304 ILLINOIS STATE HORTICULTUKAL SOCIETY. 



One attributes it to the agency of fire. The annual burnings of the 

 dry fall grasses by the Indians, in all the years they roamed over the 

 broad expanse, is said to be a potent cause to keep down the growth of 

 trees. The prairies have been kept swept clean of forests by a broom of 

 flame ; not only kept clean, but the devouring element has constantly 

 encroached on the domain of the timber, and as constantly enlarged the 

 province of the grasses. We all know the omnipotent power of fire, 

 when unchained and wild in its devouring rage. It has melted and 

 licked up great cities of stone and iron, and wrapped green woods in its 

 devouring crimson and black mantle. But I find no satisfactory evidence 

 that our grand prairie was ever covered with an arborescent growth. The 

 soil contains no history of its decayed roots, and the chemical analysis 

 of its materials no trace of the ashy and mineral residuum of its burnt 

 tops. 



Another theory supposes that the prairies are caused by receding 

 waters; another still, by the original constitution of the soil; another, 

 by the supposed hostility existing between the trees and grasses ; while 

 the true theory would embrace them all, some operating in one locality, 

 some in another, and combined in various degrees in others, modified 

 by atmospheric agencies, bounded by certain isothermal lines, inclosing 

 certain zones and belts of moisture and dryness. 



The annual fires which were supposed to sweep through the grass, 

 killing every tree germ and young tree almost before they could take 

 root, is the theory entertained by many of our old settlers, and it is much 

 favored by Judge Caton, in his thoughtful and cautious essay upon this 

 subject. In some places the fires are supposed to have encroached year 

 by year upon the forests ; in other places, as along the moist places and 

 by the margins of streams, where the fire would be checked, the timber 

 springs up and displaces the herbaceous vegetation and grasses. 



The treeless character of these plains cannot satisfactorily be 

 accounted for by the lacustrine origin and nature of the prairie soils and 

 subsoils. It is said that trees will not naturally grow in this sedimentary, 

 finely comminuted soil and subsoil covering the prairies. Others attempt 

 to explain prairie phenomena by atmospheric and climatic influences 

 marking out certain zones of moisture and dryness by isothermal lines. 



Foster argues that where moisture is equable and abundant, there 

 forest growths take place and reach their grandest development ; where 

 it is unevenly distributed, there we have the grassy plains ; and where 

 it is mostly withheld, there is the sterile desert. Where the ocean 

 breathes its moist atmospheric breath over the land, there forest growths 

 spring up, or green grasses if in less degree, or waste saharas if the 

 moisture of its breathing is taken away. The pampas of South America 

 and the verdureless plains of the West would seem to confirm him in his 

 well-settled conviction. 



Lesquereaux, with force and plausibility, argues that all our prairies 

 originate from causes similar to those which form our peat-bogs and beds, 

 and that they are in fact incipient, dried-out peat-beds, drained while 

 in process of growth and before completed. In his own language he 



