PLANT ASSOCIATIONS OF WESTERN PENNSYLVANIA 143 



the same in chemical composition. Except in the more exposed 

 situations, it bears an assemblage of forms which displays a 

 high degree of mesophytism. When such talus deposits come 

 upon exposed points, the water table is lowered, and they bear a 

 flora adapted to dry situations, including with other forms 

 Rhododendron maximum, Kalmia latifolia, Melilotus alba, Eqiiise- 

 tum arvense, Aster Shortii, Aster Drummondii, Aster oblongifolius, 

 Vaccinium pennsylvanicum, Qiiercus velutina, Quercus alba, 

 Clematis virginiana, Pteris aquilina, etc. 



When the talus occurs in protected positions, it is usually well 

 supplied with moisture which enters from the layers of stone and 

 shale above. This environment is well adapted to sustain a 

 dense stand, and under such favorable conditions the vegetation 

 is luxuriant. Rhododendron and Kalmia develop profusely here, 

 occupying especially the rocky portions of the talus near the 

 river banks. Other conspicuous members include Tilia, Mag- 

 nolia, Acer rubrum, Acer saccharinu7n, Betula lenta, Betula liitea, 

 Quercus alba, Quercus rubra, Fraxinus americana, Tsuga cana- 

 densis, Juglans nigra, Prunus serotina, Sambucus racemosa, 

 Ribes Cynosbati, Aralia racemosa, Aspidium margiyiale, Aspidium 

 spinulosum, Asplenium Filix-foemina, Tiarella cordifoUa, Aris- 

 cema triphyllurn, Habenaria orbiculata, Habenaria Hookeri, 

 Osmorhiza longistylis, Gaultheria procumbens, Cypripedium acaide, 

 Trillium undulatum, Vitis vulpina, Psedera quinquefolia, Rhus 

 toxicodendron, Smilax hispida, Liriodendron tulipifera, Poly- 

 stichum acrostichoides, etc. 



One noticeable feature associated with the talus, is the pro- 

 lific development of the lianas. They reach their strongest 

 development on the talus and frequently, when exposed cliffs 

 appear above, clamber up the surface, or more commonly de- 

 scend from above and by developing a shade upon the cliffs aid 

 greatly in retaining moisture, so that the crevice species are 

 better enabled to retain their position. A second feature char- 

 acteristic of the rocky river slopes is the abundance of Rhodo- 

 dendron and Kalmia. 



Not uncommonly the river bluff is of a different nature from 

 that already described. Steep slopes may occur where sand- 



