MEDULLOSEAE 



43 1 



normally three (see Fig. 164, st) ; each has a somewhat 

 elongated and irregular transverse section ; traced longi- 

 tudinally, they divide and again fuse with one another 

 at long intervals. The structure of the individual stele 

 is almost identical with that of the single vascular 

 cylinder of a Heterangium. The central part of each 

 stele is completely occupied by the primary wood, 

 consisting of groups of tracheides intermixed with 



L.A.B. 



Fig. 164. — Medullosa cmglica. Transverse section of .stem, showing three large leaf- 

 bases, a, /', and c. a/', be, position of next leaf-bases above, st, the three steles ; /./, 

 leaf-traces; an, accessory rings of wood and bast; J>d, periderm, forming a ring 

 round the group of steles, and also enclosing one of the accessory strands; r, adven- 

 titious root ; o.c, hypoderma ; sc, sclerenchymatous band between leaf-base and stem. 

 Slightly reduced. Phil. Trans., S. S. Coll. 737. 



conjunctive parenchyma. The primary tracheides are 

 for the most part pitted, just as in Heterangium ; the 

 spiral tracheides of the protoxylem, accompanied by a 

 few scalariform or reticulated elements, occur in several 

 groups near the outer margin of the primary wood 

 (see Fig. 165, which includes parts of two steles). 



Each stele is surrounded separately by its own zone 

 of secondary wood and bast (Figs. 164 and 165, x*,pk), 

 so that we have in this family a combination of polystelic 



