PHYLOGENY 81 



Uredinales, as now known, and that attributed by Claussen 

 (1912) to Pyronema confluens. In his paper, which is a con- 

 clusive reiteration and confirmation of his earlier work, he shows 

 that the numerous male nuclei of the antheridium enter the 

 ascogonium, and in it pair with the numerous female nuclei, 

 but without fusing with them. These synkarya then pass out 

 into the ascogenous hyphae, and there multiply by numerous 

 conjugate divisions. Finally a pair of descendants of these 

 nuclei are seen in the young ascogenic-cell, one being male 

 and the other female : here they divide conjugately into two 

 pairs, one pair being the ascus-nuclei, and the other pair 

 reserve-nuclei which may repeat the process in several ways. 

 The two non-sister ascus-nuclei fuse ; then the fusion-nucleus 

 divides, the first division being heterotypic (meiotic, reducing, 

 possessing synapsis and diakinesis stages) and the two following 

 ones, by which eight spores are formed, being homotypic. 

 There is thus in the life-cycle a single fusion, followed by a 

 single reduction. The ascus is a spore-mother-cell, comparable 

 to the teleutospore of the Uredinales, but forming an octad, not 

 a tetrad of spores. The two "reserve-nuclei," left after the 

 formation of the ascus, answer to the two nuclei left in the 

 " basal " cell of the ajcidium. Compare in this respect especially 

 the process as it takes place in Endophyllum. The sporophyte 

 generation consists then in Pyronema only of the ascogenous 

 hyphce, whose cells contain the diploid number of chromosomes 

 though arranged within two nuclear membranes. 



In certain species of Laboulbenia (Faull, 1912) there is a 

 similar cytological history. The ascogenic hyphse contain two 

 nuclei which divide homotypically by conjugate division, and 

 two non-sister nuclei pass into each ascus where they fuse ; the 

 two left in the ascogenic cell may repeat the process. The 

 fusion-nucleus of the ascus divides to form eight nuclei of which 

 four soon degenerate : the first division is meiotic and the others 

 homotypic. There is no double fusion in this group and the 

 same statement may justifiably be inferred to be true of other 

 Ascomycetes. 



On the other hand, Harper (1900), Blackman, Welsford, 

 Eraser, Brooks, Carruthers (1911) and others, maintain that in 



o. u. 6 



