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Show 180 JJAR WIN IAN A. ina- to their obvious resemblances, into groups of appa~ ently identical or nearly identical forms, whic~ were severally examined and compared. Where speCImens were few, as from countries little explored, the work was easy, but the conclusions, as will be seen, of small value. The fewer the .materials, the smaUer the likelihood of forms intermediate betw~en any two, and-what does not appear being treated upon the old . iaw-maxim as non-existent-species are readily enough defined. Where, however, specimens abound, as in the case of the oaks of Europe, of the Orient, and of the United States, of which the specimens amounted to hundreds, collected at different ages, in varied localities, by botanists of all sorts of .views and predilections- here alone were data fit to draw useful conclusions from . . Here, as De Candolle remarks, he had every advantage, being furnished with materials more complete than any one person could have procured from his own herborizations, more varied than if he had observed a hundred times over the same forms in the same district, and more impartial than if they had all been amassed by one person with his own ideas or predispositions. So that vast herbaria, into which contributions from every source have flowed for years, furnish the best possible data-at least are far better · than any practicable·amount of personal herborization -for the comparative study of related forms occurring over wide tracts of territory. But as the materials increase, so do the difficulties. Forms, which appeared totally distinct, approach or blend through intermediate gradations; characters, stable in a limited number of instances or in a limited district, prove unstable SPECIES AS TO VARIATION, ETO. 181 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 generaUy 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 enumeration : 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 monstrosities. 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 quite uniform in different trees of the same species, even these characters must be taken with allowance. In fact, having first brought together, as groups of the lowest |
