WATER IN PLANT CELLS. 



33 



Movement of water 

 in a single cell. 



Immerse the leaves of some in water, and of another set in a 5$ salt solution. 

 The petioles of the leaves should not be immersed, for it is desirable to keep 

 the cut ends out of the water or salt solution. In fifteen minutes to half an 

 hour, lift the leaves and seedlings from the water and note the result, and 

 compare. Those which were in the salt solution now rinse in fresh water 

 and immerse for a time in water. Now note the result. Explain the results 

 of this experiment from the results obtained in the previous experiments. 



Synopsis. 



A strong salt solution draws water out of the cell-sap, and 

 the protoplasmic membrane is pushed inward. The 

 cell becomes flabby. 



Remove the salt and surround the cell with water, and 

 I the cell-sap draws water inside again, so that the pro- 

 toplasmic membrane moves out and presses strongly 

 against the cell wall and the cell becomes rigid 

 ("turgid ") again. 



The cell-sap then is a solution of certain salts. 

 The beet slice is a cell mass, or a mass of tissue. 

 Placed in salt solution some of the water is drawn out 

 of the cell-sap of all the cells by the salt solution ; 

 the mass of cells, or the slice, becomes flabby. 

 Placed in water it becomes rigid, or turgid, again. 

 The action is the same as in the single cell, but all the 



cells act in concert. 



I The action is the same with leaves, and other soft cell 

 (^ masses, or plant parts. 



When water and a salt, or sugar, solution are separated by an animal 

 membrane, the current of water is stronger toward the salt, or sugar, solu- 

 tion. The membrane holds back for a time the substance dissolved in the 

 water. So the protoplasmic membrane acts in the same way when it sepa- 

 rates two different liquids, where one is a stronger salt than the other, or 

 where one is a salt and the other is water. 



When the protoplasm is killed it cannot act as a diffusion membrane. 

 Material. Fresh material of spirogyra. 

 Fresh beets, dark red ones (winter-stored beets are good). 

 Leafy shoots of some succulent plants, in a fresh condition, or seedlings. 

 Common table salt, a 5$ solution in water. 

 95$ alcohol, and hot water for exercise 15. 



Wide-mouth bottle, thistle tube, small piece of bladder membrane, and 

 sugar, for demonstration 12. 

 Microscope, etc. 



Movement of water 

 in cell masses. 



