222 PHOTOSYNTHESIS 



It was found that there was an increase of from 2.2 to 3.6 calories 

 in the heat of combustion of the leaf material for each gram of carbon 

 dioxide absorbed. The calculated amount for the formation of carbo- 

 hydrate from this amount of carbon dioxide is 2.6 calories. From these 

 results it appears that while there are probably some substances besides 

 carbohydrates formed in the photosynthetic process, the amount is variable 

 and, considering the uncertainties of the experimental determination, not 

 very large. 



Bose has endeavored to determine the relation of the amount of oxygen 

 evolved to the increase in weight of the plant during photosynthesis. He 

 employed the aquatic plant Hydrilla in his experiments and determined the 

 difference in weight of the plant by weighing it in water on a torsion 

 balance and taking the gas emitted from the plant during photosynthesis 

 as being oxygen. This should give a factor on the assumption that the 

 oxygen-carbohydrate factor will be according to : 



Oxygen __ CeH,,Oe _ 180 _ . q.-. 

 Glucose " 6O2 ~ 192 -^•^'^^^• 



In no case was this value realized, but in "normal" specimens a factor 

 of 0.8906 was obtained. The difference between the observed and cal- 

 culated values Bose attributes to the formation of substances other than 

 glucose and if starch is assumed to be a product of photosynthesis a lower 

 carbohydrate-oxygen factor would be expected. It is essential to bear irt 

 mind that the gas emitted from a submerged plant during photosynthesis 

 is not pure oxygen but a mixture of oxygen, nitrogen and carbon dioxide. 



As is discussed in the chapter of this book on Methods of Measuring 

 Photosynthesis the proportion of oxygen in the gas emitted varies with 

 the rate of photosynthesis. In order to arrive at a true carbohydrate : oxy- 

 gen value it would be necessary to determine the amount of oxygen in 

 the emitted gas. As far as can be judged from Bose's "^ observations 

 if this were done, the results would be close to the calculated values. 



That starch or other carbohydrates are not the only products of photo- 

 synthesis has been frequently reported. In some of the algae oil drop- 

 lets appear instead of starch when the plants are illuminated. These 

 observations have usually been made by the aid of the microscope and 

 the composition of the oil and its relation to photosynthesis have not 

 been definitely established. On account of the small quantities and the 

 fact that substances of a fatty nature may result from the metabolic 

 activity of the plant it has been difficult to determine the nature of the 

 oil and its manner of formation. It is a well-known fact that in the plant 

 under certain circumstances, carbohydrates are converted into fats. It is 

 therefore very difficult to determine definitely whether the oil observed 

 in the cells is a direct product of photosynthesis or whether it is a con- 



""Bose, "The Physiology of Photosynthesis," 1924, p. 198. 



