THE CELL. 7 



cell without plasm does not grow, does not tal\e in food, does not 

 live. There is no mechanics of plasm ; cell-life is still wrapt in 

 obscurity. Direct observation shows that plasm gives rise to 

 the cell-wall, as in the case of Stigeoclonium.^ The plasmic utricle 

 contracts, escapes from the opening in the cell-wall, and in time 

 surrounds itself with a new wall. To trace a phenomenon back to 

 plasm is as a rule the present limit of our ability. 



II. PRIMORDIAL UTRICLE AKD CELL-WALL 



IN THEIR MUTUAL RELATIONSHIP. 



TURGOR. PLASMOLYSie. 



The primordial utricle is usually of immeasurable thinness. In 

 order to represent it in a figure such cells or portions of cells are 

 selected in which it is of perceptible thickness as it lies in contact 

 with the cell-wall. As a rule it can be made visible only by caus- 

 ing it to separate from the cell-wall either through causes inherent 

 in the cell itself or by artificial means. When this plasmic 

 contraction is artificially induced it is recognized as " plasmoly- 

 sis." The phenomenon of plasmolysis can be explained only from 

 the inherently different properties of the cell-wall and primordial 

 utricle. It is at once evident that the endosmotic properties of the 

 bladder of an animal filled with a solution of some salt cannot be 

 compared with a living cell. It can only be compared with a dead 

 cell-wall. 



If a living cell with cell-sap (ex., hair-cell of petal of Tradescantia) 

 of a given concentration is placed in distilled water, then the endos- 

 motic flow of water through cell-wall and primordial utricle into the 

 cell is greater than the outflow of cell-fluid. The endosmotic sub- 

 stances within the cell attract the water, which therefore increases the 

 cell volume. The limit of this increase is determined by the cell- 

 w^all because it is less extensible than the primordial utricle, although 

 much more elastic. (Elasticity is that force which replaces dis- 

 placed molecules. It is very great in the cell-wall and very small in 

 the plasmic utricle.) The cell-wall is therefore a hindrance to the 

 excessive expansion of the primordial utricle. Action induces 

 reaction : the cell-sap which exerts a given pressure upon the cell- 

 wall in turn receives an equal pressure. This mutual pressure 

 of cell-sap upon cell-wall and cell-wall upon cell-sap is called 



Studied by Nageli. 



