LETTUCE, known botanically as Lactuca sativa (family Compositae), a hardy annual, highly esteemed as a salad plant. It is generally believed to have arisen from the wild species F. scariola which grows wild in Europe, Canary Isles, Madeira, Algeria, Abyssinia and Eastern Asia, and has become naturalized in the United States. The market-gardeners round London pre pare for the first main crop of Cos lettuces in the open ground early in August, a frame being set on a shallow hotbed, and, the stimulus of heat not being required, this is allowed to subside till the first week in Oct., when the soil, consisting of leaf-mould mixed with a little sand, is put on 6 or 7 in. thick, so that the surface is within 41 in. of the sashes. The best time for sowing is found to be early in Oct. When the seeds begin to germinate the sashes are drawn quite off in favourable weather during the day, and put on, but tilted, at night in wet weather. Very little watering is required, and the aim should be to keep the plants gently moving till the days begin to lengthen. In Jan. a more active growth is encouraged, and in mild winters a considerable extent of the planting out is done, but in private gardens the preferable time would be February. The ground should be light and rich, and well manured below, and the plants put out at I ft. apart each way with the dibble. Frequent stirring of the ground with the hoe greatly encourages the growth of the plants. Young let
tuce plants should be thinned out in the seed-beds before they crowd or draw each other, and transplanted as soon as possible after two or three leaves are formed. Some cultivators prefer that the summer crops should not be transplanted, but sown where they are to stand, the plants being merely thinned out ; but transplanting checks the running to seed, and makes the most of the ground.
There are four races of the lettuce, the Cos lettuce, with erect oblong heads, and the Cabbage lettuce, with round or spreading heads—the former generally crisp, the latter soft and flabby in texture—the Asparagus lettuce with narrow lanceolate basal leaves, the Cut-leaved lettuce with the leaves deeply cut at the edges.
Lactuca virosa, the strong-scented lettuce, contains an alkaloid which has the power of dilating the pupil and may possibly be identical with hyoscyamine. No variety of lettuce is now used for any medicinal purpose, though there is probably some slight foundation for the belief that the lettuce has narcotic properties.