I IO 



ASCOMYCETES AND RHODOPHYCE^. 



vegetative nuclei, while that of the antheridium is correspondingly 

 smaller. 



The cell- walls between the antheridium and oogonium are dissolved, 

 the male nucleus passes through the opening thus formed into the 

 oogonium, 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 



,-UnM 



Ue^affir 



G 



FIG. 40. Development of ascogonium of Sphcerotkeca 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 Rhodophycecz 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 



