PERMEABILITY OF MEMBRANES AS RELATED TO 



THEIR COMPOSITION 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 23 1 



F. E. Denny 



(with six figures) 



Introduction 



In a previous paper (1) measurements were made of the rate 

 at which water passes through known areas of certain membranes. 

 Different species of plants and different membranes of the same 

 species showed large differences in the rate of penetration. From 

 these facts the following questions arise. What substances in the 

 membrane are determining the rate at which water can pass 

 through it ? Of what relative importance in this process are lipoids, 

 proteins, tannoids, suberin, pectic substances, etc. ? An attempt 

 was made to answer these questions by quantitative measurements, 

 and this paper records the results. 



The role of different substances in the membrane in regulating 



its permeability to water was determined by comparing the per- 

 meability of a membrane before and after extracting it with the 

 solvent of the material studied. Thus, for example, to determine 

 the effect of lipoid materials upon the permeability of the membrane, 

 its permeability in the normal condition was first measured; it 

 was then extracted with a lipoid solvent (for example, acetone), and 

 its permeability again measured. These two measurements 

 were then compared. To accompany these measurements, micro- 

 chemical tests were made to give information as to the nature of 

 the materials composing the membrane, and the effect of these 

 extractions upon its composition; and for comparison chemical 

 analyses were made of the membrane and the extracted materials. 



Methods 

 The osmometer used has been described and figured in a 



previous 



immersed 









stant temperature water bath and the temperature 



Botanical Gazette, vol. 63] 



[468 



