THE LIGHT FACTOR IN PHOTOSYNTHESIS 1051 



carbon dioxide only in the light and Gaffron has shown that various fatty 

 acids may apparently serve as hydrogen donors. Whether this is a true 

 photosynthesis, that is, an accumulation of energy at the expense of the 

 light absorbed, is in the present state of our knowledge difficult to say. 

 To what extent reactions here play a part analogous to some known in 

 organic chemistry in which carbon dioxide is taken up by organic mole- 

 cules, which in themselves are probably exothermic reactions, is as yet 

 uncertain and open to speculation. The observations on these organisms 

 clearly demonstrate that they can absorb carbon dioxide in the presence 

 of light with a simultaneous catabolism of organic compounds. It lends 

 support to the supposition that in the photosynthetic process two 

 mechanisms, carbon dioxide absorption and oxygen liberation, may not 

 be involved in the same reaction but in integrated reactions, either or 

 both of which may be photochemical, a concept which has engaged the 

 attention of plant physiologists for many years. 



In conclusion it may be said that from the observations thus far 

 assembled, the photosynthetic process is known to be an endothermic, 

 energy storing process, in which the energy accumulated is a result of a 

 photochemical reaction. The mechanism of the conversion of the light 

 into the chemical energy is, however, still a mystery, because we are in 

 ignorance of the nature of those conditions and factors essential for the 

 reaction which are intimately associated with the protoplasmic activity 

 of the living cell. 



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