Bower . — Studies in the Phytogeny of the Filicales. VL 21 
difficulty in identification. This is minimized by these conventional signs. 
The series reads from below upwards. 
Starting from Text-fig. 9, 1, which comes from an internode just below 
a leaf-insertion, there is an obvious leaf-gap (w) with five strands of the 
leaf-trace already detached. Below is a continuous semicircular vascular 
tract. In No. 2 the left-hand end of this has separated as a relatively 
large strand, and the space between is the lowermost limit of the next 
higher leaf-gap (x). From this it follows that the leaf-gaps overlap, and 
technically the structure is dicty ostelic. Also it follows that at certain 
points the upper and lower vascular tracts may be fused. The series 1 to 9 
show the gradual separation of the leaf-trace (w), the last step being the 
giving off of the two large marginal strands (4-6). Meanwhile the leaf-gap 
X widens, and at section 6, where the leaf-trace W has passed off, the 
stele consists of two meristeles, the larger being the lower, the smaller the 
upper. The latter soon divides (7-9), to form small leaf-trace strands, and 
does not appear to maintain its identity throughout. Additional strands 
may be given off from the lower meristele (10- 11 and 14-16), while the 
foliar strands undergo irregular branchings and fusions among themselves 
(20-23), forming a semicircle of 5 or 6, to which finally the marginal 
strands are added (25-27). This completes the leaf-trace of leaf-gap X. 
But again the leaf-gap Y is already formed in section 22, and widens in 
successive sections with formation first of the median strands of the trace, 
with irregular fusions of them as before, but not corresponding exactly in 
number or position (26-32). 
