GREEN ALGM 



215 



normal condition of working cells they are in a condition of 

 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 tur- 

 gor the tissues become 

 limp or wilted. The 

 inside pressure (or en- 

 dosmotic pressure) is 

 due to the presence of 

 certain salts, sugars, 

 etc., in the cell sap 

 which are separated' // 



from the water outside 

 of the cell by the cell ' Fig. 171. 



n 1,1 11 i Amoeba, showing pseudopodia. Ect. ectoplasm, End. 



Wall and the Wall layer endoplasm, N. nucleus, Pv. pulsating vacuole. (After 



or membrane of proto- 

 plasm (or more strictly speaking by the ectoplasm). 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 walls. The cell wall being 

 elastic, yields slightly and thus is pressing in the opposite direction 

 against the plasma membrane. This produces the state of turgor 

 in the cell. The opposite condition of turgor in the cell is plas- 

 molysis, or shrinking of the plasm. This can be produced arti- 

 ficially by mounting some threads of spirogyra in a five per cent 

 solution of common table salt, or in a strong sugar solution. 

 This solution being of a greater concentration than that of the 

 cell sap, the .flow of^the water is now m_the outward direction 

 through the plasma membrane, and this is pressed inward from 



