OP SOUTH AUSTRALIA. 
29 
tlie bare ring. One is drought, or relative dryness, for rain falling in the ring 
of fungus-infiltrated soil will not sink in as readily as elsewhere, but will tend 
io run off on either side, supplying those zones with additional water, or will 
lie on the snrfaee rather than sink in by capillary attraction and so be 
evaporated. The other factor is clogging of the interstices with mycelial threads, 
which would lead to relative exclusion of the air with its oxygen, and this would 
tend to prevent the germination of seeds or the development of leaves from 
roots, processes which require the presence of oxygen for respiratory purposes. 
In addition, other factors may participate. Actual crowding of the area with 
mycelium may make it difficult for other plants to> find space to grow in, just 
as an established community of cue species of plant may prevent individuals of 
another species from growing in the same place. It is possible also that the 
nutriment necessary for the grasses is absorbed beforehand by the mycelium, 
and is no longer available for the former, and it may be, in addition, that 
definite toxic substances are produced by the mycelium which are deleterious to 
the grass. 
The more vigorous growth of grass just outside the ring lias been attributed 
to chemical changes in the organic materials of the adjacent soil, due to the 
proximity of the mycelium, these changes favouring the plant growth. This is 
not necessarily contradictory to the view that the mycelium may manufacture 
toxic substances, as such toxic substances may be stimulant in nature when much 
diluted, as in the zone outside the ring, but destructive when more concen- 
trated, as in the ring itself. The more luxuriant growth within the ring is 
explained by the old and exhausted mycelium in this situation undergoing decay 
and breaking down into materials that act as food stimulants to the grass coming 
up there. In places where the rainfall is low and precarious, both these zones 
may benefit bv the additional “run off,” when such occurs, of rain-water from 
t lie bare zone. 
The fairy ring has another aspect that deserves consideration. It will lie 
noticed, if measurements are kept, or marks made, that it increases in diameter 
by a few inches each year. Each season it grows larger. As a matter of fact, 
it began in the centre of the ring from a spore, or spores, which fell on suitable 
i ground, germinated and produced n .mycelium, and in due course a little crop of 
trailing bodies, mushrooms in the case off this fungus. Then the oldest central 
part of the mycelium died and disintegrated, ldaviug a peripheral ring of living 
and active mycelium. Season after season the. ring increased in size, the inner 
zone of spent mycelium dying after yielding its crop of fruiting bodies as a 
result of exhaustion of the food contents of the soil, an outer zone laying up food- 
stores to furnish the fruits of the next season. By measuring the average annual 
increase in size of the ring and its diameter, rough estimates can be made of the 
ages of rings. Some of these in America have been estimated to be 250, 420, and 
even 000 years old. As regards our own fungus rings, some of these must have 
been in existence long before Captain Cook sighted Australia, and probably were 
already established when Tasman named Van Diemen’s Land. The annual 
increase of the rings of our Horse Mushroom ( Psaltiota urvensis SehaefP.) have 
not yet been ascertained. Rings have been measured, however, one on the Bluff nt 
Encounter Bay being 3.0 feet in diameter in 1020, and another on the Millicent 
Rond near Kalangadoo being Ml feet across in 1928. (Figure 2.) In those 
instances in which the mycelium lias been developed from a single spore, we can 
look upon the mycelium of the whole ring ns belonging to one plant, even though 
all the threads may no longer be in organic continuity with each other. We may. 
in fact, consider the ring as a fungus tree, buried in the soil, bearing annual 
autumnal crops of fruit in the shape of mushrooms. These we pluck, but without 
injuring the plant as a whole, just as the oranges or apples that we take off a 
fruit-tree to eat leave the tree itself unimpaired. It is even possible that our 
eating the mushrooms, provided we did not cook them, might lie of advantage to 
the species, as the spores can probably pass through our alimentary tract 
Uninjured, and so finally find a resting-place wherein they might develop to 
produce a fresh fungus ring. 
There are only two species as yet known in South Australia which produce 
well-defined rings. Probably a number of other kinds do so also, but the situation 
in which they grow does not lend itself to the recognition of the ring form. The 
rings of the Horse Mushroom ( PmlUota arvensix Rehaeff.) have already been men- 
tioned ns occurring near Kalangadoo and on and near the neck of the Bluff at 
Encounter Bay — tile bare ring of the latter, situated just above a small planta- 
tion of trees on the landward side of the Bluff, can often be seen from the beach 
near Yelki, at a distance of nearly a mile. 
