74 THE POPULAR SCIENCE MONTHLY. 



some special peculiarity of its own, which has insured for it an advan- 

 tage in certain situations over all its nearest congeners ? 



Clover is, of course, by family, a pea-llower, one of the great group 

 of the Pcqnlionaceie, a tribe of the vast leguminous race. Now, every- 

 body knows the general appearance of the pea-blossom, a form of 

 flower which reappears throughout the whole group, in such different 

 plants as gorse, laburnum, peas, beans, vetches, wistaria, lupine, and 

 acacia ; and it is clearly this form of flower which gave the original 

 ancestor of the papilionaceous plants its main advantage in the strug- 

 gle for existence over almost all its compeers. In other respects, the 

 various members of the pea-flower tribe differ widely from one an- 

 other. Some of them are tall, woody trees, like the laburnum ; some 

 are bushy shrubs, like the broom ; some are low, creeping herbs, like 

 the clover ; and some are lithe, trailing climbers, like the pea and the 

 scarlet-runner. So again with their foliage : some have hard, spiky 

 leaves, like furze ; some have regular trefoils, like medic ; some have 

 long sprays of many leaflets, like the sainfoin ; and some have clinging 

 tendrils, like the peas and vetches. Once more, in the pod and seed 

 there are infinite varieties of shape, size, and arrangement, as one may 

 see by comparing peas with horse-beans, or the short, hairy pod of 

 gorse with the long, smooth capsule of the vetch, the inflated globe of 

 the bladder senna, and the twisted, snail-like spiral of the medic. In 

 fact, there is hardly a single particular in w^hich the papilionaceous 

 plants do not differ from one another immensely, except only their pe- 

 culiar flower. Clearly, then, it is the flower almost alone which has 

 given them their fair start in the struggle for life. I say almost — not 

 quite — alone, because, as we shall see hereafter, they owe much also to 

 their relatively large and richly stored seeds. In this one point they 

 early reached a state of equilibrium ; in other points, they went on 

 varying and adapting themselves to an infinite variety of external cir- 

 cumstances. 



Though it is not my intention to deal at any length here with any 

 of the papilionaceous tribe except the clovers, a few words must first 

 be premised about this peculiar and successful type of flower. It con- 

 sists, like most other blossoms of the dicotyledonous race, of flve petals, 

 inclosing ten stamens, and with a single ovary, or embryo pod, in its 

 very center. But anybody who has ever looked at a pea-blossom 

 knows very well that it is not regular and radially symmetrical like a 

 dog-rose ; it has its parts bilaterally arranged, so that an insect light- 

 ing upon the flower in search of honey necessarily brushes his breast 

 against the stamens and pistil, and therefore cross-fertilizes the em- 

 bryo y)ods by carrying pollen from one blossom to the sensitive sur- 

 face of the next. The five petals have undergone special modification 

 so as to suit this special mode of impregnation. The upper petal, 

 known as the standard, is usually broad and expanded, serving as an 

 advertisement to attract insects ; and in many advanced species it is 



