INTERNAL STRUCTURE OF TRUNKS. 497 
I must refer to the memoir, in which these 
sections are described, for specific details as to 
the varied proportions and numerical distribu- 
tion of these concentric circles of laminated wood 
and cellular tissue, in the trunks of living and 
fossil species of Cycadeae.* 
A strict correspondence is also exhibited in 
* Plates 60, Fig. 1, and 61, Fig. 1, represent very perfect 
specimens of fossil Cycadites from Portland, now in the Oxford 
Museum; both having the important character of Buds pro- 
truding from the Axillse of the leaf stalks. 
The section given in PI. 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 ; (PI. 60, Fig. 2) each presents a single 
circle of radiating laminae 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 persis- 
tent bases of fallen leaves, and of abortive scales. The continu- 
ation of the same structure is seen at the summit of the stem, PL 
60, Fig. 1, A. B. C. D. 
The Cycadites microphyllus, PI. 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 cel- 
lular 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, (PI. 
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 
Cycadeae ; and is figured in Geol. Trans. N. S. vol. ii. PI. 46, 
GEOL. K K 
