234 CHAP. XXV. PHOTOSYNTHETIC STORAGE OF SOLAR ENERGY 



of combustion the mean value 3-9 X io 3 gm. eal., the heat 

 of combustion for glucose being 3-76 X io 3 and for starch 

 4-1 X io 3 . 



Having explained the theory of the method, I proceed 

 to give experimental details. A dozen experiments were 

 carried out, the results of which were practically the same, 

 with plants from the same pond. 



Determination of Photosynthetic Efficiency 



The photosynthetic efficiency is the ratio of the energy 

 stored E s to the energy E A absorbed by the plant. 



Efficiency = =r 



The observations were taken in the following sequence : 



1. The Calorimeter out of the way : the intensity of full 

 radiation I passed through the blank Bubbler b' was measured 

 by the deflection D of the Radiometer. 



2. The Calorimeter was interposed and the number of 

 heat-units H, produced by full radiation acting for three 

 minutes, determined by the rise of temperature G, as indi- 

 cated by the deflection of the Galvanometer. 



3. The Calorimeter was put out of the way, and the 

 Bubbler b containing the plant interposed in the path of 

 light. The intensity of transmitted radiation d was now 

 measured by the Radiometer. 



4. With the Bubbler b containing the plant interposed 

 in the path of light, the transmitted radiation was made to 

 act on the Calorimeter for three minutes, and the number of 

 heat-units h determined by the rise of temperature g indi- 

 cated by the Galvanometer. 



While the energy of radiation absorbed was being measured, 

 a simultaneous determination was made of the energy stored in 

 photosynthesis by counting the number of bubbles of oxygen 

 given out by the Bubbler b during the three minutes' exposure 

 of the plant to incident radiation. 



