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



they tapered to fine points ; at the same time they differ considerably in size even at 

 the point of their insertion on the petiole. The thin-walled tissue of the spine is con- 

 tinuous at the base with the peripheral parenchyma of the petiole (fig. 50), into 

 which the sclerotic core is also clecurrent as a definite strand of fibres (fig. 48, scl. 1 ), 

 which may be traced downwards for a considerable distance, gradually approaching 

 the sclerotic ring of the petiole, with which it eventually becomes completely confluent. 



Diagram 2. — Diagrammatic restoration of a transverse section of an outer petiolar base of Bathypteris rhomboidea 



to show the arrangement of the sclerenchyma. 



The leaf-trace in the outer petioles is typically horse-shoe shaped. The xylem 

 strand has numerous endarch protoxylems, the elements of which are probably annular 

 or spiral or perhaps both, while those of the metaxylem are multiseriate. The endo- 

 dermis abuts directly on the internal sheath of sclerenchyma, and at many points has 

 conspicuously dark radial walls. The cells of the pericycle when preserved appear to 

 have possessed somewhat dense contents (fig. 53). The phloem is very poorly 

 preserved, being represented merely by a dark line indicating its crushed and collapsed 

 elements. The xylem sheath, on the other hand, presents a feature of peculiar and 

 unique interest. A large number of its cells are vertically elongated, and possess very 

 dark and lamellated walls similar to those described in the cortical sclerenchyma 

 (figs. 53 and 54, xy. sh. scl.). It is believed that these elements were actually sclerotic ; 

 and if this is so we know of no perfect parallel in the Filicales, the nearest analogy 

 being found in Adiantum trapeziforme, var. Funckii, where the xylem parenchyma 

 becomes thick-walled and fibrous. In Bathypteris the sclerotic elements of the xylem- 

 sheath are more plentiful in the outer leaf-traces, and especially on the adaxial surface, 

 where they may occupy almost the whole of its extent (fig. 53). 



The Root. 



A large number of roots run outwards in the interstices between the petioles, and 

 branch frequently as they pass out. The majority of them possess a diarch xylem 

 strand, but a considerable number of triarch roots were also met with (fig. 56). The 



