30 ALFRED DACHNOWSKI 



gonum sagittatum, Impatiens pallida, Sagittaria sp., and Aspidium 

 thelypteris are the representative undergrowth. 



4. Calamagrostis canadensis association. This type of shore 

 succession, with Phragmites communis on drier parts as a princi- 

 pal component, occupies comparatively large areas in counties 

 along the divide. Cladium mariscoides, Aspidium thelypteris, 

 Hypericum virginicum and Onoclea sensibilis are listed here to 

 give a better idea of the composition and general appearance of 

 this association. The condition of unstable equilibrium which 

 exists is more favorable for Calamagrostis during wet years and 

 more favorable for Phragmites during dry years. 



5. Phragmites communis association. It occurs more typi- 

 cally along the shores of Lake Erie, between the bar sections and 

 the mainland, where it is preceded by Scirpus validus and S. 

 americanus, and Zizania aquatica. In the earlier stages of devel- 

 opment the association includes, as in inland localities, Typha 

 sp.-; Sparganium eurycarpum, Sagittaria heterophylla and others 

 form a secondary layer, alternating and mingling with Carex 

 comosa, C. aquatilis, Juncus ca?iadensis. The Phragmites asso- 

 ciation often succeeds a bog meadow (cranberry-sphagum asso- 

 ciation) in localities where the peat is grounded solid and well 

 drained. 



These various types of associations in the shore succession are 

 often to be seen along the shore of one lake. Correlations with 

 soil conditions are more easily established than with any other 

 one factor. Differences in light and evaporation affect the plants 

 less critically as yet. Competition becomes intenser in the later 

 stages of the succession. Of the several types the Phragmites 

 association indicates the better physical condition of the soil, 

 favorable also for agricultural purposes. 



IV. THE BOG SUCCESSION 



Without change of climate or of mineral salt constituents, 

 the aquatic and marsh vegetation becomes suppressed under 

 certain conditions. Organic processes in the substratum, as 

 they approach the limit of favorable conditions, become of greater 

 importance than variations in light, temperature or evaporation. 



