President's Address. 345 



stance wliich is a constant and essential product of assimilation in 

 tlie corpuscles is hypochlorin. The idea that the primary product 

 of assimilation may vary in different plants, and that these sub- 

 stances may thus aU be direct products under different conditions, is 

 improbable, and of no explanatory value Xo fact positively for- 

 bids such a notion, but the similarity in structure and composition 

 of the chlorophyll-corpuscles, and the great agreement in gas inter- 

 change amongst green tissues, indicates an identity in all of the 

 assimilation process. Whatever theory be adopted, there remains 

 to be explained how it is that in one plant starch or fat, or it may 

 be both these substances, in another tannin, or perhaps sugar, and 

 in all hypochlorin, are formed and deposited inside the chlorophyll- 

 corpuscles. 



The theory here advanced is based upon the absorption of oxygen 

 by the chlorophyll-corpuscles, and upon the chemical nature of their 

 included bodies. These all agree chemically in this, that they are 

 non-nitrogenous, and they are visible products of assimilation, 

 derivates, differing from one another in oxygen content, of the car- 

 bonic acid and water decomposed in the process, the extent of their 

 oxygenation being determined, on the hypothesis of a single primary 

 assimilation product, by the amount of respiration in the corpuscles 

 as governed by the intensity and colour of light. From the side of 

 chemistry this view is not contradicted, but its admissibility depends 

 on anatomical and physiological considerations. 



The primary reduction product, of which, by oxidation, the 

 ternary compounds in the chlorophyll-corpuscles are in the widest 

 sense derivates, is to be sought for in the drops exuded from the 

 corpuscles after treatment with dilute acid or moist warmth, as 

 these contain all the constituents of the corpuscle sensitive to light, 

 and with strong affinity for oxygen. AU the nitrogenous com- 

 pounds and stable ternary assimilation products^ — starch, fat, tannin, 

 &c. — remain intact within the corpuscles. In the exuded mass, 

 hypochlorin, which is the only very sensitive substance besides the 

 colouring matter itself, is present as is known. Its universal occur- 

 rence has already been referred to. "Wherever chlorophyll occurs it 

 is to be found ; so constant, indeed, is this, that in epidermal cells 

 and hairs of phanerogams, or the cells of phanerogamic parasites, in 

 which clilorophyll-corpuscles are exceedingly sparsely distributed, 

 their assimilatory activity may be readily proved by the demonstra- 

 tion of hypochlorin through treatment with acid or other suitable 

 reagent. It is found along with and without the other constituents 

 above mentioned. They may be derived from it ; it cannot arise 

 from them. Its sporadic occurrence in the chlorophyll-corpuscles 

 of one and the same cell indicates its employment in assimilation. 



