58 AGRICUI^TUEAL AND INDUSTRIAL BACTERIOLOGY 



The following key based upon asexual spore production 

 differentiates nine genera of molds : 



Key for DirrEKENTiATioN of Common Genera of Molds 



A. Spores borne in sporangia. Mycelium non- 

 septate. 

 B. Sporangiophores arising in clusters from 



the nodes of runners or stolons 1. Rhizopus. 



BB. Sporangiophores arising singly, without 



stolons 2. Mucor. 



AA. Spores (conidia) never borne in sporangia. 

 B. Neither conidia nor hyphae smoky or 

 dark in color. 

 C. Conidia one-celled. 

 D. No distinct conidiophores. Conidia 



formed as oTdia 3- Oospora. 



DD. Conidia on distinct conidiophores. 

 E. Conidiophores enlarged or club- 

 shaped at tip 4. Aspergillus. 



EE. Conidiophores branched at tip 5. Penicillium. 



CC. Conidia two-celled, pear-shaped 6. Trichothecium. 



BB. Either conidia or hyphae smoky or dark, 

 or both. 



C. Conidia one-celled, in branched chain. . . 7. Hormodendrum. 

 CC. Conidia more than one-celled. 



D. Like Hormodendrum, but condidia two- 

 celled when old 8. Cladosporium. 



DD. Spores many-celled, club-shaped, in 



chains 9. Alternaria. 



Rhizopus. — Molds belonging to this genus are frequently 

 termed the black or bread molds. They are among the 

 most common, occurring upon bread, decaying vegetables, 

 and similar material. "When young they are cottony and 

 white, as they grow older they become grayish because of 

 the development of numerous dark sporangia. The vege- 

 tative mycelium spreads through the medium upon which 

 the organism is growing. When ready to produce spores, 

 long slender threads are thrown out which grow until the 

 tip touches some solid material. For example, in the labo- 

 ratory the tip may touch the glass side of the dish in which 

 the organism is growing. From this tip are sent out clus- 

 ters of dark brown, short branches, termed rhizoids. These 

 act as holdfasts, they are not roots in any sense. The 



