348 DR. W. R. M‘NAB, 
not matted together. Loew thinks that defective nutrition 
is the cause of this fusion, but the phenomenon is one of 
minor importance. 
Penicillium begins at a very early stage to produce conidia, 
even when the mycelium is growing rapidly. This production 
takes place more or less rapidly, according to the external con- 
ditions. If the mycelium is near the surface of the nutrient 
fluid, and obtains access to the air, conidia are produced 
sooner than when the mycelium is deeper. ‘The earliest 
appear on the third day, the latest on the fifth after sowing 
the spore. No marked change in the mycelium precedes 
the process; special branches are not formed, and it is only 
those hyphe that rise into the air that form spores. They are, 
therefore, not specially formed branches, and have the same 
position as the lateral branches of the mycelium, while in 
thickness, 0°0047 to 0:0050 mm., they do not differ from 
ordinary hyphe. The conidiiferous hyphe generally appear 
first on the older parts of the mycelium, and, therefore, in 
the centre of patches of it. In general they are inserted 
behind a transverse septum, and may be the youngest lateral 
branches which are produced perpendicularly to the sub- 
stratum, and first reach the top of the fluid in the centre 
of old mycelium; frequently many of them are placed 
close together. After the development of conidia has 
commenced the individual hyphe grow over all parts of 
the mycelium exactly as before, the end-cells increase the 
circumference by apical growth and branching, while the 
hyphal cells form branches and increase the number of 
threads in the centre of the mycelium. As growth goes on 
and conidia are developed, it ultimately becomes impossible 
to observe the spore from which the whole system was 
developed. 
The hyphze which produce conidia very soon cease to 
grow in length, the apical cell ceasing to grow after a 
septum has formed a short distance from the apex. Imme- 
diately below the last septum the youngest cell of the 
thread forms a lateral branch, the end-cell of which turns 
vertically upwards. Before this has attained its full height 
the main axis of the hypha forms a projection like a 
portion of the hypha, but which is a spore-forming basi- 
dium (or conidiophore). The apex is narrowed into the 
sterigma, which enlarges at its end into the first spore 
(conidium). Beneath the first another forms as soon as it 
attains its normal size, then another, and so on until a chain 
of spores is produced as in Aspergillus, Cystopus, &c., the 
apical spore being the oldest, that nearest the sterigma the 
