LIGHT AND VEGETATION 119 



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would be better described by two equations, one of which 

 expresses this liberation of oxygen of the water. Wurmser 

 propounded it in 1930 as 



2HaO — >2H2+02 

 2H2+CO2 — ^CHaO+HaO 



This then is a new fact which the theories must take into 

 account. The result should be compared with the photosynthesis 

 effected by purple sulphur bacteria using luminous energy for 

 the synthesis of carbohydrates from COg and HgS. The latter 

 compound, hydrogen sulphide, is chemically analogous to 

 water, the oxygen being replaced by sulphur, but more easily 

 dissociated. 



This photosynthesis may be written in the following 

 form: 



C02+2H25'+light=CH20+H20+25' 



Just as the element liberated, sulphur, can come only from 

 hydrogen sulphide, so also, in plant photosynthesis, the 

 oxygen Hberated comes, as we have just seen, from water. 

 The overall formula of plant photosynthesis should be 

 written, by analogy: 



C02+2H20+light=CH20+H20+20 



a formula in which the oxygen of the water initially used is 

 identified by the sign O. 



Rabinovitch has evolved a theory, although there is still 

 insufiicient evidence to support it, of a rather complicated 

 process taking these data into account. 



He assumes the existence of two unknown catalysts, 

 A and B, one of which is perhaps chlorophyll. A is capable 

 of removing the hydrogen from water and of giving it up to B. 

 B in its turn is capable of yielding this hydrogen to carbon 

 dioxide. These three phases are written: 



4A+4H2O = 4HA+2H2O+O2 

 8HA+8B = 8A+8HB 

 4HB+4[C02]= 4B+4[HC02] 

 The square brackets indicate that [CO 2] and [HCOg] are 

 in combination with other substances. 



