298 NATURE STUDY AND AGRICULTURE 



must have air to breathe as well as food to eat. They 

 cannot live without the oxygen of the air any more than 

 animals can. In our study of germination we proved that 

 air was necessary for the beginning of growth from the 

 seed. Is it necessary for further growth of the plants ? 



Experiment. — Place a plant that is growing in a very 

 small pot or can in a quart Mason jar. Put water enough 

 in the jar to stand almost to the top of the pot. Screw the 

 top on tightly, using a rubber as in canning fruit. Allow 

 it to stand several days. What takes place ? What have 

 you deprived the plant of? The plant droops because 

 you have cut off the supply of fresh air or oxygen. If 

 you leave it long enough here it will die. Do the roots 

 need oxygen as well as the leaves and stem ? In a can or 

 pot in which a corn or other plant is growing, pour water 

 until the soil is completely saturated and the water stands 

 on top around the stem. Now set the plant in a jar of 

 water completely covering the brim of the pot. Keep in 

 this condition several days and note effect. What part of 

 the plant is deprived of air? Is there any air in the soil 

 when all the spaces between the soil particles are filled 

 with water ? Fill a tumbler full of dry soil. Pour water 

 in one spot. Watch for bubbles of air that the water is 

 driving out. What happens to corn or oats on which the 

 water stands for several days? They are "drowned out" 

 because air is cut off from their roots. It is well to know 

 that plants in the act of breathing throw out carbon 

 dioxide just as animals do. It is worth while knowing also 

 that breathing or respiration in plants goes on all the time 

 both night and day. 



