SUGGESTED LABORATORY EXERCISES 425 



and is lifted up with a bit of agar and the germinated spore. Another 

 needle may then be used to transfer the bit of agar and spore to a tube or 

 plate. This method requires a steady hand but has the advantage of 

 being rapid and simple. It may be employed with high magnification 

 of the stereoscopic microscope or the low-power objective of the com- 

 pound microscope. 



EXERCISE 2 



The Influence of Temperature on Growth and Sporulation 



This exercise is outlined to illustrate three main points: (1) the general 

 effects of different temperatures upon growth; (2) the approximate 

 optimum temperature for growth of a few fungi ; (3) that the temperature 

 limits for sporulation are narrower than those for vegetative growth. 

 Inasmuch as the composition of the medium may influence temperature 

 limits, only one medium should be used in this experiment. 



Mediimi 



1. Malt extract, 20 g.; j^east extract, 2 g. ; agar, 20 g.; distilled water, 1,000 ml. 



Adjust the pH, if necessary, to approximately 6, and autoclave. Pour 

 into sterile Petri dishes, about 20 ml. per plate, and inoculate them at the 

 center. Inoculate plates in duplicate or in triplicate for each condition. 

 Incubate the plates at a range of temperatures with con^^enient intervals. 

 The range and the exact temperatures used will depend upon the facilities 

 available. Suggested temperatures are 10, 15, 20, 25, 30, 35, and 40°C. 

 Since light affects some of the species listed below, it is desirable to have 

 the cultures illuminated for a part of each day. 



Records. Observations of growth should be made daily or at least 

 every 2 days. For the purpose of this exercise the radial extension of the 

 mycelium may be used as a measurement of growth. This usually can be 

 easily measured by placing a rule (preferable one calibrated in millimeters) 

 on the bottom of the Petri dish and looking through it towai'd a light. In 

 order to have an accurate measure of the effect of different temperatures, 

 the cultures must be compared before the mycelium reaches the edge of 

 the Petri dish. A more accurate measure of growth may be obtained by 

 determining the dry weight of mycelium grown in liquid medium. Rec- 

 ords may be made in table form for each fungus, giving the days of incuba- 

 tion and the diameter of the colony. The average daily radial extension 

 of the mycelium may then be calculated for each temperature. The 

 amount of sporulation should likewise be recorded each time. 



List of test fungi: Alternaria sp., Aspergillus rugidosus, Botryis cinerea, 

 Cephalothecium roseum., Ceratosiomella fimhriala, Choanephora cucur- 

 hitarum, Glomerella cingulata, Guignardia hidwellii, Monilinia fructicola, 

 Penicillium expansum, Phytophthora infestans, Sclerotinia sclcrotiorum, 

 Septoria nodorum. 



