Barley Grain in Relation to Localized Water Absorption . 403 
method, for it enabled one to test the grain with regard to imperfections 
in the membrane, for wherever a fault occurred a black patch appeared. 
Since such flaws in the grain-coverings affect the results in all estimations 
of the semi-permeability of the barley by steeping methods, a test of this 
kind should be made with a sample of the grain to be used. A few tests 
made by the writer showed that appreciable differences existed in the 
various samples used. 
With the hope of tracing the path taken by the iodine, both transverse 
and longitudinal sections of the grain after immersion in the iodine were 
made. Leaving for a moment the 
very difficult question of its mode and 
place of entry and circulation in the 
embryo itself, it was quite clear that 
after the initial coloration of the starch 
in the neighbourhood of the germinal 
end of the furrow and around the 
scutellar rim, the layer of small cells 
with small starch granules immediately 
subjacent to the aleurone layers was 
the first to show the effects of the 
iodine. Indeed it can be said that 
the iodine travelled along this layer 
before spreading to any extent towards 
the centre of the grain. The stronger 
the solution of iodine used the more 
quickly did the blueing spread, and 
the absence of this layer from the region 
of the flanks of the furrow seems a suf¬ 
ficient reason for the tardy coloration 
of this area. During the coloration of 
this layer, blueing spread across the surface of the endosperm cells below 
and parallel to the surface of the scutellum. There was good reason to 
suppose that the iodine did not find a ready path along the aleurone cells, 
for, although they became yellowed progressively in the distal direction, 
the blueing of the adjacent starch grains proceeded more rapidly. 
Fig. 8 shows a number of transverse sections cut from the grain after 
steeping in iodine solution ; the blackened areas indicate the distribution 
of colour in the starchy endosperm. The approximate position of these 
sections is indicated in Key Fig. 8<?. 
From the fact that iodine is adsorbed by the starch grains, wetting by 
water probably precedes coloration by iodine. If this be so, then the 
rapidity with which water normally passes along the peripheral layer of 
the starchy endosperm is striking. 
Key Fig. 8a. Diagram sketch of a median 
longitudinal section of the barley grain, upon 
which are plotted the approximate positions 
of the sections shown in Fig. 8. 
