The potato crop is now an important one in almost all the rotations practiced in Britain, although its cultivation is in most districts not quite so extensive as before its failure front the potato disease in 1845 and subsequent years, and farmers arc more careful not to depend too much upon it. It very commonly succeeds a grain crop, but some times is advantageously planted ou land newly broken up from grass.
The potato is subject to a number of diseases, of which the most important is the potato disease (q.v.) or potato murrain. Before it began to prevail, the chief diseases the potato were those called earl, scab, dry-rot, and wet-tot. Of all these dis eases, it would seem that one principal cause, however combined with other causes, is the exhaustion of the vegetative powers of the plant, from frequent propagation by tubers or cuttings of tubers. It is to be borne in mind that propagation by tubers is not properly reproduction, but one plant is divided into a multitude; and the whole anal ogy of nature seems to show, that although it may live longer in this way and more healthfully than if left to the spot where its seed first germinated, its existence ,will come to an end, and the species must be preserved by reproduction from seed. It was long since qbserved as to CURL, the dread of farmers and gardeners before the potato disease was known, that it most readily attacks potatoes which sprang from weak sets. Curl is a disease affecting the foliage and general health of the potato plant, and does not seem to be necessarily connected with the presence of any vege table parasite or insect enemy.—ScAn is a disease of the tubers, which become cov ered with brown, oblong, and finally confluent and cup-shaped spots, whilst under the surface is a powdering of minute olive-yellow grains, a fungus called tubercinia scabies, of the division hyphontycetes.—Dny-noT is also ascribed to the growth of a fungus of the same order, fu.sisporiuin solani, and attacks the tubers either when stored for winter or
after being planted. It was very carefully investigated by Martins, and described in a memoir published in 1842. It was first observed in Germany in 1&',0, and caused great loss in that country throughout many years. The tissues of the potato tuber become hardened and completely filled with the mycelium of the fungus, which at last bursts Forth iu little cushion-shaped tufts loaded with fructification.—NETnoT differs from dry-rot in the tubers becoming soft and rotten instead of hard and dry, and is always characterized by the presence of a fungus referred by Fries to his genus periola, but which Berkeley regards as another form or stage of the same fungus which causes or is inseparably connected with dry-rot. Both dry-rot and wet-rot have often been observed along with the potato disease, which, however, is always characterized by the presence of another peculiar fungus.
But, besides its value as a culinary vegetable, the potato is important in other respects. Its starch is very easily separated, and is in large proportions; hence it is cheaper than any other kind. It is manufactured on a very large scale both in this country and on the continent. It is chiefly used in textile manufactories under the name of farina, which is converted into dextrine or British gum. See STARCH. In Holland and in Rus sia; where there is much difficulty in keeping potatoes through the winter. and there is consequently a necessity for using the crop quickly, large'quantities of starch are made, and this is converted irito.sngar or syrup. See SUGAR. The refuse of the starch-menu factories is all economized; it is pressed out from the water, and either used for pig feeding or for manure. In the north of Europe, much apirit for drinking is made from potatoes; it is called potato brandy