VISCOSITY, PERMEABILITY, PROTOPLASMIC STREAMING 575 



streaming did not, however, cease altogether in the two last-mentioned 

 forms of light. 



As a result of the aftereffects of light, protoplasmic streaming continues 

 during the night in the summer, as has been shown by Fitting (1925). 

 During the winter, on the contrary, it stops during the night. The after- 

 effect of light on the protoplasmic streaming thus resembles its after- 

 effects on the viscosity. The processes that are started by the daylight 

 continue during the night and, to all intents and purposes, do not cease — 

 at any rate, not during the lightest part of the year. 



After protoplasmic streaming has decreased or ceased as a result of 

 continuous illumination, it can be stimulated or restarted by means of 

 an increase in the strength of the light. Moore (1888), Schroter (1905), 

 and Andrews (1912) were able to observe an increase in the rate of stream- 

 ing with an increase in the strength of illumination, as long as the latter 

 was kept within moderate limits. Greater intensities of light caused 

 cessation of the streaming, as had already been noted by Hofmeister 

 (1867), Pringsheim (1882), and other workers. As a rule, however, this 

 effect of light appeared to be only a secondary effect and a result of the 

 destructive processes caused by illumination. 



Mast (1932) studied the effect of partial illumination of Amoeba. He 

 found that the different parts of the cell varied in their reaction to an 

 increase in the intensity of illumination. In some cases the streaming 

 of the protoplasm ceased; in others it. changed in direction or increased 

 in rate. He also concluded that light causes gelation of the plasmasol 

 adjoining the plasmagel of the amoeba, making it thicker and increasing 

 the elastic strength of the portion illuminated. 



Bottelier (1933, 1934) made an interesting observation, namely, that 

 illumination for a short period (3 4 min) can give rise to both an acceler- 

 ation and a retardation of the protoplasmic streaming. He studied this 

 phenomenon on the epidermal cells of the Avena coleoptile and found 

 that the nature of the reaction was dependent on the quantity of light 

 applied. A very slight amount of light (2-11 ergs/cm^) caused a retar- 

 dation, lasting about 4 min, whereas a larger amount (800 ergs/cm^) 

 accelerated the streaming. The intensity of the reaction followed the 

 law of products. Bottelier also noted that blue light had the greatest 

 effect, followed by violet, ultraviolet, and green, in that order, and that 

 yellow and red Hght had no demonstrable effect. His comparisons were 

 based on experiments with the same quantity of energy (in ergs per square 

 centimeter per second). 



In connection with his other studies on protoplasmic streaming and its 

 conditions, Fitting (1925) also investigated the effect of hght, which he 

 named "photodinesis." He expressed the opinion that protoplasmic 

 streaming is not induced by light alone but by a transition from weak 

 to stronger illumination. Ewart (1903) had earlier noted that a change 



