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But obviously this is only of secondary importance, and has no influence on the fact that a number of new types, analogous to the older swarms of Draba, Viola and of many other polymorphous species, have been seen to arise directly in the wild state.
A question highly interesting to the history of the progressive marks of organization on the globe has been very warmly discussed in our own times, that of ascertaining whether the polymorphous plants are more common in the volcanic islands. The vegetation of Teneriffe is unfavourable to the hypothesis that nature in new countries is but little subject to permanent forms.
In other instances the groups of elementary forms as they are shown by direct observation, have been adjudged by many authors to be too large to constitute species. Hence the polymorphous genera, concerning the systematic subdivisions of which hardly two authors agree.
M. Broussonnet, who resided so long at the Canaries, asserts that the variable plants are not more common there than in the south of Europe. May it not to be presumed, that the polymorphous species, which are so abundant in the isle of Bourbon, are assignable to the nature of the soil and climate rather than to the newness of the vegetation?
The local races are uniform and come true from seed; the variability of the species is not of a fluctuating, but of a polymorphous nature. A given elementary species keeps within its limits and cannot vary beyond them, but the whole group gives the impression of variability by its wide range of distinct, but nearly allied forms.
Starting from this conception the pedigree of our mutations must be considered as only one small group. Instead of figuring a fan of mutants for each year, we must condense all the succeeding swarms into one single fan, as might be done also for Draba verna and other polymorphous species.
It is true that about forty of them range from British to high northern latitudes; but several of them, as, for example, Lutraria rugosa and Pecten polymorphous, which are abundant, are not known at present to range farther north than the coast of Portugal, and seem to indicate a warmer temperature than now prevails on the coast where we find them fossil.
All we know is, that varieties are themselves variable, and that very diverse forms have been educed from one stock. Species of the same genus are not distinguished from each other by equal amounts of difference. There is diversity in this respect analogous to that of the varieties of a polymorphous species, some of them slight, others extreme.
In a flora so small as the British, 182 plants, generally reckoned as varieties, have been ranked by some botanists as species. Selecting the British genera which include the most polymorphous forms, it appears that Babington's Flora gives them 251 species, Bentham's only 112, a difference of 139 doubtful forms.
It occurs in widely distant families, but has a special interest for us in two genera, which are generally known as very polymorphous groups. One of them is the hawkweed or Hieracium, and the other is the dandelion or Taraxacum officinale.
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