A YEAR IN SCIENCE 33 



change ? What causes it ? Do the papers on the upper 

 and lower surfaces change at the same time? What 

 does this indicate? Repeat this experiment on leaves 

 of the nasturtium and of several other plants. At 

 what rate do you find water is given off from their 

 leaves? Do all plants transpire at the same rate? 



Exercise 54. Is Air Necessary? 

 Object: To determine whether air is necessary for 

 the growth of plants. 



Apparatus 



Wide mouth bottles Paraffin 



Kubber stoppers Glass plate 



Seeds (well soaked) Bell jar 



Geranium plant Blotting paper 



Directions: A. Place blotting paper to the depth 

 of an inch in the bottom of each of two wide mouth 

 bottles. Saturate the paper thoroughly with water. 

 Fill each bottle three-fourths full of soaked pea seeds. 

 Close one bottle tightly with a rubber stopper to 

 exclude the air and leave the second bottle open to 

 the air. Place the two bottles under the same condi- 

 tions of temperature and light. Make and record daily 

 observations for one week on the growth of the seeds 

 in the bottles. What do you conclude from the results? 



B. Do other forms of plant life require air? To 

 determine this select two potted plants of equal size. 

 Water both plants thoroughly and place one under 

 a belljar. Make this air-tight by sealing the open 

 end of the belljar to a glass plate. Now place the 



