Various appliances are now available for keepingconstantly moist and cool by automatically spraying them with water at fairly frequent intervals. Broadly these devices may be divided into two Types: those that are controlled by the actual rate of water evaporation and those that work on a simple time basis. Rate of evaporation may be determined by electrical contacts placed in the bed. As long as these contacts remain moist current flows between them. As soon as they become dry the flow of current ceases and a sensitive electronic control unit switches on more powerful current which operates a solenoid valve which itself turns on the water supply to the misting jets. These wet and electric contacts alike so that after a few seconds current flows between the contacts, the electronic control unit switches off the current to the solenoid valve and the water ceases to flow.
Time switches can as a rule be set to give any sequence of stop and flow desired but are not sensitive to changing conditions of evaporation. A third alternative is a device which measures the amount of light reaching the cuttings and controls the frequency of mist bursts accordingly. Other devices work purely mechanically, as by water dripping into a little ‘bucket’ which, when full, tips a valve to start the water flow and at the same time empty itself; or a tiny piece of sponge on the arm of a balance which, when dry, allows it to rise and turn on the water.
Mistis most satisfactory in spring and summer. The cuttings are not kept close, as they are in a normal propagating frame, but are usually rooted on the floor or staging of a . Coarse sand and peat is the most satisfactory rooting medium and the best results are obtained when this is warmed to about 65°-70° F. from below as, for example, with an electrical soil-warming cable. Cuttings should be removed to ordinary or soil, sand and peat as soon as they are rooted.