1905.] Mechanism of Carhon Assimilation in Green Plants. 373 



starchless filament within three minutes of exposure to light, and it is 

 probable that some sort of carbohydrate is formed much sooner than this, 

 for it has been shown by Brown and Morris* that starch is probablyjnot 

 elaborated within the cell until the supply of nutriment is in excess of the 

 cell requirements. 



It would therefore seem as though the arrangement which exists in the 

 plant for the removal of formaldehyde is at least as efficient as any external 

 arrangement we can make to remove it in a different way, without at the 

 same time killing the plant, and thus eliminating one of the essential 

 factors, namely, the vitality of the protoplasm. 



For this reason it is useless to look for formaldehyde in healthy 

 assimilating leaves. It is well known that certain chemical substances 

 possess the property of condensing formaldehyde to various carbohydrates, 

 chiefly formose, a-acrose, and methylenitan. It has been found by Loewf 

 that such condensing agents are chiefly metallic oxides and acid sulphites, 

 substances not likely to occur in plants. 



Moreover, condensation by these bodies is a comparatively slow process, 

 and quite inefficient when applied to the requirements of a plant. 

 Nevertheless, if the condensation in the plant were due to some chemical 

 agent stored in the neighbourhood of the chloroplast, it should still be 

 capable of taking place when the protoplasm of the leaf is killed and its 

 enzymes destroyed. 



Some healthy green sprigs of Elodca were immersed in boiling water for 

 30 seconds, in order to kill the protoplasm and destroy the enzymes. They 

 were then placed in water saturated with carbon dioxide and exposed to 

 sunlight. In the course of a few hours the deep green colour of the leaves 

 had been completely bleached, and on immersing the bleached sprigs in 

 a solution of rosaniline decolourised with sulphurous acid, a red colour was 

 developed. 



The original green material when treated in this way exhibited no 

 colouration. There was, therefore, some substance of an aldehydic nature 

 present in the killed and bleached leaves which was absent in those which 

 were alive. The sequence of events in this experiment may be described 

 as follows : — Photolysis of carbon dioxide begins in the normal way, giving 

 rise to hydrogen peroxide and formaldehyde. The enzymes having been 

 destroyed, the hydrogen peroxide, instead of being catalysed in the usual 

 manner, oxidises the chlorophyll to a colourless substance, at which point 

 the reaction necessarily comes to an end. Meanwhile a quantity of 



* « J. C. S.,' 1893, ' Trans.,' p. 632. 

 t ' Berichte,' 1888, p. 271. 



