Oct. 29, I9I7 
Fungus Fairy Rings 
209 
of each of these fungi occurred on August 16, 1915, following a rain on 
August 14 of 0.43 inch. Similarly C. cyathiformis produced on July 13, 
1909, a second crop following a series of heavy rains (2.80 inches) on 
July 7-9. 
Calvaiia polygonia fruited later in the season. The earliest record of 
its occurrence was June 21, 1915. In 1909 it was found in fruit on July 6 
and again on August 10. It did not fruit as freely as did Calvaiia cyathi¬ 
formis , and often the rings produced only one or two fruiting bodies at 
a time. 
In Table III is shown a summary of the weather conditions 1 for each 
of the years here considered, with the exception of 1907, during which 
year no determinations are available. The data are summarized for the 
months of May, June, July, and August. 
Soil moisture was the chief factor in controlling the fruiting of these 
fungi. If during May and June the soil of the first and second foot was 
moist throughout, these fungi fruited rather abundantly. If the soil 
was dry even during a part of this period, the fruiting bodies were not 
produced. These data are not taken from moisture determinations in 
the fungus ring but from determinations in the typical short-grass sod. 
As will be shown later, the moisture conditions in the Agaricus rings 
are not as favorable as those shown in this table. 
In 1909 and 1915 the soil of the first and second foot was moist dur¬ 
ing the month of June, and the fungi fruited abundantly throughout 
this period. In 1912 soil moisture conditions seem to have been favor¬ 
able during June. The failure of Agaricus tabularis to fruit at this time 
may have been due to the very extreme conditions of drouth during 
the preceding season. In 1914 Calvaiia cyathiformis fruited sparingly 
but A. tabularis produced no fruiting bodies. The impervious nature of 
the soil in Agaricus rings probably explains the absence of fruiting bodies 
of this fungus in 1912 and 1914, following the dry years 1911 and 1913. 
On the basis of soil moisture, 1909 and 1915 were the most favorable 
years. 
The rainfall was heavier in 1909 and 1915 than in any other year. 
The combined rainfall in May and June, the period during which it would 
be most important as a factor in fungus growth, was especially low in 
1910, 1911, 1913, and 1916, the years during which fungi did not fruit. 
The number of rainy days gives a better idea of the general conditions 
of humidity than does the amount of rainfall. Rainy days were more 
numerous during May, June, July, and August in 1915 than during 
any other year, including 1909, when a good crop was produced. In 
the period for 1915 more than half the days were rainy. Evaporation 
was lowest in 1915. A comparison of the evaporation rate in June, 
1915, with that of the same month in 1909 shows conditions to have been 
1 For the weather data here recorded the writers are indebted to Dr. L. J. Briggs, Biophysicist in 
Charge of the Office of Biophysical Investigations, Bureau of Plant Industry. 
