50 THE WATERLILIES. 



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 



FJO. 21. Transverse section of caudex of N. flava. h, base of leaf with bundles and 

 air-canals; e, exocortejc ; g, leaf gap; (, 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, /, 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 



