228 CHAP. XXV. PHOTOSYNTHETIC STORAGE OF SOLAR ENERGY 



are at the same temperature, there being no variation of 

 temperature in the plant-vessel caused by the passage of 

 light which had its heat-rays previously absorbed by a thick 

 stratum of water ; the experiment, moreover, lasts for three 

 minutes only. These precautions are sufficient to maintain 

 a constant temperature of the water in the vessel. Finally, 

 the serious and unknown loss through transpiration is com- 

 pletely absent in aquatic plants immersed in water. 



The efficiency of the photosynthetic organ is the ratio 

 of the energy stored to the total energy absorbed. The 

 energy stored can be accurately determined from the photo- 

 synthetic evolution of oxygen. The energy absorbed is 

 found from the difference in intensity of the incident and 

 of the transmitted light, as measured' by the two inde- 

 pendent methods of the Calorimeter and the Radiometer. 



I will describe the experimentation for the determina- 

 tion of photosynthetic efficiency in the following order : 



Experimental methods and appliances. 



The Bubbler. 



The Magnetic Radiometer. 

 The Calorimeter. 



Measurement of energy by the Calorimeter. 

 Thermo-electric couple for measurement of temperature. 

 Elimination of loss of heat by radiation. 

 Determination of coefficients of transmission and absorption. 



(i) By Calorimetric Method. 

 (2) By Radiometric Method. 



Determination of the stored energy. 

 Determination of the photosynthetic efficiency. 



Experimental Methods and Appliances 



A diagrammatic representation of the apparatus and 

 method of experimentation is given in the illustration 

 (fig- 55)- A is tne aperture 2x1-5 cm. through which 



