156 PHYCOMYCETEAE 



\i Source of light 



Fig. 52. Mucorales, Family Pilobolaceae. Pilobolus sp., showing growth of sporangio- 

 phores toward the light. (Courtesy, K. B. Raper.) 



numerable ellipsoidal indehiscent one-spored sporangioles, mostl}^ in 

 closely crowded whorls. (Fig. 54.) 



Another direction of sporangial modification is found in the Pipto- 

 cephalidaceae. In this family the sporangiophores or their branchlets are 

 somewhat swollen terminally and from these swollen portions there grow 

 out radially numerous cylindrical sporangia. In these the spores are 

 formed in a single row, the number ranging from 2 to 6 or 8, or more — 

 rarely, up to 30. As the spores approach maturity they may enlarge so 

 that the sporangium is constricted between them and breaks apart into 

 one-spored pieces or the whole sporangium becomes detached and the 

 spores escape one by one from the open base. In the former case the 

 earlier students of these forms interpreted the structure as a chain of 

 conidia. In the genera Coemansia, Kickxella, and Martensella, which are 

 included by Linder (1943) in a distinct family, the Kickxellaceae, these 

 sporangia are reduced to indehiscent, one-celled structures which are 

 borne on distinct sterigma-like structures arranged pectinately on one 

 side of lateral, several-celled sporocladia. (Figs. 55, 56.) 



Sexual reproduction is typically by the union of two approximately 

 equal gametangia to form a so-called zygospore which usually occupies 

 the cavities of the two gametangia and develops thick walls. The game- 

 tangia are multinucleate. The zygospores germinate, usually after con- 

 siderable time, by the formation of a germ tube which may branch and 

 start new mycelium or remain unbranched and terminate in a sporangium. 

 The study of the sexual reproduction of the Mucorales reveals an 

 interesting state of affairs. In perhaps the majority of species tested in 

 this respect a culture started from a single spore as well as all cultures 

 derived from sporangia produced on this culture will, when grown sepa- 

 rately or in contact with each other produce no zygospores. On bringing 

 such cultures into contact with other cultures of the same species, origi- 



