Tissue System: Each plant organ has: * dermal * vascular and * ground tissues
In nonwoody plants, the dermal tissue system consists of the epidermis.
A waxy coating called the cuticle helps prevent water loss from the epidermis.
In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots.
Trichomes are outgrowths of the shoot epidermis and can help with insect defense.
The vascular tissue system carries out long-distance transport of materials between roots and shoots.
Xylem conveys water and dissolved minerals upward from roots into the shoots.
Phloem transports organic nutrients from where they are made to where they are needed.
Tissues that are neither dermal nor vascular are the ground tissue system.
Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex. Both have plastids for storage.
Ground tissue includes cells specialized for storage, photosynthesis, and support.
Some major types of plant cells:
Parenchyma - ground: thin flexible cell walls: photosynthesis, storage.
Collenchyma - ground: thicker cell walls for flexible support.
Sclerenchyma - ground: thick secondary cell walls reinforced with lignin for rigid, sturdy support.
Xylem - vascular: water-conducting cells.
Phloem - vascular: sugar-conducting cells.
Parenchyma cells in Elodea leaf,
with chloroplasts (LM)
Sclerenchyma cells are rigid because of thick secondary walls strengthened with lignin.
They are dead at functional maturity.
There are two types:
Sclereids are short and irregular in shape and have thick lignified secondary walls.
Fibers are long and slender and arranged in threads.
Sclereid cells in pear (LM)
Fiber cells (cross section from ash tree) (LM)
Differentiated Plant Cells in the Xylem - Dead at Maturity