WICHUEA. ON HYBEIDS. 



63 



but deserve mention as characteristic phenomena in hybri- 

 dization. 



The following degrees of failure may be noted : — 



1. The catkins submitted to hybridization wither as soon as the 

 flowering is complete, like those which have not been impregnated, 

 and fall off. 



2. The ovaries swell and ripen, but do not contain a trace of 

 seed. 



3. The ovaries are quite filled with the silky hairs which clothe 

 the umbilical end of the seed, but contain no embryo. 



4. Seeds are present, but small, languid, and incapable of ger- 

 mination. 



5. Seeds apparently perfectly developed, but do not germinate. 



6. Seeds germinate, but the young plants are weak and wither 

 in a short time without further development. 



The gradation in the number of seeds next demands our notice. 

 The results of different experiments were very various. Sometimes 

 the seeds were few, but fertile and active ; sometimes, on the con- 

 trary, numerous, but with only a few fertile mixed with a number 

 of abortive seeds ; sometimes tolerably numerous, without any 

 such admixture ; but in general hybrids yielded on the whole a 

 smaller number of seeds than plants impregnated with their own 

 pollen. 



This imperfection depends on the nature of hybrids, which, 

 according to our author, are never so active as pure plants — a 

 position which is perhaps doubtful. This weakness he believes to 

 arise from a comparative want of potency in the pollen, though 

 hybrids often exhibit a peculiarly luxuriant but rank growth. 



It is not necessary to describe the structure of willow-pollen. 

 It is sufficient to observe that in hybrid willows many modifica- 

 tions occur. 



The imperfection of the pollen in hybrids is often adduced as 

 a decidedly distinctive mark between them and pure species, but 

 this is incorrect. There are hybrids whose pollen is scarcely less 

 regular than that of the parents, as for example in Petunias, and 

 there are pure species which have more irregular pollen than 

 many hybrids. It is, however, true that in the greater number 

 of cases the pollen of hybrids is less regular than that of pure 

 plants. 



In willows this is a law without exception. Amongst pure 

 species, only 8. fragilis (though not the nearly allied 8. alba) and 

 single individuals of 8. triandra had a large number of irregular 



