106 HEART-ROT 
favour their formation are not always present, but probably 
the chief reason is that owing to their insignificance they 
are generally overlooked. Olsen (Brefeld, 1889, p. 177) 
has, however, found layers of the conidiophores on fallen 
trees in Norway, growing in such a way as to have a super- 
ficial resemblance to a species of Corticiwm. He does not 
state the time of the year at which they were found. This 
is important, as it is possible that climate plays an important 
part in their formation. 
Brefeld, who has had unrivalled success in producing the 
fructifications of this higher fungi in the laboratory, was 
unable to stimulate their growth in the case of Fomes 
annosus, and suggested that under pure-culture conditions 
a conidial race is produced which becomes incapable of 
bearing fructifications. In one of my own cultures, how- 
ever, a sterilized larch block, which was infected with 
conidia, produced normal, though small, fructifications 
(fig. 44), and it must be presumed that Brefeld did not 
experiment with the most suitable medium. 
The germination of conidia is in every way similar to 
that of basidiospores. They germinate at once, and with 
great regularity, both in pure water and in nutrient solu- 
tions. The possibility of making inoculations from old, 
apparently dried up, cultures of more than a year’s standing 
testifies to the longevity of the conidia. 
Pure cultures on artificial media. Cultures of the fungus 
grow readily in 15 per cent. gelatine or 3 per cent. agar-agar 
when appropriate food-stuffs are added. I have found that 
meat extract 0-3 per cent., malt extract 3 per cent., give 
suitable nutriment. If the medium is at all alkaline it may 
be neutralized with citric acid. Cultures were first obtained 
from rotted portions of pumped trees. Small lumps of 
wood were sterilized externally by holding for a few seconds 
in a weak flame. The central portions were then cut out 
with a sterilized knife and placed on the gelatine in culture’ 
flasks, which had been suitably sterilized prior to inocula-- 
tion. Cultures grew slowly at first and then fairly rapidly, 
and were similar on gelatine and agar. The mycelium is 
