64 Henderson — Comparative Study of Pyrolaceae and 



is quite old. The less saprophytic ones have a fair amount 

 of wood developed and a comparatively small amount of phloem 

 as seen in Chimaphila and Pyrola. In Sarcodes, Pterospora, 

 and Monotropa the wood is less developed, the amount of phloem 

 being considerably greater. This greater production of phloem 

 and reduction in the amount of wood is characteristic of sapro- 

 phytic plants. 



The Rhizome 



Transverse and longitudinal sections of the underground 

 rhizome of Chimaphila umbellata were examined. On the ex- 

 terior is an epidermis composed of somewhat rectangular cells 

 (on transverse section) with rounded angles and thick walls. 

 The outer wall is much thicker than the others and has on its 

 exterior a layer of ridged cuticle. Interior to this is the cor- 

 tex, composed of 7-9 layers of rounded thin-walled cells. The 

 walls of the outer two layers of the cortex and those of the 

 epidermis become thickened, forming a cork-like region, so 

 that in cutting sections these all split off together. The cor- 

 tical cells gradually increase in size toward the interior. The 

 innermost layer, the endodermis, is composed of narrow rect- 

 angular, but somewhat irregular, cells. These are thin-walled 

 and show in section four to five cells filled with tannin. Internal 

 to this is the fibrovascular system with an external small area of 

 phloem and much larger area of wood. The pitted vessels ap- 

 pear square on transverse section and there are numerous uni- 

 seriate medullary rays through the wood. In C. umbellata there 

 were found as many as four annual rings, an evidence that the 

 rhizome is perennial. Inside the wood is a cylinder of rounded 

 thin-walled cells, the pith; starch grains occurring as either single 

 or aggregate clusters are numerous in the epidermis, cortex, 

 and pith. 



The structure of the rhizomes of C. maculata, P. rotundifolia, 

 P. elliptica is very similar to that of C. umbellata. Conglomer- 

 ate crystals are present in P. rotundifolia and P. elliptica but 

 absent in C. umbellata and C. maculata. There is no rhizome 

 in Moneses uniflora or Monotropa. 



The Ascending Axis 

 Transverse sections of all the species of Pyrolaceae and Mono- 

 tropaceae investigated were taken at the base of the ascending 

 axis just below the lowest set of scale leaves. 



