_Cultivation._--There are no set rules for the cultivation of medicinal plants, and the grower's experience with other plants must be relied upon as a guide in many of the details of cultivation. As a general rule, the soil should be worked with the hoe or cultivator at frequent intervals and kept free from weeds. It is a good practice to cultivate after a hard rain as soon as the ground is sufficiently dry. During dry, hot weather loss of moisture from the soil will be diminished by frequent shallow cultivations. HARVESTING. Drug roots are usually harvested in the fall or at the end of the growing season of the plant, but they may also be harvested early in the spring while still dormant. Roots collected during the growing season often shrink excessively in drying and so do not form the most desirable product. On small areas either a spade or a potato fork is a suitable tool for digging most roots; but if the area is large, labor will be saved by using a plow to turn out the roots, especially with such crops as belladonna or burdock. Most roots require thorough washing, and when the quantity is large this may be easily done if the roots are placed on a frame covered with wire mesh and water is applied by means of a garden hose. All roots must be thoroughly dried. Large or fleshy roots are usually split or sliced, spread in thin layers on clean floors, and stirred or turned frequently. Good ventilation is essential, as several weeks usually elapse before the roots are dry enough to be stored with safety. The proper point of dryness is indicated when the roots break readily on being bent. The time of drying may be reduced to a few days by the use of artificial heat. For this purpose the walls of a well-inclosed room are fitted with racks or shelves to receive the roots, or large trays with bottoms made of slats or wire screen are suspended one above the other from the ceiling. The room is heated by a stove, and the temperature maintained between 125° and 150° F. Ventilators must be provided at the top of the room to carry away the moisture which is driven off from the roots. Ordinary fruit driers have been used successfully in drying roots on, a small scale, but special drying houses or kilns will be necessary for successfully handling crops grown on an acreage basis. Leaves and herbs are usually harvested when the plants are in flower. Picking the leaves by hand in the field is a slow process, and time may be saved by cutting the entire plant and stripping the leaves after the plants have been brought in from the field. If the entire herb is wanted, it is preferable to top the plants, for if they are cut too close to the ground the herb will have to be picked over by hand and all the coarse stems removed. As a rule, leaves and herbs may be dried in the same manner as roots, but almost without exception they are dried without exposure to the sun, in order that the green color may be retained so far as possible.