8 COTTON SELECTION ON THE FARM. 



has been due to previous crossing or to some other cause. Experi- 

 ments with cotton have shown that a change to new conditions, or 

 even an unfavorable season, may call forth an unusual amount of 

 individual variation in a previously uniform variety of cotton. New 

 variations aroused in this way are very likely to come true to seed, 

 so that the seed of the same stock appears pure in one place and 

 impure in another." 



Each new variation constitutes, in effect, a new variety. The sub- 

 sequent crossing of the different variations with each other and with 

 the parent type produces hybrids just as if the variety had never 

 been pure or as if it had been mixed with seed of other varieties by 

 intention or by accident. 



The farmer must understand, therefore, that even if he should suc- 

 ceed in keeping a new stock of cotton completely isolated from all 

 other kinds it would still be Hable to deteriorate as the result of 

 spontaneous changes of characters or changes aroused by differences 

 of external conditions. If selection be neglected long enough, even 

 the most superior variety can deteriorate into an inferior mixture of 

 varieties, like an unselected stock. This return to diversity is what is 

 usually meant by the "running out" of a variety of cotton. 



WHY SELECTION MUST BE MAINTAINED. 



There is no known method or alternative by which the farmer can 

 avoid the necessity of selecting his own cotton unless it be that of 

 buying from neighbors who may be more wilHng to take the necessary 

 trouble. 



All that breeders and seed growers have said of the importance of 

 obtaining pure strains of our varieties of cultivated plants may be 

 admitted, but it also appears that even the purest strains can not be 

 expected to stay pure unless selection is maintained. Now and then 

 an individual plant will depart from the characters of the variety 

 and show a tendency to small bolls or some other undesirable feature. 

 It is important that all such plants be recognized as early in the 

 season as possible and removed from the field. 



Even if the farmer is skillful enough to detect all inferior plants at 

 the end of the season and rejects their seed, he can have no assurance 

 that the degenerate tendency has been removed. It is to be expected 

 that insects have already infected other plants with the pollen of the 

 degenerate individuals, and the undesirable characteristics may 

 therefore be expected to reappear, even in the progeny of the best 

 plants. 



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

 U. S. Dept. of Agricultiu-e, 1909. 

 [Cir. 66 J 



