Plant food known generally as vegetables, fruits, grains, nuts, consists of various parts of the plant. The root, stem, stalk, leaves, flower, fruit, seeds all serve as human foods, but not all these parts of the same plant. Each vegetable food is the edible part of the plant from which it comes. Beets are roots; celery is stem; cabbage, leaves; cauliflower, flowers; tomato, fruit; cocoa, seed. Different parts of some plants are edible at different seasons, as bean pods when young and beans when older.

Vegetables containing much starch are not edible raw, because starch cannot be digested uncooked; such are pota-toes. Vegetables containing a large percentage of starch are called starchy vegetables (see pp. 6, 9) to indicate this fact and designate in general what their use will be as a human food, for it is only their use in the body which makes them of importance as foods. Starchy vegetables keep well. They are therefore suitable for out-of-season use.

Starch develops in plants as they mature, as fat does in animals as they grow old.(Starch eaten in excess of the daily need stores fat in the body as body-fat. Cooked starchy foods supply the body with energy that endures and body-heat.

Other constituents beside starch are present, too, in so-called starchy foods. These are water, mineral matter, often some sugar, fat in the form of oil, and a very complex substance called protein that always contains some nitrogen compounds.

Protein is present in all living matter.

This constituent (protein) enables food to build up body-tissue as growth requires and living necessitates. Mineral matter serves in body-building too (the skeleton is largely mineral matter) and also aids digestion in various ways. Water does the latter too. Sugar and fat furnish heat-energy that is used more quickly than that supplied by starch.