Barley Grain in Relation to Localized Water Absorption. 413 
of the grain, and here must be sought the structure which is the seat of the 
remarkable selective permeability which keeps out mineral acids and most 
salts whilst passing water with considerable freedom. 
3.,Solutes such as iodine and acetic acid, which have been recorded 
as penetrating the grain more or less readily, hardly pass at all through 
the general surface of the grain, but, like water, enter by the restricted region 
at the germinal end. 
4. The penetration of nitric acid, which also takes place at the germinal 
end of the grain, is the result of selective action ; the acid neither destroys 
the enveloping membrane nor impairs the efficiency of the selective 
structure. 
5. The barley grain does not appear to possess perfect impermeability 
to any solute. Sulphuric acid gradually enters if the grains are kept in 
the solution for many days. In correlation with this it is observed that 
the initial concentrating effect of barley upon dilute sulphuric acid gradually 
falls back, and ultimately the steeping solution becomes even weaker than 
before it was brought into contact with the grain. 
6. It is at the outer cuticularized wall of the tegmen that the 
recorded arrest of silver nitrate and sodium chloride penetration takes 
place. 
7. This cuticularized membrane is permeable to water and solutes only 
to the extent usually associated with cuticle. It is possible to construct 
an osmotic cell by blocking a glass tube with a plug of the grain- 
covering. If this cell is filled with a salt solution on one side and with 
water on the other, slow passage of water takes place for months, but 
no salt passes in the reverse direction until some considerable time has 
elapsed. 
8. The initial uptake of water supplies the need of the embryo ; the 
grain-coverings form a well-constructed system for ensuring that the supply 
of water shall be carried along superficially to that part of the grain where 
it can be readily absorbed by the embryo. 
9. The subsequent distribution of liquid in the endosperm is precisely 
the path of enzyme disintegration within the endosperm during the 
germination of the embryo. It is suggested that the uptake and distri¬ 
bution of water in germination prepares the way for the distribution of, or 
the water even takes up and carries with it, the enzymes active in the 
solution of the reserves. 
In conclusion, I desire very cordially to thank Mr. F. F. Blackman, 
F.R.S., for his interest, advice, and criticism, during the course of this 
research, which was carried on in the Botany School, Cambridge, 1914* 
