CHAPTER LV. 



PLANT SOCIETIES OF ROCKY AREAS, MEADOWS, 

 AND MARSHES. 



I. Vegetation of Rocky Places and New Land. 



1093. Most of the convenient opportunities for the study of 

 the vegetation of rocky places are in the later stages of the forma- 

 tion. We rarely have an opportunity to see the beginning and 

 to watch the development for several years. Nevertheless rock 

 slides occur where areas of bare rock are exposed, or falling rock 

 at the base of a cliff may form a recent talus, or the river or 

 stream at flood may wash the soil from a rocky area, or may 

 pile rocks along the shore, leaving a rock area small or large 

 exposed and entirely devoid of soil or vegetation. These places 

 should be sought out and observed from time to time. In lieu 

 of these opportunities one can observe rocky places where the 

 plant formation represents different stages in its evolution. On 

 rocky shores, whether of the precipitous bluff type, or sloping rock, 

 smooth or creviced, of large or small boulders, the plant formations 

 are often modified greatly by the proximity to water, in comparison 

 with those of the interior; for example, the effect of surf action 

 or spray. The most striking difference is perhaps seen in the 

 tendency to a zonal arrangement of formations on the gradual 

 slopes, whether on seashore, lake, or river, but on the irregular 

 surface-rock shore the distribution is azonal. 



1094. Open formations in rocky places. First, rock lichens 

 and algae grow on the bare rock. If there are no crevices in 



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