Florida Agricultural Experiment Station


31), as described in this connection under gummosis (See page
69). It is only in the late stages of psorosis, after the disease
has been present for probably five or more years, that the wood
begins to be seriously injured. This starts as a drab discolora-
tion just under the diseased bark. Almost the entire interior,
with the exception of a narrow layer of wood just beneath the


Fig. 31.-Cross-section of orange branch on which psorosis has been
 active for the past few years. Note the dark concentric lines in the
 outer layers of growth, which consist of compact rows of gum canals.
 (Natural size.)
cambium or growing layer may, in certain cases, become dis-
colored in this way but remains firm and hard unless wood-de-
caying fungi invade the dead tissue.
 After the inner bark tissue becomes involved the growth of
the tree is reduced and the cambium may be killed in scattered
spots or even over large areas. This results in the decline of
the top of the tree in so far as it was dependent upon the part