CHAPTER XXIII 

 TUBERALES 



In the Tuberales we meet for the third time a hypogaeous develop- 

 mental series. The first group we met in the Endogonaceae among the 

 Zygomycetes; the second in the Terfeziaceae and Elphomycetaceae of 

 the Plectascales ; the third group is related directly to the Pezizales in the 

 Discomycetes. 



In many cases the mycelium surrounds the roots of forest trees and 

 forms mycorrhizas. Their fructifications are connected with this myce- 

 lium over their whole surface or only at their base. Because of their 

 hypogaeous growth, the young stages of these fructifications are little 

 known. In Tuber, the ascogenous hyphae, as in Leotia lubrica of the 

 Geoglossaceae, are present even in the earliest stages and have kept pace 

 with the expansion of the fructification (Bucholtz, 1897). The asci of 

 Tuber brumale var. melanosporum (Dangeard, 1894), T . dryophilum and 

 Hydnobolites (Faull, 1905) arise according to the hook type while those of 

 T. aestivum (Schussnig, 1921), are intercalary, as in the lower Plectascales. 



Similarly, the systematic position of many genera is still uncertain, 

 since only a knowledge of the youngest stages is needed for an interpreta- 

 tion of the mature fructifications. At present, within the order two 

 series, the Hydnotrya-Tuber and the Genea-Genabea series, may be 

 distinguished. 



Hydnotrya of the first series connects directly to the Sphaerosoma and 

 Mycogalopsis of the Pezizales. In some species of Sphaerosoma, the 

 fructifications show a semihypogaeous, tuberous, hollow sphere whose 

 whole exterior is covered by hymenium ; the surface of this hollow sphere 

 is divided by irregular folds into flat warts and grooves. Hydnotrya is 

 thus a Sphaerosoma in which the folds have penetrated still deeper into 

 the fructification, and become passages or canals (Fig. 237,1). The 

 formation of the asci is limited to the walls of these passages, while on 

 the exterior the walls of the hyphal palisade remain sterile and change to 

 a brown rind. Thus, in a cross section through a Hydnotrya fructification 

 one finds outside a thin rind layer of brown swollen hyphal tips which at 

 the entrance of the cavities continue into the paraphyseal palisade. In 

 the interior of the fructification, there is a confused system of canals or 

 passages which generally open outwards at many points, more rarely con- 

 verge to a single point; their wall is covered by a true hymenium com- 

 posed of paraphyses and asci. The asci generally form a layer, as in the 



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