Ilo ASCOMYCETES AND RHODOPHYCE. 
vegetative nuclei, while that of the antheridium is correspondingly 
smaller. . 
The cell-walls between the antheridium and oégonium are dissolved, 
the male nucleus passes through the opening thus formed into the 
oégonium, wanders toward the egg-nucleus, and soon fuses with it 
(Fig. 39, C). After the entrance of the male nucleus the antheridium 
still remains filled with cytoplasm which is in direct communication 
with the cytoplasm of the oogonium. Very soon, however, the open- 
ing between the two organs is closed by a new wall, when only a 
small quantity of cytoplasm is to be seen in the antheridium. 
Immediately after fecundation the oogonium begins a steady growth. 
The egg-cell does not round off by means of self-plasmolysis either 
before or after fecundation, thereby becoming separated from the 
Fic. 40.—Development of ascogonium of Sphaerotheca castagni.—(After Harper.) 
F, ascogonium with two cells; upper cell has two nuclei. 
G, mature ascogonium ; the penultimate, or ascogenous cell, contains two nuclei. 
H, the two nuclei in the young ascus have fused, fusion nucleus containing two nucleoli. 
wall of the oogonium. In this respect the Ascomycetes differ from 
all other plants except the Rhodophycee with which they form a 
striking parallel. 
A few steps further in the development of the fecundated egg will 
be traced to show the relation in the course of development of the 
fusion of the sexual nuclei to the vegetative nuclear fusion occurring 
in the young ascus. In speaking of this part of the development the 
term ascogonium will be used. 
A series of nuclear and cell-divisions now follow in the developing 
ascogonium, so that ultimately a row of five or six broad cells result 
(Fig. 39, D, E, and Fig. 40, F, G). Nuclear and cell-division are 
not dependent upon each other, and they do not seem to follow in the 
same order. In different stages of this growth, from one to three 
nuclei are to be seen in the distal cell of the ascogonium, but when the 
definite number of cells is formed two nuclei are always to be found 
