organisms of the sea. "It might be supposed at first thought that these phosphorescent organisms are not observed to emit light during the day because of the pressure of sunlight, and that if taken into a dark room they would be found to phosphoresce just as brilliantly as at night. Such is, however, not the case, not a spark can be elicited from them even by vigorous shaking, so long as there is daylight in the outer world. But if one stands by and watches in the dark room, as twilight is falling outside, although the organisms have been exposed to light all day, one observes the little lamps light up and flash out one by one like coruscating diamonds in the darkness till the whole fish is studded with flashing and disappearing light, a glorious sight in the darkness and stillness. Regularly every evening the lights come out, and as regularly every morning they are extinguished, although all the intervening time the tiny living creatures have been kept in darkness." 36 .. It should be noted that changes within the body may make a fixed environment act as a stimulus. Animals change in many ways when physical maturity is reached. Thus the queen ant remains quietly in the dark nest while young. On the advent of maturity she leaves the earth, flies toward the light and keeps away from the ground. When fertilized she again seeks the earth, burrows into it and starts a new colony. The rhythm of nature can hardly fail to impress the observer. The revolution about the sun, the ebb and flow of the tides and the waves of light and sound illustrate rhythm in the purely material world. Birth, youth, maturity, old age and death, show the cycle of life. The alternating periods of rest and activity, the pulsations of the heart and the inhalation and expiration of the breath display it in the activities of organisms. Whether such rhythm also characterizes human institutions must be considered elsewhere. 36 MOORE, B. The Origin and Nature of Life, pp. 250-251. Against such changes as have come in western Asia even man is largely powerless unless he moves. He may invent new measures which enable him to survive, but more likely he starts his migrations. No wonder then that Huntington says: "Finally it appears that the changes of climate have caused corresponding changes, not only in the distribution of man, but in his occupations, habits and even character." 37 It is not a matter of accident that the weather is the common basis of conversation the world over. Each and every primitive man came into close, daily, personal contact with nature. From this contact he had to get all the goods of everyday life. He was exposed to wind and storm. He saw the sun rise and set, the glory of the moon and stars. Now the civilized man has multiplied the contacts with nature in a sense he has weakened the force of each. His contact becomes more and more at second hand insofar as the great fundamentals are concerned. Hence he often ignores or denies even the great guiding forces sketched in this chapter. Yet in the qualities of the elements of the earth and man's adjustment thereto is the basis and start of all man's vaunted achievements as well as the limits thereof. SUGGESTIONS FOR READING CHAMBERLIN, T. C. Origin of the Earth. 1915. 37 HUNTINGTON, E. The Pulse of Asia, p. 359. DEXTER, E. G. Weather Influences. 1904. HANN, J. Handbook of Climatology. 1903. HELLPACH, W. Geopsychischen Erscheinungen. 1911. HUNTINGTON, E. The Pulse of Asia. 1907. MOORE, B. The Origin and Nature of Life. 1912. SEMPER, K. Animal Life. 1881. SEMPLE, E. T. American History and Its Geographic Con ditions. 1903. Influence of Geographical Environment. 1911. WOODRUFF, C. W. The Effect of Tropical Light on White Men. 1905. CHAPTER II MUTUAL AID AND THE STRUGGLE FOR We have seen that life exists because of the nature of the elements and that it continues to exist if the environment is favorable. We must now consider the various ways in which the different forms of life affect each other. The reader is warned not to interpret all the phenomena to be mentioned as if they resulted from some conscious purpose in the plants or animals. Most of the service rendered, or the harm done, results solely from the nature of the organisms. Thus plants produce purely mechanical effects of the utmost importance. By forming a dense sod they keep the soil on the hillsides from which otherwise it would quickly be removed by water. Their roots extend into the subsoil, then die and decay, thus making openings for air, water and frost which tend to break up the soil, to expose new particles of plant food and thus make increased vegetation possible. Plants absorb a considerable part of the carbon dioxid given out by animals. Thus they help to make the air fit for animals to breathe just as in water they perform a similar service. They also take up large quantities of water from the earth which pass into the air through the leaves, the amount increasing as the temperature increases, diminishing as it falls. The Washington Elm at Cambridge, Massachusetts, was studied by Professor Pierce of Harvard. He reported that the tree bore some 7,000,000 leaves having a surface area of 200,000 square feet or about five acres. It being estimated that one acre of grass furnishes 6,400 quarts of water in twenty-four hours, this tree supplied some 32,000 quarts of water daily. The influence of forests is very large. They reduce the mean temperature of the air, increase the humidity, decrease the violence of the winds, offer protection against very hot winds and regulate to some extent the flow-off of the water. Significant as these mechanical changes are they become as nothing when compared to the chemical changes produced by plants. The common chemical elements found in plants are carbon, nitrogen, hydrogen and oxygen. Plants get the nitrogen and hydrogen largely from the soil, the carbon and oxygen from the air. Now there is very little nitrogen in the rocks, whereas it forms 80 per cent of the air. How is it, then, that cultivated soil contains from .1 per cent to .2 per cent nitrogen, while rich prairie soils have perhaps 25,000 pounds per acre in the top three or four feet? That the leguminous plants (clover, alfalfa, peas and beans) enriched the soil and increased the yield of other crops was known to the Romans of old. It was not until 1886 that Hellriegel was able to show that this was chiefly due to colonies of bacteria which collected in nodules on the roots and were able to draw the nitrogen directly from the air and make it available for plants. It is estimated that an acre of alfalfa adds nitrogen worth at least $25.00 per year to the soil. Most of this supply of nitrogen in the soil must have been taken from the air by earlier generations of bacteria. Plant tissues contain much carbon. Forty per cent of the weight of rye straw is carbon. An acre of beech forest consumes almost a ton of carbon yearly. This must be |