2. Other plants of the pea family.—Examine also bean, vetch [Pg 101] (Fig. 69), meadow vetchling (Fig. 70), clover (Fig. 71), laburnum (Fig. 73), and broom. Compare the habits of growth of the plants, and notice that they all have the same peculiar shape of flower. Dissect a flower of each. Notice that in laburnum and broom the ten stamens are all united. In clover the flowers are in heads. Notice how the leaflets of the clover plant close at sunset. 3. Fertilisation.—Dig up several red clover plants in early summer and pot them. Cover about half the plants with gauze, so fixed on wire frames that insects cannot get inside, and then put all the plants together where they will get plenty of sun. Water them regularly, and notice which plants ripen seed. How do you account for the differences? Fig. 70.—Meadow Vetchling. (× ¼.) Fig. 71.—Red Clover. (× ⅙.) [Pg 102] Fig. 72.—Bird’s-foot Trefoil. 1, flowering branch (× ⅔); Fig. 73.—Flowering branch of Laburnum; st, 2, flower; 3, pistil and stamens; 4, pistil (× 1¹ ₉); 5, standard; w, wings; k, keel; 1, 2, 3, the flower fruit (× ⅔); 6, corolla; a, standard; b, wings; c, keel; 7, from different points of view. (× ½.) diagram of flower. The pea family.—Plants of the pea family are found in all quarters of the earth. They are of very diverse size and habit of growth; the laburnum, for example, is a tree; the gorse is a bush; the broad bean has a strong, erect, herbaceous stem; the pea is a weak-stemmed climbing plant; the clovers are small herbs with flowers forming “heads.” Most of the members of the family agree in having a “butterfly-shaped” corolla (Figs. 72 and 73), which consists of three well-marked parts, viz., a large standard, a pair of wings, and two closely-connected petals which form a boat-shaped keel. There are ten stamens, and the filaments of nine of these usually cohere to form a tube surrounding the ovary. In the laburnum, gorse, and a few others, all the ten stamens are united. When a bee visits the flower, in search of nectar, it alights on the “wings” of the flower, and its weight depresses these and pulls down the keel. The anthers of the stamens are so placed with respect to the keel that this results in a mass of pollen being scraped off the anthers and forced [Pg 103] out at the beak of the keel, or in the stamens being suddenly liberated and scattering pollen on the bee. The pollen sticks to the bee’s body, and some of it is almost certainly transferred to the stigma of the next flower visited. The quaint shape of the corolla is thus definitely adapted to the visits of insects; for the nectar is so placed that to obtain it the insect must carry off some of the pollen. The calyx, corolla, and stamens are not obviously—as in the wallflower and buttercup—inserted separately on the receptacle, but seem to spring from a common base.