Page:History of Iowa From the Earliest Times to the Beginning of the Twentieth Century Volume 1.djvu/51



upon which most of the trees of neighboring forests flourish luxuriantly when protected should have failed to have been covered with them in a state of nature, is the question. It is answered by some vegetable physiologists thus:

“'The excrements of vegetable growth from the roots of trees and plants, and even the annual accumulation of their own leaves after a continuous growth of the same species, become poisonous to the genera which emit them, though perfectly nutritious to plants of different families. It is claimed that the long continuance of forest growth on a rich soil made constantly richer by its own annual deposits of leaves, dead wood and excretions from the roots, finally makes it unfit for their growth. Sickliness and decay produce more dead wood so that fires finally destroy utterly what the soil refuses to nourish. Rank weeds and grasses follow, which in their turn ripen and dry in autumn, make food for new flames that destroy the remnant of tree vegetation, and even the young wood of new species which might otherwise hold their ground. Tree roots cannot live when their tops are destroyed. Perennials, on the other hand, have an extraordinary power to preserve life in their roots under the action of prairie fires. Once in possession of the soil it is easy to see that annual autumn fires, where there are not animals enough to feed down the summer growth, will not only preserve the ground won from the forest by grasses, but will singe the surrounding forests, and wherever they are sickly from the cause first named will finally consume them. Ages of the continuous growth of grasses and other perennials have assimilated those qualities of the soil that become noxious to trees; and in nature's rotation of crops, the soil has again become fitted for their growth. It is only necessary to check the prairie fires for a new crop of forest to dominate the grasses. Trees were beginning to resume possession of the prairies when the settlements began. The increase of the buffalo decreased the food for autumn fires by so much as they pastured upon the grasses. The moisture of the ground contiguous to streams, and the sweetness of the late summer grasses in those places, would naturally make spots where the trees could have time to get rooted in the absence of fires.”

It will be seen from these quotations that the subject of the origin of the prairies is by no means settled. Little, if anything new, has been developed during the last quarter of a century by scientific investigation to throw new light upon a subject that will always be of interest in the Mississippi Valley. The fact that prairie and forest conditions have been found on all of the continents, and among the islands, when first seen by men, show clearly that the solution of the problem cannot be found in local or