CONDUCTIVITY AND PERMEABILITY 231 



the pigment. This can easily be shown by killing the cell, 

 whereupon the semipermeable membranes are destroyed 

 and the pigment at once begins to diffuse out. In this 

 case, we have to do with variety of semipermeable mem- 

 branes, such as the plasma membrane, the surfaces of the 

 plastids, the vacuolar surface,^® and the nuclear surface. 

 It is to be expected that these surfaces may differ some- 

 what in permeability. Each of them is in contact with 



FlQ. 96. — A cell of Griffithsia Bornetiana (in optical section), a, cell wall; b, protoplasm 



c, chromatophore containing chlorophyll and a red pigment (phycoerythrin) which is soluble 



in water; e, vacuole filled with cell sap. (Diagrammatic). 



a somewhat different environment, and this, as we have 

 already seen, might produce differences in permeability. 

 That such differences really exist is indicated by treating 

 the cells with NH4CI (neutralized by adding NII4OH) 

 which is not strong enough to plasmolyze. The vacuolar 

 surface then contracts while the plasma membrane main- 

 tains its original position. At the same time the surfaces 

 of the plastid become permeable and the red pigment 

 comes out: it cannot, however, pass through the plasma 

 membrane or the vacuolar surface. We see that all three 

 sorts of surfaces act differently, and to these we may add 



"de Vries (1885) states that certain dyes penetrate the outer sur- 

 face more easily that the surface of the vacuole. It has been objected 

 that the dye may combine with the protoplasm and hence cannot penetrate 

 the vacuole until the protoplasm is saturated. This might cause an 

 appearance of a difference in permeability. 



