Page:Popular Science Monthly Volume 23.djvu/77

Rh, and never one-sided, because the conditions are the same all round, and the visiting insects can light upon them equally from every side. But flowers which grow sideways from a spike are very apt to become bilaterally symmetrical; indeed, whenever they are not so, one can always give an easy explanation of their deviation from the rule. Probably the blossoms of the monk's-hood began by arranging themselves in a long and handsome spike, so as more readily to attract the eyes of insects; and that was the real starting-point of all their subsequent modifications. Or, to put the same thing more literally, those monk's-hoods which happened to grow spike-wise succeeded best in attracting the bees, and therefore were most often fertilized in the proper manner. Next, we may suppose, the large green sepals, being much exposed to view, began to acquire a bluish tinge, as all the upper parts of highly developed plants are apt to do; and the bluer they became, the more conspicuous they looked, and therefore the better they got on in competition with their neighbors, especially since bees are particularly fond of blue. As each bee would necessarily light on the middle or lower portion of the flower, he would begin by extracting the honey from the two upper petals; but it would be rather awkward for him to turn round head downward, and suck the nectaries of the three bottom ones. Hence, in course of time, especially after the flower began to acquire its present shape, the two top petals became specialized as nectaries, while the three lower ones gradually atrophied, since the colored sepals had practically usurped their attractive function. But as the flower can only succeed by being fertilized, all these changes must have been really subordinate to the great change which was simultaneously going on in the mechanism for insuring fertilization. Slowly the blossoms altered to the bilateral shape—they adapted themselves by the bee's unconscious selection to the insect's form. The uppermost sepal grew into the hood, so arranged that the bee must get under it in order to reach the long nectaries containing their copious store of honey. At the same time the bee must brush against the stamens, and cover his breast with a stock of adhesive pollen-grains. When he flies away to the next flower he carries the pollen with him and, as he rifles the nectaries in the second blossom, he both deposits pollen from the last plant upon the sensitive surface of the carpels in this, and also collects a fresh lot of pollen to fertilize whatever other flower he may next favor with a call. The increased certainty of fertilization thus obtained enables the plant to dispense with some of the extra carpels which its buttercup ancestors once possessed; and, by lessening the number to three, it manages to get the whole set impregnated at a single visit. But, as three seeds would be a small number to depend upon in a world of overstocked markets and adverse chances, it makes up for the diminution of its carpels by largely increasing the stock of seeds in each.

Thus the whole shape and arrangement of the monk's-hood bear