On the Application of Manures, 



233 



During my late tour through the western portions of the Uni- 

 ted States I had frequent opportunities of witnessing the sys- 

 tem adopted by those who first established themselves in a new 

 settlement. 



In these wild regions, unlike to those portions of the globe 

 with which we Europeans are familiar, forest and pasture land 

 are seldom found intermixed, but we meet at one time with vast 

 tracts altogether destitute of timber, and at another with forests 

 taking such entire possession of the soil as to leave no intervals 

 for any sort of culture for many hundreds of miles. 



The former description of country constitutes the prairies, the 

 latter the woodlands, of North America. 



With regard to the former, various theories have been pro- 

 pounded to account for the entire absence of timber over such 

 extensive tracts. 



Monsieur Decandolle offers the following solution: — ''The 

 right of prior occupation," he says,'^ "explains how it happens 

 that forests and prairies are found mutually to exclude each 

 other. For if by any cause a forest is established in a given 

 place, the shade of the trees, together with the greediness with 

 which their roots absorb the nutriment, and the manner in which 

 the fibres of the latter are interlaced, Avill prevent the grasses 

 from shooting up underneath. If, on the contrary, the prairie 

 is first developed, then, even supposing that the ^eeds of the 

 trees do from time to time germinate, yet their roots in the young 

 state cannot easily pierce the close network of roots and stems 

 already existing on the spot, and even if they succeed in doing so, 

 are starved by the voracity of the grass roots, which are more 

 numerous and more developed than their own." 



But still the question occurs, What has given to the forest in 

 the one case, and to the meadow in the other, that prior occu- 

 pancy, to which their power of maintaining entire possession of 

 an extensive tract may perhaps be justly attributed? 



It is probable, I think, that in the climate and latitude alluded 

 to, forests would usurp dominion over the greater portion of the 

 country, if no extraneous cause interfered to arrest them. It is 

 only necessary therefore to explain why large tracts should be 

 found wholly denuded of timber j and this it seems most reason- 

 able to attribute to the practice that prevails amongst the abori- 

 gines of annually setting fire during summer to the plains in or- 

 der the more readily to take deer and other wild game. 



For the extreme dryness which prevails at that season causes 

 a fire, when once kindled, to spread in all directions, until it is 

 either stopped by the intervention of a river or put out by meet- 



Physiologie, vol. iii. 



R 2 



