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INTRODUCTION TO PLANT GEOGRAPHY 



[chap. 



and their restriction to tangled dwarfs in sheltered depressions 

 (Fig. 82, B). In strong dry winds young parts of plants may even 

 become shrivelled and killed in a few hours, and surface soil may 

 become dried out. Such effects may be observed in the warm foehn 



Fig. 82. — Effect of wind on trees. A, deformed outliers of Black Spruce (Picea 

 mariana) near Churchill, Hudson Bay. The pre\ailing winds are from the left. 

 Note in foreground the luxuriant prairie-like tundra of the arctic-subarctic ecotone. 

 The lower branches of such Spruces tend to form a dense layered mat that is well 

 protected from desiccation in winter hy drifted snow, the farthest outliers (on 

 left) often being limited to such growths. Upper branches (on right) ' trail 

 away ' to leeward. B, deciduous broad-leafed and evergreen coniferous tree 

 species forming a dwarfed tangle in sheltered depressions on exposed hill-side on 

 coast near North Berwick, Scotland. The Grasses and other herbs reach the 

 height of the gnarled ' trees ' which scarcely anywhere exceed the level of the sur- 

 rounding terrain. 



