Bower.—Studies in the Phytogeny of the Filicales. 435 
which is taken from a stolon of considerable thickness, but with long inter¬ 
nodes ; that is in fact the usual structure in such cases. 
The details of relation of the stolon to the subtending leaf do not, 
however, appear to be constant, as is 
taken from a thicker stolon with a 
since the leaf-gaps overlap the con¬ 
dition is dictyostelic though of a 
simple type. A comparison of these 
with Fig. 6, from a larger stock, 
shows that the former is constructed 
on the same plan as the latter, but 
simpler. It will be noticed that the 
leaf-trace is a single V-shaped strand, 
and that as it is given off the stele 
opens, a portion of its vascular tissue 
separating off first from one then 
from the other of the margins of 
the meristeles which remain: as in 
the larger axes a strand of scleren- 
chyma parts from the central sclerotic 
core of the axis, and passing out¬ 
wards inaugurates the involution of 
surface which finally separates the 
leaf from the axis. The origination 
of the leaf is marked externally by 
the projecting keel, which is apparent 
even below the level of separation 
of the leaf-trace. In Fig. 12, I, 
Text-fig. 4. A typically solenostelic stolon 
of P. pycnophylla ; the dark shading indicates the 
sclerenchyma, the lighter shading shows the 
stele. ( x 4.) 
shown by Fig. 12, I-V. These were 
closer arrangement of the leaves, and 
Text-fig. 5. Three successive sections trans¬ 
versely through a stock of P. pycnophylla , of 
which a is the lowest, showing the origin of 
a stolon (si) in place of a leaf; b and c show its 
complete separation from the dictyostele of the 
axis, with a protostelic structure. ( x 2). 
which is the lowest of the series, a leaf-trace has passed outwards from the 
stele, together with its accessory sclerenchyma, which also isolates itself 
from the central sclerotic core. It may be noted further that roots have 
arisen right and left from the meristeles near to the points where the 
leaf-strand had separated from them. In section II each of the shanks 
F f 2 
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