12 



CONCEPT AND HISTORY. 



The successional relations of the dominants have been discussed as well as 

 graphically illustrated by Shantz (1916:234). The primary succession ex- 

 hibits two adseres, one from Salicornia and Allenrolfea to Artemisia, and the 

 other from Allenrolfea through Distichlis and Sporobolus to Chrysothamnus. 

 These serai facts give much additional value to the indicator studies of the 

 Great Basin, especially in establishing the indicator sequence and in imparting 

 a distinct significance to the various mixed communities, (plate 2.) 



OUTSIDE (5) 



OUTER STIMULATED ZONE (4) 

 (WITH FRUITS) 



OUTSIDE (5) 

 WITHERED ZONE (4 a ) 



BARE ZONE (3) 



€.^' 



~Y~ 



^S$y$k j'j)^^'-^ 



_^ PLANT SURFACE 

 ^#^gU~SOIL SURFACE 



T 



Fig. 1. — Zones of a fairy ring due to Agaricus tabularis: A and C, during a moist 

 period; B, during a dry period. After Shantz and Piemeisel. 



Shantz and Piemeisel, 1917. — In their exhaustive study of fairy rings in 

 the Great Plains, Shantz and Piemeisel (1917:191) have shown the causal 

 relation between the rings of mushrooms and grasses, as well as the indicator 

 significance of the latter. They distinguish three types of fairy rings, based 

 upon the effect shown by the vegetation: (1) those in which the vegetation is 

 killed or badly damaged, caused by Agaricus tabularis (fig. 1); (2) those in which 

 the vegetation is only stimulated, produced usually by species of Calvatia, 

 Catastoma, Lycoperdon, Marasmius, etc. ; (3) thoee in which no effect can be 

 noted in the native vegetation, due to species of Lepiota. In the Agaricus 

 rings, the vegetation shows three zones concentric to the central area of normal 

 short-grass sod (1) : the inner stimulated zone (2) is a broad one, differing in 

 botanical composition, the more luxuriant growth, and the deeper green color 

 from the center. The bare zone (3) is narrower and somewhat more irregular, 

 while the vegetation is either dead or consists of a few very poor perennials or 

 short-lived annuals. The inner zone is the most prominent feature of the ring 

 in spring or wet seasons, the bare one in late summer or fall or in dry seasons. 

 The outer stimulated zone (4) is rather narrow and is made up for most part 

 of species peculiar to the short-grass sod, though resembling the inner zone 

 somewhat. The mushrooms occur in the outer zone near the outside edge. 



