BIO 2137 Lecture Notes - Lecture 10: Welwitschia, Gnetophyta, Double Fertilization
8 Nov 2016
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Document Summary
First megafossils, early cretaceous period 130 mya in tropical regions. Many modern families and some modern genera by 75 mya. Mystery of how dominance spread so quickly called "abominable mystery" by darwin. X titles are time eras, increasing in units of mya. Aperturate is number of holes in pollen grain (first fossils were of pollen because of pollenin being super resistant) Tracheids (membrane and little holes) and vessel elements (literally a tube) in xylem. Double fertilization kinda in ephedra (no endosperm produced) Flowers double fertilization producing 3n endosperm sieve tubes and companion cells closed carpels. 8-nucleate megagametophyte (embryo sac) stamens with two pairs of pollen sacs. Trees and shrubs - generally robust bisexual flowers with numerous. Low (but variable) numbers of tepals, stamens and carpels. Usually the one to decided with major groups. The magnoliids (anita) found at bottom of tree. Indefinite number of floral part --> definite, reduced number of parts. Number of whorls reduced, fusion of floral parts.
