5 1 8 Boodle . — Comparative A natomy of the 
represented in Fig. 25, E and F (at i.t). The group of 
tracheides and the adjacent endodermal ring, shown diagram- 
matically in Fig. 25, F , are represented in detail, with the 
adjacent parenchymatous cells, in Fig. 26, G. Internal 
tracheides are not often found. When present, they may 
behave in different ways, as will be seen from the two follow- 
ing cases. The strand of tracheides, represented in Fig. 25, E , 
was followed through a series of sections and was found to 
become gradually reduced to only two or three elements, and 
then to disappear both above and below, the tracheides being 
at no time very far from the centre of the stele. In the 
second case, there were a few tracheides at some little distance 
within the ring of xylem, but when followed in the acropetal 
direction they were found to decrease in number to one or 
two, which then passed outwards and joined the xylem-ring 
just where a gap in the latter became closed. In both these 
cases, in the region where the tracheides are most numerous, 
they form a solid strand, but, when the tracheides are reduced 
in number, they become separated from one another by 
parenchymatous elements (this separation has begun in 
Fig. 2 <5, G). 
Thus the internal tracheides may or may not have a con- 
nexion with the tracheides of the ring. 
5. Deductions from the anatomy of the mature plant. 
We may now enter into a discussion of the conclusions to 
be drawn from the occurrence of internal endodermis and 
tracheides. 
Jeffrey (’02, p. 129), applying the conclusions he reached in 
the Osmundaceae to the Schizaeaceae by analogy, regards 
it as probable that the type of central cylinder found in 
Schizaea is derived by reduction from that which is character- 
istic of Mohria and Anemia (i. e. from dialystelic structure). 
This view is not accepted here (though the theory put forward 
by the writer is similar in some respects), firstly, because the 
case of Osmunda is not admitted as proved, and secondly, on 
account of the nature of the structural evidence derived from 
Schizaea itself. 
