FERTILIZATION 



291 



on Humaria rutilans 1907, 1908; Carruthers on Helvetia crispa 1911; 

 Blackman and Welsford on Poly stigma rvbrum L912 , P>.\ the above 

 investigators this early fusion was regarded as a sexual one, thai in the 

 ascus being vegetative in nature; and some described a "double reduc- 

 tion" in the ascus to compensate for the two nuclear fusions. 

 p. 223.) 



In a series of somewhat later researches another group of observers 

 found the evidence for an early fusion to be very unsatisfactory, and 

 concluded that the only nuclear union in the life cycle is thai occurring 

 in the ascus: with Dangeard they saw in this union the sexual act. Fur- 

 thermore, no "double reduction'' was found in the ascm. Among the 

 researches supporting this view, which now appeals to be the more 

 probable, may be cited the following: Claussen on Pyroncma confliu 



Fig. 116. 



A, nuclear fusion in the ascus of Peziza vesiculosa. 

 fusion in aeciospore sorus of Phragmidium speciosinn. 







- 





B 



{After Dangeard, 1894 

 AfU r Christman, L90S 



B. cell 



1907, 1912; Schikorra on Monascus 1909; \V. H. Brown on Pyronema 

 confluens 1909, Lachnea scutellata 1911, and Leotia 1910; Faull on Lab- 

 oulbenia 1911, 1912; Blackman on ColUma pulposum 1913; Nienburg on 

 Polystigma rubrum 1914; Ramlow on Ascophanus cdrneus and Ascobolus 

 immersus 1914; Brooks on Gnomon in erythrostoma 1910; McCubbin <>n 

 Helvetia elastica 1910; H. B. Brown on Xylaria terUaculaia L913; and Fitz- 

 patrick on Rhizina undulata 1918'/. 



As the two nuclei fuse in the young ascus Harper I L905 observed in 

 the case of Phyllactinia corylea that not only the chromatin Bystems but 

 also the nucleoli and "central bodies' centrosomes upon which the 

 chromatin strands converge, unite In the Ascomycetes generally the 

 fusion nucleus, or "primary ascus aucleus,' undergo* - three successive 

 mitoses to form the eight ascospore nuclei, the spore walls in each case 

 being formed in association with the curving astral rays which focus upon 

 the centrosome. (See p. 80.) 



