PHYSIOLOGICAL SCALE AND LAWS OF PHOTOSYNTHESIS 279 



formation of quantities of carbohydrate as small as the 

 millionth of a gramme. 



Efficiency of Photosynthetic Storage of Energy 



The estimates hitherto obtained indicate generally a low 

 efficiency; but the experimental methods employed have 

 been defective from absence of means for the exact measure- 

 ment of the incident energy, of the indeterminate losses of 

 this energy, and of the energy stored in photosynthesis. 



I have been successful in obviating these difficulties by 

 the new methods devised. The incident and the absorbed 

 energy were determined by the Calorimetric Method, the 

 rise of temperature being measured with great accuracy by 

 a thermo-electric couple ; the loss of heat by radiation was 

 completely eliminated. The accuracy of the calorimetric 

 determination was tested independently by the Magnetic 

 Radiometer. The coefficient of transmission and that of 

 absorption were both found to be practically the same by 

 the two methods. The methods employed are extremely 

 sensitive, the determination being completed in the course 

 of a few minutes. 



The energy stored was simultaneously found from the 

 volume of oxygen given out by the plant, the carbohydrate 

 factor of which had been very carefully determined. The 

 photosynthetic efficiency of the leaves of Hydrilla is fairly 

 high, being about 7-4 per cent. 



The Physiological Scale and the Law of Photosynthesis 

 under Variation of Different Factors 



The expansion-curve of a permanent gas when produced 

 backwards cuts the abscissa at — 273°, which is taken as the 

 absolute zero of temperature. When the temperature T is 

 measured on the absolute scale, the volume of a given 

 quantity of gas is found from the relation 



- is a constant. 



