



1917J DENNY— PERMEABILITY 469 



approximately o?i C. In all experiments reported in this paper 

 the temperature was 25 C. Sodium chloride solutions were 

 used to induce the osmotic movement of water through the mem- 

 brane. With the peanut membrane (Arachis hypogaea), which is 

 rather highly permeable, concentrations of 0.5 M or 0.6 M were 

 found to be suitable; but for squash, cocklebur, etc., which have 

 fairly high resistance to water penetration, strong solutions of 

 sodium chloride were necessary; for use with such membranes a 

 saturated solution was used, that is, saturated at room temperature. 

 As noted in the previous paper, different membranes of the 

 same species differ in their permeability to water. This difficulty 

 was overcome by using the same membrane under the various 

 conditions of the experiment. In the tables of results each line of 

 a table represents data obtained from a single membrane; it is not 

 possible to compare one membrane with another; the data given 

 by an individual membrane under different conditions must be 

 compared. 



Effect of extracting membranes with boiling water 



It was noted that heating the seed coat of Arachis hypogaea in 

 boiling water increased the rate at which water passed through. 

 Measurements were made to determine the extent of this increase; 

 and other membranes were tested for similar behavior. The 

 method employed was as follows. A membrane was removed from 

 a soaked seed, fitted into the osmometer, and a measurement made 

 of its permeability. It was then removed from the apparatus, 

 placed in cold distilled water, and heated to boiling point and 

 allowed to remain in boiling water for 5 minutes. It was then 

 placed in the osmometer and a reading made of its permeability. 

 This process was then repeated with other membranes. Table I 

 shows the results, which are expressed in milligrams of water 

 passing through a membrane per hour; the same unit is also used 



in subsequent tables. 



The data show that heating the membrane in boiling water 

 increased the permeability of the peanut and almond membranes, 

 but not that of the grapefruit and squash coats. However, the 

 last two membranes are so slightly permeable that a considerable 



