DEPARTMENT OF BOTANICAL RESEARCH. 59 



It is obvious that the osmosis resulting in these cells was not proportional 

 to that which might have ensued if the walls of the cells had been constructed 

 of membranes such as parchment or collodion, which would not have been 

 affected by the substance in the filling solution. Their ions, however, exert a 

 marked effect on the colloidal condition of the colloids of the wall of this cell, 

 producing changes which modify its permeability in a very marked manner. 



Effect of Lipins in Interchanges between Cells and the Environment, 



by D. T. MacDougal. 



Accumulating evidence, including biochemical tests of the occurrence of 

 lipins or phosphatides in cells, microscopic and ultramicroscopic examina- 

 tions of plasma and wall, and the use of reagents which would liquefy such 

 lipins, supports the conclusion that the external layer of protoplasm is essen- 

 tially a deposit of these fatty substances. Not only are the lipins abundant 

 in this part of the cell, but strands are found to extend into the protoplasm 

 and into the wall. 



An experimental consideration of these new aspects of the cell was made 

 by osmotic tests with the artificial cell described in the report of this depart- 

 ment for 1921, and has been perfected further, as noted in the present report. 

 The results thus obtained have been correlated with measurements of hydra- 

 tion tests of biocoUoids and with the swellings of living and dried cell-masses 

 in solutions identical with those used in the artificial cells. 



The incorporation of lecithin representing the lipins in a biocoUoid repre- 

 senting protoplasm did not materially affect the water-holding capacity of 

 the mass. When this material, however, formed a layer on the outside the 

 absorption of water from solutions of various salts was modified in an impor- 

 tant manner. That such a layer is present in the living cell is demonstrated 

 by the fact that when saponin as a substance which will displace or liquefy 

 lipin is used, the cell becomes highly permeable and salts readily pass into 

 and out of it. 



That the lipin may exert a decided influence on permeability is shown by 

 the results obtained with the artificial cell. This material is less permeable 

 to salts than such pentosans as agar in a jelly form, so that when a layer of 

 it is placed between the agar plasma of a cell and the outer wall, the osmotic 

 effect is increased. 



The immersion of a living cell in water is followed by the absorption of 

 water until the full capacity of the protoplasm is reached and the cell attains 

 the greatest possible size under the restraining influence of the wall. If the 

 water in which the cell is immersed contains substances in solution which 

 penetrate the wall and make it and the outer layer of protoplasm more per- 

 meable, the amount of swelling shown will be reduced. In accordance with 

 these facts, a cell which will show an increase of 40 per cent of its volume in 

 distilled water will not increase more than one-fourth of this amount in a 

 0.005 M solution of saponin. Potassium hydroxide, which liquefies fatty 

 substances, exerts a similar effect on swelling at 0.01 N. 



The hydration, swelling, or absorption of water by living and dead cells 

 are of a kind which might be displayed by a coUoidal mass surrounded by a 

 laj^er of lipin or fatty material and inclosed in an extensible and highly per- 

 meable wall. 



