6< H ; mr. Wi CARRUTHERS ON FOSSIL CYCADEAN STEMS 



cnmpcici bundle, which as it passes outwards breaks up into the different bundles required 

 I i- the service of the leaf. The woody portion of the stem is composed of a single layer, 

 which, in transverse section, is seen to be repeatedly broken by the large meshes for the 

 , s > -•' of the trundles (Plates LVIL fig. 3, LVIII. fig. 1, and LXIL fig. 2). The ana- 

 logy lx i t ween these fossil stems and the caudex of a tree fern is very remarkable. Indeed, 

 excluding the nature of the component tissues of the stem, they differ only in that the 



fossil i ye I has medullary rays, and a cortical layer separating the vascular cylinder from 



the bnsi - of the petioles. 



The vascular bundle in B. Saxbyanus rises as a rounded swelling in the lower angle of 

 the mesh on tin- inner surface of the woody cylinder (Plate LVIL fig. 5). A depression 

 soon shows itself on the upper surface of the swelling, and the bundle extends upwards at 

 the (mils until, where it leaves the cylinder, it has a lunate transverse section (fig. 6). As 

 it passes upward^ and outwards through the cortical parenchyma the two ends are still 

 more produced; then the arc which joined them below separates from them; afterwards 

 the Lower free ends curve inwards until they meet, forming a slightly interrupted oval 



figure with somewhat swollen sides (fig. 7). This finally breaks up into more than 

 twenty separate small bundles, forming an upper and under series for the petiole (fig. 8). 

 In B. Gibsonionus the vascular bundles pass directly outwards in an almost horizontal 

 direction. The mass for each leaf separates from the woody cylinder as a whole, and has 

 here the same form as in B. Saxbyanus (Plate LVIII. figs. 1-4); but it speedily breaks 



up into the numerous small bundles seen in the section of its leaf-stalk (fig. 3). 



Th letiole ifl rhomboidal or lozenge-shaped in transverse section, with the keel some- 

 what more pronounced than the angle on the upper surface. It is composed of large 

 cells, somewhai elongated in longitudinal section (Plate LX. fig. 9), with numerous large 

 -um-canals, and a double series of vascular bundles parallel to the surface, except below 

 the upper angle, where they form a loop into the interior of the petiole. A very dense 

 i mem um clothed the under surface of the base of the petiole, which was developed to 



chan extent as to separate very considerably each petiole from its neighbour. The 

 petrifying mat. Hal, having obtained speedy access to these delicate scales, has preserved 



them in a remarkably p< ifect condition. In some specimens, like that figured at 

 Plai L\ II. Bg. 2, the petrified ramentum stands out as a network of ridges, while the 



_,— il for 



Uy mm durable petioles have decayed and left rhomboidal cavities, represents 



but, in another specimen, the hard bases of the petioles have resisted 

 th, operation of the marine animal that burrowed in the ramentum, and they are left as 

 pr tnmeneee andmg out from the body of the fossil (PlateLXIL fig.l). The ramentum 

 is eompo* I _ nerally of but a single series of cells ; but sometimes it is two or more cells 

 m hictaieas (Rate LX. fig 11). The leaf disarticulated at a point some distance from 



ortex '; hl - * ^Jorahle portion of the bases of the petioles permanently 



S 



»r 



raiding the stem (Tab. LVIL fi 



tat an! inl I ^7 mimhei ° f #the Peti ° leS b0rG Sll0rt h ™^™' TheSe aXiUaTy 



- ; _ n por tant features in this group of fossil plants. In some fragmentary speci 



men 



fte ', ,hv' fit "!'""' '^ a bud > as described by Mr. Brown; but more frequently 



n,„o„ t> «, fte ,,,ves are without them. The proportion of the buds to the leaves 



