Variation, Geographical Distribution, and Succession. 83 



or in a limited district, prove unstable occasionally, or when 

 observed over a wider area ; and the practical question is forced 

 upon the investigator, What here is probably fixed and specific, 

 and what is variant, pertaining to individual, variety, or race ? 



In the examination of these rich materials, certain characters 

 were found to vary upon the same branch, or upon the same 

 tree, sometimes according to age or development, sometimes 

 irrespective of such relations or of any assignable reasons. Such 

 characters, of course, are not specific, although 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 DeCandolle, 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 enumeration. 



(1.) Of characters which frequently vary upon the same branch : 

 upwards of 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 monstrosities. 



Then he enumerates characters, ten in number, which he has 

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

 have better claim to be employed as specific. But, as among 

 them he includes the duration of the leaves, the size of the cu- 

 pule, and the form and size of its scales, which are by no means 

 wholly uniform in difi'erent trees of the same species, even these 

 characters must be taken with allowance. 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 here- 

 after fall to the rank of simple varieties. I have not been inclined 

 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 particular case ; 

 while the botanists to whom I refer do so on the ground of analogous 

 variations or transitions occurring in the same genus or in the same 

 family. For example, resting on the fact that Quercus Ilex, Q. cocci- 



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