Barley Grain in Relation to Localized Water Absorption . 411 
facts relating to the structure of the grain and the evidence obtained by the 
use of penetrant liquids. 
Real contact between the tegmen and the embryo is made only at the 
micropyle by means of the so-called embryonic appendage, and again over 
the peripheral rim of the scutellum through the agency of a single layer of 
modified aleurone cells. The tegmen, it must be remembered, possesses 
a thick cuticle on its outer side and a much thinner one on the inner. 
From the evidence obtained experimentally two points of entry 
suggested themselves, one the micropyle and the other the tract of 
chalazal tissue in the furrow where it meets the dorsal margin of the 
scutellum. One regards the micropyle as a natural rapid inlet when seeds 
are steeped in water. The barley ovule shows a normal open micropyle 
giving access to the embryo sac, and it can hardly be doubted but that it 
remains available for the uptake of liquid after the maturation of the grain. 
Immediately underlying the micropyle is the embryonic appendage, a small 
mass of cells without apparent contents, which forms the apex of the root- 
sheath ; the mass is fused with the tegmen, and from its position it is 
assumed that it represents cells which have not been utilized in the 
formation of the embryo proper. This appendage swells and contracts 
rapidly when a section of the grain containing it in position is alternately 
irrigated with water and alcohol. No definite conclusion was reached con¬ 
cerning the chemical nature of the cell-walls of the appendage, but there 
was some evidence that they were modified in the direction of pectic, 
mucilaginous, or gum compounds. Such a tissue might act differentially in 
that water would readily pass, whilst a selective action, possibly adsorptive 
in nature, would be exercised upon a solute, and its filtration would be 
rapid, slow, or wellnigh impossible according to the nature of the action of 
the solute. Moreover, the capacity of the liquid to swell the tissue of the 
embryonic appendage, or rather perhaps the capacity of the tissue to imbibe 
the liquid in which the grains are steeped, must be considered in connexion 
with the question of penetration. Anhydrous liquids are not able to pass 
into the grain, but in association with water they enter freely. Association 
with water leads to imbibition and swelling and the subsequent entry of 
the solutes. 
Careful consideration has been given to the possible passage of 
solutions along the cells of the tegmen, between its inner and outer cuti- 
cularized membranes, and the selective action of the inner. The inner 
cuticle is the less prominent and resistant, and might fail after a time. The 
embryonic appendage might serve as a temporary hindrance to the passage 
of solutes into the embryo, whilst the main stream would pass between the 
cuticularized membranes and be distributed in the distal direction. It 
should be said here that such a method of distribution assumes that the 
connecting anticlinal walls between the inner and outer membranes at the 
