ROSELLINIA 



237 



external weft is formed it produces two types of sclerotia. 

 The most general type consists of numerous minute blackish- 

 violet sclerotia which resemble in size and general appearance 

 the perithecia of some Sphaeria. If a section of the host- 

 plant bearing such micro-sclerotia is examined, the sclerotium 

 is seen to be more or less dumbbell-shaped, a short, thick 

 neck penetrating the tissue of the host, consisting of closely 



FIG. 68. Swede, lower half covered with mycelium 

 of Rhizoctonia violaceo. 



packed, more or less parallel, septate hyphae, which spreads 

 out above into a subglobose head of compactly interwoven 

 tissue; and at the lower or basal end, again expanding into a 

 large mass of compactly interwoven hyphae, buried in the 

 tissue of the host. It is the mycelium of the micro-sclerotia 

 that alone enters the living tissues and kills the host ; the 

 superficial felt of mycelium does not send mycelium into the 

 tissues, and is so loosely attached that it can usually be 

 rubbed off with the fingers. The second type or macro- 



