274 COMPARATIVE MORPHOLOGY OF FUNGI 



gyne nuclei takes part in this migration; they appear to have fulfilled 

 their function and soon degenerate together with the trichogyne and 

 antheridium. 



The septa of the ascogonium are successively dissolved. The male 

 nuclei, thus, have unhindered access to the ascogonium itself and fuse with 

 the female nuclei. The middle portion of the ascogonium elongates, 

 assumes an irregular lobate appearance (Fig. 181) and grows in the 

 spring to ascogenous hyphae. 



Meanwhile the wall of the perithecium becomes three- to four-layered. 

 Uninucleate paraphyses grow from the cells of the inner wall layer, sepa- 

 rate the perithecium from the remains of the ascogonium and make space 

 for the penetrating asci (Fig. 182). At maturity, the ascospores may be 

 shot up as much as 1.5 cm. The meaning of this ontogeny will be clear 

 only when more species of the Sphaeriales have been studied cytologically ; 

 still there can be no doubt that the Venturia type is connected directly 

 to that of the Plectascales. 



Gnomoniaceae. — This second family with immersed perithecia in 

 the non-stromatic Sphaeriales has been thoroughly studied in culture by 

 Klebahn (1905 to 1918). Gnomonia veneta (Apiognomonia veneta) on 

 Platanus, causes characteristic brown spots, following the veins of leaves, 

 in spring until the middle of June. About the end of June, the spots 

 develop brown or black, warty acervuli of Gloeosporium nervisequum on the 

 upper surface of the leaf, usually only along the veins. Later the same 

 sort of acervuli erupt from the petiole; as they remain there a long time, 

 covered by the epidermis, the dimensions of their acervuli and conidia 

 are smaller. Therefore they were earlier described as a distinct species, 

 Gloeosporium Platani. 



Besides the brown spots on the leaves, G. nervisequum produces a 

 sudden wilt of the young shoots. Numerous conidial sori, earlier de- 

 scribed as Discula Platani (Myxosporium valsoideum) are formed in the 

 cork tissues with conidia like those of G. nervisequum (Fig. 183, d) ; Kle- 

 bahn proved experimentally their position in this developmental cycle. 

 In late autumn and winter black structures with peculiar conidia arise 

 under the epidermis of the dead leaves, raise and rupture it by their 

 growth (Fig. 183, c) ; this form was originally described as Sporonema 

 Platani and Fusicoccum veronense. When the fallen leaves have over- 

 wintered, the perithecia of Gnomonia veneta are formed. These are 

 nearly spherical with a short beak (a characteristic feature of the Gno- 

 moniaceae, Fig. 183, a). Normally they are completely immersed in the 

 dead leaf tissue with the beak reaching the upper surface of the leaf or 

 projecting slightly above it. The wall consists of about four layers of 

 cells with brown walls. 



The asci are clavate, with a thickened tip provided with a pore. 

 The hyaline, two-celled ascospores germinate in nutritive solutions to a 



