英文科學讀本 第六冊·Lesson 12 Plants Useful for Food (Ⅲ)

Lesson 12 Plants Useful for Food (Ⅲ)

Useful Vegetables

In addition to the plants which furnish man in all parts of the world with some form of bread material, there are others of a different character on which he depends to a large extent for his daily food supply. He uses the root of one, the stem of another, the leaves of another. In some cases it is the underground tuber which yields the food supply.

Among the useful roots are the carrot, turnip, and parsnip—the fleshy taproots of the respective plants. The mangold-wurzel—one of the turnip family—is a valuable root used by the farmer for feeding cattle.

The potato, although obtained from that portion of the plant which is in the ground, is not a root, but a swollen part of the underground stem. We call it a tuber.

It does not require very much explanation to show that these underground parts of the plant (roots and tubers) must of necessity contain a large amount of water, for they are always absorbing water from the soil. Every 100 lbs. weight of turnips contains 92 lbs. of water and only 8 lbs.of dry solid matter. The same weight of carrots contains 88 lbs. of water and 12 lbs. of solid matter; while potatoes yield 75 lbs. of water and 25 lbs. of solid constituents.

If these roots and tubers be dried until all the water is driven out of them, the dry solid matter will be found to consist mainly of the same substances, gluten and starch, with which we have become familiar in the breadstuffs. It is because they contain these substances that they are valuable as nutritious foods. The dried solid substance of the parsnip, for instance, yields a meal which consists of gluten in addition to starch and sugar combined. The turnip is said to be quite equal in its composition to the meal of the Indian corn, except that it is deficient in fatty matter. Therefore to make turnips really nutritious, they should be eaten with some fatty or oily food. The farmer makes turnips combined with oil-cake the main food of his cattle during the winter months, when they are for the most part housed, and unable to seek their own food in the meadows.

Next to the cereals, the potato is the most valuable of all vegetable foods. It feeds domestic animals as well as man, and is more extensively and universally grown than any other cultivated plant. It is very largely cultivated in mild climates, and to some extent in warm, and even in cold regions.

The 25 percent of dry solid matter which it contains consists largely of starch, with less gluten than is found in rice, banana, or breadfruit, yet in conjunction with other food it forms a valuable article of diet. To the Irish peasant it is as much the staple food as rice is to the Hindu and the Chinese, or the banana to the Black man.

The sweet potato of Central America, and the yam of the East and West Indies and the South Sea Islands, are varieties of the potato which form important articles of food in the regions where they are grown.

The onion is a most valuable and nutritious article of food; its solid substance when dried is found to contain from 25 to 30 percent tissue-forming gluten. In its sustaining power it is said to equal the gram of the Eastern desert-lands. It is largely cultivated in this country, and is also imported from Spain and Portugal to the extent of seven or eight hundred tons yearly.

The Spanish peasant works contentedly from day to day on a diet of bread and onions—the onions contributing very largely to the amount of nourishment provided by his simple meal. The onion is the lower part of the stem of the plant swollen out to form a bulb.

The leaves of plants provide a by no means inconsiderable proportion of our daily food, both directly and indirectly. Our sheep and oxen and other animals, whose flesh supplies us with food, live for the most part on grass.

The cabbage family of plants, including the cauliflower, broccoli, etc., are extensively grown in all European countries. They contain a large proportion of water—as much as 90 percent; but their dry solid matter is rich in tissue-forming gluten, and this makes them a highly nutritious article of diet.

A common dish in Ireland and in the South of France is made of potatoes and cabbage beaten up together. The potato supplies abundance of starch, but little gluten; the cabbage is rich in gluten; the two combined approach the composition of wheaten bread. Add to the mixture a little fat pork, and the whole gives as nearly as possible the composition of Scotch oatmeal.

One important constituent of every variety of vegetable food we have hitherto ignored. If we burned any one of the food substances we have examined, we should leave a residue—the mineral ash. This ash represents the earthy or mineral matters absorbed from the soil by the plant during its life. These mineral matters are of the highest importance to the growth and well-being of the body— particularly in the work of bone-making. At the same time, most of them are valuable as storehouses of potash, a mineral matter of great importance to our health and well-being from its anti-scorbutic properties—that is, as a preventive of scurvy and other eruptions of the skin. People who from any cause are deprived of these fresh vegetables are sure to suffer from such diseases sooner or later.