VEGETATION OF CONGLOMERATE ROCKS 389 



the moss stages the number of herbaceous plants steadily 

 increases. 



On north slopes, after a short succession with numerous in- 

 stances of telescoping, and on east and west slopes, after a much 

 longer and more complete succession, the most advance her- 

 baceous stage of the rock succession is reached. This is a meso- 

 phytic closed association dominated by walking fern, CaMpto- 

 sorus rhizophyllus (fig. 3). Where best developed, this fern 

 grows in dense tangled masses in a moss mat composed of the 

 mosses of the second or Mnium moss stage. With the walking 

 ferns are a large variety of other herbs, most characteristic of 

 which are Mitella diphylla and Cystopteris bulbifera. Other 

 plants of the association are maidenhair fern {Adiantum peda- 

 tum), great chickweed {Stellaria pubera), rue anemone {Anemo- 

 nella thalictroides) ,Corydalis fiavula, Carda?nine Douglassii, Dutch- 

 man's breeches {Dicentra Cucullaria) tall bellflower {Campanula 

 americana), and a number of the plants of the preceding stage. 



4. Shrub stages. On shelves, on the upper surface of the 

 rocks, and in large pockets wherever several inches of soil have 

 accumulated, are a number of shrubs — bladder nut {Staphylea 

 trifolia), gooseberry {Ribes gracile), fragrant sumac (Rhus cana- 

 densis), nine-bark {Physocarpus opidif alius), and poison ivy 

 {Rhus Toxicodendron) in dry parts, and wild hydrangea {Hy- 

 drangea arborescens) in damp places. In only a few rock areas, 

 the shrubby plants form definite communities with a well es- 

 tablished place in the rock succession. A shrub stage when 

 represented, may follow either of the closed herbaceous associa- 

 tions. The shrubs of dryer parts of the rocks, only one or two 

 of which are usually represented in any one rock area, follow 

 the Sedum association (fig. 1). The hydrangea shrub stage is 

 seen only in very moist places, and follows some phase of the 

 mesophytic closed herbaceous association. 



Transition to surroundiiig forest. Only on the tops of the 

 rocks, where the accumulated soil is relatively deep, does the 

 vegetation show any transition to that of the surrounding hill- 

 sides. Herbaceous plants of the hillsides, and occasional sap- 

 lings, grow in the deep soil on the rocks. But the covering of the 



