MISCELLANEOUS PARASITIC AND SAPROPHYTIC ORGANISMS. 23 



and generally by a sudden wilting of the leaves during the latter part 

 of the spring. 



Hoot diseases may be caused by unfavorable soil conditions as well 

 as by fungi, but it has been the experience of the writers that there 

 is a decided difference in the behavior of diseased trees where soil 

 conditions are responsible, as compared with diseased trees affected 

 with some fungous trouble. In the former case the tree dies gradu- 

 ally and the stag-headed condition, together with a gradual decrease 

 in the annual rate of growth, is very pronounced. Where fungi are 

 responsible for root-rot the trees ordinarily show slight indications of 

 the disease in the trunk and crown until it has reached an advanced 

 stage. They then usually send out an unusually large number of 

 leaves and exhibit a strong tendency to overdevelopment of the 

 flowers and fruits. 



Two fungi have been found in the United States which have been 

 definitely connected with one or the other type of root-rot. It is 

 probable that there are several others. While it is easy to find a 

 fungous mycelium in diseased roots, it is a comparatively difficult 

 matter to determine with any degree of certainty that the fruiting 

 bodies found near diseased trees bear any direct relation to the myce- 

 lium which occurs in the diseased root system. 



Only brief reference can be made here to the manner of growth and 

 attack of the two root-rotting fungi. The more important of these 

 is the ordinary ' ' Hallimasch " of the Germans, or the so-called honey 

 mushroom (Armillaria mellea (Vahl.) Quelet) (27, 32, 34, 35, 102), a 

 form of which may be what has been named Clitocybe parasitica by 

 Wilcox (113). The fruiting bodies of this fungus usually occur in 

 large numbers around the base of the trunk of a diseased tree. They 

 are also found frequently in dense masses on and around dead tree 

 stumps. The fruiting bodies are honey colored and the tops have a 

 more or less viscid appearance, speckled with white. The stems are 

 somewhat swollen at the base, and a short distance below the pileus 

 they have a distinct ring, or annulus. The gills are white, and from 

 them large quantities of white spores are shed, which frequently cover 

 the ground around the fruiting bodies, like a mealy white powder. 



The most characteristic parts of the honey mushroom are the 

 so-called rhizomorphs, known popularly as "shoe strings." These 

 consist of hard, black strands which occur singly or in large numbers, 

 frequently much interlaced and branched, extending in all directions 

 through the ground and along the roots or stumps of affected trees. 

 Where they grow under the bark and in the cambium layer, they 

 become much flattened. The fruiting bodies of the honey mushroom 

 are found to develop at the ends of these rhizomorph strands. 



149 



