PMYI.OGKNV 



107 



swarmers of Saprolegnia and other related genera. 

 In /.. Cyclotellae, however, they arc more similar 

 to those of Ectrogella, while the markedly hetero- 

 cont zoospores of /.. enecans and Mysocytium, de- 

 scribed by Scherffel ('25) and Dangeard ('(Mi) are 

 somewhat like those of 0. Ricciae, 0. irregularis, 

 Pteudolpidium Glenodineanum, I'. Sphaerita, and 

 Pseudosphaerita. Additional evidence of relation- 

 ship between the Lagenidiaceae, Olpidiopsidaceae, 

 Saprolegniaceae and Peronosporaceae is suggested 

 by the fact that the zoospores of Resticularia and 

 Mysocytium and probably other genera have one 

 tinsel and one whip lash type <>f flagellum. 



In sexual reproduction some species of the La- 

 genidiaceae may perhaps show a slight advance 

 over that exhibited by the Olpidiopsidaceae by the 

 fact that the oospore lies free in the oogonium and 

 the gametangia are slightly more differentiated. 

 In species of Lagenidium the oogonium is usually 

 larger, more vesicular and frequently barrel-shaped, 



while the antheridium is tubular and elongate. 

 In L. enecans, for example, the antheridium may 



be closely applied to the oogonium as in the 

 Saprolegniaceae, according to Scherffel. In other 

 genera like Mysocytium, Lagma and Resticularia, 

 however, the gametangia are less differentiated and 

 often appear to be nothing more than potential 

 sporangia, with which they are morphologically 

 equivalent. In no genus is an egg cell differentiated 

 in the oogonium in preparation for plasmogamy, nor 

 is periplasm present. In both of these respects the 

 Lagenidiaceae differ from most of the Peronospo- 

 rales, but show some resemblance to the Sapro- 

 legniaceae by the absence of periplasm. The con- 

 traction of the ooplasm during plasmogamy in L. 

 rabenhorstii may perhaps foreshadow a tendency 

 toward differentiation of an egg cell before fertiliza- 

 tion. That some differentiation docs occur in the 

 oogonium and antheridium is suggested by Dan 

 geard's report that the supernumerary nuclei in 

 8f. Vermicolum degenerate and only one from each 



gametangium functions in karyogamy as in species 



of the PeroUOSporales. Only one species of the La- 

 genidiaceae has been studied cytologically in this 

 respect, and whether or not this type of nuclear 

 behavior is characteristic of the family as a whole 



remains to be seen. Tin- so-called oospores are never- 

 theless similar in appearance and structure to those 

 of the Saprolegniales as well as the resting spores 

 of many chytrids and species of the Proteomyxa. 



Since the gametangia and gametes are not highly 

 differentiated. Atkinson. Barrett, Cook, and others 

 regarded sexual reproduction in the Lagenidiaceae 

 as a generalised oomycetous type with tendencies 

 in more than one direction. Atkinson in particular 



emphasized the isogamous and zygomycetous po 



tentialities and their relation to the origin of the 

 Zygomycetes from this family. As noted previously. 



sexual reproduction in Resticularia, Ziagena, and 



Lagenidium sacculoides is isogamous. which lends 



support to the hypothesis that the Zygomycetes also 



may have originated from lagenidiaeous ancestors. 



It is apparent from this discussion of origin and 

 relationships that the so called holohitlagelloiiiyceti s 

 have some characteristics in common with tin- I'ro- 

 teomyxa. Plasmodiophorales, Chytridiales, Sapro- 

 legniales, Peronosporales, and Zygomycetes. As to 

 their origin, three principal theories have been pro- 

 posed: (1) that they are reduced and degenerate 



oomycetes resulting primarily from submersed para 



sitism; (2) that they have been derived from hetero- 

 COnt unicellular algae through the loss of chloro- 

 phyll and the assumption of a parasitic mode of life, 

 and (3) that they have originated from simpler fungi 

 like the Chytridiales or the more primitive Proteo- 

 myxa. Their resemblance to the Chytridiales appar- 

 ently is due more to parallelism of development or 

 convergent evolution than close relationships. The 

 genera included in the provisional family Woronina- 

 ceae show varying degrees of similarity to certain 

 proteomyxean species and the Plasmodiophorales 

 by their mode of nutrition and the presence of plas- 

 modia and sori. The remaining families, on the 

 other hand, exhibit marked Oomycete relationships 

 by their diplanetic zoospores and predominantly 

 hetcrogamous type of sexual reproduction. These 

 affinities involve principally the Saprolegniales and 

 Peronosporales. 



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