Bulletin 159 Local Adjustment of Cotton Varieties (1909) pp. 10-19
O. F. Cook

DIVERSITY AS A NEW-PLACE EFFECT.

When a high-grade variety of cotton or of any other cultivated plant is grown in a new place and fails to give as good results as in its home locality, it is usual to draw the conclusion that the conditions of climate or soil of the new locality are unfavorable to the variety. Even when no unfavorable factors are known, it is still usual to trust to the assumption that some peculiarity of the variety renders it less suited to the new surroundings than to the old. It does not surprise us that a carefully selected variety fails to appear to the same advantage outside of the region in which it was developed. The selection of plants for purposes of agricultural improvement must always have reference to the external conditions under which the selection is made. Nevertheless, it is as distinctly a mistake to ascribe too much to the special adaptations of varieties as to leave this factor out of account. We must learn what we can regarding the nature of the changes that take place under new conditions, and of the possibility of avoiding .them.

When a variety of Upland cotton planted in a new district fails to attain the standards of the variety, it is usually very easy to show that inferiority of the new conditions is not the only cause of the failure, or even the chief cause. Comparison of the individual plants with each other will soon make it evident that they are much more unlike among themselves than any reasonable supposition of inequality in the conditions would explain. Many individual plants are likely to be found which have not fallen below the previous standards of the variety.

The best of the plants, rather than the worst or the general average, represent the proper test of the possibilities of the variety under the new conditions. The unequal behavior of the plants will often be found to be a larger factor in the low general average than any definite limitation set by the external conditions. If the best plants are as good as in the home locality of the variety we may have an assurance that the new conditions are not in themselves directly and essentially unfavorable, for in that case none of the plants would be able to attain the fully developed characters of the type. The crop may be damaged as much by changes that arise in the plants as a result of new conditions as by factors that actually limit the growth of the plants, but the nature of the damage is different in the two cases.

The more carefully the matter is studied the more evident it becomes that the failures of many individual plants to show the true characteristics of their variety when grown in a new place are connected with differences in the plants themselves and are not directly connected or proportioned to the differences in the conditions occupied by the various individuals. The greater diversity shown among the members of the variety in the new place explains the apparent deterioration. To avoid this diversity and thus maintain a more general conformity to the normal characters of the type is the object of local adjustment.

External conditions that are actually unfavorable to the growth of the plants may be less conducive to undesirable new-place effects than conditions that are distinctly better for an acclimatized or locally adjusted stock of the same kind of plants. This was conspicuously shown in an experiment with imported types of Upland cotton at Falfurrias, Tex., in 1907. In the rows that ran out into drier and more sterile soil a large proportion of the smaller plants in the dry soil kept nearly the normal characteristics, whereas among the larger plants in the better soil only a few individuals remained small and normal. The few small plants in the moist soil and the few large plants in the dry soil showed that individual differences in the plants were able to fully counteract the differences in the conditions.

The inspection of even a few fields with such distinctions in mind is likely to convince any person who is at all familiar with such cotton that diversity among the plants themselves is a factor of practical importance in the diminution of crops and deterioration of varieties. Something in the way of special training or of natural aptitude may be required to give one a full appreciation of this diversity as a concrete, scientific fact, and to enable comparisons to be made between amounts of diversity that are present in different stocks of cotton or in different localities. Some persons appear to be as distinctly lacking in the necessary powers of perception of minor differences of form as others are of shades of color, but it is believed that most people will be able to recognize the forms of diversity that figure in the local adjustment of cotton varieties.

NEW-PLACE DIVERSITY DISTINCT FROM FLUCTUATING VARIATION.

The chief difficulty that has interfered with the recognition of the phenomena of diversity by scientific students and experimenters is not that they are not readily visible, but that they have been confused with other types of variation, such as the ordinary fluctuating differences, accommodative changes, direct effects of environment, and diversity due to hybridization,

Diversification under new conditions represents a fourth group of facts quite different from the other three and much more related to the phenomenon of mutation, as described by De Vries. The progeny of divergent plants may be expected to show fluctuating differences like the members of other varieties, and mutative changes may affect the same characters that are subject to accommodation, but such facts need not prevent the recognition of essential differences. That seedling plants are able to become more diverse among themselves when grown in a new place, even in the first season, and that these diversities have a relation to external conditions are facts not commonly recognized.

The recognition of these new-place diversities does not depend upon the systems of measurements that have been applied to fluctuating variations. Careful measurements of large numbers of plants or animals may lead to the recognition of differences that would not otherwise be detected, but in this case the differences are readily appreciable by direct observation. If the cotton plants that show diversity had to be detected by elaborate systems of measurements, local adjustment would be altogether impracticable. A considerable body of scientific workers would be needed for a whole season to give an adequate statistical account of the diversities of a single field of cotton. It may be obvious at a glance that the leaves of a plant are narrower than those of its neighbors, but many hours might be required to measure, record, and compute with proper care the data that are necessary for a mathematical determination of the actual differences of proportion that are responsible for the general impression. The leaves of the same cotton plant are so variable among themselves that a large number would need to be measured before general averages could be established.

And even after a statistical difference has been ascertained it might still convey a very inadequate idea of the diversities that figure in local adjustment. Mutative changes seldom appear to affect one character alone, and do not obey the law of regression established by Galton. Unlike the fluctuating variations which may be thought of as mere deviations from the same course or standard of heredity, mutative changes render the plants essentially different throughout, often quite as different as the members of distinct species, or even more so. Indeed, one of the serious objections to the idea of mutations as new species lies in the fact that the members of mutative varieties of domesticated plants are much more alike among themselves than are the members of wild species living under natural conditions.

To describe the mutative variations of our cotton varieties as new species would be a very formidable undertaking and may be left to those who believe that mutations are really species. The present report is intended only to call attention to the fact that such variations are of frequent occurrence in cotton, that their numbers are still further increased by changes of external conditions, even to the extent of injuring crops and causing varieties to deteriorate, and, finally, that these dangers are to be avoided by continued selection for local adjustment.

NEW-PLACE DIVERSITY DISTINCT FROM ACCOMMODATION TO EXTERNAL CONDITIONS.

Changes of characters that have definite relations to external conditions are usually called adaptations or accommodations. Writers on evolution and heredity have recorded many examples of plants and animals that show accommodations to different conditions. Among the most familiar instances are the amphibious members of the buttercup family that have ordinary rounded leaves when growing on land, and very narrow, finely divided leaves when growing in water. The same individual can be induced to change the form of its leaves by planting it in water or taking it back to dry land.

The larger, thinner leaves that the coffee plant produces in the shade will not endure exposure to the sun, so that shade-grown seedlings usually lose all their leaves when planted in open places. If the change is not too severe the plant is able to adapt itself to the new conditions by putting out smaller, narrower leaves of firmer texture able to endure exposure to the sun.

Similar changes occur in the stature and habits of growth of the cotton plant in response to differences of environment. In one locality every individual will be larger and have more numerous vegetative branches than any individual of the same variety as it grows in some other locality. In localities where the winds are strong some varieties develop stiffer stems that resist the wind, while others avoid the need of such resistance by assuming a prostrate habit of growth and sending their branches out along the ground. Two selections from the same stock of Mexican cotton showed the same habits of growth at Victoria, Tex., but at Del Rio one of these developed a stronger central stem than at Victoria, while the other became notably prostrate.

Our experiments with the acclimatization and local adjustment of cotton varieties have made it certain that there is another class of changes of characters, those that accompany changes of external conditions, and yet stand in no such direct relations with the external conditions as do the adaptive or accommodative changes. Though accommodative changes may often appear to make members of the same species unlike they are not thought of as rendering them more diverse or individually different. An accommodative change may be shared by all the plants with as much uniformity as any other feature.

Many of the changes of characters that occur in new places, instead of rendering the plants better fitted for the new conditions, render them less fitted. This is certainly true of the instances in which the plants that change their characters are rendered unproductive or completely sterile. A wild plant that behaved as many of our newly imported varieties of cotton have done would have no prospect of surviving. And yet several of the varieties that were nearly sterile in the earlier generations have returned to normal habits of growth and fertility after a few years of acclimatization.

Experience with these more profound changes that attend the process of acclimatization has made it easier to appreciate the nature of the diversity that necessitates the careful adjustment of varieties to local conditions, even in our United States Upland type of cotton, where the stage of acclimatization was long since passed.

Since many of the changes of characters that occur under new conditions obviously do not serve purposes of adaptation, and often result in wide individual differences, even under the same external conditions, it is evident that they ought not to be considered as due to accommodative changes of characters, but rather as resulting from loss or disturbance of adjustments of heredity previously established by selection or by mutation. We may inquire, therefore, into the nature of the adjustment of characters that is disturbed when a variety is planted in a new place, to gain an indication of the possibility of restoring the adjustment and regaining a uniform expression of characters under the new conditions.

The fact that the diversity that appears under a new environment is not the same as a regularly established accommodation does not compel us to deny that new-place diversity may have an adaptive value, since it allows a species to make tests, as it were, of the many forms that its members are able to assume. The forms that prove to be best adapted to the conditions are most likely to survive, and the species may thus secure a better footing than if compelled to keep to a form less suited to the new surroundings. Thus we may consider new-place variations as experiments in accommodation or as affording the materials from which the more definitely accommodative characters may be developed.

It is often assumed that natural selection must have the same tendency as artificial selection to reduce the members of a stock to a condition of uniformity in their environmental relations. Natural selection, however, is a composite of many factors often completely opposite. A dry season that gives the plants a selection for drought resistance may be followed by a wet year that tests their progeny for ability to endure excessive moisture. The advantage would not lie with the lines of descent that specialized exclusively on drought resistance or on flood resistance, but with those that kept the two contrasted qualities represented in the family, either by producing progeny of two kinds or by combining the two qualities in the same individuals. Even though all the drought-resistant individuals were wiped out in a particularly wet season the drought-resistant characteristic need not be lost to the species, but might continue undiminished in transmission.

* For a better appreciation of these tendencies of natural selection to maintain diversity in species and preserve the extremes of expression of environmental characters, the writer is indebted to Mr. A. F. Woods. The point has an evolutionary bearing, since it suggests a way in which natural selection may assist evolution by preserving diverse tendencies among the members of the same species and thus allowing the most advantageous combinations to be built up.

Much emphasis has been placed upon natural selection as an agency for producing greater uniformity through the weeding out of the lines of descent that yield weak or defective individuals, but this is not a reason for holding that the survivors are made more uniform among themselves by natural selection. The tendency is rather to preserve and combine all the different characters that give increased abilities or powers of resistance.*

RELATION OF NEW-PLACE DIVERSITIES TO HEREDITY.

The agricultural superiority of a carefully selected variety depends largely upon the greater uniformity that follows persistent selection. Wild or unimproved types differ from our high-grade varieties not so much in a complete lack of the desirable characters as in a failure to produce the desirable characters with sufficient regularity. Success in the art of breeding is largely a matter of securing uniform progeny from desirable parents.

With seed-propagated field crops like cotton, uniformity of characters is established by persistent selection. The breeder reduces and eliminates the individual diversity that renders a wild or unimproved stock inferior for agricultural purposes to stocks that have been improved by selection. By rejecting all the individuals that express other than the desired set of characters, much higher averages of the desirable features are secured by the breeder. A still more effective method is to preserve only those individuals that bring the desired characters to the highest degree of expression.

It is often supposed that a sufficiently thorough course of selection is able to completely eliminate the undesirable diversity of characters from a domesticated variety, but it is very doubtful whether the ancestral diversity is ever destroyed, in the sense of ceasing to be transmitted. With the most favorable conditions and in varieties that have been bred with the utmost care, individual examples of diversity continue to appear more or less frequently. No complete uniformity is ever attained. Even in vegetative varieties of plants grown only from cuttings or in varieties of wheat that are regularly self-fertilized, variant individuals are still to be found. That the original diversity of characters has continued to be transmitted, even in these most uniform types, is also shown when hybrids are made, and a large number of the ancestral diversities reappear at the same time and under the same external conditions.

These considerations make it quite unnecessary to-suppose that the diversities that crop out among the members of a variety in a new place are impressed upon the plants by the external conditions. We are fully warranted in believing that much of the diversity represents inherent transmitted characters which have been able to come back into expression because the change of conditions has disturbed the previous adjustments that selection had established. It is not necessary to suppose that the diversities shown in the new place are different in any essential respect from the relatively rare individual sports or mutations that appear in the varieties, even under accustomed conditions. The chief difference is that the new conditions call forth many of these variations at the same time. Instead of sporadic mutations of single individuals, we often obtain in a new place a simultaneous promiscuous mutation of many individuals, sometimes of all the individuals, each becoming definitely unlike any of its neighbors, even when large numbers are carefully compared.

Viewed in this way it is possible to understand what our experiments show to be a fact, that even a relatively large disturbance of heredity shown by a variety of cotton planted in a new locality does not afford a sure indication that the conditions are unfavorable. And where the conditions are not unfavorable it ought not to be considered impossible to restore the previous uniformity of the stock by renewing the process of selection that established the uniformity in the first place. Experiments have also shown that such readjustments are readily established, at least in the cotton varieties with which experiments have been made.

A COMPARISON OF DIVERSITY IN TWO LOCALITIES.

To gain definite information regarding the nature and extent of the diversity which is aroused by planting a variety of cotton under slightly different conditions, a careful comparison was made between two fields of Triumph cotton—one at Lockhart, Tex., the other at Kerrville, Tex., in the season of 1907. Both of these localities are in the west-central part of Texas. Lockhart lies 63 miles northeast of San Antonio, at an altitude of about 500 feet, while Kerrville is 71 miles to the northwest, with an altitude of about 1,700 feet. The soil conditions as far as they affect the size of the plants do not appear to be seriously different.

The Triumph cotton is known to breeders as one of the most regularly uniform varieties. It was originated at Lockhart by Mr. Alexander Mebane, and has been carefully selected by him for a considerable series of years. It would be difficult to imagine better examples of uniformity in a variety of seed-propagated plants than are afforded by Mr. Mebane's fields of Triumph cotton. A careful inspection of about 50 acres of Mr. Mebane's cotton resulted in finding only three plants that appeared to be definitely different from their fellows.

Immediately after this test of diversity had been applied at Lockhart, and with the uniformity of the Triumph cotton at that place as a basis of comparison, a similar study was made of a much smaller field of cotton raised at Kerrville, Tex., from seed grown by Mr. Mebane at Lockhart. The difference in diversity between the two places was very striking. Adjacent individual plants were often obviously unlike, and a considerable percentage of the plants could be reckoned as showing distinct departures from the Triumph type.

If the facts were to be interpreted in the usual manner, any observer would have felt fully justified in saying that the conditions at Kerrville were much less favorable than at Lockhart, for many of the plants were distinctly inferior in size and fertility and many of the smaller individuals remained quite sterile. It would be very natural, of course, to use these small and unproductive plants as examples of unfavorable conditions, but other facts showed that this explanation was insufficient. In addition to many small plants that remained completely sterile, there were numerous others that had unusually small bolls, different from those of the Triumph cotton. Other peculiarities of habits of growth rendered these small-bolled plants closely similar to inferior plants that appear among our Central American cottons during acclimatization. Moreover, these peculiar plants with the small bolls were notably later than those that kept the normal Triumph characteristics, so that no ripe seed could be obtained.

In addition to the small-bolled plants there were many other individuals that showed less violent departures from the normal Triumph characters, but still very definite differences. The nature of these differences is indicated in the following notes that were made on a series of selections of variant plants, in order to test the inheritance of their divergent characters:

  1. Plant tall; bolls rather varied in size and shape, broad but long pointed, sometimes with groove in the middle of the carpel at the tip; lint abundant, long. The next plant in the row, apparently normal, had lint only half as long.
  2. Plant very open; basal internodes of the branches very long; lint long; seed smooth.
  3. A very small, low, short-jointed plant, with two branches at each node, possibly a result of injury to the main stem.
  4. Rather larger than its neighbors. Branches all rather long, only one from a node; bolls rather large, all but one with five locks; seeds very large, smooth, with a light-brown ridge along one side.
  5. Plant vigorous; bolls large, not notably different from Triumph; seed rather small, greenish; lint very fine, silky, especially in one boll.
  6. Small plant, about 1 foot high, with light foliage; small bolls, rather narrow and pointed; fruiting branches very short, with only two or three internodes, three of the branches with only one leaf and a boll; lint fine, medium; seed small; bracts connate at base.
  7. Plant large and vigorous, notably more fertile than neighbors; branches long; lint very abundant and of good length; seed green, rather small.
  8. Plant medium, open, either not vigorous or very early and determinate. Most of the leaves already moribund (determinate). Leaves rather long pointed, but some entire without lobes; bolls small, narrow, pointed, some with only three locks, others with four and five; seed smooth.
  9. A small, low, spreading, double-branched plant. Seed with short green fuzz in upper part and long white fuzz below.
  10. A very large plant with long, simple, and double branches and long basal internodes; large Triumph-like bolls; seed very smooth with a small brown tuft at base; lint of medium length, fine.
  11. A large, open plant with long branches, ripening more bolls to date than any of its neighbors, perhaps also determinate; lint not long, but abundant; numerous aborted seeds with lint developed.
  12. A small, open plant with four rather long slender vegetative branches; fertile branches of one or two internodes; only one boll, very small.
  13. A vigorous, long-branched plant; very hairy, notably more so than any of its neighbors, on the stalks, branches, petioles, peduncles, and bracts, and on the veins of the lower surface of the leaves.
  14. Plant vigorous, but not oversized; leaves rather gray-green with long, rather narrow lobes; very short primary branches pushing out at all the nodes and giving the main stem a leafy appearance; stems unusually hairy, but somewhat less than in the preceding; bolls small; lint short; more fertile than the neighboring plants.

It became evident that the diversity alone would account for a considerable diminution of the crop at Kerrville without resorting to the idea that the conditions were really less favorable than at Lockhart. Many individual plants that retained their normal characters were also as fertile as at Lockhart. A further test of the possibilities of normal behavior for the Triumph cotton under the Kerrville conditions was afforded by the adjacent experiments with cotton of the same variety which was being grown for the second time at Kerrville. In this there was no such amount of diversity and no such obvious disparity of yield among the individual plants as in the plot grown from the seed newly brought in from Lockhart.

The fact that our Upland varieties of cotton are not uniform, but usually show a large amount of diversity among the individual plants, has been generally remarked by breeders and experimenters. Stress has usually been laid upon the idea that breeders of varieties have not been sufficiently careful and persistent in selection or that there has been a relapse to diversity through admixture of seed in ginning or through cross-fertilization with other varieties in the field. The following conclusions were reached by Dr. J. F. Duggar, director of the Alabama Agricultural Experiment Station, where a long series of tests of cotton varieties has been made:

* Descriptions and Classification of Varieties of American Upland Cotton.
Bulletin 140, Alabama Agricultural Experiment Station, July, 1907
, p. 24

Man has done quite as much as nature to increase the confusion as to the varieties of American Upland cotton. The chief difficulty that has been encountered in the attempt to describe and classify cottons grown at Auburn under several hundred different names has been the absence of uniformity anions the plants of a single variety. While this variability is partly due to natural agencies, it is also largely due to the failure of growers to avoid the mechanical admixture of the seed of other varieties, which so easily occurs at public gins. Worse still, in the case of many, perhaps most, of the so-called varieties, there has been no long period of selection through successive years with a view to fixing a uniform type.*

But whatever the causes of diversity in other varieties, it is evident in the case of the Triumph cotton that a variety which has been brought to a notable degree of uniformity in its home locality may at once become diverse when transferred to another district, at no great distance, and even under conditions that are not really unfavorable to the variety, as shown by the readiness with which it returns to uniformity after selection for local adjustment.


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