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 Corticium. 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 



