56 
Journal of the Mitchell Society 
[Ji 
me 
the transportation of infested trees or plants. It is on account of 
this last feature of its spread that all of the eastern states have 
adopted measures providing for the the inspection of fruit-tree 
nurseries and the condemnation of stock found to be infested. 
The San Jose Scale is not capable of living and thriving on all 
kinds of plants. For convenience its food-plants may be divided 
into three clases. First, the ordinary food plants on which it is 
most commonly found, and including peach, apple, plum, pear, 
cherry, and apricot. Second, the not uncommon food plants, 
including currant, gooseberry, rose, grape, osage-orange, thorn- 
apple, Japan walnut, Japanese (or flowering) quince, 
poplar, elm, and linden. Third, what we may call the uncommon 
or rare food-plants including persimmons, walnut, sumac, catalpa, 
willow, ash, dogwood, maple, spruce, cedar, raspberry, strawberry, 
milkweed, and even crabgrass. 
In short, while it is found on a great variety, yet its economic 
aspect is principally concerned with its occurrence on our culti- 
vated deciduous fruit plants, (especially orchard trees) and such 
ornamental plants as belong to the botanical family Rosaceae. 
Only in rare cases has it been found in the actual forest and the 
forests are not appreciable factors in harboring or disseminating it. 
The length of time that a tree will live after it becomes infested 
depends upon the hardiness of the tree and the age at which it 
becomes infested. With peaches from two to six years (depending 
on age) will usually be fatal, while for apples from two to ten 
years is required to kill, or perhaps they may not entirely die at 
all from the scale. 
There are certain natural enemies which have a tendency to 
reduce the numbers of the scale, or at least to prevent its becom- 
ing so abundant as it otherwise might. Several species of internal 
insects parasites infest it, while more than one of our native lady- 
beetles devour it. A fungous disease also does some good work, 
while only in recent years the U. S. Department of Agriculture 
introduced a Chinese species of lady-beetle for which great things 
were hoped but which has been unequal to the emergency. 
For nearly ten years after this pest was discovered in the 
eastern states fruit-growers relied upon emulsions of kerosene or 
