WICIIURA. ON HYBRIDS. 



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complicated combinations the object was to combine as many 

 species as possible ; the species, therefore, most nearly related to 

 each other were chosen, and fresh pollen was nsecl. It is not to be 

 doubted, moreover, that the more favourable results amongst 

 complicated hybrids depended on the more favourable circum- 

 stance selected for their production ; besides, it should seem that 

 willows have a great tendency towards the production of compli- 

 cated hybrids, which must be regarded as a very peculiar circum- 

 stance. Exceptional cases doubtless often depend upon unfavour- 

 able accidents ; for combinations which failed one year succeeded 

 the next, and it is only after a large continuous series of observa- 

 tions that we can arrive at any perfectly satisfactory result. 



"Wichura does not consider it necessary to repeat in willows the 

 experiments of Kcelreuter, Grsertner, and others, which show that 

 plants have a superior appetency for their own pollen to that of any 

 other species. This depends probably on the circumstance that 

 the strange pollen does not push forth the pollen-tube so rapidly as 

 that which is native, so that if both kinds of pollen are applied to- 

 gether, the tube of the strange pollen, supposing it to be properly 

 protruded, finds the micropyle occupied on its arrival. Gsertner 

 informs us that in different plants a different number of genera- 

 tions must pass by to secure the conversion of one species into 

 another. In willows, it appears from "Wichura's experiment 

 that it requires only four years. 



A small-leaved form of 8. {purpurea + viminalis) was used for 

 this experiment, which was continued for two generations. A fe- 

 male hybrid between 8. purpurea and viminalis was impregnated 

 by 8. viminalis, the result of which was a hybrid scarcely distin- 

 guishable from 8. viminalis. Again, a female hybrid, the result of 

 a hybrid between 8. purpurea and viminalis, impregnated by 8. 

 viminalis, impregnated in its turn with 8. viminalis, produced a 

 hybrid still more near 8. viminalis, and a further crossing would 

 in all probability have perfected the change. It was a matter of 

 interest to observe how far the peculiar smallness of the leaves 

 would be recognizable in the result of the first-mentioned experi- 

 ment. This was distinctly the case, and it seems clear that the 

 propagation of individual peculiarity may be effected in a hybrid. 



A hybrid fertilized with its own pollen produces plants the 

 same as or resembling both the parents. The peculiarities of the 

 parents are moreover repeated in the hybrid. Quaternary hybrids 

 fertilized with their own pollen, produced seed which germinated, 

 but the young plants soon failed. 



