Another fungus attacking the leaves is Macrosporium Solani (fig. 3), but this attack usually comes earlier in the season than the foregoing. It is characterized by the curling of the leaves, which later show black spots due to the production of numerous dark spores in patches on the diseased leaves. The damage is often considerable, as the crop is greatly 
Fig. 3.—Portion of Leaf of Potato-Plant showing patches of a black mould, Macrosporium Solani, on the surface.lessened by the interference with the functions of the leaf. The parasite may be held in check by spraying with Bordeaux mixture early in the season. The fungus passes the winter on pieces of leaf, &c., left on the ground. All such refuse should be cleared up and burned. A third fungus, Cercospora concors, also forms spots on the leaves and may be kept in check by the same means.
Wilting of the foliage followed by the discoloration of the stem and branches is characteristic of a disease of the potato known as “Blackleg.” This disease is due to the presence of large numbers of Bacillus solanacearum in the tubes through which water is conveyed to the leaves from the roots. Their presence causes the appearance of blackish streaks in the stem and a dark ring some little distance below the surface in the tissues of the tuber. Tubers showing any trace of such a ring should not be used for seed, and rotation of crops should be observed as a means of preventing the infection of the crop with the germ. Biting and sucking insects have been found to carry the bacilli from one plant to another.
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| (From the Journal of the Board of Agriculture and Fisheries, by permission of the controller of H. M. Stationery Office.) |
| Fig. 4.—Chrysophlyctis endobiotica (Oedomyces leproides) in the Potato. |
| 1 and 2, Tubers deformed by the fungus. |
| 3, Section through diseased tissue showing dark masses of spores. |
| 4 and 5, Tissue-cell, more highly magnified, showing enclosed spores. |
The tubers frequently show scurfy or scab-like spots upon their surface, thus greatly depreciating their value for market purposes. The fungus, Sorosporium scabies, which is the cause of the scab, does not penetrate into the flesh of the tuber, nor detract from its edible properties. Excess of lime in the soil is said to favour the development of the fungus. Similar spots are produced on potatoes in America by the fungus Oospora scabies, and in both cases, if affected “seed” potatoes are steeped in a solution of 12 pint formalin in 15 gallons of water for two hours before planting, the attack on the resulting crop is materially lessened. The fungus, Oedomyces leproides, produces large, blackish, irregular warts which sometimes involve the whole surface of the tuber. This disease is of recent introduction into Great Britain, but bids fair to become very troublesome. The spores of the fungus pass the winter in the soil and the delicate mycelium attacks the young shoots in the summer. These become brown, finally blackish and greatly contorted until a large scab is formed on the developing tuber, whence the name by which the disease is known—“black scab.” Diseased potatoes left in the soil and even slightly diseased “sets” are a source of infection of succeeding crops. Rotation must be observed and no diseased sets planted.
The rotting of tubers after lifting may be due to various causes, but the infection of the tubers by the Phytophthora already mentioned is a frequent source of this trouble, while “Winter Rot” is due to the fungus Nectria Solani. This fungus finds conditions suitable for growth when the potatoes are stored in a damp condition; rotting from this cause rarely occurs when they are dried before being placed in heaps. The first signs of this fungus is the appearance of small white tufts of mycelium bursting through the skin of the tuber, the spores of the fungus being carried at the tips of the threads forming these tufts. This form of fruit is succeeded by others which have received different names, and lastly by the mature Nectria which forms minute red flask-shaped perithecia on parts of the rotted potatoes that have dried up. The intermediate forms are known as Monosporium, Fusarium and Cephalosporium. The pieces of dried-up potato with the spores of Nectria upon them are a source of infection in the succeeding year, and care should be taken that diseased tubers are not planted. Flowers of sulphur plentifully sprinkled over the potatoes before storing has been found to check the spread of the rot in the heap.
Potato race, a running contest, where the winner is the first who collects in a basket or other receptacle a number of potatoes, usually eight, placed, as a rule two yards apart, along a straight line, and then crosses a finish line five or ten yards farther on.
Potato War, (Kartoffelkrieg), the name given by the Prussians to the War of the Bavarian Succession in 1778–79. The Prussians and a Saxon contingent, commanded by Frederick the Great and his brother Prince Henry, were opposed to two Austrian armies under London and Lacy. The operations consisted almost entirely of manoeuvres which had for their object the obtaining or the denial to the enemy of food-supplies. The war thus acquired the name of Kartoffelkrieg. Its duration was from the 3rd of July 1778 to the assembly of the congress of Teschen on the 10th of March 1779, and its total cost £4,350,000 and 20,000 men to all parties. The war may be studied from the military point of view as an extreme example of what Clausewitz calls “war with a restricted aim.”
Potawatomi (properly Potewatmik, fire-makers, in allusion to their secession from the Ojibway, and their establishment of a separate council-fire), a tribe of North-American Indians of Algonquian stock. When first known (about 1670), they lived around Green Bay, Wisconsin. They subsequently moved south and eventually settled in lower Michigan. They were allied with the French in their wars against the Iroquois and took part in the conspiracy of Pontiac (q.v.). In the War of Independence they fought for England, as also in that of 1812. In 1846 most of them were removed to a reservation in Kansas. Of these the majority have abandoned their tribal relations and become citizens. Others are in Wisconsin and the bulk in Oklahoma. They now number some 2500.
Potchefstroom, a town of the Transvaal, 88 m. S.W. of Johannesburg and 222 m. N.E. of Kimberley by rail. Pop. (1904), 9348, of whom 6014 were whites. The town stands 4100 ft. above the sea on the banks of the Mooi River, 15 m.
