1915] 



ATKINSON PHYLOGENY IN THE ASCOMYCETES 343 



from adjacent vegetative cells, give rise to the ascogenous 

 threads. 



The results of recent work tend more and more to show 

 that there is no fusion of the associated nuclei in the as- 

 cogonium, or ascogenic cells, whether certain of the nuclei 

 have been derived from an antheridium {Pyronema, Claussen, 

 '12; Monascus, Schikorra, '09), or not. Conjugate division 

 in the ascogenous threads has been abundantly proven, though 

 in some cases it may occur only one or a few divisions prior 

 to the formation of the ascus. 



What the peculiar features of nuclear fusion in the ascus 

 are which characterize it as vegetative, seem to rest more on 

 an ex parte judgment of a fusion of nuclei in the ascogonium 

 than upon any well established idea of the nature of vegeta- 

 tive nuclear fusion. Thus, Miss Fraser ('08, p. 37) states 

 that in Humaria rutilans the two nuclei in the ascus enter in- 

 dependently upon the prophases of the first division, fusing 

 in the spirem stage. This she regards as evidence in disproof 

 of the sexual nature of the fusion of nuclei in the ascus 

 ('08, p. 44). Harper ('05) raises a similar objection. On 

 the other hand, it seems to me that it is excellent evidence 

 that it is not of a vegetative nature. It is well known in a 

 number of cases that the Qgg and sperm nuclei, lying side by 

 side in the egg, undergo the prophase stages of division up 

 to the formation of the chromosomes before fusion of the two 

 takes place. I cite certain examples in the Abietineae: Pinus 

 sylvestris (Blackman, '98) ; P. strohus (Miss Ferguson, '01, 

 '04); Tsuga canadensis (Murrill, '00). 



In support also of the supposed vegetative nature of the 

 fusions in the ascus Miss Fraser ('13, p. 559) cites ''vegeta- 

 tive nuclear fusions ' ' in the quadrinucleate ascus of Humaria 

 rutilans and her work on this plant in 1908. But she no- 

 where describes or figures the fusion of the. four nuclei in 

 such asci. She says ('08, p. 41) "trinucleate (Fig. 50) and 

 quadrinucleate (Fig. 51) asci are sometimes formed; their 

 fate could not be determined." It is very likely that such 

 tetranucleate young asci found by Miss Fraser in Humaria 

 result from further conjugate division prior to the prolifera- 



