TEAK-STAIN OF CITRUS FRUITS. y 
HISTOLOGICAL EXAMINATION. 
To the unaided eye, rust-mite russet with its several patterns and 
the so-called wither-tip russet or tear-stain intergrade imperceptibly. 
Ordinarily the grower calls the streak tear-stain and the solid area 
rust-mite russet. 
It was deemed important to make careful microscopic examina- 
tions to determine whether distinctive features exist in the rind 
tissue of the affected parts. Fruits were examined showing typical 
patterns of rust-mite russet as well as those showing several degrees 
of the so-called wither-tip tear-stain. Under the microscope there 
appears to be no material difference between these types of injury. 
The examination of the injured parts in both instances indicates 
that the cuticle and epidermal cells appear to be punctured, and 
beneath, depending upon the degree of russeting, one to three layers 
of cells, together with their contents, are of a rusty brown color. 
Quite frequently mycelial threads and spores of fungi are found 
adhering to the affected parts. These fungi prove to be the types 
commonly found on citrus, such as species of Colletotrichum and 
Cladosporium. 
The histological examinations have not revealed any feature that 
would serve to distinguish between the rust-mite russet and the 
so-called wither-tip tear-stain. 
The presence of punctures in the epidermal cells of the tear-stained 
areas would strongly suggest the work of sucking parasites rather 
than that of parasitic fungi. This suggestion is further substantiated 
by the following observation: In July, 1919, by the aid of a hand 
lens, numerous tear-stained immature grapefruits were examined 
while still hanging on the tree in an unsprayed grove near Orlando, 
Fla. The rust mites and their castings were more or less generally 
distributed over the fruits, but were present in especially large 
numbers over the tear-stained areas. This condition was very notice- 
able early in July. By August 2 such a marked segregation of 
mites in streaks was not particularly evident, and the mites them- 
selves, as well as their castings, were nowhere present in very large 
numbers, but the tear stains, presumably caused by rust mites, 
were quite evident. 
INOCULATION EXPERIMENTS. 
An inoculation experiment was conducted the last week in June, 
1919, on immature grapefruits which were about 2 i iches in diameter 
and so far as could be determined free from blemishes. Fifty fruits 
were used in this experiment. The inoculum was derived in part 
from dead sweet-c range twigs which had been held in moist chambers 
and on which developed a copious growth of the wither-tip fungus 
and in part from pure cultures of Colletotrichum gloeosporioides, 
