V] 



Colours of Sweet Peas 



93 



and round-pollened respectively, which outwardly were 

 indistinguishable from the two original parents. As we 

 now know, by the redistribution of factors a great variety 

 of whites is in reality produced in /%, and only those pairs 

 which bear the complementary factors C and R can ^\v^ 

 coloured offspring. This apparent dissimilarity between 

 the behaviour of the extracted forms and that of the pure 

 types from which they are derived has been adduced as 

 being inconsistent with Mendelian principles. When how- 

 ever the factorial composition of the various individuals is 

 correctly represented it is evident that this multiplicity of 

 composition in F^ is what must be expected, and there is 

 abundant evidence that such complications exist in all the 

 plants and animals that have been experimentally studied 

 on an adequate scale '^. 



Subordinate Types in F^, 



We have now to consider the meaning of the appearance 

 of subordinate types in the purple and in the red classes 

 which is a feature of some F^ families. Of these there 

 are frequently two. The first is characterized by having 

 the wing-petals much more fully coloured than those of the 

 F^ purple, or of the Painted Lady. These distinctions are 

 due to the operation of an epistatic factor for the lighter 

 wing-colour. When this factor is absent the wings are 

 dark, and the flower, if a purple, has the wings deep purple 



* Factors which may thus exist without making their presence visible 

 have been named by Tschermak **Cryptomeres." The term is open to 

 the objection which zoologists especially will feel, that it may cause con- 

 fusion owing to the fact that the series of words containing " mere " are 

 now universally understood to refer to phenomena of division — or Meristic 

 features. When the study of that part of genetics which is concerned with 

 meristic variation is more fully developed this confusion will be aggravated. 

 For the present moreover the expression " factor," qualified, if necessary, 

 as unseen, seems sufficiently precise. 



The words "latent" and "latency" must be applied in these cases 

 with great care, if at all. Various writers have, for instance, spoken of the 

 purple colour as "latent" in a white flower. This description is quite 

 misleading, for the colour need not be present in such plants. The term 

 "latent" is only admissible in application to the factors (as here, to the 

 factor which can turn the colouring matters purple) not to the characters^ 

 except loosely to those which are actually present but hidden owing to the 

 operation of some epistatic factor. 



