30 THE SYNTHESIS OF CARBOHYDRATES 



present, the amount of formaldehyde is increased in an aqueous 

 solution of carbon dioxide, since the action of such substances 

 is to protect the formaldehyde from polymerization. These 

 are test tube observations : the plant can flourish under con- 

 ditions which entirely withhold radiant energy of these short 

 wave lengths. In such cases a photocatalyst is required and 

 Baly and his collaborators find that in ordinary visible light 

 the photosynthesis of formaldehyde and its polymerization to 

 carbohydrate can be achieved in two separate stages : in the 

 first stage formaldehyde is produced from carbon dioxide and 

 water in the presence of coloured basic substances such as 

 methyl orange ; in the second stage formaldehyde is poly- 

 merized to a reducing sugar, without the aid of a photocatalyst, 

 when exposed to the rays from a quartz mercury lamp. 



The authors point out that if a photocatalyst capable of 

 bringing about both changes in the same vessel in the labora- 

 tory were known, then the separate existence of formaldehyde 

 would not be demonstrable since the formaldehyde pro- 

 duced from carbon dioxide and water would at once be poly- 

 merized into carbohydrate. Such a photocatalyst has yet to 

 be found, and if chlorophyll be one such, then the small amount 

 of formaldehyde in carbon-assimilating leaves is to be expected. 

 This investigation is still in progress : as yet Baly and his 

 fellow-workers have not found the desired photocatalyst and 

 so far have not ascertained to what degree chlorophyll meets 

 their requirements in this respect ; their results are not in ac- 

 cord with those of Osterhout * nor do they examine the con- 

 tention of Spoehr, outlined above, regarding formic acid. 



Chemical change may be brought about by electrical 

 energy ; indeed, in connection with plants, the effect of elec- 

 trical currents on vegetable growth is a not unimportant 

 branch of applied botany. 



Royer f brought about the electrolytic reduction of carbon 

 dioxide, and by similar means Coehn,J in 1904, produced 

 formic acid from this same compound. Brodie found that 

 by means of a silent discharge formaldehyde, together with 



* See Vol. I., p. 61. 



f Royer: "Compt. rend.," 1870, 70, 731. 



JCoehn: " Ber. deut. chem. Gesells.," 1904, 34, 2836, 3593. 



Brodie : " Proc. Roy. Soc.," Lond., 1874, 22, 171. 



