ASCOMYCETES 



357 



remain wholly closed. The spores escape from them by the decay or 

 the rupture of the wall by external agencies. The Tuberacese, which 

 possess undoubted asci of peculiar form, are necessarily included 

 among the Ascomycetes, and, since little more is known of them than 

 the structure of the sporocarps, they may be most fittingly dealt 

 with here at the conclusion of the consideration of the mature sporo- 

 carp. 



The formation of ascospores within the asci of Tuderacecs{txuffie{a.mi[y) 

 differs from the typical mode already described. In Tuber (Mich.) the 

 asci are globular, and a differentiation of glycogen from protoplasm takes 

 place, the glycogen forming as it were a layer next the wall. In the proto- 

 plasm cavity, which is separated from the glycogen by a sharply outhned 



Fig. 301. — Tuber ritfmu Pico, a, section seen in reflected light. The white veins, /, contain air, 

 the dark ones, w, fluid ; A, hymenial tisyue. ^, a thinner section seen in transmitted light, lettering 

 as in ffl, white and dark apptarance of veins reversed, (a x 5, ^ x 15.) (After de Bary.) 



layer, the nuclei (4-6 in number) are formed, and young ascospores 

 appear — one or more only, however, developing, while the rest are 

 arrested and ultimately disappear. In Elaphomyces (Nees ab Esenb.) 

 the process is somewhat similar, though here no glycogen is dif- 

 ferentiated. 



The sporocarps of the Tuberacese, which are mostly large subter- 

 ranean bodies, are borne on a fine mycele, usually vanishing at the time 

 of maturity. They are either attached to the mycele only at their bases 

 or are completely invested by it; Very little is known as to the life- 

 history of any of the forms, but the structure of the sporocarps has been 

 accurately and exhaustively detailed. These are enclosed by z. peridium, 

 the outer surface of which is frequently corrugated irregularly (Tuber) 

 or regularly (Hydnobolites, Tul., Genabea, Tul.), sometimes covered 



