310 President's Address. 



Perhaps the most widely accepted hypothesis of carbou- 

 assimilation and the physiological significance of chloro- 

 pliyll is a modification of that supported by Sachs and 

 Pfeffer, whereby the chlorophyll is recognised as the cause 

 of the process (how is inexplicable at present), and the 

 first visible product is either starch or oil. The process by 

 which this is brought about being probably that suggested 

 by Bayer, the formation as the primary product of formic 

 aldehyde. 



This brings us to the publication of Pringsheim's views. 

 For some years past he has been engaged with an investi- 

 gation of the character of chlorophyll-corpuscles, of the 

 action of light upon them, and the function performed 

 by chlorophyll in the plant. His investigations, whether 

 we agree or disagree with his conclusions, form a most 

 valuable contribution to the elucidation of a complex sub- 

 ject, and his hypothesis regarding the part performed by 

 the green colouring matter is an ingenious and a very 

 interesting one. 



His method of investigation, in addition to that of 

 ordinary micro-chemical observation, has been w^hat he terms 

 microscopical photo-chemistry, by which the action of light 

 on the contents of the plant cells, and the light and heat 

 absorption in the several elements of the cells, and the 

 activity stored up within the tissues by the sun's rays, may 

 be observed directly under the microscope. Light is 

 concentrated on the plant-cells under the microscope, and 

 the effect of the sun's rays and the component parts thereof 

 are readily studied. 



And, firstly, must be noticed his observations on 



Structure and Composition of Chlorophyll-corpuscles. 



In micro-chemical investigations of clilorophyll-corpuscles hitherto 

 made a solvent has been generally used for separating the colouring 

 matter from the ground-substance of the corpuscle, a method 

 possessing the disadvantage that other substances besides the 

 colouring matter are extracted in the solution from the corpuscle, 

 and these have not been sufficiently distinguished and separated from 

 the colouring matter. In Pringsheim's investigations a new method, 

 against which such objection cannot be raised, has been employed. 

 It consists in warming green tissues in water or subjecting them to 



