RACES, HYBRIDS, ETC. 357 



often proceeds one step farther, in certain cases, and gives rise to a 

 different kind of cross-breeds, viz. 



G95. Hybrids. These are cross-breeds from diiferent but nearly 

 related species. It is well known that, by proper precautions, the 

 pistil of a flower of one species may often be fertilized by the pollen 

 of another of a similar constitution, and that the plants raised from 

 the seeds so produced combine the characters and properties of 

 both parents. Some kinds, such as Azaleas and Pelargoniums, hy- 

 bridize very readily ; in others hybridism is effected with difficulty 

 between nearly related species. The gardener produces hybrids 

 among most of his favorite plants, and variously cross-breeds and 

 mingles them, so as to confuse the limits of many cultivated species. 

 But in nature hybrids rarely occur. Not more than fifty wild kinds 

 are clearly known as of continued or frequent occurrence. Others 

 may perhaps be originated from time to time ; but their existence 

 is transient. For hybrids are generally, if not always, sterile, and 

 therefore incajmble of perpetuation by seed. But their ovules may 

 be fertilized by the jiollen of either of their parents, Avhen the 

 progeny reverts to that species, probably retaining, howevei-, some 

 traces of the mixture, unless this should be obliterated by successive 

 fertilizations from individuals of the same parent species. It is 

 probable that cross-fertilization between different individuals of the 

 same species is more common than is generally supposed, and that 

 it is one of Nature's means for repressing variation. On the other 

 hand, continued self-fertilization (or breeding in and in) is almost 

 sure to perpetuate, as well as farther to develop, individual pecuUari- 

 ties, i. e. those of variety or race. 



GOG. However plants may be modified by art and man's device, 

 the systematic botanist proceeds upon the ground that the distinc- 

 tions between species, whether small or great, are real, and in nature 

 are permanent, — that variation, wide as it may be, is naturally re- 

 stricted within certain limits. And this appears to be true. As dis- 

 tinctions subordinate to species are in nature both indefinite and 

 transitory, these, however important to the cultivator, are of little 

 account with the systematic botanist. 



G97. Species are the true subjects of classification. And the end 

 and aim of systematic botany is to ascertain and to express their 

 relationship to each other. The whole ground in nature for the 

 classification of species is the obvious fact that species resemble 

 or differ from each other unequally and in extremely various de- 



