374 Messrs. F. L. Usher and J. H. Priestley. [Dec. 16, 



formaldehyde, equivalent to the hydrogen peroxide required to destroy the 

 chlorophyll, accumulates, and thenceforward the reaction is strictly 

 reversible. 



The following experiments were performed to settle the points involved in 

 this explanation : — It was in the first place necessary to show whether the 

 colouration referred to above was due to formaldehyde. For this purpose 

 some leaves, killed and bleached in carbon dioxide solution as described, 

 were soaked for 12 hours in aniline water, and were then examined micro- 

 scopically under a high power. Some leaves which had been killed and 

 simply decolourised with hydrogen peroxide were treated in the same way. 



In the first case the decolourised chloroplasts were observed to be the 

 centres of clusters of well-defined crystals, identical in appearance with those 

 of methylene aniline, artificially prepared from aniline water and form- 

 aldehyde. They were soluble in dilute mineral acids and also in warm 

 alcohol, from which they crystallised in the cell on cooling. The leaves 

 artificially decolourised with hydrogen peroxide showed no crystals. 



An attempt was then made to obtain the formaldehyde outside the 

 plant. For this purpose a large quantity of Ulva and Enter omorpha was 

 killed and bleached in carbon dioxide solution, and subjected to steam 

 distillation. The distillate was divided into two parts. To the larger of 

 these was added some aniline water. 



A white precipitate was formed after some time, which was collected, 

 and heated side by side with a comparison tube containing methylene aniline. 

 It melted, not quite sharply, three or four degrees below the pure artificially 

 prepared substance. The other portion of the distillate was evaporated with 

 ammonia on the water-bath, and the residue dissolved in water and treated 

 with bromine water, gave the characteristic tetra-brom derivative of 

 hexamethylene-tetramine. 



Hence, leaves in which both protoplasm and enzymes have been killed, when 

 placed under conditions favourable for assimilation, develop formaldehyde, 

 until the photolytic process is brought to an end by the destruction of the 

 chlorophyll. 



It was next necessary to determine whether the condensation of the 

 formaldehyde is due to an enzyme secreted by the chloroplast, or whether 

 the protoplasm of the granule itself effected it. Some Modea was suspended 

 in air charged with chloroform vapour for two hours, by which means the 

 protoplasm was killed without affecting the enzymes. It was then exposed 

 to sunlight in saturated carbon dioxide solution. In a few hours the 

 chlorophyll became bleached, and formaldehyde was subsequently found in 

 the plant. 



