No. 556] SHORTER ARTICLES AND DISCUSSION 



245 



brids, may be more important thar the breeding of hybrid va- 

 rieties. At least this is the suggestion to be drawn from the fail- 

 ure of many attempts to develop superior useful varieties of cot- 

 ton and other seed-propagated plants from interspecific hybrids. 

 As a barrier to a permanent union of two species degeneration 

 in the second or later generations of a hybrid stock may be as 

 effective as sterility in the first generation. It may prove very 

 fortunate that Mr. Borden has imported Brahma cows as well as 

 bulls, for this may make it possible to perpetuate the Indian 

 breeds in Texas. 



A tendency to deterioration in the later generations of hy- 

 brids is likely to be masked as long as hybrids are crossed back 

 on one of the parental stocks, instead of being bred with each 

 other. This is because even dilute hybrids share some of the 

 stimulation effect shown in the first generation. But these ques- 

 tions of vigor and fertility, though of fundamental importance 

 in practical breeding, lie outside of the range of the Mendelian 

 theory. Vigor and fertility are phenomena of expression in the 

 first generation, whereas the theory of Mendelism relates to the 

 transmission of characters to the second and later generations. 

 Mendelism has served a useful purpose in opening the way to a 

 better understanding of the various forms of alternative inherit- 

 ance, but the overshadowing Mendelian theory of heredity as a 

 process of alternative transmission of character-unit particles 

 needs to be cleared away. 



This theory that alternative inheritance is due to alternative 

 transmission does not lead to more correct ideas of the nature of 

 heredity or to better methods of breeding. Instead of providing 

 us with a simple method of making any desired combination of 

 characters of different species, as writers on Mendelism have led 

 the public to believe, the facts of alternative inheritance indi- 

 cate that it is very difficult, if not altogether impossible, to se- 

 cure permanent combinations of characters of different species. 

 In plants that can be propagated from cuttings, hybrid combi- 

 nations can be maintained, but this affords no assurance regard- 

 ing types that are limited to sexual reproduction. 



0. F. Cook 



Bureau of Plant Industry, 

 U. S. Department of Agriculture, 

 December 27, 1912 



