258 BOTANICAL GAZETTE [September 



also with a 32 C.-P. electric lamp as light source, tie found an 

 increase of permeability up to a certain light intensity (50 cm. from 

 the lamp), and then a decrease at the higher intensities (35-10 cm. 

 from the lamp). 



method 



The method for determining permeability is essentially that of 

 Lepeschkin (6). This method is based on the fact that the per- 

 meability of protoplasm to sucrose does not change under varying 

 conditions, while the permeability to potassium nitrate does change. 

 That is, with increasing permeability, higher concentrations of 



asm 



Weight molecula 



o 



the percent- 



ages in any series varied by 0.02 mol. The tests of permeability 

 at the temperatures from 20 to 50 C. were carried on in a constant 

 temperature oven, electrically controlled; those below 20 C, in an 

 ice chest. Of course, all were in darkness. Seeds were germinated 

 on filter paper in large Petri dishes. When the roots were about 

 1 . 5 cm. long, they were put in covered watch glasses containing 

 the solutions and left for 20 minutes. Then they were put on a 

 slide in a drop of the solution and observed as quickly as possible. 

 Repeated examination of sections of roots plasmolyzed at vari- 

 ous temperatures showed that the degree of plasmolysis of the root 



asmo 



tical cells of the root. When the urotoulasm 



from 



asmolyzed. When the DrotoDlasm 



hair is beginning to break up into several parts, the walls of all the 

 cortical cells of the corresponding part of the root are slightly 

 shrunken. In complete plasmolysis the protoplasm of the root 

 hairs is rounded up into three or four parts, and the cortical cells 

 are plasmolyzed. The criterion then for slight p 



asmo 



slightly drawn back from the tip. 



which 



DATA 



The effect of temperature on permeability is shown in the 

 accompanying figures. The ordinates give the percentage weight- 



