76 ] The Classification of Lower Organisms 



Family 11. Achnanthea [Achnantheae] Kiitzing op. cit. 81. Families Achnan- 

 thaceae and Cocconeidaceae West op. cit. 289, 290. Achnanthes, Rhoicosphenia, 

 Cocconeis. 



Class 3. OOMYCETES Winter 



Class OoMYCETEs Winter in Rabenhorst Kryptog.-Fl. Deutschland 1, Abt. 1: 32 



(1879). 

 Phycomyceten de Bary Vergl. Morph. Pilze 142 ( 1884), in part. 

 Class Phycojnycetes Engler and Prantl Nat. Pflanzenfam. II Teil: 1 (1889), in 



part. 

 Reihe Oomycetes Fischer in Rabenhorst Kryptog.-FI. Deutschland 1, Abt. 4: 310 



(1892). 

 Stamm Phykomycophyta Pascher in Beih. bot. Centralbl. 48, Abt. 2: 330 (1931), 



in part. 

 Biflagellatae Sparrow Aquatic Phycomycetes 487 (1943). 



Organisms of fungal or chytrid body type, that is, non-pigmented saprophytes or 

 parasites whose bodies are walled filaments or cells with or without rhizoids; the 

 walls consisting partially of cellulose; reproducing asexually by zoospores with 

 paired unlike flagella which are, so far as is known, respectively pantoneme and 

 acroneme, and usually sexually by fertilization, the eggs being distinct cells within 

 the oogonia. The regularly cited example and evident standard genus of the group 

 is Saprolegnia. 



Conventional botanical classification recognizes within the group of Fungi a sub- 

 ordinate group named Phycomycetes, which is in turn divided into Oomycetes and 

 Zygomycetes, the former including the chytrids. This arrangement suggests an evo- 

 lutionary series, originating perhaps among non-pigmented flagellates, and leading 

 through chytrids, typical Oomycetes, and Zygomycetes to the typical fungi. It does 

 not now appear tenable. Couch (1939) pointed out differences between Oomycetes 

 and Zygomycetes which make any direct connection between them appear quite 

 improbable; and his observations on flagella showed that only a small minority among 

 organisms of chytrid body type have anything to do with the proper Oomycetes. 



There is an old hypothesis (Sachs, 1874) that Vauchcria may represent the direct 

 ancestry of Saprolegnia. This hypothesis could not be taken seriously while Sapro- 

 legnia and its allies were known to produce heterokont zoospores, while Vaucheria 

 was supposed to be a typical isokont green alga. Now it again appears probable. It 

 implies that in the present group the fungal body type is more primitive than the 

 chytrid. 



The Oomycetes may be organized as three orders. 

 l.Of fungal body type, i.e., consisting of fila- 

 ments. 



2. Essentially aquatic Order 1. Saprolegnina. 



2. Mostly not aquatic, parasitic on higher 



plants Order 2. Peronosporina. 



1. Of chytrid body type, i.e., the cells not elong- 

 ated to filamentous form, though sometimes 

 proliferating or producing rhizoids Order 3. LAGENroiALEA. 



