SEXUAL REPRODUCTION 85 



In Erysiphe, a genus allied to Sphaerotheca^ the process 

 is more complicated. The nucleus resulting from the 

 fusion of the male and female nuclei in the oogonium 

 undergoes repeated division at once until five to eight 

 nuclei are present in the oogonium, which in the meantime 

 has increased in length and become somewhat curved. 

 Then, as in Sphacrotheca, the oogonium develops into a row 

 of cells, each of which contains a single nucleus, except 

 the second from the apex or the penultimate cell, which 

 contains more than one nucleus. This cell becomes the 

 ascogonium, and gives off from all parts of its surface 

 ascogenous hyphae. These hyphae become divided by 

 cross- walls into two or three cells ; one of these cells, 

 always an intercalary one, contains two nuclei and grows 

 into an ascus. Five to eight asci become fully developed. 

 The two nuclei in the cell forming an ascus fuse and form 

 a fusion-nucleus, which again divides to form the nuclei of 

 the ascospores. 



In Pyronema confluens, also one of the Ascomycetes, 

 investigated by Harper, the sexual apparatus is exception- 

 ally large and conspicuous. The cells of the vegetative 

 mycelium are multinucleate, as are also the antheridia and 

 archegonia, which originate as in Sphaerotheca and Erysiphe. 

 A small papilla soon appears at the apex of the oogonium, 

 which grows into a long conjugating-tube or trichogyne. 

 The trichogyne, like the oogonium, contains many nuclei, 

 and, when fully developed, is cut off from the oogonium by 

 a cross-wall, but before conjugation with the antheridium 

 takes place, this cross-wall is dissolved ; the nuclei in the 

 trichogyne also undergo disintegration. A pore is formed 

 at the point where the trichogyne and antheridium touch, 

 and the nuclei and some of the cytoplasm of the antheridium 



