A RICH FIELD FOR WORK IN THE TEXTILE PLANTS
IMPROVING THE FIBERS OF FLAX, HEMP, AND COTTON
The cultivation of flax in America gives a very striking illustration of the extravagance of our agricultural methods. Something like two and a quarter million acres of land are given over to the cultivation of flax, the harvested product being about twenty-five million bushels of seed. But the stalks of the plants covering this vast acreage are for the most part regarded as waste material, notwithstanding the fact that the fiber of the flax plant is everywhere recognized as the most aristocratic of vegetable textile materials. Flax fiber, the material from which linen is made, bears somewhat the same relation to cotton fiber that silk bears to wool. Unfortunately, the plant that bears good seed does not make good fiber; although it can be used as a second quality flax, and has been used as stock for paper. Flax in America is usually grown for the seed only, as the high cost of labor makes competition with the foreign product difficult. Contrariwise the hemp plant (Cannabis sativa), a plant belonging to the mulberry family and distantly related to the hop, which resembles the flax only in the fact that it produces a tough and resistant fiber that may be used for textile purposes, is cultivated in this country exclusively for the fiber, its seed being almost altogether neglected. Yet the seed of this plant is prized in other countries for its oil, and its neglect here illustrates the same principle of wasteful use of our agricultural resources. Hemp, however, is not very extensively grown, being chiefly confined to regions of the bluegrass country centering about Kentucky and Tennessee. Its fiber is coarse, and is used chiefly for making cordage and warp for carpets. At best the cultivation of hemp does not constitute an important industry in the general scale of American agriculture.
COTTON FOR SEED AND FIBER
But when we turn to the third textile plant, cotton, we have to do with an industry that ranks second only to the cultivation of Indian corn. And here there is a story of waste that assumes more significant proportions. For the cotton plant also produces seeds as well as fiber; and it is only in comparatively recent years that these seeds have been regarded as other than a waste product the handling of which gave great annoyance. Fortunately, however, this has been changed in recent decades, and the cotton grower now understands that the seed of the plant is a product quite rivaling in importance the coveted fiber itself. Not only does the seed contain an oil that when pressed out makes a very palatable substitute for the oil of the olive, but the residue constitutes cattle food that sells for from fifteen to twenty dollars a ton-a residue that until recently was used only as fuel, until its value for starch was discovered. So the cotton plant takes high place among producers of commercial seeds, quite aside from its significance as a producer of the most beautiful, useful, and abundant textile fibers. In the present connection, however, it is the quality of the cotton as a producer of textiles rather than as a producer of seeds that chiefly claims attention. The importance of the plant as a producer of fiber is too well-known to require extended comment. Suffice it that America now produces not far from three-quarters of the world's total cotton crop, the land devoted to this crop aggregating more than twenty-five million acres, and the annual yield averaging something like twelve million bales, with a value of much more than half a billion dollars. It is obvious that a plant that has such commercial importance is one that beckons the plant developer. For even slight improvements, when applied on so magnificent a scale, may have vast significance.
CULTIVATON AND IMPROVEMENTS
Some very good work has been done in the improvement of the cotton by selection, without the aid of hybridizing. The cotton plant came originally from the Orient, having been cultivated in India from time immemorial. It belongs to a large family that includes the hybiscus, bearing beautiful flowers, and the vegetable called in the South the Gumbo. The Egyptian and Peruvian cotton and Sea Island cotton falls into one group and the American upland cotton and India cotton into another. It is doubted, however, whether the wild prototypes of the cultivated species are known. The newer classifications recognize twenty-four species or sub-species of cotton, including a number of American species that have attained great commercial importance. The American upland cotton is a perennial plant, now cultivated as an annual, that had its original home somewthere in the heart of South America, but which has proved adapted to the climate of the North American cotton belt, and is now the chief producer of cotton in America, and hence in the world. Sea Island cotton is a species indigenous to the West Indies. It is of larger growth than the upland cotton, attaining a height of three to eight feet, and the bolls that contain the cotton fiber are sharp-pointed and characterized by having only three instead of four or five divisions or locks. Sea Island cotton yields less fiber per acre and is more costly to pick and gin than upland cotton. But it commands a higher price. It is grown chiefly on islands, and along the coast of South Carolina and Georgia. It has peculiar value as material for the making of the foundation for automobile tires. The India cotton and the Egyptian are not grown extensively in this country, although varieties have been introduced and grown by the United States Bureau of Plant Industry for experimental purposes. It is probable that these species will prove valuable when the method of hybridization is applied to the development of new races of cotton modified to meet special needs. The cotton has a large, attractive flower, and cross-fertilization occurs to a considerable extent through the agency of bees and other insects. There is no difficulty in hybridizing different species. On the contrary, it is difficult to prevent cross-pollenation where different kinds of cotton grow in the same vicinity. There is danger of contamination of the strain of any particular cotton in this way. But, on the other hand, there is also the possibility of the production of new and important varieties through such crossing.
IMPROVEMENT THROUGH SELECTION
Until very recently, as already intimated, the improvement in cotton has taken place almost or quite exclusively through the selection of seed, without any conscious effort on the part of the grower to pre-determine the characters of the seed by cross-fertilizing the parent plants. Indeed, until somewhat recently, cotton growers in common with other agriculturists, have been more or less oblivious to the need of care in the selection of seed. And even now, according to so good an authority as Professor Thomas F. Hunt, of the New York College of Agriculture, probably half the cotton seed planted is taken at random from the public gin. Yet the importance of selection has come to be understood in recent years by a good many growers, and the old slipshod methods have been abandoned by such cotton raisers-as appreciate the advantages of applying scientific methods to the betterment of their crop. The method that has produced excellent results is one that has been illustrated over and over in connection with one after another of my experiments in plant development. It consists essentially in selecting for seed the products of plants that are observed to be more productive than their fellows, and which at the same time produce cotton fiber of superior quality. With the cotton, as with other plants, it does not at all suffice to select merely the individual bolls that chance, through some nutritional advantage, to grow to large size. It is necessary to consider the plant itself and its total product as well as the average quality of that product. We have seen that, under precisely similar conditions, different individual plants of every species show a more or less wide range of variation as to size and productivity, resistance to disease, and other qualities. This variation is quite as notable among cotton plants, even of the most fixed varieties, as among most other cultivated plants. The practical method employed by the most intelligent cotton raisers is to send trusted employes through the fields to select the plants the product of which is to be saved for seed. The seed cotton thus obtained is ginned separately, and the owner who has taken this trouble is sure to be repaid by the improved average quality of his crop the ensuing season. The United States Bureau of Industry has published details as to a method of selective breeding that has been practiced for several years by some growers of Sea Island cotton, through which the staple has been increased from 1.75 to 2.5 inches in length. The method requires four years of selection to secure enough seed for general planting. The first year, five or more plants are selected as the best in the field. It is urged that it is important to take the seed of at least five plants, not merely of one, because an individual plant of fine appearance may fail to transmit its characteristics. Yet my own experience with a wide range of plants would lead me to have much confidence in the progeny of the one best plant in the field. However, the practical cotton growers have thought that they secured better results by selecting several plants instead of depending on a single one. The second year, five hundred or more seeds are selected from each plant for the next year's planting. The second year's crop is examined with great care to see whether the desired qualities are being strongly transmitted. If such is the case, several of the best plants are again selected to furnish seed for a new planting. Meantime the seed of the remainder will suffice to plant a patch of about five acres in the third year. The third year five hundred or more plants will be grown of each of the individual selections, and as many five-acre seed patches to produce seed for general planting as there were individuals of the first year whose progeny was considered worth propagating. In the fourth year there will be seed for general planting from the five-acre seed patches of the previous year. There will be several five-acre seed patches from the specially selected individuals of the second year; and five hundred or more plants of each of the individual selections. That is to say, in this fourth year we shall have a general crop of cotton plants all of which are the descendants in the third filial generation of the five plants or thereabouts selected in the first year. And inasmuch as each successive year the five or so best plants have been selected out to start a new series, the process of betterment will go on indefinitely. The general crop in each successive year will represent the progeny, not of the crop of the preceding year, but a third-generation offshoot from the best plant of an earlier year. And the crop of this year will of course supply five best plants to become the progenitors of the general crop four years from now. And this, it will be obvious, is merely the applying of the familiar rules of selection which we have seen illustrated in the production of specialized races of flowers and fruits and vegetables of many types. The only difference is the practical one that, in my experiments, the inferior members of a fraternity are usually destroyed when the best half dozen have been selected for preservation, instead of being preserved for cropping purposes. This modification obviously in no wise alters the principle, but it is a practical change that is clearly necessary to meet the needs of a cultivator who, while striving to improve his crop, must at the same time take such crop as can be grown year by year, without waiting for the best ultimate product. Of course there are limits to the amount of development that is possible through such selective breeding. The plants operated with have certain hereditary limitations, and these are pretty surely fixed by long generations of inbreeding. When these limits are attained by the practical plant developer, through the carrying out of such a system of rotation as that just outlined for a good many years, the best pure types of cotton represented in the strains under investigation will have been isolated, and the experimenter will find it difficult or impossible to make further improvement by the mere process of selection. Then it will be necessary to introduce the method of hybridizing, to give new vigor to the plants and to produce new segregations and combinations of characters that will be equivalent to the production of new varieties. And for this purpose, as I have already suggested, the mixing of strains of the American cotton with the Oriental ones, and also doubtless, the utilization of some hitherto neglected wild species may be expected, reasoning from analogy, to prove of value. A beginning is said to have been made by H.H. Webber, through combining the fine, long, strong lint of the Sea Island cotton with the large bolls and productiveness of the upland cotton.
INSECT FOES OF COTTON
It goes without saying that a highly specialized plant like the cotton, and in particular a plant growing in sub-tropical regions, is subject to the attacks of many insects. In point of fact, the distinguished entomologist, Dr. L. 0. Howard, enumerates no fewer than 465 species of insects that feed upon the cotton plant. But among these there are four that are so preeminent in their destructiveness as to make the ravages of the others seem insignificant. These are the cut worm (Aletia argillacea), the cotton worm, the cotton boll-worm (Heliothis armiger), and the Mexican cotton boll weevil (Anthonomus grandis). The cutworms are dangerous to the young plants as to other seedlings. The cotton worm may appear in hordes, but has not been especially destructive in recent years. The cotton boll-worm is an insect which, notwithstanding its name, prefers other crops, in particular maize, to cotton, so that the cotton crop may be protected from its aggression by planting a few rows of maize at intervals of twenty-five cotton rows throughout the cotton field. But the newest and most aggressive of the pests, the cotton boll weevil, is an enemy that is not so easily reckoned with. This little insect has been known a long time in Mexico as a pest that attacks and destroys the tender portion of the cotton boll itself. But it is only in recent decades that this insect has worked its way northward and into the cotton region of the United States. It must now be reckoned as one of the most destructive enemies of the cotton plants in the more southerly districts. Quite recently, however, an enemy of the boll weevil has been found in Guatemala by Mr. W. F. Cook, the botanist in charge of investigations in tropical agriculture of the Bureau of Plant Industry. This enemy of the boll weevil is described as a large, red-brown, ant-like insect. It is known to the native of Guatemala as the kelep; entomologists describe it as the Guatemala ant, Ectatomma tuberculatum. This insect is described by Mr. Cook as strikingly adapted by structure and instinct for the work of protecting the cotton against the weevils. It has large jaws or mandibles that fit neatly about the weevil and hold it firmly, and a sting that penetrates a vulnerable point in the shelly armor of the weevil. The sting paralyzes the victim, somewhat as wasps paralyze spiders and caterpillars to supply food for their young. After paralyzing the weevil with the poison injected by the sting, the kelep carries its prey to its subterranean nest, to feed the larvae. The kelep does not confine its predaceous attacks to the boll weevil but kills also many other insects found upon the cotton, including the larvae of boll worms and leaf worms. It has the curious habit, Mr. Cook tells us, of storing the dismembered skeletons of captured insects in special chambers of its subterranean home. Through Mr. Cook's efforts, this enemy of the boll weevil has been introduced. It has shown its ability to breed both in captivity and in the cotton fields of Texas. The insect forms colonies that are said to be even more highly developed than are the colonies of ordinary ants. New colonies are formed by a sub-division of the older communities, as among the honey bees, not by solitary females as is usual among ants. It is expected that the insects will thrive in the cotton districts, and will serve at least to keep the boll weevil in check, although it is not to be hoped, according to Mr. Cook, that it will altogether banish the pest; inasmuch as the weevils have not been exterminated in Guatemala, although the kelep has there imposed a very important check on their increase. It is urged, however, that additional protection from the boll weevil must be sought through such development of the cotton plant itself as will make it resistant to the attacks of the insect. The authorities of the Department of Agriculture have observed that in the cotton plants of Guatemala, where the weevil is native, the buds do not always drop off after being penetrated, and that the young bolls continue to develop in spite of the attacks of the weevil. It was found on examination that such resistance was due to the actual growth of new normal tissue into the cavity eaten out by the weevil larvae, with the result uniformly fatal to the larvae itself. It appears that the larvum in its younger stages subsists entirely on the highly organized food material to be found in the pollen grains of the unopened cotton flower. The new tissue formed by a mere swelling or proliferation from the central column of the flower is watery and innutritious, and may starve the larvum to death even if it does not act as a poison. Here, then, is a method by which the cotton is able to offer effective resistance to the weevil. It is suggested that if a variety of cotton could be developed in which the tendency to the growth or proliferation of the new tissue was pronounced, as it is in certain individuals, the weevil might be exterminated. It is considered possible that such a variety may exist at the present time in some parts of tropical America, and that if such a resistant variety can be found, it may be possible to develop the characters in the cultivated plant through selection. Inasmuch as individual plants show this power of resistance, there should be no difficulty in developing and raising cotton plants in which this resistant quality is a uniform characteristic. The problem is obviously identical in principle with numberless other problems of plant development that have been solved in the same way. And here, also, we may reasonably assume, aid may be secured through the careful cross-pollenizing of resistant individuals, even if no resistant species can be found with which to effect hybridization. It is reported that a tree cotton indigenous to southern Mexico is partially resistant to the weevil. It will be of interest to determine whether the peculiar characteristic as to growth of new tissue that makes the individual cotton plants resistant to the weevil constitutes a unit character that will be transmitted along Mendelian lines, comparable therefore to immunity and susceptibility to rust as revealed in Professor Biffen's experiments with the wheat. Whether or not such is the case, it may be expected that the cotton plants that show resistance will transmit this propensity to some of their offspring. It is obvious that an investigation of the hereditary tendencies of the cotton in this regard, coupled with experiments looking to the improvement of the quality of the fiber itself, should have at once a high degree of interest for the plant developer and the promise of large reward to both grower and consumer. The geographical location of my experiment farms makes it difficult for me to experiment with so tender a plant. But I have thought that a somewhat extended account of the work of others in the selective breeding of this plant would be of interest, partly because it suggests such close analogies with numerous experiments already detailed. I would urge upon the attention of plant experimenters who are located within the cotton belt the possibility of applying the principles that we have seen outlined in many hybridizing experiments to the improvement of a plant which, despite the excellence of its product, is by no means perfect. The fundamental principles of plant development are everywhere the same, and the methods that have been employed at Santa Rosa to perfect flowers and orchard fruits and vegetables may be applied with full confidence to the improvement of the cotton plant. In my own studies, I have come upon a variety of cotton grown in a far northern climate, that of Corea, for ages, and as it appears to be very much hardier than any cotton heretofore known, I have thought it of peculiar interest. The bolls, though produced abundantly, are small and have a short staple, growing on compact, low-bushing shrubs. This matures at Santa Rosa when other cottons seldom reach even the blossoming stage. I have sent seed of this to experimenters better located; and this unusually hardy dwarf cotton may yet prove of value for crossbreeding purposes.
-The function of cotton fiber is, of course, to protect the seed and to facilitate its distribution. But Nature would scarcely have carried the elaboration of the protective fiber to such a length, had she not been aided by man, who has selected, generation after generation, among the cotton plants, the ones that produced the best quality of fiber as gaged by his own needs.
This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 8 Chapter 4