SUGGESTED LABORATORY EXERCISES 437 



If one desires to demonstrate these principles in the laboratory, pure 

 cultures must be used, and by combining two or more of these species in a 

 culture vessel, the associative effects may be studied. This exercise is 

 outlined to demonstrate the main types of associative reactions between 

 species of fungi in the laboratory under controlled conditions and to 

 show that a species may react differently in its association with different 

 fungi. 



Media 



77. Malt extract-yeast extract agar 



78. Glucose-asparagine purified agar (vitamin-free) 



79. Glucose-asparagine liquid (vitamin-free) 



A. Each student should select three pairs of the fungi and test their 

 interaction on agar plates of media 77 and 78. Duplicate plates should 

 be inoculated for each condition. It is suggested that the two pairs of 

 fungi be inoculated on opposite halves of the agar plates 1 to 2 in. apart. 

 This will allow both fungi to make some growth before they come in 

 contact. Incubate all cultures at 25°C. Notes should be taken on about 

 the fifth day and the tenth day, and for most cultures the final observa- 

 tions may be made after 2 weeks. Carefully made sketches may add 

 greatly to the value and clarity of your notes. 



The types of reactions may be grouped under (1) none, (2) stimulation, 

 (3) symbiotic, (4) antagonistic. Each type of reaction should be 

 explained on the basis of the present experiments. 



B. Using vitamin-free liquid medium 79, inoculate flasks with Phyco- 

 viyces blakesleeanus and Sordaria fimicola separately and with both species 

 together. After a few days observe the results. This part of the exercise 

 may be conducted as a demonstration for the entire class. 



List of test fungi: Actinomyces sp., Alternaria sp., Aspergillus rugulosus, 

 Botrytis sp., Cephalotheciimi roseum, Guignardia hidwellii, Helmintho- 

 sporium sativum, Monilia sp., Monilinia fructicola, Penicillium, chryso- 

 genum, Phycomyces blakesleeanus, Sordaria fimicola, Trichodermalignorum. 



Suggested Demonstrations 



In addition to the experiments outlined in the above exercises, the 

 following are suggested as demonstrations for the entire class. These 

 may be expanded into complete exercises for individual student 

 participation. 



1. Need for micro elements for growth and sporulation. Steinberg (1919) 

 describes the procedure for preparing a medium essentially free of micro 

 elements to which the desired elements may be added. Use Aspergillus 

 niger as a test species. See Chap. 5 for other methods of removing micro 

 elements from media. 



