334 President's Address. 



matter, so likewise might the destruction of the cell-contents 

 of the green cells in intense light be referred to the colouring 

 matter as the starting point and, by its light absorption, agent 

 of the decomposition, or, the cell-contents might be regarded as 

 not sensitive to light, and the changes taking place in them 

 as merely secondary effects of the destruction of the colouring 

 matter. But such assumptions are improbable, and, indeed, 

 are contradicted by the facts that red light, in spite of its 

 stronger absorption in chlorophyll, is inactive ; that the visible 

 changes, whether paralysis or death, in intense light in the proto- 

 plasm of the cell are seen to be the direct effect of the light ; and 

 that in non-green cells there is an undeniable light-effect. Direct 

 proof that the colouring matter plays no necessary part is afforded 

 in the possibility of destroying green cells by the insolation of a 

 portion where there are no chlorophyll-corpuscles, e.g.,m a pro-embryo 

 or branch pro-embryo of Chara, where there are but few corpuscles 

 lining the wall, or the part of a living Nitella cell bared of chloro- 

 phyll-corpuscles. In such cases destruction proceeds as rapidly 

 as it would if chlorophyll were present. Again, those species of 

 Spirogyra are the most sensitive which have feebly coloured 

 chlorophyll bands, and the most widely separated bands. Cells 

 with approximated and deeply coloured bands are not more strongly 

 affected by light, as would be the case were the destruction of cell 

 contents a consequence of that of the chlorophyll colouring matter ; 

 on the contrary, there is greater immunity from light effect. 

 Differences in this respect are often very marked in one and the 

 same species of S^yirogyra. The effect of dissemination and 

 aggregation of chlorophyll in retarding the action of light on the 

 shaded part is easily observed in all green cells. The colouring 

 matter is less sensitive to light than the other sensitive elements of 

 the cell ; and this is the case, as experiments in red light show, not 

 only for lights of different intensities, but also of different spectral 

 breadths. 



The destruction, then, of protoplasm and the death of cells in 

 light'is a true light effect, independent of the destruction of chloro- 

 phyll coloiu'ing matter, taking place in green cells, as well as in 

 those otherwise coloured, before complete destruction of the colour- 

 ing matter, and it is not brought about through light-absorption in 

 the chlorophyll-corpuscles. It is developed by absorption in the 

 protoplasm itself of all the iUuminating rays of the spectrum, the 

 red rays up to those of wave lengths of -00061 mm. being excluded 

 from the action, and the chlorophyll colouring matter, instead of 

 increasing the light-effect upon the cell-contents of the part it 

 shades, lessens the same. This, the evident, and, indeed, necessary 



