BIOL 2P93 Lecture Notes - Lecture 18: Eusporangiate Fern, Psilotaceae, Psilotopsida
24 Jan 2016
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Each eusporangium has 2+ cells wall thick + makes many spores. Tapetum: innermost wall layer give nourishment to developing spores, stretch + compress development = single layer cells at maturity. Eusporangia is larger than leptosporangia + many spores, primitive sporangia formation. Leptosporangium made from single superficial initial cell = divide transversely/obliquely inner cells made either part of sporangial stal, or inactive. Precisely dividing = outer cells make a stalked sporangium w/ a spherical capsule ofl one cell thick wall. W/in wall = two-layered tapetum characteristic of leptosporangia. Inner mass differentiate into spore mother cells = each making 4 spores by meiosis. Material from tapetum deposited around spores = creating ridges, spines + other features. Spores exposed after development of crack in lip cells of sporangium. Each sporangium stalked + contains special layer of cells = annulus. Sporangium dries out = annulus contracts, snaps back-forth + catapults spores. Sporangia cluster in structure = sorus covered by flap of tissue (indusium).
