APPLE DISEASES 
thin black covering. The dead bark and 
wood is penetrated by a whitish fungous 
growth and has a strong mushroom odor. 
Sometimes rhizomorphs are found on the 
roots of an entirely healthy tree apparent- 
ly causing no injury. 
The disastrous effect of the disease re- 
sults from the girdling of the main roots 
and the trunk, and from a destruction of 
the activity of the sap-wood. This brings 
about root starvation, a checking of the 
ascent of water through the wood and, as 
a consequence, the eventual death of the 
whole tree. 
Cause 
The cause of this disease is one of the 
higher fungi known as Armillaria mellea 
(or varieties) and commonly called, from 
its usual light, yellowish-brown color, the 
honey mushroom. Several forms or vari- 
eties of this fungus have been found on 
the Pacific coast attacking fruit trees or 
growing from the decaying stumps and 
roots of oaks and other native forest trees. 
The following general description of the 
typical Armillaria mellea, however, will 
serve sufficiently well to identify the 
mushroom causing the disease under con- 
sideration. 
Fruiting bodies or toadstools occurring 
in tufts or clusters, honey-colored or light 
brown; irregular ring (annulus) on stem 
near the top; cap slightly elevated at 
center; margin inrolled; later flat or con- 
cave with margin upturned. Cap varying 
from nearly white to reddish-brown, 
darker toward center. Caps vary in size 
and stems in length. Gills under cap radi- 
ating from center shed innumerable 
spores which are blown about or other- 
wise disseminated. 
Life History and Method of Spread 
It is believed by many that the fungus 
gains its entrance, more often, if not ex- 
clusively at points where the root or the 
crown of the tree has been injured by 
cultivation, by the attacks of borers, or 
by the presence of a crown gall, ete. When 
once it has entered the tree, it sends out 
delicate filaments both into the bark, 
where, given the right conditions, it 
spreads rapidly, and also, by way of the 
473 
medullary rays (silver grain), into the 
wood, where it spreads more slowly. 
The disease spreads fast from the point 
of attack up and down the root or trunk, 
apparently working most rapidly in the 
cambium region. Little effect on the tree 
is at first noticeable until the decay com- 
mences to girdle the trunk, after which 
the progress of the disease is rapid and 
the death of the tree only a question of 
one or two seasons. 
When the decay has progressed suffi- 
ciently and the fungus is thereby richly 
supplied with reserve nutriment, the 
fruiting bodies or mushrooms may be 
formed. In their young condition these 
are edible. Abundant moisture is neces- 
sary for their development, consequently 
they are not met with, as a rule, till the 
fall rains have begun. The clusters of 
mushrooms usually appear at the point 
where the trunk enters the earth and may 
encircle its base. Often they rise through 
the soil from a diseased root or they may 
be attached to rhizomorphic strands con- 
nected with crown or roots. 
Control Measures 
The suggestions presented in the fol- 
lowing paragraphs regarding possible 
modes of treatment for this disease are 
in no way to be considered as definite 
recommendations. The reason for this 
appears when it is said that nowhere, to 
the writer’s knowledge, have thorough or 
long-continued investigations of possible 
orchard control methods been carried out 
to a successful conclusion. Furthermore, 
information as to the way in which the 
trouble may enter an orchard and the 
exact manner of its spread, is incomplete 
and unsatisfactory. Consequently, the 
writer is not warranted in stating that 
any of the methods described here are 
sure to give satisfactory results. It is to 
be hoped, however, that intelligent grow- 
ers will try out various methods of treat- 
ment experimentally. 
The prevalent, but not yet convincingly 
substantiated, idea that buried roots of 
forest trees in newly cleared land are a 
dangerous source of infection for young 
orchard trees, has led to the suggestion 
