SAGE TS 
ne 
Seb, 
I = 
and Woody Tissues of Ferns. 317 
of the rhizome. A horizontal section of the rhizome shows these 
tracts in section as dark spots on the contiguous margins of such 
of the vascular bundles as have been divided a little above the 
point of convergence (PI. V. fig. 6). 
In Asplenium Ruta muraria, instead of these dark lines, we 
have, near the base of the petiole, a complete sheath of brown 
tissue surrounding the single central vascular fasciculus (Pl. V. 
fig. 8). In the rhizome, the sheaths of the petiolar fasciculi be- 
come reduced to dark lines on the outer and inner margins of 
the vascular bundles which go to join the netted cylinder ; and 
on a horizontal section, they are represented by a series of black 
spots on each side of the interrupted circle formed by the cut 
extremities of these bundles, but most distinctly on the inside. 
In Asplenium Trichomanes the arrangement is somewhat similar, 
but the dark sheaths round the petiolar fasciculi appear to be 
mainly derived from the brown cortex or tegumentary invest- 
ment of the bases of the petioles. 
But the darker spots seen in a horizontal section of the rhi- 
zome are not always due to the prolongation downwards of the 
lines of brown tissue belonging to the petioles. In Lastrea dila- 
tata there occur in the medullary parenchyma (that is, inside 
the circle formed by the netted vascular cylinder) numerous 
isolated fusiform nodules, with their long diameter parallel to 
the axis of the rhizome. Each nodule consists of a few short 
cells placed end to end and filled with a very dark, almost black 
deposit (Pl. V. fig. 7)*. This species has its petiolar fasciculi 
ensheathed with dark tissue, as in its congener L. Filiz mas ; but 
these sheaths disappear near the base of the petiole, and there 
is no connexion between them and the nodules in the centre of 
the rhizome. 
The nodules in L. dilatata may be considered as an example 
of the first degree of induration in the rhizome; in the species 
which remain to be noticed the amount of dark tissue is much 
more considerable. In Pteris aquilina and Allosorus crispus 
there are continuous bands or cords running the whole length 
of the stems; and in Blechnum boreale, Osmunda regalis, and 
Hymenophylium, the dark tissue really makes up the principal 
mass of the rhizome. 
In Pieris aquilina the creeping rhizome is invested by a villose 
integument of a hard leathery consistence, formed of rounded 
cells indurated by the dark deposit. In the pulpy and lubricous 
parenchyma immediately underneath, there is a series of vascular 
* The allied ore or variety L. Fenisecii, which, I am informed by 
Prof. Balfour of Edinburgh, is remarkable for the dark colour of the cen- 
tral part of the rhizome, probably owes this peculiarity to the great deve- 
lopment of these dark nodules. 
