THE STUDY OF MOLDS 107 



EXERCISE 37. THE STUDY OF MOLDS 



Apparatus. Ten sterile Petri dishes; four tubes of 

 sterile slanted agar; ten tubes of sterile agar, for plates; 

 four tubes of sterile cider or wort; four tubes of sterile 

 gelatin; clean glass rings, slides and cover-glasses; hand 

 lens; compound microscope; centimeter scale. 



Cultures. Pure or mixed cultures of the following four 

 molds: Rhizopus nigricans; Aspergillus niger; Penicillium 

 italicum; Oospora lactis. Mixed (or impure) cultures of 

 two molds growing in their natural habitat will be found 

 on each table. 



Method. 1. Plate out each mixed culture* making three 

 straight needle dilution plates for each. Use agar as a 

 medium. Place the plates in the constant-temperature room 

 in the place assigned. Note the temperature. 



2. When the plates are twenty-four hours old, mark 

 and draw a well-isolated typical colony of the mold from the 

 most thinly populated plate. Measure and record the 

 diameter of the colony in millimeters. 



3. When fruiting bodies begin to show, isolate a pure 

 culture of each mold in cider (see Exercise 16). 



4. (a) As soon as growth begins to show in the tubes of 

 cider (about twenty-four to thirty-six hours) make a 

 macroscopic drawing of each. State the age of the culture. 



(b) When mycelium is well developed and fruiting 

 bodies appear (as noted on plates) make a second drawing. 



* Two mixed and two pure cultures are furnished for study. These 

 cultures owe their color to the presence of fruiting bodies or spores. 

 Always endeavor to obtain spores when making inoculations from 

 molds. 



DESCRIPTION OF PLATE IV 



Sexual Reproduction of Penicillium, Ascus Formation. 

 Formation of Chains of Asci in Process of Ripening, Some Con- 

 taining Ascospores, Section of a Ripe Ascus. 

 Saccharomyces, Budding, Colony Formation, Produc- 

 tion of Ascus and Germination of Ascospores. 



