18 Bulletin 313 



Rhizopus nigricans Ehr. — On sweet potatoes and other vegeta- 

 bles, and also on fruits in storage. Causes a soft rot. Luxuriant 

 growth of white mycelium becoming almost black at maturity. 

 Rhizoids abundant. Sporangiophores erect, fascicled and without 

 septa. Sporangia almost spherical, blackish-olive. Columella hemi- 

 spheric. Spores abundant, almost spherical, gray or brown, 11-14 /x. 



48. Entire plant, 2/3. 49. Base of plant, 2/3. 50. Sporangia spores, 1/12. 



Rhizopus batatas Nakazawa. — On sweet potato. Causes a 

 storage rot. Colonies snow-white, gradually becoming black. Spor- 

 angiophores in groups of 1-7 and 100 to 500 mm. in height, walls 

 smooth and thick. Sporangium globular and 50-150 fi in diameter 

 averaging 110 to 120 fx, white becoming black. Columella usually 

 globular, 42-100 fx.. Spores irregular in form with a wrinkled outer 

 wall, gray to dark brown in color, 3.5-5.2 x 4.4-12.3 fx. Inter callary 

 cells variably formed, 12-60 fi. 



51. Sporangia spores, 1/12. 52. Stages in the formation of the zygospore, 

 2/3. 53. Wall of immature zygospore, 1/12. 54. Wall of mature zygospore, 

 1/12. 55. Crystals from zygospores, 1/12. 



