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STEM
Bud
The stem, together with leaves and flowers,
develops from terminal bud which is an immature
shoot.
The stem is more complex than root:
Presence of nodes and internodes;
 Terminal bud produces leaves, flowers and
axillary buds giving branches (root apex does
not produce lateral organs).
The stem functions as support and conducting;
sometimes also as storage and photosynthetic
organ.
Leaves are involved only in photosynthesis.
Bud
•Terminal bud produces primary
meristems: protoderm, procambium
and fundamental meristem, which in
turn produce adult tissues (primary
thickening) such as epidermis, vascular
bundles and fundamental tissues,
respectively.
•Terminal bud is a dynamic structure
producing continuously young leaves
and lateral buds which in turn have the
same
pattern
of
development
described above.
Primary thickening of stem
•It is due to the intense cell division activity of
apical bud producing new cells. As the latter
move away from the apex they undergo
elongation and differentation giving primary
growth of stem.
Stem
Types of primary thickening
Gymnosperms
Vascular system forms a
continuous circle around
the pith
Angiosperm
Dicotyledones
Vascular bundles
form a discontinuous
ring around the pith
Angiosperm
Monocotyledones
Vascular bundles
scattered in the whole
parenchyma
•Primary thickening of linden
•Primary thickening of Dicotyledones and
Monocotyledones
•Primary thickening of Dicotyledones
Vascular bundles
•Vascular
bundles
bearing
procambium residues are called
opened and give rise to secondary
thickening (secondary xylem and
phloem). Conversely, they are called
closed and did not give raise to
secondary
structure
(e.g.
Monocotyledones and herbaceous
Dicotyledones).
• Each bundle is surrounded by a
sheath, composed of sclerenchyma
fibres, that controls movement of
substances and protects conducting
cells.
Closed vascular bundle
t.s. of stem of
Monocotyledone
Stem modifications
•Tuber is a swollen stem that
functions as an underground
storage organ. Stem tubers, for
example potatoes, often produce
buds along the stem from which
aerial stems arise the following
season. Root tubers produce no
buds.
Potato tubers
Stem modifications
•Bulb is an underground storage organ,
comprising a short, flattened stem with
roots on its lower surface, and above it
fleshy leaves or leaf bases, surrounded
by protective scale leaves, and one or
more buds often enclosed in protective
scales. It may provide the means for
vegetative reproduction, or for the
survival of the plant from one season to
the next.
Garlic bulb
Stem modifications
Turmeric rhizome
•Rhizome is a horizontally creeping, underground, root-like
stem which bears buds or shoots and adventitious roots and
usually persists from season to season.
Stem modifications
•Stolones are stems growing horizontally at ground level,
rooting at the nodes and producing new plants from its
buds (e.g. vegetative reproduction).
Stem modifications
Cladode or phylloclades of asparagus, branches
taking on the form and functions of a leaf
Cladodes of Epiphyllum
Stem modifications
•Thorns of Crataegus are modified branches,
woody, projecting structures with a sharp point that
are derived from the stem, or branch of the plant
and is connected to its vascular system.
Pharmaceutical importance of stem
•Stem provides numerous plant
drugs
through
bark
(e.g.
cinnamom, Rhamnaceae, cinchona
tree), rhizome (e.g. rhubarb, ginger
etc.), resin (e.g. conifers), latex (e.g.
Ficus, rubber) and exudates (e.g.
arabic gum, myrrh).