. 
338 MANUAL OF FRUIT DISEASES 
was observed several years ago that the Bosc, Sheldon, Seckel, 
Anjou, Bartlett and others are injured more than the Flemish, 
Clairgeau and Duchess. The Kieffer, Lawrence and Mount 
Vernon are relatively resistant to leaf-spot. In the nursery, 
budded pear-stock, after the first year, may show occasional 
lesions, but budded stock of two or more years is often badly 
injured late in the summer. 
Symptoms. 
Only the leaves are affected. The mature spots are recog- 
nized by their well-defined angular margins and their grayish 
white centers in 
which a few pyc- 
nidia develop (Fig. 
93). They are 
found on the upper 
surface. The for- 
mation of a spot 
proceeds as follows. 
The affected tissue 
becomes brownish, 
which discoloration 
enlarges until the 
. mature size of the 
spot is reached. 
These usually measure about one-sixth of an inch or less in 
diameter. The margin, while sharply defined, is angular and 
crenulate. With age the brown color at the center turns 
grayish white and becomes somewhat. transparent. About 
this light-colored central area is a brown zone which merges 
into a purplish zone and finally into the healthy green portion 
of the leaf. Ordinarily lesions are not abundant, but under 
exceptionally favorable conditions numerous spots develop 
over the leaf-surface. Several may merge, involving large 
areas of leaf-tissue. 
Fic. 93. — Mycospherella leaf-spot on pear-leaves. 
