Barley Grain in Relation to Localized Wafer Absorption . 405 
Similar experiments with solutions of acetic and nitric acids showed an 
initial weakening effect, but the subsequent action was obscure; further 
experiments will be necessary to elucidate this. 
It will be seen from these results that when grain is immersed in 
a solution of sulphuric acid, water initially penetrates faster, whilst the acid 
penetrates relatively faster as the period of steeping is prolonged, hence the 
‘concentration effect * at any time measures the temporary balance and 
cannot have any static significance into which a time factor does not enter. 
In tracing the path of entry into and the distribution of acids in the 
grain, the blue variety of barley was particularly useful. Acetic, trichlor¬ 
acetic, lactic, sulphuric, and nitric acids were experimented with. With the 
first two acids, solutions of which Brown found to penetrate the grain 
rapidly, a colour change was first noticeable at the germ end of the furrow ; 
from this point the pink coloration due to the acid reaction with the blue 
pigment contained in the aleurone cells proceeded round the rim of the 
endosperm, spreading slowly in the distal direction at the same time. 
Progress of the coloration was more rapid on the curved side. In general 
the mode of entry and path of distribution of these acids were identical 
with those of iodine. With lactic acid, owing to its slower penetration, the 
colour reaction was not so well marked, but there was sufficient evidence to 
show that entry was obtained and distribution occurred as indicated for 
acetic and trichloracetic acids. In grains immersed in sulphuric acid solu¬ 
tion the colour change could not be followed with certainty, as selected 
grains had to lie for a long time before any distinct signs of entry were 
manifest. Changes occurred meanwhile which obscured the acid reaction. 
It was thought that in some grains entry occurred through passage of the 
tissues of the furrow. 
With regard to nitric acid, Brown stated that entry was gained at 
a point at the germ or proximal end, and that penetration was due to the 
destruction of the membrane. 
So far as this statement relates to the mode of entry of a penetrant 
solute, it supports the theory put forward by the present writer, whose 
experiments further showed that immersion in nitric acid neither destroyed 
the enveloping membrane nor impaired the efficiency of the selective tract, 
whatever this might be. The evidence upon which this assertion is based 
will now be detailed* 
Grains, after immersion in 1, 5, or 10 per cent, solutions of nitric acid 
for considerable periods, with subsequent soaking in water and drying, were 
placed in iodine solution. In all cases the first appearance of starch 
blueing occurred in the usual place, namely, the germinal end of the furrow 
and coloration proceeded in the usual way. It was evident that the 
general impermeability of the membrane had not been altered by the 
treatment with nitric acid. 
