Yam, or Dioscorea bulbifera, L. is a native of Ceylon, whence its culture has been introduced into the West Indies, and other parts of America : it is divided into two varieties, known under the names of red, and white ; from the colour of their bulbous roots.
Yams flourish best on poor soils; and retain their beautiful verdure till a late period in the year: hence, they are said to ameliorate the ground nearly as much as a crop of turnips. Being propagated by setting the eyes, their culture corresponds with that of potatoes;
A and, like these roots, yams often prove an excellent preparatory crop for wheat. Farther, they are very productive ; so that the red variety yields in general, 12 tons per acre: the white sort is less fruitful; but, being more delicate, it is chiefly raised for the table, in the West Indies.
The culture of these bulbous roots in Britain is, at present, we understand, confined to the counties of Mid-Lothian and Stirling; where they are given to cows; the milk of which is thus considerably increased, without affecting its quality or flavour.
As an article of food, the yam possesses similar properties with the potatoe, excepting that it is less mealy, in a raw state, it is viscous; but, when roasted, this bulbous root is equally wholesome and nourishing, so that the inhabitants of the West Indies prefer it even to bread. In some respects, therefore, yams are more valuable than potatoes; because the former are much lighter, and more easily digested : - when first dug out of the ground, then dried in the sun, and preserved from humidity, in casks full of dry sand, they may be kept for several years, uninjured by frost, and without losing any part of their nutritive quality. - These beneficial roofs may also be peeled, deprived of their moisture by pressure, and dried in the same manner as Mr. Millington directs potatoes to be preserved (see vol. iii. p. 438). In this manner, yams may be packed in casks, like flour, and imported in a perfectly sound state, from the West Indies : when grated, and mixed with wheaten or barley-flour, they may be formed into a light and salubrious bread. Nor are they less nourishing, when converted into pottage, or pudding, with the addition of milk. Thus, Mr. R. PeaR-son ("Annals of Agriculture, " vol. 35), informs us, that the meal, obtained from the boiled and grated roots, when beaten up with milk and eggs, without any flour, yielded a firm and well-flavoured dish ; which could with difficulty be distinguished from a common batter-pudding. By this treatment, the yams are divested of their saccharine taste, which renders them at first disagreeable to some persons; though such property is, on the whole, of considerable use; as it saves the expence of sugar.