Lettuce is probably the most important salad plant grown in America. In most lettuce plants, the leaves are the edible part. Some lettuce plants form cabbage-like heads. Others have loose, crinkly leaves. Romaine or cos lettuce plants have tall, columnlike heads. Seed catalogs or packages tell when and what kind of lettuce should be planted for a continuous harvest. In the home garden, loose-leaf varieties are the easiest to grow. Planting of a four to six foot row of thinly sown seed should be enough for an ordinary family. Soil should be well-drained and well-cultivated. Lettuce needs plenty of water and food.