WIOHURA ON HYBRIDS. 75 



thou, they grow in company with their parents, they are soon 

 overgrown, and so gradually die out. 



Erom all these circumstances it is clear that spontaneous hy- 

 brids must be rare. If we except those which, like hawkweed, 

 sedges, or brambles, are propagated in certain localities by suckers, 

 they are of rare occurrence. In Silesia perhaps there is one 

 hybrid amongst 500 individuals. There is perhaps of S. (alba+ 

 fragilis) one per cent, of the parent species, § per cent, of S. (pur- 

 purea -\-viminalis), -J- of S. (aurita -\-repens),-^-- - of 8. (purpurea -{-re- 

 pens), - 5 \y of S. (cinerea-\- purpurea), ^J-^ of S.(triandra + viminalis). 

 These are, it is to be observed, only rough approximations. Com- 

 plex hybrids are so rare that no estimate is made respecting 

 them. 



In some confined localities, as in swampy wastes, sandbanks, 

 river-beds, &c, certain hybrids sometimes grow together in con- 

 siderable numbers. This is the case with S. (purpurea + viminalis) 

 on the Breslau river-banks, and with S. (aurita-\-repens) and S. 

 (purpurea-^ rep ens) in swamps. According to Andersson, S. (Lap- 

 ponwm-\-myrtilloides) (S. versifolia,~W&h\.) surpasses its parents in 

 number in some parts of Lapland. This depends probably on 

 a little-noticed biological peculiarity in willows. They cannot 

 bear being overshadowed, but become sickly, while the young 

 plants perish, even amongst herbs of small stature. Moist places 

 in districts bare of vegetation, either from artificial or natural 

 circumstances, are the favourite places of the development of the 

 light seeds. All therefore in a particular spot have vegetated in the 

 same year ; and so it may happen that, if these have come from 

 some hybrid, the hybrids may surpass the pure parents in number. 

 In other spots of the same locality not a single hybrid can be found. 



Finally, hybrids have been widely cultivated in some districts 

 by means of cuttings, as S. (alba + fragilis) and S. (fragilis +pen- 

 tandra), which are used for enclosing the roads, and 8. (pupurea-\- 

 viminalis) for basket-work. 



"We pass over the systematic chapter, which, however excellent, 

 is not especially suitable to the objects of this Journal. It is, 

 however, remarkable that the great similarity between S. caprea, 

 cinerea, and aurita is rather apparent than real. Though they do 

 not absolutely refuse intercrossing, like the Gacurbita JPepa, maxima, 

 nielanosperma, and moschata, they comport themselves differently 

 towards different species. Hybrids of these three species are by 

 no means more frequent than other hybrids ; and while many 

 hybrids of S. caprea and aurita, with other uninectariferous wil- 



