The peculiar flowers of the pea tribes are explained in Figs. [187], [188].
Fig. 187.—Flowers of the Common Bean, with one flower opened (a) to show the structure.
Spathe Flowers.—In many plants, very simple (often naked) flowers are borne in dense, more or less fleshy spikes, and the spike is inclosed in or attended by a leaf, sometimes corolla-like, known as a spathe. The spike of flowers is technically known as a spadix. This type of flower is characteristic of the great arum family, which is chiefly tropical. The commonest wild representatives are Jack-in-the-pulpit, or Indian turnip, and skunk cabbage. In the former the flowers are all diclinous and naked. In the skunk cabbage all the flowers are perfect and have four sepals. The common calla is a good example of this type of inflorescence.
Fig. 188.—Diagram of Alfalfa Flower in Section:
C, calyx; D, standard; W, wing; K, keel; T, stamen tube; F, filament of tenth stamen; X, stigma; Y, style; O, ovary; the dotted lines at E show position of stamen tube, when pushed upward by insects. Enlarged.
Composite Flowers.—The head (anthodium) or so-called “flower” of sunflower (Fig. [189]), thistle, aster, dandelion, daisy, chrysanthemum, goldenrod, is composed of several or many little flowers, or florets. These florets are inclosed in a more or less dense and usually green involucre. In the thistle (Fig. [190]) this involucre is prickly. A longitudinal section discloses the florets, all attached at bottom to a common torus, and densely packed in the involucre. The pink tips of these florets constitute the showy part of the head.
Fig. 189.—Head of Sunflower.