ZYGOMYCETES . 113 



whose sporangia the separation into + and — spores is continued (Bur- 

 geff, 1912): 



+ Spore — > + Sporangium PC R ._> + Spores 



+ Mycelium — -> +Gametangia 



— Mycelium — » — Gametangia 



— Spore ^ —Sporangium 



T T 



Zygo — >±Spor — >±Spores— ►+ Mycelium—* + Sporangia 

 spore angia~~*- —Spores 



I 



Diagram XI. 



The systematic classification of the Mucoraceae is based on the 

 asexual organs of fructification; but since these merge into one another 

 through numerous transitional forms, the dividing lines are drawn by 

 various authors in entirely different places. Four tribes should be 

 mentioned: the Mucoreae, Cephalideae, the Chaetocladieae and the 

 Mortierelleae. 



The Mucoreae (including Piloboleae) are characterized by a com- 

 pletely developed sporangium provided with a typical columella. They 

 include Mucor, Rhizopus, Sporodinia, Absidia, Phy corny ces, Zygorhynchus 

 and Parasitella. They are generally saprophytic on all possible sub- 

 strates, but Sporodinia occurs mostly on pileate fungi; Parasitella alone 

 is preponderantly parasitic on other Mucoraceae. 



The Cephalideae are distinguished from the Mucoreae by the retarda- 

 tion of spore formation which generally occurs in the extrasporangial 

 partial sporangia. They include Choanephora, Cunninghamella, Blakes- 

 lea, Syncephalastrum, Syncephalis and Piptocephalis. Choanephora is a 

 feeble parasite on wilted floral organs of many phanerogams, e.g., Cucu- 

 mis, Hibiscus and Gossypium, and causes in part a rotting of the fruit; 

 Piptocephalis is parasitic on other Mucoraceae, the other genera are 

 saprophytic. 



The Chaetocladieae form a series parallel to the Cephalideae. They 

 are characterized by the increasing degeneration of the sporangium. Of 

 the genera here discussed, they include the saprophytic Thamnidium 

 and Chaetocladium, which is generally parasitic on other Mucoraceae. 



The Mortierelleae, finally, are marked by the absence of a columella 

 and by their ability to form fructifications. The only well-known genus, 

 Mortierella, is generally saprophytic; M . Bainieri is parasitic on Basidio- 

 mycetes. The genus Haplo sporangium, which perhaps also belongs 

 here, is saprophytic. 



Endogonaceae. — On account of the structure of their sporangia and 

 the formation of fructifications, this family is closely connected to the 

 Mortierelleae; in contrast to the latter, however, the relationships of 



