SECTION IV., 1907. [353] Trans. R. S. C. 
XX.—On the Development and Function of Certain Structures in the 
Stipe and Rhizome of Pteris Aquilina and other Pteridophytes. 
By Simon Krrsou, M.A., McGill University. 
Communicated by Prof. D. P. Penhallow. 
(Read May 15, 1907.) 
In the following pages the function and probable significance of 
certain structures in the Pteridophytes in general, end more especially 
in Pteris aquilina, will be dealt with. Before proceeding with the ac- 
count of the results arrived at from experimental work, it will, however, 
be well to glance at the history of what will be shown to be both ana- 
logous and homologous structures in fossil Pteridophytes and in the 
Phanerogams. At the same time an attempt will be made to refer 
briefly to any previous work bearing on the subject, and to place before 
the reader the various interpretations of the above mentioned structures 
by the different observers. 
As will be seen below, the structures in question are strictly limited 
to the vascular bundle, and so, in most of the cases to be described, very 
little attention will be paid to the general structure of the various 
stems and petioles dealt with. 
There are essentially two phenomena to be discussed in this 
treatise :— 
1. The formation of a more or less regular canal in the vascular 
bundle, such as is well known in the carinal canals of the Equisetaceæ 
or in the xylem of phanerogamic plants like Zea mays, Tradescantia 
fluminensis, etc. 
2. A more or less complete blocking up of this canal by outgrowths 
from adjacent parenchymatous cells, these outgrowths being of the nature 
of thyloses,— structures frequently found in many trees and grasses, and 
_ which, as will be seen below, have also been described for some fossil 
Pteridophyta. 
The structures in question are not mentioned in any of the standard 
text-books on botany, and no reference to them was found in any of the 
older works. Ina few cases, however, they are either shown in illustra- 
tion, or described in connection with some other structures, but in no 
case is their true nature interpreted. 
The first mention of these strnctures appears to be by Thomé (28). 
In a figure of Pteris aquilina there are shown two vascular bundles of 
Sec. IV., 1907. 22. 
