STRUCTURE OF STIGMARIA. 433 



circumference of the stem, and circumscribed by a dark line : this line 

 probably indicates the surface of the deep cavity, to the base of which 

 the rootlet is attached. 



The apices of those bases of the rootlets are marked with a circular 

 depression, and so is the lower extremity of the rootlet figured at Plate 

 2, fig. 1, suggesting the possibility of the point of the latter (rootlet; 

 having been jointed unto the basal portion, at the level of the aperture 

 through which it emerges from the root. These corresponding depres- 

 sions may, however, have been caused by the collapse of the cellular 

 tissue at the fractured end, and thus indicate no articulation at all. In 

 none of M. Goeppert's figures is any such articulation represented, but 

 there is something of the sort in Corda's Tab. XII., Fig. 4. 



For the highly interesting specimen of a rootlet in which the cellular 

 tissue is preserved, the Museum is indebted to Mr. Warington Smyth 

 (Mining Geologist to the Geological Survey). It is figured at Plate 2, 

 Fig. 1, and consists of the silicified lower portion of a rootlet, whose 

 sides have collapsed, so as to reduce its originally cylindrical form to 

 that of an irregularly four-sided prism. The substance is formed of a 

 network of exceedingly delicate cellular tissue, (Plate 2, Figs. 2 and 3,) 

 composed of hexagonal cells ; and it is traversed throughout its length 

 by a dark line, (Fig. 2 a,) no doubt indicating the prolongation of one 

 of those slender bundles of vascular tissue which issue from the medullary 

 rays of the axis, {a of Figs. 6 and 7,) and thence proceed to themamillae 

 on the surface of the specimen, figured at Fig. 4, or the bases of the 

 cavities in the figures in Plate 1. 



This very simple structure of rootlet is similar to that of several 

 Lycopodia, and indeed of many other plants, both Monocotyledonus and 

 Dicotyledonus, so far as can be ascertained without a further knowledge 

 of the axis of the organ ; of whose structure, however, there can exist 

 no reasonable doubt, since it may be confidently assumed to consist of 

 a bundle of vessels, similar to those represented at Fig. 7 a. 



In M. Goeppert's* figure (Table XIII. Fig. 8, Erf) this axis is 

 represented as formed of such tissue, surrounded by cellular tissues dis- 

 posed in two concentric rings, between which a black line is interposed. 

 There is no appearance of any similar arrangement in the specimen I 

 have examined, the net-work being continuous from the vascular axis to 

 the circumference. As there appears to be a rupture of the tissue to a 

 considerable extent in M. Goeppert's figure near this line, and as where 

 there is no such disunion the cellular tissue is continuous across the line, 

 I am inclined to regard the latter as a coaly deposit, consequent possibly 

 upon the process of petrifaction having been arrested at that point. 



Mr. Henry Beckett of Wolverhampton having forwarded to the Geo- 

 * Goeppert, 1. c. t. xvi. fig. 48. 



