TRUFFLE, the name of several kinds of subterranean fungi of the family Ascomycetes. (See FUNGI..) Truffles have been famous for their esculent qualities from classical times. Several were recognized by the ancient Greeks and Romans ; Theo phrastus (c. 30o "Lc.) gives one of them a name which apparently refers to a common belief that truffles were produced by thunder. Pliny thought that they were amongst the most wonderful of all things in springing up and living without a root. There are numerous references to truffles in classical writings and Coelius Apicius gives six recipes for cooking them.
The subterranean Ascomycetes are usually placed in two main groups, the Tuberales and the Plectascales, depending upon the possession of fruit-bodies with or without an opening to the ex terior during development. The suggestion is that these have arisen along parallel lines. A point of interest is that we also have subterranean forms of similar external appearance in Phycomy cetes and Basidiomycetes.
The best-known genus of the Tuberales is Tuber, which is mainly native to temperate regions. The different species range in size from that of a pea to that of an orange. A section of a young specimen shows a whitish homogeneous flesh which, as maturity is approached, becomes a rich dark colour showing a lighter "marbling." Microscopical examination reveals that the trama plates bearing the hymenium are thrown into elaborate folds (venae interne) whereas other plates of tissue which are light-coloured, sterile and joined either directly or indirectly to the exterior run between them (venae externem). This compli cated arrangement is reached by a series of advances which may be traced in the allied genera. The spores of Tuber are large and are usually not more than four in an ascus ; in the same fruit-body a range from one to f our may usually be seen. These were the first ascospores to be observed ; Tournefort described them in 1710--11 and Micheli figured them in 1729. It was a common belief that they became truffles merely by enlargement, though fermentation of the earth, exudations of branches and leaves, excretion of roots, gall production by insects were frequently regarded as reasonable explanations of their formation. Truffles principally occur in open woodland on calcareous soil, being rare in or absent from sandy soil and pastures. They are usually associated with the roots of trees and are possibly mycorrhizal fungi.
The most valued truffle in French cookery is the Perigord truffle (T. melanosporum) which is said to have first gained favour towards the end of the 15th century. It is brownish black, roundish and covered with polygonal warts having a depression at their summit; the flesh (gleba) is first white, then brownish grey, and when mature becomes violaceous black, with white veins having a brown margin. The odour is well-marked and not un
pleasant. The main French truffieres are in Perigord and the Department of Vaucluse, though truffles are gathered throughout a large part of France. The truffle industry is an important one and about one-third of the gatherings are now exported ; foreign trade began seriously about a century ago and before the World War reached to as much as £3,000,000 annually. As the truffles often occur at the depth of a foot it is difficult to detect them unaided. Truffles, when occurring near the surface of the ground, crack it as they reach full size and experienced gatherers are thereby enabled to locate them. Further, many species of fly live on truffles and in the morning and evening columns of small yellow flies (Helomiza lineata, etc.) may be seen hovering over the place where truffles are present.
Occasionally man is sufficiently "susceptible" to the scent of truffles to be able to locate them. Several kinds of animals, how ever, recognize the scent without difficulty. Truffle hunting is therefore carried on with their aid ; pigs and dogs being generally used, though goats are said to be so trained in Sardinia.
The truffle industry has proved so profitable in France that the government has taken in hand the reforesting of many large and barren areas, for many of the best truffle regions have become productive by the private planting of the appropriate trees. These are oaks (Quercus coccifera, Q. Ilex with admixture of Q. robur, Q. sessiliflora and hazel) ; "si voulez des truffes, semez des glands" is an adage which has been handed on for generations. Direct attempts at cultivation have so far proved unsatisfactory. Calcareous ground is dug over and acorns or seedlings planted. Soil from truffle areas is usually spread about and the ground is kept in condition by light ploughing and harrowing. After three years clearings are made and the trees are pruned. Truffles if they are to appear do so only after five years or so ; gathering begins then but it hardly pays until after from eight to ten years. The yield is at its maximum from five to twenty-five years later. Tuber melanosporum has not been recorded for England.
The English truffle is T. aestivum which is found principally in beech woods. It is bluish black, roundish and covered with coarse polygonal warts ; the gleba is white when immature, then ochrace ous and finally brownish with whitish, branched, labyrinthine markings. It was formerly hunted on the south downs by the aid of mongrel terriers and was sold in Covent Garden. (J. Rm.) •