Page:Popular Science Monthly Volume 51.djvu/729

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Ups and Downs of the Tussock Moth.—After the English sparrows had quite exterminated the voracious measuring worms that used to make our city trees naked, the uneatable tussock moths took advantage of the opportunity and filled the trees for a few years with their uneatable larvæ. Now the tussock moths have nearly disappeared, and A Study in Insect Parasitism, by L. O. Howard, entomologist of the Department of Agriculture, tells us how it came about. It appears to be a kind of process of Nature that as soon as any living thing becomes numerous parasites find it, and shortly reduce it to its normal proportions or below. These in turn are subject to secondary parasites which keep them in check. Thus twenty one parasites have been found upon the tussock moth, with fifteen hyperparasites. While, after having passed its culmination in the farther Eastern cities, the proportion of tussock moths has been about the same, it took a rapid and enormous increase in Washington in 1895. But the parasites appeared in force with the third generation of that year; and when in September several species of trees had been cleared of leaves and others badly injured, "it was an exception to find a healthy caterpillar which one of them was not engaged in stinging." There was a moderately abundant hatching of Caterpillars in 1896, but the parasites were ready for them, and the first generation was practically exterminated by them. In the later months of 1896 the hyperparasites took their turn, and the tussock-moth caterpillars were not so hard to find, but were still rare. Even where parasites do not step in to keep down increase, the excessive multiplication of animal pests is at length inevitably checked by disease. Thus the chinch bug has no parasites, "but when it increases beyond the bounds of what may be called Nature's law, for want of a better term, bacterial and fungous diseases speedily carry it off."

Objects of National Forestry.—The policy and aims of those who are seeking the establishment and maintenance of a national forest policy have been misunderstood and misrepresented; and the misapprehension has been strengthened by some glaring defects in some of the forest laws, which the friends of forestry do not approve and desire to have remedied. It is not by their work, but contrary to their intentions, that these laws embody no provisions by which citizens can obtain wood from the public domain by purchase, and that timber-stealing flourishes under their operation. The laws which they propose are designed to remedy these evils. Reservation is the first purpose sought in them, regulation of the use of the timber the second; perpetuation of a valuable resource for coming generations the object. The programme of those urging these laws, as defined by Mr. B. F. Fernow, chairman of the American Forestry Association, is to withdraw from sale or entry all lands not fit or needed for agriculture and to constitute as objects of special care by the Government the lands at the head waters of streams and on mountain slopes in general; to permit prospecting, mining, and other operations under such regulations as will prevent unnecessary waste, and to cut and sell the timber under such methods as will secure perpetuation and renewal of the forest growth; to provide for protection against fire, theft, and unlawful occupancy; to respect all existing vested rights and arrange an exchange, if necessary, for private lands included in reservations; and, finally, to restore to the public domain for entry all lands that are found in the reservations fit for agriculture. The interests of the miner, the lumberman, the settler, and every citizen in the present and the future are regarded in the policy they advocate; the free herding of sheep, by which forest tracts are destroyed and rendered unfit for renewal, being the only industry not considered. "Just like the proverbial incompatibility of the goat and the garden, the growing of wool and wood on the same ground is incompatible."

Sewage Purification by Filtering.—Filtration through the soil is regarded by M.