232 Photochemical Formation of Formaldehyde in G^-.een Plants. 



hexamethylenetetramine, the hydrolysis of the methyleneamino-derivative, 

 which is a somewhat stable compound, is only very small (the reaction 

 represented by the arrow pointing to the left in the above equation is only 

 very incomplete). In such eases, the formaldehyde reaction can only 

 proceed to completion after warming or allowing the mixture to stand for 

 some time in the presence of the phenylhydrazine reagent. The hydrolysis 

 proceeds to completion, that is to say, when the formaldehyde that is set 

 free is removed from the sphere of action. A similar stable compound 

 appears to be formed with the chlorophyll* and formaldehyde. The reaction 

 may be schematically represented by the following equation : — 



As the condensation product is somewhat stable, equilibrium will be 

 maintained when only a very small amount of free aldehyde is present. As 

 this is removed by synthesis into sugars, etc., more of the chlorophyll-aldehyde 

 condensation product will decompose. It can furthermore be reconstituted 

 in the presence of carbon dioxide and sunlight. The fact, therefore, that such 

 a stable compound is formed, which undergoes only limited hydrolysis, 

 explains the mechanism by means of which the quantity of formaldehyde in 

 the plant available for siigar synthesis can be regulated. In the presence of 

 sunlight and carbon dioxide, tliere is probably a continuous synthesis of 

 formaldehyde, and a continuous condensation of the latter to sugars, without 

 at any time an accunjulation of the aldehyde in sucli quantity as to be toxic 

 to the plant. It is possible that the synthetic formation of sugar is due, as 

 Usher and Priestley have suggested, to the living protoplasm, as this 

 liypothesis explains certain phenomena to which they have called attcnLion 

 in their paper. 



Summary. 



1. A reaction is described by means of whicli minute quantities of 

 formaldehyde, Itoth combined and free, can be detected and estimated. 



2. Formaldehyde can be detected in chloropliyll, and exists therein in 

 a state of combination. 



3. By means of the reaction described, the photochemical synthesis of 

 formaldehyde by chlorophyll can be demonstrated. 



4. From the fact that formaldehyde exists in a state of comliination in 

 chlorophyll, it is possible to explain how the .sii])ply of iddehyde ncuessary 

 for sugar synthesis in the plant is regulated. 



* See note, p.' 229. 



