164 PLANTS MODIFIED BY THEIR SURROUNDINGS 



little light during the short days of the long winter, and a slight 

 amount of moisture all act upon the vegetation of the arctic region, 

 tending toward very slow growth and dwarfed and stunted form. 



Polar limit of trees, northern Russia. All these trees are full grown, and most of 

 them are almost one hundred years old. 



Vegetation of the Tropics. A rank and luxuriant growth is 

 found in tropical countries with a uniformly high temperature and 



large rainfall. In 

 general it may be 

 estimated that the 

 Region of Lichens. rainfall in such 



countries is at 

 least twice as 

 great as that of 



Limit of ordinary large trees. New York state, 



Regions of the vine. and in many cases 



Region of Tree-ferns. three to four timeS 



as great. An 

 abundant water 



Plant regions in a tropical mountain. Explain the diagram, supply, together 



Shrubby Region. ' 

 Limit of Cinchona trees. 



