Distribution of Plants in Nature 



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comes a " timber line/' beyond which only low-growing plants 

 related to those of the frigid realm occur ; the summits may be 

 clothed in snow and ice. Increasing altitudes bring about the 

 development of vegetation similar to, or corresponding to, the 

 vegetation of higher latitudes. 



Summary. A study of vegetation shows that the plants are 

 naturally grouped into plant associations. The plant associa- 

 tions of any uniform climatic region are essentially similar and 

 may be grouped into climatic plant formations. Climatic plant 

 formations in turn are conveniently grouped into plant realms 

 characterized by torrid, temperate, and frigid climates. 



