G08 U. S. DEPARTMENT OF AGRICULTURE. BUREAU OF PLANT INDUSTRY— BULLETIN NO. 88. B. T. GALLOWAY, Chief of Bureau. WEEVIL-RESISTING ADAPTATIONS OF THE COTTON PLANT. O. F. COOK, BiONOMiST IN Charge of Investigations in the Agricultural Economy of Tropical and Subtropical Plants. Issued Janttaey lo, 190t>. WASHINGTON: government printing office. 1906. J Book— 1^ € $ 76 S^l^ Bui. 88, Bureau of Plant Industry, U. S. Dept. of Agriculture. Plate I. U. S. DEPARTMENT OF AGRICULTURE. BUREAU OF PLANT INDUSTRY— BULLETIN NO. 88. B. T. GALLOWAY, Chiif i,f Bureau. WEEVIL-RESISTING ADAPTATIONS OF THE COTTON PLANT. O.^F. tOOK, BiONOMiST IN Charge of Investigations in the Agricultural Economy of Tropical and Subtropical Plants. Issued January 13, 1906. WASHINGTON: GOVERNMENT PRINTING OFFICE. liM)6. eff V •:•; :: BUREAU OF PLANT INDUSTRY. B. T. GALLOWAY, Pathologist and Physiologist, and Chief of Bureau. VEGETABLE PATHOLOGICAL AND PHYSIOLOGICAL INVESTIGATIONS. Albert F. Woods, 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. Ja.mes E. Jones, Chief Clerk. INVESTIGATIONS IN THE AGRICULTURAL ECONOMY OF TROPICAL AND SUBTROPICAL PLANTS. SCIENTIFIC STAFF. j f(yi O lyUf o. F. Cook, Bionomist in Charge. G. N. Collins, Assistant Botanist. F. L. Lewton, Scientific A.isistant. H. Pittier, Special Agent. D.ofD. LETTER OF TRANSMITTAL U. S. Department of Agriculture, Bureau of Plant Industry, 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 Phmt," and to reconniiend it for pnblication as Bulletin No. 88 of this Bureau. This report has been prepared by Mr. O. F. Cook, biononiist in charge of investiga- tions in the agricultural economy of tropical and subtropical plants. It 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 i^roblem. 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 100"2, and it was hoped that the innnunity 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 Deculiar cliaracter of which the com- mercial value of the crop depends, appears to find its chief use to the plant in excluding the weevil larvse 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 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 Avhich 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. Galloway, Chief of Bureau. Hon. James Wilson, Secretary of Agriculture. CONTENTS Page. Introduction . 7 Selective iniinence of the boll weevil 10 General protective characters 11 Dwarf habit and determinate growth of Kekchi cotton 11 Variations in the Kekchi cotton 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 Early rejection of superfluous squares 20 Seasonal bearing of perennial varieties 23 Annual cutting back of perennial varieties 24 Hairy stalks and leaf stems . 25 Pendent bolls 27 Extrafloral nectaries . 28 Nectaries of the leaves 30 External nectaries of the involucre . 31 Inner nectaries of the involucre . 31 Nectaries of Guatemalan Sea Island cotton 32 Continued secretion of nectar 32 Brac'tlets subtending inner nectaries 33 Efficiency of the kelep protection 34 Other nectar-bearing plants visited by the keleps 36 The involucre as a protective structure 37 Involucral bracts grown together 37 Appressed margins of bracts _._..-. 38 Large involucres of Kekchi cotton 39 Opening, or flaring, of bracts avoided 40 Hairy margins of involucral bracts . 41 Extent of protection by involucre . . : . . . 41 Advantage of open involucres 42 Behavior of parasitized buds 43 Shedding of weevil-infested squares ... 43 Cotmtings of flared and fallen squares 45 Prolifc ration of internal tissues of buds 46 Causes and conditions of bud proliferation 49 Proliferation in other varieties 50 Protection of the bolls 51 Persistence of flowers 51 Immunity of very yovmg bolls 52 Rapid growth of young bolls . 55 Thick- walled bolls . 56 Tough linings of chambers of bolls 56 5 6 CONTENTS. Protection of the bolls — Continued. Page. Proliferation from the wall of the boll 58- Time required for proliferation 60 Efficiency of adaptive characters of bolls 61 Bacterial diseases following weevil injuries 62 Breeding in buds a derived habit 62 Relation between proliferation in buds and in bolls 64 Protection of seeds by lint . . 65 Protective seed arrangement in Kidney cotton 66 Cultural value of Kidney cotton 67 The nature and causes of adaptations 67 Conscious and imconscions selection 70 Summary of adaptations 73 Classification of adaptations 72 Adaptive characters of different types of cotton 73 Concluding remarks 74 Description of plates 78 Index 79 ILLUSTRATIONS Plate I. Valley at Secanqnim. 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 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 jorolif eration 78 VII. Weevil-infested bolls of Kekchi cotton 78 VIII. Carpels of Kekchi cotton, showing proliferation 78 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 _ _ . 78 B. r. I. — ISO. 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- niity 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 ditferent 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. Wliether 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 w^eevil-resisting variety of cotton. It had been observed a Cotton Culture in Guatemala. Yearhook of the Ignited States Department of Agriculture for 1904, 475-488 ; Science, N. S., 20 : GG6-G70. November 18. 1904. 8 WEEVIL-RESISTING ADAPTATIONS OF COTTON. two years before that a field of chvarf cotton cultivated by the Indians did not suffer from the boll weevils, though these pests were abundant on a " tree cotton " a short distance away. The kelep afforded an entirely unexpected and yet very striking explanation of the fact that cotton was being grown as a regular field crop in a region which had probably been infested with weevils for many centuries, if it were not, indeed, the original home of the species. That there Avas an insect in existence specially qualified by structure and habits to attack, disable, and devour the boll weevil, was Avelcome news in the United States, and in accordance with cabled instructions from the Secretary of Agriculture numerous colonies of the keleps Avere 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 residts 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 minimum. The Guatemalan cotton protected by the keleps is a genuine Ujd- 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 Kckchi^ represents a very distinct type of this important cultivated plant. It belongs to Gossypium hirsutinn, the Upland species or series of varieties, in the sense that it is not a Sea Island, Egyptian, or Kidney cotton,"' but it is 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 o The Sea Island cotton is so called because cotton of this type is cultivated on the Sea Islands of South Carolina, lonjj famous for the excellence of their product. The Sea Island cotton came origlnall.\' from Barbados, whence also its botanical name, Gossypium barbadensc. 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 Linnjeus 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. (PL ILfig. 1.) Although cotton was not found to be planted as a regular field cul- ture in any localities in (juateniala where the keleps do not exist, small quantities are produced in the interior plateau region about Ivabinal 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 t-tudy of the question, but it shows at least that the weevil problem has many avenues of approach on the botanical side. The cotton of (ruatemala 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 allies, 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 Aveevils which is now so serious a menace to the cotton industry of the United States. 'Some of these Aveevil-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 ^i laboratory for this class of experiments. Texas Avas 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 Avhich nature has forged. The present report was planned and partly written before the dis- covery of the true nature of the best of the Aveevil-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 Aveevil has subjected the Central American varieties of the cotton plant. have erroneously confused it with tlie Old World species Go^syplum herhaccnm, wbifh 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 conmiercial scale, but they are very widely distrilmted in tropical America. The name refers to the fact that the seeds rf each comi)artment of the boll are grown together into a small comjiact mass, in shape suggesting a kidney. 10 WEEVIL-KESISTING ADAPTATIONS OF COTTON. SELECTIVE INFLUENCE OF THE BOLL WEEVIL. The boll \A'eevil exerts a most prejudicial eliect 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 larvae 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 shoAvs 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 if the selection were consciously carried on by the planter or the plant breeder. The case is different from that of the recent improvements of man^^ 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 larvae often developing even better when the buds fall off and lie 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, 11 It is now known that in the plateau region of jMexico the long dry season eli'ectnall}' excludes the weevil, so that varieties of cotton from the Mexican highlands, instead of being weevil-proof, as sometimes represented, may have no immmiity whatever Avhen 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 Ignited 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 l)e the biological and agricultural history of the cotton plant in Central America. GENERAL PROTECTIVE CHARACTERS. DWARF HABIT AND DETERMINATE GROWTH OF KEKCHT 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 Ignited 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 approaching 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 ncA-er come to maturit}^ 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-RESISTfXG ADAPTATIONS OF COTTON. as soon as the Kokclii, but they show far less tendency to determinate growth. The development of earliness has been assisted, no doubt, b}' the (?limatic 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 Uie roots, during the rainy season. Seeds scattered accidentally in the plantation at harvest time are rotted by the rain and do not germi- nate, so that little or no volunteer cotton is carried over from one season to another. If the Kekchi cotton Avere the onl}' 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 oi!' between April or May, M'hen the cotton is pulled up, and October, when the next crop is planted. There is, however, enough perennial '' tree "" cotton in the countrj^ to keep the pest from becoming exterminated. ^loreover-, 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 hardl}^ 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, Avhere the cotton could survive the winter, the destruction of the plants as soon as possible after the maturing of the crop Avas the only measure calculated to seriously reduce the number of weevils. It w^as also essential to plant cotton as early as possible in the spring to aA'oid the Aveevils bred on the volunteer, or hold-over, cotton Avhich 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, Avhere the cold comes earlier and the temperature remains loAver throughout the winter, it may often happen that there will be no period in Avhich the weevils can l)e reduced by starvation, unless time can be secured for this purpose in the spring by the i^lant- ins: of short-season varieties of cotton. a Cook, O. F., 1905. Progress iu the fotuuy of the Kelep, Science, N. S., 21 : 552. PROTECTIVE CHARACTERS OF KEKCHI COTTON. 13 Instead of colder winters being unfavorable to the Aveevils, there is every probability that cold sufficient to keep them in a torpid, inactive condition will jDreserve 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 tlie boll AA-eevil 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 suH'ered 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 a few weeks later, would be large enough to furnish the Aveevils 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 Avould seem to be little object in planting cotton Avhere the weevils are as abundant as in some places in southern Texas in the spring of the present year, 1005. Xevertheless, the opportune occurrence 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 14 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 Avinter had favored the survival of many weevils, planting could well be deferred 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 tlie etfects of applying Paris green to the very young cotton as a means of destroying the weevils Avhich had lived through the winter. Numerous dead weevils were found in the poisoned fields, but equal or even greater numbers were found in those to Avhich no Paris green had been applied, and the conclusion Avas 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 or 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 Avarm Aveather while they are going actively about, so that it is the autumn and spring which must be relied upon to reduce the numbers of the weevils rather than the cold periods of the Avinter months. Messrs. Hunter and Hinds haA'e also noted as significant the fact that of AveeA'ils captured at the middle of Decem- ber, 15.8 per cent passed the Avinter successfully, Avhile of another lot captured a month earlier, only 1 per cent survived. Their conclu- sions were as folloAA^s: It is evident that the \A'eevils wliicli pass tlie 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 "A 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. 6 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 IX KEKCHI COTTON. 15 quick-miituring varieties of cotton from tropical countries on the ground that cold weather will exclude them from the United States. The early spring is the only time in which they will be likely 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 Avinter months in mountain valleys where tempera- tures of between 40° and ()0° F. are not infrequent. (PI. I.) VARIATIONS IN THE KEKCHI COTTON. Very great diversity of size, habit of groAvth, 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 II. figure 1, might have cultural, disadvantages if these tendencies were to be maintained in regular field cultures. Such, however, is not likel}^ to be the case. AVlien growing closer together the plants are more upright and less leafy below. To wdiat 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, wliich might well conduce to the formation of separate strains. The low germinating power of the seed may pos- sibly be due to such inbi-eeding, though it is more likely that it deteri- orates because of the humidity of the climate.'' Xevertheless, 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. & 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 ?>0 bolls. At Rabinal from fi to 10 plants in a cluster is the rule, the product of the individual being still further reduced. 16 WEEVIL-RESISTING ADAPTATIONS OF COTTON. differences, sufficient to liave a very practical bearing upon tlie ques- tion of securing strains having the special characters required in the United States. Indeed, there was nearly as much diversity anions 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 ncAV 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, Avhile 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 Avide diversity of mutational charac- ters may be exj^ected when once the varietv has been brought under careful observation. The stems and petioles of the Kekchi cotton plant are dark red, or at least spotted Avith red. and the leaves turn dull red Avith matu- rity. The bracts and bolls are green Avhen young, but Avith age and exposure to the sun become more or less tinged or spotted Avith reel." The outer iuA'olucral nectaries also turn deep red, especially the tAvo upper ones, eA'en Avhile the buds are still A-^ery young. The great majority of the leaA'es are simply three-pointed, but*many of them liaA'e an additional smaller lateral point on each side near the base. a One plant at Secanquim showed a Aery decided instance of A-ariegation A\-ith white and red. though the latter color might haA-e been due to an increased tendency of the AAhite portions to take the red discoloration common on normal leaA-es. The lower branches of the plant show only normal green coloration, and a part of the upi)er branches is also normal in color and size, and \Aith fruits rather above the aAerage size. The A-ariegated branches do not regu- larly alternate, nor do they come all from one side, but they might still haA'e connection with the phyllotaxy. There seem to be two stages of the A'ariega- tion, a white and a light greenish-yellow; the latter may belong only to young leaA-es. Both are distributed with the utmost irregularity, and both may affect the upper surface of the leaf while the under surface remains green, or A'ice A'ersa, though the latter condition is much less common than the former. The etiolated portions of the leaA'es. InA-olucres, 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 A-ariegation is slight this result may be apjiarent, or if It be complete the symmetry is not affected. Except for two premature bolls the seed was not ripe, and these AA'ere from the nor- mal lower part of the plant. ACCLIMATIZATION OF KEKCHI COTTON. 17 KI'I'Kl TS OF (;l ATKM AI.AA COX DITION.S ON I'NITEI) STATES VARIP:T1ES. The behavior of the United States varieties under changed climatic conditions in (rnateniahi 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 np into a variety of types, many of which wonld 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 ])lants of the normal type, and seemed likely to be more i)rodnctive. but only a few bolls developed, and these [)roved to be of abnormal form, with deep grooves or notches across the ti]). One of the features in which the change of climate seems to pro- duce remarkable eft'ects 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,'^ Avhich 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 floAvering 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 OK KEKCHI COTTON IN THE UNITED STATES. It was not unexpected that the Kekchi 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 Avithout shoAving the slightest tendency to produce fruit or even floAvers. In lOO-t cotton from Peru planted at Victoria, Tex., grew most Aagoro.isly to a height of 18 feet, but remained quite sterile. It is possible, hoAvcA-er, that even in their oAvn country these Avere Avhat are called " tree cottons," Avhich usually groAv to considerable size before beginning to floAver. Letters from Mr. Kinsler, in charge of our exi)erimenta] plot at Pierce, Tex., relate a similar behaAaor on the part of the Kekchi cotton, Avhich at that place has groAA^n large and rank; but toward the end of July it Avas 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 ncAv conditions, and per- mit a return to the normal earliness of the variety. Similar results 9962— No. 88—05 m 2. 18 wep:vil-reststing adaptations of cotton. have attended the introduction into Texas of Mexican varieties of corn. The phmts grew 1 ! feet higli the first year and bore very littk; seed; in the foUowing 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 indicated by the results of an experiment at Lanham, Md. (1905). In favorable sea- sons cotton can be grown to maturity as far north as AVashington, but the present year has been very unfavorable, the suunner 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- eign 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 ditfereuces between individual plants. Tw^o plants in particular were found to have numerous buds, some ready to blossom before any of the others had begini 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 w'hen 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, to do appreciable damage to cotton in 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 foliage. Many annual plants, even those of tropical origin, are most vigor- ous and productive at their northern limits of growth, not, as has l)een supposed, because this is the coldest part of their range, but l)ecause the heat and sunlight, necessary to plant growth, are greater during our summer months than can be secured in a sinular time in the Tropics, owing to the nuich longer days of our northern latitudes." The Pachon cotton from western Guatemala, though it has grow'n taller at Victoria, Tex. (52-79 inches), than at Lanham, Md. (30^0 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. a Cook, O. F., 1902. Agriculture in the Tropical Islauds of the United States, Yearbook of the United States Department of Agriculture for 1901, p. 367. EARLY BEARING AIDED BY LONG BASAL BRANCHES. 19 It is very possible, therefore, that if the (iiuitenialiiii variety is able to thrive^n the United States it will ripen its crop here in even less time than it re(i[uires in Gnateniala, 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 is short and uncertain. For two years, 1908 and 1004, the Indians were miable to burn their clearings, so that the corn crop failed and the connnunity was reduced to the verge of starvation. The cotton crop, in jiormal seasons, is said to be planted in the latter half of October and ripens in March. The introduction of a dwarf, short-season cotton woidd i-e()uire, of course, something of a change in cultui'al methods in the South, since the smaller size of the plants will ueed to be comi^ensated by closer l)lanting. It Avill l)e readily understood that to secure the setting of a crop in the mininunn of time as many plants as possible should be set at work. The question is not that of the maxinunn product for each plant or for a given area. AVith the weevil in the field the time factor becomes of chief importance. Little is gained in reality by the rank growth of the largei- vai-ie- 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- oAved 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 BEAR1N(; EACILITATED BY LONG BASAL BRANCHES. The earliness of the Kekchi cotton is 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 2:)lant has tAVo kinds of branches — the true or })rimary branch, Avhich arises in the normal position of branches in the axil of the leaf, and the secondary or fruit branches, one of Avhich arises at the side of each primary branch. In most A^arieties only a fcAV of the true branches are deA'eloi)ed; often none at all. They are almost ahvays plainly indicated, hoAvever, by a small bud or a stunted leaf or tAvo, 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 secontlary 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 tlic two sorts of l)ranchcs does not alwaA's remain as distinct as in the cotfee and cacao. A primary branch, like the main stem, never bears any flowers; it prochices only leaves and other branches, mostly secondary. Secondary l)ranches, on the other hand, produce normally a flower bud at the axil of each leaf, and this rule holds very generally, except that at the lower part of the plant it sometimes happens that a branch which has the secondary position functions as a primary; that is, instead of bearing buds and flowers it produces only leaves and sec- ondary branches. In the Kekchi cotton, as grown crowded together in the Indian fields, the prinuiry branches seldom a})pear, but when more space is allowed and the soil is fertile it is usual for two branches to start from the axil of each of the lower heaves, one promptly i)ro- ducing flowers, the other assisting in the rai)id increase of the leaf surface of the plant and of its power to elaborate food. Under the ])opular idea thirt plants draw their food from the ground the possession of branches which bear little or no fruit might be looked upon as an undesirable character, but when we take into consideration the fact that the leaves instead of the roots are the true assimilating t:)rgans of the plant it becomes apparent that a variety of cotton which develops its lower primary branches ma}^ have an advantage in earliness over one which is obliged to depend for its foliage upon secondary or fruit-bearing branches. In the matter of determinate habits of growth these primary branches are also a fea- ture, because they enable a plant to produce a full quota of leaves without unduly increasing the number of fruiting branches and thus continuing to add to the number of superfluous buds. The most obvious characteristic of the Kekchi cotton as it grows in our experimental plots is the long basal branches, Avhich often equal or exceed in length the main stem itself. The most prolific branches of the United States varieties are those Avhich come out from the main stem at the height of about a foot, but the bulk of the crop on the Kekchi cotton is borne much closer to the ground. (PI. II, fig. 2.) The long basal branches facilitate the early ripening of a uniform crop of cotton, but they will not be an advantage under all circum- stances ; as, for example, in dry regions Avhere the Aveevil can be held in check by open culture. The necessary exposure of the fallen squares to the full sunlight on hot, dry soil would be interfered Avith by a plant of low spreading habit and dense foliage. EAKLY KEJIX'TION OF SUPERFLUOUS SQUARES. That the Kekchi cotton has a limited or determinate growth and does not take advantage of the perpetual summer to become a tree or even a large bush is evident from the fact that in the latter part of EARLY REJECTION OF SUPERFLUOUS SQUARES. 21 the season most ol' llic flower hiuls and leal" biiils blast and fall oil' wliHe still \-ery yoiiiis of this j)rotective habit. ANNUAL CUTTIN(; BACK OF TEKENNIAL VARIETIES. T^liile the annual variety of cotton protected by the keleps is the basis of the only held culture found in eastern Guatemala, the Indian population of the central plateau about Salama and Rabinal raise small (juantities of cotton in their dooryards by means of another cultural expedient, apparently of great antiquity, as indicated by the extent to which the plant is adapted to the cultural conditions. The variety is perennial and has very small and inactive nectaries, pos- sibly as an adaptive result of the dryness of the climate. Most of the perennial varieties begin bearing only after the plants have attained considerable size, but the Ral)inal cotton is a notable exception to this rule and avoids injury from weevils by the very prompt flowering and fruiting of the new^ shoots. The weevils are present in numbers, and are frequently seen crawl- ing about on the plants in a leisurely manner quite different from that which they affect in regions stocked Avith keleps. At the time of our visit not a single boll or bud of any except the smallest size could be found which had not been attacked by them. Nevertheless, a crop of cotton is secured at another season. In the month of April the Indians cut back all the bushes to the ground, and as the cotton is always planted immediately about the doors of their houses, where the chickens and turkeys congregate, the mortality of Aveevils at this time is probably very great. The protection of the domestic birds doubtless continues until the new shoots have grown out of reach. As soon as the plants are a few inches high they begin flowering, and l)efore the Aveevils are sufficiently increased in numbers to become injurious a crop has been set. FloAAcrs and fruit are commonly borne on the lower branches, only 6 or 8 inches from the ground. The Indians say that if the cotton is not cut back, but allowed to grow tall, they get no crop. The fact is that by that time the weevils are too numerous to permit normal bolls to be formed. Our search for such was quite in vain on both our visits to Rabinal. One boll which gave no certain external proof of injury was wrapped up in a paper and retained as a sample, but was overlooked in packing and not transferred to the preserving fluid. When the paper was unwrapped a few weeks later three dead boll Aveevils were found. The Rabinal cotton crop is evidently not large, but the harvest is said to be regular, and the area of fertile land in this district is so small that none of it is wasted. Much foreign thread is now HAIRY STALKS AND LEAF STEMS. 25 imported, however, for \veavin<^ in the native h)<)iiis. The industry has greatly declined in the last century, perhaps because chickens have been generally substituted for turkeys, which were formerly the only domestic fowl possessed by the Indians. All attempts at establishing field cultures of cotton in this region have failed. The local public, which does not take the weevil factor into consideration, is firmly persuaded that cotton will not bear ex- cept in the heavy, rich soil of the dooryards of the Indian villages. irAIUV STALKS AXD LEAF STEMS. The weevil on foot is a rather slow-moving, clumsy insect, and it has been ascertained in the course of the investigations conducted by Messrs. Hunter and Hinds that its movements on the plants are to a great extent impeded by luiiry stalks and leaf stems. The smooth Egyptian and Sea Island varieties were found to be more susceptible to Aveevil injuries than the hairy Upland sorts. The Kekchi cotton is still more hairy, however, than the United States varieties, and gains an added advantage from this fact." The longer it takes the weevils to climb from one biul to another the greater are the chances of their being caught by the keleps. The latter insects, owing to their nnich longer legs and the claws with which their feet are armed, are not only able to travel readily over the hairs, but find them of definite assistance. On smooth surfaces they are much less adroit in catching and stinging the boll weevils. In our experiments, too, they seemed to prefer the hairy I'pland cottons to the smooth Sea Island varieties. The difference between the two insects in this respect may also be illustrated by the fact that the keleps are unable to ascend a ])erpen- dicular siu'face of clean glass, a feat which the weevils accomplish without difficulty. That the Guatemalan cotton was more attractive to the keleps than the United States Upland and Sea Island varieties planted in ad- jacent roAvs seems to be indicated by a census of our plot experiment, taken April 19 by Mr. Argyle McLachlan. Kelep nests were found at the bases of 41 per cent of the plants of the other varieties, a Though distinctly hairier than our ordinary Uph^nd varieties, the Kekchi cotton is exceeded in tliis respect by two other Guatemalan types, as well shown in a field tfst at Lauhani. Md. The Pachon cotton obtained by Mr. William R. Maxon in the Retalhuleu district of western Guatemala is distinctly more hairy than the Kekchi variety, though it seems to be lacking in other weevil- resisting features. The iiivolucral bracts are not closed any more than in the Sea Island or Egyptian types. The most hairy cotton of all is the Rabinal variety, at least in the form it has taken at Lanham. The plants are very much more robust in eveiy respect than at home in Guatemala, and the hairy covering shares in this increased vigor. 26 WEKVTL-RESTSTINCr ADAPTATIONS OF COTTON. while 7(5 per ceii^ of the phiiits of the Kekchi cotton were faA'ored with kelep nests. This apparent preference may be somewhat exaggerated, j)erhaps, in view of the fact that the phuits were often farther apart in the rows of the Kekchi cotton, the seed having germinated very irregularly. Moreover, the superior attraction of the Kekchi cotton for the keleps may not have consisted entirely in the greater hairiness or the more abundant nectar. The compact foliage and spreading lower branches of the Kekchi cotton give greater protection from the midday sun, which the keleps utilize by greater activity in the middle of the day. With the Sea Island varieties it seemed obvious, however, that the smooth stems, more open liabit, and smaller supph' of nectar result in distinctly less attention from the keleps. From or 10 o'clock on hot days the}^ foraged very little, and seemed to have quite disappeared from these varieties, though still to be found in considerable numbers on the stems of the Upland varieties and most of all on the Kekchi cotton, which appears especially adapted for the coriifort and con- venience of the keleps. It was noticed, how ever, that the keleps Avent much more often into the involucres of the Sea Island and Egyptian varieties than into those of the Kekchi cotton, for the simple reason, probably, that they can get in more easily. In the latter part of the season, after the weevils had gained a foot- ing in this field. Professor Pittier noticed a very decided preference on their part for the Egyptian varieties, though it seems certain that this type of cotton had never been planted in the country before. The ])artiality of the w^eevils might be explained, perhaps, on such grounds as the relative absence of the keleps, and also the ease of access to the buds of the Egyptian cotton allowed by the more open involucres. However, a slight change of food or of conditions of growth is often a distinct advantage to plants and animals, so that a direct preference for a new^ variety as food might reasonably be expected, and similar instances are known. The greater hairiness of the stems and the presence of the keleps may also explain why the weevils in Guatemala were seldom seen walking about on the cotton plants as they do in Texas. On the other hand, they take to wing very readily and seem to prefer to alight in the open flow^ers, the only places on the cotton plants where they are safe from the keleps. The petals are so smooth that the keleps seldom descend into the flowers, and when they do sometimes appear to be unable to climb out. The petals of the Sea Island sorts are smooth even on the mar- gins, sometimes entirely so, while those of the Upland varieties are fringed with fine hairs w'ell up on the sides, if not all the w^ay round the apex. PENDENT BOLLS. 27 The liiil)ilily 1<» caijliirc by such an insect as the kelep may also aiford an explanation of the peculiar sedentary habits of the male weevils, which often remain stationary in one involucre for long; periods, or as long as their food snpply lasts. It is necessar}^ for the females to go about in search of fresh squares for egg laying, but similarly active habits on the part of the males would subject them to nnnecessary danger. PENDENT BOLLS. The early bearing of the Kekchi cotton is made possible, as already noted, by the nnusual devel()i)ment of the lower lateral brandies, which often have a drooping habit, leaving the buds and bolls in pendent position, intead of upright. There are several advantages in this arrangement, one being that the instinct of the weevils leads them to the upper portion of the plant. In a very badly infested field without kelep protection, the only bolls which escaped the weevils were a few lying close to the ground on these lower pendent branches of the Kekchi cotton. Only at the time of flowering does the peduncle curve upward and give the flower its normal upright position. Thus these drooping lateral branches of the cotton, which seem to hide the buds and bolls away from the weevil, may be looked upon as a short step in the direction of such })henomena as the cleistogamous flowers of violets which i-emain buried in the ground, or those of the peanut which, after flowering, burroAV into the soil to ripen their seeds. The flowers of the cotton plant open in a more or less directly up- right position, and this is retained by the boll in most varieties. In the so-called " stormproof " sorts, however, the bolls hang down, and this is looked upon by many i^lanters as a distinct advantage, since when the boll is ri^Dii' and oj^en the rain does not beat into it and wet the cotton or wash it out, but is shed by the protecting outer shell and involucre. On pendent bolls the external nectaries are brought upward, so that there is no danger of an abundant secretion of nectar being lost by dropping off. The surface of the nectary is papillate and has a somewhat Avaxy appearance. 'Jlie secretion often collects as a dis- tinct drop. The nectaries are also more readily visited by the keleps, and the young bolls are likely to be better protected by them. If these remained upright, the weevils would be more likely to alight and enter the involucre at once. The drooping habit may have a mechanical explanation as the re- sult of the weakness of the comparatively slender lateral branches. It is also to be connected, perhaps, with the habit of early flowering and fruiting, since this would bring heavier bolls upon smaller and softer branches which would be twisted over by their weight. In 28 weevil-kf:ststtng adaptations of cotton. (lie ]:i((M- niul more iipriiilit varieties tho flowoi-s are not formed until the wood of the branches has hardened and become strono- and rigid. Pendent bolls may thus be said to l)e incompatible with the cluster habit, which is brought about by the abnormal shortening and thick- ening of the'lateral branches, which are al)le to hold theii- flowers and fruits rigidly upright, except as they may be turned sidewise by being crowded together. The cluster cottons, too. have the undesirable tendency to an abnormal multiplication of squares and young bolls, many more than the restricted leaf surface of the plant will enable it to ripen. This superabundance of flowers and fruits gives, how- ever, the greater encouragement to the weevil, and uses up vegetative energy which could be better employed in the prompt ripening of the bolls already set. It is no unconnnon thing, however, for even half- sized bolls of cluster cottons to die without any sign of external injury or disease, while other varieties close by remain perfectly healthy. The cause is probably to be found in inadequate nutrition, but this might also be expected to give them increased susceptibility to injury from parasitic enemies of every kind. It is not unlikely, too, that the drooping habit may be connected with the greater size of the inside nectaries of the Guatemalan vari- ety. These are, as far as we have seen, larger than in any other American variety yet known ; but the Asiatic cottons, which have the inside nectaries still larger and more active, are also more definitely pendent. The involucre is grown together at the base, as though to more thoroughly protect the nectaries from above — from the sun, which would dry up the secretion, and from the rain, which would wash it off. The nectar is formed in great abundance, and Mr. F. J. Tyler, of this Department, has called attention to the fact that the surface of the nectaries of the Asiatic cottons, instead of being merely papil- late, as in the American Upland varieties, has a coA'ering of close- standing fine hairs, to which its velvety appearance is due. Finally, it may be remarked that for cotton with upright bolls the inside nectaries are often an element of danger, since when the secre- tion is abundant and is not removed it flows along the bases of the involucre and may serve as a medium for the germination of parasitic fungi or bacteria. Bolls are not infrequently found diseased arou.nd the base, apparently from this cause. EXTRAFLORAL NECTARIES. The cotton plant is not without fl(jral nectaries similar to those of related genera, consisting of fringes of nectar-secreting hairs lining the pits inclosed between the bases of the petals. The nectar serves, doubtless, the same purpose as in other plants, the attraction of the KXTRAFLOKAL NliCTAKIES, 29 lioney-loviiig insects tlu'(>iiermanent resi- dents, and this is the end secured by the extrafloral nectaries of the cotton. It may be objected by some that no use or benefit to the plant has been ascertained in the case of many species which have extrafloral nectaries and other insect-attracting devices. Much remains to be learned concerning these marvelous biological sjiecializations, and there are two obvious alternatives which need to be canvassed before belief in the adaptive nature of extrafloral nectaries and analogous structures can be destroyed. The character and extent of many such specializations show that they have existed for a long time. They may have served protective purposes no longer apparent. The other consideration is that some of the symbiotic sj^ecializations existing between such plants as Cecropia and Acacia and their insect inhab- itants have arisen through selective encouragement, nnich as the special characters of our domestic i)lants and animals have been developed. It may be sufficient, in other words, that the nectaries or other structures be of use to the insects which have done the selecting. It ma}' seem absurd to think of bushes or trees as having been domesti- cated by ants many thousands of years ago, but the wonder is no greater than that ants and termites regularly maintained subter- ranean fungus gardens ages before mushroom culture was undertaken by man. 80 WEEVIL-RESISTING ADAPTATIONS OF COTTON. NECTARIES Oi THE LEAVES. The midrib of each leaf bears on the under side an oblong: pit, from which a drop of nectar may often be seen to exude. Tliis is collected and eaten by the keleps, which are thus induced to visit all parts of the plants, especially while they are still small. The habit of collecting the nectar was not previously known to exist among the insects of the family (Poneridse) to which the kelep has been referred. Nevertheless, the fact is not open to question. The process is easy of observation in even greater detail than Avith the true ants or the bees, because the keleps do not, like these insects, have the art of regurgitating their food. They merely lap the nectar up to form a drop, which, protected by the widely ()j)ened mandibles, is carried into the nest to feed the queen and the young. Nectaries, or at least nectary-like depressions, are to })e found probably on the leaves of all vai'ieties of cotton, though very small and apparently inactive on some of the larger tree sorts." The shape of the nectaries also vai'ies greatly in the ditfei'ent sj^ecies and varieties, some being longitudinal, others transvei'se, and still others crescentic or even sagittate. Some varieties have nectaries on the three principal veins, and some even on five veins. The leaf nectaries of the Kekchi cotton are to l)e found on the midrib of the leaf about 1.5 cm. from the base. They consist of a rather shallow longitudinally oval depression surrounded by a broad raised rim. The midrib often appears distinctly narrower above the depression than below it, as though there were extra tissues to supply it. The secretion is quite active, nearly all the nectaries shoAving a small amount of liquid, which sometimes spreads out on the adjacent surfaces. These nectaries furnish, as might be expected, a medium favorable for the growth of molds or fungi, and there is often a considerable network of dark-colored fungus mycelium creeping in and about the moistened depressions, and with occasional erect, needlelike points, which may be fruiting bodies. « This was not true, however, of a Mexican " tree cotton " of the Upland type grown in the Department's experimental plots in Texas last year. Large nectaries were generally present on three veins of each leaf, and the midvein often had two. They were of the crescentic or sagittate type, bnt often extremel:' long and distorted. Another Mexican tree cotton, with a different type of lighter green foliage, suggesting that of Bixa, had nectaries only on the midvein and these reduced to a narrow groove?. The vein was not thickened nor the niiirgins raised. Tlie two vai-ieties were about as different as could well he with resi>e(t to nectaries. Neither produced either flowers or fruit, so that their true relationshii)s were not to be ascertained. NECTARIES OF THE INVOLUCRE. 31 EXTERNAL NECTARIES OF THE INVOLUCRE. The Guatemnlaii cotton protected by the keleps has three broadly oval or reniform pits at the base of the involucre, one at the middle of the base of each of the involucral leaves." These are larger, dee])er, and more active than the nectaries of any of the Texas varieties as yet observed, though there is very great diversity of size and nectar- secreting activity. In some of the varieties these nectaries are reduced to mere rudiments or are entirely wanting. The depres- sion may be present, but with no secreting tissue. The variety nearest approaching the Guateuuilan cotton in having large and active necta- ries is the Redshank, but the King and other related sorts also have fairly large nectaries. The drooping or pendent i)osition of the bolls in the Kekchi cotton may be correlated with the special development of these nectaries, as already noted. In the middle of the day the keleps are not vei*y active, but the nectaries are sometimes full to overflowing. If the bolls kept the erect position usual in the varieties cultivated in the (Jnited States the nectar would frequently dro}) off and Iw lost, but when the fruits hang down the cuplike nectaries are brought upper- most and hold the liquid much longer. The evolutionary origin of these nectaries is fairly obvious. The bracts are to be looked upon merely as modified leaves, with nectaries which have increased in size and activity as the leaves have become smaller and more specialized. INNER NECTARIES OF THE INVOLUCRE. As though to induce the keleps to come inside the involucre and thus more effectually i)rotect the young buds and bolls against the Aveevil, the Guatemalan cotton is also provided with unusually large interior nectaries, alternating in position with those of the outer series and thus placed opposite the edges of the involucral leaves or bracts. These inside nectaries, like the outside ones, are larger and more active than those on most of the cottons cultivated in the Southern States, but the closing of the involucre and the devolopment of the inside nectaries have been carried much farther in the Old World cottons belonging to the species (ro.s.'^ypk/m lierhacewm. Here the external nectaries are quite wanting, but the internal ones are enormously larger and heartshaped, and secrete nectar in such quantities that it often flows out in the groove between the adnate '' Instances are occasionally found wliere only two nectaries are developed, but such deficiencies are niucli less tre(inent than in other varieties of the Upland and Sea Island series. Tlie Iial)inal cotton counnonly has only two external nectaries. The Old World cottons thus far observed have uo nectaries in this position. 32 WEEVIL-RESISTING ADAPTATIONS OF COTTON. bracts to iiioistcii the ed^es of the iiivohicre. As yet, however, the purpose of these achiptatioiis in the Asiatic cottons is entirely unknown, both the boll weevil and the kelep being absent in the Eastern Hemisphere. The botanical homology of the inner nectaries is somewhat different from that of the outer. They correspond in all probability with the nectaries which are found on the calyx of some of the species of Hibiscus, but there the calyx is large and covers the buds and each sepal bears a nectary near its middle. NECTARIES OF GUATEMALAN SEA ISLAND COTTON. A variety of Kidney cotton planted in small (juantities by the Indians at Trece Aguas, Guatemala, has the outer nectaries very variable in size and commonly ((uite wanting." The inside necta- ries seem always to be developed and are unusually large, l)eing ex- ceeded, as far as known, only l)y those of the Asiatic varieties. The nectar secretion is' also very abundant. No weevils were found upon this cotton, nor any keleps. On the other hand, the free-seeded Sea Island cotton found by Mr. Kinsler in the San Lucas '' neighborhood, not far from the kelep cotton culture of Secanquim, reverses again the tendency of the Kidney cotton to the great development of the inner nectaries and the suppression of the outer. The latter are, in the San Lucas cotton, nearly alwaj^s present, of rather large size, and of a red color. The inner nectaries are often rudimentary or quite absent. CONTINUED SECRETION OF NECTAR. Our Upland varieties commonly secrete nectar only at the time of flowering, but in the Kekchi cotton the liquid continues to exude until the boll is nearly or quite full grown, thus securing the protec- a This variety not infrequently produces flowers with only two bracts, closely appressed, like a clam shell. In one such instance there were two nectaries at the base of each bract, or, to be more exact, two separate nectaries on one side and one partly divided nectary on the other, as though the nectary belonging to the deficient third bract had separated into two ])arts and joined the other necta- ries. ^ This San Lucas Sea Island cotton is probal)ly the variety in which the weevils were found alaindant in 1902, when the first intimation was gained that the Kelvchi cotton had means of protection against the weevil. The San Lucas cotton is attaclced not only by weevils, but by another long-bodied in- sect larva, evidently lepidopterous, that gnaws through the boll at the ends, both from above and below, and eats out the seeds. Nothing of the sort has been seen in the fields protected by the keleps. There was also noticed in this cotton an occasional abnormality closely comparable to the navel orange. Rudimentary parts like a small secondary boll were found in the middle of bolls otherwise normal. The orange tree and the cotton plant belong, it may be remembered, to related families. BRACTLETS SUBTENDING INNER NECTARIES. 33 lion of the keleps for a longer period. The temporary character of the secretion in our United States sorts Avas reported by Professor I'release several years ago. In Guatemala, however, the young bolls seem to be quite as effi- cient as the flowers. It is even possible that this generosity on the part of the plant is excessive, since if the number of keleps is small they may find all the nectar they need on the lower bolls, and hence have less inducement to inspect other parts of the plant. Under favorable conditions in Texas the cotton plant produces a much larger number of flowers than in Guatemala, so that what is lacking in quantity may be made up by numbers, in case it should become possible to utilize the keleps in Texas. RACTLETS SUBTENDING INNER NECTARIP:S. The Kekchi cotton is distinguished from all our Upland and Sea Island types by the more regular presence and nnich larger size of a series of bractlets. a pair of Avhich usually subtends each of the inner nectaries. In other varieties these are either wanting entirely or are rare and rudimentary.* The bractlets are inserted somewhat obliquely, with their margins in contact below the nectary. Sometimes they serve to conduct nectar to the edge of the involucral bracts, the nectar following along between the slender bractlets like ink between the nibs of a pen, as though to coax the keleps inside the involucre. This must happen rather infrequently, however, to judge from the great irregularity in the size of the bractlets. Sometimes they are half an inch or more long, and extend well into the angles of the involucre, or even project outside. (PI. III.) Nevertheless, it « Professor Trelease, who studied the American Upland varieties, ai)i)ears not to have found the bractlets in pairs. He says: "These glands (the inner nec- taries) belong in reality to an inner whorl of three bracts, alternating with the outer ones, but generally wanting. In stunted plants, especially as cold weather comes on, one or more of these inner bracts may be found." (See Comstock. 1875, Report upon Cotton Insects. .324.) The shape and position of the bractlets seem to warrant the suggestion tliat they represent the stipules of the outer bracts instead of an independent inner whorl of bract leaves which luis first become specialized and then become rudi- mentary. The suggestion has the further warrant in that it may help to explain the numerous involucral appendages of some of the related plants, which range about the number 9 — that is, 3 leaves and 6 stipules. The normal number should be 6, if the two whorls of leaves were represented. One of the Guatemalan species of Hibiscus examined with this interpretation in mind seemed to con- firm it by showing very often .3 of the appendages broader than the others, though the total number varied from 8 to 11, with an irregularity quite compar- able to that of the bractlets of the cotton. Even the bracts of the cotton some- times vary, involucres of 2 bracts being found occasionally, and in rare instances 4. 9962— No. 88—05 M 3 34 WEEVIL-KESISTING ADAPTATIU^'S UJb' CUTTOJS. may Avell be (juestioned Avhether these inner bracllets have remained unusually large in the Kekchi cotton because they have a definite function or because of tlie greater size and activity of the adjacent nectaries. A variety of cotton called Pachon. planted rather extensively in the Retalhuleu district of western Guatemala, and likeAvise protected by the keleps, is similar to the Kekchi cotton in many respects, including the possession of these large stipular bracts subtending the inner nectaries, but with the addition that the bracts are fringed with long hairs, as though to hold the nectar the better. This may also be the function of the hairs which cover the nectaries of the Old World cottons EFFICIENCY OF THE KELEP PROTECTION. The special development of the extrafloral nectaries in the Kekchi cotton has been noted in former reports, it being the nectaries wdiich attract the keleps to the cotton plant. That the kelep preys upon boll weevils and protects the cotton crop was learned last year, but it was still possible to question the practical value of this form of defense. Such doubts would not have survived an inspection of our recent experiments in Guatemala. A small field of cotton just outside the kelep area was attacked by the weevils in such numbers that not a single normal boll developed on any of the United States Upland and Sea Island varieties. In the field protected by the keleps the weevils obtained no footing until the plants were well grown and an excellent crop of full-sized bolls had been developed. To test the efficiency of the keleps as destroyers of boll weevils and as protectors of cotton Would be possible in Texas only by stocking a large area with keleps — a difficult and expensive undertaking. No small tract would give a fair indication, since the weevils from the whole neighborhood would continue to come in, and, although they might soon be captured, would be able to do vastly more damage than would be possible if the whole region were stocked with keleps. In Guatemala, however, it was quite possible to contrast a protected with an unprotected piece of cotton by the simple exj^edient of plant- ing outside the area occupied by the keleps. A more striking result could hardly be imagined. For several weeks, during wdiich the two plots w^ere under continuous observation, the one remained almost entirely free from weevils and Aveevil injuries and set an excellent crop. Avhile in the other scarcely a flower opened or a boll developed. The very few exceptions were on the concealed drooping branches of the native Kekchi cotton. The weevils became, indeed, too numerous for their own prosperity and fed upon and destroyed the very young buds before they were old enough to breed larvae. Twenty-five fallen squares collected and EFFICIENCY OF THE KELEP PROTECTION. 35 examined from under the plants of the plot without keleps yielded only 6 larvae, or 24 per cent. They even attacked the young leaf buds, as observed last year at Rabinal. A large proportion of the injuries were caused by feeding punc- tures, but this only emphasizes the fact that the number of weevils which migrated into this plot Avas sufficient for a complete destruc- tion of the crop, and since the other experiment protected by the keleps was much nearer to the fields of the Indians there is every probability that the weevils would have been, if possible, even more numerous if the keleps had not been at hand to catch them. The unprotected plot Avas located at about one-quarter of a mile outside of the belt of Indian cotton culture, on land not inhabited by keleps. The weevils lost no time in finding the new field. Infesta- tion was complete, and quite as destructive as in Texas, the Aveevils being so numerous as to OA^ercome AvhatcA^er resistance the cotton might liaA^e been able to oppose to smaller numbers of the pests. The Sea Island, Egyptian, and United States Upland varieties A\'ere not permitted to produce floAvers or eA^en full-sized buds, and even the natiA'e Guatemalan varieties shed their squares before the per- sistent onslaughts of the Aveevils. Cotton is regularly cultiA^ated by the Indians in this immediate neighborhood, and Indian plantings more or less infested Avith weevils Avere to be found within short distances of the protected field. Nevertheless, the keleps proA^ed to be sufficiently abundant on this piece of ground to completely exclude the AveeAdls. There Avere enough, indeed, to protect Avith apparent impartiality all the kinds ■ of cotton included in the experiment, but if the numbers had been less and the plants had been closer together, as in the Indian fields, Ave may be sure that those producing the most nectar Avould haA'e recei\^ed the most protection from the keleps. The Aveevils Avere seldom to be found in the plot stocked Avith keleps as long as the Indian cotton remained in Adgorous groAving condition, but about the time the Indian cotton ripened, the weevils seemed to make a more determined raid on our field, and along one side nearly cATry plant suffered somcAvhat, though the weevils could rarely be found except in the open floAvers, Avhich seem to be recognized as their only safe roosting places. In a A\^eek or ten days there Avas a distinct falling off, so that A^ery little damage Avas being done, and there Avas another short interA^al of practically complete protection. But after this a reneAved onslaught began and the • numbers of AvecAals gradually increased, the Upland and Sea Island plants continuing to produce thousands of ncAv squares in Avhich the weevils Avere able to breed, quite as in the United States. That the keleps are definitely attracted to the cotton plants, as stated in previous reports, is fully demonstrated by the fact that 36 . WEEVIL-KESISTING ADAPTATIONS OF COTTON. liiaiiy of the colonies iiio\'ed their nests to new buiTows excavated immediately at the bases of the cotton plants. In some parts of the field the proportion of cotton plants having kelep nests established about their roots reached nearly 75 per cent, whereas the chance that the positions of the cotton plants which stood in regular rows would coincide with those of kelep nests would not be one in hun- dreds. The success of this experiment would seem to justify fully the suggestions made in connection with the first announcement of the discovery of weevil-resisting adaptations of the cotton plant, namely, that the protection which these Central American varieties had been able to Secure from the kelep had afforded them an opportimity, perhaps unique, of developing other resisting adaptations. The Kekchi and other related cottons, though having no monopoly of weevil-resisting characters, furnish, however, the only instance as yet known to scientific observation in which a field culture of cotton has been maintained for long periods of time under climatic condi- tions favorable to the boll weevil. In Central America, at least, the secretion of nectar by the cottori is not a useless or meaningless function, as observers of the plant in other parts of the world have sometimes supposed. The cotton is not the only plant upon which the kelep can live, nor the boll Aveevil the only insect upon which it preys. To secure the attention and obvious preference of the kele]) tlie cotton has been obliged to put forth the superior attractions provided by its numerous extra floral nectaries. This additional proof of the \'alue and efficiency of the kelep does not affect, of course, the possibility of acclimatizing it in the United States. A more extended search in Guatemala resulted in finding the insects under a wide range of conditions, and at altitudes of from "200 to 2,000 feet. It lives and thrives, moreover, in soils very nuicii drier than those to which it was supposed last year to be confined. Last year's experiments in Texas indicated likewise that the kelep with- stands drought much better than it does standing water in its barrows, and care is being taken this season to locate colonies with a view to adequate .drainage. OTHER NECTAR-BEARING PLANTS VISITED BY THE KELEPS. The honey-collecting habits of the keleps are not confined to the cotton. Another favorite is a si3ecies of Bidens {B. pUosa) called by the Indians '' tshubai," which has considerable value as a forage plant, being of quick grow^th and succulent texture. The preference of the kelep for the tshubai as a second choice after cotton w-as noted last year, but no explanation was found, though THE INVOLUCRE AS A PROTECTIVE STRUCTURE. 37 the plant was searched foi nectaries. It was noticed by Mr. Kinsler that the keleps seemed to be giving especial attention to the midrib near its jmiction with the veins of the lower divisions of the leaf. Our lenses then revealed the fact that there are two minute raised Avings or margins running along the upper side of the midrib and petiole, forming two narrow grooves in which the nectar is evidenth^ secreted. The grooves are also protected by a row of fine hairs Avhich project across them from the raised margin. The behavior of the kelep thus receives a practical explanation, and the tshubai finds a )-egular place next to the cotton among the plants protected by tjie kelep. The nectar-secreting habit of the tshubai nuiy also explain its being eaten so readily l)y stock, and may help to give it standing as a forage plant, in spite of its weedy and unpopular relatives. A second member of the composite family often visited b}^ the keleps is the '' sajal," a species of Melanthera (probably M. deltoklea) , which also has local value as a forage plant, being eaten greedily by horses and inules, even in preference to grass. No nectaries have been found on this, A third composite, not A^et identified, produces nectar in small depressions at the base of the leaf on the under side. THE INVOLUCRE AS A PROTECTIVE STRUCTURE. Cotton is the only plant known to be attacked by the boll weevil, and it is also unicpie among its relatives in the possession of a large leafy involucre. This may be a mere coincidence, or it may be that the weevil has had a considerable influence in the development of the involucre, depending iii)on the antiquity (»f the contact between the insect and its host })lant. The involucre has, it is true, functions other than the exclusion of the weevils, since it takes the place of the calyx in protecting the young bud. but the reduction of the calyx probably followed the enlargement of the bi'acts, instead of preceding it. But however originated, the large Ijracts have, at the present time, a definite value in the j)rol)lem of weevil resistance. There are several specialized chai-acters which appear as though definitely cal- culated to increase the efficiency of the involucre in excluding the weevils from the young buds. INVOIJTCHAL lUiACTS (JROWN TOGETHER. Both the Kekchi and lAal)inal cottons frequently have the involucre closed at the base, the three bracts being grown together, thus making it impossible for the weevils to enter from below. In the Sea Island and Egyptian varieties, as well as in some of the Upland sorts, the bracts are not merely divided to the base, but they often have the low^er corners rolled back, thus leaving an open passage for the weevils. The Rabinal cotton much excels all the other varieties thus 38 WEEVIL-RESISTTNG ADAPTATIONS OF COTTON. far studied in the extent to which the bracts are grown together at the base. Sometimes they are united for a quarter or even a third of their length. (PL IV," fig. 1, and -PL X, fig. 1.) APPRESSED ]MARGINS OF BRACTS. In both of these Gucltemahm varieties the margins of the bracts of young invobicres are firmly and closely appressed, in strilving con- trast with the Sea Ishind and Pjgyptian varieties, where the Vxid is commonly exposed e\'eii when very young. This form of i^rotection is effective while it lasts, but in the Rabinal cotton the involucre is too small, and the growth of the young bud soon separates the bracts and permits the entraiu-e of the weevil. The United States Upland varieties are intermediate between the Sea Island and the Kekchi cot- tons in the degree to which the involncres are closed and the margins fitted together. A large proportion of the Upland involucres give ready access to the weevils, while most of those of the Kekchi cotton remain effectively closed for a longer jjeriod, as will be understood after a survey of the other involucral characters which conduce to the same resnlt. In one respect the firmly closed involucres of the Rabinal cotton seemed almost like an advantage to the Aveevil rather than the con- trary, for the insect is not admitted to the bud until it is about large enough to furnish a place of development for a larva. The plant having taken control, as it w^ere, of this relation, the weevils have not needed to possess an instinct against the destruction of 5^oung buds. Those of the open involucred Sea Island varieties often were attacked while still altogether too small to bring a larva to maturity. The advantage of the closed involucres lies, no doubt, in the fact that they shorten the period of access and allow some of the buds to escape which would be punctured either for feeding or for egg laying if the weevil has a longer opportunity. (PI. IV.) The Rabinal cotton culture is that in which the plants are cut back yearly to the ground. During the next month, or until the buds begin to develop on the new^ shoots, the weevils have no breeding places and nothing to feed upon except the leaves and leaf buds. In patches where the weevils are abundant the leaf buds are eaten out so persistently as to seriously interfere with the growth of the plants, and the very young floAver buds were also reached in some instances by boring through the involucres. When attacked at this stage the buds wdther and drop off. They serve the w-eevils only for feeding purposes, and their use in this way only postpones the time "when breeding can be resumed. The cotton at Rabinal was often overrun by two species of small black ants, identified by Dr. W. H. Ashmead as belonging to the LARGE INVOLUCRES OF KEKCHI COTTON. 39 genera Solenopsis and Tapinoma.'* There was no indication, how- ever, that these afforded any protection against the weevils, although they might, perhaps, act as Avatchmen and scare weevils away when they happened to be present on buds or bolls where weevils had alighted, like other small ants which have been reported as attacking the boll weevil. The keleps belong in an entirely distinct category in being able to sting and carry off the weevils and make regular use of them as food. Instead of being of service to the cotton these small ants at Rabinal were a distinct injury; the Solenopsis was taking care of plant lice,'' which often infested the cotton to a decidedly harmful extent. It continues and supplements the work of the boll weevils in stunting and distorting the plants. When the aphids are very numerous, the leaves are badly curled and growth is greatly impeded. LARGE INVOLUCRES OF KEKCHI COTTON. The Kekchi cotton has the bracts of the involucre much larger in proportion to the contained bud than the Rabinal cotton or than any of our Upland varieties. The possession of larger bracts constitutes a distinct weevil-resisting adaptation, since it permits the involucre to be more effectively closed and the protection to be continued for a longer time. Sooner or later, of course, the bracts must be separated by the growing bud. The larger the bracts the longer the bud can continue to grow before spreading the bracts apart. (PI. IX, fig. 1.) Prof. II. Pittier, who had charge of the Secanquim experiment in the latter part of the season, was especially impressed with the pro- tective utility of the larger bracts of the Kekchi cotton, as shown by the following summary of his observations: The large size of the bracts in proportion to the floral bud is a very important protective feature. In the Kekchi cotton the amplitude of these bracts is such as to completely inclose the bud at all times before the anthesis. and even in cases when they happen to be slightly separated the occlusion is maintained by the long hairs which fringe them on all sides. The length of these hairs con- stitutes a serious obstacle to the progress of the weevils, whose tarsi can not obtain a firm hold on the solid surface. I have seen them droit to the ground after many awkward attempts to gain access to the squares, while on the other hand the keleps did not seem to be impeded at all by the bristles. " The material was not sufficient for a conclusive determination of the species. I)(((tor Ashmead says: "You have two distinct species of ants here. One, No. 1, belongs to the family ]\Iyrmicid;Tp and is apparently the worker of (Solenopsis pieea Emery ; the other. No. 2, belongs to the family Dolichoderidiv and is apparently the worker of Tvpinonia raiinilonini Emery. I am sorry you did not have the different sexes, so that I could make positive of the species. In Solenopsis, as you probably know, there are four or live different forms, and it is not easy to identify from a single form.'" 6 These have been identified by :\Ir. Theodore Pergande as Aphis f/ossi/pii, a species well known in the United States. 40 WEEVIL-RESTSTING ADAPTATIONS OF COTTON. To show the increased size of the bracts in the Kekchi cotton, I have carefully measui'ed over 250 squares of five of the most promising varieties of the Upland species. The dimensions taken were the length of the floral bud, and the length and bi'eadth of the bracts. The table, in which these data are condensed in a comprehensive form, shows a decided advantage in favor of the Kekchi cotton. Table I. — Dimensions of pnrol hiids and bracts of sercral rarirtirs of coiion compared. Length of floral bud (millimeters). Kekchi. Parker. King. Allen. Jewett. 1 O o .a o mm. 20 28 39 42 42 42 47 52 37 47 42 ^t w w mm. 11 18 27 30 30 30 33 30 27 36 30 C(-t CM mm. O IS m mm. CM O o ►J m.m. 1-1 o St o 0) to o o +^ o CM o CM O CM ! ■Si SI ,Q 5- 6 1 1 6 5 3 4 3 ! 3 2 mm. m.m,. mm. mm. wtm. 7- 8 2 13 16 18 8 6 3 3 1 3 2 2 1 25 31 36 39 38 39 43 48 36 ■SJ 44 45 47 19 20 24 25 23 26 24 26 25 25 25 24 30 1 18 10 18 13 5 1 1 5 1 5 26 34 34 37 39 39 49 40 40 33 42 20 21 23 23 24 25 29 26 23 21 25 9-10 5 . 7 I 6 4 1 2 33 34 40 44 40 43 43 41 19 23 24 25 24 26 25 26 3 2 10 5 1 38 36 39 41 39 52 47 26 21 26 28 i» 38 34 11-12 13-14_. 15-16 17-18_ 19-20 21-22 23-24 25-26 1 48 33 27-28_ 2 1 40 49 25 28 29-80 _-.. , 31-32 33-34 1 32 42 32 Total.. 31 78 48 li" 1 The advantage i.s 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. ■ EXTENT OF PROTECTION BY INVOLUCRE. 41 All exaiiipk' of the pr()nn)tness 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. in., a small cage was placed over a small i)lant of Parker cotton, and .1 female and 2 male weevils were introdueeil. The plant jwssessed ?.G squares. 4 flowers, and 9 bolls. The morning after the weevils were put into the cage several of the scpiares had flared and one had fallen. It would seem that the mechanical forces of the square are quickly affected by the woi-k 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 Avithout flaring. HAIRY 3IARCJ1NS OF INVOLUCRAL BRACTS. In addition to their larger size, the bracts of the Kekclii cotton have the marginal teeth or lacinia^ 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 Kabinal 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 lacinia' few and small ; sometimes the edges are nearly entire, or merely toothed. The liaiiy 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 •i2 WEEVIL-RESISTING ADAPTATIONS OF COTTON. weevils commonly attack them in their very early stages, and even Avhile they are altogether too small to jiermit 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 nnich more readily susceptible to injury by the boll w'eevil 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 Aveevils 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 involucres 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 appeal' 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 Avere to be caught by insecti^'orous l)irds, like the Cuban oriole, Avhose Aveevil-eating habits have lieen discovered by Mr. E. A. Schwarz, open involucres Avoukl 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 Avill need, however, to be considered from another standpoint. It must be ascertained whether the young buds will bear full exposure. Unlike most of the related plants, the cotton bud is not protected by a calj^x. The inA'olucre may be necessary as a substitute, especially in dry climates. In humid a Dr. H. J. Webber states that the desirability of open invohicres has been appreciated and that selections of Upland varieties with a view to the develop- ment of this character have be^u made. BEHAVTOR OF PARASITIZED BUDS. 43 regions, hoAvevor, this iv(iuireiuent might be rehixed, and it is in such places that the injuries of the Aveevils are the greatest/' BEHAVIOR OF PARASITIZED BUDS. SHEDDING OF WEEVIL-IXFESTED 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 larA'je 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 Avithout 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 Avhen they fall to the ground. " It is generally true that scjuares seriously injured by the weevil sooner or later fall to the jjround. Some plants, however, shed the injured s(iuares 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 foi'mation 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 tii). In this |)osition it dries thoroughly and becomes of a dark brown color. Plants showing () or 8 of these dried brown squares are quite conmion in infested fields. Although exposeil to complete drying and the direct rays of the sun, the larva:" within are not all destroyed. * * * " It 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- rjge * * * rpjjg observations made, however, certainly show that a complete o After the above had been written it was observed that the Pachon cotton from western Guatemala, grown in an experimental plot at Lanham, iMd., 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 l)racts are much smaller and much more oi)en than in the Kekchi and Rabinal varieties, but the laciniie, or teeth, along their margins are rather stiff and are clothed with nmnerous hairs, sti'onger and more bristlelike than in the Kekchi and Rabinal varieties, and able to keep the lacinife from closing together. It may be that the greater rigidity of the lacinia> 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-RESISTIKG ADAPTATIONS OF COTTON. (Iryiiifi (if the s(iii;ire does not necessarily destroy the lai'\:i, and that a square may undei'go far more exposure to direct sunshine than had been su])posed l)Ossil)Ie 'without causing the death of the hirva or pupa within." a 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 fnll 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 developme'nt 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 Avhich they came has not been ascertained. Some of the Texas varieties are said to have l)een 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 onl}" under such conditions that the weevil would be effectually pre- vented from increasing to the fatal degree of destroying its host ])lant, and thus cutting off' its only means of subsistence. On the other hand, it was only in a humid countr}^ like eastern Guatemala that many of these weevil-resisting adaptations would be likely 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 Hnnter, W. D., and Hinds, W. E.. 11M)4. The Mexican Cotton Boll Weevil. Bui. 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 conhnned by the fact that it depends upon the existence of a sjjecial layer of soft cells Avhich readily break down when the bud is injured. Many plants have such cells as a means of shedding their fruits, !)ut 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. AVhether there are other adaptations thus especially suited to dry climates is not yet knoAvn, our studies having l)een 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 Aveevil 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 numl)ers and complete the devastation of the crop, (piite as in Texas. The irrigated soil affords a situation favorable for the development of the larva> 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 l)etween San Luis and Tampico, and on the Pacific side of Mexico, along the Santiago River above San Bias, as well as about Tepic. Doctor Palmer saAv cotton growing in a wild condition in the fences at the old nussion, San Jose de Guaynuis, (> miles from the commercial port; again at Mulege, LoAver 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 ISOf) at San Jose de Guaymas. COUNTINGS OF FLARED AND FALLEN SQLTARES. 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 larvte, proliferations, etc., found inside them. The results in percentages do not agree, however. 46 WEEVIL-KESrSTlNd ADAPTATIONS OF COTTON. with the facts obvious m the fields: indeed, they greatly misrepre- sent them. Thus the j^ercenlage of Aveevil injuries in 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 Aveevil 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 Aveevil 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 is also possible for the plant to heal the wound, and bring the injured bud to maturity by preventing the growth of the weevil larva. Where the climate is dry the Aveevil iarva^ in the rejected Inids are killed, as already explained. The humid climate alternative of the falling of the parasitized squares is proliferation, the growth inside the l)ud 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 ):ie no adequate substitute for the highly nutritious pollen grains on which the infant larva Avould 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 oi weevil jjunctures rendered ineffective by prolifera- tion was found to run well above ."iO per cent, sometimes between 80 and 1)0. (PI. V.) 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 pai't 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. Init 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 ut 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 staniinal tube, is probably also less elect- ive, since the weevil larva^ could escape before it into the ct",ter of the flower while the proliferation from the staniinal tube groAvs outward, as though to meet the intruder and keep him separated from the more special organs. The habit of the larvie to seek the center of the bud and gnaw^ off the style is responsible for the loss of large numbers of younger bolls Avhich have suffered no direct injury from the weevil. Even though the larva be subsequently killed by proliferation or though the flower dro])s off and carries the larva with it, the lack of polli- nation must prevent the development of the young boll unless par- y thenogenesis takes place, which seems improbable. Larva^ 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 someAvhat 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 someAvhat upon the degree, if any, to Avhich they might return to the habit shoAvn 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 betAveen the Aveevils of Texas and those of Guatemala. CAUSES AND CONDITIONS OF Bl I) I'UOLIFEHATION. That the i)roliferation is occasioned by the injuries of the weevil is too obvious to admit of doubt, but it may be of much practical importance to learn the exact Avay in which the ucav growth of tissue is brought about. The disturbing factor might be either mechanical or chemical. The new growth nuiy be a direct response to injury of the AveeA'ils in feeding or laying eggs, or it might be stinudated indi- rectly by the secretions of the yoimg 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 groAving bud. 99G2— No. 88—05 m 4 50 \VEEVlL-RESISTIN('r ADAPTATIONS OF COTTON. The bun'owiiiii' of tlic weevil ivlieves 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 staniinal tube. It seems not improbable that a relation will l)e 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 in 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 larvae to develop, as in Texas, except that there was still a distinct tendency on the part of the larvte to attack the pistil and ovary first, before eating out the pollen. PROLIFERATION IN OTHER VARIETIES. l^roliferation 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 w-as 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 P^gyptian 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 staniinal tube are too nearly mature. By that time, how^ever, the style may be sufficiently developed to furnish adequate food. It is well known, hoAvever, that the period of development of the weevil larvte may be greatly prolonged, and this would seem likely 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 w'ould permit the young boll to become larger. a This variety is iieculiar in having about half of each seed covei-ed only with a very tine, short, bright I)lnish-green lint. The upper half bears the long white fiber, and is smooth and I)ladv 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 w«*r(& ;ill occupied by small black ants. On some of them no weevils nor any indications of weevil injury were found, but others only a few rods away ^ere badly infested. PROTECTTON OF THE BOLLS. 51 But as the power of eifective 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 l)ud will mature and the flower Avill open and turn the weevil larva out of its qiuirters to die. And since l)uds 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 eifective 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 larvse 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 jjossible 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 larva' develop as in the squares which are far enough advanced to show definite residts. 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 thi'ough the withering tissues, Avhich seems not to be attempted. In the Kekchi cotton the flow er falls only when detached by the swelling of the young boll. This may also be true of other varieties. (See PL IX.) The frequent sequel of proliferation in the bud, as noted above, is the loss of the young boll through lack of i^ollination. This is espe- cially true in Guatemala, owing to the tendency of the w^eevil larva* to eat away the style. On one occasion Mr. Kinsler collected from a field of Indian cotton 28 young bolls showing signs of debility. These measured from 18 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 sliriveling 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 larva* to maturity 52 WEEVTL-RESISTING ADAPTATIONS OF COTTON. i^eeiiied 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 adecjuate polleu, 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 in most instances such bolls renuiin 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 Avhich 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 A^ery young bolls. This may be due to a con- servative instinct on the part of the weevil, like that wdiich 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 nuiy have a protective function. As the boll growls larger the glands do not appear to increase in numbers, but become separated much more widely. On bolls of the Kekchi cotton the oil glands are usually al)sent 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 w^all is thicker here, and the w^eevil 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 Aveevil 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, o Hunter. W. D.. and Hinds. W. E., 1005. The Mexican Cotton Roll Weevil. Bui. 51. Bureau of Entomology. V. !^. Department of Agriculture, p. 7S. 6 This peculiarity of a glandless longitudinal band in the middle of each carpel was also noticed in a variety of cotton cultivated I)y the Moqui Indians of Arizona, grown in 1904. in the Department's ]ilant-l)reeding 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 arc excessively oily, is on this acconnt innnnne from the holhvonn." The oil contained in the glands has a deep-brown color, a sticky, niolasses-like consistence, a disagreeable, pnngent odor, and a sharp, resinons taste, suggesting turpentine or Canada balsam. The development of the oil glands seems to be especially great in the Egyptian variety knoAvn as Mit Afifi, a;id 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 Ujiland varieties have the oil glands much more scattering and deep set than the Egyp- 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 slight superficial depressions, but a cross section shows them to be well below^ the surface, with several layers of chlorophyll-bearing cells betw^een. On the Egv^j^tian 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 spontaneousl}' in some in- stances; at least there are frequently small spots of hardened resin, and very slight 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 a{)plied 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 consf)icu- ously developed, like the Egyptian varieties, but the Old World cotton {Gossyjnum herhaceum) is in this, as well as in other respects, more nearly related to the American Upland cotton (Gossypiifm hir- svtum). The Aidin (Asia Minor) variety of GoHHypmm herhaceum 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 Entomologj% U. S. Department of Agriculture, p. 71. '' The Kidney cotton at Trece Aguas is called iHihi'i. and seems to have little or no relation in the minds of the Indians with the dwarf Upland cotton, which is called uok. 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 cJie nolc, or tree cotton. 54 WEEVTL-RESISTING ADAPTATIONS OF COTTON. half specked with minute brown . The Mexican Cotton Boll Weevil, Bui. ."tL Bureau of Entomology, U. S. Department of Agriculture, p. 113. 56 WEEVIL-RESTSTTNG 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 ail'ects 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 longest 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 larvse, though numerous attempts may have been made. Large larva' or pupoe 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. Pearly development of the thick walls Avas indicated by the fact that the young seeds and lint 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 &gg 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 Kekclii cott(m scarcely any young larva? were found, in spite of the fact that most of them had been punctured not once only, but many times. TOLTGH 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, e^^en in bolls not yet fidl grown and in which the seeds are not yet fully formed. This membrane is readily separable from the more fleshy external layers of the l:)oll, and though flexible, it is very TOUGH LININGS OF CHAMBEKS OF BOLLS. 57 (ii'iii and incoiiiprcssiblc. aiul resists tcariii*;" unless considerable 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 show\s, 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- qnent, the new tissue, develoi)ed as a result of the irritation of the attempted pimcture, 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 slightly 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 to this 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 nmnbers of instances where the weevils had gnaw'ed 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 Avail on the inside to form a blister- like, rounded protuberance. (PL VIII.) Eggs laid outside the parchment are firmly embedded in the new " 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 larger bolls, when opened, were found to have 28 weevil eggs deposited in them ; C, 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." 58 WEEVTI^-RESISTTNG ADAPTATTOXP OF COTTON. growth and do not appear to hatch, or if tliey do the hirva- are not able to do any damage, since they can not penetrate into the interior of the bolL It (juite freciiiently haj)j)ens that eggs are laid in the ^iniLs or groove between the linings of two locks, but without penetrat- ing the parchment of either. The tissue is here somewdiat looser than in other parts of the wall. In a few instances it was observed that the larva^ had hatched, but no case was found which indicated that larva^ hatched outside the parchment lining had been able to penetrate to the interior cavity. PROLIFERATION FROM THE WALL OF THE BOLL. The w^all of the boll offers an active form of weevil resistance by proliferation, in a manner somewhat analogous to that of the pro- liferation of the square. The channel excavated by the weevil is closed by the new growth, wdiich continues to push out on the inner surface of the wall in llic form of a rounded, blister-like protuber- ance of loose tissue. This surrounds and encysts the weevil egg, and prevents its development. A section through the mass of new tissue shows the egg embedded in it or pressed against the lint. Prolifera- tion often takes place even when the tough lining of the chamber has not been penetrated, and then appears as a prominence underneath the membrane. It has been seen from the preceding paragraph describing the thick walls and tough lining that in the Kekchi cotton, at least, the weevil is practically excluded from the boll after the boll has reached about three-quarters of its full size; but even in its younger stages also there is a measure of defense through the formation of new tissue as a result of the irritation set uj) by the weevil's injuries in a manner analogous to that which induces the formation of galls and other vegetable excrescences. The first result of the proliferation is to fill up and heal the wound bored out b}^ the weevil. The cavity is not only completely filled, but in most cases a wartlike prominence is formed on the out- side, and if the parchment lining or the inner wall has been pene- trated the new j^roliferating tissue also grows through on the inside and often spreads out as a biscuit or button shajied protuberance of soft white or transparent tissue several millimeters in diameter and readily visible to the naked eye. (PI. VIII.) There are two alternatives in the fate of an egg destroyed by proliferation. Either it is completely surrounded in the proliferating tissue outside or inside of the parchment wall or it is carried on the apex of the proliferation down against the lint and flattened between the growing surfaces. After the egg has disintegrated and disappeared its position is frequently shown by a minute brown PROLIFETtATTON FBOM WALL OF BOLL, 5V) stain. Such a discoloi-atioii often jspreuds back into the loose tissue and then gradually extends over the whole lock of cotton of that particular chamber. The seeds fail to develop and tinally shrivel up. If the proliferation results, as usual, in the death of the weevil egg or young larva, the process of abnormal growth ceases with the formation of a knob or button of the new tissue on the inside of the Avail of the boll. When, however, the young weevil escapes destruction and continues to eat and grow, the proliferating tissue also continues to increase, until in some instances the whole compart- ment is filled with a silvery-white cheesy material which seems to arise not only from about the original perforation of the outer wall, but also from other ]:>arts which have been injured and irritated by the presence of the weevil larva. This, with other facts already stated, seems to show that in some varieties of cotton, at least, the tendency to proliferation is very general, or, in other words, con- stitutional, which warrants a larger hope of increasing this character and making it uniform by selection. 'WTien proliferation, which results from the presence of the weevil larva, has become very extensive and fills the entire compartment, the weevil larva is sometimes found to have eaten through the dis- sepiment into the next chamber, perhaps to escape starvation. Such extensive proliferation, accompanied by the failure of the seeds to develop, means, of course, that the weevils gained entrance while the boll was still very young. Moreover, if the boll had been older there would have been plenty of food for the larva without the necessity of entering a second compartment. Finally, the dissepi- ment would have been too tough for the larva to penetrate easily. Further proof of the fact that the weevil larva^ are seldom or never able to gain a footing in the larger bolls is to be found in the fact, already stated, that the weevil larva^ found in them are nearly always in undersized compartments, much smaller than those which have remained uninjured, and have thus been able to continue their normal development. It is to be supposed, perhaps, that if the weevils could gain access to large bolls and feed upon the nearly adult seed they would be able to develop in less time than they usually spend in reaching maturity on the rather poor provender they secure among the abnormal tis- sues which arise after they have entered the young bolls. The exclusion of the weevil from the large bolls has been evidently not only an important measure of protection for the cotton, but it has probably compelled the weevil to accustom itself to a gradually longer and less prosperous development in the boll. The develop- ment of the weevil-resisting adaptations on the part of the cotton plant has left the insect Avith two opposite alternatives. It must enter the boll early and submit to a very long period of development 60 weevil-reststtnot adaptattonr of cotton. or filter the s(iiiare late and develop very promptly. The insect has been able, as we know, to avail itself with a hir<>e measure of success of both these alternatives, but it is not without encouragement for future progress in weevil resistance to know that the plant has so successfully guarded itself in two parts of its life history. If additional evidence be needed to show that the food supply obtained by the weevil larvse in the bolls is very dilferent from that in the squares, it is to be found in the large, firm-walled cells of com- pacted excrement with which they surround themselves in the bolls before reaching maturity. The food being of a much coarser nature and the period of development about three times as long, the amount of waste material is naturally very much greater. If feeding upon the boll is, as now^ appears probable, the ancestral habit of the wee- vil, it need not surprise us that the protective adaptations of the boll are more numerous and effective than those of the bud, which maj' have been attacked by the weevil in comparatively recent times. TIME REQUIRED FOR PROLIFERATION. In connection with the experiments in Texas, Mr. McLachlan at- tempted to ascertain the time required for proliferation to take place after the injury had been inflicted. The amount of proliferation and the time required for it to develop ma}^ be expected to depend much on external conditions. Squares of Parker cotton showed no development in six hours, but observation on bolls showed that pro- liferation w'as complete in twenty-four hours. Two of Mr. McLach- lan "s observations are described in the following notes : Ou August 14, at 0.15 a. m., a wii'e cage was placed over a plant of King cotton, and four weevils, of which at least two were females, were put inside. Later, three more were introduced. At the time there were 11 bolls, 39 squares, and 1 flower on the plant. On August 17, at 1 p. m., 11 bolls and 18 squares were picked, a little more than three days being allowed for the weevils to work. There was no rain, and of the 18 squares examined only one revealed proliferated tissue, though the weevils had scarred the buds in more th.ui .S3 sei)arate places and had deposited 15 eggs. But the bolls showed better results. They had been scarred at 32 different points, and 23 eggs were discovered when the bolls were exit oi)en. In 12 cases inward proliferation of the " shuck " had destroyed the eggs. Several of the incited growths had caught the egg, encysted it, and carried it along, inclosed at the apex, as they pushed their way into the lint. As in the Parker cotton examined a short time ago, weevils seem to have some difficulty in getting the egg through the shuck of the boll. In dry weather it appears that the King cotton is as backward as the Parker in proliferation in the squares, but in bolls proliferation goes forward as well in dry as in wet weather. On the 30th of August, at 10.15 a. m., a boll (half grown and tender) was bagged with a weevil. At p. m. of the same day an egg puncture was found on the fruit, but at 8 a. m. of the 31st no further injury had been inflicted. At 12 m., September 1, four more egg ininctures were discovered, and the boll was EFFICIKNOV OF ADAPTIVE CHARACTERS OF EOLLS. 1.7° F.. and the average total effective temi)erature retiuired for development in bolls was therefore 1,933.7° V., or nearly two and one-half times as much as in sciuares. Several larvie often develop within a single boll. They appear to remain in the larval stage until the boll l)ecomes sutticiently mature or so severely injured as to begin to dry and crack open. When this condition of the boll is reached, pupation takes place, and by the time the spreading of the carpels is sufficient to permit the escape of the weevils they have become adult. — Hunter, W. D.. and Hinds. W. E., The Mexican Cotton Boll Weevil, Bui. 45, Division of Entomology, U. S. Dept. of Agriculture, 1904, p. 75. PROTECTION OF SEEDS BY LINT. 65 Moreov'er, it seems that the adult weevil does not come out through the wall of the boll, but waits to be liberated when the boll opens to maturity. This would mean that if proliferation can exclude the weevil from breeding in the squares it would afford a practical solu- tion of the problem, since instead of merely delaying the emergence of the first brood of weevils for two or three weeks, none of them would be able to set about the work of destruction until the crop had begun to ripen, and all danger of appreciable damage would have passed. It seems, therefore, that the proliferation in the squares is the much more valuable characteristic to be considered in seeking for a weevil-resistant cotton. Proliferation in the bolls is very desirable, but the absence of it should not be allowed to figure very largely against a variety which might have a pronounced tendency tow^ard proliferation in the bud. Nevertheless, other factors must enter the calculation, for thin-walled bolls might allow the weevils to escape earlier. In moist weather the bolls might not crack open, but give the weevils comfortable shelter all winter, as would seem to have been the case in the spring of 1905, when various observers noted that some of the weevils seemed to have the appearance of having emerged only recently from the piipal condition, their very light color showing that their outer covering of scales Avas still in place. The probability is, however, that the proliferation in both places , will be found to depend upon the same internal factor or quality, so that it will be safe to assume that a high degree of proliferation in the bud could be taken as an index of what might be expected from the bolls. This would simplify the problem of selection by permitting us to confine our attention to the buds. PROTECTION OF SEEDS BY LINT. Like the large leafy involucre, the lint is also a peculiar feature of the cotton plant which may prove to have a practical connection with the weevil. Cotton is the only food plant of the boll weevil, and only the cotton, of all the related plants, has an abundant pro- vision of lint. Some of the species of Hibiscus have the seeds slightly silky, but the cotton stands quite alone in the length and abundance of the hairy covering which grows out from the seeds at (he time the bolls are most subject to weevil injuries. From the standpoint of those who believe that all characters are useful to the organisms which possess them, the interpretation of the lint as a weevil-resisting adaptation will not appear unreasonable, since it can scarcely be claimed that there is any other use of the lint so important to the ]:)lant as j)rotection of the seeds from the weevils. In other respects the lint seems rather a disadvantage than other- 99()1!— No. SS — K)Ti M 5 66 AVEEVIL-RESISTING ADAPTATIONS OF COTTON. Avise. In a humid tropical country the seeds, if left to themselves, remain inclosed in the tangled mass of lint and usualh' rot. Birds might carry the lint away to build nests, and in so doing might assist in scattering the seeds, but in most of the varieties the seeds are to be detached only with difficulty. Composed as it is of nearly pure cellulose, the lint can aiford very little nourishment, even in the younger stages. Between the lint and the watery proliferating tissue the weevil larva must find the inside of a cotton boll a very inhospitable place unless it can penetrate to the seeds. Dead and moribund larvte are occasionally found in these unfavorable situations. And even the seeds themselves do not pro- vide so favorable a food as the pollen, as shown by the nmch longer tmie required by the larva- to develop in the boll than in the sc^uare. PROTECTIVJ: seed arrangement in kidney rOTTON. Further intimation of the protective value of the lint is to be found in the very peculiar Kidney cottons, so called l)ecause the seeds are crowded together in the central angle of the chaml)er and adhere firmly to each other, thus forming a small, kidney-like mass. This unique arrangement brings all the lint to the outside of the seed, and may be the explanation of the fact that the Kidney cottons are the only representatives of the Sea Island tyix> which have gained a wide distribution on the mainland. The separate-seeded Sea Island cot- tons came from Barbados, where the boll weevil did not exist and has not yet been introduced. (See PI. X, fig. 2.) The outer wall of the boll of the Kidney cotton is notably thinner than that of Kekchi cotton, so that the beaks of the weevils could reach through without difficulty. But with the layer of lint to sup- plement it the wall becomes, for practical purposes, much thicker than in the free-seeded varieties. The inner parchment lining is rather tough, though ap])arently less so than in the Kekchi cotton. The Indians about Trece Aguas, Guatemala, are said to recognize the weevils as enemies of the dwarf cotton, but it is the local opinion that the Kidney cotton is proof against them. No weevils Avere found on the two bushes of Kidney cotton exam- ined in that locality, but these w'ere single plants growdng near Indian houses several miles away from the nearest field culture. In a forest- covered country like this part of Guatemala the luxuriant and tangled vegetation may Avell impede the flight of such an insect as the Aveevil. And if it lives, as supposed, only on cotton, its chance of }-eaching a single bush of tree cotton would be very small. That the buds and young bolls of the Kidney cotton are able to offer any abso- lute resistance to the -weevil seems very imi)robable, and the abundance of weevils found on the large tree of Kidney cotton at Tucuru last year proved that the immunity, if an3% is not general. NATURE AND CAUSES OF ADAPTATIONS. (i7 The Kidney cotton, though commonly treated as a distinct species under the name Gossypuim peruvianum, agrees with the Sea Island type in all its characters except the peculiar arrangement of the seeds. If this should prove to be an adaptive feature the idea of specific distinctness would have little left to support it. CULTURAL VALUE OF KIDNEY COTTON. The possession by the Kidney cotton of a definite weevil-resisting adaptation would naturally raise a question regarding its cultural Aalue. It belongs to the Sea Island series, and has the long, fine fiber and smooth seeds. The growing of the seeds together in masses would still further facilitate picking and ginning operations. The bolls, too, of this Guatemalan Kidney cotton, at least, are larger than those of any of the Sea Island varieties. It is not likely, however, that any of the varieties of Kidney cotton thus far known will l)e found of use in the United States, for all are perennial '' tree cottons." which have refused thus far to flower or fruit in the period of growth allowed by the shorter summers of our Temperate Zone. In tropical regions this objection would not hold, and there appears to V)e no reason why the Kidney cottons shoidd be disregarded in the search for varieties suited to the various soils and climates. The Trece Aguas Kidney cotton, for example, seems to thrive well in a humid mountain climate considered by the natives to be unfavorable for the annual Kekchi cotton, which is planted several liundred feet lower down. THE NATURE AND CAUSES OF ADAPTATIONS. To explain how such characters as the weevil-resisting adaptations arise invoh'es an interpretation of general evolutionary questions upon which the scientific world is still by no means agreed. Nevertheless, it is evident that students of such subjects should conduct and describe their investigations in accordance with some consistent plan or policy, if th.eir writings are to be understood or their facts intelligibly recorded. Moreover, it would be scarcely reasonable to maintain that such characters can be further increased by selective influence unless it could be believed that they had been assisted in the past by the same agency. It seems necessary to state that in the present report it is not assumed that the weevil-resisting characters have arisen as direct pro- tective responses to the injuries, or that they are the results merely of stimulation or irritation caused by the weevils, as other writers on evolutionary subjects might hold. Nor have they been thought of as caused by selection in any strict sense of the word. Though consti- tuting a most striking instance of the results of selective influence, it 68 WEEVIL-KESLSTING ADAPTATIONS OF COTTON. is believed that the cotton phmt must first have originated in some measure the protective characters before the external conditions (in this instance, the Aveevils) could make them of advantage to the plants and thus encourage their further development. The older theory that environment and natural selection are the efficient or actuating causes of evolutionary change has lost many adherents in the last decade, especially among those who found themselves unable to credit any longer the idea that all the characters and differences of i)lants and animals are, or have been, of use to them. It has been shown, too, by Professor AVeissman and his fol- lowers, that direct adaptations or responses of individual organisms to the environment are seldom or nevei' inherited by their offspring. To take the ])lace of the doctrine of direct environmental influence in evolution it has been suggested that there may be an internal '' hereditai-y mechanism."' as it has been called, which determines adult characters in advance, in the reproductive cells, so that modifi- cations of the specific or varietal type can arise suddenly. Selection would determine, of course, wdiich of such new ''mutations" should survive, but it Avould be a mere accidental coincidence if the new character happened to fit the conditions better than the old. It is possible, however, to explain evolutionary progress and select- ive adaptations without ascribing them either to external causes or to theoretical internal mechanisms. The diversity which plants or animals of the same parentage often show under the same conditions makes it evident that there is no j)recise mechanism which determines their form in advance, and all attempts at securing any absolute uni- formity or "' fixity " of form and color have failed. The fact is that organisms, even of the same species or variety, are normally diverse, and must have ancestry mixed by interbreeding if bodily vigor is to be maintained for any great number of generations. The generalized "" specific type,'" which is a ])roduct, as it were, of this diversity and interbreeding, is constantly and gradually chang- ing, and in many Avays at once, though in some characters more rap- idly than in others. Selection, while in no strict sense a cause of this vital motion of the species or variety, may profoundly influence the direction and rate of change. Selection, in other Avords, explains adaptation, but does not explain evolution." The word adaptation is used in more than one sense by writers on biological subjects. Some treat as adaptations the changes of form or structure by which many plants and animals are able to conform to the needs of different conditions. There are several plants, for example, which have nornuil broad leaves when they grow on land, and very narroAv and nuich-divided leaves when they grow submerged "Natural .Selection in Kinetic Evolution, Science, N. S., 19:549. 1904. NATURE. AND CAUSES OF ADAPTATIONS. 69 in Avatcr. Some plants arc haii'v in dry localities, but arc nearly naked in humid districts. Others treat these direct responses to external conditions under the heading of accommodation, and reserve the word adaptation for characters which appear regularly in a spe- cies or variety, but which fit it for some special condition, such as that presented to the cotton plant by the boll weevil. It has seemed j^roper, therefore, to discuss as protective adaptations any characters which seem to give the Central American varieties an advantage in withstanding the attacks of the weevil, particularly if it can be shown also that the presence of the weevil would tend to the preservation and extension of the given character. In the strict sense of the words, the weevil-resisting ada])tations of the cotton plant would include only those characters which have been increased by the selective influence of the boll weevil, but in the broader practical sense we may treat as a weevil-resisting ada])tation any feature which tends to limit the destructiveness of the insect. The adaptive nature of some of the characters of the Central American varieties discussed in the present paper is reasonably obvi- ous, but in other instances extended studies in developmentaTbiology and primitive agriculture might be necessary to determine the origin and development of a varietal characteristic which may have signifi- cance in the weevil problem. It is easy to understand that so injurious an insect as the boll weevil has exerted a definite selective influence ever since its remote ances- tors turned their attention to the cotton. Perhaps its earlier food plants were completely exterminated. The nearest living relatives of the cotton are the species of Hibiscus, Paritium, and Thespesia, none of which is known to have any attractions for the weevil. It is evident, too, that in the presence of the weevil the cotton plant would have met long ago a like fate if it had not been able to take on its various adaptive characters. That so many of the features by which it differs from its nearest relatives have such obvious connection with the weevil would certainly justify the belief that strong adaptive influence had been at work, even if the other circumstances were unknown. In thinking of the relation between two organisms like the weevil and the cotton we often fall into the error of too great humanizing, so to speak ; that is, we ascribe too great intelligence or too complete a reaction to cause or conditions. Thus the weevil, although highly specialized in some of its instincts, has, of course, no equivalent for the human judgment. It will puncture, as already seen, buds much too small to raise a larva, and will lay its eggs in the rind of the boll, where the larva' can never develop. If the conditions are too favor- able to the weevil, as in humid regions, it would undoubtedlv exter- 70 WEEVIL- RESTRTTNG ADAPTATTONR OF COTTON. niinate its own host ])liiiit l>y jx'riiiittiiiij;" the cotton to [)roduc(' no seed. Paradoxical as it may at first seem, we may. nevertlieless, believe that the best conditions for the per})et nation of the weevil are those Avhich are not altogether favorable to its unlimited multi- plication. CONSCIOUS AND UNCONSCIOUS SELECTION. There are two principal ways in which improved varieties of cotton and other cultivated plants come into existence. The first is by sud- den or abrupt changes, or sports; also called mutations, saltations, and discontinuous variations. These are represented in cotton by the occasional appearance of a plant with brown lint." deeply divided leaves'* (okra cotton) or very short branches (cluster cotton). The Guatemalan varieties represent a second type of evolutionary history, in which improvement is accomplished by more gradual prorgressive change, fostered and accelerated by selection. Two forms of selection are commonly recognized, natural and arti- ficial, the latter eifected by man, the former by circumstances of the enviromnent. This distinction is of doubtful value in any case, and quite obscures the important point in the evolutionary history of cotton and other plants domesticated by primitive man. It would be much better to think of selection as either conscious or unconscious, and between these two a very practicable difference exists. Conscious selection implies the preservation of individuals having a desired quality in the highest degree, while unconscious selection, whether by man, animals, or inanimate conditions, means nierely the rejec- tion of the most unfit, so that the improvement of the species or variety is gradual. Conscious selection acts, of course, much more o In Guatemala several tribes of Indians prefer brown cotton, and for certain garments use brown cotton only. Sei)arate plantings of brown cotton are not made in the neighborhood of Secanquim, where our experiment was located, but there were said to be such at Cajabon and Lanquin, only a few leagues away. The Cajabon people have a dark -brown cotton called " canch nok," and a lighter brown called " canni nok." On the Pacific slope Mr. William R. Maxon found considerable culture of a brown cotton called " ixcaco." At Antigua a similar brown variety is said to have been grown formerly in considerable quantities, the conmion name of which is " cuyuscate." It was not learned tliat any special religious use or significance is attached to brown cotton in Guatemala, as is said to be the case in Peru and in India. t> Some may be inclined to interpret these as reversions and to argue that the deeply divided involucral leaves may be a reminiscence of an ancestral charac- ter of the cotton. Or it may be that the divisions attained by the involucral leaves represent a tendency of specialization which the remainder of the leaves sometimes share by mutation, in accordance with the principle of translocation of characters recently formulated by Dr. R. G. Leavitt (Contrib. Ames Bot.- Lab. No. 3). CONSCIOUS AND ITNCONSCIOUS SELECTION. 71 s})eedily than uiicouscious. but is suhjecl to the srrious danger of weakening" its proteges l)v inbreeding, if the selection be too rigid and persistent. The unconscious selection by Avhich the development of the pro- tective characters of the Guatemalan types of cotton has been encour- iiged differs in no respect from the progress by which adaptive evolution takes place in nature. The Indians have planted and har- vested the crop, it is true, instead of the birds or other natural agents, but they have been entirely unconscious of the struggle for existence to which the cotton plant was being subjected by the presence of the boll weevil. The Indians were only another factor, along with the dry and moist climates, the keleps, and the turkeys. The problem has been solved in a genuinely natural fashion, and affords an excel- lent illustration of the nature of selective influence in evolution. Instead of representing the final possibilities of improvement in characters which give protection against the boll weevil, the Indian varieties of cotton may be looked upon rather as affording materials which conscious selection can render still more valuable. The proliferation character, for example, might never be brought to uniform expression by unconscious selection, because the possession of it would give the individual plant no advantage over its neighl)ors in the production of seed. The i)rolif crating plant might produce no weevils itself, but the free movement of the insects would keep the general average the same. Indeed, a plant uiight easily sacrifice all its buds, set no fruit at all, and thus fail to perpetuate itself. Pro- liferation can become a direct advantage to the individual plant oidy under conscious selection. The full value of the newly ascertained protective adaptations will not be known until they have had the direct selective encouragement now commonly accorded to desirable characters of other cultivated plants. It may appear remarkable that such definite and potentially valu- able characters as the weevil-resisting adaptations of the Kekchi cot- ton should have remained so completely unrecognized hitherto. The explanation of this doubtless lies in the fact that cotton culture is practiced in Central America largely by the Indians and very little by the foreigners or the more intelligent part of the native community, so that it had not received scientific study. Even the existence and utility of the keleps, though apparently known to the Indians from ancient times, had entirely escaped the attention of the European residents of the country. That the Indians should have come to recognize the keleps as l^eneficial and necessary to a full crop of cotton, although not knowing that the weevils injure the cotton or that the keleps eat the weevils, only shows in higher relief the completely unconscious character of the selection conducted in this system of primitive agriculture. The Indians of Alta Vera Paz are extremely 72 WKEVTL-RESIRTINO ADAPTATTOKS OF COTTOX. stolid, nnconiiiiuuicative people, fi-om whom little inforination is likely to be obtained except as replies to direct questions. Familiar from their earliest childhood with the agricultural lore of their own tribe, it does not occur to them that these everyday incidents can he of interest to the white stranger, or if they perceive his interest they learned long since to fear it as a danger of further intrusion. Even our own cotton experiments Avere misunderstood as a menace of addi- tional demands for lands from the white men who now own so large a part of the country. SUMMARY OF ADAPTATIONS. If the facts stated in the present report have been correctly observed and interpreted, Ave must admit that the cotton plant is in a high state of adaptive specialization in its relations Avith its noAv famous insect enemy, the boll Aveevil. Indeed, it may be that the most dis- tinctive and important characters of the plant, from both the botan- ical and the agricultural standpoints — such as the iuA^olucre, the nectaries, the oil glands, the large bolls, and the very lint itself — are adaptiA^e features Avhich the selectiA^e influence of the Aveevil has brought to their present degree of deA^elopment. CLA8SIFICATIOX OF ADAPTATIONS. The adaptations of the cotton plant might be summarized from three different standpoints. A historical treatment Avould proceed from the adaptations of the bolls to those of the buds. Breeding in the buds, for instance, was evidently a later adaptation on the part of the AveeA'ils Avhich has called for a second set of the protectiA'^e characters on the part of the plant. It may be better, hoAvcATr, to classify the adaptations as such, Avithout special regard to their historical sequence of derivation. The more practical purposes are serA^ed by dividing the adaptations into four groups: (1) Those calculated to aA^oid the Aveevils by gen- eral habits of groAvth ; (2) those Avhich exclude the Aveevils, or at least hinder their operations in the buds and bolls; (3) those Avhich attract insect enemies such as the AA'eevil-eating kelep: (4) those Avhich prevent the development of the weevil larvae, even after the eggs haA^e been laid. ADAPTATIONS TO AVOID WEEVILS. 1. Determinate growth. 2. Earlj- bearing. ^. Long basal branches. 4. Early rejection of superfluous squares. ^. Seasonal bearing of perennial varieties, fi. Prompt bearing after cutting back. 7. Hairy stalks and leaf stems. 5. I'endent bolls. 0. Rapid growth of young bolls. SUMMARY or ADAPTATTONS. 78 ADAPTATIONS TO EXCLUDE WKEVIl.S. 1. luvolueral brnrts gi'owu toj^ether at base. '2. riosely a pi tressed margins of iiivolueral bracts. '.]. Margins of involucral bracts strongly laciniate and hairy. 4. Unusual size and width of involucral bracts. r». Calyx produced into slender hairy lacinijie. new problems and adjustments of cotton culture occasioned by the invasion of the weevils, and no assurances can be given in advance regar(Hng the utility of the weevil-resisting adaptations, any more than with the kele}), or so-called '" (iuatemalan ant." Both have a present value, however, in proving that the weevil is no invulnerable dragon which it is hopeless to resist. Instead of having no enemies, as long supposed, the Aveevil is regularly preyed upon by the active and efficient kelep. And instead of there being no remedies which can l)e used against the weevil, it is now found that the cotton plant itself has a whole series of weevil-resisting characters — a whole boll weevil armory, as it were, from which we may select and sharpen the Aveapons which prove best suited to our purposes. The weevil period of each year, that in which the damage is done, extends from the time when the squares are lai'ge enough for egg laying to the period Avhen a full crop would normally be set. If the value of the cotton croj) be divided by the number of days of this period, the result will show the value of each day of protection. It has been estimated by Mr. W. I). Hunter that the l)oll weevil damaged the cotton crop in 1904 to the extent of $20,000,000. It is therefore a very conservative estimate that when the pest shall have spread over the other cotton-growing States the damage will be well beyond a million dollars a day for the growing season — in unfavorable years probably two million dollars or more a day. P^ach day of protection Avhich can be secured by the utilization of weevil-resisting adapta- tions will have, therefore, very definite and considerable value, so that the study and perfection of this group of characters are sure to be the objects not only of formal scientific study on the part of special- ists but of general interest and consideration on the part of the prac- tical cotton-growing public. PLATES. 77 DESCRIPTION OF PLATES. Plate I. (Frontispiece.) Valley at Secanquliii. Alta Vera l*az, (iuatemala. the scene of experiments with weevil-resisting cotton. Plate II. Fig. 1. — Mature plant of Kekchi cotton, to show small size and determinate habits of gi'owth, compact foliage, and long basal bi-anches. Fig. 2. — I'lant shown in figure 1. opened to show numerous large bolls and habit of fruiting on basal branches. Plate III. Involucres of Kekchi cotton, opened to show external and internal nectaries, bracts, and bractlets. (Natural size.) Plate IV. Fig. 1. — Involucres of Rabinal cotton, showing connate and closel.v appressed involucral bracts. (Natural size.) Fig. 2.— Open involucres of Egyptian cotton. (Natural size.) Plate V. Fig. 1. — Young buds of Kekchi cotton, showing numerous weevil punc- tures. The buds were split in half so that the full number of punctures could be seen. (Natural size.) Fig. 2. — Buds of Kekchi cotton (same as fig. 1), showing successful proliferations. (Natural size.) Plate VI. Large buds of Kekchi cotton, the distortion indicating proliferation. (Natural size. ) Plate VII. Weevil-infested bolls of Kekchi cotton, showing larger number of punctures along the middle line of the carpel, where the oil glands are absent. (Natural size.) Plate A'III. Carpels of Kekchi cotton, showing method of proliferation. (Natural size.) Plate IX. Fig. 1. — Kekchi cotton, successive stages of the boll. Fig. 2. — Kekchi bolls (right): King bolls (left), to show comparative size. (Re- duced to about one-half natural size.) Plate X. Fig. 1. — Rabinal cotton, showing foliage, connate bracts, and weevil- infested bolls. (Reduced.) Fig. 2. — Bolls and seeds of Kidney cotton, showing oil glands and protective arrangement of lint and seeds. ( Reduced. ) Bui. 88, Bureau of Plant Industry, U, S Dept of Agriculture Plate II. Bui. 88, Bureau of Plant Industiy, U. S. Dept. of Agriculture. Plate 111. Involucres of Kekchi Cotton, Showing Nectaries and Bractlets. (Natural size.) Bui. 88, Bureau of Plant Industry, U. S, Dept. of Agriculture. Plate IV. Fig. 1.— Involucres of Rabinal Cotton, Showing Connate and Appressed Margins. (Natural size.) FiQ. 2.— Open Involucres of Egyptian Cotton. (Natural size.) Bui. 88, Burpau of Plant Industry, U. S. Dept of Agriculture. Plate V. Fig. 1.— Young Buds of Kekchi Cot- ton WITH Weevil Punctures. (Natural size.) FiQ. 2.— Buds of Kekchi Cotton WITH Proliferation. (Natural .size.) Bui. 88, Buieau of Plant Industry U. S. Dept. of Agriculture. Plate VI. Large Buds of Kekchi Cotton with Proliferation. (Natural size.) Bui 88, Bureau of Pla-Tt Industry, U. S. Dept. of Agriculture. Plate VII. Weevil-infested Bolls of Kekchi Cotton. (Natural size ) Bui. 88, Bureau of Plant Industry, U. S. Dept. of Agriculture. Plate VIII. Carpels of Kekchi Cotton, Showing Proliferation. (.Natural size.) Bui. 83, Bureau of Plant Industry, U. S. Dept. of Agriculture. Plate IX, ^ 9 ?? C) reau nf Plant Industry, U. S. Dept. of Agriculture. Plate X. INDKX Page. Abbasi cotton, flaring of squares 40 Acacia, symbiotic specialization 29 Acclimatization of Kekchi cotton 17 Acconnnodation, direct responses to external conditions 69 Adaptation, discussion 68, 69 explained by natural selection 68 Adaptations, attractive to the kelep 73 classification 72 climatic effect 1 0, 4H, 44 commercial value 76 historical treatment 72 nature and causes 67 periods when most effectiAc 74 of Asiatic cottons unknown 32 Kekchi and Rabinal cottons 73 Kidney, Pachon, San Lucas Sea Island, and Upland cottons.. 74 summary 72 to avoid weevils 72 exclude weevils 73 prevent development of weevil larva* 73 Adaptive characters, extent 69 origin -. 67 Aidin cotton, character 53 Allen cotton, earlier than King in Guatemala 17 Anthonoraus, behavior of species related to boll weevil 48 Antidromy in cotton 19 Antigua, Guatemala, culture of brown cotton 70 Ants caring for plant lice 39 injurious to cotton 39 no protection against weevils 39 plants domesticated by 29 Aphids injurious to cotton 39 Aphis Qossf/pii, infesting plants at liabinal, Guatemala 39 Arid climate, inactive nectaries an adaptive result 24 regions, behavior of cotton -1 3, 44, 45 type of plant adapted : 20 Artificial selection, an indefinite term 70 Ashmead, William H., ants identified 39 Asiatic cottons, comparison with other varieties . . , 53 nectaries 28, 31 Bacterial diseases following weevil injuries 62 Bidens pilosa, nectar produced 36 Birds, value as weevil destroyers 42 Boll weevil larvae, adaptations to ])revent development 73 behavior in Guatemala and Texas 47 destruction by drying out of squares 43 proliferation 46 development in bolls 46 effect of opening of flowers 47, 63 rapid development in buds 63 weevils, absence from Eastern Hemisphere 32 Mexican plateau region 11 adaptations to avoid 72 exclude 73 aid to cross-fertilization 55 79 80 WEEVIL-RESISTING ADAPTATIONS OF COTTON. Boll weevils — Continued. Page. bacterial diseases following injuries 62 behavior in aVjsence of keleps 24 on foot 25 within bolls 59 best conditions for perpetuation 70 change of habits 63 destruction by chickens and turkeys 24 determination of life cycle in bolls and squares 64 development of pollen-eating habit 63 diverse habits of males and females 27 diversity in size 64 effect on unprotected cotton field 35 under favorable conditions 69 eggs, fate 58 exclusion from large bolls 59 feeding in bolls 61 general effect on cotton plants 10 in fields cultivated by Indians 35 injuries in Guatemala 47 injurious nature unknown to Indians 71 ^ mortality in spring 14 not attracted by nearest relatives of cotton 69 pollen diet 55 preference for upper portion of plant 27 selective influence 10 self-destruction 34 short-season varieties of cotton for control 22 starvation 12, 14 Bolls, diseases from superfluous nectar 28 efficiency of adaptive characters 61 fed upon by boll weevils .- 61 feeding punctures 61 infestation by weevils 55 injured, discoloration 56, 59, 62 Kekchi cotton, descriptit)n 16 immunity 56 linings of chambers, toughness as protection from boll weevil 56 normal, absence at Rabinal, Guatemala 24 oil glands 53 outer walls, proliferation 58 variation in thickness 56 pendent, discussion 27 periods of iuununity 74, 75 position 27 proliferation 59 in relation to that of buds 64 protection 51 unconscious selection for uniform ripening 11 very young, iuununity 52 weevil punctures i 61 weevil-proof lining 57 young, rapid growth 55 Bractlets of involucre 33 Bracts, appressed margins 38 dimensions 40 flaring 40 involucral, grown together 37 hairy margins 41 lacinia' 43 of Kekchi cotton 16 protective feature of lajge size 39 Branches, long basal, disadvantages of 20 of Kekchi cotton 19 of cotton, compared witli those of otlier plants 19 dimorphic 19 INDEX. • 81 Brown cotton, origin - ~_p preference of Indians^ 70 Brues, C. T., observations 52 Buds, breeding in, a derived habit 62 falling in Kekchi cotton 20 floral, dimensions -10 method of rejection 21 ovaries of, attacked by weevils 48 parasitized, l)ehavior _ 43 periods of immunity "4, / o persistence of injured 4 (^ proliferation 46 causes and conditions 49 in relation to that of l)olls . .■ 64 protection by involucre 39, 41 recovery from weevil punctures 41 superfluous 21 detrimental 22 weevil-infested, shedding "4 Cacao branches compared with cotton 19 Cajabon, Guatemala, cotton grown in vicinity 15 planting of brown cotton 70 Cecropia, symbiotic specialization 29 Chickens, boll weevil destroyers 24 Climate, effect of change on Upland varieties 16 on earliness •- 17 germination of seed 15 Climatic conditions, effect on United States varieties ^ 17 effects on adaptations 10, 43, 44 variations in cottou 17 Cluster cotton, discussion 28 origin 70 pendent bolls 28 rejection of buds 21 variety of King cotton 17 Coffee branches compared with cotton 19 Cold, effect on tropical varieties 18 weevils 12,13 Collins, G. N. , observation 54 Conscious selection 70 Corn, effect of clianged conditions 18 Cotton aphis, infesting cotton - 39 production, prol)al)le extension 44 short-season varieties 12, 14, 22 stimulus of new conditions 17 Cross-fertilization aided by Ix >! 1 weevils 55 effect of sinndtaneous blossoming 23 secured through nectar 29 Cuba, native cottons 23 Culture of cotton, methods, in eastern Guatemala 19 on Pacific slope of Guatemala 70 Mexico 45 Determinate growth of Kekchi cotton 11 habit, disadvantages of early planting avoided 14 primary branches a factor : - - - 20 Dimorphic branches 19 Dry climate, region, etc. See Arid. Dwarf cotton, effect on cultural methods 19 habit of Kekchi cotton 11 Earliness, effect of development of primary branches ' 20 climatic conditions 12, 17 not shown 1 )y date of flowering 13 Early bearing, facilitated by long basal branches 19 planting, disadvantages 14 9962— No. 88—05 m 6 82 WEEVIL-EESISTING ADAPTATIONS OF COTTON, Page. Early planting, discussion 13 essential in southern Texas 12 Egg puncture sealed by weevil 61 Eggs of boll weevils, encystation 58, 61 Egyptian cottons, immunity from bolhvorm 53 involucral bracts 37 less hairy than Upland varieties 25 not immune to boll weevil 42 oil glands 53 of American origin 9 precocious in Guatemala 17 preference of weevils 26 proliferation 50 susceptibility to injury 42 Environment not actuating cause of evolutionary change 68 Evolution, illustration of inlluence of natural seiecti(jn 71 Evolutionary origin of external nectaries 31 Fertilization, discussion 52 prevention by rain 21 Field cultures, failure in plateau region of Guatemala 25 Flower bud, position , .• 20 Flowering period, short 23 Flowers, failure of pollination 51 keleps imprisoned 29 of Kekchi cotton, color 54 Kidney cotton, color 53 opening, effect on larvfe 47, 63 persistence 51 position 27 Foliage, compact, effect on keleps 26 Food, change, advantage to plants and animals 26 Fungi, growth in nectaries 30 (Termination, cotton seed in Guatemala 15 (iossiipium harbadense, origin 8 herhaceum, Asia Minor A'arieties 53 confusion with G. Jiirsutum 9 nectaries 31 peruvianidn, specific validity 67 Growth, alternating periods in tropical plants 23 utility of acceleration 55 Guatemala, central plateau 24 eastern, climate 12 methods of cotton cuUure. „ 19, 70 nature of the country 15 field experiments 34 importation of foreign thread 24 Indian methods of cultivation 12 western, cotton 25, 70 Guatemalan conditions, effect on United States varieties 17 cottons, preference of keleps 25 Hairs, cotton plant, assistance to keleps 25 Hairy Guatemalan varieties of cotton 25 stalks and leaf stems of cotton 25 Heredity, mechanism 68 Hibiscus, involucral appendages of species 33 nectaries of species 32 species not attractive to boll weevil 69 Hinds, W. E., observations 25, 42, 43, 44, 55, 61, 62, 64 Howard, L. O. , observations 45 Humid districts, behavior of cotton 43, 44 Hunter, W. D., observations 14, 25, 42, 43, 44, 48, 55, 61, 64, 76 Immunity of buds and bolls, periods 74, 75 Inbreeding of cotton by Indians 15 Indeterminate varieties unsuited to early destruction of plants 13 INDEX. 83 Pace. Indian methods of cotton culture 11, 35 names of cotton 53, 70 Indians, agricultural habits 11, 15, 35, 48 cotton culture 11, 35, 71 cultivation of peppers 11 customs at Ral)inal, Guatemala 24 formation of new varieties 15, 71 Guatemalan, observations on boll weevils 66 of Alta Vera Paz, ( ruatemala, characteristics 71, 72 selections of cotton 15, 16, 71 utilization of cotton 45 Interbreeding necessary to vigor 68 Involucral appendages of plants related to cotton 33 bracts of Pachon cotton 25 Involucre, as a protective structure 37 bractlets 33 external nectaries, discussion 31 inner nectaries, discussion 31 protection to inside nectaries 28 protective value 37 Involucres, closed, advantages 38, 41 Egvptian cottons 41 Kekchi cotton 37, 39, 40 Kidney cotton 32 open, advantage 42 Rabinal cotton 37 Sea Island cotton, attractive to keleps 26 Upland cottons 38 value in jirotecting buds 39, 41 Irrigation, effects 45 Ixcaco cotton in Guatemala 70 Jannovitch cotton compared with Allen 17 proliferation 50 Jewett cotton, dimensions of buds and bracts 40 Kekchi cotton, adaptations 73 at northern limit of cotton culture 18 behavior, in Texas 17 bolls, variation in thicknesg of walls 56 characteristic feature 20 comparison with other varieties, at Lanham, Md 18 date of planting in Guatemala 15 developed in weevil-infested regions 4 distinct type of (joiiftj/pmm hirsutum 8 effect of crowding on character 20 fruiting 17 habits of growth 15 in the United States 17 most promising short-season variety 22 quality of lint 7 rapidity of development 55 shortness of season, explanation 11 stems, petioles, leaves, and l)olls 16 tolerance of cold 15 variations 15 weevil resistance, high value 11 Keleps, absent from Eastern Hemisphere 32 adaptations, attractive 73 definitely attracted to cotton plants 35 effect of dense foliage 26 habitat extension 36 hairs of cotton plant, assistance in climbing 25 imprisonment in flowers 29 preference for Egyptian and Sea Island cotton and Biilens pll(mt. . 26, 36, 37 protection to cotton 8, 34, 35 unknown to European residents in Guatemala 71 84 wp:p:vil-resisting adaptations of cotton. Page. Keleps, usefulness in comparison with ants 39 value known by Indians 71 visitation of other nectar-bearing plants than cotton 36 Kidnej' cotton, adaptations 74 at Trece Aguas, Guatemala 32, 53 Tucuru, Guatemala 24, 66 characters 67 cultural value 67 of A nierican origin 9 oil glands 53, 54 origin of name 9 protective features 42 seed arrangement 66 thin outer wall of boll 66 King cotton, l)ehavior in Guatemala 17 cluster variety 17 dimensions of buds and bracts 40 flaring of squares 40 large nectaries 31 proliferation 60 rapidity of development 55 Kinsler, J. H., observations 17, 29, 37, 47, 50, 51, 55 plants cultivated in Guatemala 15 Lacinife of involucral bracts 43 Lanham, Md., experiments 18, 25, 43 Lanquim, Guatemala, planting of brown cotton 70 Large varieties, disadvantages 19 Late planting in northern localities 13 Leaves, Kekchi cotton 16 nectaries, general discussion 30 Leavitt, R. G. , principle of translocation of characters 70 Limbless variety of King cotton 17 Lint, disadvantages 65 protection of seeds 65, 66 Locks, number in Kekchi cotton 16 Mackay , Tex. , examination of cotton 75 Maxon, W. R., cotton obtained 25 oliservations , 70 McLachlan, Argyle, observations 18, 25, 41, 47, 57, 60, 61, 75 Melanthera deltoidea visited l)y keleps 37 Mexican plateau, absence of weevils 11 region, advantages 43 Mexico, cotton culture 45 Mit Afifi cotton, oil glands 53 Molds, growth in nectaries 30 Moqui Indian cotton, character 52 jNIutations in Kekchi cotton 16 Natural selection by boll weevil 54, 69 cotton 9 conscious and unconscious 70 effect of oil glands 54 illustration of influence in evolution 71 in simultaneous flowering ■ 23 not actuating cause of evolutionary change 68 the explanation of adaptation 68 Nectar, continued secretion by plants 32 purpose 2S secretion in Kekchi and Upland cottons 32 on bolls 33 Nectaries, external, discussion 31 position in pendent bolls 27 secretion 27 extrafloral, connection with bacterial diseases 62 discussion 28 functions 29 INDEX. 85 Page. Nectaries, extrafloral, in Kekclii cotton 34 floral, no connection with weevil resistance 29 homology 32 inactive, of Rabinal cotton 24 inner, bractlets subtending 33 connected with drooping habit 28 of involucre, discussion 31 of different varieties 31, 32 Kekchi cotton 16 leaves, general discussion 30 species of Hibiscus 32 Oil glands, of bolls 53 protective feature 52, 54 Okra cotton, origin 70 Old World cottons. See Asiatic. Origin of cottons in arid regions 21 improved varieties of cotton 70 Upland varieties of cotton 10, 44 Pachon cotton, adaptations 74 characters 34, 43 comparison in Texas and jNlarylanA 18 • hairiness 25 involucral bracts 25 Palmer, Dr. Edward, discovery of weevil 45 observations on cotton 45 Paris green, effects on boll weevils 14 I'aritium, species not attractive to boll weevil 69 Parker cotton, dimensions of buds and bracts 40 experiments 41, 57, 60 flaring of squares 40 proliferation 60 Pendent bolls, discussion 27 Peppers, importance to Indians 11 Perennial cottons, annual cutting back 24 not likely to be of use in the United States 67 seasonal bearing 23 Pergande, Theodore, identification of aphids 39 Peruvian cotton in Texas ] 7 Petals, smoothness an obstacle to keleps 26 Petioles, Kekchi cotton 16 Pittier, H. , observations 26, 39, 46 Planting, date in Guatemala 19 late in northern localities 13 Plant lice injurious to cotton 39 Plants, destruction in the fall, difficulty 22 Pollen, diet of weevils .55 eaten by weevil larvte 47 necessity for sexual maturity of weevils 55 Pollen-eating haVjit, development 63 Poneridie, nectar collected 30 Proliferation, advantage only under conscious selection 71 best weevil-resisting adaptation 9 diminution of power in larger buds 51 effect of dry weather 60 efficiency 46 from staminal tube 49 wall of boll 58 in buds and l^olls, relation 64 Kekchi cotton 46, 49, 75 King cotton 60 Parker cotton 60 varieties other than Kekchi 50 of bolls 55, 56, 59 bud, cau.ses and conditions 49 corolla 48 internal tissues of buds 46 86 WEEVIL-RESISTING ADAPTATIONS OF COTTON. Page. Proliferation, probable effects of culture 50 summary of results of study .-49 time required 60 value 65 Protection afforded by adaptations, commercial value 76 when most effective 74 the involucre 37 tough linings of chambers of bolls 56 by keleps, efficiency 34, 35 of seeds by lint 65 Protective characters, first originated by cotton plant 68 general 11 of bolls 51 value of involucre 37 Quaintance, A. L., observations 52 Rabinal cotton, adaptations 73 bolls fed upon by boll weevils 61 characters 41 hairiness - 25 involucres 37, 38 nectaries 31 Guatemala, ants - S9 cotton culture 9, 38 customs of Indians 24 Rain, effect at time of flowering 21 Redshank cotton, characters 53 large nectaries 31 Retalhuleu district of (.Guatemala, cotton planted 25, 34 Rivers cotton, character in Guatemala 17 Rul)ber, Central American, branches compared with those of cotton 19 Sajal, plant often visited by keleps 37 Salama, Guatemala, cotton culture of Indians 24 San Lucas, Guatemala, Sea Island cotton 24 adaptations 74 attacked by other insects 32 disco veiy 50 nectaries 32 Schwarz, E. A., observations 42, 48 on Cuban cottons 23 Sea Island cotton, Guatemalan, discovery 50 nectaries 32 of San Lucas, Guatemala, annual flowering 24 cottons, comparison of petals with Upland varieties 26 flaring of squares 40 involucral bracts 37, 38 lacking in protective features 4 less hairy than Upland varieties 25 not immune to boll weevil 42 oil glands 53 origin 8 precocity in Guatemala 17 smoothness a disadvantage to keleps 25 Secanquim, Guatemala, cotton grown in vicinity 15 experiments 39, 41 Seed, low germination in Guatemala 15 Seeds, protective arrangement in Kidney cotton 66 Selection, conscious, unconscious, natural, and artificial, discussion 11, 70, 71 in cotton, time required 10 provided by boll weevil 10 Selective influence of boll weevil 10 Short season varieties of cotton 1 2, 14, 22 Solenopsis picea, ant inhabiting Rabinal cotton 39 Specific type, generalized, the product of diversity and interbreeding 68 Squares, boll weevil injuries 41 flared and fallen, countings 45 flaring -10, 41 INDEX. O i Page. Squares, multiplication in cluster cottons 28 small, ])ree(ling places for weevils 11 superfluous, early rejection 20 weevil-infested, shedding 43, 74 Staminal tube, proliferation 49 Stipules of outer bracts represented by bractlets 33 Stormproof varieties of cotton 27 Superfluous buds, discussion 21 Symbiotic specializations between plants and animals 29 Tap'moma ramulonun, ant inhabiting Rabinal cotton 39 Temperatures at localities where Kekchi cotton is grown 15 Terrell, Tex. , experiments : .- - 52 Texas, early advent of weevils 9 southern, method of checking weevil 12 Thespesia, species not attractive to boll weevil 69 Top crop, effect of weevil 22 Tree cottons, dimensions 23 discussion 17 immunity to weevils, reported 23 in Guatemala 12 infestation by weevils 8 Mexican, nectaries 30 rejection of buds 21 weevil adaptations 23 {See also Perennial cottons.) Trelease, William, observations 33 Troi^ical A merica, field for experiments 9 Tshubai, plant protected by the kelep 36 Tucuru, Guatemala, Kidney cotton 24, 66 Turkeys, boll weevil destroyers 24 Tyler, F. J. , observations 28 United States cotton varieties, effect of Guatemalan conditions 17 Upland cottons, adajjtations 74 eff ett of change of climate 16 indeterminate habit in United States varieties 13 native in Central America 10 origin : . 10, 44 preference of keleps 25 secretion of nectar 32 Variations, climatic, in cotton 17 in Kekchi cotton , 15 Variegation in Kekchi cotton IH Varieties, new, formation by Indians 15 Victoria, Tex. , experiments : 60, 61 Volunteer cotton, absence in eastern Guatemala 12 breeding of weevils 12 AVeather, dry, effect on crop 13 exclusion of boll weevil from Mexican plateau 11 Webber, H. J. , statements 13, 42 Weaving by Guatemalan natives, use of foreign thread 25 Weevil. See Boll weevil. Weevil-proof lining of bolls 57 Weissman, Professor, doctrine of inheritance 68 Winters, severe, no protection from weevils 12 o c LB Mr '08 ^