22 ISOLATION AND CULTIVATION OF FUNGI 



Fungi generally grow best in media abundantly supplied with 

 carbohydrates. Another requisite is that the pH be within the 

 ranc^e of 5 to 6. 



Since carbohydrates and proteins are decomposed by heat, 

 especially if the medium is acid or alkaline, they should be steri- 

 lized separately and added to the other constituents, care being 

 taken to prevent contamination. 



Agar media enriched by the addition of fruit juices may not 

 solidify unless the fruit juices are sterilized separately and then 

 aseptically added after the constituents have been cooled to 

 about 50° C. Wolf and Shunk (1921) demonstrated that, if 

 agar or gelatin media are cooled before being made acid or alka- 

 line, they will jellify at hydrogen- or hydroxyl-ion concentra- 

 tions far greater than those permitting growth of microorganisms. 



In manuals [Rawlins (1933), Riker and Riker (1936)] con- 

 taining formulae for compounding various kinds of media may 

 be found instructions regarding such essential matters as clearing 

 of media, filtration, adjustment of reaction, and steriHzation. For 

 this reason these subjects will not be given consideration here. 



Most kinds of organic media contain meat extract and peptone 

 as essential constituents. The meat extract supplies mainly the 

 ash constituents, organic nitrogen, and certain organic acids. 

 Peptone supplies decomposable proteins that can be cleaved by 

 many fungi to yield essential amino acids. When media con- 

 taining these materials are enriched by the addition of plant sub- 

 stances extracted by boiling, like those from potatoes, corn meal, 

 or fresh beans, they constitute satisfactory substrata for the cul- 

 tivation of a large number of different species of fungi. Such 

 media, in fact, are widely used in mycological and phytopatho- 

 logical laboratories. 



Mineral nutrient media have a more limited usage than organic 

 media. They are employed especially in physiological studies 

 of the suitability of a single carbohydrate, amino acid, or mineral. 

 A mixture of mineral salts in liquid cultures or jellified with agar 

 furnishes the basis for such media. 



In the cultivation of certain groups of fungi specific media 

 have come to be used quite generally. Members of the Sapro- 

 legniales and related orders, for example, are commonly culti- 

 vated on boiled hempseeds placed in water. The Polyporaceae 

 and Thelephoraceae usually grow well and may be made to fruit 



