344 



time, very little has been accomplished. The most widely distributed 

 is the oak-hickoi"y association, in which the following species are 

 the most important: bur oak {Qiiercus macrocarpa) , red oak (Quer- 

 cus rubra), white oak (Querciis alba), shell-bark hickory {Carya 

 ovata), Carya cordiformis, and Jiiglans nigra, together with many 

 secondary species. It is an association of essentially loamy or clayey 

 soil, and does not readily invade the sandy areas. On moister 

 ground occurs a more mesophytic association of trees, the Uhmis- 

 Acer association, whose characteristic species are elm {Ulrniis aiiieri- 

 cana), soit maple (Acer saccharinuui), basswood {Tilia americana), 

 and white ash (Fra.vinus americana). This in turn is succeeded by 

 the climax association of this region, the sugar maple (Acer sac- 

 chanim) association, which at the present time is in the infancy of 

 its development in northeastern Illinois. 



The following cross-sections, or transects, taken in the southern 

 part of the region, will aid in the understanding of the region. The 

 sections were obtained by listing the changes in the associations, while 

 walking across the area from east to west. 



SECTION OF THE ASSOCIATIONS OE THE BEACH AREA MADE AEONG THE 

 LINE OF THE WAUKEGAN SEWER, AUGUST, I909 



1. Lake Michigan. 



2. Open sand of lower beach. 



3. Beach pool with Clilaniydonionas and Oscillatoria. 



4. Open sand. 



5. Cakile-Xanthiiini association on the middle beach. 



6. Sali.r syrticola dune. 



7. Potentilla anserina association. 



8. Salix syrticola dune with a little Calaniovilfa. 



9. Andropogon scoparius bunch-grass prairie. 



10. Popnlus-Salix dune, o.i to 0.4 meter high. 



11. Calaniovilfa growing on the edge of bunch-grass prairie. 



12. Andropogon scoparius bunch-grass prairie. 



13. Calaniovilfa ridge. 



14. Bunch-grass prairie with a few very low Calamovilfa ridges. 



15. Potentilla fruticosa association. 



16. A thicket of Salix. 



17. A swale. 



18. Popidus-Salix ridge. 



19. Heath. 



20. Heath with blowouts and a little Calamoz'ilfa. 



21. Scirpns aniericanus association. 



