Regarding the first method, that of covers, it may be said that the practice goes back to the early husbandmen; but only in the last few years has the true function of the cover been properly interpreted and we are still far from obtaining maximum efficiency. Nor is there yet a suitable, scientific cover available. Any medium that interferes with loss of heat through free radiation before and after sunset is a cover. The best type of cover is a cloud; and clouds, whether high or low, are good frost protectors. On cloudy nights there is little likelihood of frost; and when we can bring about the formation of a layer of condensed water vapor we can practically eliminate frost. We have mentioned above the fact that the earth radiates the heat it has received not in the same but in longer wave-lengths perhaps three times as long. These are easily trapped and held by the vapor of water. Furthermore, the rate of radiation is a function of the absolute temperature and so the rapidity of loss depends somewhat upon the heat received. Therefore the cover should be used as early in the afternoon as possible, that is just before sunset. Aside from the water cover or vapor cover there are cheap cloth screens, fiber screens and in some places lath screens. The second method, that of direct heating, has met with much success in the orange groves of California and elsewhere. Modern heating and covering methods date from experiments begun in 1895. A number of basic patents granted to the writer in this connection have been dedicated to the public. At the present time there are on the market some twenty forms of heaters, which have been described with more or less detail in farm journals and official publications. It is not necessary to refer to them further here. The fuel originally used was wood, straw and coal, but these are now supplanted by crude oil or distillate. It has also been seriously proposed to use electric heaters; also to use gas in the groves. With modern orchard heaters properly installed and handled, there is no difficulty in raising the temperature of even comparatively large tracts five degrees and maintaining a temperature above freezing, thus preventing refrigeration of plant tissue.