ZYGOSACCHAROMYCES. 373 



(Fig. 81). The prolongations of two neighbouring cells grow 

 towards each other until they come in contact. At the place 

 of contact the projections fuse together, and the protoplasm 

 of the two cells flows together. At a later stage the protoplasm 

 separates in each cell, and two rounded corpuscles appear 

 which become spores. According to Barker, staining shows that 

 this process is accompanied by a fusion of the cell nuclei, and 

 Barker, therefore, denominated it a sexual process. According 

 to Guilliermond, the conjugation of the Zygosaccharomycetes 

 is exactly identical with that of Schizosacch. Pombe and Schizo- 

 sacch. mellacei. The nuclei of the two cells fuse together 

 always in one of the cells, and never in the conjugating passage. 

 It may be assumed that in the formation of asci in conformity 

 with the Ascomycetes an isogamous conjunction takes place. 



Fig. 8I.Zygogaccharomyceg Barker!. 



The spores swell up, and cause the walls of the mycelium 

 to burst, and then the spores develop in the usual way by 

 means of budding. On gypsum blocks and on gelatine the de- 

 velopment proceeds in a similar way to that already described. 

 The spores are chiefly round, seldom oval, and rather strongly 

 refractive. They form readily and rapidly at 25 to 23 C. 

 The maximum temperature appears to be 37 to 38 C., and 

 the minimum 13 C. Spore-formation may take place without 

 fusion of the cells, as sometimes occurs in the case of Schizo- 

 saccharomycetes. The cells are oval ; it forms no film, but a 

 yeast ring develops in ten to fourteen days at 25 C. The cells 

 in the latter are oval, and occasionally elongated. Spore- 

 forming cells also occur in the ring. Colonies formed on the 

 surface of the gelatine have a smooth edge, whilst the colonies 

 immersed in the gelatine have a fringed edge. 



Dextrose, laevulose, and saccharose are fermented, but 

 neither maltose, lactose, nor dextrin. 



