CULTURE MEDIA 9 



dioxide and water or to intermediate products. By this process the 

 fungus obtains the chemical energy which it requires for the processes of 

 synthesis. 



KINDS OF MEDIA 



No one knows when man began to cultivate fungi, but certainly it was 

 many thousands of years ago. This cultivation was no doubt uninten- 

 tional at first and was later developed into an art, in connection with the 

 preparation of foodstuffs and beverages. The use of leaven (yeast) 

 extends back to the beginning of agriculture. The yeast culture was 

 preserved in a piece of dough which in turn was added to the next batch, 

 much as buckwheat batter is prepared today. In the Orient, species of 

 Mucor and Aspergillus have been used from the dawn of civilization in 

 preparing food from rice and soybeans. Brewers used yeast many cen- 

 turies before it was learned that yeast is a living organism. On the other 

 hand, the science of growing fungi in pure culture is fairly recent. 



Natural media. It was quite natural that, when mycologists and 

 others began to cultivate fungi in the laboratory, they should turn to 

 natural materials as media. A natural medium is one which is composed 

 entirely of complex natural materials of unknown composition. Among 

 the natural substances so used are the following: plant parts, malt, yeast, 

 peptone, manure, bread, wort, fruit, and vegetables. Many of these 

 substances are used in the form of extracts, infusions, or decoctions. The 

 very diversity of these natural media is strong testimony to the fact that 

 different species have different nutritional requirements. Brefeld (1881) 

 was among the first to grow fungi in pure culture, and many of his tech- 

 niques are in use today. Since his interest in cultivating the fungi was 

 largely for the purpose of observing their development, it was necessary 

 for him to select suitable media. He found two natural media to be of 

 great utility: a decoction prepared from dried plums or raisins and a 

 manure extract. This latter medium he considered "als Universal- 

 nahrlosung flir Pilzculturen." This medium is still used in some labora- 

 tories. Natural media have many advantages. They are cheap and 

 easy to prepare. In many instances it is necessary only to add water to 

 the base material and autoclave. More important yet is the fact that 

 many fungi grow well upon a wide variety of natural media. 



Certain of the more fastidious fungi have never been cultivated in the 

 laboratory. These obligate parasites live only upon or ^^^thin the living 

 tissues of their hosts. Puccinia graminis tritici lives only on wheat, some 

 species of grasses, and some species of barberry. These host plants when 

 killed will no longer support growth of this fungus. However, many 

 species, which in the past were considered to be obligate parasites, have 

 since been cultured on nonliving media. 



