INTRODUCTION 65 



The Temperate zone is divided into two sub- 

 zones, the Cool Temperate and the Warm Temperate. 

 The former lies between the latter and the Arctic 

 zone, and the average temperature varies from 40 to 

 60° F. It is characterised by the predominance of 

 deciduous forest trees or rarely evergreens. The bulk 

 of the herbaceous plants are perennials. Many of 

 the trees are tropophytes. 



The Warm Temperate zone is equivalent to the 

 Subtropical zone, and the temperature is much higher 

 than in the Cool Temperate zone. The vegetation 

 consists of shrubs, grasses, cereals, cotton, a few 

 palms. Many plants are annuals or biennials. 

 Many of the southern British plants are members of 

 the floras of this zone, as the northern types are 

 derived from the Arctic and Cool Temperate zones. 

 There are numerous rainless areas and deserts in this 

 area, but they are not so frequent as in the Tropics. 



In the Tropical zone the temperature is highest, 

 as this zone lies on either side of the equator, where 

 the sun is vertical at mid-day and the air is moist 

 and the sun's rays intense. This is the region of 

 Palms, Screw Pines, Tree Ferns, Bamboos, and 

 many epiphytes. It is in this region that jungles 

 occur and rain is excessive at certain seasons. 

 Growth is luxuriant. There is no winter, and the 

 trees are not deciduous but evergreen. In some 

 areas there are extensive deserts and the plants are 

 adapted to dry conditions, as Euphorbias, Cacti, 

 Aloe, etc. 



VOL. III. 5 



