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Bul. 88, Bureau of Plant Industry, U. S. Dept. of A
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U.S. DEPARTMENT OF AGRICULTURE.
BUREAU OF PLANT INDUSTRY— BULLETIN NO. 88.
B. T. GALLOWAY, Chief of Bureau.
WEEVIL-RESISTING ADAPTATIONS
OH THE COTTON PLANT.
BY
Oa. COOK,
BIONOMIST IN CHARGE OF INVESTIGATIONS IN THE AGRICULTURAL
Economy oF Tropica AND SuprroprcaL PLanrs.
IssuED JANUARY 13, 1906.
WASHINGTON:
GOVERNMENT PRINTING OFFIGE,
1906.
BUREAU OF PLANT INDUSTRY.
B. T. GALLOWAY, ;
Pathologist and Physiologist, and Chief of Bureau.
VEGETABLE PATHOLOGICAL AND PHYSIOLOGICAL INVESTIGATIONS.
ALBERT F. Woops, Pathologist and Physiologist in Charge, Acting Chief of Bureau in Absence of Chief.
BOTANICAL INVESTIGATIONS.
FREDERICK. V. COVILLE, Botanist in Charge.
FARM MANAGEMENT.
W. J. SPILLMAN, Agriculturist in Charge.
POMOLOGICAL INVESTIGATIONS.
G. B. BRACKETT, Pomologist in Charge.
SEED AND PLANT INTRODUCTION AND DISTRIBUTION.
A.J. PIETERS, Botanist in Charge.
ARLINGTON EXPERIMENTAL FARM.
L. C. CORBETT, Horticulturist in Charge.
INVESTIGATIONS IN THE AGRICULTURAL ECONOMY OF TROPICAL AND SUBTROPICAL
PLANTS.
O. F. Cook, Bionomist in Charge.
DRUG AND POISONOUS PLANT INVESTIGATIONS, AND TEA CULTURE INVESTIGATIONS,
RODNEY H. TRUE, Physiologist in Charge.
DRY LAND AGRICULTURE AND WESTERN AGRICULTURAL EXTENSION.
CARL S. SCOFIELD, Agriculturist in Charge.
EXPERIMENTAL GARDENS AND GROUNDS.
E. M. BYRNES, Superintendent.
SEED LABORATORY.
EDGAR Brown, Botanist in Charge.
J. E. ROCKWELL, Editor.
JAMES E. JONES, Chief Clerk.
INVESTIGATIONS IN THE AGRICULTURAL ECONOMY OF TROPICAL AND SUBTROPICAL
PLANTS.
SCIENTIFIC STAFF.
O. F. CooK, Bionomist in Charge.
G. N. COLLINS, Assistant Botanist.
F. L. LEWTON, Scientific Assistant.
H. PITTIER, Special Agent.
LETTER OF TRANSMITTAL.
U. S. DepartTMEentT oF AGRICULTURE,
Bureau oF Piant INpustry,
OFFICE OF THE CHIEF,
~ Washington, D. C., September 26, 1905.
Sir: I have the honor to transmit herewith a report on “ Weevil-
Resisting Adaptations of the Cotton Plant,” and to recommend it
for publication as Bulletin No. 88 of this Bureau. This report has
been prepared by Mr. O. F. Cook; bionomist in charge of investiga-
tions in the agricultural economy of tropical and subtropical plants.
Tt contains an account of his observations and experiments which
show that some of the varieties of the cotton plant have definite
weevil-resisting characters. The establishment of these facts opens
new and unexpected lines of approach to cultural solutions of the
weevil problem.
The investigation of cotton referred to in this report was begun
in March, 1904, through the Laboratory of Plant Breeding, there
having been set aside for it from the emergency cotton boll weevil
appropriation a part of the funds which had been devoted to the
breeding of weevil-resistant cotton. The existence of a field culture
of cotton in the presence of the boll weevil had been ascertained by ,
Mr. Cook during a visit to Guatemala in 1902, and it was hoped that
the immunity of the cotton might prove to be due to some weevil-
resistant quality.
The first result of detailed observations was the discovery of the
weevil-eating -kelep or so-called Guatemalan ant, which has been
made the subject of previous reports through the Bureau of Ento-
mology. It now appears that the usefulness of this insect is not
limited to the boll weevils which it catches and kills. By making a
regular field culture of cotton possible in the presence of the boll
weevil it has contributed in an important manner to the development
of the weevil-resisting characters here described. The cotton plant,
it seems, has been greatly modified in protecting itself against the
ravages of its insect enemy. Not only has it attracted the kelep to
its service and developed other means of defense which are more
3
4 LETTER OF TRANSMITTAL.
direct, but even the lint, on the peculiar character of which the com-
mercial value of the crop depends, appears to find its chief use to the
plant in excluding the weevil larve from the seed. Our Sea Island
and Upland varieties have been raised for long periods ‘in regions
where the boll weevil did not exist and, as was to have been expected.
are largely lacking in protective features. The Kekchi cotton, on the
other hand, which has continued its development in a weevil-infested
region under the protection of the keleps, has by far the largest
number of weevil-resisting characters.
The fact that weevil-resisting adaptations really exist, as s shown in
numerous instances in the present report, emphasizes the necessity of
a thorough study of our cultivated cottons for the purpose of taking
advantage of any and all protective characters.
It is possible, as Mr. Cook suggests, that the Guatemalan variety
of cotton which he has discovered, and which has such a-surprising
number of weevil-resisting adaptations, may not prove suited to culti-
vation in the United States, but even in that case the value of the
present paper on weevil-resisting characters would not be diminished.
for it will serve as a help to all who may engage in seeking and
developing such characters in the types of cotton now cultivated in
our country.
Respectfully, B. T. Gartoway,
Chief of Bureau.
Hon. James Witson,
Secretary of Agriculture.
CON TENE S.
Page
1 Bra Fy COLO KON) C0) cB Regge meester Sg a 7
Selective: mmiimence or therbolliwee vill asec ce es ee a 10
Generaleprotective Charachersncs =) cee aa ene gs ee ee 11
Dwarf habit and determinate growth of Kekchi ecotton______-______--- 11
Wariationssm tnenKekchiccottonmse ste eee ee 15
Effects of Guatemalan conditions on United States varieties_ .____- 17
Acclimatization of Kekchi cotton in the United States __.__..____- 17
Early bearing facilitated by long basal branches ____-_...--_/--------. 19
HAnharejyectlonsolcupertiWOUs SGUALCS 6 seen so = hoes eee 20
Seasonal bearing of perennial varieties ____._-__.___-___----.-- Seen 23
Annualcuttine; backiof perennial varieties ©2222 22222-2222 2222-2 -e- 24
riievastalksandeleaissteMgs sass ene epee mm es ee ee 25
Pendent bolls. 22.2: Ns as ag ena ais fe NL eA ep gee TE gl: 27
Hxtratloralmectariess = <2. 2. 2 RUE Fs Ree SiMe syed Sos sece ie eta eh Scum des Bc 28
Nectaries of the leaves ______. ._--- BSc ae 5 Vad IAS Ra ap aOR si, eae eS 30
Exbermnalenectaries-of theanvolucres. 255 22 2a ee ow
Innermnectariesiotethetinvolucre ssa 5 2) tees ee 31
Nectaries of Guatemalan Sea Island cotton _____.._.____.-.._-___- 32
Continued secretionOob mec tan. sso! Se mare a Se ee 32
Bractlets subtending inner nectaries____- Sa ESE Ser eh poe hes SU Ta 33
ficiency ofthe: kelep protectiony <2 ke ee ee Sy 34
Other nectar-bearing plants visited by the keleps_.__.____-._______- 36
Mheanvolucreyas aprotective StnuCtUre “25. co 5522 22 2 ee 37
Imvolucralsoractssorowmsalogetheris was. es ee 37
epkesseauimareimston bracts: 2 sce ok er er es 38
Harceinyvolmcres of Kekchi: cotton ss: 229 2 2s a Ae ah ee 39
Openineo1r faring ot bracisya voided. 922 23a ha ee 40
ElaimyemMaLeinscOLimVvoOluGcral DRAGS 522222222 2 ee 4]
iP XbeMGrOLprOLvecLlOM Dy MNVOlUGTE 2s Wak. Mee le ee ee Ee 41
Naame SesOOPeNoImVOlUCT eS 26 eat = Se se ee 42
Behan OmoisparasitizeG@sbUds eas e=esse fee Lao a ee 48
sheddime.oisweeval-infested squares:. 227 225-22 ee 43 |
Coumipneciottlared and: fallen/squares 42. 24252228 2 ee ee 45
Promieracion. of internal tissues of buds. 299.2 2-2 Soe 46
Caucsegandiconditions of bud proliferation: 2-_—. 22-222 222-12 49
Rrohteranonsinother ivarietles)225 22) 529 gs ee ee ek 50
Protec hionsotabiesbolls ais 2 so eae So ace ook ge ee ea ee aS 51
IBErsiScenccrOLenlOnviOls ear a te an eae 00 Myke rege ren d1
Immunity of very young bolls______.__- AME yh a Wem snapipe Seni Nie). os Oa Lit oe 52
ap ee TOWN Ol VOUN SONG ps4 aly selene ena orate eek be 55
he wvallled solicits ee tense Ere ee ser eye ee er 56
Touch lamne sor chambersiot bOllsm seme sso eee tem ea oe 56
6 CONTENTS.
Protection of the bolls—Continued. Page.
Proliferation from the wall of the boll.________._- Sd afte eee d8
Time required tor proliteratione. 2. 25S. 5 joe se ee 60
Efficiency of adaptive characters of bolls__.._._.___._-_..______.. oes 61
Bacterial diseases followmeg weevil Injuries _=-_2_._- 2222222 62
Breedingin/ buds aderived habit ==. => eae eee AN nt en eee 62
Relation between proliferation in buds and in bolls ____________- ne se 64
Protection-of seeds: bylimts=5 ~ == Ses eB ee ee 65
Protective seed arrangement in Kidney cotton ___.___.._-_.__-__._+__- 66
Cultural value or kudney,.cottom 2S, ee ee i
The nature and causes of adaptations-_-_-___-__- Sieh aro Se gee ele fe
Conscious and unconscious) selection: 22-25 25s = 9es a es 70
Summary -of adaptations << 1-20 eee 2 ee ee eee 72
Classificationtomadapta tions =e eee oe eee i 72
Adaptive characters of different types of cotton__-.._____.______._--.- 7
@Goncludine remarks 2555-2 222s. ee ea ee ee ee eee 7
Description.of plates <2 g..\/ 220 Fe Sai eee ee, eee eee ie ee eee ee 7
nex tert Se iss ee Hen eh ee ee ef PS ee See aN A ir he RS 79
JPEN TEas BOITIOS
PLATE I. Valley at Secanquim, Alta Vera Paz, Guatemala, the scene of
experiments with weevil-resisting cotton-____--_-_____- Frontispiece.
II. Fig. 1.—Mature plant of Kekchi cotton. Fig. 2.—Kekchi cotton
plant: with bolls=. = 5-22 2 a ee ee ee ee 78
III. Involucres of Kekchi cotton, showing nectaries and bractlets___- 78
IV. Fig. 1.—Involucres of Rabinal cotton, showing connate and ap-
pressed margins. Fig. 2.—Open involucres of Egyptian cotton_ 78
V. Fig. 1.—Young buds of Kekchi cotton with weevil punctures.
Fig. 2.—Buds of Kekchi cotton with proliferation____________- 78
VI. Large buds of Kekchi cotton with proliferation ____.___....____- 78
VII. Weevil-infested bolls of Kekchi cotton <--->. => 78
VIII. Carpels of Kekchi cotton, showing proliferation ______._______-- a
IX. Fig. 1.—Kekchi cotton, successive stages of the boll. Fig. 2.—
Kekchi cotton bolls (right) compared with King bolls (left) __- 78
X. Fig. 1.—Rabinal cotton with bolls. Fig. 2.—Bolls and seeds. of
Kidney. cotton 2.2. 02 22-m oe ee 78
BP: k—180.
WEEVIL-RESISTING ADAPTATIONS OF THE
COTTON PLANT.
INTRODUCTION.
The fact that Central American varieties of cotton have developed
weevil-resisting adaptations has already received preliminary notice.“
A third visit to Guatemala, in the spring of 1905, has given opportu-
nity for further studies of the protective characters of the native
varieties and for comparing them with the types of cotton now cul-
tivated in the United States. For this purpose plantings of Upland
and Sea Island varieties have been made in Guatemala, and as the
season advanced other tests of the Guatemalan and United States
varieties were arranged under very different climatic conditions in
Texas and at Washington.
These opportunities of comparative observation have revealed a
series of protective adaptations of such number and nicety as to fur-
nish a unique and well-nigh incredible instance of selective develop-
ment. The statement of the former paper may be repeated with
emphasis, that the presence of the weevil-eating kelep has enabled
the Indians of eastern Guatemala to maintain since very ancient
times field culture of cotton in the presence of the weevils, with the
result that there has been developed a dwarf, annual, short-season
variety with numerous features which, in the absence of sufficient
numbers of keleps, afford material assistance in protecting the crop
against the ravages of the weevil. :
Whether this Guatemalan cotton can be made of direct use in the
United States or not, it demonstrates the existence in the cotton
plant of weevil-resisting characters. The new variety has lint of
good length and quality, so that its utilization in the United States
depends upon its adaptability to our climate and methods of culture.
As already explained in publications devoted to the kelep, the
weevil-eating propensities of that insect were discovered in 1904
during a visit to Guatemala which had been undertaken in the hope
of finding a weevil-resisting variety of cotton. It had been observed
a Cotton Culture in Guatemala. Yearbook of the United States Department of
Agriculture for 1904, 475-488: Science, N. S., 20: 666-670, November 18, 1904.
7
8 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
two years before that a field of dwarf cotton cultivated by the Indians
did not suffer from the boll weevils, though these Pees were abundant
on a “ tree cotton ” a short distance away.
The kelep arta an entirely unexpected and yet very striking
explanation of the fact that cotton was being grown as a Seentan
field crop in a region which had probably been infested with weevils
ror many centuries, if it were not, indeed, the original home of the
species. That there was an insect in existence specially qualified
by structure and habits to attack, disable, and devour the boll weevil,
was welcome news 1n the United States, and in accordance with cabled
instructions from the Secretary of Agriculture numerous colonies
of the keleps were brought home and colonized in the cotton fields
of Texas.
The finding of the kelep explained the failure of the weevils to
prevent cotton cultivations in eastern Guatemala, and seemed at first
to diminish the prospects of weevil resistance in the cotton itself.
Nevertheless, the intention of studying Guatemalan varieties of cot-
ton and the cultural methods in use in that country was not aban-
doned, and the results are not without bearing on the original ques-
tion of the causes of the apparent immunity of the Guatemalan
cottons, and also upon the more practical question of securing cotton
varieties and cultural methods by which the injuries of the boll
weevil in the United States may be reduced to a mmimum.
The Guatemalan cotton protected by the keleps is a génuimne Up-
land variety, very early and productive, with a fiber of good length
and texture, as already stated. In addition to features which di-
rectly favor the keleps, it has many other qualities which may
render it useful, even without its insect guardians. In former reports
it has been compared with the very early Upland varieties, such as
King and Parker; but comparative tests made in eastern Guatemala
show that the native variety, which it is proposed to call Hekchz,
vepresents a very distinct type of this important cultivated plant.
It belongs to Gossypium hirsutum, the Upland species or series of
varieties, 1n the sense that it is not a Sea Island, Egyptian, or Kidney
cotton,’ but it 1s distinctly more different from any of the Upland
varieties now cultivated in the United States than these are from each
other. It has not been ascertained that the Kekchi cotton in its
a@The Sea Island cotton is so called because cotton of this type is cultivated
on the Sea Islands of South Carolina, long famous for the excellence of their
product. The Sea Island cotton came originally from Barbados, whence also
its botanical name, Gossypium barbadense.
Upland cotton gained its name as a means of distinguishing it from the Sea
Island, being cultivated in the interior, or “upland,” districts of the Southern
States. The Upland type of cotton was recognized as a distinct species by
Linnzeus under the name Gossypium hirsutum, but many subsequent writers
INTRODUCTION. 9
present form is suited to cultivation in the United States, but it has,
without any doubt, new and significant characters which must be
regarded as factors in cultural solutions of the weevil problem. (PI.
eho b)
Although cotton was not found to be planted as a regular field cul-
ture in any localities in Guatemala where the keleps do not exist,
small quantities are produced in the interior plateau region about
Rabinal by what may be called dooryard cultivation, and these, too,
have suggested cultural factors and expedients which may not be
without practical bearing.
The present paper can claim to make only a beginning in the
bionomic study of the question, but it shows at least that the weevil
problem has many avenues of approach on the botanical side.
The cotton of Guatemala and neighboring countries has maintained
‘an existence, at least, in the presence of the weevils, and has suffered’
an acute natural selection with reference to its ability to protect itself
against the weevil or to secure the assistance of alles, such as the
keleps. That no commercial cotton crop is raised or exported from
such districts does not prove that they are unworthy of scientific
investigation, or that they are not likely to yield materials and sug-
gestions of practical value in meeting the invasion of weevils which
is now so serious a menace to the cotton industry of the United States.
Some of these weevil-resisting adaptations have been of use in
securing for the cotton the assistance of the keleps. There are others
which, if properly utilized, might render these interesting insects
unnecessary. Tropical America has been serving for thousands of
years, evidently, as a laboratory for this class of experiments. Texas
was invaded only yesterday—a decade ago. Now that we are forced
to engage in the strife, the first preliminary should be, it would seem,
to take stock of the weapons which nature has forged.
The present report was planned and partly written before the dis-
covery of the true nature of the best of the weevil-resisting adapta-
tions—the proliferation of the tissues of the buds and bolls. Some
of the characters here described may have no value except as sug-
gestions, but taken together they may be of interest as an outline of
the results of the very long period of selection to which the presence
of the boll weevil has subjected the Central American varieties of
the cotton plant.
lave erroneously confused it with the Old World species Gossypium herbaceum,
which is not cultivated in the United States, though often so reported.
The Egyptian and Kidney cottons belong to the Sea Island series, and are of
American origin. The Kidney cottons seem not to have been cultivated on a
commercial scale, but they are very widely distributed in tropical America. The
name refers to the fact that the seeds cf each compartment of the boll are
grown together into a small compact mass, in shape suggesting a kidney.
10 ' WEEVIL-RESISTING ADAPTATIONS OF COTTON.
SELECTIVE INFLUENCE OF THE BOLL WEEVIL.
The boll weevil exerts a most prejudicial effect upon the cotton
crop, but, unlike most parasites, it does not cause disease or debility
in its host plant. The young buds and bolls are merely pruned away,
as it were, the purposes of the weevil being the better served when the
plants remain vigorous and continue to produce more buds and bolls,
in which more eggs can be laid and more larve brought to maturity.
Nevertheless, if no bolls are allowed to develop no seed can be set.
The fate of the cotton crop in wet seasons in Texas shows that with-
out some form of protection the plant would have been extinct long
since in all localities reached by the boll weevil.
The long contact between the boll weevil and the cotton plant in
Central America has given ample opportunity for the latter to profit
by the selection which the insect itself has provided. Every differ-
ence by which a cotton plant was able to resist or to avoid the weevil
and thus ripen more seeds than its fellows would give it a distinct
advantage, quite as 1f the selection were consciously carried on by the
planter or the plant breeder. The case is different from that of the
recent improvements of many of our cultivated plants by selection
for the increase of some particular quality already existing. Such
improvements can often be made appreciable, or even highly valu-
able, in comparatively few years, but under the desultory Indian
methods of cultivation long periods of time would be required for
the origination and accumulation of such characters as these pro-
tective adaptations.
Climate and other local conditions must also be taken into consid-
eration. An adaptation which would be effective in one set of cli-
matic conditions may be of little use, or even a positive disadvantage,
in others, as, for example, the prompt shedding of the parasitized
buds. In a dry region the falling of a bud to the superheated,
sun-baked earth insures the death of the weevil larva, either by the
heat directly or by the complete drying out of the tissues in which
the larva is embedded. In the moist districts of eastern Texas, how-
ever, this expedient is quite ineffective, the larve often developing
even better when the buds fall off and le on moist soil than when they
remain attached to the plant.
It need not surprise us to learn also that the weevil-resisting adap-
tations shown by the Kekchi and other cotton varieties of Central
America are shared, to some extent, by those already known in the
United States, since the whole Upland type of cotton appears to have
been, originally, a native of the Central American region. Varieties
which reached the United States from Mexico and the West Indies
may, however, have had little or no contact with the weevil for many
centuries, while in Central America the struggle for existence has
remained severe and continuous down to the present day.
GENERAL PROTECTIVE : CHARACTERS. sta
It is now known that in the plateau region of Mexico the long dry
season effectually excludes the weevil, so that varieties of cotton from
the Mexican highlands, instead of being weevil-proof, as sometimes
represented, may have no immunity whatever when brought into
the much more moist climate of the cotton belt of the United States.
The Kekchi cotton of Guatemala, on the other hand, has to a much
greater degree than any of the varieties now grown in the United
States the very qualities which experiment has shown to be effective
for the mitigation by cultural means of the injuries inflicted by the
boll weevil. That it has, in addition, other features not possessed
by our United States varieties, or not hitherto interpreted as weevil-
resisting adaptations, need not be looked upon as anything outside
the normal order of nature, but is entirely in accord with what
appears to be the biological and agricultural history of the cotton
plant in Central America.
GENERAL PROTECTIVE CHARACTERS.
DWARF HABIT AND DETERMINATE GROWTH OF KEKCHI COTTON.
Although Guatemala is a tropical country and the climatic condi-
tions are suitable for the growth of cotton throughout the year, the
Kekchi cotton is cultivated only as an annual, and is smaller and
more determinate in its habits of growth than the Upland varieties
now known in the United States. It soon attains its full height,
and after a crop of bolls has set on the lower branches there is a
definite tendency to cease growing or producing new buds. The
later upward growth of the plants seems to be supplementary, as it
were, to the formation of the bolls; often there appear to be no
more flowers formed, and many of those which come seem to be
undersized, as though the plant were really mature and were
«pproaching the natural termination of its existence. Our Upland
varieties, on the contrary, continue to produce throughout the season
hundreds of small squares on each plant which serve only as breed-
ing places for the weevils.
The explanation of the high development of these short-season
qualities of the Kekchi cotton is doubtless to be found in the custom
of the Indians, who pull up the cotton as soon as the bulk of the crop
has ripened to make room for the peppers, which are always planted
with the cotton. For the Indians the peppers are an even more
important crop than the cotton, so that when the time comes for
clearing away the cotton they do not wait for the plants which may
have delayed maturity. Late bolls, even, would never come to
maturity or furnish seed for planting. The result has been a very
long-sustained selection for early bearing and uniform ripening of
the crop. Some of our earliest Upland sorts may begin blossoming
12 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
as soon as the Kekchi, but they show far less tendency to determinate
erowth. :
The development of earliness has been assisted, no doubt, by the
climatic conditions which prevail in eastern Guatemala. The rainy
season oftens begins before the cotton harvest is completed, so that
the later bolls are very likely to become diseased, or, if they reach
maturity and open, the lint is often beaten to the ground and made too
dirty for use in spinning and weaving. In either case the seed. is not
harvested.
The Indians believe that even if they did not pull the cotton up it
would not become a perennial, but would die out completely, even to
the roots, during the rainy season. Seeds scattered accidentally in
the plantation at harvest time are rotted by the rain and do not germ1-
nate, so that little or no volunteer cotton is carried over from one
season to another. :
If the Kekchi cotton were the only variety planted in Guatemala
and the weevil had there, as in the United States, no other food plant
than the cotton, the insects might all die off between April or May,
when the cotton 1s pulled up, and October, when the next crop is
planted. There 1s, however, enough perennial “ tree” cotton in the
country to keep the pest from becoming exterminated. Moreover,
the question of additional food plants in Guatemala is still open.
The importance of securing short-season varieties of cotton for the
United States can hardly be overestimated, since, as already intimated
elsewhere,“ there is no longer any reason to hope that the more severe
winters of the northern districts of the cotton belt will give any pro-
tection against the weevils.
As long as the weevil was confined to the southern part of Texas,
where the cotton could survive the winter, the destruction of the
plants as soon as possible after the maturing of the crop was the only
measure calculated to seriously reduce the number of weevils. It
was also essential to plant cotton as early as possible in the spring to
avoid the weevils bred on the volunteer, or hold-over, cotton which
negligent planters had left in the ground. The extension of the pest
farther north and the possibility of securing cotton varieties with
determinate habits of growth introduce several new considerations.
The hold-over cotton is eliminated from the problem, but in the more
northern latitudes, where the cold comes earlier and the temperature
remains lower throughout the winter, it may often happen that there
will be no period in cn the weevils can be reduced by starvation,
unless time can be secured for this purpose in the spring by the plant-
ing of short-season varieties of cotton.
a Cook, O. F., 1905. Progress in the Stuuy of the Kelep, Science, N. S., 21:
ays
PROTECTIVE CHARACTERS OF KEKCHI COTTON. 13
Instead of colder winters being unfavorable to the weevils, there is
every probability that cold sufficient to keep them in a torpid, inactive
condition will preserve their noxious lives much better than warm and
pleasant weather, which enables them to continue active and thus
deplete their vital energies. The winter of 1904-5 was one of un-
precedented severity in Texas, both in absolute temperature and in
continued cold and wet, and yet the weevils were able, in many locali-
ties, to infest heavily the early plantings of cotton to a far greater
extent than in previous years.
The farther north the locality the more will the efficiency of cul-
tural methods of avoiding the boll weevil depend upon the plant-
ing of quick-maturing varieties of cotton. It is true that in a
favorable season the cotton planted first would set its crop soonest,
and thus escape a part of the damage suffered by adjoining fields
of later growth, the earlier fields breeding weevils to attack in
larger force the later plantings. But instead of insuring a decrease
of the number of weevils in a given locality and checking the
propagation of the pest, very early planting by a part of the farmers
of a community might tend, after an early fall and a cold winter,
to the opposite result, since it would save the lives of large numbers
of weevils which would otherwise perish before the cotton, if sown
« few weeks later, would be large enough to furnish the weevils
with food. Dr. Herbert J. Webber states that planting could
probably be deferred even to the middle of June without impair-
ing the chances of a crop as large as that which can be obtained
in the presence of the weevil.
There would seem to be little object in planting cotton where
the weevils are as abundant as in some places in southern Texas in
the spring of the present year, 1905. Nevertheless, the opportune
-oecurrence of a few weeks of dry weather was able, even then, to
greatly improve the prospects of a crop. No matter how bad the
weevils,the planter still has hope that dry weather may come and save
his crop from being a total loss. As long as indeterminate varie-
ties are planted this possibility will always make it difficult to carry
out a general policy of early destruction of the plants.
Some of our Upland varieties of cotton are early enough in the
sense that they begin flowering and fruiting very promptly, but
unless the season is very dry they will produce a continuous succession
of buds until they are pulled up or frost cuts them off. The earli-
ness of practical value is not to be shown merely by the date of
flowering, but by the date of ripening the crop of bolls and of
ceasing to form new buds in which weevils can breed. If the im-
provements noted in other parts of this report can be realized in
practice, it would no longer be necessary to destroy the cotton plants
4: WEEVIL-RESISTING ADAPTATIONS OF COTTON.
in order to put an end to the breeding of the weevils. It would
then become practicable and desirable to regulate planting so as to
bring the growing period of the cotton at the most favorable season
for a rapid development of the crop, and thus to give the weevils
the shortest possible opportunities for breeding.* If the fall and
winter had favored the survival of many weevils, planting could well
be deterred until the weevils had disappeared, a fact which could be
ascertained by starting early a few observation plants from which
the weevils could be carefully picked by hand as long as they con-
tinued to appear.
The extent of the mortality of the boll weevil in the spring has been
well shown in the investigations reported by Mr. W. D. Hunter on
the effects of applying Paris green to the very young cotton as a
means of destroying the weevils which had hved through the winter.
Numerous dead weevils were found in the poisoned fields, but equal
or even greater numbers were found in those to which no Paris green
had been applied, and the conelusion was drawn that a large propor-
tion of the weevils, which pass the winter in a state of hibernation
or torpidity induced by the cold, perish through starvation er other
causes in the spring, after the weather has become warm enough to
render them active again and permit them to renew their search for
cotton plants on which to feed and lay their eggs.”
It is easy to understand, too, that after the weevils have been re-
duced by the cold to a condition of inactivity involving an almost com-
plete suspension of the vital functions, the lack of food and the lapse
of time can make very little difference with them. Starvation comes
much quicker during warm weather while they are going actively
about, so that it is the autumn and spring. which must be reed upon
to reduce the numbers of the weevils rather than the cold periods of
the winter months. Messrs. Hunter and Hinds have also noted as
significant the fact that of weevils captured at the middle of Decem-
ber, 15.8 per cent passed the winter successfully, while of another lot
captured a month earlier, only 1 per cent survived. Their conclu-
sions were as follows:
It is evident that the weevils which pass the winter and attack the crop of
the following season are among those developed latest in the fall and which, in
consequence of that fact, have not exhausted their vitality by oviposition or any
considerable length of active life.
With these facts in mind it becomes plain that no objections need
be raised on general biological principles to the introduction of new
aA determinate variety of cotton would also avoid the cultural disadvan-
tages incidental to very early planting, for if the weather happens to turn
cold and wet the cotton is often either killed outright and has to be replanted
or, what is still worse, it becomes permanently stunted and unproductive.
b Hunter, W. D., 1904. The Use of Paris Green in Controlling the Cotton Boll
Weevil, Farmers’ Bulletin No. 211, U. S. Department of Agriculture.
VARIATIONS IN KEKCHI COTTON. 15
quick-maturing varieties of cotton from tropical countries on the
eround that cold weather will exclude them from the United States.
The early spring is the only time in which they will be hkely to
encounter adverse conditions in this respect, and if varieties can be
secured which are able to mature a satisfactory crop in a short season,
these quick-maturing qualities will far more than compensate for any
lack of ability to withstand cold weather in the early spring.
The Kekchi cotton may prove, however, to be quite as tolerant of
cold as the other Upland varieties now cultivated in the United
States. In its native country it is planted in October and grows
throughout the winter months in mountain valleys where tempera-
tures of between 40° and 60° F. are not infrequent. (PI. L.)
VARIATIONS IN THE KEKCHI COTTON.
Very great diversity of size, habit of growth, and other features
exists in the Indian cotton of the vicinity of Secanquim and Cajabon.
The plants cultivated by Mr. John H. Kinsler on the United States
system were also very different from any grown by the Indians,
being much more robust and compact than in the more crowded
native fields. The spreading lateral branches and low, compact
growth of the Kekchi cotton, as shown in Plate I, figure 1, might have
cultural disadvantages if these tendencies were to be maintained in
regular field cultures. Such, however, is not likely to be the case.
When growing closer together the plants are more upright and less
leafy below.
To what extent the differences observed thus far represent varietal
characters can scarcely be determined without a field test of the
apparently different strains, side by side. The broken, precipitous
nature of the country renders it impossible to rely upon comparisons
of the conditions of the different fields.
The conservative agricultural habits of the Indians would tend to
the continued planting by one man or family of the same seed for
long periods of years, which might well conduce to the formation of
separate strains. The low germinating power of the seed may pos-
sibly be due to such inbreeding, though it is more likely that it deteri-
orates because of the humidity of the climate.’ Nevertheless, our
experiments were sufficient to prove that even among plants grown
from seed raised by the same Indian there were very appreciable
a@'This was shown to be a fact before the report was printed. See p. 18.
6 The Indians appreciate the fact that the cotton seed does not germinate well.
They are accustomed to plant six seeds together, from which two or three plants
usually reach maturity, often with one or two insignificant dwarfs underneath.
The yield per plant in these crowded fields is naturally very small, but the larger
individuals often bear from 20 to 30 bolls. At Rabinal from 6 to 10 plants in a
cluster is the rule, the product of the individual being still further reduced.
16 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
cfferences, sufficient to have a very practical bearing upon the ques-
tion of securing strains having the special characters required in the
United States. Indeed, there was nearly as much diversity among
the Guatemalan plants as among all the Upland varieties, though
these were in some cases unusually variable, as a result apparently
of the transfer to new and unwonted conditions of climate and soil.
The usual number of locks or cells in a boll of the Kekchi cotton is
four, but bolls containing three or five are not uncommon; often they
are on plants which have otherwise the usual number.
There is also considerable diversity on the same plant in the shape
of the bolls, some, for example, remaining quite conical and pointed,
while others round out to near the apex. One plant was observed
in which the bolls were very nearly spherical. The involucre was
also unusually large. The plant had an unusually deep red or black-
ish color, and was distinctly more vigorous than its neighbors, as
often happens with mutations.
It is not at all probable that a close selection has ever been prac-
ticed by the Indians, so that a wide diversity of mutational charac-
ters may be expected when once the variety has been brought under
careful observation.
The stems and petioles of the Kekchi cotton plant are dark red.
or at least spotted with red, and the leaves turn dull red with matu-
rity. The bracts and bolls are green when young, but with age and
exposure to the sun become more or less tinged or spotted with red.*
_The outer involucral nectaries also turn deep red, especially the two
upper ones, even while the buds are still very young. The great
majority of the leaves are simply three-pointed, but many of them
have an additional smaller lateral point on each side near the base.
@One plant at Secanquim showed a very decided instance of variegation
with white and red, though the latter color might have been due to an increased
tendency of the white portions to take the red discoloration common on normal
leaves. The lower branches of the plant show only normal green coloration,
and a part of the upper branches is also normal in color and size, and with
fruits rather above the average size. The variegated branches do not reg :
larly alternate, nor do they come all from. one side, but they might still have
connection with the phyllotaxy. There seem to be two stages of the variega-
tion, a white and a light greenish-yellow: the latter may belong only to young
leaves. Both are distributed with the utmost irregularity, and both may
affect the upper surface of the leaf while the under surface remains green, or
yice versa, though the latter condition is much less common than the former.
The etiolated portions of the leaves. involucres, and fruits do not attain the
full size of the corresponding normal organs, so that the parts affected are
more or less unsymmetrical, though where the variegation is slight this result
may be apparent, or if it be complete the symmetry is not affected. Except
for two premature bolls the seed was not ripe, and these were from the nor-
mal lower part of the plant.
ACCLIMATIZATION OF KEKCHI COTTON. ILG
EFFECTS OF GUATEMALAN CONDITIONS ON UNITED STATES VARIETIES.
The behavior of the United States varieties under changed climatic
conditions in Guatemala is interesting in several ways. The * King,”
which in the United States appears to resemble the Guatemalan
variety most nearly, here loses most of its distinctive characters and
breaks up into a variety of types, many of which would not be recog-
nized in the United States as at all related to King. One of these is
a “limbless ” or “cluster ” variety, which for a time appeared to
Mr. Kinsler as a very promising new sort, It was smaller and dis-
tinctly earlier than King plants of the normal type, and seemed
likely to be more productive, but only a few bolls developed, and
these proved to be of abnormal form, with deep grooves or notches
across the tip. ,
One of the features in which the change of climate seems to pro-
duce remarkable effects is that of earliness. The King, which in the
States is looked upon as the earliest variety, is found by Mr. Kinsler
to, be somewhat exceeded in this respect by “ Allen,” which has not
been looked upon as a competitor. The Sea Island and Egyptian
varieties, too, prove to be much more precocious than was expected.
Some of them begin flowering almost as soon as the Upland sorts.
The Rivers variety of Sea Island cotton, in particular, was very
early, robust, and productive, distinctly ahead of the near-by Janno-
vitch, though not so tall.
ACCLIMATIZATION OF KEKCHI COTTON IN THE UNITED STATES.
It was not unexpected that thesKekchi cotton would show a change
in its method of growth on being transferred to Texas. New condi-
tions of soil and climate often cause notable disturbances of the
organism. Some of the tropical cottons planted in Texas for experi-
mental purposes have grown into large bushes without showing the
shghtest tendency to produce fruit or even flowers. In 1904 cotton
from Peru planted at Victoria, Tex., grew most vigorously to a
height of 18 feet, but remained quite sterile. Jt is possible, however,
that even in their own country these were what are called “ tree
cottons,” which usually grow to considerable size before beginning
to flower. Letters from Mr. Kinsler, in charge of our experimental
plot at Pierce, Tex., relate a similar behavior on the part of the
Kekchi cotton, which at that place has grown large and rank; but
toward the end of July it was beginning to fruit, so that the ripening
of seeds in Texas is to be anticipated.
Two or three years will probably suffice to diminish this abnormal
vegetative vigor, due to the stimulus of the new conditions, and per-
mit a return to the normal earliness of the variety. Similar results
9962—No. 88—00 M——2
18 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
have attended the introduction into Texas of Mexican varieties of
corn. The plants grew 14 feet high the first year and bore very little
seed: in the following seasons they became smaller, earlier, and more
productive.
The probability that the Kekchi cotton can be grown even at the
northern limits of cotton cultivation is strongly imdicated by the
results of an experiment at Lanham, Md. (1905). In favorable sea-
sons cotton can be grown to maturity as far north as Washington, but
the present year has been very unfavorable, the summer months being
for the most part cool and rainy, and with several intervals of
unusually low temperature. The cotton, which was planted intention-
ally in rather poor soil, to avoid too great luxuriance of growth, ger-
minated very badly and remained small and stunted until August.
The Kekchi rows have, however, produced more plants, and more of
these have grown to maturity than with any of the domestic or for-
elgn varieties included in the test. The Kekchi type has also remained
more constant in Maryland than did the King variety when grown in
Guatemala, though there are obvious differences between individual
plants. Two plants in particular were found to have numerous buds,
some ready to blossom before any of the others had begun to show
signs of productive maturity.
It might be feared that a variety newly introduced ‘from a tropical
country would be likely to suffer more from low temperatures than
our United States varieties, but this seems not to be the case with the
Kekchi cotton, even when the cold is carried down to the freezing
point. There were light frosts in Lanham about the end of Septem-
ber, just sufficient, as it happened, toalo appreciable damage to cotton
im low ground. The Kekchi plants did not suffer more than the
American Upland varieties. The difference, if any, was in favor of
the Kekchi cotton, perhaps on account of the closer fohage.
Many annual plants, even those of tropical origin, are most vigor-
ous and productive at their northern limits of growth, not, as has been
supposed, because this is the coldest part of their range. but because
the heat and sunlight, necessary to plant growth, are greater during
our summer months than can be secured in a similar time in the
Tropics, owing to the much longer days of our northern latitudes.’
The Pachon cotton from western Guatemala, though it has grown
taller at Victoria, Tex. (52-79 inches), than at Lanham, Md. (30-40
inches), has produced numerous buds in Maryland, but none in
Texas. The Kekchi cotton also appears to have been more productive
at Lanham than at Victoria, to judge from a recent partial report
from Mr. Argyle McLachlan.
2 Cook, O. F., 1902. Agriculture in the Tropical Islands of the United States,
Yearbook of the United States Department of Agriculture for 1901, p. 367.
EARLY BEARING AIDED BY LONG BASAT. BRANCHES. US)
It is very possible, therefore, that if the Guatemalan variety is able
to thrive in the United States 1t will ripen its crop here in even less time
than it requires in Guatemala, and this is rendered the more probable
from the fact that in Guatemala the cotton has to be planted in the
rainy season and is obliged to exist for the first few months under
conditions of excessive moisture. The dry season of this district 1s
short and uncertain. For two years, 1903 and 1904, the Indians were
unable to burn their clearings, so that the corn crop failed and the
community was reduced to the verge of starvation. The cotton crop,
in normal seasons, is said to be planted in the latter half of October
and ripens in March.
The introduction of a dwarf, short-season cotton would require, of
course, something of a change in cultural methods in the South, since
the smaller size of the plants will need to be compensated by closer
planting. It will be readily understood that to secure the setting of
a crop in the minimum of time as many plants as possible should
be set at work. The question is not that of the maximum product for
each plant or for a given area. With the weevil in the field the time
factor becomes of chief importance.
Little is gained in reality by the rank growth of the larger varie-
ties; in fact there is a distinct loss in earliness, even though some
bolls are set in the early part of the season. If these are overshad-
owed and starved by the continued upward growth, the crop is delayed
and the lower part of the plant becomes, on the whole, distinctly
unproductive. :
EARLY BEARING FACILITATED BY LONG BASAL BRANCHES.
The earliness of the Kekchi cotton 1s made possible by the fact that
the bolls are nearly all borne at the base of the plant, the upper
branches and their foliage serving merely to assist in bringing to
maturity the fruits which are set while the plant is still very young.
Like several other tropical economic species, such as coffee, cacao,
and the Central American rubber tree, the cotton plant has two kinds
of branches—the true or primary branch, which arises in the normal
position of branches in the axil of the leaf, and the secondary or fruit
branches, one of which arises at the side of each primary branch. In
most varieties only a few of the true branches are developed; often
none at all. They are almost always plainly indicated, however, by
a small bud or a stunted leaf or two, in case the bud has not remained
entirely dormant. |
Cotton plants are either right-handed or left-handed in the sense
that on the same plant all the secondary branches come out on the
same side of the primary branches. It is possible, therefore, to de-
termine by its position whether any particular branch is a primary or
20 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
a secondary. But the function of the two sorts of branches does not
always remain as distinct as in the coffee and cacao. a ae masa
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| | |
The advantage is particularly notable with respect to the greater
width of the bracts, which enables them to remain much more effect-
ively closed at the angles. In the Parker, King, and Allen varieties
the bracts very seldom attain a width of 30 mm., while in the Kekchi
cotton the average width for all except the smallest buds is above
30 mm.
OPENING, OR FLARING, OF BRACTS AVOIDED.
The unusually large and well-closed bracts of the Kekchi cotton
have another practical use in keeping the bud from drying out, as
explained in the discussion of proliferation.
The external indication of this difference is that in the Kekchi
cotton punctured squares commonly do not open, or flare, by the
spreading apart of the involucral bracts, while among the Upland
and Sea Island varieties flaring is the regular rule. Quite a per-
centage of the squares of Abbasi, Parker, King, and other varieties
stand well open normally before any injury has occurred, but the
Kekchi cotton seldom or never exposes its squares before flowering.
The larger and broader involucre is also able to permit the protrusion
of the flower without losing the power of closing and remaining
shut for a considerable period after flowering, while the Parker and
King varieties often remain quite open, so that the young boll is
fully exposed to the weevils.
lt
EXTENT OF PROTECTION BY INVOLUCRE. 4]
An example of the promptness with which weevil injuries cause
the involucres of our Upland cotton to open is well shown in a note
by Mr. McLachlan:
On August 8, at 2 p. m., a small cage was placed over a small plant of Parker
cotton, and 5 female and 2 male weevils were introduced. The plant possessed
36 squares, 4 flowers, and 9 bolls. The morning after the weevils were put
into the cage several of the squares had flared and one had fallen. It would
seem that the mechanical forces of the square are quickly affected by the work
of the weevils. Here, of course, the punctures were numerous, because of the
many weevils on the plant. Some of the squares were riddled with feeding
and egg punctures.
The buds of Kekchi cotton often recover from three or four punc-
tures, though they might not do so if these were all made at the same
time. But it often’ happens that squares with numerous feeding
punctures remain closed and wither up without flaring.
HAIRY MARGINS OF INVOLUCRAL BRACTS.
In addition to their larger size, the bracts of the Kekchi cotton have
the marginal teeth or lacinie more numerous and more hairy than
those of our Upland varieties and able to afford more of an impedi-
ment to the entrance of the weevils. The difference was very pro-
nounced in our experimental plot, where King, Parker, and other
familiar American sorts were planted beside the Kekchi. It is as
superior in this respect to the other Upland varieties as they are to
the Sea Island.
The Kekchi and Rabinal varieties, though both belonging to the
Upland series and having many similarities, have also very distinct
differences, as, for example, in the present character. The small,
firmly appressed bracts of the Rabinal cotton have the marginal
lacinize few and small; sometimes the edges are nearly entire, or
merely toothed. The hairy covering is also reduced to a fine, short
coat, which can afford little or no impediment to the weevils.
EXTENT OF PROTECTION BY INVOLUCRE.
That the closed involucres do indeed contribute to the protection of
the young buds from the weevils became very obvious in one of our
experimental plots at Secanquim, located about a quarter of a mile
outside the belt of Indian -cultivation of cotton. There being no
keleps to afford protection, the cotton soon became thickly infested
with weevils, and very few bolls were allowed to develop on any of
the plants. There was a notable difference, however, in the age at
which the buds were punctured. As already stated, the edges of the
bracts of some of the Sea Island and Egyptian varieties separate at
a much earlier period than those of the Upland varieties, and the
49 - WEEVIL-RESISTING ADAPTATIONS OF COTTON.
weevils commonly attack them in their very early stages, and even
while they are altogether too small to permit the development of a
weevil larva. It has been pointed out already by Messrs. Hunter
and Hinds that the smooth stems and petioles of the Sea Island and
Egyptian cottons render them much more readily susceptible to
injury by the boll weevil than are the Upland types, and if we add
to this the disadvantage arising from the later development and the
more open involucres the possibility of protecting the long-staple
cottons against the weevils seems small indeed.
Instead of being immune to the boll weevil, as at one time hoped,
the Egyptian and Sea Island varieties seem to be most lacking in
weevil-resisting adaptations, as might, indeed, have been expected in
view of the fact that they have been developed in regions to which the
weevil has not yet penetrated. The Kidney cottons, which may be
looked upon as representing the Sea Island type on the mainland of
the American continents, have, as will be seen later, a peculiar
feature of protective value.
ADVANTAGE OF OPEN INVOLUCRES.
It will be apparent from the facts already recited that the partly
closed invelucres of the Sea Island and Upland varieties now culti-
vated in the United States serve little or no purpose in resisting the
boll weevil. On the contrary, they often appear to be an advantage
to the insect, serving, as they do, to hide the parasite from its enemies
and protect it against the application of insecticides or capture by
insectivorous birds.“
The great variation in the size and shape of the involucre in the
different varieties of cotton suggests the practicability of securing
sorts with open involucres or with these structures reduced to small
dimensions. If the weevils were to be caught by insectivorous birds,
like the Cuban oriole, whose weevil-eating habits have been discovered
by Mr. E. A. Schwarz, open involucres would be a distinct advantage.
It might then be possible also to apply Paris green or other insecti-
cides to young buds which are, except in the early spring, the.
exclusive feeding places of the weevils.
The practicability of an open involucre will need, however, to be
considered from another standpoint. It must be ascertained whether
the young buds will bear full exposure. Unlke most of the related
plants, the cotton bud is not protected by a calyx. ‘The involucre may
be necessary as a substitute, especially in dry climates. In humid
apr. H. J. Webber states that the desirability of open involucres has been
appreciated and that selections of Upland varieties with a view to the develop-
ment of this character have been made.
BEHAVIOR OF PARASITIZED BUDS. 43
regions, however, this requirement might be relaxed, and it is in such
places that the injuries of the weevils are the greatest.”
BEHAVIOR OF PARASITIZED BUDS.
SHEDDING OF WEEVIL-INFESTED SQUARES.
In a dry climate, like that of the Mexican plateau region, the drop-
ping of the squares in which the weevils have deposited eggs would
constitute a very effective adaptation. The weevil larve do not sur-
vive a thorough drying out of the squares. It is only in the arid
districts of Mexico that the cotton plant has shown its ability to
escape from cultivation and maintain itself without human assistance,
if indeed it be not in some places a truly indigenous wild plant, as
several botanists have reported. But in a moist region like the cotton
belt of eastern Texas this habit of the plant has no practical use,
since as many of the weevils die when the injured squares remain
attached to the plant as when they fall to the ground.
“Tt is generally true that squares seriously injured by the weevil sooner or
later fall to the ground. Some plants, however, shed the injured squares more
readily than do others. It seems to be a matter of individual variation rather
than a varietal character. Thus occasional plants retain a large proportion of
their infested squares. which hang by the very tip of the base of the stem.
Normally the squares are shed because of the formation of an absciss layer
of corky tissue across their junction with the stem. In the case of the squares
which remain hanging, the formation of this layer seems to be incomplete, or
else it becomes formed in an unusual plane, so that while the square is effectu-
ally cut off, it merely falls over and hangs by a bit of bark at its tip. In this
position it dries thoroughly and becomes of a dark brown color. Plants
showing 6 or 8 of these dried brown squares are quite common in infested
fields. Although exposed to complete drying and the direct rays of the sun,
the larvyze within are not all destroyed. * * #*
“Tt seems a conservative estimate, therefore, to say that fully one-third of
these exposed dried squares may be expected to produce adults. Considering
the exposed condition of such squares this seems to be a very high percent-
age. * * * The observations made, however, certainly show that a complete
aAfter the above had been written it was observed that the Pachon cotton
from western Guatemala, grown in an experimental plot at Lanham, Md., has
the peculiar feature of a large calyx. which completely covers the young bud
and extends above it into long, slender, hairy tips. It may be that this is to be
looked upon as still another weevil-resisting adaptation. The weevils would be
able, undoubtedly, to bore through the calyx, but the hairy tips might hinder
their access to the bud. The bracts are much smaller and much more open
than in the Kekchi and Rabinal varieties, but the laciniz, or teeth, along their
margins are rather stiff and are clothed with numerous hairs, stronger and
more bristlelike than in the Kekchi and Rabinal varieties, and able to keep the
laciniz from closing together. It may be that the greater rigidity of the laciniz
and the bristles gives better protection than the open position of the bracts
would indicate. The case is in reality quite different from that of the Sea
Island varieties, where the bracts are both naked and open.
——
~~
—_——
44 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
drying of the square does not necessarily destroy the larva, and that a square
may undergo far more exposure to direct sunshine than had been supposed
possible without causing the death of the larva or pupa within.” @ ?
It is to be remembered, however, that such disconnected squares are
thoroughly dampened every night by the dew, and that a small
amount of moisture may pass out from the plant through the shred
of dead tissue. In either case the hanging boll might get more moist-
ure and less heat than if lying on the dry ground, exposed to full
sunlight. Suspended bolls are exposed to air temperatures only.
If no other means of avoiding the weevil becomes practicable a
great extension of the cotton production into the semiarid districts of
western Texas, Oklahoma, and even Kansas is to be expected. The
long days of the more northern districts will conduce to the shorten-
ing of the growing season, and if dry weather cuts down the yield the
loss is likely to be neutralized by more or less complete protection
against the weevils.
These contradictory effects of the same adaptation depending upon
climatic condition may render necessary a complete differentiation of
the cotton varieties of wet and dry regions.
It is not improbable that the Upland varieties previously known in
the United States came originally from the more or less arid regions
of Mexico, where absence or very small development of the basal
branches keeps the ground from being constantly shaded and gives
better chances for the weevils to be killed by the drying out of the
fallen squares.
Our Upland cottons are undoubtedly of American origin, but the
region from which they came has not been ascertained. Some of the
Texas varieties are said to have been brought from Mexico. Coro-
nado’s Journal of the earliest Spanish exploration in Arizona and
New Mexico contains many references to the cultivation of cotton by
the Indians. There can be little doubt that the agricultural Indians
of the Gulf region also cultivated cotton, though no documentary
evidence of the fact seems to have come to light as yet.
It is highly probable that the original Home of the cotton plant, and
of the boll weevil as well, was in a somewhat arid region, since it Is
only under such conditions that the weevil would be effectually pre-
vented from increasing to the fatal degree of destroying its host
plant, and thus cutting off its only means of subsistence. On the
other hand, it was only in a humid country lke eastern Guatemala
that many of these weevil-resisting adaptations would be hkely to
develop if, as now appears, it has required the selective influence of
the boll weevil itself to bring them to their present advanced develop-
ment.
a Hunter, W. D., and Hinds, W. E., 1904. The Mexican Cotton Boll Weevil,
Bul. 45, Division of Entomology, U. S. Department of Agriculture, pp. 73 and 74.
COUNTINGS OF FLARED AND FALLEN SQUARES. 45
The adaptive character of this habit of shedding the parasitized
squares seems to be confirmed by the fact that it depends upon the
existence of a special layer of soft cells which readily break down
when the bud is injured. Many plants have such cells as a means of
shedding their fruits, but they seem not to be prevalent among the
relatives of the cotton. The cotton itself does not drop the ripe bolls,
and even the empty shell often remains long after the seeds are gone.
The drier the climate the more effective is the prompt shedding of
injured squares. Whether there are other adaptations thus especially
suited to dry chmates 1s not yet known, our studies having been con-
fined mostly to humid regions.
Dr. Edward Palmer, who has spent many years in botanical ex-
plorations of the dry plateau region of Mexico and who discovered
that the boll weevil was a cotton pest, states that in several localities
where the cotton was formerly grown without difficulty the introduc-
tion of irrigation improvements has proved disastrous. With the
assistance of the moist soil the weevils are now able to reach maturity
in large numbers and complete the devastation of the crop, quite as
in Texas. The irrigated soil affords a situation favorable for the
development of the larvee in the fallen squares.
This is said to have been the case about Parras, and at Rio Verde,
below San Luis Potosi. The culture of cotton has declined also in
the “Huasteca Potosina,” the tropical district between San Luis and
Tampico, and on the Pacific side of Mexico, along the Santiago River
above San Blas, as well as about Tepic. Doctor Palmer saw cotton
growing in a wild condition in the fences at the old mission, San José
de Guaymas, 6 miles from the commercial port; again at Mulege,
Lower California, across the Gulf from Guaymas, the latter a much-
branched, prolific tree, producing a nankeen-colored lint. About
Guaymas cotton was formerly utilized by the Indians as tinder, after
being dipped in a solution of saltpeter. The same facts were observed
by Dr. L. O. Howard in 1899 at San José de Guaymas.
COUNTINGS OF FLARED AND FALLEN SQUARES.
An attempt was made in connection with our Guatemalan experi-
ment to secure data on which a definite statement might be based
regarding the extent to which the different varieties were protected
by their involucral characters, but the problems are too complex to
be reached except by more elaborate statistical studies than were prac-
ticable at that time.
Countings were made, for example, of the flared and fallen
squares—that is, of those which it might be supposed that the weevils
have injured—and of the number of weevil larvee, proliferations, ete.,
found inside them. The results in percentages do not agree, however,
46 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
with the facts obvious in the fields; indeed, they greatly misrepre-
sent them. Thus the percentage of weevil injuries jn flared and
fallen squares does not appear very much higher in the Kekchi cotton
‘than in the Sea Island and Upland varieties; yet as a matter of
fact the squares of the Kekchi cotton seldom flared for any other
reason than weevil injuries, and much less often for this cause than
did those of other varieties. Many small squares of the Kekchi cot-
ton fall off, however, before they are large enough or open enough
to be attacked by the weevils.* This takes place in the other varie-
ties to a much smaller extent, but with them the apparent percentage
of weevil injuries among flared squares is much diminished, because
many squares stand open and appear as though beginning to flare,
even before the weevils have attacked them.
PROLIFERATION OF INTERNAL TISSUES OF BUDS.
The protection of the buds does not end with devices for the exclu-
sion of the adult weevils, nor with the rejection of those in which they
have laid their eggs. It 1s also possible for the plant to heal the
wound, and bring the injured bud to maturity by preventing the
erowth of the weevil larva. Where the climate is dry the weevil
farvee in the rejected buds are killed, as already explained. The
humid climate alternative of the falling of the parasitized squares is
proliferation, the growth inside the bud of loose, watery tissue in
which the larva does not develop. Whether the larva is killed by
smothering, starving, or poisoning, or by some combination of these,
is not yet known. Starvation is a sufficient explanation, since the
material with which the larva becomes surrounded can be no adequate
substitute for the highly nutritious pollen grains on which the infant
larva would otherwise feed.
Proliferation is much more frequent in the Kekchi cotton than in
any of our United States varieties, as far as known. The first and
second punctures are commonly resisted successfully, but the third,
fourth, or fifth attempt may succeed in the development of a larva.
The proportion of weevil punctures rendered ineffective by prolifera-
tion was found to run well above 50 per cent, sometimes between 80
more) GOs (ele Wa)
The promptness and efficiency of proliferation bear an inverse pro-
portion to the size of the buds. As the latter grow larger the mass of
anthers inside becomes less compact, and the other tissues become too
a@Professor Pittier found in the latter part of the season that the buds of
the Kekchi cotton were sometimes cut away at the base and left hanging in a
wilted condition. These were at first taken for flared squares as the result
of weevil injuries, but it was later ascertained that this was not the case,
though the true cause was not learned. The damage was done in the night.
PROLIFERATION OF INTERNAL TISSUES OF BUDS. 47
nearly mature to put forth new growth. If the presence of the larva
at this stage is sufficient to cause the bud to fall off, the development
of the parasite to maturity is well assured, the large bud affording
good protection and adequate food.
In the Kekchi cotton, however, such late attacks very seldom cause
the bud to fall off. Larvee developed in the larger buds are turned
out of doors, as it were, by the opening of the flower. The tendency
of injured buds to persist is notably greater than in the United
States, either because of some physiological difference between the
varieties, or because of the larger and more firmly closed involucres
of the Kekchi cotton, which keep the buds surrounded with a moist
atmosphere and protect it against drying out while the new tissues
are forming to heal the wound and encyst the egg.
In the closely planted Indian fields the squares seldom flare as in
the Texas varieties. They generally remain in place and continue to
grow until the bracts have reached nearly their full normal size. In
fields partially protected by the keleps the weevil larvee do not
seem to develop in buds as small as in Texas. Proliferation may
partly explain this delay and also the more firmly closed involucres,
but in our unprotected plot the weevils were able by repeated punc-
tures to infest smaller squares and reach maturity in them, after they
had fallen to the ground.
The behavior of weevil larve inside the squares in Guatemal:
seems also to differ appreciably from that observed in Texas where
younger squares are usually much more accessible to the weevils, and
are commonly punctured. In Texas the larve regularly grow to
maturity, depending for food upon the pollen, which is completely
eaten out. In Guatemala this very seldom occurs. Small squares
with well-developed weevil larve are rarely found under normal con-
ditions, nor do the larve depend upon the pollen as their principal
article of diet, as in Texas.
Several reasons for this difference may be considered. The first is
that the larger and more firmly closed involucre of the Kekchi cotton
gives the buds several days of protection, so that the average size
would naturally be larger. The examination of large numbers of
squares picked at random from the Indian cotton fields by Messrs.
Kinsler and McLachlan show also that a very large proportion of the
punctures are followed by proliferation, and that this means of pro-
tection is much more efficient in the younger squares. Another rea-
son must be sought, however, for the failure of the larve to eat the
pollen of the large buds where proliferation is less prompt and less
frequent. The impression might be gained that the pollen of the
Kekchi cotton is in some way not acceptable to the weevils, since even
when there is an abundance of pollen at hand they prefer to eat out
48 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
the style and central column of the flower, and thence down into the
ovary or young boll. After this has been consumed the larve return
to the upper part of the bud to finish the remainder of the pollen.
Nevertheless, this suggestion of a protecting quality in the pollen
itself can not be accepted with much confidence because the weevils
showed in numerous instances that they could live and thrive upon the
pollen of the young squares, quite as in the United States. This oc-
curred in the experimental plot where there were no keleps, and the
weevils were very numerous and persistent in their attacks. After
two or three punctures the squares flared and fell to the ground in
the usual manner, and in these the weevil larve were able to reach
maturity. |
A more probable reason for the usual failure of the larve to eat the
pollen as freely as in the United States is furnished by the opinion of
Mr. W. D. Hunter, that the original habit of the weevil was to attack
the bolls, like related species of Anthonomus, which live upon various
kinds of fruits. If this be true with reference to the boll weevil we
may think of the Guatemalan members of the species as having
retained somewhat more of the ancestral habits which with them are
definitely useful, because the cotton variety with which they have to
deal has perfected, to 2 larger extent than the Texas varieties, the art
of proliferation.
_As a further indication of the greater strength among the Guate-
malan weevils. of the instinct of attacking the ovary of the bud
may be mentioned the fact that a very large proportion of the
punctures occur low down—that is, on or below the level of the apex
of the young boll. The larva commonly eats directly to the center of
the bud and hollows out the. apex of the young boll. This habit
gives rather less opportunity for successful proliferation than in
‘Texas, because the cavity hollowed out by the larva lies below the
level of the staminal tube, the tissues of which are the most active
in proliferation. The Kekchi cotton shows occasionally another
form of proliferation not recorded from Texas, namely, that of the
base of the corolla. Sometimes this enlargement takes place in an
outward direction, forming a wart or protuberance on one side
of the bud, as shown in Plate VI. In other instances the diree-
tion is reversed and the ingrowing edges of the wound made by
the weevil fill the internal cavity and prevent the development
of the larva. The proliferation of the corolla, besides being less
a\ new species of Anthonomus with habits closely identical with those of the
boll weevil, but parasitic on the pepper plant (Capsicum), has been discovered
recently in Texas by Mr. E. A. Schwarz. This gains an added interest from the
fact already noted that it is the regular custom of the Indians of Alta Vera
Paz to plant peppers among the cotton.
CAUSES AND CONDITIONS OF BUD PROLIFERATION. 49
frequent than that of the staminal tube, is probably also less effect-
ive, since the weevil larve could escape before it into the center of
the flower while the proliferation from the staminal tube grows
outward, as though to meet the intruder and keep him separated
from the more special organs.
The habit of the larve to seek the center of the bud and gnaw
off the style is responsible for the loss of large numbers of younger
bolls which have suffered no direct injury from the weevil. Even
though the larva be subsequently killed by proliferation or though
the flower drops off and carries the larva with it, the lack of polli-
nation must prevent the development of the young boll unless par-
thenogenesis takes place, which seems improbable.
Larve were found in several instances in nearly full-sized buds
about to open, and in another case a more than half-grown larva
was found inside the central column of an open flower. More or less
distorted flowers with unmistakable signs of previous proliferation
in the bud stages are commonly found in the Kekchi cotton fields.
Summarizing the results of the study of proliferation in the
Kekchi cotton, it may be said that although the frequency of pro-
liferation in the young squares is very great, its efficiency in prevent-
ing the breeding of the weevils is somewhat less than might be ex-
pected in Texas, owing to the difference of food habits among the
weevils. If the Texas weevils are as consistent in their habits as
now supposed, the introduction of the Kekchi cotton or of a similar
proliferating variety might be of great benefit as a preventive
measure. The extent, however, to which it could be made to compass
the complete destruction of the weevil would depend somewhat upon
the degree, if any, to which they might return to the habit shown in
Guatemala of feeding upon the ovaries or boll rudiments rather
than upon the pollen of the young buds, an important and hitherto
unsuspected difference in habits between the weevils of Texas and
those of Guatemala.
CAUSES AND CONDITIONS OF BUD PROLIFERATION.
That the proliferation is occasioned by the injuries of the weevil 1s
too obvious to admit of doubt, but it may be of much practical
importance to learn the exact way in which the new growth of tissue
is brought about. The disturbing factor might be either mechanical
or chemical. The new growth may be a direct response to injury of
the weevils in feeding or laying eggs, or it might be stimulated ind1i-
rectly by the secretions of the young larva, or by chemical changes
or decay of the damaged tissue. A second mechanical possibility is
that of pressure developed in the young and rapidly growing bud.
9962—No. 88—05 m——4
5O WEEVIL-RESISTING ADAPTATIONS OF COTTON.
The burrowing of the weevil relieves this pressure at one point, and
may thus furnish the exciting cause of the rapid growth in this direc-
tion of the tissue of the staminal tube. :
It seems not improbable that a relation will be found between the
method of culture and the extent and frequency of proliferation.
Open-field conditions, with much bare ground about the plants, would
increase the daily exposure of heat and dry air, and this would con-
duce to the wilting of the punctured squares, which might then be
expected to flare and fall off instead of remaining to proliferate. The
result of weevil work tn our open-culture plots was obviously differ-
ent from that in the more crowded cotton fields of the Indians. On
the widely separated plants the squares often fell off and permitted
the larvee to develop, as in Texas, except that there was still a distinct
tendency on the part of the larve to attack the pistil and ovary first,
before eating out the pollen.
PROLIFERATION IN OTHER VARIETIES.
Proliferation is by no means confined to the Kekchi cotton, but
probably occurs, occasionally at least, in all the Upland and Sea
Island varieties. A noteworthy Guatemalan Sea Island cotton was
found by Mr. Kinsler in the aldea of San Lucas, a few miles from
Secanquim." Both the buds and the bolls afforded fine examples of
effective proliferation. Even the Egyptian varieties showed a dis-
tinct ability in this direction. In one instance no less than 17 of 23
punctured squares of Jannovitch had proliferated, and 15 cases
seemed to have been effective. |
Proliferation ceases to occur when the bud has become too large.
The anthers are no longer so closely packed together and the tissues
of the staminal tube are too nearly mature. By that time, however,
the style may be sufficiently developed to furnish adequate food.
It is well known, however, that the period of. development of the
weevil larve may be greatly prolonged, and this would seem hkely
in the present instance, since the tissues of the styles must be less
nutritious than the pollen. The delay also would be advantageous,
since it would permit the young boll to become larger.
a@'This variety is peculiar in having about half of each seed covered only with a
very fine, short, bright bluish-green lint. The upper half bears the long white
fiber, and is smooth and black when this has been removed. Some of the
plants had excellent crops of bolls, unusually uniform in size and apparent age,
as though the habit of seasonal flowering were well accentuated. The variety
is evidently perennial and grows to a height of from 6 to 8 feet, but on the
other plants the leaves, flowers, and bolls were much reduced in size. The
plants were all occupied by small black ants. On some of then: no weevils nor
any indications of weevil injury were found, but others only a few rods away
were badly infested,
PROTECTION OF THE BOLLS. 51
But as the power of effective proliferation declines in the larger
buds another factor of protection comes into play. The later the
attack of the weevil the greater is the chance that the bud will mature
and the flower will open and turn the weevil larva out of its quarters
to die. And since buds commonly mature which have been attacked
while still young enough to proliferate, it is easy to understand why
attacks made in the later stages seem to be effective only in excep-
tional instances.
An element of uncertainty often attaches to the enumeration of
weevil injuries because of the difficulty of finding the egg or very
young larve of the weevil in the squares which have been only
recently attacked. This is especially true in small squares where the
anthers are still white and of about the same color, size, and general
appearance as the eggs. The possible error does not, however, mate-
rially affect the result, since it is to be expected that the same propor-
tion of bolls will proliferate and the same percentage of weevil
larve develop as in the squares which are far enough advanced to
show definite results.
PROTECTION OF THE BOLLS.
If it be true, as already intimated, that the original habit of the
weevil was to attack the boll instead of the bud, the opportunity for
the selective development of protective characters of the boll has
been greater. This suggestion seems to accord with the results,
since the boll of the Kekchi cotton has a series of protective characters
even more striking and effective than those of the involucre and the
bud.
PERSISTENCE OF FLOWERS.
As long as the flower remains in place the young boll is thoroughly
protected, the weevils having no means of access except by boring
through the withering tissues, which seems not to be attempted. In
the Kekchi cotton the flower falls only when detached by the swelling
of the young boll. This may also be true of other varieties. (See
PPX.)
The frequent sequel of proliferation in the bud, as noted above, is
the loss of the young boll through lack of pollination. This is espe-
cially true in Guatemala, owing to the tendency of the weevil larve
to eat away the style.. On one occasion Mr. Kinsler collected froma
field of Indian cotton 28 young bolls showing signs of debility. These
measured from 13 to 20 mm. in length, most of them about 15 mm.
None of the smaller bolls showed signs of weevil injury, but in many
of them the ovules were already shriveling up. A few punctures were
found in some of the larger bolls, and in some of these proliferation
had occurred. The development of the weevil larve to maturity
5Y WEEVIL-RESISTING ADAPTATIONS OF COTTON.
seemed unlikely in any case, because the unfertilized ovules were
already withering.
Presumably there are various stages and degrees of fertilization.
Some of the stigmas of proliferated buds seem to have adequate
pollen, so that the bolls can develop normally, while others obtain
none at all or only a little. The persistence of injured flowers is
much greater. They may not fall off at all, and often remain at-
tached by the withered style to the boll when nearly full size.
It thus happens that injured flowers protect their young bolls
longer than the others, but 1 most instances such bolls remain small
or unsymmetrical, presumably as a result of inadequate fertilization.
It is quite possible, however, for normal bolls to develop occasionally
from weevil-infested buds which never open, for the style often
pushes through and becomes fully exposed, so that fertilization by
pollen from another flower might readily take place.
IMMUNITY OF VERY YOUNG BOLLS.
For reasons not yet ascertained, the weevils in Guatemala seldom
or never attacked the very young bolls. This may be due to a con-
servative instinct on the part of the weevil, like that which forbids
the laying of any additional eggs in a bud already parasitized. It
is not impossible, however, that the oil glands with which the sur-
face of the young boll is very thickly beset may have a protective
function. As the boll grows larger the glands do not appear to
increase 1n numbers, but become separated much more widely. On
bolls of the Kekchi cotton the oil glands are usually absent from a
distinct longitudinal band running down the middle of each carpel.
(Pl. VII.) A large proportion of the weevil egg punctures are
made along this naked band, although very few of them take effect.
The wall is thicker here, and the weevil in boring meets the tough
lining of the boll chamber at an angle, and is seldom able to penetrate.
If this interpretation of the facts be correct, the naked band consti-
tutes a veritable weevil trap, a device for inducing the weevil to
make its punctures and lay its eggs in the part of the boll where they
can do no harm.?
To ascribe a protective value to the oil glands is not unreason-
able in view of the fact reported by Messrs. Quaintance and Brues,
a@ Hunter, W. D., and Hinds, W. E., 1905. The Mexican Cotton Boll Weevil,
Bul. 51, Bureau of Entomology, U. S. Department of Agriculture, p. T8.
6 This peculiarity of a glandless longitudinal band in the middle of each
carpel was also noticed in a variety of cotton cultivated by the Moqui Indians
of Arizona, grown in 1904, in the Department’s plant-breeding experimental
field at Terrell, Tex. The Moqui cotton is interesting also by reason of its
short, squarish, distinctly apiculate bolls. more like some of the Old World
cottons than are those of other members of the Upland series.
IMMUNITY OF VERY YOUNG BOLLS. 53
that the Egyptian cotton, the bolls of which are excessively oily, is
on this account immune from the bollworm.” The oil contained in
the glands-has a deep-brown color, a sticky, molasses-like consistence,
a disagreeable, pungent odor, and a sharp, resinous taste, suggesting
turpentine or Canada balsam.
The development of the oil glands seems to be especially great in
the Egyptian variety known as Mit Afifi, and the glands are more
superficial. By slight pressure, or by drawing the nail across the sur-
face, the oily liquid is freely obtained. Most of the Upland varieties
have the oil glands much more scattering and deep set than the EKgyp-
tian sorts, and it is not possible to squeeze the resin out of them in
any such manner.
On Redshank and other Upland types the resin glands are marked
by shght superficial depressions, but a cross section shows them to be
well below the surface, with several layers of chlorophyll-bearing
cells between. On the Egyptian sorts the glands are also set in de-
pressions, but the gland itself is very close to the surface, and makes
the bottom of the depression again convex, the superficial layer of
cells being very thin. It seems to break spontaneously in some in-
stances; at least there are frequently small spots of hardened resin,
and very shght pressure brings out the dark, gummy fluid. The
fingers receive a permanent brownish stain, which with the acrid,
biting sensation experienced when the liquid is applied to the tongue,
increases the probability that substances of a definitely protective
character are present. It is well known that many of the aromatic
oils are for some reason highly distasteful or even fatal to many
insects.
The Sea Island and Kidney cottons have the oil glands conspicu-
ously developed, like the Egyptian varieties, but the Old World
cotton (Gossypium herbaceum) is in this, as well as in other respects,
more nearly related to the American Upland cotton (Gossypium hir-
sutum). The Aidin (Asia Minor) variety of Gossypium herbaceum
has the oil glands rather small and deep set, with the superficial pits
rather shallow, more so than the Ceylon or Korean types.
Even the petals of the Guatemalan Kidney cotton found at Trece
Aguas” contained oil glands. The color of the petals was a uniform
pale yellow, without purple spots on the inside, but in the upper
a@Quaintance, A. L., and Brues, C. T., 1905. The Cotton Bollworm, Bul. 50,
Bureau of Entomology, U. S. Department of Agriculture, p. 71.
+The Kidney cotton at Trece Aguas is called paiyi, and seems to have little or
no relation in the minds of the Indians with the dwarf Upland cotton, which is
called nok. In the Secanquim district, only a few miles away, this name paiyi
(pronounced like the English words pie ye) is not recognized. Kidney cotton,
though apparently not now planted by the Indians, is not entirely unknown to
them. They call it simply che nok, or tree cotton.
54 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
half specked with minute brown glandular dots. The oil glands of
the bolls of this Kidney cotton are apparently quite as strongly devel-
oped as in the Egyptian varieties, or even more so. They are distrib-
uted very irregularly over the surface, and are not lacking above the
dissepiments, along the middle of the carpels. The position and
structure of the glands seem also to be the same as in the Egyptian
cottons. They are close to the surface and show as distinct black
spots, there being no green tissues over them as in the Upland and
herbaceum types.
I am indebted to Mr. Guy N. Collins for the suggestion that the
present inefficiency of the oil glands as a means of protecting the
cotton from the boll weevil furnishes no argument against the
adaptation of the glands nor their development through the selective
agencies of the boll weevil itself. This fact is sufficiently obvious
when once stated, but it 1s not commonly taken into account in con-
sidering questions of this kind. We may be sure that the gradual
development of a protective character like the oil gland would carry
with it a corresponding increase in the power of the weevil to avoid
or to endure the injury. The ultimate value of the device would de-
pend on whether the glands were able to keep ahead of the weevils
in quantity and distastefulness. The readiness with which the boll
weevils attack the Egyptian cotton renders it obvious that oil 1s now
no adequate protection, but the preference of the weevils for the un-
protected strips of the bolls of the Kekchi cotton indicates that the
weevils still dislike the oil, though they may have foiled the attempt
of the plant to protect itself in this way.
There are two attendant facts which under certain circumstances
might readily obscure the immunity of the young bolls. Many such
small bolls fall off, a particularly large number it seemed from our
row of Parker cotton, but an examination of these failed to show
anything in the way of weevil injuries, except such as had been in-
flicted while the bud or flower was still in place, the style and a
small apical cavity having been eaten away in numerous instances.
Many small bolls were to all appearances quite uninjured. They
may have been rejected by the plant as supernumerary, the plant
being unable to furnish the food material needed to bring them to
maturity, or they may have failed of fertilization as a result of
weevil injuries to the bud or from other causes, such as the absence
of bees, which were extremely scarce in the Guatemalan cotton fields.
The frequency with which the boll weevils were found inside the
a'The flowers of the Kekchi cotton are pure creamy white when young and as
long as they remain open. When old and rolled together they become a pinkish
red. They are not yellow or bluish at any stage. The stamens and pistils are
also nearly white, the latter with rows of oil glands showing as small grayish
dots.
RAPID GROWTH OF YOUNG BOLLS. 55
cotton flowers and well dusted over with pollen suggests the possi-
bility that in this district at least they were a not unimportant
agency of cross-fertilization. The performance of such a service by
the boll weevil would be comparable to the famous case of the yucca
and its moth, the plant being dependent for cross-fertilization upon
its insect parasite. The weevils eat the pollen from the bud; that
they visit the flowers for the same purpose seems highly probable.
The investigations of Messrs. Hunter and Hinds have shown, indeed,
that a pollen diet is a necessity for the complete sexual maturity and
reproduction of the weevils; if without buds to feed upon they
seldom copulated and never laid eggs."
RAPID GROWTH OF YOUNG BOLLS.
Mr. John H. Kinsler, who gave careful attention to the earher
stages of the Guatemalan experiment, gained an impression that the
young bolls of the Kekchi cotton imereased in size with a rapidity
distinctly greater than that of the United States Upland varieties
planted alongside. It was not practicable to establish the fact by
carrying out a series of daily measurements, though it was possible
to ascertain from dated tags used in connection with the hybridiza-
tion experiments that the Kekchi cotton can grow bolls to full
size in less than a month from the time the flower opens. Plate LX,
figure 2, shows on the right two bolls of Kekchi cotton less than a
month from flowering. On the left are the two largest bolls from an
adjoining plant of King, the seed of both varieties having been sown
the same day.
Such an acceleration of the growth would be of very obvious utility
in lessening the period in which the danger of infestation is greatest.
A large proportion of the weevils found in adult bolls of Kekchi cot-
ton were in “locks” or compartments of diminutive size, showing
that the infestation had taken place while the boll was less than half
grown. Indeed, the weevils seldom seem to be able to affect lodg-
ment in bolls more than half grown, although numerous attempts
are made in fields where the weevils are numerous. The following
field note describes such an instance:
A boll showing many external marks of weevil punctures was found on being
cut up with care to have been attacked at least fourteen times. In five cases
the outer wall seemed not to have been penetrated, but in nine others there had
been complete perforations. All of these had been closed, however, ‘by prolifer-
ation from the inner surface, and no living larvze were found.
Such persistent attacks, however, may finally induce a diseased
condition which interferes with the normal growth of the boll, even
@ Hunter, W. D., and Hinds, W. E., 1905. The Mexican Cotton Boll Weevil,
sul. 51, Bureau of Entomology, U. S. Department of Agriculture, p. 113.
56 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
though the weevils be successfully resisted. Such injured bolls often
show a brownish discoloration of the interior tissues near the base
and connecting with the nectaries, which may indicate a bacterial
disease, to be discussed later. Sometimes this affects the walls only,
sometimes one or more seeds and the surrounding lint.
THICK-WALLED BOLLS.
In the Kekchi cotton there are considerable variations in the thick-
ness of the outer wall of the boll. Not infrequently the wall equals
or exceeds the length of a weevil’s snout, so that only the largest or
iongest snouted weevils would be able to make an opening into the
interior cavity. It was noted, also, that on the inside such bolls are
often quite free from these injuries or small larvee, though numerous
attempts may have been made. Large larve or pups may be found,
but these have come, obviously, from eggs laid while the boll was still
young. On some plants the development of large thick walls takes
place very promptly, so that a protective character of considerable
value might be obtained if this feature could be increased and ren-
dered constant. Early development of the thick walls was indicated
by the fact that the young seeds and hnt did not fill the cavity, and
the seeds were still far from mature. Instances might be drawn
from other plants where the growth of the pod or seed vessels far
outruns the seeds at first, so that the development of such a character
in cotton might reasonably be expected.
Even when a wall thicker than usual has been bored through, the
ego must be laid on the outside of the mass of lint which still inter-
venes between it and the young seed, so that the larva’s chances of
development are greatly lessened. As will be shown later in the dis-
cussion of proliferation in the bolls, the instances are very numerous
in which, although the wall is penetrated, no further damage results;
either the egg is not laid or the development of the larva is pre-
vented by proliferation. In any event the boll escapes further
injury, and it is a very significant fact that in the dissection of a large
number of such bolls of Kekchi cotton scarcely any young larve
were found, in spite of the fact that most of them had been punctured
not once only, but many times.
TOUGH LININGS OF CHAMBERS OF BOLLS.
The three, four, or five chambers which contain the locks of cotton
in the unopened boll have each a complete membranous lining. In
the Kekchi cotton, at least, this is extremely tough and parchment-
like, even in bolls not yet full grown and in which the seeds are not
yet fully formed. This membrane is readily separable from the
more fleshy external layers of the boll, and though flexible, it is very
TOUGH LININGS OF CHAMBERS OF BOLLS. 57
firm. and incompressible, and resists tearing unless consicerable
strength be exerted.
A large percentage of attempted punctures of the larger bolls
failed because the weevils are unable to penetrate this protective lin-
ing. This fact is readily determined by the study of radial sections
of the outer wall through the warts which mark the weevils’ points
of attack. The different texture of the new tissue which has closed the
wound shows, usually, that the cavity eaten out by the weevil extended
down to the tough basal lining, even when no evidence of the injury
has become apparent on the inside. In other instances, also very fre-
quent, the new tissue, developed as a result of the irritation of the
attempted puncture, exceeds the cavity and causes an inward swelling
or prominence of the inner lining analogous to the projecting warts
which are the usual external indication of weevil punctures.
It occasionally happens, too, that the projection of the new tissue
occurs almost entirely in the inside, the external wart being very
shghtly developed or not at all, though the new tissue and the inner
swelling show that a puncture had been attempted.
The utility of this lining as a means of excluding the boll weevil
seems not to have been considered heretofore, and there has been no
opportunity as yet to compare the Kekchi cotton with other varieties
with regard tothis feature.*. Certain it is, however, that in the Kekchi
cotton the parchment lining is almost as firm and tough as that which
surrounds an adult coffee seed. And it is certain, also, that a very
large proportion of the attempted punctures of the bolls failed to
bore through this inner wall of defense.
The examination of a large number of bolls, which were full size or
nearly so, though still far from maturity, in most cases failed to find
more than a very few instances, if any, of very recent perforation,
though there were large numbers of instances where the weevils had
gnawed their way down through the parchment and deposited an
egg. In many such cases the proliferation or new growth induced by
the injury causes the parchment to be raised up from the wall on the
mside to form a blister-hke, rounded protuberance. (PI. VIII.)
Eggs laid outside the parchment are firmly embedded in the new
a Since this was written Mr. McLachlan has reported the existence of the same
form of protection in Upland varieties in Texas. The following note describes
the results of injuries inflicted upon the bolls of a plant of Parker cotton in four
days from August 8 to August 12, 1905:
“The 9 larger bolls, when opened, were found to have 28 weevil eggs deposited
in them; 6 had struck the dissepiment ; 12 were not entirely through the shuck of
the boll (either not more than half way there or else stuck in the tough inner tis-
sue of the shuck) ; the others were embedded in the lint. In only two instances
was there any proliferation apparent. The outer shuck had proliferated at the
wound and in one case had encysted the egg. The other had merely forced the
egg to one side, having begun the development too late.”
5S WEEVIL-RESISTING ADAPTATIONS OF COTTON.
growth and do not appear to hatch, or if they do the larve are not
able to do any damage, since they can not penetrate into the interior
of the boll. It quite frequently happens that eggs are laid in the
sinus or groove between the linings of two locks, but without penetrat-
ing the parchment of either. The tissue is here somewhat looser
than in other parts of the wall. In a few instances it was observed
that the larve had hatched, but no case was found which indicated
that larve hatched outside the parchment lining had been able to
penetrate to the interior cavity.
PROLIFERATION FROM THE WALL OF THE BOLL.
The wall of the boll offers an active form of weevil resistance by
proliferation, in a manner somewhat analogous to that of the pro-
hferation of the square. The channel excavated by the weevil is
closed by the new growth, which continues to push out on the mner
surface of the wall in the form of a rounded, blister-lke protuber-
ance of loose tissue. This surrounds and encysts the weevil egg, and
prevents its development.
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Bul. 88, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE VIII.
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CARPELS OF KEKCHI COTTON, SHOWING PROLIFERATION.
(Natural size.)
——EE———————— - — ee ee ee ee
PLATE |X.
Bul. 88, Bureau of Plant Industry, U. S. Dept. of Agriculture.
FiG. 1.—KEKCHI COTTON, SUCCESSIVE STAGES OF Fic. 2.—KEKCH! COTTON BOLLS (RIGHT) COMPARED
THE BOLL. WITH KING BOLLS (LEFT).
(Reduced. ) (Reduced. )
PLATE X.
. S. Dept. of Agriculture.
U
Bureau of Plant Industry,
ul. 88,
B
FiGand.
—RABINAL COTTON
(Reduced. )
WITH BOLLS.
Fia, 2.—BOLLS AND SEEDS OF KIDNEY COTTON,
(Reduced. )
: Page.
EA bASikcOtOn HarinorOl: SQUALCS => += = Seen eee a ek ee eos 40
Nea cinacyinil OUlCiS PCCM Za bION 2 17
Colee branches compared. with cotton = = 950-2. 2. Sas eee see oe ee 19
Coldmetiectionttropicaléyaricticsi =. 220-22 5. en eee 18
AVC Oil Sie chee apie nene 2e POG She RA eae gle Me at LT 2s
Collinge GeeNereOOsSehyallOne . sass ee OTe te ae ee 54
WonsclOlciseleGit Ole seta a ee se ee Te es 70
Corn, effect of changed conditions..... ..... Bae ey Soa akc SSE ae ec 18
Cotton-aphis.iniestimecottom=. = 2424/0. 225222. 222 Ree ee re Be SE 2 39
PLOGMEMOUsRpLOOAble-extension: 12.225 122.2 tacos see ot ce ee 44
SOT soasOmMavGlellCa pen tetera et ean eee oe 2e An?
SHiMmmlncee iene wa CONGUMONG* tv: {ks eee Say ee eh iL
Crocs-ienimuizapion-aided: by boll. weevils: 22-53 25) oe 5d
CiiechOlmsimilltaneous;blossomine 2.2252 =) 2. Pees. 23
SECURE Cet kOuoinen eClaberens- aes. oo. cae yee Se ee 29
COU DE TODAS SOUL ODI GS we en 8 a a me 23
Calture of cotton, methods, in eastern Guatemala...........-...-.-.---2---- 19
Onezacine:slopevor Guatemala: — 2222-55242 sos: 70
IN (OSI) es 2 pe pes a Se SES ae 45
Weterminaewmnowoool Kekchi cottons ...-...2.-.-2.. 22 5.- o.oo ce ee cee bee e ila
habit, disadvantages of early planting avoided....._-- IRS Sete 14
prmanrvebranchestatactor 2%. sso: seek ee ee 20
Dp miretalnlemptane@niecs shia oa te Re ee ee ee eee 19
Dry climate, region, etc. See Arid.
Dwakecononeeciecmon cultural methodses:—*: 2-02 -. 8 se. 19
ina ope eK Chine OLbOT ete a oe ree ee AS Pe orien he ee 11
Harliness, effect of development of primary branches _.....-......2--.-2--.- 20
GS LUTINEVAN CRC OMG O TA Gee es oe em ne ann eng Sp 2 ae SUE aes IRS
MOWSUOWMaD Ve Gate Ol hOWeTiNe. eis stan ee eee yet ene 13
Rani bearins -tacilitated: by long lasal branches. =2s-...22-.5-2.<.--2_...--- ig)
TDUHAN GHEY ACUTE NGA EOS. ok A ee a ae ie at eS a 14
9962—No. 88—05 m
82 WEEVIL-RESISTING ADAPTATIONS OF COTTON.
Marly, planting, Wdiscussiomys 9-356 ecser eee PO es ee eee ei 1133
essential simrcoutlmermyl excise es es en eee SON! ci hae 2
Kee puncbure| sealed by, svelte are ee eee eee 61
Eoes of boll-weevils, encystation’ 2°22 2.01) 2 oye ayer 58, 61
Eeyptian cottons, immunity from: bollwerm (2.2251. 0s sss 3 see 53
involueral bracts =<. 225.20. ce =i he ee ee Ey FSS Bil
less-hairy than Uppland wanieties== 2 == =e eee 25
not TmamuMe toy WollE wee valle pease oe eae eee 42
Ol glade: eee eee eee Ce. See a ae Z By)
of American OTieins of 333.6055 ee 9
Precocious nl Gia terme se sae sere = ee 17
prelerenceé 70h Weevils sa eee ee ee On
proliferatione ihe gn Sone eee ee ee ee ee 50
Susceptrbilibys to simi Uy ee ae sees Sees ok renee ee 42
Environment not actuating cause of evolutionary change.................--- 68
Evolution, illustration of influence of natural selection ................-...-. i
Hvolutionary origin ovextermaly mectanies ses sere ee ee 31
Fertilization), Gis @ uss ispecies sega ge eee genet ees eee ee 52
PLEVEN CLOIWycPa see ee oe: Rea stereo 21
Field cultures, failure in plateau region of Guatemala ...................-.-- 25
Flower bud) positron fe cee oe caterers ape a nr gee 20
Flowering: periods short)! 2222 =e e2 savin pte ia ve MOEA yticega i Ne Den an oe ee A 23
Blow ers, tarluresof pollination sss 3 yc ke se eee ee 51
kelepsimnaprisomed sie eee eas Sas ORR era t,o See ease 29
OL Kekebixcottonss color a0 sales ee eee cele | eee ae eae 54
Kidney cotton, Colorgsa aan Digan das Sees Sit ee ears 53
opening, elle ctr om lar vce sisters ote eee te ee mene ee 47, 68
POLSISCEM CO eR ees es een al ae gee 51
POSIELON: Foe ee ee EG Se ee eels a eee eae AEE oes 7
Foliagecompact, ertect Onekeleps tay se eee ree i eae ee 26
Food, change, advantage to plants and animals...-.--- oe RSIS EE Sine ees 26
Puneierowth in meetaries: = Sasa eee ares rel eee 30
Germination, cottonseed am Guatemala yes ore 6 ee a ee 15
Gossypium (DGrDACeEMmSe™ ONS IN ier see eee eee 8
herbaceum: Asia Minor varieties... sa. Sas oe 53
COMMUSIOMS WAC IG. VeeSUl UT ie 9
MECtATICS «oo Rape ee na ol
penuvianum, Specie validity eae se ere ee re eee 67
Growth, alternating periods umstropical plants -ses senses se eee 23°
utility of acceleration ss cc cpees Se pene, seme ate epee ere are a ae 5d
Guatemala, central plateau...........------ Feats Bs eee Ee. cake ee 24
eastern. climate: soo Goa 2 ee Se Oo ee cee ee tag See 12
methodsiof.cottonieulitwre ss eco eee 19, 70
nature: or the: country <2 ectaa is ae an oe ee ee 15
field experiments 22 Sse eee eee ee eee ee 34
Importation Olctorergn threads. 2 ee =e eee 24
Indianimethods otcultivations 4.2. «52. 32a ee 12
western, cotton. soles) oe fs nee ooo ee ee ee eee 25, 70
Guatemalan conditions, effect on United States varieties -..........-..------ LZ.
cottons, preference of Keleps) 22.) ---- a=. een ee ee eee 25
Hairs, cotton, plant; assistance to kelepse: aes =¢e 5 aes ee eae 25
Hainy Guatemalan varieties of: cottoms 22e a oe 2 as ree 25
stalks and leat‘stemis) of Cotton: yaks oo ar eee st 25
Heredity, mechanism 225 2022 2 sso55 5c aa eee ee eee 68
Hibiscus; involucral appendages of Species\= yp .e erie ee eee 30
nectaries:of species. se2.% CNS. occ Bae Soe eee Bu
species not attractive’ to boll weevils sss 5 soe eee 69
Hinds; \W ES Observia tome tose oes ae ery ae nee 25, 42, 438, 44, 55, 61, 62, 64
Howard, ..0:, observations’. 2" 2520-2 sek as oo a ee ee 45
Humid districts, behavior of cotton....._.-.- i LORE. wie oh.s Saari ei ape 43, 44
Hunter, iW. D= observations. sees ae ee ees 14, 25, 42, 43, 44, 48, 55, 61, 64, 76
Immunity of peas and bolls, periods. ee Se Sues 2 eae, ee ane 74, 75
Inbreeding of cotton ‘by Indians2. 222. 125. Pe ee 15
13
Indeterminate varieties unsuited to early destruction of plants......-..------
INDEX. Se
Page.
Indian methods of cotton culture .........-- pL ra ee er a ae ee ec 1 Be
TEE TIES OTE BON ONG a a ea eee a ee ae 53, 70
Prchiancsaehicni tural na pitcs eae oat a ee ee Te SS 11, 15, 35, 48
CGiCO Ne CULE NE oe ery eee nt ee een Set RE A ie Soa feb
SulinvablOnlOr DED DEES etn a Se eee arene eS ee se a's se SaaS ae 11
Customs abehabimalb: Guatemalac 2 5 eee es eo lo ee Sk 24
FORMEAG ON: OF MEMEVALLChIC Gan. = aries sessees== eee 71
in) simultaneous tloweriney se - 19s see oe ee 23
not actuating cause of evolutionary change -..-.----------- 68
the explanation of adaptations .siese&. ose ee see ere een ees 68
Nectar, continued secretion by plants. -42 525s =o ee eee ane 32
PUYDOSE: Sse eco Sisia Ws te rcithle ci eee ace 28
secretion im KekechiiandeU pland) cottons se ee eee on
on bolls: 232. 222 oe ns ae Se 30
INectaries; external, discussion: