2 74 George E. Nichols, 



September 8 (30°), eighteen days earlier than at the Ingonish 

 station (September 26: 31°). There is little doubt that on the 

 plateau, during some seasons, the temperature falls below freez- 

 ing during every month of the year. And not only are the daily 

 minimum temperatures here during the growing season lower 

 than in the lowland, but the growing season is considerably 

 (probably from six weeks to two months) shorter here than 

 there. 



Precipitation, Evaporation and Wind. — No exact observations 

 have been made regarding precipitation on the plateau, but 

 from the writer's experience and from numerous inquiries it 

 can be stated with certainty that during summer the rainfall is 

 somewhat heavier here than along the coast. The evaporating 

 power of the air in clear weather, at least during the summer, is 

 apparently greater than along the coast. This observation is 

 deduced from atmometer readings, taken for the brief period 

 of three and a half clear days in August, when an instrument on 

 the barrens indicated a daily evaporation rate of 28.4 cc, as 

 '^ompared with 22.6 cc. near the shore at Ingonish. But, on the 

 whole, the humidity of the atmosphere is greater on the plateau 

 than on the lowland. This is due to the prevalence here of 

 fogs. During dull weather the clouds hang low, covering the 

 slopes and summits of the mountains above an elevation of seven 

 or eight hundred feet, sometimes for days at a time. Even 

 though it may not actually rain, everything is saturated with 

 moisture. The higher rate of evaporation during clear weather 

 is correlated with the heavy winds which sweep across the 

 plateau at all seasons. So effective are these that a wet, spongy 

 bed of cladonias may become dry and brittle within a few hours. 

 The effect of wind on the vegetation, as seen in the barrens, 

 is even more pronounced in winter than during the growing 

 season. This will be discussed later in connection with the vege- 

 tation of the barrens. 



VI. ECOLOGICAL CLASSIFICATION OF MATERIAL; 

 NOMENCLATURE 



The ecological classification adopted in the present paper has 

 already been described in considerable detail elsewhere (Nichols 

 '17), and need be only briefly outlined here. The fundamental 

 unit of vegetation from the standpoint of physiographic ecology 



