94 LABORATORY AND FIKLD EXERCISES 



SPECIAL STUDIES OF MOLDS 



RmZOPUS NlGRICANS (BLACK MOLD) 



THE MYCELIUM AND NUTRITION 



1. Spores and spore germination. Study spores which have 



been growing on prune juice or some other nutrient 



medium for different lengths of time ; for example, 



twenty-four, forty-eight, and seventy-two-hour periods. 



a. Early stages in spore germination. Use cultures which 



have been grown from twenty-four to thirty-six 



hours at 25 C. 



(1) What is the earliest stage of spore germination that 



you can find ? What change takes place in the 

 form and structure of a spore when it begins to 

 germinate? Does the entire spore cell elongate, 

 or only certain portions of it, to form the begin- 

 ning of a hypa or mold filament ? Do you find 

 branched hyplue growing from spores ? Note the 

 structure of the longer hyplue, including details 

 of cellular structure. Are there vacuoles ? Is 

 there a cytoplasmic sac or is there solid cyto- 

 plasm in the young hyphse ? (The nuclei of 

 KhizopuM cannot be seen in fresh material.) Is the 

 hypha produced by spore germination unicellular 

 or rnulticellular ? 



(2) Draw two or three stages in spore germination, to 



show the spore, the progressive growth of a 

 hypha from a spore, and the cellular structure of 

 the hyphal cell. 



2. Development of the mycelium. Study later stages in 



spore germination from cultures which have grown for 

 forty-eight and seventy-two hours. 



