196 



noted later, the grasses and other vegetation indicate the presence 

 of the myceUam in the soil as a ring like or crescent-shaped 

 growth. During eight seasons at the mountain laboratory 

 four years (1909, 1912, 1913, 1914) showed excellent develop- 

 ment of sporophores, with many fairy rings easily recognized by 

 even the non-botanist. In each of these years there were heavy 

 rains in August. 



Although requiring wet weather for the production of sporo- 

 phores, Tricholoma praemagnum is a distinct xerophyte, or is at 

 least associated with xerophytic plants. It seems to occur only 

 in dry grassland areas. This is strikingly shown in many places 

 by the fairy rings on dry knollsides which are not complete 

 toward the lower part of the slope where they seem unable to 

 invade mesophytic grassland. Thus, instead of a ring, there is 

 frequently produced a semicircle or a crescent with the points 

 extending toward the area of moister soil. 



The vegetation at the margin of the fairy rings is always some- 

 what different from that of the ordinary dry grassland. Usually 

 there is a rather bare zone in which may develop mountain sage 

 {Artemisia frigida) , or chickweed {Cerastium occidentale) , or other 

 plants. Figs, i and 2 illustrate these facts. The limits of 

 these fairy rings can usually be recognized at all times during the 

 growing season because of the unusual vegetation just within and 

 without the limits of the ring. An ecological study of the dis- 

 turbances caused by the mycelium of these mushrooms Is now 

 under way and will be reported upon after observations have 

 been made during another season. 



University of Colorado, 

 Boulder, Colorado 



