HALONIA. 91 



eighth of an inch across the major, and six eighths of an inch across the minor axis. The 

 outside shows numerous small superficial papillse, and four circular tubercles, each having 

 a depressed areola, with a small projection in the centre. The medulla and vascular 

 cylinder are in a most perfect state of preservation ; but the zone of fine parenchymatous 

 tissue, so well preserved in Specimen No. 34, is for the most part wanting, having been 

 replaced by carbonate of lime. In this mineralized portion is seen a vascular bundle, 

 showing structure. Next comes a zone of parenchyma, increasing in the strength of its 

 cells until it gradually passes into elongated utricles (or tubes), arranged in radiating series, 

 constituting the outside next the bark. 



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

 showing the medulla composed of orthosenchyma, and a woody cylinder, formed of large 

 scalariform utricles (or tubes) in the interior of the circle, and smaller ones next the out- 

 side, ftom which proceed the vascular bundles. One of the last is seen considerably dis- 

 torted in appearance, but showing the structure in the central part. The thick zone of 

 parenchyma gradually increases in strength, until it passes into the outer zone of elongated 

 utricles or tubes. It may be objected that the vascular bundle has been introduced into 

 the interior of the stem after the decomposition of the delicate parenchyma surrounding 

 the woody cylinder ; but this argument, if good for anything, would prove that the latter 

 had also been introduced. The position of this woody cylinder, however, and of the vas- 

 cular bundle, occupying their original places, is clearly shown in the specimen, No. 34, 

 last described, where those parts are seen imbedded in the parenchyma as when growing. 

 No doubt the structure of this vascular bundle is much the same as that found in Stic/maria, 

 and might easily be mistaken for it ; but it seems more reasonable to suppose that 

 this vascular bundle belongs to the stem in which it is now found than to another that 

 is not even seen near it. In other specimens in my cabinet there is abundant evidence to 

 prove that Halonia regularis was furnished with vascular bundles proceeding from the 

 woody cylinder to the outside, in all respects like those found in Lepidodendron and 

 Stigmaria, and previously described in this Monograph. 



Fig. 3 is a longitudinal section of a portion of the whole root (magnified ten dia- 

 meters), showing the medulla (a), composed of orthosenchymatous tissue, the large 

 scalariform tubes forming the inside of the woody cylinder (b), and the smaller ones, com- 

 posing the exterior (c), the fine parenchyma (<?), and the elongated utricles or tubes, 

 forming the outer radiating cylinder (/). This section does not very distinctly show any 

 vascular bundles proceeding from the woody cylinder, except a trace of one on the right 

 hand side in the specimen; but this is not more than might have been expected, for the 

 section is only one quarter of an inch in length, and the tubercles or rootlets on the out- 

 side of Halonia are very few in number, when compared with the leaves on Lepidodendron 

 and the vascular bundles seen in that plant. 



Fig. 4 (magnified ten diameters) is a transverse section of the medulla, composed of 

 orthosenchyma, surrounded by a woody cylinder of scalariform tubes or utricles, all in a 



