INJURIES INDUCED BY PLANTS 



93 



duced without the part of the tree on which they occur having 

 been previously injured, Fig. 42. The familiar state of things 

 where certain trees are covered with canker-spots, while adjoining 



trees of the same spe- 

 cies are tolerably clear 

 of them, can hardly be 

 explained in any other 

 way than by assuming 

 that the fungus travels 



FIG. 39. Branch of 

 a beech showing 

 two hailstone 

 wounds, of which 

 the upper one, b, 

 has been infected 

 by Nectria, while 

 the lower one, a, 

 has escaped infec- 

 tion and has been 

 occluded by a 

 callus. 



FlG. 40. Hornbeam 

 infected by N. ditis- 

 stma, which has en- 

 tered at the angle 

 formed by the branch 

 and the stem ; na- 

 tural size. 



FIG. 41. Hazel showing the 

 canker due to IV. ditissima, 

 the spores of which have 

 germinated in the bifurca- 

 tion of two branches which 

 have been somewhat pulled 

 asunder ; a, b, b, the bound- 

 ary of the canker-spot, 

 where red perithecia are 

 abundant ; c c, the healthy 

 side of the branch ; half 

 natural size. 



in the wood. This subject, however, requires further inves- 

 tigation. 



As the mycelium spreads in the cortical tissues of trees, it 

 produces innumerable extremely minute gonidia resembling 

 bacteria, which apparently assist in no small degree in the 



