THALLOPHYTES FUNGI 279 



in sac-like structures, known as asci (singular ascus) and are 

 usually eight in numter. The asci are borne in a body known 

 as the ascocarp. They do not produce zoospores. The sexual 

 reproduction is very similar to that of the red algae from which 

 they have probably descended. For this reason, they are of very 

 great importance in the study of the evolution of the plant king- 

 dom. The fact that so many of the species belonging to this* 

 group are very destructive to our agricultural crops makes it one 

 of the most important groups of plants, but we cannot give much 

 attention to it at this time. The following genera may be taken 

 as good examples of the Ascomycetes : Saccharomyces, Taphrina, 

 Aspergillus, PenicUlium, Microsphcera, Peziza, Sclerotinia 

 and Morchella. 



The genus Saccharomyces (or yeast) (Fig. 128) is one of the 

 very simplest and most important of the 

 Ascomycetes. Each plant is a single, very 

 small, spherical cell which reproduces by the 

 formation of small buds. These buds be- 

 come separate from the parent plant. Very 

 rarely, under conditions of starvation, the 

 cell becomes transformed into an ascus bear- 



,. FIG. 128. Yeast. 



ing lour spores. 



These plants cause fermentation or decomposition of sugar, 

 resulting in the formation of alcohol and carbon dioxide. They 

 are used extensively in the making of bread, and in brewing, 

 distilling alcoholic liquors. They feed on the sugar contained 

 in the flour, the carbon dioxide gas is caught in the sticky protein 

 of the dough, expands and causes the phenomenon of " rising." 



The genus Taphrina contains a number of species that cause 

 diseases on plants, more especially the stone fruits. One of the 

 most important is T. deformans, which causes the leaf curl of the 

 peach. The fungus grows within the tissues of the leaf, produc- 

 ing asci on the lower surface. There is no ascocarp and, there- 

 fore, the asci are said to be naked. 



The genus Aspergillus contains a number of species of the 



