6 Cmitributicms towards Establishing the General Character 



Sipillaria elegans, — a species common in the coal-mines of Eschweiler, 

 near Aix-la-Cliapelle, and of Werden, near Dusseldorf. 



By making various microscopic sections of this specimen, M. Brong- 

 niart has been enabled to study nearly the whole of its internal structure. 

 A complete transverse section shews it to consist of the following parts, 

 proceeding from the periphery to the centre.* First, a broad external 

 zone, fl, o", a", answering to the bark ; second, a narrow radiated cylin- 

 der b, supposed to constitute the ligneous system ;| third, a broken but 

 regular circle of bundles c, considered to represent the medullary sheath ; 

 and, fourth, a large column d in the situation of the pith. In addition, 

 there are on the outside of the ligneous cylinder, in some places in con- 

 tact with it, and in others at a little distance, several apparently isolated 

 bundles c, which, it is supposed, were connected with the medullary 

 sheath, and continued into the leaves or other external appendages ; as 

 such, they may be termed leaf-cords. Of these parts, the tissue of the 

 pith and the bark is, for the most part, destroyed, and replaced by 

 amorphous mineral matter ; where it is preserved, which is the case in a 

 few places, there are seen traces o? parenchyma and prosenchyma : the tissue 

 of the ligneous cylinder, of the medullary sheath, and of the leaf-cords, 

 on the contrary, is distinctly preserved. We are, consequently, furnished 

 with the most essential character of the internal structure of this plant.J 



In order to establish the true relations of ^igillaria eleqans, it will be 

 necessary to examine in detail, and under a high magnifying power, the 

 character and arrangement of its cellular, woody, and vascular tissues. 

 On a transverse section, the broken but regular circle of bundles sup- 

 posed to represent the medullary sheath, or vascular system, gives to 



* Vide the diagram (fig. 1, Plate I.), which is copied from a drawing by 

 Brongniart, three times the natural size of the specimen. 



t Brongniart, when speaking of this cylinder, appears to be undecided as to 

 whether it should be called ligneous or vascular. For reasons which will be 

 more fully noticed hereafter, I intend in this paper to apply the term ligneous 

 to it, and that of vascular to the broken circle of bundles lying within it. Al- 

 though the tissues composing the ligneous cylinder and the vascular system, or 

 medullary sheath of SigiV.aria elegans, differ in many respects from the woody 

 and the vascular tissues of ordinary Dicotyledons, yet the relative situation of 

 these parts is eminently in favour of the proposed nomenclature. 



J The figure of Artis' Rhytidolepis fibrosa (Plate IX.), which is a true Sigilkt- 

 ria, shews by the two concentric rings (which are probably the inner and outer 

 margins of the ligneous cylinder and medullary sheath conjoined), that the lig- 

 neous system of this genus does not increase in proportion to the size ac- 

 quired by the stem. Perhaps the two concentric rings of this plant represent 

 two ligneous cylinders, placed one within the other, as in Encephalartos spiralis, 

 and other Cycadacece (a supposition of which I am certainly not much in favour) ; 

 if so this character would go far to prov« that Artis' fossil is generically distinct 

 from Brongniart'a Sigillaria elegant. 



