CULTURE MEDIA 



17 



alcohol and acetone have been used. Hansen and Snyder (1947) have 

 recommended the use of propylene oxide for the sterilization of plant 

 parts used for culture media. Frequently a seemingly insignificant 

 change in the method of preparing a medium may result in significant 

 changes in the composition of the medium, which in turn may be reflected 

 in the behavior of the organisms grown upon it. Even the volume of 

 medium in culture vessels affects the amount of decomposition during 

 autoclaving. Cotton plugs may introduce hnt into the medium. Less 

 refined grades of cotton release a volatile substance which affects the 



Table 2. The Effect of Different Methods of Sterilizing Glucose upon 



THE Growth of Sex Fungi, at 25°C. 



Growth reported as milligrams of dry mycelium. 



The entire medium, containing a mixture of amino acids, was autoclaved in the 

 control experiment. In the other experiments the glucose was sterilized by either 

 Seitz filtration or treatment with acetone and added aseptically to the remainder of 

 the sterile medium. (Margolin, thesis. West Virginia University, 1942.) 



germination of some spores {Phycomyces blakesleeanus, Robbins and 

 Schmitt, 1945). Paper or aluminium caps may be used to replace cotton 

 plugs. Residual soap films on improperly rinsed glassware may cause 

 trouble in some cases. 



Preparation of media. Directions for the preparation of specific media 

 are given at the end of the text in the section Suggested Laboratory 

 Exercises. Additional details concerning various media are to be found 

 in Riker and Riker (1936) and Rawlins (1933). 



WAYS OF EXPRESSING CONCENTRATION 



Concentrations are frequently expressed in the literature as percentages. 

 Unless the basis for calculating these values is given, percentage is an 

 ambiguous way of reporting concentration. Buchanan and Fulmer 

 (1928) have pointed out that there are six ways of calculating the percent- 

 age composition of a solution. A 10 per cent sulfuric acid solution may 

 represent six different concentrations. For any precise work it is best to 



