Kelley — 130 — Mycotrophy 



rather as proliferations induced by the growth promoting stimulus 

 of the cell-sap. 



Ericaceous Mycorrhizae : — As described by Kamienski (1884), 

 Monotropa's epidermis is covered with a fungal mycelium of septate 

 hyphae which form a compact pseudoparenchymatous mantle 2 or 3 

 times as thick as the epidermis. The fungus lives on the surface and 

 never penetrates living cells, but sometimes does so in older portions 

 where these cells are filled with a brown content. In older parts of 

 Monotropa roots the epidermis disorganizes at the same time the 

 mycelium develops. But Francke (1934) said that in epidermal but 

 never in deeper layers of cells, hypae are found entering and surround- 

 ing the nuclei, becoming filled with reserves that are emptied into the 

 host-cells as "plasmoptyse". The reserve is now absorbed but no 

 excretion was observed, and no significant change in nuclear condi- 

 tion was seen. After digestion has occurred, vesicular swellings of 

 hyphae dwindle. Only one hypha enters an epidermal cell. Tannin 

 is no protection from the fungus for hyphae are found in tannin cells 

 as well as in tannin-free. MacDougal (1900) said that the mycelium 

 of Monotropaceae consists of an external absorbing system and an 

 internal one which fills the epidermal cells. In the Monotropas, 

 vesicles, sporangioids, and sporangioles fill the cells, and "probably 

 serve as organs of interchange." 



In Arbutus (Dufrenoy, 1917) the roots are clothed with a dense 

 mantle of hyphae protected by a thick greyish membrane. The fungus 

 penetrates external layers of cortex and sends haustoria towards starch 

 grains. Late in the season (Rivett, 1924), hyphae penetrate more 

 deeply in the cortex, but digestion continues all the time the host is 

 growing and the reserve storing tissues packed with content. In 

 Calluna (Rayner, 1927), in young roots the cortex consists of a 

 single layer of large cortical cells each of which encloses a dense 

 branch system of mycelium that is continuous with hyphae upon the 

 external surface of the root. Intracellular hyphae are of relatively 

 large and uniform diameter with abundant oily content. 



Vaccinium is infected by hyphae passing through the cell- walls 

 (Coville, 1910) and the epidermal cells are completely filled with 

 coiled hyphae; and in Andromeda polifoUa also the epidermal cells 

 are infected by very fine hyphae (Frank, 1887) ; while in Vaccinium 

 Oxycoccos connection was found between external mycelium and 

 intracellular hyphae. Voss & Ziegenspeck (1929) found digestion 

 stages ("clumps") in Andromeda and curious mamillae in the cran- 

 berry. In Ledum these authors found that in winter roots the fungal 

 hyphae roll together to form a brown mass; in Erica there was less 



