CHAP. V. COMPARATIVE REVIEW. ASCOMYCETES.TUBERACEAE. 195 



an evident basal portion resting on the mycelium, as in Terfezia and Delastria, 

 or are entirely enveloped when young in the mycelium and are connected with 

 it, as in Tuber, the mycelium disappearing when the sporocarp is mature and 

 leaving it naked and detached in the soil. Its surface, if we disregard the frequently 

 occurring warts and roughnesses, is either smooth and marked only with quite 

 irregular and so to speak accidental large unevennesses, as in Tuber aestivum, 

 T. melanosporum, &c. and in Terfezia, or it shows typical pit-like depressions or narrow 

 deep sinuous furrows, as in Hydnobolites and Genabea. 



The sporocarp in its simplest form, as in Hydnobolites, consists of a fleshy tissue 

 formed of closely woven hyphae, in which numerous asci on the extremities of the 

 branches are everywhere imbedded ; the outermost layer of tissue only forms a kind 

 of wall or peridium, a delicate down composed of sterile hyphae. 



In a second series of forms we can distinguish between a sterile fundamental mass 

 and a large number of groups or nests of fertile tissue, i. e. tissue containing asci im- 

 bedded in it. The fertile tissue is a more or less compact hyphal tissue in which 

 asci springing from the ends of the branches are distributed irregularly and in large 

 numbers. This tissue fills the spaces between the fertile groups in the form of broad 

 bands constituting much the larger part of the sporocarp, as in Genabea, or 

 comparatively narrow plates which show in section as veins with many fine rami- 

 fications, as in Terfezia and Delastria. The sporocarp is surrounded on the outside 

 by a layer of sterile tissue of varying thickness, forming a peridium from which the 

 veins and bands in the interior take their rise ; the hyphae of the fertile groups originate 

 in the adjacent sterile hyphae. 



A third type is represented by the genus Balsamia. The outside of the compound 

 sporophore is a thick perfectly closed peridium, and the interior is divided by means 

 of thick plates of tissue springing from the peridium into many narrowly sinuous air- 

 conducting chambers. The wall of each chamber is covered with a hymenial layer 

 the elements of which are placed at about a right angle to the wall. 



A similar structure is found in the genus Tuber, or at least in several species of that 

 genus in the young state (T. rufum, T. mesentericum, T. excavatum, &c. J ), only the 

 chambers are very narrow and very much coiled and branched. But nevertheless 

 hyphae from the adjacent tissue grow into the cavity of the chambers at an early 

 stage in the development, and fill it quite full with a dense tissue which contains air 

 in its interstices and is therefore white. At the same time the hymenial layer on the 

 walls of the chambers increases considerably in thickness, and assumes the character 

 of a massive irregular tissue which everywhere bears asci. The middle layer of the 

 wall of the chamber retains its original condition in some species. It is these relation- 

 ships which produce the characteristic marbled appearance of a section through a ripe 

 or ripening truffle (Fig. 91), in which two kinds of branched veins run through a 

 dark-coloured fundamental mass, the fertile tissue ; the one kind dark-coloured and 

 therefore less striking to the sight, which answer to the walls of the chambers and 

 contain no air (venae lymphaticae, veines aquiferes of Tulasne, venae internae of 

 Vittadini), the other white" and conveying air (veines ae'riferes, venae externae). The 

 former always originate in the inner surface of the peridium. The latter and probably 

 the previous cavities, which they are formed to fill, extend at certain points to the 

 outer surface of the peridium, and form a kind of opening there to the outside ; this 

 takes place either at spots irregularly distributed over the surface, or in such a way 

 that the veins from all parts unite into a chief trunk with an orifice at a fixed spot 

 in the circumference. In some species of Tuber, T. dryophilum, for instance, and 

 T. rapaeodorum, air-veins only can be distinguished in the fundamental mass, which 

 is traversed uniformly in all parts by asci ; this is the case at least in all the states of 

 development in which they are at present known. 



1 Tulasne, Fungi hypog. tt. XVII, XVIII. 

 O 2 



