TRANSPIRATION 2 7 



intervals thereafter, as directed by the instructor, 

 measure and record the height of the mercury in 

 the glass tube. 



5. Make two drawings of this apparatus in longitudi- 

 nal section : (a) as soon as the experiment is set up ; 

 (b) at the close of your final observation. Label 

 all essential parts. 



6. You have made this last experiment with a living 

 plant. The question now naturally arises: Is the 

 result observed due to the life-factor involved, or 

 is it merely the result of some physical condition, 

 as, e.g., the evaporation? The question may be 

 easily answered by setting up an experiment similar 

 to the preceding, but using non-living material, 

 as follows: 



Experiment 9. To see if evaporation exerts a " lifting 

 power." 



1 . Tie a piece of porous animal membrane (e.g., bladder) 

 over a thistle-tube, being sure that there is no 

 chance for a leak between the glass and the 

 membrane. 



2. Fill the thistle-tube with water. 



3. Prepare a dish of mercury and also a clamp to hold 

 the tube in place. 



4. Invert the thistle-tube and place the lower end in 

 the mercury, being sure that no air enters the tube. 

 By this arrangement all' factors of Experiment 8 

 have been eliminated except evaporation, and the 

 evaporation takes place through only one mem- 

 brane, and that a non-living one. In other words, 

 we have Experiment 8 reduced to its lowest terms. 



5. Observe and record the heights of the mercury in 

 the tube as in Experiment 8. 



