Cultivation of Truffles.—The truffle may only be grown in the midst of very favorable conditions of climate, altitude, mellowness of the soil, moisture, and proper shade. The planting of truffle trees serves as a vehicle for the spores which are later to give birth to the mycelium which itself produces the truffle. The spores of the truffles usually reach the forests in which they are grown by natural means without being particularly planted. Sometimes, however, the spores are carried directly to the soil where the new crop is to be grown.
Geographic Distribution.—The truffle, like the mushroom, is spread over all parts of the earth. In Europe it is especially abundant in France and Italy. The provinces in France where it grows in greatest abundance are Provence, Dauphiné, Languedoc, and Périgord.
Principal Varieties.—The varieties of truffles are not so numerous as mushrooms, of which perhaps a thousand different varieties are known, but still they are sufficiently numerous. One of those frequently cultivated in France is known as truffles of Périgord (Tuber melanosporum Vittad.). It grows best under the shade of a growing walnut or a young oak. The tubers of these plants, which are the part valuable for food, may weigh from 60 to 500 grams. Other botanical varieties which are much cultivated are Tuber brumale Vittad., Tuber æstivum Mich., Tuber magnatum Vittad., and many others.
Harvesting of Truffles.—The truffle comes into production from the sixth to the tenth year after planting the appropriate forest trees. It is easy to determine the year when the harvest should begin, since during the preceding year there is found in the soil some hypogæan mushrooms which may be considered as precursors of the truffles. Moreover, the soil under the tree becomes practically free of all vegetation. The truffle ripens from November to April, according to its variety. It is important that it should not be harvested except at the period of complete maturity. For harvesting purposes certain animals are made use of, such as the dog and hog. These animals have a delicate smell in these matters and only bring out of the soil the ripe truffles while they leave the others. Man is not able to make this nice distinction, and harvests all indiscriminately, from which there results great financial loss. In the harvesting of truffles the ground should be gone over about once in eight days in order that the tubercles may be secured during the whole winter at the proper time of maturity. When the truffles are developed the soil above them is hilled or cracked, especially after rains. These are the places which are selected for the harvesting when it is done by the hand of man.
Harvesting by Means of Flies.—When the weather is warm and clear there is seen above the place where the tubers are lying, a multitude of flies,—these mark the place where the harvest should be made. The best time for this kind of a harvest is about nine o'clock in the morning. Good results are not obtainable from this sign except when the sun rises clear and becomes
