n i I ' ' 
 
 
 U. S. DEPAR IMI'A r OF AGRICULTURE 
 
 BUREAU OF PL \N I INDUSTRY Circular No 
 K. l GALLOW v> I in. I ol Bui 
 
 MUTATIVE REVERSIONS IN COTTON. 
 
 O. I-. COOK. 
 
 •-10 — 1 
 
 .ton : Govt"... . orncc : i»u 
 
 * T^Jk^ 
 

 BUREAU OF PLANT INDUSTRY. 
 
 Chief of Bureau, Beverly T. Gallows r. 
 
 Assistant Chit] of Bur tan . ('.. Harold 1'owell. 
 Editor, J. E. Rockwell. 
 Chuf Clerk, James E. Tones. 
 [( ir.53] 
 2 
 
II p I 
 
 MUTATIVE REVERSIONS IX COTTON. 
 
 INTRODUCTION. 
 
 It is customary hr writers on heredity and breeding to look upon 
 reversions and mutations as rare and exceptional phenomena, but 
 mutative variations of the cotton plant are of frequent occurrence 
 ami many of them appear to I)'- reversions. Knowledge of the nature, 
 extent, and causes of such reversions would throw light upon many 
 problems of breeding and adaptation <>f varieties, for variations <>f 
 this kind appear to be onr of tin* chief factum of deterioration. 
 
 Many pronounced variations occur in cotton as sequels of hybrid- 
 isation and among the diversities aroused by new conditions. Indi- 
 vidual variations seldom appear to differ from the parent stock by a 
 single feature, l>ut usually show numerous peculiar characteristics 
 outside of the ordinary range of variation of the parental types. 
 The cotton plant affords an unusually favorable opportunity for the 
 
 observation of such facts because SO many of its parts are readily 
 seen and compared. 
 
 Changes of characters are not confined to stocks thai have been 
 recently hybridized. Even in the most uniform varieties, such as 
 the Triumph Upland cotton of Texas, many individual plants ma\ 
 show sudden departures from the normal characters of the variety, 
 especially when the conditions are new or extreme. The nature of 
 such variations and the frequency with which they occur indicate 
 that they represent reversions to the earlier diversities of the type thai 
 have been suppressed by selection." 
 
 Reversion may he defined as the return of ancestral characters to 
 expression. Plants or animals that differ from their immediate rela- 
 tives in showing characteristics .>f remote ancestors are described 
 
 isions, or "throw-backs." Striped pigs, black lambs, blue 
 pigeons, red ears of corn, and brown-linted cotton plants that appeal 
 occasionally in pure-bred white varieties may he looked upon 
 reversions to the characteristics of colored ancestors. Reversions 
 may he reckoned as partial if the variant individuals bring into 
 expression only a few of the ancestral peculiarities ami in other 
 respects continue to resemble the typical members of the* breed. 
 
 il Adjustment of Cotton Varieties. Bulletin 159, Bureau of Plant Industry, 
 - Dept. of Agriculture, 1909, j- 
 
 iClr. 531 
 
4 MUTATIVE REVERSIONS IN COTTON. 
 
 Reversions may be called total or complete when there are changes 
 of whole series of characters of parent varieties. ♦ 
 
 REVERSIONS SIMILAR TO MUTATIONS. 
 
 Whether wild species originate by sudden mutative variations or 
 not, there can be no doubt in the case of the cotton plant that definite 
 variations occur and that they can give rise to new cultivated varieties. 
 The great majority of such variations are not preserved because they 
 are inferior to existing types. In a uniform, big-boiled type of cotton, 
 such as the Triumph, many small-boiled individuals with different 
 habits of growth and other peculiarities may suddenly appear. 
 
 In dilute hybrid stocks of Egyptian cotton, with only a small pro- 
 portion of Upland or Hindi blood, individual plants of apparently 
 "pure" Upland or Hindi cotton are found, while the other plants of 
 the same ancestry show only the usual Egyptian characters. If the 
 Egyptian parentage of these variations were not known it would not 
 be suspected from any of the characters that are brought into expres- 
 sion. If the experiments had been conducted on a smaller scale 
 and only the Upland or the Egyptian type had been familiar, these 
 changes of characters might have been looked upon as rare muta- 
 tions into new species, like those that occur in the garden variety of 
 the evening primrose studied by Professor De Vries in Holland. 
 
 It does not seem probable that the mutative changes of characters 
 that often occur in cultivated stocks of cotton represent the attain- 
 ment of new characters, for the characters that come into expression 
 in this way are commonly found among the more primitive types of 
 cotton. Even the characters that have received the largest amount 
 of selective "improvement" from breeders, such as large bolls and 
 long, strong lint, have been found to exist in equal or greater degree 
 in related types of cotton that have been cultivated only in tropical 
 America without any conscious methodical selection by the Indians. 
 
 The more degenerate variations of the Upland cotton, with very 
 small bolls and very short lint, are inferior to any of the varieties 
 cultivated in the United States, so that they can not be looked upon 
 as results of crossing with other varieties, except as crossing may 
 be supposed to induce reversions. It is not necessary to suppose 
 that these inferior characters are new, for some of them are closely 
 paralleled among the very "diverse forms shown by the Kekchi and 
 other primitive Upland types that have been introduced from tropical 
 America and acclimatized in the United States in the last few years. 
 
 Several of these newly introduced varieties also share the same 
 characters that render the Hindi variations of the Egyptian cotton 
 so strikingby different from the typical Egyptian plants, such as the 
 
 « Local Adjustment of Cotton Varieties, Bulletin 1">9, Bureau of Plant Industry, 
 U. S. Dept. of Agriculture, 1909, p. 17. 
 [Cir. 53] 
 
MUTATIV] 1:1 VERSI0N8 IN COTTON. D 
 
 Bhorter lobes of the leaves, the paler preen color, and the thinner 
 texture. Two <>r three of the calyx lobes of the Hindi cotton are 
 usuall) drawn oul into a long, slender tooth, a peculiarity previously 
 observed onl) among the Central American cottons. Mr. Rowland 
 M. Meade has found thai the lobes of the calyx of the Hindi cotton 
 are Bometimes three-toothed, as also occurs in the Rubelzul cotton, 
 a perennial Upland type from eastern Guatemala with long, pointed, 
 Egyptian-like bolls. The bolls of the Hindi cotton have a rounded 
 conic form and are abruptly apiculate. The surface is Bmooth ;i m I 
 even, with the oil glands deeply buried in the tissues, another tendency 
 shared with several of the Central American Upland cotton 
 
 The agreement of the Hindi with the Central American types of 
 cotton extends even to the frequent display of two types of foliage 
 
 anions unaccliinat i/.ed plants. Both types yield occasionally la: 
 
 luxuriant, sterile, or late-maturing plants with deeply channeled 
 
 ti\edohed and seven-lohed leaves. Smaller and more fertile plants 
 have the leaves more nearly plane, with only the usual three lobes 
 
 regularly developed. Very vigorous Hindi-like plant- often have 
 the same general appearance as Egyptian-Upland hybrids and may 
 represent hybrids between the Egyptian cotton and the extreme 
 
 form of (he Hindi. The large si/.e may he connected with the fact 
 that characters of both of the parent types are brought into ex- 
 pression. Nn tendency to unusual luxuriance appears in Egyptian- 
 Upland hybrids that -how the characters of only one of the parent 
 types. The unusual vigor appears to he a physiological phenomenon 
 in some way connected with the tension or conflict in the expression 
 of the divergent characters rather than a consequence of sterility. 
 The abnormal vegetative vigor l>c:_ r ins to he manifested in the earlier 
 stages of growth, before any of the plants have reached bearing age.* 
 
 The close similarities of the variant forms of the many different 
 kinds of- cotton may be taken to indicate that ancest ral charade fist ica 
 are returning to expression. Otherwise it would need to he assumed 
 that the many diil'crent kinds of cotton are engaged in the formation 
 of closely parallel series of new species. Whether the cotton varia- 
 tions lx> looked upon as mutations or not, it is equally desirable to 
 recognise their relation to lever-ions. It might he as proper to call 
 them revertive mutations as mutative reversions, except that the 
 idea of reversion is older and better established than that of new 
 species or new character- originating by mutation. 
 
 The range of ancest ral diversit ies that may he expected to reappear 
 in reversions must be learned by the study of the wild relatives of 
 
 • Origin o! the Hindi Cotton. Circular 42, Bureau of Plant Industry, U. 8 Dept. 
 of Agriculture 19 
 ►The Vegetative Vigor of Hyl>ri<ls :ui<1 Mutations. Proceedings, Biological Society 
 
 <>t Washington, vol i;. vmw, pp v. DO. 
 
 (Cir. 53] 
 
6 MUTATIVE REVERSIONS IN COTTON. 
 
 our domesticated plants. It is a mistake to think of natural species 
 ;is uniform groups of plants that show only one set of characters, 
 like our carefully selected varieties. Very few of our cultivated 
 plants have so many wild or unimproved relatives as does the cotton, 
 to serve as a basis of judgment regarding ancestral diversities and 
 reversions. 
 
 RELATION OF REVERSION TO COHERENCE OF CHARACTERS. 
 
 Complete reversions may be considered as related to a phenomenon 
 already described as coherence of characters. In cotton hybrids 
 there is a general tendency for the characters derived from the same 
 ancestor to come into expression in groups or combinations. It sel- 
 dom or never happens that a single character of one ancestor comes 
 into full expression in a hybrid; that is, without being accompanied 
 by the expression of other characters of the same parent. Coherence 
 of characters appears to have a physiological significance. Among 
 the hybrid plants that are superior to the parent stocks in vigor, fer- 
 tility, and quality of lint, characters of both of the parental types are 
 brought into expression in coherent groups. Hybrids that bring the 
 characters of only one parent to full expression are not superior, 
 while those that show incongruous combinations of characters are 
 notably deficient in fertility. A notable example of this relation 
 appeared in a field of Jannovitch cotton raised from imported seed at 
 Somerton, Ariz., in 1909. The plant had the habit of growth, leave-. 
 and bracts of the Egyptian cotton, but changed suddenly to Hindi 
 characters in the long-toothed calyx, white flowers, and broadly conic 
 light-green bolls. At the same time it retained the Egyptian charac- 
 ters of short stamens and long exserted stigmas. Though having 
 great vegetative vigor, this plant was quite sterile. The anthers con- 
 tained pollen, but did not open to shed it. The stigmas were abun- 
 dantly cross-pollinated by insects, but no ovules developed and not 
 a single boll matured. 6 
 
 VARIATIONS OF DIVERSITY IN THE SAME STOCKS. 
 
 The fact that plants with a preponderance of Egyptian ancestn', 
 such as three-quarters or upward, may show little or no sign of Upland 
 admixture accords with the general tendency toward coherence in 
 
 •^Suppressed and Intensified Characters in Cotton Hybrids. Bulletin 147, Bureau 
 of Plant Industry, U. S. Dept. of Agriculture, 1909, p. 16. 
 
 b The empty carpels of this plant showed a further peculiarity not hitherto observed. 
 The ridge that marks the middle of the wall of the carpel, the line of dehiscence of the 
 ripe fruit, gave rise to a series of long slender hairs that projected into the cavitj . 
 Hairs of the same kind were found afterwards in normal plants and may be looked 
 upon as an additional storm-proof character, since they undoubtedly help to hold the 
 lint and seeds in place after the carpels have opened. 
 [Cir. 53J 
 
Mi i \ i i\ i REVERSIONS IN COTTON. « 
 
 the expression of characters, bul coherence alone would i>< >i explain 
 the further fad thai plants of preponderantly Egyptian ancestry 
 may depart from the Egyptian characteristics and appear as com- 
 pletely un-Eg) ptian Upland <>r Hindi. In Btocks where the crossing 
 upon tin' Egyptian is limited to half-blood Uplands there is a general 
 reduction of the expression of Upland characteristics as compared 
 with iIh 1 crosses of full-blood Upland upon the Egyptians, bul such 
 dilutions do not preclude reversions to complete Upland forms. 
 
 Upland or Hindi characters that remain completely latent or without 
 expression in one generation maj recover their potency and return 
 to complete expression in Borne of the members of the next generation. 
 One planting of hybrid seed may shoi* a preponderant resemblance 
 to one patent, another planting to the oilier parent. One planting 
 of a stock of seed may show none of the Hindi or Upland reversions, 
 while another planting of the same stock of seed or another part of the 
 same field ma\ show very pronounced examples. Three plantings 
 of the Jannovitch variety of Egyptian cotton in 1909 Bhowed Hindi 
 individuals of extreme form, although a large planting of the same 
 stock of seed in L908 gave only a lew aberranl individuals in which 
 comparatively slight evidences of Hindi contamination were detected." 
 
 A question may Mill he raised regarding the authenticity of this 
 extreme example where complete reversions have seemed to take 
 place, as it were, by wholesale. Although there is no reason to doubt 
 the equality and genera] uniformity of the imported Egyptian seed, 
 
 it is still possible to imagine that the seed planted in 1908 was of dif- 
 ferent origin from that grown in 1909, even though both came from 
 the s;mip imported stock. Such possibilities :i^ the sinking of the 
 smooth Hindi seeds to the hot to m of t he bag, or failure to germinate, 
 or early death of the Hindi BeedlingS have also to he reckoned with, 
 though the chances that BUch accidents could afford any complete 
 explanation of the facts appear very remote. The consistent general 
 behavior of the Egyptian plants in the different fields and experi- 
 mental plats and the general scattering of the Hindi individuals in 
 the plantings of 1909 give no support to the idea that the Beed was 
 different. An absolute determination of the matter will require the 
 study of more numerous am! -till larger plantings of Beed, mixed with 
 special thoroughness t<> avoid the possibility of accidental segregat ion 
 of any of the different qualities that may he included. 
 
 Regular field plantings of Egyptian cotton can he made to serve 
 
 the purposes of such experiments, but it is desirable to present in 
 
 advance the collateral evidence for expecting that reversions will 
 
 ur and that they tire likely to appear in different numbers and 
 
 ■ A Study of Diversity in Egyptian Cotton Bulletin 156, Bureau oi Plant Industry, 
 i - Dept. of Agriculture, 1909, pp is--_>l. 
 
 [Or. S3] 
 
8 MUTATIVE REVERSIONS IX COTTON. 
 
 degrees in different plantings, even when the seed is of the same stock. 
 Though breeding is undoubtedly a very important factor in reducing 
 diversity, it is no less important to ascertain the relations of environ- 
 ment to the occurrence of reversions. Such differences of behavior 
 arc frequently shown by the reversions of the Upland cotton, and the 
 irregular variations of the Egyptian cotton appear to be susceptible 
 to such influences. 
 
 Other forms of reversions, both partial and complete, have shown 
 relation to differences of environment in experiments with cotton. 
 Ancestral characters that are prominent in one locality may be 
 entirely suppressed in another place where some of the same lot of 
 seed has been planted. Xot only the amount or degree of reversion 
 but also the frequency with which particular characters are brought 
 into expression is subject to change through differences of external 
 conditions. The failure of any complete Hindi reversions to appear 
 in the Jannovitch planting of 1908 does not appear merely arbitrary 
 or accidental from the point of view of other experiments, but nmy be 
 connected with the facts that the seed was sown rather late and that 
 the plants developed under conditions of abundant moisture ami heat 
 that have shown a very general tendency to bring the extreme 
 Egyptian characters into expression. Grown under such conditions, 
 plants that are known to be Upland hybrids usually take on the 
 complete Egyptian form and show very few Upland characters — 
 sometimes none at all." 
 
 THE HINDI COTTON CONSIDERED AS A REVERSION. 
 
 Young plants of the Egyptian cotton share the foliage characters of 
 the Hindi, including the reddening of the pulvinus, the wrinkled, 
 swollen cushion where the veins meet, at the base of the leaf. If the 
 Egyptian plants are kept small and stunted by unfavorable conditions 
 the resemblance to the Hindi continues longer, so that plants that 
 finally develop with typical Egyptian characters may be mistaken for 
 Hindi. Late in the season there is another partial approximation 
 of the foliage characters, for the Hindi plants generally lose the red 
 color of the pulvinus that serves as one of the most conspicuous 
 diagnostic features of the Hindi at earl} T maturity and during the 
 preceding stage of growth. The general colors of the leaves are also 
 less distinctive in the latter part of the season, the Egyptian cotton 
 often appearing somewhat lighter and some of the Hindi plants 
 becoming darker. 
 
 Plants that do not show very distinct Hindi features in their habits 
 of growth, leaves, bracts, flowers, or bolls may still betray Hindi 
 
 " Suppressed and Intensified Characters in Cotton ITybrids. Bulletin 147, Bureau 
 of Plant Industry, U. S. Dept. of Agriculture, 1909, pp. 17-23. 
 [Clr. 53] 
 
\l I I \ I I \ I I 
 
 9 
 
 tendencies in their naked seed* >rt, sparse linl In man} bucIi 
 
 , g the petals are "l a somewhal lighter yellov than usual, or the 
 purplespol ma} doI be w deepl} colored, but palei petals and spo 
 ma} .»r. -in- wnli. 'in aii> other departure I I jyptian chai 
 
 No one character can be trusted as e\ idence of the presei i Hindi 
 
 tendencies, nor is their an} reason to suppose thai a failure to sho* 
 Hindi characters in one generation excludes their appearance in an 
 other, any more than withthesmall boiled andothei inferior reversions 
 that appear in Upland varieties Some of the Hindi charactei 
 such as tin- naked black Beed with short, sparse linl confined to one 
 .•ml. air a feature of man} small-boiled reversions thai appear in 
 1 1 pi and col ton. 
 
 Instead of thinking of the Hindi cotton as a distinct independent 
 type which has become hybridized recently with the Egyptian, it 
 ma} be considered thai the Hindi characters merely represenl some 
 of the extremes of variation of the Egyptian. Whether the two 
 types were originally distincl or nol ma} make little difference with 
 the presenl facts. There seems to be no definite evidence of the 
 independent existence of the Hindi cotton, either as an indigenous 
 wild plant or as a domesl icated \ ariety. It would doubtless be easy 
 to establish the Hindi cotton as a uniform "pure" stock in tin- -am. • 
 wax thai selection can establish uniform types from other variati( 
 of the Egyptian cotton, but it is a type that would hardly invite 
 cultivation, even among ~ \ pale-flowered tree cotton 
 
 without a petal spot was described in Egypt by Vesling about 1640, 
 and Fletcher is inclined to believe that this W as the prototype of the 
 llmdi cotton. The Egyptian cotton itself is supposed to have hem 
 brought from India to Egypl only about a centur} ago, bul even on 
 this reckoning the time hascertainl} been ample foi themosl complete 
 intermixture to ha\ e taken pla< 
 
 The general absence of intermediate plants ma} be taken as an 
 indication that recenl interbreeding with Hindi has been avoided 
 in the besl of the imported Egyptian stocks, bul at least a tew ii 
 viduals of the extreme Hindi type have been found in all. The 
 remarkabh close similarity of the extreme Hindi plants in all of the 
 newly imported stocks also supports the idea that such plants rep- 
 resent complete reversions. It is ven difficult to believe that all 
 the stocks have had the same opportunities of securing icent inter- 
 mixtures of pure Hindi seed. The more pronounced of the Hindi 
 plants are as uniform anion- themselves a- the Egyptian plants in 
 the same stage of acclimatization. Indeed, they appear even more 
 
 tcher, 1 Thi ir " i ' 1 - 
 
 vol J. m 
 
 J7JH7 I ir 53 L0 
 
10 MUTATIVE REVERSIONS IN COTTON. 
 
 uniform, perhaps as a result of the strong contrast between tnem 
 and the norma] Egyptian plants. 
 
 If the Hindi plants stood alone, they would be identified at once 
 as members of a series of Mexican cottons related to our Upland type, 
 but with definite 1 differences. Some of the varieties contain many 
 plants that combine the Egyptian with the Hindi characters, plants 
 that may be viewed as ordinary hybrids, hut the persistence and 
 remarkable uniformity of the Hindi type can hardly he understood 
 except by the analogy of complete reversions to the Upland type 
 already known in experiments with Egyptian-Upland hybrids. 
 
 CONTRASTED CHARACTERS OF COTTON REVERSIONS. 
 
 Though complete reversion may not have been formally recognized 
 as a phenomenon of heredity, it is believed that an examination of 
 related facts will show a very general tendency of reversions to 
 extreme expression of characters rather than to slight or intermediate 
 expression. Even when only one character appeals to be changed 
 there is more likely to be a complete change than a partial one. 
 Uniform, deep-red ears are a much more frequent reversion in corn 
 than ears that are pale red or that have only a part of the kernels 
 red. Black lambs are generally black all over, and only very rarely 
 spotted, except upon the head. This remains true even when black 
 males are regularly hied with white females, as on the elevated 
 plateaus of Guatemala, where the Indians prefer the black wool. 
 A few- piebald sheep were finally seen in one flock, but only after 
 many of the mixed Hocks had been looked over in vain. 
 
 Similarly accentuated contrasts are found between the Egvptian 
 cotton and the Hindi. The veins of the leaf of the Hindi cotton are 
 united at the base into a larger and more prominent cushion, or 
 pulvinus, than in the Egyptian cotton, and the pulvinus of the Hindi 
 cotton is rendered the more conspicuous by its red color, which is 
 shared by the upper side of the somewhat swollen end of the petiole, 
 for about half an inch. In normal Egyptian cotton the pulvinus is 
 pale green, like the other portions of the veins, or only slightly tinged 
 with reddish, like the end of the petiole. Under some conditions the 
 stalks and petioles of the Egvptian cotton take on a bright-red color 
 like the pulvinus of the Hindi, but in spite of the reddening of most 
 of the petiole the swollen terminal part and the pulvinus of the 
 Egyptian leaf remain distinctly paler. Exactly those parts that are 
 the mosl promptly and deeply reddened in the Hindi plants are per- 
 sistently paler in the Egyptian. 
 
 The stalks and petioles of the Hindi plants may also redden with 
 age, as in the Egyptian, and when this occurs the contrast of color 
 is destroyed, for the red of the pulvinus and the swollen end of the 
 
 [bit 53J 
 
Ml i A 1 1 \ i. i;i.\ BBSI0N8 IN COTTON. 11 
 
 petiole fades out, bo thai these parts become paler than the remainder 
 
 of the petiole, as in the red stemi I condition of the Egyptian 
 
 cotton Bui even on the old Hindi plants the verj young lea 
 whose petioles art pale have the pulvini red. 
 
 The contrasl is aol limited to the color alone, i > ■ 1 1 i^ carried over 
 into the hain coverings of the same parts The lhn.li cotton, like 
 the Kekchi and other Central Aanerican types of Upland cotton, lias 
 the pulvinus and the adjacenl reddened pari of the petiole naked or 
 uiih onlj a few scattering hairs, even when the real of the petiole is 
 densely hairy. In the Egyptian cotton, on the contrary, the petiole 
 generally naked, excepl thai hairs arc to be found on the small 
 pale area at the end where the Hindi cotton i^ naked and red. The 
 pale-green pulvinus <>f the Egyptian cotton is also distinctly hairy, 
 especiallj on \ oung lea^ es. 
 
 A similar case of completely conl rasted characters has 1 n brought 
 
 to m.\ attention by Mr. G. N. Collins. Some of the Mexican varieties 
 of coin have the leaf sheaths almosl complete!} naked, while others 
 have them almosl completely clothed with a coal of line hairs. The 
 contrast is strangely accentuated by the facl thai the sheaths thai 
 are otherwise naked have a oarrovs hand of hairs along the margins, 
 while the marginal hand i-> naked in the types thai have the hairy' 
 
 sheaths. 
 
 REVERSION IMPLIES CONTINUED TRANSMISSION. 
 
 The facts of complete reversion have a practical bearing upon 
 problems of breeding and acclimatization. They warn us not to rely 
 upon the hope of being able to effeel a complete elimination of unde- 
 sirable ancestral characters, in the sense of excluding transmission. 
 There does not appear to be any direct relation between the visible 
 expression of characters in a plant and their invisible transmission in the 
 germ cells. Characters that remain latent in one generation may lie- 
 come patent in another. A stock that appears pure under one gel of 
 conditions may appear in another place to be seriously contaminated. 
 The latent transmission of an undesirable character does no harm 
 as long as the latent condition continues, but the return of such a char- 
 acter to expression may be a serious injury in a crop like t he Egypl ian 
 cotton, where the uniformity of the fiber is a prime requisite. 
 
 Experiments with cotton do not indicate that tendencies to rever- 
 sion are limited to particular descendants or to single characters 
 acting independently, as sometimes inferred from the behavior of 
 Mendelian hybrids. Though regular Mendelian relations are found in 
 cotton, the phenomena of heredity are evidently nol limited to the 
 strictly Mendelian reactions between the chi "•indents of 
 
 Mendelism usually limit then- studies to reactions between varieties 
 
 I 53] 
 
12 MUTATIVE REVERSIONS IX COTTON. 
 
 thai have been brought into a condition of uniform expression of 
 
 characters, but other kinds of reactions are not less interesting and 
 important. The uniformity or " breeding true" of a few generations 
 of individuals docs not show that a stock is "pure"«in the sense em- 
 ployed by many writers on Mendelism. The idea that the Mendelian 
 relations of expression determine the " presence" or " absence ' of the 
 characters is a convenient assumption when the typical Mendelian 
 behavior appears, but reversions to "latent" characters show that 
 expression is no complete index of transmission. 
 
 The idea that the ancestry of our cultivated plants is to be traced 
 hack to uniform "pure" stocks that transmitted only single sets of 
 characters finds no warrant in the study of the more primitive types 
 and wild relatives of our domesticated species. Diversity of expi 
 sion, instead of uniformity, is the rule in nature, and the transmission 
 of the diverse characteristics does not cease when uniformity of 
 expression is enforced through selection. Reversions show that the 
 underlying inheritance of diversity is not completely lost, nor the 
 power of the ancestral characters to reappear, even after long periods 
 of suppression. 
 
 REVERSIONS INTERFERE WITH MENDELIAN EXPRESSION OF 
 
 CHARACTERS. 
 
 The tendency to reversion has to he reckoned as a serious obstacle 
 to the utilization of hybrid varieties unless the external conditions 
 and the processes of reproduction are under much more complete 
 control than with an open-fertilized field crop. 
 
 Mendel pointed out a very useful distinction in showing that two 
 kinds of combinations of characters are represented among hybrids, 
 some stable in expression and others unstable. Intermediate char- 
 acters or reversions that arise from divergent tendencies of expression 
 may occur with much regularity in the first generation of a cross, but 
 may afterwards diminish or disappear. Even when the first gener- 
 ation shows uniformly intermediate characters, the later generations 
 tend to revert to more complete expressions of the parental characti 
 The typical Mendelian relations appear in crosses between strains 
 that differ by definite tendencies to bring certain characters to full 
 expression or to leave them without expression, but it does not appear 
 that the analogies of such characters are applicable to all kinds of 
 plants or to all classes of hybrids. 
 
 Some writers on Mendelism have supposed that inheritance is 
 governed by protoplasmic determinants, or "units." that are entirely 
 separate and independent, so that some of them can be changed with- 
 out disturbing the others, like changing the letters of a word or the 
 words of a sentence. Individual words from related languages can 
 
 [Cir. 53] 
 
Ml I \ I l\ I 1:1 \ i KSION8 in COTTON. 
 
 often be combined into a hybrid sentence withoul disturbing the 
 general grammatical Btructure, much .1- nun characters app< 
 to be substituted for each other in strictly Mendelian hybritls. In 
 other cases the words of two languages <li> not prove t" be direct 
 equivalents, bul require differenl grammatical relations. Sentero 
 can ito longer be translated piecemeal, by individual words, l>ui have 
 to be recast by whole phrases i>r clauses. Words derived from the 
 same language tend to keep together in the hybrid sentence, in the 
 Minic way that characters of diverse parental types hold together in 
 expression. 1 1\ brids that gave intermediate or combined expression 
 of Egyptian and Upland characters in the earl} generations have 
 shown a distinct tendency toward more exclusive expression 
 Upland characters in later generations, even when selected for the 
 expression of Egyptian or intermediate characters. 
 
 [f ilic existence of determinant particles or character units is to be 
 assumed, it is more reasonable to suppose that the expression of the 
 characters is governed by positional relations among the particles 
 than by mere presence ot absence of particles. The theory of posi- 
 tional relations of determinants was suggested by Mr. Walter T 
 Swingle, of this Department." It has the advantage of accommodat- 
 ing a wider range of facts than the Mendelian theory . The establish- 
 ment of definite position- among the particles would account for con- 
 ditions of uniformity and for regular Mendelian ratios of expression, 
 while mutative reversions and diversified hybrids can be ascribed to 
 disturbances of the positional relations. Thus the positional theon 
 admits the transmission of latent characters as a general condition of 
 
 inheritance, whereas Mendelian writers have treated laten<\ as an 
 exceptional phenomenon requiring to be explained by additional 
 theories. 
 
 Mendelian combinations of characters do not promise to attain 
 great importance in cotton because of the general tendencies to rever- 
 sions and correlations of characters that interfere with stable combi- 
 nations between characters derived from different types. Reversions 
 transgress the Mendelian program. They interfere with Men- 
 delian dominance in the firs! generation and with Mendelian combi- 
 nations and segregations of characters in the later generations. A 
 Mendelian combination of the naked seeds of one variety with the 
 abundant lint of another mighl be desirable, but naked-seeded hybrids 
 are prone to revert to sparse lint, so that the yield is not likely to l>e 
 maintained. Fuzzy-seeded types are preferred because of the greater 
 abundance of lint. 
 
 " I11 a paper read at a meeting <>f the Society Cor Plant Morphology and Phyi 
 entitled "Some Theories ol Heredity and of the < Origin of Species • onsidered in B 
 tion to the Phenomenon ol Hybridisation." Abstract published in the Botai 
 c. vol, 25, do. 111. '• 
 
 [Cir 
 
14 .MUTATIVE REVERSIONS IN COTTON. 
 
 REVERSIONS OF LATER GENERATIONS OF HYBRIDS. 
 
 Many attempts have been made to obtain early and prolific Egyp- 
 tian or Sea Island varieties by crossing with Upland, and the first 
 generations of" such crosses often appear very promising. The diffi- 
 culty is that the later generations not only revert to the parental 
 types, but often go farther hack, to the condition of remote unim- 
 proved ancestors. Instead of having longer lint than the Egyptian 
 parent, as the first generation usually does, the later generations 
 become inferior even to the Upland parent. Hybrids representing 
 the fourth and fifth generations, grown at San Antonio. Tex.-, in the 
 season of 1909, did not show a single plant with good Egyptian lint, 
 and very few that were better than ordinary Upland. This extreme 
 deterioration might he ascribed partly to adverse conditions, hut first- 
 generation hybrids grown under the same conditions produced excel- 
 lent lint, longer and stronger than the Egyptian parent. These con- 
 trasts between the different generations show that the hybrids do 
 not merely fail to fix particular combinations of the parental charac- 
 ters, hut may first exceed the parents and then suffer serious deteriora- 
 tion. The characters of the lint that have received the most selec- 
 tion show the most striking deterioration. Such hybrids promise to 
 have practical value only in the first generations. The prohlem of 
 utilization turns upon the possibility of raising commercial quantities 
 of hybrid seed." 
 
 The fact that hybrids of later generations often show characters 
 different from those of the first generation has been taken as proof 
 of the Mendelian theory of separate transmission of contrasted char- 
 acters. Characters that appear in all of the individuals of the first 
 generation but not in all of the second or later generations have been 
 ascribed to the presence of two independent Mendelian "factors'" 
 that are supposed to be transmitted separately, and not recombined 
 in all the members of the later generations, but in only half of them. 
 
 This theory would explain why half of the second generation might 
 fail to show a. character that appeared in all of the first generation, 
 but it gives us no suggestion of the complete disappearance of the 
 long lint in the later generations of the cotton hybrids. There is no 
 reason to suppose that the internal '"factors" that produce the long 
 lint in the first generation of a hybrid cease to be transmitted to the 
 later generations, but there are serious differences in the external 
 expression of the characters. Factors that influence the expression 
 of characters have to be considered, not merely the possibilities of 
 alternative transmission. A character that has been expressed in 
 
 a Suppressed and Intensified characters in Cotton Hybrids. Bulletin 147, Bureau 
 of Plant Industry, 1". S. Dept. of Agriculture, 1909, p. 15. 
 [Clr. 53] 
 
Mi ; \ i i\ i. REV] RBI0N8 IN COTTON. L5 
 
 intensified form in the firsi generation maj I"- reduced or suppressed 
 in later general ions. 
 
 It mux be thai more strictl) Mendelian reactions might have been 
 secured if the experiments had been preceded bj courses "I Btricf 
 line breeding, as in many Mendelian investigations, bul this would 
 not insure results of practical value, because there is no waj to enforce 
 the Mendelian condition of Belf-fertilization in field cultures of cotton. 
 It is also possible that a course of self-fertilization would have the 
 
 effecl of more definitely fixing the expressi f the desirable charac 
 
 ters, and render the later generations less liable to shoM variations 
 and reversions. These questions are worthj of careful investigation, 
 though such physiological effects of line breeding upon expression 
 are DOl taken into account in the Mendelian doctrine of pure germ 
 
 cells. 
 
 Uniformity is much greater and more easily maintained among 
 the descendants of an individual mutation than in a hybrid stock. 
 From the breeding standpoint this greater tendency to uniformitj 
 ma\ be reckoned as the chief difference between the reversions that 
 
 OCCUr as mutation-, and those that are found among hybrids. The 
 
 range of variation among the mutations appears to be as great as 
 among the hybrids, and warrants the expectation thai almost any 
 desirable combination of characters may be found by persistent 
 
 search. 
 
 The apparent tendency of mutative reversions to come true from 
 seed suggests another possibility of making combinations of charac- 
 ters between diverse type- n hose hybrids fail to show definite Mende- 
 lian reaction-. Instead of attempting to establish immediate unions 
 between the character- of such species as the Egyptian and Upland 
 cottons, attention may be given to the occasional mutative reversio 
 that appeal- in dilute hybrid stocks. Such mutation-, mighl nol have 
 the special vigor and fertility of first-generation hybrids, hut they 
 might yield more uniform progeny. A stock of Egyptian cotton that 
 had once been hybridized \\ ith Upland mighl furnish a series of muta- 
 tive variations more promising for breeding purposes than a stock ol 
 diverse hybrids. The application of this method involves the diffi- 
 culty of producing and giving careful study to the large number ol 
 reversions that might need to he inspected before a particular com- 
 bination <>f characters could be found. Most of the reversions will be 
 inferior, hut an occasional superior type ma\ he expected. Even 
 among the Hindi-like variations of the Egyptian cotton there are 
 some that are above the average of the Egyptian, in Bpite of the 
 extreme inferiority of the lint characters of the extreme Hindi type. 
 [dr. 53] 
 
16 Ml DATIVE REVERSIONS IN COTTON. 
 
 AGRICULTURAL SIGNIFICANCE OF REVERSIONS. 
 
 II' the Hindi characteristics continue to reassert themselves in the 
 Egyptian cotton, complete reversion is a less serious obstacle to com- 
 mercial uniformity than partial reversion. Jt is much easier to recog- 
 nize and destroy the complete Hindi plants than the intermediate 
 individuals that give only slight expressions of the Hindi character- 
 istics. 
 
 In plantings of the superior Jannovitch and Nubari varieties the 
 proportion of the complete Hindi reversions has exceeded that of the 
 plants that show an intermediate or partial expression of the Hindi 
 characters. This is in notable contrast with the behavior of a planting 
 of the older and less improved Ashmuni variety, where a large pro- 
 portion of the plants show some of the Hindi characters. Whether 
 these differences should be ascribed to the more careful breeding of 
 the Jannovitch and Nubari varieties or to the different conditions of 
 the fields is not certain. It may be that the intermediate plants 
 represent new or relatively recent crosses between the Hindi and 
 Egyptian forms of plants, rather than partial reversions, but the 
 large numbers of plants that show Hindi seed characters indicate a 
 very general presence of Hindi tendencies, at least in the Ashmuni 
 stock. In any case, the recognition of the complete reversions will 
 assist the careful planter in learning to detect the Hindi characteris- 
 tics, even in their less conspicuous degrees of expression. 
 
 Hybrids and extreme forms of reversions are not the only types of 
 deterioration that must be guarded against if the need of a high degree 
 of uniformity is to be met. Many plants that do not depart from the 
 Egyptian characteristics will be found to fall far below the standards 
 of an improved variety, either in fertility or in the qualities of the 
 lint. There is no reason to suppose that uniformity can be main- 
 tained without continued selection in any field crop grown from seed. 
 
 If reversions were to be looked upon as ordinary hybrids like those 
 that result from recent crossing, it would appear impracticable to 
 guard the crop from contamination, and hence impossible to obtain a 
 uniform commercial product. No matter how carefully the fields of 
 the Egyptian cotton may be isolated, variations may still occur that 
 can easily be mistaken for hybrids. The difficulty of securing ade- 
 quate isolation of the Egyptian cotton will be serious enough in any 
 regions where Upland cotton is grown, but it need not be exaggerated 
 by the condemnation of stocks that may continue to show reversions 
 without recent contamination. 
 
 The occurrence of reversions in one locality or in one season need 
 not stand in the way of early return to practical uniformity if an 
 
 "Local Adjustment of Cotton Varieties. Bulletin 159 Bureau of Plant Industry. 
 U. S. Dept. of Agriculture, 1909, pp. 56-62. 
 
 [C'ir. 53] 
 
Ml I A I l\ I K! \ I RSI0N8 I.N I <>| l".\. 1 7 
 
 adequate selection is maintained and favorable conditions air pro 
 Tided. Familiarity with the vegetative characters « « f the plants \nll 
 enable the undesirable reversions to be rogued out before tin- time of 
 flowering, so that crossing with such plants ma) be avoided. Tend 
 encies to variation that are shown in the lint and the seeds can be 
 rejected when the necessary selections are made in the fall to sei 
 high-grade seed for tin* next season's planting. The influence of the 
 external conditions upon reversions is onl) one "f many indications 
 thai the uniformit) of the crop, as well as the yield of fiber, will dc 
 pend upon cultural methods as well a> upon the Beed that i- planted. 
 
 CONCLUSIONS. 
 
 The phenomenaof reversion in cotton are n<>i confined to the changes 
 of single characters, hut ma) result in wide departures from parental 
 types and bring different series of \ ariet al characters into expression. 
 
 Tin' return of ancestral characters to expression does ool depend 
 upon recent hybridization, l>ut ma) be shown in abrupt, mutative 
 variations of "pure-bred" stocks that have been selected for the uni- 
 form expression of a Bingle set of characters. 
 
 Reversions may be aroused b) new or unfavorable conditions ol 
 environment and may vary in extent and frequency with changes of 
 external conditions. The uniformity of a stock in one place affords 
 no assurance that diversity will not reappear in another locality. 
 Diverse characteristics continue to be transmitted and may return 
 to expression after many generations. 
 
 The variations of the different types of cotton have general simi- 
 larities and may be arranged in parallel series. The general range 
 of the ancestral diversities of cotton is also to be learned .from the 
 study of wild or unimproved types and from the diversities that in- 
 terfere with t lit* Mendelian expression of characters in hybrids. 
 
 The uniformity <>f the progeny of mutative variations renders them 
 greatly superior t«> hybrids for breeding purposes. The possibility 
 of obtaining superior mutative reversions from later generations of 
 dilute hybrid stocks is worthy of investigation, especially in cases 
 where desirable Mendelian combinations are not obtained in the earlier 
 general ions of hybrids. 
 
 The Hindi \ ariat ions of t he Egypt ian are similar in their characters 
 and behavior to some of the reversions that appear in Upland varie- 
 ties and may prove to he forms of reversion rather than result- of 
 recent contamination with a distinct type of cotton. 
 
 The more pronounced form- of reversion in Upland cotton, like the 
 Hindi variations of the Egyptian cotton, are readily distinguished by 
 Vegetative character-, so that they can he rogued out before the time 
 [dr. 53] 
 
18 MUTATIVE REVERSIONS IX COTTON. 
 
 of ilowering, to avoid the contamination of the stock by cross- 
 pollination. 
 
 Partial expressions of Hindi and other inferior characters can often 
 be detected in the lint and seed, even when not shown in the vegeta- 
 tive characters of the plants. Such tendencies are to be taken into 
 account in the annual selection of seed. 
 
 It is also of practical importance to distinguish between the Hindi 
 variations of the Egyptian cotton and the variations that result from 
 crossing with Upland cotton. If reversions are mistaken for results 
 of recent hybridization it may appear impossible to guard the Egyp- 
 tian or other superior types of cotton from Upland contamination, 
 though there is every reason to believe that distances of a few miles 
 will afford complete isolation. 
 
 Approved: 
 
 James Wilson, 
 
 Secretary of Agriculture. 
 
 Washington, D. C, February 2, 1910. 
 
 [Cir. 53] 
 
 O 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 08928 9903