308 



PLANTS 



(cf. 272 and 298); but the temperature is also very 

 important. As the earth is divided into temperature 

 belts, or zones, plants are also found distributed in belts, 

 or zones. The limits of temperature, below or above 



FIQ. 252. Cacti: the Cereus, Arizona. Negative by Geo. D. Fuller. 



which plants find it hard to continue their existence, are 

 about 32 F. to 122 F., or C. to 50 C. 



In the polar regions, lichens, mosses, and willows can 

 just support themselves. In the colder part of the 

 temperate zone there are conifers, such as spruce, fir, 

 hemlock; in the warmer part of the temperate zone 

 deciduous (leaf shedding) trees are more abundant. 

 Examples of these are the beech, maple, birch, oak, 

 hickory, and chestnut. In the tropical zone, the palm, 



