ORDER MUCORALES 165 



340 species and subspecies, excluding the Endogonaceae and a few other 

 forms. Including these the number would reach 44 genera and about 

 370 species. 



Family Mucoraceae. Sporangia relatively large and many spored, 

 oval or spherical, with a well developed columella. The sporangia are all 

 alike and are borne singly, or several may be produced on a racemosely 

 or otherwise branched sporangiophore. The wall of the mature spo- 

 rangium may dissolve in the presence of moisture or may break into 

 pieces and fall away, thus releasing the contained spores. The most impor- 

 tant genera are : Mucor, whose unbranched or branched sporangiophores 

 arise from the main mycelium; Sporodinia, whose sporangiophores are 

 repeatedly and closely dichotomously branched ; Rhizopus, in which long 

 stout creeping hyphae (stolons) form tufts of sporangiophores at the 

 points where the stolons attach themselves by rhizoids. Ahsidia, Zygor- 

 hynchus, and Circinella belong in this family as do several other genera. 

 The zygospores are naked or more or less protected and are produced by 

 both the Mucor type and the Piloholus type as described above. It should 

 be noted that some of the names used above, e.g., Mucor, Rhizopus, and 

 Sporodinia, do not conform to the international rules of nomenclature 

 requiring the earliest generic names to be used. Until some future Inter- 

 national Botanical Congress shall settle the status of Syzigites vs. 

 Sporodinia, Rhizopus vs. Mucor, Mucor vs. Hydrophora, it will perhaps be 

 well to use the more customary generic names. (Figs. 50, 53A, 57.) 



Family Pilobolaceae. Sporangia more or less flattened vertically 

 with a thick dark colored apical wall which does not break or dissolve. 

 The sporangiophore is swollen at the base in Piloholus and has a pro- 

 nounced enlargement or subsporangial vesicle (in Piloholus) or a slight 

 one (in Pilaira) subtending the sporangium. The columella is more or less 

 conical or may project almost to the top of the sporangium. In Piloholus 

 when the maximum osmotic pressure has been attained in the subspo- 

 rangial vesicle it ruptures in a circular slit so that the columella and 

 adhering sporangium are violently expelled by the mass of liquid forced 

 out by the contraction of the ruptured vesicle. This sporangium turns 

 over in flight or on striking some object, such as a blade of grass, and 

 adheres by its gelatinous base. In Pilaira the elongating sporangiophore 

 places the sporangium in contact with some near-by object to which it 

 remains attached when the sporangiophore collapses. The dung-inhabiting 

 species of Piloholus are very easily obtained by bringing freshly dropped 

 horse manure into the laboratory and enclosing it in a large dish. After 

 a very few days the spores, which have passed unharmed through the 

 alimentary canal of the horse, will produce an abundant growth of my- 

 celium and the large conspicuous sporangiophores will appear in large 

 numbers. When the dish is placed in a box closed on all sides except for a 



