enclosing the Seeds of some of the Gramineae. 83 
the case of a small number of the grains a similar result was obtained after 
48 hours’ steeping, but eventually it was found that all the grains admitted 
acid 1 . 
A similar condition was noticed, but after a much shorter interval of 
time, when the grains were immersed in 5 per cent, nitric acid. From the 
appearance of the grains after steeping, there is reason, however, to believe 
that the passage of nitric acid to the interior of the grains does not result 
from a selective action of their semi-permeable envelope, but from 
destruction of the semi-permeable property of the envelope by the 
chemical action of the acid. 
Apparently, however, an instance of the envelope exhibiting a power 
of selection for matter other than water is found in the passage of iodine 
into the barley grain. 
When barley grains are steeped in a 1 per cent, solution of iodine in 
iodide of potassium (5 per cent.) solution for 24 hours, the passage of iodine 
through the envelope into the interior of the grains is evidenced by the 
contents of the cells of the embryo and of the aleurone cells being stained 
brown, and also more markedly by the starch granules of the starch- 
containing cells of the endosperm being stained blue. 
The latter phenomenon, which renders it easy to study the manner in 
which iodine passes into the grain, indicates that it penetrates all parts of 
the skins enveloping the endosperm at approximately the same velocity, 
with the exception of the part in the neighbourhood of the ventral- furrow, 
through which it appears to pass with difficulty. 
In the first instance it seemed probable that access of iodine to the 
interior of the grain was only obtained after destruction of the semi- 
permeable property of the envelope by the chemical action of the iodine, 
but experiments in which grains of barley previously stained with iodine 
were steeped in a solution of sodium hyposulphite, appeared to show that 
such is not the case. Under such condition, if the semi-permeable 
character of the envelope of the grains was destroyed, the sodium 
hyposulphite would diffuse into the grains and discolour the starch- 
containing cells of their endosperms which had previously been coloured 
with iodine ; and, in confirmation of this, direct experiment showed that 
when grains of barley stained with iodine were steeped in a solution of 
sodium hyposulphite after their skins were punctured or otherwise damaged, 
the sodium hyposulphite diffused into the grains and discoloured them. On 
the other hand, when iodine-stained grains with uninjured skins were 
steeped in a solution of sodium hyposulphite, no discoloration was 
observed even after the grains had been immersed in the solution for five 
days. 
1 It appeared that entrance of the acid was always obtained at the germ, or proximal, end of 
the seed. 
G 2 
