Peb. 15,1925 Root Rot of Grapevine Caused by Clitocybe Tabescens 343 
the disease, but contributes nothing to 
the identity of the causal organisms 
involved. The vineyard in which an 
exceptionally severe form of root rot 
was observed was planted on a slope 
shortly after the land had been cleared 
of its oak timber, and the lower part 
was poorly drained. From his experi¬ 
ence with California conditions, the 
writer would attribute the form of root 
rot prevailing there to Ar miliaria 
mellea. 
SYMPTOMS OF THE DISEASE 
Often, without any cause apparent 
to the vineyardist, the vines will 
exhibit a sickly appearance which 
becomes quite evident in midsummer, 
when the demand for water conduction 
is greatest. At this time the margins 
of the leaves on diseased vines suddenly 
turn brown, usually shortly before the 
ripening of the fruit. Later the leaves 
may dry up entirely and the vine sud¬ 
denly die, leaving the fruit to shrivel 
in the sun (pi. 1), or the crop may 
mature and the vine linger until fall, 
being entirely dead at the winter prun¬ 
ing. In other cases only a part of the 
vine will die, some branches putting 
forth a feeble growth for two or three 
seasons longer. 
The root crowns and larger roots of 
diseased vines, when dug up and the 
outer fibrous bark peeled off, invariably 
show a whitish to creamy white or 
isabelline mycelial coating or sheet, the 
marginal portions of which spread out 
in a fan-shaped manner, the older parts 
often forming a feltlike layer of fungous 
tissue between the outer bark and the 
wood (pi. 2). Often there is present 
also a number of more or less flattened, 
black rhizomorphs. The inner living 
bark has been killed by the mycelium, 
which usually can be traced from 1 to 3 
inches above the ground line and down 
to all the larger roots. In well- 
advanced cases the smaller fibrous 
roots may be rotted away, although 
in less advanced cases only the crown 
and the larger roots may be affected, 
the smaller ones remaining for the most 
part healthy. There is comparatively 
little decay of the wood of the root 
crown or larger roots until after the 
death of the vine, in which case trans¬ 
verse sections through the root crown 
or larger roots exhibit whitish radial 
streaks of more or less delignified wood. 
The course and nature of the decay 
are essentially the same as those 
described by Wilcox (58) for fruit trees. 
Within the wood the mycelium attains 
its greatest development in the medul ^ 
lary rays, probably by reason of the 
fact that these are centers for the stor¬ 
age of reserve food materials. This 
great growth of mycelium within the 
larger medullary rays soon leads to the 
formation of radial cracks in the wood, 
which become stuffed with light tan- 
colored sheets or feltlike mats of my¬ 
celium often extending into the pith. 
This tendency of the mycelium to 
develop most abundantly within the 
larger medullary rays explains why the 
decay first appears as whitish more or 
less delignified radial streaks. Within 
the centers of decay the cell walls fail 
to respond to microchemical tests for 
lignin and various stages of dissolution 
are to be seen there. Within the 
individual cell the dissolution proceeds 
outward from the laminae bordering 
on the lumen, the middle lamella or 
primary layer being the last part to 
disappear. Contrary to the statement 
by Wilcox (58, p. 15) that the hyphae 
find their way into the cells only 
through the pits, the writer finds that 
they may penetrate the walls regardless 
of the presence of pits, as is the case in 
virtually all fungi causing an enzymatic 
digestion of the wood elements and the 
consequent decay of the wood. 
The mycelial growth through the 
inner bark is by no means confined to 
vines in which the foliage has shown 
signs of disease, but frequently may be 
found on those that are still making a 
fairly strong growth and on which the 
foliage is perfectly healthy. This point 
can be determined readily in an in¬ 
fected vineyard by making a slicing 
cut down through the outer bark at the 
ground line. The presence of the my¬ 
celium in the inner bark of the roots 
is by no means an indication of speedy 
death, however, for the disease works 
comparatively slowly and vines may 
be affected for a number of years before 
they succumb. Although the writer 
has no definite figures on this point, it 
is believed that at least from two to 
four years are required for this root rot 
fungus to kill a well-established vine. 
When the mycelium has progressed 
sufficiently through the wood and the 
inner living bark to cut off, either wholly 
or in part, the water supply, the vine 
dies more or less suddenly. 
During the late summer and autumn, 
in favorable years, one often finds in 
vineyards and orchards suffering from 
root rot clusters of the mushrooms 
fruiting from the root crowns of vines 
and fruit trees. These may be found 
even more abundantly in forests, espe¬ 
cially in oak stands (pi. 3). 
