INSECTICIDES, PREVENTIVES, AND MACHINERY. 441 



sirable, because they shelter rather than repel insects, and the 

 water falling upon them takes out the nicotine too slowly. An 

 extract may be made by boiling chopped stems and other refuse 

 until one pound of tobacco is completely extracted in one gallon 

 of water. This extract is effective against most plant-lice and leaf- 

 hoppers, and against soft-bodied insects generally ; it is also an 

 almost perfect protection against flea-beetles, and will kill many 

 of the smaller leaf-feeders. Under ordinary conditions it does 

 no injury to plants, but may spot delicate foliage or flowers. 

 Extracts are now on the market that are condensed to a soft 

 paste, and these, when diluted, are as effective as the boiled ma- 

 terial, and of course much less troublesome to {)repare. As a 

 stomach poison tobacco is not much relied upon in field work, and 

 as a contact poison the soap and petroleum mixtures are cheaper 

 when large quantities are used ; but in the garden and in the 

 conservatory it holds its own. In the greenhouse, tobacco is the 

 main reliance for green fly and many other pests, and fumigation 

 is commonly practiced. Of late, smearing the pipes with the ex- 

 tract to secure the effects of a slow fumigation has l)een much 

 resorted to ; but greenhouse jjlants differ so much in suscepti- 

 bility that it is impossible to prescribe generally ; each case mu«t 

 be worked out by individual experience. Tobacco extract is 

 sometimes added to .stxips and the combination is quite effec- 

 tive, though not enough so to authorize payment of the prices 

 charged for it. 



Lime as a whitewash has been already referred to, and tlie use- 

 fulness of the dry hydrate as a carrier and the method of making 

 it have been described. But this same dry hydrate is in itself use- 

 ful for many purposes. If properly prepared it is yet quite 

 caustic, and each particle of lime needs one more particle of water 

 to complete the change to the carbonate. Applied to any moist, 

 soft-bodied slug or other larva, it gets that extra particle of water, 

 and incidentally burns a hole through the skin of the insect. The 

 larvae of asparagus beetles may be reached by this form of lime 

 better than in any other way ; the fme, feathery foliage offers no 

 hold to insecticides, and stomach poisons are therefore of little 

 use ; but a dusting of the dry lime early in the morning reaches 

 the moist larva-, and few escape a thorough application. Any 

 other soft-bodied, slug-like larvae may be similarly dealt with, 

 when direct poisoning is not feasible. 



