The third method, that of utilizing the heat of higher levels by mixing, has not yet been commercially developed; but the methods of applying water, either in the spraying of trees or the running of ditches or the flooding of bogs, together with methods of sanding, cleaning; and draining, have all been proved helpful. Methods available and most effective in one section may not necessarily be effective in another section or with different crop requirements. Certain devices most effective in the groves of California may not answer in Florida or Louisiana because of entirely different weather conditions. In the Gulf coast states where water is available it may be advantageously used to hold back ripening and retard development until after the cold waves of middle and late February have passed, whereas in the west coast sections conditions are very different, water having a definite value and the critical periods coming in late December or early January. In what precedes stress has been laid chiefly upon the fall of temperature and the congelation of the water vapor. There is, however, another important matter connected with injury to plant tissue, and that is the rise in temperature AFTER the frost. A too rapid defrosting may do considerable damage where no damage was originally done by the low temperature. It is in this connection that water may be used to great advantage. Water, water-vapor and ice have, compared with other substances, remarkably high specific heats. If the specific heat under constant pressure of water be taken as unity, that of ice is 0.49; of water-vapor 0.45 and of air 0.24. Or in a general way we may say that water has four times the capacity for heat that air has. Therefore it is apparent that water will serve excellently to prevent rapid change in temperature. This is important at sunrise and shortly after when some portion of the chilled plant tissue may be exposed to a warming sufficient to raise the temperature of the exposed portion ten degrees in an hour. The latent heat of fusion of ice is 79.6 calories and the latent heat of vaporization of water is nearly 600 calories (a gram calorie is the amount of heat that will raise the temperature of a gram of pure water one degree) or in exact terms from 273 degrees A. to 274 degrees A. Therefore in the process of changing from solid to liquid to vapor, as from ice to water to vapor, there is a large amount of heat required. The latent heat serves to prevent fall in temperature and also serves to retard a too rapid rise. This does not mean, as is generally assumed, that the air will be warmed, but it does mean a retardation of temperature change. And it is essential that the restoration of the tissues and juices to their normal state be accomplished gradually, neither too rapidly nor yet too slowly.