Frey—Physiology of Venturia Inequalis. 
305 
ascogenous hyphae are outgrowths from a parthenogenetic egg and 
the ascus is the result of this vegetative growth, an organ which has 
no equivalent in the lower fungi. 
Harper (1895) began his studies of the Ascomycetes with Peziza 
stevensonia and Ascoholus furfurmeous and later investigated 
Sphareotheca castagnei. He found that the asci arise from ascoge¬ 
nous hyphae substantially in the manner described by de Bary 
(1865-66), Janzewski (1871), and Kuhlman (1883), and described 
the fusion of two nuclei in the ascus of Peziza stevensonia to form 
the primary ascus nucleus. The fusion nucleus grows and either 
migrates to the periphery or remains in the center of the ascus. He 
followed the processes involved by the three successive divisions of 
the fusion nucleus resulting in the formation of eight nuclei. 
Harper found the chromosome number to be eight and believed 
that in the first division, which differs in appearance from the 
other two, a reduction in the chromosome number occurs. Fur¬ 
ther research indicated that the process of spore formation in 
Ascoholus furfuraceus was similar. 
De Bary had decsribed the formation of the antheridium and the 
ascogonium from the mycelium of Sphaerotheca castagnei. Har¬ 
per (1896) found that the antheridium and ascogonium are pro¬ 
duced on neighboring hyphae. Each sex organ has one nucleus at 
the beginning of development and each cell is cut off from the 
mycelium by a wall. When the ascogonium has completed its de¬ 
velopment the antheridial hypha elongates, its nucleus divides, one 
daughter nucleus passes to the tip of the cell and a partition wall 
is laid down between the two nuclei. The antheridium lies against 
the oogonium, the wall between the two organs is dissolved at the 
point of contact, and the male nucleus pushes through the pore 
and fuses with the egg nucleus. Sterile hyphae grow from the 
female stalk and surround the sex organs after the completion of 
nuclear fusion. Similar hyphae grow from the stalk cell of the 
antheridium; the antheridium itself disintegrates after fertiliza¬ 
tion. 
The nucleus of the ascogone after fusion with the male nucleus 
divides and a wall is laid down which separates the two daughter 
nuclei. The upper cell nucleus divides again and a second wall is 
formed. Five or six uninucleate cells may be formed but the penul¬ 
timate cell is binucleate. The two nuclei of the penultimate cell 
fuse, forming the primary ascus nucleus. Harper holds that this 
fusion is vegetative, the sexual fusion occurring in the ascogonium. 
