22 ENVIRONMENT OF PLANTS AND ANIMALS 



TliL' effect of water upon the growth of trees. These trees were all planted at the 

 same time in soil that is sandy and uniform. They are watered by a small 

 stream which runs from left to right in the picture. Most of the water soaks 

 into the ground before reaching the last trees. 



weak intensity of light and live in shady forests or jungles, 

 prowling about at night. Others seem to need much and strong 



light. And man himself 

 enjoys only moderate in- 

 tensity of light and heat. 

 Look at the shady side of 

 a city street on any hot 

 day to prove this state- 

 ment. 



Heat. — Animals and 

 plants are both affected 

 by heat or the absence of 

 it. In cold weather green 

 plants either die or their 

 life activities are temporarily suspended, — the plant becomes 

 dormant. Likewise small animals, such as insects, may be killed 

 by cold or they may hibernate under stones or boards. Their 

 life activities are stilled until the coming of warm weather. Bears 



The effect of light upon a growing plant. 



