5.1Plant Systematics Laboratory #5EVOLUTION 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) APOMORPHIESEustele 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 sieveelements. 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. WoodStudy 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 PLANTSObserve 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) APOMORPHIESThe Seed Observe an ovule (immature seed, prior to fertilization and embryo development) from the available material. Preparea longitudinal section of an ovule or observe the demonstration material. Note the outer seed coat and the inner tissue of the female gametophyte. Observe the prepared slides of ovules with a dissecting and compound microscope. Note the outer seed coat, if present. Observe the megasporangium (nucellus), having a distal pollination chamber. Look closely here for male gametophytes: pollen grains with pollen tubes. Note the massive tissue of the female gametophyte. Look for the archegonia at the distal end of the female gametophyte. Draw and label the prepared slide of a seed, noting the above components. Observe the parts of a seed, from a Cycad, Ginkgo, or Conifer. What different functions does the seed have in all thesetaxa?5.2If available, dissect a "pine nut" (Pignolia), which is the edible seed of a species of pine (Pinus pinea) minus the outer seed coat. Carefully split open (with fingernails or razor blade) the outer, whitish female gametophyte tissue to reveal the central, longitudinally-oriented embryo. With care, you can remove or expose the embryo intact. Observe the radical (attached to long, stringy suspensor cells), cotyledons (3-18 in Pine), and epicotyl (observed by removing some cotyledons).Draw and label the dissected Pine seed, noting the above components. Observe the prepared slide of a seed longitudinal section, noting the female gametophyte and embryo parts described above. Draw. DIVERSITY OF SEED PLANTS Fossil "Seed ferns"Observe the available material of the fossil seed ferns. "Seed ferns" are a paraphyletic (non-natural) group of fossil plants that had fern-like foliage, yet bore seeds. Medullosa is one example of a seed fern; note the fossil stems. As in manyfossil plants, different organs of Medullosa are placed in separate "form genera." For example, the fern-like leaves of Medullosa are in the form genera Alethopteris and Neuropteris. Dolerotheca (having huge pollen grains) refers to the pollen-bearing organs of Medullosa. Also note the fossil seed Pachytesta; both longitudinal and cross-sections are on display. Cycads (Cycadales) Cycads are a relatively ancient group of plants, now fairly restricted in distribution. None are native to our area, although many, especially Cycas circinalis, are planted horticulturally. Observe the potted specimens of cycads on display. Note the generally short, erect stem, lacking axillary branching (a possible apomorphy for the group). Stems bear spirally arranged, coriaceous (leathery), pinnately compound leaves (bipinnately compound in the tropical Australian Bowenia). Note that immature leaves have circinate vernation. Note the available reproductive material. All cycads are dioecious, either male or female. Each male cone (strobilus) has a central axis bearing microsporophylls, which bear microsporangia on the abaxial surface. The microsporangia formmicrospores, which develop into pollen grains. Draw and label a male cycad cone plus a close-up of a microsporophyll with microsporangia. Note female cones (strobili) with megasporophylls, each bearing two seeds. The genus Cycas itself is the only cycad that lacks cones, having large megasporophylls bearing several seeds. Draw and label a