WICHURA ON HYBRIDS. 



71 



isolated, and not apparently to agree with those of Grirou de Buza- 

 reingues on the proportion of male and female individuals in 

 Cannabis sativa, Rosa cinnamomea, Humex acetosella, Spinacia ole~ 

 racea, and Lychnis dioica. 



Since willows have no petals, they will teach us nothing re- 

 specting the different variations of colour which are so striking in 

 many hybrids. "We must therefore look rather to the different 

 forms which they assume. When we consider the form of a 

 hybrid with reference to that of its ancestor, we must distinguish 

 three categories of characters. 



1. Constant characters in which the parent species agree. 

 These enter unaltered into the hybrid. 



2. Constant characters in which the parent species are distin- 

 guished from each other. These enter only by halves into a 

 hybrid, so that it is intermediate between them. 



3. Variable characters. In these the hybrid is equally variable. 

 If the parents agree with each other in their variable characters, 

 these are not necessarily inherited by the hybrid ; and if they 

 differ in their variable characters, the hybrid is not always inter- 

 mediate. 



As regards the first and second, the following may serve as an 

 example. S. purpurea has two stamens whose threads and anthers 

 are so intimately united that they seem to have only one thread 

 and a four-celled anther. The stamens in the other European willows 

 are free, S. incana only being exceptional, in which the threads are 

 united halfway up. If a hybrid is formed between S. purpurea 

 and another willow, the threads are confluent below in accordance 

 with the first rule, while they are free above and divergent. S. 

 purpurea, moreover, has sessile stigmas. The style of other 

 species, as for instance S. viminalis, is rather long. The hybrid 

 has the style about half as long as that of the second species. 

 Similar examples may be adduced as to the position of the stigma, 

 the leaves, the pubescence, the rough under surface of the leaves, 

 the bark, the stature, the time of blooming, and finally the quan- 

 tity of salicin in the bark. "Wichura has seen only a single excep- 

 tion to this law in S. ( 2 arbuscula+ <$ purpurea) art. As regards 

 foliage, it was exactly intermediate ; but it had nothing in com- 

 mon with the upright habit of S. purpurea, but rather lay com- 

 pletely prostrate on the ground, being in this respect an exagge- 

 ration of 8. arluscula. It is possible, however, that this was only a 

 sign of the weakness inherent in hybrids, and so the exception is 

 only apparent. More complicated hybrids exhibit the same law, 



