368 ROOT CROPS. 



is simple. It consists in laying cuttings a foot long in square 

 pits a foot deep, and covering them with mould, leaving the upper 

 ends open. From two to four pieces may be placed in each square. 

 The planting ought to be in the rainy season. The cuttings must 

 be made from the full-grown stem. A humid soil causes the root 

 to decay, a dry soil is therefore more adapted for its cultivation. As 

 blossoms are occasionally plucked from potato plants, so the mani- 

 hot or cassava is deprived of its buds to increase the size of its roots. 

 The raw root of the bitter species, when taken out of the ground, 

 is poisonous if exposed, however, to the sun for a short time, 

 it is innocuous, and when boiled is quite wholesome. 



The starch of the root of the manioc is prepared in the follow- 

 ing manner, as described by Dr. Ure : " The roots are washed 

 and reduced to a pulp by means of a rasp or grater. The pulp is 

 put into coarse strong canvas bags, and thus submitted to the 

 action of a powerful press, by which it parts with most of its 

 noxious juice. As the active principle of this juice is volatile, it 

 is easily dissipated by baking the squeezed cakes of pulp upon a 

 plate of hot iron. The pulp thus dried concretes into lumps, 

 which become hard and friable as they cool. They are then broken 

 into pieces, and laid out in the sun to dry. In this state they are 

 a wholesome nutriment. These cakes constitute the only pro- 

 visions laid in by the natives, in their voyages upon the Amazon. 

 Boiled in water, with a little beef or mutton, they form a kind of 

 soup similar to that of rice. 



The cassava cakes sent to Europe are composed almost entirely 

 of starch, along with a few fibres of the ligneous matter. It may 

 be purified by diffusion in warm water, passing the milky mixture 

 through a linen cloth, evaporating the straining liquid over the 

 fire, with constant agitation. The starch, dissolved by the heat, 

 thickens as the water evaporates, but on being stirred it becomes 

 granulated, and must be finally dried in a proper stove. 



2. Bitter cassava (Jcmipha Manihot, of Kunth ; Jatropha 

 Manikot, of Linnams ; and Manilwt utilissima, Pohl). This species 

 has a knotty root, black externally, which is occasionally 30 Ibs. in 

 weight. In the root there is much starchy matter deposited, 

 usually along with a poisonous narcotic substance, which is said to 

 be hydrocyanic acid. The juice of the plant, when distilled, 

 affords as a first product a liquor which, in the dose of thirty drops, 

 will cause the death of a man in six minutes. It is doubted whe- 

 ther this acid pre-exists in the plant; some suppose it to be 

 generated after it is grated down into a pulp. It can be driven 

 off by roasting, and then the starch is used in the form of cassava 

 bread. It is principally from the starch of the bitter cassava that 

 tapioca is prepared by elutriation and granulating on hot plates. 

 This serves to agglutinate it into the form of concretions, con- 

 stituting the tapioca of commerce. This being starch very nearly 

 pure, is often prescribed by physicians as an aliment of easy 

 digestion. A tolerably good imitation of it is made by beating, 

 stirring, and drying potato starch in a similar way. 



The grated starch of the roots, floated in water, is spontaneously 



