90 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



bility that it is not identical to the latter species thus 

 remains to be shown. 



Sparrow ('36, p. 463, fig. 4q) further described 

 an elongate th alius consisting of a linear series of 

 elliptical segments, 20-22 p X 18-20 p., connected 

 by narrow cylindrical, refractive isthmuses in Syne- 

 dra sp., which he believed may likewise relate to 

 Myzocytium. He did not, however, observe any de- 

 velopmental and reproductive stages. 



In connection with the above report of doubtful 

 Myzocytium species it may be pointed out that Stein 

 ('51, pi. 18, figs. 1-7; '59, pi. 4, figs. 49-55) figured 

 an elongate body in Vorticella microsoma which he 

 believed relates' to the developmental cycle of this 

 animal. At maturity this thallus becomes contorted 

 and lobed and give's rise to bean-shaped spores in a 

 spherical, extramatrical vesicle. The structure and 

 appearance of the sporangia and spores suggest very 

 strongly that they may relate to a species of Myzo- 

 cytium'. He ('59,' pi. i, fig. 9) also showed another 

 vesicle with spores in V. nebulifera which may also 

 possibly belong to a similar parasite. 



Preissecker ('05, p. 3, fig. 43) figured and briefly 

 described a linear series of oval pale golden cells in 

 the roots of tobacco which he believed might repre- 

 sent a dwarf individual of Myzocytium sp., the larg- 

 est cell of which measures 28 X 37 ^ (fig. 52). Zoo- 

 spores and oospores were not observed. As Preis- 

 secker pointed out, the extremely thick walls of the 

 cells militate against the possibility that this is a 

 species of Myzocytium. 



It is not improbable that the heterogamous sexual 

 stages which Borzi ('84) included in the life cycle 

 of Rhizomyxa hypogea may relate to a root inhabit- 

 ing species of Myzocytium. This is the viewpoint 

 expressed by Schroeter ('97) and Minden ('11). 

 "More recently Barrett ('35) found similar sexual 

 stages in association with a plasmodiophoraceous 

 species in roots of Stellaria media and likewise con- 

 cluded that they relate to a species of Lagenidiaceae. 

 In view of these observations two of Borzi's figures 

 have been included in plate 22 of Myzocytium. 



Whether or not the fungus figured by Turner 

 ('92) in Oedogonium sp. relates to Myzocytium or 

 to the Lagenidiaceae is very doubtful. Superficially, 

 it bears some resemblance to the thallus of Myzocy- 

 tium, but the presence of several connecting isth- 

 muses between adjacent segments militates against 

 its inclusion in this genus. 



LAGENA 



Vanterpool and Ledingham, 1930. Canad. Jour. 

 Res. 2: 177. 



(plate 23) 



Thalli intramatrical, unicellular, coenocytic, soli- 

 tary or numerous, sac-shaped, oval, elongate, tubu- 

 larj lobed and branched; attached to the host cell 

 wall by a short neck the end of which fits into a 

 thickened collar; transformed holocarpically into 



zoosporangia or gametangia at maturity. Zoospor- 

 angia hyaline, smooth, and of the same shape as the 

 thallus; content emerging at maturity through a 

 short exit tube into an extramatrical vesicle and 

 cleaving into zoospores. Zoospores bean-shaped, iso- 

 cont, flagella inserted in a lateral depression. Male 

 and female thalli fairly equal in size and usually in- 

 distinguishable, hyaline, smooth, oval or slightly 

 elongate; conjugation canal of variable length, de- 

 veloped by the male thallus ; no differentiation of an 

 egg cell and periplasm; multiple fertilization rare. 

 Oospores single or rarely numerous, hyaline, smooth, 

 oval, spherical, thick-walled, simple or compound 

 with one or two large refractive globules ; germina- 

 tion unknown. 



This monotypic genus has many characteristics 

 in common with Lagenidium, Myzocytium, and Py- 

 thium. The isocont bean-shaped zoospores (fig. 8) 

 have two laterally inserted flagella and the same 

 characteristic method of swimming as in these gen- 

 era, but sexual reproduction is predominantly iso- 

 gamous. In germination the zoospores form an in- 

 fection tube which penetrates the host cell wall (fig. 

 1 ), and after it has grown into the host cell its tip 

 begins to enlarge and eventually develops into the 

 mature thallus. The extramatrical zoospore case 

 gradually disappears in the meantime, but the intra- 

 matrical portion of the germ tube remains attached 

 to the thallus as a neck in contact with the host wall. 

 A thick collar is formed around its upper end by the 

 host cell wall at maturity, which gives it a character- 

 istic appearance when viewed from above (figs. 2, 

 11-16). 



The mature thalli may be comparatively small, 

 oval and oblong as in Olpidium (figs. 1, 2) or greatly 

 elongate, curved, lobed, branched, and hypha-like 

 (fig. 3), as in Lagenidium. A single thallus may com- 

 pletely fill a host cell, or several small ones may be 

 present in one cell. They may develop directly into 



plate 23 



Lagena radicicola 



(Figs. 3, 17, and 18 drawn from photographs after Tru- 

 scott; other figures after Vanterpool and Leding- 

 ham.) 



Fig. 1. Stages of infection and development of the thal- 

 lus. 



Fig. 2. Two mature thalli and an empty sporangium. 



Fig. 3. An elongate, tubular branched thallus. 



Fig. 4. Mature sporangium with elongate exit tube. 



Figs. 5-7. Stages of the emergence of the protoplasm 

 into a vesicle and cleavage into zoospores. 



Fig. 8. Rupture of vesicle and liberation of the zoospore. 



Fig. 9. Encysted zoospore. 



Fig. 10. Empty sporangium and an encysted zoospore 

 on surface of host cell. 



Figs. 11-15. Stages in oospore development; content of 

 male thallus passing into female thallus. 



Fig. 16. A free mature oospore. 



Fig. 17. Multiple fusion; contents of three male thalli 

 passing into one female thallus. 



Fig. 18. Compound oospore. 



