CHLOROPHYLL AND ENERGY 155 



predominant, while, if photosynthesis predominates, the result 

 will be the reverse. 



Many physiologists vied with one another in determining 

 these quotients, for, although it is possible to suppress 

 assimilation by keeping the plants in darkness, it is impossible 

 to suppress respiration. Also, the respiratory quotient varies, 

 being sometimes higher, and sometimes lower, than unity. 



After very detailed analyses and calculations, first 

 Maquenne and Demoussy, and then Willstater and Stoll, 

 concluded that the photosynthetic quotient was constant, 

 whatever the external conditions might be, and that it was 

 always equal to unity, the oxygen given off corresponding 

 exactly to the carbon dioxide absorbed. 



Thus the balance of the gaseous exchanges between the 

 plant and the surrounding air can be fairly accurately deter- 

 mined. Some of the experiments showed great ingenuity; for 

 example, the younger Schloesing succeeded in making a stem 

 of meadow soft grass accomphsh all its Ufe cycle in a con- 

 fined atmosphere, perfectly conditioned and frequently 

 analysed. 



After noting the quantity of carbon dioxide introduced, 

 estimating what was given off from the soil and calculating 

 what remained in the air at the end of the experiment, he 

 concluded that the plant had absorbed 1,527 cubic centimetres 

 of carbon dioxide; then, making the same calculations for the 

 oxygen, he found that 1,734 cubic centimetres came from the 

 plant. The total assimilation or photosynthetic quotient 

 O2/CO2 was therefore greater than unity, namely, 1-12. The 

 additional oxygen was provided by the degradation of 

 oxidized substances of the soil, such as nitrates, which are 

 used by the plant. 



First Hypotheses on the Chemistry of Photosynthesis 



During the last ten years great progress has been made in 

 the investigation of the chemical processes which take place 

 in the interior of the cell. One of the first problems was to find 

 how carbon dioxide was transformed into glucosides. 



