general; but the petroleiun oils are internal insecticides as well. 

 Tobacco decoctions and all dry powders act only when they enter 

 the spiracles and get into the body of the insect. Dry powders are 

 eflfective in proportion to their fineness; coarsely gTound tobacco, 

 for instance, will be absolutely useless, where a sample that is finely 

 ground may be effective. In the one case the particles cannot pene- 

 trate through the spiracles and hence do not affect the insects at all; 

 in the other they get where they can exercise their specific effect 

 and the insects suffer accordingly. In any case thoroughness in 

 application is absolutely demanded. 



Experience has shown that sprays are better than dry powders, 

 as against plant lice, and that the finer and more forcible the spray 

 the better its effect. The cleanest, and on the whole a very satis- 

 factory application on flowering plants, is a tobacco decoction. There 

 are now upon the market several tobacco extracts, which may be 

 diluted with water and applied without further preparation. All 

 these extracts, so far as I have used them, are more or less satisfac- 

 tory: but in every case it is necessary to use them aboiit twice as 

 strong as is recommended on the label. Furthermore, it will be 

 found that not all Mnds of aphides respond equally well. Green lice. 

 in general, succumb more readily than brown or black lice, and some 

 of the very smooth black forms resist so sti-ongly that it is almost 

 impossible to kill them with tobacco alone. Instead of the extract, 

 a tobacco soap may be used, and that is more effective, because it com- 

 bines a clogging with the direct poisoning action. 



Among the soaps tlie whale or fish oil preparations are much the 

 most effective. They usually come in paste form, although some are 

 dried out so as to cut into cakes; but in either case about one pound 

 of the soap in from four to six gallons of water will be satisfac- 

 tory. The tobacco preparations are usually harmless to plants at all 

 strengths. The soap mixtures are caustic and tend to burn or other- 

 wise injure foliage so they must be more carefully used. One pound 

 to four gallons of water is usually harmless to aU but the tenderest 

 of plants: but where there is any doubt, one pound to six gallons 

 should be first tried, and if tliis is not effective -within a day or two, 

 another application should be made, increasing the strength imtil the 

 insects are killed or the plant shows signs of becoming injiu-ed. 



In the garden plant lice are rather easily kept in check by the use 

 of tobacco" or soap mixtures; but in all cases the applications should 



