124 Brown.—Experiments on the Grozvth of 
one could always get distinct improvement in Sphaeropsis cultures by 
simply increasing the volume of free atmosphere over the cultures, i. e. by 
growing the cultures in large containers, the corresponding effect with 
Fnsarium was in many cases only slight. This indicates that the ammonia 
factor is relatively less important in the staling of Fnsarium than in that 
of Sphaeropsis. On the other hand, the effects produced by a moderate 
concentration of carbon dioxide are in every respect as marked with 
Fnsarium as in the other case. 
An experiment with Colietotrichum Lindemuthianuin indicated that 
its behaviour was very similar to that of Fnsarium. 
On examining the results given in Table X one sees that the general 
result can be expressed in the following form : 
(a) The growth of Sphaeropsis (on a medium from which ammonia 
is evolved) is improved by any treatment which causes dilution of the 
ammonia or its removal. 
(b) The growth of the same fungus is improved by allowing the accumula¬ 
tion (within limits) of the carbon dioxide of respiration. Over soda, which 
keeps the carbon dioxide concentration down to practically zero, growth 
is least; over water, where under the experimental conditions a concentration 
of about 2 per cent, carbon dioxide may be reached,-intermediate growth 
is obtained ; in 5 per cent, carbon dioxide the growth is best of all. 
To Fnsarium statement (a) applies to a less degree, statement 
(b) equally well. 
The only criterion of a staled culture so far given is based on measure¬ 
ment of the diameter of the mycelium at stated intervals. Staling begins 
when the daily rate of growth begins to diminish. Staling, however, brings 
on certain characteristic appearances in a fungal colony, so that a staled 
culture can be recognized as such at a glance. 
If the initial inoculum is very sharply localized, the resulting colonies of 
Sphaeropsis or Fnsarium on potato agar are in their earlier stages very 
nearly perfect circles, and as long as there is no staling at the margin— 
as determined by day-by-day measurements —the colonies remain circular. 
Also the various controls are extremely uniform in their rate of growth. 
Once staling at the margin appears, the colonies tend to depart from the 
circular outline, the margin becoming wavy or indented. Such a sinuous 
margin is in the writer’s experience an invariable indication of staling, 
at least in the two fungi here dealt with. 
The staled cultures further begin to show considerable variation in 
their rate of spread, so that the variation between the individual cultures 
becomes much greater. This variability is much greater as a rule in plates 
where the medium is shallow than where it is deep. Shallowness of 
medium in many cases accelerates the incidence of staling, and therefore 
the small differences in depth which occur from plate to plate and from 
