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Plant Systematics Laboratory #5




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5.1 Plant Systematics Laboratory #5 EVOLUTION AND DIVERSITY OF WOODY AND SEED PLANTS OBJECTIVES 1. To be able to recognize and name (on sight) the major apomorphies of the groups described and evaluate their adaptive significance. 2. To be able to recognize and name (on sight) all taxa listed below in bold type. 3. To be able to recognize and name (on sight) the major organs or structural components of these taxa, including knowing all terms listed in bold type. LIGNOPHYTA (WOODY PLANT) APOMORPHIES Eustele Observe the cross-section of a young stem (before wood formation) of a seed plant. Note the eustele, a single ring of vascular bundles, each bundle consisting of an inner group of xylem tracherary elements and an outer group of phloem sieve elements. Observe a eustele, identifying and labeling vascular bundles, xylem, phloem, cortex, pith, and epidermis. Note, at higher magnification, one of the vascular bundles, illustrating a few tracheary elements of the xylem, sieve elements of the phloem, and fibers (if present). Check off these terms from the illustrations in your book. Wood Study the slide of a young woody stem cross-section. Note the incipient vascular cambium, consisting of specialized cells that divide and form secondary tissue. Check off the terms from the illustrations in your book: primary xylem, primary phloem, vascular bundle, vascular cambium, cortex, and pith. Study the slide of an older woody stem cross-section. Observe the vascular cambium, which has deposited layers of secondary phloem to the outside and secondary xylem (wood) to the inside. Note the annual rings of wood, each layer corresponding to one year's growth, and the rays which traverse the secondary tissue. Also note the formation of a periderm, from the cork cambium at the stem periphery. Check off the terms from the illustrations in your book: secondary xylem, secondary phloem, vascular cambium, cortex, pith, and periderm. Observe the demonstration slide of a close-up of the junction between one annual ring and the next. The rings are caused by the fact that the tracheary elements at the beginning of a growth season are larger and thinner walled, constituting the spring wood; those at the end of the season are smaller and thicker walled, constituting the summer wood. Draw a few cells of each annual ring (at their junction) and label which is the spring wood and which summer wood. Observe the wood samples on demonstration. Note the rays, tracheary elements (tracheids or vessels), and annual rings. What is the adaptive significance of wood? Note also the difference in thickness of the annual rings. What might these differences reflect? How can scientists use this data? What is this science called? DIVERSITY OF NON-SEED WOODY PLANTS Observe the available material or illustrations of the fossil plant Archeopteris (not to be confused with the very famous, ancient reptilian bird, Archeopteryx), a non-seed Lignophyte. Archeopteris was a large tree, with wood like a conifer but leaves like a fern. Sporangia born on fertile branch systems produced spores. SPERMATOPHYTA (SEED PLANT) APOMORPHIES The ...





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