Febeuabt 3, 1911] 



SCIENCE 



163 



The displacement of equilibrium due to 

 cultivating large areas to one crop has led 

 to an enormous increase in the number of 

 insects and fungous enemies in any given 

 region.^- 



The excessive ravages of insects in the United 

 States are largely owing to the cultivation of 

 their food-plants in extended areas. Two hundred 

 years ago not even the wild crab, the earliest 

 representative of the apple, existed in this coun- 

 try, and consequently there were no apple insects. 

 Later when a few apple trees became the adjunct 

 of the simple homes of the early settlers, those of 

 our insects to which they offered more desirable 

 food than that on which they had previously 

 subsisted were obliged to wing their way often 

 for many miles in search of a tree on which to 

 deposit their eggs. If birds were then abundant, 

 how few of the insects could accomplish such 

 extended flights! But in the apple orchards of 

 the present day — some of them spreading in 

 almost unbroken mass of foliage over hundreds 

 of acres — our numerous apple insects may find 

 the thrifty root, the vigorous trunk, the succulent 

 twig, the tender bud, the juicy leaf, the fragrant 

 blossom, and the crisp fruit spread out before 

 them in broad array, as if it were a special offer- 

 ing to insect voracity, or a banquet purposely 

 extending an irresistible invitation. . . . Careful 

 cultivation has made it the best of its kind; 

 appetite is stimulated; development is hastened; 

 broods are increased in number; individuals are 

 multiplied beyond the conservation of parasitic 

 destruction; facilities of distribution are afforded 

 with hardly a proper exercise of locomotive or- 

 gans; and when these almost useless members 

 have become absorbed, as in the wingless females 

 of the bark-louse and the canker-worms, the 

 interlocking branches afford convenient passage 

 from tree to tree. 



As Bailey^^ says : 



We, as horticulturists, are every year planting 

 new invitations to insect and fungous attacks. 

 If we take this extra risk, we must certainly 

 prepare ourselves to meet it. Our fathers' 

 weapons can not avail against the horde of in- 

 vaders which we are inviting to our doors. They 

 are coming up out of the woods and the swamps 



"Lintner, First Report State Entom. N. Y., 

 10, 1882. 

 '= " The Survival of the Unlike," 187, 1898. 



and the bare fields to regale themselves at the 

 banquet which we have spread. 



Cultivation affords places of less struggle tlian 

 organisms are forced to occupy under normal 

 conditions. Man disturbs the equilibrium or re- 

 moves the pressure in some direction, and a mul- 

 titude is waiting to spring into the void. The 

 great potato fields not only provided food, but 

 there were few other insects to dispute the pos- 

 session of them; the Colorado solanum beetle saw 

 his opportunity, and improved it. He has been a 

 successful bug. This release of the natural ten- 

 sion, which cultivation affords, is to my mind the 

 most potent factor in the increase of our little 

 foes. 



TEMPERATURE 



One effect of a lower temperature is ob- 

 viously to produce a better protective coat- 

 ing on animals, while a higher temperature 

 acts in the opposite way. I quote a few 

 special cases from Darwin.^* 



According to Roulin, the semi-feral pigs in the 

 hot valleys of New Granada are very scantily 

 clothed; whereas, on the Paramos, at the height 

 of 7,000 to 8,000 feet, they acquire a thick cover- 

 ing of wool lying under the bristles, like that on 

 the truly wild pigs of France. 



Eoulin asserts that the hides of the feral cattle 

 on the hot Llanos are always much less hea^y 

 than those of the cattle raised on the high plat- 

 form of Bogota; and that these hides yield in 

 weight and in thickness of hair to those of the 

 cattle which have run wild on the lofty Paramos. 

 The same difference has been observed in the 

 hides of cattle reared on the bleak Falkland 

 Islands and on the temperate Pampas. 



Great heat seems to act directly on the fleece: 

 several accounts have been published of the change 

 which sheep imported from Europe vmdergo in the 

 West Indies. Dr. Nicholoson, of Antigua, in- 

 forms me that, after the third generation, the 

 wool disappears from the whole body, except over 

 the loins ; and the animal then appears like a 

 goat with a dirty door-mat on its back. A sim- 

 ilar change is said to take place on the west coast 

 of Africa. On the other hand, many wool-bearing 

 sheep live on the hot plains of India. Roulin 

 asserts that in the lower and heated valleys of the 

 Cordillera, if the lambs are sheared as soon as the 

 wool has grown to a certain thickness, all goes 



" " Animals and Plants under Domestication," 

 2d ed., 1, 81, 95, 102, 1890. 



