"Plant Anatomy 3 stems"
Plant Anatomy – Stems METHODS: The key to understanding plant anatomy and physiology is to equate structure with function. For this lab, draw the structure you are observing, label the structure and list its function. Use your text and the photographic atlases. PRIMARY GROWTH: STEM Apical Meristem Coleus stem tip LS [Slide 12]; Identify: apical meristem, bud primordium, leaf, procambium (this is a meristematic region giving rise to the vascular tissue of the stem) Herbaceous Stems Monocot Stem XS Compare a 'typical' monocot stem with a 'typical' dicot stem using the following: Zea mays (monocot) and Helianthus (dicot). Identify: tissues: epidermis, vascular bundle, pith, phloem, xylem, procambium, cortex cell types: vessel elements, fibers, sieve tube members, companion cells (if present, identify collenchyma) Zea mays (maize) [Slide 10]; showing typical 'scattered' bundles of monocotyledons; each bundle has a sheath of fibers around it; most bundles have two large metaxylem vessels and one smaller protoxylem vessel; primary phloem is exterior to the xylem and companion cells are easily seen; note fibers in epidermis. Dicot Stem XS Helianthus (sunflower) young stem XS [Slide 10]; showing early cambial development, note the separate bundles of xylem and phloem; Helianthus (sunflower) mature stem XS showing xylem and phloem development by vascular cambium, note how the vascular bundles have almost completely merged. Dicot Vascular Bundle Drawings are not required for the following slides, but observing them will provide you with an idea of the diversity found in various stems. Medicago (alfalfa) XS [Slide 14]; showing early cambium (but this plant is an herb and doesn't develop very much secondary vascular tissue). Cucurbita (cucumber) stem XS, LS [Slide 13]; is another example of a dicot stem; secondary growth is restricted to vascular bundles in this vine. Nymphaea odorata (water lily) XS showing large air spaces and relatively small vascular bundles. Note development of vascular tissue in these other examples of dicot stems: Sambucus (elderberry), Arctium minus (burdock), Ranunculus acris (european buttercup), Linum (flax), Nicotiana tabacum (tobacco). Drawings are not required for the following slides, but observing them will provide you with an idea of the diversity found in various SECONDARY GROWTH/WOOD woody stems. ANATOMY Cambial Variants Young Woody Stems Aristolochia (a vine) stem XS [Slide 11]; showing a type of Tilia americana (linden or cambial production common in vines. Note the unequal- basswood) stems 1 year old sized bundles; protoxylem and metaxylem; secondary [Slide 19]; and older xylem; note fascicular cambia producing bundles, but [Slide 20]. interfascicular cambia producing only parenchyma (thus Identify the following tissues: producing broad rays). pith, primary xylem; annual Vitis (grape) stem XS [Slide 21]; showing another example of rings for each year; vascular a vining dicot. Note that the interfascicular cambium is only cambium; secondary xylem weakly developed and therefore the bundles from the (wood) and narrow rays primary state retain their identities, even through secondary (parenchyma cells that are used for lateral transport), growth. secondary phloem and wide phloem rays; outer groups of Yucca brevifolia XRT and maceration. In the few monocots fibers are part of the primary phloem, whose sieve tubes are producing secondary growth (Yucca, Dracaena, Cordyline, being crushed; cork cambium and cork; remains of Aloe, etc.), the vascular cambium arises in the cortex epidermis and cuticle. outside of the atactostele. It produces entire vascular Identify the following cells: vessel elements, tracheids, fibers, bundles to the inside, and a secondary cortex to the outside. sieve tube members, companion cells Note also, that there is a cork cambium at work. Quercus (oak) XRT [Slides 17 & 18]; Periderm Sambucus (elderberry) lenticel; note cork, cork cambium, complementary tissue. Euonymus alatus branch with 'winged' cork, so called because the cork cambium is more active in 4 arcs than elsewhere. Pinus (pine) cork showing 'lens' nature of the cork, which is best seen at the small end in cross section. Quercus phellos (cork oak) showing what is called commercially 'corkwood' but which is botanically just work. This is the source of most commercial corks. . Note the location of the largest vessel elements within each growth ring. What does this tell you about vessel diameter in relation to tree rings? Pinus (pine) [Slides 15 & 16]; Compare this stem to the flowering plants, Quercus and Tilia. Pinus is a conifer (a more ancient phylum than flowering plants) and therefor lacks vessel elements. Can you see xylem rings even though this species lacks vessels? Why? Mature Woody Stems Observe the wood samples provided in lab and identify heartwood, sapwood, knots and cork. What do these samples tell you about their growing conditions?