70 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



Pythium. The other unidentified species occurred as 

 a saprophyte in Ceramium diaphanum which had 

 been kept in a laboratory aquarium for several 

 weeks. One to several spherical (figs. 13—14) and 

 irregular thalli of variable size, 20-96 fi in diameter, 

 were found in a single internode. Each thallus de- 



veloped into a sporangium at maturity with up to 

 ten or more radiating, narrow tapering exit tubes, 7 /x 

 in diameter, which penetrated the host cell wall. 

 Zoospores and resting spores were not observed, and 

 it is accordingly uncertain whether or not this spe- 

 cies belongs in Petersenia. 



Chapter VI 



Lagenidiaceae 



Schroeter, 1897. Engler und Prantl, Die Nat. Pflanz'f . I, 1 : 88. 



This family includes a number of saprophytes and 

 parasites of algae, higher plants, nematodes, insects, 

 and other animals which are characterized primarily 

 by reniform, laterally biflagellate zoospores, and 

 sexually formed resting spores. The family was 

 formerly included in the Aneylistales, but in light of 

 Miss Berdan's ('37, '38) discovery that Ancylistes 

 is a genus of the Entomophthorales, the name Ancy- 

 listales is no longer tenable. Accordingly, in 1939 

 the author raised the family Lagenidiaceae to ordi- 

 nal rank, and since that time Sparrow ('42) has in- 

 eluded the Olpidiopsidaceae. and Sirolpidiaceae as 

 well as the Lagenidiaceae in this order. Whether or 

 not these families constitute a distinct order of equal 

 rank with the Saprolegniales, Leptomitales, Perono- 

 sporales, etc., is very questionable. According to 

 Sparrow's interpretation the Lagenidiales include 

 species with iso- and heterogamous types of repro- 

 duction as well as iso- and heterocont zoospores, and 

 as such it obviously cannot be regarded as more than 

 a temporary and convenient expedient of classifica- 

 tion. In view of our lack of knowledge relative to 

 many of the species, genera, and families included 

 in this order, it is perhaps wiser for the time being 

 to avoid placing the Olpidiopsidaceae, Sirolpidia- 

 ceae, and Lagenidiaceae in a distinct order. 



The thallus of the Lagenidiaceae varies from a 

 simple ovoid, unicellular, Olpidium-\ike cell to an 

 extended filamentous, branched, septate mycelium 

 which may be confined to a single host cell or occupy 

 several cells. These parasites and saprophytes gain 

 entrance info the host by an infection tube from 

 germinating zoospores. The thallus develops as an 

 extension and enlargement of the tip of the germ 

 tube and soon becomes long and filamentous or en- 

 larges into a globular, oval, lobed, and irregular 

 structure. It may remain unicellular and continuous 

 in some species or divide transversly into several 

 segments. With further growth these segments may 

 become oval, ellipsoid, and spherical, making the 

 thallus deeply lobed at the septa, or they may remain 

 cylindrical with little or no constrictions in the re- 

 gion of the cross walls. At maturity these segments 

 are holoearpically transformed either into zoospo- 

 rangia or slightly differentiated gametangia. In all 



species which have been tested the walls of the thal- 

 lus give a marked positive cellulose reaction. The 

 protoplasm, particularly in Lagenidium and Myzo- 

 cytium, usually includes a large number of refrac- 

 tive globules of various sizes, which give it a char- 

 acteristic refringent and gleaming appearance, but 

 at maturity and as sporogenesis begins it becomes 

 more greyish granular. 



In the majority of species the content of the spo- 

 rangium emerges as a globular mass from the exit 

 tube and undergoes cleavage into zoospores on the 

 outside in much the same manner as in Pythium. The 

 presence of a vesicular membrane around the proto- 

 plasmic mass and the zoospores which are subse- 

 quently formed has been reported in a number of 

 species, but appears to be lacking in others. There 

 is considerable disagreement in the literature about 

 the presence of this structure, and further intensive 

 study of its occurrence in the Lagenidiaceae is 

 needed. In a few species the zoospores are com- 

 pletely developed in the sporangium, emerge, and 

 swim directly away, or they are discharged prema- 

 turely, come to rest in a mass and complete their de- 

 velopment on the outside. In other species they en- 

 cyst in a loose mass at the mouth of the exit tube as 

 in Achlya and exhibit marked diplanetism. It is ac- 

 cordingly obvious that the process of zoosporogene- 

 sis and the initial behavior of the zoospores vary 

 from the Olpidiopsis to the Pythium and Achlya 

 types. The zoospores throughout the family are pre- 

 dominantly reniform and somewhat pyriform in 

 shape, and in some species a distinct ventral groove 

 is present in which the flagella are inserted. Hetero- 

 cont zoospores have been reported in two species. 



Sexual reproduction is predominantly heterogam- 

 ous, but in Lagena and Resticularia it is reported to 

 be isogamous. Isogamy is present in Lagenidium 

 sacculoides also, according to Serbinow ('07). The 

 segments of elongate thalli, as well as entire uni- 

 cellular thalli, which function as male and female 

 gametangia are only slightly or not at all differen- 

 tiated as sexual organs. They may occur among the 

 sporangia in the same thallus or in separate thalli, 

 but the presence of heterothallism has not been defi- 

 nitely proven. No monozoospore cultures and infec- 



