RELATION TO ENVIRONMENT. 



which favors, 4th, strong solar radiation, and 5th, strong radia- 

 tion from the ground bringing about great changes in tempera- 

 ture between night and day; 6th, the high winds; ;th, alter- 

 nation of night and day, there not being the continuous lighting 

 present in polar lands, and 8th, alternation of heat and cold 

 during the growing season, again very different from the arctic 

 summer. 



1074. Characters of alpine vegetation. The characteristic 

 alpine vegetation lies above the limit of tree growth, which often 



Fig. 518. 



Perennial rosette plant, dandelion. P, lowland culture; M, alpine culture pro- 

 portionately same size, but showing difference in length of stem, leaves, and the larger 

 root of alpine plant. (After Bonnier. ) 



forms a very distinct line on the mountainside. The vegeta- 

 tion forms are similar to those of the arctic zone: the stems are 

 short, the leaves smaller, forming rosettes near the ground, or 

 scale- or needle-like and adpressed close to the stems. The 

 leaves are also thicker, often protected with a thick cuticle or by 

 a covering of hairs, and the structure of leaves and stems is 

 xerophile. The roots are usually much more strongly devel- 



