208 



DISEASES OF TREES 



and on the roots, when a firm snow-white mycelium (Fig. 127 y cc) 

 is observed, which, in the case of the older class of trees, some- 

 times ascends under the bark while the tree is still alive to the 

 height of ten feet or more. Brownish black lustrous strands, 

 ' 2*5 to iV mcn m thickness, which occa- 

 sionally anastomose, are observed in 

 greater or less abundance adhering to 

 the roots. These are met with in con- 

 junction with the sheets of white my- 

 celium under the cortex, though some- 

 times they merely embrace the roots 

 externally. 



A great deal of turpentine and resin 

 frequently adheres to the outside of the 

 stronger roots, and this, mixing with the 

 particles of soil, forms a firm mass round 

 the collar (Fig. 128). The diseased trees 

 speedily succumb, and are seldom to be 

 recognized more than a year before their 

 death by their pale colour or stunted 

 shoots. If we carefully dig up a plant 

 that appears to be perfectly healthy, in 

 the immediate neighbourhood of one 

 that is manifestly diseased or dead, we 

 will as a rule discover on the roots one 

 or more places of infection where a black 

 rhizomorph strand has bored into the 

 cortex (Fig. 127, a). When the cortex is 

 carefully removed the strand will be ob- 

 served expanding from the place of 

 entrance into a snow-white body (Fig. 

 127, $), which spreads in. the cortical 

 tissues and causes browning and death, 

 as far as it reaches (Fig. 127, c c). The 

 mycelium that grows in the living cortex 



is characterised by its fasciated and skin-like appearance. It 

 very easily resumes the round strand-like form, which may 

 either grow to the outside of the roots or proceed to develop 

 between the wood and cortex. W T hen, owing to the death of 



FIG. 127. The living root 

 of a spruce, showing two 

 spots, a, b y where the 

 rhizomorph has entered 

 and infected the cortex. 

 The cortex has been re- 

 moved from the larger 

 root, d to d, in order to 

 show the mycelium, c c, 

 which has gained an en- 

 trance at b. 



