by the organs of adult plants, especially while
these are in a healthy state. It is necessary to consider in con-
clusion a special case; namely, that of the seed, and the earliest
phases of its independent existence.

1187. When a fertilized ovule approaches maturity, its activi-
ties become notably lessened in degree until, with perfect ripe-
ness of the seed, the embryo manifests no indication of life. In
a few cases the seed is so precocious that it will germinate even
before it is detached from the parent plant; but there is usually
a period of suspeuded activity.

1188. Two views are held as to the nature of the life of the
embryo during this period of arrested activity: (1) that it is
simply potential, and may be roughly compared to the fire in a
match, ready to manifest itself under favorable conditions ; (2)
that it is a sluggish, dormant state, which differs from active life
only in degree.

1189. From the first point of view it is easy to regard the
seed as representing a certain amount of potential energy indi-
rectly derived from solar radiance, and held for a time in a con-
dition from which it may be released in many ways: thus, it may
be liberated by rapid combustion, as when corn is burned for
fuel; by slow oxidation, as when seeds decay ; or by the act of
germination.

1190. The second view takes into account, although it does
not explain, the slight changes which take place in certain seeds
and some other parts, especially buds, during what has been
called the resting state.

1191. It has been stated (976) that many seeds cannot be
made to start into active growth, even under the most favorable
external conditions, until after the lapse of a definite period.
Nothing is yet known as to tne exact structural and other changes
which go on by virtue of this peculiarity.

460 THE SEED AND ITS GERMINATION.

1192. Ripening of fruits and seeds. The structural changes
attending this process, taken together, result in adaptations for
providing the embryo with an ample supply of food, for giving it
adequate protection during its resting state, and for securing
its dissemination.

1193. The chemical changes comprise chiefly the storing up
of a sufficiency of food of a proper character to support the
embryo for atime. In pulpy fruits they are mostly associated
with the consumption of a certain amount of oxygen and the
liberation of more or less carbonic acid. Many of the chemical
changes can go on after the separation of the fruit or seed from
the parent plant.

In the ripening of pulpy fruits the important changes in
texture are attended by the formation of sugars, acids, ete., and
by modifications in the character of the walls of cells.

1194. Dissemination is most frequently secured by (1) some
mechanism for transport by air, water, fleece, or plumage; (2)
the construction of some expulsive apparatus ; (3) the existence
of certain attractions of taste, color, and odor, by which the
seeds are made the food of birds. In the last case the germ
itself, protected against the action of digestive juices, is often
carried to great distances from the parent plant.

1195. Ripeness of seeds. The embryo is sometimes viable, or
capable of independent life, at a very early stage. Immature
seeds are of course deficient in their supply of proper food for
the embryo, which is only imperfectly developed, and their in-
teguments are not yet adapted to protect the germ adequately.
But in certain instances such seeds may germinate, giving rise
to strong and healthy plants. Cohn? has shown that seeds which
are not perfectly ripe germinate somewhat sooner than those
which are more mature; this means that the store of food is in
a condition which admits of immediate use. He has further
pointed out that seeds separated from the plant, but still enclosed
in the pericarp, ripen; and he believes that those seeds which
have reached a medium stage of ripeness germinate most readily.
“* Viability does not coincide with ripeness ; it precedes it.” 2

1196. Shortly before the period of ripening, the part which

1 Flora, 1849, p. 481.

2 There is some reason to believe that in the case of certain cultivated vege-
tables unripe seeds may give rise to earlier varieties than come from ripe seeds.
For numerous citations from the extensive literature of the subject see a paper
by the author in the Report of the Secretary of the Massachusetts Board of
Agriculture for 1878.

VITALITY OF SEEDS. 461

connects the fruit or seed with the parent plant undergoes marked
changes, which ultimately effect or permit complete separation
of the seed from the plant without any injury. The process of
separation has been compared to that by which the leaf is de-
tached from the branch in the autumn.

1197. How long can a seed retain its vitality? Some seeds
perish shortly after separation from the parent unless they are
at once planted, while others preserve their vitality for long
periods. In experiments by De Candolle seeds of three hun-
dred and sixty-eight species of plants were kept in the same
place and under the same conditions for fifteen years. The
following results are recorded : —

Of 1Balsaminacee. . . . . . . ~ ~. 1 came up, or 100 per cent,
“© 10 Malvacee . 5 $8 $6 FE BO ee. ne
“© 45 Leguminose ew Os Qe GE i AE. SEE HES
“ 30 Labiate. 2.0. 1 8 ee 1 gE ee ee
‘¢ 10 Scrophulariacee . . . 1. . OS ot

‘© 10 Umbellifere . . . . . .. iQ a 8

** 16 Caryophyllacee . . . . i ie

“© 32Gramineew . - . 2.» 2. ew ed

fe 34 Crucifere . 2 «© 4 © 2 & * & Qi ER 88

“© 45 Composite. . . . . - Qh se

1198. Daubeny, Henslow, and Lindley found that the seeds
of a species of Colutea germinated when forty-three years old, and
those of a Coronilla when forty-two years old. They ascertained
that the seeds of plants belonging to twenty genera experimented
on, germinated after from twenty to twenty-nine years’ separa-
tion from the parent plant.

There is no unquestioned evidence that wheat-grains from the
wrappings of mummies have been made to germinate.?

1 Report of the British Association for the Advancement of Science, 1850,
p. 165.

2 The following notes of cases of prolonged vitality may be of interest : —

M. R. Brown ma dit avoir fait germer des graines de Nelumbium specio-
sum extraites par lui de l’herbier de Sloane, c’est-a-dire ayant au moins .150
ans (De Candolle: Géographie Botanique raisonnée, 1855, p. 542).

Seeds of Nelumbium (jaune) have sprouted after they had been in the ground
for a century (Lyell’s Second Visit to the United States, ii., 1849, p. 228).

The grains of wheat found in mummy-wrappings are uniformly blackened
as if by slow charring (eremacausis), and there is no evidence of a trustworthy
character that such seeds have ever been made to germinate. The account
by Count von Sternberg of the germination of wheat supposed to have been
procured at the unrolling of a mummy will be found in Isis, 1836, col.
715-717.

462 THE SEED AND ITS GERMINATION.

GERMINATION.

1199. Germination,? the process by which an embryo unfolds
its parts, is complete when the plantlet can lead an independent
existence.

1200. The conditions necessary for germination are (1) moist-
ure, (2) free oxygen, (3) warmth.

1201. The amount of water required to initiate the process
of germination is, in general, that which will completely saturate
and soften the seed. Germination does, however, begin in cer-
tain cases even when only the radicle and the albumen directly
around it have become soaked.

The amount of water requisite for the saturation of a seed has
been determined for a large number of plants, and will be seen
by a comparison of the results to vary within wide limits, depend-
ing on the percentage of water already present and the character
of the albumen. It is plain that in very exact determinations
account must be taken of the possibility of a loss by the seed
of a portion of its contents while in water; in three days this
amounts in the common bean to a little over two per cent. The
cereals require a comparatively small amount of water for satu-
ration, while leguminous seeds absorb a much larger quantity.”

1 Jt is well to distinguish between two stages in the process of germination,
(1) that marked by the protrusion of the first rootlet, (2) the subsequent de-
velopment of the embryo into an independent plant. The reason for making
this distinction is, that most of the experiments upon the relations of tempera-
ture, etc., to germination have usually terminated at the first stage ; whereas
the vigor of the plantlet as seen at a later stage is an important factor in
deducing results to guide practice in sowing seeds.

2 The table below, by Hoffmann (Versuchs-Stationen, vii., 1865, p. 52), hasa
parallel column of results obtained at Tharandt (Nobbe: Samenkunde, p. 119):

Percentage of liquid water absorbed.
Species. Observations by Observations at
Hoffmann. Tharandt,
Indiancorn, . . + « . + eee, 44, 89.8
Wheat: 3: 2 we we i OH 45.5 60.
Buckwheat. . . 1... 1. ew eee 46.9
ARV Bia: fay car Se Geb ct gee Geek Ge ees ee GS 57.7
ORB co, eae 8 ee Va RE ORE ee nay a asm 59,8
White beans . . 2. 1 ee we wae 92.1
Windsor bean. . « «2. ee wae 104. 157.
Péas ce ek eh Se ww ww a 106.8 eels
b. 71.
Redclover . . 2. + + ww ee ee 117.5 105.3
Sugar beet. . . +. 2. 2. ewe, 120.5 :
Whiteclover ....... 8 6% 126.7 89.

ABSORPTION OF WATER BY SEEDS. 463

1202. The increase of seeds in size accompanying the absorp-
tion of water is ascertained by placing them from time to time
in a narrow graduated cylinder, pouring over enough water
to completely cover them, and noting the height at which the
water stands; then pouring it into another graduated glass and
accurately measuring it. The difference in amount of water in
each case indicates the volume of the seeds. The work must
be done expeditiously in order to avoid the error arising from
absorption during the period of measuring; but this error in
any case is slight.

1203. The following results may be of interest and serve as a
guide to the student.?

65.418 grams of air-dried peas, having a volume of 43 cubic
centimetres, were soaked in water at a temperature of 19°
21°C. The soaked seeds were at each measurement carefully
dried by blotting-paper : —

1. In absolute figures. 2. In percentages,
Time.
Weight. Volume. Weight. Volume.
14hows. . .| 46.41 gr. 46 cc. 70.9 107
ce ne 8.02 ‘* 9c <8 12.3 44.1
008 we 8.52 a 88 13 16.3
70 hours. . . | 62.95 gr. 72 ce. 96.2 167.4

The gain in weight in 70 hours was therefore 96 per cent, and
in volume 167 per cent.

In another experiment the changes were as follows: Phaseolus
vulgaris gained in weight, in 48 hours, 100.7 per cent, and in
volume, 134.14 per cent. In still another experiment, with the
same species, the gain in weight in 72 hours was 114.5 per cent
(or, taking into account some loss by extraction, 117.5 per cent),
and in volume, 140.9 per cent. The gain in volume is con-
siderably greater than the gain in weight.?

1 Nobbe : Handbuch der Samenkunde, 1876, p. 122.

2 It must be noted that in many dry seeds, for instance between the coty-
ledons of some peas and beans, there are cavities which must be filled before
there can be any marked increase of volume (Nobbe: Handbuch der Samen-

kunde, 1876, p. 125).

464 THE SEED AND ITS GERMINATION.

1204. The greater part of the increase in weight and volume
from the absorption of water by dry seeds takes place in a short

time ; for example : —

Phaseolus vulgaris.

Increase in
weight.

Increase in
volume,

In 6 hours 13.99 per cent. | 28.28 per cent.
BQ Es as te aes a a ty a AES} SOE 13.10 “*
DB Eas ce i gh a a ee cee we |] BDA EE EE 62.07 “* &€
“ce 98 ee Fe 3.35 ce 6 3.45 “cc ee

After this there was very little gain either in weight or volume.

1205. Access of free oxygen must be provided to secure
germination. Even if all other conditions are favorable, germi-
nation does not take place in pure water devoid of any free
oxygen, or in an atmosphere of nitrogen.

1206. The oxygen accessible to the seed must be diluted to
about the degree found in common atmospheric air, although it
is not necessary that the dilution should be made with nitrogen,
as is the case with air. Boehm?! has shown that a mixture of
proper proportions of hydrogen and oxygen answers about as
well as a mixture of nitrogen and oxygen for germination of
seeds, provided it is furnished to them under ordinary atmos-
pheric pressure. That the degree of pressure is an important
factor, is proved by Bert’s? experiments. Barley gave the
following results : —

Percentage germinated.

In ordinary air (76 cm. pressure). . . . . 2. . 8d
In air 50 a he Sw ai a SO
Be ee 25 * fe woe ato ge a A oa D8
in ss 6 se a or aa - 10

The proportion of oxygen to nitrogen in atmospheric air is
approximately 1: 5 (oxygen, 21, nitrogen, 79 parts).

1207. The temperature requisite for germination to begin
differs considerably in different species. The lowest tempera-
ture recorded is the following, noted by Uloth:* In a perfectly
dark ice-cellar seeds of Acer platanoides sprouted on ice, the
rootlets penetrating to a depth of 5 to 7.5 em. into the dense

1 Sitzber.: Wien Akad., Ixviii., 1873, p. 182.
* Comptes Rendus, Ixxvi., 1875, p. 1493.
® Flora, 1871, p. 185.

TEMPERATURE REQUISITE FOR GERMINATION. 465

clear ice; the seeds themselves being in hollows on its surface.
The temperature must of course be given as 0° C. Uloth found
also that wheat-grains germinated in the same cellar upon pieces
of ice. Kerner? placed seeds with some earth in glass tubes and
exposed them to the cold springs on the edge of snow-fields in
Alpine regions. He found that the seeds of most Alpine plants
could germinate at 2° C., and that some might even at 0°. It
was shown that at all growing points there is some heat evolved.
In Uloth’s observations, above noted, attention is called to the
fact that the rootlets descended into solid ice in a number of
cylindrical cavities which they melted out for themselves.

1208. The minimum temperature for germination of the seeds
of many plants in common cultivation is given by Haberlandt ?
as 4°.75 C. (although some can start even below this). Be-
tween 4°.75 and 10°.5 we have the minimum temperature for
Indian corn, timothy grass, sunflower ; between 10°.5 and 15°.6,
that for tobacco and squash; between 15°.6 and 18°.5, that for
cucumber and melon.

1209. The maximum temperature, or that beyond which germi-
nation cannot begin, differs greatly in different species. Haber-
landt has shown that degree of ripeness, freshness, the ‘+ race,”
and several other influences considerably modify the result.
The maximum temperature for a few of the more common plants
is here noted : —

co.
Wheat, rye, barley, oats, peas, timothy a ni POPPY: flax,
and tobacco - . 81-37
Red clover, lucerne, hidomhent; ‘andl aontlowet . wee we w+ 875-44
Indian corn, millet, squash, cucumber, and sugar melon . . «. . 44-50

In no case was germination observed above 50° C.

1210. Between the minimum temperature below which and
the maximum temperature above which germination of a cer-
tain kind of plant does not ordinarily take place there lies an
optimum temperature; that is, the degree at which germina-
tion begins most speedily.2 The short table on the following
page is by Sachs: —

1 Berichte der naturw-med. Vereines in Innsbruck, 1873, and Botanische
Zeitung, 1873, p. 437.

2 Versuchs-Stationen, xvii. p. 104.

8 The difference in regard to the degree of warmth demanded by seeds of
the same species raised in different climates has been examined by Schiibeler
(Die Culturpflanzen Norwegens, 1862, p. 27).

30

466 THE SEED AND ITS GERMINATION.

Minimum, Maximum. Optimum.
BATE? yey se vee ny, Rs 5° 38° 29°
Wheat. « « » @ & 5° 42° 29°
Scarlet runner . . . 9.95 46° 33°
Indian corm, 5 « = 4 9.25 46° 33°
Squash... ... 119 46° 33°

1211. The time required after planting for germination to
begin, a point indicated by the protrusion of the radicle, has
been determined? for a large number of plants. A few exam-
ples are here mentioned : —

Indian corn. Red clover. Birch.
Atlé°C.. . 2... 144 hours. 32 hours, 120 hours.
iia 1s} 0 a ee 56 24 =* sa
EA BLOC 3. a se ae 48 «8 24 = * 24 “
Oe STo5iC, 6 & a 3 48 « 24 =< 24“
#5 AAPO. ce es os 80 72

1212. The influence of light upon the earliest stages of germi-
nation has been shown by careful investigations to be inappre-
ciable so far as most plants are concerned.” -

The unqualified statement found in some works,? that light is
in general prejndicial to germination, is not borne out by facts.

1213. The phenomena of germination are: (1) forcible absorp-
tion of water, (2) absorption of oxygen, (8) solution of nutrient
matters, (4) their transfer to points of consumption, (5) their
employment in building up new parts. After the initial step
these processes may go on simultaneously.

1214. The enormous imbibition power of dry seeds can be
demonstrated by confining sound seeds in a strong receptacle
to which water can obtain access. If a closed manometer is
attached, the pressure they exert can be measured. Boehm 4

1 Versuchs-Stationen, xvii., 1874, p. 104; and Storer: Bulletin Bussey
Inst., 1884,

® Hoffmann : Jahresber., iiber Agricultur-Chem., 1864, p. 110.

3 Ingenhousz ; Senebier, Physiologie végétale, iii. 1800, p- 396 ; Johnston’s
Lectures on Agricultural Chemistry, 1842, p. 194.

* Miiller: Botan. Unters. ii, 1872, p- 29, quoted by Nobbe (Hand-

buch der Samenkunde, p. 118). Similar experiments at Wellesley College
gave results somewhat lower than this,

PHENOMENA OF GERMINATION. 467

found that peas in swelling could overcome a pressure of 18
atmospheres, corresponding to a height of the mercurial .column
of 13.5 metres.

1215. The influence of oxygen upon the absorption of water
by the seed is not marked, as will be seen by the following
experiment : + —

200 fresh seeds of red clover were placed in pure water for 20
hours; 200 more were placed in water into which oxygen gas
was conducted ; 200 more in water through which carbonic acid
gas was conducted for a while and then the water covered with
a layer of oil to exclude the air. The results, so far as swelling
is concerned, were as follows : —

Seedsin water . . . . . . . . 83 per cent swollen.
fs “with oxygen. . . . 86 ee
ss te “ carbonicacid. . 71 a

1216. The oxygen absorbed by seeds in germination was
thought by Schénbein to undergo the active or ozone modifica-
tion. By his experiments the seeds of two plants, Cynara Scoly-
mus and Scorzonera Hispanica, were shown to possess to a con-
siderable degree the power of converting atmospheric oxygen
into ozone.

1217. Oily seeds absorb a large amount of oxygen. Siewert
has pointed out the fact that the neutral oil of the rape-seed very
soon after access of oxygen and water to it possesses an acid
reaction. Oleic acid can absorb at ordinary temperatures about
twenty times its volume of oxygen.

1218. Nutrient matters must become liquid before they can be
utilized by the embryo. Some of these in the form in which
they are stored up in seeds are soluble in water; such are the
sugars, dextrin, and a part of the albumin. The other nutrient
matters, such as starch, the oils, and most nitrogenous sub-
stances, must undergo changes before they can enter into solu-
tion. Some of these changes have already been alluded to in
Chapter XI., and are here presented in brief review.

1219. The conversion of starch into soluble matters is effected
in the seed by means of one or more ‘‘ ferments.” In the pro-
cess of malting,? which consists essentially in forcing germination
up to the point of protrusion of the radicle and then checking it,
the starch appears to undergo little change. But if the ground
malted grains are kept in water of a temperature of 68° C. for

1 Nobbe: Handbuch der Samenkunde, 1876, pp. 102, 108.
2 See Watts’s Dictionary of Chemistry, under ‘‘ Beer.”

468 THE SEED AND ITS GERMINATION.

two hours, all the starch will be found to have been converted
into and dissolved as soluble carbohydrates, sugar, and dextrin.
The change in this case is attributed to the ferment, diastase,
one part of which, it is claimed, can convert two thousand
parts of starch into sugar. It will be noted that in the pro-
cess above described the temperature (68° C.) is much higher
than that at which ordinary germination proceeds.

Dubrunfaut? has given the name maltin to a ferment far more
active than diastase, found in all germinating cereals. This is
able to convert into a soluble state from one hundred thousand
to two hundred thousand times its weight of starch. It forms
with tannic acid an insoluble compound which retains its power
for a long time. In good barley meal there is one per cent of
maltin.

1220. The oil in oily seeds is in germination carried through
a long series of changes. It is first transformed into starch, and
then follows the same course as starch, already described.?

1221. Van Tieghem has shown that oleaginous albumen, rich
in aleuron, has an activity of its own which enables it to digest
itself, so to speak, and thus become at once fit for the embryo
to use; on the other hand starchy albumen and cellulosic albu-
men must be first acted on by the embryo, and thus become
dissolved and ready for use.®

1222. The changes which take place in a germinating seed
are accompanied by direct or indirect oxidation of a portion of
the nutrient matters, a release of energy, and an evolution of
carbonic acid.4 The amount of CO, given off by germinating
seeds and the rise of temperature serve as measures of the
process of oxidation.

1223. It is not proved that germination can be hastened by
chemical means. Experiments with dilute chlorine water seem
to show that the time can be somewhat lessened, but the results
are discordant.°

1224. It has been asserted recently that the presence of mi-
crobes, the minute organisms to which putrefaction is due, is

1 Comptes Rendus, Ixvi., p. 274.

2 Peters, Versuchs-Stationen, iii., 1861, p. 1; Miintz, Ann. de Chimie et
de Physique, sér. 4, tome xxii. p. 472.

3 Ann. des Sc. nat., sér. 6, tome iv., 1877, p. 189.

4 For the changes in the horny endosperm of the date palm see Sachs,
Botanische Zeitung, 1862, p. 241.

5 See M. Carey Lea, American Journal of Science, xxvii., 1864, p. 373,
and xliii., 1867, p. 197.

FIRE-WEEDS. 469

essential to the beginning of the process of germination. It is |
said that in soil which has been completely sterilized, that is,
freed from microbes or their germs, seeds provided with all other
requisites for germination will fail to sprout. These experiments
by Duclaux! have not been repeated by other observers.

1225. The appearance of abundant crops of certain plants
upon ground recently cleared by fire is one of the most note-
worthy phenomena in connection with germination. At the
North, two plants have obtained, par excellence, the name of
‘*fire-weeds;” namely, Evechtites hicracifolia, and the more
common willow-herb, or Epilobium angustifolium. They are
later replaced by shrubs, and later still by soft-wooded trees,
which are characteristic of burnt districts. The following sug-
gestions have been made in regard to their appearance: (1) that
the seeds have been long buried in the soil, under conditions.
which have preserved their vitality, but which did not permit
them to germinate; (2) that the seeds find their way to the
ground of a clearing which affords, in the ash released from
wood by burning, a soil most fit for germination. But no exact
observations have yet been made upon the subject.

1 Comptes Rendus, ¢c., 1885, p. 67.

CHAPTER XVI.:
RESISTANCE OF PLANTS TO UNTOWARD INFLUENCES.

1226. Craupr Bernarp has shown that life presents itself
under three forms: (1) latent, dormant, or inactive, illustrated
by the seed ; (2) variable, or oscillating, exemplified by the plant
during periods of apparent rest, when its activities are nearly
suspended, but when, in fact, some chemical changes are going
on, though very slight in degree; (3) active, or free, exhibited
by a plant in full vigor.

It has been repeatedly pointed out in previous chapters that
during their resting periods seeds and other parts can be sub-
jected to the action of influences which would destroy the life
of plants in full activity.’

1227. Inquiry as to the kind and amount of injury caused to
active plants by hurtful agents must deal with the influence of
extremes of temperature, too intense light, improper food, poi-
sons, and mechanical agents. Many of these injurious influences
and their effects upon special parts of the plant have already
been alluded to in previous chapters; but it is proper to con-
sider them now with regard to the whole organism.

1228. Effects of too high temperature upon the plant. Here,
as in most other cases, there is wide diversity among plants,
depending upon their constitutional peculiarities ; thus, plants of
the tropics not only demand higher temperatures than those of

1 For some account of various recent views in regard to the nature of life,
the student is referred to the following works : Herbert Spencer, Principles of
Biology, 1870; Claude Bernard, Legons sur les Phénoménes dela Vie communs
aux Animaux et aux Végétaux, 1879; and Niigeli’s recent treatises.

For an interesting account of the reactions of living matter to very dilute
solutions of certain substances which are poisonous when used in greater
strength, see Loew and Bokorny. These investigators use a dilute alkaline
solution of argentic nitrate in the discrimination between living and dead
protoplasm ; upon application of the reagent the former turns black, the latter
remains uncolored. The solution is made hy mixing 1 cc. of a one per cent
solution of the nitrate in distilled water with an equal amount of a solution
containing 13 parts of potassic hydrate solution, 10 parts of ammonia, and
77 parts of distilled water (Pfliiger’s Archiv. xxv., 1881, p. 150).

EXTREMES OF HEAT AND COLD. 471

colder climates for the exercise of their normal functions, but
they will also generally sustain much higher degrees of heat with-
out injury. The differences of temperature in favor of tropical
plants are not, however, always very marked.

The following table! indicates sufficiently the highest tempera-
tures which a few common plants can bear. The line at the top
shows what were the immediate surroundings of the plants ex-
perimented upon; the columns marked A show the highest
temperatures short of proving fatal; those marked B, the low-
est fatal temperatures. The plants were exposed to the high
temperatures from fifteen to thirty minutes.

Name of Plant. Koots in WACCT, Roots in soil, Plant in water.
stems in air. stems in air.
A. B A. B A B
° Cc. oo fe} fe) fe} fe
Zea Mais 45.5 47. 50.1 52.2 46. 46.8
Tropeolum majus 45.5 47. 50.5 52. 44.1 45.8
Citrus Aurantium 47.8 50.5 50.3 52.5
Phaseolus vulgaris | 45.5 47. 50. 51.5

1229. After a plant has been subjected to too high a tempera-
ture, its foliage wilts and soon becomes dry; and its leaves,
having once taken on a scorched appearance, are unable to
recover their turgescence. it may happen, however, that the
injury does not proceed so fa: as to affect the latent or even the
partially developed buds; if this is the case, partial recovery
takes place through their unfolding. The curious fact? that
many alg can resist very high temperatures has been already
adverted to (see 566).

1230. Effects of cold upon the plant. Certain plants are seri-
ously injured by low temperatures which are considerably above
the freezing-point of water, but these are exceptional cases.
Most northern plants can readily endure cold, provided their
tissues are not frozen.

Frost produces very different effects upon different plants. In
some of our familiar spring plants the leaves may be frozen and
thawed without apparent mischief, but in general the thawing
must take place slowly ; if it proceeds rapidly, the plant may be

1 De Vries: Archives Néerlandaises, v., 1870.
2 Consult also American Journal of Science and Arts, xliv., 1867, p. 152.

472 UNTOWARD INFLUENCES.

irreparably injured. There are well-known cases in which plants
may be thawed quickly without serious injary.?

1231. Géppert? and others have shown that the flowers of
certain orchids, turned blue by the formation of indigo in their
cells when they are slightly frozen and suddenly thawed, will
preserve their usual colors unchanged if made to thaw very
slowly .®

1232. As to the length of time during which the vitality of a
frozen plant persists, we have no exact observations; but it is
stated that after the recession of a glacier in Chamouni sev-
eral plants which had been covered by ice for at least four years
resumed their growth.*

1233. It is still an open question whether much of the injury
to certain plants by freezing is not strictly mechanical, resulting
from the expansion during the formation of ice in the cells.®

1234. ° Winterkilling.” The destruction of many plants by
exposure to the influences of a variable winter is sometimes
attributed to the injurious effects of drying winds rather than
to cold alone. It has been shown (748) that the ainount of
water absorbed by roots-is governed largely by the temperature
of the soil. Although the exhalation of moisture from the leaves
of evergreens in winter is not large, it is, however, sufficient to
create a certain demand upon the soil for a supply. This de-
mand, slight as it is, is of course greater during very dry
weather; and it is from this that the injuries may be supposed
largely to result.

1235. The behavior of certain plants during exposure to low
temperatures affords some of the best illustrations of the adap-
tation of vegetation to its surroundings; and the question as
to increasing the tolerance of a given species or variety to the

1 Sachs has shown that the leaves of cabbage, turnip, and certain beans
frozen at a temperature of from —5° C. to --7° C., and placed in water at 0°C.,
are immediately covered with a crust of ice, upon the slow disappearance of
which they resume their former turgescence (Versuchs-Stationen, ii. 1860, p.
167). If such frozen leaves are placed in water of 7.5° C. they become flaccid
immediately,

2 Botanische Zeitung, 1871, p. 399.

5 According to Kunisch (quoted by Pfeffer: Pflanzenphysiologie, ii., p.
436), this blue discoloration is observed when the flowers, placed in an atmos-
phere of carbonic acid, are subjected to a freezing temperature: in this case, of
course, the indigo is produced from chromogen without free oxygen.

4 Botanische Zeitung, 1843, p. 13.

© Hoffmann (Grundziige der Pflanzenklimatologie, 1875, p. 325) attributes
a part of the mechanical injury from freezing to the separation from the cell-
sap of the air previously contained therein.

IMPROPER FOOD AND POISONS. 473

untoward influence of cold, by careful selection of seed for a
series of years, has been successfully answered by cultivators in
some northern countries of Europe.?

1236. Among the protective adaptations of seedlings to cold
is that described by De Vries,? who has noted that in certain
instances there is a marked retraction of the caulicle into the
ground upon the approach of a lower temperature. The with-
drawal is due to the contraction of the cellular tissue composing
the root.

1237. Effects of too intense light upon the plant. All other
conditions being natural, living plants containing chlorophyll can
perform their functions normally when placed in the brightest
sunlight. Even when the rays of light are moderately concen-
trated upon the foliage by a large convex lens there is no seri-
ous disturbance of function. But when, as in Pringsheim’s
experiments (see 824), the sunlight is rendered very intense,
assimilation is arrested and destruction of the protoplasm soon
ensues.

1238. Effects of improper food upon the plant. It bas been
shown (Chapters VIII. and X.) that certain substances are in-
dispensable to the healthful growth of plants; and it has further
been pointed out that most of these substances may be offered to
the plant in excess with no marked results. It should now be
noted that a few of these substances, notably nitrogen com-
pounds, applied in excess may induce a more luxuriant growth
than is desirable to the cultivator. Penhallow* and others have
pointed out that certain maladies of plants are largely dependent
upon malnutrition. In such maladies fungi are frequent con-
comitants, in many cases invading plants already enfeebled by
improper or insufficient food; in others, obviously causing by
their presence and activity the diseased conditions.

1239. Effects of poisons upon the plant. Woxious Gases. The
most hurtful of these, considered from a practical point of view,
come as products of the combustion of inferior sorts of coal,

1 Schiibeler (see note on page 465).

For an account of the formation of ice in plants, and the different degrees
of temperature at which it takes place, consult Miiller : Landwirthschaftl.
Jahrbiicher, ix., 1880.

2 Botanisclie Zeitung, 1879, p. 649. Haberlandt has also examined the
same mechanism to some extent.

3 It is a familiar fact that many plants thrive best in deeply shaded glens.
Success in the cultivation of such plants is attained only by regarding their
natural condition.

4 Houghton Farm Experiment Department, series 3, no. iii.

474 UNTOWARD INFLUENCES.

especially those which contain sulphur compounds as impurities.?
Formerly, in the vicinity of large chemical factories, the escaping
gases were productive of wide-spread injury to vegetation ; but
improved methods of manufacture have diminished this evil to
a considerable extent.

1240. Sulphurous acid, formed by combustion of sulphur in
the open air, produces, even when existing in the air in the pro-
portion of only one part in 9,000, the following effects upon
leaves: their blades shrivel from the tips, become grayish yel-
low, and soon dry so that they fall off at a slight touch. The
phenomena observed are somewhat like those occurring at the
time of the fall of the leaf in autumn. Yet in the experiments by
Turner and Christison mentioned in the note,? the amount of
sulphurous gas present in the air was so small as to escape
detection by smell.

Hydrochloric acid gas, nitric acid in vapor, and chlorine are
also very destructive to plants, even when in such minute
amounts as to be unnoticed on account of their odor.

Injarious effects are often produced upon shade trees by the
leakage of illuminating gas from street mains.

1241. Wardian Cases. In 1829 Ward accidentally discovered
that plants could thrive in tightly closed cases, in which there
could not be any interchange of the air with the outside atmos-
phere. This discovery led him to institute experiments rela-

¥

1 R. Angus Smith: Air and Rain, 1872, pp. 465, 553.

2 For accounts of experinents in this interesting field, the student may
consult the following works: Turner and Christison, Edinburgh Medical and
Surgical Journal, xxviii. p. 356; and Gladstone in Report of British Association
for Advancement of Science, 1850.

3 N. B. Ward: On the Growth of Plants in Closely Glazed Cases, 1852.

The table on the following page, based on researches by T. W. Harris, shows
the agents, the effects of which were tried upon chlorophyll, and the results in
each case as to the extrusion of chlorophyll pigment (see 772). The figures
in the third column indicate results as follows: —

1. Chlorophyll grains large and well defined. Sponge-like structure evi-
dent. One or two globules of large size on almost every grain ; sometimes
almost as large as the grain itself, which is colorless or nearly so.

2. Globules still plentiful but smaller; frequently several on each grain.
Structure of the grains evident. The protoplasm in this and the two following
grades (3 and 4) is often contracted by the chemicals used, rendering the result
more or less obscure.

8. Globules small, and fewer than in 2. Grains still retain some coloring-
matter in their substance, and are not so well defined either in form or
structure.

4. Globules few; only seen on a few grains. Structure of the grain not
defined, but under a high power it frequently has a granular and sometimes a

NOXIOUS GASES. 475

tive to the systematic cultivation of plants in such cases in the
impure air of manufacturing towns. In the glass cases, now

stellate appearance. In the latter case each grain is generally surrounded by
an irregular mass of colored protoplasm, these masses being often connected
together by threads. This stellate structure is also often brought out after
dissolving out all the coloring-matter by prolonged treatment with benzoic
acid.

5. No result.

Agent. Time of Action. Result.
2 Grains bleached, but form

Alcohol (95%) . . . . . . . . + day. remiaiiish
Steam... . . .. ee e) 6) «6L hour. 2
Boiled in H,O . . .. . .. . . 7min 2

s ‘© then coldin HCl. . . 2 days. 3

6c 73 “e 6c HNO, - ay 3 Chlorophyll

ce ce te “ Benzoic Acid . ss atellote.

2
2
HgSO, cone, 6 2 6 we we 1 Specimen destroyed.
H,SO, dilute . F Po 4S 1
HNO, cone. 1 ‘ — Protoplasm contracted.
HNO, dilute . Bs can A fie SELES 1
HO... : ‘ 1 $s
1
2
2
2
7
7
7

2
HCl -} HINO, (3 parts HCI, 1 part Te ee aa es

t tracted.
H,S0,-+ HCl (equal parts) . . $e ee 3
H,S0,+ HNO, “ . 3
H,S0O, + HCl-+ saiis, (equal parts). ss 3
HC,H3;02 . . . - : ; x ee 3
H,C.04 : ahs ; és 3
HPO, . go OD ag “ 2
H,C,H,0, (Tartaric acid) { sah } de 8 2
H,CrO, . 2S es Rs Ye 4
Picric Acid (ies 4
Citric Acid ass 3
Boracic Acid . 28 box wy & a 3
E «7 § sat.sol. in a sol. of 13 parts se
Benzoic Acid i NagHPO, to 100 iPo ' 1 1
Benzoic Acid. . 2. 1 ew ee 2 ‘* — Grains bleached.
Salicylic Acid . . 2... 3S 3
NaHPO,. . . . BEAD, vad Specay AOE 5
Na(NH,)HPO, . . . ...... 6 * 5
NeHSQy 2 @ ¢ & 8 a we ye e ES 5
Grains destroyed and pig-
NAOH 2 ade ig ei we a A ment diffused through
the protoplasm.
NHOB es eo ae ae ew wee 2S 5
KjCOs 6 ens, ee ee we eS 5

Grains swell and become
homogeneous, but no
extrusion or escape of
the pigment.

Bther ie 4. jae 6 ae Soe oe ae at

476 UNTOWARD INFLUENCES.

everywhere known as Wardian cases, the plants are supplied
with sufficient water, and the atmosphere is practically satu-
rated with moisture. When exposed to sunlight, the plants in
the cases can carry on all the operations of assimilation, growth,
and respiration.

Comparing the conditions which surround the plants in a
Wardian case with those which prevail in a furnace-heated house,
it is plain that the plants in the case are placed in what is es-
sentially a humid tropical climate, while those in the house
are exposed to excessive dryness, an to an. atmosphere which
may contain minute traces of the poisonous gases arising from
combustion.

1242. Liquids and Solids. Comparatively few substances
except those possessing strong acid or alkaline properties are
injurious to a plant. As indicated in 685, preparations of arsenic
which are extensively employed for the destruction of insects
upon crops in cultivated fields are not absorbed by plants to an
appreciable extent. This is further illustrated by the impunity
with which various other insecticides can be applied to green-
house plants.

1243. Numerous experiments, more curious than profitable,
have been made to test the effect of poisonous alkaloids upon
vegetation. Many observers have proved that some plants
yielding poisonous alkaloids may be poisoned by applications
to their roots of solutions of the very alkaloids which they have
themselves produced ; thus morphia may poison the poppy
(see 961). Strasburger’ says that.morphia speedily kills motile
spores.

Kiihne* has noted that the protoplasmic movement in the
stamen-hairs of Tradescantia is not wholly arrested, even after
many hours, by a solution of veratrin; and Pfeffer ® has observed
that the cells in sections of certain fleshy roots are not killed
even when immersed for several days in a saturated solution of
morphia acetate.

As Frank * suggests, these discrepancies in effects depend on
the differences in the power possessed by the various parts in the
absorption of such matters.

1244. Effects of mechanical injuries upon the plant. The most
important of these are caused hy destructive fungi. The destruc-

1 Wirkung des Lichtes und der Warme auf Schwiarmsporen, 1878, p. 66.
2 Untersuchungen iiber das Protoplasma, 1864, p. 100,

8 Pflanzenphysiologie, ii., 1881, p. 454.

* Pilanzenkrankheiten, 1879,

LIGHTNING. ATT

tion primarily affects the cell-contents, and later the cell-wall.
It is very highly probable that in certain cases various pro-
ducts of decomposition arising from the progress of the fungi may
themselves prove poisonous to contiguous parts of the plant.

One of the most important problems of practical horticulture
and agriculture is the search for efficient means by which invad-
ing fungi may he destroyed without at the same time injuring
the host-plant to which they have attached themselves.!

1245. The presence of certain fungi in plants sometimes gives
rise to abnormal growths and to various distortions. When once
their disturbing influence is felt, the subsequent growth may be
affected for a long time, and the malformations become of an
extraordinary character.

1246. Considerable distortions are often produced by bites
or other injuries by insects.” Galls — for instance those of the
oak and willow — are among the most noteworthy instances of
this kind.

1247. The effects of lightning upon trees have been examined
by many observers. Cohn?® and Colladon* have pointed out
some of the characteristic injuries sustained by species of poplar,
elm, and oak, stating that the stroke does not usually affect the
summit of the first two, but that oaks are frequently struck at
their uppermost branches. The course of the injury is often
spiral, winding around the trunk in stripes which involve part of
the sap-wood and bark.

It is not now believed that any species of trees are exempt
from injury from lightning, although the ash was formerly
thought to possess a remarkable degree of immunity.

1248. Partial or complete blanching of otherwise healthy leaves
exposed to light has been regarded by some observers as an indi-
cation of a diseased condition. In some cases the blanching is
dependent upon a lack of iron in the soil (see 791), but in others
it appears to be strictly hereditary, being propagable both by
bud and by seed. Nothing is known, however, as to its causes
in these cases, and they are generally referred to the unsatis-
factory category of sports.

It is worthy of notice that a considerable proportion of the
so-called variegated plants, especially of those which have only

1 For an account of some experiments in this field, see Frank : Pflanzen-
krankheiten, 1879 ; and Nobbe: Handbuch der Samenkunde.

2 For a bibliography of this subject, see Frank’s PHanzenkrankheiten.

8 Denkschrift. d. Schles. Ges. f. vaterl. Kult. Breslau, 1853, p. 267.

4 Mém. de la Soc. de Phys. et d’ Hist. Nat. de Gentve, 1872, p. 501.

A478 UNTOWARD INFLUENCES.

white spots intermingled with the green of the leaf, come from
eastern Asia, notably from Japan.!

1249. The lease of life of any given plant is fixed primarily
by the inherited character:? hence we have annuals, biennials,
and perennials ; but these differences are not in all cases abso-
lute, in some they are even ill-defined. The lease of life is
modified secondarily by external influences, which have been
sufficiently discussed in the present volume. In conclusion,
attention should be called again to the fact (see Chapter V.)
that in many instances the duration of the life of the plant is
determined largely by mechanical factors, especially the strength
of materials.

1 Morren : Hérédité de la Panachure, 1865, p. 7; Frank ; Pflanzenkrank-
heiten, p. 465.
2 The student should examine Minot on “ Life and Growth.”

GLOSSARIAL INDEX.

GLOSSARIAL INDEX.

The numbers following the titles refer to pages.

An italicized page-number

indicates that the term which it follows is defined on the page to which it refers.

ABSOLUTE ALCOHOL (C,H,O), use of,
as a medium, 5, 9.

Absorption, chemical, by soils, 243; de-
pendence of rate of, upon temperature,
279; of ammonia by leaves, 332, 341;
of aqueous vapor by leaves, 283; of
carbonic acid by plants, 299; of gases
by water, 300 2.; of liquids through
roots, 230; of moisture by soils, 239;
of oxygen during germination, 465;
of saline matters from soils by roots,
Q44; of water by seeds, 463; of water
during germination, 466; of water
previous to metastasis, 267; relation
of transpiration to, 279; through the
cut end of a stem, 263.

Absorption-bands, 292, 293.

Acetic acid (HU2H;O0.), as a reagent,
9, 54; as a mounting-medium with
glycerin, 21.

Achromatin (4, without; xe®ue, color),
375.

Acid azo-rubin, 19.

Acid nitrate of mercury (Hg[NO,],), 13.

Actinic rays of the spectrum. See Chem-
ical Rays.

Active protein matters of plants, 44.

Adaptation of plants to ary climates,
280.

Adenophore (467, a gland; $opéw, IT
bear), 451.

Bsculin (C,,H,40,3), 362.

ZEthalium septicum, composition of pro-
toplasm of, 197; locomotion of, 397;
preparation of plasmodium of, for ex-
amination, 196.

Agamogenesis (4, without; yéuos, mar-
riage; yéveots, origin), 426.

Age of trees, 140.

Aggregation, 340, 343, 421, n.

31

Air, composition of, 303; contained in a
plant, 100; contained in fresh woods,
261; removal of, from specimens, 9.

Air-passages, 100.

Air-plants. See Epiphytes.

Albumen of the seed, 181.

Albumin, diffusion of, 223; of plants, 363.

Albuminoids, 325, 2.; formation of, in
the plant, 335; tests for, 28; transfer
of, 356.

Alburnum. See Sap-Wood.

Alcohol (C:H¢O), action of, upon cer-
tain parasites and saprophytes, 294;
action of, upon chlorophyll, 41, 290;
use of, as a medium, 5; use of, asa
preserving and hardening agent, 9;
use of, in preparation of specimens for
mounting, 23; use of, in removing air
from specimens, 9.

Aldrovanda, 344.

Aleurone grains (4Aevpov, wheaten flour),
47. See also Protein Granules.

Algx, absorption by, 230; growth of
certain, at low temperatures, 385; in
hot springs, 205.

Alkaloids, 327, 365; cannot be utilized
by plants, 335; effect of, upon plants
365, 476. .

Alkanna (alkanet root), 18, 363, 2.

Alum (K,A1[SO2], + 24 120 or [NH,],
Al,Oe[SO,],+ 24 HO), 10.

Aluminium, occurrence of, in plants, 256,

Amides, occurrence of, in grasses, 336.

Amidoplasts (éuvdov, starch; tAdcow, [
form), name proposed by Errera for
leucoplastids.

Ammonia (NH,OH), absorption of, by
leaves, 332, 341; absorption of, by
soils, 243; formation of, in putrefac-
tion, 333.

482

Ammonia-carmin, 16.

Amoeboid movement of protoplasm
(440-87, change; etSos, form), 201.

Amylogenic bodies (auvdov, starch; yer-
vdw, I produce), 43. See also Leuco-
plastids.

Amyloid (auvaov, starch; eiSos, form), 32,7.

Anesthetics, effect of, upon protoplasmic
movements, 211; effect of, upon the
Sensitive plant, 424.

Anaplast (avamAdcow, I shape), 287, 2.

Andrecium (4jp, a man; olkos, a
house), 426.

Angiosperms (dyyetov, vessel; omépua,
a seed), fertilization in, 426.

Angle formed by the union of a branch
and the trunk, 193.

Anilin blue, action of, upon callus, 94.

Anilin chloride, use of, as a test for lig-
nin, 10, 37.

Anilin sulphate (2 [CsH;NH2]S0,H;),
use of, as a test for lignin, 10, 37.

Animals, occurrence of chlorophyll in,
288.

Annual growth of roots, 114; of stems,
137, 189.

Annular markings (annulus, a ring), 30,
85.

Anther (4v@npés, flowery), development
of the, 171.

Antheridia, 441, n.

Antherozoids, 440, m., 441, 2.

Anticlinal planes (avr, against; «Aivew
[xAtvw], to incline), 382.

Antipodal cells (4vri, against; ovs, a
foot), 434.

Apheliotropic curvatures (476, from;
HAvos, the sun; zpéros, a turn), 393.

Apical cell in roots of the higher crypto-
gams, 117.

Apogamy (a7é, without; ydéuos, mar-
riage), 446.

Apogeotropic organs (476, from; yj, the
earth; tpdmos, a turn), 392.

Apospory (é7é, without; omdpos, seed),
the substitution, in reproduction, of
budding for asexual spore-formation.

Apostrophe (476, from; o7p0d%, a turn-
ing), 399.

Apposition theory concerning the growth
of the cell-wall, 219.

Approach grafting, 152.

Aquatics, absorption by, 230; epidermis
of, 67.

Aqueous tissue. See Water Tissue.

Arabin (2CsH,,0,;+H,0), 358.

Archegonium, 441, 7., 442, n., 443, n.

GLOSSARIAL INDEX.

Archesporium (4x4, beginning; o7épos,
seed), 171, n., 379.

Areolated dots (areola, a small, open
place), 30, 82.

Argentic nitrate (AgNOs), 10.

Arsenic, occurrence of, in plants, 256; use
of compounds of, as insecticides, 476.

Artificial cell, 226.

Asexual reproduction, 426, 444.

Ash, amount of,in plants, 236,247; compo-
sition of, in plants, 247; of autumn and
spring leaves compared, 281; office of
the different constituents in plants, 252.

Asparagin (C4HgN,03+ H,O), 10, 364,
372.

Asphalt-cement, 20, 24.

Assimilating system of the plant, 285.

Assimilation, 185, 284; a process of re-
duction, 285, 820; chlorophyll acts as
a screen in, 823; conditions for, 285;
contrasted with respiration, 356; course
of transfer of the products of, 356;
Draper's experiments upon, 310; early
history of, 323; effect of artificial light
upon, 316; formic aldehyde hypothe-
sis, 322; free oxygen not necessary
for, 318; influence of colored light
upon, 3810; measure of activity of, by
the bacterial method, 315; measure-
ment of the amount of, 312; portion
of the spectrum causing maximum
activity in, 814; practical study of,
305; products of, 320; products of,
necessary for growth, 384; raw ma-
terials required for, 299; relations of
carbonic acid to, 318; relations of tem-
perature to, 316; storing of products
of, in perennials, 373.

Atavism (atavus, an ancestor), 447.

Atom, 213, 2.

Auric chloride (AuCl;), 10.

Automatic (autonomic) movements, 413.

Autoplast: (airés, self; wAdcow, I form),
287, n.

Autumn wood, 138, 395.

Autumnal changes in color in leaves,
297.

Auxanometers (aténots, increase ; «ézpov,
measure), 383.

BactTerta, measurement of activity of
assimilation by, 815.

Balsam, Canada, 22; Copaiba, 363; of
Fir, 363; of Peru, 363; of Tolu, 363.

Balsams, 97, 363.

Barium, occurrence of, in plants, 256.

GLOSSARIAL INDEX,

Bark, 147, 149.

Basifugal growth (basis, base; fugo, I
flee), 156.

Basipetal growth (basis, base; peto, I
move toward), 156.

Bassorin (CgH100;), 358.

Bast-fibres, 87; clinging together of, in
inner bark, 147; in cribose portions of
fibro-vascular bundles, 104; forming
sheaths of collateral bundles, 123; re-
actions of, 90; separation of, from the
stem, 147; size of, 90; solubility of,
33, n.; strength of, 189.

Beald’s carmin, 17.

Benzol (C,H,), a sulvent for fats, 10;
use of, in preparation of specimens
for mounting, 23; use of, in section-
cutting, 3; use of, in treatment of the
chlorophyll pigment, 231.

Benzol-balsam, 23.

Bibulous paper, use of, 5.

Bicollateral bundles, 104; in stems,
123.

Bifac’al arrangement of leaf-parenchy-
ma, 158.

Biformes (diforis, having two doors),
53, n.

Blanching of leaves, 254, 297, 477.

Blastocolla (2447795; shoot; “Aa, glue),
the balsam produced on buds by glan-
dular hairs.

Bleaching processes, 11.

Bleeding of plants, 264.

Bloom, 67, 294.

Bordered pits, 30, 82.

Boron, oceurrence of, in plants, 256.

Branches, rudimentary and transformed,
153.

Branching of roots, 115, 232.

Bristles, 69.

Bromine, occurrence of, in plants, 256.

Brownian movement, 429.

Budding, 152, 444.

Buds on leaves, 162.

Bud-variations, 444.

Bundle-sheath, 104.

Burnettizing, 142.

Byblis, 345.

C-xstum, occurrence of, in plants, 256.

Caffeine (C,H,,.N,O.), 827.

Caleareous soils, 239.

Calcic chloride (CaCl,), use of, as a
clearing agent, 10; use of, as a mount-
ing medium, 21; use of, in the meas-
urement of transpiration, 274.

483

Calcic hypochlorite (CaCl,0,), use of, as
a bleaching agent, 11.

Calcium, occurrence of compounds of, in
p ants, 39, 54, 247, 337; office of, and
its compounds in the plant, 253.

Callus, as a means of healing plant
wounds, 150; in sieve-cells, 93.

Calyptrogen («advmrpa, a cover; yevvdw,
T produce), 107, x.

Cambiform cells, 122.

Cambium, 104, 123, 235, 136;
division in, 377.

Cambium-ring, 137.

Cambium fibres, 81, 1.

Camera lucida, 4.

Camphors, 363.

Canada balsam, 22.

Cane-sugar (C,,H,,0,,), amount of, in
plants, 359; diffusion of, 223; test
for, 52.

Capillary water, 242.

Caramel, diffusion of, 222, 223.

Carbohydrates, 51, 357 ; transfer of, 356.

Carbolic acid (C,H;.OH), use of, as a
clearing agent, 167; use of, as a test
for lignin, 11, 37.

Carbon, appropriation of, by plants,
285

cell-

Carbon disulphide (CS,), 11.

Carbonates, test for, 9, 54.

Carbonic acid (used in this work as a
term for carbon dioxide, CO.), absorp-
tion of, by plants, 299, 305; amount
of, decomposed in assimilation, 319;
amount of, decomposed by plants pro=
portional to the distribution of effective
caloric energy in light, 314; amount
of, in natural waters, 800; amount of,
in rain-water, 299, 300, 7.; amount of,
most favorable to assimilation, 319;
effect of a large supply of, upon vege-
tation, 804, 318; roots do not take up,
300.

Carmin, 16; with picric acid, 17.

Carnivorous plants, 338.

Carpogonium, 440, nr.

Carpophytes, reproduction in, 440, n.

Casein of plants, 363.

Castor-oil, use of, as a medium, 5.

Caulicle (cculiculus, a small stem), 403 ;
movements of the, 403; sensitiveness
of the, 415; structure of the, 106, 118.

Caustic soda. See Sodic Hydrate.

Cell, 25; an osmotic apparatus, 229;
origin of name. 25.

Cell-division, 374: directions of, 389;
in plant-bairs, 380; in the cambium

484

of Pinus, 377; in the development of
pollen-grains, 879; in the formation
ef stomata, 376; method of demonstra-
tion of, 380.

Cell-plate, 376.

Cell-sap, carbohydrates in the, 51; color
of the, in flowers, 170; culor of the,
masks that of chlorophyll, 294. .

Cells, animal, analogous to vegetable,
220; classification of, 56, 59; develop-
ment of, 58; method of determining
the density of the contents of, 390;
morphological changes in, during
growth, 3873; turgidity of newly
formed, 38).

Cellular system, 57, 60, 102.

Cellulose (Cy.HiO5), composition of, 31;
formation of, in cell-division, 376; oc-
currence of, with crystals, 54; rela-
tions of, to moisture, 219; solubility of
the modilications of, 33, n., 35, n.; spe~
cific gravity of, 145; stability of, 354,
857; tests for, 8,11, 15, 31. See also
Cell-wall.

Cell-wall, capacity of the, for transfer
of water, 258; direction in which the,
is laid down, 380; formation of, 20,
218; growth of, 218, 855; markings
of the, 29; modifications of the, 34;
plates of the, in cork-cells, 38; rela-
tions of the, to protoplasm, 218; rela-
tive amount of space occupied by the,
in fresh wood, 261; structure of, 29,
257; tensions in the, 390.

Central cylinder, changes in the, 113;
structure of the, 110.

Centric arrangement of leaf-parenchyma,
158.

Cerasin, 358.

Chemical absorption by soils, 243.

Chemical rays of the spectrum, 308; least
efficient in assimilation, 310, 311, 313.

Cherry-wood, use of, in testing for lig-
nin, 14.

Chloral hydrate (CCls;CH[OH],), 11, 42.

Chlorine, occurrence of, in plants, 247;
office of, in the plant, 254.

Chloroform (CHCls), effect of, upon
protoplasmic movements, 211; effect
of, upon the Sensitive plant, 424; use
of, in preparation of specimens for
mounting, 23.

Chloroform-balsam, 23.

Chloroiodide of zine, 8, 33.

Chloroleucites. See Chloroplastids.

Chlorophyll body (xAwpés, green; pvAdov,
leaf), 41.

Chromoleucites.
Chromoplastids (xe®“a, color; wAdcow,

GLOSSARIAL INDEX.

Chlorophyll granules, 26, 41, 286; action

of alevbol upon, 41; action of darkness
upon, 42; action of hydrochloric
acid upon, 290, 475, ”.; action of
steam upon, 200, 475, .; action of
various agents upon, 474, 2.; break-
ing up of, at autumn, 298; formation
of, 287; in epidermal cells, 67; in
evergreen leaves, 298; occurrence of,
288; position of the, during the day
and at night, 398 ; Pringsheim’s study
of, 13, 289; stroma of, 290; structure
of, 289.

Chlorophyll pigment, 41, 286; alfSence

of, in certain plants, 2J4; changes in
the, at autumn, 207; color of a solu-
tion of the, not permanent, 296; ex-
traction of the, 290; fluorescence of
the, 204; in Floridee, 295; spectrum
of the, 292, 313.

Chlorophyllan, 291, 2., 292, 2.
Chloroplastids (xAwpés, green; mAdcow,

I form), 41. See also Chlorophyll

Granules.

Chlorosis, 297.
Chromatin (xe®ua, color), 375, 378.
Chromatophores (xe®#e [gen. xp5zar0s],

color; dopéw, I bear), 41, ., 287,
Chromic acid (CrQs3), action of, upon
the cell-wall, 11, 39.
See Chromoplastids.

I form), 41, 287.

Cilia (célium, an eyelash), movements

by means of, 398.

Cinchona, bast-fibres of, 148, 7.

Circumnutation (circum, around; nuta-
tio, a nodding), 490; in seedlings, 403;
methods of observation of, 401; modi-
fied, 401, 407; of the radicle, 403, 415;
of tendrils, 417; of the young parts of
mature plants, 405.

Citric acid (CeH,O7). 360.

Clathrate cells (clathri, a lattice), the
name given by Mohl to cribriform
cells.

Clayey soil, 238.

Clearing agents, 7, 10, 11.

Cleft of a stoma, 269.

Climate, adaptations of plants to a drv,
289.

Climbing plants, 405.

Clinostat (<Aivw, I
placed), 408.

Close-fertilization, 447; results of, con-
trasted with those of cross-fertilization,
448,

incline; orarés,

GLOSSARIAL INDEX.

Closed bundles, 104, 128.

Coal-tar colors, 18, 39.

Cobalt, occurrence of, in plants, 256.

Cochineal, 18.

Cold, effects of, upon plants, 471.

Coleorhiza (koAcés, sheath; p'iga, root),
107, 2.

Collateral bundles, structures of, 104,
121.

Collenchyma (xéAda, glue; éyxvua, an
infusion), 64; in roots, 110; strength
of, 191.

Colloids («éAAa, glue; eldos, like), 222,
223, 1.

“Colored” plants, 294.

Colors, as nectar guides, 453; of flowers,
170, 453; of fruits, 177; of plants de-
veloped in darkness, 288; of seeds,
178; of woods, 141.

Community in plants, 425.

Compass plant, arrangement of paren-
chyma in leaf of the, 160.

Complete oxidation, 355.

Compound hairs, 68.

Compound microscope, 1.

Compound pistils, 173.

Concentric bundles, structure of, 104,
123.

Concentric rings in roots of annuals, 115.

Conductive tissue of the ovary, 432; of
the style, 431.

Conglutin, 363.

Coniferin (Cy>H..0, + 2H,0), 362.

Consanguinity, fertilization in different
degrees of, 446.

Continuity of protoplasm in cells, 214.

Copper, occurrenee of, in plants, 256.

Copper salts, use of, in making precipi-
tation-membranes, 225.

Corallin (CoH ¢Os), 15.

Cork, as a means of healing plant-
wounds, 150; character of cell-walls
of, 75; color of cells of, 76; formation
of cells of, 75; origin and formation
of, 74, 148; reaction of, with iodine,
84, 2.

Cork cambium. See Phellogen.

Cork-cortex cells, 148. 2.

Cork meristem. See Phellogen.,

Corpuscles (conpusculum, a little body),
438.

Corrosion by roots, 246.

Corrosive sublimate. See Mercuric Chlo-
ride.

Cortex (cortex, the bark), in parasitic
roots, 116; in roots, 110, 113; in
stems, 119.

485

Cortical sheath, a term applied by Ni-
geli to the whole of the primary bast-
bundles,

Cotton, 179.

Cotton-blue “B,’’ 19.

Cover-glasses, 4, 6.

Crevsoting, 142.

Cribriform tissue (cribrum, sieve; forma,
form), 91.

Cribrose-cells. See Sieve-cells.

Cross-breed, 455.

Cross-fertilization, 447; results of, con-
trasted with those of close-fertilization,
448,

Crown of the root, 153.

Cryptogams, reproduction in, 439, x.;
roots of, 116; stems of, 154.

Crystal-cells, 97.

Crystalloids (xpioraAdos, a crystal; ldosy
form), 45, 47, 183.

Crystalloids in diffusion, 222.

Crystals, composition of plant, 54; for-
mation of, by Vesque’s method, 55;
forms of plant, 52; in bast, 89, 147;
occurrence of, in plants, 52, 54, 2.

Cultivated plants, supply of nitrogen to,
334.

Cuprammonia (Cu2[NH,]JO,), 11.

Cupric acetate (Cu[C,H30,],), use of, in
examination of resins, 12.

Cupric sulphate (CuSQ,), 12.

Curvature of concussion, 390.

Cuticle (cuticula, the skin), 65; solubil-
ity of, 34, x.

Cuticularization. See Cutinization.

Cuticularized layers, 66.

Cutin (cutis, skin), 38.

Cutinization, 34, 38.

Cutose, 35, n.

Cyanic flower colors (xtavos, dark blue),
454.

Cystoliths (xvors, bladder; A/os, a
stone), 40.

DaMAR, 23, 380.

Darkness, color of plants developed in,
288 ; effect of, upon opening and clos-
ing of stomata, 270; effect of, upon
protoplasmic movements, 206.

Darlingtonia, 349.

Defoliation, 163.

Degradation changes in the cell-wall, 40.

Degradation products, 40, 362.

Density of wood, 144.

Depth to which roots branch, 233.

Derivative hybrids, 458.

486

Dermatogen (8¢pua [gen. Sépuaros], skin;
yevvaw, I produce), 205, 118, 155.

Desmids, movements of, 398.

Desmodium gyrans, 413.

Dextrin (CoH0s), 51, 358.

Dextrose. See Grape-sugar.

Diageotropic organs (&é, through; v4,
the earth; tpé70s, a turn), 392.

Diaphragms, for controlling the illumi-
nation of microscopic objects, 2; of air-
passages, 100.

Diastase (Stéoracts, separation), 468.

Diatoms, movements of, 398.

Dicotyledons (Sis, twice; KoTvAndiv, a
cup-shaped hollow), distribution of
mechanical elements in, 193; secon-
dary structure of stems of, 186; stems
of, 129.

Diffusion, laws of, 222; of liquids, 221;
of gases, 301.

Dionxa muscipula, 342; related to Dro-
sera, 351.

Dipsacus, 350.

Discoid markings (5ioxos, a round plate;
eidos, form), 30, 82.

Diseases of plants, 470.

Dissecting instruments, 2.

Distances to which roots extend, 235,

Division of labor in the plant, 185.

Double-staining, 19.

Drainage of soils, amount of solid mat-
ter dissolved in water from, 244; rela-
tions of rain-fall to, 242.

Drawing of preparations, 4.

Drawn shoots, 388.

Drosera rotundifolia, 339; related to
Dionza, 351.

Drosophyllum, 345.

Dry mounts, 20.

Ducts. See Vessels.

Duramen (durare,
Heartwood.

Dwelling-houses, plants in, 368.

to harden). See

Eartu-worms, ivfluence of, upon the
character of the soil, 239.

Egg-apparatus, 435.

Electricity, effect of, in forming nitrogen
compounds in the atmosphere, 332;
relations of protoplasm to, 207.

Electric light, effect of, upon assimila-
tion, 316.

Embryo, life of the, 459.

Embryo-sac, 434.

Enchylema (¢yxé, I pour in), 198.

GLOSSARIAL INDEX.

Endodermis (évSov, within; Sépya, the
skin), 63, 104, 110, 120.

Endogenous stems (Sev, within ; yevvdw,
I produce), 123.

Endopleura (év6ov, within; mAcvpé, the
side), 178.

Endosmose (évSov,
thrusting), 229.

Endosperm (év6ov, within; oépua, seed),
437.

Energy, 307, 322; supply of, for work,
354.

Eosin (CaH,BrsOs), 19.

Epiblema (é7iBAqna, a cloak), 230.

Epicotyl (é7, upon; «oTvAy, a cup), 403.

Epidermal spines, 69.

Epidermal system, 102.

Epidermis (é7, upon; 6€pua, the skin),
58, 64; cells of, 65; diffusion of gases
through, 302; multiple, 67; of the
flower, 170; of the leaf, 161; of the
ovary, 172; of the stem, 119; waxy
coatings upon the, 66.

Epinastic curvature (€7, upon; vaords,
pressed close), 408.

Epiphytes (7, upon; $v76v, a plant),
352.

Episperm (27, upon; o7épua, seed), 178.

Epistrophe (émorpop%), a turning about,
399.

Epithelium of air-spaces (é/, upon; OnAj,
nipple), 101.

Equilibrium of water in the cell, 258.

Equisetum (equus, a horse; saeta [seta],
hair), epidermis of, 154; stem of, 154.

Erythrophyll (¢pv@pds, red; pvAAor, leaf),
291, m.; 297.

Ether (CyH,,0), effect of, upon proto-
plasmic movements, 211; a solvent
for fats, 12.

Ether (of space), 806.

Ethereal oils, 362.

Etiolation, 288, 291, 295, 388.

Etiolin, 291; spectrum of, 296.

Evaporation, compared with transpira-
tion, 275; from an animal membrane,
275; from soils, 241; from the surface
of a plant, 257; relation of growth
to, 271, ».; relation of rain-fall to,
242.

Evergreen leaves, 164; changes of chlo-
rophyll granules in, at autumn, 298.

Exine. See Extine.

Exogenous stems (éf, outside; yervdw,
I produce), 129.

Exosmose (éf, outside ; doués, a thrust-
ing), 229.

within; @opés, a

GLOSSARIAL INDEX.

Extine (exter, on the outside), 428.

Exudation of water from uninjured parts
of plants, 267.

Eye-pieces, 2.

Fatt of the leaf, 162, 217.

Fascicles of mosses (fasciculus, a small
bundle), 155.

Fascicular system, 102.

Fats, occurrence of, in plants, 360; sol-
vents for, 10, 11, 12.

Fermentation, 333, ., 369, ~., 372.

Ferments, 326, 365, 467.

Ferns, epidermis of, 154; reproduction in,
442, 446; stems of, 154.

Ferric acetate (Fe[C,H 0, ]o) used as a
test for tannin, 12.

Ferric chloride (Fe,Cl,) used as a test
for tannin, 12.

Ferric sulphate (Fe,[SO,]s) used as a
test for tannin, 12.

Fertilization, close, 447; cross, 447;
grades of partial, 456; in angiosperms,
435; in different degrees of consan-
guinity, 446; in gymnosperms, 487;
in hybrids, 456; results of different
methods of, contrasted, 448.

Fibres (fibra, a fibre), 57, 79; bast, 7;
cambium, 81; liber, 87; libriform, 00;
septate, 80; substitute, 80; woody,
80.

Fibro-vascular bundles (jira, a fibre;
vasculum, a small vessel), 103; bicol-
lateral, 104; closed, 104, 128; col-
lateral, 104, 121; concentric, 104;
parts of, 104, 111; course of, 105, 125;
distribution of, in dicotyledons, 130;
distribution of, in palms, 127, 130,
131, ~.; formation of, 186, 137; in the
flower, 170; in the leaf, 156; in the
ovary, 172; in the stem, 120; number
of, in the central cylinder, 111; open,
104; radial, 104; relation of the num-
ber of, in the leaves to the number of,
in the stem, 125.

Fibro-vascular system, 57, 108.

Filtering-paper, use of, 5.

Filtration through soils, 243.

Fire-weeds, 469.

Fixed air, 304,

Floral clock, 412.

Floridee, coloring-matters of, 295.

Flowers, colors of, 170, 453; develop-
ment of, 166; odors of, 454; regarded
as modified branches, 166; times of
opening and closing of, 412.

487

Fluorescence of the chlorophyll pigment,
204.

Fluorine, occurrence of, in plants, 256.

Foliar trace (fulium, a leaf), 125.

Food, effects of improper, upon plants,
473; materials for, in seeds, 182, 437,
467; methods of utilization of, 354.

Foramen of the ovule, 175.

Force exerted during growth, 395.

Forcing, 444.

Forests, effect of, upon the amount of
water in the soil, 283; effect of, upon
rain-fall, 282; humidity of, 281.

Formic aldehyde (CH,O) hypothesis in
assimilation, 322.

Forms of life of the plant, 470.

Fovilla (foveo, I cherish), 429.

Franchimont’s test for resins, 12,

Fraunhofer’s lines, 293.

Free nitrogen not available to plants,
327.

Free veins in leaves, 157.

Tremy’s process for extraction of the
chlorophyll pigment, 290.

Frey’s glycerin-carmin, 17.

Fronds of the palm-stem (frons, a leafy
brancl), 131.

Frost, effect of, upon plants, 471; not
necessary to the production of the au-
tumnal changes of color in leaves,
298.

Fruits, changes in the ripening of, 460;
classification of explosive, 400; color-
ing-matters of, 177; fastening of, in
the soil by hygroscopic movements,
899; hard parts of, 176: movements
due to changes in ripening of, 400;
nature of, 176.

Fruit-sugar, 359.

Fundamental cells, 56, 60.

Fundamental system. See Cellular Sys-
tem.

Fungi, injuries to plants by, 474, 476;
solutions for cultivation of, 251, n.

Funiculus (funiculus, a slender cord),
175.

GALLIC ACID (C;H,05), 361.

Gamogenesis (yéuos, marriage; yeveots,
formation), 426.

Gases, absorption of, by water, 300, 2.;
condensation of, by soils, 244; diffu-
sion of, 801; effect of noxious, upon
plants, 473; effect of various, upon
growth, 384; in rain-water, 300, x.;
passage of, through epidermis free

488

from stomata, 802; passage of, through
stomata, 303; proportions of varivus,
in the air, 303; relations of protoplasm
to various, 210.

Gelatin, of plants, 364; tannate of, 226.

Gelatination, 34.

Genera, 447.

Genlisea, 346.

Gentian-violet, 380.

Geotropic organs (7, the earth; 7pd70s,
a tum), 392.

Geotropism, 392.

Gerlach’s ammonia-carmin, 16.

Germination, changes during, 468; con-
ditions of, 462; not hastened by chem-
ical means, 468; of oily seeds, 368,
468; phenomena of, 466; relations of,
to light, 466; relations of, to tempera-
ture, 464; stages in, 462, ~.; time re-
quired for, at various temperatures,
466; when complete, 462.

Girdling of stems, 258.

Glaciers, aid of, in the formation and
distribution of soils, 288.

Glands, nectar, 451; of the Drosera leaf,
339; of leaves, 161.

Glandular hairs, 68.

Gliadin, 364.

Globoids (globus, a round body) 47

Glucose (CsH,,0u), 52, 359; held to be
the first product of assimilation, 322.

Glucoside, 292, n., 362.

Gluten-casein, 363.

Gluten-fibrin, 364.

Glycerides. See Fats.

Glycerin, effect of, upon protoplasm in
cells, 199; use of, as a medium in mi-
croscope work, 5; use of, as a pre-
servative medium, 21; use of, as a re-
agent, 12.

Glycerin ethers, 360.

Glycerin-jelly, 22.

Gold orange, 19.

Gold-size, 24.

Graft-hybrids, 445,

Grafting, 152, 444.

Grains of the cereals, 181.

sales (granulum, a small grain),

Grape-sugar, 359. See also Glucose.

Gravelly soil, 238.

Great curve of growth, 389.

Green, brilliant, 19; emerald, 19; methyl,
19.

Green chlorophyll, 322.

Grenacher’s alum-carmin, 17,

Growing-point, 106.

GLOSSARIAL INDEX.

Growth, 355, 373; assumption of definite
form during, 394; basifugal, 156;
basipetal, 156; changes which accom-
pany, 373; conditions of, 384; direc-
tion of, 392; effects of atmospheric
pressure upon, 889; effects of gases
upon, 384; effects of light upon, 387,
392; effects of temperature upon, 385;
external pressure retards, 395; force
exerted during, 395; great curve of,
389; instances of rapid, 384; in what
it consists, 373; measurement of, 383;
not always associated with increase of
weight, 373; observation of, 874; of
the cell-wall, 218, 882; of the leaf,
155; periodical changes in rate of,
389; planes of walls at point of, 381;
relations of oxygen to, 388.

Guardian cells, 70; development of, 376;
mechanism of, 269.

Guin-resins, 98.

Gums, 51, 358; diffusion of, 222, n.

Gymnosperms (yvuvés, naked; omépua,
seed), 426, 437.

Gyneecium (yj, a woman; olkos, a
house), 426.

HLmmatoxytty (CiH,40.+3H,0), 18,
46, 211, 380.

Hairs, 68; cell-division in, 380; com-
pound, 68; occurrence of, in air-pas-
sages, 100; of seed-coat, 179; simple,
68; used in study of protoplasm, 198.

Hales, device of, for noting the growth of
a leaf, 156; experiments of, upon trans-
piration, 271; observations of, upon
the transfer of water through the
stem, 258.

Hartig’s carmin, 16.

Healing of plant-wounds, 150.

Heart-wood (Duramen), 141.

Heat, absorption of, by soils, 2453 effect
of, upon the direction of growth, 394;
effect of, upon opening and closing of
stomata, 270; effect of, upon transpi-
ration, 277; effect of, upon vitality of
seeds, 205; evolution of, during res-
piration, 370; relations of, to germina-
tion, 464; relations of, to protoplasm,
201. See also Temperature.

Heat-rays of the spectrum, 308.

Heliotropic curvatures (jAvos, the sun;
tpdmos, a turn), 393,

Heliotropism, 392.

Hepatics, absorbing organs in, 117.

Heterogeneous pith, 124.

GLOSSARIAL INDEX.

Hilum (hilum, a little thing), 48.

Holnel’s tests for lignin, 10, 14.

Homogeneous pith, 124.

Honey of flower, 451.

Hot springs, occurrence of plants in, 205.

Hoyer’s mounting-media, 23.

Humus, 337, «.

Humus-plants, 337.

Humus soils, 239.

Hybridization, £47, 455; reciprocal, 455.

Hybrids, 455; derivative, 458; produc-
tion of artificial, 423; strength of, 458;
tendency of, to vary, 458.

Hydrochloric acid (HCI), 12; diffusion
of, 223; used in the examination of
chlorophyll granules, 12, 290; used
in the examination of plant-crystals,
54.

Hydrostatic water, 242.

Hydrotropism (i8wp, water; tpdémos, a
turn), 393.

Hygroscopicity (iypés, wet; oxoméw, I
look at), 239.

Hygroscopic movements, 399.

Hygroscopic water, 242.

Hypochlorin (iaéxAwpos, greenish yel-
low), 290, 322.

Hypocotyl (i7é, under; corvdn, a cup).
See Caulicle.

Hypoderma (i7é6, under; Sépua, the skin),
119.

Hyyonastic curvature (i76, under; vacrés,
close-pressed), 408.

Hysterogenic intercellular spaces (dore-
pos, after; yevvdw, I produce), 99, x.

IDIOBLASTS (idios, peculiar; BAagrés,
offshoot), 59, n., 97.

Inclination of the wood elements to the
axes of trees, 143.

Individual, 425.

Indol (CisHN 2), use of, as atest for lig-
nin, 18, 37.

Inferior ovaries, arrangement of fibro-
vascular bundles in, 174.

Initial cells, 105.

Injuries, of the stem, 149; to the plant,
470.

Insectivorous plants, 338; list of works
relating to, 351.

Integuments of the seed, 178.

Intercellular spaces, 60, 99; modes of
development of, 99; occurrence of
protoplasm in, 217.

Intermediate zone, 134.

Internal glands, 100.

489

Internodes, characteristics of growing,
399; movement in twining plants of
young, 406.

Interstices, 100.

Intextine, 428, n.

Intine (intus, within), 428.

Intramolecular respiration, 370.

Intussusception theory regarding mode
of growth of the cell-wall (intus with-
in; susceptio, a taking up), 219.

Inulin (Cel100;), composition of, 51; oc-
currence of, in plants, 858; tests for,
12, 50.

Inverted sugar, 359.

Iodine, action of light on solutions of,
9; action of, upon callus, 98; occur-
rence of, in plants, 256; solubility of,
8; as atest for cellulose, 8; as a test
for starch, 8.

Ipomeea, experiments upon fertilization
of, 448.

Iron, necessary for development of chlo-
rophyll granules, 254, 297; occurrence
of, in ash of plants, 247; occurrence
of, in plants, 254.

Isodiametric cells (iaos, equal; dé,
through; «érpov, measure), 60.

KARYORINESIS (xépvov, kernel; xvéw, I
change), a term used to designate the
series of changes which the nucleus
goes through in cell-division.

Kinetic energy («wéw, [ move), 307.

Knot, 154.

Kraus’s process for extraction of the
chlorophyll pigment, 291.

Kyanizing, 14%.

Kyanophyll («éavos, dark blue; dvAdov,
leaf), 291.

LABURNUM, continuity of protoplasm in
cells of cortex of, 215.

Lactuca Scariola, structure of leaves of,
160.

Lacune (lacuna, a cavity), 100.

Latex, 96.

Latex-cells, 94.

Latex-tubes. See Latex-cells.

Laurel-camphor (CoH 0), 363.

Layering, 444.

Lead, occurrence of, in plants, 256.

Leaf-trace, 131, 2.

Leaves, absorption of ammonia by, 332,
341; absorption of aqueous vapor by,
283; adaptations of, to climate, 280;

490

alterations in the color of, when ex-
posed to bright light, 296; ash-con-
stituents of autumn and spring, com-
pared, 281; autumnal colors of, 297;
buds on, 162; chlorophyll in evergreen,
298; development of, 155; epidermis
of, 161; exogenous structures, 155;
fall of, 162; fibro-vascular bundles
in, 156; glands of, 161; growth of,
156; midrib of, 157; of mosses, 164;
of submerged phenogams, 161; pa-
renchyma of, 158; quality of light
which penetrates, 309; relation of age
of, to transpiration, 279; roots pro-
duced from, 162; sensitiveness of, 419;
transpiration from opposite sides of,
274.

Legumin, 363; compared with asparagin,
365.

Lenticels (lenticula, a freckle), 151.

Leucites. See Leucoplastids.

Leucoplastids (Acuxés, white; mAdoow,
I form), 41, 43, 287; detection of, 44.

Lianes, 138.

Liber-fibres. See Bast-fibres.

Libriform fibres, 80, 143.

Lichenin (C,H190s), 358.

Life of the plant, forms of the, 470.

Light, amplitude of waves of, 306; classi-

_ fication of rays of, 308; depth to
which green tissues are penetrated
by, 309; effect of absence of, upon
plants, 388; effect of, upon the move-
ments of twining-plants, 407; effect
of, upon opening and closing of sto-
mata, 270; effect of, upon protoplas-
mic movements, 206; effect of, upon
transpiration, 277; effect of too in-
tense, upon plants, 473; influence of,
upon germination, 466; influence of,
upon respiration, 369; influence of,
upon the structure of leaves, 160;
intensity of, 306; Jength of waves of,
306, z.; nature of, 306; quality of
the, penetrating leaves, 309; relations
of growth to, 387, 392; relations of the
various kinds of, to assimilation, 305,
307, 309, 310, 312, 316; use of, in
microscope work, 2.

Lightning, effect of, upon trees, 477.

Lignification (lignum, wood; facio, I
make), 34, 36. 62.

Lignin, composition of, 86; solubility of,
36, n., 87; tests for, 10, 11, 13, 14,
37.

Ligniréose, 37, 2.

Lignone, 36, n.

GLOSSARIAL INDEX.

Lignose, 36, n-

Ligules (ligula, a little tongue), arrange~
ment of fibro-vascular bundles in,
158.

Lithium used in the determination of the
rate of transfer of water through the
plant, 260.

Lithocysts (aidos, a stone; xiors, blad-
der). See Crystal-cells.

Living parts of a plant, 195.

Locomotion, 397.

Luminous rays of the spectrum, 308.

Lycopodiacez, stems of, 154.

Lysigenic development (Avors, a parting ;
yevvaw, I produce), 99, 2.

MACERATION, 7, 12, 14, 77, 7., 80.
Macrocytis pyrifera, size of, 188.
Macrospore, 443, 7.

Magenta, 19.

Magnesium, occurrence of, in plant-ash,
247; office of, in the plant, 253.

Malic acid (CyHsOs), occurrence of, in
plants, 360.

Maltin, 468.

Malting, 467.

Manganese, occurrence of, in plants, 256.

Manures, 334.

Markings, annular, 30, 85; discoid, 30,
82; of tue cell-wall, 29; reticulated,
30, 85; scalariform, 84; spiral, 30, 84.

Maskenlack, 24.

Measurement, of the amount of assimi-
Jation, 312; of growth, 383; of micro-
scopic objects, 3; of transpiration, 271;
unit of, in microscope work, 4.

Mechanical elements, distribution of, in
dicotyledons, 193; distribution of, in
monocotyledons, 191.

Mechanical injuries, effect of, upon
plants, 476.

Mechanical irritation, effect of, upon
protoplasmic movements. 208; effect
of, upon transpiration, 278.

Mechanics of tissues, 188.

Media, for examination of microscopic
eRe 4; mounting or preservative,

0. ;

Medullary rays (medulla, the pith), 61,
114, 124.

Medullary sheath, the primary xylem
bundles projecting into the pith from
the cambium-ring.

Member, a term employed to designate
any part of a plant when it is treated
with reference to position and struc+

GLOSSARIAL INDEX.

ture but not with reference to func-
tion.

Membranogenic substances (membrana,
amembrane; yévetv, to be born), 227, n.

Mercuric chloride (HgClz), 18; solution
of, for treatment of protein granules,
45.

Mercury, occurrence of, in plants, 256.

Merismatic (meristematic) tissue. See
Meristem.

Meristem (ueptorés, divisible), 59, 105.

Mesophyll (uéoos, middle; @vAdov, a
leaf), the fundamental tissue of the
leaf.

Mestom, 191.

Metacellulose, 35, .

Metals found in plants, 247, 255.

Metaplasm (era, in the midst of; rAdopa,
that which is formed), the name given
by Haustein to the granular substances
mingled with protoplasin.

Methyl-green, 19, 380.

Metastasis (jerdoraccs,
See Transmutation.

Methyl-vivlet ‘‘ BBBBBB,”’ 19.

Micelle, 222, 257, 893; attractions of,
212, 218.

Micrometer, 3.

Micro-millimeter, 4.

Micropyle (uixpés, small; may, orifice),

3B.

a removing).

Microscope, 1.

Microsomata (uixpds, small; cua, body),
211.

Microspectroscope, 292.

Microspore, 443, 2.

Microtome, use of the, in section-cut-
ting, 3.

Mikroskopirlack, 24.

Milk-sacs, 99.

Millon’s reagent (Acid Nitrate of Mer-
cury), 13, 28, 33.

Mimosa pudica, 429.

Mineralization, 34, 39.

Mirror of microscope, 2.

Modifications of the cell-wall, 34.

Moisture, effect of amount of, in the air
upon transpiration, 275; effect of
forests upon the amount of, in the
air, 281; effect of, upon the direction
of growth, 393; exhalation of, by
desert plants, 276; relations of proto-
plasm to, 209; relations of soils to,
239. See also Water.

Molecule, 212, ~.

Monocotyledons, distribution of mechan-
ical elements in, 191; secondary struc-

491

ture of stems of, 135; stems of, 129;
types of stems of, 133.

Morphia (CyHiyNO3 + H.O), 827, 365,
476,

Mosses, absorbing organs in, 117; aid
the soil in retention of water, 282;
leaves of, 164; reproduction in, 441, 2.;
stems of, 154.

Mother cells, of pollen, 171, 879; of sto-
mata, 72, 376.

Mounting-media, £0.

Movements, cause of autonomic, nut
fully known, 414; due to changes in
structure during ripening of fruits,
400; hygroscopic, 399; of ciliated
structures, 398; of Desmids, 398; of
Diatoms, 398; of leaves, 419; of proto-
plasm, 199, 398; of seedlings, 403; of
the Telegraph plant, 413; of tendrils,
409, 417; of twining plants, 405; of
young parts of mature plants, 405;
revolving, 400; sleep, 409; sleep, of
cotyledons, 411; sleep, of floral or-
gans, 412; spontaneous, 413; utility
of sleep, 411.

Mucedin, 364.

Mucilage, conversion of the cell-wall
into, 34; in the cell-sap, 51; solubility
of vegetable, 33.

Mucilage-cells, 99.

Mucilaginous modification of paren-
chyma cells, 63.

Mucus, 220.

Mulder’s hypothesis concerning the ori-
gin of albuminoids, 326, x.

Multiple epidermis, 67.

Myxomycetes, 196, 414.

NAEGELI’S HYPOTHESIS concerning the
structure of organized hodies, 212.

Nascent tissue (nascens, arising). See
Meristem.

Natural grafts, 152.

Nectar, 451; protection of, from the
visits of unwelcome insects, 455; secre-
tion of, 452; specific gravity of, 452.

Nectar-glands, 161, 451. |

Nectar guides or spots, 453.

Nectaries, 452.

Negative geotropism, 392.

Negative heliotropism, 393.

Nepenthes, 349.

Nervation of seed-coats, 180.

Nerves of leaves, 156.

Nickel, occurrence of, in plants, 256.

Niggl’s test for lignin, 13.

492

Nigrosin, 19, 380.

Nitrates, as a source of plant-food, 335;
test for, 326, n.

Nitric acid (HNOs), 13; as a source of
plant-food, 335.

Nitrogen, amount of, in plants, 827;
amount of, in rain-water, 331; appro-
priation of, by plants, 325, 330; com-
parative needs of wild and cultivated
plants for, 334; compounds of, in the
atmosphere, 3831; in coloring-matters
of leaves, 292; in the soil, 333; mode
of formation of atmospheric com-
pounds of, 332; sources of, for plants,
327.

Non-sexual reproduction, 426, 444.

Nucellus, 175, 182, 433.

Nuclear disc, 376.

Nuclear spindle, 376.

Nuclein, 375, 376, 378.

Nucleus, 25, »., 28, 199, 220, 874; be-
havior of the, with reagents, 375; dem-
onstration of changes in the, in the
development of pollen-grains, 380;
structure of the, 375.

Nucleus cellule, 27, x. See Nucleus.

Nucleus of astarch-granule. See Hilum.

Nucleus of the ovule. See Nucellus.

Nucleolus, 28, 375.

Nutation (nutatio, a nodding), 400.

Nutrition, 355.

Nyctitropic movements (»vé [gen. vuxrés],
night; tpémos, a turn), 409.

Oaxs, histological classification of,
143, Me

Objectives, 2.

Odors, of flowers, 454; of wood, 142.

Oil in seeds, 351.

Oil of cloves, 3, 23.

Oleic acid (CisHs,0-), 360.

Olein (C5;H,o,0s), 860.

Olive-oil, use of, in experiments on pro-
toplasmic movements, 211.

Oédphytes, reproduction in, 440, 7.

Odsphere (#6, an egg; opaipa, a sphere),
435, 440, ~., 441, .

Obspore (29v, an ega; omépos, seed), 436,
440, 2.

Open bundles, 104.

Opening and closing of flowers, 412.

Orange ‘‘R,"? 19.

Orchids, tracheids in roots of, 109.

Organ, 102, 186; rank of an, 186, ».

Organic acids, effect of, upon turges-
cence, 414.

GLOSSARIAL INDEX.

Organic matter, appropriation of, by
the plant, 337; changes of, in the
plant, 354,

Organic products,
357.

Osmie acid (perosmic acid) (OsQO,), 14,
46.

Osmometer (dopés, impulse; wérpov, Mea-
sure), 224.

Osmosis (douds, impulse), 221, 224.

Osmotic equivalent, 225.

Osmundacez, stems of, 154.

Ovary (ovum, an egg), arrangement of
fibro-vascular bundles in an inferior,
174; arrangement of fibro-vascular
bundles in a superior, 178; structure
of the, 172; varieties of conductive
placente in an, 432,

Ovules, changes in the fertilization of,
435; development of, 433; formation
of, 175; ripening of, 178; structure of
the, in angiosperms, 432; structure of
the, in gymnosperms, 438,

Ozone, 304.

Oxalates, test for, 9, 54.

Oxalic acid (C2H,0,), 360.

Oxidation, 355.

Oxygen, an agent in the disintegration
of rocks, 237; amount of, absorbed
during respiration, 368; amount of,
evolved in assimilation, 319; necessary
for germination, 464; necessary for
protoplasmic movements, 210; of air
ample for respiration, 368; relations
of growth to, 888; required by roots,
245.

classification of,

PALISADE-CELLS, 61, 159.

Palmate venation in leaves (palmatus,
bearing the mark of a hand), 157.

Palinatin (Ci Hys0n), 360.

Palmitic acid (CjHs202), 360.

Palins, fibro-vascular bundles in, 130,
131.

Paper-pulp, manufacture of, 145.

Paracellulose, 35.

Paraffin, use of, in section-cutting, 3.

Parallel venation in leaves, 156.

Parasites (mapdéovtos, one who lives at
another's expense), 289, 338; chloro-
phyll lacking in certain. 294; food of,
338; roots of, 116; union between, and
their hosts, 153, 338.

Parchment paper, 82, . use of, in
making osmometer, 224.

Parenchyma (mapeyxéw, I pour in beside),

GLOSSARIAL INDEX.

57, 60; elements of, 60; forms of
cells of, G1; in the fascicular system,
102; of the flower, 170; of the fruit,
176; of the leaf, 158; of the petiole,
160; of the stem, 119, 124; sclerotic,
62; thin-walled, 62.
Parthenogenesis (7ap8€vos,
yéveors, production), 446.
Path of water through tl.e plant, 259.
Peaty soils, 239,
Pectin bodies, 358.
Pectose, 34, n., 358.
Pellicle-membrane, 227.
Perennials, storing of assimilated matter
in, 373.
Periblem (wepiBdyua, a covering), 105,
118, 155.
Pericambium, 113.
Periclinal planes (mepé, around; «aivw, I
incline), 382.
Periderm (wepé, arcund; dépya, skin),
75.
Periodic movements of organs, 409.
Peripheral tissue of rootlets, 108.
Perisperm (7epé, around; omépya, the
seed), 437,
Peristome, 441, n.
Perosmic acid. See Osmic Acid.
Petiole (petiolus, a little foot)» paren-
chyma of the, 160; sensitiveness of
the, 419.
Pfeffer's experiments with artificial cells,
226.
Phelloderm (gearss, cork; 8pua, skin),
75, 148, n.
Phellogen (eadss, cork; yervdw, I pro-
duce), 74, 148.
Phenol. See Carbolic Acid.
Phlo&m (gross, inner bark), 104.
Phloroglucin (C,H.O3), use of, as a test
for lignin, 14, 37.
Phosphorus, occurrence of, in plant-ash,
247; office of, in the plant, 253.
Phosphorescence, 870.
Phototonus, 423.
Phycocyanine (ixos, sea-weed ; xvavos,
_ dark blue), 295.
Phycoérythrine (idxos, sea-weed; épu-
Opds, red), 295.
Phycophaine (pikes, sea-weed; ¢atds,
brown), 295.
Phycoxanthine (#5«os, sea-weed ; favO0s,
yellow), 295.
Phyllocladia (¥vAdov,
a young branch), 280.
Phyllocyanin (#vAdov, leaf; «vavos, dark
blue), 290.

a virgin;

leaf; xAd8os,

493

Phyllodia (#vAddéys, like leaves), 280.

Phyllophore (vAdor, leaf ; popéw, I bear),
132.

Phylloxanthin ($vAdov, leaf; Eavéés, yel-
low), 290.

Physical properties of soils, 239,

Picric acid (CsH,[NO2],0H), 18.

Piliterous layer (pilus, hair; fero, I
bear), 108.

Pinguicula, 345.

Pinnate venation in leaves (pinnatus,
feathered), 157.

Pistils, changes of, in ripening, 176;
fibro-vascular buudles in, 173; sensi-
tiveness of, 124; structure of angio-
spermous, 427.

Pith, 124; solubility of, 34, 2.

Planes of the cell-wall at the point of
growth, 681.

Plasmolysis (mAéoua, what has been
formed: Avors, a loosing), 390, n.

Plasmolytic agents, 27, n., 890; effect of,
upon protoplasm, 210.

Plastids (wAdcow, I form), 40, 287.

Pleon (aaAcor, full), 212.

Plerom (wArjpwya, that which fills), 105,
118

Poisons, effects of, upon plants, 473.

Polarizing apparatus, 4.

Pollen (pollen, fine flour), amount of,
produced by flowers, 432; bursting of
grains of, in water, 429; contents of
grains of, 428; development of, 171,
879; effect of sugar solutions on
grains of, 429; of angiosperms, 427;
of gymnosperms, 437; structure of,
428; vilality of, 481.

Pollen-tube, emission of the, 430; time
required for descent of the, 431.

Pillinia, 427.

Pollinic chamber, 438.

Polyembryony (7voAvs, many; &Bpvor,
embrvo), 446.

Ponceau, 19.

Poplar, glands on leaf of the, 161.

Potash (KOH), diffusion of, 222; use of,
as areagent, 6; use of, in examina-
tion of ch'oroplastids, 42; use of, in
section-cutting, 3, 2.

Potassic acetate (KC2H30.), use of, as a
mounting-medium, 21.

Potassic bichromate (K,Cr,0;), 14.

Potassic chlorate (KC1O3), 14.

Potassic ferrocyanide (K,Fe[CN]«), use
of, in making precipitation-mem-
branes, 225.

Potassic nitrate (KNOs), 15, 390, 2.

494

Potassium, occurrence of, in plants, 247;
office of, in the plant, 252.

Potential energy, 307.

Precipitation-membrane, 225.

Preparation of specimens, 21.

Preservation of wood, 142.

“Pressure, effect of atmospheric, upon
germination, 369, 464; effect of atmos-
pheric, upon growth, 389; effect of,
upon movements of protoplasm, 208 ;
growth retarded by external, 395; of
sap in the stem, 264.

Prickles, 69.

Primary cortex, 119.

Primary membrane, 36.

Primary structure, 105; of the root, 106;
of the stem, 119.

Primine (primus, first), 178.

Primordial tissues, 58.

Primordial utricle, 27, «., 220.

Procambium, 104.

Prosenchyma (mpés, near; éyxvua, an in-
fusion), characteristics of, 58, 76; 1
the fascicular system, 102.

Proteids, 28, 326, n.; formation of, in the
plant, 335.

Protein basis, 46.

Protein granules, 44; classification of,
in seeds, 182.

Prothalli, 442, 2.

Protogenic developmer.t (patos, first;
yevvaw, | produce), 99, 2.

Protophytes, 439, 2.

Protoplasm (mparos, first; wAdoua, What
has been formed), amceboid movement
of, 201; appearance of, 26; chemical
properties of, 197; circulation of, 199,
898; composition of. 28, 197; continuity
of, in cells, 214; discrimination between
living and dead, 10, 470, n.; effect of
mechanical irritation upon, 208; ex-
amination of, 196, 198, 202; film of,
envelops many crystals, 54; historical
note regarding, 219; in young cells,
198; movements of naked, 200, 201,
897; movements of, dependent on the
absorption of moisture, 212, ».; nitro-
gen in, 825; passage of, through imper-
forate cell-walls, 217; physical proper-
ties of, 197; rate of movements of,
200; reaction of, 198; relations of, to
anesthetics, 211; relations of, to elec-
tricity, 207; relations of, to gravita-
tion, 209; relations of, to light, 206;
relations of, to moisture, 209; relations
of, to plasmolytic agents, 210; rela-
tions of, to temperature, 201; rela-

GLOSSARIAL INDEX.

tions of, to various gases, 210; rela-
tions of the cell-wall to, 218; rotation
of, 200; structure of, 211; tests for,
28; vitality of, in seeds and spores,
205; water contained in, 198, 257.

Pulsation of vacuoles, 397.

Pulvini (pulvinus, a cushion), 160, 404,
410; continuity of protoplasm in the
cells of, 215; in the Sensitive plant,
420; in the Telegraph plant, 414.

Putrefaction, results of, 333.

Pyrenoids (svpjv, a kernel; tos, form),
287, 2.

QUEKCITRIN (CosH 507), 362.
Quinia (CooHaN202 + H,0), 827, 365.

RAvIAL BUNDLE, 104.

Radial planes, 382.

Radicle, 118; movements of the, 403;
structure of, 106.

Rain-fall, effect of forests upon the,
282.

Rain-water, gases in, 800, 2.; nitrogen
compounds in, 331.

Ranvier’s picrocarmin, 17.

Raphides (é¢/s [gen. pagidos], a needle),
52.

Razor, use of the, in section-cutting, 3.

Reagents, 4; employment of, 6.

Receptacles for secretions, 97, 110.

Recording auxanometer, 883.

Red anilin, 19.

Rejuvenescence (re, again; jurenesco, T
become young), the formation of a
single new cell from the protoplasm
of a cell already in existence.

Repair of waste, 355.

Reproduction, 425; by budding, 444;
contrast between methods of, as ree
gards results, 443; in cryptogams,
439, n.3 methods of, 426.

Reserve protein matters, 44.

Resin-cells, 97.

Resins, 98, 363; detection of, 12.

Respiration, 355, 356, 867 ; accompanied
by evoluti:n of heat, 370; contrasted
with assimilation, 356; early history
of, 367; influence of light and temper-
ature upon, 3869; intramolecular, 370.

Resting state, 369, 389, 459.

Resurrection plant, 399.

Retention of moisture by soils, 239.

Reticulated markings, 30, 85.

Reticulated venation in leaves, 156.

GLOSSARIAL INDEX.

Revolving nutation, 400.

Rhizogenic cells (pig, a root; yevvdw, I
produce), 115, 2.

Rhizvids (pige, a root; «Sos, like), 117,
230.

Rhizomes (/‘Gwua, that which has taken
root), structure of, 153.

Rhodospermin (d5ov, rose ; apa, seed, )
295.

Ripening of fruits and seeds, 460.

Rocks, disintegration of, 237.

Root-cap, 106, 107.

Root-hairs, 108; corrosive action of,
246; distortion of, 231; increase the
absorbing surface of a root, 231; meth-
od of obtaining for study, 109; num-
ber of, on different plants, 231; office
of, in absorption, 231; size of, 231;
walls of, 108, 109.

Rvots, absorption by, 230, 244; amount
of branching of, 232; central cylinder
of, 110; colors of, 116; cortex of, 110;
crown, 153; depth to which branching
of, occurs, 233; extent of, 232, 235;
formation of, 107, 155; from leaves,
162; growth of, 107; influence of the
soil upon, 234; of cryptogams, 116; of
orchids, 109; oxygen needed by, 245;
parasitic, 116; piliferous layer of, 108;
primary structure of, 106; secondary
structure of, 112; types of branching
of, 115, n.

Roridula, 845.

Rose of Jericho, 400.

Roselic acid. See Corallin.

Rotation of protoplasm, 200.

Rubidium, occurrence of, in plants, 256.

Rudimentary branches, 153.

Russia matting, 147.

Russow’s potash-alcohol, 7.

SAFRANIN (C,,H.,N,), 19, 380.

Salicin (C,3H,,0,), 362.

Saline matters, absorption of, by roots,
244.

Sandy soil, 238.

Sap, amount of, in plants, 265; flow of,
from plants, 264; pressure of, 264,
265.

Saprophytes (campés, putrid; $utév, a
plant), 289, 294, 337.

Sap-wood, 141.

Sarcode, 220.

Sarracenia, 347.

Scalariform markings (scalaria, a lad-
der; forma, form), 30, 84.

495

Scales, 69.

Schizogenic development (cxisw, IT
cleave; yevvaw, I produce), 99, n.

Schleim, 220.

Schulze’s macerating liquid, 14, 38, 39.

Schulze’s reagent, 9, 33, 76, 77, n.

Schweizer’s reagent, 12, 15, 32.

Scion, 152, 444.

Sclerenchyma (oxAypds, hard; ¢yxvpa, an
infusion), 87.

Sclerotic parenchyma (c«Aypés, hard),
62.

Secondary liber, 113.

Secondary structure, 105; of roots, 112;
of stems, 135.

Secondary wood, 113.

Secretions, of nectar, 451; receptacles
for, 97, 110; stigmatic, 427.

Section-cutting, 3.

Secundine (secundus, second), 178.

Seeds, albuminous and exalbuminous,
181; arrested activity of, 459; changes
during the ripening of, 460; dissemina-
tion of, 400, 460; food in, 182, 437,
467; germination of, 462; germination
of oily and starchy, compared, 368; im-
mature, 460; increase of, in size, upon
the absorption of water, 463; integu-
ments of, 178; minute structure of,
178; protein granules in, 182; ripeness
of, 460; vitality of, 205, 461.

Selenium, occurrence of, in plants, 256.

Sensitiveness, 414: effect of anesthetics
upon, 424; of leaf-blades, 419; of peti-
oles, 419; of roots, 415; of stamens,
423; of stems and branches, 417; of
styles, 424

Sensitive plant, 420, 424.

Sensitive tissues, 415.

Shell-lac, 24.

Sieve-cells, 97, 103, 112; contents of, 94;
development of, 122; of cryptogams,
94; of gymnosperms, 94; size of, 92.

Sieve-plates, 91, 92.

Sieve-pores, 91, 93.

Sieve-tubes. See Sieve-cells.

Silica (SiO,), deposits of, in plants, 39.

Silicium, office of, in the plant, 255.

Silphium laciniatum, arrangement of
parenchyma in the leaf of, 160.

Silver, occurrence of, in plants, 256.

Simple hairs. 68.

Simple microscope, 1.

Simple pistils, 173.

Sleep-movements, 409; of cotyledons,
411; of floral organs, 412; utility of,
411.

496

Slides (slips), 2.

Sodic chloride (NaCl), 15; diffusion of,
222, 223.

Sodic hydrate (NaOH), use of, as a
reagent, 7; use of, in the manufacture
of paper-pulp, 147.

Sodie hypochlorite (NaClO), 11.

Sodium, can partly replace potassium in
plants, 255; occurrence of, in plauts,
247.

Soft bast, the unlignified cells of the
liber portion of a fibro-vascular bundle.

Soils, absorption of heat by, 245; ab-
sorption and retention of moisture by,
239, 282; chemical absorption by, 243;
classification of, 238; condensation of
gases by, 244; effect of transpiration
upon, 283; evaporation from, 241, 282;
filtration through, 242; formation of,
237; influence of, upon roots, 234; in-
fluence of, upon transpiration, 276;
mechanical ingredients of, 239; nitro-
gen available to plants in, 333; physi-
cal properties of, 239; root-absorption
of saline matters from, 244; tempera-
ture of, 245; transportation of, by
water, 238.

Solanum Pseudocapsicum,
matters in berries of, 177.

Solid yellow, 19.

Sources of nitrogen for the plant, 327.

Specitic gravity of wood, 144.

Spectrum, classification of the rays of
the, 308; effect of the rays of the, upon
protoplasmic movement, 206; effect of
the rays of the, upon transpiration,
278; of chlorophyll, 292, 313.

Spermoderm (cépua, seed ; dépua, skin),
178.

Spheraphides (cpaipa, sphere; fpadis,
needle), 53.

Sphere-crystals, 53.

Spines, 69.

Spiral markings, 30, 84.

Spongiole (spongivla, a little sponge),
230.

Spongy cortex, 120.

Spongy parenchyina, 61.

Sports, 444.

Spring wood, 138, 396; transfer of water
through, 258.

Staining agents, 15; effect of, upon pro-
toplasm, 210.

Stamens (stamen, a thread), development
of, 171; sensitiveness of, 423.

Starch, amount of, in plants, 357; ap-
pearance of, when examined. with

coloring-

GLOSSARIAL INDEX.

polarized light, 50; conversion of, inte
sugar, 357, 467; composition of, 50;
first. visible product of assimilation,
321; in latex, 96; in seeds, 182; pres-
ence of, in chloroplastids, 42; produc-
tion of, in a plant dependent on potas-
sium, 252; solubility of, 49; structure
of, 47; tests for, 8, 50.

Starch cellulose, 50.

Starch generators. See Leucoplastids.

Steam, action of, on chlorophyll gran-
ules, 290, 475, n.

Stearic acid (C,gH,,02), 360.

Stearin (Cs7H1100¢), 360.

Stellate hairs (stedla, a star), 69.

Stellate scales, 69.

Stems, 118; bleeding of, 264; course of
fibro-vascular bundles in, 125; cortex
of, 119; development of, 124; dicoty-
ledonous (exogenous), 129, 136; epider-
mis of, 119; fibro-vascular bundles of,
120; injuries of, 149; monocotyle-
donous (endogenous), 129, 133, 135;
of mosses, 154; of vascular crypto-
gams, 154; pith of, 124; pressure of
sap in, 264; primary structure of, 119;
secondary structure of, 185; sensitive-
ness of, 417; transfer of water through,
248 ; wilting of cut, 263.

Stereom (crepeds, firm), 191.

Stigma (oriywa, a mark made by a
pointed instrument), 427; character of
the cells of the, 172; extent of surface
of the, 427, 430.

Stigmatic secretion, 427.

Stock, 152.

Stomata (o7éza, the mouth), 70, 268; de-
velopment of, 72, 376; guardian cells
of, 70, 269; mechanism of, 269; occur-
rence of, 70, n., 71, m., 72; passage of
gases through, 303; relations of, to
exter al influences, 270; size of, 71.

Stratification, 30.

Striation, 30.

Stroma (crpdya, a bed), 198.

Strontium, occurrence of, in plants, 256.

Structural characters of wood, 146, n.

Strychnia (Co:Hs:N.0,), 365.

Style (stilus, a style), 427; character of
the cells of the, 172; conductive tissue
of, 431: sensitiveness of, 424,

Suberification (suber, cork; jfacio, I
make), 34, 38,

Suberin, 388; tests for, 7, 14, 39.

Submerged phxnogams, leaves of, 161.

Substitute fibres, 80.

Sugar, diffusion of, 222; effect of a solu

GLOSSARIAL INDEX.

tion of, on pollen-grains, 429; in the
cell-sap, 52; use of, as a reagent, 15,
199.

Sugar group of non-nitrogenous prod-
ucts, 358.

Sulphur, appropriation of, by the plant,
235, 284, 836; in the ash of plants,
247.

Sulphuric acid (H:SO,), effect of, upon
cellulose, 15, 31; effect of, upon cuti-
nized membranes, 39; use of, as a sol-
vent for callus, 93.

Sulphurous acid (SOz), effects of, upon
leaves, 474.

Superior ovaries, arrangement of the
fibro-vascular bundles in, 173.

Suspensor, 436.

Synergidx (cuvepyés,
435.

Syntagma (cvvrayya, that which is put
together in order), 218, x.

Synthesis of albuminous matters in the
plant, 335.

Systems, 102.

working together),

TABASITEER, 89, 2.

Tagma (réyna, a company), 213, n.

Tannate of gelatin used in the formation
of Traube’s cell, 226.

Tannin (CyHc0o), diffusion of, 222; in
pulvinus of Mimosa, 361, 420; occur-
rence of, in plants, 361; tests for, 12,
14.

Tapetum (tapete, a carpet), 171, n.

Tartaric acid (CsH.Oc), 360.

Teasel. See Dipsacus.

Tegmen (tegmen, a covering), 178.

Telegraph plant, 413.

Temperature, effect of, upon absorption
by soils, 240; effects of too high, upon

- plants, 470; elevation of, during intra-
molecular respiration, 872; influence
of, upon absorption by roots, 245; influ-
ence of, upon assimilation, 306, 316;
influence of, upon respiration, 369; in-
fluence of, upon transpiration, 277; of
air inside a spathe, 370; of pulvinus
of Mimosa, 421; producing rigidity
in Sensitive plant, 423; relations of
growth to, 385; relations of protoplasm
to, 201; relations of soils to, 245; rela-
tions of, to germination, 464.

Tendriis, circumnutation of, 409, 417.

Tensions of the cell-wall and tissues,

390.
Terpene (CiH;), 362.

497

Tertiary formations in the root, 115.

Testa (testa, a shell), 178.

Tetrad (tezpds, four), 171.

Thallium, occurrence of, in plants, 256,

Thallophytes, 164, 440.

Tharandt normal-culture solution, 250.

Thermotropic curvatures, 394.

Thermotropism (Gepudv, heat; rtpdmos, &
turn), 394,

Thiersch’s borax-carmin, 17.

Thiersch’s oxalic-acid carmin, 17.

Times of opening and closiug of flowers,
412,

Tin, occurrence of, in plants, 256.

Tissues, 102; classification of, 187; con-
ducting power of ligneous, 261; cribri-
form, 91; depth to which light pene-
trates, 309; hardening of, 9, 11; rela
tions of water to, 257; sensitive, 415;
tension of, 390.

Titanium occurrence of, in plants, 256.

Trabecular ducts (trabecula, a little
beam), 86.

Trachew (rpaxeia, rough), 82, 84. See
also Vessels.

Tracheal cells, 81.

Tracheal portion of a fibro-vascular
bundle, 104.

Tracheids, 82; in roots of orchids, 109;
in stems, 121; size of, 143; walls of,
84.

Transfer of water through the plant, 257;
compared with that through porous
inorganic substances, 262, n.; effect of
exposing a cut surface to the air upon,
263; effect of motion upon, 263; path
of, 259; rate of, 259, 261.

Transformed branches, 153.

Transformed cells, 56.

Transmutation, 354, 355.

Transpiration, 268; amount of water
given off in, 271, 275, 281; apparatus
for registering, 273; checks upon, 280;
compared with evaporation proper,
275; effect of various salts upon,
279; effect of heat upon, 277; effect
of light upon, 277; effect of mechani-
cal shock upon, 278; effect of moisture
in the air upon, 275; effect of nature
of the soil upon, 276; effects of, upon
the air, 281; effects of, upon the plant,
281; effects of, upon the soil, 283;
experiments upon, 273; methods of
measuring, 272; relation of age of
leaves to, 279; relation of, to absorp-
tion, 279; relative amounts of, from
opposite sides of a leaf, 274,

498

Trausverse planes, 382.

Trees, age of, 139.

Trichoblast (epg [gen. tprxés], hair;
BAaorés, shout), a name proposed by
Sachs for such idioblasts as are es-
pecially distinguished by size and
branching.

Trichogyne, 440, ».

Trichomes (@pié, hair), 65, 68, 220.

Trinitrophenic acid. See Picric Acid.

Triolein. See Olein.

Tripalmatin. See Palmatin.

Tristearin. See Stearin.

Trommer’s test for dextrin, 51.

Trophoplast (7poés, a feeder; TAdoow, I
form), 287.

Tiillen. See Tyloses.

Turgescence, effect of organic acids upon;
414.

Turpentine (C,oHi,), use of, in prepara-
tion of specimens for mounting, 23.

Twining plants, 405.

Tyloses (7¥Aos, a protuberance), 87.

Typical cells. See Fundamental Cells.

UNORGANIZED FERMENTS, 865.
Utricularia, 346.

Vacuo.rs, 26, 177, 200, 212, n., 280,
875, 397.

Variegated plants, 477.

Varieties, 447.

Variety-hybrids, 455.

Vascular system. See Fibro-vascular
System.

Vasculose, 35, 2.

Vasiform elements (vas, vessel; forma,
form), 81.

Vasiform wood-cells.

Vegetable acids, 360.

Vegetable mucus, occurrence of, in
plants, 358; test for, 15.

Vegetable parchment, 32, x.

Venation of leaves, 156.

on method of producing crystals,

5.

Vessels, 55, 77, 82, 84; classified, 60;
size of, 86.

Viola tricolor, coloring-matters in flowers
of, 170.

Vitality of seeds, 205, 461.

Vitellin, 364.

See Tracheids.

WaArDIAN cases, 474.
Water, absorbed previous to metasta-

GLOSSARIAL INDEX.

sis, 267; absorption of gases by, 300,
n.; action of steam upon chlorophyll,
290, 475, n.; an agent in the formation
of soils, 237; amount of, contained in
plants, 236; amount of, given off in
transpiration, 271; amount of, required.
for germination, 462; direction in
which tissues most readily conduct,
262, n.; effect of absorption of, upon
seeds, 463; effect of, upon protoplas-
mic movements, 209; effect of, upon
opening and closivg of stomata, 270;
equilibrium of, in the plant, 258; ex-
udation of, from uninjured parts of
plants, 267; method of determining
amount of, in dry wood, 261; rate of
ascent of, in stems, 261, 263; relations
of, to tissues, 257; relative amount of
space occupied by, in fresh wood, 261;
transfer of, in plants, 257, 269; trans-
port of soils by, 238; use of, as a
medium, 5; use of, as a mounting-
medium, 21. See also Moisture.

Water-culture, 248; directions for, 249;
first application of method of, 249; so-
lutions for, 250.

Water-plants, size of, 188; structure of
land-plants compared with that of,
257.

Water-pores, 73.

Water tissue, 62, 280.

Waxy coatings upon the epidermis, 66.

White chlorophyll, 322.

White lead as a varnish, 24.

Wiesner’s tests for lignin, 10, 14, 37.

Wild plants, supply of nitrogen to, 384.

Wilting of leaves, 471.

Winterkilling, 472.

Withering of stems, how prevented, 263.

Wood, autumn, 138, 395; color of, 141;
density of, 144; identification of, by
histological features, 145, .; odor of,
142; preservation of, 142; spring, 138,
396; structural characters of, 146, 7.

Wood-cells, 57, 78, 82; size of, 86, w.,
143. See also Tracheids.

Wood elements, inclination of, to the
axes of trees, 143.

Wood-fibre used for paper-pulp, 145.

Wood-parenchyma, 77.

Woodward’s carmin, 17.

Woody fibres, 57, 80. See also Wood-
cells.

Woody rings, 114, 187; demarcation
between, 189; size of, 140; two,
formed in a single year, 129.

Work of the plant, 185.

GLOSSARIAL INDEX. 499

Works of reference relating to insectiv-
orous plants, 351; relating to micro-
scupe manipulation and micro-chem-
istry, 24; relating to the cell and its
modifications, 55; relating to the his-
tology of the organs of vegetation, 165.

Wounds of plants, healing of, 150.

XANTHIC FLOWER COLORS (éav@ds, yel-
low), 454.

Xanthophyll (€av6ss, yellow; ¢vAdov,
leaf), 290, 291, 297.

Xerophilous plants (gepés, dry; $rAcw,
I love), 280, x.

Xylem (Aor, wood), 104.

Z1Nc, occurrence of, in plants, 255; re-
lated to changes of form in the plant,
256.

Zygophytes, reproduction in, 439, n.

PRACTICAL EXERCISES.

SUGGESTIONS FOR STUDIES IN HISTOLOGY
AND PHYSIOLOGY OF PHANOGAMS.,

Tue following hints are designed chiefly to aid students who
have at their command the simpler appliances described in the
foregoing pages. In addition to the simpler exercises there are
also suggested a few which are quite within the power of students
having access to a small chemical laboratory and a small cabinet
of physical apparatus. The chemical and physical outfits now
found in many of our high schools will prove ample for the
successful prosecution of these experiments.

HISTOLOGICAL PRACTICE.

Material for study. The supply of material for histology
should be abundant and of the best quality, all inferior or imper-
fect specimens being carefully excluded. It (except that dis-
tinctly referred to as fresh) should be collected at proper seasons
and preserved at once in strong alcohol, great care being exer-
cised to have every specimen accurately labelled ; name, locality,
time of gathering, etc., being noted. When alcoholic material
is required for immediate use in the preparation of sections, it
can be softened, if necessary, by soaking in pure water, as
directed in 37.

Delineation. When a, satisfactory section or preparation has
been secured, the student should make an accurate drawing of
its essential features. The employment of a camera lucida (12)
insures correct proportions in all parts of the sketch, and is
always to be recommended. Drawings made by its aid are con-
veniently designated by the following abbreviated term, ud nat.
del. It may seem scarcely necessary to caution students against
obscuring any part of their histological sketches by meaningless
shading ; a few clean and clear outlines suffice to express the
character of the preparation better than any attempt to give the
eflects of light and shade. There are some exceptions to this

2 STUDIES IN HISTOLOGY.

broad statement; for instance, preparations of nascent flowers
are shown equally well by shaded figures, and the same is true
of many pollen-grains, etc. The use of slips of drawing-paper
of uniform size and the arrangement of these under appropriate
heads will render the keeping of a systematic record of work
much easier.

Permanent preparations. In most cases the sections or other
preparations should be permanently mounted in some suitable
preservative medium, and properly labelled with the name of the
plant and of the special part exhibited, date of preparation,
medium in which it is mounted, etc. The drawings should be
numbered or labelled to correspond with the permanent prepa-
rations.

Histological elements, their modifications and combinations.
In the following enumeration of the more important elements
the sequence is (1) form, (2) contents, (3) distribution, (4)
development. ,

FORMS OF THE STRUCTURAL ELEMENTS AND SIMPLE
TISSUES.

J. ParENcHYMA Proper AND ITS CateF MopiFICATIOoNs,

(a) Soak a few peas or beans in water until they become soft
enough to be cut without difficulty, remove the seed-coats, and
make with a wet razor (see 8) three very thin sections through
the cotyledons. These sections for comparison should be at right
angles to one another, in order to exhibit the length, breadth,
and thickness of the cells. On removing them from the knife
or razor (by means of a camel’s-hair brush), float them in water
and move them gently about, in order to detach the cell-contents
which have partly escaped from the cut cells. When the sections
appear clear, transfer them to the middle of a glass slide, add
a little pure water and cover with thin glass, being very careful
to exclude all air-bubbles. If the sections are thin and wholly
free from bubbles of air, compare the outlines of the cells with
one another, making drawings of the specimens.

(6) Make similar sections (1) through the pulp of any unripe
fruit — apple, pear, snow-berry, etc.; (2) through the pith of
Elder, Lilac, or any soft shoots; (8) through the pulp of any
succulent leaves, for instance those of Sedum, Purslane, or
Begonia.

PARENCHYMA AND ITS MODIFICATIONS. 3

(c) Make a transverse and a vertical section through the
petiole of any water-lily, or through the soft interior of any rush
(Juncus).

(d@) When, after considerable practice, the student succeeds
in making very thin sections of the foregoing plants, let the
reagents for the demonstration of cellulose be applied to them,
as directed in 143.

It is not superfluous to state (1) that success in the application
of these and most of the other reagents employed under the
microscope is generally preceded by many failures, and (2) that
carelessness in the use of some of the reagents may irreparably
ruin the microscope lenses.

Sclerotic Parenchyma. Excellent material can be obtained
from the flesh of pears and quinces (see 211 and Fig. 40).

From the tough shells of many sorts of nuts and seeds (see
Fig. 41) good preparations can be made by the method described
in 495. For the Canada balsam there recommended good
shellac can be advantageously substituted.

Collenchyma cells are well exhibited by cross-sections of the
stem of any common Labiate, for instance Spearmint, or of the
stem of almost any of the Umbelliferze (see 216). Apply dilute
hydrochloric acid to the sections.

Wood parenchyma cells are easily obtained by careful macer-
ation (70). Dilute solutions of Schulze’s liquid are preferable
to strong, although much slower in action. Excellent material
is afforded by most of the oaks and other hard woods (see 254,
255). Nearly all possible intermediate forms can be found by
careful search. Apply the tests for “lignin” (154). Use also
upon different specimens red and blue coal-tar colors.

II. Eprpermat Cr.is.

(4) Examine a film removed from the upper surface of some
fleshy leaf; for instance, Sedum, the cultivated Cotyledon or
Eccheveria, Purslane, or Begonia, ete.

(6) Compare the cells of this film with those found on the
upper surface of a shining petal; e. g., that of Buttercup or
Poppy.

4 STUDIES IN HISTOLOGY.

(c) Remove a moderately thin film from the young stem or
branch of some Cactus, and examine the exposed surface of the
epidermal cells for cutinization (156 and 224). Apply any of
the coal-tar colors to similar fragments, and note differences
of tint.

(d) Examine the ‘‘ bloom” (226) on the following: (1) stem
of Indian corn, (2) stem of castor-oil plant, (8) leaf of cabbage,
(4) fruit of plum, juniper, or Myrica cerifera (Bayberry).

(e) Make a thin vertical section through the leaf of Ficus
elastica (India-rubber plant), noting the epidermis and cystoliths
(see 164 and Fig. 6).

(f) Examine the examples of multiple epidermis afforded by
many of the cultivated species of Begonia.

Trichomes. (a) Examine the velvety petals of any flower,
and compare their very short trichomes, or hairs, with those on
downy, rough, and bristly stems and leaves.

(6) Examine also a vertical section of a young rose-prickle.

The variety of glandular trichomes at hand in any locality
is so great that no special directions need be given for their
selection.

(c) Root-hairs are easily obtained by allowing the seeds of
flax, or the grains of corn, wheat, etc., to germinate on wet
filtering-paper, or even on moist glass.

Stomata (pp. 70-73). For the proper study of these a mi-
crometer eye-piece (11) is very necessary. By its employment
the dimensions of individual stomata and the number of stomata
on a given space can be easily determined.

Sections of stomata are made best by aid of the processes of
imbedding (8). Examination of the table by Weiss (page 71)
will afford hints as to the selection of large stomata for examina-
tion in section.

Watr-pores and rifts (242). (a) Water-pores are furnished
by the tips of the teeth of the leaves from some species of Fuchsia.
Sections showing their constituent cells are best made vertically
and lengthwise through the leaf. Tropzolum, or the so-called
Garden Nasturtium, also gives good examples.

(0) Compare with these water-pores the irregular rifts in the
leaves of some grasses ; for instance, Indian corn.

PROSENCHYMATIC WOOD-ELEMENTS. 5

Il. Corx-Crts.

For the examination of these cells, the student should begin
with the soft and close-textured ‘ velvet” cork procurable at
any apothecary shop. Let the sections be made in at least two
directions at right angles to each other, and if possible let them
pass through one of the lines of demarcation of the cork: note
any differences of shape and size presented by the cells at that
place.

The young stems of any of our common currants give in cross-
section excellent illustrations of cork-cells (see pages 74-76)
and of their development. ‘Test these and similar specimens of
cork-cells for the presence of cutin or suberin (see 26, 54, 161).

IV. ProsexcuymMatic Woop-ELemMents.

These clements (see pages 78-87) can be studied to best ad-
vantage after very careful maceration, as directed in 70. Long
wood-cells, woody fibres, and trachese (or ducts), are easily
separable from each other by such chemical means, and are
generally identified with facility. Abundant inaterial for the
demonstration of trachew is afforded hy the fibro-vascular bundles
(198) of herbs and by the ligneous parts of our common trees
other than the Conifer. There appears to be no special need
of specifying the ligneous plants which can be most successfully
employed for demonstrations of the woody elements. Magnolias,
Tulip-tree, woody Leguininose and Rosaces, Urticacee, and
Cupuliferze are all satisfactory as sources of material.

Good examples of tracheids are procurable from species of
Coniferee, such as Pines, Firs, Spruces, ete. These should be
examined in all stages of development and from all points of
view, particular attention being directed to the marked difference
between the radial and tangential aspects of the cells.

Cells which have been separated from each other mechanically
and have not been previously acted on by chemicals should be
studied with reference to their behavior under the action of
iodine and other reagents, it being possible to demonstrate the
existence of thin layers or ‘* plates” which compose the wall.
Jodine colors the fresh cells yellow; investigation shows, how-
ever, that the inner wall or plate of the cell is not much, if at
all, colored by the reagent, the color being confined to an outer
and a middle wall or plate. When the cells thus treated with
iodine are touched with concentrated sulphuric acid, the outer
and middle plates remain yellow, while the inner plate turns

6 STUDIES IN HISTOLOGY.

blue. Soon the inner and middle plates dissolve, the outer not
being attacked until] somewhat later. If Schulze’s macerating
solution (full strength) is employed, the outer plate dissolves
quickly, but the others are not much affected for some time.
Careful management of these powerful solvents is demanded to
insure even a moderate degree of success in this demonstration.

V. Bast-Finnres.

Isolation of these cells is easily effected by teasing with needles
under the dissecting microscope. The use of macerating solu-
tions for this purpose is also adinissible, but the results are not
quite so satisfactory as with the wood-elements. Examination
of the table on page 90 shows the wide difference which exists
between the dimensions of the raw fibres and their structural
elements, into which they can be separated mechanically.

Most bast-fibres take the coal-tar colors very well, and it would
be best for the student (without giving too much time to it) to
note the different effects which are produced on various fibres by
the colors described on page 19. ‘The changes produced in the
dimensions of the fibres by dilute acids should also be observed.
After this preliminary practice the reactions given on page 90
should be carefully repeated with such material as is at hand.
Full directions for the preparation and use of the prescribed
reagents will be found in the introductory chapter. Lastly, de-
terminations of the average dimensions of the commercial fibres,
flax, hemp, jute, etc., should be carefully made.

VI. Cribrosr-CELLs orn Sreve-CELis,

These can be very easily demonstrated in thin vertical sec-
tions of the stems of any large Cucurbitaceous plants; for in-
stance, squashes, melons, etc. If the student fails to detect in
fresh material forms similar to those shown in Fig. 73, a little
tincture of iodine should be added to the specimen, in order to
contract the lining and other contents of the cells. By this
reagent the contents become more or less distinctly colored, and
the discrimination hetween the cells and the surrounding tissues
is generally very plain. In other common plants, grape-vines,
ete., the detection of cribrose-cells is not always easy, but a
diligent search will bring out these characteristic constituents of
soft bast.

The study of the structure of the sieve-plates requires the use
of much higher powers of the microscope than most beginners

LATEX-CELLS. 7

are likely to possess. Much can, however, be done in the ex-
amination of the callws by the employment of the reagents
mentioned in 282 and 283. The student should not fail to sub-
mit a thin section showing the larger cribrose-cells to the action
of concentrated sulphuric acid, and remove in this way the whole
of the cell-wall, leaving (if the manipulation has been careful)
the contents slightly connected together and showing the inter-
communication between the cells.

VII. Latex-Cetts.

Latex-cells are abundant for demonstration in many wild and
cultivated plants; but few afford material better adapted to the
use of beginners than the greenhouse plant, Euphorbia splen-
dens. Other cultivated species of the same genus are about as
good. With the younger and softer stems of this plant one has
merely to secure thin sections through their outer or cortical
portion, when, in a good section, the latex-tubes can be found
ramifying irregularly. The peculiar dumb-bell shaped grains in
the tubes form a characteristic feature.

When a thin section of any tissue containing latex-tubes is
gently heated in a dilute solution of potassic hydrate, or for a
shorter time in a stronger solution, the parts become so much
softened that the tubes can be easily separated from the sur-
rounding tissue, after which they can be floated on to a fresh
slide and examined by themselves.

Abundant material for the study of latex-cells is furnished
by plants of the following groups: Lobeliaceee, Campanulacez,
Liguliflore, and many Papaveracez.

VIII. Sprcran RECEPTACLES FOR SECRETIONS.

These are constantly met with in sections of many stems,
leaves, and fruits. A few examples for study are here given.

(a) Crystal-cells. Look for these in the leaves of the Aracese,
Onagrace#, and Chenopodiaces, and in the bark of almost any
of the ligneous Rosacezee (Pome), where they are especially
associated with the bast-fibres.

(0) Resin-cells and resin-reservoirs ave found in the bark of
many Coniferze and Umbelliferz, etc., in the leaves of Rutacer,
Hypericaceee, and Myrtacez.

(c) Tannin receptacles are found in very many kinds of bark.
For the detection of tannin, solutions of potassic chromate or
ammonic chromate may be employed, a brown coior being

8 STUDIES IN HISTOLOGY.

promptly produced. This test is preferable in some respects to
the solutions of iron alluded to in 59.

Intercellular spaces of various shapes and sizes containing
air, or air and water, are met with in many of the plants already
enumerated. ‘The most interesting are found in monocotyledo-
nous plants, notably Araceze and Juncacee.

CELL-CONTENTS.
J. ProtTorpiasm.

No better material for the demonstration of the physical and
chemical properties of protoplasm in its active state can be em-
ployed by a beginner than the young stamen-hairs of Spiderwort.
Several garden species of Spicderwort are available for this pur-
pose, especially Tradescantia Virginica and pilosa. The green-
house species can also be employed. If none of these are at
hand, any young large plant-hairs with thin transparent walls
will answer for the demonstration. If the hairs are sufficiently
young, the protoplasm appears as a nearly transparent mass
filling the cell-cavity; but even when they are only slightly
advanced in development the mass becomes honey-combed by
sap-cavities or vacuoles. With further development these be-
come confluent, and traversed here and there by slender threads ;
the wall of the cell, however, as long as it is alive, being lined
by a delicate film of protoplasm.

When the protoplasm exists in a cell only in the latter condi-
tion, it is well to place the cell in a solution of sugar (a five per-
cent one will answer) or in dilute glycerin. By this means the
protoplasmic lining is contracted somewhat by the withdrawal
of water from its cavity, and in shrinking from the wall its shriv-
elled contour can be easily distinguished.

It is best for a beginner to use in his early demonstrations
very young plant-hairs in which the vacuoles do not occupy much
space within the ccll. The cells composing the growing points
of most roots, stems, and leaves are too small for satisfactory
study at the very outset; it is well to defer the examination of
the protoplasm in these until its reactions have been clearly
demonstrated in young plant-hairs.

Directions for the demonstration of active protoplasm can be
found in section 124. The tests there given should be repeated
by the student four or five times with different kinds of cells,

PLASTIDS. 9

after which the effect upon fresh material of potassic hydrate,
both the concentrated and the dilute solutions, should be care-
fully watched. In these examinations it will be well to practise
with the reagents without lifting the cover-glass (see 17 and 20).

II. CHLOROPLASTIDS.

Examine the chlorophyll granules (see page 41) in the fol-
lowing material : —

(a) The parenchyma cells of any thick leaves, for instance
those of Purslane, Begonia, etc., noting in the drawing the rela-
tive size and abundance of the granules in different cells.

(6) The epidermis of the same leaves, noting in what cells, if
any, the granules are found.

Examine also the green bodies in the leaves of any true moss,
and in any filamentous alga, ¢. g., Spirogyra, and the cotyledons
of the following seeds for any green granules: sunflower, maple,
and pine.

Raise three seedlings of flax and pine. Let one of the seed-
lings of each be kept in darkness, to the second seedling of each
give only a very little light, to the third give as much light as
possible ; and when the plumules have begun to develop, examine
the cotyledons and young stems for any color-granules.

Do well-blanched celery petioles contain chlorophyll? To
answer this, examine the base, middle, and summit of the leaf-
stalk.

The next three studies can be advantageously deferred until
after that of starch.

III. Lrvcoprasrips.

These bodies (see 174) require for their detection very careful
manipulation, but by following the directions given on page 44
they can usually be made out without much difficulty. For the
pseudo-bulb of Phajus, which is there recommended, the same
organ in almost any of the cultivated exotic orchids may be
substituted.

IV. CHRoMOPLASTIDS.

These can be examined in any of the colored fruits; for
instance, in winter, the berries of Solanum Psendocapsicum
(Jerusalem Cherry) may be used (as directed in 498). The
granules there found should be compared with colored granules
in the petals of almost any flower. For examination of the color-
granules in flowers, common pansies answer very well (see 477.)

10 STUDIES IN HISTOLOGY.

V. Prorein GRANuLEs (pages 44-47 and 182).

Examine thin sections of the endosperm of the seed of Ricinus
after the specimen has been treated as directed in 176, and also
of the seed of Bertholletia (Brazil-nut). Permanent preparations
from the latter should be made as directed on page 47.

Search also for cubical crystalloids in the cells just under the
skin of a potato-tuber.

VI. Srarcu.

In the examination of starch (pages 47 and 181) make thin
sections of (a) a potato-tuber, (6) the cereal grains figured in the
pages cited, (c) seeds of the pea and bean.

Detach some medium-sized starch-granules and measure them
with the micrometer; after this apply a solution of iodine, em-
ploying the most dilute one which will impart a decided color to
the granules. Is the color given by iodine permanent? Does
exposure of the colored specimen to light make any difference in
permanence of color?

In all cases note very carefully any appearance of stratifica-
tion which the different granules present, and determine the
distinctive characters by which each of the common commercial
starches can be recognized, such as rice-starch (toilet-powder),
laundry starch (either wheat or potato), ete. After sufficient
familiarity has been acquired by an examination of all the
kinds of starch figured in Part I., try to identify under the
microscope specimens of laundry starch and of various kinds
of flour.

Can starch be detected in the following : —

Seeds of flax and mustard?

Roots of beets and turnips?

Pulp of the ripe and the unripe apple?

Bark of willow and maple?

Young shoots of pine?

For the detection of starch in minute amount in chlorophyll
granules the directions given on page 42 must be carefully
followed.

From this time on, the character of the granules seen in any
specimen should be determined by iodine and the result noted
in the drawing.

CRYSTALS, CARBOHYDRATES, AND OIL-GLOBULES. 11

VIT. Crystats.

In many of the sections already spoken of, for instance those
of Begonia, single crystals and clusters of crystals have at-
tracted attention. For a brief study of different forms of
crystals (see pages 52-55) the following are very serviceable:
petioles of Begonia, scales of onion, leaves of Tradescantia,
Fuchsia, and the common ‘ Calla” (Richardia), bark of many
woody plants.

If a thin section of the leaf of almost any Araceous plant, for
instance ‘‘ Calla,” is placed in a little water under the micro-
scope, it frequently happens that the discharge of acicular
crystals (raphides), described on page 52, can be seen without
difficulty.

Apply to the specimens containing crystals the two reagents
spoken of in the table on page 54, and carefully note results.

Repeat Vesque’s experiment (188).

VIII. CarnonynpRATES DISSOLVED IN THE CELL-SAP.

(a) Inulin (183) is deposited from its solution in cell-sap
whenever the cells are placed for a time in alcohol or even in
glycerin. Its characteristic forms are not likely to be mistaken
for anything else met with in the tissues. Excellent material is
afforded not only by the common Dahlia, but by Cichory and
Dandelion (see Fig. 35).

(6) The sugars. Examine a thin section of beet-root by the
method described in 184. Compare with it a thin section of any
ripe fruit.

IX. OTHER CELL-CONTENTS.

Oil Globules, sometimes of large size, but generally minute,
are to be looked for in those seeds which do not contain starch
(compare 511). Examine in these the effect of ether on the par-
ticles of oil, and also make sections through the leaves of St.
John’s-wort, Rue, and Dictamnus, and through the rind of an
orange or lemon to determine the shape of the receptacles con-
taining oily matters.

Resins, etc. For a study of these, proceed as directed in 56,
employing young shoots of Pine.

Tunnin, ete. For the detection of tannin, solutions of iron (see
59) may be used; but the results are generally more satisfactory
when a solution of potassic or ammonic dichromate is employed.
The color imparted to the cells containing much tannin is brownish

12 STUDIES IN HISTOLOGY.

or even almost black. The student should examine the very
peculiar globules of tannin-solution found in the sensitive pulvi-
nus, or cushion, at the base of the petiole of Mimosa (Sensitive
plant). Similar globules have been detected in different barks.

DISTRIBUTION OF THE HISTOLOGICAL ELEMENTS.

The various histological elements after being examined as
directed in Chapter II. should be investigated with regard to
their mutual relations. It is advisable to begin with the skele-
ton or framework of the plant, afterwards taking up the latex-
cells, ete.

As shown in Chapter III., the framework of the higher plants,
which we are now to consider, consists of fibro-vascular bundles
variously arranged and conjoined. ‘The bundles, which in some
cases may run for some distance as isolated threads, and in
others exist as compact masses, are surrounded with larger or
smaller amounts of cellular tissue, the exterior portions of which
are specially adapted to come into contact with the surroundings
of the plant.

J. Srrvucrure or Frero-vascuLarR BUNDLES.

For the demonstration of the structure of fibro-vascular
bundles, seedlings of the following plants will afford good
material: Bean, Indian corn, Castor-oil plant, and Squash. The
roots of these plants give examples of radial bundles (313), in
which the strands of liber and of wood are in different radii,
while from their stems (including the hypocotyledonary stem of
the bean, castor-oil, and squash) may be obtained excellent
illustrations of collateral bundles.

The sections for displaying the structure of the bundles are
best made in the three directions, transverse, vertical-tangential,
and vyertical-radial. In a few cases sections made obliquely to
the axis of the organ are instructive; but unless great care is
exercised in observing all their relations, they may be rather
misleading.

In all cases examine fully the character of the bundle-sheath
(see 212). The student should not be satisfied with anything
less than a clear interpretation of all the structural elements
which he meets in a given bundle. If the structure of a bundle
is not revealed by the sections already prepared, fresh ones
should be made and carefully compared with the others, and

FIBRO-VASCULAR BUNDLES. 13

with the figures in Part I. In order to identify some of the
structural elements composing a bundle, it is sometimes advis-
able to resort to cautious maceration (see 70), so that the parts
may be isolated. It has been found advantageous, in a few in-
stances, to very securely fasten the section under examination to
thin rubber membrane by means of the best ‘+ rubber” cement
or marine glue, and then subject the membrane and section to-
gether to the action of the macerating liquid, great care being
exercised to have the process gradual. After the maceration is
complete, the membrane is removed from the liquid, washed,
and then slowly stretched until the adherent wood-elements are
somewhat torn apart. It will be observed that by this method
their former relations need not be greatly disturbed.

After examining the fibro-vascular bundles in the seedlings
above named, proceed to the study of the bundles in the roots,
stems, and leaves of two adult herbaceous plants, for instance
Indian corn and Bean, in order to ascertain what differences, if
any, exist in the composition of the bundles in a given organ at
different periods of growth.

It was stated in 309 that the simplest form of a fibro-vascular
bundle consists of merely a few tracheal cells (or sometimes tra-
cheze) together with some cribrose or sieve cells. The student
should search for tracheids, which may occur disconnected from
any bundle; as for example in the stems of species of Salicornia
(a seaside plant of succulent texture), and in the petiole and
pitchers of Nepenthes. Tracheids occur also, often in a con-
tinuous layer, as a sheath of the aerial roots of orchids. Sieve-
tubes may be looked for at a little distance from the bundles in
the stems of potato and tobacco, where they occur in the periphery
of the pith.

Two supplementary studies are strongly advised: (1) of the
bundles in ferns, (2) of those in aquatic phenogams. In the
former, ‘* concentric” bundles are met with; in the latter, rudi-
mentary bundles.

II. Course or Tur BUNDLEs.

The course of the fibro-vascular bundles can be traced in-some
cases, especially in young and rather juicy stems, like those of
Impatiens, with little or no difficulty ; but it is generally neces-
sary to treat somewhat thick sections of the stem under ex-
amination by a macerating liquid, for instance potassic hydrate,
after which the course can be made out. In most cases the
course of the bundles can also be made out by series of sections

14 STUDIES IN HISTOLOGY.

made at different points in the organ, care being taken to arrange
the sections in their proper sequence.

The following material will be useful for practice in the deter-
mination of the course of the bundles: young shoots of Clematis,
Vitis, and Phaseolus (all dicotyledons) ; and, after these, shoots
of Spiderwort, the rootstock of Convallaria (Lily of the Valley),
or of Smilacina, and if possible the bud of a young palm.

The course of the bundles in leaves and dry fruits can be
easily demonstrated by “ skeletonizing” them. This is effected
by keeping the leaves for a long time in a dilute solution of
calcic hypochlorite (see 50).

DEVELOPMENT OF THE ELEMENTS.

This must be examined in the youngest seedlings of the plants
now spoken of. The sections must be through the growing
points, and should be well cleared by one of the processes de-
scribed in 16 or 24. For the development of special structural
elements, for example latex-cells, see Part I.

HISTOLOGY OF THE VARIOUS ORGANS.
I. Tuer Roor.

The student may use, for demonstration of the histology of
the root-tip, any seedlings which have been grown either in water
or on a clean support, and are therefore free from grains of
earth. Root-hairs are best examined on seedlings sprouted upon
moist sponge or bibulous paper.

Il. Tue Stem.

It is advised that the student now prepare, in addition to the
sections of stems previously examined, sections through two and
three year old shoots of any common dicotyledon, and note all
differences which exist between the different woody elements
forming the rings, and all changes in the bast. The growth of
cambium should be carefully examined in the young shoots of
Pine and of Oak.

For the study of the secondary changes in the bark, the
twigs of black currant or of white birch afford good material,
the successive changes being easily followed.

The occurrence of true cork in out-of-the-way places is illus-
trated hy Catalpa, Professor Barnes reporting that it sometimes
occurs between the annual layers in the stem of Catalpa speciosa.
Other cases should be looked for.

LEAF AND FLOWER. 15

Ill. Tuer Lear.

The leaf presents few difficulties in histological manipulation.
For all necessary details consult pp. 155-164. The following
plants afford excellent material for study : —

Of the centric arrangement of parenchyma in the blade, Trit-
icum vulgare, Acorus, and many of the Cactaceze.

Of the bifacial arrangement of parenchyma, many plants with
flat horizontal leaves.

IV. Tue Fiower.

It is assumed that the student has thoroughly familiarized
himself with the morphology of the simpler flowers as explained
in Volume I, and has acquired some facility in examining, as
there directed, those of more complicated structure.

The study of the microscopic anatomy of all the floral organs
in their adult state should precede any attempt to examine their
development. Since the flower should be examined in ad/ stages
of its development, it is well to select for study only those flow-
ers which can be readily obtained in large numbers, and further-
more, by preference, those which are not thickly covered with
hairs. The common weeds Lepidium Virginicum and Capsella
Bursa-pastoris afford excellent material for the study of the
flower and its development, and have the signal advantage of
being much alike in the most essential respects, yet possessing
minor differences which are not likely to be overlooked.

An exhaustive examination of the histology of the organs of
the flower should begin with the study ot the sepals, the other
organs being taken up in their turn, and the following points
receiving special attention: (1) the possible occurrence of stom-
ata upon all the parts of the blossom; (2) the peculiarities in
the proper epidermal cells of the petals ; (3) the character of the
pareachyma in all parts of the flower, and all differences in the
nature of the cell contents, notably the plastids; (4) the charac-
ter and the distribution of the fibro-vascular bundles in their
course from the pedicel to their ultimate attenuated ramifications
in the several organs.

Stamens. The character of the pollen demands special atten-
tion, and its examination should be followed by a comparison
between as many kinds as possible taken from various flowers.
The character of the integuments and the contents of the grains
should also be demonstrated.

16 STUDIES IN HISTOLOGY.

The pistil requires little special study, except in regard to its
development. It will be well to examine the conductive tissue
of the style and trace it down to the ovarian walls. (Other
minute matters connected with the stamens and pistils are con-
sidered under ‘‘ Fertilization.”)

V. DEVELOPMENT OF THE FLOWER.

From the youngest flower-cluster of any plant having indeter-
minate inflorescence, fur instance that of Lepidium or Capsella,
cut squarely off a short piece of the tip, place it on a glass slide
in a little alcohol, in order to remove the air, and cover with
thin glass. (If the student has an air-pamp, the specimen can
be placed at once in water on the slide, and then subjected to
the action of a partial vacuum, which will of course free the
whole preparation from any air-bubbles.) After the air has
been removed, add water, and if the specimen requires clearing,
as is usually the case, some potassa. On gently warming the
slide the specimen will grow somewhat darker, but after a time
will be made tolerably clear. If not, proceed as directed in 25.
The specimen, if a good one and well prepared, ought to show
all the relations of the several flowers of the cluster to each
other. Prepare a second specimen by removing the flowers in
succession under the dissecting lens, beginning with the larger,
and placing them in a row which will comprise all the stages of
development. With the material thus obtained, which it is well
to keep moist with glycerin, the examination of all the different
parts can be successfully carried out. The study will be far
more instructive if the student makes a parallel series with an
allied species. Comparison of the two species above mentioned
shows exactly when and where some of the parts are arrested in
development.

VI. Di vELOPMENT OF THE POLLEN.

The examination of the anther for this study should begin at
a very early stage in the growth of the flower, and particular
attention should be given to the cells which line the pollen cavi-
ties. Great advantage is gained from the skilful employment
of staining agents, by which the parts are brought out more
clearly (see 77 e¢ seq.). All changes in the character of the
nucleus of the grains during their differentiation demand for
their identification the use of staining agents without the pre-
vious application of potassa.

STRUCTURE OF THE SEED. 17

VII. DerveLopment oF OVULEs.

In this examination the wall of the ovary must be removed,
and the minute eminences which are to become the ovules ob-
served in their earliest stage. The successive external produc-
tions which are to becoine the integuments of the ovule should
be traced with great care. It is also well to examine minutely
the changes in form of the embryonal sac in the nucleus (or
nucellus) of the ovule. These will be further adverted to under
‘ Fertilization.”

VIII. Mixure Srrucrure or THE Serb.

Since in the previous exercises some parts of the seed have
been already examined, it is necessary here merely to call atten-
tion to the desirability of studying the character of the integu-
ments in at least two common and a few exceptional cases.
For the former, no seeds are better than those of the common
Bean, Pea, or Lupine. After a clear idea has been obtained of
the nature of the cells. which compose the greater part of the two
integuments, the student should make careful sections through
the hilum in order to display the peculiar sac-like body there
seen. For the exceptional types of integuments, examine the
seeds of Flax (showing the gelatinous modification, etc.), or
better, if they can be procured, the seeds of Collomia and Cot-
ton. It will be well also to examine the closely united ovarian
and ovular coats in the common grains, like Wheat or Indian
corn.

The student should examine as many seeds as possible, includ-
ing those containing much, little, and no starch, and observe also
whether or not there is any difference between ripe and unripe
seeds in the amount of starch which they contain. He should
examine the contents of the cells nearest the integuments in any
of the seeds above mentioned, and ascertain the relative amount
of albuminoid matters present compared with those in the cells
in the interior of the seed.

Further microscopic examination of the seed is to be taken up
when germination is studied.

18 STUDIES IN PHYSIOLOGY.

PRACTICAL EXERCISES IN VEGETABLE
PHYSIOLOGY.

This course of experiments in Vegetable Physiology is divided
into two parts: the first series comprises a few exercises which
can be undertaken by any one having only the simplest appli-
ances; the second requires more complicated apparatus. The
first series, if faithfully and intelligently followed, should place
the student in possession of the leading facts regarding the prin-
cipal activities of the plant; while the second series should ac-
quaint Lim with the chief methods employed for the investigation
of the special offices of the organs of the plant, and fix the
principal results in his mind. It should, however, be frankly
stated that for the proper and satisfactory performance of the
experiments detailed in this second or special series the student
should first become familiar with the ordinary methods of chemi-
eal and physical manipulation, and have at command the funda-
mental principles of chemistry and of physics.

FIRST SERIES.

In this series are discussed experimentally the following car-
dinal topics: (1) The behavior of protoplasm in a living cell;
(2) The gain in substance by assimilation and the loss of sub-
stance by growth; (3) The chief conditions under which plants
assimilate ; (4) The dependence of the principal activities of the
plant upon certain external conditions.

The experiments can be conducted with the following ap-
pliances : —

1. A small balance with weights ranging from twenty grams
to one centigram. Ifa balance is not procurable, ordinary hand-
scales with horn or brass pans will answer very well.

2. A water-bath, or in place of it a small porcelain-lined
kettle of one or two pints capacity, fitting into a larger iron
kettle. Water placed in the larger kettle prevents the inner one
from being heated above the boiling-point of water.

3. Half a dozen test-tubes.

4. Three or four pieces of glass tubing, six inches long.

5. A small camel’s-hair pencil, and India ink.

6. Pieces of colored glass or colored gelatin (red, yellow,
green, blue, violet), six inches square or larger.

MOVEMENTS OF PROTOPLASM. 19

For the first study, the examination of protoplasm, a micro-
scope magnifying from two hundred to six hundred diameters
will be required, together with a small outfit of slides and covers ;
and for the examination of growth a zinc box constructed as
directed in ‘¢‘ The Dependence of Growth upon Heat.”

I. Tut BeHAvior OF PROTOPLASM IN A LIVING VEGETABLE CELL.

For all necessary details as to the chemical reactions of proto-
plasm, see 124 and the exercise on page 8 of this ‘‘ Praxis.”
At present it is proposed to call attention to the various

Movements of Protoplasm.

(a) Material. The delicate hairs from the young leaves of
almost any pubescent plant will serve for the demonstration
of these movements, but the following are recommended on
account of their abundance and excellence: stamen-hairs of
Spiderwort (Tradescantia), hairs from the young leaves of
squash and nettle, and from the velvety leaves of many culti-
vated exotics.

(6) Preparation of specimens. Remove by needles, forceps,
or scalpel a very little of the epidermis with its attached hairs,
and place it at once in a little water on a glass slide. In placing
the thin glass cover on the specimen be careful to exclude all air-
bubbles and not to crush the cells. If necessary, put a fragment
of glass under one edge of the cover, to lighten the pressure on
the object. If the hairs are suitable for the examination, the
delicate threads of protoplasm ought to be distinctly seen through
the cell-walls, and, after a little time, a movement of translucent
granules should be scen in them. If, after a few moments, no
movement can be detected, warm the slide a little with the hand
and again observe. If no movement should now be seen, add
to the water on the slide a little dilute glycerin; this causes
slight contraction of the protoplasmic lining of the cell, and
probably the movement can then be observed in the threads. If
not, do not waste time over the specimen, but try a fresh one. A
power of 200 diameters will answer for this work, but one of 500
is better.

(c) Questions to be answered by the specimen. If the student
has secured a good preparation, in which the movement of gran-
ules in the threads can be seen distinctly, he can easily answer
the following queries: What is the rate of motion of the gran-
ules at the temperature of the room? Do the threads remain

20 STUDIES IN PHYSIOLOGY.

unchanged in shape? Do any granules pass from one cell to the
next one? Where is the motion fastest?

While the observations are in progress, be careful not to allow
the preparation to become dry: add a, little water occasionally,
and note whether tbe rate of motion is increased or diminished
for the next minute or so.

(d) Questions to be answered by experiment. (1) What effect
upon the rate of protoplasmic movement does increase of tem-
perature produce?

In order to keep the slide with the specimen, prepared as
above, from touching the metallic stage of the microscope, place
under each end of it a piece of thick pasteboard, and then clamp
it down firmly by means of the stage-clips, so that it cannot
be easily displaced. After the slide has been in position for a
few minutes, note the rate of movement of the granules at the
ordinary temperature of the room. When this has been accu-
rately determined, place near the specimen, on the slide, a coin
or other small piece of metal which has been heated to 40° C.,
and note the change of rate. Afterwards apply more and more
heat by a second and a third application of the coin, heated each
time higher by immersion in hot water, and note the result. Of
course this very simple method of experiment does not allow one
to determine the exact temperature to which the specimen is
heated, but its temperature is only a little lower than that of the
coin. :

For exact experiments employ the apparatus described in
557 or 558.

(2) What effect upon the rate of movement does a decrease of
temperature cause?

Prepare a fresh specimen as directed under (0), lower the tem-
perature of the slide by the application of a coin which has been
immersed in ice-water, and note all changes in the rate of move-
ment. Still lower temperatures are easily secured by placing in
a small copper cup on the slide (an ordinary copper cartridge-
shell answers very well) a mixture of ice and salt.

If in either of the preceding experiments the motion of the
granules has been arrested, endeavor, by reversing the applica-
tion, to re-establish movement: thus, if the movement was ar-
rested at the higher temperature, apply cold ; if it was arrested by
cold, apply heat.

ASSIMILATION AND GROWTH. 21

IJ. Tue Gain IN SuBsTANCE BY ASSIMILATION, AND THE Loss oF SvuB-
STANCE DURING GrowTH.

Select a number of beans (Windsor, Horticultural, Lima, or
white), of nearly the sane size, weigh ten of them, and dry them
carefully in a water-bath to ascertain the amount of water which
they contain. Take two other lots of ten each, weigh them
carefully, pliant them on moist blotting-paper or wet sponge, ana
keep them in a warm place until they have sprouted. When
the beans have fairly started, suspend them over the surface of
water, with their roots in it, as directed in 669. From this tim2
on, keep one set of the seedlings in the light and the other set
in the dark, being careful in each case that the water is supplied
in sufficient quantity to make up for all loss by evaporation, and
that it is changed every third day. Let all the conditions und w
which the two sets are cultivated be as nearly alike as possil >,
with the single exception that light is present in one case a.d
completely absent in the other. In a couple of weeks the two
sets of seedlings will have become large enough for further
study: the set grown in the light will be green and thrifty, the
others may be as large, but they will have a yellow, unhealthy
appearance. Remove the two sets from the water and carefully
dry them separately over the water-bath as directed in the case of
the seeds. When they do not further lose weight, weigh carefully.
Compare the weight of the dried seedlings with the weight o7
the dried seeds.

Jif. Tue Cnicr Conpirions oF ASSIMILATION.

In the examination of these, repeat with great care the experi
ments detailed on page 305.

1V. Tue Depexpesce or Growtn vvox Heat.

This may be shown in the following manner: Take a sheet of
tin or zine about 6 to 8 inches in width and 24 inches in length.
Turn up its ends at right angles 6 inches. Turn them once
more at right angles, rather less than half an inch at the top
and two anda half inches at the bottom. ‘This last turn will
hold a sheet of glass which will form the fourth side of a box,
narrower by two inches at the bottom than at the top; that is,
the glass side will not be vertical, but inclined. Cut out a piece
of wire-gauze of the right size for the bottom, and either solder
or rivet it in place. Fill this box with well-moistened sawdust.
Plant a row of six or cight large Windsor beans in regular order

22 STUDIES IN PHYSIOLOGY.

in the sawdust, near the glass side, so that the tip of each radicle
will start down about one fourth of an inch from it. If the glass
is properly inclined, the radicle will quickly press itself against
it and thus be the more readily seen and studied in its subse-
quent growth. When the radicles are about two inches in
length, withdraw them, and by the aid of a fine camel’s-hair
brush and India ink mark them off with precision at regular
intervals of one or two millimeters, then place each in the same
place and position from which it was taken. It will be found
that only their tips grow; the marks above the tips remaining
the same distance apart.

Put a thermometer in the sawdust in order to observe the tem-
perature, upon which it will be found the rate of growth depends.
Place the seedlings near the stove or over a register where the
temperature of the sawdust can be gradually raised to from 28°
to 30°C. Having previously measured and noted the exact
length of the radicle of each plant, observe its increase, while
the temperature remains constant, for a given period of say from
five to ten hours. Next place the case containing the seedlings
in an improvised ice-chest (any box which can be well closed will
answer), and when the temperature has been reduced to 10° C.,
or nearly that, measure the roots carefully again. Hold this
degree of cold as nearly constant as possible for five or ten hours,
whichever may have been the period of time in the first case.
Compare the growth in the two periods and note the difference.

SECOND SERIES. —SPECIAL EXPERIMENTS.

J. Dirrusron.

Place a tumbler containing an inch or two of pure water upon
a firm shelf where it will not be subject to any jarring, and put
in it a vial filled to the brim with some colored liquid, for instance
blue or purple ink. Then by means of a tube or ‘‘ thistle-funnel”
resting on the bottom of the tambler pour into the tumbler water
enough to come up to the mouth of the vial, and very cautiously
add more until the mouth is covered to a depth of about an inch.
If the pouring has been skilfully done, there will be scarcely any
of the ink mixed with the surrounding water. Let the apparatus
stand undisturbed for a week or so, and note any changes in the
color which may be cbserved from day to day.

Try the same experiment with a saturated solution of common
salt in place of the ink, and at intervals of three days cautiously

OSMOSE. 23

remove a little of the water from the bottom of the tumbler by
means of a small tube or pipette, and test it for chlorides.

II. Osmosr. Dirrusron trroucn A Membrane.

Scoop out a small cavity in a fleshy root, for instance that of
a carrot, and carefully dry it with a cloth. Then fill it with fine
sugar, and let the root stand in some place where it will not
be disturbed. Note any changes which take place in the sugar
and in the condition of the root. By comparative examinations
of the tissues removed and those remaining, ascertain whether
any of the sugar has entered the cells.

Tie a thin, sound piece of parchment paper (or, better still,
parchment) over the mouth of a thistle-funnel, and fill the bulb
of the funnel with a strong solution of common salt. Then sus-
pend the funnel in pure water, so that the level of the water
outside corresponds to that of the brine inside, and keep the ap-
paratus in a warm place, noting any change of level of the liquid
in the funnel tube. Try other substances in the tube; for in-
stance, dilute potassic hydrate, concentrated potassic hydrate,
syrup, and dry powdered gum-arabie.

Carefully examine the upper surface of the leaf of Lilac, Olean-
der, or Echeveria for the presence of stomata, and if none are
found, make the following trial with a good, sound. young leaf,
being careful to see that the plant is well watered. Put a drop
of water on the upper surface of the leaf, and dust upon it
either finely powdered sugar or salt, until the drop has taken
up all it can, and the mass looks nearly dry ; then blow off the
residue, and cover the leaf or plant with a bell-jar. Keep it in
a warm place and water well. Observe in the course of a few
hours, and at frequent intervals during the next four or five days,
any changes which the spot of sugar undergoes. It is a good
plan to prepare several such spots with different substances.

Ul. Prvzircre Precrvrrates. — TrauBr’s ARTIFICIAL CELL.

Dissolve 5 grams of pure potassic ferrocyanide in 100 cubic
centimeters of pure water. Place some of the solution in a test-
tube having a foot, and drop into the tube a small fragment of
moist chloride of copper. Observe the changes which take place
in the shape of the film which instantly forms around the frag-
ment. Try the same experiment with a saturated solution of
potassic ferrocyanide, and afterwards with solutions containing
respectively 1 and 10 per cent of the ferrocyanide.

24 STUDIES IN PHYSIOLOGY.

What effects are produced when a solution of potassic ferro-
cyanide is shaken up with a solution of copper chloride?

The pellicle precipitates can be further examined as directed on
page 226. Calcic chloride and sodic carbonate can be employed
in the examination instead of the substances there mentioned.

IV. Prerrer’'s ARTIFICIAL CELL.

Repeat Pfeffer’s experiments (page 227), with all the precau-
tions there advised.

In every case where a manometer, or pressure-gauge, is to be
used, corrections must be made for temperature and for baro-
metric pressure according to the directions given in such works
as Bunsen’s ‘‘ Gasometry.”

V. ABSORPTION OF WATER.

Moisten one side of a perfectly flat, thin piece of hard wood,
for instance the holly-wood used for sceroll-sawing, and note
any change of form which occurs. What effect is produced by
moistening, in the same way, the other side of the wood?

Fill a strong stone bottle with large dry seeds of known weight,
for instance beans, and put it in a pail of water so that the
water can pass into its mouth. Ifthe bottle should break in a
few hours, remove quickly with blotting-paper all the outside
moisture from the seeds, and determine their increase in weight
due to absorption of water.

Place a thermometer bulh in a tumbler half full of dry starch ;
slowly add to this water of exactly the same temperature, and
note any change of temperature which accompanies the absorp-
tion of the water by the starch.

Weigh a fleshy root, and carefully dry it in a water-bath, to
determine the amount of water which can be expelled at 100° C.
Then raise the temperature of the root to somewhat above
100° C., by carefully heating it in a sand-bath, and observe any
loss of weight. Determine also the amount of water contained
in a fibrous root of Indian corn, a small woody stem, ‘' dry ”
wood, leaves of Indian corn, Begonia, and Sedum, the pulp of
an apple, grains of wheat.

After the above substances have been thoroughly dried and
weighed, immerse them in water for one hour, wipe them as dry
as possible by means of blotting-paper, and weigh again. How
much water can each absorb in one hour? In like manner as-
certain how much they will absorb in ten hours and in twenty-
four hours.

ao

RELATIONS OF THE PLANT TO WATER. 2

VI. Root-ABSORPTION.

Repeat the following experiments by Ohlert : —

Cut off the so-called spongioles, the very tips of the roots of
sound seedlings which have been cultivated for a few days upon
moist sand or sponge (or, better still, with all the roots in water),
and cover the wounds with asphalt-varnish. The wounded end
of the root must be quickly dried with blotting-paper before the
varnish is applied. Then put the roots of the plant again upon
their moist support or in water, and endeavor to answer by care-
ful observation the question: Does or does not the plant absorb
enough water for its needs without the ‘* spongioles”’?

Cultivate seedlings of one or two plants, for instance radish
and wheat, upon (1) rather dry sand; (2) moist sand; (3) wet
sand, or upon blotting-paper of these three degrees of moisture,
and notice if there is any appreciable difference in the number of
root-hairs produced. Cuan the development of the hairs be in-
creased by increasing slightly the temperature of the support?

VII. Roor Pressure.

Cut off squarely the stem of a young dahlia or sunflower well
rooted in a flower-pot of moderate size, and to the stump fasten
immediately a T-tube, with its pressure-gauge as directed on
page 264. Ascertain the pressure shown by the mercurial gauge
at intervals of an hour, and determine also the efect of chang-
ing the temperature of the soil in the flower-pot.

VIII. Srem Pressure.

Apply a pressure-gauge to the cut stem of some woody plant
well established in a flower-pot (for instance, a strong rose), and
ascertain the amount of pressure exerted by the sap.

In the winter time or early spring try the experiments referred
to on pages 264-267.

1X. TransFer oF WATER THROUGH STEMS.

Repeat De Vries’s experiments described on page 263. For
these, stems of sunflower and tobacco answer very well, while
those of heliotrope are not very good. Ascertain the height to
which a color (as anilin red) will rise in the cut stein of a young
woody plant under different conditions of warmth, exposure of
the leaves to light, etc. Repeat the experiment with a strip
ot blotting-paper, described on page 260. Try the foregoing

26 STUDIES IN HISTOLOGY.

with the substitution of a salt of lithium for the dye, and deter-
mine the rate of ascent.

It will be well for the student at this point to review carefuliy
the principal facts regarding the amount of moisture which the
atmosphere can take up at different temperatures. In all trans-
piration experiments he should determine the percentage of
moisture in the atmosphere to which the leaves of the plants
are exposed, and for this purpose the well-known Hygrodeik,
or Hygrophant, may be employed. But if only the simple wet
and dry thermometer bulbs are at hand, the student can find
all necessary data for his calculations in the tables published by
the Smithsonian Institution.

Place in a watch-glass under the microscope water containing
finely powdered ind‘go, and immerse in it the clean-cut surface
of a leafy shoot. Observe in which direction the indigo particles
move.

X. TRANSPIRATION, OR EXHALATION.

Repeat the following experiment devised by Henslow: ‘‘ Take
six or eight of the largest, healthiest leaves you can find, two
tumblers filled to within an inch of the top with water, two
empty dry tumblers, and two pieces of card each large enough
to cover the mouth of the tumbler. In the middle of each card
bore three or four small holes just wide enough to allow the
petiole of a leaf to pass through. Let the petioles hang suffi-
ciently deep in the water when the cards are put upon the tum-
blers containing it. Having arranged matters thus, turn the
empty tumblers upside down, one over each card, so as to cover
the blade of the leaves. Place one pair of tumblers in the sun-
shine, the other pair in a shady place. In five or ten minutes
examine the inverted tumblers.”

Tie a piece of thin rubber-cloth around the flower-pot and
lower part of the stem of any young leafy plant, and weigh the
whole upon a common balance capable of turning with a deci-
gram, under a lead of two or three kilograms. If nothing better
can be procured, one of the best forms of small platform balance
will answer. A thistle-funnel should be tied up with the stem,
so that water can be supplied to the plant as required. Ascer-
tain the amount of transpiration from the foliage of the plant
during twenty-four hours under the following conditions: (1) at
a temperature not falling below 60° F. (about 16° C.); (2) ata
temperature not rising above 40° F. (about 4° C.).

What is the loss of moisture in one hour under direct exposure
to the brightest sunlight? Note temperature and inoisture in the

ASH OF PLANTS. 27

air. What is the effect upon transpiration of placing the flower-
pot in some crushed ice, the temperature of the air remaining
about the same as before?

Determine the minimum, maximum, and optimum temperature
for transpiration of any suitable herbaceous plant, for example,
a Pelargonium (House Geranium).

XI. ExrravasaTion From Lraves.

Cover a young healthy plant of Indian corn or wheat with a
bell-jar, being careful to keep it warm. If, after a little time,
a drop of water should appear at the tip of any of the leaves,
remove it by blotting-paper, and replace the bell-jar. What is
the lowest temperature at which water is thus given off by young
leaves of the above plants?

If a young Caladium is at hand, examine the tip of the leaf
for the jet of water (page 268) which can sometimes be seen.
If the plant is a suitable one, and the jet can be seen at all,
ascertain the lowest temperature at which it is ejected.

XII. IncombBusTiBLeE Matters In THE PLANT.

Burn upon platinum foil (free access of air being permitted),
known weights of the following substances, and weigh the ash
left in each case: (1) oak-wood, (2) pine-wood, (3) a young
leaf of any plant, (4) a much older leaf of the same plant (for
instance raspberry), and (5) some grains of Indian corn.

If no platinum foil is at hand, burn the substance in a hard
glass tube open at both ends and held slightly inclined in the
flame of an alcohol lamp or of a Bunsen burner. If the glass
tube is used instead of platinum foil, weigh the tube and the
substance together before heating, and afterwards weigh tube
and ash together to obtain the difference in weight.

XIII. ExamixatTion oF THE ASH OF PLANTS.

If the student has facilities for conducting qualitative chemical
analyses, he would do well to examine the ash of the following
plants: Sugar-beet, Buckwheat, and Oat.

If he has had sufficient practice in quantitative chemical
analysis to warrant it, an examination of the ash of some one
of the plants which have been spoken of in 664 and 665 would
form a useful exercise. The investigation of the ash of a single
species at different seasons is recommended.

28 STUDIES IN PHYSIOLOGY.

XIV. Warer-Cutrunre.

In the study of water-culture no plants can be more easily
managed than buckwheat and Indian corn. Secure good seed-
lings, and treat them as described in 669. After the plants
have become well established in their new surroundings, use for
the nutrient liquid the following solutions in a fixed order, and
with the precautions laid down on page 249.

1. Well-water, or other drinking-water.

2. Distilled water with potassic nitrate.

3. Hs ue ue ** chloride.

4 ue “ ‘¢ magnesic sulphate.
5 «6 ee ** ealcie chloride.

6. = es ee ** sulphate.

7. tg es ‘* potassie phosphate.
8. Nutrient solution I. (672).
9. ee “« TT. (6738).
10. Distilled water alone.

XV. ASSIMILATION PRoPER.

Chlorophyll and other coloring-matters. Make a solution of
the pigment by placing bruised leaves of grass in strong alcohol
for a few hours, and keeping them from the light. It is well to
prepare at least ten ounces of the strong extract, which can be
used in all the following experiments.

Examine the color of about an ounce of the above extract held
in a small vial. What is its color by transmitted and by re-
flected light? In the latter examination it is better to throw a
strong light from a burning-glass or double convex lens upon the
surface of the liquid. How long will the liquid keep its color in
the strong light?

Treat, as directed in 774, one ounce of the extract which has
not been exposed to light, and place the turbid mixture aside in
a dark place until it becomes clear. What are the colors of the
upper and the lower layer into which it separates?

If a microspectroscope is available, make on paper projections
of the spectra of the following substances: (1) Chlorophyll solu-
tion, (2) the upper iayer of the liquid just mentioned, and (3)
the lower layer of the Lqaid. Examine also the spectrum of a
thin green leaf.

Tf possible, examine the colors of autumnal leaves, and of
alcoholic extracts from colored flowers and colored fruits.

ASSIMILATION. 29

Place a few red sea-weeds in pure water, and Ict them remain
there for ten hours. What is the color of the water by (1) trans-
mitted light? (2) by reflected light? Extract the coloring-matter
of red sea-weeds by means of alcohol, and compare the alcoholic
with the aqueous solution.

What is the color of an alcoholic extract of the bruised tissues
of Monotropa uniflora?

Etivlation. Keep seedlings in a warm, dark place until they
have lost their green color, and then, having removed some of
their leaves for immediate examination, place the plants, with the
remaining leaves attached, in the light. Make alcoholic extracts
of the blanched leaves and of the green ones, comparing them
from all points of view.

Examine pine seedlings grown in complete darkness, and ascer-
tain the nature of the pigment which their green cells contain.

Carbonic acid and assimilation. Compare at the end of two
or three weeks the dry weights of two seedlings grown under the
following conditions: Both the seedlings have furnished to them
exactly the same kind and amount of soil, and are provided with
equal amounts of nutrient solutions at corresponding times;
both are placed under tubulated bell-jars, and have the same
amount of moisture in the atmosphere to which they are exposed.
The seedling in one bell-jar obtains a supply of carbonic acid
gas, since there is an opening in the jar through which the en-
closed air communicates with that outside containing its normal
proportion of carbonic acid. The seedling in the other jar has
no carbonic acid supplied, since a cup which contains potas-
sic hydrate deprives the air already in the jar of all its carbonic
acid, and an open receptacle, filled with pumice-stone satu-
rated with potassic hydrate, removes all carbonic acid from
any air entering the jar. One plant is thus furnished with
enough available carbonic acid, the other is in an atmosphere
wholly free from it.

In a modification of the foregoing experiment, supply a known
quantity of carbonic acid in aqueous solution to the sod of the
second plant, being careful to prevent by means of a cover of
rubber-cloth any escape of the carbonic acid from the soil of the
flower-pot into the air of the jar, and after a few days compare
the weights of the plants as before.

Can a water plant derive its carbonic acid from water contain-
ing a small amount of sodic bicarbonate in solution ?

Add to the normal air contained in a freshly filled bell-jar, in
which a seedling is growing, a known quantity of pure carbonic

30 STUDIES IN PHYSLOLOGY.

acid.’ Later, double and quadruple the quantity added, and
observe the effect produced upon the plant. Experiment with
different species of ferns and club mosses in the same manner.
Observe in another series of experiments the effect of sunlight
in modifying the inflaence of an excess of carbonic acid gas in
the atmosphere.

The measure of assimilative activity is to be found either
in the amount of pure oxygen evolved in assimilation, or in the
amount of carbonic acid decomposed in it.

1. Determinations depending upon the amount of oxygen
evolved: The gas which is given off during assimilation, espe-
cially by water plants, is never absolutely pure oxygen; but
since it contains so small a proportion of other matters under
most circumstances which the student is likely to meet, the
amount of it evolved may be taken safely as the approximute
measure of assimilation. ‘The method of measurement by count-
ing bubbles emitted by water plants in water (see 814) is always
practicable and easy of execution. The evolved g:s can be
easily collected in any convenient inverted receptacle. If the gas
collected and measured is analyzed eudiometrically, as dir2cted
in Bunsen’s ‘‘Gasometry,” the determination leaves utle to be
desired.

2. Determinations depending upon the amount of carbonic
acid decomposed. ‘To the air contained in a glass vessel in-
verted over mercury a known quantity of carbonic acid is added.
The plant previously placed in the receptacle decomposes a part
of this, and after a given time the amount decomposed is ascer-
tained by measurement of the carbonic acid that remains.

Liffects of different gases upon assimilation, A few plants
and two or three small Wardian cases, or, better, capacious bell-
jars, will answer for this study. Select only sound plants for
examination, and be careful to have those in one bell-jar as nearly
as possible of the same size and strength as those in the others.
Let the air in one of the jars be ordinary atmospheric air; to that
in the others add a known but small quantity of one of the fol-
lowing gases ; namely,(1) common coal gas ; (2) sulphurous acid ;
(3) chlorine. Compare the growth and vigor of the plants from
time to time, and observe whether insolation makes any difference
in the appearance of the plants exposed to the gases menticned.

1 In all cases where an additional amount of gas is introduced into 2 bell-
jar, allowance must be made in some way for the possible increase of pressure.
For the necessary correction in these cases, and for other details regarding the
management of gases, consult Bunsen’s ‘‘ Gasometry.”

RESPIRATION, bl

XVI. Resprrarion.

The measure of this process is usually found in the amount
of carbonic acid given off by plants. The methods of deter-
mination of this amount are, although apparently simple. open
to some objections; but by the exercise of great care in the
management of the simple appliances, their results are in gen-
eral trustworthy.

The carbonic acid which is given off by the plant may he
measured in one of the two following ways: (1) A current of
air freed from all its carbonic acid by means of wash-bottles con-
taining potassic hydrate is allowed to pass into a receptacle in
which are confined the plants to be examined. The air with-
drawn from this receptacle passes slowly through Liebig’s potash
bulbs in which are held a known amount of potassic hydrate.
At the conclusion of the observation the amount of carbonic acid
which has been given off by the plants and been taken up by the
potassic hydrate in the bulbs can be accurately determined.
(2) The current of air which is withdrawn from the receptacle
containing the plant is permitted to pass very slowly through a
long slightly inclined tube in which is held a solution of pure
baric hydrate. As the bubbles of gas pass through this liquid
and give up their carbonic acid, they cause an abundant precipi-
tation of baric carbonate in it. The second method, which is
essentially that of Pettenkofer, yields uniform results, and is
in general to be preferred to the first. It is better applicable
to observations upon intramolecular respiration; in which, as
pointed out in 981, some gas like nitrogen or hydrogen, wholly
free from any trace of oxygen, is allowed to come in contact with
plants or parts of plants, and the amount of carbonic acid given
off is determined as in the former case. Interesting results are
obtained by placing in the receptacle very young seedlings, or
buds which have just begun to unfold.

XVII. GrowrH.

The measurement of growth. Growth can be satisfactorily
measured in the three following ways, each of which is adapted
to particular instances : —

1. Direct measurement. Determine the place and rate of
growth of young internodes of any rapidly developing plant, for
instance Morning Glory, by marking the whole space of the
internodes into equal intervals, and subsequently determining

32 STUDIES IN PHYSIOLOGY.

the actual inzrease in distance between any two or more lines.
In all cases mark the part under examination with good India-
ink, making clear, narrow lines. To avoid any possible error
caused by influence of lines marked only on one side, make
lines on both sides of a part whenever possible. To measure
the growth of leaves, use the method spoken of on page 156.

2. Measurement by a micrometer eye-picce. With the tube
of the microscope kept perfectly horizontal, cxamine the position
of a line of India-ink, upon a perianth leaf of Crocus, or upon
the root-cap of Windsor bean. Observe the space which the
image of the line appears to pass through in a given time, and
refer this to the previously determined values of the spaces of
the micrometer.

3. Measurement by an index. (a) On a simple are. For
this use the simple and admirable modification of Sachs’s aux-
anometer, devised by Bessey (American Naturalist).

(0) On a recording drum. A slender brass or steel shaft is
attached to the hour-spindle of a cheap clock, and from the shaft
is suspended firmly a stiff pasteboard drum of about the same
size. This revolves with the spindle, and if well made is
carried without any appreciable vibration. A piece of glazed
paper of the size of the drum is moistened, and a little mucilage
placed on one edge, so that when the paper is rolled around the
drum, its edges can be firmly fastened together. Be careful to
have the seam in the paper so placed as to avoid any catching
of the needle index attached to the plant. When the paper on
the drum is dry, it is smoked lightly and evenly over a smoky
turpentine flame. The ncedle at the tip of the index is now
placed against the smoked paper so as to press lightly upon it,
and, as the drum revolves, leave a clean mark. When a suffi-
ciently long record has been registered, the paper is carefully
removed and dipped in (not brushed with) a solution of common
rosin in alcohol, which upon drying prevents any of the lamp-
black from coming off.

Two corrections are necessary with this simple apparatus :
(1) for the curve of the descending needle at the end of the
radius ; (2) for any changes in the position of the needle caused
by the varying amount of moisture in the air.

For recording temperature, it is possible to use a metallic
thermometer with a long index, and have the two records side
by side. It is well, however, to have the needle for the ther-
mometer give a different mark in order to prevent any subsequent
confusion.

MOVEMENTS OF PLANTS. 33

The proper methods of examining the formation of new cells
in a simple case are indicated in the studies upon a stamen-hair
of Tradescantia noted on page 380.

XVIII. Movements oF PLANTS.

The student is advised to select some one plant in a vigorous
condition and make a thorough examination of all the phenomena
of movement which it presents. The plants named below are
among the best for such an examination, and they can be made
to grow even under rather unfavorable conditions, like those
affurded by schoolrooms.

Spontaneous movements. Desmodium gyrans, the Morning
Glory, or Hop, may be used. The first requires a high tem-
perature and a fair amount of moisture in the air in order to
exhibit its peculiar movements satisfactorily.

Movements following shock. The Sensitive plant (Mimosa
pudica) should be observed. It can be experimented upon with
various kinds of irritants, both mechanical and chemical, at
various temperatures, and under the influence of anesthetics.
For the experiments with anesthetics only very young plants
are suitable, and they cannot well be used afterwards for other
investigations.

In the case of all of the above plants note any changes which
the leaves undergo during the day and at the approach of
night.

The details given in 1045 suffice to indicate the general method
of exaggerating by means of slender glass threads the slow and
slight movements of plants, and do not need further treatment
here. For observations with such threads, the following plants
are very useful: seedlings of the Morning Glory, clover, cress,
cabbage, and sunflower.

XIX. TENSION oF TISSUES.

Make sections of young internodes as directed in 1025, secur-
ing in every case accurate measurements of all the parts, both
before and after their separation. It will be well to examine in
like manner a large number of young roots, stems, leaves, and
parts of flowers, noting in all cases the age of the part examined.

XX. InsEctivorous PLants.

In the study of these plants the student is advised to read
carefully Mr. Darwin’s work on the subject, and verify, by means

34 STUDIES IN PHYSIOLOGY.

of good specimens of Drosera rotundifolia, the facts there re-
corded. Students are reminded that Mr. Darwin’s observations
were made with the simplest appliances, and with a degree of
care never excelled.

For independent study abundant material may be found in the
common Sarracenias of the North and South, in regard to which
very much still remains to be learned.

XXI. Cross-FERTILIZATION.

For this study, repeat the observations of Darwin as they
are given in his work on Cross and Sell Fertilization ; or if that
is not at hand, as they are bricfly stated in the abstract in the
present volume, pages 448-450.

XXII. Hypnripizine.

With the precautions given on page 456 the student should
be able to undertake experiments in hybridizing species of the
following common genera, all of which lend themselves readily
to this process: Nicotiana, Verbascum, Lilium, etc. Be care-
ful to exclude foreign pollen in all cases.

XXIIL Tur Rirexine or Frvirs anp Skreps.

Good material for this study is afforded by the following
plants: Solanum, Impatiens, Pyrus, Prunus, and Tecoma.

XXIV. GERMINATION.

Sclect sound seeds of some common plant, for instance beans
or Indian corn, and test with them the truth of the following
statements: (1) Water is essential to germination. (2) Germi-
nation cannot begin without access of free oxygen. (3) Seeds
of the plants selected require the same temperature for the be-
ginning of germination. (4) When the process of germination
has once hegun, light is necessary to any increase of the plant in
dry substance (compare experiment Series 1, No. II.). (5) Car-
bonic acid is constantly given off during germination. (6) In
some cases carbonic acid will continue to be evolved even when
no more oxygen is supplied (compare intramolecular respira-
tion). (7) The temperature of germinating seeds is higher than
that of the surrounding atmosphere (compare respiration).

What is the optimum amount of water required for the speedy
germination of the following seeds, — Windsor beans, peas,
clover, squash, and sunflower? :

EFFECTS OF FROST. 35

What is the optimum amount of oxygen required ?
What is the optimum temperature required ?
Compare the precocity of unripe and ripe seeds of any plant.

XXV. EFFECTS OF FROST.

Wrap up a leaf of Begonia in thin rubber-cloth, to protect it
from moisture, and place it in a freezing mixture of powdered
ice and salt. After an hour examine the tissues of the leaf with
special reference to any mechanical injury which they may have
sustained. Having completed this preliminary study, proceed
to the examination of any well-developed seedlings, and note in
every case (1) the effect produced upon the parts which have
been quickly thawed; (2) the effect where thawing has been
allowed to go on very slowly.

Freeze any strong seedlings and after a time thaw them
slowly. Place them then under favorable conditions for growth,
in order to ascertain whether their vitality has been destroyed.
In cases where death of the part or plant ensues, does it appear
to come from the freezing or from the thawing?

36 TABLE OF MEASURES.

MEasurzes or LENGTH.

Inches.
. Meter. . ae . F a ar 89.87079
Millimeter . . . . . . 0.08937

Micro-millimeter (,) the unit of microscopic measurement . 0.000039

Measures OF Capacity.

Pints. Cubic Inches.

Liter. . eo we ee 4 ~ % 1.761 . 61.02705

Cubic centimeter or milliter . . » « » 0176 . « 006108
Measure or WEIGHT. .

Grains,

Gram. . sae G2 ote «a ae tip SO ee . 15.48285

Measures OF TEMPERATURE.

Cenhigrade, Fahrenheit. Réamur. Sen tetsae > | Fahrenheit Réamur.
° ° ° ° ce) oO
+100 4212 +80 416 4608 | +128
90 194 72 15 59 12
80 176 64 14 57.2 Wa
70 158 56 13 55.4 10.4
60 140 48 12 53.6 96.
50 122 40. 11 i 51.8 8.8
49 1202 39.2 10 | 50 8
48 118.4 38.4 9 48.2 7.2
AT 116.6 37.6 8 46.4 6.4
46 114.8 36.8 7 44.6 5.6
45 113 36 6 42.8 48
44 T12 35.2 5 Al 4
43 } 109.4 34.4 4 39.2 8.2
42 107.6 33.6 3} 87.4 24
41 105.8 32.8 2 35.6 1.6
40 104 32 +1 +83.8 +0.8
89 102.2 31.2 0 +32 0
388 100.4 80.4 —1 +380.2 —0.8
37 98.6 29.6 2 28.4 1.6
36 96.8 28.8 3 26.6 2.4
35 95 28 4 24.8 3.2
34 93.2 27.2 5 23 4
33 91.4 26.4 6 21.2 4.8
82 89.6 25.6 7 19.4 5.6
31 87.8 24.8 8 17.6 6.4
30 86 24 9 15.8 7.2
29 84.2 23.2 10 14 8
28 82.4 22.4 11 12.2 8.8
27 80.6 21.6 12 10.4 9.6
26 78.8 20.8 13 86 10.4
25 ie 20 14 6.8 11.2
24 75.2 19.2 15 5. 12
23 73.4 18.4 16 8.2 12.8
22 71.6 17.6. 17 14 13.6
21 69.8 16.8 18 —0.4 14.4
20 68 16 19 22 15.2
19 66.2 15.2 20 4 16
18 64.4 14.4 30 Ze 24
17 62.6 13.6 —40 —40 —32