ZYGOPTERIS 309 



form the xylem of a foliar bundle (Fig. 1 15, l.t.). In 

 the wood of the stele, a central and a peripheral region 

 may be distinguished. The peripheral tissue consists 

 principally of large scalariform tracheides. Towards 

 the ends of the more projecting arms, and especially at 



Fig. 116. — Zygopteris Grayi. Transverse section of stele, showing wood and remains of 

 phloem. 1-5, the five angles of the wood, from which leaf-traces are given off, in 

 order of the phyllotaxis, No. 5 belonging to the lowest leaf of the series ; x principal 

 ring of xylem ; xi, small tracheides of internal xylem ; xe, small tracheides at peri- 

 phery ; ph, phloem; r, base of adventitious root. X 14. Will. Coll. ior9 B. 

 (G. T. G.) 



the angles of the most prominent of them, much smaller 

 elements occur (Fig. 1 1 6, xe). The central tissue, like 

 the wood as a whole, has a stellate form ; the main 

 mass, which occupies the middle of the stele, sends out 

 prolongations into each of the arms. The central tissue 

 used at one time to be described as a pith, but that is 

 not its true nature, for in addition to the delicate 



