TURGIDITY 



l8l 



D 



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NN 



parchment in a cylinder filled with water and note the rise of 

 the column in the capillary tube during the next few hours, due 

 to the attraction of sugar for water. Wash 

 the membrane thoroughly and fill the capsule 

 with a solution of di-sodic phosphate colored 

 deeply with methylene-blue. Note the rise 

 of the column and also that some of the color 

 is diffused out into the water of the cylinder. 

 Refill again with di-sodic phosphate and me- 

 thyl-blue and immerse the capsule in a solu- 

 tion of calcium nitrate (i per-cent.) for a 

 short time. Now place in a cylinder of water 

 as before. The calcium nitrate forms a pre- 

 cipitate in the membrane, and this changes 

 its permeability so that it does not allow the 

 coloring matter to pass through it to any 

 great extent. Similar changes take place in 

 walls and membranes with analogous re- 

 sults. 



252. Turgidity. If the outlet tube of the 

 osmometer in the last experiment is closed, 

 the parchment cylinder is expanded to its 

 fullest capacity for stretching and becomes 

 hard and rigid, resembling the condition of a 

 cell under similar circumstances. The princi- 

 pal substances in protoplasts which attract 

 water from the outside are sugars, salts of 

 organic acids and potassium nitrate. ,The 

 plasmatic membranes show specific resistance 

 to the diffusion of these substances outwardly, 

 or else the cell would quickly lose its power of inducing 

 endosmosis and maintaining turgidity. The substances ab- 

 sorbed in this manner are quickly changed into some form not 

 so readily diffusible, so that a turgid cell has a constant stream of 

 solution passing through its walls and plasma into the vacuoles. 



B 



V 



Pig. 87. Osmometer. 

 A, glass vessel contain- 

 ing distilled water. B, 

 parchment cylinder. C, 

 stopper. ' D, Ttube. £, 

 capillary extension tube. 

 G, joint made with rub- 

 ber tubing and wired. 



