STEMS

• What is the direction of growth for an erect stem?


  It ascends perpendicularly to the ground.
• How does an ascending stem grow?


  It rises obliquely (slanting).
• What is the growth direction of a decumbent stem?


  It is more or less reclining to the ground.
• What does a prostrate or procumbent stem do?


  It lies flat on the ground.
• What characterizes a creeping stem?


  It is closely pressed to the ground and roots at the nodes.
• How do scandent or climbing stems grow?


  They ascend using support offered by other plants or objects.
• What are the characteristics of herbaceous stems?


  • Lack secondary growth
  • Most monocots are herbaceous
  • Dicots can be herbaceous or woody
  • Primary tissues present: epidermis, cortex, endodermis, vascular bundles, vascular cambium, pith (visible in dicots only)
• What are the features of monocot stems?


  • Vascular bundles scattered in the cortex
  • No pith
  • No secondary growth
  • Growth in diameter depends on primary tissues
  • Parenchyma tissues dominate
  • Collenchyma and sclerenchyma provide support
• What distinguishes dicot stems from monocot stems?


  • Vascular bundles arranged in an orderly ring
  • Presence of pith
  • Vascular cambium is present
  • Secondary tissues are poorly developed
  • Collenchyma and vascular fibers provide support
• What are the characteristics of woody stems?


  • Formation of secondary tissues
  • Conducting tissues in concentric circles/cylinders
• What is the role of vascular cambium in woody stems?


  • A layer of meristematic cells between xylem and phloem
  • Produces secondary xylem and phloem
  • Causes the mature stem to increase in thickness
• What is secondary xylem and its significance?


  • Inner derivative of vascular cambium
  • Comprises about 90% of a typical tree
  • Contains tracheids and vessels
  • Forms annual rings
• What is sapwood?


  Wood in the outer few rings of the xylem that transports water and nutrients.
• What is heartwood?


  Older dark rings near the center where metabolites are deposited.
• What constitutes bark in woody plants?


  • All tissues outside the vascular cambium
  • Includes secondary phloem and periderm
• What are the three tissues comprising the periderm?


  • Phellogen/cork cambium: produces periderm
  • Phellem/cork cells: waterproof and protect the plant
  • Phelloderm/secondary cortex: alive and not suberized
• What is the composition of wood?

  • Chiefly composed of cellulose and lignin
  • Annual rings consist of summerwood and springwood
• What are the characteristics of summerwood and springwood?


  • Summerwood: smaller, thicker-walled cells formed in summer
  • Springwood: larger cells formed by cambium in spring
• What is the function of xylem?


  • Upward conduction of water and dissolved nutrients
  • Xylem cells are differentiated into tiny tubes
• What causes sap to rise in plants?

  • Transpiration pull: loss of water through stomates
  • Cohesion and adhesion of water molecules
• What is root pressure?


  It is the result of osmotic uptake of water into the vascular elements of the root.
• What is guttation?


  Excretion of droplets of water by plants from hydathodes.
• What is the function of phloem?


  • Distributes products of photosynthesis via translocation
  • Involves mass flow/pressure flow theory
• How does active transport function in phloem?


  • Moves solutes into sieve tubes
  • Increases solute concentration, making them hypertonic
• What is the role of meristems in plants?


  • Contain small cells with thin walls
  • Produce stem and leaf tissues
  • Can switch to floral meristems
• What is the function of the epidermis in stems?


  • External layer of cells covered with a cuticle
  • Prevents water loss and protects against pathogens
• What is the cortex in plant stems?


  • Layer of cells between epidermis and vascular tissue
  • Functions as a storage organ in many woody plants
• What are the components of vascular tissue?


  • Comprised of phloem, cambium, and xylem
  • Organization varies between monocots and dicots
• What are the major cell types in phloem?


  • Sieve tube members: responsible for transport
  • Companion cells: support sieve tube activity
• What is the function of vascular cambium?


  • Provides new cells for vascular system growth
  • Essential for radial expansion of the stem
• What is the role of xylem in plants?


  • Required for transport of water and nutrients
  • Contains tracheids and xylem vessels
• What is the pith in plant stems?


  • Innermost tissue comprised of parenchyma cells
  • Functions as a storage tissue
• What distinguishes monocot stems from dicot stems?


  • Monocots: vascular bundles scattered, distinct epidermis
  • Dicots: vascular tissue arranged in a cylinder, pith present
• What is primary growth in stems?


  • New cells produced at root tips and shoots
  • Increases stem length
• What is secondary growth in stems?


  • Increases stem width
  • Involves vascular cambium and cork cambium
• What is the formation of wood in plants?

  • Layers of xylem produced year after year
  • Older xylem becomes heartwood
• What is the function of bark in woody plants?


  • Consists of outermost layers of dead cork
  • Functions to waterproof the plant
• What are the differences between mature structures of woody and herbaceous stems?

  • Herbaceous: lack secondary growth, soft and flexible
  • Woody: have secondary growth, increase in diameter
• What are the types of stems that grow aboveground?

  • Tendrils: for attachment and support
  • Searcher shoots: long internodes
  • Stolons/runners: horizontally oriented
  • Thorns/spines: modified for protection
  • Cladodes/cladophylls: for photosynthesis
  • Culms: hollow or solid stems of grasses
  • Succulent stems: store water
• What are the types of stems that grow underground?

  • Bulb: large, roundish bud
  • Corm: stubby, fleshy stem
  • Rhizomes: underground stems near soil surface
  • Tubers: swollen regions that store food