310 STUDIES IN FOSSIL BOTANY 



parenchyma, it contains a system of small tracheides, 

 quite distinct from those of the external xylem (Fig. 

 1 1 6, xt). This internal tracheal system forms a group 

 or irregular ring about the centre of the stele, and from 

 this central group radial bands of small tracheae extend 

 outwards, up the middle of each arm (Fig. 1 1 6). The 

 groups of small external tracheides (xe in Fig. 1 1 6) were 

 no doubt continuous with the protoxylem of the foliar 

 bundle, but they were also continuous, in the downward 

 direction, with the smallest internal tracheides of the 

 xylem-arms (see Fig. 1 16, at 2, which, however, is not 

 cut quite at the right level to show continuity). Hence 

 the transverse section shows both internal and external 

 protoxylem. 



Some remains of the phloem which surrounded the 

 wood of the stele are preserved ; it includes a single or 

 double series of large elements, which probably represent 

 the sieve-tubes (Fig. 1 1 6, pJi). The phloem evidently 

 followed the contour of the wood. The whole is 

 surrounded by a zone of delicate tissue (which may 

 best be regarded as an inner cortex), filling the spaces 

 between the arms of the stele, and cylindrical in form 

 (Fig. 1 1 6). Beyond this is the wide outer cortex, the 

 internal layers of which are thick-walled, forming a kind 

 of sheath to the inner cortical zone. The epidermis 

 was provided with multicellular hairs. 



The course of the leaf-trace bundles can be very 

 clearly followed ; a single large bundle entered each 

 petiole. To form the trace the whole distal part of 

 one of the prominent arms (cf. Fig. 116, 5) became 

 detached, forming an approximately triangular con- 

 centric bundle, with the base directed outwards. In 



