The potato is of great importance as affording food both for human beings and for cattle; and next to the principal cereals, is the most valuable of all plants for human food. It is also used for various purposes in the arts. No food-plant is more widely diffused; it is cultivated in subtropical countries; and struggles for existence in gardens. %even within the arctic circle, yielding small and watery tubers; although the effects of late spring frosts, or early autumnal frosts, upon its foliage often prove that it is a plant properly belonging to a climate milder than that of most parts of Britain. No more important event of its kind has ever taken place than the genera] introduction of potato culture into the husbandry of Britain and other European countries. It has exercised a most beneficial influence on the general welfare of the people, increasing national wealth; and preventing, as a few far-seeing thinkers had anticipated, the once-frequent returns of famine. That in 1846 and 1847 terrible famine resulted in Ireland and elsewhere from the failure of the potato crop itself, was owing only to the excess to which its culti vation had been carried. The results confirmed two great laws, that plants long very extensively or almost exclusively cultivated in any district, however successfully they may be cultivated for a time, are sure to fail at last, and that the exclusive, or almost exclusive, dependence of a people on one source or means of support is unfavorable to their welfare in respect to all their interests. • Humboldt calculates that the same extent of ground which would produce thirty pounds of wheat, would produce 1000 pounds of potatoes. But potatoes are not nearly so nutritious as wheat, and the constant employment of them as the chief article of food is not favorable to the development of the physical powers, and is consequently in its protracted influence unfavorable to mental energy. All this is too well illustrated in Ire land and the Highlands of Scotland, in a race capable of the highest development of both. It is calculated that 100 parts of good wheat-flour, or 107 parts of the grain, con tain as much actual nutriment as 013 parts of potatoes. The inferiority of the potato in nutritious power is very much owing to the comparatively small quantity of nitrogenous substances which it contains, in consequence of which it is most advantageously used along with some very nitrogenous article of food, in Britain generally with animal food, in some parts of Europe with curds or with cheese. The potato tuber, in a fresh state, contains about 71 to 80 per cent of water; 15 to 20 of starch, 3 to 7 of fiber or woody matter, 3 to 4 of gum, dextrine, and sugar, and 2 of albumen, gluten, and casein. There are considerable differences, however, in different varieties, in different stages of maturity, and in different soils and seasons.
Potatoes are used, both raw and boiled, for the feeding of cattle. For human food, they are variously prepared by roasting or boiling, but now chiefly by boiling, a process by which they are freed from all that is narcotic and noxious in their juice. The water in which potatoes have been boiled is not wholesome, and those modes of preparing them for the table which do not admit of its complete rejection ought to be avoided.
The herbage or haulm of the potato has been used for making paper, but the results were not encouraging. The berries are sweetish, but not pleasant; nauseous when fer mented, but yield by distillation a tolerable spirit.
The varieties of the potato in cultivation are extremely numerous. Any enumeration or classification of them is impossible. New ones are continually appearing, and old ones passing away. Those most advantageously cultivated in particular soils and climates are often found to degenerate when removed to a small distance. Many- of the new varieties of potato are raised in Lancashire, but particularly of the garden kinds, which generally differ from those preferred for field culture in their greater earliness, and not unfrequently in their inferior productiveness, and in their being less mealy and less nutritious. Potatoes differ considerably in the character of their herbage—which is some
times erect, sometimes straggling—and in the size and color of their flowers; but arc more generally distinguished by the size, form, and color of their tubers, which are round, long, or kidney-shaped, white, red, dark purple, variegated, etc.
New varieties of potatoes are produced from seed; but potatoes are ordinarily propa gated by planting the tubers, or cuttings of the tubers, each containing an eye or bud. Late crops of early potatoes are sometimes procured by cuttings of the stalks or by layers; methods which might probably be pursued with more advantage where the sum mer is longer than in Britain. Much has been written by gardeners and agriculturists on the comparative advantages of planting whole tubers or cuttings; but the latter method generally prevails.
Potatoes are planted in drills, made either by the spade or plow; or in lazy-beds, which are always made by the spade, and are beds in which the sets of potatoes are cov ered over with earth dug out of the alleys. The alleys serve, although imperfectly, for drails in undrained land. The cultivation of potatoes as a field-crop seems to have been first attempted in lazy-beds. They are still common in many parts of Ireland, but are now rare in most parts of England and Scotland. They are very suitable for strong, heavy, and somewhat moist land, and are profitably used in reducing some kinds of soil to cultivation; but are generally unsuitable for field-culture, owing to the expense of labor required. In strong heavy land, potatoes are cultivated in raised drills; in lighter and drier soils, the raising of the drills is unnecessary. Manure is given, con sisting generally of dung and well-rotted straw from the farm-yard. Guano and other strong artificial manures are apt to produce an excessive growth of stalks and leaves, which is to be guarded against by diminishing or even withholding manure in certain soils, potatoes of too luxuriant growth being always particularly liable to diseases. The cultivation of potatoes, after they are planted, whether in the field or garden, consists chiefly in keeping the ground clear of weeds, and in earthing up the plants, to promote the formation of tubers. Potatoes are taken up either by the fork or by turtling over the drills with the plow. Garden potatoes are generally used long befc•e they are really ripe, forming a favorite dish in a very unripe state, when they are far from being a safe article of food, and contribute not a little to the prevalence of cholera and kindred dis. eases in summer. Field potatoes, unless when intended for the supply of the markets of towns, like garden potatoes, are allowed to ripen thoroughly, and are then capable of being stored for winter and spring use. Early potatoes are forced in hot-beds, and in the spare ground of hot-houses, that they may be obtained very early; also, after being thus brought forward in some degree, they are planted out in gardens, for a succession of young tubers. The planting of potatoes in the open air cannot be successfully prac ticed in most parts of Britain before February or March, and in many seasons the later planted are found as early as the earlier planted, and more productive. The storing of potatoes is variously accomplished in dry lofts or sheds, in airy cellars or barns, and in pits, which are sometimes holes excavated to a small depth in the earth, and the potatoes piled up above the surface of the ground, in a conical, or in a roof-like form, sometimes mere heaps of one or other of these forms upon the surface of the ground. and covered with straw and earth to keep out light and frost. The access of light makes potatoes green, bitter, and unwholesome, as is often seen in those which, whilst growing, have been partially above ground. Potato pits are often ventilated by means of pipes, as without ventilation the potatoes are apt to heat and sprout. Potatoes taken from the ground before they are quite ripe are extremely apt to heat and sprout.