66 Henderson — Comparative Study of Pyrolaceae and 



preceding, as in Monotropa the axis becomes fleshy. The epi- 

 dermal cells are not papillate, and have a cuticular and waxy 

 covering which is not as thick as in Chimaphila. There is no 

 outer thick-walled area of cortex. It is composed of about 

 ten rows of large thin-walled hexagonal cells, some of which 

 have slightly thickened walls and contain tannin. The inner- 

 most layer of the cortex consists of narrow elongated cells — 

 the endodermis. The central vascular cylinder consists of 

 several bundles separated from each other by medullary rays. 

 Each consists externally of a wide patch of phloem — equal in 

 width to that of the wood. The wood consists of 10-15 ce ^ s 

 in each group. Those according to Kamienski (39) are tracheids 

 with either spiral or annular thickening. This ring of wood 

 consists of both primary and secondary wood. 



The structure in M. uniflora is exactly similar to that of 

 M. hypopitys. 



Sections of the base of the ascending axis of Pleuricospora 

 fimbriolata were taken from boiled up herbarium material. The 

 cortex is wider than in Monotropa. The vascular cylinder is 

 more united than in the others, there being a continuous ring 

 of phloem and an almost solid interior of wood — the pith being 

 very small in amount. The wood is much greater in amount 

 than in Monotropa. 



Epidermis 



The epidermis was examined at the middle of the ascending 

 axis or flowerstalk. In C. umbellata, it is composed of rect- 

 angular cells with thick walls and with an exterior covering 

 of ridged cuticle. Chloroplasts occur in the cells. Small 

 papillae, also with ridged cuticle, are present on some of the 

 cells. Stomata are present, but not numerous. They are 

 small and appear normal and functional; some are of the nor- 

 mal type with the slit parallel to the longitudinal axis — others 

 show all stages of twisting of the guard cells until the opening 

 between them becomes exactly transverse. The series is the 

 same as in M. uniflora except that in the latter the guard cells 

 are greatly enlarged and distorted. These transverse stomata 

 are present on the stems of Viscum album, Arceuthobium, Anti- 

 daphne, Loranthus, Lepidoceras, Nuytsia of the Loranthaceae; 

 Choretrum, Mida, Myoschilus, Anthobolus, Santalum album, 



