Taxonomy and Ecology Of Inland Sand Dune ... - Mycorrhizae

8(Schenck et al., 1984), a sporiferoussaccule (Walker et al., 1984), asporogenous saccule (Berch, 1985), or aswollen sac (Morton, 1988).Microscopic examination shows thatspores in species of Acaulospora maynot develop from the side of the chamberneck. Spores develop within a lateralswelling of the chamber neck since theouter wall of the spore may becontinuous with the wall of the chamberitself (Walker et al., 1984). Berch(1986) first used the term "sporogenousvesicle" to describe the hyphal swellingassociated with spores ofEntrophospora. Walker (1987)suggested that the so-called azygosporesin Acaulospora are sporangiospores andthat the saccule is a sporangium.Species of Gigaspora and Scutellosporaform large spores in the soil. Spores areproduced terminally on a single,bulbous-shaped, subtending hypha thatis called a bulbous suspensor cell(Morton, 1988). The subtending hyphahas one or more small lateral projectionspointing toward and sometimes incontact with the outer surface of thespore wall. No one knows the functionof the small lateral projections.Nicolson and Gerdemann (1968) usedthe term azygospore to describe sporesin Gigaspora because of the similarity ofthe single subtending hypha to agametangium in Endogone. There is noevidence that spore development inGigaspora or Scutellospora isparthenogenic or that developmentevolved from zygospores via thereduction of one of a pair of gametangia(Powell and Bagyaraj, 1984).A sporangiospore is separated from thesporangium by a separate and distinctwall. Most species of Gigaspora andScutellospora produce spores with a thininner wall and thick and laminated outerwall. These characteristics led Walker(1987) to suggest that such walls form asporangium in Gigaspora andScutellospora.Gigaspora and Scutellospora areseparated from other VAM fungi by themode of spore formation and from eachother by the mode of spore germination.When Scutellospora spores germinate,the spore forms an internal structure (thegermination shield) and then forms anendospore. In Gigaspora, no