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Tissues and the Primary Growth of Stems, Within xylem are two types of…
Tissues and the Primary Growth of Stems
Basic Types of Cells and Tissues
Sclerenchyma:
Primary walls plus secondary walls. Many dead at maturity. Provides elastic supposed and some (tracheary elements) are involved in water transport.
Collenchyma:
Has unevenly thickened primary walls. Typically alive at maturity and provide plastic support.
Parenchyma:
the most common type of cell and tissue, constituting all soft parts of a plant. Soft leaves, petals, fruits and seeds are composed almost completely of parenchyma.
Cells that have only primary walls that remain thin. These cells are actively metabolically and usually remain alive after they mature.
The tissue is a mass of parenchyma cells.
External Organization of Stems
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The stem and shoot are sometimes used inter-changeably, but technically, the stem is an axis, whereas the shoot is he stem plus any leaves, flowers, or buds that may be present
There are
nodes
where leaves are attached
Internal Organization of Stems: arrangement of primary tissues
Epidermis:
The outermost surface of an herbaceous stem. All internal change of material between a plant and its environment occurs by means of its epidermis.
Cortex:
Interior to the epidermis. The cortex is quite simple and homogeneous, composed of photosynthetic parenchyma and sometimes collenchyma. It can also be very complex in some species, containing many specialized cells that secrete latex, mucilage, or pitch (resin). Some cortex cells containing large crystals of calcium oxalate or deposits of silica.
Vascular Tissues:
Two types of vascular tissues occur in plants,
xylem
and
pholoem
Xylem:
conducts water and minerals
Phloem:
distributes sugar and minerals
Vascular Bundles
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Stem Growth and Differentiation
Evolution of Land Plants
When the first land plants evolved about 420 million years ago, they were basically just algae that either washed up onto a shore or were left there as lakes and streams evaporated.
They had no roots, stems, or leaves
, and they just lay on the mud.
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As early populations of land plants continued to evolve and became taller, their stems functioned primarily as
transport and support structures
, and they do still. However, stems of modern flowering plants have additional roles.
The Way Water Moves Through Tracheids, as compared to Vessel Elements
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The Processes of Primary Growth
The
body of an herb
contains just three basic parts: leaves, stems, and roots.
Within xylem are two types of conducting cells,
tracheary elements
and vessel elements
The evolution of a plant to a herb
Xylem and phloem occur together as
Vascular Bundles
Modifications to basic stem components
