98 IOWA ACADEMY OF SCIENCES. 



Prof. Lesquereux carries the idea of suitability of soil a little 

 farther. He traces all prairies to old time lakes; declares 

 that prairie soil is "neither peat nor humus, but a soft, black 

 mould, impregnated with a large proporton of ulmic acid, pro- 

 duced by the slow decompo>itic;n, mostly under water, of 

 aquatic plants, and thus partaking as much of the nature of peat 

 as of that of true humus." * * * "It is easy to understand," 

 he says, "why trees cannot grow on such kind of ground. The 

 germination of seeds needs free oxygen for its development, 

 and the trees, especially in their youth, absorb, by their roots, 

 a great amount of air, and demand a solid point of attachment 

 to fix themselves, etc." That is, the reason why our prairies are 

 treeless is that they are too wet. and they contain, in virtue of 

 their origin, certain elements to trees inimical. Professor 

 Whitney also finds explanation of our prairies in the nature of 

 the soil, "as the prioie cause of the absence of forests and the 

 predominance of grasses over this widely extended region. 

 And although chemical composition may not be without 

 influence in bringing about this result, * * * yet we con- 

 ceive that the extreme fineness of the particles of which the 

 prairie soil is composed is probably the principal reason why 

 it is better adapted to the growth of its peculiar vegetation than 

 to the development of forests." 



Whitney makes also another very suggestive statement, the 

 importance of which he did not himself realize. He says: 

 "Wherever there has been a variation from the usual condi- 

 tions of soil on the prairie or in the river bottom there is a cor- 

 responding change :'n the character of the vegetation. Thus 

 on the prairie we sometimes meet with ridges of coarse 

 material, apparently deposits of drift, on which from some local 

 cause there has never been an accumulation of fine sediment; 

 in such localities we invariably find a growth of timber. This 

 is the origin of the groves scattered over the prairies for whose 

 isolated circumstances and peculiarities of growth, we are 

 unable to account in any other way." 



It is interesting to notice the emphasis which Whitney here 

 places on the character of this soil. No doubt there is some- 

 thing about prairie soils which makes them different from all 

 other soils with which we are acquainted, and no doubt diifer- 

 ence in soils is responsible for the difference in the forms of 

 vegetation which they carry, but while both these excellent 

 students, Lesquereux and Whitney, came in their surmises 



