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Notable Plant Families: Pulse

Pulse Family.--The Pulse family includes many of our common wood and field flowers. The majority of its members are easily distinguished by those irregular, butterfly-shaped blossoms which are described as papilionaceous. The sweet pea is a familiar example of such a flower, and a study of its curious structure renders easy the after identification of a papilionaceous blossom, even if it be as small as one of the many which make up the head of the common pink clover.

The calyx of such a flower is of five more or less-and sometimes unequally--united sepals. The corolla consists of five irregular petals, the upper one of which is generally wrapped about the others in bud, while it spreads or turns backward in flower. This petal is called the standard. The two side petals are called wings. The two lower ones are usually somewhat united and form a sort of pouch which encloses the stamens and style; this is called the keel from a fancied likeness to the prow of an ancient vessel. There are usually ten stamens and one pistil.

These flowers are peculiarly adapted to cross-fertilization through insect agency, although one might imagine the contrary to be the case from the relative positions of stamens and pistil. In the pea-blossom, for example, the hairy portion of the style receives the pollen from the early maturing stamens. The weight of a visiting bee projects the stigma and the pollen-laden style against the insect's body. But it must be observed that in this action the stigma first brushes against the bee, while the pollen-laden style touches him later, with the result that the bee soon flies to another flower on whose fresh stigma the detached pollen is left, while a new cargo of this valuable material is unconsciously secured, and the same process is indefinitely repeated.