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The Story of Lettuce
{let'-uhs}
Lettuce, Lactuca sativa, of the family Compositae, is the most popular of all salad crops. It is a cool-season vegetable, growing best at temperatures between 15 and 18 degrees C (59 and 64 degrees F). It will often bolt, or produce seed prematurely, if it is grown in midsummer heat. Of the four principal lettuce types, the most popular, the crisp-heading lettuces (iceberg is a well-known variety), have brittle, prominently veined leaves; butterhead types (Boston, for example) have softer leaves and a smooth texture; loose-leaf varieties, such as oak leaf, do not form heads but grow as clusters or bunches of leaves; and cos lettuce, or romaine, forms a long, loaf-shaped head. Cos is slower to bolt than other lettuces and is therefore useful as a warm-weather crop. No cultivated lettuce variety has been found growing in the wild, although there are many wild lettuces, and it is assumed that domesticated varieties may be cultivars of the weed L. serriola (prickly lettuce). Lettuce is usually propagated by seeding directly in the soil, although head-lettuce types are sometimes transplanted. Leaf lettuce is harvested about 40 days after seeding, head lettuce from 70 to 90 days. Of the U.S. states, California is the major commercial lettuce producer, followed by Arizona and Florida. Lettuce shipped from these areas is often kept fresh by a process known as vacuum cooling, in which the tender leaves are cooled by rapid evaporation of water. O. A. Lorenz
Images and text from: 1998 Grolier Multimedia Encyclopedia http://gi.grolier.com |
