

f 



1917] 



DENN Y—PERMEA BILI T I 



375 



in which a portion of the seed coat was used as the membrane, and 

 made preliminary measurements on the rate of penetration of 

 water. The problem of getting quantitative measurements of 

 the permeability of various plant membranes was then undertaken 

 by the writer with the results here reported. 



The rate of penetration of water through membranes was 

 measured with an osmometer of the design shown in figs. 1 and 2. 

 A, B, and C are hard rubber discs, 3 . 5 cm. in diameter and 2 mm. 

 in thickness. Brass discs also were used, but are not suitable for 



Fig. r. — Photograph of osmometer: explanation in text 



use with salt solutions. In the centers of A and B at K is a hole 

 of known diameter. Between A and B and over this hole the 

 membrane to be studied is placed ; thus the area of the membrane 

 used can be calculated. D is a hard glass cylinder with ground 

 edges fitting snugly against the hard rubber discs. Soft rubber 

 gaskets are interposed between the glass cylinder and the discs 



made 



admitt 



The 



latter is tilled with distilled water until water appears in the hori- 

 zontal capillary tube. The position of the meniscus in G may be 



nf tV»f <;tonrork in F. G is a 



means 

 ro cm. 



capillary tube with about 10 



capillary bore of approximately i mm. Scale divisions on G were 



