32 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



wavy exospore; warts, spines and knobs non-cellu- 

 losic ; content coarsely granular with one to several 

 large or small refringent globules ; male or com- 

 panion cells when present, single or numerous, oval, 

 spherical, elongate or vermiform, hyaline, smooth 

 or warty and spiny. Resting spores transformed di- 

 rectly into zoosporangia in germination and liberat- 

 ing zoospores through exit tubes. 



General Considerations 



As is shown in the synonomy above species of this 

 genus have undergone the usual taxonomic vicissi- 

 tudes and have been bandied about from one genus 

 to another. Cornu created the genus Olpidiopsis in 

 1872 for five parasites which he found in various 

 species of the Saprolegniales. In three of these para- 

 sites he observed thick-walled resting spores to 

 which were attached one or more smaller empty 

 vesicles which he assumed to be male cells or anther- 

 idia. Although Cornu did not specifically mention 

 the presence of attached cells as the distinguishing 

 generic character of Olpidiopsis, it subsequently 

 came to be regarded as such. Reinseh ('78) later 

 observed the passage of the protoplasm of the small 

 cell into the larger thallus, and since that time the 

 resting spores of Olpidiopsis have been generally 

 believed to arise from fusions of unlike and sexually 

 differentiated thalli. In a subsequent study of these 

 parasites, Fischer ('80) failed to find empty male 

 companion cells attached to what he believed to be 

 the resting spores of 0. Saprolegniae. Accordingly. 

 two years later ('82) he rejected the cellule adja- 

 eeiite character as diagnostic for the genus, and re- 

 dlagnosed and described Olpidiopsis as having 

 asexual resting spores. Further studies in the mean- 

 time, however, convinced Fischer that his earlier ob- 

 servations were incorrect, and in 1892 he inter- 

 preted the genus in the original sense and estab- 

 lished a second genus, Pseudolpidium for the 

 Olpidiopsis-\ike species with asexual resting spores. 

 In this genus he included P. Saprolegniae and P. 

 fusiforme, for which he described resting spores, 

 and four additional doubtful species in which rest- 

 ing spores were unknown. 



In the meantime Zopf ('84) and Fisch ('81) had 

 described two similar parisites, 0. schenkiana and 

 Pleocystidtum parasiticum, with uniflagellate zoo- 

 spores and sexual resting spores in Spirogyra. Two 

 years later Schroeter established a new genus, Di- 

 plophysa, for Cornu's O. Saprolegniae and his own 

 D. elliptica which parasitizes Mesocarpus sp. 

 Fischer ('92), however, reduced Diplophysa and 

 Pleocystidtum to synonyms of Olpidiopsis and di- 

 vided Cornu's genus into two subgenera — Olpidiop- 

 sis with biflagellate zoospores, and Pleocystidtum 

 with uniflagellate zoospores. In the former he placed 

 0. Saprolegniae and 0. minor (0. fusiformis), while 

 O. schenkiana and 0. parasitica were included in 

 Pleocystidtum. The sporangia and resting spores of 

 several additional algal parasites were described by 



de Wildeman in 1895, and in 1911 Minden estab- 

 lished a new genus Pseudolpidiopsis (synonymous 

 with Pleocystidium and Diplophysa), in the family 

 Olpidiaceae for these species as well as 0. schen- 

 kiana and 0. parasitica. Inasmuch as the number of 

 flagella on the zoospores of de Wildeman's fungi 

 were unknown, Minden was not justified in refer- 

 ring these species to Pseudolpidiopsis. Since that 

 time the zoospores of 0. schenkiana and its synonym 

 0. parasitica have been shown to be biflagellate and 

 heterocont, so that Pseudolpidopsis also becomes a 

 svnonym of Olpidiopsis. In the meantime, Butler 

 ('07) added two additional species to the genus 

 Pseudolpidium. 



Since the time of Fischer and Butler until quite 

 recently very little critical study was made of Pseu- 

 dolpidium, although several new Olpidiopsis and 

 Pseudolpidium species were described, and these 

 two genera have been distinguished respectively by 

 the presence and absence of male cells on the rest- 

 ing spores. In 1939, however, McLarty and Shanor 

 independently discovered that the spiny structures 

 which Fischer had interpreted as the resting spores 

 of Pseudolpidium are nothing more than spiny 

 evanescent zoosporangia, thus showing that Fisch- 

 er's genus, based on the misinterpretation of these 

 sporangia, is no longer valid. McLarty found in ad- 

 dition that the majority of resting spores of 0. Ach- 

 li/ae develop parthenogenetically without sexual 

 fusion, which suggests further that other Pseudol- 

 pidium species, i.e., P. Pythii, P. gracile, and P. 

 stellatum, etc., with true resting spores lacking in 

 attached male cells are only parthenogenetic mem- 

 bers of Olpidiopsis. He ('41) accordingly amended 

 the diagnosis of Cornu's genus to include such spe- 

 cies and listed Pseudolpidium as a synonym. The 

 present writer is following this diagnosis almost 

 completely but retaining Pseudolpidium provision- 

 ally as a dumping ground for the species in which 

 no resting spores have yet been found, i.e., P. Glen- 

 odinianum, P. Sphaeritae and P. deformans. The 

 first two of these species will probably be included 

 eventually in Olpidiopsis, but P. deformans, because 

 of its amoeboid schizogonic thallus, appears to be- 

 long to a different group of organisms. 



McLarty and Shanor furthermore demonstrated 

 quite clearly from monozoospore infection experi- 

 ments that the number, size and shape of the zoo- 

 sporangia as well as the character of the spines, 

 warts, and knobs on the resting spores are highly 

 variable and of little diagnostic value in distinguish- 

 ing closely-similar species. It is accordingly almost 

 impossible to determine with certainty the identity 

 of most of the Saprolegnia- and .ic/i/^a-inhabiting 

 species which were only briefly and meagerly de- 

 scribed prior to 1939 and 1941. Until all species 

 have been as intensively studied as O. varians and 

 O. Achlyae, an accurate diagnosis of this genus is 

 well-nigh impossible, and for this reason the classi- 

 fication given below is to be regarded as temporary. 

 Particularly significant in diagnosis are the re- 

 sults of Shanor's ('40) and Miss Whiffen's ('42) 



