IV] 



TUBERALES 



137 



Bucholtz was able to examine, showed a system of internal chambers lined 

 by the hymenium and communi- 

 cating at one or more points with 

 the exterior. As development pro- 

 ceeds these cavities increase in size 

 and the hymenium becomes further 

 convoluted, so that additional cham- 

 bers are formed. 



In Tuber the ascocarp is ir- 

 regularly globose, fleshy or some- 

 times almost woody; internally the 

 walls which divide the gleba are 

 extensively branched, and the free 

 space between them is diminished, 

 so that the layers of the hymenium 

 are brought close together and 

 constitute the fertile "veins." Other 

 "veins," white and sterile, run be- 

 tween the hymenial layers and serve 

 as air chambers (fig. 97). The asci 

 are often globose, and the spores 

 usually four in number, but the 

 number varies, and is sometimes 

 reduced to two or one (fig. 98). 



The development of the fruit 

 has been studied by Bucholtz in Tuber puberulum (fig. 99). The very 

 young ascocarp consists of a mass of hyphae, the outer rather more loosely 

 interwoven than the inner.. Around the lower part a dense basal sheath is 

 differentiated. Soon the first signs of the fertile veins appear as invagina- 

 tions of the upper surface, and internally the loose tissue of the sterile veins 

 becomes recognizable. 



Owing to the rapid growth of the upper portion of the young fruit, the 

 basal sheath is bent backwards, while at various points along the fertile veins 

 the first signs of asci appear. Later the peripheral tissues become thickened, 

 together with the remains of the basal sheath, and form the peridium. This 

 ultimately closes over the points where the fertile veins are in communication 

 with the exterior. Thus the young 'fruit is open at first, the hymenium 

 becomes internal by invagination and the peridium which covers the mature 

 ascocarp is a secondary formation. 



The development of the fructification in Choiromyces macaudriformis 

 approaches that of T. puberulum, but the basal sheath and peridium are 

 less conspicuous. 



Tuber rufutn Pico; section through 

 hymenium ; after Tulasne. 



