1917] 



DEX N Y—PERMEA BILI T Y 



475 



for proteins. — Biuret reaction; those containing tyrosine 









Millon 



those containing trypto- 



phane give a violet color by Liebermann's reaction; other protein 

 tests were not found to be suitable because the color of the mem- 

 branes interfered with the tests. 



Tests for cellulose. — Blue color with sulphuric acid and iodine, 

 and dissolves in copper-oxide-ammonia. 



..-£ 



Membrane of peanut (Arachis hypogaea) 



The cells in the layer at a (fig. i) have walls of cellulose and 

 pectin, and their contents consist of granular lipoid substances. 







The layer at b contains 

 coloring matters, of 

 which tannin was shown 

 to be one. A water ex- 

 tract of this seed coat 

 also gives a positive re- 

 action for tannin. The 

 color in this layer is not 

 completely removed 

 either by treatment with 



hot water or with lipoid 

 solvents. The layer at 

 c consists of the old 

 walls of a parenchyma- 

 tous tissue that, in the 

 mature seed coat, is 

 much compressed. 

 These walls are of cellu- 

 lose and pectin. It requires a long period of heating in acid and 

 dilute base to cause these cells to fall apart. The membrane at d 

 has no visible contents. The outer walls are of cellulose and 

 pectin, but of a type very resistant to chromic acid. When sections 

 of this membrane are treated with chromic acid these walls are the 

 last to be broken down. Furrows extend across the thick wall of 

 this layer, but the remains of protoplasmic connections between 

 the cells could not be detected. Fatty bodies could be seen 



.. b 



....a 



Fig. i. — Cross-section of seed coat of Arachis 

 hypogaea, X45°- 



