[Chap. XLIV THE FUNGI 557 



mycelia develop from spores sown on boiled grain in sterilized culture 

 bottles. 



Fairy rings. When growth conditions are favorable in lawns and pas- 

 tures, the fruiting bodies of the common meadow mushroom often occur 

 in so-called "fairy rings" (Fig. 248). The rings were thought in ancient 



Fig. 248. A fairy ring of a common mushroom {Lepiota) on a ranch in Colorado. 

 Photo from the New York Botanical Garden. 



times to represent the paths traversed b\' dancing fairies. The circular 

 appearance is due to the outward growth of the underground mycelium 

 from the original center. The hyphae are perennial, and their radial ex- 

 tens'ion is accompanied each year by the death of the older portions of 

 the hyphae in the central areas. The fruiting bodies thus appear in circles 

 which increase in diameter from year to year. Nearly perfect rings of 

 this mushroom 160 feet in diameter have been reported, but the diameter 

 is usuallv less than 20 feet. Similar rings are developed by many^ other 

 fungi, including morels and puff balls. Some haxe attained diameters of 

 nearh^ a quarter of a mile and could have resulted only after hundreds 

 of years of outward extension of the mycelium from the original center 

 of growth. These largest rings are usually irregular, and occur in incom- 

 plete circles. 



An eruptive skin disease of man and other mammals, known as "ring- 

 worm," is caused by a fungus. Pustules appear in irregular circles about 

 the point of infection because of the radial growth of the hyphae in the 

 skin. The lesions are caused by the fruiting bodies of the fungus as they 

 break the skin, and thus appear as miniature fairy rings. 



