8 
these being placed at intervals of about 25 feet on the floor of the 
house. In each receptacle first pour the proper amount of water and 
then the acid. Beginning with the end of the house farthest from the 
exit, drop into each receptacle, in succession, the package of potas- 
sium cyanide, proceeding as quickly as possible toward the exit. 
During the few seconds the operator is in the house after the genera- 
tion of the gas is started, the breath should be held to prevent even 
the least bad effects. Close and lock the door of the house and, after 
three hours, partially ventilate it by opening the ventilators, pre- 
viously arranged for opening from the outside. One ventilator for 
every 25 or 30 feet, opened for ten or fifteen minutes, is sufficient to 
protect the plants from possible bad effects of overexposure to the 
gas. Before inhaling air in the house, however, the ventilation should 
be more thorough, so that no odor of the gas, which is much like that 
of peach pits, can be detected. The morning after the fumigation the 
contents of the receptacles should be buried. 
Time for subsequent fumigations.—A single fumigation, according 
to the directions given above, will destroy practically all of the insects 
except the eggs and some of those in the late pupal stage. Although 
one such treatment might check the insects so that they would not cause 
noticeable damage for weeks, in many cases it would be the part of 
economy to give two more fumigations at times which a knowledge of 
the life history of the white fly indicates would be most advantageous. 
Knowing that the egg and late pupal stage of the insect are not to 
any great extent affected by the treatment recommended, while all the 
other stages may be destroyed, and knowing the duration of each 
stage, we can outline a plan of treatment which will practically eradi- 
cate the pest in the worst-infested greenhouses. Two subsequent 
fumigations two and four weeks, respectively, after the first will sub- 
ject to the gas all of the white flies in the house in stages wherein, 
under ordinary circumstances, they are unable to withstand its destruc- 
tive effects. 
Treatment when the use of hydrocyanic-acid gas is undesirable.— 
Fumigation with tobaceo fumes, made by burning the refuse stems 
and leaves, has no effect on the greenhouse white fly beyond tempo- 
rarily stupefying the adults. The adults may be destroyed, however, 
by vaporizing in the infested house certain tobacco extracts which 
are sold in liquid form. To accomplish this result preliminary tests 
should be made, first using the amount recommended in the directions 
accompanying the preparation. The attempt to control the green- 
house white fly by means of tobacco extracts alone has never, to the 
writer’s knowledge, proven successful, while many cases of failure 
have been reported. The frequent fumigation necessary to control 
the insect when once it has become abundant would be impractical 
and costly. However, in connection with syringing the plants with a 
