VARIATION AND DISTRIBUTION OF SPECIES. 133 



many of them are such as would have been expected to be 

 constant in the same species, and are such as generally enter 

 into specific definitions. Variations of this sort, De Candolle, 

 with his usual painstaking, classifies and tabulates, and even 

 expresses numerically their frequency in certain species. The 

 results are brought well to view in a systematic enumera- 

 tion : — 



(1) Of characters which frequently vary upon the same 

 branch : over a dozen such are mentioned. 



(2) Of those which sometimes vary upon the same branch : 

 a smaller number of these are mentioned. 



(3) Those so rare that they might be called monstrosi- 

 ties. 



Then he enumerates characters, ten in number, which he 

 has never found to vary on the same branch, and which 

 therefore may better claim to be employed as specific. But, 

 as among them he includes the duration of the leaves, the 

 size of the cupule, and the form and size of its scales, which 

 are by no means wholly uniform in different trees of the 

 same species, even these characters must be taken with al- 

 lowance. In fact, having first brought together, as groups 

 of the lowest order, those forms which varied upon the same 

 stock, he next had to combine similarly various forms which, 

 though not found associated upon the same branch, were 

 thoroughly blended by intermediate degrees. 



" The lower groups (varieties or races) being thus constituted, I 

 have given the rank of species to the groups next above these, which 

 differ in other respects, i. e., either in characters which were not 

 found united upon certain individuals, or in those which do not show 

 transitions from one individual to another. For the Oaks of regions 

 sufficiently known, the species thus formed rest upon satisfactory 

 bases, of which the proof can be furnished. It is quite otherwise 

 with those which are represented in our herbaria by single or few 

 specimens. These are provisional species, — species which may 

 hereafter fall to the rank of simple varieties. I have not been in- 

 clined to prejudge such questions ; indeed, in this regard, I am not 

 disposed to follow those authors whose tendency is, as they say, to 

 reunite species. I never reunite them without proof in each partic- 



