CHAPTER XXV 

 BOTANICAL GEOGRAPHY 



395. Regions of Vegetation. The earth's surface (that 

 of the land) has been described by one of the greatest of 

 geographical botanists 1 as divided into twenty-four regions 

 of vegetation. This classification takes account of all the 

 principal continental areas which have a characteristic set 

 of plants of their own, as well as of the most important 

 islands. But a simpler arrangement is to consider the 

 plant life of the earth as distributed among the following 



regions : 



1. The tropical zone. 



2. The temperate zones. 



3. The arctic zones. 



4. Mountain-heights. 



5. Bodies of water. 



Any good geography gives some account of at least the 

 land vegetation of the earth. It is necessary in the pres- 

 ent chapter only to point out a few of the most important 

 characteristics of the plants of the zones and other areas 

 mentioned above and to give some reasons why the plant 

 population of each has its special characteristics. 



396. Tropical Vegetation. Within the tropics two of 

 the great factors of plant life and growth, namely, light 

 and heat, are found in a higher degree than elsewhere 

 on the earth. Moisture, the third requisite, is in some 



1 A, Grisebach, 

 324 



