36 



BOTANY OF THE LIVING PLANT 



solution of potassium nitrate is hypertonic and will withdraw water 

 from the cell-sap. The effect of immersion in such a solution can be 

 most readily observed microscopically in cells which contain a soluble 

 pigment in the cell-sap, giving greater definition to the outlines of 

 the vacuole and of the protoplast. Sections of the Red Beet may be 

 used, or strips of epidermal cells of leaves such as Cyclamen, where 

 a red pigment is again present. The initial effect of immersion is a 

 shrinkage of the whole cell as the pressure of the contents on the 

 wall is relaxed (Fig. 18, i. and ii.). In a very short time the protoplast 

 breaks contact with the cell-wall and shrinks to a further extent. 

 The cell is now said to be plasmolysed (Fig. 1 8, iii.). The space between 



Fig. 18. 



Young parenchymatous cell (i.) in the turgid state, (ii. and iii.) successive ap- 

 pearances of cell after immersion in a hypertonic solution of potassium nitrate. 

 it'=wall; c = cytoplasm; n = nucleus ; s = cell-sap; e= nitrate solution which has 

 passed through the cell-wall. (After De Vries.) 



the cell-wall and the protoplast is filled with the nitrate solution, 

 illustrating the fact that the cellulose cell-wall is readily permeable 

 to water and to dissolved, crystalloidal substances. Turning to the 

 cytoplasm, it will be noticed that there is no outward leakage of the 

 red pigment, the colour of which is intensified by the concentration 

 of the sap. The cytoplasmic lining constitutes a membrane that is in 

 life to some degree semi- permeable to the sap. 



If plasmolysis be carried out slowly by means of dilute solutions, fine 

 threads of cytoplasm may often be seen to stretch from the cell-wall to the 

 contracted mass (Fig. 19). This indicates under normal conditions of the 

 cell an intimate relation between the two bodies, which is in accordance 

 with the deposit of the cell-wall from the protoplasm. But it is uncertain 

 what relation, if any, these cytoplasmic threads have to the threads that 

 establish protoplasmic continuity through the cell-wall (Chapter II.). 



