366 RESEARCHES ON FUNGI 



the bare zone is simply due to the fact that in dry weather the green 

 plants in the zone are killed owing to the mycelium in the ground 



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FIG. 131. Fairy rings formed by two Basidiomycetes in the short grass north-east 

 of Yuma, California, U.S.A. The signs represent the positions of fruit-bodies. 

 The large outer almost complete ring, which has a diameter of 65 metres, was 

 formed by the mycelium of a Puff-ball, Calvatia cyatkiformis. The clear discs 

 on the outside of the ring represent the positions of fresh fruit-bodies and the 

 black discs on the inside of the ring dry fruit-bodies of the previous year. 

 Interrupting the continuity of the Puff-ball ring, and also within the area 

 bounded by the Puff-ball ring, are numerous rings formed by the mycelium 

 of Psalliota cumpestris the Common Mushroom. Mapped by H. L. Shantz 

 and R. L. Pierneisel. Courtesy of the United States Department of Agriculture. 



beneath cutting off the supply of water from their roots, and the 

 stimulated zones are due to the mycelium increasing the avail- 

 ability of the soil's nitrogenous contents. These observers have 

 also shown that the subterranean mycelium has essentially the same 



