20 
J. H. Priestley 
the suberin seems to form an intermediate median lamella unmixed 
with cellulose, and its solution is accompanied by a distortion of the 
inner cellulose wall which is often left free in the interior of the cell. 
In stating this we are travelling beyond von Hohnel who con¬ 
sidered that when the suberin had been removed from the lamella 
a basis was left behind consisting of cellulose. His main argument 
for this belief is that after and during the treatment with potash 
the suberin containing lamella gave a violet or reddish-violet re¬ 
action with iodine or sulphuric acid or with chlor-zinc-iodine, a 
reaction that he considered due to the cellulose present when it is 
no longer masked with suberin. 
We owe to von Hohnel the conception that the normal cork wall 
consists of three layers—the outermost or the middle lamella, a 
median one or the suberin lamella, and an inner one of cellulose. 
All subsequent investigators have confirmed this conclusion, but one, 
of the most careful of them, van Wisselingh (15), has modified von 
Hohnel’s description in one important particular. Von Hohnel 
described the median lamella as suberin on a basis of cellulose, 
van Wisselingh describes it as suberin without admixture of cellu¬ 
lose. Before describing van Wisselingh’s work, however, it will be 
desirable to describe some macro-chemical observations of Eugene 
Gilson(8). Van Wisselingh’s observations, made with great care and 
precision, are entirely micro-chemical in nature. They are published 
in a long series of papers which were appearing during the time that 
Gilson’s work was published. 
Gilson’s work, dealing with appreciable quantities of material by 
the normal manipulations of organic chemistry, threw great light on 
the nature of suberin and incidentally enabled van Wisselingh to 
assess the critical value of his own micro-chemical observations with 
much more confidence. 
The Macro-Chemical Investigation of Suberin 
Gilson’s work is based upon the solution of suberin on warming 
with potash. Recognising that the process was probably accompanied 
by the formation of soluble potassium salts of organic acids as in the 
saponification of an ester or true fat with alkali, he proceeded, by 
the customary methods of organic chemistry, to attempt the isolation 
of any organic acids and alcohols that might be present in solution. 
As suberin seemed to dissolve more completely in an alcoholic 
solution of potash, he carried out his original saponification of 
powdered bottle cork with three per cent, alcoholic potash. 
