326 President's Address. 



plays no part in the destruction of the green colouring matter, is of 

 considerable importance in view of the theory of the function of 

 chlorophyll colouring matter here advanced. 



The cells once colorised, whether to a great or slight extent, 

 never, even though they be not killed, regenerate the chlorophyll 

 colouring matter. The decolorisation sets in relatively slowly, be- 

 coming manifest only after a minute or so of exposure. The case of 

 Nitella, as previously described, is a very typical one. 



It may, then, be concluded, from such facts, that the destruction 

 in nature of chlorophyll is a pathological process, hurtful to the 

 plant, and not, as has been supposed, a normal process associated 

 with the breaking up of carbonic acid, and the fixing of carbon in 

 the green tissues. 



Ever since the days of Senebier opinions have widely differed 

 upon the destruction of chlorophyll in light, upon the relative energy 

 in the process of the diiTerent rays of the spectrum, and upon the 

 significance of the process, in the life of the plant ; the decolorisation 

 is ascribfed by one to frost, by another to heat, and by others to 

 light. The only accurate method of investigation is to study the 

 changes in the plant cells, and, as a result of the investigations here 

 recorded, the possibility of the destruction of chlorophyll colour 

 ing matter by intense light in the light in the living cells is 

 proved. 



Not only chlorophyll colouring matter, but also yellow, blue, and 

 red, are in presence of oxygen destroyed within the plant cells when 

 exposed to intense light. Yet all colouring matter found in plant 

 cells is not so acted on ; different colouring matters under like con- 

 ditions behave differently. Observations are still wanted to show 

 which are destructible and which are indestructible, and to supply 

 the key to the relation between destructibility of these colouring 

 matters of the cells in light and their genetic connection AAith chloro- 

 phyll colouring matter. As illustration: the red colouring matter 

 of many resting spores of Ahjw, especially oospores, is not destruc- 

 tible, or only with extreme difficidty, by exposure to intense light. 

 On the other hand, the steel-blue colouring matter of the Phyco- 

 chromacece (Osdllaricce, Nosfocacece, &c. ), the hrown oi Diafomacece, 

 Phceosporcce, and Fucacece, and the red of Floridew, in all their modi- 

 fications, are, it appears, as easily destroyed in intense light as the 

 chlorophyll colouring matter of green plants. 



Colouring matter of flowers seems to behave differently. The 

 yellow-red colouring matter of the ligulate flowers of Calendula is 

 with ease completely destroyed in intense light, whilst that of Nar- 

 cissus poeticus, in the same circumstances, remains unchanged. The 

 blue cell sap of Tradescantia virginica loses its colouring matter 



