72 Henderson — Comparative Study of Pyrolaceae and 



layers of rounded thin-walled cortical cells. There is a very 

 great development of hard bast (about 8-9 layers) which dips 

 in between the numerous phloem patches and joins with the 

 indurated medullary rays. It is greater in width than the soft 

 bast, which is well developed in this species. The latter has 

 a width about twice that of the wood, which is extremely re- 

 duced in amount, there being only about five to eight cells in 

 a group interior to the many celled phloem patch. 



The structure in M. uniflora (Fig. 7) resembles that of M. 

 hypopitys except that no hairs are present on the epidermis, 

 and the amount of hard bast is not as great, there being only 

 about 4-5 layers. 



■H8 



Fig. 7. T. S. ascending axis Monotropa uniflora X 200. 

 L = lignified pith. 



MacDougal (48) describes the structure of the ascending axis 

 of Pterospora andromedea as follows: "The epidermis is com- 

 posed of elongated spindle-form elements. The epidermis and 

 the two underlying layers are slightly lignified. The outline 

 is exceedingly crooked, and shows deep invaginations directly 

 over large air-chambers, while in other places distinct fixed 

 stomata are to be found. The cortex is composed of cylindrical 

 elements arranged in circles with intercellular spaces which 

 increase in size outwardly. The fibrovascular bundles contain 

 one or two annular and two or three spiral vessels, with a few 

 alongated elements of slight differentiation, which are perhaps 



