While the spring frosts are injurious to the grapes, winter frosts are on the other hand most beneficial, if not necessary to a continued raisin cult. The raisin grape must have a season of recuperation, and winter frost is the only climatic phenomenon which, without injury to the vine, can procure it that rest which is so necessary for all deciduous trees, by nature destined to enjoy alternate periods of growth and sleep. The absence of frost causes the sap of the vine to circulate more or less in the wood, and the vine never ceases to grow. This is one of the reasons why our deciduous vines do not succeed well in the tropics, where there are no cold seasons to cause the leaves to fall and the sap to become dormant. In the tropics, therefore, our deciduous vines keep on growing, set little or no fruit, and prove unprofitable. This phenomenon is shared there with other trees, and peaches, pears and apples act in the same manner. They all appear to need the rest afforded them by the winter frosts. It is also a question of very great importance, whether the continued and unnatural activity of the vine, at a time when it should be dormant, does not invite diseases of various kinds, which find the exhausted vines unfit to withstand their ravages. It may be possible that _mal nero_, the vine plague and other similar and as yet insufficiently understood diseases, are especially destructive to vines growing in frost-free climates, while in colder climates they make but little headway, the vines as it were being protected by the heavy frosts, which either kill the enemies of the vine or enable the latter to gather the necessary strength to battle with them through the growing season. There can be little doubt that at present the healthiest vineyards are those growing in countries where winter frosts are severe, but on the other hand we know that grapevines have been growing for ages in temperate climates, where the frosts, even if not entirely unknown, are still of very rare occurrence.