GROUPS OF PLANTS. 23 



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

 only after a period of rest. 



EUMYCETES : TRUE FUNGL Ascomycetes. The As- 

 comycetes are distinguished for the most part, hke the other 

 higher Fungi, in having a septate myceHum, i.e., one celkilar 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 one 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. 15. Species of Saccharomyces (Yeasts). A, S. cerevisicE or beer yeast; B, 

 5. Pastorianus; C, S. glmneratus; D, 5. Piculatns: a, vegetative cells reproducing by 

 budding; b, formation of ascospores. After Reesz. 



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 

 Pedsa conflucns (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, from which it is then separated by the forma- 



