34 THE FLORIDA ENTOMOLOGIST 
the atomizer, was shown by a tiny brown spot. Where the ap- 
plications had been so heavy that considerable areas were cov- 
ered with a continuous film, these areas showed up of the same 
size and shape as brown blotches. On closer examination the 
outer skin of these oil covered spots was found to have been 
killed, leaving a rough outer surface consisting of broken, dead 
skin tissue adhering to an imperfect substitution skin under- 
neath. In a few cases of extra heavy application of orange oil 
the entire bark was killed to the wood on twigs as large as a 
lead pencil, thus resulting in the death of the twigs. 
In making these tests with needle pricks and atomizer, I was 
trying out a suspicion that melanose and ammoniation spots 
may be due to the bursting of oil glands and the consequent 
exudation of their contents to the outer surface where the effect 
of the oil would damage the epidermal layer or outer skin of 
newly grown leaves, fruit, and twigs. It is evident that the oil 
is a factor in the development of melanose and ammoniation or 
dieback spots but the reasons for the escape of the oil from the 
sacks to the outside must be found before a full explanation can 
be given. In case of the disease known as melanose it appears 
that probably abortive infections from spores of the stem-end- 
rot fungus permit the leakage of the oil and thus result in 
melanose spots. 
Coming back now to the appearance we call rust, one need 
only examine a very rusty orange that had an early infection, 
with a hand lens, to see that the outer skin has been killed and 
that its broken fragments are adhering to an imperfect inner 
one. This is true only of russeting that is due to an early attack 
of rust mites on fruit. In case rust mite does not become very 
numerous until after the fruit has attained considerable size, 
however, the oil injury following is not so serious and usually 
gives rise to smooth russets. The rough russets due to the early 
attacks of rust mites are commonly called buck-skin or shark- 
skin fruits. 
The effects, then, of rust mite on fruit are considerable and 
various, depending upon the relative earliness and intensity of 
the infestation and on the weather conditions prevailing during 
the period of greatest activity. For example, tear-staining can 
probably result only during periods of comparatively dry weather 
so that the exuded oil accumulating in spots of intense mite 
activity may be carried down the sides of fruit in streaks by 
dew deposits thus allowing concentrated action of the oil, while 
