Lecture VIII — 115 — Mycodomatia 



Allium: — In an extended study of A. roseum, Capelletti (1931) 

 isolated a fungal endophyte which he referred to Rhizoctonia. 



Orchids: — Tuber formation of orchids was described by Fabre 

 in 1855 but interest in its significance dates from Bernard (1902). 

 The latter found, as in potato, the causal fungus is Fusarium {Rhizoc- 

 tonia), and that tuber formation takes place very early in develop- 

 ment of the plant ; yet the tuber itself, at least the parenchymatous in- 

 terior, remains fungus-free. Beau (1914) also said that in the adult 

 plant, tuberisation may take place without fungal invasion. Bernard 

 found a retardation of development in the orchid plant which goes 

 hand in hand with nodule formation and storing of food-stuff, and to 

 him it seemed the result of a sort of poisoning caused by the endo- 

 phyte. So long as the plant is free from infection there is active growth 

 of leaves, flowers and fruits ; but tubers are formed only after en- 

 trance of fungus. Later (1909), Bernard classified orchids as 

 facultatively mycotrophic (as in epiphytic members) and constant 

 mycotrophs. According to Burgeff (1910), the fungus is found in 

 roots and protocorms of almost all orchid plants. Gallaud (1905) 

 classified orchid tubers in Series Four, and stated that the endophyte 

 is intracellular and produces coils (pelotons) which sometimes remain 

 inactive (host-cells) or are digested (digestion cells). A curious 

 condition was described by Barsali (1921) in which two horizontal 

 tubers are formed in addition to the ordinary ones, the former tubers 

 supposedly making use of humus of the top-soil. 



