OMPHALIA FLAVIDA 435 



been brought back into the fruiting condition, was used to inoculate 

 malt-agar in Petri dishes. The mycelium grew radially outwards 

 from the centre of each dish. Certain of the cultures which were 

 exposed to diffuse daylight on a table in the laboratory formed 

 concentric zones in which broader fluffy sterile rings of mycelium 



Fig. 221. — Omphalia flavida. Alternate zones of sterile fluffy myceliixm (white) 

 and of gemmifer-bearing mycelium (dark) in a malt-agar culture of Omphnlia 

 jlavida originating from Trinidad. The culture was started by placing 

 a single gemma in the middle of the agar. The sterile zones of mycelium 

 were formed during the night and the fertile zones during the day. The last 

 two dark zones are narrower than the previous ones because, on the days 

 when they were formed, the plate was exposed to light only from 9.30 a.m. 

 to 5.30 P.M. Natural size. 



alternated regularly with narrower, non-fluffy rings of mycelium 

 bearing gemmifers (Fig. 221). By marking the plates it was soon 

 found that the sterile zones were formed during the night and the 

 fertile zones during the day. These facts indicated that the pro- 

 duction of gemmifers by the mycelium is initiated by a morphogenic 

 stimulus of light. Some further observations supporting this 

 deduction will now be recorded. 



The Porto Rican culture, referred to in the last Section, was sent 

 from Porto Rico in a dark wooden box and, after arrival in Winnipeg, 



