SOIL FUNGI 247 



A. PHYCOMYCETES 61 (algal fungi). Mycelium unicellular, unseptated, 

 branched profusely, sexual reproduction by zygospore or oospore. 

 I. Oomycetes. Conjugating cells differing in appearance and function 

 and consisting of a large oogonium and small antheridium. 



1. Saprolegniales (water fungi), unicellular, abundantly 



branched vegetative mycelium, asexual reproduction by 

 means of conidia or swarm spores, produced in separate spor- 

 angia; sexual reproduction by means of an oogonium. 

 Aphanomyces laevis has been found to live saprophytically in 

 the soil; 62 the same is true of Pythium de baryanum. 



2. Peronosporales (downy mildews) : Species of Pythium are 



found abundantly on rotting manure at the first stages of 

 decomposition of organic matter. Butler 53 isolated 6 species 

 of Pythium from the soil, including P. de baryanum and 

 P. intermedium. Various species of Phytophthora can live 

 in the soil saprophytically. 

 II. Zygomycetes: Sexual reproduction by fusion of terminal cells of 

 branches of mycelium similar in appearance but different in sex. 

 The most important group is the order Mucorales. 

 1. Reproduction asexually by spores contained in sporangia, sub- 

 order Sporangiophorae: 



1'. Sporangia generally only of one kind, spherical or pyri- 

 form with a membrane that dissolves or fractures easily. 

 The septum separating the sporangiophore from the 

 sporangium curves into the interior of the latter to form 

 a columella. Sporangioles with persistent membranes 

 occur very rarely and in such cases are disposed without 

 order along the principal sporangiophore. Zygospores 

 naked or surrounded by appendages, but never with a 

 complete envelope. Mucoraceae. 

 l". Sporangiophores arising from stolons (runners): 



(a) Sporangiophores produced from the nodes of 



the stolons; spores often striated longitu- 

 dinally; sporangia globose. Rhizopus. 

 This genus is represented in the soil by five 

 or more species, only three of which (Rh. 

 nigricans (88, PI. XIII), Rh. nodosus and 

 Rh. arrhizus (89, PI. XIII)) have been iso- 

 lated in different parts of the world by 

 Hagem, Lendner, Dale and others. 



(b) Sporangiophores produced from the inter- 



node of the stolon, sporangia pyriform. 



61 Fischer, A. Pilze. In Rabenhorst's Kryptogamen Flora. I, 4: 1, 5. 1892; 

 Lendner, 1908 (p. 237); Hagem, 1908 (p. 237). 



62 Busse, W., Peters, L., and Ulrich, P. Uber das Vorkommen von Wurzel- 

 branderregernimBoden. Arb. K. Biol. Anst. Land- u. Forstw., 8: 260-302. 1911. 



" Butler, 1907 (p. 238). 



