42 THE SAX JOSE OR CHINESE SCALE. 
The most commonly infested ornamentals are purple-leaved plum, Crataegus, Japa- 
nese quince, mountain ash, red-twigged dogwood, and Rosa rugosa. Poplar, willow. 
Persian lilac, Cotoneaster, elm (both American and European), and osage orange 
have been found thoroly incrusted by the insects, especially when growing near 
infested trees. 
Of the plants which are reported as noninfested in this list 
probably many of them may be subject to slight or occasional 
infestation. Notwithstanding the San Jose scale's wide range of food 
plants, strangely enough certain varieties of pear seem to be almost 
never attacked, and are practically exempt from injury. This holds 
true also, to a less extent, with different varieties of other fruits. 
The striking illustrations are the Leconte and Kieft'er varieties of 
pears, and the reason for this immunity is difficult to explain. Differ- 
ences in the density and texture of bark could hardly account for it, 
because that would scarcely protect new and comparatively tender 
growth. A notable instance of the immunity of the Leconte pear is 
seen in the little grove connected with the insectary of this Depart- 
ment. This grove has been thickly planted to pear and apple trees, so 
that the branches are interlacing all the time, and it has been pretty 
badly infested with the San Jose scale off and on for ten years, and 
yet the 10 or 12 Leconte trees have been clean the whole time, while 
the rest, representing different varieties of pear, apple, peach, and 
plum, have died out or have been replaced, some of them over and 
over again. 
CITRUS FRUITS AXD THE SAN JOSE SCALE. 
The susceptibility of the orange and lemon and other citrus plants 
to the San Jose scale is a matter of great interest to citrus growers. 
In catalogs of the food plants of the San Jose scale the orange and 
lemon and other citrus fruits are listed, notably in Mrs. Fernald's 
Catalog of Coccidae. The facts on which this statement is based are 
rather meager, and, when examined, do not warrant any grave fears 
of injury to the ordinary cultivated citrus fruits. It is well known 
that the San Jose scale will infest rather freely the trifoliate orange. 
a hedge plant somewhat closely related to the orange and lemon. 
Some trifoliate trees, for example, on the Department grounds, are 
now rather thickly covered by the San Jose scale, hut even in the case 
of this hedge plant the infestation is, as a rule, not serious, and. 
according to Mr. Gossard, the plant seems to throw the scale off as it 
grows. The first undoubted example of San Jose scale on orange was 
on certain hybrid sorts produced by crossing the trifoliate orange 
with the sweet orange, and was received in 1903 from Mr. Gossard 
from Florida. Mr. Gossard stated that in a single instance where a 
small sweet orange tree interlaced with the branches of a badly 
infested trifoliate orange the former had matured perhaps half a dozen 
San Jose scales. 
