THE STEMS 99 



The stele from -5 to 6 mm. in diameter occupies the centre of the 

 rhizome, and near its periphery are the vascular bundles, generally 10-15 

 in number, distributed somewhat irregularly in one or two zones, the 

 larger bundles to the outside. 



Each bundle is usually of the ordinary collateral type with V-shaped 

 xylem and a narrow sheath of sclerenchyma. Some of them have only 

 one large vessel ; in others, two vessels are present, these being irregular 

 in size and not arranged symmetrically. The centre of the cylinder, 

 though sometimes hollow, is more often filled with soft pith. 



