DIMORPHISM IN CONIOTHYRIUM PIRINUM SHELDON 465 
accounted for by the fact that the proUfic spore production in the 
plus strain requires food material and energy which would otherwise 
be used for vegetative growth. 
Color Phenomena and Spore Production in Relation 
TO Temperature 
The production of an olive green color is characteristic of the 
mycelium of C. pirinum. On some media color production is more 
pronounced than on others. The present observations have been 
made on the two strains growing on starch agar in Petri dishes. 
An interesting correlation between color production, sporulation 
and incubation temperature has been studied. It was found by 
experience that vegetative growth was most rapid at 25° C, and that 
sporulation was most active at 18-20° C. It was therefore customary 
to grow the cultures in moist chambers for 3-6 days at 25° C. and 
then at i8°-20° C. The moist chambers, each consisting of a plate 
of water and a tall belljar, maintained an atmosphere of absolute 
humidity and prevented the drying of the culture medium. The 
dishes were incubated upside down to prevent moisture from running 
over the surfaces of the cultures. Under the above conditions the 
following observations have been recorded. 
Plus Strain. — Plus colonies grow rapidly but remain white 2-5 
days. In three days pycnidia are usually present in abundance. 
Most of them are pink at this time but a few may be black due »to 
the dark color of mature spores within. About the 5th day the 
mycelium just back of the growing ends begins to take on an olivaceous 
color. Later as the pycnidia mature in abundance this color is all 
absorbed, leaving the mycelium hyaline (Fig. 13). At the same 
time more color is formed farther out toward the margin of the radi- 
ating colony. The result is that an olivaceous zone migrating con- 
tinuously outward always exists just behind the growing ends of the 
mycelium. 
Microscopic study shows that the olivaceous mycelium is replete 
with refringent droplets of oil. In the inner zone of spore production 
the mycelium is hyaline and contains no oil drops. It is evident that 
the oil supplies the color. It is manufactured and stored temporarily 
in the mycelium. Later it is withdrawn and passes into the spores 
as they develop the dark color characteristic of the species. In. 
cultures only 1-3 days old, spore production precedes color formation 
