CHAP, V.—COMPARATIVE REVIEW.—ASCOMYCETES.---TUBERACEAE. 195 T 
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.'), 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 aquiféres of Tulasne, venae internae of 
Vittadini), the other white and conveying air (veines aériféres, venae externae). The 
former always originate in the inner surface df 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 i 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. 

' Tulasne, Fungi hypog. tt. XVII, XVIII. 
02 
