HOP, Humulus lupulus, L., an herbaceous twining plant, belonging to the family Moraceae. It is of common occurrence in hedges and thickets in the southern counties of England, but is believed not to be native in Scotland. On the European conti nent it is distributed from Greece to Scandinavia, and extends through the Caucasus and Central Asia to the Altai Mountains. It has been introduced into the northern and western states of North America and also into Brazil, Australia and the Himalayas.
It is a perennial plant, producing annually several long twining roughish striated stems, which twist from left to right, are often 15 to 20 ft. long and climb freely over hedges and bushes. The roughness of stem and leaves is due to lines of strong hooked hairs, which help the plant to cling to its support. The leaves are stalked, opposite, 3-5 lobed, and coarsely serrate, and bear a general resemblance to those of the vine, but are, as well as the whole plant, rough to the touch ; the upper leaves are sometimes scarcely divided, or quite entire. The stipules are between the leaf-stalks, each consisting of two lateral ones united, or rarely with the tips free. The male and female flowers are produced on distinct plants. The male inflorescence forms a panicle; the flowers con sist of a small greenish five-parted perianth enclosing five stamens, whose anthers open by terminal slits. The female inflorescence is less conspicuous in the young state. The catkin or strobile consists of a number of small acute bracts, with two sessile ovaries at their base, each subtended by a rounded bractlet. Both the bracts and bractlets enlarge greatly during the development of the ovary, and form, when fully grown, the membranous scales of the strobile, they are known as "petals" by hop-growers. The bracts can then only be distinguished from the bractlets by being rather more acute and more strongly veined. The perianth is short, cup shaped, undivided and closely applied to the ovary, which it ultimately encloses. In the young strobile the two purple hairy styles of each ovary project beyond the bracts. The ovary con tains a single ovule which becomes in the fruit an exalbuminous seed, containing a spirally-coiled embryo. The light dusty pollen is carried by the wind from the male to the female flowers.
The ovary and the base of the bracts are covered with a yellow ish powder, consisting of minute sessile grains, called lupulin or lupulinic glands. It is to the lupulin in these glands that the medicinal properties of the hop are chiefly due. Besides the com mon hop there are two other species, the American hop (H. americanus) and the Japanese hop (H. japonicus), both of which are cultivated. (V. H. B.)