CROWN-ROT OF FRUIT TREES: HISTOLOGICAL STUDIES 
J. G. Grossenbacher 
Introduction 
The term crown-rot" is used to designate a bark disease of fruit 
trees (chiefly apple — Pyrus malus and pear — Pyrus communis), occur- 
ring in most of the tree-growing portions of the United States. The 
affected bark eventually dies in various sized patches, and the sur- 
rounding living tissues produce callus, which thus separates the living 
tissues from the dead. This disease most characteristically affects 
the bark of the lower trunk and that of the adjoining portions of the 
upper roots. The location of affected patches of bark seems to depend 
very largely upon the interrelation of growth and weather conditions; 
in some cases the disease involves chiefly the upper roots, while in 
other cases it occurs most frequently at the base of the trunk. An 
affected patch of bark that dies to the wood decays more or less 
rapidly, depending upon its distance from the ground or other sources 
of moisture. The wood exposed by the decayed bark is usually dis- 
colored at its surface but may be alive within and active in the con- 
duction of water. When the crown-rotted patch extends around 
three fourths or more of the trunk, the downward current of elaborated 
food in the bark is interfered with to such an extent as to permit much 
less than the normal amount of radial growth in the roots. The 
enfeebled roots thus absorb less soil solution, and therefore smaller 
leaves are formed. The wood under the wound dies in time, and 
thus the water-conducting tissues are reduced. Such trees usually 
die in a few years unless radial growth produces much new wood about 
the wound in the meantime. In some instances the bark dies entirely 
around the base of the trunk, and in many cases of this sort the width 
of the dead girdle determines the length of time such a tree will live. 
Crown-rot has an important economic bearing upon the fruit 
industry of this country, owing to the fact that it involves the lives 
of trees and is therefore much more serious than fruit- and leaf-spotting 
diseases which after all are essentially matters of a season. 
Crown-rot and related bark diseases have been investigated inter- 
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