May 2i, 1917 
Xylaria Rootrot of Apple 
271 
occurrence of an excessively large set of small fruits, a phenomenon fre¬ 
quently displayed by plants weakened by disease. 1 In the following 
season such trees may produce only a few flowers, and only a score, or 
even a less number, of fruits are set. The apples on affected trees never 
develop to normal size, but ripen prematurely. Certain varieties may 
exhibit a reddish flush when they are no larger, perhaps, than an inch in 
diameter, and normal apples of the same variety on trees near by will be 
considerably larger and entirely green. 
All of the foliage and fruit throughout affected trees usually exhibit 
these symptoms equally strikingly. A few cases have been observed, 
however, where the fruit and leaves on one or two limbs only mani¬ 
fested symptoms of disease; and in such cases the roots are quite normal, 
except on the side corresponding to the one which bears the abnormal 
parts. 
The effect of this disease upon the twigs is indicated by a decrease in 
the annual increment of growth when comparison is made with healthy 
trees of the same variety grown under the same conditions. This de¬ 
creased growth would naturally be expected to follow any impairment 
of the root system. In consequence of it there is a more or less marked 
bunching or rosetting of the leaves. 
The roots of affected trees are covered with a thin, compact growth 
of mycelium, which is snowy white at first; after a few days, however, 
the superficial portion develops into a black incrustation or stroma. 
Under conditions favoring the optimum development of the fungus this 
stroma is sufficiently thick so that the outer black crust may be separated 
from the snowy-white weft beneath without at the same time removing 
any of the cortical tissues of the root. Minute, black, threadlike rhizo- 
morphs are seen to radiate from the margin of the stroma and extend 
for several inches along the surface of the root. These rhizomorphs 
may anastomose more or less, forming a network, and are in such inti¬ 
mate relation with the cortex that it is impossible to separate intact 
even small portions. These strands become obscured in the stroma, 
except in its most recent growth. The disintegration of the cortex 
beneath the stroma proceeds rapidly and follows closely upon its advance. 
The bark then becomes fissured, and, when it has dried, it can be readily 
crumbled. Affected roots are soon girdled, and the distal portions die. 
New roots are sometimes developed above the diseased parts, thus 
enabling diseased trees to live for a term of years. 
Observations made in the field indicate that soil type, drainage, expo¬ 
sure, elevation, age, and variety of trees seem to have no bearing upon 
the presence of the disease, since rootrot has been found under the 
widest variation of these factors. Diseased trees occurred in fields that 
had been in cultivation for several years before the orchards were set. 
1 Schrenk, Hermann von. A root rot of apple trees caused by Thelephora galactina Fr, In Bot. Gaz., 
v. 34, no. r, p. 65. 1902. 
