Plant Structures Stems Horticulture I 2014

Specialized Tissues in Plants Plants are as successful if not more successful than animals Plants are as successful if not more successful than animals Seed plants have three main structures: Seed plants have three main structures: Roots Stems Leaves Linked together by various means Linked together by various means

Specialized Tissues in Plants Stems Stems Support for the plant body Carries nutrients throughout plant Defense system to protect against predators and infection Few millimeters to 100 meters

Specialized Tissues in Plants Plant tissue systems Plant tissue systems Exist within the root, stems, and leaves Exist within the root, stems, and leaves Dermal tissue Dermal tissue Vascular tissue Vascular tissue Ground tissue Ground tissue

Specialized Tissues in Plants Dermal Tissue Dermal Tissue Outer covering Single layer of cells Cuticle – waxy coating Trichomes – Spiny projections on the leaf Roots have dermal tissue Root hairs Guard Cells

Specialized Tissues in Plants Vascular Tissue Vascular Tissue Transport System Transport System Subsystems Subsystems Xylem Xylem Phloem Phloem Subsystems are used to carry fluids throughout plant Subsystems are used to carry fluids throughout plant

Specialized Tissues in Plants Xylem Xylem Two types Seed plants Angiosperms Tracheid – long narrow cells Walls are connected to neighboring cells Will eventually die Vessel Element – wider that trachieds

Specialized Tissues in Plants Specialized Tissues in Plants Phloem Phloem Sieve Tube Elements Sieve Tube Elements Cells arranged end to end Cells arranged end to end Pump sugars and other foods Pump sugars and other foods Companion Cells Companion Cells Surround sieve tube elements Surround sieve tube elements Support phloem cells Support phloem cells

Specialized Tissues in Plants Ground Tissue Ground Tissue Cells between dermal and vascular tissue Parenchyma Thin cell walls, large vacuoules Collenchyma Strong, flexible cell walls Sclerenchyma Extremely thick, rigid cell walls

Specialized Tissues in Plants Plant Growth Plant Growth Meristems – tissues responsible for growth Meristems – tissues responsible for growth Undifferentiated cells Undifferentiated cells Apical Meristem Apical Meristem Produce growth increased length Produce growth increased length Differentiation Differentiation Cells will assume roles in the plant Cells will assume roles in the plant Flower Development Flower Development Starts in the meristem Starts in the meristem

Stems Stem Structure Stem Structure Produce leaves, branches, and flowers Hold leaves up Transport substance between roots and leaves Essential part of transport system Essential part of transport system Function in storage and photosynthesis Function in storage and photosynthesis

Stems Xylem and phloem – major tubule systems Xylem and phloem – major tubule systems Transport water and nutrients Transport water and nutrients Composed of three tissue layers Composed of three tissue layers Contain nodes – attachment for leaves Contain nodes – attachment for leaves Internodes – regions between the nodes Internodes – regions between the nodes Buds – undeveloped tissue Buds – undeveloped tissue

Stems Stem Types Stem Types Monocot – vascular bundles are scattered throughout Distinct epidermis Dicot – vascular tissue arranged in a cylinder Pith – parenchyma cells inside the ring

Stems Stem Growth Stem Growth Primary growth – new cells produced at the root tips and shoots Primary growth – new cells produced at the root tips and shoots Increases the length Increases the length Secondary growth – increase in stem width Secondary growth – increase in stem width Vascular cambium – produces tissue and increases thickness Vascular cambium – produces tissue and increases thickness Cork cambium – produces outer covering of stems Cork cambium – produces outer covering of stems

Stems Stems Formation of Vascular Cambium Formation of Vascular Cambium Xylem and phloem bundles present intially Secondary growth initiates production of a thin layer The vascular cambium divides Produces new xylem and phloem

Stems Formation of wood Formation of wood Wood – layers of exlem Wood – layers of exlem Produced year after year Produced year after year Results from the older xylem not conducting water – heartwood Results from the older xylem not conducting water – heartwood Becomes darker with age Becomes darker with age Sapwood – surrounds heartwood Sapwood – surrounds heartwood

Stems Formation of Bark Formation of Bark All the tissues outside the vascular cambium Consists of outermost layers of dead cork Water proof