314 Dr. G. Ogilvie on the Vascular 
how unsatisfactory all the systems of classification are which 
have been proposed in this order, these particulars may possi- 
bly have a certain value, as increasing the store of facts bear- 
ing on the general organography of the group, from which 
it is to be hoped that some botanist may yet draw materials for 
a more natural method of arrangement than any which has yet 
been brought forward. The peculiarities, too, in these points, 
are in some cases so striking that they appear worth recording 
as specific characters *. 
A brown-coloured principle is very extensively distributed in 
the organization of Ferns. It is particularly conspicuous in the 
sporangia and other parts of fructification, and in the epidermis 
of the stem, and the ramenta or scales with which it is clothed ; 
and it is so characteristic of the group, that it communicates a 
peculiar rusty tint to the vegetation of districts in which (as in 
some parts of New Zealand) Ferns form a prevailing feature. 
It is probably identical with the brown principle which occurs 
in other foliaceous Cryptogamia, particularly in the stems and 
capsules of Mosses; and, whatever may be its chemical relations 
—a point on which I can say nothing,—it at least resembles the 
woody matter of phanerogamic plants in being deposited in the 
interior of cells, in concentric pitted layers, on the inner aspect 
of the first-formed wall of cellulose. The tissues in which it is 
deposited often acquire great hardness, but are deficient in the 
toughness of true wood; on drying, especially, they become very 
brittle. 
This brown matter is very constantly met with in the epider- 
mic cells of the Fern-stem. The hardening of the cortical layer 
in these plants, as in arborescent endogens, is even more neces- 
sary for the support and defence of the stem than the accumu- 
lation of the layers of bark in exogenous trees, on account of the 
occasional deficiency of hard tissues in the interior of the rhi- 
zome. Generally, however, there is a certain limited amount of 
internal induration also ; for we find that particular tracts of the 
(see a criticism by Mr. Moore, Phytol., n.s., i. p.378). There is a still 
greater indefiniteness about the sectional views in Mr. Francis’s ‘ Analysis 
of the British Ferns.’ Another reference given me by the same gentleman 
(Duval Jouve, ‘ Etudes sur le Pétiole des Fougéres,’ in Billot’s ‘ Archives 
de la Flore de France,’ pp. 50-149) I have been unable to verify, though I 
have made inquiry for the work in the principal libraries in London. I 
have not had access to the works either of Mohl or others of the German 
botanists who have discussed the structure of Fern-stems, so that I cannot 
say how far they may have gone over the same ground. 
* Tn this connexion I may refer to the great similarity in the disposition 
of the dark tissue in the petioles of Scolopendrium vulgare and of Ceterach 
oficinarum (Grammitis Ceterach), once referred to the first-mentioned 
genus. 
