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Before the publication of Darwin's first volume, M. Alphonse de Candolle had summed up the result of his studies in this regard, in the final chapter of his classical "Geographie Botanique Raisonnee," in the conclusion, that existing vegetation must be regarded as the continuation, through many geological and geographical changes, of the anterior vegetations of the world; and that, consequently, the present distribution of species is explicable only in the light of their geological history.
In the mean time, no botanist of any distinguished note, except M. De Candolle, has confidently ventured to question this migration theory, so imposing and formidable has been the array of names which have frowned down, like so many gigantic ghauts, upon the audacious questioner.
The actual geographical distribution of species any species does not depend solely on lines of ancestry, however great their persistence of specific characters; nor on any principle of natural selection, nor on the possibility of fertile monstrosities, but on the simple incidence of conditions; and M. De Candolle, in his "Geographie Botanique," virtually concedes this, while treating of geographical considerations in connection with distribution.
De Candolle makes the important announcement that, in the oak genus, the best known species are just those which present the greatest number of spontaneous varieties and sub-varieties. The maximum is found in Q. Robur, with twenty-eight varieties, all spontaneous. Of Q. Lusitanica eleven varieties are enumerated, of Q. Calliprinos ten, of Q. coccifera eight, * etc.
The Quercus robur may furnish the maximum test to-day, but a few concealed pockets of nature may bring some other variety of the congeneric species to the front to-morrow, requiring M. De Candolle to correct his classification.
One of De Candolle's young-lady pupils was present when he received the letter and expressed his regret at losing the drawings: she exclaimed, "We will copy them for you." De Candolle said it was impossible 1500 drawings in eight days!
The fact of the larger fruits often floating longer than the small, is interesting; as plants with large seeds or fruit could hardly be transported by any other means; and Alph. de Candolle has shown that such plants generally have restricted ranges. But seeds may be occasionally transported in another manner.
We saw thirteen folio volumes of these drawings done in the eight days! Of course some were much worse than others, but even this I liked: it showed that individuals were ready to sacrifice their own amour propre in a benevolent undertaking. De Candolle went himself with the original Flora to the frontier; he was to send it by Lyons.
Just as we come to know them better, intermediate forms flow in, and doubts as to specific limits augment." De Candolle insists, indeed, in this connection, that the higher the rank of the groups the more definite their limitation, or, in other terms, the fewer the ambiguous or doubtful forms, that genera are more strictly limited than species tribes than genera, orders than tribes, etc.
Some few persons have the power of contracting the superficial muscles on their scalps; and these muscles are in a variable and partially rudimentary condition. M. A. de Candolle has communicated to me a curious instance of the long-continued persistence or inheritance of this power, as well as of its unusual development.
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