BIOL120 Lecture Notes - Lecture 7: Dicotyledon, Asexual Reproduction, Cellular Differentiation
4 Feb 2017
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Protosteles are found in: stems of most seedless vascular plants. In monocots, the embryonic root: embryonic root dies, arises from lower part of stem and therefore are adventitious. Are considered equivalent to animal stem cell niches: plant meristems. Plant stems: called a shoot, stems move leaves toward light and away from shade, defining features: Axillary buds that give rise to branching: grow in length but also produce leaves and axillary branches, lengthening simultaneously at the internodes. Increase in height: some plants have intercalary meristems. Stem vascular tissue: variation exists, siphonostele: continuous vascular cylinder that surrounds a pith, evolved from protosteles, eusteles: ring of vascular bundles, some dicots, some gymnosperms, phloem towards outside, xylem in middle, loose ring. In a stem, xylem will always be towards a central axis and phloem towards the outside: monocot stem, no ring! Instead, vascular bundles, called stele: xylem still points toward centre and phloem towards outside, most roots have the primitive arrangement.
