imi\ LOOENY 



10o 



Achlfia to Lagenidium and Pythium. As noted be- 

 fore, however, 0. Oedogoniorum may possibly be a 

 species of Lagenidium while /'. vernalis may relate 

 to another family. In these events, the occurrence of 

 true diplanetism in the Olpidiopsidaceae remains to 

 be conclusively demonstrated. So far nothing is 

 known of it> occurrence in Pseudosphaerita and 

 BUutulidiopsis. The Bagella of Olpidiopsis, particu- 

 larly of 0. Saprolegniae, are structurally similar to 

 those of the Lagenidiaceae, Saprolegniales and 

 Peronosporales, according to Couch ('41). One of 

 the fiagella bears hairs or tinsels, while the other is 

 of the whip lash type. 



Except for Pseudosphaerita, which is a doubtful 

 member of this family, tin- appearance of the vacuo- 

 late protoplasm and the method of zoosporogenesis 

 of most species are very similar to those of the re- 

 timed members of the Lagenidiaceae, and unless the 

 type of sexual reproduction is observed it is diffi- 

 cult and almost impossible to tell the species apart. 

 On these grounds then the Olpidiopsidaceae and 

 Lagenidiaceae appear to he directly related. 



To many mycologists the type of sexual repro- 

 duction exhibited by the Olpidiopsidaceae is primi- 

 tive and indicates an even closer relationship to the 

 Lagenidiaceae. In Olpidiopsis the degree of sexuali- 

 ty varies considerably in the same and in different 

 species, .and sex does not appear to be well estab- 

 lished for the genus as a whole. The resting spores 

 i oospores? | in sonic species are entirely asexual or 

 parthenogenetic and appear to be nothing more than 

 encysted, thick-walled vegetative tballi. while in 

 other species. (). Achlyae, for example. 75 per cent 

 of them may be parthenogenetic and the remainder 

 zygotic. At the other extreme are species in which 

 the spores are 100 per cent zygotic. Further evi- 

 dence of variability in degree of sexuality is shown 

 by some partially parthenogenetic species in which 

 only a portion of the male gamete fuses with the 

 female. Also, one male gamete may occasionally 

 "serve" two females, or one female may be fertilized 

 by two to eight male gametes. Furthermore, except 

 for size differences, the gametes are not markedly 

 differentiated as such. Structurally, they do not ap- 

 pear to In- very different from ordinary vegetative 

 thalli or sporangia and are morphologically equiva- 

 lent to these structures. The male thallus is usually 

 smaller than the female, but occasionally the two 

 are equal in size. Sexual reproduction in the Olpi- 

 diopsidaceae is. nevertheless, predominantly hetcrn- 

 gamous. However, no egg cell or oospore is differ- 

 entiated in tin- so-called oogonium in preparation 



for fusion, and except for the questionable species. 



(). Oedogoniorum, the oospore completely rills the 

 thallus in which it develops. The type of undiffer- 

 entiated gametes together with the great variability 

 in degree of sexual expression in Olpidiopsis suggest 

 very strongly that this genus and other members of 



the Olpidiopsidaceae are primitive, but on tin- other 

 hand they may equally well indicate reduction .iiiil 

 degeneration. Nonetheless, Barrett. Cavers, Scherf- 

 felj Cook, and others regarded Olpidiopsis as primi- 



tive. Cavers and Cook derived it from tin Olpidia- 



ceae in the Chytridiales. but Schertl'el believed that 

 it originated from an /•'.ctrot/clla-Mkv ancestor (dia- 

 gram 1 ). He reg.arded <). Schrukiana as representa- 

 tive of the genus as a whole, and from such species 



evolution proceeded along the line of (). Oedogonio- 

 rum to the Ancylistineae ( Lagenidiaceae). The lasl 

 named species, according to him. is very significant 



phylogenetically, since the oospore lies free in a 

 vesicle or rudimentary oogonium and is difficult to 

 distinguish from species of Lagenidium, particularly 

 L. Oedogonii. In Pythiella vernalis sexual repro 



duction resembles that of 0. schcnkiana but differs 

 from that of Olpidiopsis in general and the Lageni- 

 diaceae by the partial differentiation of an egg 

 cell in the oogonium and the presence of a small 

 amount of periplasm. By these characters P. vernalis 

 resembles species of Pythium with which it may 

 possibly be closely related. Scherffel's interpreta- 

 tion of the relationships of Olpidiopsis and related 

 genera has been followed very closely by Sparrow 

 ('42) and Bessey ('42). Sparrow, as noted before, 

 included the Olpidiopsidaceae in the I.agenidiales. 

 The Lagenidiaceae is the most complex group of 

 the holobifiagellomycetes and is generally regarded 

 as the climax family. Due largely to the fact that 

 many of the species are incompletely known, tliis 

 family has undergone the usual vicissitudes of classi- 

 fication and in mycological literature may be found 

 in various relations to the Archimycetes and higher 

 Oomycetes. The similarities of Myzocytium and 

 Lagenidium to reduced specimens of Pythium were 

 so striking that Schenk ('59). Pringsheim ('58). 

 and W'alz ('70) at first included the type species of 

 these genera in Pythium. Since that time a great 

 many mycologists have recognized this close resem- 

 blance to the Pythiaceae and included the Lageni- 

 diaceae among the higher Oomycetes, but as in the 

 case of the other families previously discussed these 

 workers were not in agreement whether this family 

 represents an ascending or degenerating line. The 

 viewpoints of many workers were influenced by the 

 generally held belief that Ancylistes and other simi- 

 lar non-ZOOSporiC genera, were closely related to the 

 Lagenidiaceae. Had they known that Ancylistes and 

 probably other genera also are members of the En- 



tomophthorales, their interpretations would doubt- 

 less have been different. The fact that their view- 

 points provided for Ancylistis must be borne in mind 

 relative to anv criticisms which arc made below. 



De Bary ('84), Schroeter ('80). Tavel ('92), 

 Butler ('07), Clements ('09), Scherffel ('25), 

 Clements and Shear ('31), Wettstein ('85), Spar- 

 row ('86, '42), and others included the Lagenidia- 

 ceae (Ancylistaceae) among tin- Oomycetes in close 

 relation to the Pythiaceae and I'eronosporaeeae. 

 but Bessey ('37) and Coker and Matthews ('87) 

 regarded it as a family of the Saprolegniales. 



Gaumann ('25) and Gaumann and Dodge ('28) 



also included the Lagenidiaceae in the Oomycetes 

 but discussed it as a family between the Blasto- 



cladiaceae and Saprolegniaceae. De Bary and Tavel 



