WI0I1URA ON HYBRIDS. 



78 



Wiclmra confirms G-sBrtner in the assertion that where hybrid 

 pollen is used for the impregnation of simple or complicated 

 hybrids, as also in pure species, there is a great predominance 

 of individual forms, while hybrid ovules impregnated by the 

 pollen of pure species, even in the most complicated combinations, 

 give very uniform products. 



On the whole, our author's experiments have far more generally 

 exhibited variety of form in the produce where the pollen of 

 hybrids, and, on the contrary, uniformity where the pollen of 

 pure species was employed. We may therefore attribute to the 

 pollen of hybrids a tendency to produce varieties, while, since the 

 ovules of the same, if fertilized with pure pollen, yield as uniform 

 produce as those of true species, there does not appear in general 

 to be any inherent propensity in them to produce varieties. 

 There is but one observation of Gsertner's which gives any sup- 

 port to the assertion that the varieties from the ovules of hybrids 

 with pure pollen may be more numerous than from those of pure 

 species. Tolerably constant forms arose from a hybrid fertilized 

 with the pollen of the male parent, if the female hybrid was fruitful, 

 but variable forms if the productive powers were weak. This could 

 not, however, depend upon the pollen, which in either case was 

 the same, but on the incipient sterility of the female, which in- 

 duced a malformation of the ovules ; so that the rule that the 

 product of hybrid pollen is more polymorphous than that of pure 

 pollen remains unshaken. 



The circumstances which favour the spontaneous production of 

 hybrids in willows, seem to be nearly the same as those which 

 facilitate artificial intercrossing. Dioecious plants, which are sub- 

 ject to fertilization by insects, must necessarily produce hybrids, 

 if they comprise, like willows, a great number of nearly related 

 species, which grow in company with each other, and which have 

 the same or nearly the same time of flowering. 



Wimmer believes that there are thirty-four undoubtedly pure 

 European species of willow, or perhaps thirty-five if S. helvetica 

 is not a hybrid. If, however, &. pedicellata, Desf. and S. arctica, 

 Br., whose hybrids in the extreme southern and northern lati- 

 tude of Europe have not yet been studied, be excluded, we have 



to be an accidental variety produced by grafting C. purpureas on C. Laburnum ; 

 and it is conjectured that a portion of the cells of the one plant must have 

 become so intimately connected with the cells of the other, that when cell- 

 division took place part of the plant assumed the type of C. Laburnum, another 

 of C. purpureas, while others were exactly intermediate between the two. 



