200 
Journal of Agricultural Research 
Vol. XI, No. s 
cases a few very poor perennials or short-lived annuals may be found. 
This zone is the distinguishing feature late in summer and fall or in dry 
seasons. If rains are frequent, scattered annuals succeed fairly well 
even on this area. Beyond the bare zone there occurs a rather narrow 
zone, the outer stimulated zone (4), resembling somewhat the inner 
stimulated zone, but being for the most part made up entirely of plants 
which characterize the native sod. The sporophores occur in this zone, 
near the outer edge. Outside this zone normal native short grass is 
found (5). 
Fig. 3 “A sketch showing the different zones in a typical ring formed by Agaricus tabularis. At A the 
appearance of the ring is shown during a period of ample moisture supply. At B the appearance during 
a period of deficient moisture supply. The vegetation on the inside (i) is normal. In the inner stim¬ 
ulated zone (2) the greatest stimulation occurs near the bare zone. The bare zone (3) is usually devoid 
of vegetation, or contains only scattered plants. The outer stimulated zone (4) contains the fruiting 
bodies of the fungus and differs from the vegetation outside only in color and in more luxuriant growth; 
outside, the vegetation is normal (5). In B the same zones are shown as in A, except the outer stimulated 
zone which is here shown as the withered zone (4a). In this zone the plants not only wither but with 
continued droughts will die, and the area of this zone be added the following year to that of the bare 
zone. 
At B the zones are shown as they appear during a period not favorable 
to fungus growth. During the late summer, when the moisture supply 
is deficient, or during a dry year following a wet year (PI. 16) the ring 
presents a very different appearance from that described above. 
The inner stimulated zone (2) ripens or dries up as dry weather comes 
on and usually presents a brown, dead appearance, although the peren¬ 
nials remain alive in a dormant condition. If the season is dry, this 
zone (2), while noticeably different from the natural sod inside (1), does 
not show the luxuriant growth so characteristic of a wet year. During a 
dry year the bare zone (3) is unusually prominent, since not even the 
short-lived annuals appear, and the zone is named from its appearance 
during drouth periods. Such periods are characteristic of eastern Colo- 
