174 MANUAL OF FRUIT DISEASES 
diameter, and they may be scattered over the whole blade or 
confined to one portion. Within a week or so the affected 
tissue becomes dark-red or reddish brown in color. Later 
developments may be one of two types; either the affected 
portions drop out, leaving circular areas in the leaf, or the whole 
leaf turns yellow (Fig. 48, center). A single leaf may show both 
types of symptoms, but with cherries, the yellowing of the 
leaves is the more common, whence the common name yellow- 
leaf. An allied trouble affects plums, and while the leaves 
show both a yellowing and a shot-hole effect, the latter symptom 
is the more common. During periods of wet weather whitish 
masses appear on the lower surface of the leaf-lesions (Fig. 48, 
center). Sometimes these pustules are found. in the center of 
the spot on the upper surface. Any time after the last of June 
premature defoliation is likely to occur on affected trees. 
Affected pedicels show spots one-fourth of an inch or less 
in length, which extend one-third or more of the way around, 
often girdling the pedicels. The presence of such lesions causes 
the fruit to ripen unevenly. Lesions on the fruit are unusual 
and probably are never important. They manifest themselves 
in the form of dead, brown spots with whitish fruiting bodies 
in their centers. 
Cause. 
The leaf-blight of sweet cherry is caused by Coccomyces 
hiemalis, a fungus with a not unusual life-history. The leaf- 
blight on mahaleb seedlings is caused by a very similar organism, 
Coccomyces lutescens. These fungi hibernate in the old fallen 
leaves as sexual structures called apothecia. In the spring 
ascospores are ejected from the apothecia, and are carried by 
the wind to the new foliage on which spore-germination occurs. 
About a week or ten days later signs of leaf-blight are visible 
to the naked eye. The reader will recall that this has occurred 
by June 1 at least. The spore on germination sends its tube 
into the young leaf and mycelium rapidly develops. The 
