206 
Journal of Agricultural Research 
Vol. XI, No. 5 
That there was no further fungus growth within the ring he attributed 
to the competition with a vigorous crop of grass. 
Westerhoff in 1859 (Ritzema Bos, 1901) attributed the centrifugal 
growth of the mushrooms to excrements of the roots of the mushrooms. 
Berkeley (1860, p. 41) noted the tendency of fungi to assume a circular 
growth not only when the spawn was perennial but where the whole 
period of existence of the fungus amounted to only a few days or weeks. 
Fairy rings originated from a single spore, the growth from which rendered 
the soil unfit for further fungus growth. The rings extended outward 
until interrupted. 
The various investigators following this period ascribed the cause of 
advance to those already recorded. Ritzema Bos (1901) likened the 
advance of a fairy circle to the progressive advance of a flame which 
results from dropping a match in dry grass, and which will spread con¬ 
tinually outward. 
Reed (1910) stated that the tannin of the bark of a hemlock tree 
marking the center of a fairy ring had caused the death of the ring on 
the downhill side. But Coville (1898) found the rings uniformly broken 
on the downhill side, which suggests the harmful influence of the decom¬ 
position substances which are washed toward the lower side. 
Investigators differ as to the exact cause of this outward growth, some 
attributing it to the exhaustion of the nutrient materials of the soil, 
others attributing the cause partially to the fact that the active mycelium 
occurs only on the outside of the ring, and that the portion of the 
mycelium on the inside is already old or dying. That the mycelium 
grows outward from a central point and continues to grow outward is 
no more strange than that the horizontal roots grow out from the tree 
and keep on growing out instead of back toward the trunk. The fact 
that the filaments grow into virgin soil by growing outward would favor 
the growth in that direction. 
Where fungus fairy rings occur, the soil is usually rather low in organic 
matter. The growth of the saprophytic fungus probably consumes the 
available supply of organic matter. In the case of the Agaricus tabularis 
ring this is replenished by the death of the grass cover and by the subse¬ 
quent increase in growth of annuals and short-lived perennials, which die 
and leave their root systems as available organic matter. Determinations 
of organic matter do not therefore show a marked difference outside or 
inside the fairy ring. The active fungus filaments are always on the 
outer edge, and a turning back into the central area would require passage 
through from 1 to 5 meters of depleted soil or a continuance in a living 
condition for a period of several years in the same spot or soil mass. In 
addition to these reasons why progression should be outward, observa¬ 
tions are numerous of the tendency of fungus filaments or even roots of 
growing plants to distribute themselves rather evenly into new soil 
areas. When fungus filaments approach each other, they turn aside 
