MUTATIVE REVERSIONS IN COTTON. 15 



intensified form in the first generation may be reduced or suppressed 

 in later generations. 



It may be that more strictly Mendelian reactions might have i)cen 

 secured if the experiments had been preceded by courses of strict 

 line breeding, as in many Mendelian investigations, but this would 

 not insure results of practical value, l)ecause there is no way to enforce 

 the Mendelian condition of self-feililization infield cultures of cotton. 

 It is also possible that a course of self-fertilization would have the 

 effect of more deiinitely fixing the expression of the desirable charac- 

 ters, and rendei- the later generations less liable to show variations 

 and reversions. These questions are worthy of careful investigation, 

 though such physiological efi'ects of fine breeding upon expression 

 are n(jt 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 uniformity 

 may be reckoned as the chief difference between the reversions that 

 occur as mutations 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 that 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 possibihty of making combinations of charac- 

 ters between diverse types whose hybrids fail to show definite Mende- 

 lian reactions. Instead of attempting to establish immediate unions 

 between the characters of such species as the Egyptian and Uplanil 

 cottons, attention may be given to the occasional nmtative reversions 

 that appear in dilute hybrid stocks. Such mutations might not have 

 the special vigor and fertility of first-generation hybrids, but they 

 might yield more uniform progeny. A stock of Egyptian cotton that 

 had once been hybridized with Upland might furnish a series of muta- 

 tive variations more promising for breeding purposes than a stock of 

 diverse hybrids. The application of this method involves the diffi- 

 culty of producing and giving careful study to the large number of 

 reversions that might need to be inspected before a particular com- 

 bination of characters could be found. Most of the reversions will be 

 inferior, but an occasional superior type may be expected. Even 

 among the Hindi-like variations of the Egj^ptian cotton there are 

 some that are above the average of the Egyptian, in spite of the 

 extreme inferiority of the hnt characters of the extreme Hindi type. 



[Clr. 53] 



