74 The Plant World. 



The Sand Deposits of Illinois. — Gleason has published a 

 report * of work on several areas in northen Illinois which are 

 characterized by sandy soil derived from glacial outwash. The 

 areas are mainly xerophilous prairies of Andropogon scoparius, 

 A. furcatus, Lepioloma cognatum, Panicum pseudo-pubescens and 

 Koeleria cristata, with numerous "blow -outs" of nearly bare 

 soil. Along the streams, or extending onto the upland, are belts 

 of forest of Quercus velutina or (juercus macrocarpa. A number 

 of associations are recognized and the successions are described 

 through which the blow-outs and grassland become forested. 



Northern Illinois lies in the transition zone between the 

 deciduous forest region and the prairies of the central states, 

 and just south of the northern coniferous forest region. The 

 author recognizes a successional series for each of these regions 

 and indicates that the vegetational activities of the area he has 

 studied comprise the several successions of the three adjacent 

 regions and also successions in which the deciduous forest series 

 is encroaching on the grassland series; each stage of the grassland 

 series being encroached upon by a corresponding stage of the 

 forest region series. 



Gleason lays emphasis on the importance of the "reaction" 

 of the vegetation upon the habitat as being responsible for the 

 successional phenomena observed, saying: "The plant itself is 

 in manv cases the controlhng agent in the environment." It is 

 of course true of sandy soils, wherever found, that the existence 

 of plants serves to fix them and to increase their organic matter 

 in a manner directly and indirectly favorable to plants of greater 

 water requirement. It is well enough to know what are the 

 effects of plants themselves on the physical environment, but it 

 should be borne in mind that features of the environment which 

 are determined by the existence of associated or precedent plants 

 are, after all, physical in their nature and in no wise different 

 from physical factors of different origin. It can not be true that 

 "undue emphasis on the environment may lead to a partial 

 neglect of the most important feature of a region, the vegetation." 

 No ecologist whose work is known to the reviewer has yet given 

 too much attention to the environment. 



Gleason says "the chief difficulty in separating associations 

 lies in the idea of the association itself, which has never been ex- 



♦Gleason, H. A., The Vegetation of the Inland Sand Deposits of Illinois. Bull. 111. State 

 Lab. of Nat. Hist., 9, 21-174, 20 pis. 1910. 



