But the best preventive is, first, to prune carefully, so as to give free access to light and air in all parts of the tree; then to rub energetically the trunk and largest branches with lime-water, or with the whale oil and sulphur preparation, and these enemies will be kept at bay; only a small portion of them, if any, will survive, to become the prey of their own enemies, which nature provides to finish the work of man, that is: of the man who knows how to help himself.
In Europe, says Du Breuil, the most dangerous enemy of the olive tree is the excessive cold of certain winters, when the thermometer runs down as low as 12° and 10° Fahr.
Looking back over a century, it has been found that the olive trees have been frozen, on an average, every nine or ten years. Among the winters most disastrous to them were those of 1740, 1745, 1749, 1766, 1770, 1789, 1795, 1811, 1820, 1830, 1837, 1843, 1859 and 1866. No more recent data is at hand.
Is it, then, surprising that this culture rather tends to decrease than to increase in the best oil regions of Europe, and that they should raise the olive tree mostly from the seed? It is true that it can thus cope more successfully against those severe winters which come at frequent intervals; but the period of bearing is considerably delayed thereby. It is for such reasons as these that many European agriculturists are deterred from engaging in this culture, the result being that
