144 MORPHOLOGY 



of propagation, therefore, exercises a most dominat- 

 ing influence in the preservation of the species, while 

 the other methods merely act as its helpmates. 



In cultivated plants, where the object is to maintain 

 the characters of the varieties and races unaltered, the 

 vegetative method of reproduction is resorted to by 

 preference, because these characters cannot come out 

 true by seeds — that is, by the sexual method. For 

 example, good varieties of Mango are always propa- 

 gated by the vegetative method of grafting, as they 

 seldom come out true if grown from seeds. On the 

 other hand, if it is intended to produce newer or better 

 varieties or races of cultivated plants, the sexual 

 method of crossing is always resorted to. This also 

 bears out prominently the dominating nature of the 

 sexual method. 



We have seen how freely the flowers of a species 

 cross-pollinate one another. But cross-pollination 

 between different but allied species is not unknown. 

 Such a process of cross -pollination is known as 

 HYBRIDIZATION, and the products of such crossings 

 as HYBRIDS. The hybrids usually combine the char- 

 acters of both the species, but seldom are the crosses 

 between the hybrids fertile. They are, however, fer- 

 tile if crossed with the parent species. 



CHAPTER XX 



DISPERSION OF SEEDS 



If the seeds of a plant fall immediately below it, the 

 ground on which they fall is necessarily restricted, 

 and if it be unfavourable for germination, the seeds 



