i6o THE CARBOHYDRATES 



chlorophyll be kept in the dark no formaldehyde is produced, 

 no matter whether moist carbon dioxide be present or not ; 

 further, if such plates be exposed to sunlight in an atmosphere 

 free from carbon dioxide, a very minute quantity of formalde- 

 hyde is produced ; on the other hand, the plates when exposed 

 to the sun's rays in the presence of moist carbon dioxide give 

 a distinct formaldehyde reaction. 



From this Schryver concludes that in the presence of 

 sunlight, water, and carbon dioxide, there is a continuous 

 production of formaldehyde, which is continually being con- 

 densed to sugar. If this condensation does not proceed rapidly 

 enough to remove all the formaldehyde, the excess enters into 

 combination with the chlorophyll, and, as the free formaldehyde 

 is used up, this compound of formaldehyde with chlorophyll 

 decomposes, setting free the former, which is converted into 

 sugar. There is thus in the plant a mechanism by means of 

 which the quantity of free formaldehyde is regulated, so that 

 at no time is the amount sufficiently large to become toxic ; 

 thus Curtius and Franzen found only -0008613 gram of 

 formaldehyde per kilo of green hornbeam leaves (see p. 150). 



With regard to questions relating to the form of energy 

 used in these photosynthetic processes, a few passing remarks 

 may be made. As is well known, the view commonly held is 

 that radiant energy, more especially those rays of the red end 

 of the spectrum, afforded by the sun, is the direct source. And 

 as this is adequately treated in most texts on plant-physiology, 

 it is not proposed to deal with it here. At the same time it 

 is to be borne in mind that other forms of energy may be made 

 use of by the plant. 



Royer * brought about the electrolytic reduction of carbon 

 dioxide, and by similar means Coehn,t 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,§ in 1906, found that formaldehyde 

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



* Royer : " Compt. rend.," 1870, 70, 731- 



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



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



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



