i 9 2o] TAYLOR— SUCCESSION OF MOSSES 473 



with some Hypnaceae as the third vertical layer. An especially 

 good example of this was found on a low rock situated on a hill- 

 side in an open pasture, and at some distance from the stream. The 

 top of the rock sloped a little in the downhill direction and was 

 slightly lower than the ground at the upper edge, but was perhaps 

 2 feet above the ground at the lower side. Numerous bushes 

 overhung the upper border, but the lower part was exposed to 

 full sunlight. On the shaded vertical face was a small quantity of 

 a liverwort and an extensive growth of crustose lichens. The 

 liverwort did not grow over the edge at the top, but the crustose 

 lichens which had spread over much of the upper surface were 

 being overgrown by foliose lichens. Growing among and over 

 these was Grimmia apocarpa. Overlying the edge of the Grim- 

 mia and in many places entirely covering it was Bryum argenteum, 

 forming a thick compact mat over a large part of the remainder of 

 the rock, except at the upper side where soil had washed over the 

 surface from the ground in contact with it above. Here Br achy - 

 thecium acuminatum, growing partly on the soil, was extending out 

 over the Bryum, forming a third moss layer. Small patches of 

 lichens and of Grimmia here and there indicated that these at one 

 time had been pioneer plants over the entire surface. When the 

 two more mesophytic species came in, they had developed more 

 rapidly on the part of the rock which received the most moisture 

 from the ground and which was also somewhat shaded by over- 

 hanging bushes. 



In shaded places along the creek in the ravine proper several 

 species of Anomodon form the moss stage following the pioneers. 

 As would be expected, the change in species occurs more rapidly 

 in spite of the slope of the rock, which more nearly approaches the 

 perpendicular. In some places the cliffs are quite closely covered 

 with Juniper us virginiana and deciduous trees and shrubs. Under 

 these and often overhanging, the edge of the cliff is an undergrowth 

 of Taxus canadensis, reminding one of the Juniperus communis 

 under the pines in the dune region, except for the greater meso- 

 phytism which is indicated by the herbaceous flora. On vertical 

 rock faces, well shaded and with water dripping over the surface, 

 a luxuriant mass of Anomodon viticulosus is the only common 



