Lettuce, a plant of the natural order compositae, the leaves of which are largely used as a salad. It has been cultivated in England for over 200 years, and has been known from the earliest times; hence, as is the case with many cultivated plants, it3 native country is uncertain; Alphonse de Candolle (Geographic botanique raisonne) says that he knows of no locality in which the plant appears to be really spontaneous, and he thinks it probable that the cultivated lettuce, usually called lactuca sativa, is only a form of the widely distributed L. scariola. Lettuce is an annual, at first forming a more or less compact cluster of leaves, or a head, which are exceedingly crisp and tender; as the plant grows older it secretes an abundant, milky, bitter juice, and rapidly pushes up a flower stalk, 2 to 4 ft. high, which has numerous branches, the subdivisions of which are terminated by small heads of pale yellow ligulate flowers. The varieties in cultivation are numerous, new ones being offered every year; these varieties are divided into two principal groups: the cabbage lettuces, which have rounded leaves and form a compact head like that of a cabbage, and the cos lettuces, which have firm and oblong leaves forming a long, erect head, largest above and tapering below.
The seeds in some varieties are white, and in others yellow, brown, or black; some varieties produce white and black-seeded sub-varieties; such is the tendency to vary that each gardener largely engaged in lettuce growing, by careful selection of plants for seed-bearing, soon establishes a subvariety or strain suited to his soil. Among the leading varieties are the Silesian, tennis-ball, and drumhead; the curled India is best for summer crops, and the Dutch and hardy green for wintering over. In the family garden lettuce is sown in the spring, transplanted when large enough, and consumed as it comes to perfection. Those who supply the markets pursue a very different method, as they must have it every month in the year. In some localities large areas are covered by the sashes of the salad growers, who by the use of fermenting manure produce crops all through the winter. Latterly pits or low greenhouses heated by hot water have been used for this purpose. The hot months of summer present the greatest difficulty to the lettuce grower, as the plants run up to seed too soon, though some varieties do this less readily than others. In the vicinity of New York many families are supported solely by the cultivation of this plant, with perhaps radishes in the spring.
Dietetically, lettuce can hardly be considered as nutritive, but it is probably a bland corrective of grosser food. When its milky juice becomes developed it is no doubt a sedative, and it may act as such on very susceptible persons before the principle becomes sufficiently abundant to make the lettuce unpleasantly bitter. It is a little singular that a plant which contains little or no nutriment should be of such general consumption over the greater part of the world. - Lactucarium or lettuce opium is the name given to the inspissated juice of the lettuce. The soporific effects of lettuce were known in early times, but Dr. J. R. Coxe of Philadelphia was the first to call the attention of the medical profession to the dried juice as a remedial agent. It has had a variable reputation, probably on account of the uncertain character of the lactucarium found in the market. If prepared, as is the practice in some parts of Europe, by expressing the juice from the lettuce and evaporating it, it is of doubtful efficacy. The best is collected by cutting the flower stalks and receiving the milk as it exudes upon pieces of cotton cloth; these when fully charged are placed in a vessel of water until the juice is dissolved out, and the solution then evaporated to the consistence of an extract.
Lactucarium has a peculiar and a bitter taste. It has the anodyne properties of opium, but in a much less degree, and does not like that drug derange the digestion and produce constipation. On account of its uncertain quality as found in commerce, the dose varies from 5 to 20 grains.