Plant Tissues (cont.) Week 14

4/9/2024 Plant Tissues (cont.) Stems Woody Twig – – – – – – – Axil: the angle between the petiole (attaches the leaf to the stem) and the stem itself o Axillary bud: located within the axil Terminal bud: found at the tip of a twig o Growth makes the tip longs (apical meristems) Stipules: leaf-like appendages at the based of a leaf, coming off the petiole (not every plant has them) Node: the region of the stem/twig where the leaf is attached Internode: the space between nodes Leaf scars: left on deciduous trees when the leaves fall off Bundle scars: the little dots within leaf scars (formerly the vascular tissue connections between the stem and the leaf) o The shape of leaf scars and the arrangement of bundle scars can be used to identify a tree Monocotyledonous Stems – – – No vascular cambium or cork cambium Xylem closer to center of stem and phloem closer to surface Parenchyma surrounds vascular bundles Sieve tube elements are always associated with companion cells Herbaceous Eudicotyledonous Stems – – – Does possess a vascular cambium, but no cork cambium Contains vascular bundles lining the inside of the stem in a ring o Within the vascular bundle, xylem is still closest to the inside of the stem & phloem is still closes to the outside Pith (parenchyma) is in the center Specialized Stems – – – – Rhizomes: horizontal stems that grow below ground and have long/short internodes Runners: horizontal stems that ground above ground and have long internodes Stolons: produced beneath the surface of the ground and tend to grow in all sorts of different directions Tubers: fleshy, underground stems that store food – – – o The eyes of potatoes are nodes! Bulbs: large buds surrounded by numerous fleshy leaves (each layer is a leaf) that store food o EX: onions, lilies, hyacinths Corms: resemble bulbs, but composed entirely of stem tissue o EX: crocus, Cladophylls: flattened, leaf-like stems o EX: greenbriar, prickly pear cactus Leaves Leaf primordia develop into leaves and bud primordia develop into buds Monocot leaves: leaf blade with a sheath Eudicot leaves: petiole comes off the stem – if there is no petiole, the leaf is sessile (comes straight off the stem) Leaf Arrangement – – – Alternate: one leaf per node Opposite: two leaves coming off at a node Whorled: three or more leaves per node Simple vs. Compound Leaves – – Simple leaf: one leaf blade at the node Compound leaf: a single leaf with many leaflets o Many leaflets are borne from the same bud o Rachis: attaches the leaflets Venation – – Monocots: parallel veins Eudicots: net-like veins o Pinnate: one center vein with smaller veins branching off o Palmate: the veins extend from a single point in the center of the leaf Leaf Margins (the outside of a leaf) – – – – – Entire Wavy Toothed Double-toothed Lobed Vascular Bundles in Leaf Veins – – Xylem is closer to the inside of the vein and phloem is still closer to the outside Stomata on the underside of the leaf Specialized Leaves – – – – – – – Tendrils: Thorns: modified stems arising in the axils of leaves of woody plants Prickles: Storage leaves (succulents) Window leaves Reproductive leaves Insect-trapping leaves o Pitcher plants o Sundews o Venus flytraps (native to NC and SC!) o THESE PLANTS DO NOT EAT INSECTS!! They merely absorb the nutrients Plant Assignment #15: Take a look at 2 plants and describe their leaves/stems (and if they are modified). Include photos.