Oct, 29, I9I7 
Fungus Fairy Rings 
201 
rado. The withered zone (4a) is characterized by the dry vegetation, 
which during the more favorable period had marked the outer stimu¬ 
lated zone (4). During a dry year the short grass in this area is withered 
and often perfectly air-dry when the adjacent sod is still green. 
RINGS MARKED ONLY BY A ZONE OF STIMULATED VEGETATION 
Most of the fungi forming fairy rings in eastern Colorado produce only 
a temporary stimulating effect on the vegetation. In this group, there¬ 
fore, the presence of fungi is indicated by an increase in the size, vigor, 
and chlorophyll content of the annuals and of the perennial grasses. 
RINGS FORMED BY CALVATIA CYATHIFORMIS 
A large number of the rings marked only by a zone of stimulated vege¬ 
tation are produced by Calvatia cyathiformis Bose (fig. 5, 6). They are 
usually much less conspicuous than those formed by Agaricus tabularis. 
Fig. 4. —A bisect of the Agaricus tabularis ring shown in figure 3 at A, The vegetation on the inside and 
outside does not differ noticeably. The outer stimulated zone in which the fungus fruits are produced 
is separated from the inner stimulated zone by a bare zone in which plants are only occasionally found. 
The distribution of the mycelium in the soil is also indicated in the illustration. 
In size they are often much larger. Several rings have been observed 
which exceed 200 meters in diameter (PL 24, B). In periods when the 
rings are not marked by fruiting bodies these rings can be distinguished 
from Agaricus by the sterile bases of the fruits of Calvatia cyathiformis 
which remain on the ground from one year to another, or by the natural 
vegetation which usually presents a stimulated appearance, but seldom, 
if ever, is damaged by the presence of the fungus. The annuals in the 
rings, which grow much taller than in the adjacent areas, are prominent 
both during their period of rapid growth and after they have ripened, at 
which time the rings appear as dark-yellow or brown circles on a uni¬ 
formly light-green short-grass cover. 
A sketch of a ring formed by this fungus is shown in figure 5. The first 
crop of fruiting bodies occurs at the outer edge of the stimulated zone. 
The vegetation in this zone consists of the same species as the native sod, 
but the growth is more luxuriant (PI. 25, A). This is especially noticeable 
in the short-lived annual plants which stand up prominently above those 
