VISCOSITY, PERMEABILITY, PROTOPLASMIC STREAMING 565 



diffuse daylight sometimes exceeded that absorbed by similar cells in the 

 dark by as much as six times. No difference could be found with regard 

 to calcium and manganese. 



A thorough study was made by Jarvenkyla (1937). He used the epi- 

 dermal cells of the underside of leaves of Rhoeo discolor and the leaf cells 

 of Elodea densa and Chara ceratophylla. The two first-mentioned objects 

 were examined plasmolytically, Chara being used for analyses of the cell 

 sap. The permeability was tested to a number of substances, such as 

 ethylene glycol, glycerol, trimethyl citrate, urea, methyl urea, monacetine, 

 hexamethylenetetramine, malonamide, potassium nitrate, and lithium 

 chloride. 



The influence of light on the permeability varied with the test object, 

 the wave length, and the nature of the substance. A 300-watt lamp at 

 a distance of 41 cm caused an appreciable increase in the rate of perme- 

 ation of the substances in the case of Elodea and Chara but had no effect 

 in the case of Rhoeo. In the last-mentioned plant a positive effect of 

 light was obtained only in direct sunlight. The effect of light on the 

 permeability increased with decreasing wave length, mainly 450-600 m/z. 

 The reactions differed for the substances studied. The influence of 

 light was greatest in the case of hexamethylenetetramine, the perme- 

 ability to which was 80 per cent higher in the light than in the dark, 

 whereas the increase was only 10 per cent in the case of trimethyl citrate. 

 The other substances studied by Jarvenkyla had values between these 

 two extremes. 



Jarvenkyla also made the interesting observation that the effect of 

 light decreases with an increase in the solubility in Hpoids and with an 

 increase in the size of the molecules of the permeating substance. He 

 explained this connection by the assumption that light loosens lipoids in 

 the plasmatic membrane. 



Osterhout (1947) expressed the view that the increased intake o5 non- 

 electrolytes in Chara noted by Jarvenkyla could not be due to a supply 

 of energy, since there was no accumulation of the penetrating substance 

 and it does not seem possible that the pH was involved. He considered 

 that there might be a direct effect on permeabihty pr on the cell wall. 



Jarvenkyla's experiments also showed that a longer period (3 days) in 

 the dark increased the permeabihty. It is therefore possible that, in a 

 comparison between the permeability of objects that have stood in the 

 light and the permeability of those which have stood in the dark, the two 

 methods of treatment may give approximately the same results. This 

 may then be interpreted as evidence that light has no influence, although 

 in both cases the permeability has been altered by the light factor. Thus 

 the pretreatment of the object is of decisive importance for the results of 

 the experiments. 



In this case the similarity between the dependence of the permeability 



