GROUPS OF PLANTS. 



23 



to withstand unfavorable conditions, and germinate (Fig. 13, C) 

 only after a period of rest. 



EUMYCETES: TRUE FUNGI.— Ascomycetes.— The As- 

 comycetes are distinguished for the most part, like the other 

 higher Fungi, in having a septate mycelium, i.e.,' one cellular in 

 structure, and in producing asci (sacs), which latter are formed 

 at the ends of the branches of the mycelia. Two main sub-groups 

 are recognized, the^ £>ne? producing an indefinite number of spores 

 in asci which are not well developed, and known as the Hemiasci ; 

 the other producing a definite number of spores, which, number is 



Fig. is. Species o£ Saccharomyces (Yeasts). 

 S. Pastorianus; C, S. glomeratus; D, S. Piculaius: 

 budduig; b, formation of ascospores. — After Reesz, 



A, S. cerevisiiE or beer yeast; B, 

 a, vegetative cells reproducing by 



characteristic for each species, in a well-developed ascus, and, 

 known as the Euasci. In the latter group the spores arise by 

 successive divisions of the primary nucleus into two, as shown in 

 'Pesiza conHuens {Fig. 14). 



Yeasts. — The simplest of the Ascomycetes is the sub- 

 group known as the Saccharomyces, or Yeasts. The Yeasts do 

 not produce a mycelium, but the plant body consists of a single 

 cell, or a chain of cells, and multiplies by a peculiar process known 

 as' "yeast budding" (Fig. 15, a). From either end of the cell 

 a wart-like process develops, which enlarges until about the size 

 of the original cell, fr'orh which it is then separated by the forma- 



