400 Collins .— The Structure of the Integumentary System of the 
fmbrjO 
namely, the penetration of iodine into the barley grain, stated that t the 
blueing of the starch grains renders it easy to study the manner in which 
iodine passes into the grain, and indicates that it penetrates all parts of the 
skin enveloping the endosperm at approximately the same velocity, with 
the exception of the part in the neighbourhood of the furrow, through which 
it appears to pass with difficulty 5 . 
The results obtained by the writer with barley are quite opposed to 
Brown’s. 
Because of the results obtained in the experiments dealing with the 
uptake of water, it was thought advisable to repeat the barley and iodine 
experiments; grains of both Hordeum vulgare var. caerulescens and 
H.vulgare var. ‘ Goldthorpe' were placed in solutions of iodine in potassium 
iodide. In both cases the first signs of blueing of the starch contents 
appeared on each side of the 
furrow at the germ or basal end. 
(See Fig. 6.) From these points 
it was easy to trace the path 
taken by the iodine. Whilst it 
spread to some extent along 
each side of the furrow towards 
the apex of the grain, it passed 
more rapidly around the starchy 
endospermic rim, immediately 
beneath the scutellum. The two 
blue arcs joined round the em¬ 
bryo, completing the circuit; at 
the same time the blueing spread 
rapidly on the curved side of the 
grain towards the apex, the lateral edge of colour as a rule being somewhat 
sharply delimited. The flanks of the furrow side were the last to be blued. 
The stronger the solution of iodine, the more rapidly the blueing occurred, 
an immersion of 12—24 hours in a very strong solution of iodine sufficing 
for complete coloration,- but the path travelled was always the same except 
when penetration occurred through the presence of injuries. 
The first trials were made with grains wholly immersed in the solution, 
but in order to confirm the results many further experiments were made 
and are described below. 
Grains were placed distal apex downward in holes in cork rafts about 
two inches square. The rafts were then floated on iodine solution contained 
in covered Petri dishes. The iodine was thus brought into contact with the 
apex of the grain, perhaps a quarter of the grain being actually in contact 
with the solution. Every opportunity was thus given for penetration of 
the solution into those parts with which it came into contact first. Never- 
Dorsal view. Median longitudinal section. 
Fig. 6. Grain with paleae removed. 
