Fig. 69.—Vetch. (× ⅓.)
Watch bees visiting the flowers. The insect alights on the wings, and its weight pulls them down and lowers the keel, bringing the stamens against the bee’s body.
Cut a complete flower down the middle with a sharp knife, and notice that calyx, corolla, and stamens seem not to be inserted separately on the receptacle, but to spring from a common base.
2. Other plants of the pea family.—Examine also bean, vetch ([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.)