5i 
Zygopteris Grayi of Williamson . 
The text-figure gives a rough idea of the arrangement of six aphlebia- 
traces, of which the course was actually followed. They are lettered (a-f) 
in the order in which they were observed to be given off from the leaf-trace 
5, to which they all belong. Probably, however, two additional strands 
from the same end as C and E were missed, owing to local damage. 
The aphlebia-strand first appears as a bulge of the peripheral loop. 
On first becoming free its xylem appears to be solid ; where any differen- 
tiation can be observed, the smallest tracheides are in the middle. As the 
strand passes further out it becomes tangentially extended, ultimately to 
an extreme degree, as shown in PI. Ill, Fig. 6 from the outer part of the 
cortex of the stem. In this condition the xylem appears to form a flattened 
c 
o 
o 
0 
0 
A 
0 
8 
Diagram of stele, with the arms, numbered in kathodic order, the leaf-trace 5, and the 
aphlebia-strands (more crowded than in nature) given off from it (a-f). 
ring, with the smallest elements in the interior ; in a longitudinal section 
there was some indication of laxly spiral elements (protoxylem) in this 
position. It is often noticeable that the tracheides on the abaxial side are 
larger than those on the adaxial side of the ring, a point of some slight 
interest, as the same difference exists, in a more marked degree, in the 
secondary strands of the rachis of Ankyropteris (P. Bertrand, ' 09 , p. 85; 
PI. X, Figs. 73 and 74). So far as I have been able to make out, the 
aphlebia-strands are given off essentially in the same way as the secondary 
rachis-strands, as described by P. Bertrand, i. e. without any interruption of 
the external xylem (‘filament’). There thus seems to be a considerable 
analogy between the scale-like aphlebiae and the ordinary pinnae of the 
leaf. 
