74 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHVCOMYCETES 



cal, oval or slightly irregular, globular mass at the 

 mouth of the exit tube. As will become more evident 

 in the diagnoses of individual species, investigators 

 are not in agreement as to whether this mass is naked 

 or enclosed in a definite membrane as in Pythium. 

 According to present data the latter is apparently 

 present in some species and lacking in others, but a 

 careful restudy of this structure is necessary before 

 the problem is settled. The protoplasmic mass may 

 be vacuolate and undergo marked rocking or oscillat- 

 ing movements shortly after emerging, and in some 

 instances it mav even move or be carried away from 

 the exit tube. In L. giganteum the protoplasm may 

 occasionally emerge in several separate masses, ac- 

 cording to Couch ('35). Cleavage begins very soon, 

 and in most species it appears to be progressive and 

 centripetal. In the masses which possess a large 

 central vacuole, i.e., L. Oedogonii and L. giganteum, 

 cleavage is largely centrifugal in direction. A\ hile 

 cleavage is going on the slow oscillating or rocking 

 movement continues, and as the process is completed 

 and flagella develop at the outer periphery of the in- 

 dividual segments, and this motion is augmented by 

 that of the rudimentary zoospores. Cleavage stages 

 in L. giganteum have been intensively studied at dif- 

 ferent time intervals by Couch. As the protoplasm 

 emerges it includes one or more large central vacu- 

 oles and numerous small peripheral ones (fig. 55). 

 The central vacuoles fuse (fig. 56), but the periph- 

 eral ones remain intact and are eventually included 

 in the zoospores. Flagella in pairs are formed on the 

 periphery of the mass opposite the small vacuoles, 

 and shortly thereafter cleavage furrows develop 

 centrifugally from the central vacuole and divide 

 the mass into biflagellate, univacuolate segments. 

 The central vacuole collapses as the furrows reach 

 the periphery, and as a result the zoospore mass con- 

 tracts (fig. 57). The zoospores soon begin to oscil- 

 late individually and glide upon each other as they 

 mature, and within a few minutes they are actively 

 swarming in a localized and restricted region (fig. 

 58) It is this localized swarming in numerous other 

 species which suggests or indicates the presence of 

 a retaining membrane, although it often cannot be 

 clearly seen. Shortly thereafter the swarmspores 

 separate very quickly as if they had been freed by 

 the rupture "or deliquescence of the membrane. In 

 species where no membrane occurs, the zoospores 

 pull apart more gradually as they mature, and soon 

 swim away. 



In L. pygmaeum and L. oophihim the incipient 

 zoospore segments are delimited in the sporangium, 

 emerge in succession, and complete their develop- 

 ment near the mouth of the exit tube, while in L. 

 Cyelotellae they are developed completely in the 

 sporangium, emerge singly, and swim directly away, 

 according to Scherffel ('25). Lagenidium Oedogonii 

 is particularly interesting and significant relative 

 to its zoospores. They may develop either extrama- 

 trically in a vesicle, as in Pythium, or within the 

 sporangium. In the latter case they collect in a 

 cluster at the mouth of the exit tube after emerging 



PLATE 20 



Figs. 23, 24. Irregular contorted thalli of L. entophytum 

 with smooth and warty oospores. Zopf, '84. 



Fig. 25. Olpidium-like thallus of L. pygmaeum with 

 partially formed zoospores emerging in a vesicle. Zopf, 



'87. 



Figs. 26, 27. Encysted and motile zoospores of L. pyg- 

 maeum. Zopf, I.e. 



Figs. 28, 29. Mature oospores of L. pygmaeum. Zopf, I.e. 



Fig. 30. Empty thallus of L. enecans from a Cymato- 

 pleura solea cell. Scherffel, '25. 



Figs. 31, 32. Heterocont secondary swarmers or zoo- 

 spores of L. enecans. Scherffel, I.e. 



Fig. 33. Oospores, L. enecans. Scherffel, I.e. 



Fig. 34. Portion of filamentous thallus of L. Closterii. 

 Couch, '35. 



Fig. 35. Inflation of exit tube before passing through 

 host wall. Couch, I.e. 



Fig. 36. Zoospore of L. Closterii. Couch, I.e. 



Fig. 37. Thallus of L. marehalianum in Oedogonium 

 cell. Couch, I.e. 



L. Oedogonii 



Fig. 38. Germinated zoospore and cellulose plug formed 

 around germ tube. Couch, I.e. 



Fig. 39. Unicellular thallus transformed into a zoospo- 

 rangium with contents beginning to emerge. Couch, I.e. 



Fig. 40. Vacuolate content of sporangium after emerg- 

 ing. Couch, I.e. 



Figs. 41, 42. Side and ventral views of heterocont, sec- 

 ondary swarmers or zoospores. Scherffel, I.e. 



Fig. 43. Encysted zoospores at mouth of exit tube. 

 Scherffel, I.e. 



Fig. 44. Oospore. L. brachystomum. Scherffel, I.e. 



Fig. 45. Elongate, unbranched thallus from Gompho- 

 nema cell. Scherffel, I.e. 



Fig. 46. Zoospores in a vesicle. Couch, I.e. 



Fig. 47. Zoospore. Couch, I.e. 



Fig. 48. Oospore. Scherffel, I.e. 



L. Cyelotellae Scherffel, '25 



Fig. 49. Olpidium-Wke thallus undergoing cleavage. 

 Fig. 50. Zoospore. 

 Fig. 51. Oospore. 



Lagenidium sp. Couch, '35 



Fig. 52. Lagenidium sp., in Oedogonium. Couch, I.e. 

 Fig. 53. Diplanetic zoospores. 



L. giganteum Couch, '35 



Fig. 54. Portion of filamentous thallus. 



Fig. 55. Vacuolate content of sporangium shortly after 

 emerging. . . 



Fig. 56. Early stage of sporogenesis; flagella arising 

 adjacent to peripheral vacuoles. 



Fig. 57. Later contracted stage following disappearance 

 of central vacuole; peripheral vacuoles incorporated in 

 the zoospores. 



Fig. 58. Zoospores in a vesicle. 



Fig. 59. Various views of the zoospores. 



L. zoophthomm Sparrow, '39 



Fig. 60. Lobed thallus in rotifer egg. 

 Fig. 61. Emergence of zoospores. 

 Fig. 62. Zoospore. 



