BIOL 2004 Lecture Notes - Lecture 4: Pollen Tube, Taxus Brevifolia, Ginkgo
12 Apr 2016
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Phyla: coniferphyta conifers, cycadophyta cycads, gingkophyta gingko, gnetophyta ephedra, welwitschia and gentum. *there are at least four exinct groups: progymnosperms, seed ferns, cordaitales, voltziales. Seeds come from a single ferilizaion of a sperm and an egg. Angiosperm seeds come from a double ferilizaion of a sperm and an egg and two nuclei of the megagametophyte. Gymnosperm seed nourishment comes from the megagametophyte. Can withstand periods of cold winter and drought. The coat is like a barrier against bacterial or fungal decay. Atracts seed eaing animals which will either destroy the seed or disperse it. Seeds have food for the embryo and the germinaing seedling. Pollen tube delivers sperm to the egg without the need for water. Gametophytes are smaller and and protected/nourished within the sporophyte. Seed evoluion is ied to the evoluion of sporophylls and sporangia on the sporophyte. Heterospory and endospory (gametophyte development taking place inside the spore walls) were key precursors to the emergence of seeds.
