128 J. H. Priestley and Edith E. North , 
aquilinum L. after brief previous treatment of the section with eau de 
javelle, the yellow suberin layer, present on the inner tangential wall 
only, standing out very clearly because it had separated from the 
lamella exterior to it. The colour reactions here obtained indicate 
that the Casparian strip is more acid in reaction than the suberin 
lamella. That the strip is acid and the suberin lamella neutral in 
reaction is also suggested by their reaction with nile blue, when the 
Casparian strip is stained deep blue and the suberin lamella violet 
to pink. 
(b) Evidence that the basis of the suberin lamella is not identical 
with that of the Casparian strip. This evidence is obtained mainly 
from examination of the tertiary stage in Potamogeton strips. It is 
b 
Fig- 3 
difficult to obtain because the lamellae are very firmly cemented 
together. In the first place prolonged maceration, lasting many days, 
seems to dissolve slowly the cementing material which is presumably 
some of the deposited fatty acid products. If the tertiary endodermal 
strips, after short maceration or boiling in concentrated potash, are 
mounted in iodine and sulphuric acid the layers described by von 
Hohnel are seen very clearly. In the joint wall between two cells is 
seen the dark wavy line of the middle lamella, outside this the suberin 
layers, and beyond these again the strongly pitted cellulose layers 
(Text-fig. 3 (a)). At a focus about i /x or i*5/x higher the dark middle 
lamella is no longer seen, in its place is a wider wavy strip of yellowish 
or greenish tinge (Text-fig. 3 ( b )). On prolonged maceration this 
strip separates from the cells on either side and then often loses its 
wavy appearance. This separation can most readily be produced by 
mounting the strips, after washing them in water on removal from 
the strong potash, in concentrated hydrochloric acid and gently tap¬ 
ping the cover glass. The strip then separates in many places from the 
