236 Intermediates [ch. 



cases where much gradation occurs is usually troublesome, 

 but it is becoming clear that the difficulty is often a practical 

 one only. To analyse the intermediates and to determine 

 the various elements that have taken part in their pro- 

 duction may be a very laborious process, still it can be 

 shown in many examples that the intermediate character is 

 only a superficial or nett result of the interaction of factors 

 which are transmitted as units The several classes under 

 which such intermediate types present themselves are worth 

 enumerating. 



I. Intermediates as heterozygous forms. Sometimes, 

 as is the case of the blue Andalusian fowl, the whole group 

 of heterozygotes forms a recognizable, distinct class which 

 might nevertheless be regarded as intermediate between 

 the two pure types black and white, with splashes of grey 

 and black. Similar intermediates occurring as heterozygous 

 forms have now been often seen and described. In the 

 case of Prim^ula Sinensis the heterozygote between the 

 star-shaped flower of the modern stellata varieties and the 

 common type with imbricated petals is always an inter- 

 mediate^. 



In fowls though no perfectly distinct heterozygous type 

 of comb exists, yet with experience it is usually possible to 

 distinguish the pure {DD) pea combs from the DR group, 

 and, though with much less confidence, the same distinction 

 can sometimes be made among the rose-combs. 



In Lychnis the crosses between white vespe^^tina and 

 red dioica are, so far as I know, always of an intermediate 

 shade of pink. In Pisum the crosses between the races I 

 have called '' half-dwarf," standing about 3 to 4 feet high, 

 and actual dwarfs, about i foot high, are usually intermediate 

 in height. The researches of Miss Wheldale on Antirrhi- 

 num have shown that in that species numerous intergrading 

 forms are definite heterozygotes, and Miss Marryat has 

 proved that the same is true for Mirabilis. 



Such instances may be multiplied indefinitely. Domi- 

 nance indeed is not often so pronounced that a practised 



* Whether any such intermediate flower shape exists as a gametic form 

 which can be bred true I do not know for certain. Mr Gregory and I have 

 not met one among our derivatives from various crosses between stellata 

 and Sinensis. 



