142 



FOSSIL PLANTS. 



purpose of showing that different transverse sections of the root give the same result as 

 to the structure of the central axis. 



Yig. 2 (magnified 8 diameters) is a transverse section of a portion of the root taken 

 near the outside of the specimen, showing the lax parenchymatous tissue (e) passing into 

 the outer radiating cylinder of prosenchymatous tissue, formed of rectangular tubes (/), 

 traversed by four bell-shaped cavities {d), connected with the pear-shaped bundle 

 of barred tubes, like those found in Stigmaria rootlets. In one of these cavities is a 

 rootlet. 



Fig. 3 (magnified 8 diameters) is a longitudinal section (unfortunately not very true, 

 being nearly diagonal across the inner radiating cylinder and the central axis) showing 

 the large and small tubes and cells {ci) which, by the direction of the section, appear like 

 utricles and cells, large and small, barred on all their sides, the small tubes (3) next to 

 the central axis and the larger tubes (e), also barred on all their sides, forming the inner 

 radiating cylinder. In this figure the small tubes appear more like cells than tubes ; but 

 under a high magnifying power they show the bars on their sides, like those seen on the 

 larger tubes. 



In all the longitudinal sections of specimens of Sigillaria vascularis (Nos. 39 and 40) 

 we have not been able to trace any vascular bundles proceeding from the central axis 

 or traversing the inner radiating cylinder, having their origin in a medulla or a medullary 

 sheath, similar to those found in the Stigmaria Jicoides with open wedges. In the 

 tangential section we cross the large vascular bundles and small medullary rays, which in 

 their sectional view do not afford any direct evidence of their being formed of barred 

 tubes, and this is all that can be said of them. In the examination of numerous casts of 

 the outside of the medulla, or central axis, of Sigillaria vascularis, as previously stated, 

 there have been found no openings in the ends of the wedge-shaped masses of the wood 

 of the inner radiating cylinder, like those found in the open-wedged Stif/maria. This is 

 the case with all the specimens of Biploxylon cycadoideum and Siyillaria vascularis that 

 have come under my observation. In tangential sections of the outer radiating cylinder 

 or inner bark of the latter plant (pi. xxxiv, fig. 2, in my Memoir in the 'Phil, 

 Trans.') there is evidence of a foliar bundle similar to that shown to exist in Sigillaria 

 spimdosa by MM. Renault and Grand' Eury. This is also seen in similar sections of the 

 small Siyillaria vascidaris described by me [loc. cit., pi. xxxv, fig. 5), and which Professor 

 Wilhamson and Mr. Carruthers think is a Lepidodendron, and which Professor Schimper 

 identifies with L. Veltheimianum. 



The large size of the tubes and cells in the medulla is very remarkable, and in a 

 great measure accounts for the absence of that part of Stipnaria ; for such bodies -were 

 not likely to have been able to resist decomposition for any considerable time and 

 it also tends to confirm the probability of the large tubes found in the pith of my 

 Staffordshire specimen, hereinbefore referred to and questioned by Professor Williamson. 



