A strict correspondence is also exhibited in the internal
structure of the scales, or bases of leaf stalks surrounding
the trunks of our fossil Cycadites, with that of the corresponding
scales in the recent species.[1]
with circles of cellular tissue, is similar to the two laminated circles near the base of a young stem of Cycas revoluta, (Pl. 59, Fig. 3.) This section was communicated to me by Mr. Brown early in 1828, to confirm the analogy which had been suggested from the external surface, between these fossils, and the recent Cycadeæ, and is figured in Geol. Trans. N. S. vol. ii. Pl. 46.
- ↑ in Pl. 61, Figs. 2, 3, represent two vertical sections of a Cycadites microphyllus from Portland, converted to Calcedony. These slices are parallel to the axis of the trunk, and intersect transversely the persistent bases of the Petioles or Leaf-stalks. In each rhomboidal Petiole, we see the remains of three systems of vegetable structure, of which magnified representations are given Pl. 62, Fig. 1, 2, 3. We have, first, the principal mass of cellular tissue (f;) secondly, sections of gum vessels (h) irregularly dispersed through this cellular tissue; thirdly, bundles of vessels, (c,) placed in a somewhat rhomboidal form, parallel to, and a little within, the integument of each petiole. These bundles of vessels are composed of vascular woody fibres proceeding from the trunk of the plant towards the leaf. See magnified section of one bundle at Pl. 62, Fig. 3, c'.
A similar arrangement of nearly all these parts exists in the transverse section of the leaf stalks of recent Cycadæ. In Cycas circinalis, and C. revoluta, and Zamia furfuracea, the bundles of vessels are placed as in our fossil, nearly parallel to the integument. In Zamia spiralis, and Z. horrida, their disposition within the Petiole, is less regular, but the internal structure of each bundle is nearly the same. In Pl. 62, Fig. A shows the place of these bundles of vessels in a transverse section of the leaf stalk of Zamia spiralis; Fig. A. c'. is the magnified appearance of one of the bundles in this section; Fig. B, c″ is the magnified transverse section of a similar bundle of vessels in the petiole of Zamia horrida. In this species the vascular fibres are smaller and more numerous than in Z. spiralis, and the opake lines less distinct. Both in recent and fossil Cycadæ the component vascular fibres of these bundles are in rows approximated so closely to each other, that their compressed edges give an appearance of opake lines between the rows of vascular fibres, (see Pl. 62, Fig. 1, c'. Fig. B, c″. and Fig. 3, c'.) These bundles of vessels seem to partake of the laminated disposition of the woody circular within the trunk.
An agreement is found also in the longitudinal sections of the Petioles of recent and fossil Cycadeæ. Pl. 62, Fig. 1, is the longitudinal section of part of the base of a Petiole of Zamia spiralis, magnified to twice the natural size. It is made up of cellular tissue, (f,) interspersed with gum vessels, and with long bundles of vascular fibres, (c) proceeding from the
