Ill] 



PLECTASCALES 



63 



succinic acid, acetic acid, and small quantities of other substances. The 

 amount of these by-products varies during the progress of fermentation 

 and according to external conditions. In particular, fermentation is affected 

 by the presence or absence of free oxygen. Under conditions of plentiful 

 aeration the yeast grows and multiplies rapidly and much of the sugar is 

 used as food ; under anaerobic conditions, on the other hand, the main part 

 of the sugar is utilized in respiration, alcoholic fermentation is more complete 

 and the quantity of alcohol produced is greater in proportion to the number 

 of cells concerned. 



On the ground that their daughter cells are produced by septation, and 

 not, as in other genera, by budding, Guilliermond postulates for the species 

 of Schizosaccharomyces a derivation from the neighbourhood ol Endornyces 

 Magnusii in which the mycelium cuts off free cells by transverse septation. 

 He refers such genera as Saccharomyces, in which budding occurs, to the 

 line which gave rise to Endornyces fibuliger where asexual multiplication 

 takes place in a similar way (fig. 24). 



ScM.c. 



L .J. ir 



Fig. 24. Diagram of the phylogeny of the Yeasts; after GuilUermond. Er. f., Eremascus fertilis. 

 'E,xA A., Endornyces fibuliger. ^3.. ^.., Saccharomycopsis capsularis. Z., Zygosaccharomyces. Sa., 

 Saccharomyces. L. J. II, Johannesberg yeast II. End. M., Enc/omyces Magnusii. End. d., Endo- 

 rnyces decipiens. Sc. o., Schizosaccharomyces octosportis. Sc. M., Schizosaccharomyces viellacei. 

 Sc. M. a. , Sch. mellacei, apogamous variety. 



Conjugation, as a preliminary to the formation of asci, was first described 

 by Schionning in 1895 in Schizosaccharomyces and was afterwards studied 

 in some cytological detail by Guilliermond (1901). In Sch. octosporus, two 

 neighbouring cells of similar size put out processes which fuse to form 

 a conjugation tube; the nuclei pass into the tube and undergo fusion, after 

 which the two associated cells enlarge and form, as a rule, a single oval 



