INSECTS AND DISEASES 47 
mixture, thereby making a compound insecticide 
and fungicide. 
The grape is sometimes subject to special 
insect troubles. The European species (Vitis 
vinifera) is liable to attacks by the dreaded 
phylloxera, both outdoors and in the greenhouse. 
This insect first infests the roots, at which time 
we should take steps against it; then it spreads 
to the stem and leaves. There are adherents 
of two methods for destroying it. First, we can 
remove most of the soil from the bed and flood 
the roots of the vines, drowning the insects. Or, 
we can place at six-foot intervals over the border, 
saucers containing a little carbon bisulphide, 
which, being a volatile liquid, heavier than the 
atmosphere, will flow out over the edge of the 
dishes and sink into the soil, killing the pest. 
Probably the former is the safer plan, for the 
carbon bisulphide is extremely inflammable and 
must be handled with caution, entirely away 
from all fire. 
The other vines, valuable-for their edible prod- 
ucts, described in Chapter XIX, have insects 
partial to each one of them. Tomatoes are 
bothered by the potato beetle, which may be 
exterminated by the use of arsenical poisons. 
By the time the fruit begins to swell, the beetle 
