115 



growth of some contradict this, as it is known often to accompany 

 suppressed fertility. The most fruitful hybrids are always less 

 so than their parents. The weakness of the generative organs 

 in very luxuriant hybrids induces an increase of vegetative 

 growth, while this is not the case in others which are too weak 

 to exhibit such a reaction. 



It is an interesting question whether the paternal or maternal 

 parent has most influence upon the form of the hybrid. A curi- 

 ous statement bearing upon this is quoted from Gcertner, that 

 the most perfect equality of production prevails. Seeds arising 

 from the impregnation of either parent, it is stated, produce 

 plants of the most complete resemblance. "Whether the female 

 of S. caprea be crossed with the male of S. viminalis, or the male 

 of caprea with the female of viminalis, the resemblance of the 

 offspring was so perfect that they might be taken for products of 

 one and the same crossing. It does not, however, follow that in 

 hybrids the sexes occur in equal proportions : it is not so in 

 nature, and it is an unsettled point as yet in the artificial pro- 

 duction of hybrids. It is stated, as the apparent result of 

 Wichura's experiments, that the pollen of hybrids has a tendency 

 to produce varieties : and on the other hand, that of pure species 

 to lead to uniformity in the offspring. It is observed that dioe- 

 cious plants, which are subject to fertilization by insects, must 

 necessarily produce hybrids, if they comprise, like willows, a 

 great number of nearly related forms, growing in company, and 

 having nearly the same time of flowering. But this seems to 

 assume first, that seedling willows are numerous ; second, that 

 they are able to hold their own in the struggle with more vigor- 

 ous forms ; and third, that the pure species do not vary much 

 from well established types. "Wimmer believes that there are 

 thirty-four or thirty-five pure European species of willows. 

 Perhaps we might put our British species, omitting varieties, at 

 about twenty-six or twenty-seven. From Wimmer' s thirty-two 

 species with hybrid-producing power sixty-six indubitable binary 

 hybrids are known, but this statement must, I think, be received 

 with caution, until fuller evidence is given in each particular 



H 



