322 President'' s Address. 



their contents, hitherto hardly recogniscahle, now appear sharply 

 circumscribed. Finally, the protoplasmic utricle separates from the 

 cell-wall, and all the signs of death from light are apparent. In the 

 insolated part the chlorophyll-corpuscles exliibit none of these 

 changes, nor does the protoplasmic utricle separate from the cell- 

 wall ; and this portion may remain in this condition for months, 

 long after the adjacent chlorophyll-corpuscles have disintegrated. 



If before death is set in and before the chlorophyll corpuscles are 

 completely decolorised the light be interrupted, then the partly or 

 almost entirely decolorised chlorophyll-corjjuscles separate from the 

 utricle ^ind fall into the rotating protoplasm, and with the formed 

 elements circulate uninterruptedly in its current, forming often 

 small heaps of corpuscles without disturbing the rotation ; and 

 though they gradually lose colouring matter, and after a time are 

 quite colourless, they suffer no further change in form or substance. 

 By degrees in this way the insolated part becomes deprived of 

 chlorophyll-corpuscles, and may get quite bare of them ; and Nitella 

 cells in this condition may be ke]Dt for months unchanged, the 

 rotation continuing vigorous, and the formed elements in the proto- 

 plasm and the chlorophyll-corpuscles in the non-illuminated area 

 retaining their normal form, colour, and arrangement. 



In other cases, again, if the action of light is of a high intensity, 

 and the insolated area is decolorised without the rotation being 

 stopped, there are often developed, especially in long cells and when 

 the insolated area is in the middle of the cell, two currents instead of 

 one, which rotate at opposite ends of the cell, each independent of 

 the other, and separated from one another by the insolated area, 

 which is a barrier to the movement. 



But this action of light is not confined to green tissues. Non-green 

 cells — for example, the blue-sapped hair cells on the stamen of Trade- 

 scantia virginica — are affected in the same way, and paralysis and 

 death may be produced. Paralysis may occur before or after destruc- 

 tion of the blue colouring matter of the cell-sap, and the circulation, 

 which is temporarily suspended, may after a longer or shorter time 

 return without the cell having suffered at all. Death occurs in them 

 also before complete destruction of the colouring matter. Whenever 

 the colour changes to violet the protoplasm is killed, circulation is 

 stojiped and never returns, and the protoplasm threads become granu- 

 lar, in part disappear or rupture irregularly, and the protoplasmic 

 utricle, separating from the cell-wall, collapses. A slight separation 

 of the cuticle over the insolated area is sometimes seen. 



All these efi'ects just described are dependent not only on the 

 high intensity of the light, but also upon its colour and the affinity 

 for oxygen of the cell-contents. All of them are produced rapidly 



