Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/299

. IX. appearing at the distance of between eight and ten miles from any place where it grew. Notwithstanding the astonishing number of seeds produced by Orchids, it is notorious that they are sparingly distributed; for instance, Kent appears to be the most favourable county in England for the order, and within a mile of my house nine genera, including thirteen species, grow; but of these one alone, Orchis morio, is sufficiently abundant to make a conspicuous feature in the vegetation; as is O. maculata in a lesser degree in open woodlands. Most of the other species, though not deserving to be called rare, are sparingly distributed; yet, if their seeds or seedlings were not largely destroyed, any one of them would immediately cover the whole land. In the tropics the species are very much more numerous; thus Fritz Müller found in South Brazil more than thirteen kinds belonging to several genera growing on a single Cedrela tree. Mr. Fitzgerald has collected within the radius of one mile of Sydney in Australia no less than sixty-two species, of which fifty-seven were terrestrial. Nevertheless the number of individuals of the same species is, I believe, in no country nearly so great as that of very many other plants. Lindley formerly estimated that there were in the world about 6000 species of Orchideæ, included in 433 genera.

The number of the individuals which come to maturity does not seem to be at all closely determined by the number of seeds which each species produces; and this holds good when closely related forms are compared. Thus Ophrys apifera fertilises itself and every flower produces a capsule; but the individuals of this species are not so numerous in some parts of