Page:Popular Science Monthly Volume 45.djvu/814

792 particular case, because the movement in question is undoubtedly useful, and as such, variations in this direction, be they fortuitous or mechanically induced, would be preserved by natural selection. In other words, an ever-recurring mechanical stimulus is presupposed even on the theory which works entirely with accidental variations, responding more or less fortunately thereto, while, if the stimulus be a direct cause of the favorable variations, its importance as a factor becomes still greater.

Our theory of the origin of the peculiar movement in barberry stamens amounts, then, to this: Stimulation by contact at a definite part of the filament for innumerable generations, increase of the protoplasmic contents by the reduction of adjacent parts, and the usefulness of such a movement at every stage of its development—these three factors, although separately incompetent, have yet in combination been the ones chiefly concerned in bringing about through the agency of natural selection such changes in the protoplasm of the sensitive cells as make its fundamental property of contractility prominent to an extraordinary degree.

Fertilization being accomplished, the single pistil ripens into a berry. In Berberis vulgaris each of the two ovules ordinarily becomes a hard-coated seed flattened on its inner face by pressure (Fig. 20) in much the same way as happens with the two "beans" in a coffee berry. Sometimes (as in the so-called "male berry" coffee) one of the ovules aborts, thus leaving the other to form a seed proportionally richer in reserve food and correspondingly round in form. Occasionally there may be found barberry bushes producing fruit in which both ovules have aborted. But accordding to Buckhout such individuals "do not constitute a permanent variety, for stoneless barberries are only found on old plants, and it has been proved that young suckers taken from them and planted in fresh soil fruit with perfect seeds." Seed production in this case would thus seem to be a question of the plant's vigor at a given period, and so to be comparable with the case of