HOW THE LEAF GETS FOOD FROM THE AIR 77 



or droops and sometimes dies. To stop the escape of 

 water as much as possible 

 the plant closes the sto- 

 mata. It opens them again 

 when the danger is past. 



Poisonous gases are 

 sometimes used to kill 

 insects on plants. This is 

 done at night when the 

 stomata are closed. Other- 

 wise the gases would go 

 through the stomata into 

 the leaf and kill it also. 



What happens if the 

 stomata become stopped 

 up? Smear vaseline on 

 both sides of some leaves 

 (without taking them off 

 the plant) . Spraying with 

 oily liquids may have the 

 same effect as the vaseline 

 if not properly done (see 

 page 412). 



To prevent the stomata 

 from being stopped up with 

 water during rain, many 

 leaves have coverings of wax or hair. Such leaves 

 when under water look like silver, and the side on 



FIG. 40. Blue gum showing leaves 

 which, by hanging straight down, 

 avoid excessive sunlight. Above, 

 two leaves from a young tree; 

 they spread out horizontally after 

 the fashion of most plant leaves. 



