284 PRINCIPLES OF SOIL MICROBIOLOGY 



growing in a calcareous soil) , symbiosis changes to parasitism of the fun- 

 gus upon the plant tissues. Under these conditions, the fungus, which 

 never forms pycnidia in nature when associated with healthy plants, 

 produces these bodies freely in the stomata which invest the roots of the 

 unhealthy seedlings. A case of symbiosis whereby the higher plant 

 depends completely upon the presence of the endophytic fungus has been 

 recorded for Gastrodia elata among the orchids. 186 This non-chloro- 

 phyllous plant is parasitic upon the fungus Armillaria mellea, 

 by digestion of the mycelium by the cells of the root, the relation being 

 obligate for the full development of the plant; the fungus itself is 

 parastitic in habit and at first invades the tuber of the orchid. Accord- 

 ing to Rayner symbiosis in the case of mycorrhiza is considered to imply 

 not a reciprocal relation involving mutual benefit to the participants, 

 but, as defined by de Bary, the living together of dissimilar organisms. 

 According to Peyronel, the phycomycetoid endophyte grows as 

 vigorously under saprophytic conditions as in symbiosis with the plant ; 

 it continues its development, after the death of the plant, at the expense 

 of the dead cortical tissues of the roots or organic matter in the soil. 



186 Kusano, S. Preliminary note on Gastrodia elata and its mycorrhiza. Ann. 

 Bot., 25: 521-524. 1911; Jour. Coll. Agr. Tokyo, 4: 1-66. 1911. 



