AUTOBASIDIOMYCETES 473 



somewhat darker in color than the pileus. Rhizomorphs are pres- 

 ent, and these, at maturity, are black in color. When growing 

 close beside the trunk or under the edge of fallen logs or brush, 

 giant forms of the mushroom may appear, single specimens of 

 which have been found weighing more than a pound, with gills 

 anastomosing and variously modified. It has been suggested by 

 some observers that Agaricus melleus is responsible for this root 

 rot of the apple, but the writer has never detected this fungus 

 associated with the typical disease in Missouri. 



Control. It is hardly possible to adopt effective control measures, 

 but it is desirable that every means possible be taken to get rid 

 of stumps ana roots in land set to an orchard, and preferably 

 such land should be grown to some grain or other field crop for 

 several years previous to its use for orchard purposes. Isolation 

 of affected trees by trenching, and the prompt removal and de- 

 struction of these, is also to be recommended. 



XIII. THE HONEY AGARIC 



Armillaria mellea Vahl. 



Hartig, R. Wichtige Krankheiten der Waldbaume. pp. 12-42. ph. I, 2. 

 Hartig, R. Die Zersetzungserscheinungen d. Holzes d. Nadelholzbaume u. d. 

 Eiche. Berlin, 1878. 



Of the Agaricaceae which may induce plant diseases there is no 

 fungus better known or more destructive than Armillaria mellea. 

 It is abundant in Europe and America, and doubtless has a very 

 general distribution. This fungus is unusual in that it is no less 

 common as a saprophyte than as a parasite. It is said to occur 

 upon all conifers which grow in Europe, and, among deciduous 

 trees, especially upon Primus avium and Prunus domestica. In 

 moist regions it has been noted upon a variety of hosts, and in 

 the small forests of central Missouri it has done greatest damage 

 to young trees of the hop hornbeam (Ostrya virginiana) and of 

 the white oak {Quercus alba). It frequently attacks saplings, or at 

 least its effects become evident upon such trees, of from 1^ to 

 3 in. in diameter. Infested trees grow very slowly, and often the 

 leaves fall in early summer. When so far affected death promptly 

 ensues. An examination of the crown of these trees would show 



