240 
Journal of Agricultural Research 
Vol. XI, No. s 
The fourth or perennial stage is shown by the entrance of Gutierrezia 
sarothrae (Pursh.) B. and R. and Artemisia frigida Willd. 
The fifth, or short-grass, stage is established gradually and Bulbilis 
dactyloides , which in this case must depend largely on reseeding, does not 
predominate over Bouteloua gracilis . As a result the two short grasses 
are established and the final stage reached without the development of 
the characteristic Bulbilis stage. 
In figure 13 a bisect and transect of a ring of Agaricus tabularis is 
shown. The zones here are unusually wide, and the mapping made in 
1916 is characteristic of a dry year. Very few annuals appear. During 
1915 the early weed stage to some extent, but especially the late weed 
stages, were marked by a very luxuriant growth and a dense stand. 
Such annuals as Festuca octoflora , and Plantago purshii occurred abun¬ 
dantly in every zone and stage of revegetation. This ring is shown 
because it illustrates the succession stages somewhat better than the 
narrower rings in which the short-lived grass stage usually occupies a 
much narrower zone. 
The zone of disturbed vegetation is usually about 3 meters broad in 
these rings of Agaricus tabularis. Estimates of the rate of advance of 
this fungus given earlier in the paper were 12 cm. per year. At this 
rate the time required for the vegetation to become reestablished would 
be 3004* 12 or 25 years. This estimate is in accord with previous studies 
in succession on abandoned plowed fields (Shantz, 1911) and on aban¬ 
doned roadways (Shantz, 1917). 
GENERAL DISCUSSION 
Under normal conditions in eastern Colorado Agaricus tabularis pro¬ 
duces an enormous superabundance of spores. From the number and 
age of the fairy rings which are shown in figure 2, new rings are only 
rarely formed. Most of the rings are fragments of old rings which 
have long since ceased to be true or complete circles. The conditions 
necessary for the germination of spores of Agaricus spp. have been the 
subject of many investigations. More recent summaries and studies 
(Ferguson, 1902; and Duggar, 1905) show clearly that the conditions 
most favorable to germination would be seldom realized on the Great 
Plains. Nor would there be chances of reproduction by fragments of 
tissue. The effects of the presence of old fruits and mycelium on germi¬ 
nation of spores would only tend to cause germination where the myce¬ 
lium already existed. Only rarely do spores germinate and produce new 
rings. At first these would not present the appearance of older fairy rings, 
but would merely represent small more or less circular areas in which spor- 
ophores are produced and the native grasses are stimulated (PI. 30, C.). 
The mycelium would spread out in all directions as practically all 
fungi do in culture media. During the first year or two there would 
be no differentiation into zones, but subsequent gradual outward growth 
