The distinction between the fruit and the vegetable is purely arbitrary, since both are parts of plants and have the same general composition. Botanically the tomato is as truly a fruit as the apple; but when it is stewed and served with meat, it is classed as a vegetable. Other parts of plants, however, besides the fruit are used as vegetables.
Vegetables are much like fruits in composition, being richest usually in carbohydrates and ash, but sometimes containing a large amount of protein. Some have carbohydrates in the form of starch, as the potato, and others in the form of sugar, as the beet; young corn is rich in sugar, old corn in starch. All have more or less cellulose, that in lettuce being very tender, while that in beets is so firm as to be softened only by long cooking. Study carefully Figs. 34 and 35. Notice how the amount of water compares with the amount in fruits. See, too, that beans, both green and dry, are richer in protein than other vegetables. Celery has the highest percentage of water, and is valuable for its ash and the bulk it gives because of the large amount of cellulose.
To explain these facts we must understand something of the physiology of the plant. The stem is the carrier of water and nutritive material to other parts of the plant. The onion bulb, the parsnip root, and the potato tuber are the winter storehouses of food for the next year's plant when the leaves first sprout. In the dry bean seed, and also in the pea and lentil, the young plant lies dormant, with a large supply of all the foodstuffs ready for its first growth when warmth and moisture are supplied in the spring. Classified according to their nutritive value, the vegetables rank as follows. Leaves are grouped with stems.
Fig. 34. - Composition of vegetables.
Fig. 35. - Composition of vegetables.
Contain all the foodstuffs. High in protein.
Roots and tubers and the bulb
Contain all the foodstuffs. Low in protein and fat. High in starch or some form of sugar.
Rinds (squash and pumpkin)
Contain all the foodstuffs in small amounts. Mineral content the chief value.
Leaves and stems
Mineral content the chief value.
Certain substances in some vegetables are supposed to have a physiological effect, but we should be cautious in accepting statements that have not been scientifically proved; for instance, that celery is "good for the nerves." It is doubt-less true that the oils which give onions and the cabbage their strong flavors do not agree with some people, and these vegetables should be eaten with caution.