Page:Popular Science Monthly Volume 28.djvu/86

78 by human agency; while our two more truly wild species are meadow and pasture weeds, and are therefore amply protected by prickles against herbivorous animals. Again, bird's-foot trefoil, whose pretty yellow flowers form such ornaments to our sunny banks in summer, has a long, hard, dry pod, too stringy to be edible, and filled with pith between the beans; while lady's-fingers, a somewhat similar type, has an inflated hairy calyx completely inclosing the short pod in its protective and inedible capsule. Strangest of all, however, is the small, matted bird's-foot, whose pod never opens to shed the seeds, but divides between them into little joints or "articles," each inclosing a single bean, and so cheating the expectant birds of their promised food. These examples, which might be multiplied indefinitely, will sufficiently serve to show the importance of protection for the seeds as a basis of differentiation among the papilionaceous flowers.

With the restricted tribe of clovers the need for such protection has almost alone produced all the species into which the genus has long since split up. Originally, of course, we must suppose that there existed one united type of ancestral clover, differing from the other papilionaceous plants in the points which now distinguish the whole clover genus, but possessing none of the special distinctive marks which specifically divide one kind of clover from another. This hypothetical ancestor had probably rather large, purplish flowers, collected in compact heads on a common foot-stalk, with the five petals separate, and with a small three or four-seeded pod completely inclosed within the faded brown petals. From some such form the existing clovers have sprung by differentiations almost entirely affecting the pods and seeds, though they have also varied a little in color, according to the individual tastes of their particular insect visitors, as well as in the degree of union effected between their petals. Without going beyond the limits of our own native clovers, we will look first at those types in which the arrangement of the pod is simplest, and then pass on gradually to those in which it is more and more complex, till we arrive at last at that most marvelous English species which actually buries its own pods entire in the ground by a wonderful series of apparently purposive movements and gyrations.

Our common English purple clover (for convenience' sake I adopt throughout Mr. Bentham's vernacular names) may be taken as a good specimen of the simpler and less-protected kinds. The mere fact that it is grown extensively for fodder shows that it has no deterrent prickles or bristles to ward off the attacks of herbivorous animals; and indeed, throughout the clover group, it may be noted that birds and insects, rather than large mammals, seem to be the enemies especially guarded against by the majority of plants. Purple clover is a perennial, with long, hairy stems, the hairs serving to prevent ants from creeping up to the blossoms and uselessly rifling the honey