DEVELOPMENT OF THE PERITHECIUM. 21 



in a fashion very difficult to show in even a large drawing. Drawing 

 the successive cells as they appear in one plane, as I have done, results, 

 for example, in causing the second cell of the ascogonium in fig. 27 to 

 appear very short as compared with the first and third. As a matter 

 of fact, however, the second cell is as large as the first, but bulges out 

 on the lower side, as the section lies, so as to appear for the most part 

 in the next section. 



From the outer cells of the perithecium in its basal region hyphse 

 have begun to sprout, which form a sort of secondary mycelium com- 

 parable to the secondary mycelium of many Discomycetes (fig. 27). 

 These hyphas grow out for a considerable distance and become inter- 

 woven with the mycelial hyphse over the stomata. Whether they give 

 rise to internal hyphal branches with haustoria I have been unable to 

 determine with certainty, as they are in no way differentiated from ordi- 

 nary mycelial hyphse in appearance and their course is not easy to trace. 

 There are good reasons, however, for doubting whether they ever pass 

 through the stomata. The latter are crowded full, with all the entering 

 branches which apparently can find room, long before the perithecia 

 are sufficiently developed to give rise to these secondary hyphas. It 

 seems likely that the latter serve merely for the better attachment and 

 support of the developing perithecium. The single stalk-cells of the 

 oogonium and antheridium together certainly seem hardly adequate, 

 from a mechanical point of view, for giving a firm and safe support 

 for the relatively immense fruit body developed on them. In a section 

 such as that shown in fig. 30 the asci seem already to lie at approxi- 

 mately the same level in the ascocarp, and to be for the most part, at 

 least in a horizontal layer slightly above the middle of the perithecium. 

 Close examination and comparison of successive sections show, how- 

 ever, that in reality the individual asci extend to quite unequal levels 

 both toward the base and toward the apex of the perithecium, as would 

 be expected from the irregular course of the ascogenous hyphse from 

 which they arise. At this stage the two nuclei of the young ascus have 

 fused to form the primary ascus-nucleus of De Bary and Strasburger. 

 The process of fusion is described fully below. 



In this stage of the development of the perithecium the old asco- 

 gonium and the sterile cells of the ascogenous hyphae are scarcely rec- 

 ognizable. The asci have grown to be swollen, oblong sacks and are 

 pressed together and flattened upon each other in their middle regions, 

 while the perithecial cells still press in between their ends. The nucleus 

 of each ascus lies in its lower end and below this the ascus is narrowed 

 sharply into a stalk. This stalk-like portion frequently does not lie in 



