FUNGI, BLACK MOLD 



249 



The spores are very numerous and float readily in the air, so that 

 if a piece of bread or cooked potato is left exposed in a room or 

 out of doors for a day or less, and then covered in a pan with 

 some moist paper, in a few days the mold will appear. The 

 mycelium is white and forms an abundant growth of threads 

 forming the white glistening mat which spreads over the bread or 

 other substances. 



403. Asexual reproduction. The mycelium is the vegetative 

 or growing stage of the fungus. Within a day or so after the 

 mycelium begins to form, asex- 

 ual reproduction begins and 

 at the same time the mycelium 

 continues to spread. Here and 

 there upon a thread of my- 

 celium, erect hyphae arise in 

 tufts of three to five or more 

 (fig. 208). The ends of these 



branches become enlarged into 

 a rounded body, the spore case 

 or sporangium, and the proto- 

 plasm is separated from that of the stalk, or sporophore (some- 

 times called sporangiophore), by an arched wall, the columella. 



Fig. 208. 



Group of sporangia of a mucor (Rhizopus 

 nigricans), showing rhizoids and the stolon 

 extending from an older group. 



Fig. 209. 



A mucor (Rhizopus nigricans); at left, nearly mature sporangium with columella, showing 

 within; in the middle is ruptured sporangium with some of the gonidia clinging to the colu- 

 mella; at right, two ruptured sporangia with everted columella. 



At maturity the sporangium wall disintegrates so that the 

 spores are easily set free. The columella is often very large 



