THE ANALYSIS OF CHARACTERS IN CORN
AND THEIR BEHAVIOR IN TRANSMISSION

>
W. B. GERNERT

THE ANALYSIS OF CHARACTERS IN CORN
AND THEIR BEHAVIOR IN TRANSMISSION

BY

WALTER BYRON GERNERT

Champaign. Illinois
1912

Submitted (May 15, 1911) in partial fulfillment of the requirements for the degree of
Doctor of Philosophy in Agronomy, in the Graduate School of the University
of Illinois.

Published by the Author

IN EXCHANGE

Univ. of [mois -
sUL 22 1012

INDEX
Page
TINO) UGA ONG pe re ep fa eievorae sett ineratcheielstvate carcccraaatase creer Me recht che, hecteate 5
WEAR TATTON AND) SEE CRON? seteyetsteet-rcte sttote eis oletorsice cialeiovern erento tee ehare eects —
ENVIRON MENIAL SNPDUIEN CES loam setrata sien saiciner sete cisere aerate cisiciee oaiare, Seiten re 6
ABN ORIMUAT [RTE S pues sewn ereisterceetctorces che ec foe Grane Srthersese oral oes iavar late oer oesloke areas ta —
WViTGORM ORM GROWDED sep caceryay cerebral eRe oie Tracer Tete cats Sheu ahimeshatiustetalorayeleleratelaneceleve 7
TENIBRIEE DION Ghee en Serpents ee PR Taian Ate Natya My Ray ove ne a ar En the es Sicud 8
FA MBREDIZ ADT ONE AND alVUEND hy SUMAN pew mrteteleyaataiae sieve ele tease ecektinitee creicrsiele 9
WiSHRUE. | CORRELATION Siva sercrercrattcleiarccesevl ora arere salaieisiel tase atectiove Gvaiaos olereicaroree II
INUNTZADE (Cad) Distt B oe reais Giaipecncy eee ering: OCA a Cae CER RoC IAI Rater oe een ae _
eft CGE TUINVIM (Gorges sere vate tects ayes ee sie cre Levey ter chev ere ere Pe Sole vagus eosy aT aVGIS ooeica ovale Caray eS ralavocs aittyenads I2
INEGORDING# pec ictee eto eT is ererernee ae ieee Piststa tele (hs heperetececsfs ow Teteieveksrsie rs —
IPL EDI CY ENON Ben Okla s Htotin Goro SOE ota MOO Ren eM CeCe nee nas —
SIVERINULNOL OG Wp ayer vst c tyepaeseetes evn aystersisce eats cle eicsepe ie fasae a roevereiel oy stoke ote tucteavore #8 ataiere 14
BPEANT (CHARACTERS *..... 2. SPean eo Uso Aa SO TOROS aires Oneho OOOO 16
(GERIMATINVAT TO Nigircteerarerevevere se ater eyerooraperevautin areola ofe ahs Sie oaereyRrere Oelevos ewes WEIS eons --
IP WANIELE DS MCE ASCIE SERRA Payee ort Serie de ress Ae Uo tae yca ey clovicva elsecte ee aise Meteo 18
MATER TONES (MMs ACM svar ce seis ova ctevst cosa tre raves a ah cv eseh cue tes (at ovate ol ss atator eran earere ee
SIGS a3 cides Gatos S aa AES BD One POET REE ORES CES en eee ree 21
TLIO arco he cea rcu Ce ao HE ORR RE ERS ORTON LE SR UES PeECEST OE EC ee ca 2 23
ECA PARRAN GEMIEINGD) ereavertcre cinvaisienterarusiols sfaccre ches ars FADO a OOM eRe OCT _
ERAS ERA Deere stoner poet iretetans esas cis: cravat ieoaionc iohahsoteoreterar oe ewe SAIS AISLE 24
EARNS SUR Bee ay crs Aecr eters: ova anal) custsrays cers Suciehntas scaldvere. Sea ane amie ia, aeiarerhoe’ 25
DD) ISHAG MACE STSMAIN GEN tops ts i sarcioss archers cic col sfaueea olekn crave tenets diejez enti aiavaresavaecnenchscate —
ATR IM CE OL OR Masten totale ease ora chsh otab ce casei Lesa tsises la/aie sccsia asia Mane //es a )syeyesieisiaieieie 25
GTO tines epee ae ert pete v ete eet Sepa TeTonone Me savage estar ace nshah sen Husterevels Slapenake _
JRYSta TAR I hoy SOME Se bas es rere CCAR a DED IES A Peas ee arte ete cs —
ID ge se1PACGl,? Ae Bg Sele Se en ale ee On orate come re ata 5 aos 27
WarieratediHoliage: cemeninecaeelcr Bo ae Aerie senaay sR tne seengeena —
PAURES GON GR a yet crece tert ohe eee Tene ay SEa ol ener oa alain Fievehe hone Seepevaraaverdveyeenee 2S
Cpe ac ate tecere eer hone ena hoo cana: seahasaes ev ataie asst ss a: Beals She cre epabcieties aie ayaa te ashes =
lSGavrerstneWojaied Si x misiomie cn oto oud ho Ran Geen Hike are ae ici oN Hoon ere ents 29
NIN FERN ODES HMR wer ycct a crerer ae seonhie cite cbesetetere roc STokeh owl evovensFonsy stare ieva tas fers ceases 32
PNERTIAT CR OOUScapacr yar rtcuehsarctese reee yon tarere 6 cdereranalie ares sotonob wists payetene ein etene sara! ak let 34
IRORTODYOR AGRO WEBEL merece eee seats eee occ cpete tee, can) acetarem Saianeres titrerensccieyCapspeests —
TINTEWORES GEN Gans ororiertte ier Wate ter starr tel ok eotiop cy ence eieVare ales oevus aie shayauahede varias eerie BF
APIS) SlEIS POR as Sh tee ches rue es BGs ENG es SN OTR EERE EOC ON Ne Cae RRR eg 38
SLAG HTELEA USN Cho caer OO. OKRA Ole GhOkS) Orc Moco MOI nineteen —
(Chal Wave Res GS aise 6 do tic o Oa ao LORCA OCI Sis Orit Cae ee eter net 39
Mia ewarnl O wien semper rcciee ts rear site, cusnie te coer atee te voice mnisheer eu —
JATIN th Go 8dd.0 HO eon UDC Ee ORS Toa Coe DOC OE aoe nn Reece 49
STP 1a soon S Cus neath DUOC SS ULEAD COURS OG) ToDo ce act —
Golan jeesicsroeiane aeievecenrals RENT pawalesus ohoalletatarele ssa ar eifevotahscomsicheae —
SGP ivereowone occa codacuo pneuon donee Gund SGonencn coer 41
Pollen parece srccrry yr harceioen proteleittrersrenh ofsisysecrecetare avai Sr ecgat aerate bene
Wila DILLVaNet inane tiatbiiacrrititerniiancatelasisierrehenieressi viele syarctscue edd

Shc Koley tc aa erate ne, SMe ME Merctistn HEA e cuinatiGodo moo acb oo 45
Barrenness. css ty tiehe- cs ats sods shot nas eat eT LR et eR RE Ee 46

FUUISKS cc es tenets afstecepare lores betes idle eee inte oicTe E Sie ee e Ped ees’ 17/

Teaminade sc stecs sccterertctaa tosis the aieate nities pen ion ar een eee 490

SI oer morarbe an an are oa ee CAH 3 AAO cacao Dobedermtn oes 50

Position of Uppet Shoot) .cmmescsso seer ieee eee 51

Number of “SHOOtS 2% aosf osc oo) cro oto econ oieiaisiclneeitee etersioie etctemine reac 52

RIE PRRENIGES yiccrreetnc atcresvavsies a7 Goths role patole sie (ole oI SETS MOC RTO ee ceo 56

INTRODUCTION.

The work, of which this paper is a partial report, has in reality been a
search for characters in the corn plant; how many and what are they; how do
they behave in transmission? In the general plan of the investigation, it was
decided to begin with the germinating seed and continue through the life history
of the plant, going as far as time and facilities would permit.* The plan followed
was to study characters wherever they might be found, rather than to make a
group study of varieties or strains as a whole. The topics used as headings in
the report of the investigation are not necessarily characters of last analysis, but
may represent more or less complex bundles of genetic units.

To a very large extent, investigators in hybridization, before Mendel’s law
was applied, saw their material in generalities. Mendel’s far-sightedness in com-
paring individual characters only and not plants as a whole, together with his
careful watch upon the behavior of these individual characters through several
generations of the progeny, enabled him to secure the facts which led to the
discovery of this great law, overwhelming in its importance, which bears his
name, Following its rediscovery in 1900, methods in the study of heredity have
been revolutionized. Thus the era of mass selection in corn breeding is also
rapidly passing and the practice is to be superseded by more rational methods.

Some general principles of heredity, which have a direct bearing on the
subject in hand, will be considered briefly before entering into the discussion of
the characters themselves.

VARIATION AND SELECTION.

In a wind-pollenated plant like corn, we must expect great diversity unless the
parents have been inbred for a number of generations. In ordinary seed corn,
then, we have the opposite to what Johannsen has called a “pure line”. “A pure line
may be defined as the descendants from one single homozygotic organism, exclu-
sively propogating by self-fertilization. ‘Pure line’ is merely a genealogical term,
indicating nothing as to the qualities of the individuals in question. A ‘line’
ceases to be pure when hybridization (or even intercrossing) disturbs the continuity
of self-fertilization.’’46)

We cannot conceive of variation being a haphazard phenomenon, but rather
that it is governed by definite laws. In such a study as this, the question naturally
arises as to the methods and causes of variations observed and the possibility of
controlling them. Anything gained in this direction, adds to our knowledge of
what we are dealing with in the selection of variations already existing.

Since we have a mixed ancestry in corn, there is much significance in the
suggestion,—that, in general, gains secured in selection in corn are not fluctuations
inherited, but rather the products from a mixture of types long existing and which
selection partially segregates.

Considerable confusion exists in literature in regard to the word “selection”.
It is improbable that any thoughtful writer claims that the act of selection itself—of
either mutations or fluctuations—produces any genetic change in an organism, since

*The tabulation of the plant characters consumed so much time that the writer was unable,
in the time allotted, to compile and report the data secured on the ear and kernel characters.

In order to save expense in publishing, the original thesis has also been considerably abbre-
viated by the removal of the voluminous tabular matter and the discussion relating to it. This
paper, therefore, contains only a general discussion of some of the plant or “vegetative”? char-
acters studied in the investigation, of which this is only a partial report,

5

the differences, which we see expressed in the soma or body, existed before the
selection was made, otherwise there would be nothing to select. The question to
be decided finally is not; whether “selection” produces anything new; but, are
small variations (so-called “continuous fluctuations”) inherited? Are small varia-
tions due to differences in environment and food only? May they not be of
greater significance in total differentiation than a limited number of mutations
(“discontinuous fluctuations”) in the evolution of a race? Selection is the tool,
not the cause.

One writer has the following to say about selection: “Within pure lines,
if no mutations or other disturbances have been at work, or within a population in
which there is no genotypical difference, selection will have no hereditary influence.”
This must be granted at once, since the clause “mutation or other disturbances”
excludes everything else. Neither is there anything left to work on if we allow
the term “small mutations”, which is used by some writers to explain the results
gained by the use of fluctuations, granting that fluctuations are cumulative.

ENVIRONMENTAL INFLUENCES,

It has long been known that corn is very responsive to environment and in
order to get normal development, which the farmer calls “best results”, the seed
should come from the region in which the crop is grown. Tests at the various
experiment stations have substantiated this principle. In investigations, such as
the present one, it is evident that environmental influences must be carefully
considered in the interpretation of results and especially upon corn which has not
come from “home grown” seed.

A number of varieties used in my study were imported from other states,
Mexico, and Central America. The behavior of these varieties including widely
different habits of growth, enabled me to compare adaptations to the environment
here in Illinois. Some of the varieties produced few or no viable seeds, because
of the short season to which they were poorly adapted. In some cases, pollen
only was secured and this was applied to silks of earlier maturing varieties. It
may be that this is the most successful way (hybridization) in which desirable
characters of varieties requiring a long growing season may be introduced into a
region having a short season. Collins 18) reported that first generation hybrids
are relatively free from the new place effects.

ABNORMALITIES.

Many abnormalities were found in this work, some of which are of particular
interest and which will be mentioned in connection with the characters to which
they are related. Blaringhem 9) described several new races which came from
mutilated plants of an eight-rowed yellow flint variety. He reports obtaining a
constant hermaphrodite form, another with white grains, and other differences in
plant structure. He states that abnormalities were much more constant in the
progeny of the mutilated plants than when found in plants not mutilated. Why
this should be, he does not explain, except in the cases that were close—or self—
fertilized. Sturtevant 80) mentioned a number of similar obnormalities, some being
secured by mutilation, but of which none were reproduced in one trial with open
pollenated seed. We have found all the abnormalities mentioned by Blaringhem
and Sturtevant, and many others during the two seasons in which our work was
in progress, and none of them, so far as known, were due to mechanical mutilations.
It is possible that the white strain which Blaringhem secured, may be the result
of segregation from the yellow variety as Shull has secured a yellow strain from
a mixed white variety by self-breeding. The corn plant undoubtedly furnishes a
rich field for inyestigation in the above mentioned class of study.

6

VIGOR OF GROWTH. ;

In varieties that are thoroughly acclimated, the question of vigor is an important
factor, and one which may obscure the development of certain characters in both
pure and hybrid plants. One of the objects of the study was to get additional
information upon this much discussed topic. Vigor in corn has been investigated
from two standpoints; wide-bred, and inbred populations.

The question was perhaps first studied from the wide-bred standpoint by
W. J. Beal 6), who concluded as follows: “To improve or infuse new vigor
into varieties—plant near each other and mix them—good results of such crossing
will last for several years, though most apparent the first year.” Other experiment
stations were asked to take part in this investigation, but the reports were generally
indefinite. Beal’s own results with yield tests were very satisfactory, as is shown
by the following proportionate yields which he obtained:

“From Crossed Seed.” “Seed Not Crossed.”
TOPS e sone stteiosie ne on ase 109.67 100
ESO Mieke esco.t vchosetera ctor ts toner are One 121 100

So far as known, Beal’s method of securing hybrid seed is the first reported
instance in which detasseling was put to any extensive use. This method was
used later by Burrill, Sturtevant, and others, and was finally adopted as a practical
method to prevent inbreeding.

Results by McCluer and Morrow and Gardner a decade later confirmed the
work of Professor Beal. McCluer 57) found that “The corn grown from the
crossed seed was in nearly all cases clearly increased in size [ears larger than those
of either parent] as a result of crossing—nearly all the corn grown a second year
from the crosses is smaller than that grown the first year, though most of it is
yet larger than the average size of the parent varieties.” Morrow and Gardner 62)
noted that “In every instance the yield from the cross is greater than the average
from the parent varieties; the average increase per acre from the five crosses being
9.5 bushels.”* But this conclusion does not give the most important part of the
results as may be seen by a rearrangement of their data.

Yields in bushels of air dry corn per acre:

Increase over Increase over

Parent Average of Yield of average of higher-yield-

No. yields. parents. Hybrid. of parents. ing parent.
lig Jaeoyl IBC, saoodosse 62.9 64.1 1.2 —.1
Zi Waaoy baal Cr Cle Bene ey nae lee 730 1.4 —6.1
3, UD OEIBAOsy lesterol ane 60.3 86.2 16.9 12.6
A, Jago) IDERUOscooons6 os 67.1 76.2 9.1 2.6
Gy JAxovbe (GRR een So abee 61.3 78.5 17:2 14.3
AWVETa cesar i 66.5 75.6 9.2 5.0

Evidently nothing would be gained by making such hybrids as No’s 1 and 2:
while such hybrids as No’s 3 and 5 would be very profitable because the yields
were, in each case, much higher than that of either parent. What might have
been secured from other combinations of these same parents could be told only
by trial. Some of the other possible combinations might have given greater yields
then either of those tried, since there is evidence that some of the hybrids were
more favorable combinations than others. Reports of a later, similiar test by the
same authors 63) show somewhat less gains from hybridization than in the first
report. The system of checking field results, used by these early workers, was
imperfect and consequently the yields reported are not absolutely reliable.

Hartley 42) states that “in some instances, cross bred seed produces less than
the average of the strains crossed.” Collins 16) found similiar cases and recom-
mends that “we should lose no time in securing information regarding the amount

*(More exactly 9.2 bushels).

of difference that should exist between the strains crossed to secure the maximum
increase of vigor—self-fertilization of corn inevitably leads to sterility.”

Shull has investigated the question of vigor in connection with self-bred
strains of corn, originating from the same field mixture, somewhat upon the plan
of “Mr. Q. I. Simpson in breeding hogs by the combination of two strains which
are only at the highest quality in their first generation, thus making it necessary
to go back each year to the original combination, instead of selecting from among
the hybrid offspring the stock for continued breeding.” Shull’s results with
hybrids of self-bred strains were similiar to those of Beal, McCluer, and Morrow
and Gardner upon hybrids of open pollenated strains, and with which it seems ‘he
was not familiar at the time of writing his first two papers on this subject, although
in his first paper 72) Shull refers the reader to an article on inbreeding by Shamel
in which McCluer’s work is mentioned and Morrow and Gardner's experiments
are discussed at some length.

Discussing the cause of increased vigor in hybrids, Shull 75) suggests in a
recent paper; “the degree of vigor is correlated with the number of characters in
respect to which the hybrids are heterozygous—heterozygosis in some elements may
be without effect upon vigor, or even depressing. The presence of unpaired genes
or the presence of unlike or unequal paired genes, was assumed [A. B. A. 1908] to
produce the greater functional activity upon which larger size and greater efficiency
depend—East suggests that this stimulation due to hybridity may be analogous to
that of ionizetion—A. B. Bruce proposed that the degree of vigor depends upon
the number of dominant elements present rather than upon the number of heterozy-
gous elements.”

Since the above propositions are nothing more than theories as yet, other
explanations might be considered. Thus, vigor (increased or decreased) might
be due to:

(a)—New size-producing factors introduced by hybridazation.

(b)—A new combination of latent size-controlling factors.

(c)—The readjustment necessary in changing from a more or less pure to a
complex heterozygous condition which expands or contracts size-pro-
ducing parts, being therefore a purely mechanical phenomenon similar to
the change in form and bull in many chemical reactions.

In any of these explanations, segregation would have the usual scattering effect
upon size in the second hybrid generation.

Again, the theories as held at present in regard to increased vigor may be
the reverse of the real truth, and instead of a plant developing above the normal,
it may be that by means of favorable combinations the plant is only enabled to
develop more or less to its full capacity. A special stimulus may be required
to bring out what is perhaps only a small part of the possibilities within its makeup.

INBREEDING.

There seems to be a question lingering in the minds of many as to whether
very much self-pollenization takes place in corn. As evidence upon this point, the
following observation may be mentioned: An ear having a large percent of sweet
(wrinkled) kernels was found growing in a field of dent corn. The seed planted
was purchased, for pure Reid’s Yellow Dent seed. The most probable explanation
is: that a grain of pollen from a white sweet corn was blown or carried to the
parent “Reid” ear, fertilizing one of its ovules, and because of the two recessive
characters—white and wrinkled—possessed by the pollen, the stray kernel was not
noticed in the seed since its external appearance was probably much the same as
that of the other kernels planted.

It is evident that the ear developing on this hybrid plant was very largely
self-pollenated, since the lower three-fourths of the ear exhibited very fair di-hybrid
Mendelian proportions in regard to color and composition of the endosperm. That

8

there may have been a difference in the blooming period of this plant and that of
the others surrounding it is recognized, but the upper part of the ear had nearly
all smooth kernels due to the effect of dent pollen only, which very probably had
come from the surrounding plants after its own tassel no longer furnished pollen.

Ears borne on isolated corn plants are generally reported to have very few
kernels 71). In the season of 1910 three isolated corn plants were found growing
far apart in a cemetery and each more or less surrounded by trees which served
as a wind-break. These plants probably grew from scattered grains in the manure
applied to the flower beds. A goodly number of kernels developed on each of
these ears, many more than had been expected from earlier observation on
isolated plants growing in gardens.

Although these plants were sheltered somewhat, the same conditions frequently
exist in an ordinary field of corn, and on a day when there is not much wind
a very large amount of self-fertilization must take place. We have frequently
obtained perfectly filled, selfed ears by one application of pollen in hand-pollenating
work. Such observations prove conclusively the desirability of detasseling corn
plants from which seed is to be obtained for general field planting.

Collins 17) has suggested that—*The production of more than one ear on each
stalk—would to some extent, correct the tendency to self-pollination, for in prac-
tically all cases, the second ear must be cross-pollinated. In regions where high
winds prevail at the time of flowering, the percentage of self-fertilized grains
would be further reduced.” This conclusion was made in connection with a
variety in which the anthers made their appearance considerably in advance of
the silks. Lazenby 52), however, in what were apparently quite conclusive observa-
tions, stated, that “almost without exception the silk appears earlier in comparison
with the maturity of the anthers, when there is more than one ear on a stalk.”

In our own notes taken daily in 1909, we learned that in some of the varieties
producing more than one ear on a plant, the silks on the second and lower shoots
appeared very soon after, and in some cases, preceded those on the upper shoot
(bagging the upper shoot and leaving the second one exposed frequently favored
this apparently abnormal behavior). In general, however, the tendency to mix-
pollenate is greatly increased on the lower shoots. This may be the principal
reason why séed from nubbins, which often represent ears delayed in development,
may produce as good or a better crop the next season than seed produced on large,
well developed ears which are more likely to be partially self-pollenated.

In 1g05 Shamel 71) reported some observations upon the effect of self-fertiliza-
tion in corn; “it was found that in four generations of continuous self-fertilization,
the vitality had become so weakened that the seed failed to germinate.” That
Shamel used a strain with an inherent weakness, or that there was some fault in
his test, seems to be shown by the results which Shull has been securing on corn
selfbred for a number of years. Shull 74) concludes that “the decrease in size and
vigor, which accompanies self-fertilization is greatest in the first generation, and
becomes less and less in each succeeding generation until a condition is reached
in which there is (presumably) no more loss of vigor.”

Experiments by East 26) corroborate the conclusions of Shull. East asserts
that in a number of families inbred two to four generations; “In all characters
of stalks, leaves, roots, male infloresence, and mature seed, the plants were normal.
It is merely in the matter of size of plant and ear, and thereby yield, that the plant
compares unfavorably with cross-bred plants. Further, there is no continuous
decline in yield.”

HYBRIDIZATION AND MENDEL’S LAW.

It is essential that the student of heredity have an accurate knowledge of the
method of reproduction of the organism in which he is interested. There is no

9

better way to gain this information than through hybridization, and the final test of
a character is to hybridize it. In our study, the work was planned so that certain
characters might meet many others in the various hybrid combinations, and that
their behavior upon close—and self—breeding might also be determined.

Because of the mass of Mendelian literature, in which the general principles
of behavior in combination and segregation have been reviewed again and again,
there is no need of their discussion at this place. Since Mendel’s Law was redis-
covered in connection with a corn hybrid and because of other earlier work upon
corn, which has a close relation to this topic, it is worth while to mention some
incidents which are of especial significance.

The history of events leading to the rediscovery of Mendel’s Law is of
absorbing interest and will always stand as a classic example of what patient,
thorough search and careful consideration of a vast array of facts and theories
accumulated from the work of others may accomplish in throwing light upon a

problem in research.

In a bibliography attached to a paper on “Cross-Breeding and Hybridizing”
written in 1892, L. H. Bailey included the reference,—(1865 Mendel, G. Versuche
uber Pflanzen-Hybriden. Brunn Verhandl iv.-3.47.)

Professor Bailey had taken this reference from Focke’s book “Die Pflanzenmisch-

linge” published in 1881, but had not, himself, seen the paper.
The following is the account in DeVries’ own words in a letter to Bailey :—

“Many years ago you had the kindness to send me your arficle on Cross-Breeding
and Hybridization of 1892; and I hope it will interest you to know that it was
by means of your bibliography therein that I learnt some years afterwards of the
existence of Mendel’s papers, which now are coming to so high credit. Without
your aid, I fear I should not have found them at all.”

DeVries had already produced hybrids of sweet and starchy corn in studying
the phenomenon of double fertilization in corn. He carried these hybrids through
the second generation allowing them to pollenate naturally and reported what we
now call “Mendelian segregation” without at first appreciating the significance of
it; “Tous ces epis [twenty-five] etaient de nature mixte. Environ un quart des
graines etaient sucress, les trois autres quarts etaient amylacess” 81). This was
at the time that DeVries was making a thorough search of literature on evolution
in preparation for his ‘““Mutations-theorie”’, 2 work containing a wealth of references
which the author used to such good advantage in establishing this theory. The
discovery of the significance of Mendel’s paper and its announcement occurred
in the year following (1900).

In looking through the available literature upon corn hybridization, other
similiar cases are to be found in which Mendelian proportions were approximated,
but not being analyzed with due care were consequently disregarded. Ten years,
previous to DeVries’ publication, Kellerman and Swingle 48) noted some results
as follows: “The ear consists of about one-fourth sweet corn and the remaining
kernels are more or less dented at the summit’—“in the large proportion (prob-
ably 34) of yellow’—"“probably seven-eighths of the kernels were flint” and
in a later publication 49)—"“By actual count, there were 370 kernels on the: ear.
Of these 206 were blue, 71 pink, 71 orange and yellow, and 22 pure white.”
Although they did not realize the meaning of these behaviors, they had recorded
very fair Mendelian results. It will be noticed that the last quotation contains
a very good di-hybrid ratio in which the theoretical expectation would have been
approximately 213 :71:71 :24.

Quoting from McCluer 57); “The self-fertilized ears [of a hybrid] showed
the same modification of kernels as those naturally fertilized, proving that each
kernel of the crossed corn had in itself the power to produce both sweet and
dent corn—the progeny had tended strongly to run back to the parent forms, while
at the same time taking on other forms different from either.”

19

In this way the ear of corn had provided most desirable material for the
deduction of a general law of inheritance, but was awaiting the insight of a second
Gregor Mendel to be made use of. Corn did finally serve for the first corroboration
of Mendel’s Law in connection with the first announcement of its rediscovery in
1900 by Hugo DeVries.

USEFUL CORRELATIONS.

The Ohio, Nebraska, and Maine Experiment Stations have been making yield
tests in selections of certain ear characteristics and have reported but slight
differences in results. Davenport, Rietz, and Smith have made use of the statistical
method in the study of correlation of characteristics of the ear in a mixed popula-
tion, and find indications of considerable correlation in some instances. Ewing 31)
has recently investigated the correlation of weight of grain with characteristics
before or at the beginning of the blooming period, and concluded that aside from
the genetic coupling of unit characters, the correlation in the fluctuating variability
of two different characteristics is not likely to prove of much assistance to the
breeder.

The perfection which Nilsson and his co-workers in Sweden have attained
in utilizing character of plant detail in agricultural species has proven highly
profitable for economic purposes and has also served as a fruitful source of
knowledge in the theory of heredity. Aside from the general use of certain
features, such as wrinkled endosperm for table use, large size of plant with relative
large amount of ear corn for ensilage purposes, and other similar cases, not a
great many distinguishing characters have been made use of in connection with
selection for desirable features in corn. The mechanical method used by Hopkins
and others in selecting for differences in protein and oil content in the corn
kernel is an example of this kind.

It would be desirable to know in a similiar way the possible relations between
certain characters which we are beginning to recognize in corn and to have a rather
comprehensive list of such characters or genetic units with complete information
upon the behavior of each, in order that we may realize more fully the possibilities
in the most important American crop. It was with no small degree of satisfaction
that this study of the corn plant was undertaken with the knowledge that much
that might be learned would be of immediate economic value.

MAIZE GROUPS.

We will perhaps never have positive evidence as to the exact origin of the six
generally accepted groups of corn, five of which are distinguished by their
endosperm characters. We know that the Indians were cultivating all of them
when America was discovered and we can only speculate as to their source.
Quoting from Sturtevant 80); “It seems almost certain that in the order of evolu-
tion (excluding from consideration the puzzling sweet-corn group) progress has
been from the pops, through the flints and the dents to the softs.” East 25) has
suggested that sweet corn “may have come about through mutation in each of
these groups [dent and flint], but from what we know of the early sweet corns,
it is more likely that the change took place among the flint types and was extended
by hybridization.”

It seems, however, that there is a much more probable source of sweet corn
than the one suggested by East. It is well known that there is perhaps no variety
of sweet corn grown that is entirely free from soft starch, aside from the very
considerable amount of corneous starch which is always found in all mature sweet
corn kernels. There are also varieties of sweet corn which have a semi-starchy
endosperm, and Halsted 37) has found that the proportion of starchy endosperm

II

may be increased by selection in hybrid sweet corn where one of the parents
possessed a semi-starchy endosperm. Sturtevant classified samples of such semi-
starchy corn received from the Zuni Indians under the name of “amyleasaccharata”.
As East has also mentioned; many of our varieties of sweet corn have been pro-
duced by the selection of segregates from hybrids of sweet with flint, dent, and pop-
corn and this has resulted in wide differences in kernel shapes, ear and stalk
characters.

East’s conclusions were based largely on results secured in sweet corn hybrids
with flint and dent corns, the new combinations suggesting flint or dent origin,
depending on the variety of sweet corn used in the hybrid. In our own observa-
tions in 1910, we find that it is possible to get results similiar to those secured by
East when we use soft corns to hybridize with the various sweet varieties. Soft
corns are quite sweet at the roasting ear stage, and were used by the early settlers
for eating from the cob and are still so used to a large extent. The first sweet
corn varieties secured from the Indians bore short, eight to twelve rowed ears
with broad shallow kernels; these are common characters in soft or “flour” corns,
to which considerable evidence points as the source of our sweet or “sugar” corn.

TECHNIC:

In this study, the arrangement and groups recognized by Sturtevant in his
bulletin on ‘Varieties of Corn” 80) were taken arbitrarily for the purpose of
classifying and numbering the varieties used.

RECORDING.

A method of numbering somewhat on the plan of the Dewey library system
was employed. The six groups were given numbers 100 to 600 and varieties within
the groups designated by units. We illustrate the system as follows:—White Pearl
Pop was the tenth variety in the list of pop corns (200) and it was given the
number “210”. It happened that this variety was planted on row 13 in 1900, so in
that season the stake and labels on this row bore the field number 210.13. A plant
in this row was pollenated by a dent variety grown on row 33, the name and number
of which was “Fairview Speckled Dent-404”. The hybrid note would then read
(210.13-2 404.33-14) and it would also include a description of the work done.
The figures following the dash (—2 and —14) indicate the particular plants used
on the two rows in making this hybrid.

When the above hybrid was planted in 1010, all of the figures except those
indicating the groups 200 and 400 were dropped and as this particular hybrid was
splanted in row No. 162 in roro, its field label for that season bore the number
24.162. This was as simple for daily use as the index of the first season and gave
all the information necessary for field work. Its previous history could readily
be found in the record book of the year before. A reciprocal (404.33-14 > 210.39-20)
of this hybrid was grown on row No. 238 in 1910, consequently its label bore the
number 42.238, indicating dentXpop and grown on row 238.

In 1909 the blooming notes were taken daily and for each individual plant, but
in 1910 these notes and also those pertaining to the husks were taken every four
days, and only for the row as a whole. The observations on size characters and
number of parts on the plant were made a short while before maturity, and the
observations on the ears were all taken in the field at harvesting time, the study
of kernel characters being left for the laboratory. In general, such characters
were chosen which could be recorded readily. Many interesting and desirable
features were neglected entirely for lack of time.

POLLEN ATING,

Some methods of technic were developed during the experience of the two
seasons, a knowledge of which would have been of much value in the beginning.

12

As some of these may be of use to others contemplating similiar work, brief
mention will be made of a few of them.

The record books should always provide room for special or general notes
upon an individual or row in addition to the regular scheme. The labels used
for marking plants should be such as will not be destroyed by wind and rain.
Cloth, wood, or metal labels with a wire tie are indispensable.

In a locality where storms are apt to occur when the corn is in bloom, tough
parchment paper bags are necessary to protect the shoots, but ordinary manila
bags will serve to collect pollen. Parchment paper is desirable because of its
semi-transparency, which allows observations on the color and especially on the
development of the silk without removing the bag. This is very convenient at
pollenating time. The most satisfactory and expeditious method of bagging shoots
was that of bending down or preferably breaking off the leaf blade in the sheath
of which the shoot to be pollenated is developing. The inverted bag with one
side between the shoot and the culm is then pulled down over the shoot with a
sawing motion till there is room to fasten the bag to the leaf sheath, or to the
shoot about which it is folded, with an ordinary brass pin. A flexible wire may
be used to split the leaf sheath in case the bag is not strong enough to accomplish
this with ease. The bagging of shoots must be done, of course, before there is
any indication of a silk and the bag should be left on ten to fifteen days after
the silk has been pollenated. In a moist climate these shoot bags should be
removed when all danger of contamination is past, since the developing ears tend to
become moulded when the bags are left on.

The bags for collecting pollen were put on early in the morning of the day
in which the pollen was to be used, preferably before the pollen begins to fall,
because there is here a possibility of collecting stray pollen grains which have lodged
on the tassel from surrounding plants. In a dry period, this may be quite effectively
guarded against by bagging the tassel on the day preceding, as, in the majority of
cases, corn pollen is no longer viable in from 24 to 36 hours after it has been
shed. For this reason best results are obtained in pollenating work when pollen
is used within a few hours or during the same day on which it has been gathered.

The inverted pollen bag is readily fastened about the base of the tassel by
means of a spring clothes-pin, which is a very handy article in general plant-
breeding work. The bag is fastened in such a manner that one side is lower
than the opening, thus providing a pocket in which the pollen may lodge instead
of sifting out through the crevices at the mouth of the bag. In this way sufficient
pollen may be secured at one time from one tassel to pollenate a number
of shoots. The pollen may be used at any time of the day and in all kinds of
weather, so long as the pollen and silks are kept reasonably dry. Studies made
on the behavior of pollen and silks will be discussed in connection with the in-
florescence.

In case the silk came in contact with the hands or apparatus in the process of
pollenating it was carefully clipped. with scissors. In general and except for
special study, all the silks were clipped at a short distance above the shoot as the
bag was being removed from it. When a shoot is young it may be clipped below
the tip and opened, thus exposing a larger number of silks. Clipping of silks was
done not only for ease in operation, but also to insure thorough application of the
pollen; clipping also prevents heating of the mass after the pollen has been applied.
When long and tangled silks are pollenated barren patches on the cob are fre-
quent because of the pollen failing to reach the silks on the inner or lower side
and sometimes due to the heating mentioned. The pollen is poured directly from
the bag and thus the silk and the pollen are never touched by the hands, except
by accident. There is therefore no need of washing the hands in alcohol after each

13

pollenation, as some workers recommend. The scissors used in clipping, and the
hands of the operator as well, may be cleaned with the silks which are cut away.

Some workers expose the shoots while pollenating them; others use an umbrella
with or without a side curtain for protection from falling pollen, the umbrella
having an extra covering to make it pollen proof; for extensive work, this re-
quires an extra man to hold the apparatus and is, at best, not very satisfactory.
During the first season, a pollenating apparatus was used which was cylindrical in
shape, mounted on a pedestal, covered with oilcloth, and large enough to admit
the operator. A slit was made in the curtain to admit the lower part of the
plant including the bagged shoot. On warm days, continuous work in this cloth
cage was very trying and a new apparatus was constructed for use in the
second season.

The new apparatus consisted of an inverted box of very light wood, which
had been carefully seasoned to prevent checking, all the joins being sealed with
glue. A short curtain was attached about the base to exclude falling pollen. The
box was large enough to provide room for the manipulation of the pollen and silk,
all but the arms of the operator being on the outside. The side of the curtain,
inserted between the shoot and the culm, was provided with a metal shield having
a narrow “A” shaped opening and sewed into the heavy duck curtain. In the box
and just above this opening was inserted a pane of glass to provide light. Glass
panes were also placed in the side opposite and in the top of the box. In this
way the operator is enabled to view his work from a number of directions, accord-
ing to the height of the shoot. The box was readily adjustable to any height
on an upright rod mounted on a “T” base with recurved sharp points to anchor it
in the soil and to allow it to be readily removed. These points were long enough
to permit straddling the ridge usually thrown up along the corn row in cultivation.

In order to secure pollen from an early blooming variety to use on a late
blooming variety, it was necessary to make several plantings. It was found, how-
ever, that the late plantings matured much more quickly, relatively, than the earlier
planted rows. It was frequently necessary to use the last tassels to mature on the
early varieties and these were found on poorly developed plants or on suckers.
This practice introduces difficulties in the interpretation of the results. We may
have thus selected genetic differences in sucker devlopment, but otherwise the
use of pollen from suckers would not be expected (of itself) to seriously affect
results. Hartley 41) states that progeny from ears fertilized with pollen from
suckers were as productive as plants from ears fertilized with pollen from the
main culm. In general, only one application of pollen to each shoot was made.
The practice of pollenating the same shoot several times is not only time consuming,
but also allows more opportunities for mixture by stray pollen grains.

East 27) has experienced difficulty in getting certain varieties to hybridize and
has concluded that there are some varieties which will not combine with others.
Similar experiences have been reported by early investigators. Collins 18) and
Emmerson 29) have later secured successful hybrids with strains similar to those
used by East. In my own work, wherever I was sure of the viability of both
pollen and silk, I have found no difficulty in securing hybrids between varieties
differing widely in regard to size, period of growth, and many other characteristics.

TERMINOLOGY,

Confusion exists in literature regarding the meaning of the words “hybrid”,
“cross”, and “inbred”. At present the terms “hybrid” and “cross” are used inter-
changeably, some writers using both words in the same sentence in referring to
the same individuals. While these superfluities of the language are permitted;
they are confusing, especially to the uninitiated. In this work some distinction was
necessary and the terms will be used throughout the report as defined below:

14

Substantive. Infinitive. Definition.
a hybrid to hybrid to interpollenate individuals of distinct varieties or
species (so called).

a cross to cross to interpollenate individuals of strains or “lines” of the
same variety.

a close to close to interpollenate individuals springing from the same
flower or mother plant.

a self to self to pollenate with pollen from the same flower—or other
flower—on the same plant.

a mix to mix to pollenate with pollen from either an unknown or hetro-

genous source (this applies to individuals pollenated
naturally in mixed populations).

The above terms are in common use and the distinction here made is no
radical departure. Although the ardent supporters of the “genotype” ideals might
maintain that there is no difference between hybrids and crosses, some distinction
should be made between a sweet cornXrice pop hybrid, as an instance, and a cross
between strains of slight differentiation coming from a well established variety
like Reid’s Yellow Dent or Boon County White corn. The general term “wide
bred” will be applied to hybrids and crosses; the general term “inbred”, which
has been confused in a number of papers with “selfbred”, will be applied to closes
and selfs.

The sign “XX” is to be interpreted as it is commonly used; meaning, ‘“‘pollenated
with”, when inserted between two variety names or numbers. The sign “&” will
be used in the tables to indicate hybrids which have reciprocals. The expressions
F (or Fy), Fi, F., Fs, ete., are being used in papers dealing with Mendelian segrega-
tion, the letter “F” being an abbreviation of the word “filial”. In discussions con-
cerning the progeny, the words “hybrid generation” are used and not “filial genera-
tion”. In reports on segregation, it is not unusual to find the expletives “Fi hybrid
generation”, “F, generation of the cross”, etc. in dealing with hybrids only.

By those who begin the use of the “F” expression and by those who are at
present employing it, a new term may not be desired, and at this late date a change
may be somewhat confusing; but in themselves the expressions , Xi, Xa:
Xs, ete, would be intelligible almost without explanation, since the sign “>” is in
common use in discussions concerning reproduction. Because we have need of
the letter “F’’ in a number of cases to designate characters in discussing segreates
and parents in corn, the above suggested expressions will be used in this report.
The term “generation” will always be used in referring to the seed produced
by the parent plant. When that seed has germinated, the plant developing from it
will be designated “>, generation”, its seed and the plants resulting therefrom as
“S<» generation”, the succeeding generations as “:”, etc. By the word “seed”,
in this instance, we refer to the germ and endosperm only and not to the seed
coat which is tissue identical with that of the generation preceding the new seed
We will apply the expression ‘“”, ete.* to the progeny of hybrids, crosses, closes,
and selfs; and whenever it becomes necessary to discuss two or more of these
classes of reproduction simultaneously or in review, it will also be necessary to
include the name of the class to which reference is being made.

*Since this paper was submitted for publication the writer has learned that Lotsy (Biol.
Centralblatt 25:97-117) has employed the expressions ‘‘x-generation’” and ‘2x-generation” as
substitutes for *‘F,’’ and “‘Fs’’. It seems, however, that the expressions “ SEXas serXo ake
more appropriate since they suggest only relative or subsequent generations rather than giving
the idea of increasing complexity or hybridization only, as Lotsy’s ‘‘2x—” and ‘3x—” terms
would imply.

15

PLANT CHARACTERS

Those who are familiar with variation in corn will appreciate the handicap
under which this work was started, with no inbred strains, and many of the
varieties imported. These difficulties are especially perplexing in the plant char-
acters to which very little attention has been paid in the developing of new varieties
and strains. From an economic standpoint, the significance of plant or “stalk”
characters was not recognized until quite recently. This fact accounts to a large
extent, for the individual variation in plant characters. Differences are often as
great within 2 variety as between distinct varieties whose classification is based
largely upon kernel and ear characters.

GERMINATION

A number of influences within the corn kernel affect germination and the
early growth of the seedling. Some individual ears and also yarieties exhibit a
much more vigorous germination than others. It has been observed that some of
the high yielding varieties frequently germinate poorly and this has been asso-
ciated with the old mistaken idea, prevalent among animal breeders at one time,
that improved strains showed the often observed loss of “vitality” as a direct con-
sequence of the “improvement”. We know now, that vitality was lost in some
of these cases by selecting the wrong segregates. It is also evident that many
economically desirable characteristics in plants and animals are in a sense degenera-
tion, in that they are not favorable to the perpetuation of the species except by the
intervention of man. It is well known that single-eared and high-yielding varieties
tend to have deep, closely packed kernels and mature late. Such ears do not dry
out well, are apt to ferment and mould, and therefore germinate poorly or not at all.

It has been noticed that starchy kernels are apt to germinate more quickly than
hard, flinty kernels of the same variety. In germination, the scutellum or coty-
ledon (the organ in which enzyme secretion takes place) uses the soft-starch portion
of the endosperm first and the horny portions, if there are any, are used more
slowly. A soft-starchy endosperm thus furnishes the more available food and
should favor a more rapid development of the germ. In order to test this theory
a number of &: kernels from hybrids of flint, soft, and sweet corn were germinated
in flats of soil in the laboratory. In this way two and, in some cases, three of the
above types of kernels could be obtained from the same hybrid ear. All the
kernels were planted at exactly the same depth by means of a wood pin having a
collar to permit uniform planting through a heavy wire screen placed on the surface
of the soil. This method insured accuracy in spacing as well as in depth of planting.

In the majority of cases, grown in the laboratory, the starchy kernels slightly
preceded the flinty kernels in germination, but the difference was not especially
noticeable and the resulting seedlings were quite similar in height and vigor. The
most noticeable difference was between either starchy or flint. as compared to
sweet kernels which contain very little soft starch. Plumules from the wrinkled
kernels first appeared above the soil at from 10 to 24 hours later than those from
either the starchy or the flint kernels, and the germination of the entire lot of sweet
kernels was extended over a much longer period of time.

The delayed and often lower percentage of germination of the wrinkled kernels
may be associated with the fact that wrinkled kernels mature later than starchy
and flinty kernels on the same heterozygate ear. This is very noticeable in the
field just before the corn ripens; at this time the kernels which become wrinkled
later are larger and much softer than the others on the same ear. This has been
noticed also by Halsted of the New Jersey Experiment Station 37). Still another
explanation must be considered. Segregation in rapidity of growth factors may

16

have taken place in these *: kernels borne on x; cobs and there may or may not be
an association of this behavior with a character in the endosperm.

Walls 84) selected kernels with large and small germs, finding that “the
heaviest grains do not necessarily have the best germinating qualities—The germ-
inating properties of the kernels containing different sizes of germs may be equal.”

Correns 19) stated that he observed no change in rapidity of germination of
the < hybrid seeds. In our own work, however, we noticed that in general, the
x hybrid seeds gave a more rapid germination than the parents. In a number of
cases, these hybrid plantlets were more vigorous and maintained a larger size
throughout the season. For lack of time we were unable to get exact field data on
germination in 1910, but during the last winter several sets of observations were
made in the laboratory in connection with other tests on the influence of the
endosperm on early growth and on which the above conclusions were based.

Indications were found that popcorn pollenated with other groups germinated
better than other groups pollenated with popcorn, while popcorn alone gave in
some cases a better germination than the other groups. In corroboration we may
cite Sturtevant and others who have reported that popcorn has a better viability
than the other groups. This may be due largely to the adaptation in kernel shape,
composition of seed coat and endosperm of the pop group.

The specific density is not always a safe guide to the viability of a corn
kernel, as was shown in a case of a partially constricted ear.

Less than a fifth of this ear was normally developed at its base, the remainder
being abruptly smaller as if the whole ear had been developed and pollenated
normally and then the nourishment cut off very suddenly from the upper four-
fifths. It was at first thought useless to plant any of the small shrunken kernels
in the field, but 1t was decided to give them a trial. Thirty hills were planted with
the large kernels and twenty hills with the small shrunken kernels. To our sur-
prise, every kernel grew and the viability of other kernels from the same ear
remained nearly as good a year later as shown by a germination test. The small
kernels germinated more slowly end there was a marked difference in the size
of the young plants, this difference diminishing Somewhat as the plants grew
older. The average comparative sizes of 100 kernels from each of the two parts
of the ear near the division line were:

Av. Wt. of I Av. Vol. of I Av. specific density
kernel (gms. ). kernel (cc.). of 1 kernel.
Wane IWernels® t-te tin. ye 0.321 0.250 1.25
Sill ISN. gaasoondadne O.112 0.101 ie ttit

The following data represents the empirical modes of 29 plants grown from
the large kernels and 19 plants grown from the small kernels:

2 a
v er n :
ol = a ay —
s OF a io) an n
a tea ae ro) 5 . : a
Pay Eliy yisand) Si MEL aioe all antatan licen as s
CM SI Sh Svat Fe ie | Meir = oo
SoS a COM say a Gel Belen ERS Ae
HOGS eae eee ee ae 22
OU CMOe CE ROL ro eh Sea Se
ey AS ua Zpeies Oe Oa
Marcelernels....... 110 16 9 2— I 8— 6.5 123
Small Kernels....... 100 15 o— I I 8— 6.0— 127

The data just given will serve two purposes :—To illustrate that the hereditary
make-up of the small kernels, which was probably the same as that of the larger
ones, enabled the plants by the end of the season to catch up with the plants
from the large kernels in three out of nine more or less fluctuating characters. On
the other hand the data serve to point out the effect of what are perhaps only

17

physiological or somatic difference in the kernels. These differences apparent in
the kernel and in the plantlet stage are not entirely overcome but have their
effect throughout the life history of the plants in which the genetic make-up was
probably identical.

The permanent root systems of Germineae develop from the stem and at or
near the surface of the soil. Thus, no matter at what depth a kernel of corn is
planted—if the depth is not excessive—the epicotyl lengthens until the node at the
base of the coleoptile is near the surface in dry soil, or at the surface in wet soil,
before the secondary roots develop. The kernel itself remains hypogeal. After
these secondary roots have become established, the primary root is of little or no

value to the plant.

In germination, other temporary roots develop from the placenta of the germ.
In our observations, we have found these to vary from o to 8 in number, some of
them arising from between the epicotyl and scutellum, the remainder from the
outside. In tests with from zo to 30 seedlings, from each of 67 individual hand-
pollenated ears in various varieties, we found differences in modal numbers of from
o to 4 of these rootlets. The counts were made on young plantlets from seeds,
which had been in soil two weeks.

That these roots play a vital part in the young plantlet stage cannot be ques-
tioned, as they often take the place of the primary root which may become
diseased, cut off by insects, or fail to develop. What relation they bear, 1f any,
to the mature plants or how they behave on hybridization has not been determined.
Numerous, small, temporary roots may also develop on the epicotyl (below the

first node.)
PLANTLETS:

It is always of great practical importance in plant breeding to be able to
recognize in the seedling stage of a plant what its adult characteristics will be
DeVries 82, 83) has made much of this point and cites a large number of instances
in which characters in the seedling are correlated with characters which become
apparent later in the mature plant. The extended use which Luther Burbank and
other plant breeders have made of seedling characters in eliminating undesirables is.
well known.

It was hoped that a number of distinct characters might be found in seedling
corn plants and from the limited studies made it is apparent that quite a large
list of such characters exists. Among the varieties red tinge stems develop soon
after germination. This character is correlated with red tinge on the mature
plant in some varieties. These are constant when homozygous, and dominant to.
pure green stems.*

Dark green leaves are distinct from light green leaves and the »;: hybrid
plantlets show dark green. Very narrow and very broad leafed seedlings are con-
stant when homozygous. Certain dents and flints show very broad, blunt seedling
leaves, while rice pops illustrate best the narrow pointed grass-like form. Broad
leaves appeared in the %. hybrid seedlings between the types. Plantlets from
closed and selfed ears in one strain showed marked differences in lezf-shape.

Large size of parts is dominant to small size in X, plantlets as well as being
an indication of increased vigor. A number of plantlet abnormalities were found
but their genetic relation has not been learned.

ALBINISM.

Albinism, partial or complete, occurs in many species of plants and animals
and, although its cause has not been determined, its behavior has been quite well

*We will designate characters as dominant when they are epistatic to another in the x
generation. The ratio or “type” of segregation for the “plant’’ characters is, of course, not
determined at the time at which this paper is written.

18

studied in a number of cases. Miss Newbegin 64) found a diminished capacity
for assimilation in plant albinos and thus the phenomenon might be expiained as a
degeneration. That it is not a consequence of the artificial conditions of cultiva-
tion is shown by the fact that many cases have been observed in nature. DeVries 83)
recites a number of examples arising as seedlings and bud variations from green
or colered ancestors to which they are more or less recessive, aud generally
inconstant in themselves.

Cuenot 21) found albinism to be a recessive character in mice. I’arabee 32}
gave an account of negro albinism which indicates this character being recessive
in man. Castle and Allen 13) report a similiar behavior in rabbits and gtimea
pigs and state that “complete albinism, without a recorded exception, behaves as a
recessive character in heredity.” Others have investigated various degrees of
albinism and so far as known, with one possible exception in axolotl, reported ty
Haecker, the statement by Castle is true of albinism in its pure state. The behavior
of white pigment, which seems to be complicated, is not to be regarded as albinism.

Bateson 3) describes results of his own and other investigators in which the
hybrids from two sweet pea parents with white flowers have all been colored in
the 1 generation, the X: splitting into the dihybrid (9:7) ratio. This behavior
is explained as due to the meeting of a complementary character from each parent,
producing no color when separated.

Corn in which albinism exists in the pure state cannot live beyond the plantlet
stage (3 to 4 leaves) since the young plants cannot elaborate plant food because
of the absence of chlorophyll. Bauer 5) reports a similiar behavior in pure albino
seedlings arising from white margined aid partial albinos in geranium.

Albinos are not uncommon in corn, but so far as known there are only three
published reports of actual counts in which close-bred or hand-pollenated seed
was used. The first case was that found by Hastead 35) in the X: generation of
Black Mexican and Egyptian sweet corn parents. No white plantlets were found

in the germination tests of the parents. By various treatments he found
that the proportion of albinos could not be affected. It was also found that both
ears from the same stalk, with one exception, produced albinos, and that the char-
acter was therefore “within the plant”.

The important test made by Halsted was that in which “inbred” (probably self-
bred) and “wide bred” (probably hybrid) seed was used from the strain in which
the number of albinos was pronounced. His counts were as follows (ratios com-
puted from Halsted’s data) :

Selfed (?) Per cent.
corn. Albinos. Green. Ratio. albinos.

[Braye INIOWiIs rerccsarerarsrerauae ous crn ai cieee 13 47 I 33.6 21.7

Ear No. 2 15 38 1:2.5 28.3

Beaty NiO sarQiserer wercncatteis lee cicusnstetorens 7 48 1 :7.0 14.6

Hybrid (?) Per cent.
corn. Albinos. Green. Ratio. albinos.

IDE VerIN or tigate occa CO OS (0) 60

BanuNigsc2 ects ccm cetioadotins o 65

IDEVE NNO hee seat ape 0 crest eg Onno fe) 65

This was soon after the rediscovery of Mendel’s Law and Dr. Halsted was
probably not studying his hybrids in sweet corn with regard to Mendelian segrega-
tion at that time. Although he has been making use of this all important law in his
hybridizing work since, we have not found that he has corrected his conclusions
upon this phenomenon, namely,—that close fertilization was probably the cause of
albinism.

19

It is plainly evident that he secured on the first two ears, with only 60 and 53
kernels germinated, very nearly the simple Mendelian ratio with the percent of
albinos 21.7 and 28.3, rspectively, and an average for the two of 24.8 per cent.
The distribution of albinos on the third “inbred” ear must have been very uneven
from the charatcer of the results obtained and should be discarded. When it is
included, we yet have the very satisfactory average of 26.3 per cent. albinos in
133 kernels from three ears. On the opposite page in Dr. Halsted’s report may be
found an interesting photograph of these three lots of plantlets by the side of the
three lots of “widebred” (hybrid?) green plantlets. This photograph not only
shows the dominance of green to albino but also, shows very strikingly, the increase
in vigor in the hybrids, a phenomenon which has since become so important in the
development of the theory of corn breeding.

Blaringhem 9) noted an instance of five albinos in 37 plantlets from a mutilated
parent of flint corn which was probably close pollenated. He also reported finding
the albinos from year to year in his various cultures. Collins’ 18) found nine
albinos.in 48 plantlets of a hand-pollenated ear (close-bred) of dent corn, while
the hybrid of this with another variety produced green plantlets only. Evidently
neither of these cases were studied with any thought of Mendelian segregation, and
the counts reported are very limited but all point to the conclusion that they were
dealing with a simple Mendelian ratio.

Dr. Smith has observed during the last few seasons an increasing proportion of
albino plantlets in the “low ear strain’ of yellow dent corn grown at the Illinois
Experiment Station and in the season of 1910, two ears were secured from this
strain for use in this experiment upon inheritance. The two ears came from
parents which showed a large per cent. of albinos in 1909. A number of plants
grown from these ears were selfbred and closebred as well as hybridized with
other varieties including some with variegated or striped foliage.

As a preliminary test, 100 or more kernels from ears obtained in 1910 were
planted in flats of soil in the laboratory, to selfed, four closed, and six hybrid ears
were used. Only green plantlets were produced from four of the selfs, three of
the closes, and six, or all of the hybrids. From the remaining six selfs and one
close, the following proportions of green and albino plantlets were obtained :

Fig. 1.—Albinism in young corn plantlets. One of the rows in the germinating
box which gave exact 3:1 ratios of greens and albinos.
20

SEGREGATION OF GREEN AND ALBINO PLAN#LETS.
Per cent. Number of

Greens. Albinos. Ratio of albinos plantlets.
2M OOOGS EB orayene Talore wie as 104 27 3-9:1 2I 131
BABS OSES SE, Serciels el sycteheiei< ois 7 20 PAPI 28 105
MEMOS OS 8 a. nee ae ene 82 20 4.031 20 102
AZASSODGS wists yarscelansleis oe%s-3, 5 72 16 4.5:1 18 88
ABUESOSR Sm ar -taiciere as sisters 61 15 4.0 :1 20 7
ABAISOS Srciaycis te cieieierelarns 76 23 3.311 2 99
BALOOXIES 5. Seri ety vie ars 75 29 2.671 28 104
MO tal ee aera. a asst 540 DSO sav 3c) cave 705

These cases, averaging 100 kernels from, each ear, show conclusively that
albinism in corn is a simple Mendelian recessive. The character is especially inter-
esting from the theoretical as well as the economic side. It is brought to view in
the homozygous state only, and in this condition is disastrous to its perpetuation;
therefore the only way it can be transmitted is in the heterozygote. It is appar-
ently due to the absence of the factor which in the green plants produces the
chlorophyl.

What appears to be an intermediate stage of albinism was found on an ear
which was selfed and produced 20 yellowish greens and no albinos in 100 plantlets.
The first test of this ear with only 64 seedlings gave 16 yellowish greens or 23.9
per cent., which is near the theoretical proportion. The final test of 3 plantlets
gave only four yellowish green individuals, and this poor distribution caused the
total proportion of 4:1, or 20 per cent. yellowish greens to fall short of the
theoretical, although it is evident that “yellowish green” is also a true recessive.
These two characters, albinism and the yellowish green, which may be an inter-
mediate form of albinism may be added to our list of those characters appearing in
the plantlet stage.

SUCKERS.

The idea prevails generally that the ancestor of corn was a much branched
grass. Harshberger 38) suggested that—‘the original form in the wild state was
propegated probably by lateral offshocts—The habit of suckering, annual in the
north, was probably perrenial in a more southern latitude, so that in the semi-
tropics the non-sexual development of suckers was the ordinary method of pro-
pagation, the vigor of the stock being rejuvinated by an occasional distribution of
seed by birds.” Under favorable conditions most of the commonly grown varieties

produce suckers.

The tendency to sucker or tiller is decreased as a variety characteristic in the
corns developing stout stalks, and those varieties growing to extreme height pro-
duce few or no suckers under ordinary conditions. There seems also to be a
decrease in number of suckers in those varieties which produce very large ears or
cobs. This variation in number of suckers is so noticeable that there is appar-
ently a direct correlation with the aboye mentioned characters but modified by
thickness of planting and other environmental influences. Dense planting, un-
fertile soil, low humidity, and excessive heat, all have a direct limiting effect on
the development of suckers, while inbreeding and consequent decrease in vigor
also tend to check their development.

Occasionally an individual plant is found, apparently constant otherwise, that
stands out from among its fellows in the production of suckers or other vegetative
growth and this is frequently attributed to reversion. Collins 15) has published an

21

account of apogamy in corn in the form of plant like branches developing from
pistillate flowers in the tassel and producing short aerial roots while attached to
their place or origin. These branches, when removed and placed in soil, produced
roots over a foot in length and growth continued in an apparently normal manner
for nearly two months.

Suckers may begin to develop on corn when the seedlings are less than a foot
in heigth. Later, in certain varieties and especially under adverse conditions, some
or all of these young suckers may wither and die. Those suckers that start at or
beneath the surface of the soil and live through the season, develop strong, inde-
pendent root systems and frequently become separated from the main stalk due to
the expansion in growth and rupture or death of the connecting strand.

In a test concerning the value of suckers in dent corn, the Nebraska Experi-
ment Station 56) reported an average loss in two consecutive seasons of 17 bushels
per acre when the suckers were removed. Similar results were reported later 61)
by the same station. They found that “Removing tillers has had a tendency also
to increase the number of two-eared stalks and decrease the number of barren
plants, although this benefit has not apparently been enough to counteract loss of
ears ordinarily produced by tillers.” In these results it was evident that the
production of suckers was an adjustment on the part of the plant to existing con-
ditions, the suckers’ developing when there was room and nutrition, disappearing
when there was not. The best yielding rows always had a good percentage of
ear-bearing suckers. Card 12), of the Rhode Island station, selected plants with
the largest total number of ears in a variety of sweet corn and found that this
was associated with the production of a large number of suckers.

It is doubtful whether suckers ever have much value to the main culm since
they at first receive nourishment from it and, later, after they have developed their
own root system, feed in the same soil mass, thus robbing the main part of the
plant continually. Lyon 55) and Hartley 41) report wide variation in the produc-
tion of suckers in dent corn, also that it is hereditary and can be controlled by
proper selection and breeding.*

During the two years in which they were under observation, several of the
strains and their hybrids produced no suckers; But, perhaps, every variety known
will produce some suckers under certain conditions. All degrees from non-suckering
to profuse suckering were found.

In the hybrid (1) the minus-fluctuations (diminished sucker production) ap-
peared to be dominant to the plus fluctuations (profuse suckering). An absolutely
non-suckering behavior would be expected to be dominant to a suckering behavior.
Suckering depends very largely on environment and vigor.

Comparing these X: results with published accounts of tillering and branching
in other plant hybrids, we find that Keyser 50) reports a wheat hybrid in which
the stooling was more abundant than with either parent. Bateson et al 3) states
that the much-branched, erect habit of the “Bush” Sweet Pea is evidently recessive
to the unbranched form. Shull 73) found a branched sunflower to be dominant

*Ninety-nine varieties and strains, representing the six species-groups, were used in the
experimental work in preparation for this thesis. The greater proportion of these strains of
corn used were found to be complex mixtures and in the second year many divisions were
made of the list as it was used at the beginning of the work.

The arrays of varieties in the parents and their hybrids, as well as the empirical modes
and summaries of the arrays, were tabulated in order to gain a definite idea of the constancy
of the character in question as well as the nature and limits of fluctuation if any variation was

found. Two generations of the parents and only one generation of the hybrids, selfs, and closes
(X11) were grown.

In the tabulation of data no aberrant individuals or populations were discarded at any
time for lack of conformity to the bulk of the array or table. Selections were made for a wide
range in combinations of characters. The hybrids, selfs, and closes, all came from carefully
controlled, hand-pollenated seed produced in 1909.

This tabular matter and discussion of it have been omitted in this paper and will be
substituted by brief general statements concerning the results.

22

to the unbranched. Balls 2) includes “branching base” in his list of dominant char-
acters in the cotton plant. Saunders (cit. Bateson 3) gave the branched form of
stocks as dominant to an unbranched type. While Keyser’s case in wheat is the
only one directly comparable to tillering in corn, there was no total absence of
tillers and perhaps no genetic difference in the parents with respect to this character,
and the increased stooling in the hybrid may have been due merely to increased
vigor. It might also have been due largely to the conditions under which the
hybrid was grown.

LEAVES:

During the growing season many noticeable differences in leaf characters are
to be found, such as; the arrangement, shape, texture, color, pubescence, vienation,
and sheath characters. The misroscope would no doubt aid in identifying many
others in addition to those mentioned.

A corn plant may give a general impression of “leafiness” from several causes—
alone or combined. A broad or long leaf may give it this characteristic appearance ;
but it is more often due to a relatively large number of leaf nodes on a short
stem, which is equivalent to very short internodes. Suckers would naturally tend
to give it the same appearance. Since number of leaves is determined by the
number of nodes or internodes, except in rare cases where there are two or more
leaves at the same node, its behavior will be identical with “number of internodes”,
to be discussed later.

LEAF ARRANGEMENT.

Perhaps the most noticeable differences in aspect of the leaves are found soon
after blooming time when they are nearly developed, but still fresh and succulent.
Zea mays exhibits the characteristic alternative, two-ranked leaf arrangement of
the Gramineae. Twisting occurs in the upper and more slender parts of the stem,
so that frequently the leaves above the ear are not in line with the lower ones
nor exactly on opposite sides of the stem near the tassel. In a number of cases the
leaves near the tassel are all warped to one side of the stem.

It is not uncommon to find plants having two or more leaves at the first and
second nodes below the tassel. These abnormal leaves are narrow and diminished
in size, giving the appearance of division rather than of addition of parts. Blar-
inghem 9) has noted a shortening or telescoping of internodes below the tassel on
poorly developed adventitious suckers produced by traumatism. Evidently these
abnormal growths represented efforts on the part of the mutliated plant to per-
petuate the species, which resulted in a contorted stem with a tufted arrangement

of leaves.

In the plants observed here in Illinois in the two seasons, only one of tu<
cases of prolification was associated with a deformity of the plant itself and in t
instance the two nodes immediately above the soil each bore a pair of leaves. Al-
though this plant had only one less internode than the empirical mode of the row,
it attained but little over one-half the modal height. This, and most of the cases
of pairing of leaves on the first or second node below the tassel, occurred upon XX:
hybrids. Three cases were observed on corn that had been selfbred for a number
of generations, one of these plants producing three leaves at the first node below
the tassel. The plants observed were generally of average height and number of
internodes, more frequently above than below the average. These cases, therefore,
cannot be explained as being due to telescoping nor to fusion of two nodes, but are
simple cases of prolification or merism, the cause of which is unknown.

During the season of 1910, a plant of rice popcorn was found having several
suckers, all normal but one which had paired opposite leaves at every node; thirteen

23

pairs in all. There was a shoot in each of the axils of these paired leaves at the
eighth, ninth, tenth, and eleventh internodes above the soil. It is not expected that
such abnormalities are inherited. :

Stray individuals having very erect leaves occur in a number of varieties.
The erect leaf accompanied by a one-sided arrangement about the tassel is notice-
able in corn which fails to develop fully. The one-sided position of leaves near
the tassel is frequently associated with very short internodes in that region. During
the season of 1910, a one-sided arrangement of husks was found to be frequent
on mature corn in general field culture and it is possible that such cases of orienta-
tion of leaves are due to warping.

Collins 18) in a paper concerning hybrids between a “Chinese corn’ and other
varieties, reports that the erect monosticious blades seemed dominant in the 1
generation hybrids at first, but later in the season the character was not so marked.
Second year plants from the original seed did not have this character so strongly
developed.

Mr. Collins kindly furnished some of the original seed for a test here at the
Illinois Station, where it was grown in 1910, and a large number of the plants
behaved as described in Mr. Collins’ original paper. It was noticed that the leaves
on the plants grown here in Illinois were inclined to be thick and rigid. It is
possible that after it has become acclimated, this variety will still retain an erect
position of leaves somewhat above the average, as other varieties possessing rigid
leaves with heavy mid ribs tend to do. Blaringhem 9) in his paper on traumatism,
figures the tassel and upper leaves of what he considered to be the normal type of
a yellow flint variety, which exhibited this erect position of upper leaves at
blooming time.

A violent storm on August 23rd, 1910, ruined the entire field for observations
on leaf arrangement. On many of the plants, which had not been broken off, only
the midribs of the leayes remained. The difference in position of these midribs
when stripped of the leaf blades was very noticeable. In general, 1 hybrids
have larger, broader leaves, consequently a heavier leaf load than the smaller of
the parents; but the rigid thickened blade and midrib is also, apparently, 2 dominant
character and tends to give the leaves an erect appearance.

Some varieties have very much smaller leaf blades near the tassel than
those lower on the stem, thus giving an open, sparse effect; other varieties have
relatively large and broad leaves near the tassel frequently accompanied by shortened
internodes. This latter condition gives a dense, crowded effect and although long
internodes are apparently dominant, large leaves are also dominant and various Xi
hybrids exhibit this leafy appearance about the tassel.

LEAF SHAPE.

Perhaps no two leaves on a single plant of any species are alike in outline.
Usually on the corn plant there is a gradual increase in length and leaf area till
the upper ear-bearing node is reached, and then a rapid decrease in leaf dimension
occurs until the upper leaf at the tassel-bearing node is reached. In some varieties
the upper leaf is often but a mere bract, while in others this leaf is quite broad,
‘but much shortened in comparison to the leaves at the middle of the stem.

Very long leaves and very broad leaves are prominent characters of some
varieties and strains. Hartley 39) found a broad leafed plant of dent corn in 1900
which he selfed, and in 1901 the progeny was very noticeable because of their
broad leaves, many being six inches in width. Seed from this row planted in
1902 produced plants which exhibited the same character. Collins 18) reports
a hybrid in which the leaf blades were slightly shorter but much broader than
those of either parent.

General notes only were taken in leaf shape in this study. Varieties with
characteristics of different dimension in length and width were found. Several
hybrid rows, the product of parents one of which had long leaves, were noted as
having very long leaves. A number of hybrids with a broad leafed dent variety
also bore broad leaves. Largeness, including both dimensions, is dominant to the
mediocre or small leaf. Leaf blades with a broad base are apparently dominant
to those with a narrow base.

Abnormal leaf shapes were frequently found. Many of the hybrids as well as
the parents produced cleft and distorted blades. Cleft leaves were found more
often on suckers than on the main clum. Blaringhem reported tubular and cleft
leaves developing on mutilated plants, and stated that the tubular development was
reproduced to a considerable extent from year to year on these weakened strains.
DeVries 83) has pointed out associations of cleft leaves with other monstrosities,
such as fasciations and twisted stems in various species.

LEAF TEXTURE,

Certain external differences in leaf structure occur which serve to distinguish
varieties as well as individuals. Among these differences which are apparent with-
out miserscopic study, are rough and smooth leaves—without reference to pube-
sence; thick, rigid blades in contrast to others which are thin and wavy, sometimes
crinkled. In a number of X; hybrids the rough and the rigid types were dominant
to their opposites.

During the season of 1910 a small variety of white rice pop produced crumpled
leaves throughout. The leaf sheaths and bases of the blades, especially, gave the
appearance of having been crushed or jammed in the process of development. No
hybrids involving this character have yet been grown. Collins 18) noted a hybrid
between Tom Thumb pop and a tall Guatemala variety, all the plants of which had
crumpled and distorted leaves.

DISEASE RESISTANCE.

Disease resistance in plants is of great economic importance and remarkable
cases are on record of the finding of single plants which withstood attacks of fungi
when all their neighbors have been destroyed by the disease. Such cases have been
taken advantage of in a number of species 65). The production of antitoxin in
these disease resistant plants has been suggested as an explanation of the behavior.

Rust resistance was found to be a recessive character in wheat by Biffen 8), but
so far as known no other cases have been reported in which this character has been
studied with regard to segregation in the hybrids, although a number of cases have
been reported of selection of disease resistant plants after hybridization.

66). This last mentioned fact seems to indicate that disease resistance is gen-
erally a recessive character. Shull 72) reported increased susceptibility to smut
on self bred corn plants.

In 1910 we noticed a number of plants which were seriously infested with rust
while others were practically immune. Very little rust was noticed in the previous
season which was a very dry year. A hybrid row in 1910 showed advanced stages
of rust (probably Puccinia sorghi) on every plant. Another 1 hybrid row con-
taining only sixteen plants produced six normal green individuals which bore small
ears, while the leaf tissue of the remaining ten plants was thickly studded with
large pale yellow spots turning later to a darker yellow. These diseased plants
were smaller and more slender than the green plants and none produced ears. The
nature of the disease has not been determined.

3 It may be that disease suscepitible combinations were unwittingly made in these
two hybrid cases and that in the latter case we secured what appears to be segrega-

2

on

tion. The diseases are not the same, consequently the causes in each instance may
differ. The rows, however, were not near each other and the conditions of infec-
tion may have varied. The green plants, as well as the spotted individuals in the
second mentioned row, were but very slightly infected with Puccinia sorghi, which
was the principal disease of the first case.

LEAF COLOR. ae

Among leaf colors in corn may be mentioned :—dark green, light green, red
tinge, dark red, and variegated (stripes of white, yellowish green, and red). In
varieties with green leaves occasional striped individuals occur, about the behavior
of which little is known. Pure albinos which perish in the plantlet stage will not
be considered under the head of leaf color.

Green.

Distinct shades of green are affected somewhat by humidity and plant food.
The X: hybrid from dark and light green parents were dark green when growing
in the same soil and-season (1910) with the parent varieties. It is possible that
the dark green of the hybrid may be partly due to vigor of growth, but segregation
of dark and light greens is to be looked for in the XX, generation. Price and
Drinkard 69) also found the green leaf dominant to the yellowish green leaf in
tomatoes.

Red Tinge.

Many varieties show a more or less red tinge on the leaf sheaths and edges of
the leaf blade; this, in general, is associated with a red tinge on other parts of the
plant, especially the culm, husks, and tassel. 1 hybrids frequently show this red
tinge intensified where one of the parents has exhibited the character. , plantlets
of two such hybrids were grown in the laboratory and gave the following results
with respect to this character :—

Total No.of

Ear number. Stems red. Stems green. Percent green. plantlets.
ALE OS GOMER ORO Oae Oe 10 3 23 13
BOOS Sint sincere iet 16 8 33 24

These numbers are too small to be of much value, but since large numbers
of &, plants growing in the field showed uniformly red tinge stems in hybrids of
green and red tinge, we place confidence in the above results, and in more complete
studies would expect perfect segregation of green and red tinge stems. Webber 85)
found this red tinge stem appearing in mature plants of the first generation hybrids
of Hickory King (green stem) and Cuzco (“purplish base”).

Red coloring matter in many plants has been generally ascribed to “anthocyan” ;
which very general name for a series of red, blue, and violet coloring substances is
usually the first and last resort in papers dealing with behavior of certain colors in
plants. A large and interesting field awaits the student in this very important
branch of heredity. In general, the theory prevails that anthocyans are produced
from glucosides by oxidation, ete. Similarly to chlorophyll, anthocyans depend
upon sunlight for their production and perhaps, in same cases, prevent the decompo-
sition of chlorophyll by very strong light 64). It was noticed that bagging shoots
retarded the production of red in the silks and on the husks which were covered
by the paper bags.

Anthocyans occur in the cell sap of many plants and are soluble in water, the
red tissues frequently giving an acid reaction. Transpiration is reported to be less

26

in red leaves than in green, and this character might be used to advantage in
developing a drought resistant variety. When a leaf or stem is broken on the corn
plant during the growing season, especially during the latter part of the season,
the ruptured and surrounding tissue on the living end develops a tinge of red.
This was noticed on many plants after the violent storm in 1910 and the color was
apparently caused by oxidation of the cell sap. Blaringhem 9) secured a con-
siderable amount of red foilage presumably as a direct result of mutilation and
cutting of the main culm.

Dark Red.

Some varieties are of a deep blood red throughout the plant, others are only
partly so in the husk, cob, seed coat, another, or sill color. K6rnicke 51) noted a
variety from Peru with blood red leaves and stem. Sturtevant 80) mentions
receiving red-husked ears from the San Padro Indians of Mexico in 1886, a red-
husked dent was advertised in 1885, a sweet variety with red stalks in 1889, and a
pop corn with red stalks in 1895, but the history of their origin is not given. Fre-
quently the new varieties introduced are from new combinations in hybrids and it
is probable that some of the above varieties originated in this way. Halsted 36)
noted the deep purple foilage of Ruby Sweet as dominant to the green foilage of a
flint variety.

Only one hybrid (green foilage & dark red) was secured in 1909 in which
the dark red foliage of one of the parents was constant, but of the kernels
planted, only two grew. These X; plants were very dark red throughout with the
exception of kernel and cob colors. The endosperms were yellow and white, while
the cobs of one plant were white and the seed coat colorless. These two plants
were the most striking in the field because of their deep red foilage and perfect
color segregation would be expected from their progeny.

Variegated Foilage.

Variegation occurs in some form in most families of flowering plants. In
many species this phenomenon does not appear to be constant. DeVries 83) gives
a large list of such instances and concludes that selection of variegated plants will
not of itself lead to constant forms. Occasional striped individuals occur in corn
as in all the Gramineae. So far as known all the groups of corn are subject to it.
Sturtevant 80) mentions finding them in flint, dent, and sweet varieties. In our
own work we found occasional striped plants in two dent varieties, one selfed pop,
and two dent hybrids. These plants were selfed, closed, and hybridized but the x:
progeny have not yet been grown. The cause of the stripes is not known, but
in some cases, they are associated with degeneration or abnormalities. Correns 20)
and Baur 4) report several types of variegation in other species which (apparently )
do not reproduce strictly true to seed, and consequently gave irregular segregation
in the hybrids. Baur 5) found a case of yellowish green variegation in Antirrhinum
majus which was always heterozygous, segregating into one-fourth clear yellow
incapable of forming pigment, one-fourth pure green, which were constant, and the
remaining two-fourths of the heterozygote form.

The first mention of constant striped varieties in corn, in so far as is known,
was in 1861 and in 1866 33). These were said to have been brought from Japan
and named “Japanese Striped” but the origin of the constant forms is not reported.
Bailey 1) hybridized Zea Canina with Zea Japonica and in 1892 reported twelve
green plants out of fourteen which indicates dominance of the green. The occur-
rence of the two striped plants may have been due to accidental self-pollenation.
Variegated individuals of these Japanese Striped varieties, when selfed or closed
in 1909, reproduced constant in 1910 without an exception. That the purity of these

a>
ai

varieties is to be questioned is evidenced by the fact that green plants were
occasionally to be found coming from a mixed lot of the parent seed. The striping
seems to be influenced by environment somewhat, more or less stripe appearing
under varying conditions, thus we find variations in the stripping from almost pure
green to almost pure albino. There is considerable fluctuation upon one plant and
suckers are frequently found having more stripe than the main culm. In plants
grown from hand-pollenated ears it was found that there were three types of the
striping, namely:—More white than either yellow or red, more yellow than either
white or red, more red than either white or yellow. It is not known whether
these three types will behave as units.

Without exception, all 1 hybrids of striped and green plants, including twenty-
seven cases and a large number of individuals, were green. This shows complete
dominance of green foilage. The striped varieties, however, tend to have red
tinge stems and leaf sheaths and, since this is a dominant character, when striped
plants—having the red tinge in addition—are hybridized with pure green plants,
the 1 progeny show the red tinge stem. There may be some variegated strains
which do not have red tinge stems but in case none such are found, the above
results might serve as an instance of broken correlation between two characters
on hybridization, one being a recessive, the other a dominant and variable character.
Whether there is an association of these characters in the X, segregates is not
known.

PUBESCENCE.

Individual plants in a number of varieties have a more or less heavy pubescence
on the leaf blades. Other plants were found which were perfectly glabrous. The
leaf sheaths of some of the rice pops have a dense, coarse pubescence. The data
secured, indicates that pubescence in hybrids is a dominant character. Ten
different ><: rows which were hybrids between varieties relatively smooth and
varieties pubescent were especially striking for their dense, coarse pubescence on
the leaf blades.

Dominance of hairs and spines has been reported in wheat, campion, stocks,
and thornapple 3). Miss Saunders 3) found a very interesting case of correlation
of purple sap color and hoariness in stocks.

The value of pubescence on the corn plant is not definitely known, although
it is probable that this character would be desirable in a dry region. Collins 18)
noted a Mexican drought resistant variety on which the leaf sheaths were densely
covered with long hairs borne on tubercles.

CULM.

The diameter of the culm in Gramineae, as in most monocotyledons, increases
by the enlargement of the cells of the young plant and not by the addition of
new tissue, as in the cambium of dicotyledons. No study of the internal structure
of culms was made but we might expect, from what is known of the method of
enlargement of the stem, that there would be considerable constancy in the cross
section of plants of the same strain.

There are two regions on the average corn stalk where most of the breaks
occur by strong winds. One common break occurs at from one to three nodes
above the soil, the other at the first above the earbearing node. Occasionally the
break occurs at a node below the ear. Of these breaks, the most objectionable is
at the base of the culm. Nearly all breaks occur on the upper border of nodes and
not along the internodes; this may be explained by the fact that at the time of the
summer storms the upper parts of the nodes are yet succulent and spongy, con-
sequently they break quite easily. Every farmer who has cultivated tall corn early

28

in the morning knows from experience that corn plants break off much more
readily at this time than later in the heat of the day when there is less moisture
in the stem.

It would appear that in order to prevent loss from broken stalks the breeder
should select individuals with firm, tough lower nodes, and large relative diameter
of stem at this point in addition to a strong root system to prevent lodging and
“down corn”. Just such characters as have been mentioned, occur in different
varieties, and unless correlations interfere, they are probably available by means of
selection or by hybridization with individuals having other desirable characters.

When varieties or strains are planted side by side, the growing periods and
relative stage of development must also be taken into account in comparing the
effect of any particular storm or season. A stalk which is nearly mature is able
to withstand a storm far better than one which is yet green and brittle.

A large proportion of the plants in several rows, some of them hybrids, were
broken off near the soil in the season of 1910. These plants were usually slender
and had a brittle appearance. Other rows also, including hybrids, tended to break
above the upper shoot or ear. Plants and entire rows which lodged, and especially
those which failed to straighten up afterwards, were those with slender stems and
long internodes; therefore, not all slender stemmed varieties tend to break. No
measurements of diameter of culms were made but, as was to be seen readily by
inspection, there is a wide difference in this regard.

The product of coarse culm % slender culm and the reciprocal gave 1 hybrids
with coarse, rigid culms. Slender culm slender culm gave only a slight, if any,
increase in diameter; which may be attributed to increased vigor. It is therefore
apparent that the coarse culm is dominant to the slender culm in the X: generation.
It was noticed that the coarse, stout culms were characterized by thickened cortex
and pericycle layers, but what relation the internal structure and the nature of
the vascular bundles may have to strength of stem was not determined.

During the season of 1909, an abnormally large stalk was found in a field of
pure-bred Leaming corn belonging to Mr. F. I. Mann of Gilman, Illinois. While
the culm was yet green, it measured approximately two and one-half inches in
diameter at the third node above the soil. An external examination revealed no
other abnormality nor disease. Seed from the open-pollenated ear borne on this
stalk was planted at the Illinois Station in 1910 and of the plants produced on
medium soil, none measured more than an inch and a half in diameter. This shows
that this peculiarity cannot have been a dominant characteristic at least, and evidently
is not a genetic character since largeness in general is probably a Mendelian
dominant.

“Vigor of plant as shown by ability to stand upright is hereditary. Ear-rows
[dent varieties] growing side by side have shown a variation of from no broken
plants to 56 per cent of broken plants—The ability to stand upright did not result
from a lighter load’ 87) Webber 85) noted much taller and thicker stems in Xx
plants from Hickory King, a slender-stalked dent variety, pollenated with giant
Cuzco.

HPIGHT OF PLANTS:

The response of the corn plant to food and environment is most significant in
height and size, and for this reason alone there is always a possibility of finding
considerable fluctuation in a study of these characters. Varieties are reported 80)
to vary in height from 18 inches for a “Tom Thumb” pop to 30 feet or more for
varieties grown in the tropics. Undoubtedly many of the difficulties which have
been experienced in interpreting the behavior of size or length of parts may be
attributed at once to abnormal environment and to impurity of strains.

29

In his original paper on hybridization Mendel 58) reported complete dominance,
in fact, increase in height of sweet pea plants, followed by complete segregation.
“The longer of the two parental stems is usually exceeded by the hybrid, a fact
which is possibly only attributable to the greater luxuriance which appears in all
parts of plants when stems of very different lengths are crossed.” He secured a
ratio of 2.84 talls to one dwarf in the next generation with 1064 plants. McCluer 57)
hybridized two varieties of pop corn and secured plants taller than an average
size of the two. Hartley 4o) states that a hybrid of Mexican Dent corns produced
plants 234 feet taller than the average height of the tallest parent and 434 feet
above the average of the shortest parent.

Tschermak 3) reported apparent inconstancy with regard to height in bean
hybrids. DeVries 83) found that extracted F, dwarf antirrhinum did not breed
true, but gave progeny of various heights. In a hybrid of giant Cuzco and Hickory
King dent corns, Webber 85) noted that the ><: generation was much taller than
either parent. The Cuzco had been stunted, however, by being started in pots
and then transplanted. Hybrids of Turkey Red wheat with Russian Winter were
reported by Keyser 50) to have made a height growth fully to inches greater than
either parent.

Lock 53) working with corn concluded that the height of 1 hybrids “was
obviously intermediate—In a number of cases the cross was made between the Fi
plants and the shorter of the parental types. The offspring of this cross showed
no such segregation into short and intermediate plants, as was to be expected if
Mendel’s Law held good.” Price and Drinkard 69) found “standard stature”
(tall) dominant to “dwarf stature” in tomatoes, giving complete segregation in
the . generation. As a result of his observations on measurements with hybrid
rabbits and guinea pigs, Castle 14) proposed that “Size variation is apparently
continuous and its inheritance blending—[but]—Blended inheritance may possibly
be only a complex sort of Mendelian inheritance, in which many independent

factors are simultaneously concerned

Emmerson 29) stated that in every case with which he is acquainted, there
has been segregation of size characters in X. following the blend in the X: genera-
tion. Crossing a Tom Thumb pop 90 em in height with a late dent 225 cm in height:
Emmerson secured approximate blending with regard to height (182 cm), number
of nodes, and growing period. He found X: plants ranging in size from the Tom
Thumb to above that of the 1 generation but none were as tall as the large dent
parent. East 28) secured X; plants from a medium sized flint and a tall dent
which were nearly equal in height to the tell dent parent. East attributes the
increase in size of the ; plants over the average of the two parents to increased
vigor as a result of hybridizing and not to dominance of tallness. The distribution
of heights in the %, generation was more variable and no definite segregation
was apparent other than this difference in fluctuation between the X: and X;
generations. He concluded that a combination of many characters may be neces-
sary to produce size.

Thus, in general, the disposal of size-inheritance has been unsatisfactory. In
the first place a size somewhere between the heights of the parents, represents no
actual increase, although it is above the average of the two. Practically we would
not concede an increase unless we secured a hybrid larger or taller than anything
we used to produce that hybrid. This complication due to vigor may perhaps never
be overcome, but we need at least an approximate method of evaluating its
influence before we can say how size segregates.

Undoubtedly a system of height classification based only upon inches or
centimeters is unsound. It is hardly rational to expect corn plants to vary in
units of the yard stick or bushel measures, and to attempt an analysis of inheritance
from this viewpoint alone, or to expect “bushels per acre” to segregate, is extremely

30

fallacious. Perhaps the division into dwarfs, intermediates, and giants is as far
as we may go at present with our limited knowledge of what constitutes height.
Tf it is not possible to find characters correlated with height, it will be necessary;
as Bateson, Castle, and others have recognized, to determine the units—of which
there are probably a number—that together control size.

In general, the 1 generation was more uniform than the parents; which is
especially true of the selfs and closes. The arrays were made in five-inch classes
since the error in finding the height of a plant of this nature can scarcely be
limited to one inch.

In my work the fluctuation in the parent rows in I910 was generally less than
in the poorer soil and season of 1909. This accords with the conclusions of
Davenport and Reitz 22) upon measurements and weights of ear corn. They
report variability to be slightly less on fertile land than on lands giving lower
yields. Love 64) has reported increased variation with increased food supply in
height the number of internodes of garden peas. Humbert 44) found indications
of a decrease in variation in night flowering catchfly with an increase of plant
food in the soil.

In general the Xi generation is more uniform than the parents, which is
especially true of selfs and closes; this accords with observations by other in-
vestigators and is explained, partially at least, by the fact that the immediate
parantage is restricted to two individuals in the case of hybrids, crosses and closes
and to one parent in the selfs. For practical purposes the aomeha : or poorly
developed plants in such cases as; 15.100, 22.120, 25.170 etc. may be neglected.

While Gregor Mendel 58) stated in his paper on hybrid peas; “It is further-
more shown by the whole of the experiments that it is perfectly immaterial whether
the dominant character belongs to the seed-bearer or to the pollen-parent; the
form of the hybrid remains identical in both cases”; a number of instances have
since been observed where this principal does not seem to hold. Bateson 3) has
proposed two possible explanations of “the remarkable fact that the mother-plant
can impress varietal characters on her offspring by influences which are not
hereditary in the ordinary sense”, namely,—the difference in food materials in the
seed, and the presence of a specific factor or factors.

From a large number of observations on plant and seed characters in corn, we
feel that either or both of these explanations may be justified in the same
individual. A summary of the reciprocals in regard to height given in Table 3
exhibits general uniformity in results :—

Reciprocal Hybrids.

No. Modal height ininches. No. of plants.
PTO GAOA ee eccisiey ohare yeieaat aes os okeenedsterobanctop eters euetske IIo 36
MODK BANG pannesoeotoovandoooorsoderecdorod 120 4
OLS Oia a aac maa TOO Rote Re pT On cre ones 45 47
SQLS ROR ne Ot ea radar roe CHE PUR IT One tOrten cten 50 49
SOR Ov EG ce arnt oor aU OO BRINE Dt MOA a TO 45 30
SHOS <A Cle Ce ROO obo AERO TOO Sere no nado n ear 125 16
MOOS RIGA home get BORSA OP NTE Coe etn roO Ree ar 125 28
OPS AOW Oa om HRA ee RU CeCe oc heen 105 13
(ETOSKEAD SA: Ba Senor en nb ROBT IAG aanH nN BOSE 105 19

With the exception of the 404210 hybrid which produced only four plants, the
results may be considered as uniform. In numerous cases—not reciprocals—it was
noticed that where dent corn was used as the female parent, taller and coarser

31

stalks resulted than when it was used as the male parent on the smaller sweet, flint,
and pop varieties; while this difference is noticeable in the mature plants, it is
especially striking in the plantlet stage as has been mentioned. Reciprocals made
in 1910 between rice pop and large dent varieties exhibited a wide difference when
growing side by side in the X; plantlet stage in the laboratory tests. In some of
these instances, at least, the difference seemed to be due to unlike food material in
the kernel,—unlike it seems, in both quantity and quality.

Thus it is apparent that differences in vigor and size exhibited in seedlings
may be noticeable in the same plants when mature. it may be that the explanation
of increased vigor of hybrids depends largely upon this one fact—vigor of seedling—
due to the quantity and composition of food material in the germinating seed, which
favors an initial, vigorous cellular—activity upon which luxurious development
depends.

The modal summary of the behavior of height shows some very interesting
results with variations from what appear to be increases in height to those cases
which appear to be perfect blends and others that seem to be decreases below the
height of the shorter parent. Twenty-three cases out of forty-five possible ones
in the 1 hybrids gave modal heights greater than either parent individuals and
modes. In five cases <1 hybrid modes were below the parent, individuals and modes.
How these hybrids would behave in the XX. generation would make a very
fascinating study indeed. The closes gave variable results, as is to be expected in
view of the unknown purity in the seed. With regard to height, there may have
been as wide difference in the majority of individuals used in the production of
hybrids. Had “pure” strains of corn been available, we would have expected a
decrease in height in the majority of 1 closes. Some of the increases in height
observed in the i closes may have been due to acclimatization; again, we may
have had a wide difference in the individual parents of some of the closed cases.

From the experience of McCluer, Shull, East, and others, we would expect all
the selfs to appear in the column, “Below the Lesser Parent’, ie; decrease in vigor
the first season because of self-breeding. To our surprise, we find one case
giving 1 progeny as tall as the parents (Equal to the Average of the Parents)
and another taller than the parents (Above the greater Parent). In the case of
increase (28.170) there were only nine plants but confidence is placed in their
behavior, although the parent mode chosen may not have been exactly correct
because of the limited array given. The hybrid kernels from this same ear
(23.170) gave plants taller than the selfed individuals although the 300 variety
averaged somewhat shorter than the 210 variety. It is suggestive that these two
varieties, both popcorns (201 and 210) may permit inbreeding for a time without
serious loss of vigor. The two closed populations (2C.163 and 2C.164) of 210
gave further evidence in favor of this conclusion.

INTERNODES.

The question arises as to what hereditary factors determine height and, as a
matter of course, it is to be expected that the number of internodes and their
relative length would determine mere linear dimension. It is also surmised that
number of internodes, within a variety, is a more constant quantity than either
height or average length of internodes.

The possibility of correlation of number of internodes with yield or production
and with some other characteristics has been investigated, but so far as known,
no correlation tables have been constructed between number of internodes and
height of plant. Ewing 31) found the coefficient of variation for number of inter-
nodes within one variety of corn to be less than for a number of other plant
characters studied. The results in selection during six successive years as given
by Smith 76) give evidence of a direct correlation between height and number of

32

internodes within each of the two strains, “high ear” and “low ear”. In the data
given by Smith, the number of internodes is plainly more constant than their
average length. Certain varieties exist, however, in which the average length of
internodes remains quite constant.

Cases of “telescoping” or shortening of internodes have been found to repro-
duce. Hartley 39) describes stalks 4 to 5 feet tall bearing 18 to 20 broad leaves
in a white dent variety whose normal height was to feet. These short plants were
pollenated with each other and the dwarf character was reproduced by their
progeny.

In the season of 1910 in a plot of Leaming, a tall dent corn, here at the
Illinois station, a stalk was found having 17 internodes, probably the average of
the variety. This plant was only 37 inches in height while the average of the
plot was approximately 120 inches, and the largest leaves of this plant were as
long as the culm of the plant itself. This average length of internode of slightly
over two inches as against approximately 7 inches in the normal plants presented
a very dense-leafed effect. No ear was produced on this plant but its pollen was
used on two other strains of Leaming corn with success. As short internodes is
expected to be recessive, if there is an inheritance of the peculiarity, it cannot
appear till the . generation has been grown.

With a given height, extreme length of internode is not desirable unless it is
accompanied with a large diameter of culm and a well developed root system.
Extremely short internodes are also undesirable, as such varieties usually produce
short leaves and small ears, with a corresponding decrease in other parts of the
plant. In general, the length of internode on a corn plant is least at the roots,
and increases toward the tassel and, in many varieties, there is again a decrease
in length of internode between the upper ear and the tassel.

In Emmerson’s 29) Tom Thumb Pop XLate Dent hybrid, an intermediate
number of nodes (8 nodes19 nodes gave 12 nodes in the 1) was obtained in
the 1 generation, but segregation was predicted for the x. generation. Assuming
that the number of nodes given by Emmerson corresponds to the number of inter-
nodes, we interpret his results as follows :—

Av.length of internodes
Height of plant. No.of internodes. (Including the tassel).

Gormelvintim bees secre go em. 8 rises} (eat.
WatemDentieneticc sect 225 cm. 19 II.9 cm.
labaoraalon eee codons 182 cm. 12 5 e2acms

While he secured a gain of 3.3 cm. in average length of internode, his %: plants
showed a decrease of 7 internodes as compared to the taller parent. This behavior
indicates either dominance of small number of* internodes, or that one or both
the individual parents used were heterozygote with respect to number of inter-
nodes; unless number of internodes can be shown to actually blend.

Because of the very short internodes at the base of the plant, some of which
may be covered in cultivation, it is impracticable in most cases to secure a count
of the total number with an experimental error less than 2 internodes.

It is practically impossible to get the exact number of internodes at the time
of maturity of the plant without dissecting the rooted portion of the stem. Care-
fully marking the sixth or seventh leaf of the young plantlet while the coleoptile
or plumule sheath is yet discernable and which is borne at the first true node, would
be, perhaps, the most satisfactory and definite method of counting internodes.

In the behavior of the hybrids it is significant that height of plant is affected
more frequently by difference in average length than by difference in number of
internodes. It was found that closing and selfing gave a decrease in average length
but no significant decrease in number of internodes.

33

Among the hybrids there were a number of cases which fluctuated considerably
from the modes of the parent strains, and the modal summary shows very clearly
that the fluctuation in results is largely due to hereditary differences in the individual
parents. The summaries show at a glance that both large number and greater
average length of internodes predominate in the 1 hybrids, the majority of cases
falling in the lists “Equal to and Above the greater Parent’. Closing and selfing
seems not to have any decided effect upon the number of internodes, while there
was a decrease in average length in the majority of cases.

From the results obtained, it is evident that more reliable data and greater
accuracy in interpretation may be expected with regard to number of internodes
and their relative length than from observations on mere height of plant in units
of measure. These two characters do not behave alike in all cases in transmission,
and do not seem to be correlated. Decrease in average length of internode seems
to be the principal cause, at least in the first season, for “decrease in vigor due to
inbreeding” in so far as height of plant is concerned.

AERIAL ROOTS.

After the secondary roots, which develop at the first few nodes on the stem,
have become established, the primary root is of very little importance and later
ceases to function, as is characteristic of monocotyledonous plants.

The first few whorls of secondary roots are usually very close together, making
it difficult to distinguish the internodes. Succeeding whorls of aerial roots, com-
monly known as “brace roots”, frequently develop at a considerable height on the
culm from which they can no longer reach the soil, unless the plant is bent or
lodged; in that case the aerial roots always start from the side of the node nearest
the soil, sending out a mass of fibrous roots after penetrating the soil surface, thus
anchoring the plant firmly in its new position.

The aerial roots are forced through the epidermis of the nodes. They are
usually quite fleshy, and have a gummy surface which is said to be due to the
breaking down of the outer cell walls. During a rain or when immersed in water
the gum accummulates at the root tips as a transparent jelly-like mass. This
gelatinous substance is tasteless and gives a neutral reaction with litmus. The gum
prevents dessication and affords protection for the tender surface of the develop-
ing roots.

Some varieties have thé aerial-root character well developed while others do
not show it at all. So far as known no selection for these roots has been
reported. The character is fluctuating in its behavior, being affected by environ-
ment and vigor. Border plants frequently produce the roots higher on the culm
than do plants in the center of the plot or field. One plant of large Mexican corn
(408) on the end of a row in 1909 produced aerial roots at the thirteenth node
above the soil. ‘

Counts of the aerial root whorls were made only in roro. The fact that very
few of the 1 generation and only a limited number of the parents produced plants
with only “one rooted node” above the soil, favors the conclusion that when
varieties produce aerial roots at all, they tend to do so on several nodes. Certain
strains produced no aerial roots which failed to reach the soil. In the large
majority of the <1 hybrids, a high number of rooted nodes predominates, when this
feature was found in one of the parents. Closing gave variable results depending
on the parentage. In the selfs the number of nodes with aerial roots decreased in
three out of four cases observed.

PERIOD OF GROWTH.

The origin of varieties with very short, and others with extended growing
periods has not been recorded, but varieties exist that are adapted to regions
34

differing widely in soil and climatic conditions. Considerable local adjustment
may take place in a few seasons in varieties whose requirements are not adapted
to the new conditions in which they may be placed. Sturtevant 80) recorded
differences in growing periods of from one to seven months in varieties growing in
different regions.

After five years of selection for high and low ears, Smith 76) observed that
the “low-ear” plot was apparently a week in advance of the “high-ear” plot at
the tasseling stage. The low ear character is associated with a decrease in height
of stalk, shorter internodes, and a decrease in number of internodes below the ear.

Pearl and Surface 67), after three years of experience in selecting sweet corn,
report; “Many of our results seem to indicate that earliness, in a large part at
least, is a physiological rather than an hereditary phenomenon—all the gain which
has been made in earliness was accomplished in the first year’s selection. No
further increase has followed the further selection practised in the two subse-
quent years.”

Emmerson 78) has found apparently little correlation between height and
earliness in the second hybrid generation of two varieties of corn, some of the
earliest plants being above medium height and some of the latest being very short.
He reported the i generation as intermediate in maturity (100 days) between
parents whose growing periods were approximately 70 and 130 days respectively.
Mendel 58) failed to complete his report on the study of this character in peas,
but found that the first hybrid generation was intermediate and predicted segrega-
tion if hybrids were made in which the parents differed at least twenty days in
maturity. Biffen 8) also noted intermediate results with hybrids of early and
late wheat varieties.

In our study of this question, the “period of growth” will be designated as the
time in days between the planting of the seed and the date upon which the husks
on the upper ear or shoot are dead. We do not assume that growth in the plant as a
whole ceases definitely at this stage, but the time at which all green has disappeared
from outside husks provides perhaps as definite and satisfactory a point as can be
secured for comparison in regard to the total growing period. After this stage in
ripening, there is undoubtedly considerable deposition of substance in the ear and
in other parts of the plant in some cases. Incidentally it was noted that some
varieties ripen their husks a number of days before the remainder of the plant
matures. The period of growth may properly be divided into two stages by the
date on which the silks of the upper shoots on most of the plants appear. This
point in the blooming period was taken because it is the time when the process of
reproduction begins.

Notes were taken daily on each plant in 1909 on the appearance and character
of the tassel, anthers, and silks, and it was found in a number of instances that the
relative time of the appearance of these three was quite irregular. Since the plant-
ing was done at three different times in the first season, only data from 1910 were
used for comparison with the x: generation. This data was taken every four
days on the appearance of anthers and silks only. The differences in length of
blooming periods are frequently due to poorly developed and abnormal plants, yet
Some varieties pass the period very quickly (10 days) while others have a very
extended period (20 days or more). In general the blooming period of the Xi
hybrids tends to be longer than the average of the parents. Eleven hybrids in the
list of those observed had a period equal to or less than that of the parent with
the shortest period, while sixteen other hybrids had a period equal to or longer
than the average of the parents: nine being equal to or longer than that of the
parent with the longest blooming period. Among the closed cases, six out of
nine required more time to finish blooming than did the parent rows in the same

35

season. Two of the three selfed cases had blooming periods identical to those of
the parents and No. 201 (selfed) finished blooming in a much shorter time than
its parent. ‘

While protandry is the most common behavior in floral development in corn,
no very extended observations on the inflorescence at the time of blooming are
necessary to bring to notice individuals which do not shed pollen till some time
after the silks appear. As examples of differences among the varieties, No. 203
had eighteen plants which showed silks on a given date while only five among
that number were as yet producing pollen. When this variety was closed and
hybridized the progeny gave a normal behaviar. Other varieties, notably 503, 603,
and 610 produced no silks. until approximately eight days after the first anthers
appeared. It is striking that a somewhat similar behavior prevails in the closes and
selfs of 503 and 603.

The reciprocals differed somewhat in time of appearance of silks after planting.
This difference varies from four to eight days, and may have some significance,
but the general result is the same; that is, the longer periods tend to be dominant
in the X: hybrids. The hybrid 24.162 was approximately a week later in blooming
than its reciprocal 42.238. It may be that the difference in location in the field
may have had an influence, but it was more probably due to the difference in the
individuality of the parents on the 210 side. This is also another example of
difference in behavior when dents are hybridized with smaller varieties. The large
dent kernels of 42.238 should give the plantlets an initial advantage over the
plantlets from the very small kernels of 24.162. Close and self pollenation delayed
the time of blooming in the majority of the 1 progeny. While the results do not
permit definite conclusions to be drawn, the balance is decidedly in favor of
“late blooming as being the dominant character.”

A partial list of the total growing periods varied, in the parent strains used,
from approximately 100 days to nearly or perhaps fully twice that length of time.
This table also showed the number of days in the latter part of the growing period.
The uniformity of this latter period in comparison with the total period is sig-
nificant in all those cases in which maturity was reached. The exact average
fraction of the total time for both the parents and the X: generation is 0.39 or
approximately 0.40.

Tf this fraction were constant for all the varieties and their progeny, it would
afford a ready means of calculating the total growing period when the time from
planting till silking is known; and thus provide a method for learning the total
growing period in those cases which did not mature because of the short growing
season. There were, however, extreme fluctuations of from 0.31 to 0.45 and there
must have been similar fluctuations in the varieties which did not ripen. In testing
this proposition on some cases which did not mature, by adding 40 percent of the
total (equal to 24 of the time from planting till the appearance of the silks) to
the number of days from planting till the silks appeared, a few of the cases should
have been ripe although they are not so shown in the field data. While further
and more conclusive tests of the relative lengths of the two periods of growth are
necessary, the results secured indicate that approximately 60 per cent of the total
growing period in corn preceeds the time of the appearance of the silks; the remain-
ing 40 per cent of the total growing period falls between the time of silking and
the time when the husks on the ear are dead.

The data are too incomplete for a summary. In a number of cases, the X:
hybrids ripened late or failed to ripen at all. There is sufficient evidence of this
nature in the tables to permit the conclusion that late maturing is dominant to
early maturity. Since the total growing period tends to be longer in the Xi
hybrids than that of their earliest parents, the period between silking and time of
ripe husks is as a consequence also longer.

36

INFLORESCENCE.

There are numerous indications that the present monecious type of inflorescence
in corn has developed from a terminal hermaphrodite form. Hackel 34), Harsh-
berger 38), and others have recognized the origin of the ear of corn, as we have it
now, as due to a union of two rowed spikelets of the floral clusters on the tillers
or plant branches. Harshberger has pointed out further that clusters of these
fasciations or ears probably existed in the primitive form, and “one ear, in the
cultivation of corn for centuries, has enlarged at the expense of the others, furnish-
ing another illustration of the law of compensation in growth.” These ear clusters
mentioned by Harshberger are of common occurrence in many varieties today, being
found in the terminal inflorescence of suckers and also upon the shanks and among
the husks of ears on the primary culm. Sturtevant 80) mentions the frequent
occurrence of such cases.

Montgomery 59) proposed that the ear has developed directly from the central
spike of the tassel without fasciation, the lateral branches of the tassel disappearing
as a consequence. It is a well known fact, however, that the large majority of
ears in many varieties are “spread”, that is;—larger in one diameter than in the
one taken at right angles to the first. (The frequent occurrence of such ears
indicates that it is a dominant character.) Quite frequently, also, ears with
enormously spread or fasciated tips are found, and such features are very strong
evidence in fayor of the fasciation theory. The fact that large husks (not enlarged
glumes) are frequently found in among the kernels near the base of the ear also
the occurrence of kernel baring branches not only at the base of the ear but at
some distance above the base of the ear are further evidences in favor of the same
theory. The recurrence of these branches indicates that they. were absorbed but
not lost.

A very interesting case arising in our own work offers evidence in favor of
the fasciation idea rather than the theory presented by Montgomery. In harvest-
ing one of the Illinois Experiment Station plots, the men found a peculiar cone-
shaped ear with a prolificated cob. A section of the ear disclosed only a large
central pithy core to which were attached the slender branches. The kernels
(borne in pairs) and glumes were irregular in size and shape (due to the irregular
distribution) but normal otherwise. Fifty plants were grown from this ear in
1910 and two of that number bore exact duplicates of the mother ear; this fact
indicates that the prolification is a character and will reproduce. The pollen
on these two plants grown in 1910 was nearly all gone before the silks developed;
it is probable that the mother plant behaved similarly and that the seed was largely
cross pollenated by normal plants.

If this behavior, which appears to be a reversion, is a recessive character, it
would account for the small number of individuals which reproduced the prolifica-
tion. One of the ears was pollenated by a normal individual in the row and in
case this character behaves as a true recessive, the . generation of the hand
pollenated ear should produce fifty per cent of proliferous cobs. The peculiar ear
character is associated with a distinct tassel type, which is also cone-shaped, bearing
numerous short branches. Advantage may be taken of this fact in the selection of
such individuals before the silks appear.

Historical investigations indicate that the number of rows on the primitive
type of ear was not very large, probably ranging in number of rows from four to
fourteen, and in some varieties there has since been a decided increase in size and
number of parts in the ear as well as in other parts of the plant. It is evident that
large proportions within paired spikes or rows in the cob are responsible for large,
broad kernels. This enlargement of parts, including kernels, appears to have taken
place at the expense of other parts, such as anthers and glumes, as well as of one

37

of the entire florets of the original pair (Embryonic kernels are paired in the row
similarly to the pairing of the rows themselves, but the lower flowers in each
spikelet are generally abortive) 80). This increase in size of the femake parts
seems also to have been associated with decrease in the leaf blade and telescoping of
the internodes on the ear bearing shank.

In regard to the origin of the ear-bearing branch Montgomery suggests that
as evolution progressed, the central tassel came to produce only staminate flowers,
the pistillate ears being produced on the tiller-like branches, which became shortened
until the leaf sheaths enclosed the ear.

Blaringhem 9) found a close correlation between the length of the supporting
stem and the type of terminal inflorescence on suckers; those having only female
flowers being borne on the shortest stems while those bearing a mixed inflorescence
were borne on longer stems. It is well known that extremely large pods in the pod
corns may develop not only at the expense of the cob, but of the entire floral parts
including the kernel. Pod corn frequently develops a large amount of grain or
very heavy glumes in the tassel, in which case it often happens that no ear
develops on the culm.

When a number of rows of kernels are combined in the central tassel spike,
there is a thickening of parts and in most cases a decrease in the number of
branches,

Development of scattered, medium sized, rounded kernels are frequent in tassels
which show no perceptible thickening or enlarging of tassel parts. This behavior
is very common among pod corns and tends to reproduce. Sturtevant 89) reported
slight or no indication of the transmissal of this character from wind-pollenated
seed. He also noted hermaphrodite flowers and staminate clusters on the cobs of
other species groups. Blaringhem 9) secured hermaphrodite ears from mutilated
flint corn parents and reports the second generation as being constant in the
production of anthers on the ear. Montgomery 60) has recently reported finding
perfect flowers in well developed ears. In our own work, a number of similar
cases have been found, but of their inheritance we know nothing except in the
case of the pod corn. In this study no instance was found (in a large number
of cases observed) where both floral parts functioned in the same flower either in
the tassel or on the cob, although both anther and pistil are present; one always
functions at the expense of the other which is poorly developed, thus insuring
pollenation between florets at least. In the season of 1910, an abnormal plant was
found which bore two medium sized ears, but no indication of a tassel.

Cases of barrenness or complete sterility will be discussed in connection with
the paragraphs on “Pollen” and “Shoots”.

Aside from notes on hermaphroditism and abnormalities, there are but few
reports upon tassel characters. Various investigators have noted differences in
the number of tassel branches. Collins 18) noted frequent cases in a Mexican
drought resistant variety in which the tassels were unbranched and the normal
form itself produced but few branches. Shull 75) reports an apparent decrease
in the number of tassel branches in a self-bred strain. Webber 86) found a correla-
tion between the kernel color in Black Mexican sweet corn and green tassel
glums and anthers. This correlation was but rarely broken.

Structure.
Styles and sizes in tassel structures are various and, in our own work at least

a dozen distinct types or forms have been found. No one tassel was found which
38

possessed all the dominant units, consequently the various hybrids gave many new
combinations not observed in the parents. To the casual observer these tassels of

the X: hybrid would apear a blends very analagous to the supposed blends in

Fig. 2—Some distinct tassel types.

height of plant. The detection and sorting of the segregates with respect to certain
tassel characters may prove as difhcult an undertaking as that of determining the
units which control height in the plant. It is evident that the twelve types chosen are
themselves the combinations of many units.

In the X: hybrids, we found the following tassel characters apparently dom-
inant :—large size, long spike, erect spike, long branches, many branches, spreading
branches, coarse parts, thick glumes, large glumes, monstrous glumes. On many of
the 1 selfs and closes, we noticed a decrease in the number of branches on the
tassel as was reported by Shull 75) on self-bred strains. It might be assumed that
the behavior just mentioned is due to segregation, but a number of observations in
our own work led to the conclusion that it is a decrease in vigor of branching.
This is very similar to the decrease in the number of suckers observed on our
self-breds and although Shull has not mentioned this fact his photographs show
his “Strain A” which was originally suckered, as no longer producing them.

Color.

In varieties that were known to be fairly pure, and especially in self-breds, the
tassel colors were fairly constant but in the majority of the varieties used con-
siderable mixture existed in these characters. Red tinges in the tassel were shown
to be dominant to green in a number of &, hybrids. As has been mentioned in
connection with colors of the culm and leaves, we were unable at the beginning
of the study to secure a variety that was constant with respect to deep red color
throughout. Dark red tassels are relatively numerous in some varieties and their
frequent appearance in the ; generation indicates that this is a dominant character.

Male Flowers.

The male florets in clusters of two or a multiple of two, one pediceled, the
other sessile, or both sessile, are usually arranged alternately in the panicle. In
the four varieties secured from Arizona an opposite arrangement of spikelets

39

occurs at many points in the tassel, similar to the behavior in a Mexican variety
reported by Collins 18). Cases of paired spikelets were found in hybrids with
these variations in IgQIo.

Differences in size and texture of glumes have been mentioned in connection
with tassel types. Colors in the glumes behave similarly to those on the stem of the
tassel, frequently, however, the glumes are colored when the tassel stems are not;
quite often a distinct red ring is formed at the base of the florets in those varieties
having red tinge tassels. “Red tinge” or “red base” in the glumes and their deeper
colored form “reddish green” are dominant to pure greens. Dark red glumes from
mixed parentage gave results which indicate. dominance of that color over red
tinges and pure greens.

ANTHERS.

The anthers in the floret of a corn tassel are usually three in number (sometimes
four to six where doubling of parts occurs) and vary in different individuals and
varieties as to size, shape, color, and fertility.

Size.

During the hand pollenating work of the two seasons, a small quantity of
anthers was preserved from representative individuals in the parents and the Xi
generation. These anthers were thoroughly dried in the tassel bags and samples
stored in small glass vials for future reference. Among these cured anthers, dis-
tinct differences exist in regard to size and shape. Such differences had been
observed in the field but since there was no opportunity for taking measurements,
only general statements regarding their behavior can be made.

Extreme length is not always associated with large circumferences in anthers,
and long anthers are not always found on tall growing varieties. Anthers below
the average in length were found in some varieties, upon very tall plants. Long
anthers were found in other varieties producing small plants. In the : hybrids,
a number of cases were found where long anthers were dominant to short anthers.
Many intermediate cases were found, which were attributed to distinct differences
and heterozygosis in parents with respect to this character. No definite statement
can be made in regard to the behavior of relative size and circumference in anthers,
but differences exist in this respect as well as in length.

Color.

Carful notes were taken on the color of anthers upon every plant grown in
1909 and upon every plant hand pollenated or from which pollen was secured in
1910; thus exact data are at hand on the behavior of anther color. The color in
dried specimens was preserved perfectly in most instances. A number of striking
colors and beautiful tints were found. None of the varieties used were absolutely
constant in anther color, consequently only a limited number of cases were found
in the , generation in which the anthers were of the same color on all the
plants of a population.

Among the many combinations made, we find cases as_ follows :—green
(anthers) green, giving only green; green % reddish green, giving only reddish
green; and other cases giving colors from pure green, reddish green, to dark red;
either green or reddish green X deep red giving all deep red and some giving mixed
results from pure green to very dark red. From this it is evident that dark red—
when homozygous—is dominant to other colors, while pure green is recessive to
colored anthers (red tinge, reddish green, and red).

40

Increzsed uniformity was secured in another color in all the closes and selfs.
This uniformity including that of glume colors was a striking feature in self-bred
strains. One closed case (502XC) in which one parent had pure green anthers
and the other reddish green, gave i progeny all having reddish green anthers.
This case gave the same results in regard to another color as was secured in hybrids
between varieties because—as is apparent—we closed a pure green with a pure and
dominant reddish green segregate. The anther color of the majority of plants of
the parent variety was green. This is another of the many instances of mixture
of characters in a variety which is popularly said to be “pure”.

Tests were made of the behavior of the light green anther which Webber 86)
reported was correlated with kernel (aleurone) color in “Black Mexican” sweet
corn. Two X; hybrid populations of this variety with others having reddish green
anthers gave X: progeny all having reddish green. In Webber’s own observations
upon 4 segregates of a hybrid of this black sweet variety with one having reddish
green anthers, he reports almost perfect correlation of the pure “black” or purple
kernels with green glumes, anthers, and silks. If the correlation is not perma-
nently broken, we should be able to pick out the X: plants homozygote to the
dominant kernel character—purple—by selecting those plants bearing green anthers.
If such results can be secured in the 2 generation it will serve not only as an
example of broken correlation in so far as its expression is concerned in the Xi
generation, but also as an instance in which a homozygote dominant can be
separated from the heterozygote dominants in the 2 generation because of the
correlation of a dominant and a recessive character.

Among the Black Mexican plants growing in 1909, four out of 108 individuals
produced red tinges on the anthers and silks. This may be due either to impurity
or to imperfect correlation. Webber also found stray individuals in the 4 segre-
gates exhibiting red tinge silks and glumes which he attributed to breaking of
correlation by hybridization.

Sterility.

Kélreuter and Gartner among other early investigators thought that sterility
in hybrids was a means of distinguishing species. Darwin investigated many
cases by which he was able to point out the fallacy of this belief. In an explana-
tory statement in connection with an instance of total sterility in corn, DeVries 82)
concludes; “barrenness is to be considered as a monstrosity, which like all other
monstrosities, is inherent in a race, but is developed only in a certain percentage
of its individuals.”

A number of instances of sterile anthers have been reported in inbred corn.
From our knowledge of heredity gained since these cases were reported we know
that they have been the result of using parents in which sterility existed, rather
than sterility being the immediate result of inbreeding itself. Hartley 40) reported
two hybrid cases in corn which showed a strong tendency toward sterility. Suckers
developing adventitiously from mutilated plants were stated by Blaringhem 9) to
have produced tassels with infertile stamens, but such a condition frequently exists
on poorly developed suckers in corn.

In a hybrid of Maryland white dent and blue Hopi corn, Collins 18) found
six out of sixteen plants which failed to produce pollen Sterility has been
reported in hybrids with other species than corn, but the behavior does not seem
to be the same in all cases. Normal anthers are reported to be dominant to sterile
anthers in sweet peas 3).

In two of the parent strains used in our experiments the majority of the
tassels bore largely sterile anthers. A number of the plants produced a small
quantity of pollen insufficient for our needs, others gave no indication of sterility.

~ All the hybrids as well as the closes with these two strains. gave, without exception,
41

1 progeny with partially or completely sterile anthers on the most of the plants.
It is therefore expected that a careful analysis of this abnormality would show
that it is a Mendelian dominant in corn. In many instances of total sterdlity, the
flowers never opened while in others the hard shrunken anthers were discharged.
These latter individuals were at first bagged, before we became aware of their
nature, with the expectation of securing pollen. Such a character if it is dominant
could of course not be transmitted unless it is pollenated by a homozygous recessive.
This is another instance of a character, fatal in itself, depending on heerozygosis
(in this case, pollen of a recessive on a pure ot a heterozygote dominant) for its
perpetuation. Thus the character, while it insures mixed-pollenation, is yet un-
desirable because it is a dominant one. Some individuals were found haying a few
fertile anthers among the many sterile ones in the same tassel.

POLLEN.

The daily field notes taken in the season of 1909 upon individual plants, recorded
the exact time of the appearance of pollen and silks upon approximately 5000
plants representing a large range in varieties and all the species groups. A number
of cases were noted in which the silks appeared on the upper shoot at from one
to three days before any pollen was shed from the tassel of the same plant
(protogyny). The large majority displayed a similar and frequently greater
variation in the opposite direction—anthers before silks (protandry), while many
instances were found in which the anthers and silks appeared on the same day
(synacmy ).

In the cases mentioned, we thus found a variation in the difference of time
in days of from minus three to infinity, if we include those plants which produced
no silks at all or were “barren” in so far as production of ears was concerned.
We may therefore expect in many varieties, a normal fluctuation of from one to
four or five days in the interval between the appearance of pollen and silk on the
same plant. Several varietial differences in this respect have already been men-
tioned under “Period of Growth” (see page 80).

Sturtevant 78) made similar observations on single plants, noting first—bloom-
ing in each row of the different varieties grown and from his data we have com-
piled these results :—

co)
=
5 o>
7p) — =o ~~
v fo) 8) fs) ™
a ay a Qa & na
: o a : v
Group é a ae. boa S g
z oS = AS) SSeS) o
= > Etsy te tie ie ss 2 o
BE ve ES Mees ol 32 ae Bw
6 | RON icnita we S23 Se
f : 5 2 eee Be) Bs yas)
fe} 3 6 Oe . Gs Y >
a Zi Aiea Zils eel alg <q
Dent peyanl chess eee 46 12 39 7 0 to 9 2.6
MUG Setccce sens ceo ieeeneernerersee 2: 12 21 2 oto 8 3.4
SWE ett rer cat tea cetecs errant: 40 27 30 8 2 —2to 8 2.4
Soe padaoe blaavearenderat ae II 2 ie) I 0 to 5 1.1
Pope(common)))) see eemee abt ee) 4 Gl I 0 to 7 3-5
l2toyo, (GoreehelD) Je sba5c Sen 8 4 7 I 0 to 6 2.0
RopwCnigei sore ween 14 7 12 2 0 to 3 1.7

With the exception of being the first to bloom in each row, these plants were sup-
posedly normal.
Lazenby 52) reported observations which extended over several years upon
15 or more distinct varieties, as follows:
42

PER CENT OF INDIVIDUALS SHEDDING POLLEN WHEN THE SILK APPEARED.

Some pollen Y pollen All pollen
shed. shed. shed.
Dente Ouvanieties.. «cles sso sys sayere 05 76 32
Biliniseetavanienles/ncr i. can ct eaerlex cece 89 60 38 +
SweebiGmvall CtleS smi saeterteriaras cisterna 08 82 44

As in our own experience, Lazenby found that it is not always easy to tell just
when the pollen is all discharged. With different tassels, we found the pollen
production to extend over a period of from four to eight days.

In 1875 Sturtevant 77a) counted pollen grains in a large number of anthers,
and the number of florets in the tassels. From his results Sturtevant concluded
that the average number of pollen grains in an anther is 2500 and the number
of stamens in a tassel 7200. Allowing two ears of 1000 kernels to each plant,
there would be approximately gooo pollen grains for every ovule to be fertilized.
Using Sturtevant’s estimate of 2500 pollen grains in an anther, Lazenby 52) com-
puted the ratio of number of ovules to number of pollen grains by counting the
flowers in several average sized panicles in dent, flint and sweet corn.

LAZENBY 'S CALCULATIONS.

Approximate ratio

No. of No.of pollen bear- No. of pollen of ovules to

ovules. ing flowers. grains. pollen grains.
DenteGonmerre ype 1520 9300 69750000 I : 45000
Rint COUN sys qatar 940 6500 48750000 Te 5 2000)
Sweet! Cone ceases t 445 1500 11700000 I : 26000

These figures would allow a range of from 25000 to 50000 pollen grains for each
silk to be pollenated where there is only one ear on the plant. However, as
Leavenby has pointed out, there is a great variation in the number of tassel flowers
on different individuals in the same variety. There is also a difference in number
of ears and from what we know now of differences in the size of anthers and the
tassels on which they are borne, the differences in number of pollen grains must
be much greater than in the cases selected by Lazenby. The fact that in some
instances a large proportion of the pollen grains are infertile must also be
recognized,

The first staminate flowers to mature are usually those in the upper part of
the axis or central spike of the tassel the sequence being in both directions, but
mostly downward and, on the branches, inward. When there is sunshine, more or
less pollen is shed throughout the day, but the most of it falls during the forenoon.
On dzys that are favorable, another, shorter period occurs in the evening, a short
time before sunset. Either cold, wet weather or excessive heat may retard the process,
Manipulation of the flower spike in the hand has an accelerating effect, probably
due to friction and warmth of the hand, and a considerable quantity of viable
pollen may be secured from mature flowers in this way.

The distance to which corn pollen is carried depends largely on the nature
of the wind. A rising or whirling wind might readily carry pollen a much greater
distance than a straight wind. Various limits have been placed upon the distance
to which corn pollen is carried by the wind,—varying from 50 feet to a half mile.
In our own work, we found the last blue kernel in a yellow variety at a distance
of zo rods (north) from our breeding plot which furnished the pollen for this
kernel.

43

Viability.

In breeding work with horticultural species, advantage has been taken of the
fact that many kinds of pollen are viable for weeks and months. Booth 10)
germinated grape pollen in New York, three weeks after it had been gathered in
California. Sandsten 70) secured apple and plum pollen from Washington, Tennes-
see, Missouri, and Minnesota; testing it in Wisconsin he found that “a small per-
centage of apple pollen retained its vitality for six months, while but little plum
pollen retained its germinating power this long.” Supposedly authentic instances
have been reported in which grape, tomato, and date pollen has remained viable
two, six, and twelve months respectively 30).

Because of the difficulty experienced in getting very early and very late
varieties of corn to bloom at the same time, it would be very desirable to store
corn pollen or to be able to ship it over long distances, for hybridizing work.
McCluer 57) reported that corn pollen seemed to retain its viability for several
days if kept dry. Webber 85) stated that corn pollen retained its viability at
least two weeks.

In our own work, more than a thousand tests were made on the viability of
pollen and silks. The time in which they were retained ranged from 0 to 25
days in all the combinations made,—tfresh pollen on old silks, old pollen on fresh
silks, and the intermediate combinations. No reliable cases were found, including
hybrids in all the groups and many varieties, in which shoots produced kernels
when pollenated with pollen that had been stored 30 hours. Many successful cases
were found in which the pollen was used in the morning and during the forenoon
Of the day after the one on which it was gathered. For satisfactory results it is
best to use corn pollen on the same day on which it is gathered, discarding what is
not used and getting a fresh supply on the morning of the next day in which
pollenating work is to be done.

These conclusions are supported by the work of others, in which corn pollen
was tested under different treatments and in various germinating solutions. Jost 47)
states that corn pollen remained viable only one to two days under optimum condi-
tions. Pfundt 68) found that pollen of corn remained viable only one day, alike
in all the conditions under which it was kept.

There are many instances in plant species in which self-pollenation results in
few or no viable seeds. Similar cases of sterility in hybrids are known. In an
attempt at hybridizing two varieties of corn many years ago Gartner reported
securing only five kernels. Sturtevant 79) stated that “The agricultural species
[sweet, flint, dent, soft, pop] have a strong tendency to resist cross fertilization
with each other.” Blaringhem 9) stated that many groups of corn do not hybridize
among themselves but cited no authority in support of the statement. East 27
was unable to secure hybrids of Giant Missouri Cob Pipe, a large late dent corn,
and Tom Thumb, an early dwarf pop variety.

On the other hand Kellerman and Swingle 48) concluded that “dent, flint,
soft, sweet, and pop corn cross as freely with each other as with the different
varieties in their own class.” Collins 18) hybridized successfully the smallest
Tom Thumb with large Guatemala and Mexican varieties. Emmerson 102) obtained
a hybrid of Tom Thumb pop and a large, late dent corn.

As has previously been stated (see page 14) wé are aware of no cases in our
work in which widely diverse varieties such as are mentioned above would not
hybridize when fresh silks and pollen are available.

In order to learn whether there are any differences in the external appearane
of the pollen grains, pollen from a number of varieties was observed under the
microscope. Fresh pollen was gathered and placed in the shade, part placed on
glass slides, both covered and uncovered, and part of it being left in the bagi

44

in which it was gathered. It was found that the grains which were plump at first
began to shrink immediately, giving it a deeper yellow ‘color under the lens. In
a number of samples, no plump grains were found after thirty minutes to an hour
had elapsed and yet this shrunken pollen was viable when applied to silks. Ten
pollen grains of from one to three representative plants, in various varieties taken
at random, were measured and the empirical modes of the length-breadth measure-
ments as well as the shape or outline of the pollen grains are given below :—

Size of freshly gathered pollen grains of various varieties (mm.).

on

Crepes 5
Variety Number and Name Se s = 3

eee ee a
104.4=A Pod Corn....:.... (medium sized kernels)....... 30.0904 .146 elipse
1044—B) /Pod!Gorn\... - .- (medium sized kernels)....... 30 .090 .098 pyriform
204.14 Yellow Rice Pop.(very small kernels..:........ 30 .078 .0o86 elipse
ZOO meaed! Peatli Pope a (Smiall’ Kkernels))io- scarier ecient 30 .086 .o98 pyriform
211.— Yellow Pearl Pop(Tom Thumbs—small kernels) 10 .090 094 elipse
212,22 White Rice Pop. (very small kernels).......... 30 .078 = .086 *
213— White Rice Pop. (very small kernels).......... 30 .078 .o86 ee
304— White Flint .... (very small plants—early)....20 .o86 .008 s
402.37. White Dent ....- (Hickory King—large kernels) 30 .082 .098 cs
442.77. White Dent .... (Cob pipe corn—med. kernels)30 .086 .o98 pyriform
Fof—» Sott \Gorn)= 52... (medium kernels)............ 30 .090 .098 elipse
612.92 Sweet Corn ..... (Egyptian—medium kernels)..30 .090 .102 2

From these measurements it appears that there is no difference in size or shape
of pollen grains which will interfere with their successful germination and subse-
quent fertilization of the ovules of any of the varieties used. The ratio between
the modal length and breadth as shown in the above data bring out the fact that
corn pollen is not exactly round as it has been reported by others. With regard
to the inheritance of shape, normal long pollen grains have been reported to be
dominant to round pollen grains in sweet peas 3). It was thought that difference
similar to this might be found in corn pollen.

Correns 19) reported differences in receptivity to pollen when that of several
varieties was applied to an ear at the same time. We have obtained similar results
by using pollen from varieties of different colors and composition of kernels all on
the same shoot and evidently there is a difference in germinating power or recep-
tivity aside from mere viability of the pollen itself.

Difference in the shade of yellow in the fresh pollen of various varieties was
found, some having light yellow and others darker yellow colors. Aside from
this difference in color and perhaps in viability, we found nothing that would in-
dicate distinguishable genetic differences in pollen grains of corn.

SHOOTS.

The immature female inflorencence of corn, composed of the undeveloped ear
with its leafy involucre of bracts or “husks” upon a short stem or “shank’’, is com-
monly known as the “shoot”. This name applies until the ovules have become
fertilized and considerable enlargement of the young ear has taken place.

45

The theory concerning the differentiation of the inflorescence of corn into
“tassel” and “ear”, as has been mentioned previously, includes the idea that the
shank or stall of the ear-bearing branch has become shortened. This idea is
substantiated by the frequent occurrence of very long shanks on individual plants
in general field culture, the increase in length of shank being most frequent on
the lower shoots. In the limited number of individuals of this nature observed in
our work, the extremely long shanks were plainly due more to the increase in
length of the internodes than to an increase in their number. Montgomery 59)
stated that the number of nodes in the ear bearing branches coincided with the
number of nodes found in the main culm above the point of attachment of the ear
bearing branch, in a sweet corn plant which he studied.

From a number of counts we have made on several dent varieties, it appears
that Montgomery’s statement will not hold in some, and perhaps all, varieties.
Only distinct internodes on the shanks were included in the counts and in the
majority of cases there was a larger number of internodes on the shank than on
the main culm above the point of attachment of the shoot; this is very evident
where the ear is borne at the second or third node below the tassel. Incidentally
it was noted that the number of these upper internodes on the culm was more con-
stant in a variety than the number of shank internodes. If each husk on the
shoot is counted and an internode assigned to all that are not paired or multiple,
we would have many more internodes on the shoot than on the upper part of the
culm (above the ear-bearing node). It is often difficult to get satisfactory counts
on shank internodes because of telescoping near the ear. Certain varieties—
notably pop corns—tend to produce secondary shoots on branches in the axils of
the husks on the main ears; these secondary branches may have as many or more
apparent internodes than are found on the main shank,

After four years of selection for erect and declining ears from a straia
which had been previously cross-bred* for seven generations, Smith 76)
reported; “that the ear branch or shank was on the average almost twice as long
in the declining ear strain as in the erect-ear strain, the averages for that year
being about twelve inches and seven inches respectively—the longer shanks had an
average of a slightly larger number of internodes and correspondingly a larger
number of husks.”

In all the groups, individual plants may be found with very long shanks, but
as yet we have no data upon their inheritance. Certain varieties tend to preduce
long shanks while others produce very short shanks but the character is a
fluctuating one. The behavior of the X. hybrids, in which flint, dent, sweet, and
soft varieties with long shanks were used with other varieties having short shanks,
indicate that long shanks are probably dominant to short shanks.

Barrenness.

“Barrenness”, or failure to produce ears, differs from sterility in that the entire
inflorescence may fail to develop, thus the fertility of the flower does not enter
into consideration. Barrenness in corn may include failure to produce a tassel, as
has already been stated, but the large majority of cases deal with the failure to
produce normal shoots.

Detasseling has been resorted to in order to prevent the pollen from barren
plants falling on the silks of individuals from which seed is to be saved for
planting. Some uncertainty exists in this practice because of the difficulty of
determining truly barren plants in some varieties at the time at which detasseling
is done. Bull 11) reported that barren plants “may be discovered by the absence
of the enlarged leaf sheath just above the joint where the ear should appear”;

*Bred by individuals within the variety or strain.

40

while Soule and Vanatter 77) stated that they were unable to distinguish barren
plants, at the time of tasseling, from those which develop-late and eventually pro-
duce ears.

We are aware of no case of reported barrenness which has not been influenced
largely by either environment or decreased vigor and it was at one time suggested
that if barrenness is hereditary, the character would tend to eliminate itself 43, 45),
but this was before it was generally known that characters detrimental or even
fatal to the perpetuation of the species in the pure or homozygous state may yet be
transmitted indefinitely by means of heterozygosis

Plants upon which shoots develop extremely late are undesirable and such
plants usually produce nubbins or poor ears and indicate weakness in general.
It has been suggested that the best way to overcome this evil would be to discard
the parent ears entirely and to select from such ear-rows in a breeding plot that
produc vigorous shoots. Varieties differ very much in regard to size and develop-
ment of shoots at tasseling and silking time, some varieties producing silks before
the shoots leave the leaf sheaths while others develop large shoots before the sills
appear. By delaying detasseling till just before the pollen begins to fall it is
possible to differentiate between vigorous and weak plants in many varieties at least.

It sometimes happens that varieties producing some barren plants possess other
characters which are desirable and since breeding blocks are generally limited in
size the small amount of additional work necessary to detassel undesirable plants
would be well worth while not only with regard to failure to produce good ears
but also with regard to other undesirable features which are known to be trans-
mitted to the progeny.

Since no case has yet been reported where the progeny of a hand-pollenated ear
fertilized by the pollen of a barren plant have all been barren, it would seem that
this behavior—provided it is hereditary—must be either a recessive or a composite
character and be transmitted contrary to the behavior of sterile anthers mentioned
on a preceeding page. .

Husks.

The arrangement of husks about the ear varies within an individual shoot.
They are most frequently two ranked and imbricate, but other arrangements are
to be found, such as; paired, convolute, mixed arrangement, and multiple—not
imbricate—arrangements, at husking time the outer ends or tips of the husks may
be found on one side of the ear. This warping of the dead husks proceeds far
enough in many cases to expose the ears on the opposite side.

In harvesting the crop in 1900, distinct differences were noted in the amount of
husks about the ear and in 1910 a number of counts were made on different
varieties and their : generations. In securing these counts, all the husks on the
shoot including those on the shank were taken. This was done at harvest time
after full development had been attained. ;

A wide fluctuation in the varieties, in number of husks on the upper ear, was
found. This wide fluctuation may be partially accounted for by the frequent
prolifications of the inner husks. The number of parts in these prolifications is
variable. Although extremes of six and twenty-eight husks were found, practically
all the varieties overlapped in this character and variable results would therefore
be expected in their progeny.

If it can be shown that the number of internodes on the shank are the same as
the normal number of husks then it is evident that many of the husks are prolifica-
tions. Had it been possible to eliminate all proliferous husks and thus determine
the number of primary ones (one to each internode) we would have expected more
definite results.

47

If prolification is a recessive character in husks, as it appeared to be in the
case of the ear mentioned on page 37, many of the contradictory cases in the X;,
generations might be explained by this one fact alone. In some instances there
may have been pairing of proliferous and non-proliferous character while in others,
both parents may have had the proliferous character. The conclusion reached
during the study of this character was that many normal husks are dominant to
few normal husks.

General notes were taken on other characters of the husks. Thick and thin
husks (without regard to number or width) were found to be varietal characters
and in a number of X: hybrids, thick husks were plainly dominant to thin husks.
Thickness of the total layer or involucre, depends not only on the thickness of each
husk and on the number of husks, but also on the width or degree of wrapping of
the ear by each individual husk. In the X, hybrids, the wide and well wrapped
husks were dominant to the narrow type.

“The Central West desires a corn with loose shucks so as to be easily husked,
while for protection against insects, the Southern States require a tightly fitting
husk” 40). Market gardeners desire young ears well covered with husks which
permit storing the roasting ears for a longer period than do the ears of those
varieties poorly covered with husks. East 24) reports finding a row of sweet corn
in an ear-row test of Stowell’s Evergreen, in which the ears were especially well
covered with husks and remained in table condition for over a week (presumably
after picking) while ears from other rows remained in prime condition only one day.

On some varieties used in this study the husks were very loose even though the
involucre was relatively thick, this was especially noticeable before the kernels on
the ear had enlarged to any extent. The husks remained loose and creased through-
out the season in some varieties while-in others they were tightly stretched and
forced to expand as the ear developed. This firm, compact, type of shoot was
dominant to the loose type in the 1 hybrids and was very noticeable as the young
ears were developing in the field.

The Mexican variety No. 408 produced shoots with many, wide, thick husks,
the inner ones of which were folded or rugose longitudinally in the upper region
and laterally rugose at the base. These rugose husks were constant in the 408
variety and dominant in its X1 hybrids. Collins 18) reports a hybrid in which the
“inner husks were crumpled at the base of the ear, a not uncommon condition with
thick husked varieties.”

The absolute length or size of husks on the hybrids behaved much like the
size of plants, being intermediate in some cases and in others equal to or greater
than those of either of the parents. Varieties producing long ears necessarily
develop long shoots and husks and length in these instances is dominant to shortness.

With regard to the relative length of the husks and ears or cobs, the behavior
discloses an interesting difference. When hybrids were produced between a variety
in which the mature husks extended beyond the tip of the ear and a variety in
which ear and husks were conterminous, the hybrid invariably exhibited the latter
character. But when either of these two types were hybridized with a type in which
the ear protruded, the protruded ear character was dominant. All the plants of
the pod variety No. 1o1 displayed the protruded ear character which was always
dominant in its i hybrid progeny. One of the Mexican varieties (No. 410)
produced approximately 50 per cent of individuals with protruded ears and this
was a distinguishing character in its &; hybrids. Collins 18) found a behavior
similar to this in two cases in which a large number of the ears protruded beyond
the husks in the Xi hybrids. In my results it appears that while long husks are a
dominant character as well as the long ear, the long ear yet exceeds the long husks
in relative as well as absolute length.

48

The husks of most varieties are green but in some a red tinge is frequent.
This red tinge, which is often associated with red tinge on the culm, appeared in
the X: generation from parents having green husks hybridized with other parents
having red tinge husks. Red husked plants were frequent in the variety No. 408
as well as in the hybrids in which it was one of the parents, and homozygote red
husks would be expected to be dominant to red tinge and pure green husks.

Laminae.

Many years ago, Goethe, the great German naturalist-poet, announced the theory
that floral parts are nothing more than modified leaves. This idea is perhaps no
more beautifully illustrated than in the enveloping involucre or husks of an ear
of corn. When the shank in the shoot is relatively long the lower husks assume
the form of true leaves. With a tendency toward a shorter shank, there is a
decrease in the leaf-blade until the leaf sheath, which has become a husk, bears a
very small blade or none at all.

In some varieties these small leaf blades or “laminae” persist on the outer husks
and in some individuals (occurring in all the species groups) these laminae may
equal the length of leaves—two feet or more in length in extreme cases. Develop-
ment of unusually long laminae is generally associated with long shanks and small
ears. In those in which extremely broad laminae were developed, the size of the
ear was also generally diminished.

As a varietal character, long laminae are more often found in the flint, sweet,
and soft groups. Varieties producing very short or no laminae are more often
found in the dent and pop groups.

In studying the behavior of length of laminae, we are dealing again with a
fluctuating character and one which, similar to the suckering character, seems not
entirely lost in any variety. In addition to this fluctuation between plants in the
parent strains, there is also another and similar fluctuation upon the individual
plant. The laminae on the lower shoots are nearly always longer than the laminae
on the upper shoot, and a similar increase in length exists on a single shoot from
the tip downward.

Because of this variation in length of laminae, it was found impracticable to
secure exact measurement and the data were taken with respect to the length of
laminae on the upper shoot only and as compared to the relative length of the
shoot on which they were borne. While this method was only an approximate one,
the data were all secured by the same person and, aside from a possible bias in
judgment, the classification was uniformly made in all the parent varieties and x:
progeny.

It was noticed that few of the varieties are constant to the “Type Group” in
which they fall and distinct genetic differences within a variety, and consequently
variable results in the hybrids, are to be expected. Seven of the ten hybrid cases
which gave an “Average” result were such in which the parents had like modes
and the hybrids produced the same. Eliminating these seven cases, the large num-
ber of the hybrid results would appear to fall at either extreme as shown in the
summary. This should not occur if there is a genetic difference in length of
laminae.

Among the remaining 29 cases on which data were taken, a small majority
indicate dominance of the long laminae. Certain hybrids displayed this dominance
of long laminae so markedly that we would expect this result in all cases where
homozygous parents are used. The mixture in varieties is evidenced by the results
secured in the closes in which there were distinct differences in behavior while all
the ; results would have been expected to fall in the “average” list. The selfed
cases as usual are limited in number but indicate a decrease in the length of laminae.

49

Occasional individuals occur having abnormally broad laminae, the inheritance
of which has not been determined. One variety (No. 214B) frequently having
short, broad laminae gave, in its hybrid with a variety (No. 210) haying short nar-
row laminae, medium and broad laminae. .

The colors of the laminae are generally the same as those of the leaves on the
plant and behave similarly in transmission.

Silks.

The most conspicuous phenomenon in connection with the development of the
shoot is the appearance of the silks. Their growth is very rapid and their period
of usefulness limited. When pollenation of these silks or “styles” is prevented they
may continue to grow for a.number of days. Lazenby 52) reported that “Some of
the silks [of a dent variety] attained a total length of over eighteen inches.”

In our study of the receptivity of silks of various ages, a number of individuals
were found which had attained a length of 8 to 14 inches beyond the tip of the
shoot. This behavior might be considered as an adaptation to provide a fresh
surface upon which the pollen may lodge, but the length to which the silks may
grow is apparently correlated with the length of the cob from which they arise.

As has been reported under “Technic”, the silks are receptive at any point and
clipping them back does not interfere with the subsequent fertilization of the ovules
by pollen applied after the silks have been clipped. This test was also applied by
Kellerman and Swingle 48), and in addition they opened the husks of some shoots
before the silks appeared and succeeded in getting poorly filled ears by applying
pollen in this way. From our own observations in repeating this experiment, it
was found that only those silks were receptive which would have appeared very
soon after the time at which the husks were opened. When the husks were stripped
back on the shoots which had silks well exposed, and pollen applied to the portion
of the silks within the shoot, successful fertilization was effected.

The silks, which are double in structure, are more or less hairy near the
extremity and an erroneous idea has been given in popular descriptions of the
process of fertilization of the silks, by the statement that these hairs catch and hold
the pollen in their grasp. The hairs provide an increased surface upon which the
pollen may lodge, but the moist surfaces of the silks and pollen grains alone serve
to hold the grains which must germinate very quickly judging from the very short
period in which corn pollen is viable when exposed in a normal atmosphere.

Some writers state that the silks from the base of the ear appear first and the
ovules from which they come are consequently fertilized before the others on the
ear 11). This statement is true only in the broad sense—meaning the lower portion
of the ear. Among the many ears secured in our work by hand pollenating silks
of various ages, we found many imperfectly filled butts and bare tips on ears which
were pollenated soon after the first silks appeared.

The double pollenated ear—No. 2S3.170—was an instance of this nature. The
dam of this particular ear was a white pearl pop (No. 210). On the first day on
which the silks appeared, it was pollenated from its own tassel (selfed). Six
days later, pollen was applied from a variety having a yellow endosperm (No. 300).
As has been stated, the selfed and hybrid kernels were determined by the differnce
in color and a distinct band of pure white kernels was found at some distance above
the butt of the ear. The remainder of the kernels below and above this band were
yellow. A number of other and similar cases were found.

At the end of the six days, the silks at the tip of this particular ear had not
yet developed for the reception of pollen as was shown by the bare cob at this
point. This regularity of distribution does not appear on all ears, many of which
have irregular patches of kernels evidently due to the uneven development of silks

50

on various parts of the spike. Irom the many hand-pollenated ears secured, the
longest interval of time between the first apeparance of-silks and the last date on
which the younger silks on the same ear were yet receptive was thirteen days, and
in this case only a few kernels at the tip of the cob were secured. Entire ears may
be pollenated fully in the natural way in a period ranging from two to ten days,
depending upon the variety and conditions.

Differences in the size and structure of silks were found but no attempt was
made to study their behavior in the hybrids. In varieties having colored siiks
(other than pure green or yellowish green) the hairs on the silks are the first
and frequently the only parts to become colored.

No variety was found which was homozygote to silk color but the populations
from selfed seed showed exact uniformity in color of silks in most of the cases.
In one of these i selfed cases (No. 201S) silks were produced having a dark
yellowish-green color; the behavior of this color on hybridization has not been
determined. Several cases were found in which dark green silks were dominant
to light green silks in the 1 generaticn. Green silks & green silks in most cases
gave green silks only, but several cases were found in which only parents with
green silks had been used, where the 1 generation showed some individuals with
red tinge or reddish green silks. Without a knowledge of the ancestry previous to
1909, we are unable to state whether such cases are due to heterozygosis which did
not shown in 1909 or whether they are due to new combinations in the & generation.

The notes on the silks were taken somewhat early in their development in
many cases and it is possible that some of the parents developed a red color after
the notes were taken. In general the order of dominance of silk color appears to be
as follows: dark red, reddish green, red tinge, to green. Numerous cases have
been reported by others in which the deep red silk appears to be dominant to the
green and red tinge silk.

The behavior of the various shades of green fall in a separate category from
that of the reds, and either of the greens may be obscured by the red color. It '5
very doubtful whether red tinges which are absolutely constant to degree of colora-

tion can be secured. :
Positicn of the Upper Shoot

Instances have been reported which permit the general conclusion that shoots
may be produced in the axil of any leaf on the culm or its branches. Among the
varieties used in this investigation we found ears at various heights on plants and
at all internodes below the tassel, while small ears at the base of the tassel are
not uncommon, but a rather definite location for the production of the main ear-
bearing shoot exists in the different varieties. The number of upper internodes
(between the tassel and the upper or main ear-bearing shoot) is more constant
throughout the varieties of corn, than is the number of lower internodes (below
the upper shoot).

The results secured at the Illinois Experiment Station 76)- in selecting for
“high” and “low” ears, gives evidence in support of the above statement. Height
of ear in inches above the soil was made the basis of selection in this instance.
Data were also secured upon the total height of the plant, number of internodes
below the ear, and the total number of internodes on the plant. If from this
data we compare the difference between the number of internodes below the ear
and the total number on the plant, we find that this difference (7 internodes) was
always the same in both plots except in one year. In this aberrant year, the
“high-ear” difference was six internodes and the “low-ear” difference only five inter-
nodes. The cause of this is not known, but it is important to note that the excep-
tions occurred on both plots in the same year. If the deviation of one were added

51

to the total number of internodes given for the “high-ear” plot and the deviation of
two to the number given for the “low-ear’ plot in that year, it would at least make
the “total internode” columns for the six years more uniform as well as .to give
exact uniformity in the number of upper internodes in both plots for all the years.

From the data, it is also evident that there has been no change in the “high-
ear” plot in the height of ear, neither in inches nor in number of internodes.
Neither is there any change evident in this plot in regard to total height of plant
and total number of internodes. The difference (three feet), which now exists
between the two plots is due solely to a change in the “low-ear” plot in which the
height of ear, both in inches and number of internodes, is but little greater than
half of what it was at the beginning. There has also, apparently, been no change
in length above the ear in the low ear selections; the average length in inches above
the ear being slightly more in the low-ear plot than in the high-ear plot.

This decrease, which has been found in the “low-ear” strain, suggests the
idea that homozygous “low-ears” have been selected and mated from within a
heterozygous population. The fact that the “High-ear’” strain has remained con-
stant with only slight fluctuations, readily attributable to seasonal differences, sug-
gests in a similar way that the parents of this strain were either homozygous “High-
ears”, or that this is the dominant character and that extracted “High-ears” have
been selected, thus maintaining but not materially increasing the height of the
strain. As in the case of the differences in oil and protein secured in other strains,
no one can say positively as yet what is happening in these experiments of far-reach-
ing importance,

Data were taken to secure exact information upon the behavior of the relative
height of the upper shoot. It is significant that there is a very close uniformity
between all the parent varieties in the number of upper internodes (above the upper
shoot), irrespective of the number of lower internodes. It is also significant in
comparing cases, that this internodal height of the upper shoot or ear is not affected
by the number of shoots on the culm.

As was stated previously; it is difficult to determine the internodes at the base
of the plant at the time of maturity, and it is evident that a shortening of inter-
nodes at this point is partially the cause of fluctuation in the number of lower inter-
nodes, apparent at maturity, in some varieties.

The reciprocals indicated small differences but in general these cases are fairly
uniform.

The summary of the data shows that a large majority of the hybrids are
above the average of the parents in number of lower internodes. The results in
the closes and selfs indicate that individual parents were used which had a greater
number of lower internodes than the mode of the variety from which they came;
a result contrary to that which would be expected from inbred progeny.

The summary of results with respect to the number of upper internodes is
indefinite and had the study of relative height of the upper shoot been made only
with respect to its distance from the tassel, no definite conclusions would have
been reached. The extremes in the number of upper internodes in all the parent
modes are five and eight, which, with the existing fluctuations, allows the parent
arrays to overlap and does not provide sufficient difference for marked differenta-
tion in the 1 hybrids. The fact that the majority of the fourteen hybrids fall in
the average group is attributable to the use of parents which were very similar in
this respect. No definite concluiosns can be made on the behavior of the ; closes
and selfs.

In order to check the behavior of the upper and lower internodes simultaneously
on the same population, the “Relative Height on the Plant” was computed from
the sum of the two modes. In the data secured in this way, we find that in the
large majority of cases the relative height of the upper shoot in the x1 hybrids

52

is equal to or greater than that of either of the parent modes, therefore, relatively
high ears on the corn plant must be a dominant character.

Number of Shoots.

Perhaps no organ of the corn plant is more dependent upon environment and
vigor of growth than the shoot containing the undeveloped ear. While certain
varieties normally produce a large number of shoots in comparison to other
varieties, adverse conditions may inhibit their development entirely.

While the large majority of shoots on the lower part of the stem may fail to
produce ears, their partial development is an indication of an ear bearing tendency,
and as such is important in a study of characters in the corn plant. How the
difference among varieties in shooting tendency and prolificacy in ear production
came to exist, is not known, but it is evident that there must be a close correlation
between this and other characters in the plant. As an example, the production of
an extremely large ear in the upper shoot is not associated with a large number
of ears, and those varieties producing a large number of shoots generally have
small ears.

It is evident that the production of shoots is closely related to the production
of suckers, and individual plants are frequently found in which it is difficult to
distinguish between the lower shoots and the suckers. Card 12) made selections
in a variety of sweet corn for large number of ears on the plant, and found that
the increase which he secured came chiefly from the increase in the number of
ear-bearing suckers.

My data was obtained by counting all the shoots which extended beyond the
leaf-sheaths on the main culm of each plant. This data, therefore, includes a very
large proportion of shoots within which ears failed to develop. Data were also
secured upon the number of ears harvested and, as would be expected, those
varieties producing a large number of shoots also tended to produce a large
number of ears. The same parents and hybrids used in the study of behavior of
number of internodes were used in this instance, and it is evident that with a
given number of internodes sufficient to permit the development of numerous
shoots, the number of shoots actually developing does not appear to have any rela-
tion to the relative height at which they are borne.

' As usual, interesting differences in behavior were found when one parent
variety was used in different combinations with other varieties. The reciprocals in
this table gave quite uniform results as is shown by the arrays in each case.

The summary of the , hybrids places the large majority above the average
of the parents in the production of shoots. As has been noted, the production of
shoots depends to a large extent upon vigor of growth and therefore hybridization
should favor the development of a large number of shoots. Leaving out the 11
cases which gave a number of internodes above those of the greater parent, which
result might be attributed to increased vigor, the remaining hybrids in the sum-
mary yet show that a “large number of shoots” on the main culm is dominant to
a “small number of shoots”.

Close pollenation in the majority of cases evidently had no limiting effect upon
the development of shoots in this one season. Among the selfed cases only two
showed a decided decrease in the production of shoots, while one (310XS) of the
six cases produced a mode slightly above that of the parent mode of the previous
year. A comparison of all the parent modes in both years shows that the modes
for 1910 were generally higher than those in 1909; therefore, the selfed case, having
an apaprent slight increase, must have been the result of difference in seasons.

As is the case with all the other characters discussed in this paper we must
consider not only environmental influences but the probable genetic differences

on

3

within the populations studied. The important fact brought out by the summaries
of the various tables is: that in order to get definite results we must have individuals
pure with respect to the character with which we are concerned, or at least observe
their behavior in the second controlled generation when the data carefully secured
may be just as reliable, regardless of the mixture in the original parents.

54

APPENDIX

The writer, Walter Byron Gernert, graduated from the Kansas State Agricul-
tural College in June 1907 with the degree of Bachelor of Science in Agriculture.
In September 1907 he entered the Graduate School of the University of Illinois,
from which he received the degree of Master of Science in Agronomy in 1909.

During the years 1905-07 he was Student Assistant in the Kansas Experiment
Station and was later connected with the Illinois State Soil Survey through the
field seasons of 1907 and 1908. He held a Fellowship in Agronomy in the Uni-
versity of Illinois during the academic years 1908-'IT.

The writer desires to express his gratitude to Dr. L. H. Smith, under whom
this investigation was made, and to acknowledge his indebtedness to others who
have rendered much valued assistance.

55

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