THE PRODUCTS OF PHOTOSYNTHESIS 221 



If the carbohydrate which is formed in photosynthesis has the empirical 

 formula CnH.nOn as, for example, a hexose, then the absorption by the 

 leaf of one part by weight of carbon dioxide corresponds to the formation 

 of 0.681 parts of the carbohydrate. If sucrose were formed, with the 

 formula C12H00O11, one part by weight of carbon dioxide would result 

 in 0.647 parts of this carbohydrate. A similar calculation for starch or 

 inulin with the formula CgHioOg, shows that each part of carbon dioxide 

 yields 0.613 parts of either of these carbohydrates. 



A more detailed study of the relation of the amount of carbon dioxide 



reduced to that of carbohydrates formed has been made by Kraschenin- 



nikoff."' The results, unfortunately, have appeared in a rather obscure 



publication in the Russian language. The question was approached in 



different ways. Five different plants were studied and the relations of 



the amount of carbon dioxide absorbed to the amount of dry matter 



formed and to the quantity of carbohydrate formed were determined. 



Thus, in the following table, A represents the ratio of the increase in 



dry weight to the amount of carbon dioxide decomposed, B the ratio of 



the carbohydrates formed to the amount of carbon dioxide decomposed, 



and C the ratio of the amount of carbohydrates formed to the increase in 



drv weight. 



A B C 



Bamboo 0.60 " 0.45 0.75 



Cherry-laurel 0.60 0.31 0.51 



Sugar-cane 0.67 0.50 0.75 



Linden 0.75 0.56 0.75 



Tobacco 0.65 0.37 0.57 



From these results it is apparent that when all the increase in dry 

 weight is taken as carbohydrate a value is obtained which is close to the 

 one demanded by the theory that the products of photosynthesis are 

 carbohydrates. It is, however, experimentally impossible from determina- 

 tions of this nature to differentiate whether the carbohydrate formed is 

 a hexose or starch; the method is not sufficiently accurate. The values 

 under B, would go to show that only a portion of the carbon dioxide 

 absorbed by the plants was recovered as carbohydrate. Similarly, the 

 values under C, would indicate that not all of the gain in dry material 

 during photosynthesis can be ascribed to carbohydrates. 



Krascheninnikoff also endeavored to gain further information regard- 

 ing the nature of the material which is formed in photosynthesis from 

 the heat of combustion of the leaf material. As in the previous experi- 

 ments the half-leaf method was used. Thus, per one square meter of 

 leaf surface the following values were obtained : 



Increase in heat of combustion of the dry matter 15.4 Kg. cal. 



Heat of combustion calculated from the amount of CO2 absorbed. . . . 14.5 

 Heat of combustion when increase in dry material is calculated as 



consisting of carbohydrate 14.0 



a li 



117 



Krascheninnikoff, "Accumulation of Solar Energy in Plants" (Russian), Mos- 

 cow, 1901. 



