Page:Popular Science Monthly Volume 45.djvu/816

794 involves the assumption of the following changes: (1) The disappearance of all but one of the pistils; (2) reduction of the number of seeds; (3) the abandonment of dehiscence; (4) increased hardness of seed coat; (5) the acquirement of succulence; (6) the development of an attractive color.

The first-named alteration we have already considered in connection with the evolution of the flower. As with this, so with the other changes, the best we can do is to imagine how they might have come about. Now, it is true of all capsular fruits that until fully ripe they are neither dry nor dehiscent. We know that variations in the time of ripening do occur, and experiments have shown that even unripe seeds will germinate and produce strong, healthy plants. In view of these facts it seems reasonable to suppose that not only might there arise varieties in which the capsule would retain something of its succulence until the seeds were nearly ripe, but if the fruit in this condition were eaten by birds or other animals the seeds might be disseminated by them, much to the benefit of the favored variety. There were doubtless seasons of scarcity in prehistoric times as well as now, when animals would be glad of even such comparatively unattractive fruits as we have described. Among the descendants of those plants whose fruits had become somewhat berrylike, those having the more succulent pericarp would, other things being equal, have most descendants, and thus in the course of many generations the present condition be reached.

The conspicuousness, depending as it does upon the same changes in the original pigment as occur in the transformations of chlorophyll in autumn leaves, may be looked upon as a result incidentally connected with the retention of succulence in the pericarp after growth had ceased, and as this tendency for the fruit to assume a color contrasting with the foliage would be beneficial as an advertisement to birds, natural selection would favor rather than hinder it.

The fact that in mahonias the berries are commonly of a dark purplish blue suggests that possibly this was the color first assumed by the fruit of the genus, the more conspicuous scarlet of the common barberry and its near relatives being acquired later, along with the higher differentiation of structure which it accompanies. Although this view gains some support from the occasional appearance of a blue-fruited variety of Berberis vulgaris (which might be thought of as a reversion to the ancestral type), still it should be remembered that our knowledge of the chemistry of plant pigments is at best too meager to justify much confidence in any theory of color change.