1915] 



ATKINSON PHYLOGENY IN THE ASCOMYCETES 337 



of the ascus in Eremascus, so that the ascus appeared to be 

 supported on two stalks. Frequently, however, in Peziza 

 vesiculosa and Helvella ephippium he observed the origin of 

 the ascus from a single hypha curving at the end in the form 

 of a hook or crozier. The four nuclei resulting from the divi- 

 sion of two were so situated in the crozier that after the forma- 

 tion of two cross walls the ultimate and antepenult cells each 

 contained one nucleus, while the penult cell contained two 

 nuclei. The association of two nuclei in the young ascus and 

 their fusion he interpreted as a sexual act, and the young ascus 

 was looked upon as an oogonium. Later, Dangeard found that 

 the crozier method of ascus formation was the usual one in the 

 forms studied and that in no case in these higher forms did 

 the ascus arise immediately from the conjugation of two dif- 

 ferent hyphae. 



This important pioneer work by Dangeard was a great 

 stimulus to further studies which has led to a more or less 

 clear knowledge of the history of the nuclei from the archicarp 

 through the ascogenous hyphae to the ascus, while the origin 

 of the ascogenous hyphae from the fertile cells of the archi- 

 carp was first described by Janczewski (71) in Ascoholus, 

 and later by Kihlman ('83) in Pyronema confluens. Harper 

 first demonstrated the origin of the ancestral ascus nuclei in 

 the archicarp of Sphaerotheca castagnei ('95'') and Pyronema 

 confluens ('00) and their migration in the ascogenous hyphae, 

 though he does not give the nuclear history in the ascogenous 

 hyphae, except the later stages at the time of formation of the 

 ascus. Their archicarp origin has been abundantly confirmed 

 by several investigators in a number of different forms, both 

 among the lichens and other Ascomycetes. 



The different opinions in regard to the significance of 

 nuclear fusion in the ascus rest upon the interpretation by 

 different investigators of the behavior of the nuclei in the 

 archicarp, or ascogenous cells, before they begin to move into 

 the ascogenous hyphae. Some maintain that there is a fusion, 

 in pairs, of the sex nuclei (1) in the archicarp when fertilized 



