The form of Penicillium which was used in the experiments was isolated
from ketchup in which it grew luxuriantly. When conidia are first
formed on the ketchup, they are a delicate blue in color; they then
become bluish green, then green, and finally olive. The development of
the color of mold growing on ketchup is practically the same as when
grown in wort, tomato bouillon, pea bouillon, or gelatin made with
these solutions as a basis. In ketchup containing sodium benzoate, the
blue color appearing first remains for a long time, and in old cultures
the mold is a dull drab, not olive, as in normal development.
In ordinary ketchup made without a preservative, the mold forms a
heavy, wrinkled mycelium, showing a large development of conidia. In
the bottles of ketchup, the mold pushes down into the ketchup, becoming
entirely submerged, a clear liquid covering the mold and separating it
from the ketchup. This occurred in more than one hundred bottles. No
secondary mycelium formed on the surface of the liquid, a method of
development which frequently occurs in ordinary media when a mass of
mold is submerged.
An exception to this was shown in ketchup which had developed the mold
in the laboratory. The bottles were then put in the refrigerator for
two weeks. During this time scarcely any development took place; but
after they were again placed in the laboratory, the mycelium pushed
down into the ketchup and a new, very thin mycelium developed on the
surface. The filaments when seen under the microscope were swollen, had
irregular outlines, and a comparatively smaller number of septa, and
were filled with a coarsely granular protoplasm. The ends were blunt
and misshapen and the sterigmata were irregular, tending more toward a
fasciculated arrangement, and forming fewer conidia. The filaments from
the vinegar and acetic acid media had the same appearance as those
developed on ketchup, but had a smoother outline.