INJURIES INDUCED BY PLANTS 



209 



the tree, the shrinkage of the cortex affords space for the de- 

 velopment of these strands, they anastomose abundantly, like so 

 many twigs, and envelop the wood of the stem in a reticulate 

 fashion. The'rhizomorphs that spring from the roots progress 

 underneath the surface of the ground, at a depth seldom exceed- 

 ing four inches, and bore into any sound roots of conifers that 

 they may encounter, and thus the disease is spread from tree 

 to tree (Fig. 127). In autumn, from the end of August till 



FIG. 128. A young pine which has been killed by 

 A. melletts. Numerous sporophores are seen which 

 have broken through the cortex at the surface of 

 the ground. Branching rhizomorph- strands are 

 present on the roots. 



FIG. 129. A sporophore 

 of A. mellens which has 

 developed on a rhizo- 

 morph, a lateral branch 

 of which has produced 

 only abortive sporo- 

 phores. 



October, the large familiar sporophores (Fig. 129) may be 

 observed developing on the rhizomorphs which grow in- 

 dependently in the ground, or projecting from the cortex, 

 especially the collar (Fig. 128), of trees that have been killed by 

 the parasite. For further details I may refer to what I have 

 published in the works already alluded to. The white spores of 

 this Hymenomycete, which are spread either by the wind or by 

 being brushed off by passing objects, develop first of all a 

 filamentous mycelium, and from this the mycelium form 

 designated Rhizomorpha is produced, as is easily proved by 



P 



