Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/377

 Rh trunk and scales, in our search for their distinguishing characters.

I have elsewhere (Geol. Trans. London, N. S. vol. ii. part iii. 1828) instituted a comparison between the internal structure of two species of these fossil trunks, and that of the trunks of a recent Zamia and recent Cycas.

I must refer to the memoir, in which these sections are described, for specific details as to the varied proportions and numerical distribution of these concentric circles of laminated wood and cellular tissue, in the trunks of living and fossil species of Cycadeæ.{{#tag:ref|Plates 60, Fig. 1, and 61, Fig. 1, represent very perfect specimens of fossil Cycadites from Port land, now in the Oxford Museum: both having the important character of Buds protruding from the Axillæ of the leaf stalks. {{parabr}} The section given in Pl. 59, Fig. 2, of the trunk of a recent Zamia horrida, from the Cape of Good Hope, displays a structure similar to that in the section of the fossil Cycadites megalophyllus from the Isle of Portland; (Pl. 60, Fig. 2) each presents a single circle of radiating laminæ of woody fibre, B, placed between a central mass of cellular tissue, A, and an exterior circle of the same tissue, C. Around the trunk, thus constituted of three parts, is placed a case or false bark, D, composed of the persistent bases of fallen leaves, and of abortive scales. The continuation of the same structure is seen at the summit of the stem, Pl. 60, rig. 1, A. B. C. D. {{parabr}} The Cycadites microphyllus, Pl. 61, Fig. 1, affords a similar approach to the internal structure of the stem in the recent Cycas. The summit of this fossil exhibits a central mass of. cellular tissue (A,) surrounded by two circles of radiating woody plates, B. b., between these laminated circles, is a narrow circle of cellular tissue, whilst a broader circle of similar cellular tissue (C) is placed between the exterior laminated circle, (b) and the leaf scales (D.) This alternation of radiating circles of wood 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.