Hemp, a plant cultivated for its fiber, seed, and oil. Hemp is also the source of several drugs. The name cannabis is sometimes used for the hemp plant or for the flowering tops of the female hemp plant. India and China are the leading producers of hemp, together accounting for more than half of the world's output.
Hemp fiber was woven into cloth as early as 3000 B.C. in China, where the plant originated. Introduced into Europe about 1500 B.C., hemp became an important source of cloth to the Mediterranean peoples. The Greeks and Romans wore a linen-like fabric of hemp. The American colonists brought hemp with them and raised it widely. When factory-produced cotton cloth replaced homespun fabrics, the hemp industry declined.
Long, straight hemp fibers are called line. Line is used to make rope, cord, and strong twines known in the trade as commercial twines. Line is also woven into sailcloth, carpeting, sacks, and webbing. Short pieces of fiber are called tow. Oakum, used in caulking wooden boats, consists of wads of tow impregnated with tar or a similar substance. Tow also makes a soft packing material. Hemp fiber of any length, treated chemically, is used in artificial sponges and certain plastics.
Most hemp seed is pressed to obtain the oil it contains. The oil is used to make soap, paint, and varnish. Hemp seed has some use as feed for poultry and cage birds.
The flowering tops of female hemp plants contain a potent resin. (Resin in lesser quantities is also found in the leaves.) The tops, leaves, or extracted resin may be chewed, smoked, sniffed, eaten, or brewed into beverages. They are so used for the intoxicating effect they produce.
Hemp is a hollow-stemmed, annual plant that grows best in rich clay loam in mild, moist climates of the Northern Hemisphere. There are many wild varieties. The cultivated plant is bushy-leaved, with a tall, straight stalk. Soon after the tiny, yellowish flowers appear above the dark-green leaves the male plants die. The female plants go on to sturdier growth. Hemp plants may be 3 to 16 feet (0.9 to 5 m) tall; in the United States, they are usually about 5 feet (1.5 m) tall.
Hemp seed is sown scattered or drilled in rows. After three or four months the plants are harvested. The seed-bearing tops and side shoots are removed for threshing.
The denuded stalks must first be retted (allowed to decompose by exposure to moisture) so that the bark-like outer fibers, called bast, will separate from the woody core. Dewretting is the simplest way. The stalks are left for weeks in the open field, where rain and dampness carry out the process naturally. In water-retting, a refinement practiced in Italy, the stalks are soaked in water tanks, and the fiber is said to be of finer quality as a result.
The retted stalks are gathered into shocks or loose bundles and allowed to dry outdoors. Breaking consists of pounding the dry stalks so that the interior woody part is broken into small pieces called chaff. Lastly, the stalks are scutched, or whipped against a solid object. The broken woody bits fall out and are discarded, leaving only the fibers.
Hemp is Cannabis sativa.