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philosophy of the case. Practically, no botanist can say what 

 amount of dissimilarity is compatible with unity of species ; 

 in wild plants it is sometimes very great, in cultivated races, 

 often enormous. De Candolle himself informs us that the dif- 

 ferent variations which the same Oak tree exhibits are signifi- 

 cant indications of a disj)osition to set up separate varieties, 

 which, becoming hereditary, may constitute a race ; he evi- 

 dently looks upon the extreme forms, say of Quercus Robar, 

 as having thus originated ; and on this ground, inferred from 

 transitional forms, and not from their mutual resemblance, as 

 we suppose, he includes them in that species. This will be 

 more apparent should the discovery of the transitions, which 

 he leads us to expect, hereafter cause the four provisional 

 species which attend Q. Robur to be merged in that species. 

 It may rightly be replied that this conclusion would be arrived 

 at from the likeness step by step in the series of forms ; but 

 the cause of the likeness here is obvious. And this brings in 

 our " motif philosophique." 



Not to insist that the likeness is after all the variable, not 

 the constant, element, — to learn which is the essential thing, 

 resemblance among the individuals or their genetic connec- 

 tion, we have only to ask which can be the cause of the other. 



In hermaphrodite plants (the normal case), and even as 

 the question is ingeniously put by De Candolle in the above 

 extract, the former surely cannot be the cause of the latter, 

 though it may, in case of crossing, offer occasion. But, on 

 the ground of the most fundamental of all things in the con- 

 stitution of plants and animals, " the fact incapable of farther 

 analysis, that individuals reproduce their like, that character- 

 istics are inheritable," the likeness is a direct natural conse- 

 quence of the genetic succession, — and it is logical to place 

 the cause above the effect. 



We are equally disposed to combat a proposition of De 

 Candolle's about genera, elaborately argued in the " Geographie 

 Botanique," and incidentally re-affirmed in his present article, 

 namely, that genera are more natural than species, and are 

 more correctly distinguished by people in general, as is shown 

 by vernacular names. But we have no space left in which to 

 present some evidence to the contrary. 



