58 Henderson— Comparative Study of Pyrolaceae and 



cap— though thinner here than over the rest of the root. As 

 in P. rotundifolia there is a development of pseudoparenchyma 

 between the epidermal cells and a continuation of this on the 

 exterior forming a sheath much greater in thickness than in 

 P. rotundifolia. This outer sheath consists of two regions, the 

 inner composed of closely intertwined hyphae, the outer of 

 more loosely arranged threads that stray out into the soil. 

 Kamienski claims that the hyphae never penetrate the epi- 

 dermal cells, but that sometimes in older parts a hypha may 

 penetrate an epidermal cell, which it fills with a brown content. 

 He also says that over the apex the sheath thins out so that 

 there are only several isolated filaments. MacDougal and 

 Lloyd (50) state that the hyphae do penetrate the epidermal 

 cells, forming swollen vesicles, and that the root tip is completely 

 invested by a thin fungal sheath. Peklo figures the penetra- 

 tion of haustoria into the epidermal cells. He states that 

 haustoria are present in all infested roots of this species. The 

 hyphae do not completely fill the cell as in P. rotundifolia be- 

 cause there is present a vacuole of yellowish brown substance. 

 Drude calls this a pigment ; Kamienski notes its presence in dead 

 cells only, and states that it is tannin; Bokorny (5) that it is 

 tannin in the living cells. The latter, noting that there seems 

 to be no difference in the quantity of this material from the 

 youngest to the oldest epidermal cells, concludes that it cannot 

 have anything to do with the nutrition of the fungus but that 

 it serves, on account of its strongly concentrated tannin con- 

 tent, as a protection against the hyphae. Peklo also notes 

 that beside this the resistant cuticle of the layer beneath keeps 

 the fungus from penetrating further into the root. He claims 

 that there are two ecological varieties of M. hypopitys, one 

 living in humus, with the roots near the surface; the other in 

 loamy soil, the roots deep underground. In the former, he 

 says that hyphae are always present and indispensable to the 

 life of the plant; in the latter, there are no mycorhiza in a great 

 majority of the roots. The writer's material, however, was 

 collected in a loamy soil with a surface covering of humus, the 

 roots about 5 dm. below the surface, and all were strongly 

 infested with hyphae. One difference between the epidermal 

 cells of this species and those of P. rotundifolia is that they are 

 not enormously enlarged in comparison with the rest of the 



