i 28 Brown.—Experiments on the Growth of 
tively tolerant of staling substances, nevertheless produces them in such 
quantity that its growth tends to be limited. 
Though the amount of staling shown by a fungus depends on the 
experimental conditions, and especially on the nature of the medium on 
which it is grown, yet it would appear that a fungus which shows staling on 
one medium is likely to show a tendency in the same direction on any other 
medium, and thus one could speak in a general way of Fusarium as being 
of the staling, and Botrytis as being of the non-staling, type. 
In interpreting the growth-curves of the same fungus when grown 
under different experimental conditions, one has to take account of the 
amount of mycelium within the body of the colony, and it is in respect of 
this point that the difficulty of this method of experiment lies. However, 
certain broad conclusions can be drawn. Take, for instance, the growth of 
Sphaeropsis on potato agar in a closed Petri dish as compared with that in 
an open one, all other conditions being the same. Here the mycelia under 
the two conditions are identical in all appearances in the early stages. The 
differences in amount of staling which appear later cannot be due to different 
rates of mycelium production, as the amount of mycelium present at the 
time of incidence of staling is obviously the same in the two cases. In fact, 
the non-staling culture has probably much more mycelium after a time 
than the staled one, and thus the unstaled type of growth is maintained in 
spite of what is probably a greater evolution of the staling substances. The 
only interpretation which will suit the facts is that the staled growth in the 
one case results from the accumulation of an active staling substance, 
an accumulation which is kept in abeyance in the other by the experimental 
arrangements. 
The more staled growth that one finds on certain media when present 
in a shallow as compared with a deep layer, is to be interpreted somewhat 
differently. Here it is obvious from inspection that there is less mycelial 
growth at all stages on the shallow layer of medium. In this case the inter¬ 
pretation must be that though a greater amount of staling substances is 
formed on the deep layer in accordance with the greater amount of mycelium 
present, nevertheless it is not so effective in producing staling at first as it 
is free to diffuse away into a larger volume of medium. The results ofi 
growth measurements on deep and shallow layers of medium depend very 
markedly on the nature, and especially on the concentration, of the nutrient 
medium, and this will be dealt with more fully in a subsequent paper. 
Throughout this paper we have dealt merely with one factor of staling, 
viz. ammonia. This, however, is not the only factor, or even the only 
alkaline factor. Thus it is easy to show that a medium on which Fusarium 
or Sphaeropsis has been grown with evolution of ammonia is still alkaline, 
even after all the ammonia has been driven off. There is thus a formation 
of fixed alkali which is more marked in the case of Fusarium than of 
