The chemical 2,4-D is one of the so-called "plant hormones," or "growth regulators." In minute quantities it stimulates some of the plant functions, but in slightly larger dosage it is toxic. A solution consisting of one-seventh ounce in 1 gallon of water sprayed on poison-ivy foliage kills all leaves hit and may kill the roots. In the concentration used in weed killing 2,4-D is not believed to be harmful to animal life, but until this point can be thoroughly clarified the chemical should be used with reasonable caution to avoid poisoning. 2,4-D is not flammable and is not corrosive to spray machinery. If the sprayer is used also for insecticides and fungicides it must be washed very thoroughly to remove the slightest trace of the 2,4-D. This is very difficult, however; it is safer to use another sprayer. To make a spray solution 2,4-D must be combined with other chemicals, as it is not soluble in water. A number of substances, including polyethelene glycols and naphthenic soaps, have been used for this purpose, but the best solvent has not yet been determined. Commercial weed killers containing 2,4-D are of varying composition. =Ammonium thiocyanate.=--This byproduct of the coal-gas industry is one of the newer herbicides. The crude commercial chemical is a pink or reddish salt, very soluble in water. It does not keep well, tends to disintegrate into a red, sludgy mass, and is difficult and disagreeable to handle. A purer form in clean white crystals is available and is well worth the slight extra cost. In either form ammonium thiocyanate is injurious to the skin and to leather articles, and in time it corrodes metals. The spray solution is made by dissolving 1 to 1½ pounds of ammonium thiocyanate in 1 gallon of water. Most annual, plants and some perennials are killed by a single application of ammonium thiocyanate. Poison-ivy usually requires three or four treatments. Ammonium thiocyanate has a high content of nitrogen, much of which remains in the soil and eventually becomes a fertilizer. Thus an area treated with this chemical is likely to produce a profuse growth of annual weeds a month or two after treatment. =Borax.=--Common borax scattered on the soil is deadly to the roots of many plants. Spread dry at the rate of 10 to 15 pounds per square rod, it kills poison-ivy slowly over a period of 6 to 8 weeks. A second somewhat lighter treatment 3 to 5 months later is usually necessary to kill all plants completely. Borax is easy to handle, nonpoisonous, and nonflammable, readily obtainable, and not expensive. It is one of the best chemicals to use around stone walls, rocky ledges, fences, and other inaccessible places.