BAEYER'S HYPOTHESIS 39 



hydrate, the realms of theory are entered. The hypotheses 

 are many and have this in common none entirely satisfy the 

 plant physiologist ; for which reason it is proposed to consider 

 but two in any detail on the present occasion, not that those 

 discarded are barren of ideas indeed, some contain valuable 

 suggestions but that their examination, more especially when 

 unsupported by experimental evidence, would tend rather to 

 obscure than to clarify the problem. 



In 1870 Baeyer put forward the hypothesis that the carbon 

 dioxide is split up by the plant into carbon monoxide and 

 oxygen, and that the water is concurrently resolved into its 

 constituent elements. The carbon monoxide and hydrogen 

 thus produced then combine to produce formaldehyde, which 

 undergoes polymerization, and so forms a hexose. 



These changes may be represented in the following equa- 

 tions : 



/ 1. co 2 = CO + o 



\ 2. H 2 O = H 3 + O 



3. CO + H 2 = CH O 



4. 6(CH 2 0) ' = C 6 H 12 8 



Thus, according to the theory, there are two distinct actions, 

 the first leading to the formation of formaldehyde, and the 

 second to the production of sugar. 



Considering the first part of Baeyer's theory, it is seen that 

 both carbon monoxide and hydrogen are supposed to be pro- 

 duced, but carbon monoxide has been found but once in a free 

 state in the living plant (p. 73), and it is a substance which 

 does not lend itself at all readily to constructive metabolism, 

 the evidence as to whether plants are able to make use of it 

 for synthetic purposes being contradictory. Bottomley and 

 Jackson * state that if the carbon dioxide normally present 

 in the atmosphere be replaced by about twenty times as much 

 carbon monoxide the increase in the amount of the latter 

 being necessary on account of its lesser solubility in water as 

 compared with carbon dioxide plants of Tropaolum formed 

 starch and flourished. Preliminary analyses also showed that, 

 in the case of seeds germinated in an atmosphere in which the 

 carbon dioxide had been replaced by carbon monoxide, there 

 was in the seedlings an increase in organic carbon. Further, 



* Bottomley and Jackson : " Proc. Roy. Soc.," Lond. B., 1903, 72, 130. 



