Phylum Phaeophyta [81 



sites attacking land plants under moist conditions. The reproductive structures act 

 as sporangia if formed in water, as conidia if formed in air. Pythium, saprophytic on 

 plant remains in water or parasitic on algae or higher plants, includes some forty 

 species (Matthews, 1931). The few other genera include perhaps a dozen species. 

 Zoophagus produces specialized branches which serve as traps for rotifers which are 

 parasitized and killed. 



Family 2. Albuginacea [Albuginaceae] Schroter op. cit. 110. Parasites of higher 

 plants, called white rusts, the masses of conidia which push up and burst through the 

 epidetmis being of a white color. Albugo. 



Family 3. Peronosporacea [Peronosporaceae] Cohn in Hedwigia 11: 18 (1872). 

 Parasites of higher plants, called downy mildews. The ovoid conidia are produced 

 solitary or in clusters, not in chains, on elongate conidiophores, usually branched, 

 projecting through the stomata of the hosts. This numerous group includes the 

 agents of some of the most important diseases of cultivated plants. Plasmopara viti- 

 cola, causing downy mildew of grapes. Phytophthora injestans, the cause of the blight 

 of potatoes which produced the Irish famine of 1846. Peronospora, the many species 

 attacking many kinds of plants. 



Order 3. Lagenidialea [Lagenidiales] Karling in American Jour. Bot. 26: 518 

 (1939). 

 Suborder Ancylistineae Engler in Engler and Prantl Nat. Pflanzenfam. I Teil, 



Abt. 1 : iv ( 1897), for the most part, not as to the type genus Ancylistes. 

 Order Ancylistales Auctt., in part. 

 Oomycetes of chytrid body type, parasites consisting of walled cells which are 

 more or less isodiametric, sometimes proliferating or producing rhizoids, but not 

 forming extensive branched filaments. The cells become multinucleate. Mitotic 

 figures of Olpidiopsis as described by Barrett (1912) and McLarty (1941) are quite 

 as in the preceding orders, with sharp-pointed intranuclear spindles apparently with 

 centrosomes at the poles. In the usual course of events, each cell develops an exit 

 tube to the exterior of the host, and the protoplast becomes divided into uninucleate 

 cells which escape as unequally biflagellate zoospores. Fertilization, by the migration 

 of the protoplast of one cell into another, has been observed; the zygote becomes a 

 thick-walled resting spore. 



1. Internal parasites without rhizoids. 

 2. The cells not proliferating. 



3. The zoospores diplanetic Family 1. Ectrogellacea. 



3. The zoospores not diplanetic Family 2. Olpidiopsidacea. 



2. The cells proliferating. 



3. Marine Family 3. Sirolpidiacea. 



3. Fresh-water Family 4. Lagenidiacea. 



1. External parasites with rhizoids Family 5. Thrau stock ytriacea. 



Family 1. Ectrogellacea [Ectrogellaceae] Scherffel in Arch. Prot. 52: 6 (1925). 

 Ectrogella, Eurychasma, Eurychasmidium, Aphanomycopsis, with about a dozen 

 known species, attacking diatoms and red and brown algae. 



Family 2. Olpidiopsidacea [Olpidiopsidaceae] Sparrow in Mycologia 34: 116 

 (1942). Olpidiopsis and a few other genera, with some thirty known species, attack- 

 ing water molds, green algae, red algae, and other aquatic organisms. 



Family 3. Sirolpidiacea [Sirolpidiaceae] Sparrow 1. c. Sirolpidium and Pontisma, 

 each with one species, attacking marine algae, respectively green and red. 



