114 J. H. Priestley and Edith E. North 
The varying structure and function of endodermal tissue at 
different stages of its development has resulted in much confusion. 
We have therefore re-defined these stages, clearly enunciated many 
years ago by the Marburg school of physiological anatomists under 
the guidance of Prof. Arthur Meyer. This method of dealing with 
the subject has involved separate discussions of the structure and 
behaviour of the same endodermis at two different stages in its 
history. The general role of the endodermis within a plant has been 
discussed in a later section after the facts as to the structure, func¬ 
tion and occurrence of the different types of endodermis have been 
given. 
Incidentally it has been possible, thanks to new technique em¬ 
ployed, to contribute some further facts towards an understanding 
of that very well-known phenomenon, the undulation of the Casparian 
strip. These facts have been gathered into a short section at the 
conclusion of the account of the micro-chemistry of the “ secondary ” 
endodermis. 
Investigation of the micro-chemistry of the endodermis has so 
far been carried out upon the cells of this tissue as seen in section. 
This material was found so unsatisfactory that in the end the 
method was abandoned for another which provided material both 
for micro-chemical and macro-chemical investigation. 
Preparation of the Endodermis by Maceration 
The study of the micro-chemistry of the endodermis was begun 
by observing the behaviour of sections towards various reagents, 
but this method of investigation soon raises problems it is unfitted 
to solve. Attempts were therefore made to isolate the endodermis 
from other tissues so that macro-chemical methods might be 
employed. The main obstacle to isolating the endodermis is the 
existence in the normal stem or root of three almost equally re¬ 
sistant tissues, cuticle (or periderm), endodermis, and xylem, all 
associated in a matrix of cellulose relatively easily removed by 
hydrolysis. 
From the work of Zimmermann ((35) loc. cit. p. 152), extended by 
Kroemer(i3), it should be practicable to separate xylem from endo¬ 
dermis by treatment with eau de javelle since in a section the xylem 
disintegrates so much more rapidly. There appeared to be the nucleus 
of a method here, as it is relatively easy in many plants to pull out 
the vascular strands and so free them from periderm or cuticle. 
