INJURIES INDUCED BY PLANTS 85 



The branches of the rhizomorph directed outwards break 

 through the cortex from within and form a new filamentous 

 mycelium, which penetrates into the soil ; or, in other cases, they 

 swell up under the cortex to form tuberous sclerotia, Fig. 33 ^, 



FIG. 31. Longitudinal 

 section of the root of 

 a vine whose upper 

 part has been killed 

 by the rhizomorphs 

 of D. necatrix as far 

 as b, and whose lower 

 portion shows an in- 

 fection-spot at a. 



FIG. 32. Magnified five 

 times. Boundary, a, 

 of the healthy and dis- 

 eased parts of the root. 

 The rhizomorphs send 

 out lateral branches, 

 which may occasion- 

 ally reach the epider- 

 mis, as at b. 



FIG. 33. A large vine- 

 root infected by D. 

 necatrix. A portion of 

 the cortex has been 

 carefully removed so as 

 to show the rhizo- 

 morphs which begin to 

 appear at a ; at b the 

 mycelial tubers, which 

 resemble sclerotia, are 

 formed, and on these 

 the gonidiophores ulti- 

 mately develop. 



which sometimes break through the cortex and appear in rows 

 upon the surface, Fig. 35. 



On these tubers the gonidiophores are developed in the form 

 of bristles, at whose apex the gonidia are abscinded, Fig. 36. 



It also happens very frequently, however, 'that these sporophores 



