The butterfly-shaped or papilionaceous corolla serves readily to identify a member of the pulse family. It is almost as unfailing as the nose of the Hohenzollerns. But we poor mortals may not flatter ourselves that it has been thus considerate to facilitate our study of the genus. The family has a very subtle way of achieving its ends in this world.
It has been observed that flowers that are dependent upon insects for cross-fertilization have usually an irregularly shaped corolla. It is so with the pulse family.
They offer no comfortable seat or resting place for Master Bee and therefore force the poor fellow to let the weight of his whole body knock against the blossom as he thumps about in search of nectar. It is for this little push that the flower has been planning. The stigma that was enclosed in the keel is knocked out, and the pollen grains that were already on the style from early-maturing anthers are dropped upon the bee's back. Little suspecting the trick that has been played upon him, he saunters off to another member of the family, as he is again allured by the irregular corolla and the purplish pink that is his favourite colour. As before, he knocks about for a seat and pushes out the stigma, which then greedily receives the pollen with which his back is covered from his last visit. In this way the pulse family manages the little matter of cross-fertilization. It has the true method of allowing others to do its work. And that its system is good is proved by the vigour and freshness of its growth.
The flowers are always arranged in fives, or multiples of five.
The stamens do not exceed ten and are usually united by their filaments. The leaves are mostly compound, with entire leaflets. Papilionaceae is the name that is now used as distinctive of this family and in preference to that of Leguminosae, under which they were formerly known.