Bulletin 229, Diseases of Citrus in Florida


phase of the so-called water relations problem in citrus, it is
also apparent that other, and less obvious, factors enter into this
question. No means for preventing fruit-splitting has been
found other than what the above discussion has suggested in-
directly.
 INTERNAL DRYING OF FRUIT
 Internal drying of citrus fruit is of frequent occurrence, es-
pecially when it has been left on the tree any great length of time
after maturity. The present discussion of internal drying deals
solely with the type commonly occurring in fruit that has not
been damaged by freezing. Tangerines and oranges are the
chief commercial fruits to be affected by this trouble, the grape-
fruit not being particularly affected. Internal drying is of great-
est importance on tangerines, since they often begin to dry out
in the midst of the. shipping season.
 Internal drying is a matter of great importance to packing-
houses, since it is difficult to detect the affected fruit or to tell
to what extent the fruit is affected.

 SYMPTOMS OF INTERNAL DRYING
 Fruit affected by drying out at the stem-end is characterized
by the juice sacs drying out more or less completely and sep-
arating from one another, thus allowing air to enter, which gives
them a rather colorless and lifeless appearance in comparison
with the bright color and turgid appearance of the normal juice
sacs. Cutting lengthwise through an affected fruit reveals a
more or less dry, spongy condition (Fig. 72). The internal dry-
ing may be confined to the region of the stem-end in the less ad-
vanced cases but, in the more pronounced cases, it may involve
the entire fruit, in which case the tissues near the stem-end are
the driest. There is little or nothing in the external appearance
of the fruit to indicate the occurrence and extent of the trouble,
although it usually can be detected readily by the feel or weight
of the fruit.
 CAUSE OF INTERNAL DRYING
 The exact cause of internal drying of citrus fruit is not known
but it is believed to be one of the water relations problems of
citrus trees. It is generally conceded that fruit on rough lemon
rootstock, at least on the lighter and drier soils, dries out from
six to eight weeks sooner than that on sour orange stock. Where