193 



chyma and medullary rays attacked by the hyphse become 

 filled with a brown substance, probably caused by the 

 decomposition of the protoplasm. This discoloration is more 

 noticeable in the roots than in the stems of the Deodar. A 

 remarkable characteristic of this fungus is the possession of 

 rhizomorphs. These are branched, cylindrical, or~ flattened, 

 bodies composed of an outer, black and somewhat brittle, 

 cortex, formed of interwoven tough brown hyphse and of a 

 central, tough, flexible, whitish portion composed of fine 

 hyphal filaments. In general appearance these resemble the 

 black petioles of some ferns and are not unlike the ordinary 

 fine Deodar roots. They are, however, blacker, of a different 

 consistency, and do not taper regularly towards the apex. 

 They can be distinguished by splitting them longitudinally 

 when the silky white medulla can be teased out with the 

 fingers. These are organs of propagation possessing the 

 power of apical growth. Springing from the mycelium in 

 the roots of diseased trees, they travel below the surface 

 of the ground and, penetrating below the cortex of any healthy 

 Deodar roots which they may encounter, develop in them 

 the ordinary mycelium, and thus spread the disease from tree 

 to tree. Trees growing close together in the forest often have 

 their roots in close contact and are frequently found grafted 

 together. It is probable that infection often takes place by 

 the mycelium thus growing directly from one root into 

 another which is in contact with it. For illustrations, see 

 Plate XVII. 



The only measures likely to be effective are the removal of 

 attacked trees to prevent the formation of sporophores and the 

 isolation of infected areas by trenches dug a few feet deep 

 and sufficiently far from the centre of infection to include 

 all diseased roots and rhizomorphs. It is doubtful if this 

 could be done profitably on a large scale. 



169. In its life-history and 



action on the plant attacked, Armillaria mellea, which has been 

 briefly noted in Part IV above, has several points of resem- 

 blance with the fungus just described, see page 133. Armillaria, 

 however, is particularly interesting as being one of those f ungi 

 which, although living at times in a purely parasitic manner, 

 are also able to exist as saprophytes. This fungus may 

 accordingly sometimes be found thriving on wood used in 

 construction, e.g. in bridges, and also on dead roots and 

 stumps, and at others as a virulent parasite attacking 

 and killing living trees. From cases such as these we 



