76 SEXUAL REPRODUCTION IN CERTAIN MILDEWS. 



EEIvATIONS OP ASCOMYCETES AND BASIDIOMYCETES. 



Maire's (62) discovery of regularly binucleated cells in the carpo- 

 phore of the Basidiomycetes, confirmed by myself (40a) and others, has 

 firmly established the conception of a phylogenetic relationship between 

 this group and the rusts. The inferences drawn by older authorities 

 from the resemblance of the promycelium of the rusts to the basidium 

 of Auricularia are thus confirmed. Maire accepts the conception of an 

 alternation of generations in the Basidiomycetes and holds that the 

 union of nuclei in the basidium involves the reduction process found 

 in the spore-mother-cell stage of the higher plants, thus rejecting spe- 

 cifically Dangeard's conception of the basidium as an oogonium. 



There can be no question, in view of the general agreement of 

 other authors (15, 8, 46, 400), that Maire, like Sappin, Trouffy, and 

 Dangeard, has been misled as to the number of chromosomes in the 

 rusts, the Ascomycetes, and the Basidiomycetes by faulty methods of 

 fixation which have caused the chromosomes to stick together in clumps. 

 Guilliermond (31, 33) finds the number of chromosomes in the divisions 

 in the ascus to be 8 in Aleuria cerea, 12 in Peziza cortinus, 16 in Peziza 

 rutilans, and 8 in Peziza vesiculosa. I have found 8 chromosomes in 

 the asci of Ascobolus furfuraceus and Peziza stevensoniana (35), 8 in 

 the asci of Erysiphe communis (40), 10 in Pyronema confluens (40), 

 and 8 in Phyllactinia. In the face of these facts it is difficult to see how 

 Maire and Dangeard can maintain that there are probably 4 chromo- 

 somes in all Ascomycetes. Dangeard originally concluded there were 

 8 chromosomes in the conidia of Sphaerotheca castagnei, but has now 

 changed his estimate to 4, in harmony with Maire. It is plain that no 

 such simple conditions eikist as Maire imagines when he contends for 

 the universal occurrence of 2 chromosomes in the rusts, 4 in the Basidi- 

 omycetes, and 4 in the Ascomycetes. Maire has apparently seen more 

 or less vaguely the true chromosomes in the prophases, but here he was 

 not able to make out any constancy in the number. 



Maire (62) holds that the stage corresponding to a true fertiliza- 

 tion is that at which the binucleated condition arises in the hyphal cells. 

 He was not, however, able to determine with certainty the method of 

 origin of the binucleated condition, nor to demonstrate the existence of 

 simultaneous or conjugate nuclear division, so that he leaves the initial 

 point of the sporophyte generation — the formation of a fertilized egg — 

 still uncertain for the Basidiomycetes. Miss Nichols's (71) researches 

 show that the binucleated condition is present in the mycelium of several 

 forms and apparently does not originate at any constant stage nor in 

 any specially differentiated structures in the life cycle of the fungus. 



