Stems & Transport

Early & Late Wood

early: larger vessels; suggest warm moist growing conditions and more precipitation

late: smaller vessels; drier, cooler conditions; denser tissues

Vascular Plants

plants with true stems

include club mosses, ferns, gymnosperms, and flowering plants

Stems

organs for attachment of leaves, buds, cones, flowers, and fruits

indispensable to plants

Woody Plant Twigs

lateral (axillary) buds, leaf scars from previous year’s leaves, bud scales on terminal buds, bud scale scars marking position of previous years’ terminal buds

Horizontal Stems

stems that lie just above or below ground

Rhizomes

underground stem, usually horizontally oriented, may be superficially rootlike in appearance but that has definite nodes and internodes (the space between nodes)

Corms

vertically oriented (upright), thickened food-storage stem that is usually enveloped by a few papery, nonfunctional leaves; underground storage stem

ex: gladiolus and cyclamen

Tubers

swollen, fleshy underground stem

ex: potato

Runners

stem that grows horizontally along the surface of the ground; typically has long internodes

Stolons

stem that grows vertically below the surface of the ground; it typically has relatively long internodes

Tendrils

thin stems that coil around supporting structures upon contact with other surface that allow plants to grow tall without putting energy into secondary wood production

usually a modified leaf or leaflet and aids the plant in climbing

Thickened Stems

used for water storage in cactus and euphorbs

stems are often main photosynthetic organ

ex: barrel cactus

Programmed Cytoplasmic Death

xylem cells are dead empty pipe-like cells at maturity

tracheid and vessel elements both undergo programmed cytoplasmic death (cytoplasm is removed)

water flow facilitated through the dead, empty cells

Movement of Water & Minerals

move by cohesion-tension

Vascular Bundles

strand of tissue that develops from procambium composed mostly of xylem and phloem; usually enveloped by a bundle sheath

in monocots: scattered

in dicots: in a ring

Fascicular & Interfascicular Cambium

meristematic cells found in stems that differentiate into xylem (inside) or phloem (outside)

inside vascular bundle: fascicular

between vascular bundle: interfascicular

Xylem

narrow tracheids (tapered cell with thick walls containing pits) with wide vessel elements

reinforced with lignin

also has nonlignified areas called pits that allow flow

Phloem Sieve Elements

Individual cells are called sieve tubes; end walls are called sieve plates

sieve cells are ALIVE unlike in xylem: have cell membrane, mitochondria, plastids, and some ER

nucleus and some cell components absent, removal seems essential for flow of phloem sap

Companion Cells

provide materials for sieve elements via plasmodesmata 

specialized cell derived from the same parent cell as the closely associated sieve tube member immediately adjacent to it

Sugar Flow in Phloem

from source cell to sink; i.e. from a place of high concentration of sugars to place where sugar will be used

Symplast

the continuous network of the living cytoplasm within a plant that is interconnected by plasmodesmata

Symplastic Loading vs Apoplastic Loading

sym: does not require energy (simple diffusion); sugars loaded directly or via companion cells through plasmodesmata; symplast present

apo: requires some transport energy expense (in the form of ATP); no symplast- sugars loaded from intercellular spaces through the cell membrane

Wood Sections

tyloses: peel-like protusions that clog and prevent conduction of water- these clogs leads to materials accumulating, which darkens the heartwood

heartwood: nonliving, darker-colored wood whose cells have ceased to function in water conduction

sapwood: outer layers of wood that transport water and mineral in tree trunk; usually lighter than heartwood

bark: the outermost layer, also called the periderm

Ray Initials

responsible for transporting food, water, minerals

Cork Cambium

lenticels

periderms