154 Princrples of Plant Culture. 
volatile. In purchasing, only fresh samples should be ac- 
cepted. If fresh and pure, these powders produce a ting- 
ling sensation when applied to the nostrils. 
292. Tobacco Smoke is much used for destroying 
“lice” or “green fly’ (aphide) on plants under glass. For 
this purpose, the partially-dry stems or leaves are burned 
upon pans or bricks, or in small, sheet-iron stoves. Many 
delicate flowers are, however, injured by tobacco smoke. 
Stems or leaves of tobacco, strewn abundantly beneath 
greenhouse benches, tend to prevent the multiplication of 
aphide. 
Several semifluid extracts of tobacco are sold which may 
be evaporated in the greenhouse, over an oil stove, or pre- 
ferably by steam under pressure. Some of these are very 
efficient for destroying insects, and do not injure flowers. 
293. A Strong Decoction of Tobacco is often used for 
destroying aphid on plants in rooms where tobacco smoke 
would be objectionable. The plants are immersed in, or 
washed with the decoction. The same is often effectually 
used on young plants of cabbage, cauliflower and turnip, to 
prevent their destruction by the flea beetle.* 
294, Kerosene is a very useful insecticide for a class 
of insects not readily destroyed by other means (316). It 
has generally been used as an emulsion made with soap and 
water, for which the following formulas are good. 
a — Dissolve one quart of soft soap in two quarts of boil- 
ing water; remove from the fire, and add at once one pint 
of kerosene. Agitate violently in a closed tin can for three 
minutes or pump the mixture while still hot through a force 
pump. For use, dilute with an equal quantity of water; or 
« Phyllotreta vittata. 
