and Woody Tissues of Ferns. 323 
masses of dark tissue. In his remarks on the structure of the 
stems of Ferns, in his ‘ Introduction to Cryptogamic Botany’ 
(p. 515), he states distinctly that the hard tracts belong to the 
parenchyma, and do not correspond to the proper wood of the 
Phanerogamia. The latter he considers to be represented by 
certain pale fibres, occurring in the substance of the vascular 
bundles. I have recognized such fibres distinctly enough in two 
species of Tree-fern which I have lately examined. They form 
a sort of surface-coating to the fasciculi, exterior to the scalari- 
form vessels, and immediately within the cambium-layer, This 
is just the position occupied by the pleurenchyma of the Endo- 
genous stem; but in themselves these fibres have none of the 
characters of woody tissue. They appear to be portions of the 
cambium-layer which have undergone an imperfect conversion 
into vascular tissue. The transformation seems to take place by 
the clustering of the minute cambium-cells into long fusiform 
masses, which then become invested by a cell-wall, on whose 
inner surface the scalariform markings are developed, by a deposit 
of cellulose at particular points, pari passu with the disappear- 
ance of the original cells of the cluster enclosed by it. I think 
I have observed all stages of this transition—fusiform masses of 
cellules, pale granular fibres, and tubules or elongated cells, 
differmg from the scalariform vessels of the fasciculus only in 
their smaller diameter and fainter markings. 
In most of our indigenous species I have been unable to re- 
cognize any distinct fibrous coating to the vascular bundles, 
though the inner stratum of the cambium-layer has certainly at 
times an appearance of faint longitudinal striation, and the sca- 
lariform vessels on the exterior of the fasciculus are generally of 
smaller diameter and less distinctly marked than those within. 
The striated layer comes nearest to the characters of a real fibrous 
tissue in the netted cylinder of Polystichum Lonchitis and Cysto- 
pteris fragilis, and in the indurated petiolar fasciculi of Tricho- 
manes radicans and Asplenium lanceolatum. In P. Lonchitis and 
A. lanceolatum some of these cambium-fibres make a still closer 
approach to those of woody tissue, by the deposit of a brown 
sclerogenous matter in their interior. In Botrychium Lunaria 
similar fibres occur, and the vessels are rather annular than 
scalariform. 
That the woody fibres of plants generally differ from the ducts 
or vessels only in being a less-differentiated form of cambium- 
tissue, is a view which was very distinctly laid down by Schleiden*, 
and one which derives some support from the replacement of 
ducts by punctated woody tissue in the Conifer, and from the 
occurrence in some species of various intermediate forms, such 
* Principles of Botany, bk. 2. c. 2. § 26. 
