47 
in (liimioter, there is a teudeiiey for the al^ae to reapjavir 
soni(^ distance from the maroin and it is not nniisual to 
i'iiid the central area sparstdy recolonisi'd and separated 
fi'om th(' shai‘pl>' (hd'ini'd ont(M* mar^-in of tlu' cii-cle hy 
a. C()mplet(dy bare' lang oft(Mi no moit' than 1-2 cm. in 
widtli. In somi‘ of the larger cireles tlu're is a tendcnicy 
towards tiie foi'iiiation of a series of c(Micentrie ring's ah 
ternately colonised and bare. 
Uncolonised rings in a stratum of blue-green algae. A foot 
rule is in the foreground. 
The occurrence over grassed aivas of soimovliat similar 
l)Ut largcn- “fairy-rings'’ is well known, ami liere the 
riims art' dm^ to the radial growth of some fungus which 
is generally a member of tlie Agarieaceae or Lycoper- 
daceae. However, in the case of the “fairy-rings” over 
the l)lue-green algae tlu‘ causative agents were found to 
l)e Aseomycetous fungi. 
After falls of rain sufficient to keep the soil moist 
for about three days small dark brown perithecia re- 
sembling grains of sand generally appear somewhat 
sparsely over the bare areas. In circles less than o cm. 
in diameter they may occur anywhere from the centrt^ 
to within about b mm. of the margin, but in larger circles 
are. generally I'estricted to a ring 1 -2 cm, wide situated 
about b mm. from the outer margin. For tlu' most part, no 
])erithecia are found in recolonised areas within the cirehe 
Algal filaments a1 the margins of bare areas have 
