THE SAC FUXGI (AS('()]MYCETES) 233 



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

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

 tures of yeast Averu iess Ukely to be secured, — " wild" yeasts 

 \ery frequently appearmg. 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 

 fermcidatiou of the dcuigli that is desired.^ 



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 breAver 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 AAdiicli brewei's formerly had from 

 impure yeasts furnished the occasion for the development of 

 the basis of modern bacteriology. The bre«-ers of Germany 

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

 in this difficulty, hie succeeded, m 1850, m devismg 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 kuid of }'east selected for use 

 ui fermentation. It A\'as this method of pure culture which 

 opened the ^^ay for bacteriologieal mvestigations. 



226. Other ascomycetes. The number of destructive asco- 

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

 tary treatise. Some of the mcire unportant ones besides those 

 discussed abo\'e are here given. Upon heads of rye the dis- 

 ease known as ergot (^L'Javiccps purpu rca') sometimes develops. 

 Its mycelium uifests the whole plant. Within and about the 

 deAeloping grams masses of summer spores are formed. Later 

 the same mycelium produces dark compact masses (Fig. IS'J), 

 which completelj' replace some of the grains. These fall to the 

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

 the sprmg the ascospores for lle^\' growth develop. The spore 



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

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



