YAM ROOTS. 
87 
for many montlis without sustainmg any injuiy. The 
usual mode of preparing the cassava is to grind the roots 
after peeling off the dark-coloured rind, to draw out the 
poisonous juice, and finally to bake the meal into thin 
cakes on a hot iron hearth. Fortunately tlie deleterious 
principle is so volatile as to be entirely dissipated by 
exposure to heat ; for when the root has been cut into 
small pieces, and exposed during some hours to the direct 
rays of the sun, cattle may be fed on it with perfect safety. 
If the recently extracted juice be drunk by cattle or 
poultry, the animals soon die in convulsions; but if this 
same liquid is boiled with meat and seasoned, it forms 
a wholesome and nutritious soup. The Sweet Cassava, 
though very similar to the Manihot or bitter variety, and 
wholly innocuous, is far less extensively cultivated. 
The yam-roots, so frequently mentioned in naiTatives 
of travel through the tropical regions, are the produce of 
two climbing plants — the Dioscorea sativa and alata — 
with tender stems of from eighteen to twenty feet in 
length, and smooth sharp-pointed leaves on long foot- 
stalks, from the base of which arise spikes of small tlowers. 
The roots of the D. sativa are flat and palniated, about 
a foot in breadth, white within and extenmlly of" a dark 
brown colour; tho.se of the D. alata are still larger, being 
frequently about three feet long, and weighing about 
thirty pounds. Both kinds are cultivated like the common 
potato, which they resemble in taste, thi^ugh of a closer 
texture. 
The Dioscorete are natives of South Asia, and are 
supposed to have been thence transplanted to the West 
Indies, as they have never been found growing wild in 
any part of America; while in the island of Ceylon, and 
on the coast of Malabar, they flourish in the woods with 
spontaneous and luxurious growth. 
The Spanish or Sweet Potato, commonly cultivated in 
the tropical climates both of the eastern and the western 
hemispheres, is an herbaceous perennial, which sends out 
