Ii 6 
J. H. Priestley and Edith E. North 
Developmental Stages of the Endodermis 
Any investigation of the endodermis at the present day naturally 
starts from the sound basis of facts, critically established, and 
published in great detail in the long series of papers issuing from the 
Marburg laboratory. To these papers we shall often refer in the 
following pages and, although we find ourselves differing from the 
general standpoint of this school of investigators as to the function 
of the endodermis, we must express our indebtedness to them 
for an extensive series of data, and for very valuable suggestions 
as to micro-chemical methods which we have employed in our own 
work. 
In one of the earliest papers in this series Kroemer(i 3 ) points out 
that during its development the endodermis of the flowering plant 
passes through a series of stages in chronological succession. These 
stages differ from one another in important structural particulars, 
and from the standpoint of physiological anatomy must receive 
separate consideration. 
They may be summarised as follows (Kroemer, loc. cit. pp. 87 et 
seq.): 
1. The Embryonal Stage, where the cells are typical constituents 
of normal merismatic tissue. 
2. The Primary Stage, in which the individual cells have re¬ 
latively thin, unsuberised membranes and in which the radial and 
transverse walls show the characteristic Casparian strip. 
3. The Secondary Stage, in which the walls are still relatively 
thin, but are characterised by the possession of a suberin lamella, 
usually deposited over the whole inner surface of the cell. 
4. The Tertiary Stage, characterised by the deposition within 
the suberin lamella of inner lamellae, consisting mainly of cellulose; 
these deposits often reach very great thickness, particularly upon the 
inner tangential wall. 
An endodermal cylinder, in which the cells have reached the 
tertiary stage, may have passed in succession through all the previous 
stages (this appears to be always the case in the root, but not in the 
stem), but the primary or any succeeding stage may represent the 
final stage for the endodermis of various plants. Thus the work of 
Rumpf( 26 ), Mager(i 5 ), and Basecke(i) makes it clear that in the 
Pteridophyta, with the exception of the Leptosporangiate Ferns, the 
primary stage is usually the final stage of differentiation reached in 
the root. In the Leptosporangiate Ferns the roots usually have as 
