FORM AND STRUCTURE OF MICROBES 67 



results from the fusion of protoplasm as well as nucleus of 

 two differentiated cells, the gametes, one male, the other 

 female. Heterogamy exists when the male gamete is manifestly 



FIG. 31. Successive stages of 

 conjugation in a Zygosac- 

 charomycete. (After Barker.) 



FIG. 32. Zygoscucharomyces yeast. 

 (a) Vegetative cells : (6) Asci. 



different from the female isogamy when they seem identical. 

 The ascus and the basidium are modes of sexual reproduction. 

 In the yeasts, examples of conjugation are not lacking. 

 In Zygosaccharomyces before the intracellular formation of the 

 spores, two neighbouring cells put out each a little bud ; the 

 two buds join and along the little canal thus formed fusion of 

 the nuclei takes place (according to Barker). The two cells 



FIG. 33. Nuclear fusions and spore formation in Schizosaccharomyces 

 octosporus. (After Guilliermond. ) 



remain united forming a dumb-bell-shaped ascus. The same 

 process occurs in certain schizosaccharomycetes, where the 

 shape of the ascus also recalls its origin from two cells. Since 



F 2 



