104 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



With a lower concentration of ammonium chloride a 

 marked contraction of the inner surface can be produced 

 while the outer still maintains its turgidity. That such a 

 condition is due, in part at least, to false plasmolysis is 

 shown by the fact that it may be brought about by hypo- 

 tonic solutions, tap-water, or even distilled water. 



In the protoplasm of thfe alga are embedded numerous 

 chromatophores, containing chlorophyll and a red pig- 

 ment soluble in water. When separation of the inner 

 and outer protoplasmic surfaces has proceeded to a certain 

 degree, the surfaces of the chromatophores becomes perme- 

 able to -the red pigment, as is shown by its diffusion into 

 the protoplasm. The outer and inner protoplasmic 

 surfaces still remain impermeable to it, so the vacuole 

 and surrounding solution are uncoloured. This condition 

 may be maintained for a couple of hours, when suddenly 

 the pigment begins to diffuse from the protoplasm. At 

 the start the nuclei are not penetrated by the colouring 

 matter, but soon after diffusion from the chromatophores 

 has taken place they also become red. 



From such researches it is clear that the various sur- 

 faces of a cell exhibit differences in permeability. For 

 these phenomena Osterhout has suggested the term dif- 

 ferential permeability. This conception may be extended 

 to all intracellular surfaces, down to those which are 

 ultramicroscopic . 



FALSE PLASMOLYSIS. 



Appearances almost or quite indistinguishable from 

 true plasmolysis may be brought about by hypotonic 

 solutions, or even by distilled water. These Osterhout 

 (1913, 2), to whom the investigations on this subject are 

 due, has termed false plasmolysis. 



The root-tips of Zostera marina were employed as suit- 

 able for study, and were mounted in their normal medium , 



