356 



COMPARATIVE MORPHOLOGY OF FUNGI 



In the cavities of Pachyphloeus, this secondary tissue has developed 

 to a pseudoparenchyma of looser structure than the ground tissue. In a 

 cross section through a mature fructification it appears penetrated by two 

 sorts of veins (Fig. 239, 1 and 2). One, the so-called tramal plates (gen- 

 erally darker) or venae internae, which arising in the tissue zone lying 

 under the rind, converge toward the top and bear the hy menial palisade 

 on their surface, and the other, venae externae (generally lighter), which 

 begin at the top of the fructification, penetrate its interior and end blindly. 

 Between the two systems of veins there lies a hymenium consisting of 

 parallel paraphyses and asci arranged in a regular palisade with tips 

 directed toward the venae externae. Ontogenetically the venae internae 

 are only the folded parts of the wall of the hollow sphere of the fructifica- 

 tion, such as we have come to know in Hydnotrya, while the venae externae 

 form the originally looser, later pseudoparenchymatous tissue which 





■'ti^'^fi;"^^ ■rwf-y-is ' 



'*'■■;* 



Fig. 238. — Pseudobahamia magnata. Median section of fructification. (X6; after E. 



Fischer, 1908.) 



has arisen by the growth of the paraphyses and secondarily has filled the 

 hollow passages in the interior of the fructification. By these venae 

 externae the fructifications of Pachyphloeus, in contrast to those of 

 Hydnotrya, form a compact mass, though ontogenetically heterogeneous, 

 such as we usually meet in Tuber. 



Apparently in Tuber, the fructifications, as in Hydnotrya and possibly 

 in the above genera, are formed gymnocarpously (Bucholtz, 1897, 1903). 

 Thus, Fig. 239, 3 shows the stage of 1.5 mm. cross section; a flat shell 

 on whose interior project several tramal plates, venae internae. This 

 flat shell is sometimes called ground plate. Apparently it corresponds to 

 the hypothecium of apothecia but is histologically more differentiated 

 and is penetrated- by special wide-lumened hyphal strands of unknown 

 function, frequently called resin canals. Outside, the ground plate is 

 surrounded by a brown pseudoparenchymatous ground tissue, the perid- 

 ium, which, extending beyond the rind, gradually merges with the pali- 



