is 
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a 
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por 
it 
: f 
~~. 
and Woody Tissues of Ferns. 315 
parenchyma become the seat of such a deposit, so that a section 
commonly shows the pale tissue of the stem relieved by a dark 
pattern of the indurated cells, as well as by the cut ends of the 
vascular bundles, which are generally of a whiter colour. This 
induration of the parenchymatous cells is sometimes not attended 
by any alteration in their form, the resulting tissue somewhat 
resembling that of the shells of nuts. In certain cases, however, 
the cells become elongated into fibres ; and we find every variety 
of brown tissue, from one of short cells like those of the husky 
structures of the higher plants, to long fusiform fibres, undi- 
stinguishable, except in colour, from the wood of the Phanero- 
gamia. The wood-like tissue generally occurs in cords or bands, 
either surrounding the vascular bundles or interposed between 
two sets of fasciculi. In the denser fibrous bands the cells be- 
come so filled up with brown matter that only a small central 
cavity is left, as in the duramen fibres of the harder woods ; but 
in the Jess indurated tracts the cells (both prosenchymatous and 
parenchymatous) have frequently a large central space filled 
with starch-grains, like those of the pale-coloured cellular matrix 
of the stem. Starch-grains, it may be observed, occur in a 
similar way in the woody fibres of the ivy, and probably in those 
of Banksia and a few other plants, though this arrangement is 
not usual among Phanerogamia. 
The disposition of the tracts of indurated tissue differs very 
much, as I have already remarked, in different species. There 
are some instances in which the brown deposit appears to be 
confined to the layers of cells forming the cuticular investment 
of the rhizome and of the bases of the petioles near their origin 
from the rhizome. This is the case, more or less distinctly, in 
all our Polypodies, in the majority of the species of Asplenium, 
and in Polystichum aculeatum, Lastrea Filiz mas, and Adiantum 
Capillus Veneris. 
The deficiency is most marked in the nodulated stems of the 
common Polypody ; their peculiar fragility is due to the soft 
watery parenchyma in which the minute and straggling vascular 
bundles are imbedded. In most of the other species there is, 
more or less, some compensating provision. Thus in Polypodium 
Dryopteris, and still more in P. Phegopteris, the parenchyma is 
much denser, and has a decidedly dark or brownish tinge. In 
Asplenium Filiz foemina, there is no such dark tinge in the fresh 
parenchyma, but it has a peculiar hardness, from the thickness 
of the walls of its component cells. In Lastrea Filix mas, again, 
the vascular bundles have a brownish tint, and a degree of tena- 
city which allows them to be dissected out with more ease than 
in any other of our Ferns. 
We find, too, that in many of these species the brown sub- 
21* 
