has been useful to man for thousands of years. The linen fiber comes not from the seed, as is true of cotton, but from the stem. The fibers of the flax are so closely held in the stems that they must be put through a long process of retting, or rotting, before the fibers can be separated. Then the fibers can be made into linen thread or cloth.

FIG. 244..

(Reproduced by permission of the Philadelphia Commercial Museum.)

- In the cotton gin (short for "engine") the cotton seed is separated from the fiber. In the figure men are shoveling up the seed.

The seeds of the flax are also used, as in the case of cotton; from them we obtain linseed oil (see § 33), which is used in large amounts for the making of paints. Do you know of any other use of flaxseed?

Hemp, like flax, is not a plant native to the United States, but has been brought here from the Old World. There are many substitutes for the true hemp. Thus, Manila hemp is a fiber obtained from a banana grown in the Philippines. For what is hemp used?

Straw is the dried stalk of many grain plants, such as wheat, oats, and rice. What is straw used for, besides as fodder for cattle?

322. What is a Fruit? What is the difference between a vegetable and a fruit? In the case of some plants the work of the plant is done when the embryo is developed, and the seed case is stuffed with food for the embryo to use when it begins to germinate. But in many plants this is not all: important changes take place in other parts of the reproductive organs as well, and we get edible fruits. Really a fruit is the ripened ovary, or egg case, and its contents; but in popular language we use the word fruit without thinking much of the seed, and only of the pulpy tissue which comes with it. We might call such fruits" fleshy " fruits.

Name some berries. A real berry (Fig. 245) is an ovary with its seeds and fleshy material, and with a thin outside "skin." Grapes, gooseberries, and blueberries are real berries,

Grape

FIG. 245.

Raspberry

Strawberry

are they not? How about raspberries? A raspberry is really a cluster of berries, which comes off from the knob, or receptacle, that forms the top of the flower stem. What is a strawberry? Have you ever bitten or cut a strawberry in two, and noticed the fine lines running from the outside of the berry to its center? These are tubes that connect the seeds with the top of the flower stalk. It is

How some of our "berries" look, when cut through. What is the real berry in each case?

this pulpy top, or receptacle, that we enjoy eating; the seeds are the gritty particles which are embedded in it. In blackberries we eat both the cluster of berries and the receptacle.

What are citrous fruits? They are fruits like oranges, lemons, and grapefruits. In their case the thin skin of the berry has become a tough, leathery hide. Pumpkins and melons go a step farther, and the ovary walls become rinds. Fruits which contain stones, or pits, such as cherries, plums, peaches, and apricots, are the result of the wall developing in two layers: (1) a hard layer surrounding the seed; and (2) a pulpy layer covered by a thin skin.

What kind of fruit is the banana? It is really a berry, as you can see if you cut it across. Its seeds are, however, mere remnants of seeds, and unable to develop into new plants. We learned in § 321 that we eat juicy vegetables, not for the fuel they give us, but for their flavor, minerals, and the like. The same is true of most pulpy fruits. But the banana has the qualities both of a fruit and of a starchy vegetable, such as a potato. How does the banana skin differ from other, tough, fruit skins, such as those of an orange or a watermelon?

323. Exercises. 1. What are some plant foods used by us that were very rare a hundred years ago?

2. Can you think how a spineless cactus could be produced from a spiny one? Of what use would a spineless cactus be?

3. How was the seedless orange developed? Who did it?

4. What was the importance to the world of the invention of the reaper by Cyrus McCormick? What was the date?

5. What is corn sirup? For what is it used? Examine a paper bag in which cornmeal has been kept. Do you get any evidence of an oily substance in corn?

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6. Examine a head of red clover. Is the head one flower, or many? What is each separate flower like? Which part of the clover ripens first, the outer, or the inner, part?

7. Why is corn allowed to stand in great stacks, or shocks, after being cut?

8. What is meant by the “ curing" of hay and clover? What is the purpose of the curing?

9. Does the value of vegetables and fruits as food depend on the energy we get from them? Explain.

10. Why is a hard-working horse fed upon oats in addition to hay? 11. What are some of the varieties of the potato? Of what value is the potato as food?

12. Is beet sugar produced in the United States? Where?

Summary. As plants carry on their life work, they produce materials which man can use.

Man brings into his own land not only the products of foreign plants but, in many cases, the plants themselves.

The grass family includes not only "grass," but our grains, cane sugar, and bamboo.

Wheat is useful for bread, not only because of its food value, but because of its sticky material, or gluten, which allows the bread to be "raised" by yeast.

Beans, peas, clover, alfalfa, and similar plants produce their seed in a peculiar pod, called a legume.

Leguminous plants capture nitrogen from the air by means of the bacteria colonies that grow upon their roots.

We eat vegetables for their starch and for their minerals and growth substances, or "vitamines."

Cotton gives us cotton and cottonseed oil; flax gives us linen and linseed oil.

From the point of view of the plant, a fruit is the ripened seed case with whatever is attached to it. From our point of view, a fruit is usually the pulpy tissue which surrounds, or is a part of, the real fruit, and which we like to eat.

CHAPTER XXXIII

OUR PLANT FRIENDS AND FOES

324. How are Trees Our Friends? - Have you ever been in a great forest and thought of Longfellow's lines? This is the forest primeval. The murmuring pines and the hemlocks, Bearded with moss, and in garments green, indistinct in the twilight, Stand like Druids of eld.

In such a forest of pines and hemlocks the lower parts of the trees have no branches, and the trunks stand straight and tall for perhaps 80 or 90 feet before the branches and foliage begin. When this is the case, it is not hard for us to imagine ourselves in a wonderful cathedral, with trees for its great columns, and leaves and branches forming its roof and letting in only a dim, green light to illuminate the floor below. As a matter of fact, the temples of the Greeks, the ruins of which show us the glory of Greek art, were originally of wood, and the columns supporting the high roof were tree trunks. Then, as the people learned to work in stone, and one by one the wooden columns decayed, stone columns, adorned in the style of each succeeding age, took their place.

Do you realize how many years large trees have been in growing; and that some of them are much older than any animal living upon the earth? Indeed, some of the Big Trees of California are believed