Physiological Studies in Plant Anatomy 135 
experiment is not conclusive but it certainly suggests that the 
endodermal cylinder, with its suberin lamellae, offers a considerable 
resistance to the ingress and egress of water. 
General Discussion 
The general consequences of the view taken in this paper of the 
functions of the primary and secondary endodermis are very far- 
reaching. Here it is only possible to emphasise the following points: 
In the absorptive region of the root a primary endodermis is 
present in all vascular plants with the exception of the Lycopodiaceae. 
A consideration of the previous pages will show that this primary 
endodermis possesses all the qualities essential for the development 
of sap pressures, as enumerated in a previous paper. Whilst many 
points in the complex micro-chemistry of the cell membranes remain 
to be cleared up, it is hoped that this general conclusion is soundly 
established. 
On the other hand when, as in the older roots and stems of many 
Angiosperms and the Filices, an endodermis of secondary or tertiary 
stage develops, an entirely new situation arises. If this endodermis 
contains no passage cells, then the vascular strands it encloses must 
be regarded as solely conducting in function. The full consequence of 
this view, when applied to the Filices requires fuller consideration 
than it has yet received. As a result of our own observations together 
with a consideration of Basecke’s fundamental researches, we reach 
the conclusion that in many Ferns the stele throughout the greater 
part of its passage in rhizome and frond is practically isolated from 
its surrounding cortical tissues. Basecke’s experiments upon the 
movement of starch from the partly shaded leaves of Scolopendrium 
supply good evidence that it can only pass from the lamina into the 
vascular strand in the region of the sorus, where alone the endodermis 
is not in the secondary stage. We note also his remarkable observa¬ 
tion that in every fern frond of the Filicineae that he could examine 
growing in its native country, when the sori were mature the vascular 
strands in the leaf become completely isolated from the lamina by 
the completion of the secondary stage of the endodermis throughout 
the course of the vascular bundle. The subsequent death of the lamina 
Basecke then attributes to lack of solute, and we would add, to lack 
of water also. 
With the help of Miss Armstead, M.Sc., some preliminary experi¬ 
ments have been carried out upon the changes in the cell membranes 
in the cortical tissues of the Filicineae. As a result the conclusion is 
reached that the “vagin” of Basecke is only a form of the phlobo- 
