406 Collins.—The Structure of the Integumentary System of the 
Again, grains were soaked in a 5 per cent, solution of nitric acid, con¬ 
taining 3 per cent, of silver nitrate; they were then rinsed and placed in 
a 5 per cent, salt solution. From this the grains were rinsed, halved in different 
planes, and exposed to light. There was no evidence of general penetra¬ 
tion ; in a few local blackening was evident, but in the majority the exposed 
surface remained white. Following these experiments, a test was made 
of the efficiency of the selective capacity of the tissues forming the path 
of entry after immersion in nitric acid. 150 grm. of barley were steeped in 
1 per cent, nitric add for sixty-eight hours. The grain swelled very con¬ 
siderably. The acid was poured off, and the grains were thoroughly rinsed 
and stood in a large bulk of tap-water for forty-eight hours with several 
changes. The last water gave no colour reaction with blue litmus paper. 
After this the grains were allowed to dry, and they ultimately weighed 
148 grm. The acidity of the grain was tested after drying. Some few 
grains were cut across and steeped in distilled water; the cut surface gave 
a slight acid reaction with litmus paper. The whole lot of grain was then 
steeped in 250 c.c. of 4-9 per cent. H 2 S 0 4 , and maintained at 30° C. The 
nitric-acid treated barley concentrated the acid solution to the same extent 
as did a similar weight of normal barley set up as a control. The results 
are shown in the following table: 
Concentration Effect obtained by steeping in H 2 S 0 4 . 
Hours. 
Hours. 
Hours. 
Hours. 
Hours. 
Days. 
Time 
0 
2 4 
48 
72 
96 
42 
c.c. 
c.c. 
c.c. 
c.c. 
c.c. 
c.c. 
‘ Nitric barley ’ 
7*5 
8.1 
8.26 
8*22 
8*12 
7-7 
Normal „ 
33 
8.14 
8.26 
— 
8.0 
7-44 
Control 
)) 
— 
7-52 
— 
7*5 
7-5 
The figures show the number of c.c. of a solution of KOH required to 
neutralize 1 c.c. of the acid. 
Because the grains gave an acid reaction after drying, the solution of 
sulphuric acid in which the grains were being steeped was tested after 
forty-eight hours for nitric acid. Neither by the coloured ring test with 
ferrous sulphate nor the starch blueing test in the presence of nascent 
hydrogen could the presence of nitric acid be detected. 1 
(c) Uptake of stains . 
Additional evidence that penetration took place at a special point or 
points at the micropylar end was afforded by further immersion experiments. 
A brief description of these follows. 
(a) Grains were steeped in aqueous solutions of methylene blue and 
safranin in shallow dishes. The coleorhiza frequently broke through the 
1 A slight tint was given in the latter test, but on repeating it, together with a control of the 
original sulphuric acid, the same slight tint was given in each case. 
