Practically, when naturalists are at work, they do not trouble themselves about the physiological value of the characters which they use in defining a group or in allocating any particular species.

If they find a character nearly uniform, and common to a great number of forms, and not common to others, they use it as one of high value; if common to some lesser number, they use it as of subordinate value.

This principle has been broadly confessed by some naturalists to be the true one; and by none more clearly than by that excellent botanist, Aug.

St.