TUBER ALES 



357 



sade tissue. Then follows the ground tissue from which the tramal veins 

 branch. In the course of development, the whole cavity is surrounded by 

 the ground plates and gradually filled by the tramal pads; as these are 

 much twisted and bent, sections of the interior of the fructification show 

 isolated cavities which probably were exposed originally. 



In the mature fructification (Fig. 240, 1), as in Pachyphloeus, one finds 

 without a verrucose rind 1 mm. thick and within a dark-colored flesh, 

 penetrated by both labyrinthiform systems of slender veins; the original 



*0m 





K 





■ Sir 





w 



-J /•' 

 Tr ve 



Fig. 239. — 1. Pachyphloeus melanoxanthus . Section of mature fructification. 2. 

 Pachyphloeus luteus. Section of fructification. 3. Tuber excavatum. Section of young 

 fructification, cavity beginning to fill with loose hyphal tissue. 4. Piersonia bispora. 

 Peripheral portion of immature fructification, tr, tramal plates; ve, venae externae. (3 X 

 26; 4X6; after E. Fischer, 1897, 1908; Bucholtz, 1897.) 



white or reddish venae externae, ochraceous at maturity, and the dark- 

 brown venae internae, often almost obliterated at maturity. In the sub- 

 genus Aschion the venae externae converge toward a point, while in the 

 subgenus EuTuber they radiate toward certain points of the periphery and 

 open outward; in some species this opening is not visible as the venae 

 externae are enclosed at the periphery by a compact hyphal tissue. 



The regular structure of the hymenium which was gradually disap- 

 pearing in Hydnotrya and Pachyphloeus, is entirely lost in Tuber (Fig. 

 240, 2). The asci (ellipsoid or pyriform) lie irregularly imbedded in a 

 tissue between the venae. The spore number has become inconstant 



