SA PROLEGNIA LES 80 1 



SYSTEMATIC ACCOUNT 



SAPROLEGNIALES 



Microscopic, saprophytic or parasitic, aquatic or terricolous fungi; 

 the thallus endobiotic or more commonly partly within and partly outside 

 the substratum ; holocarpic or eucarpic ; when eucarpic the hyphae with- 

 out constrictions and of unlimited growth; septa formed only in eucarpic 

 species, where they delimit reproductive organs; walls turning blue 

 with chloriodide of zinc ; contents granular, refractive only in growing 

 tips ; gemmae present or absent ; zoospores formed in sporangia, which 

 in certain genera may be internally proliferous; zoospores biflagellate 

 or (in Geolegnia) lacking flagella, mono- or diplanetic (mono- or dimor- 

 phic), if diplanetic the primary zoospore somewhat pyriform or pip- 

 shaped, with two anterior flagella, the secondary zoospore reniform or 

 grape-seed-like with two lateral or subapical oppositely directed flagella, 

 capable in some individuals of repeated encystments and emergences 

 before germination; sexual reproduction oogamous, plants homo- or 

 heterothallic, gametes never flagellate nor set free in the medium; 

 oogonium producing one or more eggs without periplasm 1 ; antheridium 

 (occasionally nonfunctional or lacking) usually forming a fertilization 

 tube; oospore thick-walled, characteristically with a large reserve globule 

 (partly or completely surrounded by one or more layers of minute 

 globules) and a lateral bright spot, upon germination forming a myce- 

 lium or a short hypha terminated by a zoosporangium. 



The order as here defined excludes the Leptomitaceae of older 

 authors, which was raised by Kanouse (1927) to ordinal rank. 



The Saprolegniales consists of three families, the Ectrogellaceae, 

 Thraustochytriaceae, and Saprolegniaceae. The Ectrogellaceae includes 

 simple endobiotic holocarpic fungi which strongly resemble endobiotic 

 true chytrids in their body characteristics. The Thraustochytriaceae, 

 based on a eucarpic marine form, Thraustochytrium proliferum, sapro- 

 phytic on Bryopsis, approximates in its bodily organization species of 

 the chytridiaceous genera Rhizophydium and Phlyctochytrium, the spo- 

 rangia being epibiotic and the vegetative system within the alga rhizoidal. 

 The members of both these families, however, show unmistakable 



1 Except Pythiella. 



