242 THE LOWER FUNGI— PHYCOMYCETES 



2. Sporangium either accompanied bj- or replaced by sporan- 

 giola or conidia. 



a. Sporangium present, accompanied by sporangiola, both 



usuall}- formed on the same sporangiophore. 



3. Thamnidiaceae, p. 253 



b. Sporangia often absent; when present sohtary, not 



borne on the same sporangiophore with sporangiola or 

 conidia. 



(1) Sporangium absent; conidia covering sub-termi- 



nal enlargements of branches of the conid- 

 iophore. 



4. Chaetocladiaceae, p. 257 



(2) Sporangium present in some genera, absent in 



others; sporangiola or conidia present in all 

 cases, and covering terminal capitate enlarge- 

 ments of the branches of the sporangiophore or 

 conidiophore. 



5. Choanephoraceae, p. 258 

 B. Sporangium when present lacking a columella; zygospore where 



known enveloped by a thick layer of interwoven hyphae; spo- 

 rangiola and conidia formed in some cases, when present isolated, 

 not covering an enlargement on the sporangiophore or 

 conidiophore. 



6. Mortierellaceae, p. 264 

 II. Sporangium narrowly cylindrical or rod-like, relatively few-spored; 



sporangiospores arranged in a single row, at maturity having the 

 aspect of a chain of conidia due to the dissolution of the sporangial 

 wall; zygospore usually formed in a bud put out by the fusion cell 

 which results from the copulation of the gametangia. 



7. Piptocephalaceae, p. 270 



Mucoraceae 



Large, globose to pyriform, multispored sporangia formed in 

 all genera, not shot away; sporangiola and conidia lacking; 

 sporangial wall thin, not cutinized; zygospore not enclosed in a 

 definite hyphal envelope. 



Key to Genera of Mucoraceae 



Sporangiophore indeterminate, elongating indefinitely, branching in a 

 cymose manner, not bearing a terminal sporangium; branches circi- 

 nate; sporangial wall persistent. 



A. Sporangium pvriforni; columella liourglass shaped. 



1. Pirella, p. 243 



B. Sporangium globose; columella cylindrical to conical. 



2. Circinella, p. 244 



