Name: When speaking of grasses one often includes such plants as Rib Grass, Poverty Grass and Cotton Grass, which botanically have none of the characteristics of true grasses. On the other hand, many people do not regard Corn and Millet as true grasses. Agriculturally a distinction is made between cereals and grasses, but botanically such a distinction is impossible, rye, barley, oats and wheat being grasses as truly as Meadow Fescue, Red Top and Timothy.
Seed: If with a sharp knife we cut through a corn grain, parallel to its broadest side, we see that a great portion of it consists of a white or yellow mass, in which the naked eye cannot discover any distinct structure. This part of the grain, which in Fig. I is marked End. is called endosperm and provides food for the young seedling. The remaining part of the grain is dull-coloured, and the naked eye can discern three distinct sections. This is the embryo or young plant before germination. It consists of a so-called cotyledon (Fig. I, Cot.) which lies close to the endosperm, a terminal bud (Fig. 1, B.) from which the stem and leaves of the germinating plant develop, and a radicle (Fig. I, Rad.) from which the first root is formed. The portion lying between the radicle and the terminal bud is the stem of the embryo.
Fig. 1. Section through a grain of Corn. Four times natural size. End.- Endosperm. Cot. - Cotyledon. B. - Bud. Rad. - Radicle.
Germination: When corn germinates the cotyledon acts as a sucker, turning the food in the endosperm over to the embryo; it remains enclosed in the grain during germination. The other parts of the embryo soon become visible. The radicle develops into a root and the bud soon displays a number of green leaves. The primary root soon dies and its function is taken by secondary roots, which sprout from the lower parts of the stem. The essential features of this process of germination are characteristic of all grasses.
Root System: Most fodder and pasture grasses are perennial; that is, their underground parts survive from year to year. These surviving parts consist of underground stems, from which roots and overground stems develop. Sometimes they are creeping with long internodes, when the overground stems appear scattered and the whole plant forms a more or less spreading mat, as in Red Fescue. In other cases the internodes are very short. The overground stems are then close together and the plant develops into one of the bunch grass type, such as Sheep's Fescue. Although characteristic of a certain species, the type may be modified by the soil. Thus, stiff, compact soil is apt to prevent the development of creeping rootstocks, and the plant may assume a more or less bunchy appearance. On the other hand, bunchy plants often develop looser tufts in open, loose soil than in stiff clay.
Stems: The stems of the grasses, generally called culms, are hollow, except in corn, in which they are solid, but are closed at intervals by variously coloured swollen parts called nodes or joints. The parts of the stems between the nodes are called internodes. Immediately above the nodes a small portion of the stem remains soft and continues to grow during almost the whole life of the plant, but the upper part of the internode soon becomes firm and stops growth. This enables the stems, if they are not too old, to regain their upright position when lodged by wind or rain.
Leaves: The leaves consist of two distinct parts. The lower encloses the stem like a tight case, usually open along one side. It is called the sheath. The upper part, the blade, is generally long and narrow. Where the plants have sufficient moisture the blades are flat; during drought they are often rolled together and bristle-like, turning their upper surface outward. A plant which during excessive drought has bristle-like leaves may display flat ones if moisture becomes abundant in either air or soil. As the moisture secured by the root evaporates chiefly through the lower surface of the leaf, the-rolling together of the blade during drought prevents loss of moisture and thus saves the plant from perishing of thirst. Where the blade is attached to the sheath there is generally a thin membranous appendage, of varying size and shape, called the ligule (Fig. 2, L.).
Inflorescence: The flowers arc in inflorescences which, however different they may look, are always constructed on the same principle. That of Kentucky Blue Grass is typical (Plate 10). It consists of branches arranged in whorls at the upper joints of the main stem. When the branches are elongated, as in the Blue Grasses,
Fig. 2-Sheath and lower part of leaf of Timothy. Natural size. L. - Ligule.
Red Top, Fescues, Oats, etc., the inflorescence is called a panicle. When they are very short, as in the Foxtail Millets, the inflorescence has the appearance of a spike. Timothy (Plate 3) and Meadow Foxtail (Plate 4) inflorescences are extremely like regular spikes, but even in these the type is that of the ordinary panicle. This is proven by the fact that branched inflorescences occasionally occur in Timothy. Even an ear of corn is a modification of a panicle, characterized by extremely short branches from a fleshy main stem. The panicles of many grasses are differently shaped at different stages of development. Thus, in Red Top and Sheep's Fescue the branches spread during flowering and the inflorescence is therefore open and broad. When flowering is over, the branches close in toward the main stem, making the inflorescence contracted and narrow.