LATENCY. 



69 



IV. LATENCY DUE TO HYPOSTASIS (MASKING). 



Sometimes a character may be hidden by the presence of another 

 character which simply obscures it. Thus, in the hair of most species 

 of mammals there are both yellow and black pigments, each of which 

 may be visible because of a certain other factor which causes them 

 to develop more or less in different regions of the same hair. But in 

 the absence of this controlling factor the black and yellow pigments 

 develop in the same regions of the hair and the black thus obscures 

 the yellow. Prof. T. H. Morgan found a case in the cross between the 

 black rat and the Alexandrian rat, in which the black color was 

 dominant over the gray color of the Alexandrian rat, presumably 

 because the black color hid the other color characters. 



Characters which are thus obscured by the presence of another 

 character are said to be latent by hypostasis — that is, they are 

 hypostatic to the obscuring character, while the latter is said to be 

 epistatic to the obscured character. These convenient terms were 

 suggested by Professor Bateson. In one of his crosses between 

 black beans and yellow beans ShuU obtained some seal-brown beans, 

 and inferred that the seal-brown had been present in the black 

 beans, but was there obscured by hypostasis. 



V. LATENCY DUE TO INHIBITION. 



The category of latency due to inhibition is much like the last and 

 was included by Shull, perhaps properly, wdth it. It seems possible, 

 however, that it may deserve separate treatment. In the cases 

 considered characters have been invisible simply because some other 

 character present obscured them. There are cases, however, where 

 the presence of one character seems to prevent the development of 

 another character. For instance. Prof. V. L. Kellogg, of Leland 

 Stanford Junior University, in crossing certain white and certain 

 colored varieties of silkworms found the white to be dominant. Simi- 

 lar phenomena have been found by Bateson and Davenport in 

 poultry, and the writer, in cooperation with Mr. Q. I. Simpson, has 

 found the same in swine. Here the presence of the white character 

 seems to prevent the color from developing rather than simply to 

 obscure the color. Perhaps we might not be justified in treating 

 this case as anything else than hypostasis. At any rate, the behavior 

 in inheritance is exactly as in the case of hypostasis, as far as the 

 ratios of the various types are concerned. 



VI. LATENCY DUE TO FLUCTUATION. 



Some MendeUan characters are highly variable. Shull cites the 

 case of certain leaf lobings which vary greatly under unfavorable 

 conditions, and sometimes entirely fail to develop. When the 



