304 MYCORRH1ZAE AND MYCOTROPHY 



zoctonia repens; from Phalaenopsis and Yanda, R. mucoroides; 

 from Odontoglossum, R. lanuginosa. 



Fundamental knowledge regarding endotrophic mvcorrhizae 

 in Ericaceae comes from the studies of Ternetz published in 1907 

 [Ravner (1927)]. Ternetz became interested in the possibility 

 of nitrogen fixation by the endophytes that she invariably found 

 in Ericaceae growing in peaty soils. From 5 ericaceous species 

 she isolated pycnidium-forming fungi, to which she gave the 

 names Phovia radicis oxy cocci, P. radicis andromedae, P. radicis 

 vaccinii, P. radicis tetralicis, and P. radicis ericae. She was able 

 to show that each, when grown in a liquid nitrogen-free medium, 

 was capable of fixing appreciable quantities of nitrogen. From 

 these results, obligatory symbiosis among Ericaceae has been in- 

 ferred to exist, as Ravner has claimed, in a series of studies involv- 

 ing Calluna vulgaris. In this species the endophyte occurs within 

 the seed and permeates the entire plant. Ravner also found (1929) 

 that the endophytic mycelium ramifies throughout the stem tis- 

 sues of Vaccinium oxy coccus and V. macro car pon and that ova- 

 rian infection occurs in V . vitisidaea, V. myrtilhis, V. pennsyha- 

 nicttm, V. ovatnm, V. vacillans, and V. corymbosam. Ravner's 

 claims, however, have been disputed. There exists a body of evi- 

 dence that ericaceous species, notably cranberries, have been 

 grown successfully for a term of years, apart from the endophyte. 

 Significance must be attached, however, to the fact that in nature 

 certain species always possess endotrophic mvcorrhizae and that 

 vigorous growth is promoted by the presence of the fungus. Re- 

 cent studies by Barrows (1941) show that an endophyte occurs 

 within the roots, stems, flowers, ovules, and fruits of trailing ar- 

 butus, Epigaea repens. 



A most unusual kind of mvcorrhizal relationship exists between 

 the tuberous, non-chlorophyllous orchid, Gastroidea elata, and 

 Arviillaria viellea [Kusano (1911)1. The rhizomorphs of this 

 fungus, which is widely known because of its ability to destroy 

 forest trees, attack the tubers in such a way that the outer layers 

 contain a dense mass of thick-walled hyphae; beneath it occurs a 

 region containing thin-walled hyphae, and the innermost layer 

 contains a few slender hyphae. Tubers associated with rhizo- 

 morphs produce offsets which remain dormant during the winter 

 and develop flowers in the following summer. If mvcorrhizae 

 are not formed, flowers are not developed. 



