No. 551] THE MENDELIAN NOTATION 649 



modifying its reaction during development. This is a 

 physiological conception of heredity, as it recognizes the 

 great cooperation between factors during development. 

 It is a very simple conception of heredity, moreover, for 

 it allows a multitude of individual transmissible differ- 

 ences with the assumption of a very few factors. Some 

 illustrations will be given later that will show the idea 

 underlying this theory. Let us now see whether Castle's 

 work can be described properly by it. 



Castle started with a peculiar character. It fluctuates 

 continually and has never been bred to as small a varia- 

 bility as have many other characters. I have worked 

 with a somewhat similar character in maize. It is a 

 variegated pericarp color. In experimenting with it I 

 have raised over a thousand progeny in one generation, 

 a thing manifestly impossible with rats. Both solid 

 colored ears and white ears have been obtained, and 

 while at present it would be unwise to draw definite con- 

 clusions, it appears that both solid red ears and white 

 ears of this kind give again variegated progeny. In 

 other words, neither the red ear nor the white can be- 

 have like a normal red or white ear, but as if the pattern 

 had fluctuated so widely that it can not appear on the 

 ear (this explanation was suggested by Emerson). At 

 any rate, we may conclude that the rat pattern fluctuates 

 widely and is therefore markedly affected by some con- 

 dition either internal or external. 



Castle began therefore with a character in a fluctua- 

 ting condition, possessed by a race which had not re- 

 cently been crossed with a different race. This does not 

 mean, however, that the various individuals forming his 

 original stock did not differ in several factors that in 

 their different combinations might have an effect upon 

 the developing pattern. Suppose for the moment that 

 this were actually the case. If he had been able to pro- 

 duce a fraternity by a single mating numbering several 

 thousands, he would have produced individuals with all 

 of these combinations of other genes. It is probable 

 that he would then have obtained his progressive ex- 



