NECTRIA. 



187 



grown over in course of time by the activity of neighbour- 

 ing living tissues, but the rapid development of the mycelium 

 of this Nectria prevents any such healing, and brings about 

 death of more bark. As a result the so-called '" cankers " are 



Fig. so. — Nectfia ditissuna. Caukci- 

 011 a stem of Beech, (v. Tubeuf 

 phot.) 



Fu;. SI. — Nectria ditissima. Canker on Hazel. The 

 place of infection, a partially broken branch-fork. 



produced. The mycelium, at first gives off tiny unicellular 

 conidia on the bark, then later white cushions bearing fine 

 conidiophores, from which are abjointed multicellular conidia, 

 shaped like a sickle. Infection is brought about by the 

 germination of spores or conidia on wounded parts of the 



