An increasing importance is coming to be attached to the use of vegetables and fruits in the diet. Not only vegetarians but many others have found from experience that it is possible to live largely upon vegetable food, while those who use meat freely lay great stress upon the vegetable accompaniments whether in the form of salads or of cooked vegetables.
A study of vegetables from the standpoint of botany would imply their classification according to the parts of the plant used; whether leaf, as in the case of lettuce, cabbage, spinach; stem, as in celery, asparagus, potato (a tuber, or underground stem); root, as in beet, carrot and sweet potato; flower, as cauliflower; or fruit, as squash, cucumber, tomato.
From the standpoint of cookery the most important classification is that of strong flavored and sweet flavored vegetables, since this modifies our method of cooking; right methods leading us to retain all the juices of the latter as far as possible, while we legitimately discard part of the extract of the former. For example, green peas and string beans, young carrots, and squash, should be cooked in a small amount of water, or have the water in which they are cooked concentrated at the end so that it may all be servedwith the vegetable; while in the case of onions we may well use a large portion of water, and throw it away. It is true that in this latter case we may lose valuable salts and some nutriment, but these we sacrifice for the sake of improved flavor.
From the standpoint of diet a better classification would be into nutritive vegetables and flavor vegetables. With the latter we should include those that contain mineral salts, but have little food value. Of this class, lettuce, spinach, cabbage, tomato and cucumber are types; while rice, potatoes, peas, beans and lentils furnish examples of the former. Many vegetables will be on the border line between the two.
The composition of vegetables varies in general from that of animal foods in that here we have the carbohydrates largely represented. The chief carbohydrates of vegetables are starch, sugar, and cellulose of various types.
The fact that cellulose forms the framework of the plant and that it is within cellulose walls that the starch as well as the proteid of the plant are contained, is important in two ways. While cellulose is only slightly digested by human beings (only so little of it in young and tender plants really serving as a food that the amount may be neglected), it does have a more or less important function in furnishing the required bulk of food. If one undertakes to live wholly upon a vegetable diet, this bulk generally becomes too great; on the other hand, one of the objections to an exclusively animal diet is in the absence of bulk. Since the digestive juices do not act upon cellulose to any extent, and the nutritive portions of the vegetables are enclosed within walls of this substance, the province of cooking is to so change the cell wall that the nutritive materials may be set free, or the digestive juices penetrate to them.
STARCH OF A POTATO ENCLOSED IN CELULOSE CELLS.