LITERATURE CITED 361 



cystidia undergo digestion progressively in the zone immediately 

 behind that from which spores have been discharged. 



Fairy rings. From time to time over a period of more than 

 100 years certain Basidiomycetes have been observed to produce 

 fructifications in rings, called "fairy rings." Such rings arise by 

 initiation of growth at some point, followed by centrifugal spread 

 of mycelium through the soil. The diameter of the ring in- 

 creases from year to year. As the mycelium advances, the or- 

 oranic matter is decomposed and exhausted, so that recession is 

 impossible. Shantz and Piemeisel (1917) made an extensive 

 study of fairy-ring formation by Agariciis tabular is in grasslands 

 of Colorado. They also noted from previous records that more 

 than 50 species of agarics, boletes, and puffballs, which they list, 

 are known to produce fairy rings. 



LITERATURE CITED 



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