38 



EXPERIMENTAL PLANT PHYSIOLOGY. 



in the air for several days and weigh. Those in darkness will have 

 lost, while those in light will have gained weight since they were able 

 f.o form food from carbon dioxide of the air and water. 



EXPERIMENT 44. 



OXYGEN IS GIVEN OFF DURING PHOTOSYNTHESIS. 



Fill a funnel of medium size with green shoots of Elodea 8 to 10 

 centimeters in length. Immerse the funnel, inverted, in a wide dish 

 filled with spring-water, and over the small end of the funnel place 

 a test-tube filled with water. Set in the sunlight. In a short time 



Fig. 33. 



Fig. 34. 



Apparatus to show excretion ot 

 oxygen by Elodea. (Detmer.) 



Action of light on Elodea. 

 (After Oels.) 



gas can be seen, collected in the upper part of the tube, which tested 

 with a glowing splinter is proved to be oxygen. 



EXPERIMENT 45. 



THE AMOUNT OP PHOTOSYNTHESIS AND OF OXYGEN GIVEN OFF DEPENDS ON 

 THE INTENSITY OF THE LIGHT. 



Fasten a shoot of Elodea about 10 centimeters long to a glass 

 rod and immerse in spring-water or water containing carbon dioxide, 

 so that the cut end is higher than the other. Set the apparatus in 

 direct sunlight, and immediately a stream of gas-bubbles — oxygen — 

 begins to pour from the cut end of the shoot. (Fig. 34.) In diffused 



