760 MR R. KIDSTON AND MR D. T. GWYNNE-VAUGHAN ON 



The wide central pith is represented by a space that is surrounded by an almost 

 continuous ring of xylem about 5 mm. in diameter (fig. 2, xy.), which in the fossil has 

 become accidentally fractured at several points. Neither the inner cortex (fig. 2, i.e.) 

 nor the peripheral tissues of the stele have been preserved, but they have left a space 

 traversed by several of the departing leaf- traces. The outer region of the cortex 

 (fig. 2, o.c.) was sclerotic, and at certain points, which appear as dark patches, it is still 

 in sufficiently good condition to show that it consisted of narrow, thick-walled fibrous 

 elements. The leaf- traces in this sclerotic region were surrounded by a sheath of 

 parenchyma continuous with that of the inner cortex, but ib has decayed away, and the 

 leaf-traces appear to lie loosely in so many cavities in the sclerotic outer cortex. Some 

 other smaller light-coloured spaces are also present in the outer cortex (fig. 2, /?.), which 

 represent roots cut across in various directions as they pass outwards. 



The actual limit of the stem itself coincides with the periphery of the cortical 

 sclerenchyma (fig. 2, a.), and this is surrounded by a thick coating of closely adpressed 

 leaf-bases which may have been more or less concrescent in close proximity to the axis. 

 In this region of the fossil, however, each leaf-base is distinguished by a special ring of 

 dense sclerenchyma which is continuous below with the outer cortex of the stem. The 

 space between the separate sclerotic rings is occupied by a large number of small sclerotic 

 strands of irregular and varied form, scattered in a matrix of finely granular matter, to 

 which attention will be presently directed. 



At first sight the sclerotic rings of the leaf-bases appear to increase in size gradually 

 towards without, at the same time becoming tangentially flattened and variously 

 twisted and contorted. If, however, the coating of leaf- traces be more closely scrutinised 

 as a whole, four more or less distinctly concentric zones (fig. 2, sc. L.) can be made out 

 in which the sclerotic rings are especially ill-developed and small in size. These zones 

 successively interrupt the regularity of the increase in size of the leaf-bases towards 

 without, and no doubt they represent zones of scale-leaves with abortive laminae similar 

 to those occurring in certain of the modern Osmundacese. 



Detailed Description of the Stem. 



The most important anatomical character of this species is the almost complete 

 absence of leaf-gaps in the xylem ring of the stem. The fact is that most of the leaf- 

 traces, if not all, depart without in any way interrupting the continuity of the xylem 

 ring, so that the " medullary rays " characteristic of the Osmundaceous stele in general 

 are almost or completely absent. The xylem ring is irregularly and rather deeply 

 indented along both its margins (PI. I., fig. 3), and before or during fossilisation it 

 became crushed at some points and broken right across at others. Most of these 

 breaks in the xylem ring are clearly due to accident, but it is just possible that some of 

 them may have been occupied by thin-walled cells which decayed before fossilisation. 

 Even if such medullary rays actually were present in the living plant, they must 



