THE SELF-FERTILIZATION OF PLANTS. 395 



finds many characters, either like its own, and with 

 which its characters may isochronize; or (as in the case 

 given above, where the plant was self-impotent), like 

 the characters, of its species, which it has lost, and 

 which fail to be represented in its own pollen. 



With the characters of another species, it may, for 

 one generation, make up its lost integrity. But, the 

 escape of the line of such individuals from extinction, 

 by means of crossing with a distinct species, is only a 

 temporary and slightly deferred one. For, on account 

 of such a cross, their hybrids become irremediably 

 sterile. Had the individual crossed with one of its 

 species, it might have continued indefinitely fertile. 

 The sterility of an individual, whose ancestors have 

 never been crossed with a different species, is not abso- 

 lute. All that makes such individual sterile, is the loss 

 or reduction of characters; which may be remedied, 

 and the fertility of the individual restored, either by 

 reversion, crossing with an individual of the same spe- 

 cies, differing positively in structure, or by grafting. 

 But, when a cross is had with a distinct species, a defi- 

 nite, and inevitable failure of issue, is entailed upon the 

 offspring. There exists a barrier to further reproduc- 

 tion. When two individuals of different species cross, 

 the reproductive element of each is capable of the pro- 

 cess of integration, because such element has been 

 normally secreted by a pure species ! If the forces of 

 such element, are isochronous with the forces of the 

 other reproductive element, as is the fact generally in 

 the case of closely allied species, the two may concur 

 in building up an organism. But, though the forces 



