BIOL 2P93 Lecture Notes - Lecture 16: Phloem, Selaginella, Sexual Reproduction
24 Jan 2016
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Lycopodium sp. engages in heteromorphic alternation of generations = w/ dominant diploid stage. = spore producing stage, haploid stage = gamete producing stage. Sexual reproduction begins when sporangia mature + ready to release spores. B/c it"s homosporous = meiosis makes spores that produce bisexual (monoecious) gametophytes bearing both antheridia + archegonia. Gametophytes can be green, irregularly lobed, subterranean/non-photosynthetic mycorrhizal structures. Development of archegonia + antheridia in gametophyte take 6-15 years + mature = gametophytes makes series of sporophytes in successive archegonia. Water needed for fertilization, biflagellated sperm swim through water to archegonium. After fertilization, zygote develops into embryo grows inside archegonium venter. Young sporophyte attached to gametophyte for a while + eventually become independent. Step 1: don"t forget that lycopodium sp. is homosporous. W/in sporangia of mature diploid sporophyte = sporogenous tissue/spore mother cells undergo meiosis = haploid spores. Sporangia located on upper surface of sporophylls w/in strobili (spore cone) of plant.
