MOVEMENTS OF WATER IN THE PLANT. 



21 



Close the small end of the tube with the finger, lift from the water,, 

 and place in an upright position with the small end immersed in a 

 dish of mercury. (Fig. 16.) Examine daily for two weeks or more. 

 As the water evaporates the mercury slowly rises. It may be drawn 

 to a height of 34 cm. if a good quality of ox-bladder is used. 



FIG. 17. 



FIG. 16. 



Apparatus to demonstrate lifting power of evaporation. (After Oels.) 



This experiment may also be carried on in the following manner 

 to determine the amount of water evaporated : Fit a thistle-tube 

 with a membrane as above, and while still under water attach to it 

 by means of a short section of rubber tubing a glass tube bent twice 

 at right angles (Fig. 17). Completely fill the apparatus with water 

 and fasten in an upright position. Place a drop of oil on the surface 

 of the water in the open tube to prevent evaporation at this point. 

 The amount of evaporation from the membrane will be shown 

 directly by the fall of the level in the open tube. 



