President's Address. 337 



diminution in amount of destniction of carbonic acid in sunlight, 

 and of its being less than in bright diffuse daylight. But it is 

 more rationally explained by an increased combustion in direct 

 sunlight, so that the assimilation and respiration cur\'es approach. 



Tissues which are not green, and plants, such as phanerogamous 

 Saprophytes and Fungi, as they want the elements, especially the 

 easily oxidised assimilation products of the chlcrophyU-corpuscles, 

 which, in green cells, so readily absorb oxygen in light, are not so 

 sensitive to light. A marked increase of carbonic acid accumu- 

 lation does not take place in them, even in diffuse daylight of low 

 intensity. Some researches in this direction by Drude on Moiw 

 tropa, and by Wolkoff and Mayer upon germinating plants, have 

 shown an increase in respiration in light. The latter found the 

 differences very small, and considered them as tending to show that 

 light had no important influence on respiration. But their results 

 may be taken as supporting the theory here set forth. In experi- 

 ments on respirating germinating seeds and green organs cannot be 

 fairly compared as regards the substances used up. In the former 

 it is the reserve materials — starch, fat, &c. — which, after metastatic 

 change, are oxidised, whilst in the active green cells these sub- 

 stances, as has been shown, take no share in the respiration, but it 

 is the primary assimilation products or their immediate derivates 

 which undergo combustion. If, therefore, with such unfavourable 

 objects, an increase in the carbonic acid formation is observed, it is 

 the more a distinct indication of the influence of light on respira- 

 tion. 



On the Relation of Assimilation and Colour, 



Priugsheim has some interesting remarks : — 



The known facts regarding assimilation in plants are not in op- 

 position to the view here advocated, that the colour only indirectly, 

 through respiration, takes part in this process, and that the colouring 

 matter has no share in decomposing carbonic acid. 



Out of the general notion that chlorophyll colouring matter plays 

 a direct part in assimilation, has developed the idea that its substance 

 enters directly into the process of decomposition of carbonic acid, 

 and that in this processs it is constantly being destroyed and re- 

 generated. This must be the basis of any chemical hypothesis of 

 its function in assimilation. It not only assumes the destruction 

 in light (and in daylight of medium brightness) of colouring matter, 

 but also that this destruction is a consequence of appropriation of 

 the carbon drawn from the carbonic acid decomposed. The carbon 

 "compounds formed through assimilation in the plant body would 



