THE CHEMISTRY OF PHOTOSYNTHESIS 269 



Pollacci's -^ views differ from these and are based upon his claim of 

 having found hydrogen and methane in the gases emitted during photo- 

 synthesis. He assumes that the hydrogen arises from intramolecular re- 

 arrangement of organic compounds and is used in the following manner : 



2 H2CO3 -f 2 H2 + Light = CH2O + CH4 -f H2O + 2 Oo 



2 H2CO3 -t- 3 H2 + Light = CHoO + CH4 + H2O -f 2 O2 -f H2 



Later he simplified these to : 



H2CO3 -f H2 = CH2O -f H2O -f O 



According to this author the function of the light is to produce electric 

 currents within the plant which bring the hydrogen into a "nascent" con- 

 dition. In the dark the hydrogen is not in this condition and is therefore 

 not capable of reducing carbonic acid. The last equation can obviously 

 not represent the photosynthetic reaction, for it would require a photo- 

 synthetic quotient (CO2 : O2) of 2 : 1 which is quite contrary to experience. 

 It is exceedingly doubtful whether assumptions such as these in which 

 the hydrogen is produced independently of the action of light, can be 

 upheld. Even if hydrogen were formed within the plant, and there can 

 be little doubt that reducing actions take place, the amount of this when 

 compared to the total oxidative reactions is small. In photosynthesis there 

 is a lift in energy represented by carbon dioxide passing to carbon : 



CO2 -» C -f O2 



or when water is added, of : 



HoCOs^fH^CO) +O2 



It is difficult to devise a rational scheme (other than the decomposition of 

 water or the formation of hydrogen peroxide) by which hydrogen could 

 be obtained from the (H.CO) material of the plant in sufficient quantities 

 to yield a total increase in carbohydrate material. INIany of the attempts 

 which have been made in this direction represent mere juggling of chem- 

 ical formulae with disregard of the fact that the plant during photosyn- 

 thesis increases in total carbohydrate content and that the ratio of the 

 volume of carbon dioxide absorbed to that of oxygen formed is unity. 

 In photosynthesis there is 10-30 times as much carbon dioxide absorbed as 

 is produced in respiration, so that any scheme which endeavors to utilize 

 the dehydrogenation in the oxidative processes of respiration as a source 

 of reduction in photosynthesis must, under the most favorable assumptions, 

 fall short by 10 to 30 times of the amount of hydrogen required for the 

 reduction of all the carbon dioxide. The fact that hydrogen is actually 

 produced in the respiratory consumption of glucose has, moreover, never 

 been definitely established. 



^^Pollacci, Atti del. IsHt. hot. Pavia, 7, 97 (1902) ; 8. 1 (1902). 



