408 
Journal of Agricultural Research 
Voi. XXV, No. xo 
TWIG INVASION FROM BUD SCALES 
There is a possibility that some of the twig infection may proceed 
from bud scales. It has been previously mentioned that out of the 129 
cankers noted on Oldenburg twigs of the current season in October, 1921, 
21, or 16 per cent, were immediately below terminal buds, and had 
apparently resulted from bud scale infection and subsequent mycelial 
invasion of the twig (PI. 1, A). No tests to prove this theory have yet 
been made, but the shape and location of such lesions indicate that they 
may originate in the manner suggested. 
LIMB INVASION FROM SPURS 
On the Oldenburg variety, encircling blotch cankers often occur on 
large limbs at nodes where spurs have developed from dormant buds 
(PL 3, A). Whether such a canker is the result of leaf-scar invasion at 
the time a leaf was borne at that point or the result of a much more 
recent invasion from a younger canker on the spur, a suggestion made 
by Mr. R. A. Simpson, is not easily determined. Because of their position 
in the lower interior part of the tree, these spurs are highly subject to 
petiole infection and subsequent canker formation. However, cankers 
are very common at nodes where no spur has developed and must have 
developed from petiole infection or direct spore infection when that 
portion of the limb was bearing leaves. It seems likely that both types 
of limb infection occur and that, if no spur has developed, the canker is 
very nearly as old as the limb at that point, whereas, if a spur is present, 
the age of the canker is uncertain. 
LONGEVITY OF FUNGUS IN CANKERS 
Cultural tests have proved that the blotch fungus may remain alive 
many years in the advancing margin of the canker where it may continue 
to produce pycnidia and spores. The diseased tissue is very rapidly 
invaded by other fungi, but portions of the extreme edge of the purple 
advancing margin cut out with a scalpel, sterilized a few minutes in a 
mercuric chlorid solution, rinsed, and planted in agar plates yielded 
cultures of the blotch fungus, as shown in Table I. 
Table I .—Longevity of blotch fungus in cankers 
Variety. 
Age of 
wood. 
Number of 
cankers 
tested. 
Number 
yielding 
blotch 
fungus. 
Oldenburg. 
Years. 
X 
8 
5 
A 
Do. 
O 
A 
A 
Do... 
*T 
5 
6 
*r 
6 
*r 
2 
Transparent. 
? 
2 
Oldenburg... 
7 
8 
0 
A 
A 
Do. 
*r 
2 
T 
2 
Do. 
14 
2 
2 
Possibly the cankers on the limb 14 years old may have resulted from 
infected spurs. In the other cases, however, it seems certain that the 
