POTATO. 313 POTATO. by hand, but where the crop is grovn on a large scale potato phmters are used. The crop is planted in the spring when danger of injury by frost has passed. After planting, the soil is har- rowed frequently until the plants are all up, when the cultivator is used until the vines shade the ground. Tlie results of experiments at dif- ferent experiment stations in the United States indicate that the use of half the tuber as a seed ])iece is preferable to using smaller cuttings or the whole tuber. In the Southern United States two crops of potatoes are sometimes produced on the same land in one year. PoT.iTO Diseases. Until comparatively recent- ly the potato Jblight or rot was believed to be all caused by a single fungus. Two distinct forms are now held accountable, the leaf or early blight, and the late blight or rot. The early blight [Al- tcriKirid soliuii) appears upon the leaves as gray- ish brown spots, which, aliout the time the tubers are beginning to form, enlarge, and in ten days or two weeks involve half the leaf. In about a month all the foliage may have succumbed. Tlie late blight or rot ( Phi/tophthora infcstans) ap- pears in August or September, attacking leaves, stems, and tubers. . The leaves are first to ap- pear to be injured. They show brown or black areas, which soon become soft and foul-smelling. Moisture and a fairly warm, but not hot, temper- ature is most favorable to its rapid development, and a few dry. hot days will cheek its spread. The tubers also become blotched or discolored on the surface and streaked within with hrown or black. Since they are likely to rot. the crop is practically worthless. Both of these diseases can he prevented by spraying w ith Bordeaux mixture, beginning when the plants are 4 to 6 inches high and continuing through the season at intervals of 10 days to 2 weeks. Brown rot, believed to be caused by Bacillus solanacearum, is sometimes troublesome in the Soxithern States. The foliage usually wilts, shrivels, and turns brown or black. .Since leaf-eating insects are held accountable for the spread of this trouble, they are combated with insecticides. Rotation of crops is recommended as a means of jirevention and care in the selec- tion of seed tubers that they do not come from infested regions. Scab api)ears as rough, dark patches of varying depth upon the tubers and upon beet roots, rendering them unsightly and de- stroying the outer portions. Scabby potatoes and infested soil should he avoided, ilany growers soak the 'seed' in a solution of 2io ounces of cor- rosive sublimate in 15 gallons of water: or 8 fluid ounces of formalin, or formaldehyde, in 15 gallons of water, after which the tubers are spread to dry. These are considered preventive measures. Food and Feeding Value. When a section of the potato is carefully examined, it will be seen to consist of three more or less well-defined por- tions, namely, the skin, cortical or fibro-vascular layer, and the flesh, which is made up of the outer and inner medullary layers. The cortical layer, immediately beneath the true skin, and sometimes designated the inner skin, is slightly colored, containing practically all the coloring matter normally present in the potato. As shown by recent analyses, the skin of the potato consti- tutes on an average 2.5 per cent, of the whole and the cortical layer 8.5 per cent. It is difficult to peel potatoes so that the skin only is removed. The amoimt of refuse and edible portion lost by peeling is estimated at 20 per cent. Doubtless, in many cases the rejected portion is very much larger. The edible portion is made up of 78.3 per cent, water, 2.2 per cent, protein (total nitrogenous matter), 0.1 per cent, fat, 18.4 per cent, car- bohydrates (principally starch), and 1 per cent, ash or mineral matter. Of the carbohydrates, 0.4: per cent, is made up of crude fibre and materials which in some of their modifications constitute the cell walls of plants and give them a rigid structure. The fuel value is 385 calories per pound. The above figures, like others for compo- sition of food materials, represent general aver- ages, from which there are wide variations in individual specimens. Though the skin, cortical layer, and flesh differ somewhat in composition, they all resemble more or less closely that of the wliole tuber. When potatoes are stored they shrink about 12 per cent, in 7 months. Although the potato contains some protein, it is chiefly valuable as a carbohydrate food, and, like all such food, is useful for supplying the body with energy. The principal ways of cooking potatoes are baking, boiling, and frying, or some modifications of these processes. Just wiiy cook- ing changes the flavor as it does has apparently never been made the subject of investigation. In. potatoes, as in other foods, the cooked starch is more agreeable to the taste than the raw. Pos- sibly also there are volatile bodies of more or less pronounced flavor which are removed or reduced by the heat of cooking. The physical condition of the potato is much affected by heat. In the raw potato the separate starch grains are inclosed in cells with walls composed of crude fibre, a material resistant to digestive juices.- If potatoes were eaten raw, the digestive juices would not reach the starch as easily, unless the cell walls happened to be ruptured mechani- cally, as in mastication. Heat, however, expands the water present, ruptures the cells, and breaks up the starch, expanding the granules, which when raw consist of tightly packed concentric layers. Over 90 per cent, of the total nutritive material of potatoes is digestible. According to statistics obtained in the large number of dietary studies made in this country, potatoes constitute about 13.7 per cent, of the total food consumed by the average American family, and furnish not far from 3.9 per cent, of the total protein and 10 per cent, of the total carbohydrates. The potato is a staple article of diet in almost every house- hold. The universality and extent of its con- sumption would seem sufficient to prove it to be a wholesome and nutritious food. Scientific in- vestigation shows that the practice, which has become so general, of serving potatoes with meat and other similar foods which contain liberal amounts of protein is based upon correct prin- ciples, one food supplying the deficiencies of the other. • Evaporated potatoes are on the market, being especially recommended for provisioning camps and expeditions. As compared with fresh, the evaporated potatoes have a high nutritive value in proportion to their bulk. Large quantities of potatoes are used for the manufacture of starch. Potatoes either raw or cooked are sometimes fed to pigs, milch cows, and other farm animals. When fed to pigs it has been found that 414
