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THE AMERICAN NATURALIST [Vol. LII 



the occurrence of new or extra-parental characters was 

 detected, although a few plants in the F 2 of the simple 

 hybrid slightly exceeded the range of one or the other 

 parent. Examination, in 1917, of the F 3 progenies of 

 the simple hybrids, and of the % back-cross progenies 

 also failed to reveal the occurrence of any extra-paren- 

 tal characters. Nor have any new characters been de- 

 tected in the first, second or third generation progenies 

 from selfed seed of the parent individuals. It is evident, 

 therefore, that nothing in the nature of a mutant has yet 

 appeared in any of these line-bred and hybrid stocks. 



It was not, however, expected that mutants would be 

 detected in these small progenies, which were grown for 

 the purpose of studying, under controlled conditions, the 

 behavior of the hybrids in the earlier generations and 

 to provide seed for the growing of each stock on a more 

 extensive scale. Statistical evidence regarding the pro- 

 duction of mutants can scarcely be expected until much 

 larger numbers of plants have been examined. The 

 stocks resulting from repeated back-crossing should be 

 especially interesting to study in regard to the occur- 

 rence of mutation. 13 



Conclusion 



The investigation here described was undertaken in 

 the endeavor to ascertain the conditions under which 

 mutants are produced, in Egyptian cotton. Simple and 

 back-crossed hybrids were made between two varieties 

 (Pima and Gila) which differ significantly in numerous 

 characters. Three generations of the hybrid progenies 

 and of progenies from selfed seed of the parent indi- 

 viduals, were grown. No evidence of the appearance of 



