THE FUNGI WHICH CAUSE PLANT DISEASE 105 



Sporangia globular; columella 



not constricted 8. Circinella. 



Sporangia pear-shaped; colu- 

 mella constricted 9. Piiella. 



Mycelium metallic; suspensors spiny 10. Phycomyces. 

 Sporangia of two kinds, the primary 

 many-spored; the secondary few- 

 spored Subfamily III. Thamnidiese. 



PUobolus crystallinus (Wigg.) Tode, a form with beautiful 

 crystalline sporangia on yellowish, evanescent sporangiophores has 

 been frequently noted as injuring or smudging chrysanthemum, 

 rose and other leaves 121-122 y^y j^g profuse discharge of spo- 

 rangia. It is not, however, a parasite. 



Of the other genera the only ones of interest regarding plant 

 disease are Rhizopus and Mucor. The others are saprophytes found 

 on a great variety of substances, manure, fungi, and many other 

 kinds of organic matter. 



Rhizopus Ehrenberg (p. 104) 



The sporangium wall is not cutinized, and falls away. The 

 sporangia are all of one kind and with columellas. The sporan- 

 giophore is never dichoto- 

 mous; zygotes are found in the 

 mycelium. The suspensor is 

 without outgrowths. Twelve 

 or fifteen species, chiefly sap- 

 rophytes. 



R. nigricans Ehr. Aerial 

 mycelium at maturity choco- ^^^ rg.-Rhizopus. Dia^am showing 



late-colored; rhizoids numer- mycelium and sporophores. After Coul- 

 , . . ter, Barnes and Cowles. 



ous; sporangiophores fascicu- 

 late, erect, aseptate; sporangia globose, blackish-olive, granular; 

 columella hemispheric; spores gray to brown, subglobose or irregu- 

 lar, 11-14 fi; zygospore 150-200 /*, epispore with rounded warts, 

 black. This is the cause of soft rot of stored vegetables, particu- 

 larly of sweet potatoes, 12' also of Irish potatoes, ^^^ apples and pears; 

 it causes death of squash blossoms ^^^ and is destructive to barley 



