to soon reach the underlying granite, permits a rapid drainage. 

 The thick Alpine-Tundra topographical irregularities, and many 

 adaptations for water retention in the lichens and mosses how- 

 ever raise this retention ratio. Yet, all in all, it is the frequency 

 of precipitation rather than amount that determines the meso- 

 phytic effect. 



c. BIOTIC FACTORS. 



A general survey of the plant world convinces us of an 

 internal and mortal combat. We see from purely physical 

 reasons that no two plants can occupy identical soil at the 

 same time. From this necessarily arises a struggle for 

 supremacy of position leading to a more favorable life relation. 

 This struggle for existence is threefold. It may take place 

 between individuals of the same species, between individuals of 

 different species, and thirdly between plant societies. The line 

 along which two societies meet is pronouncedly that of great- 

 est aggression and struggle. It is along this tension line that 

 the ecologist finds his most interesting study. For it is here, 

 above all other places, that he may analyze the influencing fac- 

 tors and study the encroachment of one society upon another. 

 Where the conditions for life are most favorable, the struggle 

 of society with society, species with species, and individual with 

 individual is the most severe and the tension line becomes the 

 battlefield of mortal combat. 



The influence of animals upon the plant life here is at a mini- 

 mum. The absence of man and the slight effect of the winter 

 grazing of droves of caribou, which come from the north to feed 

 upon the lichens and heaths laid bare upon the higher slopes, 

 leaves the flora of the mountain in a delightfully primeval state. 



D. THE HISTORICAL FACTOR. 



This factor deals with and involves a question of time. Hence 

 it gives us a conception of movement and of change, for we 

 recognize that our world is not one of statics but of dynamics. 

 Nothing is fixed; all is movement. There is a continual and 

 progressive change in the physiography of any region, a 

 destructive and constructive cycle, tearing down there, building 

 here. This progressive introduction of new physiographical 



