Hemp
Family Cannabinaceae
Cannabis sativa, hemp, is a dioecious annual herb, up to several meters high, with angular stems. The palmate leaves (Ca. sativa 1) are opposite near the base of the stem and spirally arranged above. The male flowers (Ca. sativa 2) are borne in axillary and terminal panicles, each flower with 5 sepals and 5 stamens, petals absent. The female flowers (Ca. sativa 3) are also borne in axillary and terminal inflorescences. Flowers in pairs, each flower enveloped by a bract with thick glandular hairs and with the calyx enveloping the ovary. The fruits are small achenes.
Distribution
Hemp is a native of Central Asia and is of ancient cultivation. It probably reached China in the 3rd millennium BC. However, in the New World it was introduced just in post-Columbian times.
Use
Hemp produces three products: fibre from the stem; oil from the seeds; and narcotics from the leaves and flowers.
The white bast fibres are used as a substitute for flax in the manufacture of yarns and twines. Greatest producers of fibre are India, Russia, Romania, Hungary, Poland and Turkey.
The oil is used as a substitute for linseed oil in paints and varnishes, and in the manufacture of soap.
The narcotic properties of hemp are the result of the presence of cannabinoids in a resin from the glandular hairs on the leaves and inflorescences, with cannabinol (THC= tetrahydrocannabinol) as the most active one. As a narcotic it is usually smoked for euphoric purposes. Marijuana are the dried leaves and flowering shoots and contains 1-5% cannabinol, depending on the climate; the hotter the conditions, the more resin being produced. Hashish is powdered resin. Most of the narcotic is produced in Afghanistan, Morocco, Lebanon, Turkey, Pakistan and Nepal. In the US it is imported from Mexico and Colombia.
Hemp shows a clear example of artificial selection. North of 30 degrees latitude for centuries the plant was cultivated for its fibres, south of that latitude for its cannabinol. This resulted in the fibre plants being longer and containing less THC.