IMPERFECT SEGREGATION 183 



while in the other they were compound, consisting of from 

 two to eight parts. In the first generation of hybrids, the 

 starch grains were intermediate in size and form between 

 the characters in the parents. Other characters were also 

 found to be intermediate. 1 



Another very striking thing about the Mendelian results, 

 suggesting that segregation is often by no means perfect 

 even in the most favourable cases, is, that when the accounts 

 of Mendelian results are examined, many individual excep- 

 tions appear, although the average may show the expected 

 figures with considerable accuracy. For instance, in the 

 account of some carefully conducted experiments with peas, 

 we find the following remark : " When a discrepancy occurs 

 in Tables II., III., and IV. between the totals for cotyledon 

 colour and totals for shape in a given plant, it signifies 

 that in the case of some of the seeds of that plant the 

 shape was determinable whilst the colour was dubious, or 

 vice versa." These tables refer to peas of the fifth inbred 

 generation from the cross, 2 so segregation should theoreti- 

 cally have been perfect. This is only one example, but 

 Mendelian results are full of such cases of individuals in 

 which segregation has not occurred. 



In considering the differences between racial and indi- 

 vidual characters, considerable stress was laid upon the fact 

 that man had probably always selected large variations. 3 

 By eliminating the usual effect of bi-parental reproduction 

 and the necessity for accurate adaptation to the environ- 

 ment, and by constantly selecting considerable variations, 

 man has produced races of animals and plants which, within 

 certain limits, breed true with regard to the particular 

 characters he has selected, for as long as he keeps on 

 selecting. These characters have generally been produced 

 in an extraordinarily short space of time in comparison 



1 Darbishire, A. D., ' ' Oil the Result of Crossing Round with Wrinkled Peas, 

 with Especial Reference to their Starch Grains," Proc. Roy. Soc., B., vol. Ixxx., 

 1908. 



3 Darbishire, A. D., op. cit. 



3 See p. 71. 



