THE FUNGI : ASCOMYCETES AND BASIDIOMYCETES 277 



groups may be found, containing up to a hundred cells, which remind us 

 that the yeasts, although normally unicellular, may be closely related to types 

 of Fungi which produce regular mycelia. When a bud is formed the nucleus 



Nucleus 



Fig. 26S. Saccharoviyces sp. A and B, Structure of vegetative cell. 

 In A, glvcogen deposit shown black. C, Development of bud. 

 D and E, Stages in mitosis. F, Separation of bud with daughter 

 nucleus. (After Kater.) 



of the cell divides and one portion passes into the bud, but whether this 

 division is a mitotic process has not been fully established (Fig, 268). 



Sexual Reproduction 



Ascus formation occurs when the food supply, and especially when 

 the water supply, is scanty. The commonest method of inducing the 

 formation of asci is by sowing an active culture on a damp plaster block in 

 a closed glass dish. Another way is to spread the yeast on a sterilized slice 

 of carrot which is kept dry. The asci are slightly enlarged vegetative cells, 

 the contents of which divide and round off into four ascospores with rather 

 dense and highly refractive walls (Fig. 269). 



