208 CLASS ASCOMYCETEAE 



trichogyne and the antherid (which he considers to be a degenerate struc- 

 ture and calls the trophogone), and the nuclei in the antherid and tricho- 

 gyne disintegrate in situ, the oogone nuclei then arranging themselves in 

 pairs. Following this stage all agree that soon 10 to 20 buds appear on 

 the surface of the oogone and elongate to become ascogenous hyphae into 

 which the diploid zygote nuclei or the pairs of haploid nuclei pass until 

 many nuclei are present in each hypha. The nuclei probably divide in the 

 oogone as some of them do in the ascogenous hyphae. The latter elongate, 

 forking somewhat. Eventually septa are formed, producing cells that are 

 plurinucleate toward the base of the hypha and fewer nucleate toward 

 the apex where the last few cells are binucleate. In the meantime from 

 the cells supporting the tufts of oogones and antherids there have been 

 growing outward and upward numerous hyphae which intermingle with 

 the ascogenous hyphae derived from the oogone and also form a mass of 

 external hyphae. 



From the terminal binucleate cell of each ascogenous hypha a lateral 

 branch forms just beneath the apex and the two nuclei divide simul- 

 taneously (conjugate division) so that the lateral cell also becomes a 

 dicaryon (binucleate) cell. This may be repeated. Eventually the nu- 

 merous terminal dicaryon cells thus produced proceed to the production of 

 the asci. The cell curves back upon itself like a hook, with a pair of nuclei 

 in the curve. The nuclei divide conjugately and cross walls are formed, 

 leaving two of the nuclei (a daughter nucleus of each of the two original 

 nuclei) at the curve and one daughter nucleus in the cell at the tip of the 

 hook and another daughter nucleus in the cell cut off at the base of the 

 hook. The two nuclei in the curve of the hook fuse while the cell elon- 

 gates. This is the young ascus. The basal and apical cells of the hook may 

 fuse and then elongate and form a new hook and a new ascus, etc. The 

 fusion nucleus of the young ascus is diploid or tetraploid according to 

 the interpretation as to the presence or absence of nuclear fusions in the 

 oogone. This nucleus undergoes three successive divisions to produce 

 eight nuclei. The first two divisions are reduction divisions (meiosis) 

 according to either theory, the third division being considered the final 

 division of a second meiosis by the advocates of the tetraploid nature 

 of the young ascus nucleus. By both theories the eight resulting nuclei 

 are haploid. From the centrosome remaining in close proximity to each 

 of the eight nuclei fibrillae appear to radiate and certain of these rays 

 curve downward around the nucleus, at some little distance from it, 

 apparently delimiting a mass of cytoplasm surrounding the nucleus from 

 the remainder of the cytoplasm of the ascus, the epiplasm. Along this 

 delimiting surface the ascospore wall is laid down. In the meantime the 

 asci have been elongating as have the vegetative hyphae surrounding 

 and between them. The latter become the paraphyses while the former 



