ON A NEW SPECIES OF DINEURON AND OF BOTRYOPTERIS. 363 



section the tracheae are seen to possess scalariform thickenings without the occurrence of 

 any porose markings. 



None of the stems yet met with show the departure of the leaf-trace from the stele, 

 but in several of them the leaf- traces are seen in their passage through the cortex. 



At fig. 4, two petioles are being given off, apparently in spiral series ; at figs. 6 and 

 7, one is seen on each stem, though in the former case it has probably become free. 



The petioles, which are larger than the stems from which they arise, are circular or 

 slightly oval in form, the largest met with attaining a diameter of 2*20 mm., with a leaf- 

 trace 075 mm. in its greatest width. The leaf- trace is thus a half larger than the 

 diameter of the stele of the stem. 



The cortex of the petioles forms a broad zone of thick- walled prosenchymatous cells, 

 the smaller of which lie at the periphery, while the larger elements are towards the 

 centre of the zone, whence they decrease in size towards the endodermis, though even 

 here they are larger than those of the peripheral area (fig. 6, pet.). 



The endodermis is clearly defined by its dark contents, and is seen at fig. 8, end. 



The whole of the soft elements of the leaf-trace have almost entirely disappeared, 

 and when any fragments remain they are too imperfectly preserved to admit of a 

 detailed description. The leaf-trace thus comes to occupy the centre of a clear space, or 

 has fallen to one side (fig. 4, pet/, pet." ; fig. 6, pet.; fig. 9). 



In form the leaf-trace is oval, with one side slightly flattened, its more pointed or 

 adaxial side being formed of protoxylem elements (fig. 8, prx.). In their distribution, 

 however, the protoxylem elements are very irregular, and though their usual condition 

 is to form a prominent band-like group at the apex of the trace, they occasionally have 

 a greater or less lateral extension in the form of a narrow band down both sides of the 

 xylem, or even extend some distance on the abaxial surface (fig. 8, prx.). At other 

 times they are almost entirely limited to the adaxial margin, with a few isolated elements 

 scattered along its lateral margins ; but in no case do the protoxylems form teeth as in 

 the other known species of the genus. 



In longitudinal section the protoxylem elements are seen to be scalariform. 



The metaxylem of the leaf-trace is composed of large tracheae arranged without any 

 definite order, but which become slightly smaller as they abut on the protoxylem 

 (fig. 8). Their walls are porose. 



The petioles underwent bifurcation. At fig. 1 1 an early stage in the dichotomy of 

 a petiole is seen. Here the trace has become transversely elongated, and an indenta- 

 tion has appeared on one side. At fig. 12 the same petiole trace is seen divided into 

 two equal arms. 



The pinnae appear to have been alternate, and their traces arise as small protuberances 

 on the trace of the petiole (fig. 9, pin.). A further stage in their departure is seen at 

 fig. 10, pin., where the pinna trace is free from that of the petiole, though still enclosed 

 in a common cortex. The protoxylem of the pinna trace is adaxial to the trace of the 

 petiole. 



