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The classification and physiology of the zoosporic plant-pathogen Olpidium brassicae and its relationships with the closely-related species are often confusing. This review focuses on these species and intends to differentiate them based on the literatures published since the discovery and establishment of the species by Woronin in 1878 under the name of Chytridium brassicae to current molecular era. The goal of this review is to help researchers better understand the taxonomy, the host range, and the potential role in plant health of O. brassicae-related species. To reach the goal, we reviewed the rationales behind the creation or reduction in synonymy of the different names for O. brassicae and its allied species in order to elucidate the evolution of the species concept on them based on the traditional morphological studies. Furthermore, the studies by molecular biology methods improve our knowledge and perspectives on O. brassicae and its host specificity. In particular, we clarify the differences between O. brassicae and Olpidium virulentus, and propose potential new research avenues. We therefore hope that this review will give a better perspective on Olpidium spp. and their potential role in the root microbiome of plants in natural environments and in agricultural settings.

The investigations csrried out on algae revealed the following species of fungi from the order of Chytridialis Hawksworth et al. (1995) parasitizing on algae: Rhizophydium subgulosum, R. ganlosporum, R. planctonicum, Entophlyctis rhizina and Harpochytrium hedinii. These species arc new to Poland. The figure of resting spore of Entophlyctis rhizina is the fint graphic documentation of this species.

A new species Chytridium caloneidis Kadłubowska is described and illustrated in the paper. The species was found in the Brześnia brook near Jedrzejów. It differs from the other species in the genus with unique corrugated wall of sporangium.

Chytridium olla A. Braun, the first described chytrid and an obligate algal parasite, is the type for the genus and thus the foundation of family Chytridiaceae, order Chytridiales, class Chytridiomycetes and phylum Chytridiomycota. Chytridium olla was isolated in coculture with its host, Oedogonium capilliforme. DNA was extracted from the coculture, and 18S, 28S and ITS1-5.8S-ITS2 rDNA were amplified with universal fungal primers. Free swimming zoospores and zoospores in mature sporangia were examined with electron microscopy. Molecular analyses placed C. olla in a clade in Chytridiales with isolates of Chytridium lagenaria and Phlyctochytrium planicorne. Ultrastructural analysis revealed C. olla to have a Group II-type zoospore, previously described for Chytridium lagenaria and Phlyctochytrium planicorne. On the basis of zoospore ultrastructure, family Chytridiaceae is emended to include the type of Chytridium and other species with a Group II-type zoospore, and the new family Chytriomycetaceae is delineated to include members of Chytridiales with a Group I-type zoospore.

Chlorophyll fluorescence imaging is a non-invasive method to monitor the metabolic state of photosynthetic organisms. We used spatially resolved (imaging) microscopic measurements of chlorophyll fluorescence kinetics to follow the fate of individual cells of the filamentous brown alga Pylaiella littoralis infected by the biotrophic parasite Chytridium polysiphoniae (Chytridiomycota). These measurements showed strong differences between individual parameters of the inhibition of photosynthesis, revealing important details about the mechanism of damage. The dark-adapted photochemistry of photosystem II itself (measured as Fv/Fm, where Fv = Fm − F0) remained unaffected until a very late stage of damage to the cell, while the light-adapted efficiency of PSII electron transport decreased earlier. A particularly complex pattern was found for the changes in nonphotochemical quenching (NPQ). The shape of the fluorescence transients suggests that the changes in NPQ during the actinic light period are caused by cha...

The Chytridiomycota is in need of taxonomic revision, especially the largest order, the Chytridiales. We analyzed 25 isolates in, or allied to, the Chytridium clade of this order. Isolates were selected based on one or more of the following criteria: (i) having a large subunit molecular sequence similar to that of the type of the genus Chytriomyces, (ii) having specific zoospore morphology, and (iii) currently classified as a species in the genus Chytriomyces . We examined ultrastructural characters and partial sequences of large subunit and small subunit rDNA and generated a phylogenetic hypothesis using maximum parsimony and Bayesian analyses. The sequence analyses strongly supported the Chytridiaceae, Phlyctochytrium, and Chytriomyces angularis clades, and each clade had a specific zoospore type. Developmental morphology of the thallus did not mirror the DNA-based phylogeny. Based on the results of phylogenetic analyses of sequences and ultrastructural characters, we emend the Chytridiaceae by including exogenous and polycentric development and define the family on the basis of a single zoospore type. Species identified as being in the genus Chytriomyces occur in several separate, well-supported clades along with species currently classified in seven other genera ( Asterophlyctis , Entophlyctis , Obelidium , Physocladia , Podochytrium , Rhizoclosmatium , and Siphonaria ), indicating that Chytriomyces as currently defined is polyphyletic.

In the cryoseston community of the Pirin Mountains, 18 species were determined. Chlorophyta: Chlamydomonas nivalis (predominant), Chloromonas brevispina, Chloromonas rostafinski, Chlainomonas rubra (new genus and species for Bulgaria, documented in Europe for only the second time), Cystococcus nivicolus and Stichococcus nivalis. Bacillariophyceae: Aulacoseira granulata var. angustissima, Hantzchia amphioxys, cf. Surirella. Fungi: cf. Chytridium chlamydococcii. Deuteromycetes: Selenotila nivalis, Chionaster nivalis, and saprophytic fungae cf. Myzocytium, Rhodosporidium toruloides, Alternaria sp. and cf. Cladosporium, in pollen grains. Bacteria: Leptothrix ochracea. Ciliata: Vorticella campanula. The composition of cryoseston in the Pirin Mountains is characteristic for high mountains where Chlamydomonas nivalis predominates.

Podochytrium dentatum occurred during spring and fall on chitin bait placed in a Maine lake. Zoospore ultrastructure is of the chytridialean type and is a variant of the Chytridium subtype. The zoosporangium forms from an apical expansion of the encysted zoospore. At maturity the dentate apical part of the zoosporangium, with orange contents, is separated from the basal part of the zoosporangium by a wall. Zoospores discharge in a mass surrounded by papillar material. Rhizoids branch from a knob-like rhizoidal base and are either fine or coarse.

Rhinosporidiosis is caused by Rhinosporidium seeberi. Most mycologists believe that R. seeberi is either a Chytridium related to the Olpidiaceae (order Chytridialis, class Chytridiomycetes) or a Synchytrium. This is the first documented case of tumoral rhinosporidiosis in a Sri Lankan and the third documented case in the world literature. A 44 year old male presented with a large mass above the thigh and a similar mass over the anterior chest wall, both masses contained R. seeberi. Later examination of the patient revealed nasal polyps, confirming that the tumors were due to systemic spread of this infection.

Unialgal cultures of the brown alga Pylaiella littoralis (L.) Kjellman infected by either Eurychasma dicksonii (Wright) Magnus (Oomycota) or Chytridium polysiphoniae (Cohn) H. E. Petersen (Chytridiomycota) were used to elaborate the host ranges of these pathogens. Infection experiments with 48 host species covering 13 orders of the Phaeophyceae showed that 45 species were susceptible to attack by Eurychasma and 23 to Chytridium. The two pathogens showed host-specific differences in generation times: while in Pylaiella the shortest cycles were 16 days for Eurychasma and 6 days for Chytridium, one and five days more, respectively, were required in Acinetospora. Heavy parasite attack on the microscopic stages of host species with heteromorphic life histories, like kelps (Laminariales), is documented and discussed as a potential regulatory factor for the population dynamics of macroalgae.

Aquatic fungi from four brackish water lakes; Edku, Burullus and Manzala lakes which are located at the northern region of Egypt and Qarun lake that located in El-Fayoum city are reported in this manuscript. Twenty-nine fungal species which belong to 19 genera of aquatic fungi were recovered from water samples collected from the studied lakes. The most frequently isolated fungal species were Chytridium conferrop, Allomyces throughout and Rhizoclosmatium globosum. Thraustochytrium amoeboidum and Leptolegniella exoosporus have a moderately occurrence frequency. The maximum fungal count of recovered aquatic fungi was recorded in Burrullus lake followed by EdKu, Manzala and Qarun lakes. This study was extended to test the ability of six selected aquatic fungi ( Brevilegniella keratinophila, Blastocladiella cystogena, Chytridium conferrop, Entophlyctis variabilis, Schizochytrium mangrovei and Thraustochytrium rosii), to uptake the radionuclide from their culture medium as a step to biologically treat the waste water or solution with radio-cesium and radio-cobalt. Fifty seven % of Cs-137 and 35% of Co-60 could be removed from liquid waste by the selected aquatic fungi.

During our survey of chytrids occuring on algae in fresh waters in the northwestern part of the Russian Federation we never observed mass development of parasites, but if cultures of Chlorococcum minutum Starr or Tribonema gayanum Pasch. were inoculated with a sample of water (0.5 L), the parasites appeared in 10% of the cases. Two-clonal (alga and parasite) cultures were obtained by plating of the material on the lawn of algal cells on the solid medium with benzyl penicillin. 22 cultures are now available. For the most part, cultures belong to Rhizophydium species. Chytridium lagenula (Braun) sensu Scherffel is grown on Tribonema gayanum cells. Cultures differ in possible host range, where some have a very wide host range, but others grow only on the cells of Chlorococcum minutum (from 40 strains of different clorococcalean algae examined). Only two Rhizophydium spp. cultures are opportunists and grow on dead algal cells and organic media. Collection is used for the examination of interaction between algae and fungi.

Entophlyctis luteolus, a new species of sap- rophytic Chytridiales from aquatic habitats, develops endogenously or exogenously on nutrient agar and usually has two rhizoidal axes, which are slightly swol- len at the base. Zoospores emerge en masse from the sporangium after deliquescence of the tip of the dis- charge tube and are surrounded by gelatinous mate- rial. Resistant sporangia form on onion skin. This is the first report of a species with monocentric, exog- enous development that has a Chytridium subtype of zoospore. Other monocentric, exogenously develop? ing species that have been studied have a Nowakows- kiella subtype of zoospore. Exogenous, monocentric development cannot be considered a homologous character state in all species of the Chytridiales.

The zoospore ultrastructure of 12 species of Rhizophydium is described. Species include the following: R. chlorogonii (Serbinow) Jaczewski; R. constantineani Saccardo; R. haynaldii (Schaarschmidt) Fischer; R. capillaceum Barr; two morphologically and cytologically different species, each previously identified as R. sphaerotheca Zopf; R. patellarium Scholz; R. biporosum (Couch) Barr; R. subangulosum (Braun) Rabenhorst; R. laterale (Braun) Rabenhorst; R. sphaerocarpum (Zopf) Fischer var. spirogyrae Barr; and two isolates of R. pollinis-pini (Braun) Zopf. The Rhizophydium zoospore is basically similar to the Chytridium zoospore having (1) the nucleus, a compact cluster of ribosomes, one or more mitochondria, and a microbody – lipid globule complex compartmentalized into the core of the zoospore by a double membrane system and (2) two to five microtubules connecting one side of the kinetosome to the rumposome on the lipid globule surface and thus anchoring the lipid globule in a lateral–posterior position in the zoospore. Rhizophydium patellarium does not have kinetosome-associated microtubules or a rumposome but does have the membrane-bound core area. In all species, a microbody and mitochondrion are associated with the lipid globule. The number of mitochondria varies from 1 in some species to several or to over 30 in other species. In one isolate of R. pollinis-pini, there is 1 large mitochondrion and in the other there were 30–35 small mitochondria. The peripheral cytoplasm of all species contains clusters of vesicles or endoplasmic reticulum which bud from the double membrane system, vesicles of moderate electron density, and vacuoles of various sizes; R. capillaceum, R. patellarium, and R. subangulosum have in addition vesicles which contain very electron-dense material. Rhizophydium capillaceum and R. sphaerocarpum zoospores have virus-like particles and the R. biporosum zoospore contains a paracrystalline body. The taxonomic significance of the observations and the relationship of Rhizophydium to other chytrids are stressed in the Discussion.

Thallus development, zoospore size, zoospore ultrastructural complexity and organization, and flagellum length are cited as important in phylogeny of the Chytridiales (chytrids) and should be the bases for this classification. Discharge of zoospores is also cited as important although emphasis is not placed on operculation. It is proposed that simple, eucarpic, monocentric chytrids which discharge zoospores following dissolution of the sporangium wall evolved into multipapilliate species of Rhizophydium and 2 lines of evolution from these species are documented with examples. In one line they evolved into single-pored species such as R. pollinis-pini , then to Chytridium and Endochytrium -like chytrids and to polycentric chytrids such as Nowakowskiella and Cladochytrium . The second line evolved from multipapilliate Rhizophydium species to Phlyctochytrium and Entophlyctis , and to the order Blastocladiales. Rhizophlyctis rosea and some olpidiaceous chytrids, because of a fibrillar rhizoplast in their zoospores do not appear close to Rhizophydium -related chytrids and may require separate subordinal rank in classification. It is proposed that zoospores of the advanced members of the class Chytridiomycetes have reached limits for further zoospore development because of size; however, the zoospore is no longer essential for them because they have developed a filamentous habit of growth.

Summary An other gall-producing Chytridiale, Chytridium sexuale Koch parasitizing on Vaucheria walzi Rothert and its first recognition in Europe are described.

In a high-rate oxidation pond, 0.1 to 1.0% of the algal population of Scenedesmus obliquus was found to be infected by a chytrid. When suitable conditions developed, these infections burst into massive epidemics that killed most of the algae. The major factors triggering massive infections were optimal oxygen concentration and low concentrations of potassium and magnesium cations. The fungicide Benomyl was effective in preventing infection at a concentration of 1 mg/liter.

Consideration of the population curves of Oocystis crassa and O. lacustris in Lake Manitoba during the summers of 1966 and 1967, and July 1968, indicated that the aquatic fungus Chytridium deltanum was able in two instances to attack growing populations of these algae. This strongly suggested that the fungus was a parasite. However, in July 1965, in Cadham Bay, the fungus bloomed as the host population stopped growing and began to decline. Probably the host cells were slightly senescent at that time and thus more susceptible to fungus attack. Consideration of the composition of the fungus population showed that during one epidemic at least, large numbers of zoospores were released every 7 to 9 days. This suggested a nearly synchronous development of the fungus population. It was also observed that zoospores, able to encyst and successfully infect one host, were sometimes unable to attack another potential host present at the same time. In 1966 and 1967 the fungus appeared a few days after the water had reached 25C. Comparison of culture data for the algae and field studies indicated that Chytridium deltanum most commonly grew on the algae at temperatures above the optimum for the algae.

A new Chytridium species, C. deltanum, is described growing on Oocystis crassa, O. lacustris, O. submarina, and O. parva. A sexual process is involved in the formation of the endobiotic resting spores. The occurrence of Chytridium oocystidis Huber-Pestalozzi on O. lacustris and O. crassa is briefly described. Three other fungi as yet not completely identified, but evidently new to science, are described on Oocystis spp. One of these appears to be a Lagenidium species.

In a survey of the incidence of parasitism of plankton diatoms by chytridiaceous fungi in the English Lake District particular attention has been paid to the occurrence of fungi on Asterionella formosa and Fragilaria crotonensis , and to the effect of parasitism on their seasonal distribution. Almost all the plankton diatoms are infected by fungi, some of which are described, including: Rhizophidium planktonicum, Chytriomyces sp., Zygorhizidium planktonicum Canter, n.sp., and Septosperma anomala on Asterionella formosa; Zygorhizidium melosirae, Septosperma sp., and? Rhizophidium fusus on Melosira italica ; and Chytridium versatile on Tabellaria . Some of the parasites cannot be named until further details of their life history are known. Parasites of plankton diatoms are also recorded from other bodies of water in Great Britain and various parts of Europe. Fluorescence microscopy has been used to follow the effects of parasitism on the host cells. The occurrence of bacteria on two of the fungi is discussed.

The life-history of Chytridium isthmiophilum sp.nov., which parasitizes Staurodesmus curvatus (West) Teiling in the plankton of Windermere and Ullswater in the English Lake District, is described.

The operculate genus Chytridium Braun is emended and restricted to approximately 25 known species and several incompletely known members which lack an apophysis and develop much like species of Rhizophydium, insofar as the zoosporangium and absorbing or rhizoidal system are concerned, and form endobiotic or intramatrical resting spores. This interpretation corresponds fairly closely to Braun's diagnosis of the type species. A new genus, Diplochytridium, is established to segregate the former Chytridium species with an endobiotic or intramatrical apophysis or prosporangium and resting spores, which may develop sexually or asexually. Some of these species have a well-defined endo-exogenous alternation of growth and development in which the apophysis appears to function as a prosporangium. As interpreted here, Diplochytridium includes approximately 20 of the known species. Another new genus, Canteria, is created for a parasite of Mougeotia which Canter first described as a species of Phlyctidium but later found to develop endobiotic resting spores or zygospores by the fusion of conjugation tubes.

Several monocentric chytrid species of the generaPhlyctochytrium,Rhizidium,Chytridium,Chytriomyces andKarlingia were isolated on various substrata from soils of Oceania. Among these are two new species,Phlyctochytrium megastomum andRhizidium endosporangiatum. The former species is characterized chiefly by sporangia with an usually large apical, subapical, or a lateral exit orifice, the persistence of remnants of the pailla wall at the edge of the exit orifice, and by small zoospores.

A chytrid is described on heterocysts of Aphanizomenon flos-aguae (L.) Ralfs from preserved material of plankton from a pond near Sedlice, South Bohemia. For the time being it is included provisionally under the binomial Chytridium cornutum Braun.

Rhizophidium coleochaetes (Nowak.) Fischer has been rediscovered and the presence of a tubular rhizoid and an operculum demonstrated. The fungus thus appears closer to Chytridium than to other genera in which it was subsequently placed.

Chytridium aggregatum occurs as a saprophyte on dead and decaying filaments of Spirogyra crassa, Cladophora sp., and Oedogonium sp. in New Jersey and New York and has been cultured to a limited ext...

Water, soil, and alga samples collected on Ross Island and the dry valleys of Victoria Land during January and February, 1971, were found to contain monocentric chytridiaceous fungi, a blastocladiaceous fungus, and filamentous Oomycetes. Of the alga-infesting chytrids, only Scherffelliomyces appendiculatus and Chytridium versatile could be identified with certainty. Saprophytic chytrids which grew on baits were represented by Rhizophlyctis rosea, and two new species, Rhizophydium proliferum and Phlyctochytrium recurvastomum. Catenophlyctis variabilis occurred as a saprophyte of keratinous substrata. The Oomycetes were represented by Pythium tenue and an undetermined sterile species of Pythium. Aside from unverified observations of Aphanomyces, members of the Saprolegniaceae were lacking. The low diversity of aquatic Phycomycetes with frequent reoccurrence of a few species is noted and commented upon.

The saprophytic soil chytrid Rhizidium richmondense sp.nov., which grows on cellulosic baits, is described together with its parasites Chytridium suburceolatum sp.nov., C. parasiticum sp.nov., and Septosperma rhizophidii Whiffen. Rhizidium richmondense is considered essentially inoperculate, but a portion of the sporangium wall may occasionally separate at dehiscence. C. parasiticum also parasitizes Rhizophlyctis sp. and Entophlyctis sp., and Septosperma rhizophidii parasitizes Rhizophlyctis sp. Further, Chytridium parasiticum hyperparasitizes C. suburceolatum and Septosperma rhizophidii.

Chytridium marylandicum Paterson is a highly specific saprophyte which grew only in the mucilage of colonies of Botryococcus braunii. During the summers of 1965–1968, Chytridium multiplied on the Botryococcus population as the alga was approaching the maximum. The year 1968 was a particularly good summer for both the alga and the fungus. The fungus maximum occurred shortly after the algal maximum and at this time 79.5% of the observed Botryococcus colonies supported fungus thalli. At this time as many as 25 Chytridium thalli were occasionally observed on a single Botryococcus colony. During the 1968 Chytridium bloom, it was observed as well that the composition of the fungus population changed with time. A marked increase in germinated zoospore cysts every 5 days suggested that the asexual development of the fungus under these apparently optimum conditions took 5 days. Botryococcus population levels showed positive correlations with conductivity and temperature. Similarly Chytridium showed positive correlations with conductivity and temperature and with increasing Botryococcus numbers. The appearance of Chytridium marylandicum, therefore, was favored by conditions optimum for Botryococcus braunii.

DURING RECENT YEARS there has been increasing interest in the use of nutritional characters in tracing phylogenetic relationships among the aquatic Phycomycetes. In 1950, Cantino gathered together all the important nutritional data on the water molds and proposed a tentative phylogenetic arrangement of orders based partly on nutritional characters interpreted in terms of Lwoff's (cf. 1932, 1944) hypothesis of regressive physiological evolution. Although Cantino considered speculation along these lines to be promising, he pointed out that the nutritional information available was not sufficient to warrant *any far-reaching generalizations. Because the order Chytridiales holds a key position in the phylogeny of the uniflagellate water molds, and because the physiology of relatively few of its species had been studied, an investigation was begun on the nutrition of two chytrids, Chytridiwn sp. and Macrochytrium botrydioides Minden. No member of either genus had been studied previously from a nutritional point of view. The principal accounts of nutritional studies in the Chytridiales are those of Whiffen (1941), Stanier (1942), Quantz (1943), Ajello (1948), and Haskins and Weston (1950). These reports present valuable information on species belonging to ten genera, but Rhizophlyctis rosea is the only species that has been comprehensively investigated thus far (cf. particularly Stanier, 1942). ORGANISMS AND METHODS.-In the spring of 1947, D. F. V. Ranzoni made collections of skeletonized leaves and debris from a stream near Pope Valley, California. Water cultures inoculated with this material were baited with autoclaved grass blades and placed in a window box where the temperature ranged between 10? .and 15?C. It was on the grass blades in one of these cultures that Dr. Ralph Emerson, almost a year later, discovered the Chytridium sp. that was used in the study reported here. Macrachytrium was also found on grass blades, in a water culture that had been inoculated with plant debris which Dr. Ranzoni had collected in the Middle River, seven miles west of Stockton, California, in the spring of 1950. Since the original discovery of Macrochytrium by Minden in 1902, it has been reported by only two other investigators, Lund (1934) and Kanouse (in Sparrow, 1943, p. 368). The first pure cultures of these organisms on

In a recent note (1937) I pointed out that the spelling of Gobi's (1879) algal genus Asterocytis differs slightly from de Wildeman's (1893) chytrid genus Asterocystis and that there were no orthographic grounds for substituting Olpidiaster for the latter, as Pascher (1917) had maintained. Shortly thereafter Arwidsson (1938), however, showed that Berkeley and Broome (1875) had used the name Astrocystis for a group of ascomycetes, and since Asterocystis is but an orthographic variation of the latter, Berkeley and Broome's genus has priority over de Wildeman's. Pascher's viewpoint has thus been confirmed, but from other evidence than that which he presented. In a study of the early mycological literature I have found another case of priority among the chytrid genera. In 1855 Braun established Phlyctidium as a sub-genus of Chytridium to include non-operculate species whose intramatrical absorbing system consists of an unbranched peg, knob, or short filament. A few years later Rabenhorst (1868) raised it to generic rank, and since that time it has been recognized as such by most students of the chytrids. A survey of the literature, however, shows that Wallroth used this name for a group of ascomycetes as early as 1833, and since Phlyctidium was thus established subsequent to Fries (1821-1832) Systema mycologicum, it has status and validity under the present rules of nomenclature. Braun was apparently unaware of Wallroth's genus, for in none of his writings have I been able to find any reference to it. The thirteen ascomycetous species included by Wallroth in Phlyctidium have since been gradually transferred to other genera as far as I am aware, and the genus is no longer recognized among the ascomycetes except as a tautonymy. As has been pointed out by numerous investigators, it is very doubtful whether the chytrids included at present in Phlyctidium are sufficiently different from those of Rhizophidium to justify a 286

Catenochytridium hemicysti is a monocentric chytrid with exogenous-endogenous development. A prosporangium develops inside the germ tube and the incipient sporangium develops from the outflow of protoplasm through the zoospore cyst. The zoospore cyst ruptures longitudinally and remains appended to the base of the sporangium. Sporangia are operculate, the single operculum is flexuous and folds up or collapses. Zoospores are released as a globose mass, and almost at once drift apart before swimming away. C. hemicysti utilizes glucose, cellobiose, sucrose, lactose, galactose, starch, cellophane (cellulose), and xylan (hemicellulose). It utilizes organic, ammonium and nitrate nitrogen, and it requires thiamine. It has a zoospore similar to Nowakowskiella, Cladochytrium and Allochytridium. The systematic relationship of Catenochytridium to Chytridium and Diplochytridium is discussed.

SUMMARY Single-sporangium isolates of Chytridium ottariensis, Chytriomyces hyalinus, Phlyctochytrium powhatanensis, and Rhizophydium sphaerocarpum have a stable type of thallus development regardless of the growth medium or substrate used. However, medium is highly influential on the size range of sporangia and resting spores. Thallus growth on standard chytrid baits is epi-endobiotic and also interbiotic; resting spores produced on these baits occur on or in the substrate. Sporangium and resting spore size ranges for 17 isolates of C. hyalinus on a given medium were not significantly different. Apophysis shape within any one strain on any medium was highly variable and ranged from spherical, clavate, elongate, to catenulate. Both lid and flap opercula occurred in five of the 17 strains but in the remaining 12 the opercula were either flap or lid but not both. Location of thallus, position of resting spore, and presence of catenulate apophyses were not constant within any strain for any medium or substrate. In an exploration of species concepts in the chytrids, it becomes immediately apparent that the constancy of the characters used to delineate families, genera, and species needs verification. The stability of many characters used for separation of genera has not been established since very few species of chytrids have been studied in axenic culture or tested for variability on natural substrates. Some indications of the morphologic plasticity of these organisms are found in recent

In the course of an examination of conjugating filaments of Spirogyra Weberi Czurda, collected in a roadside ditch near Seymour, Wisconsin, in the early summer of 1938, a rhizidiaceous fungus was found parasitizing the zygospores but not the vegetative cells. Because of its characteristic aculeated zoosporangia and its general habit of growth the organism was recognized as one described by Blytt in 1882 as Chytridium spinulosum. Study of the method of zoospore discharge and the appearance of empty zo6sporangia revealed that the apical structure, taken by Blytt to be an operculum of the Chytridium type, is actually an apical ornamentation similar in certain respects to the apical spine of Obelidium. It plays no part in zo6spore discharge since the spores escape through a sub-apical exit pore. On the basis of this difference it seems necessary to separate this species from Chytridium as the type of a new genus. The name Blyttiomyces is thus proposed in commemoration of the man who first collected this interesting fungus. Since Blytt (1882) was unable to see zoospore discharge in his material, he concluded from the general appearance and location of the sporangial apiculus that its function was that of an operculum. This, in addition to the intramatricality of the resting spores, led him to conclude that he was dealing with an undescribed species of Chytridium, and he accordingly described the chytrid under the binomial of Chytridium spinulosum. The present observations are not the first to show the inoperculate nature of the sporangium; it was recognized by Petersen (1910) since he described its dehiscence by a lateral orifice. It was also recognized later by Scherffel (1926) since he stated clearly that the apical 558

Rhizophydium androdiocles sp.nov. is described from the plankton of Loch Leven, Scotland, where it parasitizes cells of the colonial alga Dictyosphaerium pulchellum Wood. Its generic placing remains tentative as dehiscence of the sporangium was not observed. The resting spore is formed after an unusual sexual process in which the female settles on a male thallus already established on a cell of the alga.

Summary The morphology and life history of seven aquatic Synchytriaceae are described. Micromyces zygogonii Scherffel, M. petersenii Scherffel and Micromycopsis fischeri Scherffel are new records for Great Britain; Micromyces laevis, Micromycopsis intermedia and M. mirabilis are new species; and Endodesmidium formosum gen.nov. sp.nov. In Endodesmidium the sporangia emerge from the sorus as non-swarming zoospores, and it is believed this represents a primitive condition within the group. References to ‘asterospheres’ in the older British literature are cited, and the validity of records of Micromycopsis and Micromyces spp. are considered.