President's Address. 333 



the influence of insolation, may cause the torsion and consequent 

 separation. It is possible, however, that clieniical changes of the 

 membrane at the limits of the cells may contribute to the result. 



Pringsheim then discusses 



Respiration in Light of Green Tissues and the Function of 

 Chlorophyll. 



All the fore mentioned results (he says) lead to the conclusion that 

 the amount of oxygen inhalation exercises a very definite influence 

 upon the assimilation by chlorophyll-corpuscles, and hence the gTeen 

 colour is of physiological value to assimilating organs, even if it play 

 no direct part in the decomposition of the carbonic acid. The 

 illuminating light rays exercise an immediately observable effect 

 upon the colourless protoplasm of the cells, especially upon the 

 ground substance of the chlorophyll-corpuscles and on their enclosed 

 substances. The destructive action within cells in intense light, 

 when oxygen is present, and the immunity observed in its absence, 

 indicate that the injurious effect of light is due to increased com- 

 bustion of the cell elements necessary to life. It is still a moot 

 point whether the cell elements which absorb oxygen in darkness 

 are the only ones that have their afiinity for the gas increased, or 

 whether the elements which, under normal conditions of darkness, 

 remain unoxidised are not also consumed in light. It is certain, 

 however, that the amount of respiration in green cells increases j>an 

 passu with the intensity of the light, and at the higher intensities 

 may reach such a degree as to kill the cell, and the light affects the 

 contents directly and not through the medium of the green colour. 



The degree of sensibility to light of the tissues of different plants 

 varies greatly, and may be ascribed to the anatomical character of 

 the contents and the dimensions of the illuminated cells. The 

 great difference between green and non-green cells is specially 

 noteworthy. The former are always more sensitive than colourless 

 cells, and, indeed, than cells having any other colour besides green. 

 It is, for example, more difficult to produce light paralysis and 

 death in blue and colourless cells of Tradescantia, or in the 

 filaments, sporangia, or oogonia of Saprolegnia, than in the larger 

 cells of Spirogijra and Eitella, or in cells of the leaves of Mnium 

 or VaUisneria. 



Naturally the cause of difference is sought for in the green 

 colouring matter, and such an explanation would be quite in accord 

 with the relation of the colour to the action of light in assimilation 

 as here demonstrated. As the seat of the action of light in 

 assimilation is usually misplaced in the chlorophyll colouring 



