FLORIDA STATE HORTICULTURAL SOCIETY. 
©1 
fused is that produced by the presence of 
insects such as the purple scale (Mytilas- 
pis citricola), on the lower surface of the 
leaf. In this case, there is only a loss of 
green color, and usually the insect or its 
remains may be found on the lower sur¬ 
face of the leaf. Again, unless the tree 
EXPLANATION OF FIG. 2. 
Cross Section of Yellow Spot Area. (A) Upper 
Epidermis, (B) Palisade Cells, (C) Spongy Tis¬ 
sue, with swollen cells (a) and gum-like deposits 
(b) ; (N) Nuclei. 
is severely infested with the scale, the af¬ 
fected leaves are confined to the lower 
branches. 
There is often a yellowing of the 
leaves on trees badly diseased with die- 
back, which much resembles the yellow 
spotting, on the upper surface of the leaf; 
but these yellowed leaves lack the greasy 
projecting appearance on the lower sur¬ 
face that is characteristic of the yellow 
spotting. The yellow spotting has been 
found to occur upon trees diseased with 
dieback, but the yellow spotted areas are 
readily distinguishable from the yellow¬ 
ing due to dieback. 
When trees are being starved, espe¬ 
cially with regard to ammonia, there is a 
yellowing of the leaves. But this should 
not be confused with yellow spotting, 
since this yellowing is merely a loss of 
green color, and does not occur in round¬ 
ed areas. 
A yellowing of the leaves similar to 
that produced by starvation, is caused by 
the withertip fungus (Colletotrichum 
gloeosporioides). It is almost impossible 
to give a description from which a branch 
diseased with the withertip fungus may 
be recognized. Besides the yellowing of 
the leaves which is caused by a poison se¬ 
creted by the fungus, the bark of the 
branch will usually have a dry, dark, iron- 
gray or steel-gray appearance. The whole 
branch will appear decidedly unhealthy. 
The withertip fungus also attacks the 
leaves, producing rounded areas of an 
ashy-gray appearance, covered with mi¬ 
nute black specks. These specks are the 
portions of the fungus that bear the spores 
by which the disease is spread. This is 
the spotting described by Prof. Hume in 
