INSECT ENEMIES AND THEIR CONTROL 115 
of each triangle may be ascertained by multiplying the height 
of the perpendicular side of the triangle by the length of the 
base line and that product by the length of the house. This 
total divided by two will give the capacity of the triangle. If 
the eaves are not on a level, the space may be divided into 
rectangles and triangles and the cubic contents of the house 
calculated similarly to the foregoing method. 
Miscellaneous insecticides, in addition to those pre- 
viously described in this chapter, are sometimes em- 
ployed in the treatment of greenhouse vegetable crops. 
Kerosene emulsion is a 
standard spray for the 
control of aphids, 
though the liquid to- 
bacco preparations are 
generally preferred for 
use in the greenhouse. 
Arsenate of lead, when 
an arsenical poison is 
needed, is most satis- 
factory for greenhouse 
purposes. Various 
soaps and soap prep- 
arations, some of them 
proprietary, are useful 
in checking the ravages 
of certain insect pests. 
It will seldom be nec- 
essary, however, to use Fig. 37.—Galls on cucumber roots produced 
5 by nematodes. 
any of these materials 
if the major treatments previously described are thorough 
and timely. 
The spraying apparatus for greenhouse use should be 
light and convenient to operate. The various forms of 
knapsack sprayers are sometimes employed. Automatic 
tank pressure sprayers are becoming popular. Some 
growers prefer.bucket pumps, but they are not the most 
