60 Henderson — Comparative Study of Pyrolaceae and 



spora. It is coated with a dense brownish septate mycelium 

 which pushes in between the epidermal cells, penetrates them, 

 forming irregular vesicles and distorted nuclei, and even enters 

 the sub-epidermal layers. A root cap is present, and MacDougal 

 states that this resembles that of Sarcodes, in having more than 

 two layers. The mycelium covers the root cap and penetrates 

 the older cells in free tips, but penetrates beneath the root cap 

 in those roots that are in the center of the clump. He states 

 that starch is present in the outer cortical layers and that sec- 

 ondary roots arise exogenously. 



Thus in the root tip region we have a gradually ascending 

 series in the amount of fungus present from C. umbellata, with 

 the epidermal cells of some roots with no hyphae — other roots 

 with hyphae, but not in every cell; to C. maculata with a still 

 greater number of the epidermal cells filled with hyphae; to 

 P. rotundifolia and P. elliptica with all of the cells infested and 

 with a beginning of a sheath of intertwined hyphae around the 

 root tip; then in M. hypopitys an increase in the width and 

 extent of this sheath and a division of it into two zones — the 

 outer a more loosely interwoven mass of hyphae, the inner 

 more compact; finally in M. uniflora a still greater width of 

 the fungal sheath. The descriptions of the presence of hyphae 

 in Sarcodes and Pterospora show a great resemblance to Mono- 

 tropa, but not having material to examine the writer cannot 

 say which has the larger amount of mycelial investment. In 

 Chimaphila the hyphae are probably not of much use to the 

 plant as the threads are only in the epidermal cells and do not 

 extend out over the surface. The development of an outer 

 sheath of hyphae in Pyrola and its great increase in amount in 

 Monotropa, Sarcodes, and Pterospora would allow the fungus 

 to be of more use to the plant and that this is true is indicated 

 by the lack of green coloring matter in the last three men- 

 tioned. 



Sections both longitudinal and transverse of the oldest por- 

 tion of the root were examined in all of the preceding. In 

 C. umbellata, as the root becomes older, the hyphae penetrate 

 more between and into the epidermal cells, completely filling 

 them all. The nuclei become disintegrated, the walls thicker, 

 the cells die and finally fall off. The outermost layer of the 

 cortex may have some of its cells penetrated by the fungus, 



