After the soil has been heated somewhat, the tubers are laid on the bed, about an inch apart, and covered with about 3 inches of good soil, and the soil, in turn, covered with leaves or hay, to increase the warmth of the bed. In a week, more or less, the sprouts will show above the surface of the soil, when the leaves or hay must be removed. The object in not connecting the flues from the furnace with the chimney is to economize heat. The air chamber under the entire bed becomes evenly heated, and the smoke escapes finally by the chimney. This chimney may be made of wood, and a height of 8 or 10 feet will afford ample draft. Either wood or coal may be burned, but preferably wood. The planting distance in the field is about 3 feet by 2, the young plants being set upon ridges. It requires about 9,000 plants to the acre. The work must not be done until the ground is warm. The crop is ready in from sixty to ninety days. =Cultivation.=--Shallow cultivation is all that is required. The vines at the North are not permitted to take root along their length, but in the South they are sometimes allowed to do so, and additional tubers thus secured. At the North the vines are lifted and turned, to clear the way for the cultivator and to prevent rooting. =Enemies.=--Black rot is one of the worst of sweet potato diseases. Stem rot is another serious enemy. The best treatment for these and other fungous troubles is prevention, and the best prevention is a healthy soil. It is, therefore, best to go to new land occasionally. =Harvesting.=--The common practice is to plow the sweet potatoes out of the ground just after the first frost has touched the vines. The tubers must be exposed to the air for a time, and partially dried. They are prepared for market, if wanted immediately, by rubbing off the soil and sorting into two sizes. =Storage.=--At the South one of the several methods of winter storage is to build a light wooden flue of lattice work, and pack about it a conical-shaped heap containing about forty or fifty bushels of sweet potatoes. Straw is used as a covering, with earth upon the straw, the earth to be increased as the weather becomes colder. Over the entire heap a rough shed is erected to turn the rain. The top of the flue or ventilator is closed with straw in really cold weather. The spot must be a dry one.