RHIZIDIACEAE 69 



WoROxixACEAE. This family is represented by 15 species of 

 endoparasites of Saproleginales and Pvthiales. They differ from 

 all other chytrids in that their zoospores are biflagellate. Olpidi- 

 opsis and Rozella commonly cause the hyphae of Saprolegnia, 

 Achlya, and Allomyces to be swollen. Asexual spores, formed 

 in ellipsoidal sporangia, are emitted through exit tubes. Thick- 

 walled, spiny oospores arise by migration of multinucleate proto- 

 plasts from small antheridia into multinucleate oogonia formed on 

 closely juxtaposed thalli. Sexuality in Olpidiopsis saprolegniae 

 was studied by Barrett (1912) and Diehl (1935), in O. hixiir'nvis 

 by Barrett (1912), and in O. achlyae by iMcLarty (1941). The 

 germination of the oospores has not been observed. 



Sparrow (1943) places Olpidiopsis in the Lagenidiales, Rozella 

 in the Olpidiaceae, and Woronina in the Plasmodiophorales. 

 This fact shows that the Woroninaceae, as formerly understood, 

 are not chytrids and are not a group of similar forms. In fact, 

 in a recent study, Karling (1942) monographed a heterogeneous 

 group of 80 biflagellate species, which he divided more or less 

 arbitrarily into five families: Woroninaceae, Ectrogellaceae, Ol- 

 pidiopsidaceae, Sirolpidiaceae, and Lagenidiaceae. The fact that 

 these species possess a pair of flagella, whereas all chytrids are 

 uniflagellate, constitutes an adequate basis for regarding them as 

 non-chytrids. He therefore regards them as a distinct group of 

 Phycomycetes and does not place all of them in a single order. 



Rhizidiaceae. The Rhizidiaceae constitute a group of ap- 

 proximately 100 species, mostly ectoparasites. They possess 

 globular or elongated plant bodies attached by rhizoidal branches. 

 They may be found on various algae, both marine and fresh- 

 water species, and upon aquatic fungi and insects. The best- 

 known species occur on Spirogyra, Oedogonium, and various des- 

 mids and diatoms. Rhizophidhim pollinis-pini is common on 

 pollen grains floating in water. 



The swarm cells are uniflagellate and may function either as 

 asexual spores or as gametes. Couch's (1935) account of sexu- 

 ality in R. ovatinn states that the male gamete settles on a fila- 

 ment of Stigeoclonium and attaches itself by a delicate rhizoid. 

 Soon thereafter a female s^amete becomes attached to the male, 

 both increase in volume, the protoplasmic content of the male 

 cell passes over to the female cell, and the two nuclei unite. 

 The zygote formed is capable of germination within a few days. 



