Physiological Studies in Plant Anatomy 119 
on edge (see Text-fig. 2 ( b)). The triple line appearance is also very 
striking in strips of Potamogeton endodermis after treatment with 
sulphuric acid. Here the groove is 1 /x deep at least; and at different 
foci either the central line or the two marginal lines are sharply 
defined (see Text-fig. 2 (c)). 
The relations of the Casparian strip to the rest of the wall must 
now be discussed. Kroemer’s results already quoted suggest that it 
consists of a basal substance easily soluble in sulphuric acid, and an 
impregnating substance resisting sulphuric acid but dissolving in an 
oxidising agent like eau de javelle. Ivroemer also points out that the 
unaltered strip gives many of the reactions of lignified membranes 
(red with phloroglucin and hydrochloric acid, etc.), and in its be¬ 
haviour to Sudan III glycerine and to other fatty stains resembles 
