ARMILLARIA 



357 



coloured, cordlike rhizomorphs have a compact cortex con- 

 sisting of short cells with thick, coloured walls ; these change 

 gradually into thin-walled hyphae towards the centre of the 

 rhizomorph, which in reality is an elongated sclerotium. 





Fig. i io. - Agaricus mellcus. Base of stem of young Scots fir 

 killed by the fungus. A portion of the stem is cut away to show 

 the dense white layers of mycelium under the bark. 



These rhizomorphs radiate in every direction in the soil, 

 growing by the tip only, and eventually attack the roots of 

 other trees, by dissolving the cortex and giving origin to a 

 sheet of white mycelium between the wood and the bark as 

 described above. 



