Page:Popular Science Monthly Volume 28.djvu/84

76 among the surrounding grasses in such a way as to get freely at the sun and air, which are necessary for the nutrition of the plant. But the chief peculiarity of the clovers is the arrangement of their flowers in dense heads. Instead of the blossoms growing separately or in pairs, as with most peas and vetches, or in long, loose bunches, as with laburnum and sainfoin, the flowers of the clovers, much reduced in size, are crowded into compact little bundles, for the most part at the end of a long stalk. What we ordinarily call the flower of a purple clover is, in fact, such a head of clustered flowers. This dense clustering of the flowers makes them, though individually small, very conspicuous in the mass to bees and other insects, and so largely increases their chance of cross-fertilization. For the same purpose they usually secrete abundant honey, and they possess in many cases the familiar fragrant clover perfume. Moreover, in most though not in all species the bases of the five petals have grown together into a narrow tube, inclosing the honey; and in the common purple clover this tube is so deep that no British insect except the humble-bee has a proboscis long enough to reach the nectaries. Such peculiarities are quite sufficient to give the clovers an immense advantage in the struggle for existence; and it is not surprising that they should have become exceptionally numerous in species and individuals, even among the richly endowed and dominant papilionaceous family.

Every race, however, has its weak as well as its strong points; and the weak point of the highly successful clovers lies in the unprotected position of their seeds and pods. Hence, in accordance with the general principles above laid down, it is in these particulars that we might expect to find the various species differ most from one another, since this is just the part on which natural selection of favorable varieties is most likely to be exerted. As in the papilionaceous family as a whole, the flower is the organ which remains almost identical throughout, because it is the organ which gives the family its true importance; so in the restricted clover group the trefoil leaflets and the clustered heads of flowers remain almost identical throughout, and for the like reason. But in any classification of the various species of clover, it will be seen by anybody who looks into the matter that all the distinctive characters are drawn from differences in the pod and calyx after flowering, because this is the weak point of the genus, and the one in which alone diversities of habit have been likely to arise and to be perpetuated by survival of the fittest. The other organs have long since reached their equilibrium; these organs alone remain in need of further equilibration.

And why is the pod a weak point? For this reason. The seeds of clover, though small, are very richly stored with starches and other food-stuffs for the growth of the young plant. Such richness is, of course, in itself an advantage to the race, because it allows the seedlings to start well equipped on the path of life, with some accumulated