280 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
cubic foot. The writer proposes to place the dosage of volatile dusts 
upon the same basis. Briefly, dosage is the number of cubic feet of 
tree volume or tree space occupied by one pound of dust. 
Definitions 
By tree volume (T v ) is meant the cubic contents of an imaginary 
right cylinder having a diameter (D), which is the mean diameter, 
and a height (H) the same as that of the tree under investigation, all 
measurements being in feet and tenths. Mean diameter is.the average 
of two diameters of the tree taken at right angles to each other. In 
mathematical symbols, T v = 0.785 D 2 H. Dividing this product by 
the number of pounds of dust used on the same tree 
© 
gives 
the 
number of cubic feet occupied by one pound of dust on the basis of tree 
volume. Since pear trees vary in shape and habit and because, when 
enveloped, the cloud does not conform closely to the contour of the tree, 
a cylinder represents the space as well as a more complicated solid and, 
in addition, the volume is easily computed. 
Tree Space (T s ) is the product of the planting distances and the 
height; for example, a tree 16 feet high, planted 20 x 18 feet would have 
a tree space of 5,760 cubic feet. This result divided by the amount of 
dust used on the tree © gives the number of cubic feet occupied by 
one pound of dust, on the basis of tree space. The difference between 
tree space and tree volume is designated open space (S G ). 
S 
Percentage of open space = 100 —°. 
T'c 
Nature of Experiments and Data 
During pear psylla experiments in western New York, 1921-23 in¬ 
clusive, a total of 15, 802 trees (86 acres) were dusted in cooperative 
field trials. These tests included dusts of varying nicotine content but 
the majority were 2 per cent lime-nicotine mixtures. Owing to cost, a 
number of growers used less material per tree than recommended, with 
the result that seme failures occurred but it gave an excellent opportunity 
to determine the effect of dosage. 
The greatest difficulty, from a biometrical point of view, was the 
limited number of trees upon which data could be secured, owing to 
