26 AQUATIC PHYCOMYCETES 



grubs, and the like. A number of interesting fungi belonging to the 

 Saprolegniaceae have been isolated from the soil (Harvey, 1925, et al.) 

 by methods similar to those described by Butler (1907) for the collection 

 of species of Pythium. In contrast to the technique noted above for the 

 isolation of Allomyces, here only a thin layer of water covers the soil 

 and the bait is allowed to float on the surface of the water as well as 

 to rest in direct contact with the earth. Since a few of these fungi lack 

 a motile stage, actual contact of some of the bait with the soil is essential. 



The Leptomitales occur primarily as inhabitants of fruits and twigs. 

 The methods of collection outlined for members of the Blastocladiales 

 in a similar habitat apply here as well. Leptomitus has been most fre- 

 quently found in water polluted by decaying organic material, such as 

 that in the outlets of drains, sugar-beet factories, and the like. 



O/pidiopsis, the commonest member of the Lagenidiales, often appears 

 in gross water cultures of saprolegniaceous Phycomycetes. The three 

 predominantly marine genera, Petersenia, Sirolpidium, and Pontisma 

 often develop in algae which have been in a tank of running sea water 

 for from several days to a week. Sirolpidium occurring in Bryopsis 

 frequently causes blackened areas on the frond which are recognizable 

 to the naked eye. Its greatest development, however, takes place after 

 it has remained under laboratory conditions for a few days. Species 

 of Myzocytium and Lagenidium are infrequently collected. Algal mats, 

 particularly those composed of Conjugatae, must be systematically 

 examined microscopically for the presence of these fungi. 



The species of the Pythiaceae considered here are, for the most part, 

 saprophytes of fruits and twigs, occurring with such forms as Rhipi- 

 dium, Gonapodya, and so on. Zoophagus, however, has usually been 

 found ramifying between filaments of green algae, or among plants 

 of the Characeae. 



The only genus of the Entomophthorales treated, namely, Ancylistes, 

 occurs exclusively as a parasite of desmids and should be looked for 

 in sites supporting growths of these algae. 



Isolation and Culture 1 

 Many of the species of fungi discussed in the present work can be 



1 See the important paper by Emerson (Mycologia, 50 : 589. 1958) on cultivation 

 and preparation of Phycomycetes for class use. 



