16 BULLETIN 684, U. S. DEPARTMENT OF AGRICULTURE. 
these two varieties were nearly healed over, and in the dead bark 
remaining the fungus was no longer alive. 
Although these experiments seemed to show rather conclusively 
that the branches of the Yellow Newtown, the chief commercial apple 
whose fruit is susceptible to bitter-rot in Virginia, are resistant to 
the disease, it was also thought possible that the fungus found in 
Virginia might not be capable of causing cankers. This, however, 
proved not to be the case, as is shown by the series of inoculations 
listed in Table II. In fact, in these experiments the fungus isolated 
from Virginia fruits attacked the branches more vigorously than 
that isolated from bitter-rot cankers from Arkansas. The results of 
these inoculations did not differ materially from those of the pre- 
vious experiments. 
TABLE II.—Comparison of results of inoculations of apple branches with bitter- 
rot fungus cultures from fruits grown in Virginia and in Arkansas, at Ar- 
lington Farm, Va., on August 21, 1916. 
Width of blackened 
Number band. 
Source of culture used. Apple variety. piseot Tea 
slits. | On Aug. 29.| On Sept. 15, 
Years. Mm. Mm. 
Varcimiatnuithesse-peeeeeee- IBENED aS seen eae 2 6 1 6 to 20 
ArkansasiCanketiee ese acs |eece GOs ea erect | 3 6 1 1to2 
Bb Gs on Sebocedeeas Sand ance On Ss SEiep see ee 2 6 0 0 
Virginiatruites:|-ce kno IMISSOUEIEt Sot: eee nee | 2 4 2 to 3 8 to 10 
Saale ees Pee ae ca erate dowel Sane re yore i + 4 1 4 to 10 
pATKansSasicankersssees =e er eeeee GOssese cae ence ees pee 2 4 0 to 2 0tod5 
Wirginiairuithncceeen ss ee Yellow Newtown.......-..-. | 1 4 1 
The importance of cankers as sources of infection is also greatly in- 
creased by the enormous number of spores which a single canker is 
capable of producing in a season. The writer estimated that the 
number of conidia in one canker 7 cm. long by 2 cm. wide, not a large 
specimen by any means, was not less than nine millions. When one 
considers that during moist hot weather the production of spores may 
be almost continuous, he realizes that the number produced from a 
single canker during one season must be enormous. 
SUMMARY OF KNOWLEDGE REGARDING BITTER-ROT CANKERS. 
Knowledge of the bitter-rot cankers may be summarized as 
follows: 
(1) Discovered by Simpson in 1902 and shown by Spaulding and Von Schrenk, 
in 1906, to be due to Glomerella cingulata. 
(2) May occur perennially on older branches of susceptible varieties and 
may survive many years. 
(3) Infections on younger branches develop rapidly but do not survive. 
(4) Slow-growing cankers are more apt to survive. 
(5) Varieties differ in susceptibility to the canker disease; the Yellow New- 
town and York Imperial are nearly immune. 
