abundance is almost certain to follow, and any abnormal increase of the former is almost sure to be checked by the corresponding increase of the latter.” 18 In other words, neglecting the tremendous destruction of life through failure to develop, whatever be the reason, and the frightful death-rate through storm or other natural agency, the fact that all life depends in large measure on other life for maintenance establishes what may be called the "balance of nature." In reality we have then an equilibrium which may be temporarily upset by any change in the conditions of life: thus giving now to one group of organisms, now to another, a peculiarly favorable chance for increase; but at the same time setting the bounds to this increase and providing the basis for the reaction. It will not be specially difficult to understand this phenomenon if we can avoid the temptation to think of this struggle for existence as a conscious activity on the part of living organisms. Even man's actions are far less deliberate than we usually think. The effort to preserve individual life and that of reproducing its kind both growing out of the nature of self is the keynote. Under favorable conditions there will be both growth and reproduction. The increase of any type of animal is conditioned in part upon the available food supply. Here man unwillingly and often unwittingly acts as host. He plants his crops but receives undesired coöperation in the harvesting thereof. The Year Book of the Department of Agriculture, 1904, estimates the damage done yearly by insect pests to the various crops in the United States as follows: 18 SMITH, J. B. o. c., p. 100. Insects are the most numerous of all the animal species. In spite of their vast number perhaps not more than five per cent do any great harm to the farmer, yet the burden is terrific. In 1894 there appeared in the southern counties of Texas a small beetle-like animal known as the boll weevil. It takes but fourteen days to develop from egg to adult and the progeny of a single pair may reach in a season 134 million. For some years it attracted little attention but, as was later discovered, kept spreading to the extent of some fifty miles a year. By 1912 it had crossed the Mississippi River, by 1915 had reached Georgia, and it is certain now to spread throughout the entire cotton-growing South. It feeds on the cotton bolls, the eggs being deposited in the unripe boll which is destroyed as the insect develops. It hibernates in cotton stalks or other plants. By 1903 it was thought that the damage done to the Texas cotton crop was some $15,000,000, but this was a wet season and particularly favorable to the weevil. Suffice it to say that in this immigrant the cotton planter finds his greatest enemy, and as yet no 19 Year Book of Department of Agriculture, 1904, p. 464. abundance is almost certain to follow, and any abnormal increase of the former is almost sure to be checked by the corresponding increase of the latter.” 18 In other words, neglecting the tremendous destruction of life through failure to develop, whatever be the reason, and the frightful death-rate through storm or other natural agency, the fact that all life depends in large measure on other life for maintenance establishes what may be called the "balance of nature." In reality we have then an equilibrium which may be temporarily upset by any change in the conditions of life: thus giving now to one group of organisms, now to another, a peculiarly favorable chance for increase; but at the same time setting the bounds to this increase and providing the basis for the reaction. It will not be specially difficult to understand this phenomenon if we can avoid the temptation to think of this struggle for existence as a conscious activity on the part of living organisms. Even man's actions are far less deliberate than we usually think. The effort to preserve individual life and that of reproducing its kind both growing out of the nature of self is the keynote. Under favorable conditions there will be both growth and reproduction. The increase of any type of animal is conditioned in part upon the available food supply. Here man unwillingly and often unwittingly acts as host. He plants his crops but receives undesired coöperation in the harvesting thereof. The Year Book of the Department of Agriculture, 1904, estimates the damage done yearly by insect pests to the various crops in the United States as follows: 18 SMITH, J. B. o. c., p. 100. Insects are the most numerous of all the animal species. In spite of their vast number perhaps not more than five per cent do any great harm to the farmer, yet the burden is terrific. In 1894 there appeared in the southern counties of Texas a small beetle-like animal known as the boll weevil. It takes but fourteen days to develop from egg to adult and the progeny of a single pair may reach in a season 134 million. For some years it attracted little attention but, as was later discovered, kept spreading to the extent of some fifty miles a year. By 1912 it had crossed the Mississippi River, by 1915 had reached Georgia, and it is certain now to spread throughout the entire cotton-growing South. It feeds on the cotton bolls, the eggs being deposited in the unripe boll which is destroyed as the insect develops. It hibernates in cotton stalks or other plants. By 1903 it was thought that the damage done to the Texas cotton crop was some $15,000,000, but this was a wet season and particularly favorable to the weevil. Suffice it to say that in this immigrant the cotton planter finds his greatest enemy, and as yet no 19 Year Book of Department of Agriculture, 1904, p. 464. enemy has been found to check it. The natural enemy of the weevil in its own home, an ant, apparently will not live in our country, hence the plague. The total loss charged to its account down to 1914 is some $500,000,000 or 10,000,000 bales of cotton. Seven Mississippi counties in 1907 produced 171,790 bales. The boll weevil entered and the production in 1909 was 89,577 bales; in 1910, 61,432; 1911, 37,816, and in 1912, 30,909. The larvæ of the corn-root worm feed upon the roots of young corn and sometimes cause the loss of the entire field. This worm and a few similar species probably destroy two per cent of the crop year by year. The ear worm eats the kernels particularly of sweet corn of which some 90 per cent of the ears are attacked and destroys not less than two per cent of the entire crop. Another two per cent goes to the chinch-bug. About fifty species of insects attack the corn and, in addition to the work of the three mentioned, probably reduce the crop another two per cent, making a total of eight per cent of the entire crop. Of the cereals wheat suffers most. The Hessian fly, chinch-bug and grain louse are its worst enemies. In some years over one-half of the acreage planted has been abandoned because of the Hessian fly alone. In 1900 Indiana and Ohio are estimated to have lost not less than $24,000,000 on account of this pest. The productiveness of the apple tree is reduced 5 per cent by the woolly aphis which attacks its roots, 2 per cent by the borers, and 10 per cent by the plant lice, scale insects and those that destroy the leaves. The codling moth, which lays its eggs in the young fruit through the country at large, causes a loss of not less than 20 per cent of marketable apples, while some estimates place the |