2 BOTANICAL GAZETTE [jULy 
and in some instances to analyze the causes of these variations, to the 
end that the factor of environmental variation may be more clearly _ 
recognized as a problem of mycological taxonomy. 
We shall consider these variations under the causes that produce 
them. 
I. Density of colonies 
SEPTORIA PETROSELINI Des. VAR. Apit Br. & CAV., FROM CELERY 
This fungus, when plated so that the spores lay thinly scattered, 
produced colonies which were ultimately black, 1 to 2”™ in diameter, 
Fic. 1 Fic. 2 
Fic. 1. Septoria Lycopersici Speg., sborits formation of normal pycnidia on ~ 
portion of thinly sown plate culture.—Fic. 2. Septoria Lycopersici Speg., showing 
absence of pycnidia on thinly sown portion i plate culture; magnification same as 
in fig. I. 
with pycnidia of normal character. If plated so that the spores lay 
in large numbers per square centimeter, it produced colonies which — 
reached a size of only about o.5™™ and became ultimately black, 
containing ordinary pycnidia, bearing spores in the normal way- 
_ When plated so that there were still more spores per square centimeter, 
the colonies never became black and no pycnidia were produced; but 
on the contrary, multitudes of spores were borne uncovered, in clumps — 
upon simple hyphae. 
