86 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



accurate in their observations. Although Dangeard 

 made a cytological study of the sporangia of M. 

 vermicolum, lie did not observe cleavage and matura- 

 tion of the zoospores. 



There is also some disagreement about the rela- 

 tive lengths of the flagella in this genus. Dangeard 

 described the zoospores as heterocont in M. vermi- 

 colum, with the shorter cilium extending forward 

 (fig. 20). None of the other investigators were very 

 definite on this point, and it is impossible to deter- 

 mine with certainty from their drawings whether the 

 zoospores are iso- or heterocont. In figure 47, for in- 

 stance. Sparrow shows one flagellum to be slightly 

 shorter, while in figure 48 they are more nearly equal 

 in length. 



The antheridia and oogonia may occur in the same 

 thallus with the sporangia, but they usually do not 

 appear in abundance until fairly late in the season. 

 They are but modified segments of the thallus in the 

 same sense as the sporangia and do not undergo any 

 marked differentiation. The so-called antheridium 

 is usually more elongate and cylindrical than the 

 oogonium, but it is not so specialized a structure as 

 in Lagenidium. According to Dangeard, the oogon- 

 ium contains approximately eight nuclei, and no 

 differentiation of an egg cell nor the formation of 

 epiplasm occurs before fusion. In preparation for 

 plasmogamy seven of the nuclei degenerate, leaving 

 the oogonium uninucleate. Shortly before or at the 

 time of fusion the protoplasm in the oogonium in M. 

 proliferum contracts markedly (figs. 8, 9) around 

 the tip of the conjugation canal according to Zopf. 

 The antheridium, on the other hand, is binucleate 

 (fig. 30), but only one nucleus functions in karyog- 

 amy. Prior to fusion a pore is formed in the wall 

 .between the two gametangia, or the antheridium 

 sends forth a short tube into the oogonium (figs. 8, 

 9, 19, 37). The cytoplasm and one nucleus of the 

 antheridium passes into the oogonium, and the two 

 protoplasts fuse. The binucleate zygote begins to 

 contract (fig. 31), and as the oospore wall begins to 

 form karyogamy occurs (fig. 32). Dangeard's draw- 

 ings and description are not very clear and convinc- 

 ing in relation to the critical stages of fusion, and 

 further study of the behavior of the gametic nuclei 

 is very essential. When an antheridium lies between 

 two oogonia it is capable of fertilizing both, accord- 

 ing to Dangeard. 



After a period of rest the zygote nucleus divides 

 and the oospore becomes multinucleate (fig. 34). 

 Dangeard did not observe nuclear division, and 

 nothing is known about when and where meiosis oc- 

 curs. It presumably takes place during the first divi- 

 sion of the oospore nucleus. Eventuallj' the oospore 

 develops an exit tube (fig. 35), but the formation of 

 zoospores and their emergence have not been ob- 

 served. 



M. PROLIFERUM Schenk, I.e. 



Pythium proliferum Schenk, 1859. (Not P. proliferum 

 de Bary, 1860. Jahrb. Wiss. Bot. 2: 182.) Verh. Med. 

 Gesell.Wurzburg 9: 27. PI. 1, figs. 30-42, 47. 

 P. globosum Schenk, I.e., p. 27. PI. 1, figs. 43-46. 



P. globosum Walz, 1870 (pro parte) Bot. Zeit. 28: 556. 



PI. 9, figs. 13-19. 

 Lagenidium globosum I.indstedt, 1872. Synopsis d. 



Saproleg., p. 54. 

 M. globosum (Schenk) Cornu, 1872. Ann. Sci. Nat. 6th 



ser. 15: 21. 

 Bicricium transversum Sorokin, 1883. Arch. Bot. Nord. 



France 2: 43. Fig. 46. 1889. Rev. Mycol. 11: 138. PI. 



78, fig. 76. 

 Bicricium naso Sorokin, 1883, p. 43, fig. 47; 1889, p. 138. 



PI. 81, fig. 117. 



Thallus usually elongate, unbranched and con- 

 stricted; consisting of 1 to 20, usually less than 10, 

 segments in a linear series. Sporangia hyaline, 

 smooth, spherical, 8-25 p., ellipsoidal, 13-16 fi, X 

 16-26 ix, and elongate with a single, 2-6 /j. X 4~ 4 8 fi, 

 exit tube which may project for varying distances 

 beyond the surface of the host cell. Zoospores bean- 

 shaped, 3.6 X 5A/x; partially formed in the spo- 

 rangium, emerging and developing further in an 

 extramatrical vesicle, freed by the rupture or deli- 

 quescence of the latter. Gametangia occurring 



plate 22 



M. vermicolum 



(All figures after Dangeard, '06) 



Fig. 30. Two binucleate antheridia and two terminal 

 multinucleate oogonia. 



Fig. 31. Incipient oospore with gametic nuclei. 

 Fig. 32. Completion of karyogamy. 

 Fig. 33. Oospore in median section. 

 Fig. 34. Oospore with divided nuclei. 

 Fig. 35. Early germination stage. 



M. megastomum 



Fig. 36. Reduced thallus with elongate exit tubes. 

 Wildeman, '96. 



Fig. 37. Portion of thallus showing sporangia, oogonia, 

 antheridia, and plasmogamy. 



Fig. 38. Ancylistes miurii Skvortzow which possibly 

 relates to 31. megastomum Skvortzow. Skvortzow, '25. 



Figs. 39, 40. Antheridia, oogonia (?) and oospores of 

 ./. miurii Skvortzow, I.e. 



M. zoophthoruin Sparrow, '36 



Fig. 41. Infection stages. 



Fig. 42. Young elongate thallus. 



Fig. 43. Infected rotifer with numerous thalli, antheri- 

 dia, oogonia, and oospores. 



Figs. 44, 45. Stages in the emergence of the protoplasm 

 from sporangium. 



Fig. 46. Cleavage of initial globule of protoplasm into 

 zoospores; additional fully formed zoospores emerging 

 from neck of sporangium. 



Figs. 47, 48. Dorsal and ventral view of zoospores. 



Fig. 49. Thallus of M. irrcgulare from Microasterias 

 cell. Petersen, '10. 



Fig. 50. Young antheridium and oogonium of Myzocy- 

 liiim (Rhizomyxa hypogea pro part) sp. (?) Borzi, '84. 



Fig. 51. Oogonia with oospores, Myzocytium sp. (?) 

 Borzi, I.e. 



Fig. 52. Myzocytium sp. (?) from tobacco root cell. 

 Preissecker, '05. 



