44 Florida Agricultural Experiment Station

face membrane completely disappears (Fig. 13). In especially
susceptible varieties, canker has been found on the bark of ma-
ture branches as large as six inches in diameter and branches
from two to three inches in diameter are quite commonly infect-
ed. While underground roots of citrus trees have been repeat-
edly inoculated, with positive results, canker has never been ob-
served occurring naturally on such roots despite numerous exam-
inations of roots of badly diseased trees that were dug in heavily
 infected
 s groves. How-
 ever, the dis-
 ease has been
 .' -, found on roots
 Fg. 1o f grapefruit
 h trees exposed
 al 1 above the sur-
 ove t face of the
 ground.
 ciad wit On the Fruit:
 Individual
 IN canker lesions
 on t he fruit
 t Cr have much the
 Ss a m e appear-
 ance as on the
 leaves except
 Fig. 14.-Canker on grapefruit. h e yl
 halo is usually
absent and the crater-like appearance is usually more notice-
able (Fig. 14). The spongy, rough eruptions may be scattered
over the surface or several may occur together, forming an ir-
regular, scurfy or scabby mass. Gumming is sometimes asso-
ciated with the spots formed on the fruits. The disease, which
does not penetrate deeply into the rind, does not cause a decay
of the fruit directly but opens the way for fungi to enter and
cause infected fruits to rot.
 Distinguishing Canker from Other Diseases:-Citrus diseases
with which canker may be confused are scab, scaly bark or nail-
head rust, and anthracnose on Mexican or Key limes. It can be
distinguished readily from any of these diseases, however, by
noting the following points:-