Ag 221Principles of Horticulture Dr. Chumbley Fall 2011
Growth • Where does the growth of plants start? • Where does cell division occur? • Differences between apex and intercalary meristem? • Differences in primary and secondary growth?
Organs of Plants • Stems • Leaves • Roots
Stems • support; trunk, branches and stems of all plant parts • conduction; through phloem and xylem • food storage; ex. Irish potato tubers • protection; ex. thorns on mesquite • propagation; ex. bulbs, runners, rhizomes • photosynthesis; ex. pads (called cladophylls) on cactus
Stem Morphology • bud - an underdeveloped and unelongated stem composed of a short axis with compressed internodes, a meristematic apex, and primordial leaves and/or flowers. • terminal bud - a bud at the tip of a stem responsible for terminal growth. • axillary budorlateral bud - buds along side the axis of a stem; they at were produced by the terminal bud during growth; once they grow out and form a lateral stem they become terminal buds of the lateral branch. • flower bud - a bud containing a floral meristem which develops into flowers; usually larger than vegetative buds. • leaf scar - a scar marking the former point of attachment of a leaf or petiole to the stem. • internode - the part of the stem between nodes • node - part of stem marking the point of attachment of leaves, flowers, fruits, buds and other stems. • lenticel - rough areas on stems (and some fruits, ex. apple) composed of loosely packed cells extending from the cortex through the ruptured epidermis; serve as "breathing pores" for gas exchange. Only occur on young stems. • growth rings - bud scale scars from the last terminal bud; they denote flushes of growth (usually per year). Can be used to age stems because usually 1 set of growth rings is produced per year on temperate trees in the Temperate Climatic Zone.
Leaves • photosynthesis; site where primarily occurs • regulate water loss; i.e. by opening and closing stomata • storage; ex. carbohydrates and water in garlic, aloe vera • support; ex. tendrils on grape • protection; ex. spines on cacti; bud scales • attraction; ex. bracts on poinsettia or dogwood • propagation; ex. bryophyllum with plantlets on leaves
Simple Leaf Morphology • tip - the terminal point of the leaf blade or lamina - the flattened, green, expanded portion of a leaf. • margin - edge of a leaf. • midrib - the most prominent central vein in a leaf. • lateral veins - secondary veins in a leaf. • petiole - the leaf stalk (connects blade to stem). • stipules - leaf-like appendages (at the base of petiole of some leaves).
Compound Leaf Morphology • leaflet - secondary leaf of a compound leaf. rachis - an extension of the petiole bearing leaflets. • petiolule - the leaflet stalk. • petiole - the leaf stalk. • stipules - leaf-like appendages (at the base of the petiole of some leaves).
Leaf Arrangement • alternate - one leaf attached per node, usually staggered (spiral) along stem. • opposite - two leaves (a pair) attached per node, usually opposite each other. • whorled - three or more leaves attached per node, usually equally spaced around the node.
Leaf Types- Simples • Types of simple leaves based on venation (arrangement of veins) • pinnate venationfeather-like, net venation with lateral veins extending from a central midrib (dicots - ex. elm, oak) • palmate venationfinger-like, net venation with several major veins diverging from the union of the petiole and the leaf blade (dicots - ex. maple) • parallel venationprincipal veins parallel to the axis of the leaf (monocots - ex. grasses).
Leaf Types- Compound • pinnately compoundleaflets arising from along both sides of the rachis (ex. rose, pecan). • palmately compoundleaflets all arising from the same location at the top of the petiole (ex. buckeye, schefflera, poison ivy, bean).
Roots • anchorage; secures plant to ground or for epiphytes to branches • absorption; water and nutrients from soil • storage; ex. sweet potato, carrot or radish tuberous roots, • propagation; ex. dahlia or sweet potato tuberous roots, blackberry
Functions of Leaf Parts • Stomata • stoma - an open aperture (the stomatal pore) in the epidermis surrounded by 2 guard cells. • stomata - plural • Usually more frequent on epidermis of lower leaf surface. • Found on some herbaceous stems, fruits and petals. • Mechanism of Opening • open when guard cells are turgid (due to water uptake in response to potassium influx) • closed when guard cells are flaccid (due to water loss in response to potassium efflux)
Function of Leaf Parts • Designed for gas exchangea) CO2 in and 02 out for photosynthesis b) CO2 out and 02 in for respiration c) H20 out during transpiration Mesophyll • Palisade parenchyma • Contains 70-80% of the chloroplasts in the leaf. • Specialized for photosynthesis - because it contains a large number of chloroplasts and it occurs towards the top side of leaf
Function of Leaf Parts • Spongy mesophyll • Contains large air spaces • Specialized for gas exchange - because of the large air space and more stomata occur in the epidermis of lower leaf surface Shad vs. Sun Leaves Sun Grown Leaf thicker, due to thicker palisade parenchyma layer Shade Grown Leafthinner, due to thinner palisade parenchyma layer, therefore, higher proportion of spongy mesophylllarger size softer and more pliable