are kerosene emulsion and the tobacco preparations. Whale-oil soap is also good. The tobacco may be applied as a spray, or in the house as fumigation; the commercial forms of nicotine are excellent. (See page 194.) Be sure to apply the remedy before the leaves have curled and afford protection for the lice; be sure, also, to hit the underside of the leaves, where the lice usually are. The presence of lice on trees is sometimes first discovered from the honey-dew that drops on walks.
Usually the emulsion is diluted with 10-15 parts of water for plant-lice (see formula, page 194); but some of the species (as the dark brown cherry-leaf louse) require a stronger emulsion, about 6 parts of water.
The lady-birds (one of which is shown in Fig. 234) destroy great numbers of plant-lice, and their presence should therefore be encouraged.