84 Brown . — On the Existence of a Semi -permeable Membrane 
The experiments described above demonstrate that the embryo and 
endosperm of the barley grain are enclosed within an envelope through 
which water and iodine can pass to the interior of the grain, but through 
which certain acids and salts cannot pass. As there appeared to be no 
known instance of the occurrence in the vegetable kingdom of a membrane 
other than one of living protoplasm, which possessed a marked semi- 
permeable property, it seemed very desirable to inquire if the semi- 
permeable property of the envelope of the barley grain was a function of 
living protoplasm, although from the first it appeared very improbable that 
it was so when the conditions ruling in some of the experiments already 
described were considered. 
In order to demonstrate the semi-permeable character of living proto- 
plasm by plasmolysis, solutions either of inert salts, or of such bodies as 
cane sugar, which do not exert an injurious action on the protoplasm of 
the living cell experimented with, must be employed, for otherwise, as the 
solute must come into direct contact with the protoplasm of the cell in 
order to exert its osmotic influence, its vitality would be destroyed and it 
would cease to function as a semi-permeable membrane. But in some of 
the previous experiments it has been shown that the semi-permeable 
property of the envelope of the barley grain is exhibited with solutions of 
sulphuric acid of very high concentration, and it appears inconceivable that 
such strong acid can come in contact with living protoplasm without 
destroying its vitality at once. Moreover it has been shown that when 
solutions of such poisons for protoplasm as silver nitrate and cupric sulphate 
are employed these salts are excluded from the interior of the barley grain. 
Additional evidence that living protoplasm does not act as the semi- 
permeable membrane of the barley grain is also furnished by the results of 
the experiments with iodine, which have already been described. In these 
experiments it was shown that iodine penetrates the coverings of the 
grain, and yet on subsequent immersion of the grain in a solution of sodium 
hyposulphite the coverings through which iodine has already passed prevent 
the passage of the salt. To regard the selective character of the coverings 
as depending on the action of living protoplasm after the passage of 
a strong poison like iodine through them seems unreasonable. 
Conclusive proof that the semi-permeable character of the envelope 
surrounding the grain does not depend on the activity of living protoplasm 
was, however, obtained by experiments conducted with grains of barley 
after they had been subjected to the action of boiling water. Some barley 
grains were immersed in boiling water, and at intervals of 5 , io 5 3°, 6°, 
and 120 minutes a number of the grains were removed. On examination 
it was found that the skins of all the grains which had been steeped in 
boiling water for 120 minutes were ruptured and their contents were 
extruding, and of those grains similarly treated for 60 minutes all but one 
