viii] ''Latency'' 145 



been if the plant had been a coloured one. Lock (176) has 

 spoken of this faint pattern as the "ghost" of the mapling. 



Mudge (204) has observed a very similar phenomenon in 

 young albino rats. When the hair is short the coat may be 

 seen to be similarly damasked, those parts which would be 

 pigmented if the animal had pigment looking different in 

 consistency from the rest. 



What the exact difference between the hairs in these 

 areas and the rest may be has not been ascertained, but 

 evidently it must be a modification due to the existence of 

 one of the factors for colour in those hairs. They are the 

 parts prepared to develop colour if the other element were 

 present in them. In black leopards and black kittens a 

 similar damask effect can often be seen, the parts which in 

 the spotted leopard or tabby cat would be light being dis- 

 tinguishable on careful examination. As it is not yet known 

 whether black is dominant or recessive in these cases the 

 exact meaninof of these marks is uncertain. 



Both in animals and plants there is satisfactory proof 

 that whiteness, the absence of colour, may be due to partial 

 or complete suppression of the pigment-factors and not 

 merely, as in the albino, to their absence. This suppression 

 is caused by a dominant, epistatic factor. White individuals 

 containing such a factor are more or less totally do?mnant 

 whites, whereas whites due to the absence of one or more 

 pigmentation-factors are recessive whites. A cross between 

 a dominant and a recessive white may obviously cause 

 coloured individuals to appear in /^5, if the factors for pig- 

 mentation were introduced by the parental types ; for in F.^ 

 there will be individuals lacking the suppressing factor. 



Confusion has been introduced into these analyses by 

 the use of the term "latency" in application to those factors 

 which cannot be perceived without breeding tests. This 

 difficulty has occurred especially in regard to albinos, though 

 it pervades the whole system of factorial analysis. Albinos, 

 for instance, in any species may have the most diverse 

 factorial composition. All that is common to them is the 

 absence of colour, i.e., if we adopt Cuenot's suggestion, of 

 the chromogenic substance. The composition of each albino 

 may be ascertained by crossing it with a coloured type and 

 raising the F^ generation. If the coloured type chosen be 



B. H. 10 



