IXSECT/CIDES, PREVENTIVES, AND MACHINERY. 455 



Nurserymen can clear their trees of most of the scale pests by 

 fumigation, and almost all insects, not in the egg stage, may be 

 killed by this process. In the orchard, the Pacific coast horti- 

 culturists have developed a practice that must be described at 

 length to be understood. In the East, fumigation has made little 

 headway, and there is no prospect of great improvement in the 

 near future. In the conservatory or greenhouse. Prof. Johnson's 

 book is a reliable guide ; but practically every kind of plant must 

 be separately studied before the gas can be safely and effectively 

 used. In factories, mills, or houses, when infested by insect pests 

 of any kind, this cyanide fumigation offers the best remedy, pro- 

 vided the inclosures can be made tight and no human beings are 

 exposed to the gas. It must always be remembered that this 

 combination is about the most poisonous mixture that can be 

 generated, and that it requires only a little carelessness to result 

 fatally. 



For some unknown reason, the gas acts more fatally upon 

 insects and less harmfully upon plants in the dark ; hence fumi- 

 gation should be made at night, under black tents or in dark in- 

 closures. Where tents are used to cover trees, or where nursery 

 stock is to be covered in bulk, eight-ounce duck soaked in boiled 

 linseed oil is the best material and most nearly gas-tight. Treat- 

 ments should never be made in the middle of a hot day nor, when 

 it can be avoided, on deciduous trees when in foliage. 



A few words must be said of patented insecticides or mixtures 

 sold under fancy names. In general such should be avoided, 

 for, though some are meritorious, they cost altogether too much. 

 The name has often covered a mere mixture of Paris green and 

 land plaster at druggist's rates, and, practically all of the combi- 

 nations intended to reach chewing insects have an arsenical 

 preparation as a base. It is also advisable to warn against 

 plausible schemes for preventing insect injury — i.e., placing some 

 substance into the body of a tree to be carried into the circulation 

 to repel or kill insects inclined to feed on the foliage. All such 

 preparations heretofore used have been frauds, and in the same 

 category belong those mixtures into which seeds or tubers are 

 to be dipped to prevent the attack of insects on the foliage that 

 comes later. 



