TRANSPIRATION 27 



4. At the beginning of the experiment, and at suitable 

 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 involved? 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 this tie- tube, being sure that there is no 

 chance for a leak between the glass and the 

 membrane. 



2. Fill the this tie- tube with water. 



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

 the tube in place. 



4. Invert the this tie- 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 height of the mercury in the 

 tube as in Experiment 8. 



