Abstract: A device for controlling the incidence of heat and light radiation on a growing area of a greenhouse or the like comprises slats of a non-self-supporting material which are tensioned to hold them in shape. The slats are arranged in parallel side-by-side relationship to cover substantially the whole growing area and can be tilted like Venetian blinds.

Abstract: An improved method of operating a water-vapor generator having a vaporization vessel containing water and provided with heating electrodes therein which are connected to an electric current supply and between which flows an electric current whose magnitude depends on the depth of immersion of the electrodes in the water in the vessel, which method comprises discharging water from the vessel from time in order to reduce the concentration of minerals in the water resulting from vaporization and introducing fresh water into the vessel to replace that which has been evaporated and/or discharged. The method employs the electrode current as a controlled condition for the control of the water supply and discharge valves to the vessel.