STABLE AND MIGRATORY PLANT FORMATIONS J45 



In the vegetation of the cHff top, the coastal profile is 

 often of first significance, and besides this, the influence of 

 the chemical and physical relations of the rock forming the 

 cliff, to leaching, water capacity, and drainage, all require 

 attention. 



Alpine crags primarily owe their features to the slow effects 

 of frost, insolation, and gravity, but many of the crags of 

 mountainous regions, including most of those in this country, 

 have been further influenced by glaciation. The late glacia- 

 tion has led to rock exposures in places where frost, insolation, 

 and gravity now only conspire towards their burial, and, on 

 the other hand, has reduced elevated summits where such 

 agents would be most active in erosion to rounded debris- 

 strewn contours. The foremost tendenc}- of these agents is 

 towards obliterating the effects of glacial erosion, eliminating 

 the crags on gently sloping ground and at lower levels, and 

 forwarding the development of those on the steeper contours 

 at high elevations. In the former case, the succession of 

 plant associations has full stabilisation as a goal in sight ; in 

 the latter, only true migratory associations can obtain a 

 footing. In the latter, the true alpine crags, all the associa- 

 tions, lithophytes or chomophytes, hold but temporary 

 habitats liable to destruction by disruption and landslip. 

 As in the case of all crags and steep banks, the more 

 elevated and exposed positions forming the tops and spurs 

 are specially liable to leaching and drought, while the lower 

 parts of the faces and protected crannies obtain the more 

 permanent supply of water and food solutions which descend 

 the surfaces and crevices of the rocks. The former are 

 leached by atmospheric precipitation, rapidly drained, and 

 exposed to insolation and the drying influence of wind, while 

 the latter are more protected from sun and wind, and obtain the 

 food materials and water draining from above. This influence 

 on plant distribution, which may be studied on any roadside 

 wall, extends to lithoph\'tes, chasmophytes, and chomophytes 

 alike, but varies much with the chemical and ph\'sical relations 

 of the rock to leaching. 



In conclusion, it may be said that all rock plant associations 

 are apt to differ according to their relations to leaching, water 

 capacity, flushing, drainage, and exposure to the sun. Alpine 



