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viii be unsymmetrical. The petals are often very different in form and size, and the flower then becomes irregular, as in the Snapdragon, Foxglove, and Monkshood. One peculiar form of irregular flower prevalent in the Leguminosæ or Pea tribe is known as papilionaceous, from a fancied resemblance of the petals to a butterfly with its wings expanded. The upper of the five petals, usually larger than the rest, termed the vexillum, is somewhat curved backwards; the two lateral ones are called alæ or wings; while the two lower, which are united slightly by their margins, are styled the carina, or keel.

Attached to the petals, or between them and the stamens, are sometimes found small processes of various form, to which the name of nectaries is usually given.

The stamens are arranged within the petals, in one or move whorls. They consist generally of a long slender column or filament bearing a small body at the apex called the anther, which contains the pollen or powdery matter by which the seed is fertilized. This anther is usually two-celled, but sometimes one-celled, and the manner in which the cells open to discharge their pollen is often a most important character in distinguishing plants. The stamens are sometimes united by their filaments into a column with the pistil, or into several groups, and in some plants the anthers are similarly connected. The anther is the only essential part of the stamen, the filament being often wanting.

The pistil is the body through which the fertilization of the seed takes place. There is sometimes only one, and sometimes many; they always occupy the centre of the flower. A pistil generally consists of a club-shaped or variously divided process called the stigma, supported on a column termed the style, by which it communicates with the ovary or embryo seed-vessel at its base; the style, however, is often absent.

Like all other parts of the flower, the ovary is formed of modified leaves variously arranged. Sometimes it consists of one leaf with the margins united so as to form a vessel in which the seeds are