FUMIGATION OF ORNAMENTAL GREENHOUSE PLANTS. 9 
conducted where the plants, beds, and walks were thoroughly soaked 
with water, and the injury which would be expected under normal 
conditions to such plants as cosmos, rose geraniums, roses, helio- 
tropes, and Asparagus plumosus did not appear, nor were such in- 
sects as aphids and thrips appreciably affected. It is obvious, there- 
fore, that in order to increase the effectiveness of the fumigation the 
plants should be syringed not less than four or five hours prior to the 
liberation of the gas, to avoid undue absorption of the gas by the 
water on the benches and walks. 
The difference in the results noted above may be accounted for by 
the fact that in the case of box fumigation only the foliage was cov- 
ered with a film of water, whereas in the case of the greenhouse ex- 
periments not only the foliage of the plants was covered with a film 
of water but the entire soil surface of the house was soaked, and the 
water undoubtedly absorbed much of the available gas, reducing the 
toxic effect of the gas on the plants and insects. 
HUMIDITY. 
Recent tests have demonstrated that a relatively high humidity 
(98 to 100), with temperature varying from 70° to 75° F., greatly 
increases the amount of injury to the foliage of the plants, whereas 
plants in the presence of a relatively high humidity (98 to 100), with 
a temperature of 60° to 65° F., do not exhibit injury in excess of that 
which would appear if the plants were fumigated with an excessive 
dosage under normal atmospheric conditions. It is apparent, there- 
fore, that a relatively high humidity alone is not responsible for 
injury unless accompanied by temperatures exceeding 70° F. 
: ADVISABILITY OF A FUMIGATION BOX. 
A fumigation box is desirable for two reasons, namely, for testing 
the amount of gas plants can stand without injury, and for ridding 
a limited number of potted plants of insects, and thus avoiding costly 
and laborious hand scrubbing of such plants. The size of the box will 
depend on the use to which it is to be put. A box with a capacity 
of 200 cubic feet can be used advantageously for nursery stock, 
palms, etc. 
Plants to be fumigated in a box in the daytime eheula remain in 
the box with the door closed at least one.hour before the gas is gen- 
erated and should be shaded from the bright sunlight for at least 
two hours after the completion of the exposure. 
HOW INSECTS ARE DISSEMINATED FROM HOUSE TO HOUSE. 
Doubtless many houses become infested with insects through the 
agency of plants commonly referred to as “ boarders.” The practice 
of turning over home-grown plants to a florist to care for during the 
71777°— Bull. 518—17——2 
