

468 , BOTANICAL GAZETTE [june 



What is probably the ultimate forest of the region and the 

 climax of the morainic series, the beech-maple type, is seen at 

 Otis and Smith, Indiana. No mosses except Catharinea have been 

 found in these forests in any place except on decayed wood or in 

 water holes. In ravines in the Otis woods where humidity is 

 higher (figs, i, 2) mosses are a little more common, not growing on 

 the ground, but on sticks, stumps, or bases of trees. These are 

 almost invariably some species of Hypnaceae. 



Of the three leading causal factors mentioned for the sand 

 association, water erosion may be substituted for wind erosion 

 and covering. As long as very active denudation continues on a 

 lake bluff or ravine slope, resulting either in a gradual wearing 

 down of the surface or in slumping, mosses have no chance to be- 

 come established. While evaporation on the bare slope may be 

 excessive, neither that nor competition with other plants is the 



1 



primary factor. In the later stages, however, these become the 

 two determining conditions. Wherever the arbor vitae and 

 juniper are present we have a repetition of approximately the same 

 conditions as under the pines and juniper on the dunes. The 

 arbor vitae is near its southern limit at Glencoe and does not 



1 



form a thick cover, and for this reason has less influence as a shade 

 producer than has the pine. On the other hand, the juniper 

 may be just as dense and as effective in producing shade and in 

 retaining moisture as in the former situation. 



Ulrich (12) has made a study similar to that by Fuller in the 

 ravines at Glencoe. Three stations were used which correspond 

 roughly to the three elevations on the ravine slope just described, 

 and the results justify the supposition that evaporation is the 

 main cause of such a difference. The station near the top in what 

 would correspond to the Polytrichum area showed the highest rate 

 of evaporation; that on the middle of the slope or the region of 

 mixed mesophytic mosses gave a lower rate; that at the bottom 

 or the area of Hypnaceae gave a still lower rate during a part of 

 the season, although at times it was slightly in excess of that mid- 

 way up the slope. This is exactly what we would expect from 

 the nature of the species present and a comparison of the conditions 

 in other regions where they are found. Competition with other 



