throughout the year and its accentuated value during the resting 

 period produces a condition very precarious to plant life. 



* TABLE III-WIND VELOCITY IN MILES PER HOUR. 



* Data from Mt. Washington. 



It is not surprising in view of this great desiccation and high 

 transpiration ratio, to find that alpine plants have suffered adap- 

 tive modifications which tend to mitigate these harmful 

 effects. The excessive development of cutin in epidermal layers, 

 producing the sclerophyll type of leaf, high development of the 

 tomentose character in several species, absence of dorsal 

 stomata, reduction in the number of ventral stomata, the reduc- 

 tion in number and size of transpiring surfaces, and the 

 cespitose habit of growth are all evidences of protective adapta- 

 tions and adaptations without which this mountain flora would 

 be unable to withstand the adverse conditions of its environment. 



B. EDAPHIC FACTORS. 



'Soil factors operate upon plants, not through the atmosphere 

 but through the substratum in which they live. The soil being 

 an anchorage as well as a source of food materials, its import- 

 ance becomes at once very apparent. Schimper has considered 

 the influence of soil and its properties so significant in the deter- 

 mination of the local distribution of plant societies that he has 

 designated those societies so determined edaphic formations and 

 the soil and its properties edaphic factors. 



