HEART-ROT 



105 



with a number of pointed sterigmata, and oven in this state 

 they are easily recognized. 



These conidiophores and conidia were first discovered by 

 Brefeld, who sought in them support for his theory that 

 basidia and basidiospores are modified conidiophores and 

 conidia. He found instances in which the conidiophores 

 bore three or four large conidia instead of a large number 

 of smaller ones. But, even so, it is unlikely that they are 

 homologous with basidia. The 

 formation of basidiospores is 

 generally, if not invariably, pre- 

 ceded by a nuclear fusion ; but if 

 these conidia are homologous with 

 the conidia of types whose cytology 

 has been investigated, the nuclei 

 which enter them are not derived 

 at all directly from a fusion nucleus. 

 This distinction between conidia 

 and basidiospores has been drawn 

 subsequently to Brefeld's work on 

 Fomes annosus, and it is sufficient 

 to justify the disfavour with which 

 his synonym ' H eterobasidion an- 

 nosum ' has been received. 



As stated above, these conidio- 

 phores occur regularly in cultures, not only on bread and 

 gelatine, but also on diseased wood and even on fructifi- 

 cations if kept in a damp chamber. They are usually simple 

 or slightly branched, but under certain circumstances, as 

 when a culture is grown on bread soaked in a solution 

 of dung and given plenty of room, the conidiophores may 

 appear in large bundles. A single conidiophore of such 

 a bundle is exactly like one of the simple conidiophores 

 and has the same dimensions, but the whole bundle may be 

 a quarter of an inch high. 



As these conidiophores are of such frequent occurrence in 

 artificial cultures it is extraordinary that they should be so 

 rarely met with in nature. No doubt the conditions which 



FIG. 43. Fomes annosus : 

 a, conidiophore from which 

 some conidia have fallen, 

 leaving the pointed sterig- 

 mata ; b, conidia ( x 400). 



