The cassava plant is a perennial that grows under cultivation to a height of about 2 4 m. The large, palmate leaves ordinarily have five to seven lobes borne on a long slender petiole. They grow only toward the end of the branches. As the plant grows, the main stem forks, usually into three branches which then divide similarly. The roots or tubers radiate from the stem just below the surface of the ground. Feeder roots growing vertically from the stem and from the storage roots penetrate the soil to a depth of 50-100 cm. This capacity of the cassava plant to obtain nourishment from some distance below the surface may help to explain its growth on inferior soils.
Male and female flowers arranged in loose plumes are produced on the same plant. The triangular-shaped fruit contains three seeds which are viable and can be used for the propagation of the plant. The number of tuberous roots and their dimensions vary greatly among the different varieties. The roots may reach a size of 30-120 cm long and 4-15 cm in diameter, and a weight of 1-8 kg or more. The plant, its flowering shoot and its various parts are shown in Figures I and 2.
Clusters of root of the Bogor variety, ripe for harvesting, are shown in Figure 3. A cross section of the root is given in Figure 4. The peel consists of an outer and an inner part, the former comprising a layer of cork cells and the phellogen. The cork layer, generally dark-coloured, can be removed by brushing in water, as is done in the washers of large factories. The inner part of the peel contains the phelloderm and the phloem, which separates the peel from the body of the root. The texture of the transition layer makes possible an easy loosening of the whole peel from the central part, thus facilitating the peeling of the roots.
The cork layer varies between 0.5 and 2 percent of the weight of the whole root, whereas the inner part of the peel accounts for about 8-15 percent. Generally in ripe roots this is about 2-3 mm thick. The starch content of the peel is only about half that of the core. The peel is much firmer in structure, hindering a smooth rasping by primitive raspers; small factories prefer to peel the roots before working them up. The loss of starch incurred by rejecting the peel. however' is not acceptable to the larger factories. which remove only the cork layer.