SOURCES OF APPLE BITTER-ROT INFECTIONS. 1 
more so than the Winesap. The York Imperial and Yellow Newtown 
are very nearly immune. While on the two last-named varieties the 
fungus may begin the development of a canker, the reaction of the 
host is such that the growth of the fungus is soon checked and the 
incipient canker itself is later obliterated by the formation of callus. 
As these two varieties are the ones chiefly found in Virginia orchards 
and as their fruits, especially those of the Yellow Newtown, are sus- 
ceptible, the writer believes that these inoculation experiments ex- 
plain why bitter-rot cankers have not been found in that State. 
~ It is also worthy of note that in these experiments the inoculations 
were eventually more successful on older branches than on 1-year-old 
twigs and water sprouts, though the growth was usually slower on 
the older branches. This is in accord with the writer’s observations 
on naturally formed bitter-rot cankers. 
The inoculations made in July were more uniformly successful 
than those made in June, doubtless owing to the fact that in July 
the temperature was much higher and the growth of the host more 
restricted. 
These experiments and the writer’s observations indicate that 
cankers in which the growth of the fungus is comparatively slow 
are apt to be much longer lived than those in which the fungus de- 
velops rapidly. This is particularly true in the case of the Givens, 
a variety which harbors more cankers than any with which the writer 
has come in contact. Cankers on Givens branches grow very slowly, 
but are exceedingly persistent. 
Young vigorous-growing twigs are able, after the hot season which 
favors the bitter-rot fungus is over, to continue growth and by the 
formation of a callus layer to utterly isolate the mycelium of the fun- 
gus in the tissues which it has killed. This explains why the writer 
has not been able to find bitter-rot cankers on young branches. 
It seems probable that another reason why cankers on branches of 
the Givens variety are so persistent is that this variety begins growth 
in the spring nearly two weeks later than most, varieties. It is in 
the spring that the most vigorous growth of the apple occurs, and 
hence it is at this time of year than the branch is in the best one 
tion to isolate the cankered areas and develop callus. The fungus, 
on the contrary, is not able to start growth until the weather be» 
comes hot. This conclusion is drawn from the inoculation experi-. 
ments of 1914 and 1915. 
On January 9, 1917, three cankered branches of each variety in- 
oculated in the 1916 experiments were cut off, brought into the 
laboratory, and placed in moist chambers for 48 hours. Masses of 
spores were produced from all cankers except those from the York 
Imperial and Yellow Newton trees. Cankers on the branches of 
