PAPERS ON BOTANY 235 



is wanting. Old residents of Evauston state tliat at one 

 time the ridges were covered with a hea\'^' forest in which 

 the white oak was much more common and that lumber- 

 ing was the first industry along the Xorth Shore. The 

 white oak, being excellent for building purposes, would 

 be the first removed. Also the artificial conditions, due 

 to the opening of the forest and draining, might destroy 

 some species. Dr. Heminway (8) mentions this as one 

 cause of the dying of the forest trees. 



DISCUSSIOX 



The distribution of the forest associations is appar- 

 ently closely related to soil and drainage conditions al- 

 though other factors may enter in. The mesophytic up- 

 land forest requires a rich but fairly well-drained soil. 

 Such a condition can only be found in this region on the 

 moraine uplands and on them the forest is fully devel- 

 oped. Along the edge of the bluff where the exposure 

 is greater and the conditions more xerophytic the red 

 oaks increase in number and a few scattered birches 

 (Betula alba), red and white cedars (Juniperus virgini- 

 ana) and white pines (Pinus strobus) are to be found. 

 The red cedars and birches appear to be natural but 

 the Thuja occidentalis and Pinus strobus may have been 

 introduced. Xo individuals whose presence naturally 

 was absolutely certain were seen though Mr. Atwell (1) 

 states that some white pines still remain from the old 

 forest. 



Where the soil is rather course and well-drained, as 

 on the crests and slopes of the ridges the xerophytic for- 

 est reaches its highest development. The red oaks are 

 on the whole the predominating species, but at the end 

 of Pine Street, Winnetka, near the lake, is a patch con- 

 sisting chiefly of bur oaks (Q. macrocarpa). There is no 

 apparent reason for this, but Cowles (5) says the bur 

 oak appears to be more abundant on the lower and less 

 drained ridges. The difference in elevation in this case, 

 however, is inappreciable. 



The swamp forest is found on the lowland clay where 

 the drainage is very poor. Its composition apparently 



