Page:Popular Science Monthly Volume 5.djvu/150

138 appears in two well-marked varieties: one, found in sunny localities, whose petals are dark yellow, with red at the base; and the other, growing by shaded ditches, with petals of light yellow, and no red at the base. The more conspicuous variety attracts insects, and, as the stigma overtops the stamens, the agency of insects is required to secure fertilization. The flowers of the less conspicuous variety are not visited by insects, and, as the stigma does not overtop the stamens, the agency of insects is not required. The flower is self-fertilizing. These two forms graduate into each other, by connecting links which are found on the sunny edges of ditches.

Here is a very instructive lesson. Greater amounts of sunlight will account for the richer color of one variety; and the agency of insects, attracted by the color, will account for the change in structure. We see Nature in the act of species-making. Insects, acting mechanically on the delicate organs of a plant, effect something more than fertilization. Let us consider this action more carefully.

Dr. Ogle has observed the manners of the bee in visiting beans and scarlet-runners. These flowers are arranged to secure cross-fertilization. The honey they offer must be taken by an insect which will enter by the open door of the corolla-tube. But Dr. Ogle observed that while certain bees visit the flower in the legitimate way, and thus carry pollen from anther to stigma, others have a trick of evading their duty by piercing a hole in the calyx-tube, thus securing the nectar by a short cut. An important fact noted in these observations is, that the same bee always visits a flower in the same way. The inference is, that this habit of nipping the calyx is the result of individual experience. As some bees have acquired the habit, and others have not, another inference is that these insects are intelligent, and that they differ from each other in degrees of intelligence. Our final inference is that, if all bees are ever schooled up to this new art, there must come an end to our beans and scarlet-runners—unless some modification should occur in the structure of their flowers.

The salvia is constructed as if with special reference to fertilization by bumble-bees. But Mr. Meehan, who first pointed out the correlation, never saw a bumble-bee enter the flower. Under his eye the bee always cut the tube of the corolla. But another observer has seen the bumble-bee enter the flower and effect fertilization. And he has seen it nipping the corolla-tube to secure the honey by a short cut. And he has noticed that the smaller bees entered the corolla-tube, and that those which were too large to get into the flower nipped the tube. This is an important observation, and brings us to the very heart of the matter. The salvia with small corolla-tube, not securing fertilization, stands but little chance of surviving. The flower with large tube invites the bee, is fertilized, and ripens seed. "Natural selection" is going on under our very eyes. Now, if, in "the struggle for existence," a larger race of bumble-bees should appear, the salvia must either vary with