BOTRYOPTERIS 329 



adaxial protoxylem-groups commonly united into one, 

 and as fusion with the stele took place, this group 

 necessarily took up an internal position in the stelar 

 wood ; every stage of the fusion is shown in serial 

 sections of B. hirsuta or ramosa. Thus the xylem of 

 the stele was endarch ; spiral elements are not often 

 to be found in the stem, which was a comparatively 



Fig. 122. — Botryopteris kirsuta. Transverse section of vascular bundle of young 

 petiole, showing the xylem in course of differentiation, px, lignified protoxylem ; 

 x, thin-walled xylem not yet lignified ; ph, phloem-zone. The dark external layer 

 may be the endodermis. X 150. S. Coll. 564. R. S. 



short and presumably rather slow-growing rhizome. 

 The small tracheides sometimes found at the periphery 

 of the wood were probably in connection with the 

 adventitious roots. 



The rachis of the English species often shows 

 branching, its branches being given off singly, and not 

 in pairs as in Zygopteris, but such knowledge as we 

 have of the form and structure of the lamina is entirely 



