CHERRY DISEASES 185 
again. In the event of renewed activity in the winter the 
bacteria spread at the edge of the old cankers, thus enlarging 
these lesions. The bacteria probably lie dormant also in the 
buds. The effect of their action is not ordinarily observed 
until the buds fail to open in the spring or until, after opening, 
they suddenly die. From the cankers, bacteria may possibly 
be carried by insects in the summer to new points where in- 
fections result. The bacteria attack the outer bark, then the 
phloem and cambium. These affected elements all turn brown. 
Brown streaks are found in the bark (between the phloem and 
outer cortex) extending above and below a canker. Gum 
pockets are formed under the bark, which splits and allows the 
gum to ooze forth. 
The theory of gum-formation has created no little interest. 
It is now generally held that gum is formed through the trans- 
formation and liquefaction of the walls of certain cells. Such 
cells are formed abnormally by the cambium as the result of 
stimulation by parasites or other factors already enumerated. 
In bacterial-gummosis of the cherry this stimulating factor is 
Bactertum Cerasi. Probably it produces an enzyme which 
dissolves the walls of the cells, with the result that gum is 
formed in pockets made in turn by the dissolution of the cell- 
walls in a local area. In order that gum may be produced, an 
abundance of water seems necessary. It also seems essential 
that the tree be in a growing condition for gum-production. 
It may then be understood why young trees exude gum more 
often than do old trees. 
Control. 
Recommendations for the control of the bacterial-gummosis 
of the cherry are made in the Northwest along three lines: 
(1) the removal of cankers; (2) the protection of susceptible 
trunks and limbs with coarse cloth or burlap; (8) the use of 
resistant seedlings and the growing of resistant varieties. . 
Cankers on old trees are rare, so that surgical methods apply 
