OMPHALIA FLAVIDA 



437 



the mould Fusarium discolor sulphureum, that shows typical zonation 

 in Petri-dish cultures exposed to daylight, Bisby ^ observed that an 

 exposure of the mycelium to bright daylight for only one-fourth to 

 one-half of a second is sufficient to cause the formation of a ring of 

 conidia which can be detected 

 with the naked eye. As we have 

 seen, exposure of the mycelium 

 of Omphaliaflavida for one hour 

 or less stimulates it to produce 

 gemmifers. Further experi- 

 ment may show that an ex- 

 posure of the mycelium to 

 bright daylight for a very few 

 minutes, or possibly less than 

 one minute, is sufficient to 

 initiate the production of 

 gemmifers. 



Luminescence of the My- 

 celium and its Value as a 

 Diagnostic Character of the 

 Coffee-leaf Disease. — For some 

 years, in the hope of discover- 

 ing luminosity in fungi in 

 which it had not yet been 

 observed, I examined system- 

 atically in the dark every 

 fungus species grown in my 

 laboratory and also many 

 isolated agaricaceous fruit- 

 bodies — but all in vain. One 



evening in the autumn of 1925, however, my efforts were at last 

 rewarded with success ; for, on taking a bread culture of Omphalia 

 flavida contained in a conical flask into the dark room, I at once 

 perceived that the mycelium emitted light (c/. Fig. 222). The 

 glow was pale but quite distinct, and the culture was used to 



^ G. R. Bisby, " Zonation in Cultures of Fusarium discolor sulphureum," 

 Mycologia, Vol. XVII, 1925, p. 92. 



Fig. 222. — The mycelium of Omphalia 

 finvida growing on either moist bread- 

 crumbs or corn-meal in a conical flask, 

 photographed by its own light. Ex- 

 posure of negative (a panchromatic 

 plate), 75 hours. Aperture 4-5. 

 Culture made by S. F. Ashby at the 

 Imperial Mycological Institute at Kew, 

 and negative by G. Atkinson, artist at 

 the Royal Botanic Gardens, Kew. 

 One-half the natural size. 



