138 



POSSIL PLANTS. 



whole of the internal radiating cylinder and the central axis, magnified 12 diameters ; 

 (a) showing the barred tubes of the central axis ; {5 b) the internal radiating cylinder of 

 barred tubes, at first next the central axis, small, but increasing in size ; {c c) as they 

 approach the outside. In this section no part of the zone of lax cellular tissue, the outer 

 radiating cylinder, the prosenchymatous tissue forming the inner bark, or of the outer bark, 

 is shown ; nor are there any traces of vascular bundles. 



Pig. 3 is a tangential section of a portion of the inner radiating cylinder, magnified 

 16 diameters; {d) showing the large bundle of vascular tubes, and {d') the medul- 

 lary rays consisting of a single row of cells traversing the inner radiating cylinder. 



Although all the tangential sections afford evidence of these two kinds of rays, they 

 have not been yet observed in the longitudinal sections ; so we cannot be certain whether 

 the larger have a bnndle of vascular tissue surrounded by cellular tissue, like those seen in 

 Sti(/maria,o\' wot; and we have no direct evidence to connect them with the pith or central 

 axis, the latter being separated from the inner radiating cylinder by a sharp and distinct 

 line, and showing no communication with the pith, such as is seen in some Stigmarice, 

 and in Corda's Diploxi/lon cycadoideum ; but exactly resembling Witham's Anabathra 

 pulcherrima in every particular. 



Pig. 4 is a portion of the outer radiating cylinder, composed of small rectangular 

 tubes, or elongated utricles, magnified 12 diameters. This band of prosenchymatous 

 tissue is traversed by wedge-shaped masses of lax cellular tissue, which gradually 

 diminish in size as they approach the outer bark. The tangential section does not 

 exhibit the vascular or foliar bundles in so good a state of preservation as ray large 

 specimen in plate xxxiv, vol. civ, of the 'Phil. Trans.,' but it shows that they are exactly 

 of the same character, so far as they have been preserved. 



Pig. 5 (No. 40). This is a transverse section of the inner radiating cylinder, enclosing 

 a central axis or pith, of a small Sigillana vascularis, in all respects, except as to size, 

 similar to the large specimen ; magnified 9 diameters. The tubes in the centre, both 

 great and small, are barred on their sides. The specimen has an outer zone of lax cellular 

 tissue, passing into the outer radiating cylinder of prosenchymatous tissue, surrounded by 

 an epidermis converted into coal. The figure is given for the purpose of showing that the 

 small specimens of Sigillaria vascularis, with piths of barred vessels, first described 

 by me in the ' Quarterly Journal of the Geological Society,' pass gradually into the 

 large specimens described in the 'Philosophical Transactions' and in the present 

 Monograph. 



A number of the central axes have been taken out of the internal radiating cylinders 

 of Sigillaria vascularis for the purpose of endeavouring to trace the connection of the 

 medullary rays with the central axes or piths ; but no evidence was obtained to show 

 where these rays originated. They could only be traced to the dark line separating the 

 pith from the inner radiating cylinder, but not passing through that hne. 



The inner Avails of * the outer radiating cylinder, next the central axis or pith, were 



