B. V. l.—rM. 



MUTATIVF. R1:VHRSI()NS IN COTTON. 



INTRODUCTION. 



It is customary for 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 

 and many of them appear to be reversions. Knowledge of the nature, 

 extent, and causes of such reversions would throw light upon many 

 problems of breeding and adaptation of varieties, for variations of 

 this kind appear to be one of the chief factors of deterioration. 



Many pronounced variations occur in cotton as sequels of hybrid- 

 ization and among the diversities aroused by new conditions. Indi- 

 vidual variations seldom appear to differ from the parent stock by a 

 single feature, but usually show numerous pecuUar 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. 



Chanires of characters are not confined to stocks that have been 

 recently hybridized. Even in the most uniform varieties, such as 

 the Triumph Upland cotton of Texas, many individual plants may 

 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 that 

 have been suppressed by selection.'^ 



Reversion may be defined as the return of ancestral characters to 

 expression. Plants or animals that differ from their immediate rela- 

 tives in showing characteristics of remote ancestors are described as 

 reversions, or "throw-backs." Striped pigs, black lambs, blue 

 pigeons, red ears of corn, and brown-linted cotton plants that appear 

 occasionally in pure-bred white varieties may be looked upon as 

 reversions to the characteristics of colored ancestors. Reversions 

 may be reckoned as partial if the variant individuals bring into 

 expression only a few of the ancestral peculiarities and in other 

 respects continue to resemble the typical members of the breed. 



a Local Adjustment of Cotton Varieties. Bulletin 159, Bureau of Plant Industry, 

 U. S. Dept. of Agriculture, 1909, p. 20. 

 [Cir. 53) 



