MUCORALES 101 



into a wall on the side next the stalk. The central portion remains sterile and 

 becomes the columella (Fig. 5, 4). Its nuclei no longer show any membrane 

 or nucleoli and degenerate, although occasionally fusions or amitotic divisions 

 appear. The peripheral, spherical cap forms the fertile sporogenous layer. 



There are three types of spore formation. In Piloholus crystallmus (P. 

 microsporus) and P. oediinis (Harper 1899) vacuoles divide the whole sporog- 

 enous protoplasm into uni-, rarely multinucleate, portions, the so-called proto- 

 spores, which round up, swell, and undergo several nuclear divisions before 

 separating into multinucleate portions. These portions again round off, are 

 surrounded by a membrane, and become 2-spored. "We shall find suggestions 

 of this mode of spore formation in the Endomycetales. {Coccidioides and 

 Profomyces, pp. 147, 157.) 



In Circinnella conica (Moreau 1913) and C. minor (Schwarze 1922) de- 

 velopment is simpler ; here the protospores are surrounded by a membrane with- 

 out further splitting and become spores directly. In most of the other genera, 

 as in Sporodinia (Hai-per 1899), Phycomyces, Ehizopus, Mucor, Ahsidia, and 

 Zygorhynchus (Swingle 1903, Moreau 1913, Green 1927), the protospore stage 

 is omitted. The division of the nuclei in Phycomyces, probably also in the 

 other genera, occurs simultaneously in the whole sporangium. The sporog- 

 enous protoplasm splits directly into multinucleate, rarely uninucleate, por- 

 tions Avhich round off, form a membrane, and develop directly into spores 

 without further nuclear division. The unicellular sporangiospores are gen 

 erally ellipsoid or spherical, hyaline or dully colored; resting free in the 

 sporangium or embedded in a granular gel, probably developed from within 

 themselves, which swells rapidly in water. At germination they swell con- 

 siderably and develop into a mycelium through one or more germ tubes. 



The original sporangial type discussed above, represented by Mucor, 

 Sporodinia, etc., is modified in higher forms. Either the individualization of 

 protospores is retarded without being suppressed or the sporangia decrease 

 successively in differentiation, size, and spore number until they appear and 

 function as conidia. 



By retardation of spore formation we have a series from Choanephora 

 to PiptocephaJis. Poorly nourished individuals of Choanephora cucurbitarum 

 exhibit sporangiophores and sporangia like those of Mucor. On the ends of 

 the brown, smooth sporangiospores are 2-3 hyaline processes from each of 

 which as many as 20 hairs may arise. AVhere there is abundant food supply, 

 the spores develop, either on swollen tips of vertical hyphae or on the short 

 secondary branches, exogenously by budding not endogenously by cleavage. 

 Spore formation is ontogenetically retarded and transferred from the interior 

 of the sporangium to its surface. 



Exogenous spore formation appears more clearly in CunninghameUa in- 

 vestigated by Moreau (1913). In C. echinulata and C. Beriholletiae, the ends 

 of the sporophores swell to sporangia whose content is differentiated into a 

 watery inner, and a rich outer, zone. The peripheral layer pushes out into 

 small spherical sacs on short sterigmata, with 3-8 nuclei each. These sacs are 



