The sagacity which characterizes these two naturalists is seen in their success in finding decisive instances, and their sure insight into the meaning of things.  As an instance of the latter on Mr. Darwin’s part, and a justification of our venture to compare him with the facile princeps botanicorum, we will, in conclusion, allude to the single instance in which they took the same subject in hand.  In his papers on the organs and modes of fecundation in Orchideae and Asclepiadeae, Mr. Brown refers more than once to C.K.  Sprengel’s almost forgotten work, shows how the structure of the flowers in these orders largely requires the agency of insects for their fecundation, and is aware that “in Asclepiadeae . . . the insect so readily passes from one corolla to another that it not unfrequently visits every flower of the umbel.”  He must also have contemplated the transport of pollen from plant to plant by wind and insects; and we know from another source that he looked upon Sprengel’s ideas as far from fantastic.  Yet, instead of taking the single forward step which now seems so obvious, he even hazarded the conjecture that the insect-forms of some orchideous flowers are intended to deter rather than to attract insects.  And so the explanation of all these and other extraordinary structures, as well as of the arrangement of blossoms in general, and even the very meaning and need of sexual propagation, were left to be supplied by Mr. Darwin.  The aphorism “Nature abhors a vacuum” is a characteristic specimen of the science of the middle ages.  The aphorism “Nature abhors close fertilization,” and the demonstration of the principle, belong to our age, and to Mr. Darwin.  To have originated this, and also the principle of natural selection—­the truthfulness and importance of which are evident the moment it is apprehended—­and to have applied these principles to the system of Nature in such a manner as to make, within a dozen years, a deeper impression upon natural history than has been made since Linnaeus, is ample title for one man’s fame.

There is no need of our giving any account or of estimating the importance of such works as the “Origin of Species by means of Natural Selection,” the “Variation of Animals and Plants under Domestication,” the “Descent of Man, and Selection in Relation to Sex,” and the “Expression of the Emotions in Men and Animals”—­a series to which we may hope other volumes may in due time be added.  We would rather, if space permitted, attempt an analysis of the less known, but not less masterly, subsidiary essays, upon the various arrangements for insuring cross-fertilization in flowers, for the climbing of plants, and the like.  These, as we have heard, may before long be reprinted in a volume, and supplemented by some long-pending but still unfinished investigations upon the action of Dionaea and Drosera—­a capital subject for Mr. Darwin’s handling.