84 TEXT-BOOK OF^FUNGI 



and at an early period of development, both are cut off 

 from their supporting hyphae by a cross-wall. When the 

 oogonium is fully developed, the antheridial branch, which 

 is closely applied to the wall of the oogonium, increases in 

 length and its nucleus divides. One of the daughter- 

 nuclei passes to the tip of the antheridial branch, which is 

 cut off from the lower portion by a cross-wall, and con- 

 stitutes the antheridium. By increase in length of the 

 lower portion of the antheridial branch, the antheridium 

 comes to rest on the apex of the oogonium. At this stage 

 of development the nucleus of the oogonium is larger than 

 the vegetative nuclei, and that of the antheridium smaller. 

 The walls of antheridium and oogonium are dissolved at 

 the point of contact, and the male nucleus passes into the 

 oogonium and fuses with the female nucleus. After this 

 fusion or fertilisation the opening into the oogonium closes 

 by the formation of a new wall. After fertilisation nuclear 

 division and cell-formation commence in the oogonium, 

 resulting in the formation of a row consisting of five or six 

 cells. When this is completed the second cell from the 

 apex contains two nuclei, the other cells one nucleus each. 

 The cell containing two nuclei forms the ascus. At a later 

 stage the two nuclei present in the ascogenous cell fuse. 



This fusion of the two nuclei in the ascogenous cell is 

 considered by Dangeard as constituting true sexual fertilisa- 

 tion. 



It is important to note that after fertilisation a portion 

 of the protoplasm of the oogonium does not separate from 

 the wall and form a distinct cell round which a wall is 

 formed, as in in the Phycomycetes. In this particular 

 Sphaerotheca and other Ascornycetes agree with the 

 Florideae. 



