The Hop (_Humulus Lupulus_) is a very interesting plant to a botanist, from the peculiarity of its flowers. The male and female ones are distinct, and generally on different plants. The male flowers are produced in loose panicles; the calyx (_fig._ 73, _a_) consists of five sepals, in the centre of which are five stamens, standing at first erect, but springing back with elasticity, when they discharge their pollen, and remaining extended as shown at _b_. The anthers open by pores at the extremity of the cells, as in Ericaceæ. The female flowers are produced in close heads (_c_). They have neither calyx nor corolla, but the ovary of each is protected by a membranous scale. Each ovary has two styles, though it produces only a single seed. As the fruit ripens the styles disappear, and the scales enlarge, so as to give the head of female flowers the form of a strobile or cone (_d_), the ripe fruit or nut being placed at the base of each scale, as shown at _e_. The surface of the scales is studded over with roundish glands, which are filled with a substance resembling pollen, called lupuline, which they give out on pressure, as shown at _f_; and this substance consists of a number of cells filled with volatile oil, which occasion the fragrance of the hop, and contain the bitter and astringent principles which make the hop so useful in compounding malt liquor. The lupuline is also somewhat narcotic; but though the fragrance of hops is said to produce sleep when inhaled in small quantities, an excess of it produces headache and vertigo, especially in nervous persons. The leaves are opposite, and three or five lobed; they are serrated on the edges, and rough on the surface. The stems are angular, covered with small prickles, and twining from left to right. The fibres of the stem when separated by soaking in water, are found to possess the same kind of tenacity as those of the Nettle and the Hemp, and may be made into cloth. The young shoots when boiled, are very good to eat as a substitute for asparagus. The leaves are furnished with stipules, and the flowers spring from the axils of the leaves. [Illustration: FIG. 74.—HEMP. (_Cannabis sativa._)]