APPLE DISEASES 103 
Armillaria root-rot, black rhizomorphs are found adhering to the 
roots; accompanying these is a peculiar mushroom odor. The 
sporophores, or mushrooms, or the causal pathogene, appear in 
groups at or near the base of the diseased tree. Their presence, 
while not constant, affords the most positive evidence of this 
root-rot. 
Cause. 
The fungus, Clitocybe parasitica, a mushroom, is responsible 
for this trouble, whence the name of the disease. It was first 
found and described in Oklahoma about 1900. The rhizomor- 
phic strands mentioned above are found on the surface of the 
roots. These can be traced to an organic connection with 
mycelial bands between the cortex and cambium, that is, just 
beneath the bark. From these latter, subcortical mats of 
hyphe, mycelial threads enter the woody tissue by way of the 
medullary rays. They grow vertically in the wood-ducts; side 
branches are given off and these enter adjoining cells through 
pits in walls, destroying the contents of the invaded cell. A gum 
is formed; this fills the sap-tubes, thus interfering with the 
ascent of sap. 
The parasite propagates itself in two ways: (1) by forming 
sporophores, or. mushrooms, from the rhizomorphs, and (2) by 
the growth of the rhizomorphs from one tree to another. In 
the cases where mushrooms are developed, countless spores are 
formed on the gills on the lower side of the cap of each. These 
spores at maturity are scattered by the wind. In suitable 
infection-courts they give rise to mycelium, and subsequently 
to rhizomorphs and sporophores. The rhizomorphic strands 
spread from one point to another by growing through the soil. 
By this means the fungus may travel several feet to other trees. 
Rhizomorphs have been found in the soil at a depth of about 
eight inches. The roots or even the crowns of trees are en- 
countered ;- entrance is gained through healthy or through 
injured bark. The flat-headed apple-borer is held responsible 
