Barley Grain in Relation to Localized Water Absorption . 389 
(e) Impermeability of the cuticular membrane of the tegmen to solutes . 
A. Brown, by using the silver salt method, in which grains were 
steeped first in a solution of silver nitrate and then in a solution of salt, 
came to the conclusion that the nucellar epidermis was acting as the semi- 
penneable membrane. It was a little unfortunate that the region of the 
furrow was chosen for closest investigation on this point, for, as remarked 
in a previous section, the nucellar epidermis is not present at this point. 
In the experiments recorded here, the same method, with a slightly 
longer period of immersion in each of the solutions, was followed. The 
grains were rinsed and exposed to sunlight. Large numbers of sections 
were cut, always from the middle of the grain, for reasons already stated; 
the sections were placed directly on slides with water, glycerine, or alcohol, 
and exposed to strong sunlight until the rims of the sections became quite 
dark. Some of the best results were obtained from those sections which 
had stuck to the glass, owing to the evaporation of the alcohol. This, to 
a great extent, prevented the escape of the particles of silver chloride from 
the seat of precipitation. The sections were stained with Scharlach R and 
finally mounted in glycerine. Examination of many sections so prepared 
left no doubt that the cuticularized outer membrane of the tegmen was 
responsible for the stoppage of the silver nitrate or the salt, for the deposit 
of silver chloride could be traced up to this point, but not beyond. In the 
region of the furrow the yellowish contents of the group of cells situated 
here were blackened, and in some sections the silver chloride deposit could 
be seen extending for a little way both into the base of the sheaf-like mass 
of cell-walls and between the inner and outer cuticularized membranes of 
the tegmen. 
(f) Summary . 
Investigation of the structure of the integumentary system shows that 
the barley grain is, with the exception of the micropyle and chalazal tract, 
completely invested by a strongly cuticularized tegmen membrane. This 
membrane is destroyed by a solution of caustic potash, which causes the 
impregnating fatty material to aggregate into droplets ; it is not altered 
when exposed to the action of solutes known to penetrate the grain, and its 
reactions are not impaired by treatment with solutions of the strong acids. 
The membrane is impermeable to salt or silver nitrate or both, for after 
grains have been steeped successively in solutions of these substances, 
a precipitate of silver chloride can be traced up to the membrane, but 
not beyond* 
