XIV, 6 Lee and Yates: Pink Disease of Citrus 661 
DESCRIPTION OF THE DISEASE ON CITRUS 
The first stage of the disease appears to be a slight gumming 
(Plate II, fig. 1, Plate IV, fig. 2), similar in many ways to the 
gumming which is produced coincident with many other injuries 
to the bark of Citrus. At this stage the bark seems dry and 
very hard, and it adheres closely to the wood. Often longi- 
tudinal cracks form in the bark at the same time with the 
gumming. 
Usually the first appearance of the fungus is in the form of 
pustules, which push through the hardened bark (Plate I, fig. 
1, Plate II, fig. 1). These pustules are dirty white to pinkish 
in color, usually 1 millimeter or less in diameter, and rather 
irregular in shape when observed under the hand lens; so far 
as known, they are sterile. These pustules appear to be the 
“Hockerchen” form described by Rant. Following the pustule 
stage, or sometimes occurring without any appearance of it, 
there is a formation of the mycelium of the fungus over the 
surface of the branch. This mycelium spreads and extends over 
the entire lesion (Plate IV, fig. 1, Plate III), forming a pink 
incrustation, which varies somewhat in shade but perhaps typi- 
cally approaches most closely the “orange-pink” of Ridgway’s ** 
nomenclature. This color is the most striking characteristic of 
the fungus (Plate I). The incrustation is at first almost entirely 
smooth and of a velvety appearance, but with age it becomes 
roughened and broken up into patches, passing through tran- 
sitional stages of color until it finally fades out to a dirty white. 
The mycelium advances up and down the branch as a char- 
acteristically delicate, smooth, fan-shaped white mycelium (Plate 
li; fe 2): 
In some cases, upon cutting through the bark beneath the 
actively advancing mycelium, no visible effect of the fungus is) 
found even though the mycelium on the surface has advanced | 
considerably beyond the cut; in others the bark is shown to— 
have a watery, darkened, greenish appearance; while in still 
other cases the affected area extends beyond the limits of the 
surface mycelium. This variation “may perhaps be explained 
by different seasonal conditions. As the disease advances, the 
watery appearance of the bark passes off, and the tissue becomes 
still darker in color and presents a dried-out appearance. The 
bark at this stage is a dry mass of shredded fibers, running 
* Ridgway, Robert, Color Standards and Color Nomenclature. Wash- 
ington (1912) pl. 2. 
