. Adventures with animals and plants. Biology. PROBLEM Our Relationship to Other Orgmimns 383 Fig. 332 Fruits of the cot- ton plant. Three have hjirst open showing where the cotton grows. ]Vhy is cot- ton an i?nportant crop plantF (u. s. department of agriculture;. ment. Some of them are rich in proteins and much cheaper than meats or fish. Plants also supply us with such minor foods as spices, sugar, tea, coffee, flavor- ing, and substances for making beer and other alcoholic liquors. Before reading further do Exercise 2. The other uses of plants are many and important. Much of our clothing i
. Adventures with animals and plants. Biology. PROBLEM Our Relationship to Other Orgmimns 383 Fig. 332 Fruits of the cot- ton plant. Three have hjirst open showing where the cotton grows. ]Vhy is cot- ton an i?nportant crop plantF (u. s. department of agriculture;. ment. Some of them are rich in proteins and much cheaper than meats or fish. Plants also supply us with such minor foods as spices, sugar, tea, coffee, flavor- ing, and substances for making beer and other alcoholic liquors. Before reading further do Exercise 2. The other uses of plants are many and important. Much of our clothing is made from cotton. From trees we obtain lum- ber, wood pulp for the manufacture of paper, firewood to heat homes and for cooking, and the raw materials for many manufactured products. One of the most important of these is rubber. From the forests we obtain also turpentine, rosin, tar, tannin for tanning leather, cork, and many other products. And from the for- est trees that lived millions of years ago we get our coal. Some stems have fibers that are used for weaving linen (flax) or for making rope (jute, hemp, and others). Some supply us with drugs; quinine, for example, is extracted from the bark of the cinchona tree originally found in Peru. (You will find The Fever Bark Tree by M. L. Duran-Reynals in- teresting reading.) How we use microorganisms. We think so often of microorganisms as causes of disease that we tend to forget how use- ful some of them are. You read in the last Problem of the bacteria and molds that restore nitrates to the soil and are useful in the carbon cycle. You have al- ready learned that yeasts ferment sugar, changing sugar to alcohol and carbon dioxide. In breadmaking the carbon di- oxide raises the dough, making the bread light. A special kind of yeast is used in this process. Other kinds of yeasts are used to produce alcohol. See Exercises 3 and 4. Some kinds are used in the brew- ing of beer where grains are acted on by yeasts; others in the ferm
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