Fungi on Culture Media. 125 
one part to another of the same plate produce a marked effect on the 
growth. 
Another striking contrast between staled and unstaled cultures of the 
two fungi in question is illustrated in Fig. 7, which represents diagrammati- . 
cally a section in elevation of two cultures of either fungus, the first unstaled 
and the second staled. In the unstaled culture the height of the ‘ surface ’ of 
the aerial mycelium slopes down gradually to the growing margin, which 
latter may have a more or less broad fringe with practically no aerial 
mycelium. The margin of a staled culture is as represented in {b) of Fig. 7. 
Here the mycelium drops suddenly at the margin, and this feature gets 
more pronounced as staling advances ; finally one may observe even an 
overhanging margin. 
On plates where the medium is poured deep, a feature of staling is 
a tendency for the submerged portion 
of the culture to grow slowly past the 
aerial portion, and thus the diameter of 
the submerged growth is greater than 
that of the aerial growth. Cultures 
showing this appearance are very stale. 
This suggests that the deeper layers of 
the plate are slightly less staled than 
the surface, though why this should 
be so is not clear. This peculiar effect is not noticeable with shallow 
media. 
A further distinction between a staled and an unstaled colony is to be 
observed in the nature of the general mycelial growth. In the colonies 
( Sphaeropsis , Fusarium ) growing in closed Petri dishes the mycelium in 
the central portion of the culture tends to collapse, giving the appearance 
as if it had been mown. On this central collapsed region Fusarium forms 
abundant masses of spores, and on the surrounding upstanding aerial myce¬ 
lium spore masses appear borne aerially, either scattered promiscuously 
or showing some kind of zonal arrangement. When the culture is 
grown in 5 per cent, carbon dioxide, where the staling effect is reduced, 
collapse of the central mycelium is much delayed, and there is every¬ 
where a greatly reduced tendency to sporulation. The exact relationship 
between sporulation and staling is probably very complex, but there would 
appear to be every probability that, if the dynamics of the staling process 
were more completely investigated, considerable light would be thrown 
on the problem of sporulation. 
The same appearances are shown by Sphaeropsis cultures, with the 
exception that no spores appeared in any case, at least during the limited 
duration of each experiment. Here it is only necessary to compare the type 
of growth in a closed Petri dish with that in an open one (in a large 
Fig. 7. (Diagrammatic.) Vertical section 
of unstaled ( a ) and staled (£) colony. 
