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58 FUNGI 



with wart-like excrescences, or quite smooth. This peridium consists of 

 a pseudo-parenchyme of densely compacted hyphce, showing, in the 

 case of Stephensia (Tul.), separate layers. The external cells are denser 

 and thicker-walled than those within, but a gradual transition takes 

 place from one to the other, and again from the latter to the cells com- 

 posing the veins or seams of tissue Avhich traverse the interior and 

 divide the spore-bearing tissue into chambers. The walls of such 

 chambers in (xenabea (Tul.) possess a pseudo-parenchymatous structure 

 like the peridium, but in general such walls consist of a looser tissue. 

 Only by the perishing of this peridium or its rupture by external agencies 

 do the spores escape. 



Certain authors divide the Tuberaceee into two families, the Tiiherece, 

 containing Tuber, with an assemblage of allied genera mentioned below ; 

 and the Elaphomycece^ containing Elaphomyces, Onygena (Pers.), and 

 Penicillium (Link). Though the sporocarps of Elaphomyces and Peni- 

 cillium undoubtedly resemble each other, there is at all events as yet 

 hardly sufficient ground for going so far as to assume for Elaphomyces 

 (or Onygena) the life-history of Penicillium. Onygena again, though 

 it may be placed beside Elaphomyces, is hardly near enough morpho- 

 logically to deserve other than a provisional juxtaposition. 



Of the TiiberecE^ Hydnobolites is the simplest, with asci distributed 

 through the internal tissue, and the peridium represented only by the 

 outer layer of sterile hyphae. Genabea, with a regularly corrugated peri- 

 dium and asci arranged in groups imbedded in tracts of sterile hyphae, 

 forms another type with Terfezia (Tul.), in which the large masses of 

 fertile hyphae are separated by branching white seams of sterile tissue. 

 These sterile tracts or seams proceed inwards from the thick peridium. 

 There is a third type, characterised by a stout peridium enclosing an 

 internal mass consisting of thick plates of tissue, which proceed from 

 the peridium, and are separated by many narrow channels or chambers. 

 The wall of these chambers bears the hymenium. This type includes the 

 remaining genera Tuber (truffles), Balsamia (Vitt.), Choiromyces (Vitt.), 

 Pachyphloeus (Tul.), Stephensia, Hydnocystis (Tul.), Hydnotria (B. and 

 Br.), and Genea (Vitt). 



Elaphomyces has a thick, hard, corky peridium consisting of two 

 distinct but united layers. The external one is thin, and either smooth 

 or warty ; the inner thicker, and composed of a dense plexus of thick- 

 walled hyphae. When ripe the internal substance consists of a dark 

 mass of spores traversed by a delicate cobweb-like capilhtiian which 

 arises from the inner surface of the peridium. Before maturity the asco- 

 genous hyphae may be recognised by their greater diameter than the 

 capillitium-hyphae, but they vanish with the ripening of the spores. 



