In a technical sense all plants are vegetables. The term, however, is usually applied to edible plants which store up reserve food in roots, stems, leaves, and fruits and which are eaten cooked, or raw as salad plants. Vegetables constitute a large and varied group of considerable importance in the world's commerce. Most of them are very old, and their origin as food plants is lost in antiquity. The food value of vegetables is comparatively low, owing to the large amount of water present (70 to 95 per cent.). Even so, they rank next to cereals as sources of carbohydrate food. This is usually present in the form of starch, although occasionally sugar, pectins, or other substances may occur. Proteins, save in legumes, are rarely available, and fats are stored only in very slight amounts. The nutritive value of vegetables is increased greatly, however, by the presence of the indispensable mineral salts and vitamins, while the roughage value of the various tissues aids digestion. For convenience the vegetables may be classified as earth vegetables, herbage vegetables, and fruit vegetables.
The earth vegetables include all forms in which food is stored in underground parts. The storage organs may be quite different morphologically. Some are true roots, while others represent modified stems, such as rootstalks, tubers, corms, and bulbs. All these structures are especially well adapted to storage because of their protected position. Many wild, as well as cultivated, species have fleshy underground parts, and these have played a role in the development of civilization and agriculture second only to the cereals and legumes. From earliest time roots and tubers have furnished food for man and beast. Even though the amount of stored material is less than that in dry fruits and seeds, these are extremely valuable since they are readily digested and have a high energy content. One objection to them is the high water content, which not only reduces the amount of available food material but impairs their keeping qualities as well. Their bulk, too, makes it impossible to transport and store them as efficiently as cereals, legumes, or nuts. Root crops, as these earth vegetables are often called, tire an important phase of agriculture all over the world. In most countries they are grown