118 THE PHYCOMYCETES 



some being restricted to the dung of herbivores, others to that of 

 carnivores. Many species of Mucor have been isolated from soils, 

 but little is known of their function therein. Sporodinia grandis 

 occurs on fleshy species of gill fungi and pore fungi. 



Mycelium. In general the Mucorales possess an extensive, 

 much-branched coenocytic mycelium. They grow readily on 

 ordinary culture media, upon which asexual fructifications are 

 commonly produced. In liquid media they may fail to fructify, 

 and the hyphae may segment and bud in yeast-like fashion. Se- 

 nescent hyphae or those grown in the presence of high concen- 

 trations of sugars may also become segmented. The hyphae of 

 Haplosporangium early become partitioned into multinucleate 

 segments. Special runner-like hyphae, called stolons and attached 

 to the substrate by specialized rhizoids, are produced by Rhizopus 

 and Absidia. 



Asexual reproduction. The sporangia of Mucorales are 

 formed on erect sporangiophores that are usually unbranched. 

 In Thammdknn elegans the sporangiophore is verticillately 

 branched; in Biakeslea trispora, Choanephora manshnrica, and 

 Sporodinia grandis, dichotomously branched; and in Circinella 

 innbellata, circinately corymbose. The formation of sporangia 

 and sporangiospores has been detailed by Harper (1899), Swingle 

 (1903), and Schwarze (1922). The sporangium is initiated by 

 a sweUing of the sporangiophore tip or the swelling of the tips 

 of its branches. A septum eventually delimits the sporangium. 

 This septum remains plane in the Mortierellaceae but forms a 

 globular, cylindric, or pyriform dome called a columella in the 

 Mucoraceae. 



Spore formation in this order is of three types. One type is 

 illustrated by species of Pilobus. Harper (1899) found in P. 

 crystallimis and P. oedipiis that the sporangial content is usually 

 cleaved into uninucleate portions along the lines of the vacuoles, 

 using up all the protoplasm. These portions round up and after 

 several nuclear divisions become invested with spore membranes. 

 A second type, in which cleavage directly results in the forma- 

 tion of multinucleate masses, is found in Rhizopus nigricans and 

 Fhy corny ces nitens [Swingle (1903)], in Sporodina grandis 

 [Harper (1899)], in Circinella conica [Moreau (1913)], and in C. 

 jninor [Schwarze (1922)]. These multinucleate portions, with- 

 out undergoing nuclear division, round up, form a membrane, and 



