1915] 



ATKINSON PHYLOGENY IN THE ASCOMYCETES 



341 



sexual process, and, therefore, it must be of a vegetative na- 

 ture. If a second fusion of the nuclei occurred it would call 

 for a triple division of the fusion nucleus in order that the 

 haploid condition should be again reached. 



The universal occurrence of the triple division in the ascus 

 in the formation of the spores is by some ascribed to a " quad- 

 rivalent character" of the chromosomes in the fusion nucleus, 

 and rendered necessary in the return to the univalent condi- 

 tion (Harper, '05; Overton, '06), and Overton states, "that 

 all these divisions persist, no matter how many spores are to 

 be produced, which shows their necessity in the process of 

 reduction." 1 Eremascus controverts this statement since 

 there is certainly but one fusion (Stoppel, '07; Guilliermond, 

 '09) and yet triple division occurs in the ascus. 



The results of cytological investigations by different stu- 

 dents in connection with the triple division show considerable 

 variation. Thus Harper ( '00, '05) finds the same number of 

 chromosomes in all three divisions (10 in Pyronema, 8 in 

 Phyllactinia) . The two ascus nuclei "fuse with all their cor- 

 responding parts" (Harper, '05, p. 67), so that the quadriva- 

 lent nature of the chromosomes in the fusion nucleus is not to 

 be seen, though he conceives it to exist. Synapsis occurs in 



the first division. 



MissFraser ('07, '08) describes Humaria rutilans as having 

 16 chromosomes in the first division where synapsis occurs 

 (heterotypic) which split transversely and the daughter nuclei 

 have each 16 chromosomes which appear on the nuclear plate 

 in the second division. In the second division the chromo- 

 somes split longitudinally (home 

 pass to each daughter nucleus. 



chromosomes are supposed to separate r.t the nuclear plat 

 without division, 8 going to each daughte 



Dtypic) and 16 chromosomes 

 In the third division the 16 



she terms " brachymeioti 



eus. This divi 

 A similar situation is de 



ier and Brooks 



scribed by Fraser and Welsford ('08), ] 



( '09) , and Carruthers ( '11) . Faull ( '05) finds the same num- 



1 Polysporoua asci resulting from several to many nuclear divisions may be 

 the retention of an ancestral character, the number of divisions being reduced 

 to three in most forms. 



