980 



THE HIGHER BACTERIA, MOLDS AND FUNGI 



structures. In the lower types met with as laboratory contaminants 

 ascospore formation is rarely observed. 



The Yeasts. The simplest forms of ascomycetes are the exoasci of 

 which the yeasts or saccharomycetes are familiar examples. These 

 develop on laboratory media as moist masses of separate round or 

 oval cells usually from 10 to 20 microns in diameter. These send 

 out buds (blastospores) which gradually assume the size of the 



FIG. 108. MUCOR MUCEDO. Formation of zygospore. 1. Two branches coalesc- 

 ing. 2 and 3. Process of conjugation. 4. Ripe zygospore. 5. Germination 

 of zygospore. 6 and 7. Mucor erectus. Azygo sporulation. No two branches 

 meet, but form spores without conjugation. 8 and 9. Mucor tenuis. Azygo 

 sporulation. The spores grow out from side branches without sexual union. 

 (1-5 after Brefeld; 6-9 after Banier, from Tavel.) 



parent cells from which they quickly separate. When grown on a 

 dry surface some of the cells divide into ascospores which remain 

 for a while enclosed in the membrane of the parent cell OF ascus. 

 Typical yeasts are unicellular but in some species the cells succes- 

 sively produced by budding adhere to the parent cells and form 

 mycelial filaments, which consist of chains of round or oval units. 

 In other cases the individual cells of such a chain elongate and form 

 a hypha with cylindrical elements. 



