8 o 
Blackman and Paine.—Studies in the 
Effect of Light on Protoplasmic Permeability of the 
Pulvinus. 
That light increases the permeability of the protoplasm has been 
demonstrated by Lepeschkin ( 3 ) and Trondle (6). The former demonstrated 
the effect of light on the permeability of the cells of the pulvinus of 
Phaseohis and of Mimosa , mainly by the use of the indirect plasmolytic 
method ; but he also showed that the total exudate from a number of 
pulvini of Mimosa in water was greater in the light than in the dark. 
Trondle relied entirely on the indirect plasmolytic method in his study of 
the mesophyll cells of the leaf of Buxus and Titia . 
It is clear that the conductivity method provides an almost ideal one 
by which the effect of light on the permeability to electrolytes can be 
studied, for the method can be made sensitive to extremely small quantities 
and readings can be for any period of time and the same organ can be used 
continuously throughout the investigation. 
The relation of light to permeability was not studied exhaustively, but 
a few experiments were made to test the value of the method. The 
pulvinus was prepared in the ordinary way with the sides sliced to increase 
the surface for diffusion, and it was illuminated through the glass side of the 
bath by a Nernst lamp of 50 candle-power placed 10 cm. from the pulvinus. 
As it was considered possible that the temperature of the water in the 
conductivity cell might be of a higher temperature than that of the bath, 
owing to the greater absorption of light by the green-coloured pulvinus, 
some of the experiments were made with a thermo-couple in the water of the 
* cell * and in the bath. A difference of not more than 0*3° C. was observed, 
which would mean that the readings in the light and dark would only differ 
by o*6 per cent, from this cause. Owing to the magnitude of the effect of 
light such a difference is, of course, quite negligible. 
Occasionally a pulvinus was met with which refused to react to light 
for unknown reasons, but the majority showed a very marked reaction, the 
rate of exosmosis of electrolytes, as measured by the increase of conductivity, 
being greatly increased. The graph shown in Fig. 4 shows the results 
obtained during an experiment of which Table IV gives the details. The 
increase in conductivity, measured in gemhos, for successive periods of 
15 min. is plotted against time; the periods of darkness are indicated by 
the dark lines on the axis of the abscissae. It will be seen that the pulvinus 
was kept in darkness during the first hour; on exposure to light exosmosis 
increased during the first half-hour, then, although still illuminated, the 
permeability began to decrease; when placed in darkness for a second 
period an initial rise in the rate of exosmosis was observed. These effects 
were repeated on further changes from darkness to light and from light to 
darkness. 
