40 



EXPERIMENTAL PLANT-PHYSIOLOGY. 



photosynthesis promoted by each can be demonstrated. The 

 red rays are principally active in photosynthesis. 



31. Division of the Spectrum.— It is found that a watery solu- 

 tion of potassium bichromate transmits only the red, orange, 

 and yellow rays of light, and that an ammoniacal solution of 

 copper oxide transmits only the blue and violet rays. Unless 

 carefully compounded, however, the latter solution will also 

 allow the passage of some of the red and yellow rays. 



EXPERIMENT 46. 



PORTION OF THE SPECTRUM ACTIVE IN PHOTOSYNTHESIS. 



Make a solution of potassium bichromate in water. To obtain 

 the ammonia-copper-oxide solution, add ammonium hydrate to a 

 soluuon of copper sulphate in water as long as the forming precipi- 

 tate is redissolved. Fill a double-walled bell-jar with each solution. 



Fig. 36. Fig. 37. 



Double-walled bell-jar. 

 (After Oels.) 



Apparatus to replace double 

 walled bell-jar. (After Oels.) 

 k, solution of potassium bi- 

 chromate or copper oxide; -o, 

 water ; />, pasteboard cover. 



Prepare three shoots of Elodea as 



in Experiment 45. Place one in 



sunlight and one under each bell-jar. 



off from the shoots in open sunlight and under the red bell-jar, but 



none from the one under the blue bell-jar. (Fig. 36.) 



Bubbles of oxygen are given 



