4 o THE SYNTHESIS OF CARBOHYDRATES 



The results obtained by the use of visible light and a 

 coloured surface are of interest in that it would appear that a 

 closer imitation for the first time has been made in the test 

 tube of what occurs in the green cell. In each the process is 

 conditioned by visible light and a pigmented surface ; the 

 presumed poisoning effect of the cobalt surface by the oxygen 

 is paralleled by the fatigue effect exhibited by leaves in strong 

 illumination and in both there is a recovery. The maximum 

 yield of organic material obtained by the authors was 0-075 

 gram in two hours, and assuming that the product be glucose, 

 it is calculated that the gain in calorific value is 0*48 calories per 

 sq. cm. of surface per hour, which just falls without the range 

 given by Puriewitsch,* 0-27-4-1 calories, for a number of plants. 

 But this for the time being has no significance ; the intensity 

 of carbon assimilation in the plant varies much with the condi- 

 tions, and, on the other hand, the material obtained by Baly 

 and his fellow-workers is not all glucose. The authors also 

 argue that the constant ratio of chlorophyll A to chlorophyll 

 B, observed by Willstatter and Stoll, is maintained by the 

 carotin which becomes oxidized to xanthophyll. Since the 

 ratio of xanthophyll to carotin tends to increase during photo- 

 synthesis, it is suggested that the slow recovery process in the 

 leaf is that in which the xanthophyll is again reduced to carotin. 



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. 



Royerf by electrical means brought about the reduction 

 of carbon dioxide, and similarly Coehn,$ in 1904, produced 

 formic acid from this same compound. Brodie § found that 

 by means of a silent discharge formaldehyde, together with 

 marsh gas, was produced from a mixture of hydrogen and 

 carbon dioxide ; and Lob,|l in 1906, found that formaldehyde 

 may be produced by the action of a silent discharge of elec- 



* Puriewitsch : " Jahrb. wiss. Bot.," 1914, 53, 229. 



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



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



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



|| Lob : " Zeit. Electrochem.," 1906, 12, 282. 



