VISCOSITY, PERMEABILITY, PROTOPLASMIC STREAMING 553 



plasma is labile. Moreover, it varies with the physiological condition and 

 development of the organism (see Seifriz, 1936). 



Weber (1929a) was presumably the first to study the effect of light on 

 the viscosity of the protoplasm. He infiltrated leaves of Ranunculus 

 ficaria with a strongly hypertonic solution of potassium chloride and cal- 

 cium chloride and observed the course of plasmolysis in the cells of the 

 spongy mesophyll. He compared leaves exposed to sunlight under 

 natural conditions or to diffuse daylight with leaves that had been kept 

 in the dark. In the last-mentioned, plasmolysis took place rapidly, and 

 the protoplasm assumed a convex form. He interpreted this as a sign of 

 low viscosity. In the leaves exposed to light, on the other hand, plas- 

 molysis was retarded, and the protoplasm freed itself from the cell wall 

 with concave surfaces. These results give the impression that the proto- 

 plasm has a high viscosity (adhesion, stickiness). In another study 

 Weber (1929b) demonstrated that, as a result of such differences, the 

 onset of plasmolysis may vary from a few seconds to a long period. 

 Weber did not, however, make any definite statements regarding the 

 mechanism of the effect of light. He left as an open question whether 

 light has a direct effect on the protoplasm or whether its action takes 

 place as a result of other effects, such as heating, transpiration, or 

 photosynthesis. 



By means of centrifugation of the objects, Alsup (1942) studied the 

 effect of light on the viscosity of the protoplasm in Amoeba proteus and 

 A. dubia and the dependence of the effect on the presence of calcium. 

 Centrifugation was performed with a hand centrifuge, and the moving of 

 the granules was observed. He used a microscope lamp of approximately 

 300,000 m-c as the source of light. The experiments showed that illumi- 

 nation increased the viscosity of the cortical protoplasm ("plasmagel") 

 approximately 30 per cent and that this change started immediately. 

 The increase in viscosity could be detected within 10 sec after the expo- 

 sure and persisted for over 15 min. Calcium was found to be essential 

 for this gelating action, since light did not increase the viscosity of the 

 plasmagel of amoebae immersed in ammonium oxalate. The ''plasma- 

 sol," or inner protoplasm, of A. dubia was also gelated by short exposures 

 to the intensive light, and the effect persisted for at least 3 min. It could 

 also be prevented by removal of calcium from the cells with oxalate. 



In investigations made by Stalfelt (1945, 1946), leaves of Elodea densa 

 served as the test object, and the viscosity was measured by centrifuging 

 the leaves. The centrifuge (angle type, about 3000 rpm) had four tubes, 

 and eight leaves could be tested at the same time. On centrifugation 

 the chloroplasts moved to the distal end of the cells. The time required 

 for this moving was taken as an indicator of the viscosity of the proto- 

 plasm. After centrifugation the chloroplasts returned to their normal 

 positions, and streaming continued as prior to it. No detrimental influ- 



