THE FOSSIL OSMUNDACE^J. 



463 



xylem-parenchyma amongst the tracheae, which in longitudinal section exhibit the 

 usual Osmundaceous multiseriate pitting. Of the soft outer tissues of the stele the 

 xylem-sheath alone is well preserved, being three to five cells thick. The phloem and 

 pericycle are too much disorganised for detailed description, but the phloem occurred in 

 greatest quantity opposite the medullary rays, forming little wedge-like projections 

 between the xylem strands. This is better shown in the other specimen than in the 

 one figured. No distinct endodermis could be made out. 



The leaf-trace departs in exactly the same way as in the modern genera Osmunda 

 and Todea (fig. 28). The soft tissues in the axil of the leaf- trace communicate directly 

 with the pith immediately upon the insertion of the leaf-trace xylem upon that of the 

 stem (fig. 28, l.t. 1 ). The arch-like strand thus formed closes in below to cut off a small 

 island of parenchyma which soon dies out, leaving the decurrent leaf-trace protoxylem 



Fig. 5. — Osmundites S'chemnitzensis. Diagram of transverse section of stipular base of the petiole in the outermost 



region of the specimen. 



completely immersed in the xylem strand of the stem, and this also eventually 

 disappears. 



At the point of its departure from the stele the xylem of the leaf-trace has the form 

 of an oblong strand with slightly enlarged and somewhat adaxially curved ends. There 

 is a single median strand of protoxylem, which is truly endarch throughout (figs. 23 

 and 24). On its way out through the sclerotic cortex the trace is accompanied by a 

 sheath of parenchyma which is usually preserved even when the sclerotic cortex itself is 

 gone ; it appears in the photograph as a dark zone (fig. 22). The leaf-trace passes 

 through the usual series of changes that result in the typical Osmundaceous curve (figs. 

 25 and 26). In the coating of leaf-bases the petioles possess well-developed stipular 

 wings. Their sclerotic rings are well preserved, and consist of homogeneous sclerotic 

 fibres (fig. 27, scl.). A band of sclerenchyma is also found lining the adaxial concavity 

 of the leaf- trace. This at first fills up nearly the whole of the concavity ; further out it 

 is confined to a layer evenly coating the inside of the trace (figs. 25 and 26, i. scl.); 

 still further out the layer thins down considerably in the median region (cf. text fig. 

 diagram 5). So far as we could make out there was no other sclerenchyma within the 

 sclerotic ring. 



TRANS. ROY. SOC. EDIN., VOL. XLVII. PART III. (NO. 17). 69 



