Page:Popular Science Monthly Volume 45.djvu/198

184 to persist unless carefully aided by artificial selection, yet they must have commenced as acquired characters. Well-broken horses and well-trained dogs transmit these qualities to their offspring, and all domestication and cultivation of animals and plants, all changes wrought in them by man, must have been first acquired to some degree, and then, by intelligent selection, the degree can easily be increased. Like produces like, and if we can not explain why, it is because we have not yet solved the problem of heredity. The elaborate theory offered by Prof. Weismann in his Germ-Plasm, plausible as it sometimes seems, true as it doubtless is in many of its details, utterly fails to solve this problem. It is altogether too rigid, too mechanical, to explain such subtle phenomena. Nature is more flexible, more self-adjusting, more delicate than his system contemplates, and is constantly doing just those things which he insists can not be done.

I trust that it has been sufficiently shown, chiefly from his own words, that in elaborating this complicated theory Prof. Weismann, guided, as he always seems to be, by the highest regard for truth, has, greatly to his credit, conceded all the essential points in the long controversy as to the inheritance of acquired characters. The discussion may therefore be regarded as narrowed down, not so much to the relative importance of the direct and indirect factors, as to the degree to which in any given case the one or the other has operated in determining the observed result.



IN many respects the Ohio is one of the most remarkable rivers in the world. Its drainage basin comprises about two hundred thousand square miles on the northwestern slope of the Alleghany Mountains. Its eastern tributaries rise at an elevation of something over two thousand feet above the sea, and hence are so situated as to carry the rainfall and the melting snows with great rapidity into the main channel, which at Pittsburg is seven hundred feet above the sea, and at Cairo, where it unites with the Mississippi, about three hundred feet; the descent from Pittsburg to Cairo being about four hundred feet in a distance, as the river runs, of nearly a thousand miles.

The whole course of the river is through sedimentary rocks, which, though of Palæozoic age, have been but slightly disturbed. The elevation of the region has been so continental in its proportions that the rocks have retained to a great degree their original 