The second family, the grasses, on the contrary, includes the most important of all food plants, all of the grains belonging here. They differ mainly from the sedges in having, generally, hollow, cylindrical stems, and the sheath of the leaves split down one side; the leaves are in two rows, while those of the sedges are in three. The flowers ([Fig. 87], L) are usually perfect; the stigmas, two in number and like plumes, so that they readily catch the pollen which is blown upon them. A few, like the Indian corn, have the flowers unisexual; the male flowers are at the top of the stem forming the “tassel,” and the female flowers lower down forming the ear. The “silk” is composed of the enormously lengthened stigmas. The fruits resemble those of the sedges, but the embryo is usually larger and placed at one side of the endosperm (N, em.).
While most of the grasses are comparatively small plants, a few of them are almost tree-like in their proportions, the species of bamboo (Bambusa) sometimes reaching a height of twenty to thirty metres, with stems thirty to forty centimetres in diameter.
Order V.—Scitamineæ.
Fig. 88.—Scitamineæ. A, upper part of a flowering plant of Indian shot (Canna), much reduced in size (Cannaceæ). B, a single flower, × ½. C, the single stamen (an.), and petal-like pistil (gy.), × 1. D, section of the ovary, × 2. E, diagram of the flower. The place of the missing stamens is indicated by small circles. F, fruit, × ½. G, section of an unripe seed. em. embryo. p, perisperm, × 2.
The plants of this order are all inhabitants of the warmer parts of the earth, and only a very few occur within the limits of the United States, and these confined to the extreme south. They are extremely showy plants, owing to their large leaves and brilliant flowers, and for this reason are cultivated extensively. Various species of Canna ([Fig. 88]) are common in gardens, where they are prized for their large, richly-colored leaves, and clusters of scarlet, orange, or yellow flowers. The leafy stems arise from thick tubers or root stocks, and grow rapidly to a height of two metres or more in the larger species. The leaves, as in all the order, are very large, and have a thick midrib with lateral veins running to the margin. The young leaves are folded up like a trumpet. The flowers are irregular in form, and in Canna only a single stamen is found; or if more are present, they are reduced to petal-like rudiments. The single, perfect stamen ([Fig. 88], C, an.) has the filament broad and colored like the petals, and the anther attached to one side. The pistil (gy.) is also petal-like. There are three circles of leaves forming the perigone, the two outer being more or less membranaceous, and only the three inner petal-like in texture. The ovary (o) is inferior, and covered on the outside with little papillæ that afterward form short spines on the outside of the fruit (F).
The seeds are large, but the embryo is very small. A section of a nearly ripe seed shows the embryo (em.) occupying the upper part of the embryo sac which does not nearly fill the seed and contains no endosperm. The bulk of the seed is derived from the tissue of the body of the ovule, which in most seeds becomes entirely obliterated by the growth of the embryo sac. The cells of this tissue become filled with starch, and serve the same purpose as the endosperm of other seeds. This tissue is called “perisperm.”
Of food plants belonging to this order, the banana (Musa) is much the most important. Others of more or less value are species of arrowroot (Maranta) and ginger (Zingiber).
There are three families: I. Musaceæ (banana family); II. Zingiberaceæ (ginger family); and III. Cannaceæ (Canna, Maranta).