LEAVES 165 



In Experiments 214-220 cells of yeast are considered. 



Note. For general consideration of the cell and protoplasm see 

 also Experiments 226-228. 



148. LEAVES 

 Object. To show that leaves purify the air- 



Apparatus. A healthy, freshly cut shoot of any vigorous green 

 plant, two tumblers and a shallow basin of water, vaseline, a piece 

 of glass or rubber tube ten or twelve inches long, and two. pieces 

 of plate glass three inches square. 



Method. Fill both tumblers with water to exclude the 

 air. Into one of them place the shoot, top down. Now 

 invert both glasses a b 



under water so that 

 they stand as in Fig- 

 ure 72. By means 

 of the tube blow 



into each tumbler 



, ., ,, FIG. 72. 



until they are com- 

 pletely filled with impure air from the lungs. 



Set the tray containing the inverted tumblers in a sunny 

 window and leave it there for two or three days. 



After two or three days grease the two glass plates lib- 

 erally with vaseline. Then very carefully slip them under 

 the tumblers so that they shut them air-tight. 



Now with a burning stick test the contents of each tumbler. 

 Is there any difference in the way the stick burns in these 

 two glasses ? Both originally contained impure air from 

 the lungs. What is the difference between the contents of 

 these tumblers now? Can you account'for this? 



Conclusion. State what effect plants have on the air. 



Query. Give reasons why the planting of shade trees 



