GREEN 



235 



turgor, that is, they are in a state of tension produced by inside 

 pressure. This makes the cell plump, as one might say, or firm. 

 When cells are united together in masses as in vegetables, in 

 leaves, or in succulent stems, all of the cells being in a state of 

 turgor, these parts of the plant are firm and held in position. If 

 the cells lose their turgor the tissues become limp or wilted. The 

 inside pressure is due to the presence of certain salts, etc., in 

 the cell sap which are separated from the water outside of the 



Fig. 180. 



Amoeba, showing pscudopodia. Ect. ectoplasm, End. endoplasm, N, .nucleus, Pv. pulsating 

 vacuole. (After Claus.) 



cell by the cell wall and the wall layer or membrane of proto- 

 plasm. Since the water outside has no salts in it, or if present 

 they are in a less concentrated form than those in the cell sap, the 

 water moves more readily through the plasma membrane into 

 the cell sap than it can move outward. The inside pressure 

 presses the plasma membrane firmly against the cell wall. The 

 cell wall being elastic, yields slightly and thus is pressing in the 

 opposite direction against the plasma membrane. This pro- 

 duces the state of turgor in the cell. The opposite condition of 

 turgor in the cell is plasmolysis, or shrinking of the plasm. This 

 can be produced artificially by mounting some threads of spiro- 

 gyra in a five per cent solution of common table salt, or in a 



