MOULD FUNGI 97 



Key to Families or the Order Zygomycetales 

 Non-sexual spores in sporangia, which in some genera are reduced 

 to conidioid bodies. 



A. Non-sexual spores formed in sporangia in many cases accom- 

 panied by conidiospores. 



(a) Sporangia (at least the main sporangia) with columella. 

 Conidiospores absent, or only sparingly found. Zygospores 

 naked, or only covered by curled outgrowths of the sus- 

 pensors. I. Mucorace^. 



(b) Sporangia without columella; zygospore surrounded by a 

 thick covering of hyphae. II. Mortierellace^. 



B. Non-sexual spores as conidiospores. Sporangia exceptionally 

 present. 



(a) Conidiospores single. Zygospores formed directly by the 

 united gametes. 



1. Sporangia present transitional to conidia; sporangia 

 monosporic and polysporic. III. Choanephorace^. 



2. Sporangia never present; parasitic on other MUCOR- 

 ALES. IV. Ch^tocladiace^. 



{b) Conidia in chains zygospore formed where the bent ends 

 of the gametes unite. V. Piptocephalidace^. 



Non-sexual spores as true conidiospores borne singly at the end of 

 conidiophores. VI. Entomophorace^. 



Family i. Mucorace^. — The mycelium of the true moulds is 

 homogeneous, or it becomes heterogeneous through differentiation into 

 aerial and nutritive hyphae. Non-sexual reproduction by the forma- 

 tion of endospores in sporangia. The sporangia here may be simple or 

 branched. The sporangia are all alike, or there are as in Thamnidium 

 two different types known as megasporangia and microsporangia. The 

 larger sporangia have a columella, while the smaller ones are mostly 

 without a columella, but occasionally a columella is present. The 

 formation of conidiospores is unknown in the family. The zygospore 

 may arise by the fusion of two similar gametes formed from the same 

 mycelium (homogamic hermaphrodites) or by the union of two slightly 

 dissimilar gametes the product of the same myceUum (heterogamic her- 

 mophrodites), or it arises by the conjugation of similar gametes (+ and 

 — races) from two distinct mycelia (heterothallic and homogamic). 



