406 
Journal of Agricultural Research 
Vol. XXV, No. 10 
ined and 2,643 of these, or 52 per cent, bore petiole lesions, and in 1922 
84 per cent of the 2,099 leaves examined bore petiole lesions. Out of 
1,206 leaves on unsprayed Oldenburg trees examined in 1921, 93 per cent 
showed petiole lesions and, out of 893 leaves from Ben Davis trees, 88 
per cent showed petiole infection. From these figures it may be seen that 
a very high percentage of the leaves on the lower limbs bear petiole 
lesions. In the majority of cases these lesions are located very near 
the base of the petiole (PI. 1, G, H, I,), often in close proximity to the 
abscission layer. 
Incidentally, it is of interest to note that pycnidia containing viable 
spores are commonly present in these petiole lesions on leaves that have 
lain over winter on the ground, but no signs of an ascigerous stage have 
been found. 
VISIBLE TWIG INVASION FROM PETIOLE LESIONS 
In some cases the lesion at the base of a petiole enlarges until it visibly 
crosses the abscission layer and invades the tissues of the twig (PI. 1, 1 ). 
On the 35 twigs tagged at Mooresville in 1920, there were 155 leaves wifi 
basal petiole lesions and in three cases the lesion extended across to the 
twig tissue. On the eight twigs tagged at Knightstown in the fall of 
1921, 65 out of the 105 leaves bore basal petiole lesions and in three cases 
the lesion had crossed to the twig. 
At Mitchell, in the fall of 1921, 129 lesions were noted on Oldenburg 
twigs of the current season, of which 79, or 61 per cent, were located at 
leaf scars, and although a large proportion of the leaves at these scars 
had fallen, 38 per cent of these leaf-scar lesions were obviously extensions 
from basal petiole lesions. 
Thus, in many cases actual twig invasion from petiole lesions may be 
observed during the current season, particularly in southern Indiana, 
but as previously noted, the great majority of the twig lesions do not 
become visible until long after the leaf has fallen. 
CORRELATION OF LEAF-SCAR CANKERS AND BASAL PETIOLE 
LESIONS 
In order to determine whether or not cankers appear only at leaf 
scars to which infected petioles have been attached, 35 twigs on a North¬ 
western tree at Mooresville were tagged in the fall of 1920 and the loca¬ 
tion of each leaf with a basal petiole lesion was recorded. There were 
leaves with basal petiole lesions at 155 scars, and at 109, or 70 per cent, 
of these leaf scars, blotch cankers appeared, mostly during April and 
May of the following year, as previously noted. A total of 146 cankers 
developed on these twigs and 109, or 74 per cent, developed where an 
infected petiole had been attached. Thirty-two cankers, or 22 per cent, 
were located at scars where no basal petiole infection had been recorded; 
the origin of these cankers is not clearly understood. It is possible that 
small petiole lesions were overlooked. 
To ascertain more accurately the correlation between petiole lesions 
and twig cankers, careful records were taken on the leaves on eight 
twigs of a Northwestern tree at Knightstown on September 27, 1921. 
There were 107 leaves on these twigs and 76 bore petiole lesions. In 
each case, the distance of the lower margin of the lowest lesion from the 
abscission layer was recorded in millimeters and in 49 instances this was 
less than 3 mm. Cankers developed at 45, or 59 per cent, of the leaf 
