" He also adds that it
is the best known species which present the greatest number of spontaneous
varieties and sub-varieties. Thus Quercus robur has twenty-eight
varieties, all of which, excepting six, are clustered round three sub-
species, namely Q. pedunculata, sessiliflora and pubescens. The forms
which connect these three sub-species are comparatively rare; and, as Asa
Gray again remarks, if these connecting forms which are now rare were to
become totally extinct the three sub-species would hold exactly the same
relation to each other as do the four or five provisionally admitted
species which closely surround the typical Quercus robur. Finally, De
Candolle admits that out of the 300 species, which will be enumerated in
his Prodromus as belonging to the oak family, at least two-thirds are
provisional species, that is, are not known strictly to fulfil the
definition above given of a true species. It should be added that De
Candolle no longer believes that species are immutable creations, but
concludes that the derivative theory is the most natural one, "and the most
accordant with the known facts in palaeontology, geographical botany and
zoology, of anatomical structure and classification."
When a young naturalist commences the study of a group of organisms quite
unknown to him he is at first much perplexed in determining what
differences to consider as specific and what as varietal; for he knows
nothing of the amount and kind of variation to which the group is subject;
and this shows, at least, how very generally there is some variation.
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