conditions has brought about a corresponding succession of 

 plant societies, a thing which must inevitably follow. This 

 succession may of course be either progressive or retrogres- 

 sive. Hence we have a continual readjustment of plant 

 societies. Considered geologically all this movement has 

 its temporary end, the pene plain for the land, the climax 

 mesophytic forest for the plant society. I say temporary 

 end, for epeirogenic or orogenic movements would rejuvenate 

 the physiography and bring about a readjustment of the plant 

 societies and inaugurate the redevelopment of the climax forest. 

 It is evident then that the stage in the plant cycle at any one 

 period is directly dependent upon the then existing physiographic 

 stage. 



The purely geological phase of this factor must not be neg- 

 lected. If we speak of the physiographic factor in terms of 

 years, so must we speak of the geological in centuries, embracing 

 vast periods of time. It is in the latter phase of this historical 

 factor that we have found the origin of the Ktaadn flora. 



Having discussed the various factors instrumental in the deter- 

 mination of the plant aspect of the mountain, we may now take 

 up in detail the study of the many plant societies which give it 

 its characteristic tone. But as we pass to this treatment let us 

 have clearly in mind that it is to the interaction of these complex 

 climatic, edaphic, biotic and historical factors that the mountain 

 presents its varied plant physiognomy. ' 



VI. THE PLANT SOCIETIES. 



The study of the historical factor and the origin of the Ktaadn 

 flora showed that the life of the plant covering of Ktaadn has 

 been one of progressive dynamics. Further, the plant societies, 

 as they are seen there to-day, represent the various and successive 

 steps of this horizontal development. For any one place, how- 

 ever, the story has been one of vertical succession. So by the 

 one the other may be interpreted. It is the object of this section 

 of the paper to trace the genetic development of these plant 

 societies in so far as it is possible. 



A. ROCK SOCIETIES. 



In the discussion of the physiography of the mountain 



29 



