306 Wisconsin Academy of Sciences, Arts, and Letters. 
Three successive nuclear divisions of the primary ascus nucleus 
result in the formation of the eight nuclei of the spores. 
The sex organs of Erysiphe communis, according to a later paper 
by Harper (1896), are borne on different hyphae, and the uninu¬ 
cleate oogonium is separated from the mycelium by a basal cell. 
The uninucleate antheridium is similar, but smaller and also has a 
basal cell. The nucleus of the antheridium divides and a wall is 
laid down between the daughter nuclei. The nucleus of the end 
cell of the antheridium passes into the oogonium through a pore 
formed by the dissolution of the cell wall at the point of contact 
between the two sex organs. The sterile hyphae arise from the 
stalk cell of the oogonium. The nucleus of the oogonium, formed 
by the fusion of the egg and the male nucleus, then divides. The 
daughter nuclei immediately divide again. The oogonium elon¬ 
gates and walls are formed between the nuclei, giving rise to a 
chain of five to seven cells. The chain of cells so formed is crooked 
and the penultimate cell has two nuclei and from this cell the 
ascogenous hyphae arise. The ascogenous hyphae branch, each 
branch forming two or three cells. One large intercalary cell in 
each branch has two nuclei; the two nuclei of this cell fuse and 
then the cell develops into an ascus. The remaining cells of the 
ascogenous hyphae degenerate. 
The cells of the ascogonium of Ascoholus furfuraceus according 
to Harper (1896) are uninucleate in the early stages, but later 
seem to be connected by openings in the walls between them. The 
ascogonium becomes a bow-like row of cells. The nuclei in each 
cell divide many times. The fourth cell from the apical end of the 
ascogonium is the largest and from it ascogenous hyphae arise. 
The nuclei of the adjacent cells flow into the ascogenous hyphae 
and the empty ascogonium disintegrates. The nuclei gather at the 
tip of the ascogenous hyphae. The ascogenous hyphae branch, and 
nuclei pass into the branches which are then separated from the 
ascogenous hyphae by walls, thereby making the cells so cut off 
ascus mother cells from which asci arise. 
In 1897 Harper described in detail the cytological phenomena 
connected with ascus development and spore formation in Erysiphe 
communis, Peziza stevensoniana and Ascoholus furfuraceus. Fusion 
of two nuclei to form the primary ascus nucleus takes place. The 
process is eventually the same in the three organisms. Harper 
does not regard the fusion in the ascus as sexual, for in Ascoholus 
furfuraceus cases occur of four nuclei fusing to form the ascus 
