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Stem Structure

Stem-pathway where foods produced from the leaves, and minerals and water absorbed form the
roots are transported throughout the plants.
Primary function: Translocation of materials
Other functions: -involved in food manufacturing
-vegetative reproduction
-for support
Eternal Structure
!odes- point of attachment of leaves and buds.
"nternodes- the distance between two nodes
# Types of Stems
a.$ %erbaceous Stems
-soft and green and have very little or no woody tissue
-little growth in diameter and are usually short-lived
-outer surface consist of a thin epidermis in which stomata are present
-color green is due to the presence of chlorophyll.
Eample: grasses, clover, wheat
b.$ &oody Stems
-hard, thic' and long-lived
-for older stems outer surface is rough and covered with cor'.
-rough surface is called lenticels, which are really openings beneath which cells are
loosely arranged. (aseous echange ta'es place through these openings
-bul' of this stem type is composed of woody tissue
-young woody stem may contain chlorophyll and carry on photosynthesis for a short
period, but as the diameter increases and cor' forms, the ability is lost.
-it is here where new stems and their leaves develop
Terminal bud-located at the tip of the twig.
*illary or +ateral )ud- occurring at regular intervals along the stem
-located in angle made by the stem and the leaf stal'.
Accessory - *n etra bud produced on ether side of an aillary bud.
Adventitious - ,sed to describe a bud that develops some place other than a stem node.
--rom roots or crown tissue or rhi.omes.
Dormant - !on growing buds, were growth is delayed due to winter or dry conditions.
Flower bud - * stem tip with embryonic flowers. /agnolia, 0herry.
Lateral - Produced on the sides of the stems
Leaf bud - * stem tip containing embryonic leaves.
Mixed bud - %aving both embryonic flowers and leaves.
Naked - !ot covered by a scaly covering.
Pseudoterminal - ,sed for lateral buds that ta'e over the function of the terminal buds,
0ommon in persimmon.
Reproductive - %aving embryonic flowers.
Scaly - *lso called 1covered buds1 which have bud scales that cover the embryonic
flowers and2or leaves.
erminal - )uds at the ends of stems.
!e"etative - )uds of embryonic leaves.
*rrangement of )uds
Opposite- two leaves at a node side by side
*lternate-only is present
&horled-three or more leaves at a node
"nternal Structure of a &oody Stem
Primary Tissues-if arises at the apical meristem
Secondary Tissues-if they arise from a cambium
Protoderm-outermost layer of the cells and will eventually develop into the epidermis as they
continue differentiating
Procambium-cells appear as isolated groups arranged in circular fashion.
-in longitudinal view cells are much longer than the neighboring cells and form
strands which is the beginning of the vascular tissue
-gives rise to primary vascular conducting tissues as they mature.
(round /eristem-cells here eventually forms the pith and the corte
Primary Tissues and 3egions
-all cells that comprise primary tissues were produced by cell division in the apical
meristem where they differentiate as they mature.
4.$ Epidermis 5 forms the surface protective layer.
- ,sually one cell in thic'ness and cell wall of cells are thic'
- Outer wall is covered with a layer of cutin.
#.$ 0orte- located 6ust beneath the epidermis which contains primarily parenchymal cells
-cells are basically spherical, although sometimes slightly elongated with thin walls
and large vacuoles.
-vary in thic'ness, but usually many cells in thic'ness
-collenchymal and sclerenchymal cells are present fro additional strengthening and
supporting factors.
-not present in older stems
7.$ Primary Phloem-several types of cells are present which enables the efficient conduction of
organic materials from place to place
Sieve tube elements-vertically elongated cylindrical cells
-primary conducting cells
-transport rate is higher than diffusion
0ompanion 0ells- narrow slightly elongated cell ad6oining a sieve tube element.
- have something to do with storage and conductions
The phloem parenchymal cells which are scattered through the tissue are mainly for storage.
8.$ 9ascular 0ambium-meristematic cells derived from the procambium or the ground meristem
-form a narrow, one or two cell thic'ness, and cylindrical sheath of tissue
-immediately internal to the phloem
-as cells in here divide, those cells that mature towards the outer part of
the stem develop into various cells of the secondary phloem.
-those that mature in the inner part of the stem develop into cells of the
secondary ylem
-tissues eternal to the cambium is called bar' only if secondary tissues
and cor' are formed
-vascular cambium and other regions eternal to the ylem are pushed
outward upon the production of the secondary ylem. The entire development results to the
increase in diameter of the stem.
:,$ Primary ;ylem-for conduction of water and minerals occurs mainly through tracheids and
vessel elements.
Tracheids-lignified, thic' walled, elongated and tapering ends which are dead at maturity.
-the hollow cavity, and the pits that are present, and the overlapping ends of
tracheids in stems and roots enable water and minerals to be transported very rapidly in a vertical
-unction: strength and support.
9essel Elements-functions in transport
-more efficient than tracheids because they have larger diameter
-many pits are present in the thic' lignified walls.
-main conducting elements of ylem
;ylem parenchyma cells and ylem fibers are similar to the parenchyma cells and fibers
found in the phloem however, fibers are more numerous.

Secondary Tissues
-reinforce or replace primary tissues
-responsible for increase in circumference as well as the diameter.
-no epidermis, corte, or pith is formed by the cambium
4.$ Secondary Phloem-cells are similar to those of the primary phloem as far as structure and
function is concerned
-difference lies in the mode of origin
Phloem 3ay 0ells-parenchymatous cells that are elongated radially and function readily
for transporting materials across stem.
-large simple pits of these cells facilitate the transport from cell to cell
-oriented end to end
-stores various materials
#.$ Secondary ;ylem-basically similar with the primary ylem however, differ with respect to
the meristematic tissue from which they develop
;ylem 3ay cells-similar with phloem rays cells.
9ascular ray-radially oriented ray cells etending through the secondary ylem and
3esin ducts or canals-scattered through the wood and bar'
-interconnected canals lined with parenchyma cells that secrete resin
7.$ 0or' 0ambium
-outer cells develop into cor' cells
-inner ones develop into phellodermwhich are parenchymal in nature
8.$ 0or'
-arise from cor' cambium
-consist of bo-shaped cells similar to the cor' cambium where they are derived but walls
are impregnated with suberin
-due to suberin cell walls results to impermeable to water and gases
-becomes protective tissue that replaces epidermis in woody plants
-protoplast of cor' cells dies after suberin is deposited in the walls.
Stem Types
4.$ %erbaceous /onocotyledon Stem
-vascular tissue eists as bundles of ylem and phloem
-vascular bundles may be numerous at the periphery
-ylem and phloem never form continuous cylinder tissues
-ylem is located at the inner side of the bundle and the phloem at the outer side
-greater part of the stem is composed of parenchymal tissues
-directly ad6acent to the epidermis are sclerenchyma and collenchyma cells which
strengthen and support the stem.
#.$ %erbaceous <icotyledonous Stem
-vascular tissue arranged in discrete bundles however is arranged in an orderly ring and
not scattered
-cambium which is visible between ylem and phloem, may be restricted from bundle to
bundle or may be continuous.
-secondary tissues are poorly developed
-stem remains non-woody
-collenchyma cells and vascular tissue may contain fiber which aid in support of the
7.$ &oody <icotyledonous Stem
-very young stem has vascular bundle, the conducting tissues of mature woody stems are
in the form of concentric cylinders in which the great development of secondary ylem results in
the characteristic woody condition.
-less pith the herbaceous dicotyledonous stems