CH. I] RICE AND OTHER CEREALS AND FOOD PLANTS 51 



tubers, even potatoes being known as yams in Ceylon. The four 

 best of the many Dioscoreas used are usually supposed to be 

 the white yam (D. alata), the negro yam (D. sativa), the Guinea 

 yam (D. aculeata), and the cush-cush yam (D. triphylld), but 

 there are very many others eatable out of the 150 species of 

 which the genus is composed. Most of them, and all the best, 

 have underground tubers like potatoes, but of very variable 

 size, from a few ounces in some kinds up to 40 Ibs. weight in 

 others. 



Yams are propagated like potatoes from pieces of the 

 tubers, and are planted in rows, with sticks to climb upon. 

 The tubers are ripe in eight to twelve months, and are usually 

 dug up and put by to keep. The yam is used as a vegetable 

 like the potato, and cooked in various ways. Properly cooked, 

 a good yam is an excellent vegetable, though English people 

 seldom enjoy it. 



Cassava, Manioca, or Tapioca (Manihot utilissima) is one of 

 the great food plants of the tropics, besides being consumed in 

 colder climates. It is a native of South America, and was very 

 early introduced into Asia, where it is extensively grown in the 

 Malayan countries, Ceylon, etc. It is also very largely cultivated 

 in the West Indies and throughout the warmer parts of South 

 America. It is a shrubby plant, usually about eight feet 

 high, and produces enormous tubers upon the roots. These 

 are full of starch, and it is for them that the plant is 

 cultivated. 



There are two varieties in cultivation, the sweet and the 

 bitter. The latter gives the best return, and is the more 

 popular, but its tubers contain prussic acid, and are dangerously 

 poisonous until the acid has been dissipated by boiling or 

 heating. 



The plants are set out as cuttings, and the roots may be 

 gathered at about eight to twelve months old. The tubers are 

 carefully dug up, and are usually washed, peeled, and grated 

 small, while the resulting pulp is hung in a compressible bag, 

 with weights upon it, so as to squeeze out the poisonous juice. 

 The meal is then baked or otherwise cooked. In some countries 

 the tubers are eaten like yams. 



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