26 ANATOMY AND PHYSIOLOGY 



the experiment is standing for an hour, each, in (a) 

 direct sunlight and breeze; (b) diffuse sunlight, and 

 the comparatively still air of a room; (c) under a 

 glass bell-jar, or large box. The breeze may be 

 secured by placing the experiment in or near an 

 open window or other draught, or by means of an 

 electric fan. 



On the basis of your observations in Experiment 7, 

 discuss the control of transpiration by external 

 conditions, and suggest differences in the condition 

 of the plant caused by its exposure in the various 

 situations suggested above, and the effect this would 

 have on the rate of transpiration. Were the results 

 observed in the three situations strictly comparable? 

 Why? 

 C. One Effect of Transpiration: 



Experiment 8. To show the so-called "lifting power" 

 of transpiration. 



1. Insert a leafy stem of a living plant (a branch of any 

 evergreen is excellent to use) into one end of a piece 

 of glass tubing about 3 ft. long, of small bore, and 

 full of tap-water, taking special care to have the 

 joint between the stem and the glass air-tight, 

 using rubber tubing for this purpose if neces- 

 sary. The experiment will be more satisfactory 

 if the stem is cut off under water, and the cut 

 end kept from contact with air, throughout the 

 experiment. 



2. After being sure that the glass tube is full of water, 

 place it upright in a dish of mercury, having care 

 not to allow any of the water to run out in so doing. 



3. Place the experiment in sunlight, if possible, but 

 do not leave it in direct sunlight for more than one- 

 half to three-quarters of an hour. 



