iQig] ■ STEVENS— PERITHECIA 475 



(tig. i). In young perithecia which do not yet show asci, the 

 whole central portion of the perithecium is filled by the pseudo- 

 parenchyma (fig. 2). It is of interest to know how the asci develop 

 within this structure, but the material did not afford all the evidence 

 desired. The asci, however, are all basal and arise from any part 

 of the base of the perithecium (figs. 3, 4), and since asci of various - 

 ages are seen imbedded in the pseu;ioparenchyma, it is apparent 

 that they grow out into it; and since there is no evidence of 

 crowding exhibited by the pseudoparenchjTna cells near the asci, 

 the asci probably digest the pseudoparenchyma as they grow 

 forward. Indeed the pseudoparenchyma is very tenuous and is 

 probably very easily disposed of. Fig. 4 shows an ascus that has 

 shrunk, leaving a free space between itself and the surrounding 

 pseudoparenchyma. The structure of this perithecium suggests 

 the condition in the perithecium of Penicillium and the Plec- 

 tascineae generally, where the asci are scattered in a pseudo- 

 parenchyma. This case is different, in that the asci in this fungus 

 are not scattered but arise basally. The similarity, however, 

 suggests a relationship between the Plectascineae and the 

 Sphaeriales. 



In the Erysiphaceae the asci develop pari passu with the peri- 

 thecium, and at certain stages may show asci with parenchyma-like 

 cells between them (cf. fig. 30, pi. 2., Harper, R. A., Carnegie 

 Inst. Publ. 37, September, 1905). In certain other fungi the 

 young perithecium is soUd throughout and pseudoparenchymatous; 

 while later the central cells disorganize and a central cavity results. 

 The asci push up into this cavity. Neither of these conditions 

 presents an exact parallel with that of the fungus under consider- 

 ation. A simple rational inference is to regard the case as one 

 of delayed dissolution of the pseudoparenchymatous central region 

 of the developing perithecium. The fact that this structure was 

 not clearly seen without good thin sections raises the question 

 whether similar conditions may not exist in other perithecia, and 

 may have been overlooked because the microtome has not been 

 employed. 



The mycelium of this fungus is interesting on account of its 

 great variation in shape and size (fig. 5). The ostiole is lined by 



