No. 499] A NEW MENDEL I A N BAT10 441 



which, when acting together, produce none. This may 

 therefore be called latency due to continuation, since 

 patency is brought about by separating the two allelo- 

 morphs whose union effaces their characteristic mani- 

 festation. If the White Flageolet carries the mottling 

 factor, M, as was at first supposed, the appearance of 

 mottling as a novelty in the first generation hybrids was 

 due not alone to that fact, but just as much to the fact 

 that the pigmented bean does not carry the mottled 

 factor; or if, on the other hand, it should prove true on 

 further investigation that the white bean does not carry 

 the mottled factor, the mottled F x is due to this very fact, 

 quite as much as to the fact that the colored bean does 

 possess it. 



The conclusion, reached in my previous papers, that the 

 primitive bean was probably purple mottled and that 

 the purple mottled condition is therefore an atavistic 

 one, seems to be left in some doubt, because of the ex- 

 istence of two types of mottling, one of which behaves 

 as a typical Mendelian unit as shown by Tschermak, the 

 other having the peculiar faculty of losing its external 

 manifestation the instant it becomes homozygous. 1 

 have no doubt that in some form the mottling unit is a 

 primitive one, but whether the ancestral bean possessing 

 that unit was mottled or self-colored would depend en- 

 tirely on which type of the mottling unit it carried. In 

 order to breed true it is necessary that both eggs and 

 sperms shall all carry the mottled factor, and if this 

 mottled factor were of the latter type, the beans pro- 

 duced by the union of such sperms and eggs, being 

 homozygous with respect to mottle, would be self-colored, 

 while if the mottle was of the former type, the homozy- 

 gous beans would be mottled. The conclusion as to the 

 allelomorphic composition of the original bean is prob- 

 ably correct, but as to its external appearance, it may as 

 well have been black as mottled. 



The peculiar behavior of the purple mottled allelomorph 

 in my hybrids and in most of Tschermak 's, may have a 



