LEAVES 



161 



Rate 

 oj transpiration. 



144. LEAVES 

 Object. To measure the amount of transpiration. 



Method. Magin's apparatus to measure the amount of 

 transpiration is shown in Figure 70. Push into one arm of a 

 U-tube a rubber stopper 

 through which a leaf or 

 branch has been passed. 

 Fill the tube with water 

 and into the other arm 

 push a stopper through 

 which passes a long piece 

 of glass tube bent at 

 right angles near the 

 stopper. The water 

 should not only fill the 

 U-tube but extend out 

 into the tube. As the FlG - 70 - 



plant transpires, the water contained in the tube will gradu- 

 ally move along the tube towards the U-tube. The rate at 

 which it moves along will indicate the rate of transpiration. 



Suggestion. Lay two large leaves like those of the hy- 

 drangea on a table in sunshine until they have begun to wilt. 

 Then place one with blade under water and leafstalk out 

 in the air. Place the leafstalk of the other in water with the 

 blade in air. After an hour or two what change has taken 

 place? Do both act alike? Account for the difference if 

 they are not alike. 



What may be inferred from this experiment? 



Do leaves absorb water from their surfaces ? 



How are leaves of cabbage, mullein, caladium, and water 

 lily adapted to prevent wetting? 

 EXP. EOT. 11 



