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Macmillai’s Science Monographs

THE COTTON PLANT IN EGYPT

MACMILLAN AND CO., LimITED
LONDON . BOMBAY . CALCUTTA
MELBOURNE

THE MACMILLAN COMPANY
NEW YORK . BOSTON CHICAGO
DALLAS SAN FRANCISCO

THE MACMILLAN CO. OF CANADA, Lrtp.
TORONTO

__ .._._......_g@°&g _. Sy ___ _

Tue ‘*SHoRtT-STYLE” FLOWER or Cotton,

THE
COTTON PLANT
IN EGYPT

Studies in Physiology and Genetics

W. LAWRENCE BALLS, M.A.

Fellow of St. John’s Co ollege, Cambridge.
Membre de PiInstitut Egyplicn ; Bo fants Ld e a
Department of Agriculture, Egyptian G melt

MACMILLAN AND CO., LIMITED
ST. SA RIIN'S SPREET, LONDON

T9Q12

RicHarp CLay AND Sons, LIMITED
BRUNSWICK ST., STAMFORD ST., S.E., AND
BUNGAY, SUFFOLK.

PREFACE

THis book has been written with the purpose of
abstracting the results of a series of researches made
upon cotton plants in Egypt, which investigations,
though diverse, were connected by the desire to know
all that could be learned about the plant itself. Portions
of these inquiries have appeared in various journals,
but most of the material here utilised has not yet
been published. Where it may appear to the reader
that a conclusion necessitates much fuller data than is
placed before him, I can only ask his clemency until
such time as a fuller monograph shall be written.

Primarily, I have written for those few Economic
Botanists who are more botanical than economic, but I
have found so much genuine interest displayed by the
pure botanist, and by the pure economist, as well as by
the cotton spinner and the irrigation engineer, that in the
hope of giving them some explanation of the relation
between my inquiries and their interests, I have written
with divided attention. The result is avowedly un-
satisfactory, but the difficulty is inherent in any application
of natural science to economic material.

While the subject is parochial in its origin, having

been studied almost entirely at Cairo, I venture to think
vii

vill PREFACE

that its interest is not purely Egyptian, if only from the
fact that American Upland cottons have been employed
extensively ; the chapters on Heredity apply equally to
the American crop.

Some of the data are not without suggestiveness to
students of even human physiology and genetics.

The views expressed are purely personal, except where
specific reference is made to the contrary. To any who
may recognise their assistance inadequately acknowledged
I herewith proffer my regrets, with the assurance that
such plagiarism has not been conscious.

The botanist may find, I fear, that the treatment is
far from thorough in its consideration of recent work,
and it may be that in many matters which I have
regarded as original the priority rests elsewhere. For
such mistakes it may be fairly pleaded that Egypt has
been a lonely place for a botanist until the current year.
Even the card index reproduced as the bibliography is
rather casual than systematic.

The economic importance of any contribution to our
knowledge of the cotton plant needs no explanation. The
industry is one of the largest in England, with almost
unlimited influence. In Egypt itself the cotton crop is the
prime factor in the finance of the country ; other crops
and industries are relatively insignificant, and a partial
failure of the cotton crop may cause a financial crisis.

It might be thought that such an important crop
would have been one of the first to which scientific
investigation should have been applied by the world in
general, so soon as the profitable nature of such inquiries
became obvious to the financier. Unfortunately, the
trail of the “ practical man” was followed somewhat

PREFACE ix

too closely in the investigations which were made before
the end of last century, with the result that many field
experiments have expressed the net result of many
conflicting factors, and have given but little indication as
to the components.

On my appointment to the staff of the Khedivial
Agricultural Society at the end of 1904, as Cryptogamic
Botanist, and hence specialising on heredity and physiology
in cotton—on account of the innate perversity of things
Egyptian—I decided to abandon the accepted method of
crop-inspection on a large scale, and to substitute detailed
examination of a few plants. The literature then extant
gave scarcely any assistance to such heterodox procedure,
and the story of the researches which followed from this
decision has been written on a tolerably clean sheet.

The work began as Genetics, but necessarily extended
into Physiology. This mental transition was accelerated
by the pronounced deterioration of the Egyptian crop,
both in yield and quality, which began to be obvious in
1905, and culminated in the catastrophic failure of the
1909 crop. The physiological researches necessitated by
demands for information as to the possible effects of
unsuitable soil-water conditions have given results of
more immediate interest, and of greater novelty, than
the weary routine accumulation of critical data for
Mendelian analysis, though the latter are probably of
higher intrinsic value.

For years it had been intended to establish a suitable
field laboratory in which the work could be conducted
efficiently, but, owing to various causes, this establishment
was delayed, and it has taken from December 13th, 1907,
when the resolution was passed, till March, 1912, to

% PREFACE

realise intentions in this respect. The.scope and utility
of the work has been limited to a regrettable extent by
the absence of this provision, and more particularly on
the economic side.

My acknowledgments for assistance rendered: must of
necessity be incomplete. In the first place, my thanks
are due to the Khedivial Agricultural Society, which for six
years gave me freedom to conduct researches as I choose ;
for this exceptional treatment I am indebted to H.H.
Prince Hussein Pasha Kamel, President of the Society, to
Mr. G. P. Foaden, and to Abdel Hamid Bey Abaza,
successively Secretary-General thereof, while my colleagues
on the staff have given every assistance. Since my
transfer to the new Department of Agriculture the work
has been continued, the Mendelian laboratory projected by
the Society has been established by the Egyptian Govern-
ment, and a pure-strain system of seed-supply is in process
of adoption.

Many of the records utilised would not have been
obtainable without the steady co-operation after 1909 of
my assistant, Mr. Francis 8. Holton, to whom I am
especially indebted. The members of the Cairo Scientific
Society, and of the Botany School at Cambridge have
displayed an encouraging interest in the work.

To specify individual assistance among so many would
be invidious, but on looking back over the train of ideas
involved, I find that the most illuminating of these have
come from the late Mr. J. R. Gibson, English Com-
missioner for the State Domains, from Mr. F. F. Blackman,
F.R.S., Reader in Botany in the University of Cambridge,
and from Mr. J. A. Todd, Professor of Economics at the
Khedivial School of Law, Cairo, while the data on the

PREFACE xi

h drology of sub-soil water garnered by Mr. H. T. Ferrar,
of the local Survey Department, have provided a founda-
tion for discussions on this most important topic.

I should like also to acknowledge the pains which
Prof. R. A. Gregory, the Editor of this series, has taken,
under all the disadvantages involved by my absence in
Egypt.

The greater part of the work would not have been
executed had it not been for the assistance of my wife,
who has also helped me in preparing the present volume,
and in working up the records on which it is based.

W. Lawrence BALLs.
Gezira House,
CatRo.

CONTENTS

PREFACE

SECTION I
HISTORICAL

SECTION II
THE INDIVIDUAL PLANT

CHAPTER I

FERTILISATION, CYTOLOGY, AND EMBRYOLOGY

CHAPTER II

DEVELOPMENT AND ENVIRONMENT. I,

CHAPTER III

DEVELOPMENT AND ENVIRONMENT. II

CHAPTER IV
THE COTTON FIBRE

SECTION III
THE RACH

CHAPTER V
FLUCTUATION

PAGE
vu

XIV

COMMERCIAL VARIETIES .

NATURAL CROSSING .

HEREDITY. I

HEREDITY. II

ECONOMICS .

BIBLIOGRAPHY .

CONTENTS

CHAPTER VI

CHAPTER VII
CHAPTER VIII

CHAPTER Ix

SECTION IV

CHAPTER X

PAGE

105

113

127

150

176

181

LIST OF ILLUSTRATIONS

e ‘‘Short-style” Flower of Cotton . . . Frontispiece
. Ovule, Seed, and Lint A

. The Mechanism of Nuclear Division

. Development of Pollen

. Fertilisation and Embryology .

29. Temperature of the Seed Bed . a a
. The Plant and the Environment. Gezira, Cairo, 1911
. Growth and Temperature of a Fungus

. Growth and Temperature of a Root

. Growth of Stem .

. The Sunshine Effect .

. The Root: Development, ASpiyation anil. Hagensration
. Seedling

. Water Jet Hxoavatinn of Buots

. Regeneration of the Root-System .

. Stomatograph Records

. Transpiration in Field Crop

. Internal Temperature of Leaves

. Comparison of Varieties

. Specific Growth-habit

. Flowering Curves. Giza. 1910.

Mean Flowering Curves in Field Crop, 1909, 1910 and 1911

. Composition of Sheddings

. Terraced Land. Giza. 1909 .

. Height of Stem . é
. Maximum Lint-length of Single Suede F
. The Impurity of Commercial Varieties .
. Netted Plants

52a.
52s. ; ‘
. Correlation Diagram for Two Bates of Alldiounerphe j

The Breeding Plot
The Breeding Plot

PAGE

103
111
117
120
121
131

XV1 LIST OF ILLUSTRATIONS

FIGe

54. Typical Plant of ‘‘77.” July 10, 1909
55. A File-sheet BY ttn, 8

56. Growth of Stem

57. Height of Stem in June .

58. Height of Stem in F,

59. Length of the Leaf .

“60. Form of the Flower

61. Width of the Boll

_ 62. Form of the Boll

63 and 64. Loculi of the Ovary

65. Loculi of the Ovary .

66. Mean Seed-Weight .

67. yy $5 in Inter- en ewes
68. ,, ‘5 in Aigypto-Upland Cross
69. Dissection of Mean Seed-Weight in F,

70. Mean Maximum Lint-length

71. Area and Yield of the Egyptian Cotton Ciro 1895- 1911

PAGE

134
135
152
153,
155
157
161
162
163
164
166
167
169
169
171
174
177

THE COTTON PLANT IN EGYPT

SECTION I
HISTORICAL © *

Tue history of civilisation in the Nile Valley can be
followed into the past for half a hundred centuries.
Textile fabrics have been found among the earliest
remains of Ancient Egypt, but in none of these can we
recognise any fragment of the plant upon which is based
the latter-day prosperity of the country.

The cloth found in the ancient remains, notably as
mummy-wrappings, was invariably made of linen, and
though a watch is being kept by the Antiquities Depart-
ment for traces of the cotton plant, none have yet been
discovered. Still there is a strong presumption that the
genus Gossypium is no modern upstart in Egypt, for in
spite of philological confusion it seems clear that cotton
was in common use during Ptolemaic times, though flax
was exclusively employed for funereal purposes. Pliny
gives an unmistakable description of a cotton plant which
grew in the upper part of Egypt, from which garments
were made for the priests, Herodotus describes how Amasis
sent a cotton corselet of wonderful fineness to the
Lacedemonians, and the famous tri-lingual “ Rosetta

* Reference numbers appearing in the text denote publications by the
Author, as enumerated in the Bibliography. References to other authors
therein enumerated are made in the usual manner, with a number in
brackets where more than one paper is given.

2 THE COTTON PLANT IN EGYPT
Stone,” which solved the riddle of the hieroglyphs, bears

a reference to cotton.

These and similar data, however, do not enable us to
trace the existence of cotton in the Nile Valley beyond
an earlier date than about B.c. 200, and such antiquity is
trivial in Egypt. There are, however, several wild cottons
in the Sudan, some of which were recorded by explorers
in the early nineteenth century; whether they are truly
indigenous, in view of the extensive movements of Arab
traders all over Africa, may well be doubted, but their
existence leads one to think that some lucky excavation,
or perhaps a casual glance through a microscope, will
suddenly extend the known history of cotton in Egypt by
two or three thousand years.

The geographical position of Egypt, on the overland
commercial route to the East, makes the recognition of
indigenous cotton a difficult matter for medizval times.
Later, at the end of the sixteenth century, we have
records by Arabic writers which describe the cultural
operations pursued in Egypt itself, and mention the
principal localities in which weaving was practised. At
the same epoch we have the first botanical record of an
Egyptian cotton plant, by Prosper Alpino and by Vesling.
Although the plant they figure was merely an ornamental
garden shrub, and apparently distinct from the cultivated
one, the record is not without interest, as it seems to
describe the same Peruvian-type tree cotton which was
taken from a garden and extended into a field crop by
Jumel, some two centuries later, and from which the
present stock has developed.

When Napoleon Buonaparte effected his famous invasion
of the country at the end of the eighteenth century, he
brought in his train a peaceful force of savants, whose
labours are fully recorded in the unique “ Description de
lEgypte.” From this we obtain much detailed informa-
tion, with the added advantage that the herbaria then

HISTORICAL 3

collected are still extant. ‘'wo entirely different species
of cotton were then under cultivation. One was a tree,
grown in Upper Egypt, and apparently identical with
Alpino’s plant. The other, an annual, peculiar to the
Delta, was possibly the same as the cultivated form which
Alpino did not describe ; in any case it belonged to the
Asiatic group of cottons, still found on the other shore of
the Levant, but now extinct in Egypt, and only repre-
sented in the Nile Valley by a tree-cotton found in
Sennaar, two thousand miles away.

The cultivation of this short- -stapled Asiatic cotton
died out,in consequence of the economic development of
Jumel’s plant, and the last trace we find is a record in
1840 stating that it was almost extinct.

The tree-cotton from Upper Egypt, probably identical
with Alpino’s garden plant, possibly even with that of
Pliny, was next brought forward under the egis of
Mohammed Ali, founder of the Khedivate, at the sugges-
tion of M. Jumel, a Franco-Swiss engineer. Taken from
the garden of Maho Bey, in Cairo, it was propagated
rapidly from the year 1820 under a system of State-
control, and soon displaced the Asiatic type. The brown,
long, strong lint, readily ginned from the almost naked
seed, quickly made its reputation with the spinners, and
this type of lint has been typical of the Egyptian product
ever since.

To trace the origin of the present cultivated varieties
from this stock is almost impossible. Still, the following
interpretation meets all the facts at present known.

The success of Jumel’s tree-cotton led to the importa-
tion and trial of other cottons, notably Sea Island.
Importations of this latter strain, an annual in habit, have
continued to the present day. It is not very successful
in Egypt, yielding lightly, and suffering unduly from
“shedding,” but the lint is often of good quality, equal
to that of Georgia’s and Florida's. The state control of the

: BQ

4 THE COTTON PLANT IN EGYPT

seed-supply became disorganised after a time, partly in con-
sequence of Mohammed Ali’s military activities, and the
inevitable mixing of the two seed stocks was accelerated.
This mixing, combined with natural crossing, led to the
formation of splitting-forms, some of which were annual
but brown-linted, and these gave rise to the Ashmouni
stock, or old “Brown Egyptian,” which dominated the
fields up to 1887. The tree-type disappeared in conse-
quence of its greater liability to damage from insect pests
such as the Boll-worm (Harias insulana) which was
definitely recorded in Egypt as early as 1876, and also on
account of the better cultivation obtained with plants of
annual habit. The only remaining trace of its influence is
the presence of abnormally tall rogues—up to four metres
in height—in the field. The Hamouli variety was possibly
an intermediate stage in this process of extinction by
artificial and natural selection.

From the Ashmouni stock came the Afifi, in 1887, by
selection, probably natural in part, and from this now
degenerate complex of sub-varieties and splitting-forms
other varieties have been selected. The Ashmouni stock
was driven into Upper Egypt, and has.there improved
itself until it is now making a reputation anew.

The relatively white lint of the Sea Island stock has
always been a feature of at least one Egyptian variety,
such as Abyad and Gallini, both extinct, and the modern
Abbassi. Gallini in particular, while possessing the bigger
boll, higher yield, and “climatic suitability” of ‘its
Peruvian-type ancestor, was a very fine cotton, which
controlled the fine-spinning market for years until it
deteriorated through mixture and crossing and was driven
into oblivion by competition with Georgia’s and Florida’s,
its own ancestors. Gallini has been revenged of late years
on its unnatural ancestors by the modern Yannovitch,
itself a single plant selection from the Afifi complex.

The apparent identity of all the modern varieties of

HISTORICAL 5

Egyptian cotton in external appearance—for even when
grown side by side they are scarcely distinguishable—
is the natural result of their origin from two related stocks.
This absence of differentiating characters, excepting for
the lint itself, has been responsible for a fund of fatalistic
ideas about deterioration, which, though possibly
appropriate to the near Hast, are nevertheless untenable.
The “running-out ” of varieties, miscalled inevitable, need
no longer be the bogey of the cultivator. A recognition
of the incontrovertible fact that the nominal varieties are
more or less heterogeneous complexes of heterozygotes,
even when first introduced to commerce, should enable us
in the future to dictate the history of Egyptian cotton
with greater definition than Mohammed Ali could ensure.

Systematy.—In this brief summary of the few
available historical facts, it has seemed advisable to evade
systematy, and the pitfalls thereof, by referring to
G. wtifoum (Cav.) as the “ Peruvian type,” and to
G. herbaceum annuum as the “ Asiatic type.” For
further details the reader should consult Mr. Fletcher’s
article* and Sir George Watt’s monograph. Though
opinions may differ as to the real importance of some of
these classifications, the latter book nevertheless forms
a standard and permanent record of specimens and
synonyms.

The three main phyla of Gossypium are all represented
in the Nile Valley, for the weed “ Hindi” cotton now
found in the fields is certainly on the same phylogenetic
line as the “ American Upland stock,” or G. hirsutum.
The author’s inclination is to believe it to be a smooth-
seeded sport from G'‘. hirsutum, since parallel cases are
well known in both the other phyla.t In any case, the
Egyptian ‘‘ Hindi” is not homogeneous, but consists of at
least two forms, one hirsute, the other glabrous.

* Fletcher (*). } Allard, H. A. (4), Fyson, P. F.

SECTION II

THE INDIVIDUAL PLANT

CHAPTER I
FERTILISATION, CYTOLOGY, AND EMBRYOLOGY

THE development of the sexual cells’ in the cotton flower
bud is not marked by many special features, but the
intrinsic importance of the gametes is such that the main
characteristics of their microscopic’ history should be
examined, if only to facilitate their visualisation when
matters relating to heredity are under discussion.

The life-story of the individual begins at the moment of
fusion between the male and female gametes, viz., between
the generative nucleus of the pollen grain and the egg-cell
of the ovule. The unicellular zygote thus formed develops
by repeated division into an embryo enclosed in the seed-
coats, and the germination of this seed is the stage
commonly regarded as beginning the life-story. For
reasons both of precision and of ultimate convenience, we
shall commence the study of an individual plant at the
union of the gametes, first, however, describing the genesis
of the latter.

The Gamete-mother Cells.—The young flower-bud
(Fig. 1) develops centripetally from the primordia of
involucral bracts, calyx, corolla with staminal column, and
lastly ovary. The latter is composed of two to six carpels,
which originate as separate ring-primordia, developing

cH. 1 FERTILISATION AND EMBRYOLOGY

Se OM fi
NEL yf

W.L.B. dol.

Frias. 1 to 7.—Ovuig, Srep, anp Lint.

8 THE COTTON PLANT IN EGYPT cuap.

into hollow cones. These unite laterally to form the 2-
to 6-locular ovary, while the combined apices of the cones
elongate to form the style (sy.). Large-celled conducting
tissue is formed at the base of the style and in the radial
walls, which afterwards facilitates transit for the burrowing
pollen-tube. On the inner side of these hollow cones
(y. ov.) there arise the ovules with their double integu-
ments ; a single cell in the centre of the nucellus enlarges
into the single megaspore mother-cell.

The microspore mother-cells are formed in plates below
the epidermis of the embryo anthers (st.) on the staminal
column. They arise from the cell-layer immediately
below the epidermis, but soon separate themselves from
it by two layers of cells, and then enlarge till their
diameter is about 40 », when they pass into the synapsis
stage. Meanwhile (Fig. 8), the cells which surround them
on all sides divide once, and thus give rise to a tapetum,
which is ultimately disintegrated.

The mechanism of nuclear division in reduc-
tion.*—This division has not been captured for observa-
tion in the megaspore mother-cell ; it appears to take place
very rapidly, judging by the ease with which the stages.
immediately precedent and antecedent can be found.
The same applies to the microspore mother-cell, where
the stage is easily observed about ten days before the
flower is due to open.

The extraordinary minuteness of the chromosomes of
Gossypium is very obvious in this division, where they are
inconspicuous in comparison with the linin threads, which
have actually been figured in error as the chromosomes
themselves. The latter appear to consist of twenty groups
of pseudo-tetrads, each unit of the group being about
06 in diameter, arranged in prophase along one side
of the somewhat tangled close spireme of linin. This
spireme splits longitudinally and the two halves separate
like loops of cotton in a broken soap-bubble, retaining

FERTILISATION AND EMBRYOLOGY 9

W.LB. del.

Fics. 8 to 18.--THe Mecuanism or Nucigear Division.
Fias. 19, 20.—-DEveLOpMENT OF POLLEN,

10 THE COTTON PLANT IN EGYPT cuap.

connection with the chromosome groups by fine fibres
(Fig. 11), which become the spindle fibres. The pseudo-
tetrads are then halved into groups of pairs, the inter-
chromosome fibre disappears in the cytoplasm, and the
two daughter nuclei rapidly divide again (Figs. 14, 15) in
the same way, never breaking the thread-rings, and thus
distribute one minute chromosome from each pseudo-tetrad
to each of the four microspores.

The prominence of the non-chromatic linin structures in
this remarkable division has enabled these changes to be
examined thoroughly. The main features are summarised
above, and the possibility of providing a physical explana-
tion for nuclear division on these lines makes the observa-
tion one of general interest. The same thread-rings are
found in the somatic nuclei (Figs. 16, 17, 18), where the
chromosomes number forty, and the same scheme is
followed.”

The spores.—The microspores, or pollen-grains, are
thus formed in groups of four. Hach member of the group
enlarges (Fig. 19), develops spiny sculpturings on its
outer wall, colouring matter—golden in the case of
Egyptian cotton—and finally floats free in the liquefied
residuum of the tapetum. Some three days before the
flower opens, the single nucleus divides into a moruloid
vegetative nucleus and a smaller ellipsoid generative
nucleus (Fig. 20). The latter again divides into two, the
male gametes, and the pollen grain is then ready to
fertilise the ovary.

The megaspores are also formed in groups of four, but
the three nearest the base of the ovule abort, and only the
fourth member becomes a megaspore. The usual nuclear
changes then take place: the three antipodals abort before
the flower opens, while the two polar nuclei have met in
the centre of the spore, though without fusion, and two
typical synergids support the egg-cell or female gamete.

Fertilisation.—We shall have ample occasion later to

FERTILISATION AND EMBRYOLOGY 11

WL B.del.

Fries. 21 to 28.— FERTILISATION AND EMBRYOLOGY.

12 THE COTTON PLANT IN EGYPT cuap.

discuss the methods by which the pollen-grain reaches the
style, whether of its own, or of another flower, and also to
inquire into the pseudo-parasitic nature of the pollen tube,
which attacks some styles more easily than others. For the
present we will examine a normal case.

The sugar solution excreted by hairs on the style retains
the pollen-grain, and causes it to germinate. The single
pollen tube traverses the tissue of the style and the
conducting tissues till its end enters one of the loculi,
along the wall of which it passes till it finds (Fig. 3)
the micropyle of an ovule. Traces of branching may be
seen at this point. Passing through the micropyle
channel to the nucellus, it bores through the tissues of the
latter, and after literally squeezing its way through the
firmer wall of the megaspore, the end of the tube swells
up and bursts (Figs. 21,22). From the torn end escape the
two male gametes, one of which passes to and fuses with
the egg-cell (Figs. 23, 24), forming a zygote, and thus
beginning a new life-history. ‘The other male fuses with
the two polar nuclei, and the triple nucleus thus formed
(Fig. 25) serves later to provide the endosperm.

The process is exceptionally rapid. Fertilisation is
normally completed within thirty hours after the first
opening of the flower, ze. by the afternoon of the
following day.

The embryo.—From the date on which the flower opens
until the boll cracks, some forty to sixty days later,
according to the weather and the kind of plant, the
embryo is developing inside the fertilised ovule, or seed.

On the third day of this period the unicellular zygote
divides along a plane at right angles to the axis of the
ovule, its forty chromosomes, formed by the addition of
two twenties from each gamete, being each halved and
distributed to the daughter-cells (Fig. 26). ‘Two more
divisions produce an octant (Fig. 27), and by the end of
the week the embryo is just visible to the naked eye,

I FERTILISATION AND EMBRYOLOGY 13

consisting of some hundreds of cells, and exhibiting a
cordate form under the microscope (Fig. 28). The
pointed end becomes the radicle, and the two lobes develop
into two cotyledons, marked with black dots caused by
the presence of the resin-glands which are characteristic
of all portions of the cotton plant other than the root.
The adult cotyledons are folded in a complex way, being
considerably broader than the seed in which they are
contained, and they envelop the straight radicle. Their
cells contain much of the food reserves in the form of oil,
which is an important commercial product. The endosperm,
formed by rapid division of the triple nucleus, is destroyed
during the growth of the embryo, so that the ripe seed is
ex-albuminous.

We shall postpone consideration of the seed coat, and
of the development of the lint upon it, to its proper place
at the end of the story of the individual.

CHAPTER II
DEVELOPMENT AND ENVIRONMENT—1.

Tue physiology of a cotton plant growing under the field
conditions which obtain in Egypt may be conveniently
considered in two stages. During the first stage, which
includes the period from sowing to flowering, the plant
is mainly under the control of aérial conditions. After
flowering, in the middle of June (near Cairo), a critical
period ensues, during and after which the soil conditions
commonly provide the limiting factors.

The subject is one of great interest, on account of the
stringent environmental conditions which prevail during
a great part of the Egyptian cotton-season. (See Figs.
30 and 33, Environment.) Thus, in the month of June at
Cairo the meteorological conditions are somewhat as
follows :—Sun temperature maximum, 75°C. ; Clouds, rare ;
Shade temperature maximum, usually 34° C., at 2 p.m.:
occasionally 42° C.: minimum about 20° C., at 6 am.;
Humidity, dropping to 20 per cent. of saturation, or even
less, during the day, and rising above 90 per cent. at
night ; Wind, strongest by day.

Such conditions result in xerophytic adaptions, unless
an ample water-supply is available, as it is in Egypt
through irrigation ; but we shall see later that even under
conditions of field cultivation, the cotton plant virtually
becomes a xerophyte every afternoon. After the month
of June, however, the increasing size of the plants

cH. 11 DEVELOPMENT AND ENVIRONMENT Os

automatically modifies the severity of the environment,
in so far as the lower portions are concerned, by producing
a “‘ surface climate” with higher humidities and less wind,
consequently less evaporation, and affording at least
intermittent shade to any given portion of plant tissue.
Germination.—The sowing of the Egyptian crop takes
place at different times, varying with the locality and with

1
1
1
1
i]

' i

[= ' March 80th.

1 I

a ee
20°C. ! : i

{

;

|
10.0 | :
5 a ‘March 81st.
20 i
10. " ——————
oe April Ist.
20
10 !
Night Gam. Noon 6pm. Night

\ a. Seed sown Bb. Irrigated
Weather normal
Fic. 29.—TreMPERATURE OF THE SEED BED,

Recorded by thermo-electric junction placed 5 cm, below surface on
south side of ridge.

the weather, from the end of February until May. The
habit of sowing on ridges running east and west secures a
higher soil-temperature on the south face. The tempera-
ture of the seed bed before, during, and after optimum
sowing-time was recorded electrically in 1911 (Fig. 29);
the sudden rise shown at the moment of sowing (a) is due
to the scorched surface soil which fell into the hole,
showing how effective is the heat insulation of dry soil,
since the depth of the hole was only 4 cm. The heat
absorptivity and conductivity of the soil after irrigation (b)

16 THE COTTON PLANT IN EGYPT cuap.

Maximum, Black-bulb in vacuo

Lower limit of Thermotoxic effect

<= aes eee Spee ee ee Acar gastos

Maximum Shade Temp.

Temperature
(Survey Dept.)

° Minimum Temp.

10 mm. Sown ae ae

s : .
3 20 mm. Mean Growth per day on Ten Afifi Plants. (main axis) ae
§

WwW

OOO ergs 7
Ieee Seterecetererececeoees | Wat i

RES SLG

The Root

SSCS SSRIS noe SRK KKS
LS earenestatatecestotecencetereeen SS ISSN

On% Oe <o Lx
IRR SKS “

Flowering Mean
Shedding Growth
Bolling mm, .
S p-p.p.d. per day Records of Individual Plant shown in Fig. 37.

Germinated caw me eer me ®

S
~~
i)
g Sown
z

a —T 7
April May dune
5 2 10 18 2% 4 12 20 28 1 9 #17

Fic, 30.—THr PLANT AND THE

are both obviously greater than that of the dry soil. The
magnitude of this daily change in soil-temperature
diminishes with increasing depth, and is negligible below
50 cm. Thus the root-tip in the early stages of germina-
tion is subject to great variations in temperature, but
after the root has grown some 15 cm., the temperature is
constant, except for the annual change. At a depth of
50 cm. the temperature is approximately 17° C. at the
beginning of March, rising to about 25° C. in the
summer.

The localisation of the optimum sowing-date will be
discussed later, in connection with the date of the first
flower. For the present it suffices to notice that sowings
in the middle of February near Cairo will take twelve
days to show the cotyledons above ground, while identical
sowings made in the middle of April may appear in five
days, temperature being the limiting factor. The sowings

II DEVELOPMENT AND ENVIRONMENT | 17

Maximum, Black-bu/b in vacuo
x Maximum Shade Temp,

ee Sn rN
Minimum Temp. NO

<I II>

es Sub-soil Water Period Autumnal Period
W
oe ae I a nN
ROIS
SoU SR

REI
x
ees ee

Environment. Gezira, Carro. 1911.

on intermediate dates take intermediate times, vary-
ing, of course, with the particular weather which they
experience.

The proportion of seeds which successfully complete
their “ field-germination” also varies—other things being
equal—with the sowing-date. The lowest proportions are
found in the very early and very late sowings, though for
totally dissimilar reasons. The failures in the first
instance are almost entirely due to a damping-off fungus,
known as ‘‘ Sore-shin,” which we must consider in further
detail, not. merely because it is the only serious fungoid
disease of cotton in Egypt, but rather because certain
conclusions drawn from the study of its relations to
temperature will be used extensively for interpreting the
growth-processes of its host.

The “Sore-shin” fungus.’*°‘—This facultative
parasite was first described in 1895 by Mr. G. F. Atkinson

18 THE COTTON PLANT IN EGYPT cuap.

in the United States. It is practically omnivorous, and is
the only damping-off fungus which seriously attacks cotton-
seedlings in the Egyptian fields. The organism is an
extremely simple one, probably a degenerate Basidio-
mycete, but devoid of any spore-forms. A resting-stageé is
produced by free branching of hyphe into clusters of short
swollen cells, which turn brown, forming irregular hard
black spots on the mycelium. Such resting-cell forma-
tion precedes the staling or exhaustion of an ample food
supply. The mycelium containing these cell-clusters has
been kept over calcium chloride for nearly two years, and
sent out abundant hyphe when moistened at the end of
the period. The hyphe are all equivalent, in the absence
of any sexual process, and are diagnosed by a curious
septum which is formed in each lateral branch immediately
above the point of origin.

When a cotton seedling has been completely decom-
posed by the fungus in a somewhat dry site, the hyphe
which grow away from it form branching brown rhizo-
morphs, seeking fresh sources of food. The fungus is
ubiquitous in Egypt, and its sterile mycelium must be
regarded as a gigantic network, stretching through the
soils of all the country.

It is strictly aérobic, grows freely on most culture
media, though with difficulty when the nitrogen is
presented as urea, and forms resting cells very quickly on
asparagin media, while it can infect cotton seedlings
under perfectly sterile conditions. The cotton plant is
‘immune when cork layers have been formed, though even
then it can be infected at wounds, but without any
notable injury.

The chief interest of the disease lies in its absolute
dependence on temperature, and the consequent mis-
apprehension existing as to the effect of cold on cotton
seed. If germinating seeds, or seedlings, are kept damp
at a temperature of 20°C. with a fragment of “sore-shin ”

1 DEVELOPMENT AND ENVIRONMENT 19

culture, they are visibly infected in three hours, and
completely destroyed in a few days. Repetition of the
experiment at 33° C. produces slight superficial brown
scars, and nothing more, while at 37° C. the seedlings
remain without injury. Moreover, if an infection has
been well established at 20° C., and is then transferred to
a temperature of 37° C. for an hour or two, or for several
hours to 33° C., the infection is arrested. The hyphe
cease to advance, and the host proceeds to delimit the
damaged portion by means of a cork cambium.’”

The effect of high temperature can be modified in one
way. If the tissue to be infected is partially immersed in ~
water and kept at 33° C., the fungus will destroy all the
cells on the water-line, though merely scarring the epi-
dermis above, as before, and leaving the immersed portions
untouched, on account of deficient aération.

The results of infections in the field depend on the age
of the plant. The brown skin of seedling roots is
commonly regarded as normal to the cotton plant, whereas
it is actually due to abortive attacks by this fungus and
possibly by a Rhizopus. Very late sown seedlings have
pure white roots. The seed is doomed if the attack takes
place as soon as the tip of the radicle emerges from the
seed-coat ; its growing point is destroyed, while the fungus
enters the seed-coats and rots the cotyledons; such seed
is commonly said to have been “killed by the cold.”
When the attack is made on an established root or
hypocotyl, the infection has to be sufficiently extensive to
reach the phloem tissues ; such destruction of the phloem
limits the supply of synthesised food from the leaves to
the root, and may check root-growth ; this check in its turn
limits aérial growth, and so produces stunted plants, which
flower lite and make the crop irregular. If much phloem
tissue is destroyed, the seedling may die through indirect
water shortage during the day, but though seedlings which
have wilted from this cause are common in the field, the

Cc 2

20 THE COTTON PLANT IN EGYPT cuap.

most serious attack is the inconspicuous one which occurs
at the beginning of germination.

A treatment of the seed with 24 per cent. of its weight
of naphthalene, mixed with gypsum as a cement, effec-
tually prevents this primary attack, though leaving the
seedling unprotected by the time of secondary infection.

A notable example of secondary infection was observed
in May, 1906, on a piece of land at Giza, which had
become very foul with weeds, and was consequently a hot-
bed of ‘‘sore-shin,” so that a third sowing had been
necessary. The clusters of seedlings from this were
’ perfectly clean, under the protection of the summer
temperature, till two abnormally cool and cloudy days
arrived. When these were over, every tenth cluster had
been completely destroyed,’ and the clean white roots had
deliquesced into a sodden brown mass.

The facts here related led the author to a conviction
that further investigation would be profitable, and after
some experimental difficulty, a method for studying the
relation of this fungus to temperature was devised. Since
the results appear to be capable of general application,
their description may be considered under a general title,
and supplemented by less precise data from cotton itself.

Temperature and growth.’—The effects of tem-
perature on the growth of the “sore-shin” fungus were
studied with special apparatus. A moist-chamber was
devised in which the concentration of the “ hanging drop”
containing the fungus remained constant, however quickly
the temperature was changed. This change was effected
through a double jacket of liquid in which the chamber
was completely immersed. The measurements of elonga-
tion of the observed hypha were made every minute
through a water-immersion objective with a micrometer
eyepiece, while the actual temperature of the hanging-drop
itself was recorded to 0°1°C. by means of a delicate
thermo-electric junction in the field of the microscope,

1 DEVELOPMENT AND ENVIRONMENT ) 21

balanced on a similar couple in a water-bath of known
temperature.

Consequently, the two variables under examination
were recorded with unusually high precision, and relatively
rapid temperature changes could be employed with safety.

The general arrangement of the initial work was
such as to ensure that temperature, and temperature
alone, should be the factor which limited the growth.
The rate of temperature-change was usually about 1° C. in
three minutes, so as partially to avoid errors from
prolonged exposure to high temperatures, and the air
space of the chamber was filled with pure oxygen. Under
these conditions growth-curves like Fig. 31 were obtained
from fresh cultures, recently renewed, and kept at low
temperatures, so as to be free from any suspicion of
staleness. These curves indicated that growth followed
chemico-physical laws, being accelerated by increased
temperature, and approximately doubled in velocity by a
rise of 10° C. This acceleration began to fail in the
neighbourhood of 36° C., and growth ceased altogether at
a mean temperature of 37°5° C., the maximum. A value
of +0°5° C. covered departures from normal in the
position of this maximum. Obviously, a second factor
was coming into play, antagonistic to the normal accelera-
tion, and probably itself accelerated by rise of temperature.

Slower rates of heating, down to the maintenance of
culture-flasks at various constant high temperatures,
showed that the time of exposure had an influence on this
factor. The more rapid the heating, the nearer the
growth-curve approached to its hypothetical form, «.e., a
sudden arrest at 37°5° C. when in full swing. The slower
the heating, the lower was the temperature at which the
slowing of the growth-rate appeared on the curve, and the
lower the temperature at which growth ceased.

Following this graduated series of conditions down to
the stage at which the change of temperature is infinitely

22 THE COTTON PLANT IN EGYPT cuap.
”
a oo
L-¥ 373 6.
35°C. = a
> fe
ae
° y oi
30 ¢. xf A 0.120 mm.
rbe7
et-
wr’
4%
25°C a : 0-090mm.
p \/
ry
AN
7)
ée. of
0-060 2 0-060 mm.
0-050
8 a
5 0-040
=
= 0-030 VA
s ra
0-020 a
:
10 20 30 40
Minutes

Maximum rate =0-0055 mm. per minute

Fic, 31.—GrowtH AND TEMPERATURE OF A FUNGUS.
Hypha of ‘‘ Sore-shin.”

slow, we find that growth stops even in a culture kept
constantly at 20°C., if kept long enough. Such cessation
of growth is not necessarily due to exhaustion of food
from the culture, for all the food-ingredients may still be
present. Further, it takes place, for any given temperature,
after a lapse of time which is directly proportional to the
volume of the culture media.
cultures” will resume their growth if they are eluted with
pure water.
Plainly, then, the staling of cultures is due to excretion

Lastly, such ‘stale

II DEVELOPMENT AND ENVIRONMENT 25

by the fungus into | , ye (ae
the surrounding ~°* —

' oy
medium, Such ex- Cal |

cretion takes place ey
s ~—

of a toxic substance xa7e

more rapidly at
high temperatures ;
than at low ones. iz
Lastly, retracing is
our series of con- |o.%, 4
ditions, the cessa- oa
tion of growth in
fresh cultures raised
rapidly to a tem-
perature of 37°5°C.
is due to poisoning
of the protoplam %

by the toxin, which Sos
is produced most
rapidly at this tem- ya

02 ee
perature. We shall ;

7 Ss

denote this hypo- 30 60 90 120. 150

thetical substance, Minutes
i Maximum rate = 0-025 mm. per minute
or mixture of sub-

M
°
‘S

Fic. 32.—GrowtH AND TEMPERATURE OF A

stances, by the sym- Race
bol “ax,” for con- Cotton seedling.
venience.

The chemical nature of “x” is obscure. It is not an
enzyme, however. On prolonged boiling, or on exposure
to air in thin films of water, it is decomposed, and by
either of these methods we can rejuvenate a stale culture
medium. Since ‘‘a” is thus unstable, and its chemical.
nature unknown, we are thrown back upon the growth-
curve as a test for its presence. Denoting completely
stale culture media as 100 per cent “x.” we find that the
depression of our growth stopping-point from the normal

24 THE COTTON PLANT IN EGYPT cuap.

37'5°C. is apparently proportional to the percentage of
“g” which we add to the culture medium. Thus, a
50 per cent. solution has a stopping point in the neigh-
bourhood of 32°0°C., however quickly the temperature
be raised.

Were it not for the accumulation of “x” in the cells,
the growth-rate would go on doubling with every ten
degrees until the death-point was reached at about 49°C.

This substance is formed only in growing cells of the
fungus, and unless the formation is very rapid it diffuses
out into the surrounding medium before an injurious
concentration can accumulate. Stale mycelium can there-
fore be rejuvenated by washing with fresh culture medium,
or with water. Conversely, when the volume of the
surrounding culture medium is of microscopic dimensions,
as in a cell of the host plant, staling takes place rapidly.

We are now in a position to comprehend the peculiar
relationship to temperature of the ‘“‘sore-shin” disease.
Owing to the minuteness of the cells of the host, a very
short exposure to temperatures above 30°C. will completely
inhibit the parasite’s growth—unless the tissue is washed
by water—and the host-plant is thus given time in which
to form the protecting barrier of corky cell-walls.

It would seem natural to assume that the host-plant
itself had a different temperature-relationship, since its
cells would otherwise become stale at the same time as
those of the fungus, and high temperatures would have no
protecting effect. This assumption is not correct, however,
and a different explanation has to be tried, in view of the
following experimental work.

In parallel with the experiments on the fungus, a few
similar measurements were made with the root of
germinating cotton-seeds. The seedling was immersed
in a double-jacketed water bath with a glass side, through
which the elongation of the root-tip was observed by a
Comparator measuring to 0‘(01 mm. ‘The reserves in the

II DEVELOPMENT AND ENVIRONMENT 25

seed formed a sufficient food supply, and. aération was
maintained by a stream of bubbles of oxygen through the
water. The rate of heating had to be reduced to about
1°C. in five minutes, in order to obtain accurate measure-
ments, but even so, the growth-curve (Fig. 32) was
identical with that given by the fungus, showing the same
acceleration, and also stopping at about 37°5°C. Slower
rates of heating were employed in the form of germination
trials in the incubator, when it became clear that some
similar “ x-substance ” was again operative. The germin-
ation of samples of seed stored at higher temperatures
is much quicker, though the ultimate germinating per-
centage is unaffected. Moreover, a 37°C. sample is
surpassed in four days by a 25°C. sample, not only in the
mean length of the radicles, but also in mean weight.
The sample at 37°C. is, in other words, stale, and needs a
prolonged exposure to lower temperatures if it is to be
restored to health.

It should be noticed that a shade temperature of 40° C.
is frequently reached during the early summer, so that
some manifestation of this process, which the author has
denoted as ‘“ Thermotoxy,” may be expected to occur
during the growth of the crop in the field. We shall see
later that such is actually the case.

Meanwhile, one other point needs to be considered.
The heat-poisoned fungus is cured through removal of
““,” whether physically by washing, or chemically by
decomposition. The first method is impossible in the
higher plants, so that chemical decomposition must be
invoked; the effect of overheating in one afternoon,
though plain during the following night, has disappeared
by the second night.

_ Now it has long been a truism that every plant has an
‘optimum temperature” for growth.* We have just seen,

* See various writings by Mr. F. F. Blackman for critique of these
terms,

26 THE COTTON PLANT IN EGYPT cuap.

however, that two such dissimilar organisms as a cotton
plant and a sore-shin fungus possess identical growth-
curves with no true optimum. On the other hand, the
cotton plant certainly grows best at temperatures near
32° C. ; we are therefore led to a final conclusion, namely,
that the general “ growth-optimum ” of any higher plant’
is that temperature at which, after prolonged exposure,
the equilibrium of growth-acceleration with “ x-produc-
tion” allows the maximum sustained value to the former.
The “x-production ” factor is itself compound, being the
balance of “‘ x-production ” against “ x-decomposition,” for
the latter of which there appear to be special facilities in
the higher plants.

Summarising this section, we have found that, in the
absence of other limiting factors, growth is accelerated by
rise in temperature along a logarithmic curve, while a
time factor (“ thermotoxy ”) acts against this acceleration,
unless the toxic katabolites are removed as fast as they
are formed. The “optimum” is essentially a variable,
but the “maximum” is normally constant, though it can
be depressed by suitable treatment. Tissue temperatures
which exceed 38° C. reduce the subsequent growth-rate of
the cotton plant to a marked extent, while prolonged
exposures above 35° C. are proportionately harmful.
Exposure to temperatures below 30° C. for a long
time appears to produce no injurious effect on the cotton
plant.

The effect of sunshine.—The conclusions of the
preceding discussion would lead us to expect that strong
sunlight might conceivably have a prejudicial effect on the
growth of the plant-stem, by over-heating the growing-
point, but thermo-electric measurements of tissue-tem-
peratures indicate that the young leaves and buds rarely
exceed the shade temperature during early summer, owing
to the regulation of their temperature by transpiration.

Actual measurements of growth, on the other hand,

II DEVELOPMENT AND ENVIRONMENT 27

show that direct sunshine inhibits it completely.” ”
(Figs, 33 and 34).

This simple discovery has had an almost revolutionary
effect on our study of plant physiology in Cotton. The
phenomenon, though almost unprecedented outside Egypt,
is exhibited by many other plants in Egypt, notably by
Helianthus.

The “sunshine effect” was first recognised in May,
1910, and has since been found to be usual from the first
appearance of the seedling till the autumn, if not through-
out the season. The elongation of the stem is checked
immediately the sun strikes upon it, and a slight shrinkage
usually follows. A cloud passing across the sun is
immediately effective in permitting growth, which ceases
again directly the cloud has passed.

The contraction of the stem in sunshine indicates that
loss of water is the direct cause of growth cessation. That
this explanation is the true one can be shown in many
ways; thus plants covered by a glass bell-jar so as to
surround them with an atmosphere of high humidity, will
grow rapidly in the sun during May. Similar conditions
occur in the field for a day or two after watering, when
the plants are large. The most striking proof is provided,
however, by leaf-removal ; if the total lcaf-area is reduced
about one quarter, by simply cutting off the lower leaves,
growth is almost instantly resumed, since the water-loss of
the stem is reduced. This last experiment shows in a
striking manner the delicacy of the water equilibrium
between root-supply and stem-loss.

Disturbances of this equilibrium are normally effected
by variations in the weather, such as abnormally high sun
or shade-temperatures, hot dry winds, etc. It should
be noticed that the equilibrium-point is probably deter-
mined by the worst normal conditions, namely, at 1 p.m. to
2 p.m.

Artificial disturbances of this equilibrium can be effected

i THE COTTON PLANT IN EGYPT cuap.
“ Monday i Tuesday / Wednesday /

T aera fae ae t T ~ r 7
8 10X12 4 6 8 10Xi 2 #6 8 10Xil 2 4 6 g 10XIl2 4 6 8 10 Xi 2 46 8 10 XII

7 Li Fi ia ‘caer pap
Wind) | Tf i PTET Te |
[eal aw / ]

ff arse Tae | Bi
ed iff

i Ges

a i an Hr it CCST ueuaul
MnnLESEUGULERUDUBELERELEEUDEELRun|

Wednesday /

6 8 10Xi2 46 8 10 XII

THT

TEMPERATURE..............-

SEER aa
VA
Wi

HUMIDITY
Fic. 33.—Growti or Sven.
June 7th was abnormally hot.
Last watering on May 28th.

Fold out

i DEVELOPMENT AND ENVIRONMENT 29

by limited defoliation, or by root-pruning, or by cul-
tivation in limited quantities of soil, as in flower pots. All
these methods give similar results as regards the “sun-
shine effect.”

The qualification “limited” is added to the mention of
defoliation methods because of the interference with photo-
synthesis which follows if too many leaves are removed,
or if they are removed from near the terminal bud.

The positive effect of day temperatures on growth is
thus almost non-existent, and the modicum of truth which

Intermittent
shade (Clouds

$
i=]
=
3 & trees)
Q SUN)
S 1 Pree :
3 SUN] Artificially screened from direct Sun
§05

“4 A
2a Sea ar
s°3 TG [_Niig ht [\[Nifgnt [7
Soi| Hy “6 r_y aaa

| ae oe —

Hour 72 6 Mid- 6 NY 72 6 Mid- 6 72
ending Noon pm. night am. Noon am. night pm. Noon

Fic, 34.--Tue SunsHINE Er rect.

Growth-rate per hour in hypocotyl of an Assili seedling sown on March 7th,
during March 19th to 2ist. Compare screened portion with temperature
in Fig. 33.

attaches to “‘ accumulated-temperature” approximations is
still further diminished. The only effect of day-tempera-
ture is the prejudicial one of “ thermotoxy,” excepting on
the rare occasions when the sky is overcast. Such days
are remarkably interesting ; usually the clouds take the
form of a dust-storm, accompanied by high temperatures,
and so long as the temperature does not reach the
“thermotoxic” limit, or 35° C., they cause abnormal
growths to be recorded, since elongation of the stem is
continuous throughout the twenty-four hours.

In view of the rarity of such weather we are justified
in deducing the conclusion that night-temperature is the
prime factor in growth during the first half of the growing-
season, provided only that no limiting factor other than

30 THE COTTON PLANT IN EGYPT cuap.

temperature operates during the night. On this latter
point, unfortunately, we are unable to generalise with
safety. The curve of growth—after sunset—leaps from
zero to 4 maximum, and thereafter follows the temperature
curve* till the small hours of the morning (Fig. 34). It
is not clear whether there is any limitation through
exhaustion of the photosynthetic food supply before sun-
rise. On the whole, the evidence is against this view,
except in rare cases, and in any case such limitation would
take place at the period of minimum growth-rate.

Night-temperatures.—Combining our knowledge of
temperature control with the elimination of day-
temperatures provided by the “sunshine effect” we are
enabled to interpret the growth-rates obtained under field-
conditions with fair exactitude.

The curve shown in Fig. 30 was obtained by daily
measurements of the axial shoots of ten cotton plants, thus
summarising the mean growth of the twenty-four hours.
The correlation between minimum night-temperature and
the growth rate up to July Ist is very close (r=0°7843+
00459) if those daily periods are excluded in which the
maximum temperature had risen above 35° C. The
correlation sinks to a value of 0°5236+0°0755 when
these are included, owing to thermotoxic effects.

At this stage of the plant’s existence there can be no
question as to the economic interest of stem-growth. The
faster the growth of the stem and branches, the sooner
will the first flowers open, and the period which we are
now considering ends with the appearance of these.

Thus, the date of “arrival” of the crop depends first
on the night-temperatures which have been experienced,
secondly, on the date of sowing, and thirdly, on the clouds,
We shall return to this subject later, in connection with
the date of the first flower.

* Except after heat-poisoning,’when it remains constant, or rises slowly
until cut by the falling temperature.

‘HI DEVELOPMENT AND ENVIRONMENT | 31

Meanwhile, we must not forget that the night-
temperature is commonly recorded as a minimum only,
and that the true mean night-temperature may be some-
what different. Moreover, the internal temperature of the
tissues is appreciably affected by clouds, which check
radiation.

- Having now discussed the main factors which control
growth during the first half of the season, we can turn to
the examination of the water factor in more detail, since
its importance will be considerable at a later date. Before
so doing, an example may be studied which will remind
us that the idiosyncrasies of the plant have to be taken as
the base-line for all environmental effects.

Length of the seedling stem.—That portion of
the stem known as the hypocotyl, situated between the
true root and the seed leaves, forms the greater part of
the “root” which emerges from the seed-coats on
germination. It is distinguished from the true root by
the black speckling of resin glands. The length to which
it attains after raising the cotyledons out of the soil
would appear to be a matter of pure chance. Seed buried
under clods of earth, or deeply sown, develops a stouter
hypocotyl in reaction against the mechanical resistance ;
much of the reserve food having been exhausted in the
effort, the aérial portion of the hypocotyl is shorter, and
the cotyledons smaller.

A series of seedlings grown under uniform conditions
showed that specific foundations were discernible in such
a trivial character even as this. The strains employed
were derived from an American Upland (King), and an
Egyptian (Sultani). Having been soaked for a night at
30°C. they were planted at a uniform depth of 2 cm., at
uniform distances of 5 cm., in finely sifted soil which had
been uniformly damped, and the hole which had been
dibbled for each seed was filled by more fine soil without
compression. The box containing the soil was kept in

44 THE COTTON PLANT IN EGYPT cnap.

the open air. Daily measurements of height were made,
and the final length of the hypocotyl when growth in this
region had ceased showed that the Upland exceeded the
Egyptian by 50 per cent. under the field conditions of an
Egyptian April. ‘I his excess was the more striking, in that
the Upland seed was much smaller than the Egyptian, and
a large seed usually displays a stronger “ field germina-
tion” than a small one.”

This difference became still more remarkable when the
first internode developed above the cotyledons had also
attained to its full length, for it completely reversed the
hypocotyl length, being 50 per cent. longer in the Egyptian
than in the Upland. The length of subsequent internodes
is correlated with that of the first one, and since the
internodes are developed at about the same time, the
height of the plant is determined by the internode length
unless other factors intervene, which we shall consider later.

A repetition of this experiment in a cool greenhouse in
England threw some light on the specific temperature-
relationships. Under these conditions the Egyptian
seedlings exceeded the American in all their dimensions,
including the hypocotyl length.

More detailed examination of the water-relationships
which we have already encountered in the “sunshine
effect” are now necessary, dividing the same into the two
components, namely, absorption by the root and loss by
the stem.

The root.—The root first makes its appearance in
germination at the end of the emerging hypocotyl as a
zone of embryonic tissue about three millimetres in length.
The growing zone is remarkably smal] throughout root-
development.

The primary root is positively geotropic, and its elonga-
tion is indefinite. The plant is consequently tap-rooted,
and the depth to which the root system extends is deter-
mined by external conditions alone. The greatest depth

Ul DEVELOPMENT AND ENVIRONMENT — 33

to which an unbroken tap-root has actually been followed
is two metres and twenty centimetres. This depth had
been attained between March 28th and September Ist, in
soil where the sub-soil water level is four metres below the
surface until September (Fig. 30).

The growth of the tap-root is arrested or diverted
horizontally upon arrival at saturated soil, and plants
grown in land with a constant high sub-soil water level
consequently possess insignificant tap-roots,* with a greater
development of laterals.

In case of injury to the growing point of the tap-root
one or more of the lateral roots nearest the tip turns
downward and replaces it.

The resistance offered to root-growth by soils of normal
texture appears to be negligible, both from the indirect
evidence of growth-rates, and from actual observation in
glass-sided boxes.

The secondary roots normally begin to develop when the
tap-root has attained a length of some 12 cm. Their
original diameter is about half that of the tap-root, and
roots of higher orders arise from them. Their rate of growth
under the same environmental conditions is slower than
that of their tap-root; this phenomenon is one of those
commonplaces of observation which have never received a
satisfactory explanation. In spite of their slower growth,
they produce an enormous increase in root area, on account
of their numbers, and if the soil is carefully washed away
from a cluster of cotton seedlings about six weeks after
sowing (Fig. 35), the root system appears as a tangled
white gossamer web. Only a few of the rays of this web
survive (Fig. 37).

Before discussing the factors controlling root growth, we
may advert to the general form of the root-system, which,
beginning as a vertical line, rapidly becomes an inverted

‘*® Audebeau.

34 THE COTTON PLANT IN EGYPT cuap.

cone. When plants are sown at wide intervals, this conical
form is maintained, the principal laterals extending radi-
ally by the autumn to distances of over two metres

Dec. 15th. or 8 months <_

+10
metre

Soi!
surface

Y) tl

A —1-0
metre

Dibposk
Zonepregched

VA yy LMM.

Notes:- The new roots shown are those from
a single lateral only.
For effects of asphyxiation, see sowing
of March 28th. in Fig.30.

on this one root.
Aged 36 days.
Fic. 35.—Tue Root: DeveLormEent, ASPHYXIATION, AND REGENERATION.

Scale drawings from measurements.

(Fig. 37); the irregular base of the inverted cone thus
becomes about five metres in diameter, while its depth
may exceed two metres. When the plants are closely

II DEVELOPMENT AND ENVIRONMENT - 35

sown, as in the field crop, the uppermost laterals from
adjacent plants begin to encroach on each other’s territory,
within three months from the date of sowing; although
interlacing takes place, the form of the effective root-system
is modified by this lateral limitation into a cylindrical
upper portion ending below ina cone. The depth of the
cylindrical portion increases as lower and lower laterals
come progressively into contact. If the downward ex-
tension of the tap-root is checked, the conical portion is
overgrown, and the whole root-system becomes a cylinder.
The interest of this ‘root-interference” will become
apparent later, when we find that plants in field crop
behave as if they were “ pot-bound.”

That the total volume of soil occupied by an adult
cotton root must be enormous is shown by the examin-
ation of pot plants. The photograph of Fig. 36 represents
an average plant from sowings in six-litre pots after
fourteen days; the tap-root had attained a length of
16 cm. and was diverted by the floor of the pot after seven
days only. Having been exposed to higher temperatures
during the day than it would have experienced in the
soil, the absolute size of the root is somewhat abnormally
large, but the ratio of increase is interesting. After
seven days the total root-length was 20cm. ; after fourteen
days, two metres; after three weeks, four and a half
metres. Yet the growth-curves from the plants during
this last week showed that their root system was in-
sutticient for the needs of the stem, though the total leaf
area amounted to less than 30 sq. cm.

On account of the more obvious importance of the
root system at a later stage, we shall at present omit
further discussion of its functions, but one experimental
result might be mentioned. With plants growing in pots
where the water content of the soil can be determined
with certainty, we find no obvious relation between this
factor of the environment and the growth of the stem

36 THE COTTON PLANT IN EGYPT cuap.

during the night until the water content has sunk below
a certain limit. Since deficient water-absorption is the
real limiting factor of the sunshine effect, it follows that
the size of the root-system is the true limiting factor of
water-absorption, and that the humidity of the soil may

Fic. 36.— SEEDLING.

Fourteen days old.

vary between wide limits without affecting it. Much
more work needs to be conducted on this question, in
view of its importance in irrigation practice.

The rate of growth of the roots under field conditions is
primarily controlled by temperature. Once the tap-root

I DEVELOPMENT AND ENVIRONMENT _ 37

has passed into soil at constant temperature, containing
perhaps 70 per cent. of the saturation quantity of water,
the growth rate can safely be predicted. We have already
examined the effect of temperature on root growth, and it
suffices to add that the mean growth rate of many roots
growing in soil in the laboratory works out at approxi-
mately 0°9 mm. per hour at 18° C., and 1:25 mm. per
hour at 22° C. When the seedlings under examination
are placed out of doors, the total growth of the roots in
twenty-four hours is considerably less than the calculated
amount (see also Fig. 35), and it seems probable, although
a complete experimental proof has not yet been obtained,
that this diminution is due to the “sunshine effect,”
which disturbs the water-equilibrium of the root conjointly
with that of the stem.

The rate of growth under field conditions is not easily
ascertained. Small plants can be grown in boxes or tubes
with glass sides, which are buried flush with the soil
surface, and pulled up as often as may be necessary for
examination of the root, which grows down the inclined
glass side. For checks on such plants, and for examina-
tion of all large plants, we have no method other than the
primitive and muddy one of excavation with a jet of water
and a trowel till the end of an unbroken root is reached.
Measurements made by these methods have given data

of which the following series is representative :—
Length of true root.

Sown ... .. . March 28... 0
Measured ... ... April 2... 0... wee 6 cm.
” SL aise ager timé’, eRe is 14 cm.
45 ott hs May 15... 1... ou. 55 cm.
a5 aaa! Liew July 1... 1... 140 cm. (abt.)
5 pede aR September 1... ... 220 cm.+

From these it follows that the root-depth in well-drained
soil certainly reaches two metres by the end of August.*

* The lower soil-temperature in the Northern Delta should diminish the
root-extension considerably. The point needs investigation on account of
its intimate relation to drainage projects.

38 THE COTTON PLANT IN EGYPT cuap.

Lastly we have to consider an abnormal limiting factor
of root-growth, namely deficiency of soil-oxygen, usually
due to water-logeing of the minute interstices which the
soil contains. Owing to the fact that its anatomical
structure does not include an elaborate system of inter-
cellular air-spaces, such as aquatic plants possess, the
cotton root is locally asphyxiated in water-logged soil, and

Fie. 37.—Water Jer Excavation or Roots.

See Fig. 35 on which the area of this photograph is marked.
Lateral from neighbouring plant on right is marked with an X.
Length, 170 cm. +.

in a few weeks even the stout, woody roots are not merely
dead, but decomposed. Here also we require precise
information as to the degree of soil saturation which
produces these effects under field conditions, but the main
facts are perfectly clear, and we shall meet with the serious
economic effects of this root-asphyxiation at frequent
intervals.

The stomata.—Certain plant physiologists have

I DEVELOPMENT AND ENVIRONMENT = 39

expressed doubts as
to the importance

of the stomata in
regulating transpir-
ation, but such is
certainly their
function in the
cotton plant. Con-
sequently, an ex-
amination of the
stomatal move-
ments, so far as
they are at present
known, is necessary
to an understand-
ing of the way in
which the stem
loses water.

The stomata of
Egyptian cotton
plants are found
on both surfaces of
the cotyledons ; on
the hypocotyl and
stem, and on both
surfaces of the foli-
age leaves.

A full grown
stoma is about 0:04
mm. in length, and
the mean fre-

quency of these
organs in each
square milli-
metre has been
found to be as
follows.

<— 144 em.
below the surface

< 00y \dvy

saocgevnes ean eniv ki gery

perenne”

Fic. 38.—REGENERATION
OF THE Root-syYstEM.

Highest level
veached by
sub-soil water

Old dead roots
threaded by
new roots

«<— 200 cm. below
the surface

Showing crop of new roots developed in six
weeks from merely one uninjured lateral (the
dotted line). Tracing from a blue-print of
the root itself, after floating it upon a sheet
of glass. See Fig. 35 and also 30,

40 THE COTTON PLANT IN EGYPT cuap.

Cotyledon : Lower epidermis ... ... .-. «+ 275
Upper 33 teh, idee Oe! Glee 200
Hypocotyl and stem ...0 ...0 cee cue eee eee 20, &c.
Leaf: Lower epidermis ... «0 ce. wee ee 176 to 116
Upper _,, sielgy| RGR sates Weta! v a 97 to 44

The total number of these apertures is consequently
enormous. Such a seedling as that portrayed in Fig. 36,
already possesses about half a million. Nevertheless, the
cotton plant is not abnormally rich in stomata, though
the fact that they are found on both sides of the leaf
should be remembered.

The functional capability of the immature stomata
found in very young leaves is not clear. The cuticle of
such leaves is yet thin, and in all probability it allows
some evaporation to take place. The density of the
stomata on such developing leaves is about the same as on
adults, so that fresh stomata are continually being differ-
entiated as the leaf expands.

Further, with changes in the age of the leaf we find
changes taking place in the degree of those reactions
which the stomata exhibit towards environmental
changes. These are by no means fully understood, and
for the present we must confine our attention to the
normal leaves, fully grown, but as yet showing no signs
of senescence, which constitute the greater part of the
leaf area. The principal observations upon which this
account is based were made during May, June, and July.

The study of changes in stomatal aperture under field
conditions has formerly been impracticable except by
personal observation, which almost precludes continuity
in the records. The author succeeded, however, in
adapting Mr. Francis Darwin’s Porometer method,* to a
self-recording system, and the first continuous automatic
records of stomatal aperture were thus obtained.

In the Porometer, the leaf is made to seal an air-tight

* Darwin and Pertz.

i = DEVELOPMENT AND ENVIRONMENT — $41

chamber, within which the pressure is higher or lower
than that of the atmosphere. The air-flow, restoring
equilibrium of pressure, can thus take place only through
the stomata and mesophyll tissues, while the square root
of the velocity of this flow is approximately directly
proportional to the stomatal aperture.

The author’s Stomatograph*® consists of a sensitive
electric air-pump, which maintains a constant pressure
gradient between the chamber and the outside air,
signalling the time of completion of every stroke—and
hence the stomatal aperture—on a chronograph drum.
The pump, with its operating battery and a relay, is
contained in a small dust-proof box, placed below the
plant under examination. From this box issues
the tube leading to the leaf-chamber, and also a
telegraph wire which leads from the relay to the chron-
ograph ; the latter may be at any convenient distance,
preferably in the field laboratory. The instrument is
independent of any meteorological change or disturbance.

In the usual simple experiments, we find that
desiccation, darkness, and poisons cause closure, while
sunlight causes the stomata to open to their maximum
aperture.

The records obtained from normal leaves in field
conditions, which in one case extended over five con-
secutive days with the same leaf (Fig. 39), reveal a most
fascinating interplay of factors. During the night the
stomata are completely closed; they begin to open
slowly at dawn, and continue to do so until a moderate
aperture has been attained, even in diffuse light. When
direct sunlight strikes the leaf, the aperture is rapidly
increased, till maximum is reached at about 9 a.m.
This maximum aperture is maintained for a varying
period, the length of which is undoubtedly determined by
the water-absorption of the root, provided that sunshine be
continuous. Immediately after irrigation it may last two

42 THE COTTON PLANT IN EGYPT cuap.

or three hours, while on hot, dry, windy days, with a
soil approaching to physiological dryness, the full aperture
has scarcely been attained before closure sets in. Such
facts indicate that the closure which follows must be due
to “water-supply shortage,” and that its utility is to
check the excessive water-loss involved by free transpir-
ation. By noon, on most summer days, this closure is

Sun-shine
Sun-| | “ |

rise
Dark | j

Sun-

Sun behind trees set
i.e. diffused tight o ny | Dark

J
o
>

%& Screened whole plant
from direct sun.

Zero.
dune 8th.

—_
=
—]
(
=
dune 9th. /) ‘

dune 10th, / |

a
=
Ss
13
oO
a
J : Vane 12thN
dune 11th. ex

effused
per minute

UNIT i
Tec. of air

dune 12th. ne
Mid- 6 Noon 6 Mid-
night am. pm night

Fic. 39.—StomatocrarH REceRDs.

Curves show volume of air driven through an area of 80 sq. num. of leaf per
: minute, under a pressure of 1 mm. of mercury.

Five-day record on the same leaf without alteration of apparatus. Fifth day
is abnormal.

almost complete, and we shall revert to its effects on
transpiration and photo-synthesis when considering these
functions.

On cloudy days, or when a screen is placed across the
plane of the ecliptic so as to cut off all direct sun from
the whole plant, the maximum aperture is not attained,

1 = DEVELOPMENT AND ENVIRONMENT — 43

but a moderate aperture persists throughout the day,
followed (Fig. 39, June 8th, from noon onwards) by
slow closure in the late afternoon, and complete closure
at sunset. In such circumstance the illumination is
the controlling factor, and there is no water-shortage ;
this might be expected from consideration of the fact
that the existing root-system has been developed to
cope with the demands of sunny weather.

If this very plausible hypothesis of diurnal water-
shortage be correct, it must mean that the water-content
of the soil which is in juxtaposition with the roots has been
reduced at a greater rate than that at which water can be
restored by capillarity. During the night there must be
a purely physical movement of water into these semi-
desiccated portions of soil, since the water-shortage is not
apparent on the following morning. We thus obtain
from the Stomatograph some conception of the severe
strain which the plant undergoes during the torrid
weather of a summer in Egypt.

The verb “to vegetate” is frequently misused as a
description of inert torpidity, but the daily experiences of
a cotton plant in Egypt almost justify this libellous
employment of the word. From noon onwards, this long-
suffering plant is neither growing, nor feeding, nor
transpiring beyond the necessary minimum, and possibly
not even breathing properly.

The supremely injurious effect of fogs has long been an
article of the cotton grower’s faith. It is difficult to see
any reason for this conviction, apart from the continued
low temperature which morning fogs entail, but it is
possible that the blocking of the stomata by condensed
water may have a prejudicial effect. Even so, a fog
should merely postpone the brief period of general activity
of the plant by a few hours, and not actually curtail that
period. On the whole it seems safer to adhere for the
present to the cynical explanation that most “fog” is

44 THE COTTON PLANT IN EGYPT cuap.

boll-worm, while the rest is either mere spoiling of the
seed-cotton in the open boll, or else a simple reduction of
temperature. .

Transpiration.—We have examined the principal
machinery by which the water-loss of the plant is
controlled and it now remains to ascertain what the
amount of this loss may be under field conditions.

On this subject we are profoundly ignorant, owing to
the experimental difficulties, and the present section is
intended rather to indicate the possible lines of attack
than to attempt a statement.

The usual methods of investigation are divided into
gravimetric and volumetric determinations, which may be
used to summarise the net result of a long period, such as
a day, or to investigate the effects of a particular set of
factors at a given moment. Direct weighings of the plant
are feasible in the earliest stages, but we have seen that a
plant aged three weeks, growing in a six-litre pot, is
already abnormal. Further, we shall come later to
evidence which shows that two plants growing in an iron
cylinder 2 metres high and 80 cm. in diameter, are
suffering from root limitation by the middle of July;
since similar signs are shown by close-sown plants in field
crop, the objection is not fatal, but the conditions cannot
be regarded as normal. Furthermore, such isolated plants
have room to develop all the branches they produce, and
their leaf area is consequently much larger than that of a
field plant. Lastly, being isolated, they are freely
exposed to wind, and this rapid removal of saturated air
must increase transpiration enormously. ‘The only serious
attempt. at determinations by weighing large tanks was
carried out by M. Audebeau. The objections just mentioned
apply to this excellent series of observations, especially
after June, when the field plants are beginning to produce
a ‘“‘surface climate.” The discrepancy between M.
Audebeau’s total transpiration and the actual state of

II DEVELOPMENT AND ENVIRONMENT 45

affairs was strikingly shown to the author by Mr. J. I.
Craig, who computed that on this basis the whole Nile
flood would be lost through the transpiration of the cotton
crop alone !

It may be possible, however, to obtain data from plants
growing under nearly normal field conditions, by under-
pinning large masses of earth to form concrete tanks in
the middle of a field of cotton, and determining the fall
of the water-table in these tanks from day to day. The
method is open to many objections, but it lends itself to
automatic recording, and if regarded in part as a problem
in soil physics, the results should form a near approxima-
tion to the truth. It is not however suitable for examina-
tion of the diurnal variation.

For the problems of diurnal change it is usual to
employ the Potometer, which compares the velocities of
intake of water by means of a tube intercalated in the
cut stem. This method has not been persuaded to work
in Egypt owing to the severity of the sunshine effect,
which promptly kills the severed stem.

The only method which holds out any prospect of
utility is the least obviously practical of any. It consists
in cutting off portions of plant tissue of known area, and
weighing them repeatedly on a Joly spring balance as
soon as possible after cutting. The weighing is done in
the field, usually under difficulties due to the wind, and
the balance is set up so that the tissue shall remain in
the same position which it occupied before being cut off.
Even whole plants may be treated in this way and
measured up with a planimeter afterwards. The curve
of weight-diminution in time is then plotted backwards
to the moment of cutting, and its value at that moment
is assumed to be the true transpiration rate. This is then
converted for purposes of comparison into milligrammes
per square centimetre per minute.

The few determinations yet made in this way have

46 THE COTTON PLANT IN EGYPT cuap.

given consistent results, four of which have been plotted
in Fig. 40. They show that transpiration is practically
in abeyance at night, slow in the early morning. By
9 a.m. in sunshine it has reached a maximum which is
maintained till past noon. The last result is perhaps
rather unexpected, seeing that the stomata are nearly

0150p— '
_ as
a res Tw,
. OY Re) ~~ 0
‘ <5 | —.%o
: My
6 em ~._ ve ye
0-100 2 ae Ss, ay
a a oo aves
”, aN “ee
a ee
(7)
&
Sed,
SN 2,
S
z é 1%,
3s Sn
Sa
5 c—)
93
i]
=
10) 5 6

2 3 4
Minutes (from moment of removal)

Fig. 40.—TRANSPIRATION IN FIELD Crop.

Rate of water-loss from detached leaves, plotted backwards to instant of
removal.

Initial weight of all four was about 0°85 gram ; areas, 30-40 sq. cm.

Time. Wet Bulb. Dry Bulb.
9°50 a.m, 25°6° 28°4°
125 p.m. 23°9 32'8

closed, but it is easily explained when we remember the
increase in stringency of the environment which has
taken place during these four hours: Sun-temperature
has risen from about 50°C. to 75° C., shade-temperature
from about 25° C. to 35° C., and humidity has fallen
from about 60 per cent. to 20 ‘per cent. of saturation.
During the afternoon the transpiration rate appears to fall

11 DEVELOPMENT AND ENVIRONMENT 47

steadily, but the shape of the curve is only known
approximately as yet.

The rate of mean maximum transpiration obtained in
these trials was 000076 g. per sq. cm. per minute, which
seems to be within the order of probability. A trial with
an entire plant in the same way indicated a rate of 0:0003
at midday on June 15th, many of the leaves being shaded
by others; there were twelve leaves, with a total area of
585 sq. cm., the wet and dry bulbs reading 24° C. and
33° C. respectively.

Tissue temperatures.—A number of records of the
internal temperatures of various tissues have been taken
by inserting a thin copper-constant in thermo-electric
couple in the tissues;* it is then balanced upon a
similar couple bedded in a rod of paraffin wax, which
is kept at shade temperature behind a screen close
to the plant. The actual shade temperature is simul-
taneously recorded by means of a thermograph near the
control couple.

Since the shade temperatures form the standard of com-
parison between various sites, this method is preferable to
direct determinations of absolute tissue temperature. The
difference between the two couples is automatically
recorded by a ‘‘ Thread Galvanometer,” a zero line being
first traced in order to show when the couples are at the
same temperature.

The results obtained in this way present a few features
of exceptional interest. Variations of +1:0°C. are shown
even by large bolls, while the stem within five millimetres
of the terminal bud varies in the same way as the
younger leaves, though with less amplitude. Young
leaves, which have not attained to a third of their ultimate
length, rarely exceed the shade temperature, but frequently
fall below it, their extreme variation being about + 0° to

* Blackman & Matthaei.

48 THE COTTON PLANT IN EGYPT cuap.

— 6° (Fig. 414). Old leaves, on the other hand, rarely fall
below air-temperature but frequently rise above it, varying
from — 3° to + 10° (Fig.41c). These oscillations in leaf-
temperature are extremely rapid, differences of 10°C.
being recorded often at intervals of only a minute.

The thermo-regulation of the leaf seems to diminish
with age, and it is not inconceivable that the senescence of
a leaf may thus be hastened by thermotoxic effects. In
general terms, the old leaf follows the sun-temperature,
but the younger leaf follows the wet-bulb temperature.
Puffs of wind, whether natural or artificial, produce no
notable effect on the old leaf, but reduce the temperature
of young leaves.

Thus it follows that in considering the effect of
maximum day-temperatures on growing tissues, we were
justified in taking the shade-temperatures as the
maximum tissue temperatures.

That thermo-regulation is real may be seen by comparison
of Fig. 414 and Fig. 418. The two records were taken from
the same tissue, at an interval of twelve days, during
which the vascular tissue had been destroyed by a “ boll-
worm.” The top of the stem wilted in the usual way
and became dry, and the recording couple inside showed
most erratic oscillations of temperature, due solely to the
intermittent cloudiness of the sky.

The night-temperature of tissues is practically identical
with the air-temperature, excepting for variations of about
2° C., which have been shown to be caused by clouds,
checking radiation. ‘The effect is not an important one.

Fogs cause no noticeable alteration in leaf-temperature,
so that any chilling effect they may have is directly
recorded by the thermometer.

The most important result obtained from these records
is one which relates to the effect of water-shortage on the
temperatures, through reduction of transpiration, and
consequent loss of thermo-regulation. On account of the

DEVELOPMENT AND ENVIRONMENT = 49

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varying nature of such controlling factors as clouds and
sun-temperature and the age of the leaf, it is not very easy
to demonstrate the progressive effect produced by desicca-
tion of the soil over a period of many days. Mimicry of
this progressive change by sudden root-pruning may be re-
garded as tolerably just, and the effect of such pruning is
to cause all but the youngest leaves to behave like old
ones; they are easily over-heated, and where they had
formerly held their temperature down below that of the air,
they now exceed the air temperature by several degrees.
Hence nearly all the plant tissues suffer from over-heating
during the day. The bearing of this fact on our interpreta-
tion of the fall in growth-rate which follows water-shortage
in July will shortly be mentioned.

Another method of demonstrating this loss of thermo-
regulation is simply to examine the tissue-temperature
record of a young leaf during a day when the stomata
had closed at an early hour. ‘This temperature-trace.
starts below the air-temperature line and slowly rises up
to it, or above it. Differences of not less than 5° C. in
mean relative tissue-temperature may thus be produced
by stomatal closure.

Photosynthesis.—We can scarcely leave the general
physiology of the cotton plant without some reference to
this prime function, but a critical and exhaustive series of
data has yet to be obtained.

The first attempts at obtaining such a series by the
Sachs-Thoday* dry-weight method were rendered fruitless
by the unexpected high error of a-symmetry in cotton
leaves. The probable error of difference between
nominally identical areas of 15 sq. cm., cut from the right
and left sides of the central segment, amounts to
+ 4 per cent. of the mean weight of each pair. Hence
at least sixteen pairs have to be examined in each

* Thoday, D.

i = DEVELOPMENT AND ENVIRONMENT 51

experiment if a result with a probable error of
+ 1:0 per cent. is to be obtained.

The evidence to hand indicates that photosynthesis
takes place largely in the early morning, the subsequent
closure of the stomata preventing free access of CO, to the
chloroplasts. The curve of increase in dry-weight follows
the temperature curve till nine o'clock, and then the
stomatograph record, with differences in detail between
old leaves and young ones during the afternoon.

The increase in dry-weight in hourly series of observa-
tions, without correction for loss by translocation, has
given record values at the highest point of the curve,
namely 25 (-+ 4) mg. per sq. decim. per hour. This rate
is reached in June, between 8 a.m. and 11 a.m., when the
stomata are at their maximum dilatation, and the tempera-
ture is above 30°C. There is reason to believe that values
of about 30 mg. may yet be obtained under certain con-
ditions, thus reaching ‘the absorption of a surface of KOH
when exposed freely to the wind.

It is improbable that the intensity of illumination should
ever be a limiting factor in the process, except before
sunrise.

No definite signs of growth-limitation by deficient
photosynthesis have yet been discovered, unless in such
circumstances as the last three hours of Fig. 34, though
here again we ultimately may find some such effect in
the autumn. ,

The first flower.—The date of appearance of the first
flower on any individual plant deserves consideration in a
separate section ; being the ultimate result of a long series
of interacting factors, morphological and physiological, it
is in itself an automatic summary of their effects and it
possesses the additional distinction of being commercially
important. The “date of arrival of the crop” is almost
entirely dependent on the “ first-flower date,” but the

grower does not seem to realise that he is given nearly two
E 2

52 THE COTTON PLANT IN EGYPT cuap.

months’ clear warning as to whether his crop will be late
or early. Specific differences between various strains of
cotton depend in the first instance on the method of
branching. If the first branches of the young plant are
sympodial flowering shoots, the flowering will probably
be early. Sometimes, however, strains have been noticed
which ought to have been early but were actually late,
owing to a propensity for shedding the unopened flower
buds. Again, specific differences due to branching may
take the form of irregularity ; all the plants of some strains
in the author's possession (notably King Upland), come into
flower almost simultaneously, even if some are stunted ;
other strains show a wide scatter among plants which
appear to be equally healthy. Other, and more subtle,
differences can only be relegated to the protoplasm itself
for ultimate explanation, some strains developing identical
flowering branches at a much slower rate than their
neighbours, just as the lateral roots grow more slowly than
the tap-root under the same environmental conditions.

A point of importance, which is still obscure, relates to
the influence of the environment upon the nature of the
branch arising from a bud. In certain circumstances,
not yet clearly understood, but apparently including
excessively high night-temperatures, the plant delays its
formation of flowering branches. In many cases the delay
is only apparent, the flower buds being formed but soon
shed. In others it is real; ‘ Nyam-nyam Kidney ”
cotton grown at Giza, though otherwise healthy and
growing strongly, forms very few flowering branches.

When dealing with most pure strains we find consider-
able uniformity in the date of the first flower. The
stunted plants, if any, flower late, so that a close corre-
lation here exists between the height of the young stem
and the flowering-date. Curiously enough, however, this
correlation vanishes when we reach the normal plants,
which all flower at about the same time in spite of notice-
able fluctuations in height.

1 = DEVELOPMENT AND ENVIRONMENT 53

Another form of the same phenomenon is presented
when we examine data for plants sown at varying times.
This was first recognised by the author when plotting
data for sowing and picking-dates in a series of years,
provided from various large estates in Egypt. The graph
was interesting as showing the influence of district on
sowing-date, and on picking-date in consequence, but
more especially so because it indicated—in spite of the
many sources of error—that it is useless to sow before a
certain critical date in any given district. However early
or late the sowing may be, the crop “arrives” at the
same mean time until this limiting date is exceeded, after
which a delay in “arrival” results, following the delay in
sowing. Ultimately, of course, the paraboloid “ arrival-
curve” will leave the “sowing-curve,” since plants sown
absurdly late will not: flower at all.

The same phenomenon was shown on a smaller scale,
though with greater precision, by weekly sowings on a single
site in a single season. The mean date of the first
flower was actually slightly later in the earliest sowing, on
account of the larger number of stunted plants. Three
Upland sowings indicated the same behaviour as the
Egyptians, but within a shorter period. Sowings made
on the critical date were not merely superior in arrival,
but also in height, in yield, and in all respects.

We cannot, of course, lay down rigid rules as to the
date on which to sow in any place, since the weather
varies a little from year to year. Nevertheless it seems
clear that the tendency in Egypt is towards sowing too
soon. Thus, March 24 was the critical date for Gizain 1911.

The variations in night-temperature from year to year
during the six weeks before flowering probably constitute
the chief cause of variations in first-flower date, and hence
in crop arrival, since the growth-rates of all the branches
are closely correlated until June. There have recently
been two striking examples of this in the early crop of
1910 and the late one of 1911.

CHAPTER III
DEVELOPMENT AND ENVIRONMENT—II

THE second half of the development of the cotton plant in
Egypt may be conveniently subdivided into three stages,
though none of these have any definite boundaries. They
are, successively, the critical period, the water-table period,
and the autumnal period. The first of these three is little
more than an abstract term which has been found useful
in discussion, while the other two explain themselves.

The chief feature of all three, though especially of the
first two, is that the main control of the environment has
been transformed from the air to the soil (Fig. 30). This
change can be seen clearly in the growth curve. During
the first period, under the modern conditions of Egyptian
irrigation, the plant can always be supplied with sufficient
water, but the adjustment of the water-supply becomes a
very delicate matter during the critical period, owing to
root-interference ; while excess of water is likely to be
present during the next period, partly from natural causes,
and hence reduction in the effective root-system follows.
When the sub-soil water period is very early, and con-
sequently overlays the critical period, the combination of
the two produces disastrous effects, of which the 1909
crop was our worst example, through an early and high
flood.

During these three periods the maturation of the crop
takes place. We are chiefly concerned with the flower, and
with the boll which ripens from it, though also with the

cH. DEVELOPMENT AND ENVIRONMENT 55

boll which does not ripen. We should also be able to
discuss the growth phenomena shown by the lint in the
boll, but the experimental difficulties of such investiga-
tion have not yet been overcome, and this section of the
development, which is of prime interest to the spinner,
must be left almost blank.

Methods of observation.—So far as this part of
the research has at present been carried, the author has
had to devise methods in which the accuracy of the
individual observation is low, while the ultimate precision
of the result isdue to multiplication of such observations.
Thus, averages are worked out for a large number of plants
and expressed in terms of “‘ per plant per day” (abbreviated
for convenience to “p.p.p.d.”), with respect to such
characters as the opening of flowers, the ripening of bolls,
the shedding of flowers, and the growth rate.

The results are usually plotted in graphic form for
convenience in examination.

The lack of moderately trustworthy assistance in Egypt
often makes it necessary to arrange the time-table of work
so as to have daily observations on special plants and
groups for three days, then for three days more on another
series, and to take those families where the number of
plants is large, such as variety-rows, only once a week,
depending on the greater number of component individuals
to compensate for the scarcity of observations. All these
observations can be plotted down to the same “ p.p.p.d.”
basis, and are directly comparable with the results obtained
by daily observation, or from large areas.

The task of working data up at any stage is lessened by
tabulating note-books at the beginning of the season,
though the balance between minimum discomfort in the
field, and facility at the writing-desk, is not always easy
to strike. The speed of desk-work can often be greatly
increased by preparing nomographs to take the place of
the slide-rule.

56 THE COTTON PLANT IN EGYPT cuap.

A natural outcome of these methods of observation has
been the employment of some of the simpler tools of the
statistician. The author having for some years depended
on detailed observation of random rows whereby to obtain
expressions for the behaviour of plots in ordinary culti-
vation, was particularly interested when Prof. Wood and
Mr. Stratton combined data and treatment in a critical
discussion of field experiment methods. The appearance
of their article implies that science has at last been intro-
duced into agricultural field experiments, and an examin-
ation of the available data respecting cotton should
therefore be profitable. The figures for the yield of
nominally identical plots in Egypt are too scanty to
provide a definite statement of the probable error; those
available work out to a probable error of + 6 per cent. of
the mean yield for the total yield of half acre plots ; the
same figure in the case of Wood and Stratton’s investi-
gations for English crops was -& 5 per cent.

The difficulty of obtaining identical plots of Egyptian
cotton, even in the same field, is extreme, since great varia-
tions in the physical texture of the sub-soil are normal,
which involve similar differences in the water-supply of
the roots, when they have penetrated thereto, though the
surface soil may appear to be uniform. Consequently, we
are not justified in expecting the Probable Error (P.E.) of
Egyptian cotton plots to be any lower than that of plots of
English wheat and we may take + 6 per cent. as a very
liberal estimate of the accuracy of cotton plot experiments
in Egypt. Taking odds of 30:1 as practical certainty it
follows that two plots of different varieties grown
for comparison side by side may show yields of four
kantars and six kantars respectively, and will yet give us
no justification for stating that the greater yield is due to
the superiority of one variety over another.

This is a very unsatisfactory state of things, since much
money has obviously been wasted in trying such useless

mr DEVELOPMENT AND ENVIRONMENT _ 57

experiments. If further application of Wood and
Stratton’s analysis can be made to enhance the precision
of cotton experiments, the attempt is worth making.

The method of examining single rows and computing
to single plants is capable of high precision. The
examination can be carried out daily, weekly, or casually,
and may be extended to any observable character, or
restricted to mere pickings of the ripe cotton. In the
latter case it is actually less laborious than the ordinary

T__,, T Total Yield eae

eZ 25-1 bolls £0
eal Sakel 18-5 ,, +0-6
SOC __assiti 19:9, «= £08
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Week August September October
ending 20 27 3 10 17 24 1 8 15 22 29

Fic, 42.—ComPaRiIson OF VARIETIES.

Yield expressed as bolling-curve per mean plant.
Six scattered groups of 30-40 plants per variety.

method, since smaller quantities have to be dealt with.
Confining attention to total yield only, the author
obtained a series of data from double rows of five varieties,
badly cultivated on an extremely irregular strip of land
(Fig. 42). Comparing two adjacent rows of the same
variety, each comprising from 25 to 35 plants in the row,
and expressing the differences in terms of the mean yield
per plant for the two rows, the final figure for nineteen
such pairs gave a P.E. of + 5°5 per cent. for number of
bolls, or 6°8 per cent. for weight of seed cotton. Two
little rows growing side by side, of 30 plants each, may
thus be made to give as good a comparison for the

58 THE COTTON PLANT IN EGYPT cuap.

particular locality between, e.g., two varieties, as can be
obtained from plots of any dimensions whatever, while
by taking more pairs we increase the precision of our
comparison to such an extent that mean divergences of
only 5 per cent. cannot be due to accident.

Having obtained from these and from similar small-scale
records some definite expression of the precision of the
“‘ observation-row method,” and knowing approximately
the limitations of plot trials, we are in a position to
arrange future tests of varieties, manures, waterings,
sowing-distances, sowing-dates, &c., with a definite fore-
knowledge of the significance of our results.

The growth-curve.—Records of the growth of the
main stem have already been discussed with respect to the
controlling factors up to the end of June. After this date
we begin to perceive remarkable differences between various
strains of cotton plants. Thus, on the same piece of land,
and in the same season, by weekly or fortnightly measure-
ments of the height, made to the nearest five centimetres
with a graduated rod; we obtain mean growth-curves like
those of Fig. 43, plotted from families of King American
Upland, Egyptian Afifi, Egyptian Sultani, and com-
mercial Afifi. The first ceases to grow during June, the
second during August, while the third continues at a fairly
uniform growth-rate until October. In the third case we find
on examination at the end of the season that the length of
the internodes is uniform throughout the adult stem.
In the case of American Upland only a few internodes of
uniform length are produced, after which some half-dozen
of decreasing length result in total cessation of growth
from the terminal bud of the main stem. The Afifi strain
behaves in the same way, but less suddenly, and at a later
date. These compressed internodes contain abnormal
quantities of calcium oxalate crystals.

Until more detailed investigation of the growth-rates of
various portions of the same plant has been completed,

mt = DEVELOPMENT AND ENVIRONMENT ~ 59

there is little profit in discussion of the phenomenon. It
should be mentioned, however, that—so far as the avail-
able data go—the cause seems certainly to be a form of
Thermotoxy, local in, and peculiar to, the particular
growing point. The differences between the various strains
thus are reduced to a specific susceptibility to thermic
effects, either in the form of increased ‘ x-production,” or
deficient “x-destruction.” The view does not claim to

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Week dune duly August September October
ending 11 18 25 2 2 16 23 30 6 13 20 27 3 10 17 24 1 8 15

Fig. 43.—Spreciric GROWTH-HABIT.

Mean growth-curves for central axis from various families in same year and
on same plot.

K. King Upland. S. Sultani. Af. Afifi. a’. Afifi, stunted plants only.
C. Commercial Afifi in field crop.

be an explanation, but it at least offers the prospect
of an answer to the question.

Leaving these specific differences, and confining our
attention to the Afifi type of growth-curve just figured,
which is fairly representative of the Egyptian cottons, we
can return to the effects of the environment proper. ‘The
curve showing the mean growth per day of the terminal
bud of ten plants of Afifi (Fig. 30, growth), from
which we have already demonstrated the effects of
night-temperature, now becomes still more interesting.
After June 15th there is a slight indication of a

60 THE COTTON PLANT IN EGYPT cuap.

lag in the growth-rate behind the night-temperature
control. After June 26th this lag develops rapidly
into the dominant feature of the curve, and some
factor is obviously at work which leads to a general
and progressive falling off of the growth-rate. A part
of this degrading is probably of the chemical nature
indicated above, which results in a decreased range of
sensitivity in the growing protoplasm; some such
inferiority would account for the slower growth of lateral
roots. To postulate such “deadening” of response is not
inadmissible, since it has often been noted in the fungus
studies,” where two hyphe in the same field, with the
same temperature relationships, were yet found to grow at
proportionally different rates, whatever their temperature
might be. In these same studies it was also found that
such decrease in the growth-rate sometimes appeared as
the result of short exposure to high temperatures, too
short to affect the stopping-point.*

Such general slowing down of the growth-rate will not
cover all the observed facts, for if we smooth the growth-
records to the basis of such an assumption, we find that
the formerly preponderant influence of night-temperatures
on the daily growth is rapidly vanishing. On the other
hand we find that the actual records show a long-period
modality, corresponding to the intervals between the
waterings ; growth attains its maximum from two to five
days after watering. Obviously the root-absorption is
partially involved, probably indirectly through thermo-
toxy, or auto-toxy of some other kind, and also through a
partial and temporary suppression of the sunshine effect.

These soil-water effects disappear in their turn after the
middle of September, when—in the particular series under
discussion—the infiltration water from the river raised the
water-table and smothered the roots. By this time, how-

* Loe, cit.,9 ‘‘ Triple curve.”

ur DEVELOPMENT AND ENVIRONMENT - 61

ever, the main axis had reduced its growth-rate below even
that which was possible under these conditions, and the
effects of root-asphyxiation are shown by the laterals only,
as in the flowering-curve.

A peculiar confirmation of the interpretation just given
as to the influence of the soil-water in July is shown by
the growth-curves of families sown at different times.
During the week ending on June 26th, 1911, a depression
of the growth-rate was recorded in the oldest family, while
the oldest but one showed it in a less marked form. The
remaining families were unaffected. When we consider
that the earlier the plant is sown, the larger its root-system
must be, we see that the drying-effect of the early plants
on the soil surrounding them will be more severe than in
the case of the later plants, and hence they will show the
soil-water limiting effect at an earlier date.

The flowering-curve.—As in the case of the growth-
curve, we meet with specific differences in the manner of
distribution of flower-production in time. The beginning
of the curve, as the date of appearance of the first flower,
has already been discussed.

The specific differences in growth-reaction to environ-
ment, which we have just discussed, affect the form of this
curve also. Thus, owing to the habit of “ early growth-
cessation” taking place first in the oldest bud, namely, the
terminal one, and then progressively in the younger ones, the
growth of the flowering branches is checked in the strain
of King Uplands by the end of July, and no flowers open
during August or September. By the end of August a
plant of King appears to be dead, but ‘the flower-
ing begins again in October, and a second crop of bolls
may be produced from these flowers. The Egyptian
Sultani strain already mentioned, with its continuous
growth-habit, continues to flower throughout the season,
while the usual Egyptian flowering-curve rises to a
maximum in the beginning of August, and then descends

62 THE COTTON PLANT IN EGYPT cnap.

steadily till the winter. The form of the later part of the
curve is usually modified by subsoil water effects, either
through root-asphyxiation, or by continuously shallow soil,
which accentuates thermo-toxic effects through water-
shortage.

The actual form of the curve is also determined by the
branching-habit, since the flowers are produced by special
branches. For our purpose it is not worth while to enter
into detailed discussion of these branches and their effect
on the utility of the plant; they have been closely
investigated by Mr. Leake.* Their general effect on the
flowering-curve may be seen best in second generation
hybrids ; continuous growth without lateral mynopodial
branches, resulting in a straight stem bearing sympodial
flowering branches only, produces a flowering-curve which
remains low and without modes throughout the season.
The substitution of discontinuous growth-habit in com-
bination with the same habit of branching, cuts out a
resting-period from this curve. Discontinuous growth
with free vegetative monopodial branches at the base of
the stem, which in their turn produce sympodia, causes
the flowering-curve to run up to a high mode, then to fall
rapidly to zero, and to rise again in the autumn. Similar
branching to this, but combined with continuous growth-
habit, builds up an enormous flowering-curve, which rises
steadily to a maximun (not infrequently amounting to
25 p.p.p.d. flowers), and then descends to the winter. A
total production of five hundred flowers in a month is
common among plants possessing this last combination
of habits.

Confining our attention again to the usual Egyptian
type of flowering-curve, the normal form of this may be
affected by the environment through the growth-processes,
but it is frequently important to remember that a normal
form exists, since these distortions often serve as useful

* Leake (? 3),

mt DEVELOPMENT AND ENVIRONMENT 63

indications of environmental changes, and especially of
changes in the condition of the root-system. A concise
example is provided by the flowering-curve of plants
growing in the two-metre cylindrical tanks already
mentioned, when compared with similar wide-sown plants
growing in ordinary soil near by, and with others growing
under the close-sown conditions of the field crop (Fig. 44).
The curves shown were all taken in the same year, and
all from an area of a quarter acre, cultivated in these
various ways with the same pure strain. Taking the

June, July Aug. Sept. Oct. Nov.

Flowers per plant per day
ix)
[o)

3
ae

Wide Planting ——-——Field Crop) -----Tank Plants
Fic. 44.—FLowerine Curves. Guiza. 1910.

Showing root-limitation of tank-plants equally with field-sowings.
Note the smaller effect of root-asphyxiation in the wide-sowings.

wide-sown plants as nearest to normal development, we
see that field-planting reduces the number of flowers
formed, presumably by the crowding of the flowering
branches, and hence reduces the height of the maximum.
Comparing these plants with the wide-sown ones grown
in the tanks, we find that the ascending flowering-curve
is checked under the latter conditions, and is not allowed
to continue at the normal maximum. Obviously a
limiting factor has supervened, and it is more than
probable that this factor is the limitation of root-develop-
ment through the confinement of the roots within the
limited capacity of the tanks. An interesting side issue

64 THE COTTON PLANT IN EGYPT cuap.

of this result is the inevitable deduction that two cotton
plants can occupy more than three tons of soil with
their roots by the end of July. In making a further
comparison of the tank-plants with those sown in field-
conditions, we find in the latter a similar arrest of the
rising curve, which is probably to be explained in the
same way, as due to root-limitation, formerly discussed.

Such variations as those just mentioned may be produced
within the same pure strain in at least two ways; either
by checks upon the growth of the flowering branches,
or by shedding of the flower-buds. The latter falls.
into the same category as the shedding of flowers
or bolls, but should be mentioned here as a possible
source of variation in the flowering- curve. With
certain strains, notably one bred by the author from
an Egypto- American cross, this effect is marked
very strongly; some plants, otherwise identical with
their neighbours, shed their flower-buds just before
opening them, while their neighbours retain them. The
first produce a scanty flowering-curve, the others a gigantic
one. Neither, however, ripen any early bolls, and the
distinction appears to be due entirely to accidental root-
differences.

Another important factor which modifies the form of
the later part of this curve is the water-table. The
coincidence in time between the contact of the roots with
the water, and the rapid cessation of flowering, is shown
very clearly in records from families sown on different
dates, the idiosyncrasies of each family being obliterated
when this contact takes place ; on continued rising of the
water the flowering curves all coalesce at or near zero.
The field-crop records taken at Giza show variations in
this respect as between 1909 when the flood was very
early, and the two following years when the flood was late
(Fig. 45).

These last records are of exceptional interest, as they

mut DEVELOPMENT AND ENVIRONMENT 65

demonstrate for the first time the effect of increasing
the head of water on the Delta Barrage and so immersing
the lower roots sooner than would normally be the case, in
the land lying up-stream.

1909 1910 1911
1-00 x x x
4

= n ee 1977
a fa
£ i— ! \ Sinieeecctwe 1910
a t
a a 1909
as & '
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3 U Sy
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= 0-20+- f Spe Ny:

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0-10;- (Tein ate
A Tae al bee
June dul Aug September October

Yy ust
ll 18 25 2 9 16 23 30 6 13 20 27 3 10 17 24 1 8 15 22 29
Fic. 45.—Meran Fiowerine Curves In Fietp Crop.

On same land, with same variety, in three successive years, at Giza.
x = Date on which Roda Gauge reached 16 m. A.S.L.

Decaudation due to rise of sub-soil water over roots. See Figs. 30, 35, 38,
and 47.

The bolling curve.—Curves plotted to show the
number of bolls opening each day in the same way as for
the flowering curve, should be identical with them, if all
the flowers which opened were ripened into bolls. Such
perfection has never been obtained by any of the author's
plants. Some of the flowers are always shed, and the
ratio of bolls formed to flowers opened has never exceeded
90 per cent., and has been known to fall almost to zero.
To take an extreme example, a certain plant, otherwise
quite healthy, in the year 1909, ripened three bolls out of
a total of 746 flowers which opened before the middle of
September.

The early part of the bolling curve, formed by flowers
which have opened at the beginning of the Critical Period,
is usually identical with the form of the originating flower-

ing curve (Fig. 30), but after the first few weeks it
_

66 THE COTTON PLANT IN EGYPT cuap.

frequently. bears no relation whatever to the latter. Hence,
the variations in form of the bolling curve have to be
studied principally in terms of “shedding.”

In order to ascertain the shedding-curve, unless sufficient
assistance permits of direct measurement, we have to sub-
tract the bolling curve from the flowering curve, allowing
a certain interval for the maturation of the flower into a
boll. This period is variable, its length being in the first
instance specific. Thus, quoting again from the same
three families, at Cairo, King Upland has a mean matura-
tion period of forty-two days, Egyptian Sultani has a mean
period of fifty-one days, while the Afifi strain takes forty-
eight from the day when the flower opens till the day
when the boll cracks and discloses the contents. The
figures are determined by labelling single flowers with the
date on which they open. Apart from these specific
differences, which are, after all, only the mean expression
of numerous environmental influences acting on specific
organisms, we find variations in this period on individual
plants. Flowers which open on the same day and on the
same plant may differ by two or three days in their
maturation-period ; we must be content for the present to
describe such differences as due to chance. Further, it
was first pointed out by Allard that in the United States
the maturation period became longer as the temperature
fell, so that the late bolls took longer to develop; he
pointed out, as a curious example of the practician’s
unreliability in practical matters, that the belief of the
farmer holds to the exact converse. The maturation
period is eight days longer in the middle Delta than at
Cairo.

Since the mean for the standard Afifi strain at Cairo
lies at forty-eight days +3 per cent., we shall not intro-
duce any serious error if we plot the mean shedding curves
of this strain by subtracting bolling from the flowering of
seven weeks previously. Such a subtraction-result is not

ut DEVELOPMENT AND ENVIRONMENT ~ 67

precise, but it is very useful in cases where direct
shedding-records have been impossible.

The shedding curve.—We have just seen that the
bolling curve, which represents not only the distribution
but also the size of the ultimate yield of the plant, and
hence of the area, is in reality the flowering curve modified
by shedding. This shedding process thus becomes a
matter of great economic importance. More than this,
the shedding of an organ of the plant is a phenomenon of
great interest from the general scientific viewpoint. The
fact that removal of a few roots should cause the abscission
of leaves or flowers, quite automatically, leads directly to
consideration of the complex interaction of stimuli
necessary to produce such transmission and conversion of
cause into effect.

The term in common use to describe the process under
discussion is “ boll-shedding.” It is not altogether satis-
factory, since the organs shed by the plant are chiefly
flowers shed three or four days after opening, and hence
only described as bolls by courtesy. Ripening bolls, up to
two centimetres in diameter, may be shed, but this is less
common. In addition, there may be extensive shedding
of unopened flower-buds, and the fall of the leaves belongs
to the same general category. Consequently, the general
term “shedding,” while sufficiently descriptive, is more
truthful.

The composition of the sheddings actually gathered from
the ground beneath a field plot of more than a thousand
plants in 1910, at Giza, is shown in Fig. 46. Shed leaves
were not counted, but the diagram shows that flower-buds
may be shed even before the opening of the first flower,
that the majority of the sheddings are flowers which have
been cut off before they had definitely “set” their ovaries,
while the percentage of true bolls of various ages up to
three weeks old is only noticeable in the autumn.

The act of shedding is, of course, under the control of

F 2

68 THE COTTON PLANT IN EGYPT chap.

the plant, its immediate cause being the formation of a
special tissue across the base of the stalk of the leaf, bud,
or flower. The facultative position of this tissue, or
“ absciss-layer,” is marked by a slight groove on the stalk.
When the determining stimulus has been received by the
cells of this layer, which are otherwise indistinguishable
from their neighbours, they proceed to divide, and the
daughter-cells separate from one another, thus destroying

Field Crop From 1,300 plaats,
Giza 1910. A collected weekly.
0-15 Ba
A
3 = S
i~% q
<
040 A
n
=
3
3
% Fl Ss
ower: x
0:05 :
_/ |
ie RT i en DO! Bulds| [~~ +~_5
Week July August September October
ending 2 6 3 1

Fic. 46.—Composition oF SHEDDINGS.

the continuity of the stalk except in such tissues as the
wood. The phloem being among the severed tissues,
synthesised food supplies are cut off, the organ dies, sooner
or later the stalk breaks, and the organ is shed. Even
before any sign of unhealthiness becomes visible, the stalk
may break at a light touch, being retained merely by the
wood-vessels, bast fibres, and cuticle.

The reaction to the determining stimulus is very rapid
in cotton, on account of the extreme simplicity of the
absciss-layer. A convenient way of provoking this
unknown stimulus is to cut off a few roots. Within four
days after such treatment, we find that complete severance
of the tissues of the absciss-layer has taken place. Micro-

ut DEVELOPMENT AND ENVIRONMENT _ 69

scopic examination at intermediate stages shows that the
plate of dividing cells is only one cell thick, that the
divisions begin at the periphery, and extend towards the
centre, and that the dividing wall between the daughter
cells splits immediately along its middle lamella. The
daughter cells which are left on the face of the scar, after
the stalk has broken away, bulge outwards, and form a
simple callus.

In many plants this stimulus is also provoked by non-
pollination, so that unfertilised flowers are shed. This
occurs in cotton, of course, but it does not seem to be
common under ordinary conditions.

For the present we are unable to form any clear
conception of the chain which extends from the severed
root to the absciss layer. It is certain that the main
factor, if not the only one, is the water-content of the
plant. Mere severance of the root does not provoke
shedding as a traumatic stimulus ; thus, plants which are
screened from direct sun after the root has been damaged,
show little or no shedding. Consequent on such root-
damage we find a general closure of the stomata, and it
seems at least probable that this abnormal closure reacts

-first of all on the absciss layer, by bringing about
abnormal internal temperatures. Much more experimental
work is required before further discussion can be
profitable.

Though the primary cause of shedding in Egypt is
a deficient root-absorption, it follows that an excessive
transpiration rate must produce the same result, since the
terms “deficient” and “ excessive” are relative. A very
dry hot day may provoke shedding, but such weather is
infrequent at the time when shedding is important. The
heavy shedding of wide-sown plants as compared with that
of plants in field crop is probably caused by excessive
transpiration, or rather, by too great irregularity in this
function, since wide-sown plants are freely exposed to wind,

70 THE COTTON PLANT IN EGYPT cuap.

and do not create a humid “surface climate.” In the
Sudan, however, spells of hot dry wind are generally
recognised as being the precursors of shedding epidemics.

Before considering a few typical shedding-curves it may
be well to insist once more on the economic importance of
these records. Plants whose flowering curves are identical
may give entirely different bolling curves ; in other words,
entirely different crops.

The record of the behaviour of families sown on various
dates in the same year may be reconsidered in this
connection. We have already mentioned a decrease in the
growth-rate caused in the older families by water-shortage,
but by the time when boll-shedding is becoming notable, all
the plants are suffering from root-interference, which in a
light soil results in periodic water-shortage. As the result.
of this we find successive modes in the shedding curves,
common to all the families. Following these modes we
have periods of less shedding, which immediately follow
irrigation. Some of these records show three such modes
in each family, followed by a fourth one.

This fourth mode is apparently due to a distinct cause.
Firstly, it comes a week sooner than one would expect ;
secondly, it is followed by a general cessation of flowering ;
and lastly, it coincides with the intersection of the
root-depth line by the level of the infiltrated sub-soil
water (Fig. 30).

Thus we have two ways of producing a mode in the
shedding-curve, relatively to the number of flowers
available for shedding. One acts through decrease of the
amount of available water in the soil, while the other way
is through increase of the soil-water-content to saturation-
point, thereby excluding air, causing root-asphyxiation,
and so reducing the size of the root-system; this root-
system, having been developed to cope with a certain
mean maximum demand for water from the aérial portions,
or, more correctly, having controlled the development of

nr DEVELOPMENT AND ENVIRONMENT 71

aérial organs of a certain size, is now insufficient to cope
with the normal water-loss of those organs. They in their
turn reduce their water-loss to meet the new conditions by
stomatal closure, but the general metabolic disturbance,
due to demolition of the delicate balance between root and
shoot, produces shedding. We have already seen how
delicate that balance is, when noting that plants would
grow in sunshine if a few leaves were removed. Here we
are dealing with the converse.

Much more experimental work is needed on such points
as the permissible degree of desiccation or of saturation in
various types of soil, on the rate of renewal of soil water
to a root-dried zone, and so forth, but the main principles
of the matter are now fairly clear.

In light soil, which has a low power of water retention,
it would seem from consideration of the shedding curve
that frequent light waterings are necessary. This practice
might, on the other hand, be unnecessary, if not injurious,
in a heavier soil, with a higher capacity for holdmg water.

A mode in the bolling curve may actually originate
from a falling flowering curve, if all the flowers had been
held during one week, so that a heavy crop of bolls is
picked seven weeks later (Fig. 30).

Some interesting shedding curves have been obtained
by the author from land arranged * in three terraces, at
half-metre differences of level. The purpose of this
arrangement was to ensure differences in the time and
intensity of the effect of rising subsoil water; the lowest
terrace was first affected, the highest last ; the water-table
in the lowest one almost reached the surface of the soil,
while in the highest it left a metre of normal soil.
The method is not ideal, on account of the soil disturb-
ances entailed, even when the top half-metre of soil is
carefully replaced on each terrace ; the remainder of the

* Tn collaboration with Mr. Hughes.

42 THE COTTON PLANT IN EGYPT cuap.

plot was not disturbed and always produced superior
plants during the three years over which the experiment
lasted, but the three terraces were quite comparable.
Each terrace carried not less than 300 plants per annum,
-sown in ten ridges, under conditions which were otherwise
those of the field crop. The water-table in this site was
chiefly controlled by changes in the level of the Nile, at a
distance of nearly a kilometre, though there were variations
due to impervious patches of soil, even wag bin this small
area. Es

In the year 1909 the Nile rose abnormally early; in
1910 it rose late; 1911 was rather later than 1910.
The curves of flowering and bolling in 1909 were taken

om daily observations of three ridges in each plot.*
They are plotted in Fig. 47, which shows that while
the flowering curves were identical within the probable
error on terraces A, B, and C, the later portions of
the bolling curves were dissimilar, and that this dis-
similarity was due to the shedding curve. The steady
progression from terrace C—the lowest—to terrace A,
becomes still more apparent when the curve of shedding
is plotted in the form of percentage of flowers shed to
flowers open. The amount of shedding thus appears to
be proportional to the depth of root-system which is
submerged by the rising water-table. In 1910 the same
set of observations gave no result which could be dis-
cerned by the methods of observation employed; this
was not unexpected, since the rise of the Nile shown by
the water-table on these plots began forty days later than
in 1909; as also in 1911 (Fig. 45).

It is noticeable that the 1909 curves show two maxima
of shedding ; one is coincident with the “critical” period
of maximum evaporation, the other with root-reduction.
The first maxtmum was very clearly shown by M. Audebeau,

* Report 1910 Cotton Commission.

ut DEVELOPMENT AND ENVIRONMENT 73

Fen days duly August September October | November Dec.

‘ending 10 20 30 9 19 29 8 18 28 8 18 28 7 7 27 7
aN
0-3k—y
3s oN
Q ‘
& \ip Flowering
o 02 _—
8 i
“.\. sire. ores
2 yl a ON ee Fh
7 al PA Ss
: lie a
: 279 Titeeee,
A
3 Bek
50-2 #L—™
<i Y/ ae :
2 i a Bolling .
2 ‘, aS
& 0-1 Ne gee —<—
Spee
. ii
3
a 1 C.
Q : ri
OPEN re Shedding
3 AS ican
oS ee
+ 90%
ae + 80%
70%
Leo Percentage of
BA ao Shedding to Flowers
C-—— 2 130%
-+-20%
A \ eee L 10%
Soil-surface R.L.-18-8 m. A
_ ——n
r=
ada
1 Geode
t- dens, Aug. 1st.

Fic. 47.—Terracep Lanp. Giza. 1909.
Three terraces, each 40 em. lower than predecessor.
Observations on 100 plants in each terrace ; flowers counted every day, bolls
every tenth day, shedding by subtraction.

74 THE COTTON PLANT IN EGYPT cuap.

who cultivated plots of cotton in small cement tanks, with
the water-table fixed at definite depths in each tank
throughout the season; his data showed that even the
absolute shedding, and much more the relative shedding,
was greatest in soil with a water-table only half a metre
below the surface, while it became proportionately smaller
in deeper soils, down to a two-metre water-table. In his
experiments there was no second mode, since no change
took place in the water level. We shall appreciate the
bearing of these data better at a later stage. In general,
they imply that a sufficiently large volume of soil must be
occupied by the roots to ensure a uniform water-supply
for the stem.

Since the “ terraces” were open to agricultural criticism
on account of the soil-disturbance involved by their
construction, a set of six cylindrical iron tanks, each
80 cm. in diameter, and two metres in height, were sunk
in a pit in the ground, until their tops were flush with
the surface, Each was fitted with an inlet pipe at the
bottom, protected by a loose brick arch, rubble, and sand,
and was finally filled with good uniform soil. A rubber tube
leading from this inlet pipe, and connected to an adjustable
reservoir of water, allowed the level of the water-table in
each tank to be maintained or adjusted to any required
level. Various combinations have been employed with
these tanks, but the results have only substantiated those
already described. Fixed high water-tables cause undue
shedding, so that the early part of the bolling curve is
abnormally small; changing water-tables cause temporary
shedding, so that a wedge is cut out of the bolling-curve
about seven weeks after the change has been initiated.”

Such small tanks are, however, open to many objections,
and the ideal method of study would be to encase an
undisturbed mass of soil with armoured concrete by under-
pinning, so as to convert it into a large tank. A set of at
east six such tanks should be arranged at intervals in a

ut DEVELOPMENT AND ENVIRONMENT 75

large cultivated field, with their rims just buried beneath
the surface; cultivation could then be normal, and the
water-level in each tank could be exactiy controlled by
pumps and tube wells.

The amount of space which we have devoted to the
subject of shedding may appear disproportionate, but the
Egyptian reader will realise its relation to recent problems
concerning deterioration of yield.

~ The centre of gravity of the root system.—A
metaphorical term is often of use in discussion, and the
words “ centre of gravity” are here used in a metaphorical
sense.

The C.G. of the root system may be considered in two:
respects ; either structurally, or functionally. The structural
C.G. is first situated in the radicle of the germinating
seed, from which it moves steadily down the tap-root so
long as the latter continues to grow. Unequal development
of laterals would displace the C.G. from the axis of the
root-system, but we shall assume that root-development is
perfectly symmetrical in its radial distribution. The
position of this structural C.G. is the resultant of the
length of the tap-root with the length, number, and
position of the lateral roots, A plant growing in shallow
soil, whose tap-root has consequently been arrested, and
whose laterals have developed uniformly over all parts of
the stumpy axis, will thus have a structural C.G. situated
mid-way between the surface of the soil and the limiting
lower stratum ; this stratum may be a rock or a water-
table. If this limiting stratum is removed, the tap-root
will descend further, and the C.G. will be lowered.

The mere structural C.G. is of less importance than the
functional C.G., which must obviously change its position
from day to day, even when the structural C.G. is
constant. The magnitude of these changes depends on
various factors, most of which we have already discussed,
and although much tedious analysis of soil samples will be

76 THE COTTON PLANT IN EGYPT cuap.

required before we can plot a curve to show this diurnal
change, yet the conception of a variable centre of gravity
for the water-absorption of the root seems so to clarify our
ideas on certain points that we will discuss it in more
detail than it probably deserves.

As a basis for discussion we may take four series of soil-
water determinations made at intervals of 20 cm. down-
wards for a depth of two metres, in the soil occupied by
the plants on which the daily growth (Fig. 30) was
measured. The bores were made within a few feet of each
other, among these plants which—it will be remembered
—were growing under field-crop conditions. The soil

contained 25 per cent. of water when completely saturated,
and the water-determinations, made by drying in the
steam oven, are expressed in terms of the saturation
amount.
‘The determinations were made under the following
circumstances :—
June 27th :—Four days after irrigation, when the maximum growth-rate
of the whole year had just been recorded during the previous twenty-four
hours. The precedent watering had arrested the symptoms of water-

shortage yet shown by the plant. We may safely conclude that the
water-distribution shown on this date was nearly ideal.

July 11th :—The day before the next subsequent watering, when severe
water-shortage was being exhibited by all plants, and the growth curve had
been falling fairly steadily since the last determination. The water-
distribution here was decidedly typical of insufficiency of water.

July 15th :—On the third day after watering, when the growth of the
main axis, having been accelerated for two days, had again begun to
decrease. The water conditions were probably very good, though no
growth-measurements were being taken on lateral branches by which this
statement could be corroborated, but comparison with the growth after the
previous watering indicates that the water-distribution in the soil had not
yet reached its optimum.

July 30th :—These determinations were made just before the next water-
ing. Water shortage was again apparent, and the period elapsing since the
last watering was the same as in the case of the determination of July 11th.

The actual changes in saturation-percentage under these
various conditions are shown in the following table. The

1 = DEVELOPMENT AND ENVIRONMENT 77

values shown are significant to plus or minus three per

cent,
Date. July 27th. July 11th. July 15th. July 80th.
Depth. Difference. Difference.
20 cm 43 -18 25 57 —43 14
40 cm 58 -17 41 73 —54 19
60 cm 62 -17 45 56 — 22 34
80 cm 84 - 9 75 77 — 2 75
100 cm 80 --11 69 82 - 6 76
120 cm 84 -10 74 86 — 22 64
140 cm. ......... 90 - 3 87 84 - 3 81
160 cm. ws... 90 +1 91 87 - 9 78
180 cm. ......... 86 + 3 89 93 — 6 87

Firstly, we seem to have found a way of ascertaining
the depth of the root-system. The depth of the roots
had been measured by excavation at the end of May, and
the mean depth for the end of June calculated from this was
approximately 140 cm. ; this depth was the last at which
a loss of water was shown. A month later, at the end of
July, when the roots had grown another 50 cm. at least,
the samples from 160 cm. and 180 cm. also showed a
definite loss of water. This is not recommended as a
trustworthy way of finding mean root-depths, but it at
least adds an extra method to the scanty stock available
for root-investigation.

For further interpretation of these data we obviously
need to intercalate observations at intermediate dates.
Certain points may however be deduced from them as
they stand. Thus, root-growth is not inhibited by soil-
water amounting to 80-90 per cent. of saturation. Again,
it would seem that less than 50 per cent. of saturation in
the soil is sufficient to produce water-shortage; on the
other hand, the pot experiments on this subject have
indicated that a lower value, perhaps 20 per cent., does
not usually limit growth at night ; the difference must be
due to the fact that a large plant with a “ limited” root-

78 THE COTTON PLANT IN EGYPT cuap.

system, having dried up the soil particles near its root
hairs, has to wait for the incoming of water from adjacent
particles as reinforcements, so that the plant is injured
during the day. The greater severity of the water-strain
during July, due partly to the higher evaporimeter read-
ings, and more to the greater leaf-area, is shown by the
greater water-loss during similar intervals, resulting in
more severe desiccation of the soil on July 30th as
compared with July 11th.

The water-loss is more severe in the upper layers of
soil, partly on account of surface evaporation, but more
from the complete occupation of such soil by the lateral
roots. Theextent of this desiccation becomes more severe
as the plant becomes larger, and it extends to a greater
depth in the same time. In other words, the centre of
gravity of the absorbing root-system shifts downwards
as the root grows larger, along with the structural C.G.
Moreover, even on the narrowest assumption, the top 40
em. of soil could have been providing little or no water to
the roots it contained on July 30th, whereas it had been
making free provision on July 15th. Thus, on July 15th
the functional C.G. and the structural C.G. probably
coincided, whereas on July 30th the functional C.G. has
descended far below the structural.

The extent of this displacement obviously increases as
the root grows larger, and as root-interference between
adjacent plants extends to greater depths. Thus, in the
germinating seed there can be no displacement ; structure
and function have a common centre of gravity. In seed-
lings with a ten-centimetre root there is a slight change
as the surface soil dries up after watering, but the dis-
placement is slight. So, as we progress to older and
older plants, the amplitude of the displacement increases,
its duration being bounded by successive waterings, till we
reach a maximum amplitude probably in early August.

Using a different method of expression, we may state

ur DEVELOPMENT AND ENVIRONMENT ~ 79

that the plant becomes more and more dependent, for
longer and longer periods, upon deeper and deeper layers
of soil for its steady water-supply.

If now we decrease the depth of available soil by rais-
ing the water-table, and at the same time asphyxiate, or
ultimately kill, the lower part of the root-system, we are
throwing more strain on the surface roots, and reducing
the deep-seated reserve. If this reduction is effected
in July or August, when the amplitude of displacement
of the functional C.G. is at its maximum, the effects—
shedding, for instance—will be much more severe than if
the reduction is effected at a later date, when the leaf-
surface has increased but little more, when the surface
climate is damper, and the sun-temperature is lower ; all
these alterations tend to relieve the water-strain on the
roots, by reducing the evaporation from the stem.

In this interpretation we find a reasonable explanation
for the otherwise disproportionate severity of the effects
produced by an early Nile flood, shown in the shedding-
curve and flowering-curve on the terraces in 1909, and—
according to the author's interpretation and forecast‘ ™ ”
—by the whole of Egypt in the same year, with disastrous
results.

Root regeneration.—The appearance of a root-system
in December is most remarkable, if it has been partially
immersed in the sub-soil water. The fullest examination
which the author has made was effected on the Gezira at
Cairo, where the sub-soil water-level is controlled entirely
by the river. By excavating a trench of three metres’
depth near the side of the plants, washing away the soil
with a jet of water from a force-pump, and using the
Ancient Egyptian method of reflecting mirrors to illuminate
the deeper portions, it was shown that the tap-roots had
descended to a depth of not less than 220 cm. Below the
depth of 160 to 170 cm., however, all the original tap-roots
and their branches were dead (Figs. 35, with 37 and 38).

80 THE COTTON PLANT IN EGYPT cu. 111

This level coincided with the maximum height of the water-
table, which had been maintained for ten days at the end
of September, and again for a day or two about October
20th. Side by side with these brown and partly decom-
posed roots, which had been traced unbroken from the
surface of the ground, there were clean, white, new roots
in abundance, which terminated at various depths up to
210 em. On following these new roots upwards they
were found to arise from those laterals which had not
been reached by the water-table. When the fall of the
water-table began at the end of October, these healthy
laterals had broken out into hundreds of tertiaries of all
sizes (Figs. 35, 38), which all turned downwards, following
the flight of the water-table, and reconquered the invaded
territory. The effect of this reconquest is shown above
ground by renewed growth of the stems in November
on a falling temperature-curve.

CHAPTER IV
THE COTTON FIBRE

WHEN the ‘sunshine effect” was first announced, a some-
what smiling denial came from many cotton experts.
When some of them had been converted to a belief in the
fact, they objected that it could not apply to the growth
of the lint. Substituting “may” for “could” this
criticism is still valid ; yet if the reader has succeeded in
gathering some conception of the fate of cotton plants
under Egyptian field conditions, he will probably expect
this criticism to yield before further experimental work.
We are, in point of fact, profoundly ignorant as to the
bearing of the two preceding chapters upon the final
commercial result, owing in the main to difficulties in the
technique of investigation. Methods for determining the
strength of small samples of fibre, for instance, are non-
existent ; true, it is possible to determine breaking-strains,
but the labour involved is enormous * if sufficient results
are to be obtained to give a reasonable probable error for
only a single seed. When uot merely a single seed, but a
thousand, have to be examined, the method becomes
hopeless. The author is experimenting with indirect
methods such as determinations of weight, specific gravity,
etc., which can be made on single fibres by suitable
appliances, but as yet we are dependent on the rule of

* Vide e.g. Yves Henry.
81

82 THE COTTON PLANT IN EGYPT cuap.

thumb, and finger, of the expert, who objects to handling
even single-plant samples. Probably a combination of all
these methods with a minimum of microscopic observation,
which is undesirable on account of its high subjective
error, will give us a line of attack, and we may be able in
the future to explain why a fibre has become strong or
weak, and how such weakness or strength is affected by
the environment.

Even such an obvious character as length of fibre is
very difficult to examine during development. The tangle
of lint hairs on the seed is almost inextricable, especially
in the early stages, when the individual fibres are too
weak to endure combing. Further, as in the excavation of
roots, a fruit once dissected for examination can be no
longer observed, and averages must be struck.

The little which we know may be summarised under
the microscopical evidence, with the evidence derived from
fluctuation and correlation.

Cytology of the fibre.—The development of the
fibre begins before fertilisation is accomplished, by radial
growth (Figs. 3, 5) of a large number of the epidermal cells
of the seed coat. These cells (Fig. 4) differ in no respect
from their neighbours, and it seems possible that the
density of the coating may be determined by the external
conditions during a day or two after flowering. Possibly
irregularity in length may arise from distribution of the
normal simultaneous “ sprouting” of these cells over
several days. ‘

The young fibre (Figs. 6, 7) at once assumes its final
diameter, which is about twice that of the unaltered cell.
It remains unicellular throughout its career, and is always
covered by the cuticle which protected the original cell.
The familiar “beading” which follows treatment with
ammoniacal copper hydroxide is simply due to constriction
of the swelling cellulose by the cuticular remains. For
the first day the nucleus lies at the tip of the swelling, but

IV THE COTTON FIBRE 83

after the third day it takes its place in the middle of the
cell axis, and there remains, either slung in cytoplasmic
bridles, or at the side. The cytoplasm, of course,
lines the whole cell-wall, and appears ie remain, alive
until the boll cracks.

The growth of the fibre is at first confined to. ae
extension. In fact, it seems that the boll attains.almost
to its full size before any secondary thickening of the
fibre wall begins. By this time the fibre has reached
to rather more than its final ripe length. This:,period
embraces about half the total maturation period, being
some twenty-five days. Presumably it is during this
period that unfavourable environment, such as is made
manifest by a mode in the Shedding Curve, could produce
irregularity in length from boll to boll. The final length
is of course constitutional, and can only be deflected from
this constitutional basis to a relatively slight extent.
Even seeds which have not been fertilised, and consist of
empty, undeveloped seed-coats alone, possess hairs of
nearly normal length, though abnormally weak. The
best evidence in respect of this constitutional basis for
length is given by measurements on the ripe seed. Thus,
a random selection of data for maximum lint-lengths,
in five seeds per plant in a pure strain grown under
conditions favouring maximum fluctuation, has given the
following figures on a total of 210 seeds.

Mean length vee eee tee ee eee = 83°50 mm.

Extremes... see aes ee eee, 27 and 39 mm.
Standard deviation vin ate ace oe, © 24am,
Probable error... «5 see vee wee): 1°44 mm.

Probable error as percentage of mean = +£4°3 per cent.

Comparison of one strain with another in this way
shows that the mean lint-length is an inherited character-
‘istic. The final attainment of the lint cell in the matter
of length is effected by intercalary growth, the form of
the tip and of the base being determined at an early stage.

G 2

84 THE COTTON PLANT IN EGYPT cuap.

The cessation of this growth is thus the result of
internal constitution, though environmental changes
exercise a limited effect. (Fig. 50 also, “310” and
i ae |

It appears, though this point is not quite clear as yet,
that linear extension has ceased before thickening of the
wall commences. It is this thickening which determines
the strength of the individual fibre. The strength of the
commercial sample depends not only on thickness, but also
on uniformity of strength as between different fibres.
Moreover, commercial strength does not merely result
from the thickness of the cell-wall, but also from the
uniformity of that thickness over the whole length of
the cell, and possibly is also affected by the ‘“ texture”
of the thickening layers.

Even as regards the simple fact of thickening, we find
many curious delusions in the extant literature of the
subject. Confining ourselves to the known data, the
matter is a simple one; concentric Jayers of cellulose,
probably delimited from night to night, are laid down on
the interior of the delicate cellulose-cuticle wall, until a
certain thickness is reached. This deposition is not uniform,
but results in the formation of simple pits at intervals,
elongated obliquely.

In consequence of this pitting we find that fibres devoid
of secondary thickening show no twisting when extricated
from the unripe boll and dried, while fibres taken from a
boll which is nearly ripe exhibit rapid and uniform
twisting as they dry, owing to the closure of the solid
portions of the cell-wall into the minute spaces formerly
occupied by the pits.

Strength.—In respect of the strength of the lint, we
have some evidence to show that the causes which provoke
shedding are simultaneously effective in weakening the
lint.

The lint from the terraces (Fig. 47) in 1909 was

IV THE COTTON FIBRE 85

submitted to an expert * for grading. The first pickings
from all were classified as uniform. The second pickings,
ripened during the rise of the water-table, were progres-
sively graded ; the top terrace gave the strongest lint, and
each step down was a stage weaker. These second pickings
came from the bolls which had ripened during the rise
of the water-table.

Another set of data came from an F, of Egyptian x
American. The lints were classified by the grader into
groups, according to their strength. The amount of
shedding per plant in this family had been computed
up to a certain date and found to range from 100 per
cent. to 19 per cent. of the flowers opened, with a mean
at 70 per cent. Grouping those plants which possessed
Egyptian lint according to their strength, the following
figures were obtained :

Strength. Mean Shedding.
Weak ase ade. aie aan Wee 70°2 per cent,
Medium... ... ... 0. oe 68°7 34
DtEONE a3. aa A Se ee 60°6 55

In this case the cause of variation in shedding is
constitutional, and the correlation is hence more striking
than when the variations were due to environment only.

This same family was dissected in the same manner for
other characters, but no other correlations were obtained,
except with regard to lint-weight (mean weight of lint per
seed), This ranged from 0021 g. to 0°060 g. with the
mean at 0°036 g. Classifying the Egyptians again by
strength we found :—

Strength. Mean Lint weight.
Weak = sas ive was ewe ea, ans 0:0348 g.
Medititi- ys wie ee aes hae aed 0-0358
Stromg ae se) Gen ake Sag SE 0:0373

Thus the heavier lint is the stronger. Further, since
lint-weight and seed-weight are closely correlated, we find

* Mv. H. C. Thomas, of the National Bank of Egypt.

86 THE COTTON PLANT IN EGYPT cuap.

that the “ ginning out-turn” is highest in the strong lints.
This ranged from 48 to 111; mean at 75 about.

Strength. Mean Out-turn.
Wreale ico skie Guxt cha, Shan 20m Gai 69-90
Medium -vsx. ase agar) age eee 72°96
Strong as. wz. ove we ces ts SOT

The last result gives a partial clue to the preference for
high “ out-turn” which the buyer—independently of the
grower—displays. A few notes on this matter should be
made.

Ginning out-turn.—The out-turn of lint from seed
cotton at the gin is expressed in Egypt as rotls of lint per
315 rotls of seed-cotton. The extreme means recorded
for a whole factory throughout a season are 113°3 (Abbassi,
Qalioubia, 1899) and 88-0 (Ashmouni, Sharkia, 1888).
Variations in this figure occur from place to place, but
when the mean out-turns of large ginning factories are
considered, we find ‘that the variation-graphs for a number
of years are closely similar in different places.” Thus 1903
showed a sudden rise of out-turn almost everywhere in
Egypt.

These variations are as yet inexplicable. Wide-sown
plants give much lower out-turns than those which are sown
in field crop,* and nitrogenous manures in field crop also
depress the out-turn, through increase in the seed-weight.t
The variation is due, of course, to imperfect correlation of
lint-weight with seed-weight.” This correlation had a
value of r= 0°810-+0°035 in a set of forty-five commercial
samples of one variety examined by the author. It has
been shown by Mr. J. I. Craig { that there has been also a
slight correlation between mean out-turn and the total
Egyptian crop in any given year; r=0°3899+40°182 for
fourteen years.

The study of variations in ginning out-turn is thus
dissected into separate studies of fluctuation in lint-weight
and in seed- weight.

* E.g. Vig. 50. ‘* Varieties.” -. + Hughes, 3. . t Craig, 3.

IV ‘THE COTTON FIBRE 87

Lint length.—The “length” of the lint is also a
complex of several factors. Chief amongst these are the
mean maximum length, and the regularity.

Some strains of cotton produce lint-hairs of the same
length on all parts of the seed-coat.” Most kinds, however,
make shorter hairs, at the micropylar end.*° Fluctuation
in this respect. does not seem to be very noticeable, and
we can restrict our present remarks to the mean maximum
length; this is ascertained by combing the lint on the
seed, and measuring from the seed to the edge of its
halo of lint.

Fluctuation in the mean maximum length is described
later, and the relation of such fluctuation to the conditions
under which the fibre develops has already been discussed.
Briefly summarised, this length is determined primarily by
the constitution of the individual plant ; secondarily, by the
experiences of the particular seed and boll during the first
four weeks after flowering.

The’ second determinant necessarily varies greatly when
we are dealing with.a commercial sample which includes
seed from bolls of various ages; the particular experiences
of each boll may be so different that on the average we
may consider the effects from year to year.as being almost
uniform. Consequently, though it is possible to-depress a
40 mm. lint to 30 mm., we find that the practician draws
a sharp: distinction between 30 mm. and 40 mm.
varieties.

We have now ‘completed: an..outline sketch of the
principal factors which’ are yet known to control the
development of a cotton’ plant in Egypt, and certain
hypotheses have been: propounded which serve for the
present as interpreters of the author’s data.

“It might seem that too much stress, has been. laid,

* Photos.

88 THE COTTON PLANT IN EGYPT cu. Iv

whenever and wherever possible, on physico-chemical
possibilities. The author’s own opinion favours such
readings of the experimental text, if only as a refuge from
disguised vitalism. Lest such opinion be made an
accusation, it may be well’ to point out that many
recorded phenomena will not yet yield to the point of
such hypotheses. One irreconcilable of this order is the
striking ‘‘ sleep-movement,” which is exhibited by all
leaves throughout the year, and even by the seed-leaves.

The organic factors of the environment, such as fungoid
and insect pests, together with the flora and fauna of the
soil, cannot be discussed within these limits. The fungi,
excepting ‘“Sore-shin,’ are of negligible importance in
Egypt, though Colletotrichium gossypii, Mycospherella
gossypina, and Meliola spp. are extremely common. The
insects, conversely, are of great economic importance,
though the blame for many of their reputed crimes really
lies at the feet of the plant, particularly in respect to the
boll-worm. Some such confusions have already been
noted in passing, and it is curious to note that a mild
attack of cotton-worm, through diminishing the water-
strain, may actually increase the yield by prolonging the
flowering-period.

The soil flora, imperfectly understood, must be left
untouched by us. In soils of the Nile Valley the
geological aspect is superior to the chemical one; texture,
and hence water-content (frequently complicated by
“ salting”) is more important than manurial mixtures.
The author's colleague, Mr. F. Hughes, has shown con-
clusively that the cotton-crop of latter-day Egypt is rarely
limited—in Blackman’s sense—by the chemical com-
position of the soil. Water, always sufficient, but never
excessive, is the principal need of the crop;” and the
desired balance between deficit and surplus is struck only
by accident as yet.

SECTION III

THE RACE

At intervals throughout the preceding pages we have had
to resort to evidence drawn from the average behaviour of
groups of plants, in default of precise data from in-
dividuals. In other words, we have considered a group as
representing an average individual. These groups have
now to be considered for their intrinsic interest.

Such groups may be derived from a “ pure strain,”
being all of identical gametic composition ; in this case we
find material to study in the fluctuation, which is the
result of slight irregularities in a normally uniform
environment. Again, the groups may be derived from
the crossing of two pure strains, in which case their
gametic composition may not be uniform; we have then
to apply corrections for fluctuation, and having done this
we search in the residuum for evidence of gametic
differences wherewith to formulate expressions for the
inheritance of each characteristic.

Lastly—though it will be more convenient to discuss
this subject in the second place—the group may consist of
many different pure strains, mingled with hybrids between
them of every generation imaginable. Such is the com-
position of the commercial “varieties.” Within limits,

and for certain purposes, we may consider such varieties
. if

go THE COTTON PLANT IN EGYPT

as uniform, since the inequalities smooth themselves out
when a sufficiently large number of plants is taken.

These group limits have been drawn for convenience, and
they are perfectly genuine. Nevertheless, the phenomena
are mutually interdependent, so that the humblest plot
of cotton cannot be understood without a knowledge of
Physiology and of Genetics. The subject of Fluctuation
forms a neutral ground between these two relative branches
of science; it belongs to both; physiology explains it,
genetics cannot be explained without it.

The author frequently had oceasion to regret the lack
of significance in his older heredity experiments, due to
lack of fluctuation data as standards, and when these
began to accumulate they were found meaningless until
the physiology had been studied.

CHAPTER V
FLUCTUATION

WHEN we desire to compare different sets of data, we
must either admit of no observational error, or ascertain
separately what error exists in each set, or else employ
standard methods of known probable error.. The last is
the most convenient method, since the yearly programme
of work can be standardised, and comparisons are easily
effected. The particular method employed for any one
characteristic, such as the form of the leaf, is a compromise
between the probable error and the. facilities for
observation.

The slide rule and nomographs, measuring dividers,
glass plates graduated in angles and lengths, the plani-
meter and pantograph, adding machine and Joly balance,
with a string of simpler appliances stretching down to the
oldest of all—a small-tooth comb—have been successfully
pressed into service with the object of economising time
in these researches.

The pure strains on which these observations have been
made were derived from single plants of. various kinds.
A few of the offspring in every year during periods of
three to six years have been covered with mosquito netting”
to prevent natural crossing ; the resulting strains are not
visibly impure, so far as our present knowledge can
ascertain.

92 THE COTTON PLANT IN EGYPT cuap.

Whenever a family is henceforth mentioned, it should
be understood to be one of these strains. Commercial
“‘ varieties ” will be specifically designated as such.

Since the fluctuation-graphs for parents will necessarily
be consulted when dealing later with genetics proper, the
reader is referred to these, except where some special
point requires to be illustrated by a special figure.

For the expression of fluctuation in statistical terms, we
shall take the percentage probable error, and not the
“coefficient of variation.” The latter is the “standard
deviation” expressed in percentage of the mean. The former

—
is roughly two-thirds of the latter, 2.e., PE = 0-67,/ 28

P, 100.

Mean ~
convenient, since half the observed cases must lie within
the limits given. The maximum possible true fluctuation
may be taken as odds of about 30:1, or 3°2 times the
probable error.

Whenever a specific figure is given for a family it
should be understood as having been checked by com-
parison with other families, and therefore considered by
the author as being fairly representative of the data
available.

Colour characters.—Such characters as the colour of
the petal anthers are devoid of appreciable fluctuation.
This uniformity is probably apparent rather than real,
since a difference of less than 10 per cent. in the
intensity of a colour cannot be perceived by the ordinary
eye.

When colours have to be classified, as in hybrid popula-
tions, standard flowers, &c. are always used, and the
unknowns are matched to them.

Characters which depend on the presence of antho-
cyanin in the tissues, such as the red spot at the junction of
petiole with lamina, fluctuate widely. Comparisons can

and our particular expression is This form is

v FLUCTUATION 93

only be made with safety when the plants are equally
healthy.

The stem.—The branching habit of the stem has not
received from the author the attention it merits. Some
evidence may be gleaned indirectly from the flowering-
curves, but systematic study of fluctuation in branching
is difficult,* unless a high subjective error is risked.

The height of the central axis is easily examined. The
plants are measured to the nearest 5 cm. every week or
fortnight, taking the soil-surface and the terminal bud as
the approximate extremes. A portion of the fullest series
of height determinations obtained as yet is plotted in
Fig. 48. This series represents an extreme case, some
plants being badly stunted. The height determinations
in this family can be compared with similar series from a
very uniform lot of seedlings belonging to family “307,”
and also with rows of commercial Afifi plants in field crop.
These last were measured to bench-marks with a water-
level. The statistical statement is as follows :

July 4th. August 29th.
x Number
Family. of Plants.

Mean. PY EB. Mean. PLE.

Per cent. Per cent.

307. Wide-sown, uniform 17 524 cm. | £12°0 || 115 cm.) + 9-2

77. $8 irregular 45 61 cm.| £18°3 || 114 cm.) +12:°0
Commercial Field - crop ;
fairly uniform... ... 98 524 cm.| £152 || 89cm.) £15°4

The fluctuation in a wide-sown pure strain decreases as
the plants grow older, stunts overtaking the normals.
This is partly the case in field sowing, though to a less
extent owing to competition, and it is further masked in
commercial varieties by their non-uniform composition.

* See, however, Leake, H.M., 2 and 3.

94 THE COTTON PLANT IN EGYPT cuap.

The same figure (Fig. 48) also shows the fluctuation in
the growth curve, which can be obtained by following the
same plant from date to date.

27 is May 23.

26
27 18 25

21 24 15 16 _dune 5,

1413 7 3°17

8.114 2°10 5

16
27 «22 12 June. 19.
24 20 6
21:23 13 15 26; 5 vw
19. 8 14:11 7 4/3]2 10
:
July 4. 27 6
2414 26 22 25 4
19 23 12 205 8
a 27 17 § 12 13:16 2
\
27
July 78, 23 21
26 22 16 12/18
8 13:15 7\7 10
24419 411 14 20 251315 2 6
27
Aug. 1. 25
23) 14 18
26 22 16)/21 u ie ae
24 19_ 20 13/4 8 15 3 5 12 2 10
Aug.) |76. i
26 2325 § 2711 1712
24 22 19/16/20 13 2115 4 14 8 3 7/1016 2
Aug. 29. ‘
24 1 10
—__2219|90/16 9513 4 5 18 3|1|12 7 8 6 2
Ped
|Sept. 12. it
14
28 24 21 ta} fiz 10
22 |ielig 251533 934] 3/5 11 8 27 8
Sept. 26. 27
Pp #
26 24 14.11 ~ 10
22 he] 19 2545 13 2123 18/3/12 4 5 8 2 6 7

10 20 380 40 50 60 70 80 90 100 NO 120 180 140 150 160 170 180 190
Centimetres

Fic. 48.—Heient or Stem.
Wide-sown, pure strain ‘‘ 77.”
This figure is a reproduction of a page in the ‘* Ledger” of this strain.

The correlation of fluctuations in height with the fluctua-
tions of other characters has occasionally been interesting.
The most curious result was obtained in this same family
77, with respect to the leaf-length. The latter was
measured in the first week of September ; plotted against

v FLUCTUATION oe 95

height on July 4th, two months previously, there was a
marked negative correlation; r= —0°67, on 81 pairs;
plants which had been short in July possessed long leaves
in September. The height on September 12th—at the
time. of leaf measurement—showed a small positive
correlation, while August Ist gave a transition stage
with no correlation at all. These data have obviously
some bearing on the inter-play of root upon shoot, and
conversely,

The correlation of height on July 4th with the data of
the first flower—which varied in one series from June 19th
to July 28—is definitely curvilinear. Plants which. were
stunted, and are therefore still short, flower proportionately
late, but this correlation vanishes after passing the mean
height, all the normal and super-normal plants flowering
at approximately the same time. Here we are probably
dealing with the data of initiation of the flowering-branch
buds.

The correlation of early height with total flower- or boll-
production is also close, and becomes less distinct. as we
pass to later height. This is effectively a statement that
stunted plants, even if they grow up later to normal
height, cannot produce a crop of normal size. This effect
of stunting acts partly through the delayed first-flower.

The leaf.—Fluctuation in absolute size of the leaf, as
expressed by measuring the length of the mid-rib, is
obviously complex. The correlation with stem-height,
previously mentioned, will serve to illustrate this. Still, even
leaf-length is tolerably definite, the PH. ranging from 6 per
cent. to 34 per cent. The discussion of leaf-form, however,
introduces us to a new set of factors, of ontogenetic, or
even phylogenetic nature. The first leaf of the seedling
plant is entire, even when adult; later leaves became
progressively more elaborate even when first unfolded,
until the five segmented typical leaf is reached. The
form assumed is nevertheless not independent of the

96 THE COTTON PLANT IN EGYPT cuap.

environment, for later buds on old stems may develop
leaves of juvenile form.

As regards the method of observation, we take three
adult leaves from every plant during August-September.
Each one is laid under a graduated glass plate, from which
its length, and two angles, are read. From these we can
complete any other constituents of the triangle thus
recorded. This triangle gives us the form of the central
segment, which is limited lengthways by the petiole and
the central tip, and laterally by the sinus at which the
leaf-margin bends sharply back on the lateral seg-
ment,

The position of this sinus is the essential feature. On
examining growing leaves we find that the sinus moves
outwards along a constant angle as the leaf enlarges, at a
rate which is directly proportional to the growth of the
leaf in length, consequently the sinus-angle relatively to the
mid-rib, either from tip (4*)or origin (4°) shows the
minimum fluctuation. More fluctuation is necessarily
shown by the length of the line from petiole to sinus pro-
portionately with the total length, but both are specific.
If we neglect such additional factors as curvature of the
segment-margin, plication of the lamina, &c., this method
of expression is comprehensive. A check on the result is
obtained by plotting sinus-positions in a pure strain,
relatively to the tip or to the base. The resulting diagram
resembles the side view of a choked shot-gun discharge,
passing along the angle-lines, the centre of the pellets
defining the mean sinus-length. The P.£. of these angles
in Egyptian strains is about +3°0 per cent.

The number of leaf-segments, or rather the development
of the second pair of lateral segments, has been mentioned
above as dependent on ontogeny. It is fairly definite
under given conditions, same strains refusing to produce
the extra pair.

Perhaps it is worth while to mention that such presum-

v FLUCTUATION 97

ably primitive cottons as G. Sturtiz, F.V.M.,* retain the
entire leaf throughout their development.

The depth of the segmentation, when present, varies
within the same sub-species, as in the two forms of
“Nyam-nyam kidney cotton;” possibly the Okra-leaf
sport in American Uplands is another example. Such
facts are suggestive of mutation, but mutations in
Gossypium ought not to be mentioned until we know
much more about natural crossing and heredity than we
are likely to acquire for several years to come.

The flower.—lIn the course of an attempt to breed
an uncrossable flower, to be mentioned again later, the
author had had occasion to measure the various floral
organs, namely, petal, style, staminal column, and fila-
ments. The sequence of development of these in the bud
begins with the petal, followed by the column and fila-
ments, and ends with the style.

The fluctuation does not follow this order. Fifty-one
plants in “77” family gave the following typical
results :— a

Petal, ase sais ape Mean, 59 mm. P. HE. +2°8 per cent.
Style acs wus xcs BD ngs P.E. 435 $9
Column ... «0... se. Anas P.#H. +56 ‘is
Filament Sears is 4°2 mm. PLE. £77

”

A portion of this increased fluctuation is probably
apparent, being due to greater errors of measurement in
the smaller organs, but much of the increase is certainly
significant. One would rather expect the external organs
to fluctuate most, but the reverse is the case.

The involucral bracts are intermediate in their fluctua-
tion. ‘Their width in the same family gave a P.E. of
+ 4:0 percent. The ratio of width to length also gives
a 4°0 per cent. probable error.

The measurements are taken with dividing compasses

* Watt, Sir G.
H

98 THE COTTON PLANT IN EGYPT cuap.

to the nearest millimetre exept in the filaments, where
half-millimetres are attempted. Three flowers are

examined on every plant, and the means for all three are
taken.

First flower and maturation.—The obvious effect
of early stunting is to provide a long tail of late-flowering
plants upon a graph which shows the date of the first
flower. If the originally stunted plants are excluded, the
P.E. of this date works out at a little more than four
days in most families, or 33 per cent. of the time elapsing
between sowing and flowering.

The maturation of the flowers opening during early
July at Cairo has been directly recorded by marking the
flowers. The results for, e.g., family “77” in 1911 gave a
mean of forty-eight days with a P.H#. of + 3:0 per cent.
The period is longer in the Delta.

Flowering and bolling.—The limits of the present
volume do not permit of detailed discussion of the
fluctuation from plant to plant in flowering- and bolling-
curves, beyond the account of the possible controlling
factors already given.

The influence of sowing-distance is shown in Fig. 44,
four times the number of flowers being found on wide-
sown plants as against field sowing. The point is important
with regard to propagation of new varieties ;* by wide-
sowing we can obtain 100 bolls per plant from a strain
which will only produce 15 to 20 in field crop.

The influence of defoliation by cotton-worm is peculiar,
the flowering being immediately arrested, but subsequently
extended much later than usual, so that a warm autumn
may enable the ultimate yield to reach the normal.

A few points of interest arise with regard to the total
production of flowers up to a certain date, and the bolls
developed from them. The correlation between these two
quantities was worked out in the wide-sown, very irregular
family of “77,” for 1910, with the following results.

v FLUCTUATION 99

E, £29 per cent.

E, £34
Correlation between total flowers and bolls : r=0°85.

(Imperfection of correlation is mainly due to shedding.)

Percentage of retained flowers: Mean, 40°6 ; P. #. +7°5 per cent.

Total number of flowers per plant Mean, 115 =P.
50 P.

” ” bolls ” ” ” ”

These figures demonstrate the manner in which errors
accumulate during field experiments. Comparison of two
rows or plots of the same variety becomes more and more
erroneous as the plants grow older; comparison by the
number of flowers has a lower P.#. than comparison by
the number of bolls; this in its turn has a lower P.E.
than comparison by weight of seed-cotton picked ; this
again is more precise than comparison by ginned lint.
Fresh sources of error creep in at every stage, and the fact
that field plots have a P.E. of +6 per cent., at least,
becomes quite comprehensible.

The boll.—The three chief characteristics of the boll
are its diameter, the number of loculi, andthe shape. The
first. and last are determined from three full-grown
bolls per plant, measured with parallel-jaw callipers, the
form being expressed as a diameter in percentage of length.
The number of loculi is determined by examination of not
Jess than twenty bolls of one kind on each plant; thus
forty bolls may have to be examined to obtain the critical
number, if half are trilocular and half quadrilocular ;
such a plant receives the designating formula of 3°5.
Plants whose bolls are all trilocular are designated 3:0; if
all quadrilocular, 4:0, &c. For certain families the critical
number has been raised to forty bolls of a kind (eg.,
Fig. 63).

Specimen data for these characters in Egyptian families
are :—

Boll width ... .. 0 « Mean, 25 mm. P. #. +3°6 per cent.
x AOL: ees: gine wae » 646 ,, P, #H, £3°8 fs
»> Loculi ... ... ve ‘5 2°81 ,, P. i. +26 33

The fluctuation of the last character is low, presumably
because the number of loculi is differentiated at an early
HQ —

100 THE COTTON PLANT IN EGYPT cuap.

stage of bud-development, whereas the diameter of the
boll is partly dependent on the environment in which it
exists during the first thirty days after the flower
opens.

It may possibly be owing to this division of boll-
maturation into two periods that we find no correlation of
seed weight with any of the boll-characters in pure strains,
though such correlation is very evident in heterogeneous
F, families.

Seed weight.—The mean weight of the seed is
determined by. weighing and counting samples of not less
than 200 seeds. There is much to be done yet in deter-
mining the causes of fluctuation, by examining weekly
pickings. ‘

The highly irregular “77” family of 1911 had a mean
at 0-097 gram, with a P.#. of +8°3 per cent.

Another family, of twenty-three very uniform plants
with a mean at 0:095, had almost as much fluctuation,
viz., P.E. +7°0 per cent.

The weight of a seed is completely determined by the
mother plant, and not by the embryo. Thus the weights
of single seeds of an F, plant show no modality, nor does
the weight of the embryo. Forty such seeds, weighed
singly, gave the following fragmentary result.

Mean seed weight... 0-180 gram P, FE, £5°9 per cent
» testa ,, ais 0-078 ,, P. EF. £67 33
>, embryo weight... 07102 ,, P. EB, +53 5

Embryo weight = 57 per cent. of seed weight.

The difference between testa and embryo is slight, and
both are equally important in causing fluctuation in seed-
weight.

The causes of this fluctuation are obscure. Correlations
have been plotted for all recorded characters, but with
very few results. The values for “7” need not be given
since a qualitative statement is sufficient for the available

data. The only connections yet shown are: Leaf length,

Vv FLUCTUATION IOI

some, positive; Height, doubtful, positive; Lint-length,
slight, negative ; Lint-weight, high, positive ; First flower,
slight, negative.

None of these are very definite and the explanation lies
in the fact that while height, leaf-length, and first-flower
represent the mean result of a long period of environmental
influence, the fluctuation in weight for any particular seed
is probably fixed within a period of a few days.

The same explanation applies to the high P.Z#. of uniform
families, which is neany equal to that of the most irregular
families.

Summarising, we may say that everything points to the
root as the controller of fluctuation in seed-weight.

Lint weight and out-turn.—We have already dealt
with the correlation between weight of lint and seed, in
discussing ginning out-turns. The correlation is
less close in pure strains, taken plant by plant (e.9.,
r=0'72) than for the crop-samples there mentioned
(r=0°81).

The fluctuation in lint-weight seems to be proportionally

less than that.in seed-weight, the P.E. being, | é.9., 275
per cent. as against 83 per cent. respectively 1 in the same
family. This. statemént probably requires revision for
field crop conditions, since wide-sown plants give
abnormally low ginning out-turns ; the crop-samples gave
a lower correlation between seed-weight and out-turn
(0°220-0°094) than between lint-weight and out-turn
(0316 + ‘091).*
‘The fluctuation in ginning out-turn for family “77”
had a mean of 92 rotls, with a P.E. of + 3°5 per cent.
This is probably an excessively high figure, as the plants
growing in the tanks gave much higher out-turns than the
rest.

Seed fuzz.—Although this amount of “fuzz” on

* See Craig, J. I. (3).

102 THE COTTON PLANT EN EGYPT cunap.

the seed scarcely admits of statistical expression, it is
sufficiently important to merit a comment. The cytology
of the “fuzz” hairs is as yet unknown. They are
certainly different from the lint hairs, but the demarcation
may not be very obvious in abnormal seeds.

The presumably primitive cottons * possess no lint, but
abundant “fuzz” covers the seed-coat. Less “ primitive ”
cottons have both fuzz and lint. In the cultivated
cottons we find groups with “entire” fuzz like the
primitive species, others with fuzz restricted to the hilum
and raphe, and others with no fuzz whatsoever. The
phylogenetic interest of the character is consequently high,
especially since some evidence as to its factorial composition
is available.

One of the chief features in this connection is the colour.
Green, brown, and white fuzz are all known in most
cultivated cottons, though—since the green is unstable—
green and brown are not easily distinguished. The lint
colour, on the other hand, ranges through browns and
creams to white, while even the browns appear to be of
various origins. There is, however, a green-linted cotton
known as “Texas Wool” which appears sporadically in
fields of American Upland, and breeds true to the green
lint. This stock is of interest because it provides a
suggestion of possible phylogenetic connection between
lint and fuzz.

Apart from colour, however, we find a certain amount
of fluctuation in the amount of fuzz. Within a pure
strain this is very slight, but when severe constitutional
changes are forced upon a semi-fuzzy stock by crossing
or by a novel environment, the fluctuation may be
conspicuous.

Lint-length.—Since data on fluctuation in lint-
strength are not yet available, we can quote for lint-

* Watt, Sir G.

Vv FLUCTUATION 103

length only of those characteristics which interest the
consumer of the crop.

Cultivation 10 Parent Year
5 =
Wide-sown Pn ain 77(B)(x) | 1909
10 77(B)(x)(1)
5r ee
Wide sown % LA 4970
| ite me
10
st N/
Wide sown f ”
10 es 77(B)(x)3
5Fr Le
Wide sown £7 1
10 do
5b
Wide sown a w
25-
36 LN 77(BYX)N1).2. | 29EE
SL ae a
10
5Fr NWN
Wide sown

io fx. 77(BUX)(1) 6
7
Field a. 57 ie f—-k i \ — ”
A

60 seeds
10 7 N78) 3
5 ss \

Field 6. >|. af] 7
60 seeds
10 — :
5 sre Pos we Me Commercial
do. do. eee pe [eee Assili
“
10 i, -
5 eo el OY pie Commercial
do. do. ape fe Teer’ wo Nees Affi “
20 25 30 35 mm.

Fic. 49.—Maximum Lint-Lencto or SINGLE SEEDS.

x Mean length of parent plant.
— Pure strain of Afifi.
... Commercial ‘‘ varieties.”’

‘Field a and 6” were different field plots carrying alternating rows of
various cottons.

Fluctuation in this respect has been shown to vary with
the season and cultivation, with the sowing distance, &c.

104 THE COTTON PLANT IN EGYPT cu. v

The extent of this fluctuation is determined on the mean
maximum lint-length of five seeds taken at random from
the plant, and gives such results asa P.H. of +2°9 per
cent. on a mean of 33°5 mm.

Taking single seeds only, we obtain such results as those
shown in Fig. 49. There is a definite bi-modality in some
of these graphs; probably further investigation of such
modes will show us how to persuade a plant into the
production of abnormally long lint as a normal preduct.

CHAPTER VI
COMMERCIAL VARIETIES

TuE probable origin of the type of cotton plant grown in
modern Egypt has been discussed in the historical section
of this volume. Many commercial varieties have been
developed within this type. Some are extinct, and are
only known to the author by name; such were Gallini,
Abyad, Hariri, Bamia, Hamouli, Zafiri, and Ziftawi.
Others which have been subjected to examination by the
author, but which have not been able to make good their
footing in the market, are Brown Yannovitch, Charara,
Kerki, and Bolanachi. Others again are cultivated to a
limited extent, such as Sea Island (both old stock and
imported seed), Sultani, and Voltos.

The main varieties at present cultivated on a commercially
important scale are Yannovitch and Sakellaridis in the
“fine-spinning” group; Abbassi, as the white and
moderately fine type ; Ashmouni, Nubari,* Afifi and Assili
in the “ bread and cheese” group.

Ashmouni is the putative ancestor of all these, by way
of Afifi. The origin of any one variety is most difficult to
ascertain, but the majority probably arose as single-plant
“selections.” In the case of Yannovitch this is definitely
known.

* Nubari is not considered as a ‘‘ bread and cheese ’”’ staple at present, but
its future probably lies that way. The matter is discussed in as yet
unpublished reports by the author on the Lancashire cotton demand,

105

106 THE COTTON PLANT IN EGYPT cuap.

Lastly we have the weed cotton, so-called ‘ Hindi.” It
is not a cultivated variety, but sporadic as a weed mixed
with other varieties. In general appearance it could
easily be mistaken for American Uplands, but the seed is
devoid of fuzz. Within the Hindi type there are various
sub-types ; thus, of some five hundred plants grown from
Hindi seed of commercial origin, only about a third were
very hirsute, while others were completely glabrous.

The seven important varieties mentioned differ in age.
Ashmouni, or rather the name, dates back to the ’fifties
of last century. Afifi was introduced commercially about
1887, Abbassi in 18938, Yannovitch in 1899, Nubari in
1907, Sakel in 1909, and Assili in 1910. These dates
are, of course, approximate, being those years in which a
conspicuous quantity of the lint reached the spinners.

Now with this multiplicity of varieties it might be
imagined that their differentiation was easy. Such is by
no means the case. All the varieties are similar in
external appearance; even when grown side by side in
field rows on the same plot, they cannot be distinguished
with certainty. There may be far more difference between
individual plants within the same variety than between
two distinct varieties.

Certain physiological differences are found, however, but
they are not very easily expressed in precise terms.
Thus Ashmouni is the crop of Upper Egypt, Yannovitch
is concentrated round a centre in the N.E. of the Delta,
and Afifi gave the best results in the Southern Delta.
Again, Yannovitch is credited with cropping lightly,
about 10 per cent. below Afifi or Abbassi, and this opinion
is supported by the scanty data available.

One of the cherished fables of the practician teaches
that heavy crops and fine staple cannot co-exist. The
inaccuracy of this belief, though long suspected, has only
recently been proved by the Sakel variety. The bolling
curves of Afifi, Sakel, Assili, Voltos, and the pure strain

vI COMMERCIAL VARIETIES 107

“77” are shown in Fig, 42, determined from weekly
pickings of five rows apiece, with a P.H. of + 10 per cent.
for any point in the curves.

The total yields of these curves work out as follows :

BOT 5) atten ~ el Yield =25'1 bolls p.p. . £06

P.E
Assili 0. 1... » =199 P.E. £0°5
Sakel v0... a ae P.E. £05
Voltos... 60 o. sp). Sey “5 P.E, £04
(ABE sa ake: one » =200? ,, P.E, £1°5)

Thus the three commercial varieties included in the list
are practically identical with regard to yield.

We have already figured the length of the lint of “77”
under these conditions, and a comparison of this pure
strain with similar rows of the two varieties Afifi and
Assili should be of interest, one being old and notably
irregular, the other new and presumably uncontaminated.
The data are plotted in Fig. 49. The P.#. of random
single seeds in respect of mean maximum lint-length being
+6°3 per cent., we find values of 7°8 per cent. for Assili
and 7°5 per cent. for Afifi.

Thus, on the statistical evidence of lint-length, the
newest “variety” is by no means uniform. This con-
clusion is abundantly confirmed by other evidence. Thus,
the Sakel cotton contains at least two entirely distinct
types of seed fuzz ; the presence of these two types might
possibly be unimportant, but in all probability it points
to a heterogeneous origin for the original plant or plants.
Such heterogeneity might occur even in the offspring of a
single-plant selection, if the gametes of this plant were
not uniform; in other words, if the plant was not pure-
bred.

Such constitutional irregularity bemg manifest even in
new varicties (see also Fig. 50), our next step must be to
examine the cause. So soon as a family becomes
heterogeneous, so soon does natural selection begin to
operate. Once natural selection has begun, any sequence
of alterations is possible. The usual result of such

108 THE COTTON PLANT IN EGYPT cuap.

sequences is to stimulate the belief which les dormant in
the minds of most people—practical and otherwise—
namely, that all man-made plant varieties suffer from an
innate perversity, due to their “ un-natural” crigin, which
causes them to “revert” at the first opportunity, and so
to revenge themselves on human interference.

Up to the present point we have considered only the
zygotic constitution of the “variety,” and have merely
laid emphasis on the fact that when a “variety” of cotton
plants is inspected, plant by plant, the component
individuals are not usually identical; we have seen, in
addition, that the differences between nominal varieties
are mean differences, which are negligible in most
morphological characters, slight in physiological characters,
aud are definite only in respect to the nature of the
commercial product—the lint hairs.

Our analysis has now to be driven much deeper. We
have to investigate the origin of these zygotes, to ascertain
whether they are derived from identical gametes or not,
and to determine what effect their constitution may have
on succeeding generations.

Gametic impurity.—In the older writings on plant-
selection we find continual references to “ transmitting
power,” coupled with advice to test this power by
examining offspring. The reasons for this precaution
are now better understood ; ‘‘ transmitting power” is not
a mysterious vital function, but can be reduced to
formulae. The causes of difference in this respect are
two-fold.

In the first case, the plant originally selected may have
been an extreme fluctuation and its offspring will
therefore regress to the mean.

In the second case, with which we are now concerned,
the original plant was heterozygous, derived from a natural
or artificial hybridisation. Such hybridisation might have
taken place in the previous year—the plant thus being an

VI COMMERCIAL VARIETIES 109

F,—or more probably several years before, in which case
the plant may be denoted as F,. In this second case we
are dealing with an entirely different set of phenomena,
superadded to fluctuation. The segregation of the
character-bearing factors in sex-cell formation, with their
reunion into new combinations at fertilisation, produces a
set of offspring which differ constitutionally amongst them-
selves. The complexity of these differences will depend
on the number of characters in which the original plant
was heterozygous.

An example of such a plant may be quoted from the
author’s records. In 1909, while examining an old field-
book of 1905, a note was found which gave the names of
plants in flower at a very early date. They were all
Uplands with one exception. This exception was a group
of plants grown from a boll of Kerki, called No. 95. The
few seeds available were taken from the files and sown. in
1910, since an early-maturing Egyptian stock was much
needed. Only five plants were raised, of which four were
slightly stunted, while the best and earliest was found in
the autumn to bear an inferior and quite distinct type of
lint. Whether this plant was an F, from 1905, or an F,
from an earlier cross, our records could not disclose. The
former is more probable. The remaining four were again
fertilised naturally, and four families raised in 1911. They
were fairly early, and—except for a few natural hybrids
from crossing in 1910—-were uniform in most respects
excepting height. The original plants had been irregular
in height, owing to stunting, but the offspring gave the
following figures for height in October.

Parent Height. Offspring. No. of Plants.
2 85 cm. Mean, 117-7cm. P.H. +12:0 per cent. 94
3 110,, » 1884, PE. +118 ,, 118
4 145 ,, , 1540, PE +15 ,, 145
5 80 ,, » 1382, PE+83 ,, 23

Inspection of the frequency curves showed that No. 95.
C. 2 was breeding true to shortness, 95. C. 4 probably

110 THE COTTON PLANT IN EGYPT cuap.

to tallness, while 95. C. 3 and 5 were throwing out
shorts.

The uniformity of the deviation, which does not reflect
the heterogeneity of 2 and 3, is due to the fact that the
plants were growing in pairs, and had not been checked
for stunting.

Such an experience is the rule rather than the excep-
tion. Thus, a series of 75 plants of various varieties
were examined in four characters, and their offspring
compared with them. The results were as follows :

a. Offspring like parent in thirty-eight cases; some
unlike in thirty-seven cases.

b. Alterations in each character, twenty-five, fifteen,
sixteen, and fourteen cases respectively.

ce. Alteration of all four characters took place in two
cases, of three characters in seven cases, of two in fifteen,
of only one in thirteen.

There is no recorded difference between the different
commercial varieties in this respect. The newest are
equally heterozygous with the oldest, though with less
intensity of difference.

The cause of the impurity—which soon appears even
when the original strain was pure—is to be found in the
act of natural cross-fertilisation, or vicinism.

The effects of this double impurity need scarcely be
elaborated. It is obvious that such a welter of unequal
individuals must form an excellent medium in which
natural selection can work. The transference of a
“commercially pure” variety to a new district will be
followed by “ acclimatisation ” ; such acclimatisation will be
perfectly genuine, but it will not be due to any mysterious
impress of the environment on the individuals.’» ”

Again, if such gametic contamination is continuous from
year to year, and if our variety is not isolated upon
an island in mid-ocean, we find a steady admixture taking
place with other varieties. Such obvious contamination

VI COMMERCIAL VARIETIES II

as takes place through seed mixture is relatively
unimportant in comparison with contamination of the
ovaries by foreign pollen. We have already laid emphasis
on the external similarity of the different varieties, and its
bearing now becomes apparent. A field grown under the
name of Afifi might consist in reality of a mixture of five
or six varieties with the original stock, together with all
possible combinations and permutations of their multi-
farious gametes, but the difference would be almost

Length of Lint in mm.

25 : 30 35 25 380 35 2. 3 35
| DUR a a La TETANY
50-51,
“310” “Variety of 1910"

60-61

g per 315

70-71

80-81

90-91

Out-turn on Ginnin

{,100-101,—

“Variety of 1909”

nome

Two Pure Strains. Two Commercial Varieties.

Fic. 50.—Tue Impurrtry or CoMMERCIAL VARIETIES.

Target-diagram plotted from random single-plant samples in 1911.
Identical treatment, site, cultivation (wide-sown) and methods.
Compared in respect of only two important commercial characteristics.
o = Variety-type, under given conditions.

invisible till the bolls opened. The mere fact that such a
cotton as Yannovitch was a simple single-plant isolation
from Afifi demonstrates this statement sufficiently without
resort to our detailed tables of plant to plant differences
(e.g., Fig. 50).

Further, although the author has quoted Egyptian
illustrations, the same arguments apply to American
Uplands, to Sea Islands, and to the few Indian cottons
which he has studied. Mr. H. Martin Leake has

demonstrated exactly similar heterogeneity in both

112 THE COTTON PLANT IN EGYPT cx.vi

zygotes and gametes for Indian varieties, but the
Egyptian examples are perhaps more striking, on account
of their higher economic value.

Even in a uniform environment, therefore, a commercial
variety of cotton must change and may deteriorate. We.
might almost say that the change must be in the inferior
direction, since a successful new variety is mostly superior
to its parent stock, and will regress if contaminated by it.
A plausible fiction declares that the life of a variety of
Egyptian cotton is limited to fifteen years. The kernel of
truth within this dogma should now be apparent to the
reader, and it should further be self-evident that the life
of a variety might be prolonged indefinitely by suitable
precautions.

CHAPTER VII
NATURAL CROSSING

WueEn the author first began his researches it was generally
assumed that cotton was self-fertilised, and the only
precise statement to the contrary was that of Webber,
who had found 5 per cent. natural crossing between
adjacent rows of distinct varieties. At the present day
the seriousness of the crossing error has been demonstrated
and admitted in many countries,* but the importance of
the subject does not end with this conversion.

Field conditions.—The author's first concern was to
investigate the amount of crossing which had taken place
in field crop during 1904 by examining the offspring from
random single bolls of that year.** It was found that when
a plant did not give uniform offspring, resembling itself,
the difference of the offspring from the parent might be of
two kinds.

In one case the offspring, or some of them, bore
characters which were dominant over those of the parent ;
thus a 40 mm. lint might be derived from a 25 mm. lint ;
the presumption here was that all or some of the parent
ovules had been crossed in the previous year by pollen
from a long-linted plant. This was the rarer case, which
“in itself defines the amount of natural crossing, if we take

* Notably Leake, H. M. (1), (4), and Allard, H. A.
113 I

114 THE COTTON PLANT IN EGYPT cuaap.

the number of such cases in proportion to the total
number of plants, or bolls, originally chosen for testing.
This number was 5 in 75 in the original trials, but it must
be remembered that not all the vicinistic pollen parents
will have characters dominant over those of the mother
plant; in any one character the chances will be even for
or against such recognition. These chances can be reduced
by taking more than one character, but when the two
intercrossed characters are identical, or nearly so, the
observational errors will prevent detection. Thus, we
shall not be far wrong if we double the number of cases
observed when working with two pairs of characters, so
that our figure becomes 10 vicinists in 75, or 13°3
per cent.

In the other case we find that some offspring bear
characters which are recessive to those of the parent. A
lint of 40 mm. in this case gives rise to some plants with
20 mm. lint. The presumption here is that the parent
was a heterozygote, produced by natural crossing in some
year antecedent to the one in which the seed was taken
from the field, having been simply self-fertilised in that
particular year. The number of such F, plants in the
original total is nevertheless dependent on the amount of
crossing which takes place every year, and should serve as
a check upon the direct observation of the former case. If
now we assume simple Mendelian segregation for the
characters we employ, or prove it by growing further
generations from these splitting forms, we see that the
number of such F, heterozygote plants depends not only
on the renewal of that number each year by fresh crossing
but also on its reduction each year by segregation of
homozygotes from them.

If crossing to the extent of 10 per cent. per annum
were naccompanied by segregation, we should find the
number of vicinists increasing along a logarithmic curve,
since some of the crossed strains would be re-crossed in

VII NATURAL CROSSING 115

subsequent years. Thus, the years would yield :—
A, 0 per cent., B, 10 per cent., C, 19 per cent., D, 27°1 per
cent., &c.

Again, if we start with F, plants, all being identical,
allow no further crossing, and consider one allelomorphic
pair only, we shall obtain the following series, P denoting
homozygotes, and H denoting heterozygotes. A, 100 per
cent. H. B, 50 per cent. H and 50 percent. P. C, 25
per cent. H and 75 per cent. P., &. In other words,
assuming the productivity of H and P to be equal, the
hybrid form will decrease to infinitely small proportions.
When two pairs of characters are involved, the rate of
decrease of H will be slower. Instead of a 1:2: 1 ratio
in the year B, or 2 H:2 P, we shall have the ratio of
1:1:2:2:4:2:2:1:1,or 12 H:4P, being 25 per cent.
instead of 50 per cent. of homozygote forms.

Combining these two antagonistic processes, crossing
and segregation, we come to the following general
algebraic statement.

For y pairs of simple allelomorphs involved in a cross
we obtain in F, :—

2y homozygotes (P) from 4y individuals.

Since crossing is renewed every year we can consider
this as a general value for purification.

In each generation let xP become H, by crossing, and
yH become P, by segregation.

Then the composition of the crop will be :

1st Year: PP only.

Qnd ,, : (l-a)P+aH.
3rd_,, : {(L—x)?+ay}P + (x(2—-a—y)}H.
4th ,, : {(l—x)+ay(3—20—y)}P

+a{3—3(a+y)+(at+y)\H.
Hence =
al —-(l-a+y)""'}
“+y

nth year: H=

116 THE COTTON PLANT IN EGYPT cuap.

When 7 is infinite (or practically in our case when it
exceeds ten) :
ofl -(1-ery) =a
ax

and =
ery

In the 75 cases already mentioned, we found, dealing
with two pairs of characters, that there were twenty-six
cases of recessives splitting out from dominants. Thus
H=28 after years.

With two pairs of characters

a 1
Y= Buz
And since
_ & 26
~aty 75
. ©=0°132.

Thus there was 13'2 per cent. of natural crossing as the
mean value for past years.

By direct observation we found five vicinists from the
previous year, implying about ten altogether, or about
13°3 per cent. of natural crossing in 1904.

The two results agree.

The absence of facilities has prevented the author from
carrying this analysis further by the use of pure strains
planted under field conditions, but a value of 5 per cent.
to 10 per cent. for natural crossing under field conditions
in Egypt has been confirmed by numerous, though non-
systematic, pieces of evidence.

This value is expressed in terms of flowers crossed to
total flowers ripening. ‘The possibility of mixed pollina-
tion should not be disregarded, since we shall see that
hybrid and selfed embryos may be formed side by side in
the same ovary. The expression of the value in terms of
ovules crossed to ovules ripening would therefore be
preferable.

VII NATURAL CROSSING 117

Prevention.—The evidence as to the means by which
the cross-pollination takes place is not yet as full as we
should like it to be, but the greater part is performed by
bees. Tests for wind-blown pollen made by the author
with glycerine smears on glass plates have given negative
results on the breeding plot, though a certain amount of
pollen must be dislodged in this way in close-sown field

Fic. 51.—-Nettep PLants.

First crosses and parents.

crop.* ‘Ihe remedy, therefore, seems to lie in the
exclusion of bees from the flower. In most countries this
can be done by covering the flowers with paper bags, but
the method fails in Egypt, since about 95 per cent. of
the flowers thus treated are promptly shed ; this shedding
appears to be due to the local interference with transpira-
tion, and consequent over-heating of the tissues. We
have therefore employed mosquito-nets, which cover the
whole plant, being supported over it on four posts.
(Fig. 51). Practically no vicinism then takes place, though

* See Allard, H. A. (2).

118 THE COTTON PLANT IN EGYPT cuaap.

one or two suspicious cases have been recorded. The
method has its own disadvantages, however, the first being
that of expense, while the second is that some strains resent
the treatment, and refuse to hold their bolls. Rattoon
plants, 7.e., plants which have been cut back and allowed to
shoot again in subsequent years, usually grow well under
the nets, as also do most American Uplands, but—though
erratically—many Egyptians are failures. When the
method was first employed we had yet to discover the
sunshine effect; this effect is precluded from its full
operation by the permanent veil of netting, and netted
plants consequently grow during the day, becoming
abnormally tall. Improvements are being made by
substituting wire gauze for mosquito net, using larger
cages, and so forth, since the perfection of some preven-
tive method of this nature lies at the very foundation of
all cotton-breeding and of seed-supply.”

Another obvious possibility is the discovery, or manu-
facture, of a cleistogamic flower, which shall obstinately
refuse to admit foreign pollen to its style. At one stage
of these researches the author seemed to be well on the
road to success in this direction, and the story of the
ultimate failure is not without suggestiveness.

The short-style flower.—At the time when it was
being realised that natural crossing would be a permanent
source of trouble, confusion, and error, the question of
floral structure naturally came under consideration. No
hint of the existence of uncrossable cotton flowers * could
be found, but it seemed reasonable to expect that if we
could decrease the opportunity for foreign pollen to reach
the style, we might expect vicinism to diminish.”

V The cotton flower has a dense brush of anthers, borne on
a cylindrical column, through the centre of which the
style projects. The length of this style, and the extent

* Compare Howard and Howard recently on the related genus Hibiscus.

vil NATURAL CROSSING 11g

to which it protrudes, varies in different strains and
species. Most American Uplands have a much shorter style
than Egyptians, and plants were noticed in F, of Upland
Egyptian crosses, whose styles did not protrude beyond
the column. The inheritance was therefore investigated
statistically, and from a cross of 29 mm. style with 20 mm.
column, upon 24 mm. style with 13 mm. column, we bred
several strains with such flowers as the one shown in the
frontispiece. The plant from which this flower was photo-
graphed was an F,, and its descendants were grown up to
F,, still breeding true to this flower form. In F, they had
a mean style length of 184 mm. with a column of
144 mm.: the anther filaments being 44 mm. long made
up the length of the brush to 19 mm., which sufficed to
cover the style completely, so that it was visible only in
end view, whereas the style of the Egyptian parent had
projected for more than half a centimetre.

The short-style flower was thus at our disposal, but
without avail. Four such plants from an F;, similar to
this respect, but otherwise differing, which had been
growing close together in 1908, gave the following
offspring in 1909: A. 26 plants; 7 rogues. B. 19 plants;
5 rogues. C. 47 plants; 16 rogues. D. 36 plants;
12 rogues.

The percentage of rogues due to undoubted natural
crossing in the four families was thus respectively
26, 26, 34, and 33. ‘The control families grown from
long-style brothers of these, gave the same range of
variation, from 25 to 35 per cent. These figures have
been extended since, but without improvement, and we
are driven to the conclusion that the accessibility of the
style is a minor factor in natural crossing, under the con-
ditions of our breeding plot.

The figures for the breeding plot had always been so
much higher than the 5 to 10 per cent. on which we
decided for field conditions, that this last reverse led the

120 THE COTTON PLANT IN EGYPT cwHar,

author to reconsider the whole subject from a_ totally
different point of view.
The breeding plot (Figs. 52a and 52b).—We have

thus far found that floral structure has no protective effect.
In addition it should be noted that the geoeraphical
position of any plant on the plot seems to make but little
difference ; in two cases we have found natural hybrids

Fic. 52s.—THr BREEDING Puov.

bearing a semi-red leaf, being first-crosses with a single
plant of Willett’s Red-Leaf, which was kept in a corner of
the plot from year to year ; these natural crosses had been
made over a distance of 50 metres, the interval being
eecupied by dozens of other plants.* Further, we have
found indications that different varieties. or even different
plants, growing side by side, show differences in their

* See, however, Leake, H. M. (4).

VII NATURAL CROSSING 121

hability to natural crossing ; we have just stated that such
differences cannot be due to any obvious cause such as
position or floral structure, so we are driven back upon a
more abstruse explanation.

The hypothesis which has been framed to account for
the facts observed is based upon an analogy drawn by

Prof. Marshall Ward many years ago, between the pollen

Fic. 528.—THE BreEepine Prior.

Irrigating Sudanese Tree-Cottons.

tube and the hypha of a parasitic fungus. We find in
mycology that within the same strain of host-plant, different
species and varieties of the same fungus possess different
infection-capabilities. Conversely, the same fungus may
he able to attack one strain of its host-plant with ease,
while another strain may be practically immune.

Using these facts to help us in forming conceptions as to
the possible behaviour of pollen, we see at once that some

122 THE COTTON PLANT IN EGYPT cuap.

such assumption as to differential susceptibility and in-
fectivity between any style-pollen pair would lead us along
way. The method which has been employed by the author in
testing this possibility, though on a very small scale as yet,
is a method of mixed pollination. Equal quantities of
foreign pollen and self pollen are placed on the style of a
flower at the same time, as early as possible in the morning
and the two sets of grains are allowed to compete with one
another in the race down the style. The fact that artificial
hybrids can easily be made between Upland and Egyptian
in either direction shows that neither style is immune
from the other pollen. Nevertheless it is quite possible
that the tube from self pollen may grow faster in its own
style than a foreign tube cando. Thus, on account of some
effect, probably toxic, but as yet obscure, the foreign
pollen-tube is beaten in the race down the style, and the
majority of ovules are fertilised by the first arrivals, or
self-tubes.

Using such a method, with all possible precautions to
ensure equal opportunity to both sets of grains, we found
that mixed pollinations of Egyptian by Upland, and the
reverse, gave us ten natural hybrids in 330 ovules
fertilised, or 3 per cent. of vicinism under the most favour-
able conditions for its manifestation. There was no
significant difference between the reciprocal mixings.
This figure is far below the minimum which we can
possibly admit for field vicinism between plants of the
same nominal variety. A new factor must therefore be
involved, and we shall, in terms of our hypothesis, denote
it as “relative immunity,” regarding the pollen-tube of
one kind as parasitic on the style of the other.

A curious side-light on this result is given by the Hindi
cotton. Though the latter plant crosses readily with
Egyptian under artificial treatment, and though it may
amount in some fields to 15 per cent. of the crop, yet

Hindi x Egyptian hybrids are merely frequent in the

VII NATURAL CROSSING 12%

field. Certainly the error of natural crossing must be less
between Hindi and Egyptian than between two Egyptians.

With a value of 3 per cent. for American and Egyptian,
and of 10 per cent. for Egyptian and Egyptian, under the
most favourable conditions, the occurrence of such values
as 85 per cent., mentioned above, leads us to suspect that
the story is not yet complete.

Before proceeding further we must define the value of
our “percentage vicinism” with more exactitude. We are
agreed that computation on the basis of the number of
ovules is the most precise, but it remains to decide how
we shall recognise those ovules. The difficulty which
arises in recognition is due to the fact that all F, hybrids,
and most F, hybrids, germinate much more energetically
than their parents. In this peculiarity lies the great
weakness of simple “selection methods.” The precise
reasons for this difference are still not clear, but knowledge
of the fact is very old. It is therefore not sufficient to
count the number of vicinists in a population raised from
contaminated seed ; we shall be nearer to the truth if we
take the ratio of vicinists to the number of seeds sown,
thus assuming that all the seeds which did not establish
themselves were pure-bred. In inter-Egyptian crossing
this factor will be insignificant as compared with its
importance in crosses of Egyptian with Upland. In the
latter case the author has been the victim of such
absurdities as the cultivation of a family which contained
100 per cent. of vicinists ; the soil tilth was not good, the
weather was cool, and between the two perils of
mechanical resistance and “ sore-shin” not a single selfed
embryo survived.

When attempting to account for amounts of real
vicinism which rise as high as 30 per cent., we must
consider the nature of the pollen to be found on the
breeding-plot. This plot has contained cottons from
Egypt, from America, from India; indigenous cottons

124 THE COTTON PLANT IN EGYPT caap.

from Arizona, from the Sudan, ete. More than this, it has
contained plants of F,, F:, F3, F,, F;, and F,, raised from
crosses between American Uplands and Egyptian. Con-
fining our discussion for the sake of simplicity to the F, of
such crosses, it is obvious that we possess an infinite
variety of pollen grains on an acre of land. To estimate
the number of allelomorphic pairs involved in the cross of
“38” (King) with “89” (Charara) at fifty would be very
conservative. The number of possible combinations of
these pairs works out at a figure which, for our present
purpose, we may consider as infinite. Now, if Mendelism
is not a delusion, this infinite number of combinations
corresponds with an infinite variety of nuclear composi-
tion, on the part of the male gametes. It is true that
these gamete-nuclei are devoted to sexual purposes, but
their relations, the vegetative nuclei of the pollen grains,
are generally admitted to control the growth of the pollen-
tube, and these are of identical composition with the
gamete nuclei. Consequently, we may reasonably expect
to find some correlation, however indirect it may be,
between the gametic differences and the physiological
differences in growth-rate of the pollen-tube. Such relation
would imply a greater ‘“‘ variability” in the growth
processes of pollen tubes from an F, flower than that
which we find in a pure strain. The standard deviation,
or probable error, in the behaviour of F, pollen-tubes
under a given set of conditions would necessarily be much
greater than that of the pollen-tubes in a pure strain,
whether Egyptian or American.

Regarded in another way, this conclusion may be stated
thus. If 3 per cent. of the pollen-tubes from Upland
pollen fluctuate sufficiently in a positive direction to enable
them to beat 3 per cent. of the Egyptian pollen-tubes in a
race down an Eeyptian style, then we may expect—
owing to greater variability—that much more than 3 per
cent. of F, plant pollen-tubes will vary sufficiently in a

VII NATURAL CROSSING r35,

positive direction. Hence, in mixed pollination of F, upon
parent, we should find a higher percentage of vicinists.

The steps of the preceding argument were taken long
before the experimental results were available. These
results were as follows :—

Mixed pollination of F, upon Egyptian ... 20/100 or
20 per cent.

Mixed pollination of F, upon er . 25/65 or 28
per cent.

Even allowing for all possible errors, and for the scanty
numbers of ovules involved, the difference between 3 per
cent. and 24 per cent. as values for the ‘“ prepotency” of
mother-parent and of F, pollen, under the same experi-
mental conditions, cannot be without significance.

Hence, we conclude that some part of the F, pollen from
an inter-specific cross is prepotent over all other pollen ;
that self pollen is prepotent over pollen from some other
species ; and that pollen from other species only makes its
way to the ovule with difficulty.

Gametic differentiation.—A conclusion which may
be immediately drawn from these differences in prepotency
of pollen is, that the error from natural crossing is likely
to be less in the field—where it is difficult to avoid—-than
on the breeding plot, where it can be avoided by appro-
priate, though expensive methods.

Again, it is within the bounds of possibility that
immune strains might be discovered or developed. Such
discovery is scarcely probable, but it may as well be
borne in mind.

The chief speculation in which we may legitimately
indulge relates to gametic differentiation. If our postulate
as to correlation between gametic composition of the
microspore nucleus and growth-processes of the pollen
tube can be substantiated, it follows that those tubes
which succeed during mixed-pollination must possess

126 THE COTTON PLANT IN EGYPT cua.vir

certain gametic characteristics. A detailed statistical
study of the composition of F, plants resulting from such
mixed pollinations has been begun, and if we can find any
constant deflection of the frequency curves from expecta-
tion, we shall have a clue as to the nature of the winning
pollen-grains.

In other words, our endeavour is to ascertain whether
differences which are manifest before fertilisation exist
between F, gametes. Further discussion® would be
worthless at present, but any clue to gametic differentia-
tion deserves to be followed up.

CHAPTER VIII
HEREDITY—I.

1. General

Having discussed physiology, fluctuation, and natural
crossing, we are now in a position to examine the
inheritance of characters in crosses between two strains
of cotton derived from separate reputed species.*

The evidence to be adduced in the following pages is
frequently most infirm beyond the second generation.
Leaving outof account the inefficient conditions under which
this part of the work has been done (Figs.52a and 52b),
the chief responsibility for this uncertainty lies with the
difficulty of preparing self-fertilised seeds. When an F,
of two hundred plants is to be studied, we desire to avoid
the use of nets (Fig. 51) owing to their disturbing
effect upon growth; yet, if nets are not employed, we
necessarily raise F, families which are contaminated.
Therefore it is better to dispense with the nets, and to
rogue out the F, vicinists; very often, however, such
decisions as to vicinistic origin are based on the appearance
of abnormal characters which might very well be due in
reality to some rare gametic combination following self-
fertilisation ; we thus argue in a circle; a plant shows an
unexpected characteristic, therefore it is a rogue. We
have endeavoured to reduce the probability of such un-
just decisions by a system of voting, whereby no plant

* The coming economic application of Mendel’s Law to cotton will at first.
be made through crosses of much more nearly related forms, and hence of
far greater simplicity than those which the author has chiefly investigated.

127

128 THE COTTON PLANT IN EGYPT cuap.

can be condemned unless it shows incredible abnormalities
in several characters. Such treatment does aot lend
itself to precision.

A way out of the difficulty which has been employed
several times has been to dispense with netting in F,,
growing the F; from natural seed, leaving the F, plants
in the ground as rattoons, and netting any of them which
appear to be important. The natural F, is thus used for
indicative, while the selfed F, is used for critical confir-
mation in the following year. The method involves waste
of a year, waste of labour, and waste of land, but it seems
to be the only plan which gives trustworthy data.

The few crosses which have been made and studied were
easily effected, taking the usual precautions.

The F, plant was invariably netted after 1906, and the
experimental error of the F, data is therefore very low.

The F, results, on the other hand, which are of supreme
importance in disentangling the complex F, data, are
subject to the errors which we have just detailed. The
same holds good for F, and F;—which is the highest
generation we have cultivated—though by this time we
usually know what plants to net, so that the data are
more likely to be trustworthy; on the other hand
many such families have been grown but not studied
critically, through insufficient opportunity.

The elucidation of inheritance in cotton is thus no light
task, and should not be undertaken without a residential
laboratury, ample skilled assistance, and __ financial
resources.

The ditticulty of obtaining accurate data beyond F, is so
much the more regrettable in that the factorial analysis of
cotton hybrids often requires the highest precision. We
shall see that the composition of an F, is commonly very
similar to a Gaussian curve of error; this similarity is
usually—probably always—fictitious, and is due to the
appression of several true modes, which blend into one

vu HEREDITY 129

another by fluctuation. Part of this blending, moreover,
is not fluctuation in the ordinary sense, but rather an
autogenous fluctuation,” provoked by correlation with
other characters. Thus the modes of seed-weight in an
F, are not only subject to a P.£. of 12 per cent., but before
this allowance can be made they have to be corrected for
correlation with diameter of the boll.

A simple way of applying such correction is to dissect
the frequency polygon of the family, isolating the wide-
boll and the narrow-boll forms, for example, and plotting
their seed-weights separately (e.g., Fig. 69). Unfortunately
this method reduces the size of the groups under examina-
tion, which has never been excessive to begin with, so
that the precision gained in one direction is lost in
another.

Again, since correlation exists between certain
characters, it might be thought that the slide-rule would
give the necessary correction. The difficulty here is to
find out the value and nature of the correlation. The
simplest Mendelian combination, ABxab, where the
characters are simply linear measurements, gives a correla-
tion diagram in F,, which consists of four groups, only
separable with difficulty even when correlation is perfect
and linear, which—worked out in the conventional way—
gives a value for 7 from 0°6 downwards (Fig. 53). There
does not seem to be any method at present extant by
which a «quantitative separation of these groups can be
made.*

The dithculties enumerated, both of experiment and of
computation, have prevented the author from making any
exhaustive statement which can be considered as honest
from the scientific viewpoint. The results are in the
main indicative, and suggestive, often strongly so, but in
all cases open to criticism.

* W,L.B. 21, and reply by Craig, J. I., Cairo Sci, Jour., August, 1910,
K

130 THE COTTON PLANT IN EGYPT cuap.

In rare cases we have been able to demonstrate the
existence of Mendelian ratios in F,, confirmed by the
behaviour of later generations. In others we have failed
to analyse the F, but have dissected the F;, where the
phenomena were simpler. In others, again, such analysis
has been utterly impossible, and we have been obliged to
rely on the bare fact that a certain character has “ bred
true” in the end, though we have been unable to trace the
steps of its purification. As a last infirmity, and last
resort, we have fallen back on comparisons from year to
year in massed data: if the graph for seed-weight in F,
shows certain modes, and if those modes reappear in the
graph for all the F; plants in the following year, we have
a claim to assume that the modes are at least due to
a systematic cause and not to accident.

The data to be quoted are drawn largely from crosses of
Egyptian with American Upland, especially from Afifi with
Truitt Big Boll (No. 252), and from Charara with King
(No. 255). Other crosses which have been made, but only
partially examined through lack of space and labour, are
Hindi x Charara, King x Russell, Russell x Charara, and
Sultani x King. In the early stages of the work many
natural hybrids were examined, which had resulted from
natural crossing between Egyptian cottons, while full
analysis has been made up to F, in an inter-Egyptian cross
between Afifi and another Sultani. The phylogenetic
relationships of the various parents is doubtful, to say the
least. The author has leaned to the designation ‘ inter-
specific,” but this has been questioned, in view of the
cultivated origin of the parents.* Perhaps a description
of them as “ reputedly inter-specific” would best meet the
case.

The cross of Afifi x Sultani was made with the object
of studying some simple examples in place of the com-

* See references ‘‘ Egypt,” in Sir G. Watt’s Monograph,

Vill

Computed.

Py.
x=60 or A.
7=80 or B.
a=0°9.

Length of Y

HEREDITY

Length of X

131

40> - - ~45- - -- 50- - --55- - -- 60- - --65-

(ab)

P, : "
(aB)

(Ab)

Exeperimental.—-F, of King x Charara.
Length of Petal in mm.

SIS BD Se SS SAF So SAG Ss Se SAG Soe) BGR Ree SEOs SSG 5 =

Length of Style in mm.
rrrrBrrrvsBrrvriBrrriBrirrira

. .
.
. ee
5 .
. . .
.
‘! . .
. cy .
ee rs
Pa 7 . ae
ee .
ee
. . .
. whee OF
= % ery
. . ote
o fete
.
oe .
‘ .
oe
+ .
eee
oe
. ee

Cus
: F,

Fig. 53.—CorRELAtION DiaGRamM FoR Two Parrs or

ALLELOMORPHS.

K 2

132 THE COTTON PLANT IN EGYPT cuap.

plexities presented by the other crosses, but it is as
complex in its own way as the Upland x Egyptian
series. It seems to be quite probable that this cross was
one between the old Peruvian and Sea Island stocks, and
was hence not very much more intimate than the Upland x
figypto-Peruvian crosses.

The author can only reiterate his conviction that all
these hybrids are subject to Mendel’s Law of segregation ;
often obscurely—on account of defective methods—
but none the less certainly. The evidence available can
all be interpreted in Mendelian terms, and it is very
significant that most of it should appear at first glance to
be completely dissociated from the classical ratios,
Mendelian students of heredity have confined themselves
to the more definable characters, such as colour, partly
because statistical characters take up an excessive amount of
time in mere determination, and partly because the use of
statistical methods is prone to provoke irrelevant criticism
from mathematicians with whom the mere biologist cannot
fairly compete. At the same time it is clear that the
frontier of Mendel’s territory is not demarcated by any
special character, and—with all their experimental
disadvantages—the only characters which admit of
complete treatment are those which can be measured with
definable precision.

There are many features of these complex results which
bear a tantalising resemblance to problems of human
heredity.

Record system.—The examples to be quoted in
these pages are drawn from a systematic set of records.
These records are compiled from three sources, the Field-
Books, Field-Cards, and the Laboratory-Books, in which
the actual observations are entered. These are then worked
up at the end of the year in two ways; first in the
Files, and secondly in the Ledgers. The Files consist of
printed forms, one to every plant, on which are entered all
particulars available ; the file-sheet of the plant shown in

VII HEREDITY 133

Fig. 54 is reproduced in Fig. 55. The Ledgers collect the
data from all plants of a family under the head of each
character separately ; this is conveniently done in the form
of frequency polygons, in which the number of each
individual is written; Fig. 48 reproduces a page of the
ledger dealing with the height of the offspring of a plant
which was brother to that shown in Figs. 54 and 55. The
polygons elsewhere reproduced have had the component
plant-numbers omitted in order to save space. Lastly, a
Card Index of the completed ledgers enables any fact about
any plant to be found immediately.

li. Qualitative Characters.

Those characters which are not easily subjected to
statistical expression are dealt with in this sub-chapter.

The Leaf-spot.—The development of anthocyanin in
the leaf, which finds its fullest expression in the Red-Leaf
sports, is usually noticeable at the point where the petiole
begins to branch into the main veins. In Uplands, and
in Hindi, this leaf-spot is conspicuous, and forms a useful
diagnostic character in the seedlings for comparison with
Egyptians, whose leaf-spot is fainter, smaller, and pink
rather than crimson. The character varies with the water
equilibrium and illumination of the plant, like all antho-
cyanin characters. ‘The F, of the ‘spotted by relatively
spotless” cross bears an intermediate spot. In F, the
ratio of the three forms accords closely with 1:2:1.
Extracted full-spot and spotless breed true, without known
exceptions.

General colour of the leaf.—The Upland cottons
possess a leaf lamina of much lighter hue than the
Egyptians. This difference in colour is real, and inde-
pendent of differences in hirsuteness, &c. The inheritance
of the character, or character-complex, is unknown, except
that large families have been found to breed true to one
or the other colour after F,.

134 THE COTION PLANT IN EGYPT cHar.

The matter might be of importance with regard to
photosynthesis.

Colour of petal.—The limb of the petal, apart from
the colour of the basal spot, which we shall discuss shortly,

Fic. 54.—TypicaL PLant or *‘77."” Jury 10, 1909.

ranges in colour from almost pure white to a rich golden
vellow. Each pure strain of cotton has a definite petal
eolour, which is white to creamy in Uplands and Hindi,
while in Egyptian families it ranges from lemon to golden.

VIL HEREDITY
FamiLy 77(B)@&) PLANT <3
Date of Sowing
Seedling Condition. . ,
Adult Condition .
Leaf.

Spot......... Werre...... Hirsuteness ... Gladic--?,
Averages: on, 3 . toaves: — L S68 fo. 18° Lb 7°

Foatriily om 165° (8) 165. (ATO C0) (6S) 170 Gy |

Cg ,
Branching... Scares ¢ 7 hati
FlOWEr. seticscigee cenistianas P Weeks ending Saturday:
Colour: — Petal, rch Y. | wre | duly | Ave. | Sept | Oc. | Nov. | Dee.
Spot, Fuk... |
Anther,, Yeeloaer ‘a Cd fa
K yp
Formon \3. . Flowers,
Petal. 60 maStyle FA mre]
Bract 099. Column, ZO m4 59
Filament 4% tm] rant H-+4 4 Total,
First Flowers. - 47. 27 (fons) dese 4 PER eet N LI 16 292.8
Maturation, //* aq 46 dap ry 2 i 3 hi =) 7 a

Boll. Goll-Shedding.. 40. Firat Boll gry!
Surface. . 27: f Divisions, on G7.. bolls: 27

Averages on ....3 bolls: — Form. 0:60. Size: 243. mt

Seed. Fuzz... Mav o£
Weight on .<3/6 | Seeds: — silliest Out-tunn .. OS Aets
Lint.

Length 27 mee (30)... Colour . Weigh. 9°94.0 4

Expert’s report: —

Notes:— .. T°Acta Fas joe.

Fru. 55,

135

136 THE COTTON PLANT IN EGYPT cuap.

White and creamy petals are not difficult to find in
Egyptian field crop, but their ancestry is dubious ; some
may be true Egyptians, but most are splitting-forms from
Hindi x Egyptian hybrids.

The hybridisation of these forms has not given a simple
result in any cross yet made by the author. Mr. Fyson
has published details from large families of Indian cottons,
which indicate that the character was there controlled by
a single pair of allelomorphs, but the data are not quite
convincing as to this simplicity, and the same uncertainty
is found by Mr. Leake (3).

The cross Afifi x Sultani was a cross of golden petal x
lemon petal. The F, was intermediate. In F, we
matched the offspring to the three forms, taking three
flowers from each plant on different days. It should be
remembered that the colour differences between these
three forms are not very great, although the parents are
quite distinct from one another. Many plants were
matched to the same type-colour each time, but many
others were matched first to one and then to another.
The probability seems to be that there are more than
three colour types in the F,, just as in Tammes’ work on
hybrids of Zanwm, so that our matchings may mean very
little.

On the simplest interpretation of the data we might
imagine that the heterozygote was a simple intermediate,
throwing outa 1:2:1 ratioin F,. The figures are too
discrepant to admit of this view. They tend more towards
the interpretation based on two pairs of allelomorphs,
giving a ratio of 9:3:3:1, where the last two are
externally similar, making the ratio into 9:3: 4.

The crosses of Egyptian with Upland have behaved in a
similar way. The cross of yellow—whether lemon or
golden—with white or cream has always given an inter-
mediate F, In F, we have obtained ratios which
approached very closely to 1;2:1, but with a constant

Vl HEREDITY i}

excess of the paler parental colour-type. Testing this on
the assumption of a 9:3:4 ratio, we obtained consistent
results up to a certain point. Whites and some full
yellows bred true, some intermediates threw out all colours
like the F,; other intermediates threw whites only,
while yet others threw only the full parental yellow,
giving approximate 3:1 ratios in both cases. It seemed
at one stage that the double-pair hypothesis had met all
contingencies, until the following test was applied.

A family raised from an F; plant which bore the
intermediate colour had given twenty-two intermediates
to seven full yellows. Six of these F, intermediates
were grown into F,; the obvious expectation was that
four should throw out yellows, while two should breed
true to the intermediate colour. The actual result was
that none threw any yellows at all, but all threw whites.
These whites were not, moreover, of the same colour as
the parent white, but much nearer the intermediate itself.
The figures for the six families, in ratio of ‘intermediate :
new white” were (4:0), 21:5, 16:9, 26:1, 10:1, 11:3.
The families were almost gametically pure in all other
known respects, and all vicinists had been eradicated.

From this evidence it is plain that petal colour
in crosses of Upland by Egyptian may be controlled by
not less than three pairs of allelomorphs. The presump-
tion is that our matching methods are not sufficiently
precise, and that some form of colorimetric grading is
needed. Even the inter-Egyptian cross shows the same
peculiarities.

We shall see that similar evidence is to hand in the
next character to be considered, together with a strong
probability for gametic coupling. If the colour and
marking of a flower’s petal is controlled by at least five
allelomorphic pairs, complicated by gametic interaction, it
need not surprise us to find that the modes of seed-weight
in F,, for instance, are not very definite.

138 THE COTTON PLANT IN EGYPT cuap.

On the other hand, far more complex analyses of flower
colour have been proved indisputably for such plants as
Antirrhinum, Matthiola, Lathyrus, &c.,* so that the
indications of our fragmentary evidence may be considered
as quite probable, even in a simple sap-colour.

Petal .spot.—The Egyptian flower is characterised
by a rich crimson spot at the base of the petal. This spot
is not so large as in G. herbacewm, where it occupies the
whole of the petal claw, but it is conspicuous. The
typical Upland cottons and Hindi have no such spot, the
petal being self-coloured. The intensity of the spot may
differ within commercial Egyptian varieties, like the petal
colour. Similarly, commercial stocks of, e.g., “ King”
Upland contain a notable proportion of plants with spots
on their petals. Such differences are probably due to
doubtful pedigree.

A cross between ‘‘ full spot”” Egyptian and “ spotless’
Upland gives an intermediate F,. The F, spot is smaller,
more vague in outline, and less noticeable than the spot of
the Egyptian parent. In cases where the latter had a spot
which was relatively small, the F, is proportionately
inconspicuous.

In F, the ratios are very erratic. Taking them in
the order “full: intermediate : none,” we find two families
from F, sister plants giving 11:22:18, and 23:42:31.
In this case the ratio approximates to 1:2:1, but it is
closer to 3:9:4, and the divergence from even this is
more than can be explained by errors of observation.
Probably, as in the case of petal colour, there are more
classes than we have admitted. This view is substantiated
by the fact that we have been unable to discriminate in
many cases between “Full” and “Full?”. As in the
case of petal colour we find that ‘‘ spotless” breeds true,
while “full” may either breed true or break, and inter-

* See Bateson, Saunders, Baur, Wheldale, Xe,

VII HEREDITY 139

mediates break in at least two different ways. Probably
there are again two allelomorphic pairs concerned.

Another series of crosses gave an entirely different set
of ratios. One of these was derived from an Egyptian
parent which possessed an inconspicuous petal spot, and
the divergence from expectation was at first * attributed to
fluctuation. The ratio in F, was 5:9:47. The other
series was not open to this interpretation, since the
Egyptian parent had a fully-developed petal spot, while
the F, ratio was 27:41:112. If we assume that the
petal spot in the latter cross was controlled by two
allelomorphic pairs, with 3:1:1:3 gametic coupling,
while the “ full spot” class consisted of two groups which
were practically indistinguishable, we obtain a theoretical
ratio which is very close to actuality, viz., 25:40:115.

It is inadvisable to discuss the point more fully, since
we require much larger series of numbers than those the
author can present, before a decision can be taken as to the
probability of this view. The consistently erratic
behaviour of the spotted and intermediate forms in F,
supports such interpretation, but the figures available are
not sufficient to substantiate it.

The only decisions at which we can arrive with certainty
are :—that the presence or absence of the petal spot in
these Agypto-American crosses is not determined by a
single pair of allelomorphs, and that there is strong
evidence for complication of this mechanism by gametic
coupling in some cases.

Anther colour.—tThe colour of the central brush of
stamens is an important feature in the general colour-
effect of the cotton flower. In Egyptians it is bright
golden-yellow, in Uplands and Hindi it is whitish, or
rather buff in colour, and the F, is intermediate.

In F, we obtain ratios which appear to be genuinely
1:2:1, and no exceptions have yet been noted in sub-
sequent generations, The characteristic thus appears to

140 THE COTTON PLANT IN EGYPT cuap.

be under the control of a simple pair of allelomorphs, so
far as evidence is available.

This presentment does not exhaust the possibilities, for
a family of King Upland, grown from seed of a selected
plant, showed itself to be a hybrid in this respect. The
anther colour of the selected parent was pale lemon, which
broke up on self-fertilisation into 24 lemon: 8 buff. The
‘latter have since bred true, as have some of the lemons. In
this case the pair was simple, with dominance of more
colour over less colour.

Hirsuteness.—The hairiness of the plant involves a
number of factors; one type of hair may be confined to
the leaf-lamina, another to the veins, another to the stem,
and so forth. During our studies of this character in
cotton we have examined only the petiole of the leaf.

The Egyptian cottons have glabrous petioles, the
American Upland petioles are more or less hirsute, and
the F, petiole is almost glabrous. The author's first
published mention of this character®* stated that the
glabrous form was completely dominant. In almost all
other plants the reverse is true, and further complications
were expected when Mr. Holton discovered that a few
long but scanty hairs were present on the F, petiole.

Early classifications of F, and F; in which glabrous and
intermediate were grouped together as non-hirsute, gave
ratios of “‘non-hirsute: hirsute” as 111:37, 58:17,
43:9, &c. On cultivating some extracted hirsutes in F,
we found six out of seven breeding true to hirsuteness,
while one broke up, giving 31: 8, the eight being of the
F, type. Moreover, we found that the extracted forms
differed in the length and density of their hairs, and that
segregation in this respect was indicated within the limits
of the hirsute group.

A very careful classification was then made on the
F, of another Upland-Egyptian cross, which gave the

following results :

Vill HEREDITY 141

Like Egyptian parent... o.oo 48
Doubtfully Egyptian dene Lhe Steer alan) cube 8
Doubtfully like PF)... 1
Like F, (scanty hairs on dorsum) sis ithe lage 71
Like F,, but with more hairs... ... 0 0... 6
Like Upland, but shorter Wale Age Gas) ase 10
Like Upland parent... ...0 6. ae 19
Like Upland, but denser... ... 0... 0.0. 12

Total. see eax’ sae? fe wee! eas 175

Thirty-five of these plants were grown on to F;, but
their families were not sufficiently large. One notable
feature was that an “F, type” plant gave thirteen off-
spring like itself, and no other forms. Other similar
plants threw the glabrous type only, while others again
behaved like the F, itself. Some of the differences
which had been recorded between the F, plants seemed
to be due to fluctuation, but the general trend of the
evidence is to the same conclusion as in the characters
already discussed, namely, gametic complexity, possibly
with length and density as component factors.

It should be added that families of fifty plants have
been grown in F;, which bred true to new types of
hirsuteness, such as the felty class described above “like
Upland, but shorter.”

Since the hirsuteness, or rather the glabrousness, of all
Egyptians is practically the same, we have no data for
simpler crosses. It might be well to investigate the
character in a cross of glabrous Hindi with hirsute
Hindi.

The stipule.—During examination of Afifi x Sultani
F, it was noticed* that the form of the stipule was
very different in the two parents. The Sultani parent
had long narrow stipules, while the stipules of the Afifi
parent were about four times as wide for the same length.

The F, stipule was long and narrow like the Sultani
parent.

* By Mr. F. S. Holton.

142 THE COTTON PLANT IN EGYPT cuap.

In F, we found, by simple matching, that 48 plants
had stipules like the Afifi, 59 like the Sultani, while 27
were recorded as doubtful.

The evidence is inconclusive, but it again points to
some slight complexity, possibly a ratio of 9:7.

The surface and glandulation of the boll.—All
parts of the cotton plant, other than the root, contain
abundant resin glands, which produce the characteristic
black speckling externally. The depth at which these
glands are situated in the ovary wall is characteristic of
different kinds of cotton plants. In most Egyptian bolls
they are near the epidermis, which is depressed above
them, forming small craters. In American Uplands we
find the glands situated much further below the epidermis,
which is not depressed, so that the surface of the boll is
smooth, and the speckling is scarcely visible. The F, of
these two forms is intermediate, though more like the
Egyptian parent.

A large number of bolls have been pickled and sectioned
in the attémpt to understand the inheritance of this
character. It appears to be straightforward, but the
evidence is not convincing. The appearance of the surface
is not solely dependent on the glandulation ; Egyptian
bolls are bright green and shiny, while Upland bolls are of
a dull, grey-green colour. Some structural differences are
also shown by the microscope.

Thus the fact that an F, was matched into 17 Uplands:
33 F, type: 14 Egyptian type, must not be taken as
evidence of simple segregation. The data from F;,, &c.,
lead to the same uncertain views as in the more definite
characters of the flower colours.

The distribution of seed fuzz.—The differences
between various strains of Egyptian cotton in this respect
range from complete nakedness to a woolly coat which
covers all but the back of the seed. The former are
’ indistinguishable from Hindi seeds, but most of them

Vill HEREDITY 143

give rise to plants which bear no sign of any Hindi
ancestor.

Plants bearing seed with entire fuzz are occasionally
found, but these appear to originate from crossing with
Hindi.

Hindi cotton, on the other hand, always bears naked
seeds, while typical American Uplands are entirely fuzzy.
Naked-seeded sports occurring in the Upland crop have
been discussed by Allard (1) and in the Indian crop by
Fyson.

Several natural hybrids have been bred on from
Egyptian cottons. In all cases they have given a simple
3:1 ratio, more fuzz being dominant over less fuzz,
and expectation has been fulfilled in F;. The cross of
Afifi x Sultani behaved in the same way ; some fluctuation
was shown, but the groups were clearly 116: 41 in F,.

In crosses of any Egyptian with American Upland, we
meet with complications. The entire fuzz is dominant,
and the F, has given such 15 : 1 ratios of “ entire : slight”
as 97:6, 180:11, &. The naked seed breeds true in F,,
and has continued to do so till F,, while the entire fuzz
either breeds true, or breaks up. There are indications
that the latter process may give either a 3:1 ratio, ora
15:1 ratio, but the figures are too small. Further, there
are indications of constant differences in the entire fuzz
group, some being woolly, while others are felted ; if a
woolly seed does not breed true, it may throw out felted
seeds in a 8:1 ratio. Felted seeds, which may be
regarded as a step towards the Egyptian fuzz type, do not
throw woolly ones.

It would seem that two pairs of allelomorphs are here
implicated, giving a 15:1 ratioin F, The fifteen appear
to consist of 12 woolly and 3 felted. In F, we find all the
nakeds breeding true, some woollys throwing felted only,
some throwing naked only, and some throwing both, while
the felted forms either breed true or throw nakeds only.

144 THE COTTON PLANT IN EGYPT cuap.

An interesting proof of the tangibility of these
gradations in fuzziness was afforded by a natural hybrid
from Abbassi, bearing normal Egyptian slight fuzz on its
seed. When selfed it threw recessive wholly naked seed
derived from an unknown pollen parent. When it was
crossed with American Upland we raised seven F, families,
four of which contained the typical Egyptian seed as one
plant in sixteen, while three contained the naked seed in
the same proportion.

The behaviour of Hindi, the seed of which is devoid of
fuzz, when crossed with Egyptian (Charara) has been
somewhat remarkable. In the first generation the seed
was entirely fuzzy, like an Upland. This was probably a
case of reversion due to the meeting of cryptomeres, and it
was naturally expected *” that the F, would show a ratio
of 9:3:3:1, both the Egyptian fuzz and the Hindi fuzz
reappearing. An unsuccessful sowing gave “ 14 entire :3
Egyptian,” which seemed to support this view. In the
following year a family of 130 F, plants was raised, but
without producing a single Hindi seed ; the result was the
same as if Uplands had been used instead of Hindi,
namely, “123 entire: 7 Egyptian.” The absence of the
Hindi type in a family of this size can scarcely be
accidental, and a few more crosses of this kind might
throw light on the phylogeny of the Hindi cotton.

This complex inheritance is made even more interesting
by the fact that a cross of the same Hindi strain with a
natural hybrid of Hindi and Afifi yielded simple
segregation of the naked Hindi seed in F).

Summarising the evidence with respect to this character
we have tolerably convincing data as to the increasing
complexity of inheritance when passing from varietal to
reputedly inter-specific crosses, this complication taking
the form of an additional pair of allelomorphs. In one
ease we have found reversion through the meeting of
cryptomeres, and in general it would seem that the less

Cal

VIII HEREDITY 145

fuzzy cottons have been evolved from primitive cottons
with entire fuzz by the loss of factors. The particular factor
lost has not been the same in certain strains of Egyptian
as in others, nor as in Hindi; hence we obtain reversion in
some crosses, though not in others. No case of reversion
in inter-Egyptian crosses has yet been noted, but it is
quite conceivable.

Colour of the seed-fuzz.—The presence and absence
of colour in the fuzz-hairs appear to form a Mendelian
pair. It is not easy to decide on the absence of colour,
since the colouring matter is unstable, and in some cases
fades very easily. There may be essential differences
between green and brown fuzz, but the former fades very
readily into the latter.

The quantity of fuzz on the parent is not coupled with
colour. Thus, seeds which are practically naked, except
for a most minute tuft of coloured hairs at the tip, will
give rise, on crossing with white entire fuzz, to an F,
possessing green entire fuzz. It is interesting to note
that this phenomenon, together with the F, resulting, has
been described * as an instance of the failure of Mendel’s
Law ; it was expected that ‘ black seed” should form an
allelomorphic pair with ‘‘ white seed.”

Distribution of lint on the seed.—Parallel with the
seed-fuzz distribution and colour, we find characters of lint
distribution and colour.

The distribution of the lint is not easily recorded, there
‘being a large subjective error involved by the combing
which is required before it can be seen. Crosses of
“irregular” with “regular” give a “regular” F,, and
segregation certainly seems to occur. The most convincing
example. of this was an F, from a “regular” F, plant.
The irregularly covered seeds were clearly defined, so that
the curve for weight of lint per seed showed a very

* Cook, O. F. (1).

146 THE COTTON PLANT IN EGYPT cuap.

definite mode at the light end, consisting of eight plants as
against twenty-two in the rest of the curve.” The
extremes of the curve were 0-012 g. and 0038 g.
while the modes were situated at 0°018 g. and 0-032 g.
respectively.

We may reason by analogy that the lint distribution
will behave in much the same way as the fuzz-distribution,
and may possibly be coupled with it in part.

Colour of the lint.—The first crosses made between
Egyptians with brown lint, and Uplands with white lint,
gave an intermediate F, of creamy hue, with simple
1:2:1 ratios in F, such as 12:21:11; the whites and
browns bred true up to the F;, while the creams
broke up.

Even in these series there were manifest complications.

Thus, while never transgressing the limits of ‘ brown-
ness,” the extracted browns were by no means uniform,
some being much darker than the Afifi parent, while
others were lighter. We have not yet decided whether
these differences were gametic, or whether they were
due to “autogenous fluctuation” with other characters.

Another cross, that of Charara x King, where the parents
were very light brown Egyptian, and white American, gave
an intermediate F, as before, but the F, consisted of
“<9 brownish: 60 creamy: 109 white.” This classification
was made by a cotton expert, and not by the author. It
is curiously reminiscent of the inheritance of petal spot,
with its suggestion of gametic coupling.

The lint from F,; of this family, and from all other
families grown since, has never been examined by an
expert, and since this is peculiarly a case where outside.
judgments are best, the author prefers to leave the
discussion at this stage.

The ‘‘style” of the lint.—At present we are
completely in the dark as to the real nature of the
differences between such lints as Upland and Egyptian.

VIII HEREDITY 147

We know that the lint hair of the former is shorter and of
greater diameter than the lint-hair of Egyptian, but there
are other differences which the microscrope cannot as yet
determine, though to the fingers of the expert grader of
lint they are far more obvious than is the colour to
his eye.

The F, of Aigypto-Upland crosses is always a superfine
Egyptian. Thus, the mating of a “ bread-and-cheese”
Egyptian with a short-staple Upland gives a first cross
bearing such lint as is required by the fine spinner. In
the early stages of these researches we denoted this general
peculiarity of these hybrids as “ first-cross intensification,”
in the hope of explanation later. In many characters this
explanation has been since obtained, but not in
respect of the “style” of the lint. Until we know the
component elements of “style” we cannot make much
advance. It is safe to expect that such intensified
characters will regress to the parental normal in later
generations, but further knowledge might enable us to
purify the particular combination of allelomorphs which
leads to this immediate improvement. In point of fact
we have raised families which breed true to an extremely
fine and strong Sea Island type of lint, from the cross of
King with Charara; the lint of the latter parent was of
the Abbassi type.

From what has been said above it will be clear that the
“style” of a lint sample is the resultant of an unknown
number of unknown factors, both zygotic and gametic.
When a set of F, samples is placed before an expert, this
becomes obvious; the expert finds one lint which
resembles Afifi, except that it has the colour of Yannovitch ;
he next meets another which has the colour of Afifi, but
which he would unhesitatingly afirm to be American
Upland if the room were darkened. The task of analysing
an F, in this way is almost hopeless, however valuable
the results may be for other purposes. The author is

L 2

148 THE COTTON PLANT IN EGYPT cuap.

much indebted to three Alexandrian gentlemen,* who have
assisted him in the past, by their expert opinion, given
under all the difficulty involved by the smallness of the
samples available, and their results, though open to these
objections, are summarised thus :—

Afifi x Truitt:—F,, Yannovitch; F, composed of
7 Afifi, 24 Abbassi, 22 Yannovitch, together with 17
Hindi or Upland. Ratio, of Egyptian to non-Egyptian,
being 53:17. The non-Egyptians bred true in F,, while
some Egyptians broke up. One plant from the F,, the
lint of which was described as being similar to that of
the Afifi cotton when first introduced in 1887, gave a
remarkable series in F,; the limits of the brown Peruvian
type of lint were never transgressed, but within these
bounds we obtained almost every known modification ;
the old Afifi, modern Afifi, Ashmouni of the Fayoum,
Upper Egypt Ashmouni, and—most remarkable of all
—the original Jumel cotton of Mohammed Ali’s time.
Within the limits of this one family there was plainly
an opportunity for much research.

The examination of the King x Charara F, was com-
plicated by the extreme range of lint length, which ran
from 18 to 40 mm. Many plants were confessedly judged
as non-Kgyptian because of their shortness, and hence the
fact that the ratio of Egyptian: non-Egyptian was 108:
71, or almost 9:7, cannot be regarded as significant.

Summarising this and similar evidence, it would seem
safe to affirm that some striking feature of the lint—
possibly the diameter—is inherited as a simple factor.
Complications may be introduced gametically, and also by
‘autogenous fluctuation.” Until we can define the reasons
which cause an expert to call one sample by one name and
another by another, our investigation must be limited to
rule of thumb.

* Mr. E. A. Benachi, now Minister of Agriculture for Greece, and Messrs.
Marco Nacamuli and H. C. Thomas, of the National Bank of Egypt.

VIII HEREDITY 149

We have now examined the nature of the problems which
the non-measurable characters present. The general
trend of the evidence is to show that inheritance becomes
more complex as the crossed parents are less and less
closely related. The amount of labour which the author
has been able to apply to these problems, under the
limitations imposed by natural crossing and accidental
circumstances, has not been enough to produce one clean
and indisputable proof for any character. Nevertheless,
he believes that the preceding discussion will be found by
later workers to represent the general position of a
complex subject.

CHAPTER IX
HEREDITY—II.

ii. Quantitative Characters.

ALL possible characters have been investigated quanti-
tatively, by the methods described in the previous
chapter on “ Fluctuation,” including flowering, bolling,
and shedding.

The same difficulties already enumerated have prevented
conclusions from being drawn with certainty, the chief of
these being the scanty F; data. On the other hand,
we are no longer troubled by doubts as to the nature of
our classification.

Presentment of all the data, the frequency polygons,
correlation tables, and dissected curves, is not possible
here, but it should be understood that one or more forms
have been bred out pure in F; to F, for every character
where a factorial analysis is suggested.

Height of stem.—The specific nature of the length
of hypocotyl and first internode has already been mentioned.
While the strains of Sultani and “ King” Upland were
being grown for this purpose, a set of F, seedlings from
these two parents was raised in the same site and soil.
Data for F, were unfortunately not available.

The plants were classified day by day, and the figures

150

CH. IX HEREDITY 151

plotted from those plants only which had all germinated
on the same day, being as exactly comparable as they
could possibly be, show a very definite segregation of the
two parental first-internode-lengths from one another, and
from a central mode. Whether the segregation is simply
in aratio of 1:2:1, or whether it is more complex, we
cannot pretend to say. It is clear, however, that in com-
mencing to analyse the height of our hybrids, we have
first to take into account the internode length.

This alone is not sufficient for us. If internode-length
was the only factor, then the height of the Upland would
be about half that of the Egyptian, whereas the early
height of the former is rather greater than that of the
latter. Again, on June 18th, in Fig. 56, the same Upland
strain whose internodes we measured is equal in height to
the same Sultani, both being grown side by side on the
breeding plot. Hence the growth-rates must have been
much the same, and the Upland merely produced more
internodes in the same time. Comparing these heights
with that of the F, on June 18th, we find that the
latter is nearly twice as tall. The internodes are no
lone so that the great height of the F, must be due to

a greater growth-rate.

The rate of growth, due to imperfectly known and
constitutional causes, is thus the second factor in the height
of the stem.

From these typical figures for June 20th, one hundred
days after sowing, we might declare that tallness was
dominant over shortness, whatever the components might
be. If we follow the height-curve on to the and of
September (Fig. 56) we shall see that this sweeping
assertion would also be untrue, for the growth-rate of the
F, has slowed down, though not as much as that of the
Upland, while the Sultani parent is still growing
steadily. :

Hence the third factor in height of stem is the amount

132 THE COTTON PLANT IN EGYPT cuap.

of change in growth-rate, or—as we have formerly inter-
preted this change—the liability to thermotoxy.

It was expected that a fourth factor would be found
operative in F,, &c., namely, the habit of branching, but
all heights and growth-habits appear to be distributed
evenly throughout all the branch-types, from plants with-

/|Sultani

150) f

i La || ™ ;
ij w

iS
°
oat gee 7
2100 =
= 4 x
> a“
iS i a
= 7 Silas
§ [ Eee aa King
~ a
*' 50 7
June July Aug. Sept. Oct.
Date 18 2 16 30 13 27 10 24 8

Fic. 56.—Growrs or STEM.

Parents F, of an Augypto-Upland cross. Means of families.

out monopodial branches at all,* up to plants in which the
main axis was scarcely recognisable.t

The heights of the F, plants are therefore dependent
on the three components first enumerated, but although
we have described them as “ factors,’ they may be each
the resultant of more than one factor in the Mendelian
sense, as 1s the colour of the petal. Within the limits of

* See Leake, H. M., (2), (3), and W.L.B. (5) (8) (15).
+ Cf Bateson, W., in Lathyrus,

_ 1 HEREDITY 153

this book we cannot compress a full set of F, data,
like the set given for fluctuation (Fig. 48), but the three
main features are as follows :—

A, The internode-length of the parents reappears in
F, forming modes in the curve.

B. The early rate of growth varies in normal plants,

Afifi x Sultani June 20th. 1910 & 1911

Sultani 1917

0
%
|
|
3
§
S

oa
ee

I9i0

Brother
} Fy families
1917

Fic. 57.—Heicut or Stem in JUNE.

Individual plants.

even if we dissect the curve of “ growth-rate in June”
into any component groups we may choose. Thus, taking
only those plants which afterwards showed the habit of
continuous growth, and omitting all but the normal
seedlings, we find the growth-rate ranging symmetrically in
thirty-five plants from 3°6 to 17°8 mm. per day. More-
over, on plotting these growth-rates against the ultimate
height of these plants at the beginning of October—which
is legitimate, since their growth curves were all “con-
tinuous ”’—we find a close correlation, with a value for “7”

154 THE COTTON PLANT IN EGYPT cuap.

of not less than 0°622. The initial growth-rate of the
F, plants therefore ranges at least as high as that of the
F, and at least as low as that of either parent. (See also
Fig. 57.)

C. Over and above this incomprehensible factor of
‘orowth-rate,” which needs the repetition of such experi-
mental work as we have described under “the Indi-
vidual” on every plant of a large F, before we can
interpret it, we have also the change in growth-rate,
affecting the height of the plants after the end of June,
or earlier, which we have endeavoured to interpret in
terms of specific lability to thermotoxy. On classifying
the individual growth-curves in a family of 179 F, plants,
we find that they were grouped as follows :

Continuous growth, like Heyplen ae Sie gen 1D?
Doubtfully continuous... aa aay 29
Doubtfully like F, ... ... .. sts: Sider. Skee, eee Ze
Semi-continuous, like F,. as we. 20
Doubtfully like F,, being st semi-discontinuous ... 30
Like American parent... 1. we ee ee

Thus a small percentage of plants reappears in F, with
the high thermotoxic susceptibility of the American
Upland parent. It might be pointed out that the figures
could be fitted toa 9:3:3:1 ratio, two pairs of allelo-
morphs being involved, namely, presence and partial
absence of ‘‘«-production” and of “‘z-removal”!

There does not appear to be any necessary correlation
between any of these factors in their distribution amongst
individuals. A plant with a low initial growth-rate may
have the habit of continuous growth and short internodes:
strains of such plants have been bred out to F, and have
remained pure. Such plants are short in the stem.
Shorter still are those plants which have the discontinuous
growth-habit, with short internodes and a low growth-rate.
At the other extreme we meet plants with a high growth-
rate, long internodes and continuous growth-habit. Con-

IX HEREDITY 155

sequently, it is not surprising that the curve showing the
height of an F, at the end of the season exhibits continuous
variation from one extreme to the other, especially since
we have seen thatthe fluctuation in height is by no means

so}
25F

20 | June
15b 18th.

July mY
July on A a
KA)

10
5

July 30th.

August 27th.
Zo]

Sept. 10th. yay
x x
Sept. 24th. ce eee
Oct. 10th. Per” | a
— ‘< =

ae 8g NEE ORR wry
ara a: =e ae
Fluctuation (pure tall strainy Sept.24th. ..|.——™~-—._. S| y
LA. = L
50 100 150cm.

Fic. 58.—Heicur or Stem in F, or Kine (0) by Caarara (x).

Stunted and damaged plants excluded. Ledger page, like Fig. 48.

inconsiderable in a pure strain. There are modes in this
curve, nevertheless, and the following result shows that
they are not due. to accident.

The F,, the heights of which in 1909 are shown in
Fig. 58, was used to provide an F; from some thirty of its

156 THE COTTON PLANT IN EGYPT cuap.

members in 1910. Most of the plants chosen for this
purpose were—for subjective reasons—short in the stem.
Plotting the aggregate height of all the normal F; plants
in 1910 against the same date in 1909, we see the same
modes reappearing, in spite of the differences of soil and
season (Fig. 58). These modes become less markedly
coincident amongst the taller F,; plants, but the general
result indicates that such modes are due to definite
constitutional causes, inherent in the plants themselves.

The form of the leaf.*—The component characters of
leaf-form appear to be the length of the mid-rib (LZ) the
distance from sinus to petiole (S), and the angle of the
sinus from the petiole relatively to the mid-rib (/s).

Two other components which we have not examined in
detail for more than one family are, the angle made by the
first lateral vein with the mid-rib, and the presence or
absence of a second lateral vein and lobe.

The three first components are concerned with the form
of the central segment alone, but even in this respect we
find more problems than we can solve.

Taking the length (Z) first, we have already seen that
it is correlated with height of stem, in some obscure
manner. King Upland, with a mean leaf-length of 75 mm.,
crossed with Charara, the mean leaf-length of which was
about 135 mm., gave an F, with leaves rather shorter than
Charara, and this by selfing produced an F, which ranged
from 70 to 195 mm., with slight indications of modal
grouping ; most of the plants lay between the parental
measurements (Fig. 59). This curve was dissected in
various ways, thus, the plants with the ‘‘ continuous”
growth-habit had larger leaves than the rest, but although
none of these plants had extremely small leaves, yet
moderately small leaves were found as a detached group.
Further dissection of this group never succeeded in

* See Leake, H. M. (1) (3).

Iz HEREDITY 159

producing a group of plants with leaves of identical
length (z.e., identical within the P.£. of fluctuation). Thus
it seems highly probable that the length of the leaf
is inherited as a separate character, although it is distorted

L Sultani Xx Afifi
BE ‘
r Ps.
F, A at A
10 —
| i . ;
| t | T | Tv | T i T ]
150 200
mm
10F King | x Charara
P.s

Two Fz families

Pies, ie | a

a a

“~

a iam Sa Uist Ue LA om a I, ea Sa ea
50 100 150 mm. 200

Fic, 59.—Lenetu or tHE Lear.

ss.
ES
T T

from the parental length by autogenous fluctuation. The
same probability is suggested by correlation diagrams for
leaf-length with height, with petal length, &c.; such
diagrams show a distinct indication of isolated groups,
such as we shall inspect shortly in the flower measurements.

158 THE COTTON PLANT IN EGYPT cnap.

The next-character “S,” or distance from petiole to
sinus, is inherited in much the same way as LZ. We can
eliminate the diversities in absolute size by expressing S
in terms of Z, 7.e., plotting for the ratio S/Z. We then
find that an Upland leaf, in which S is relatively long
when crossed with an Egyptian in which S is relatively
short—or, in other words, slightly and deeply dissected
leaves—give rise in F, to a leaf very like the Egyptian,
but with a slightly longer S. In F, we obtain the same
modal curve, stretching to the parental extremes. Cor-
relation diagrams for Z and Sin F, show modal grouping
and no general correlation. In other words, the length of
the sinus is inherited independently of the length of the
mid-rib. Now this sinus-measurement is determined by
the plant at a very early stage in the primordia, since we
find freshly expanded leaves showing the same form as
adults; hence a factorial determination is highly probable.
It is necessary to express S in terms of ZL, on account of
the diversities of Z. Thus, if we plot S simply, we find,
e.g., in the King x Charara cross, that the parents are
identical, while the F, is 60 per cent. longer. It is, of
course, quite possible that our use of Z as the expression
for mere size may be fallacious, but this would not affect
the general argument for factorial inheritance of form.

The last component of the form of the central segment
is -s. We have formerly seen that the position of the
sinus fluctuates along the angle-lines, so that instead of
using S and .s we might employ 4s and cé, the latter
being the angle made by the sinus with the mid-rib from
the tip of the latter.

On crossing the narrow angle of Upland with the
wide angle of Egyptian we obtain a wide angle in F;. In
F, we obtain the same wide and modal curve on plotting
the angle values, with some indication of simple segregation
of narrow angle from wide, which is probably fallacious.

The next point to consider is the inter-relationship of

1X HEREDITY 159

these angles, and whether a wide ~s is necessarily linked
with a narrow -¢ as in the Egyptian parent. The result
of dissecting our curves in this way is very definite ; there
is no such linking. Thus, taking the 26 plants which had
the narrowest 4¢ in an F, of 180 individuals, we find that
while 24 had very wide 4s, there were two with a very
narrow <5, far removed from the rest. Conversely, taking
out the 26 plants with the widest 4¢, we find from one to
five possessing very wide 4s, while the rest had narrow <s.
Thus the two angles may definitely be said to be inherited
factorially, and the origination of new leaf-forms in F,
need no longer be surprising.

Flower form.—The characters studied in the flower
were the length of the petal, style, and column, measured
from the apex of the ovary cavity, the length of the
filaments, and the width and length of the involucral
bracts. The form of the corolla has not been examined;
it ranges from an open cup to a long narrow one.

The story of the inheritance of all the first four
characters is much the same. In the first cross studied
we found that by correcting for fluctuation, taking the
petal length as the standard because it has been the same
in both parents, our graphs for the F, composition assumed
the 3:1 form.” “ Long was dominant over short, and all
the extracted shorts tested bred true up to F;. Here, in
spite of the Aigypto-American crossing, the characters
seemed to be under the control of a single pair of factors.
In this way we bred out the “short-style flower”
mentioned in connection with natural crossing (Frontis-
piece).
~ In the King x Charara cross we found indications of
segregation in petal length also, and it was in this con-
nection that we developed the correlation-diagram method
of seeking for segregation (Figs. 53 and 60). The method
is essentially the same as the use of the slide-rule, but it
enables us to deal with two variables, without correction.

160 THE COTTON PLANT IN EGYPT cuap.

If long and short petals are represented by d and a, and
the style lengths similarly by B and 8, and there is no
mutual interaction, then we obtain

9 Long petals with long style, AB.

3 Long petals with short style, db.

3 Short petals with long style, @B.

1 Short petal with short style, ab.

Now if the correlation of the two dimensions within any
given flower is almost perfect, we shall obtain such a
correlation diagram from the F, as that shown in Fig. 53
(upper). The ab group is almost continuous with the 4B
group, and is scarcely to be differentiated from it. The
aB and Ab groups lie on either side of this diagonal
compound scatter. Thus, on working out the value of
“»” for the whole table we shall obtain quite a low
value, whereas it is in reality a case of almost perfect
correlation. Comparing this with the observed result
obtained for the King and Charara F, as shown in the
lower half of the figure, there can be no possible doubt
that some such grouping is really present. The parents
and the F, are marked on the diagram as A, E, and F.
The F; data of the cross confirm this conclusion, so
far as they go, and the probability is high in favour of
the view that even the semi-smooth Gaussian curves of
error shown by the length of petal, style, column, and
filament in the F, of this cross are (Fig. 60) essentially
nothing more than simple 3:1 curves, which have been
deformed by fluctuation, both autogenous and ordinary.

With regard to the form of the bract and its width there
is nothing definite to be said. Narrow bract is dominant
over wide, just as narrow leaf segments are dominant over
wide segments, and narrow bolls over wide bolls. The F,
ranges from one extreme to the other in a modal curve,
and pure strains have been extracted, but no details are
available by which the stages of this segregation can be
traced.

1X HEREDITY 161

ase

+ Filament. - Style.
30F : \

5 20F
25,- F

F 15
=} /\

9 10F V (7
BE F

at 5[- x
L Ns

10 Pe NN ey

FE 1 ag a as ee ee) TT a es a ee |

E ‘ ‘ 20 25 30 35 mm.
5c ws.

q if - wma

7: .

Petal.

°
oo °
ox ox o° °
T T T T T T | ee Sa fies Dames Com) a
40 45 50 55 0 mm.
40(- In Fy | X 12 smallest leaves
- Column. Petal \ 0 14 largest leaves
35F
30F
25-- —— Charara

oeee- King

TTT rs ar eer Sa es

15 20mm.

Fic. 60.—Form oF THE FLOWER IN AN AlGypro-UpLanp Cross.

Width and form of the boll.—The Upland boll is
usually wider and more nearly spherical than the Egyptian
boll. Differences also exist within the Egyptian strains,

162 THE COTTON PLANT IN EGYPT cuap.

some approaching the long narrow boll of the Sea Island
type. The form is expressed as — A cross of
Upland with a mean form of 0°75 and a width of 31 mm.,
upon an Egyptian with a form of 0°58 and a width of 27
mm., gives an F, with a form of 0°60 and a width of 32
mm. In other words, the long narrow form is dominant
though very much

= Charara x| King larger than the

5L
t Ps, ea a long narrow parent.
i i 4 (Figs. 61 and 62).
The F, of such a
F,. ~—-————_ cross ranges up to
20} the F, width and
E form, but includes

mes i plants the bolls of
5 2.
tok y which may be as

c narrow as 0°44 and
BE ne 22 mm. So far as
i mere width is con-
"20°" 25" ~30.~-—~S 35mm. _— cerned, this might
Fic. 61.—WiptH oF THE BOLL. well be due to auto-
genous fluctuation,
but the new form of the extremely narrow bolls cannot be
attributed to this cause. As in the case of leaf-form, we
are probably dealing with a compound inheritance, and
the new forms are the result of recombinations of
allelomorphs.

A side-light on this interpretation is provided by plotting
the correlation table of form against width in F,. While
the general trend of the diagram indicates positive correla-
tion between wider boll and more spherical boll, yet on
comparing such a diagram with that from a pure strain, it
becomes clear that the F, family is heterogeneous.

Again, families have been raised in F, which showed no
more fluctuation in width than the parent strain, while the

1x HEREDITY 163

form varied over double the range which could be attributed
to fluctuation.

One autogenetic factor in the width of the boll is the
number of boll-loculi. Without attempting to correct for
any possible modality in the diagram we found the value
for correlation between these two characters in F, to be
“pr” = 0°331 (+ 0:061). The explanation is presumably
mechanical; the bolls with more loculi have more septa,

Charara xX King

Po ee

iiive
bE A [OV

T v T T T T T T * T

LaLa
0-50 0-60 0-70 Width

Length
Fic. 62.—Form or THE Bott.

and these occupy more space, hence the boll diameter is
greater.

More information on these two characters is highly
desirable, because of their economic importance.

The loculi of the ovary.—The inheritance of this
meristic character is of peculiar interest, since it is not a
character of form, but of distribution, and analogous to
such things as the number of ray-florets in the Composite.

A cross (Fig. 63) between an Upland with its mean at
4°3 and an Egyptian with a mean at 3:0 produced an
intermediate F, with the formula 4:1. In F, this family

M 2

164 THE COTTON PLANT IN EGYPT cnap.

gave a range of 3:0 to 4°7, with modes at 3:2, 3°6, 4'1,
4°4, and possibly elsewhere. In F, a 4°8 bred true to

y Charara x | King
F P.s =
3:0 3-5 A10 4:5 5:0
FE A_A
i /\
aoe
5 t-F, A
' A
x x
es ive
3 ie LE

Afifi x Truitt
P.s. Q Skeleton, showing new|F, forms Q
ee

—

F, es Osx

F, (two) ee
/

.
L ! bs
i. ‘
5 a F4 ; %,
q . ‘y
. ae 4
_:

ar’; an, nae’, i Co 5-0

Fics. 63 anp 64.—LocuLi oF THE OvaRyY.

4°8, and a 3°1 bred true to 3°2. On the other hand, 3:3
broke up into a scatter from 3°1 to 3°7, as did also a 3°6.
A 3-9 plant appeared to breed true round a mean of 4°1,

1x HEREDITY 165

while a 3°8 scattered from 3°8 to 3°3. Similarly, a 4:0
scattered from 3°9 to 3'2, and soon. On the data avail-
able it seemed clear that the parental forms could be
extracted and bred true, while the intermediate forms
represented new gametic combinations which broke up in
new ways, giving new forms. No large family having
been raised beyond F, in this cross, we may examine
the data from another one.

The Afifi x Truitt cross had 2°8 and 4°5 as the parental
values (Fig. 64). The figure 4°5 is uncertain, because there
was every indication that the American parent was
heterozygote in this respect. The F, had 36 loculi, and
the F, spread from 2°9 to 4°8. Only five F; families
were raised ; one of these was derived from a 3°3 plant,
and its twenty-one offspring ranged from 2°9 to 3°4, thus
resembling the Egyptian parent closely but not exactly.
Another 3°3 behaved in the same way, and repeated this
behaviour in Fy, Conversely, a 4°8 gave only 4°6 to
4:9; while a 4:5 gave 4:2 to 46. The offspring of a
4:3 form broke up into a wide scatter from 3°3 to 4:9;
several small families of these were bred on into F,, but
the largest and most interesting was one from a 4°5
plant, which consisted of twenty-nine plants, ranging only
from 4°5 to 5:0, and giving a frequency polygon with the
same probable error as the parent.

The inter-Egyptian cross was expected to unravel a
portion of this tangle, but although the critical numbers
were doubled, and the data classified to half-grades the
result was much the same (Fig. 65). Sultani (3°20)
crossed by Afifi (2°80) gave an F, at 3:00. The F, of
this broke up with great symmetry over the parental
extremes with a single mode at the F, value. The
spread of this curve of the F, is too narrow to be the
expression of a 1:2:1 ratio, so it is probable that at
least two factors are involved even here. There is a slight
indication of the possible nature of these factors, namely,

166 THE COTTON PLANT IN EGYPT cuap.

differentiation and coalescence, but it is not worth fur-
ther consideration until we possess the data from later
generations.

This Afifi x Sultani cross was made principally in the
hope of obtaining a simple inheritance of this particular

fr, :
10h Afifi x =; Sultani
°F Ps, PA t . MeL
PA ra aN
i. F.;. “ x
35
30f
25-- x
20F an
C ny
15 ae
10-Fi3-F5. r {
3 oe
SS es a
27 3-0 3:3

Fic. 65.—Locuni oF THE Ovary.

character. Although it has failed to give the expected
simplicity it is still less complex than the Mgypto-
American crosses. The graphs are most strongly
indicative, to the unbiased mind, of the formation of a
new character in F,, which subsequently breeds true;
nevertheless, in the light of the other crosses, there can be
little doubt that such is not the true interpretation.

IX HEREDITY 167

The weight of the seed.—The inheritance of the
mean seed-weight is particularly interesting. In the first
place it fluctuates more than any other character, except-
ing the height, and it further shows clear evidence of
autogenous fluctuation.

The first cross in which this character was carefully
examined was Afifi x Truitt (Fig. 66), where the mean
seed weights were.0°105 g. and0°135 g. The seed weight
in F, was 0165 9. In F, the weights ranged from 0°08
to 0°175 g., with two marked modes at 0°095 and 0°115.
The form of this F, graph suggested that light seed was

P.g. Pa F,

10F

100 =) 150
Fic. 66.—MeEaAn Seep-Weicur.

Afifi x Truitt, showing extraction of small seed in F;.

segregating from heavy seed, and on testing this by breed-
ing on, we found no reason to modify this conclusion ;
thus, a plant with seed weighing 0°100 regressed slightly
in F, to amean of 0090, with a scatter from 0°070 to
0°110, and no higher probable error than the parent strain ;
and F, raised from a 0°090 plant of these gave the same
result, ranging from 0°:065 to 0:110. ‘he plants of the
F, had been extremely diversified in most other characters,
such as height, while the F, was almost a pure strain.

Whether the segregation was simple or compound, it
was clear that the size of the seed—expressed by us as
weight—was an inherited characteristic.

In another cross, namely Charara x King (Fig. 68), the
matter became more interesting, and the inheritance

168 THE COTTON PLANT IN EGYPT cuap.

obviously complex. The seed weights of the two parents
were substantially the same, being 0°085 for the American,
and 0°095 for the Egyptian. The weight of the F, seed
was 0°145. Thus a very marked “ intensification” had
taken place, and the problem of finding the cause was set
to the author. The seed weight in F, gave an unexpected
frequency polygon; instead of a 3:1 form we obtained a
modal curve, otherwise fairly symmetrical, which ranged
from 0°055 to 0°170; the principal modes were situated
at 0°085, 0°105, 0°120, and 0°140.

Before discussing this graph any further we may note
that the F, data were of the same nature as those described
under the preceding character; the parental small seed
was extracted and bred true, while larger seeds sometimes
threw small ones in a way which suggested a 3: 1 ratio, or
less commonly bred true. In the latter case a new
character, not found in either parent, had been “ fixed.”
In the ordinary Mendelian characters such phenomena are
usually due to the meeting of cryptomeres, but we shall
see that our cryptomeres in this case are even less cryptic
than Miss Wheldale’s enzymes in Antirrhinum.

The attempt to dissect the F, graph into its components
led to the plotting of numerous correlation tables, and to
the preparation of ‘dissected graphs” (Fig. 69). In the
latter method, which is more rapid than the former, we
take plants possessing some character in common, such as
a very large boll, and mark off their position on the graph
of the whole family. The mean of the special group, as
compared with the general mean, serves to indicate any
displacement, while the form of the “ dissection ” is usually
less complicated than that of the general graph. On
dissecting in this way for the fifteen plants which had the
greatest boll-width of the whole 181 F, individuals, the
mean seed-weight was raised by 00105 g.; moreover,
though these large-boll plants constituted the greater part
of the 0°140 mode, yet four of them were found in the 0°085

IX HEREDITY

» Sultani x Afifi
10 a es
5 ,
r Ps, '
i
Fy.
20}
15 EE
10F ov
t
- 1
5 Fo. Fz -
i T nee i | cf a | qT T aN T q
0-050 0-100 0-150 gram
Fic. 67.—Mxran Seep Weicut in Inrer-Ecyrrian Cross,
; King x Charara
BE P.s a ae
F. L
20
15 a |
A Pr \ re
5 = F,
L T T T T ae | T T T T T T T TT T T | Fn aa |
0-050 0-100 0-150 gram

Fic, 68,—Mzan Sexp-Weicut 1n ‘Ecypro-Urtanp Cross,

170 THE COTTON PLANT IN EGYPT cuap.

mode. This result indicated correlation of big-boll and
big-seed, with segregation of big seed from small within
the group. Similarly, on dissecting for the twenty-four
smallest bolls, the modes were at 0°105 and 0°075. On
plotting the correlation diagram it was found to give
a value for “7” of about 0°3, but this diagram was
distinctly modal, the points being grouped, so that the
true value of “7” was probably very much higher.

Similar dissections were made in respect of almost every
character available. In no case did the groups show
uniform seed weight within the error of fluctuation.
Either the new group was evenly distributed over the
graph, there being no correlation, or else it moved to one
side. In the latter case, the group always assumed the
3:1 form. The most interesting of these for comparison
with the big-boll dissection was the dissection for “ dis-
continuous habit of growth”; the twenty plants which
most resemble the Upland parent in this respect did not
exceed 0°130, and formed two modes, one on and behind
0085, the other on 0°105. Again, though classification
according to habit of branching showed no marked shift-
ing of the group-centre, yet the ‘“‘ unbranched” plants
filled up the 0°120 mode, while “freely branched”
occupied the mode at 0°140 (Fig. 69).

Two general conclusions result from this analysis.
Firstly, that the modes in the F, curve are genuine, and
largely due to autogenous fluctuation.

Secondly, that the F, curve consists of superposed
curves having the 3:1 form, but mutually obscurant until
groups of comparable individuals are taken.

Thus we have shown that light seed is segregating from
heavy seed in F,, probably as a simple pair of allelo-
morphs, just as in the Afifi x Truitt series. The only
serious weakness of this view lies in the fact that both
the parents were light-seeded! The Upland parent, how-
ever, bore these light seeds inside a boll of 32 mm.

Ix IX HEREDITY
Fifteen
‘ F Largest Bolls PI S\ \ ee
100 S50 V V V/
5E
FE °°
r 3 2 ° ° ° 5 . ° Kn
E Thirteen
Y Largest Leaves a La \ \\ ran
10l-see V V
BE V
a °° oo
Ss 2 © oo°o oOo 9° TaN
—+— Total of all F,
\ families
|. Shedding ; :
r less than 50% / \ A!
fF 900 / VN ra
rE = V ;
BE -
vs
F AA A
—-—- Unbranched
aecreen Branched
10F a L\
AV
5 C entity / 3 n\/
= aos dane “sf. wa sv
~ Ae Ph
® — a > Tl aN T
0-050 0-100 0-150 grams.

The F, curve of Fig. 68,

Fic. 69.—Dissection or Mean Seep-Weicut 1n F,.

characters,

dissected in respect of four correlated

171

172 THE COTTON PLANT IN EGYPT cuap.

diameter, while the Egyptian boll was only 27 mm. in
diameter. On crossing the two strains we effectively
placed the Egyptian seed inside a boll whose cubic
capacity had been doubled, and an increase in seed-size
followed. Thus we may regard the Egyptian seed as
being constitutionally large, and dominant over the
genuinely small Upland seed. At gametogenesis in F,,
the two seed-weight allelomorphs separate from one
another, and the 3:1 ratio appears in F, if we clear
away the lumber brought in by autogenous fluctuation.
We have discussed this masking of the difference in
seed-weight, and the development of the difference under
equal opportunities, in terms of boll-width alone for
convenience, though other factors are also involved. The
displacement of the means for such dissected graphs,
when compared with the probable error of a pure strain,
which is obviously too stringent a test for these hetero-
geneous groups, gave significant deviations in respect of
“ discontinuous growth” ; a slight but significant deviation
with respect to branching ; a slight indication of connec-
tion between extensive shedding and heavy seed, which
is probably indirect, since “‘ discontinuous growth” sheds
less than the other types; and a very marked relation
between wide or narrow boll and heavy or light seed
respectively. In the last case the figures were as follows :—

36 Widest bolls. Mean seed-weight + 9°4% (P.E. x 3:2
3-2

4:3%)
24 Narrowest bolls. 4 ie -13:2% (PE. x 5°37)

= 53%
The simple cross of Sultani x Afifi showed dominance
of heavy seed over light in F, (Fig. 67), and although
the difference between the two parents was very small,
yet some indication of segregation is shown. This takes
the form of two modes in the F, curve, which appear in
both the brother families; since the mean weights are
computed, and hence do not suffer from any subjective

error, this coincidence is probably significant, and due to

1X HEREDITY 173

the superposition of a small-seed mode on the flank of a
large-seed mode.

Summarising the evidence, it would seem that beneath
all the complexity involved by fluctuation, by autogenous
fluctuation and by correlation, there existed in all these
hybrids a straightforward segregation of seed-size, con-
trolled by a single allelomorphic pair of factors.in every
case.

The mean maximum length of the lint.—The
inheritance of this character has been curiously similar
to that of seed-weight, but the evidence is not so clear.
The Afifi x Truitt cross showed segregation which was
ostensibly simple, long being dominant over short; the
Charara x King cross gave dominance of length in F,,
with subsequent modal composition in F,. Sultani x
Afifi again gave dominance of length, and the F, curve
was almost symmetrical between the parental extremes
(Fig. 70).

Subsequent generations have shown that pure parental
length can be extracted, while new intermediate lengths
may also breed true.

Dissection of the F, revealed a similar series of
phenomena to those shown by seed-weight. In this case,
the most definite result was obtained by grouping to seed-
weight; the 28 largest seed-weights had a mean lint-
length which was 5:9 per cent. above the general mean,
with modes at 264 and 32 mm., the form of the dis-
section being that of the 3:1 type (Fig. 70). Conversely,
the 27 smallest seed-weights were 59 per cent. below
the mean general lint-length, with modes at 21 and
27 mm. .

It thus seems highly probable that lint-length is also
inherited simply, in spite of the seeming complication
of the Charara x King second generation.

Miscellaneous.—All the characteristics mentioned in
the chapter on Fluctuation have been made the subject of

174 THE COTTON PLANT IN EGYPT cuap.

Afifi | x Sultani
15

10h

20-F

Treryt

oa
ae

bas Sy King x] Charara

5
rP.s a

Tiventy-eight
Largest Seeds

=
a
a

ar
a

Fic. 70.--Mgean Maximum Lint-Lenora.

IX HEREDITY 145

statistical records in the ordinary course of routine
observations. Thus we possess the curves for growth,
flowering, bolling, and shedding for almost every indi-
vidual studied. Data for weight of lint per seed, and for
ginning out-turn are also to hand, but the majority of
these records are of more value as supplementary sources
of information in physiology than from the standpoint
of Genetics. At the same time, they are frequently of
interest as showing the commercial resultant of those
conflicting gametic forces whose lines we have endeavoured
to trace.

SECTION IV

CHAPTER X
ECONOMICS *

Wiruin the limits of this volume we can do no more than
glance at the many matters of economic interest to which
those researches are linked. Their most direct and im-
mediate application has been found in the Sub-Soil Water
controversy, from which many of the inquiries originated.
No attempt has here been made to emphasise the economic
importance of root asphyxiation and restriction, but the
text and diagrams should show that a deep water-table
is essential, and that a rise of the water table to the roots
is deadly in July, prejudicial in September, and almost
harmless in December. For several years the yield per
acre in Egypt had been lessening (Fig 71), and many
causes * had been invoked to account for it, but the matter
was obscure until Mr. J. R. Gibson, assisted by M.
Audebeau, showed that the level of the water-table had
risen on the State Domains, and pointed out the pro-
bability that such a rise, produced by improvements in the
system of irrigation, might suffice as a general cause. ”
Mr. Gibson’s death deprived the author of his collaboration

* See Todd, J. A., for discussion of the purely economic problems of
cotton in Egypt and Lancashire.
176

CH. X ECONOMICS ee

in developing the biological side of this hypothesis, which
—after three years of animated discussion ' 1% 1 % 2
has now become a factor in the administration of Egypt.*

The original hypothesis is still unproven, and must so
remain, in the absence of extensive records to show the
water-levels of past years, but so strong a case has been

‘
’
,

, ra % a

- 1,500,000

Area in-------
Feddans (acres)

=
°
9
2
°
°
°

ice)

Yield per Feddan in Kantars (100 /bs. lint.)

Area and Yield of the
Egyptian Cotton| Crop

1895 - IQII

Year 1895 1900 1905 1910
Fic, 71.—AREA AND YIELD oF THE Eayrtran Corron Crop, 1895-1911.

made out for the presumption t that, when taken in con-
junction with the physiological evidence summarised in
the present volume, the proof may be regarded as exhaus-
tive. The preliminary solution of one of the neatest
problems ever set to agricultural science has thus been

* Report of Cotton Commission, 1910; Reports of H.M. Agent and
Consul-General on Egypt and the Sudan (Egypt No. 1) 1910, 1911, and 1912.
} Ferrar, H. T. ; Lucas, A ; Audebeau, C.

178 THE COTTON PLANT IN EGYPT cnap.

achieved, on a crop which is worth twenty to thirty
millions of pounds per annum.

Concurrently with the depreciation of yield, there had
also been a depreciation of quality in the chief variety
grown.” * This latter trouble was partly due to the
same cause, but chiefly to varietal “ deterioration.”

The coincidence was extremely unfortunate, for the
short crops led to inflated prices,* which were intolerable
with a degrading quality.; the consumers, driven to
experiment with inferior cottons, succeeded beyond all
expectation in the substitution of long-staple Upland, and
even of ordinary Upland, for Egyptian cotton. The
typical Egyptian cotton has thus lost the monopoly which
it formerly enjoyed.

The remedies for these two troubles are now being
applied,t to wit, drainage and restricted irrigation in the
first case, together with the supply of better seed in the
second. With regard to seed-supply we have seen that
the problem is essentially the avoidance of natural crossing,
since “deterioration” must ensue if a single foreign
pollen-grain enters the pedigree. By cultivating pure
lines in bee-proof cages, propagating from these in
isolated sites, or in plots protected by related populations,
and by renewing continually the seed-supply of any
strain in this way from the laboratory through seed-farms,
the varieties of the future will be proof against “ deteriora-
tion,” unless mutation takes place. It cannot be too
strongly insisted upon, that any scheme for the intro-
duction of new cottons is doomed to ultimate failure unless
continual replacement of contaminated stocks is taking
place every year from the original pure strain.* ”

The demands of Egyptian cotton upon the cotton-
breeder,” ” apart from this question of purifying and

* Todd, J. A. ;
+ Lord Kitchener’s Report on Egypt and the Sudan, 1912.

x ECONOMICS 179

distributing the existing varieties, have sunk of late years
into insignificance, through contrast with the urgent call
for physiological information. Still, they are by no means
trivial, and once stability is restored to the supply of
Egyptian cotton, there will be room for much improve-
ment in detail. The chief interest of the data on
genetics ®* 1° relates to the extension of cotton cultiva-
tion into fresh countries and climates. ‘The reader will
probably concede, whatever may be the soundness of
the interpretations given, that there is no doubt as to
the formal nature of the inheritance of various characters
in cotton crosses, even where such inheritance appears
most dependent on simple chance. Such characteristics
as yielding-capacity, earliness of maturity, climatic
suitability, and others of agricultural importance, are
the outcome of complex and interacting combinations
of allelomorphs, and must in no way” ** be con-
sidered as simple things; but sufficient time and
research will ultimately deduce the laws of their trans-
mission, now that the said research has been placed on
a precise basis. The outcome of such deductions must be
that the colonial agriculturist of the near future will no
longer carry a bag of seed, searching for a district in
which it will grow to the consumer’s liking, but will choose
his district first, and then manufacture a cotton plant to
suit it. A further impetus towards the precise study of
genetics will be given by the specialisation of manufactur-
ing processes, demanding more various types of raw
material, each suited to special purpuses, and therefore
worked up with greater. economy. The aeroplane is
already beginning to affect the Egyptian fellah.

An important advantage of seed-supply projects lies in
their simplicity from the viewpoint of the native cultivator,
who is usually prejudiced and frequently unskilled. A
change in the variety of cotton supplied to him causes no
change in his habits or methods, and interferes less with

N 2

180 THE COTTON PLANT IN EGYPT cx. x

his personal freedom than any other manifestation of the
‘march of progress.”

With regard to the general cultivation of cotton,
these researches have thrown into prominence the im-
mense importance of the root-system, whereof—in a
limited sense—the aérial portions are only the visible
expression.” 17%55°° Tt seems probable that a great
deal of botanical research in the coming twenty years will
be subterranean. Researches have also cleared up the
causes of seed-failure, have obtained some general ex-
pressions for, the effect of environment on development,
and by means of a system of records, which can be kept
with no more trouble than meteorologists’ observations,
they have thrown light on the causes of variation in crops
from year to year, and from place to place, in the form
of certain curves of flowering, bolling, and growth, which
have a precise value.

The designation of lines upon which to drive our wedges
still further into the mass of available material is almost
impossible, since the most valuable results are usually
obtained by following out a side line, which in its turn has
been detected through the accidental direction of attention
to a commonplace phenomenon. Knowledge of the
changes in water-content of various layers of soil can be
applied directly to irrigation practice, study of the growth
processes in the fruit will demonstrate the causes of
fluctuation in the grade of the commercial product, and
any information about the infectivity of foreign pollen
may reveal the way by which the contamination of
varieties can be eliminated. Lastly, it should be borne in
mind that most of these researches are based on evidence
collected at the apex of the Egyptian Delta, so that there
is a long field of operations in which our present results
may be re-examined, stretching from the Mediterranean
into the heart of the Sudan.

BIBLIOGRAPHY

Allard, H. A.

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2. “Preliminary Observations concerning Natural Crossing in
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Atkinson, G. F. ‘Some Diseases of Cotton.” Alabama Exp. Sta.,
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Audebeau, Bey C. Rapports présenté a la Commission des Domaines
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182 BIBLIOGRAPHY

Balls, W. Lawrence (cont.)
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x 25. “The Application of Mendel’s Law to Cotton-breeding.” Report
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+26. “The Physiology of the Cotton Plant.” Cazro Sci. Jour.,
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27. “Investigations of Water-logging.” Manchester Guardian,
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28. “The Mechanism of Nuclear Division.” Annals of Botany,
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30. ‘The Inheritance of Measurable Characters in reputed Species-
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on Genetics. Paris, 1911.

BIBLIOGRAPHY 183

Balls, W. Lawrence (cont.).

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Bateson, W. ‘‘ Mendel’s Principles of Heredity.” Cambs., 1910,
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Beaman, A. H. ‘“ Egypt Revisited” XI. “ Agriculture and Cotton
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Feb, 1908.

Biffen, R.H. “ Mendel’s Laws of Inheritance and Wheat Breeding.”
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Blackman, F. F. ‘‘Optimaand Limiting Factors.” Ann. Bot., 1905.

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Bowman, F. H. ‘Structure of the Cotton Fibre.” Manchester,
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Bowring, Sir J.“ Report on Egypt and Candia.” London, 1840.

Brodie, D. A. ‘Building up a run-down cotton plantation.” U.S.
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Brownlee, J. “The Inheritance of Complex Growth forms such as
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1910.

Burkill, I. H. ‘Pollination of Cotton in Behar.” Jour. and Proc.
Roy. Asiat. Soc. Bengal, N.S. III. 7, 1907.
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(Botanical).
Burns, G. ‘Soil Moisture.” K.A.S. Year Book, 1905.
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Club, 1900.
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Clouston, D. “ Artificial Fertilizers for Cotton in Central Provinces.”
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184 BIBLIOGRAPHY

Commission, the, of the Egyptian Government, on Cotton, 1910,
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Connell, E. T. ‘ Cotton Gins. How to erect and work them.” Imp.
Dept. Ag., West Indies.

Cook, O. F. McLachlan, A., and Meade, R.M. “A study of
Diversity in Egyptian Cotton.” U.S. Dept. Ag. Bur. Pl.
Industry. Bull. 156. July 24, 1909.

Cook, O. F.

1. “Reappearance of a primitive character in Cotton Hybrid.”
U.S. Dept. Ag., Bur. Pl. Industry. Cire. 18, Nov., 1908.

2. Local Adjustment of Cotton Varieties.” U.S. Dept. Ag., Bur.
Pl. Ind. Bull. 159. Sept. 28, 1909.

3. “ Origin of the Hindi Cotton.” U.S. Dept., Ag., Bur. Pl. Ind.
Bull. 42. Dec. 11, 1909.

4. “ Weevil-resisting Adaptations of the Cotton Plant.” U.S. Dept.
Ag. Bur. Pl. Ind. Bull. 88. Jan. 13, 1906.

5. “Suppressed and intensified characters in Cotton hybrids.”
U.S. Dept. Ag., Bur. Pl. Ind. Bull. 147. April 7, 1909.

6. “Danger in judging Cotton Varieties by Lint percentages.”
U.S. Dept. Ag., Bur. Pl. Ind. Cire. 11. Aug. 25, 1908.

7. “Cotton Culture in Guatemala.” U.S. Dept. Ag., Year
Book, 1904.

Craig, J. I.

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