THE SAC FUNGI (ASCOMYCETES) 233 



the air spaces are enlarged and at the same time the alcohol 

 is evaporated. In former methods of bread baking pure cul- 

 tures of yeast were less likely to be secured, " wild " yeasts 

 very frequently appearing. With modern methods, quite sim- 

 ilar to those used in bacteriology, pure cultures may be ob- 

 tained, and it is therefore possible to secure the exact kind of 

 fermentation of the dough that is desired. 1 



The processes of fermentation by yeasts are used in the 

 manufacture of alcohol, wine, beer, and other liquors which 

 contain alcohol. Certain definite kinds of yeasts produce cer- 

 tain kinds of alcoholic fermentation, and it is necessary for 

 the brewer to keep pure cultures of the desired yeasts in order 

 to insure the particular quality of his product. It is worthy 

 of note that the difficulties which brewers formerly had from 

 impure yeasts furnished the occasion for the development of 

 the basis of modern bacteriology. The brewers of Germany 

 appealed to the great scientist, Louis Pasteur, to assist' them 

 in this difficulty. He succeeded, in 1856, in devising methods 

 of pure culture by isolating single yeast plants and growing 

 a colony from each. Thus the particular result to be secured 

 could be determined by the kind of yeast selected for use 

 in fermentation. It was this method of pure culture which 

 opened the way for bacteriological investigations. 



226. Other ascomycetes. The number of destructive asco- 

 mycetes is too large even to be enumerated in this elemen- 

 tary treatise. Some of the more important ones besides those 

 discussed above are here given. Upon heads of rye the dis- 

 ease known as ergot (Claviceps purpurea) sometimes develops. 

 Its mycelium infests the whole plant. Within and about the 

 developing grains masses of summer spores are formed. Later 

 the same mycelium produces dark compact masses (Fig. 189), 

 which completely replace some of the grains. These fall to the 

 ground and lie dormant through the winter, and from them in 

 the spring the ascospores for new growth develop. The spore 



1 An especially interesting paper is "Bread and the Principles of Bread 

 Making," by Helen W. Atwater, Farmers' Bulletin 11%, U. S. Dept. Agr., 1900. 



