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! 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 : 
. The tropical zone. 
tS — 
. The temperate zones. 
The arctic zones. 
Mountain-heights. 
Bodies of water. 
Re og 
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. 
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