io8 Brown.—Experiments on the Growth of 
described as showing staling at its growing margin, and in accordance with 
the amount of falling off will be described as more stale or less stale as the 
case may be. Further, as the basis of measurement is that of increase in 
diameter, the term staling will in the present paper have reference to growth 
at the margin of the colony only. 
Experimental Method. 
The general method of experiment was the same as that described in 
the earlier paper dealing with the growth of fungal colonies (loc. cit., p. 270), 
so that it is unnecessary to repeat the details here. Certain further particulars 
will be given below in describing particular experiments. 
The fungi mainly dealt with were Sphaeropsis malorum and a species 
of Fusarium} both of which show well-defined staling phenomena. Both 
have also advantages in this respect, that there is no trouble in either case 
from air-borne spores, the former only producing spores, if at all, in very old 
cultures, the latter forming its spores in moist masses. Fungi which 
possess air-borne spores are troublesome in this kind of work, as the 
disturbance incidental to measurement is liable to scatter spores on to the 
uninvaded portion of the plate, thereby producing colonies which interfere 
with the free growth of the mother colony. The removal of the lids of the 
Petri dishes for purposes of measurement brings in the risk of contamination 
from outside, and this has to be guarded against. This trouble has been 
met in two ways—by disinfecting the laboratory at fairly frequent intervals 
and by cutting out contaminating organisms when they are first noticed. 
By carrying out these precautions and by avoiding any work with such 
fungi as Penicillium glaucum and Rhizopus nigricans during the course of 
these experiments, no appreciable trouble was met with in the way of 
contamination of the plates from outside. 
The stock cultures from which the inocula are taken are of course kept 
pure in the usual way in sterile tubes. 
The actual measurements were made in each case in two directions at 
right angles to each o£her, each measurement being made to the nearest 
half-millimetre. In cases where the colony for some reason or other had 
not grown circularly, measurements were made along the long and the 
short diameter, and the average taken. When the greatest accuracy was 
required, successive measurements were made along marked directions. 
When the object was to compare successive daily growths with each 
other, the cultures were kept at uniform temperature in an incubator. In 
a large number of experiments, however, where it was only sought to draw 
comparisons between different cultures under the same temperature condi- 
1 This is the same fungus as was dealt with in the earlier paper already cited. Its systematic 
position will be set out in a subsequent publication. 
