173 



Antennaria plantaginifolia Lespedeza Nuttallii 



Aster linariifolius Liatris scariosa 



Aster patens Poa pratensis 



Carex pennsylvanica Pteris aquilina 



Cerastium arvense Pycnanthemiim virgmianiim 



Comandra umbellata Sericocarpiis asteroides 



Helianthus divaricatus Solidago nemoralis 



Lespedeza capitata Viola pedata 



Up to this point in the succession herbaceous plants have pre- 

 dominated. But some shrubs usually appear in the crevice 

 stage (fig. i) and by the time the rock has become sod-covered 

 they may have increased in number to such a degree as to become 

 the controlling element of the vegetation. Very often it is 

 possible to recognize a distinct shrub stage. Of the shrubs 

 present at this time, a number may be cited as about equally 

 characteristic, viz. 



Ceanothus americanus Rhus copallina 



Gaylussacia baccata Rhus glabra 



Myrica asplenifolia Rhus hirta 



Prunus virginiana Rosa humilis 



Quercus ilicifolia Vaccinium pennsylvanicum 



Quercus prinoides Vaccinium vacillans 



The next advance toward mesophytism is seen in the advent 

 of trees. Like the shrubs, trees begin to appear early in the 

 series, and their presence often exerts an appreciable effect on 

 the character of the rock face and crevice vegetation. Poly- 

 podium vulgare, for example, grows in crevices beneath the shelter 

 of these scattered trees, but almost never out in the open. Many 

 mosses are likewise restricted. Succession invariably is more 

 rapid in the shade than in the open sunlight. Foremost in 

 importance among the pioneer trees in the trap ridge succession 

 near New Haven are the red cedar {Juniperus virginiana) and 

 the post oak {Quercus stellata). The transition from the shrub 

 stage to the pioneer tree stage is not abrupt, and, as a matter of 

 fact, so simultaneously may the shrubs and trees make their 

 appearance that quite as often as not the stages are telescoped 



