368 



RESEARCHES ON FUNGI 



inclined to believe that in fairy-ring-less pastures, where Mush- 

 rooms make their appearance year after year, much of the 

 mycelium is perennial and capable of producing fruit-bodies 

 annually. 



It seems to me that, although much of the turf in certain fields 

 may be capable of supporting the mycelium of Psalliota campestris, 

 and although spores may be deposited upon it in great numbers, 

 yet new infections from such spores only take place very rarely ; 

 and the same statement holds for Marasmius oreades and for other 



-/oo 



-o 

 -so 



-/OO 



FIG. 133. A vertical section through a fairy ring caused by the mycelium 

 of Psalliota (= Agaricus) tabularis in a wheat field in 1915, a year 

 of ample moisture supply. Colorado, U.S.A. Sketched by H. L. 

 Shantz and B. L. Piemeisel. Courtesy of the United States 

 Department of Agriculture. 



ring-forming fungi. This view is based on the following reasoning. 

 A fairy ring is produced from a mycelium which grows radially 

 outwards from a single point and progressively exhausts its sub- 

 stratum. The older parts of the mycelium die progressively, death 

 taking place in a radial direction. Thus a fairy ring, so far as the 

 fungus is concerned, is a living zone of mycelium which develops 

 centrifugally. This centrifugal growth continues often for a con- 

 siderable number of years. Now the turf outside the ring is evi- 

 dently extremely well suited to support the mycelium of the fungus, 

 for otherwise it would not be progressively invaded. Yet each 

 year the surface of this turf must receive a vast deposit of spores 

 from the fruit-bodies occurring in the same pasture. The spores, 

 although thus showered by the million on the top of ground per- 

 fectly suited for infection, rarely cause infection ; for, if infection 

 frequently took place, the turf outside the ring would quickly 



