86 Brown. — On the Existence of a Semi-permeable Membrane 
In order to investigate this point further, grains of H. vulgare , var. 
caerulescens , and of several varieties of H. distichum were steeped for 
48 hours in solutions of methyl-violet and of fuchsin, and also in solution 
of various salts which could be readily traced by micro-chemical means, 
and subsequently sections of the grains were prepared for the purpose of 
studying microscopically the limit of passage of the reagents employed 
through the coverings of the grains. 
The best results were obtained with grains which were in the first 
instance steeped in a 3 per cent, solution of silver nitrate for 48 hours, 
and afterwards steeped for 48 hours in a 5 per cent, solution of sodium 
chloride. By this means the limit of penetration of the silver nitrate 
through the skins of the grain was rendered visible by its precipitation 
as silver chloride in the cellular tissues and subsequent blackening on 
exposure to light. 
Microscopic examination of sections of barley grains treated in this 
manner demonstrates that silver nitrate passes through the pales and 
pericarp into the spermoderm, which, in part at least, is coloured by the 
silver salt. A thin layer of uncoloured membrane, however, remains 
between the stained portion of the spermoderm and the walls of the 
aleurone cells of the endosperm. Probably this layer of the spermoderm 
is derived from the epidermis of the nucellus, but its identity has not been 
satisfactorily determined at present. 
When transverse sections of a barley grain treated with silver nitrate 
and 'sodium chloride are examined in the neighbourhood of the funicle 
a very well-defined line is found, indicating that the silver salt, after 
penetrating the spermoderm some distance, stops abruptly at the outer- 
most layer of the sheaf-like mass of empty cells, which are usually regarded 
as the remains of the cells of the nucellus ; but it appears undesirable to 
draw any definite conclusion from this observation owing to the complex 
character of the envelope of the barley grain in the neighbourhood of the 
funicle. 
There seems to be no doubt that the semi-permeable property of the 
barley grain centres in the spermoderm, but whether the property is 
confined to one of its layers only has not been definitely determined 
as yet. 
As it appeared interesting to ascertain if the grain of other of the 
Gramineae than Hordeum exhibited the phenomenon of semi-permeability, 
grains of Avena , Triticnm , and Secale were steeped in a normal solution 
(4-9 per cent.) of sulphuric acid for 48 hours, and subsequently examined. 
It was found that they all evidenced the .possession of a semi-permeable 
covering, as in the case of Hordeum. In the case of Triticum and Secale , 
however, a much larger proportion of damaged grains not capable of 
excluding acid were found as compared with Hordeum and Avena. 
