ORDEK LAGENIDIALES 99 



the zoospores become visible in the zoosporangium and after a few 

 moments the contents again appear homogeneous, the zoospores again 

 becoming visible and actively motile just before the tube opens. Depend- 

 ing upon the number of zoospores infecting the host cell there may be 

 from one to many sporangia formed. The host cell may not show much 

 enlargement or may be quite strongly hypertrophied. In the species para- 

 sitic in fungi the zoosporangium may be ornamented by few or many, 

 short or elongated, slender or stout spine-like processes which are pro- 

 duced by the host protoplasm, not by the parasite. Sexual reproduction 

 where known is by the union of two adjacent equal or unequal cells of 

 the parasite which at the point of contact produce a perforation of the 

 walls through which the multinucleate contents of one cell pass into the 

 other, also multinucleate, cell. Barrett (1912) reported the apparent union 

 of these numerous nuclei in pairs. The zygote cell enlarges somewhat and 

 then forms a thick, angular, smooth, or coarsely spiny or knobby, wall. 

 After a little while this resting spore becomes a zoosporangium and the 

 biflagellate zoospores emerge through an inoperculate exit tube. The 

 empty male cell, sometimes more than one, remains attached to the 

 oospore and is sometimes partly covered by the thickened wall of the 

 latter. Over 20 species have been described but careful culture work with 

 pure cultures is necessary before the validity of all these species can be 

 established. The genus was first set up by Cornu in 1872 for several 

 species occurring in the hyphae of Saprolegniaceae. He described the 

 zoospores as posteriorly uniflagellate but Fischer (1882) studying what he 

 believed to be the same species found that the zoospores were anteriorly 

 biflagellate. In 1884 the great German mycologist Wilhelm Zopf described 

 0. schenkiana in the filaments of Spirogyra, but described and figured the 

 zoospores as posteriorly uniflagellate. On this account von Minden (1915) 

 transferred the species to a new genus which he named Pseudolpidiopsis. 

 Scherffel and others studying what they believed to be the same species 



» found that the zoospores were biflagellate. If the usually accurate ob- 

 : server Zopf was incorrect the genus Pseudolpidiopsis (tentatively included 

 in this book in the Olpidiaceae) must be rejected but if he was correct 

 the genus must be maintained. It must be noted that several cases are 

 known where apparently almost identical species have been found on 

 careful study to differ in their flagellation (e.g., Sphaerita dangeardii 

 Chat, and Brod., in the Olpidiaceae and Pseudo sphaerita euglenae 

 Dangeard, in the Olpidiopsidaceae, both parasitic in Euglena). (Fig. 36.) 

 In some species of Olpidiopsis the resting spores may arise partheno- 

 genetically under certain conditions and sexually under other conditions, 

 while in other species the sexual stage is unknown as yet. These were set 

 apart by Fischer (1892) as a separate genus Pseudolpidium. Probably this 

 does not deserve this generic distinction but Karling (1942) uses this as a 



