146 



PLANT SOCIOLOGY 



The extremes are quite remarkable. For example, at Sonnblick, 

 the mean for one hour was 38.1 m. per second; on the Santis the ane- 

 mometer registered on Jan. 27, 1890, a daily mean of 32.3 m. per second, 

 with a velocity between 1 and 2 p. m. of 46.1 m. per second. The 

 maximum in Zurich during 1890-1900 was 24 m. per second. Such 

 winds can snap off or uproot a whole stand of trees and tear off slabs of 

 rock from frozen ground and whirl them aloft (Braun-Blanquet, 1913, 

 p. 53). 



Winds act mechanically by their pressure and physiologically by 

 increasing evaporation, i.e., water loss. Continuity of wind action is 

 the factor that most affects the form of vegetation. 



Fig. 81. — Wind form of trees. Cup>'pssus macrocarpa delormed by ocean winds, 



Pacific Coast, California. 



Mechanical Effects of Continuous Winds. — Winds effect the polli- 

 nation of anemophilous plants and facilitate the distribution and migra- 

 tion of many plants by increasing the range of dissemination of seeds. 

 Transport of wind-blown seeds over distances of 10 to 20 km. is not 

 unusual. Seeds of Picea, Pinus silvestris, Larix, Alnus viridis, and 

 Acer pseudoplatafius have been collected on snow fields far above their 

 last outposts and 10 to 15 km. from the nearest seed-bearing trees. 



more important contributions are those of Klinge (1890), Vogler (1901), Friih 

 (1903), Warming (1902-1903), Buchenau (1903), Hansen (1904), Kraus (1910), 

 Skottsberg (1916), Th. C. E. Fries (1913), Braun-BIanquet (1913-1915), Szym- 

 kiewicz (1924), Flaiiault (1925), and Haumau (1927); 



