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Rh whether it be a distinct species or a mere variety, the points to be considered, independently of direct experiment, will be chiefly the following:—

Are the distinctive characters such as can be accounted for by station, climate, or other known influences, of which I have enumerated several in my Handbook? (Introd. p. 31 and 32.)

Are the circumstances under which it was growing, and its general aspect, such as to suggest its being a hybrid between the allied and some other species?

Are the distinctive characters such as are known to occur in mere varieties of other species, more especially of such as are systematically allied to the one in question?

Is the plant in question, an isolated individual (including in the same category any number of individuals naturally propagated from a single one by runners, suckers, bulbs, &c.); or has it been observed in more or less abundance in any variety of stations over any considerable independent geographical area, or in any important part of the area of the allied species?

Is the distinctive character relied on confined to a single organ, or is it more or less accompanied by differences in other organs of the plant; and, if so, how far does the plant retain all the characters in all the different stations and localities where it has been observed?

Have intermediates between the plant and its allied species been sought for in any considerable portion of the area of the latter, and especially in those countries where it is most liable to variations? And, if such intermediates exist, what is their relative number, and how far do they vary, or pass one into another in all, or any, and which, of the points in which the plant in question differs from its allied species?

It is only in proportion as the evidence on all these points is full, satisfactory, and reliable, that our decisions on the value of a species can be fair, independently of any want of tact, experience, powers of observation or judgment, which we are all liable to; and not to mention the cases of but too frequent occurrence where ignorance, a false pride, vanity, a love of controversy, a desire of flattering, or even mercenary motives, have influenced the reckless splitting or over-hasty reunion of species.

With regard to direct experiment in aid of inductive reasoning, it has been said that cultivation is a sure and easy test of the identity or distinctness of species; and nothing is more common than to find as an argument in support of a "critical" species, that it has been growing for many years in a garden, always retaining its distinctive characters.