8 



EOTAL HORTICULTURAL SOCIETY. 



Further, whatever opinion we may form in this respect, we must 

 allow that these forms, not transmissible by way of generation, 

 want in this very respect the essential character of species and 

 true races, which is to perpetuate themselves faithfully by seed and 

 to increase. "We may say strictly that these varieties are no longer 

 represented sometimes after ages of duration, save by a single 

 individual, always the same, and always renewed by grafting, that 

 is to say, by the indefinite division of its branches. 



But if crossings have produced these phenomena of irregular 

 variability in cultivated plants, would it not be possible that the 

 same cause had made them arise in plants remaining in a wild 

 state ? One is led to believe, when we cast our eyes on certain 

 generic groups, as those of Salix, Potentilla, Rubus, &c, where 

 species well characterized at first sight are connected nevertheless 

 with one another by intermediate forms so numerous and so well 

 graduated, that at last we do not know where to place the limits 

 of these species ; thus, in spite of the most laborious studies, these 

 genera have remained a matter of dispute amongst botanists. 

 What renders this supposition probable is, that the species of 

 these different groups are precisely those which occur under phy- 

 sical conditions the most calculated to favour crossing. But it is 

 sufficient here that two species, when crossing, give place to fertile 

 hybrids which do not all revert to the specific types, in order that 

 the irregular variability should come into play, and induce, after 

 some generations, that chaos of undecided forms in the face of 

 which all the efforts of botanical describers miscarry*. 



After having related how hybrids vary, it is time to examine how 

 pure species behave themselves, when their forms are modified. 

 Let us state first, that in respect of variability they are very un- 

 equally gifted. There are some which we never see varying, at least 

 in the sense which we attach to this word ; there are others which 

 vary, and sometimes within extremely wide limits. We know 

 not what causes determine these variations ; it is nevertheless 

 allowable to believe that emigration and cultivation are not with- 

 out influence, for we see many remarkable varieties spring up in 

 their course. But species, when they vary in consequence of their 

 innate tendency to do so, do it in a very different manner from 



* The translator of this memoir was peculiarly struck three years since with 

 the infinite variety of forms of Salix which occur along the course of the Dee. 

 It really seemed as if every bush possessed some character of its own, and in 

 consequence a neighbouring botanist, who set out with the intention of collecting 

 every variety of willow in Aberdeenshire, gave up the matter in despair. 



