LIFE-HISTORY OF PENICILLIUM. 349 
youngest. The spores when first found are colourless, but 
soon assume a bluish colour (turning to sage-green when 
dry), which is not noticeable in the single spores, although 
evident when they are in the mass. At the time the basi- 
dium on the main axis forms its first spore, a basidium 
forms on the lateral branch, which in turn begins to form 
spores. At the same time a second and third basidium form 
at the apex of the main axis and also on the lateral axis, so 
that in a few hours the formation of spores is proceeding on 
all. ‘Two cases of formation of spores are figured by 
Brefeld. 
The spores in the chain are not all of the same size; they 
decrease in size from the apex to the sterigma. At first this 
is well marked, but later it is not so distinct. Between 
the spores the small connecting neck remains for some time, 
and unites the spores into a chain ; this disappears when the 
spores fall off, and leaves no trace of its existence. The 
neck is a short portion of the sterigma which remains 
between every two swollen parts, either permanently, as in 
Cystopus, or for a short time, as in the present instance, and 
Aspergillus. Loew thought that there was a special mem- 
brane outside the true wall of the spore which formed 
a neck between the spores; but Brefeld considers this a 
mistake and distinctly states that the wall of the spore is 
single. 
If the spore be germinated in a very rich and concentrated 
nutrient solution it produces many hyphe, which branch fre- 
quently and form so thick a felt that the mycelium 
resembles a skin and can be raised from the solution as a 
firm, tough layer, like soaked cartridge paper. The thick- 
ness of the layer of mycelium depends on the number of the 
branches which come to the surface to form spores. These 
are placed so close together that the spore-forming basidia 
give rise to a kind of crust; hence the Linnean name 
crustaceus applied to the species. ‘The growth of the my- 
celium and formation of spores are unlimited, and continue 
as long as the nutrient material lasts. Sometimes the dense 
aerial hyphe unite into bundles and form an almost tree-like 
fungus, the crown being formed of numerous closely aggre- 
gated, spore-forming basidia. This form of Penicillium, 
which is only found when the plant is rankly nourished, 
was described by Link as a special fungus under the name 
of Coremium glaucum. 
When the spore is germinated ina solution poor in nutrient 
material, as in water with a minute trace of organic matter, 
it only sends out one hypha, which is narrower than usual 
