IV] 



DISCOMYCETES 



97 



may, by invagination of the fertile surface, have produced the closed fruit 

 of the truffles. The simpler Tuberales may have had a similar origin, or 

 may have arisen direct from a pezizaceous 

 form, such as Sepultaria, with which Genea 

 has several points in common. 



It is not impossible that theRhiziita group, 

 by the development of a sterile stalk, has also 

 produced the Helvellaceae and it may be the 

 Geoglossaceae as well. But the latter family, 

 because of the characteristic method of dehis- 

 cence of its ascus (by the ejection of a plug 

 of wall material), has sometimes been looked 

 upon as related to the Helotiaceae and their 

 allies which show a similar dehiscence. 



Massee has developed a theory that forms 

 with large, coloured, and elaborately sculp- 

 tured spores, tend to be primitive. He thus 

 regards the Tuberaceae and Geoglossaceae 

 as ancient groups from both of which pezi- 

 zaceous forms have sprung. 



Bucholtz's work on the development of 

 Tuber diminishes the probability that this is 

 a primitive type, or one that has given rise 

 to cup-shaped forms, and it seems easier to 

 think of Genea and its allies as derived from 

 the Pezizales by the diminution in size of 

 the external aperture, the shortening and 

 broadening of the ascus and the increased 

 convolution of the hymenium, than to regard 

 them as giving rise to that group by the 

 contrary changes. It is, however, not impro- 

 bable that the Pezizales are polyphyletic in 

 origin, and that some of them may have been 

 derived from the higher Geoglossaceae. 



So far we have considered mainly the 

 external characters of the fruit and the struc- 

 ture of the ascus, but when we turn to the 

 Pezizales we find a further, and possibly a more valuable, criterion in the 

 structure of the sexual organs. 



The antheridium is known in very few cases. A large, oblong coenocytic 

 cell has been described in Ascodesinis, and a similar, though larger, organ 

 in Pyronema and in Lachliea stercorea, and \ve have also, if its position 



G.-V. / 7 



Fig. 55. Sepultaria coronaria Mass.; 

 uniseriate spores ; ascus opening by 

 a lid ; branched, septate, clavate 

 paraphyses ; x 600. 



