Barley Grain in Relation to Localized Water Absorption . 383 
of water, whilst the final weight reached by grains immersed in these 
solutions was above that of grains steeped in water. 
Whilst discussing the various theories advanced to explain the 
semi-permeability of membranes, Schroeder suggested the possibility of 
a localized entry, or perhaps an increasing impermeability of the coverings 
from the basal towards the apical end of the wheat grain. He also 
suggested the possibility of a reaction -between the solution and some 
constituent of the membrane leading to increasing impermeability, an 
assumption based upon his experiments with osmic acid. 
Reichard, in a first paper, called attention to the presence Uf a tannin 
layer in the coverings of the grain of barley, and later, after the discovery 
of the semi-permeable membrane, sought to connect the presence of tannin 
with the phenomenon of semi-permeability. As will be seen later, the 
present writer has failed to confirm the presence of a tannin layer. 
Shull dealt particularly with the seeds of Xanthium , and concluded 
that cellulose walls might form efficient semi-permeable membranes. 
Moreover, in a general review, he regarded semi-permeability in seeds as 
a widespread phenomenon,” and enumerated the various orders and genera 
of plants whose seeds possessed this type of covering. 
Consideration of the investigations that have been made shows that 
attention has been focused more particularly upon the molecular state of 
water and the action of the solutes upon this state, a physical rather than 
a biological study, and that the barley grain has been exploited largely 
from this point of view. In the present work it is intended to consider the 
structure and properties of the various layers of the investment, not as 
a physico-chemical ^problem, but rather as a biological study in liquid 
absorption. 
The general results of this research may be summarized as follows: 
1. Very restricted permeation over the general surface of the grain, 
either of water or solutes, is indicated. 
3. The area of absorption and semi-permeability is located chiefly at 
the germinal end. 1 
3. The structure of the integumentary system is significant in relation 
to the path of penetration of water and solutes into the grain. 
Section II. Structure and Reactions of the Investing 
Integumentary Layers. 
(a) Morphology and structure of the layers . 
For the purpose of determining the structures, grains were steeped in 
water for two days and sections were cut from the mid region transversely. 
After a number of trials it was found that sections cut by hand gave the 
1 The germinal, basal, or proximal end of the grain is the end at which the grain is attached 
to the rachis; the germ is situated on the ventral or curved surface. 
