93 



FOSSIL PLANTS. 



most beautiful state of preservation, with scarcely a cell wanting, and nearly as perfect as 

 when they grew. 



Fig. 5 (magnified forty diameters) represents a nearly right-angled transverse section 

 of the vascular bundle in the middle of the root. This we take for one of those which 

 proceeded from the outside of the woody cylinder to the rootlets. It consists of an axis 

 of scalariform tissue, composed of two different sizes of tubes, the one being much larger 

 than the other, and formerly imbedded in a zone of orthosenchyma, which has disappeared 

 in the specimen. This is succeeded by a zone of regular parenchyma. 



On comparing this section with a similar one of Stigmaria, figured and described by 

 me many years since, scarcely any difference can be detected.^ 



§ 3. Specimen No. 36, Ilalonia re()ularis. Plate XVII, figs. 1, 2, 3. 



Specimen No. 36 (Plate XVII, fig. 1, natural size) is another example of Halonia 

 regularis from the Upper Brooksbottom seam of coal. It is imbedded in a nodule of 

 limestone, and only shows a portion of one side of the fossil. Its transverse section is 

 irregularly oval, measuring one and a half inches across its major and three quarters of an 

 inch across its minor axis. The length of the specimen is two and one quarter inches. 

 So far as it is exposed, no one would be able to distinguish it from a small specimen of 

 Stigmaria Jicoides. Unlike No. 35, it presents no appearance of tubercles ; but in their 

 places are depressed areolae of a circular form, having a raised ball in the centre, and 

 arranged in quincuncial order. From its external characters the most experienced judge 

 of Carboniferous fossils would not be able to distiuguish it from a Stigmaria ; but when 

 we proceed to examine its internal structure, we find that it is exactly the same as that of 

 Halonia regularis, and very different from that of Stigmaria jicoides. 



Fig. 2 (magnified five diameters) represents a transverse section of the same specimen, 

 which displays a medulla composed of orthosenchyma and a woody cylinder, formed of 

 large scalariform tubes in the interior of the circle, and smaller ones next the inside, 

 whence proceed the vascular bundles ; a trace of one of these is seen. A portion of the 

 delicate parenchyma, next to the woody cylinder, has been destroyed, and replaced with 

 mineral matter ; but the greater part of it is preserved, and shows it to increase in 

 strength as it approaches the circumference, assuming a prosenchymatous structure and a 

 radiating appearance. Outside of this is a dark line, succeeded by an epidermal layer 

 whose structure is apparently destroyed. It is upon the surface of the latter, however, 

 that the Stigmarioid areolae occur; and, if it were carefully removed, we should most 

 probably find the tubercles generally seen, as in specimens Nos. 35 and 38, and 

 other common forms of Halonia regularis^ in the place of the areolae in this 

 specimen. 



' 'Quart. Journ. Geolog. Soc.,' vol. vi, pp. 18, 19. 



