1915] 



ATKINSON PHYLOGENY IN THE ASCOMYCETES 



335 



way of the descent of the Ascomycetes from the Florideae. 

 Some (Bessey, E., '13, p. 151) have attempted to overcome this 

 difficulty by suggesting the homology of the ascus and tetra- 

 sporangium. But this effort leads to so many suppositions 

 and supporting hypotheses because of the fundamental dif- 

 ference between the process of spore formation in the ascus, 

 and the processes of carpospore or tetraspore formation, that 

 the descent of the ascus fungi from the red algae would re- 

 quire a far more labyrinthian course than would be necessary 

 in deriving them from the Phy corny cetes. 



NOTE III 



NUCLEAB FUSION IN THE ASOUS OF A VEGETATIVE OB SEXUAL 



NAT UBE ? 



It is unfortunate that there is 



h great diverg 



of 



opinion in the interpretation of the nuclear phenomena in the 

 archicarp and ascogenous threads. These conflicting results 



are probably, in a large measure, du< 

 sented in the minute size of the nucl 



the difficulties 

 The divergen 



of 



opinion relates primarily to the question as to whether the 

 fusion nucleus of the ascus is the result of two successive 

 nuclear fusions, the first taking place in the ascogonium and 

 the second in the ascus, or whether the nuclear fusion in the 

 ascus is the only one. 



The principle of a single nuclear fusion, that in the 

 interprets this act as the final stage in the process of fertiliza 

 tion, by the fusion of two nuclei of more or less remote an 



cestry 



At some time prior to ascus formation these two 

 may possibly become associated in pairs into 



in pairs into a syn- 

 karion and multiply in the ascogenous threads by conjugate 

 division, or the synkarion and conjugate division may be post- 

 poned to the ascus hook and the complicated series of fusions 

 between the ultimate and antepenult cells of the crozier, or 

 proliferations of the young ascus with accompanying con- 

 jugate divisions of the synkarion. 



Dangeard ( '94) first described the presence of two nuclei 

 the young ascus, and their fusion, in several species (B 



ciliaris, Peziza vesiculosa. Hel 



hippium, Geoglossum 



