EXERCISE 24 

 A WASTE PRODUCT OF PHOTOSYNTHESIS 



Materials. Submerged water plants, such as the common pond 

 weeds. 



Directions for work. 1. Place the plants in a large glass jar 

 or aquarium filled with water. Allow the sun to shine upon it. 

 After ten minutes observe the plants and look for evidence 

 of any gas escaping from the plants. 

 Darken the aquarium and note the 

 effect. Try several degrees of shad- 

 ing and note effect, counting number 

 of bubbles per minute, but always 

 allowing several minutes for the new 

 conditions to produce its effect. 



The gas escaping may be collected 

 by proper methods (see " Introduc- 

 tion to Botany," Fig. 27) and shown 

 by tests to be oxygen, but experience 

 shows that under laboratory conditions 

 such tests are often unsatisfactory. 



2. If a good projection lantern is 

 available, the experiment may be per- 

 formed as follows : 



Place a branch of a water plant in 

 water in a thin glass tank, which can be substituted for the. 

 slide carrier. Illuminate the plant by the electric lamp, which 

 will project its image upon the screen. After some minutes the 

 plant will begin to give off bubbles of gas. 



This method offers the advantage of being available on cloudy 

 days, and the experiment may be shown to all members of a 

 large class simultaneously. 



References 



BERGEN and CALDWELL. Practical Botany, pp. 15-17. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 38, 39. 



[27] 



