CHAPTER VII 

 SAPROLEGNIALES 



The fungi composing this order are commonly termed the 

 water moulds. By certain early students (Pringsheim, 1858: 

 284) they were incorporated in the algae. They occur more or 

 less abundantly in all fresh waters, usually preferring those 

 which are clear and relatively pure. In stagnant or polluted 

 waters their development is retarded by the presence of bacteria 

 and infusoria. A striking exception exists in the case of Lep- 

 tomitus lacteus which grows in waters containing large amounts 

 of organic substances, such as occur in the drains from certain 

 types of manufacturing establishments, paper mills, sugar 

 factories, etc. The members of the order are usually saprophytic, 

 being often found on plant or animal remains lying in the water. 

 In recent years many species have been isolated from the soil. 

 A few are known to be parasitic. The saprophytic forms occur 

 on a wide variety of substrata including decaying algae, woody 

 or herbaceous parts of vascular plants, the bodies of insects, 

 and other types of non-living organic matter. Practically all 

 the species may be grown in pure culture. Sterihzed flies 

 immersed in sterilized water in watch glasses afford perhaps 

 the most commonly used source of nutriment. Bits of egg 

 albumen, ant pupae, aphids, and cooked peas also have been 

 extensively used. More satisfactory and constant results may 

 be obtained if sterilized synthetic media are used, and if isolations 

 are made from single spores or hyphal tips. Marked variation 

 in the development of the mycelium and reproductive bodies 

 may be obtained by altering the chemical constitution of the 

 medium. The physiological treatises of Klebs (1899), Kauffman 

 (1908), Obel (1910), and Pieters (1915 a) are extremely important 

 in this connection, and should be consulted before any attempt 

 to do critical taxonomic work is made. 



The mycelium of the Saprolegniales is profusely developed. 

 It usually consists of two sorts of hyphae, internal threads 

 (rhizoids) which ramify throughout the substratum and taper 



14t) 



