1905.] Mechanism of Carbon Assimilation in Green Plants. 375 



It follows from this that the protoplasm of the chloroplast is the con- 

 densing agent. The bleaching of the chlorophyll in this case is due to the 

 fact that the enzyme, though unharmed at the commencement of the 

 experiment, quickly becomes poisoned by the accumulating formaldehyde. 

 Tn this last experiment the limit to the accumulation of formaldehyde in a 

 plant is realised, since there is formed an amount equivalent to that amount 

 of hydrogen peroxide which is catalysed before the enzyme ceases to act- 

 together with an amount equivalent to the hydrogen peroxide required to 

 destroy the chlorophyll. 



That a certain amount of hydrogen peroxide is catalysed when the 

 protoplasm only is dead was shown in the following manner. Approxi- 

 mately equal quantities of Elodca, were taken, one of which (A) was killed 

 by immersion in boiling water, another (B) was suspended for two hours in 

 air saturated with chloroform vapour to kill the protoplasm and not the 

 enzymes, while the third (C) served as a control. 



All three were placed in carbon dioxide solution under funnels with 

 inverted test-tubes, and exposed to artificial light for 12 hours. From A 

 there was no evolution of oxygen, from B 03 c.c. were given off, and from 

 C 2 - 8 c.c. In the case of B, after exposure to light, no catalytic action on 

 hydrogen peroxide could be observed, while previously vigorous decomposition 

 had taken place. 



Summary. 



1. The photolysis of carbon dioxide may take place outside the plant in 



absence of chlorophyll, provided one of the products is removed. 



2. The normal products of the photolysis are hydrogen peroxide and 



formaldehyde, though under certain conditions formic acid may be 

 formed. 



3. In the plant the decomposition of the hydrogen peroxide is provided 

 for by a catalysing enzyme of general occurrence. 



4. The condensation of the formaldehyde is dependent on the healthy 



condition of the protoplasm. 



There are therefore three factors essential to photosynthesis from carbon 

 dioxide and water in the plant, they are (i) vitality of the protoplasm, 

 (ii) presence of a catalysing enzyme, and (iii) presence of chlorophyll. If 

 any one of these factors be interfered with, the process of photosynthesis 

 ultimately comes to an end, through the destruction of the optical sensitiser, 

 chlorophyll. 



LXXVII. — b, 2 E 



