204 
Journal of Agricultural Research 
Vol. XI, No. s 
the grass is short and yellow. Gilbert (1875) stated that it is known 
that fairy rings occur chiefly, though not exclusively, on poor pastures, 
and that they are discouraged by especially high nitrogenous manuring. 
Ritzema Bos (1901) stated that the best fairy rings are produced during 
rather dry seasons, and that mushrooms usually occur in meadows 
where the organic matter is not abundant. 
On the Great Plains fairy rings have been noted in all sections from 
Texas to Montana. Their abundance in certain areas is illustrated in 
figure 2. This map covers an area of three-fourths of a mile by one-half 
a mile of unbroken native sod lying just west of the Akron experiment 
farm, near Akron, Colo. 
A total of 62 rings or 
fragments of rings is 
shown on this map. 
From 0.5 to 1 per cent 
of the total soil area 
lies within the zone of 
influence of these rings. 
This area contains 35 
Agaricus rings, 14 Cal- 
vatia rings, 3 Cata- 
stoma rings, and 10 
unidentified rings. 
Throughout the whole 
of eastern Colorado, 
especially on the 
“hard” land (charac¬ 
terized by the pure 
short-grass cover), 
fairy rings occur often 
in great abundance. Many other areas might have been chosen which 
would show an equal or possibly even greater number of rings. 
About one-half of the area shown in this map was plowed in the fall 
of 1915 and seeded to Turkey wheat. During 1916, an exceptionally 
dry year, the area was remapped. The results of this remapping are 
shown in figure 8. 
CAUSE OF ADVANCE 
Hutton (1790) noted the regular annual progression of fairy rings, but 
Wollaston (1807) was the first to discuss the cause of this progression. 
He came to the conclusion that the ring was formed by a progressive 
increase from a central point due to the exhaustion in the central area 
of some particular “pabulum” necessary for the further growth of the 
fungus; hence, the new growth of the fungus “roots” extended solely 
in the opposite direction—that is, outward. He confirmed his theory by 
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Fig. 7.—A sketch of a fairy ring formed by Lepiota morgant southeast 
of Yuma, Colo. No effect could be noted on the vegetation. 
