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TREE ROOT-ROT. 

 [Agaricus [Armillaria] mellezts, Vahl.) 



The following article, prepared by Mr. G. Massee, F.L.S., 

 has been published in the' ICew Bulletin as the first of a series 

 of illustrated articles on the subject of the diseases of plants 

 produced by parasitic fungi. 



Agaricus melleus is one of the most generally distributed 

 and destructive of " toadstools," attacking all kinds of fruit 

 trees, many broad-leaved forest trees, also all European and 

 many imported conifers. Hartig records having recognised 

 its mycelium in fossil wood of Cupressinoxylon. As a sapro- 

 phyte it occurs in dense clusters at the base of stumps, and 

 also on posts and worked timber. 



The cap or pileus is 2 to 3 inches across when expanded, 

 pale honey-coloured, and ornamented with numerous minute 

 scales ; stem 4 to 6 inches long, coloured like the pileus ; 

 gills white, with just a suspicion of pink, and, when young", 

 hidden by a membrane stretching from the stem to the edge 

 of the pileus. As the latter expands this membrane breaks 

 away from the edge of the pileus and forms a ring or collar 

 round the stem. The spores are white, and settle on objects 

 under the gills in the form of a dense white powder. 



The fruit of the fungus is usually not formed until the tree 

 has been killed, or nearly so, by its mycelium ; nevertheless, 

 the disease is indicated by the pale colour of the leaves and 

 the stunted branches, and, in the case of conifers, by the 

 great accumulation of extruded resin round the collar. 



The spores of the fungus dispersed by wind and carried by 

 the fur of animals, &c, germinate and first form a delicate, 



