ORDER HYSTERIALES 239 



and unite above the latter to form a thick pseudoparenchymatous epi- 

 thecium or "secondary cortex" which is generally not so thick as the 

 "primary cortex" (the excipulum and its outer layers). The folding of 

 the surface of the cavity may lead to the formation of canals leading to 

 enlarged chambers. In some of these the hymenium lines both but in 

 Piersonia and some other genera the asci arise only in the chambers while 

 the canals are lined only with rudimentary paraphyses. With this increas- 

 ing complexity the single external opening is lost and several openings 

 develop at points where the canals converge near the surface. In Tuber 

 the canals are filled at a very early stage by the ingrowing paraphyses 

 and appear as "veins" in the tissue of the sporocarp. The hy menial 

 chambers become obliterated by the ingrowing asci and paraphyses. In 

 this genus the asci are ovoid or spherical and often but few-spored. They 

 do not form a single hymenial layer at maturity but project into the 

 epithecial tissues at various levels. A number of other genera are recog- 

 nized with varying degrees of modification of the foregoing structural 

 types. Of all the species of the order a few species of the genus Tuher 

 (the truffle) are of economic importance. These species, especially T. ■ 

 aestivum Vitt. and T. melanosporum Vitt., occur in the rather open forests 

 of Southern Europe (mainly under species of Quercus), where they are 

 collected by the use of trained animals (dogs or pigs) which find them 

 by their odor. In recent years many species of Tuberales have been dis- 

 covered in the Pacific Coast states where the climate is quite similar to 

 the regions of Europe where they are best known. Miss Gilkey (1939) 

 described and figured nineteen genera and fifty-seven species of North 

 American Tuberales. She included in the Tuberales the genera for- 

 merly placed by Fischer (1896) in the family Terfeziaceae in the Order 

 Aspergillales. (Fig. 84.) 



Order Hysteriales. In this order of plant-inhabiting saprophytes and 

 parasites the apothecia are much reduced in size and compressed later- 

 ally, to elongated, often somewhat boat-shaped, structures, opening by 

 a long narrow slit. They are dark-colored, leathery or hard, and show a 

 strong contrast between the dark-colored excipulum and the light-colored 

 hymenial layer. The latter consists of ovoid to elongated cylindrical asci 

 intermingled with mostly septate paraphyses which are frequently en- 

 larged at the apex or branched, even forming at times a well-marked 

 epithecium. The apothecia may be single or in closely packed groups, 

 superficial or emerging from the substratum. The asci open by a pore, 

 not a lid. The ascospores are of very many different forms, as in the 

 Phacidiaceae, to which this order shows many points of relationship. They 

 are ellipsoid and one-celled, or several-celled, or divided both longi- 

 tudinally and transversely into many cells, or needle-shaped. In color 

 they vary from hyaline to brown. Conidial formation has been reported 



