14 THE PLANT SOCIETIES OF 



From this time on the slopes become reduced and the ravine widens 

 more than it deepens, by reason of lateral cutting, landslide action, 

 and side gullies. After a time a sufficient stability is reached to per- 

 mit a considerable growth of. vegetation. If the erosion is slight 

 enough to allow a vegetation carpet to develop, a high degree of 



Fig. 1.— Embryonic ravine in the lake bluff at Glencoe. Entire absence of vegetation on the 

 unstable clay slopes, with the exception of shrubs and grasses that have slid down from the top. 



luxuriance may be attained. In fact, ravine conditions are usually 

 extremely favorable for plants, after the initial stages have passed. In 

 a comparatively few years the vegetation leaps, as it were, by bounds 

 through the herbaceous and shrubby stages into a mesophytic forest, 

 and that, too, a maple forest, the highest type found in our region. 

 Nothing shows so well as this the brief period necessary for a vegeta- 

 tion cycle in a favored situation as compared with an erosion cycle. 



Of such interest are the facts just noted that it is worth while to 

 mention some of the characteristic ravine plants. Perhaps the most 

 characteristic trees of the Glencoe ravines are the basswood {Tilia 

 Americana) and the sugar maple (Acer saccharinuni) , though the ash, 

 elm, and other trees are frequent. The most characteristic under- 



