30 BOARD OF AGRICULTURE. [Pub. Doc. 



even in the willows and oaks, in which, perhaps, hybrids 

 arc better known than in any other American plants. The 

 great genus carex or sedge, which occurs in great numbers 

 and many species in almost every locality in New England, 

 and in which the species are particularly adapted to inter- 

 crossing by the character of their inflorescence, furnishes 

 but few undoubted hybrids. Among one hundred and sixty- 

 seven species and prominent varieties inhabiting the north- 

 eastern States, there are only nine hybrids recorded, and all 

 of them are rare or local, some of them having been col- 

 lected but once. Species of remarkable similarity may 

 grow side by side for years, even intertangled in the same 

 clump, and yet produce no hybrid. These instances prove 

 that nature avoids hybridization, — a conclusion at which 

 we have already arrived from philosophical considerations. 

 And we have reason to infer the same conclusion from the 

 fact that flowers of different species are so constructed as 

 not to invite intercrossing. But, on the other hand, the 

 fact that all higher plants habitually propagate by means of 

 seeds, which is far the most expensive to the plant of all 

 methods of propagation, while at the same time most flowers 

 are so constructed as to prevent self-fertilization, proves 

 that some corresponding good must come from crossing 

 within the limits of the species or variety; and there are 

 purely philosophical reasons, as we have seen, which war- 

 rant a similar conclusion. But experiment has given us 

 more direct proof of our propositions, and we shall now turn 

 our attention to the garden. 



Darwin was the first to show that crossing within the limits 

 of the species or variety results in a constant revitalizing of 

 the offspring, and that this is the particular ultimate function 

 of the operation. Koelreuter, Sprengel, Knight and others, 

 had observed many, if, indeed, not all, the facts obtained by 

 Darwin ; but they had not generalized upon them broadly, 

 and did not conceive their relation to the complex life of the 

 vegetable world. Darwin's results are, concisely, these : 

 self-fertilization tends to weaken the offspring ; crossing 

 between different plants of the same variety gives stronger 

 and more productive offspring than arises from self-fertiliza- 

 tion ; crossing between stocks of the same variety grown in 



