Phylum Inophyta [ 123 



columella undergoes cleavage to form spores, which may remain plurinucleate 

 (Swingle, 1903). Other members of the order exhibit transitions (apparently two 

 distinct series of transitions) from sporangia as just described to typical conidia. 



Syngamy occurs when the tips of pairs of hyphae meet and are cut off by crosswalls 

 to act as multinucleate gametes. The process is regarded as conjugation, although 

 the gametes of a pair are usually not of the same size. Conjugation does not occur 

 at random, but, in most Zygomycetes, between branches from hyphae of two mating 

 types, designated plus and minus (the distinction of mating types is not identical 

 with the differentiation of sexes). Zygomycetes were the first group reproducing by 

 conjugation in which a distinction of mating types was discovered; the discovery was 

 by Blakeslee (1904). 



Syngamy is preceded by a flare of mitoses in the gametes. The mitotic figures are 

 sharp-pointed, as though centrosomes were present; the haploid chromosome number 

 appears to be 2. The process is not meiotic (Moreau, 1913). After these divisions, 

 the walls between the gametes break down and the nuclei unite in pairs. Unpaired 

 nuclei, presumably contributed in excess by one gamete or the other, undergo disso- 

 lution (Keene, 1914, 1919). Ordinarily, the zygote enlarges and becomes a thick- 

 walled resting spore; in some examples, the resting spore forms as an outgrowth on 

 what was one of the gametes. In Phycomyces, Absidia, and Syncephalis, the hyphae 

 which have produced the gametes, and to which the zygote remains attached, .send 

 out branches which form a layer about the zygote. These branches might be inter- 

 preted as making up fruits. Endogone produces definite fruits of considerable size. 



A zygote germinates by production of a hypha bearing a sporangium (Blakeslee, 

 1906). Meiosis is believed to occur in the course of germination. 



While Mucorina in general are saprophytic, some of them are parasitic on others, 

 Piptocephalis and Chaetocladhim on Mucor, and Parasitella on Absidia. Drechsler 

 (1935, 1937) discovered a number of organisms apparently of this group parasitizing 

 amoebas and nematodes in the soil. 



The Mucorina may be treated as five families. 

 1. Not producing macroscopic fruits. 



2. Not parasitic on amoebas or nematodes. 

 3. All spores produced in sporangia 



with columellae Family 1. Mucoracea. 



3. Not as above. 



4. Producing sporangia or else 

 conidia as outgrowths from a 

 knob, homologous with a 

 sporangium, solitary on an un- 



branched stalk Family 2. Piptocephalidacea. 



4. Sporangia or conidia solitary 

 and terminal on branches of a 

 branched sporangiophore or 

 conidiophore; sporangia, if 



produced, without columellae Family 3. Mortierellacea. 



2. Parasitic on amoebas or nematodes Family 4. Zoopagacea. 



1. Producing macroscopic fruits Family 5. Endogonacea. 



Family 1. Mucoracea [Mucoraceae] Cohn in Hedwigia 11: 17 (1872). Mucorina 

 whose spores are produced exclusively in sporangia with columellae solitary on un- 

 branched sporangiophores. Mucor L., typified by M. Mucedo, is now limited to a 



