II. SOME QUANTITATIVE RESEARCHES ON THE PER- 

 !\IEABILITY OF PLANT CELLS' 



W. J. V. OSTERHOUT 

 Harvard University, Cambridge, Mass. 



The preceding speaker has said that our ignorance of some 

 physico-chemical aspects of our subject is nearly perfect. If this 

 be true of a field where accurate quantitative methods have long 

 been employed what shall we say of the biological branch of our 

 subject, W'here such methods have scarcely begun to be used? 

 It is this point of \'iew which leads the speaker to lay emphasis 

 upon some quantitative investigations of permeabihty. 



It is well known that qualitative methods have played the 

 chief part in the stud}' of this subject. The most important of 

 these may be briefly mentioned. 



The penetration of dyes has been commonly used as a criterion 

 of permeability, although the entrance of the dye can not as a 

 rule be demonstrated unless the dye becomes more concentrated 

 in the cell than in the external solution. It is, however, quite 

 clear that a dye may be able to penetrate the protoplasm freely 

 without becoming so concentrated within the cell. 



It can not be said that this method has led to any trustworthy 

 results of great importance. It appeared at one time to furnish 

 a substantial basis for Overton's theory that the outer layer of 

 the protoplasm is composed of lipoid substances.^ If this theory 

 were correct we should expect that only those dyes which are 



' Address delivered at the Symposium on Permeability and Osmotic Pressure 

 before the Botanical Society of America at Cleveland in January, 1913. 



' The term lipoid has been variously used to designate (a) non-saponifiable 

 substances soluble in ether and chloroform, (b) any fat -like substance soluble in 

 ether and chloroform. To many authors "lipoid soluble" apparently means sol- 

 uble in ether: to some it means soluble in oil; to others soluble in lecithin or chol- 

 esterin. In testing solubility some regard it as important to use lecithin or chol- 

 esterin which has been purified and freed from water, while others pay no attention 



129 



THE PL.^NT WORLD, VOL. 16, NO. 5, M.\T, 191.3 



