SUGGESTED LABORATORY EXERCISES 433 



cient. The fungus will be harvested at intervals and the amount of 

 growth determined by obtaining the dry weight of the mycelium. If 

 there is sufficient growth in the flasks, the first harvest should be made 

 after 3 or 4 days. 



Harvesting of the mycelium is accomplished by filtering the medium 

 through a fine cloth and washing the mycelium with distilled water. 

 Harvest duplicate cultures at each time. The mycelium is then trans- 

 ferred to small aluminum pans of known weight, dried for 12 to 24 hr. at 

 90°C., and weighed. The subsequent harvests should be made at inter- 

 vals of 2 to 4 days, depending upon the growth rate of the fungus used. 

 A convenient method of presenting the results is in the form of a graph, 

 ploting time against weight of mycelium for each of the four media used. 



EXERCISE 10 

 The Influence of Vitamin Concentration on Growth and Sporulation 



This exercise is designed to illustrate a few important principles regard- 

 ing the need for an adequate supply of vitamins in the medium for vita- 

 min-deficient fungi. Some of these points are (1) that vegetative growth 

 may be limited by an inadequate supply of the needed vitamins ; (2) that 

 higher concentrations of vitamins are needed for reproduction than for 

 vegetative growth; (3) that the absolute amount of a vitamin necessary 

 to induce reproduction varies with the amount of sugar in the medium; 

 (4) that the number of perithecia (or other reproductive structures) is 

 partiality dependent upon the concentration of the vitamins in the 

 medium ; (5) that fungi may be used in bioassays for the vitamin content 

 of various products. 



The following experiments are suggested (these may be conducted as 

 demonstrations before the whole class, if desired) : 



A. Thiamine concentration and growth; thiamine assay 



Media 



51. Basal glucose-asparagine medium, no vitamins 



52. As above, but with 100 ng thiamine per liter 



53. As above, 25 fig thiamine per liter 



54. As above, 12.5 ^g thiamine per liter 



55. As above, 6.25 Mg thiamine per liter 



56. As above, 3.12 ng thiamine per liter 



57. As above, 1.56 ng thiamine per liter 



58. As above, add 0.5 g. cake flour per flask 



59. As above, add 0.5 g. whole-wheat flour per flask 



Other amounts of cake and whole-wheat flour may be used, or polished 

 and brown rice may be used instead. 



Adiust the pH of the above media to 6.0 and distribute 25 ml. each to 



