260 GENERAL BOTANY 



fungi, while the blue-green molds belong to the sac fungi. 

 They are, however, conveniently studied together on. account of 

 the similarity in their general structure and mode of life. 



/The black molds are readily distinguished by the naked eye 

 on account of the dark spore cases, or sporangia, which are borne 

 by the older portions of the aerial mycelium. If examined 

 closely, these sporangia look like black spheres supported upon 

 minute stalks, or hyphse, springing from the white aerial mycelium 

 of the mold. The younger sporangia are white, becoming gradu- 

 ally darker with age. Another characteristic of the black molds 

 is the peculiar structure of the hyphal filaments, which, though 

 long and frequently branched, are yet composed of single cells, 

 like Vaucheria, without partitions or septa but with many 

 nuclei. They have been likened to a greatly elongated yeast 

 cell which with its growth has failed to form new cell walls 

 to inclose the repeatedly dividing nuclei of the growing cell. 

 A convenient species for study is the common black mold of 

 bread, known as JKhizopus niyru-am. 



RmZOPUS NIGRICANS (BLACK MOLD) 



Habit. Rliizopus has the same branched multinucleate and 

 unicellular hyphse as the rest of the black molds. It is peculiar 

 in that it spreads over the surface of bread or other nutrient 

 media by means of special hyphse termed runners or stolons. 

 The mold spreads by these stolons in much the same manner as 

 strawberry plants spread by runners growing out from the 

 mother plants. The stolons are hyphse which grow out radially 

 from centers where the mycelium is already established. At cer- 

 tain intervals these hyphal stolons send out rootlike submerged 

 hyphal branches, which penetrate the nutrient medium on which 

 it grows and anchor the aerial mycelium. The sporangia and 

 spores are borne on erect aerial hyphse which spring from the 

 points on the stolons where the rootlike hyphse grow out. The 

 sporangia and spores are thus borne at the most favorable points 

 for receiving food from the submerged hyphse, as these digest 

 and absorb the starch and other nutrient substances of the bread. 



