BIOL 2P93 Lecture Notes - Lecture 25: Habitat Destruction, Ovule, Starch
24 Jan 2016
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Document Summary
The gymnosperms other living gymnosperm pt 1. Cycads resemble palms/tree ferns, differ in structure + reproductive behaviour, found in tropical + subtropical areas, appeared at least 250mya during permian period + mesozoic era, = 11 genera + 300 species of living cycads, few grow in only mild winters, some in moist areas in dense forests, exposed places + in semi desert regions. All cycad species are endangered (due to habitat destruction + over collecting) + covered by import/export restrictions of convention on international trade in endangered species (cites). Seeds produced in range of size, shape, + surface texture. fleshy seed coat attracts birds, rodents, small marsupials + others as dispersal agents. Reproductive units reduced leaves w/ attached sporangia, clustered into cones near top of plant. Pollen tubes formed by microgametophyte unbranched/slightly branched, growth destruction of nucellus. Before fertilization, basal end of microgametophyte swells + elongates, = sperm close to eggs. Basal end ruptures multiflagellated sperm swim to eggs.
