218 ILLINOIS ACADEMY OF SCIENCE 



the island, all of the trees were small, probably averaging 

 about four inches in diameter. Fraxinus nigra has 

 developed as coppice, and Qucrcus hicolor occurs as a 

 small tree. These were the three dominant tree species 

 comprising the hydro-mesophytic association. Quercus 

 eUipsoidalis was the dominant tree of the more meso- 

 phytic portion of the island. The pioneer xerophyte, 

 Pyrus coronaria, was the most abundant member of the 

 trees in the lower stratum. The extremely dense under- 

 growth is comprised largel}^ of the trees of the lower 

 stratum, and vines. The latter were represented by all of 

 the different species noted in the plant list for the 

 hydrarch mesophytic association. The herbaceous under- 

 growth indicated a high degree of mesophytism. 



The island in N. T. 1, 8 presented an entirely different 

 aspect from the one in N. T. 1, 23 and 26. It was elevated 

 somewhat higher above the Skokie than the one just de- 

 scribed. The cutting here had evidently been more severe, 

 because there were no large trees on the entire island. The 

 dominant vegetation was shrubs. These formed almost a 

 l)ure stand, entirely excluding trees from the northern 

 end of the island. Rhus tyjyhina ^and Rhus glabra occu- 

 pied a narrow zone to the north and west end of the island. 

 The remainder of the island was covered with a thicket of 

 Coryliis americana and HamameUs virginiana about 12 

 feet in height which was almost impenetrable. Of these 

 two Corylus americana was the most abundant. Shrubs 

 fewer in number and importance found near the edge of 

 this mass were Rosa (sp.), Ruhus occidental is and Physo- 

 carpus opulifolius. The tree species listed were Quercus 

 ellipsoidaUs, Quercus rubra, Quercus macrocarpa, Quer- 

 cus alba, Carya ovata, Populus tremuloides, Populus 

 grandidentata, Prunus serotina, Crategus (sp.), and 

 Pyrus coronaria. Qucrcus alba, Carya ovata, and Pyrus 

 coronaria were the most abundant trees. 



In comparing the two islands it is to be noted that the 

 more severe cutting and the slightly higher elevation of 

 the land in N. T. 1, 8 has evidently been the cause of the 

 development of a more xerophytic vegetation than that 

 found in N. T. 1, 23 and 26. Severe cutting would mean a 

 very marked retrogression in the development of the for- 

 est succession, which is best illustrated in the appearance 

 of xerophytic shrubs as the pioneer vegetation. Higher 



