THE FOOD OF PLANTS. 



37 



material we now place a double-walled bell-glass filled with a 

 solution of Potassium bichromate, and once again count the number 

 of bubbles escaping. We then remove the bell-glass, and after 

 again determining the number of bubbles escaping in bright 

 diffuse daylight or in direct sunlight, replace it by a bell-glass 

 containing ammoniacal solution of Copper oxide, and once again 

 count the bubbles of gas. It is well to place a thermometer in 



FIG. 12. Apparatus 

 for collecting the 

 Oxygan produced by 

 assimilating water 

 plants. 



FIG. 13. Apparatus for the same purpose. 



FIG. 14. Api 



paratus for ob- 

 serving the liberar 

 tion of bubbles of 

 gas from assimi-. 

 la ting w ater 

 plants. 



the water surrounding the research material so as to control the 

 conditions of temperature during the separate stages of the 

 experiment. Proceeding as above we easily succeed, as I have 

 satisfied myself, in determining the interesting fact that the less 

 refrangible rays transmitted by a solution of Potassium bichromate 

 induce almost as energetic a liberation of Oxygen from green 

 plant structures as does mixed white light, while the liberation 

 of Oxygen proceeds under the influence of the more refrangible 

 rays transmitted by an ammoniacal solution of Copper oxide only 

 with very slight energy. l 



Twigs of Elodea or Hippuris are placed, together with a ther- 



