54 PLANT PHYSIOLOGY 



which are condensed to form a molecule of glucose. There are 

 thus seen to be two distinct reactions, (1) the formation of the 

 formaldehyde and (2) its polymerization into the sugar, of which 

 only the first may be dependent upon light. 



Among the serious objections to this theory are that carbon 

 monoxide is never found in the free state in the plant (except in 

 a few cases as a product of respiration) and that it is a very poison- 

 ous anaesthetic. According to Kraschennikov and Sulander, no 

 green plants are able to use carbon monoxide and 0.5% was 

 sufficient to inhibit the growth of lupine seedlings. Although 

 Bottomley and Jackson (1903) have reported that if carbon 

 monoxide is substituted for carbon dioxide Tropxolum forms 

 starch and grows well, the majority of evidence points the other 

 way. 



Erlenmeyer (1877) tried to modify von Baeyer's theory to 

 make it acceptable, and suggested that the carbonic acid is re- 

 duced to formic acid and oxygen, after which the formic acid is 

 then further reduced to formaldehyde and oxygen, or that the 

 reducing action may give rise directly to formaldehyde and 

 oxygen : 



C0 2 +H 2 = H 2 C0 3 

 H 2 C0 3 = H 2 C0 2 +0 

 H 2 C0 2 = CH 2 0+0. 



According to the first view, both formaldehyde and formic acid 

 are produced while, according to the second, only formaldehyde. 

 Formic acid is also poisonous to the plant, but the fact that it is 

 never present in large quantities, being reduced (as soon as formed) 

 to formaldehyde (which in turn is immediately polymerized), 

 might answer this objection. 



Bach, who was the first to attempt to produce formaldehyde 

 in vitro from carbon dioxide and water, proposed that carbonic 

 acid was reduced to a peroxide and formaldehyde, after which 

 the peroxide was also reduced. This hypothesis, in a somewhat 

 modified form, is held today by many workers, who consider 

 that the reactions occur in the following steps : 



C0 2 +H 2 = H 2 C0 3 

 H 2 C0 3 +H 2 = HCOOH (formic, acid) +H 2 2 

 HCOOH+H 2 = CH 2 0(formaldehyde)+H 2 2 

 2H 2 2 = 2H 2 0+0 2 . 



