Betts. — Rosette Plants at Cass. 



263 



The endodermis is a single layer of cells ; opposite the vascular bundles 

 the cell-walls in this layer are suberized, but not in the vicinity of 

 the medullary rays. The pericycle consists of small, thin-walled, paren- 

 chymatous cells. 



There are five vascular bundles, arranged in a circle. The xylem con- 

 sists of vessels of fairly large diameter, together with small wood-fibres. 



Fig. 17. — Cardamine heterophylla. Transverse section of root ( x 175). 

 a, suberized ceils ; b, cortex with starch ; c, phloem ; d, xylem- 

 vessel ; e, xylem parenchyma. 



The phloem group is nearly as wide as the xylem. Between the bundles the 

 medullary rays are lignified, consisting of small, rounded, thick-waUed cells ; 

 the xylem and these lignified elements together form an undulating band. 

 The pith is not lignified, and consists of large, thin-walled, circular cells. 



Root (fig. 17). — Diagram is from a section of the tap-root. On the out- 

 side are a couple of layers of small, irregular, thin-walled, dead cells which 



