Bulletin 229, Diseases of Citrus in Florida


branches to from two to three, or even more, feet on the larger
branches, main limbs and
trunks. In long-standing
cases of psorosis, the dis-
ease frequently involves
the entire main trunk
above the bud union and
also many of the main
limbs. Independent le-
sions may occur farther
up on the limbs and even
on the smaller branches
of the tree (Fig. 30).
 In the well advanced
stages of the disease, in-
ternal gum formation
begins in the cambium
and embryonic wood
cells and a yellowish dis-
coloration of the inner
bark may appear, due to
the gum infiltrating the
tissues. Gum may ap-
pear on the surface of
the bark, especially dur-
ing the active growing
period of the tree, but its
exudation is never a s
copious as in gummosis,
usually being reduced to
scattered drops at either
end of the lesion. A
cross-section of an at-
tacked trunk or branch
in the late intermediate
stage of the disease may
not show any discolora-
tion except dark brown
lines of closely crowded
gum canals in the outer
 Fig. 30.-Psorosis lesion on orange
layers of the wood (Fig. branch which is virtually girdled.