No. 556] 



SHORTER ARTICLES AND DISCUSSION 



243 



Mendelian relictions arc likely to be obtained when defective 

 mutations, such as cluster cottons or hornless breeds of cattle, are 

 crossed with normal varieties, but not when normal representa- 

 tives of two species are crossed, like the Upland and Egyptian 

 cotton or the cow and the zebu. Though there can be no ques- 

 tion of the purity of the parental stocks with reference to many 

 contrasted characters, interspecific hybrids seldom show the 

 typical Mendelian behavior. 



Non-Mendelian Behavior of the Bovine Hybrids 

 The facts stated by Dr. Nabours regarding the bovine hybrids 

 do not show that the behavior of the characters is essentially 

 Mendelian. Even if the parental breeds were segregated in the 

 same proportions as in simple Mendelian hybrids, the result 

 would still be essentially non-Mendelian, for the parental types 

 differ by many sharply contrasted characters. Such a segrega- 

 tion of "pure Brahma and pure Durham" would mean that 

 there had been a complete coherence of all of the characters of 

 the two parental stocks, instead of a Mendelian segregation and 

 recombination of independent units. The actual facts appear to 

 lie somewhere between complete coherence and complete segre- 

 gation. 



If the Mendelian conceptions of heredity applied to these 

 bovine hybrids, the segregation of "pure Brahma and pure 

 Durham," instead of appearing to be the rule, would occur only 

 in extremely rare eases, because of the numerous differences of 

 the parental types. Indeed, my own impression on this point is 

 somewhat more Mendelian than the account given by Dr. Na- 

 bours. Though it was noticed that several individuals of the 

 second generation were distinctly more Brahma-like and more 

 Durham-like than any of the first generation, there were only 

 two or three that suggested the idea of complete segregation of 

 the parental types. The fact that impressed me was not that so 

 much segregation of the contrasted parental characters had taken 

 place in the second generation, but so little. The various colors 

 and textures of hair and skin, the horns, humps and dewlaps 

 were generally brought into coordinated, harmonious expression, 



puhl 



Leaves ami Hulls. 



