330 President's Address. 



cell of Nitdla be exposed. In this plant, however, it sometimes 

 happens that nohypochlorin shows on the green chlorophyll-corpuscles 

 of the non-isolated portion of the cell. The light effect in this case, 

 it would appear, has spread beyond the immediately exposed area, 

 and this may be explained by the fact that hypochlorin is one of the 

 most easily affected bodies in the cell Small increments of tem- 

 perature, mechanical stimuli, spontaneous disease, as already shown, 

 are, even when the chlorophyll colouring matter is intact, able to 

 destroy it in the cell. From these facts we may conclude that the 

 disappearance of hypochlorin is the earliest indication of a hurtful 

 influence affecting the plant cell, and its destruction results in 

 intense light earlier than does the destruction of the chlorophyll 

 colouring matter. 



(c) The protoplasm of the cell and turgescence as affected by intense 

 light. — The turgescence of cells is diminished by exposure to intense 

 light. In large-celled Algce this is shown by the vertical division 

 wall between insolated and non-insolated cells becoming curved 

 into the former. The tension of the insolated cell is decreased 

 relatively to the non-insolated by the greater permeability (as shown 

 by its behaviour to coloured solutions) for cell sap of its protoplasmic 

 utricle. If a filament of Spirogytv, some cells of which have been 

 insolated, be laid in a watery solution of aniline blue, the insolated 

 cells become rapidly coloured, the non-insolated are, even after some 

 days, still uncoloured. Nitella is very favourable for such an 

 observation, as the differences, owing to the length of the cells, may 

 be observed in one and the same cell, and moreover, as the rotation 

 is not stopped, one may study the difference in permeability between 

 the cell wall and the protoplasm, the former becoming rapidly 

 coloured, whilst beneath it the rotating protoplasm remains for a 

 time unchanged. 



The greater j^ermeability after insolation is associated with a 

 distinct change in structure and in mass of the protoplasm lining 

 the cell wall. It loses, as has been shown, a considerable amount of 

 its contractile power. The addition of plasmolytic agents, such as 

 iodine in iodide of potassium, causes little or no retraction of the 

 utricle in an insolated cell, and it depends upon the intensity and 

 duration of exposure to light, as well as upon the thickness of the 

 layer of protoplasm, to what extent the power of contraction is lost. 

 In Nitella this may be well studied. Here, as has been already 

 described, the contraction consequent upon death from insolation 

 advances gradually over those portions of the cell which have not 

 been insolated and are green, the protoplasm at first slowly separating 

 from the cell wall and then subsequently collapsing. Only at the 

 insolated part does the utricle show no, or almost no, contraction, 



