INTRODUCTION 205 



ture within which numerous perithecia are imbedded or on which the 

 perithecia are seated, each with a thin outer stromatic layer. The true 

 perithecial wall is colorless or light-colored and is formed from one or 

 more layers of hyphae arising from the supporting cell of the oogone or 

 antherid, producing a hollow structure surrounding the ascogonium and 

 the ascogenous hyphae and the asci which arise from it. 



In the works of the older mycologists other structures were also called 

 perithecia, which they often resemble very greatly. The studies of von 

 Hohnel (1902-1923), Theissen (1913), Nannfeldt (1932), and others have 

 shown that these structures are entirely stromatic, without any true 

 perithecial wall, and with single asci or tufts of asci without paraphyses, 

 arising in cavities of the stroma. Fungi with this type of spore fruit form 

 the group Ascoloculares of Nannfeldt (1932) in contrast to the Asco- 

 hymeniales which produce apothecia or perithecia in the sense indicated 

 above. A third type of ascocarp with perithecium-like structures, usually 

 without any ostiole, and with the asci scattered throughout the interior, 

 neither in tufts nor forming a hymenium, is considered by some my- 

 cologists to be a true perithecium, by others to be of a different nature. 

 Fungi with this type of spore fruit form the Plectascales of Nannfeldt and 

 others. 



What seems to be, in the author's opinion, a rather primitive but 

 characteristic type of sexual reproduction is that described by Higgins 

 (1936) in MycosphaereUa tulipiferae (Schw.) Higgins. In this species, as in 

 other species of the genus studied by the same investigator (1914, 1920, 

 1929), the male gametes are nonmotile, thin-walled sperm cells produced 

 usually by fours within sperm mother-cells in the interior of more or less 

 spherical, hollow spermogonia. The sperms are imbedded in a mucilagi- 

 nous mass and escape through an apical opening in the spermogonium 

 as the mass expands with the absorption of moisture. Within a loose mass 

 of hyphae an archicarp is formed consisting of a spherical or ovoid cell, 

 the oogone, with a single large nucleus, and a trichogyne, extending as a 

 slender hypha several times the length of the oogone. The loose hyphae 

 surrounding the archicarp grow and those at the exterior eventually 

 cohere into a dark-colored, firm outer wall, the interior hyphae forming 

 a pseudoparenchymatous mass of thin-walled colorless cells. In the mean- 

 time one or more sperm cells have adhered to the trichogyne which forms 

 a papilla at whose tip an opening is formed through which the sperm 

 nucleus enters and passes down into the oogone. The male nucleus gradu- 

 ally enlarges as it progresses and eventually the two nuclei are approxi- 

 mately equal in size and side by side in the oogone. The trichogyne dis- 

 integrates, a wall cutting it off from the oogone. The latter enlarges and 

 becomes more or less lobed, the two nuclei in the meantime dividing 

 conjugately many times. From the lobed oogone arise ascogenous hyphae 



