184 PHYCOMYCETEAE 



sometimes circinately curved ; not dark-colored, nor of a metallic appear- 

 ance. Sexual reproduction practically isogamous. Not parasitic on fungi 

 (but sometimes saprophytic). Mucor 



Like Mucor but parasitic upon Mucorales. Parasitella 



Much like Mucor but sporangiophore much broader below, tapering upward, 

 somewhat metallic in appearance. Parasitic upon Basidiomycetes. 

 Mycelium often with short lateral spine-like branches. Spinellus 

 Much like Mucor but sexual reproduction very strongly heterogamous; 

 homothallic. Zygorhynchus 



Primary sporangium missing at the apex of sporangiophore which is cymosely 

 branched with circinately recurved branches. 

 Sporangia spherical, without apophysis, spores spherical. Circinella 

 Sporangia pyriform, with apophysis, spores ellipsoid. Pirella 



Sporangiophores repeatedly forked dichotomously; homothallic, isogamous. 



Sporodinia 

 Sporangiophores arising from stolons. 



Sporangia mostly large, mostly spherical, spores dark and striate; sporangio- 

 phores arise at rooting nodes of the stolon. Rhizopus 

 Sporangia small, pyriform, spores colorless or colored; sporangiophores 

 arising from the summit of the arch of curving stolons which mostly 

 root at the nodes. 

 Stolons forming a series of regular, rather short arches with the sporangio- 

 phores arising from their summits. Absidia^ 

 Stolons forming longer, less regular curves, the sporangiophores mostly 



clustered at their summits but some scattered singly. Tieghemella 

 Stolons as in Tieghemella but the sporangiophores in a whorl midway along 

 the curve. Mycocladus 



Key to the Genera of Family Pilobolaceae 



Sporangiophore swollen to a subsporangial vesicle which is broader than the 

 sporangium, which is violently discharged. Pilobolus 



Sporangiophore uniform in thickness, without subsporangial vesicle. Sporangium 

 not discharged. Pilaira 



Key to the Genera of Family Thamnidiaceae 



Sporangiophore terminated by a primary sporangium that is many-spored and 

 with a columella, and bearing lateral variously branched clusters of secondary 

 sporangiophores with dehiscent or indehiscent sporangioles. 



Sporangiole-bearing branches dichotomously forked, walls of sporangia not 

 strongly cutinized. Thamnidium 



Sporangiole-bearing branches dichotomously forked, walls strongly cutinized. 

 Very strongly heterogamous. Dicranophora 



Sporangiole-bearing branches in whorls, many of the hyphae terminating in 

 awl-like extensions. Chaetostylum 



Sporangiole-bearing branches circinately curved. Helicostylum 



No primary spoi-angiuin formed, main axes of sporangiophore and of the branches 

 terminating in awl-like extensions. Chaetocladium 



2 Tieghemella, Mycocladus, and three other genera, Proabsidia, Protoabsidia, and 

 JAchlheimia, are often all included in Absidia. 



