SUGGESTED LABORATORY EXERCISES 435 



E. Effects of hiotin starvation on a biotinr-deficient fungus 



Media 



65. Glucose-asparagine, purified agar; no bio tin 



66. As above, 5 ng biotin per liter 



67. As above, 1 ng. biotin per liter 



68. As above, 0.5 Mg biotin per liter 



69. As above, 0.1 ng biotin per liter 



Pour into Petri dishes and inoculate each medium in tripHcate with 

 Sordaria fimicola. Observe the results after about 6, 8, and 10 days. 

 Note the amount of growth, the time of perithecium formation, and the 

 relative numbers of perithecia. Examine microscopically the perithecia 

 formed in the low concentrations of biotin, and look for deformed asci 

 and ascospores. Add a drop or two of sterile biotin solution to some of 

 the nonfruiting, biotin-starved cultures. Observe the effects in a few 

 days. 



Records. Take full notes on all observations of the above experiments. 

 Write out a full explanation of the results with interpretations based 

 upon physiological processes in fungi (see Chap. 14). 



EXERCISE 11 

 Factors Affecting Spore Germination 



This exercise demonstrates the effects of nutrients, humidity, pH, and 

 temperature upon the time and percentage of germination of the spores 

 of some common fungi. While the germination of fungus spores may be 

 influenced by a number of factors, only a few of them can be easily studied 

 in the laboratory. See Chap. 16 for a discussion of factors which influ- 

 ence spore germination. 



A. Effects of nutrients upon spore germination. Place filter paper in the 

 bottoms of Petri dishes. Cut two holes in the filter paper about }^ in. 

 in diameter and place a glass slide over these. Add water to moisten 

 the paper, and autoclave. Make up a spore suspension in media 70 and 

 71, and place drops of this suspension on the slide over the holes in the 

 paper, which must be kept moist w^ith sterile water. Incubate at 25°C. 

 After incubation the slide may be examined by placing the Petri dish on 

 the microscope and removing the lid. 



Media 



70. Distilled water 



71. Distilled water plus 2 g. yeast extract per liter 



72. Same as medium 71 but solidified with agar; adjust to pH 8.0 



73. Same as medium 71, but pH 7.0 



74. Same as medium 71, but pH 6.0 



75. Same as medium 71, but pH 5.0 



76. Same as medium 71, but pH 4.0 



