426 PHYSIOLOGY OF THE FUNGI 



EXERCISE 3 

 The Influence of Light on Growth and Sporulation 



This experiment is designed to illustrate the variable effects of visible 

 and ultraviolet light, particularly upon reproduction of some common 

 fungi. Exposure to light is essential to spore formation in some fungi, 

 while other fungi may sporulate abundantly in total darkness. For a 

 more complete discussion, see Chaps. 3 and 15. 



Media 



2. Same as medium 1 



3. .\ny semisynthetic medium, such as the basal medium in Ex. 4 



Adjust the pH of the media to approximately 6.0, autoclave, and pour 

 into sterile Petri dishes. Inoculate plates in triplicate for each condition. 

 Place the inoculated plates under the following conditions: 



A. Continuous total darkness at 25°C. 



B. Continuous artificial light at 25°C. 



C. Alternating light and darkness at 25°C. 



D. Same as C, but expose to ultraviolet three times for 2 min each time, at intervals 

 of 2 days 



The exposure to ultraviolet light should be made in an inoculating 

 chamber, with the lids of the dishes removed, at a distance of approxi- 

 mately 10 to 12 in. from the source (the G.E. germicidal lamp is quite 

 satisfactory). Wearing of spectacles or sunglasses will protect the eyes 

 from the ultraviolet rays. The first exposure should be made when the 

 fungus colony is approximately 1 in. in diameter. Subsequent exposures 

 should be timed so that the last one is made before the mycelium reaches 

 the edge of the plate. With rapidly growing species, the interval between 

 exposures may be shortened. At the time of each exposure, use a wax 

 pencil to outline the extent of the mycelium by marking the bottom of the 

 Petri dish. The plates kept in total darkness should be wrapped in paper 

 or stored in a lighttight cardboard box. Examination of most fungi 

 should be made after about 7 days. The rapidly growing species should 

 be placed in a separate box which can be opened earlier. 



List of test fungi: Botrytis cinerea, Cephalothecium roseum, Cerato- 

 stomella fimbriata, Choanephora cucurhitarum, Dendrophoma obscurans, 

 Endothia parasitica, Moniliniafructicola, Neocosmopara vasinfecta,Penicil- 

 lium expansum, Septoria nodorum, Trichoderma lignorum. 



EXERCISE 4 

 The Effect of the Carbon Source on Growth and Sporulation 



This exercise is designed to show that fungi differ in their ability to 

 utilize certain compounds as a source of carbon. For discussion of this 



