MEIOSIS 



281 



Very little is known concerning nuclear behavior in the phycomycetes, 

 largely because of the minuteness of their nuclei. According to Woycicki 

 (1927), meiosis in Basidioholus ranarum occurs when the zygote nucleus 

 divides, three of the four nuclei then degenerating. Kniep (1930) 

 reports an alternation of gamete-producing and spore-producing plants in 

 Allomyces javanicus. Here reduction probably occurs in the "resting 



*^' - 'laa! 



f 



Fig. 163. — "Double reduction" in Pyronema confluens. a, prophase in germinating 

 spore, showing 6 chromosomes, b, vegetative hypha. c, nuclei in tip of ascogenous 

 hypha, showing 12 chromosomes, d, first meiotic mitosis in ascus, showing 24 chromo- 

 somes disjoining into groups of 12. e, metaphase of second mitosis. /, metaphase (below) 

 and anaphase (above) of third mitosis, showing 6 chromosomes passing to each pole. 

 {After Gwynne-V aughan and Williamson, 1931.) 



cells" producing zoospores from which the gamete-producing individuals 

 arise. 



In the ascomycetes meiosis occurs in the mitoses by which the fusion 

 nucleus in the ascus gives rise to the nuclei of the ascospores. The chief 

 question at issue concerns the nature of the third mitosis, for ordinarily 

 eight spores are formed. Most observers'*^ have contended that meiosis 

 is completed in the first two divisions; but it has also been claimed by 

 some investigators^" that a further " brachymeiosis " is accomplished in 



*8 Maire (1905a) on Galactinia, Faull (1905, 1912) on Hydnoboliles and Laboul- 

 benia, P. Claussen (1912) on Pyronema, W. H. Brown (1909, 19116) on Pyronema 

 confluens and Lachnea, Bagchee (1925) on Pusiularia, E. Schultz (1927) on Peziza. 

 Researches on ascomycetes are reviewed by Atkinson (1915). 



^ Fraser (1907, 1908) on Humaria; Fraser and Welsford (1908) on Otidea and 

 Peziza; Fraser and Brooks (1909) on Lachnea; Carruthers (1911) on Helvetia; Gwynne- 

 Vaughan and Williamson (1930, 1931, 1932) on Humaria, Pyronema confluens, and 

 Ascobolus; Tandy (1927) for some asci in Pyronema domesticum. 



