396 



INTRODUCTION TO PLANT GEOGRAPHY 



[chap. 



narrow cracks or troughs that afford shelter for plants which in the 

 Far North often grow better in such microhabitats than in surround- 

 ing areas. 



On steep slopes and below weathering crags, still more dynamic 

 and often poorly vegetated ' screes ' are common. Also often con- 

 stituting barrens of one sort or another are ' raised beaches ' near 

 sea-shores ; for although some are well vegetated, many others are 

 the reverse, owing to exposure, recent emergence, or an unfavourable 





*«.-»«3CS8rr- 



FlG. 1 20. — ' Polygons ' in northernmost Spitsbergen. The stony intervening 

 tracts are here almost barren, but often in other instances are covered with 



vegetation. 



substratum. Altogether these poorer types of vegetation — or ter- 

 rain, for often plants are scarcely at all in evidence — are so numerous 

 and variable in the Arctic that only a few examples can be mentioned 

 here. 



In low-arctic regions fell-fields, barrens, and the like, are found 

 chiefly in upland districts and in exposed areas near the coast — 

 especially where the substratum is of porous material. Here, owing 

 to lack of stability, to local aridity, or to extreme exposure, such 

 fell-field or ' half-barren ' areas as that shown in Fig. 121 occur, 

 in which Mountain Avens, Nard Sedge, and various tufted Saxifrages 

 and other herbs form irregular patches of vegetation. A fair number 

 of cryptogams are often admixed, though usually they are of poor 



