Some flowers are gathered while scarcely open and others as soon after opening as possible, and in general they should be carefully dried in the shade to prevent discoloration. Hand picking is very laborious, and mechanical devices similar to a cranberry scoop (fig. 2) or seed stripper (fig. 3) may often be used to good advantage. A homemade picker may be constructed as follows: From a stout wooden box, about 10 inches wide, 14 inches long, and 6 inches deep, remove one end and connect the opposite remaining sides at the top with a stout strip, which will serve as a handle. Drive long, slender wire nails through an inch strip of wood at quarter-inch intervals, thus forming a "comb" the teeth of which should be about 2 inches long. This comb is fastened to the bottom of the box in such a manner that the teeth will project outward through the opening left by the removed end. On swinging this device, teeth forward, through the flowers, the heads will be snapped off by the comb and will fall into the box, from which they may be emptied into suitable containers. [Illustration: Fig. 2.--A berry scoop suitable for harvesting flower heads of large size.] [Illustration: Fig. 3.--A seed stripper which may be used for gathering flower heads.] Seeds are harvested as soon as most of them have ripened and before the pods or seed capsules have opened. Seedlike fruits, such as anise, coriander, fennel, and wormseed r are harvested a little before they are fully ripe, in order that they may retain a bright, fresh appearance, which adds to their market value. The machinery used for thrashing and cleaning ordinary seed crops will frequently serve a similar purpose for seeds of medicinal plants, provided the proper adjustments have been made. Most seeds must be spread out to dry and turned at intervals until thoroughly dried before they can be stored in quantity. DISTILLATION. The volatile oil obtained from many aromatic plants by steam distillation is often their most valuable product. The equipment necessary for distilling volatile oils consists essentially of a steam boiler, a retort, and a condenser. A constant supply of cold water must also be available. A common type of retort consists of a circular wooden vat, about 6 feet in diameter and 8 to 10 feet deep (fig. 4), fitted with a removable cover, which can be made steam tight. Metal retorts made of boiler iron three-sixteenths of an inch thick and jacketed with wood to prevent the radiation of heat are also used. A pipe leads from the steam boiler to the bottom of the retort and another from the top of the retort to the condenser, one form of which consists of a coil of tin-lined or galvanized-iron pipe inclosed in a jacket through which cold water is kept flowing when the still is in operation. [Illustration: Fig. 4.--A still used in the production of wormwood oil.]