Bower. — Studies in the Phytogeny of the Filicates. 455 
was essentially the same as in other cases, viz. on the back of the leaf-base. 
The material was thus at hand for anatomical observation. Externally, the 
surface was covered by dermal appendages. These were of two sorts : soft 
woolly, but unbranched hairs, and in less numbers long stiff dark-coloured 
bristles (‘ Borsten ’). 
If a section be cut of the petiole of a small leaf, an undivided horse- 
shoe-shaped trace is seen, with incurved margins, and not very markedly 
crinkled. The xylem is more massive in the neighbourhood of the marginal 
crooks, but towards the median plane it thins out to a single layer of 
tracheides (Fig. 15 , c ). In a large leaf the trace may be separated into 
three portions (Fig. 14), having the same relative positions as those in 
Lophosoria (see ‘Ann. of Bot./ xxvi, p. 284). The trace is very much 
convoluted and crinkled and the number of the ‘ divergents ’ is very large, as 
many as eighty having been counted. 
Where the axis is small, for instance about the base of a small runner, 
its vascular system may be a simple solenostele (Fig. 15 , a). But where 
larger, a single strand, or sometimes more than one, may be found in the 
pith (Fig. 15 , b). Tracing the origin of the medullary strand it is found 
that it separates at the opening of the leaf-gap preparatory to receiving the 
leaf-trace, as described by Gwynne-Vaughan for Pteris data , or Dennstaedtia 
rubiginosa (‘ Ann. of Bot./ xvii, PI. XXXIII, Figs. 13, 14). It runs down the 
centre of the pith, and frequently ends blind where the runner is small ; 
but in stronger axes it may connect up with that from the next lower leaf- 
gap, and constitute a continuous rod. In larger shoots the same method 
is found, but the medullary strands connect so as to form a considerable 
medullary system. This is illustrated by the series of sections shown in 
Text-fig. A, 1-8, which show transverse sections taken at short intervals 
from a thick stock, and arranged in succession from below upwards. In all 
of the sections it will be seen that the continuity of the solenostele as a ring 
is unbroken, even where a leaf-trace is being given off. This is a point of 
difference from what is seen in the young runner, where the ring opens on 
the giving off of a leaf-trace. This continuity is maintained in the old stem 
by a broad strap of vascular tissue — the compensation strand, or tongue of 
Tansley (‘Ann. of Bot./ xix, p. 507, &c.), which connects with the medullary 
system. It is in fact the correlative of the small strand already noticed in 
young runners (Fig. 15), and it arises like it from the anterior margin of the 
foliar gap. But notwithstanding the fact that the ring as seen in transverse 
section appears always as a complete one, there is still indirect communica- 
tion between the outer parenchymatous system and the inner by a passage 
down the hollow of the gutter-shaped trace. 
The sections may now be described in detail. In Text-fig. A 1, 2, 3 
show the steps of separation of the leaf-trace (a), and in 4 the petiole itself 
has separated from the axis, leaving only a flattened side to the section. 
