Chap. I] CHARACTERS OF THE ARCTIC CLIMATE 



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At a depth of 08 m. the soil is frozen, except in September. The strongest winds are 

 E. and ESE. ; the greatest average strength of wind is attained by the ESE. in summer 

 with nearly 10 meters per second. 



2. EFFECTS OF THE ARCTIC CLIMATE ON PLANT-LIFE. 



i. SURVEY OF THE CLIMATIC FACTORS. 



The elements of the polar climate that appear effective in influencing 

 plant-life deeply and characteristically, may be grouped together as 

 follows : — 



(1) Continuous light during summer: — Retarding action on growth. 

 Furthering of assimilation, of the formation of pigments and other sub- 

 stances. Effects on the histological structure. 



(2) Loiv temperature of the air during summer : — Inhibitory action on 

 most of the vital processes, specially on the growth of foliaged shoots. 



(3) Low temperature of the soil during summer : — Inhibitory action on 

 the growth of subterranean members. Retarded absorption of water by the 

 roots, and hence effects similar to those induced by dryness of the soil : — ■ 

 inhibition of the growth of foliaged shoots, promoted formation of sexual 

 organs, danger of desiccation. 



(4) Heating by insolation : — Temporary removal of the action of the low 

 temperatures of air and soil. 



(5) Dry winds in winter: — Danger of desiccation, effects similar to those 

 under (3). 



(6) Shortness of the warm season : — Acceleration of periodic phenomena. 

 Dangers to the ripening of seed. Limitation of the growth in thickness 

 of axes. 



It is at present impossible to assign to each of the above-mentioned 

 factors its part in the characteristic features exhibited by plant-life in 

 arctic countries, yet, owing to Kjellman's and Kihlman's researches, the 

 first steps have been taken in this direction. 



