Phylum: Oomycota
This division contains about 450 species, and includes water
molds, white rusts, and downy mildews. They are distinguished from the chytrids
by having exclusively diploid assimilative hyphae. The cell walls of these
organisms are composed largely of cellulose or cellulose-like polymers, thus
differing markedly from the cell walls of the fungi. They range from
unicellular forms to highly branched, coenocytic filamentous ones.
Most species of Oomycota can reproduce both sexually
and asexually. Sexual reproduction is said to be "oogamous" A gamete
nucleus from an antheridium (male gametangium) moves into an oogonium (female
gametangium), through direct contact of the antheridium and oogonium, and fuses
with an oosphere (egg). The result is an oospore (the zygote, a thick walled
sexually produced spore) which is not motile. Asexual reproduction is by means
of zoospores, that have two flagella - one tinsel and one whiplash. In this lab
you will examine two orders of Oomycota, one aquatic, and one terrestrial.