258 



STUDIES IN FOSSIL BOTANY 



distinct centripetal primary xylem, surrounded by a 

 wide zone of secondary wood. This fossil was originally 

 described by Williamson as an advanced condition of 

 the stem of Lepidodendron (now Bothrodendrori) mundum. 

 It is probable that it really belongs to that plant, 



Fig. 106. — Stigmaria, sp. Transverse section ot an axis, showing pith and large-celled 

 centripetal primary xylem, with broad zone of secondary wood. At the top of the 

 figure the bundle of a rootlet is seen. X 24. From a photograph lent by Professor 

 F. E. Weiss. 



representing its root or rhizophore. The primary wood 

 gives the axis its stem-like character, but it is shown to 

 be of the nature of a Stigmaria by the structure of the 

 cortex and by the bases of rootlets attached to it. The 

 rootlet-bundles are remarkable for having, usually, a 

 mesarch xylem, with secondary growth on all sides, 



