37 



protoplasm, and this retaining property is due, then, to the 

 protoplasm lining the cell-wall. For if a section of beet-root 

 is placed in a tolerably concentrated solution of some salt, such 

 as nitrate of potash, or common salt, the cell-wall will not be 

 found to alter much in shape, but the layer of protoplasm lining 

 the cell-wall will contract away from it towards the centre, and 

 form an irregular bag in the middle of the cell, leaving a large 

 space between it and the cell-wall — i.e., we have produced a 

 plasmolytic condition of the protoplasm. Yet, though the 

 protoplasm has contracted, the red fluid contained in the 

 vacuole has not escaped ; and since it is plain that the fluid in 

 its integrity could not have remained in the cell in its now 

 reduced size, something must therefore have passed out, what 

 has done so being simply pure water. The protoplasm, then, 

 so long as it is living, prevents coloring matter passing out 

 through it, and this is true also of other substances — e.g., grape 

 sugar, which occurs abundantly in the beet-root's cells, dissolved 

 in the red cell-sap. While an objection might possibly be 

 entertained to the evidence of the red coloring matter, inas- 

 much as it belongs to the class of bodies denominated "colloids" 

 by Graham, the case of the sugar presents no such ambiguity, 

 because it is a crystalline substance belonging to Graham's 

 class of" crystalloids," and, therefore, should dialyse through a 

 membrane such as the cell-wall, were it not for the retaining 

 power of the protoplasm exercised upon it ; for even in the 

 plasmolytic condition above described it is still impossible to 

 detect any trace of cane sugar outside the cell. But it may be 

 objected that in plasmolysis you have destroyed the life of the 

 cell. That this is not the case may be satisfactorily demon- 

 strated; for it is possible, by gradually diluting the salt solution 

 with water, to bring the cell back again from the plasmolytic 

 condition into a turgid state, yet during all this time there has 

 been no escape of the coloring matter. Precisely the same 

 effects will occur if these experiments are repeated on a 

 growing plant, which will go on growing as before after they 

 are over, so that this is proof enough that they do not 

 destroy the plant's life. As we shall see, these observations 



