Monotropaceae with Reference to Ericaceae 73 



tracheides. A number of closed sieve tubes are present. The 

 xylem bundles do not form a ring, but immediately external to 

 the bast-region is a complete cylinder of heavy sclerenchyma 

 composed of ten to fifteen layers of cells. Both the xylem and 

 the sclerenchyma are distinctly lignified. The medulla is from 

 3 to 6 mm. in diameter, making up about half of the cross sec- 

 tion of the stem, and is composed of cylindrical elements with 

 ample intercellular spaces." In the material examined by the 

 writer (Fig. 6) the hard bast area was found to be composed of 

 even more than fifteen layers of cells. The phloem was found 

 to be greater in width than the xylem. The xylem in Pterospora 

 is better developed, i. e., has more cells and more heavily thick- 

 ened walls, than in Monotropa, but is less so than in Pleuri- 

 cospora. 



Sections of the axis of Pleuricospora fimbriolata were taken 

 from a boiled-up herbarium specimen. The axis is wider than 

 in Monotropa, about the same thickness as in Pterospora, and 

 consists mainly of cortex and pith composed of rounded thin- 

 walled cells. The vascular system (Fig. 5, 2) forms an irregular 

 ring placed nearer the exterior than the center of the section. 

 No hard bast is present; the area of soft bast is about equal 

 to that of the wood which is better developed than in any other 

 members of the Monotropaceae examined, there being more 

 cells and the walls more heavily thickened. 



According to Solereder (73), the axis of Schweinitzia odorata 

 resembles that of Sarcodes and Pleuricospora in that it does 

 not possess a ring of hard bast fibers. 



Sections of the axis of Sarcodes sanguinea were cut some 

 distance below the middle. They showed a great increase in 

 size over any of the others examined. The main bulk of the 

 axis is made up of thin-walled cells of the cortex and pith. The 

 bundles as in Pleuricospora form an irregular ring which in 

 position is nearer the exterior than the center. There is no 

 hard bast produced in Sarcodes. In the section examined by 

 the writer, the phloem was about equal in width to the xylem. 

 The phloem forms a continuous ring; the groups of xylem being 

 separated from each other by medullary rays. Oliver (58), 

 Fig. 49, figures three of these bundles. At the level where he 

 examined it, the phloem is less in extent than the xylem. He 

 states that the bundles undergo no secondary thickening. 



