18 Bower.—Studies in the Phytogeny of the Filicales. VII. 
P 
Professor Gwynne-Vaughan. As he did not find opportunity to examine 
it, it was returned to me after his death. From the very hard sclerotic 
stock sections were cut in series. Fig. 17, a-l, represent selected sec¬ 
tions from one of those series, arranged in succession from below upwards, 
their actual numbers in the series being marked in plain figures at the base 
of each drawing. It will be seen that they correspond in essentials to 
previous descriptions. 1 
The structure of the leaf-trace at the base of the petiole is shown 
in Fig. 16 as an elaborate horseshoe, accompanied in its sinuous course 
by outer and inner coverings of sclerenchyma. Right and left are venti¬ 
lating pneumatodes, while the surfaces of the petiole and stock are covered 
by broad scales. The continuity of the horseshoe is interrupted on 
the abaxial side, three strands being quite separate, while the rest of 
the trace is continuous right and left, extending into deep adaxial hooks. 
The protoxylem groups are indicated in the drawing by dark dots, and 
it will be noted that the three isolated strands 
contain one each. Thus they represent in¬ 
dividual ‘ divergents \ 
The stelar structure of the axis is poly¬ 
cyclic. The outer and middle rings are in 
this stem complete. The innermost is repre¬ 
sented by variable strands. It is probable 
that in different examples, as also in different 
species, there may be some latitude of detail. 
The leaf-trace comes off exclusively from the 
outermost ring, essentially in the way de¬ 
scribed by Mettenius. It appears first as 
a thinner region of the ring, which soon arches widely outwards, and 
becomes sinuous in its middle region. Presently the base of the arch 
becomes narrowed by a sharp angle or kink in the ring on either side, 
and about the same time the outermost part of the arch is dissociated 
to form the three strands (divergents) above mentioned, which are separated 
before the trace is detached from the stele. This differs from Mettenius’s 
account (see his PI. VI, Fig. 6), as also does the point of detachment. 
Mettenius represents this as coinciding with the kink or angle already 
mentioned. But I find that it is constantly below that point (Fig. 17, 
a, 3 , c), and that the vascular tissue is continuous at the angles or kinks. 
Root-steles come off at irregular points from the outer surface of the outer 
ring, without disturbing it, or having any connexion with the inner system. 
The inner ring seems never to be completely closed. It is interrupted 
1 Karsten, Vegetationsorgane der Palmen, 1847, PI. IX, Figs. 5 and 6 ; Mettenius, Bau von 
Angiopteris , Abhandl. K. Sachs. Ges. d. Wiss., Bd. vi, p. 531, PI. VI, Figs. 1-6. Subsequent 
writers appear to have used these earlier observations without reinvestigation. 
Fig. 16. Transverse section 
near to the base of the petiole of 
Saccoloma elegans. p, p = pneuma- 
tophores. (x 3.) 
