A layer of active cells that separates the xylem and the phloem. These cells produce new xylem and phloem that are represented by the annual rings of trees. Camellia spp.
See: Thea spp. Camote
See: Ipomea batatas. Canker
A necrotic, sunken lesion on a thick part of a plant, such as a stem. Cankers are usually caused by fungi. Canna edulis
Known as 'achira' in South America, where it originated, this crop is usually called Queensland arrowroot, or purple arrowroot, in English. It is grown commercially in Australia for extraction of starch from the rhizomes. Hybrids of wild species of Canna are a popular ornamental known as the Canna Lily. Rather too specialised for amateur breeders . Cannabis sativa
- Hemp. Tall varieties grown especially for the stem fibres. The stems are retted either wet or dry in order to extract the bast fibres, which make up about 25% of the stem tissues. The cultivation of hemp has often been legally restricted because of its close similarity to the drug varieties that produce marijuana (see below). However, the crop is becoming popular and offers scope for amateur breeders in areas where it has not been previously cultivated. The fibres, gathered from wild plants, have been used since Neolithic times, and the plant has probably been cultivated in China and Central Asia, for fibre production, for more than six thousand years. It is still cultivated in many countries for its fibres, although competition from synthetic fibres has greatly reduced its importance.
- Marijuana. Short varieties grown for drug purposes. Known as 'ganja' in India, 'marijuana' in the Americas, and 'bhang' elsewhere, this is a relatively harmless drug plant. This crop, which is illegal in many countries, provides an excellent example of what can be achieved by amateur breeders. A great number of breeders working independently have increased the strength of the plant's psychoactive component, tetrahydrocannabinol (THC) by about 100 times the naturally-occurring concentration. But the general advice to plant breeding clubs is to remain legal.
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