ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 769 
MM. Berrranp and Renautt have expressed on purely theoretical grounds a 
somewhat similar view of the origin of the Cycadean type of bundle, and they also 
have cited Lyginodendron for comparison, relying not on any original investigations 
but on the figures published in Wiiutamson’s Memoir IV. ‘They have, however, 
misunderstood the structure, owing to their assumption that the whole of the 
centrifugal wood is secondary and the whole of the primary wood centripetal. This, 
as we have shown, is not in accordance with the facts. It is, to a great extent, 
in consequence of this error that they are led to derive Lyginodendron and Heter- 
angium, as well as their own genus Poroxylon, from Lycopodiaces, a conclusion 
which, as regards the genera investigated by us, is completely negatived by the 
whole. organization of the leaf, while it is quite unnecessary as an explanation of 
the stem-structure.* 
In Lyginodendron then, we have this remarkable combination of anatomical 
characters, namely, collateral, mesarch Cycadean bundles in the stem, passing over 
into concentric Fern-bundles in the petiole. In Heterangium we have the further 
complication, that the mesarch bundles in the lower part of their course occupy the 
periphery of a pithless stele, the whole interior of which consists of wood. 
We wish to add one word as to the roots; we have called attention above to their 
great similarity, when young, to Marattiaceous roots, and to their regular mode of 
secondary growth recalling that of a typical Dicotyledon. They are less similar to 
roots of Cycads than we might have expected, but then we must remember that 
Cycadean roots are generally fleshy, and consequently much modified in structure. 
We may reasonably regard the roots of Lyginodendron and Heterangium as those of 
Fern-like plants, which have already thoroughly adapted themselves to secondary 
growth by means of a cambium. Certainly they bear no resemblance whatever to 
any known roots of Lycopodiacez. 
We have seen how extraordinary a combination of characters belonging to various 
groups these genera present. In different parts of their structure they have been 
found to present points in common with Gleicheniaceze, Osmundacez, Marattiacez, 
Ophioglossex, and Cycadez. 
The view of the affinities of Lyginodendron and Heterangium, which we desire to 
suggest, is, that they are derivatives of an ancient and “generalized” (or rather non- 
specialized) Fern-stock, which already show a marked divergence in the Cycadean 
direction. Of the two genera Heterangium appears to be the more ancient, and 
certainly stands nearer to the Filicinean ancestry. Lyginodendron, while still 
retaining conspicuous Fern-like characters, has advanced much further on Cycadean 
lines. 
We do not intend to suggest that in these plants we have the actual ancestors of 
* BortRanD et Renavwt, “ Remarques sur les faisceaux foliaires des Cycadées actuelles,” é&c., ‘ Arch. 
Bot. du Nord de la France,’ 3rd année, No. 35, 1886, p. 237. ‘“ Recherches sur les Poroxylons,” loc. cit., 
p. 382, &e. 
MDCCCXCV.—B, 5G 
