466 
C. H. CRABILL 
No oil is at that time stored in the myceHum but passed directly into 
the spores. 
In some old cultures the greenish color diffuses out into the agar 
(Fig. 15). This is especially noticeable in colonies which have reached 
the edge of the Petri dish in which they are growing. In many cases 
it has been subsequently absorbed on sporulation. 
Cultures 20 days old kept at 13°-! 5° C. for 10 more days become 
quite black in the outer zones. This temperature is too low for 
active production of spores but does not materially hinder the growth 
and manufacture of oil by the mycelium. The oil is therefore not 
used as rapidly as produced and necessarily accumulates in the 
mycelium and imparts to it a dark color. 
Cultures incubated constantly at 25° C. produce much less color, 
as well as fewer pycnidia, than those incubated at lower temperatures. 
Minus Strain. — Minus colonies remain white 10 to 20 days. 
The olive green color then appears in minute spots usually around 
very young immature pycnidia. The color spreads gradually some- 
times appearing more pronounced in some sectors than in others. 
The pycnidia on maturing absorb the color from the mycelium im- 
mediately surrounding them but owing to the fact that these are so 
few in number, the cultures retain most of the olive color which 
darkens with age until the culture is quite black (Fig. 14). Minus 
cultures incubated constantly at 25° C. produce very little color. 
The optimum temperature for spore production is i8°-20° C. Some 
cultures will scarcely fruit at all at 25° C. but fruit typically at i8°- 
20° C. Color production and sporulation are both maximum at the 
latter temperatures. 
Mixed Cultures.- — In mixed cultures in which plus and minus strains 
grow in respective sectors, the plus sectors develop and later absorb 
color as described for pure plus strains. The minus sectors on the 
other hand may never develop this color or if they do it is in small 
amounts and very tardy in appearing (Fig. 15). In many cases there 
is no spore production whatever. Normally a few pycnidia appear 
with characteristic tardiness. 
Inoculations 
The plus and minus strains of Coniothyrium pirinum have been 
used to inoculate apple leaves. Holes were seared in the leaves with 
a hot needle, wetted and smeared with spores. The leaves were then 
bagged. 
