The principal _use of hops_, in brewing, is for the preservation of malt liquor, and to communicate to it an agreeably aromatic bitter flavour. The best hops are used for ale and the finer kinds of malt liquor, and inferior kinds are used for porter. The odour of hops hung over a bed, or a pillow stuffed with hops, has been said to promote sleep, after the application of opium has failed. The _young shoots_ and tops are often gathered from the hedges, by poor people, and boiled and eaten in the manner of asparagus. Of the woody part of the _hop-binds_, after having been steeped in water, and worked into a pulp, a coarse kind of paper may be made. HEXANDRIA. 261. _YAMS are an American and West Indian root of very irregular shape, which possess properties somewhat similar to those of the potatoe, but they are less mealy, and, in a raw state, are very viscous._ _The plants_ (Dioscorea bulbifera) _which produce these roots have heart-shaped leaves, and a stem that creeps along the ground like ivy._ In some of the rich lands of South America, yams are said to grow to the weight of fifty or sixty pounds each; and are so productive that an acre of ground planted with them has been known to produce roots to the weight of from 20,000 to 30,000 pounds. Yams are propagated by setting the eyes, in the same manner as we plant potatoes; and, in six or eight months, they arrive at maturity. When they are dug out of the ground, they are, for a little while, exposed to the sun to dry; and if, after this, they be packed in casks full of dry sand, they may be preserved, without injury, for many months. They are consequently often used as sea-store for vessels about to sail on long voyages, and are frequently brought into England. Several attempts have been made to cultivate yams in this island; and these have been attended with a certain degree of success in the counties of Mid-Lothian, Perth, and Stirling in Scotland, where they are used for the feeding of cattle. There are two kinds, one red, and the other white. The former of these contain a more nutritive food than the latter, though their flavour is much less excellent. With the negroes, in the West Indian islands, the yam is a very important article of food. When roasted, it is so wholesome and nutritive that it is preferred by them even to bread. Like potatoes, yams may be converted into bread, by mixture with a portion of wheat or barley flour. They are sometimes made into soup, puddings, and other useful dishes. OCTANDRIA. 262. _The ABELE, or GREAT WHITE POPLAR-TREE_ (Populus alba, Fig. 74), _is a British tree which grows in hedges and woods, near brooks, and is known by its leaves being nearly triangular, irregularly jagged at the edges, and cottony underneath._