of perpetual snow in the Himalaya, and having specially devoted his attention to 'geographical varieties,' or those changes of character which plants exhibit, when traced over wide areas and seen under new conditions; being also practically versed in the description and classification of new plants, from various parts of the world, and having been called upon carefully to consider the claims of thousands of varieties to rank as species, no one was better qualified by observation and reflection to give an authoritative opinion on the question, whether the present vegetation of the globe is or is not in accordance with the theory which Mr. Darwin has proposed. We cannot but feel, therefore, deeply interested when we find him making the following declaration: 'The mutual relations of the plants of each great botanical province, and, in fact, of the world generally, is just such as would have resulted if variation had gone on operating throughout indefinite periods, in the same manner as we see it act in a limited number of centuries, so as gradually to give rise in the course of time, to the most widely divergent forms.'
In the same Essay, this author remarks, 'The element of mutability pervades the whole Vegetable Kingdom; no class, nor order, nor genus of more than a few species claims absolute exemption from it, whilst the grand total of unstable forms, generally assumed to be species, probably exceeds that of the stable.' Yet he contends that species are neither visionary, nor even arbitrary creations of the naturalist, but realities, though they may not remain true for ever (p. 11). The majority of them, he remarks, are so far constant, 'within the range of our experience,' and their forms and characters so faithfully handed down, through thousands of generations, that they admit of being treated as if they were permanent and immutable. But the range of 'our experience' is so limited, that it will not account for a single fact in the present geographical distribution, or origin of any one
