Evergreens 



107 



ciduous tree grows better than the evergreen. The 

 abundant water supply and the low rate of evaporation 

 from the leaves enable it to support a great crown of 

 leaves, and the long growing season allows it to keep 

 these leaves for so long a time that in the course of a 

 summer it can manufacture more food than an ever- 

 green can, even though it keeps its leaves during the 

 whole year. 



The evergreen, on the other hand, succeeds where the 

 water supply is not so great, where evaporation is more 

 intense, or where the winters are long and cold. In 

 sandy soils and on steep and rocky mountain slopes; 

 where the air is dry ; and in the far north, it is the pre- 

 vailing type of tree. Its small, tough leaves demand 

 only a small amount of water, and by working through 

 a longer season they make more food for the tree than 

 the leaves of a deciduous tree can produce in dry loca- 

 tions or during short summers. Do you think ever- 

 greens are not found in deep, moist soils because they 

 will not grow in these locations, or because in such 

 places the deciduous trees grow more rapidly and crowd 

 them out? 



In the moist tropics where there are no cold seasons the 

 trees do not need to shed their leaves and are all ever- 

 greens. But these evergreens have broad leaves like 

 our deciduous trees and differ in type from the ever- 

 greens of dry and cold regions. Just why the trees in 

 many swamps are evergreens has not been fully ex- 

 plained, but one reason probably lies in the fact that 

 under -swamp conditions only a feeble root system can 

 be developed. 



