472 
Hosts 
From numerous parts of Europe and 
America it is reported that many forest 
trees, including various evergreens, the 
birch, beech, walnut and oak, as well as 
such fruit trees as the apple, plum, 
cherry, peach, citrus and olive, besides 
certain bush fruits and the grape, are 
attacked by very similar, if not identical, 
mushroom root rots. Along our Pacific 
coast, mushroom root rot is prevalent on 
many kinds of trees and shrubs. In 
Western Washington, Lawrence reports 
its presence among several native trees, 
both evergreen and deciduous, and men- 
tions that in orchard and field the apple, 
plum, cherry, gooseberry, currant, black- 
berry, raspberry and loganberry were 
found to be badly injured or killed. In 
California, Horne has reported that it 
occurs throughout the state, attacking a 
great variety of hosts. He says that it 
appears to be capable of attacking almost 
any plant, in fact, that it is somewhat 
woody and long-lived. 
Symptoms 
The symptoms of the disease vary 
somewhat, depending upon the point at 
which the tree is attacked, the rapidity 
or slowness with which the parasitic 
fungus spreads, and other conditions. It 
is generally not until the trouble has 
made considerable progress that the first 
external evidence of the attack appears 
in its effect on the health of the tree. The 
earliest indication is usually a retarded 
growth, attended by early dropping of the 
leaves. The foliage generally presents an 
unnatural appearance. Often this is con- 
fined to that side .of the tree correspond- 
ing with the side of the trunk first at- 
tacked. The fruit is usually poor and 
stunted. A tree may sometimes show 
such symptoms for two or three years be- 
fore it finally succumbs, but death fre- 
quently occurs during the season in 
which the symptoms first appear, or dur- 
ing the following year. In rapid attacks, 
the leaves often become yellow early in 
the summer. Not infrequently the entire 
foliage suddenly withers and the whole 
tree dies in midseason. Again, death may 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
occur during the winter, in which case 
the tree fails to leaf out in the spring. 
Sometimes, but not always, clusters of 
mushrooms of a light brownish color 
come up in the autumn around the base 
of the trunk, or push through the soil 
above diseased roots. In some cases, this 
occurs before the tree is totally dead. 
As soon as a tree shows the first signs 
of trouble, it should be examined by 
digging the soil away from the base, and 
a search should be made for decayed areas 
on the trunk and roots (Fig. 2), and for 
Cee. es ay. Sea, 
Vig. 2. Trunk of Apple Tree Which Died in 
Midsummer. Dead bark removed to show 
layers of white fungus under bark. 
peculiar black, rootlet-like branching 
strands, mostly about the thickness of the 
lead in a pencil, clinging to the bark. 
These strands, known as rhizomorphs, are 
characteristic of the disease, since they 
are a special form of the fungus which 
causes the rot. They can be distinguished 
from the roots of any small plants which 
may also be present in the soil, by their 
peculiar irregular method of branching 
and by the white interior substance. which 
can be rather easily separated from the 
