THE PERMEABILITY OF ORGANIC MEMBRANES 147 



to be the nucellar epidermis. It consists of nearly pure 

 cellulose, and is unsuberized. Both layers contain some 

 tannin, but as this does not form a continuous layer, and 

 as semi-permeability is not destroyed by treatment with 

 tannin solvents, the evidence is adverse to Reichard's 

 (1909) theory, which regards semi-permeability in such 

 cases to be due to the deposition of tannin compounds. 



