LIFE AS AFFECTED BY CLIMATE 



257 



wide range of climatic conditions. Moisture, sunlight 

 and temperature are the chief factors which determine the 

 growth and development of plants. If the temperature is 

 too high or too low, they cannot exist. If sunlight or 

 moisture is wanting, they cannot build their tissues. 



In regions where the temperature is constantly below 

 freezing, there can be no plant life. Where the tempera- 

 ture is above freezing for only a short time in the year, 

 plant growth is slight and whatever plants there are must 

 be small and stunted. Only where there is a long grow- 



AN OASIS IN THE MOJAVE DESERT. 



MESQUIT BEANS. 

 From this desert plant some In- 

 dian tribes made their bread. 



ing period can large 



plants exist. That is 



why there is almost no 



plant and therefore almost no animal life on the upper 



parts of lofty mountains, while somewhat farther down 



the life is stunted, and still lower down life flourishes. 



Changes in latitude have the same effect. 



Where moisture is lacking, no plants can grow. Where 

 there is but little moisture, only those plants can grow 



