39. Miscellaneous food-products. Under this head we must consider the products of certain plants which do not properly belong to any of the foregoing groups. Thus in the common garden rhubarb or pie-plant (Fig. 112) the part commonly used is the leafstalk, just as in celery; but it can hardly be called a vegetable, for it is used quite like a fruit on account of its strongly acid sap; in spite of its fruit-like qualities, however, it can still less be called a fruit.

Similarly in the olive (Fig. 113) we have a fruit which is put to a peculiar use. The pulp instead of being sour or sweet, abounds in a rich oil, which when extracted by pressure, is the most highly valued of vegetable oils for salads and in cookery. Peanuts and various other oily nuts, as also cotton seed and others rich in oil, yield a similar product which is often substituted for olive-oil; but although equally wholesome and of practically the same chemical composition, the nut-oils and seed-oils are inferior in flavor.

The sugar used in this country is obtained very largely from sugar-cane (Fig. 114). When full grown the stalks are crushed between rollers, which press out the sweet sap. This, upon evaporation of a certain amount of the water, yields crystals of cane-sugar which are separated from the thick, sweet liquid known as molasses. The crystals after further removal of impurities form the cane-sugar of commerce.

Exactly the same kind of sugar as that obtained from the sugar-cane is extracted also from the sugar-beet (a variety of the common garden beet) and from the sap of the sugar maple (Fig. 248). Beets form the chief source of the sugar used throughout Europe and nearly half of that consumed in the United States.

As already stated in the last chapter (section 29) large quantities of what is known commercially as "glucose" (which is a honey-like syrup), are manufactured from the starch of maize or Indian corn, particularly for the use of confectioners. This product is chemically much the same as the sweet substance found in fruits, and is perfectly wholesome; it has, however, the disadvantage of being only about three-fifths as sweet as cane-sugar.

Another food-product, very much used in confectionery, is what is commonly called "cocoa," or when sweetened and flavored, "chocolate." This name "cocoa" is somewhat misleading, since it is also applied to the palm which yields the "cocoanut" and which is a plant totally different from the one that gives us chocolate, as may be seen by a glance at Figs. 115 and 34. Cacao is a much better name for the plant and product from which chocolate is manufactured, for it is the name commonly used in tropical America where the plant grows, and is applied to no other sort. It is the seeds which afford the cacao of commerce. Separated from the fleshy pulp of the somewhat squash-like fruits, the seeds are placed in tight boxes or otherwise massed with exclusion of air, and allowed to undergo for some days a process of fermentation or "sweating," whereby their peculiar flavor is developed. This accomplished, they are dried by exposure to the sun, daily, for two or three weeks, when they assume a rich red tint and are ready for market. As will be seen from the chart, cacao possesses a very high nutritive value.

Starch in the particularly palatable forms known as sago and tapioca, is obtained from certain tropical plants which are especially rich in this form of food. The best sago comes principally from the spineless sago-palm, shown in Fig. 116. When full grown the tree is felled and the trunk cut into sections to facilitate the removal of the spongy pith-like interior, which is gorged with starch. By repeated washings the starch is separated from the indigestible material, and is then finally dried and granulated into small pearl-like masses for the market. A single tree will yield from four hundred to six hundred pounds of sago.

Tapioca is manufactured chiefly from the large fleshy roots of the bitter cassava (Fig. 117). Curiously enough the starch in these roots is associated with a milky juice which is decidedly poisonous. The poison, however, is of such a nature that it entirely disappears in the process of preparation.

This is essentially as follows. The roots are first reduced to a pulp, and then subjected to pressure, which forces out the milky sap together with a large quantity of starch. After standing a while, the starch settles from this poisonous fluid. The latter is then poured off, and the starch, spread upon iron plates, is heated until all vestige of poison has disappeared, and the starch-grains becoming somewhat gummy adhere together into small irregular masses which constitute the tapioca of commerce.

A seaweed known as carrageen or "Irish moss" (Fig. 118), found along the North Atlantic coast on both sides of the ocean, is used for food, generally in a sort of pudding, somewhat as tapioca. The whole plant is cooked, after having being dried and bleached in the sun at the time of gathering. The principal chemical constituent (see chart) is a mucilaginous carbohydrate which swells greatly in water and gives to Irish moss blanc-mange its jelly-like character.

Finally must be mentioned as widely cultivated for food the common field mushroom (Fig. 119) which, as the chart will show, compares favorably with many vegetables in the percentage of nutritious constituents. The statement is frequently made, however, by writers who ought to be better informed, that mushrooms are as nourishing a food as meat. That this is an absurd exaggeration is seen from the fact that a pound of mushrooms contains less than one-sixth as much proteid as a pound of meat. Furthermore it has been ascertained that while the proteid of meat is almost entirely digestible, scarcely more than half of the proteid in mushrooms is available as nutriment. Still, mushrooms are sufficiently nutritious to warrrant our using them much more than we do, especially certain wild forms which abound in our fields and woods, and of which some at least are preferable even to the cultivated species. The reason these wild forms are allowed to go to waste, is chiefly that there grow along with them certain poisonous species so nearly similar in appearance to the edible sorts as to have led ignorant persons to gather and eat them unwittingly, with fatal result; for unlike the poison in cassava root, that in poisonous mushrooms is not rendered harmless by cooking. Unless one is well acquainted with the peculiarities by which edible and poisonous sorts may at once be distinguished, it is surely both foolish and dangerous to gather wild mushrooms to eat; nevertheless, such knowledge is not difficult to acquire with the aid of good pictures and careful descriptions, and to those who spend much time in the country the information may be of not a little value.