Guilliermond - Atkinson — 126 — Cytoplasm 



their vacuoles an anthocyanin pigment which gives them a natural 

 color, it is observed that as the cells become plasmolyzed the color 

 of the vacuole is considerably accentuated. The pigment therefore 

 is becoming concentrated in the vacuole. 



The phenomenon of plasmolysis takes place only in living cells. 

 A dead cell has become permeable and can no longer be plasmolyzed. 

 Therefore the capacity of the cell for being plasmolyzed serves as a 

 criterion as to whether the cell is living. 



When carried out with certain precautions, plasmolysis does 

 not cause the death of the cell and may be followed by the converse 

 phenomenon, if the cell be placed in a solution of pure water. 

 Endosmosis then occurs which again brings about the dilation of 

 the vacuole and the cytoplasm once more becomes pressed to the 

 cell wall. The cell now recovers its normal aspect. It is said to 

 have been deplasmolyzed. 



As the ectoplasmic layer which lines the interior of the cell 

 wall is generally only relatively semi-permeable, plasmolysis is fol- 

 lowed, at the end of a period varying according to the case, by a 

 spontaneous deplasmolyzing action which is brought about by the 

 gradual penetration into the vacuole of the substance dissolved in 

 the surrounding medium. Thus there is re-established an osmotic 

 equilibrium between the vacuolar sap and the external medium. 



If plasmolysis is brought about too brusquely, however, it leads 

 to the death of the cell. As soon as this happens, the ectoplasmic 

 layer disorganizes and water enters the cellular cavity. The proto- 

 plasm is coagulated and the cell cavity now contains nothing but 

 protoplasmic coagulations floating in the water which has accumu- 

 lated within the cell cavity. Now, during this phenomenon the 

 vacuole, which is more resistant, remains stretched out in its 

 habitual shape and, if it contains anthocyanin, this pigment remains 

 localized within the vacuolar sap. The vacuole appears to be sep- 

 arated from the medium by a limiting semi-permeable layer. This 

 layer is resistant much longer than the ectoplasmic layer. The 

 vacuole may thus be preserved for a very long time. Then its 

 limiting layer is destroyed in turn, and the contents of the vacuole 

 blend with that of the cell cavity. In this way the vacuole may 

 subsist within the cell cavity after the death of the cell. This 

 phenomenon DE Vries called the isolation of the vacuole, a classical 

 phenomenon which has been seen since by numerous investigators : 

 TswETT, Guilliermond, Kuster, Weber, Hofler, Eichberger, etc. 



This phenomenon demonstrates that the vacuole is limited ex- 

 ternally by a peripheral, semi-permeable layer. It is of the same 

 nature as that which surrounds the outside of the cytoplasm and 

 is called the endoplasmic layer, or perivacuolar layer. It is how- 

 ever much more resistant than the outer cytoplasmic layer. 



As a result of his work, DE Vries was led to consider this semi- 

 permeable layer as a differentiated membrane and the vacuoles as 

 permanent components of the cell. He considered that the vacuoles 

 are made up of vacuolar sap, containing in solution various crys- 

 talloid substances, are surrounded by a semi-permeable, differen- 



