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most widely effective of all the great factors in determining the distribution of human activity and productivity. 16

REFERENCES

I. C. W. WOODRUFF, Effects of Tropical Light on White Men,

pp. 85ff.

2. J. W. GREGORY, The Menace of Color.

3. Ibid., Chap. viii.

4. E. HUNTINGTON, Civilization and Climate, pp. 41-42.

5. G. TAYLOR, Environment and Race, pp. 264ff.

6. E. HUNTINGTON, West of the Pacific, pp. 349ff.

7. E. C. SEMPLE, Influences of Geographical Environment,

pp. 34ff.

8. E. G. DEXTER, Matter Influences, pp. 81-82.

9. E. HUNTINGTON, Civilization and Climate, p. 47.

10. J. HANN, Climatology, p. 57.

11. M. L. DAVIS, Scribner's Magazine, July, 1926.

12. O. T. MASON, Origins of Invention.

13. HUNTINGTON and WILLIAMS, Business Geography, Fig.

38, p. 110.

14. Ibid., pp. 110-111.

15. E. HUNTINGTON, Civilization and Climate, pp. 200ff.

16. HUNTINGTON and WILLIAMS, op. cit., p. 127.

CHAPTER IV

MUTUAL AID AND THE STRUGGLE FOR EXISTENCE

So, naturalists observe, a flea

Has smaller fleas that on him prey;
And these have smaller fleas to bite 'em

And so proceed ad infinitum.

THE ORGANIC COMPLEX

-SWIFT

Long, long ago the seer could state that "no man liveth unto himself." Only yesterday did man begin to understand that this statement was but a small part of the truth and to see that every form of life influences every other form, directly or indirectly. Even this statement is inadequate, for the surface of the earth is itself modified by the activities of the various organisms. Though countless details still escape our observation, the main outlines of the picture are becoming clear. Our first task is to find the facts, the second, to interpret them. A word of warning is necessary. It is as hard for us to avoid a man-centered interpretation of the interrelations of the different forms of life as it was for our ancestors to avoid an earth-centered interpretation of the universe. We are likely to ascribe human motives to the actions of animals. The fact is, however, that we have no right to assume that the influences to be described have any deliberate or conscious cause in the plants or animals themselves. In most cases they must be in entire ignorance of the results of their actions and, not infrequently, this is true of man himself. In other words, they do what they do because of what they are and for that they are not responsible. Therefore such words as "good" or "bad" are inapplicable, and misleading. In as much as language must be used the reader will have to make the necessary corrections to avoid

error.

Effects of Plants

Plant life has no small effect on the contours of the earth. One has but to compare the arid with the humid regions of our own country to see this. In the humid parts the grass binds the soil on the hills and valleys and on embankments made by man. The rain comes and the floods overflow the valleys. Rarely is any great harm done. In the arid country the rain causes great washes in the hills, destroys railroad embankments, and leaves an impassable mass of rock where yesterday was a good highway. The trees and the grass hold the moisture, delay the melting of the snow in spring, thus maintaining a more even water supply as well as preventing the dangerous floods which come when the hillsides are laid bare. Plant life markedly affects the make-up of the air and water either by increasing or decreasing the amount of various gases they contain. The excess of nitrogen in the aquarium so injurious to fish may be removed by plants just as the carbon is taken from the air. Plants furnish a considerable amount of water vapor to the air. The Washington Elm at Cambridge, Massachusetts, was studied by Pierce of Harvard. He found that it had some 7,000,000 leaves with a surface area of 200,000 square feet, or nearly 5 acres. He estimated that this one tree supplied some 32,000 quarts of water daily to the air. The influence of a great forest can be imagined. Thus the forest will increase the humidity of the air, decrease the violence of the storms and offer protection against hot winds as well as furnish shade, welcome to many smaller plants as well as to the animals and man. The roots of trees penetrating the lower layers of the soil, ultimately dying and decaying, will modify the conditions of the soil itself. Indeed, the formation of the soil is largely a matter of the activity of organisms, as will be shown in a later paragraph.

Effects of Microörganisms

For ages man had divided the organic world into plants and animals and had thought it easy to distinguish one from another. How easy such a definition is the reader will discover if he tries to make it. In 1683, Leeuwenhoek, a Dutch maker of lenses, put a couple of them in a tube and found that he had a compound microscope. It magnified objects about 150 diameters, or only about one-tenth as much as our present microscopes, but it revealed a new world. With it he examined many things and found all sorts of minute organisms moving under the lens. He called these "animalculæ," for plants were not supposed to have the power of motion. Even to-day there is a dispute between botanists and zoölogists as to the proper classification of many of them. For present purposes we may divide the organic world into microörganisms, plants and animals.

The microorganisms are divided into four main classes. Among them we find minute animals, the protozoa, which appear to feed on bacteria and other minute organisms. They multiply by fission and have the power of encysting themselves and thus of surviving through bad conditions for considerable periods. Some of them are causes of disease. The bacteria, proper, are single cells averaging about 1/25,000 of an inch in diameter. It takes about 15,000,000 typhoid bacilli to weigh an ounce. They multiply by fission, though some of them produce spores which are, however, very different from the spores of ferns as each bacterium produces but one or a very few spores at most. This seems to be a device of nature to enable them to survive in time of need, as they live indefinitely in spore form. Bacteria produce nearly all the putrefaction and decay found in nature. The yeasts are single cells, round or oval in form and about 1/5,000 of an inch in diameter. They are the cause of fermentation. The fungi are a large and varied group having two common characters. They have their cells arranged in long threads, often almost microscopic in diameter, although the fruiting bodies above ground are often large as in the case of the mushrooms and puffballs, and they contain no chlorophyll. The molds are simple fungi whose fruiting bodies are usually visible, and which cause over half of all known plant diseases. The fungi increase by spores. It is but a short step from the fungi to the lowly plants called algæ which contain chlorophyll.

From the standpoint of their food supply there are three main groups of bacteria. Some are autotrophic, growing in the darkness of the soil and feeding directly on mineral matter, getting their energy from simple compounds such as ammonium salts and methane. Most of them are saprophytes, feeding on the dead tissues of organisms. Some are parasitic, attacking live tissues and producing diseases. It is to be noted further that while a few bacteria may utilize the sunlight, most of them are killed by direct exposure to the sun, the short rays being most fatal to them. Few bacteria attack the living tissues of plants or animals.

All animals must get their food by breaking down the compounds prepared by green plants. Here lies a great difference between plants and animals. In some way not clear to us, plants under the influence of the sunlight are enabled through their chlorophyll (leaf green) to build up out of a few common elements the great series of hydrocarbons and other compounds which animals can incorporate but cannot produce. "All flesh is grass," as the poet sang. Man may eat a little salt or take small doses of chemicals as medicines but he must depend on presynthesized food.

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