CRYPTOGAMS 355 



are of a much more complicated structure than in the Erysipheae. They 

 first appear as spirally -coiled fertile hyphte, which soon become enveloped by 

 other sterile hyphse (Fig. 275, A, B), Entirely enclosed by a tissue of pseudo- 

 pareuchyma, tho ascogenous hypha gives rise to branches penetrating the perithecial 

 envelope and producing numerous asci containing eight small round spores (G). 

 In the ripe ascus- fruit the walls of the tubes become disorganised and also the 

 investing pseudo-parenchyma, except the outermost layer, which, by suddenly 

 bursting, releases the spores. 



3. The Tuberaccae or Truffle Fungi are saprophytic Ascomycetes whose mycelium 

 is entirely subterranean, ramifying in humus soil, particularly in woods under 

 decaying leaves. They belong to the Fungi which give rise to the formations 

 known as Mycorrhiza (p. 210). The ascus fructifications familiar under the name 

 of truffles are underground tuberous bodies (Fig. 277), consisting of a thick, 

 investing, cortical layer of pseudo-parenchyma enclosing an inner mass of looser 

 hyphal tissue. The internal tissue is traversed by air-passages (d) and pervaded 

 by anastomosing veins of more compactly united hyphae (c), in consequence of 

 which it has a marbled or veined appearance in cross-sections. 



The club-shaped asci are disposed in nest-like groups (Fig. 277, 2) throughout 

 the interior of the tuberous fructifications, or they form a hymenial layer coating 

 the walls of narrow, winding chambers. The asci contain only a small number 

 of spores ; in the case of the true truffles (genus Tuber) they are usually only four 

 in number, and generally have a spinous or reticulately-thickened epispore. When 

 the fructifications are fully mature, the sterile tissue in the interior and also the 

 walls of the asci disappear, leaving the ripe spores enveloped only by the outer 

 cortical layer. 



The fructifications of many of the Tuberaceae are edible, and have an aromatic 

 odour and taste. They are, for the most part, obtained from France and Italy, and 

 from the neighbourhood of the Rhine, where they are regularly collected on account 

 of their commercial value as articles of food. Of the edible varieties, the most 

 important are the so-called black truffles belonging to the genus Tuber, viz. 

 Tuber brumale, melanosporum, aestivum, mesentericum. The fructifications of 

 these species have a warty cortex of a black, reddish-brown, or dark brown colour ; 

 the two first named frequently attain the size of a man's fist, and often weigh over 

 two pounds. The white truffle, Choiromyces meandriformis, which is also edible 

 and resembles a potato in form and size, is light brown externally, but in the 

 interior is white with yellowish veins. The fructifications of Tuber rufum, which 

 are about as large as a walnut, and have a leathery cortex enclosing a hard internal 

 substance, are not edible, nor are those of Elaphomyces granulatus, the Stag- 

 truffle, whose yellowish-brown cortical layer is hard and woody or corky. 



Order 3. Pyrenomycetes 



The Pyrenomycetes comprise an exceedingly varied group of Fungi, some of 

 which are parasitic upon different portions of plants, particularly on the 

 cortex and leaves, and others are saprophytic upon decaying wood, dung, etc., 

 while a few genera occur as parasites upon the larvee of insects. The flask-shaped 

 fructifications or perithecia are characteristic of this order. The perithecia are 

 open at the top, and are covered inside, at the base, with a hymenial layer of asci 

 and hair-like paraphyses (Fig. 278). The lateral walls are coated with similar 

 hyphal hairs, the paraphyses. The spores escape from the perithecia through the 

 aperture. In this process one ascus after another elongates in consequence of the 



