70 
AMERICAN JOURNAL OF BOTANY 
[Vol. io. 
after the fruit has become ripe and serves in many instances as an indication 
of internal abnormality. If the peel of the lemon is comparatively thin, 
the breaking down of some of the internal tissues will cause the formation 
of a depression at the base of the nipple on the stylar end of the lemon. 
In some cases the depression appears on one side only, thus causing the 
nipple to curve or bend over in that direction. These depressions are 
often, but not always, a sign that the lemon is affected and that it should 
be discarded. 
In all the three classes of fruits the external signs are such that usually 
50 to 90 percent of the lemons having internal decline may be detected and 
culled out. 
Internal Symptoms. There is little or no indication of a further breaking 
down of the cells in the peel, but the pulp tissues continue to lose water 
and collapse as long as the fruits remain on the trees. When f to J of the 
stylar end of the lemon has become affected (see d, PI. VII), an abscission 
layer usually forms in the stem and the fruit drops. 
After the trouble has progressed to a considerable extent, the stylar end 
of the lemon becomes lighter in weight than the opposite end. On this 
account many of the badly affected lemons may be distinguished and culled 
out at the time of washing, because these lemons, unlike the sound ones, 
will float with the affected ends upward. 
In the above description of the symptoms of internal decline, a typical 
example has been cited in which the collection of gum and the destruction 
of the tissues begin while the fruit is still green. As has already been stated, 
the malady may appear only in the silver or tree-ripe fruit. In such cases 
the course of development of the abnormal conditions is like that which 
begins while the fruit is still green, except that in some instances gum 
formation may be a little less abundant and discoloration of the tissues 
less pronounced. 
EXPLANATION OF PLATE VII 
a. Vascular bundles clogged with gum. 
b. Initial collapse of pulp tissues. 
c. Affected area in peel; vessels and adjoining cells becoming filled with gum. 
d. Collapse of placental and adjoining tissues. The lemon usually falls from the tree at 
about this stage. 
Note: The earlier stages of development of the malady cannot be satisfactorily shown 
in an ordinary photograph, and in fact none of the stages can be most advantageously 
shown without the use of a colored plate. 
