The caulicle usually elongates, and from its lower end roots are emitted. The elongating caulicle is known as the =hypocotyl= (“below the cotyledons”). That is, the hypocotyl is that part of the stem of the plantlet lying between the roots and the cotyledon. _The general direction of the young hypocotyl, or emerging caulicle, is downwards._ As soon as roots form, it becomes fixed and its subsequent growth tends to raise the cotyledons above the ground, as in the bean. When cotyledons rise into the air, germination is said to be =epigeal= (“above the earth”). Bean and pumpkin are examples. When the hypocotyl does not elongate greatly and the cotyledons remain under ground, the germination is =hypogeal= (“beneath the earth”). Pea and scarlet runner bean are examples (Fig. 48). When the germinating seed lies on a hard surface, as on closely compacted soil, the hypocotyl and rootlets may not be able to secure a foothold and they assume grotesque forms (Fig. 17). Try this with peas and beans. The first internode (“between nodes”) above the cotyledons is the =epicotyl=. It elevates the plumule into the air, and _the plumule leaves expand into the first true leaves of the plant_. These first true leaves, however, may be very unlike the later leaves in shape. [Illustration: FIG. 18.—COTYLEDONS OF GERMINATING BEAN SPREAD APART TO SHOW ELONGATING CAUDICLE AND PLUMULE. ] [Illustration: FIG. 19.—GERMINATION OF BEAN.] =Germination of Bean.=—The common bean, as we have seen (Fig. 15), has cotyledons that occupy all the space inside the seed-coats. When the hypocotyl, or elongated caulicle, emerges, the plumule leaves have begun to enlarge, and to unfold (Fig. 18). The hypocotyl elongates rapidly. One end of it is held by the roots. The other is held by the seed-coats in the soil. It therefore takes the form of a loop, and the central part of the loop “comes up” first (_a_, Fig. 19). Presently the cotyledons come out of the seed-coats, and the plant straightens and the cotyledons expand. These cotyledons, or “halves of the bean,” persist for some time (_b_, Fig. 19). They often become green and probably perform some function of foliage. Because of its large size, the Lima bean shows all these parts well. [Illustration: FIG. 20.—SPROUTING OF CASTOR BEAN. ] =Germination of Castor Bean.=—In the castor bean the hilum and micropyle are at the smaller end (Fig. 20). The bean “comes up” with a loop, which indicates that the hypocotyl greatly elongates. On examining germinating seed, however, it will be found that the cotyledons are contained inside a fleshy body, or sac (_a_, Fig. 21). This sac is the endosperm. Against its inner surface the thin, veiny cotyledons are very closely pressed, absorbing its substance (Fig. 22). The cotyledons increase in size as they reach the air (Fig. 23), and become functional leaves. [Illustration: FIG. 21.—GERMINATION OF CASTOR BEAN. Endosperm at _a_.] [Illustration: FIG. 22.—CASTOR BEAN.