212 
Mycologia 
other groups. The use of these terms has been fully discussed 
by Westling 3 who prefers the term sterigma. These fertile cells 
are uninucleate, tubular ratber than flaskshaped. While not uni- 
form in diameter such swelling as is found is usually about the 
middle of the length. The variations in shape are such as may be 
easily attributed to the effect of crowding many such cells into 
compact verticils upon the dome-like apex of the fertile branch. 
The diameter of the cell is usually a little less than that of the 
branch below it. The tubular form with an average diameter is 
maintained to a length varying somewhat but fairly characteristic 
for each species. There is, then, a more or less abrupt reduction 
to a smaller tube (figure a ), from which the conidia arise. 
This tube may be found to vary within the field of the microscope 
from imperceptible to several microns in length. 
Conidium Formation 
The process of conidium formation as far as it has been fol- 
lowed cytologically, involves the division of the cell nucleus, the 
migration of one of the daughter nuclei to the tip of the tube 
which grows rapidly in length, the formation of a cross-wall in the 
tube at a distance from the tip characteristic for the species, and 
the swelling of the new conidium to the size and shape typical for 
the species. Some preparations give no hint of this process. If 
conidium formation be for some reason arrested, the newest conid- 
ium may rest directly upon the basal cell without a vestige of a 
tube between. In other cases, a tube several microns long may 
separate the conidium from the main body of the parent cell. 
Every gradation may be found in the same culture if it is watched 
over a period of several days to several weeks. No species has 
shown conidia globose from the first. Such appearances may 
be easily found but examination of fresher or younger colonies 
shows them to be misleading. However quickly the stage may 
pass, the conidium of Penicillium arises as a cylindrical or barrel- 
shaped segment cut by cross-wall from the end of the fertile tube 
of the conidiiferous cell. This tube was designated by the writer 
in a previous paper as the sterigma because of its really permanent 
character as a conidium-forming organ of the cell. One might 
reasonably designate it a character of the genus. 
3 Westling, R., Arkiv. f. Bot. Bd. II (1911), no. 1, pp. 1-156- 
