5o 



The Wateri.ilies. 



species has an additional interest as representing probably the most 

 primitive member of the syncarpous series. 



In a transverse section of the caudex of N. flava (Fig. 21), one finds 

 a pretty well marked cortex, a broad vascular ring with one to three leaf- 

 gaps, and a well defined pith which is continuous with the cortex through 

 the leaf-gaps. The vascular ring, however, presents a most peculiar 



Fig. 21. Transverse section of caudex of JV. flava. b, base of leaf with bundles and 

 air-canals ; e, exocortex ; g, leaf gap ; I, point of branching of leaf trace ; m, medio- 

 cortex ; n, endocortex ; p, pith (medulla); r, root trace ; t, central leaf trace. 



structure. Projecting slightly into the pith from the inside of the ring are 

 seen seven or eight vascular bundles, t, of varying size, cut transversely, 

 each with its phloem against the pith, and its xylem (of equal or greater 

 amount) next to the vascular ring ; these are the central leaf-traces. 

 The greater part of the "ring " consists of horizontal or oblique elongated 

 elements, mostly of phloem, but with some spiral tracheae ; these are 

 derived from root-traces and lateral leaf-traces. In this ring and 

 sometimes on the outer side of it, next the cortex, are additional bundles 



