9: Stem (k)

shoot

- the above ground portion of the plant

- Includes stems, leaves, buds, flowers and fruits

Leaves

are sites of food production and stems function in conduction and support

epicotyl

Shoot growth is initiated in the embryo from the _______, which may or may not have one or more leaf primordia

epicotyl

segment of a seedling; pt where cotyledon is attached and becomes upper part of stem and leaves

hypocotyl

segment of a seedling; pt where cotyledon is attached and becomes lower part of stem and leaves

nodes

areas where leaves arise

internodes

the intervals between the nodes

Axil

upper angle between a leaf stalk (or any lateral structure) and the stem

axillary structure

anything that arises from axil

buds

an external meristem; can be protected by a bud scale; could become branch or flowers

Lateral buds

buds along the side of the twig; may be for new leaves, flowers or branches

Terminal buds

buds at the end of the twig; only for extending length of stem

- Support leaves and reproductive structures

- Produce carbohydrates

- Store materials

- Transport water and solutes between roots and leaves

functions of stems

Herbaceous stem

soft, green & short- lived stem

Woody stem

hard, brown & long-lived stem

Corpus

adds bulk to the apical meristem by increase in volume (anti + peri)

Tunica

surface growth to maintain their continuity over corpus (anticlinal growth)

primordia

develop into all the above ground organs of a plant from shoot apex

leaf primordia and axillary buds

lateral appendages from shoot apex

primary stem

- Product of the apical meristem

- Tissues include dermal, ground (cortical) and vascular

- Epidermis from protoderm via tunica

- Ground tissues: cortex and pith

- Vascular bundles

3 main tissues primary stem

stele

- Primary vascular tissues + associated ground tissues (e.g. pith)

- Central cylinder

protostele

The simplest type of stele, consisting of a solid column of vascular tissue.

siphonostele

A type of stele containing a hollow cylinder of vascular tissue surrounding a pith.

eustele

A stele in which the primary vascular tissues are arranged in discrete strands around a pith; typical of gymnosperms and angiosperms.

atactostele

- Stem contains a ring of vascular bundles, and then a spiral towards the centre.

- This represents the highest level of development of the vascular system in the stem.

cortex

- betw epi and stele

- Mainly parenchyma (with some collenchyma and sclerenchyma)

- May see aerenchyma in aquatic plants

aerenchyma

a soft plant tissue containing air spaces, found especially in many aquatic plants

pith

- Internal from vascular tissue

- Typically parenchyma

- cortex

- phloem fibers

- phloem

- metaxylem

- protoxylem

- pith

dicot stem parts

epidermis

- One layer thick with cuticle

- With trichomes

- Presence of stomatal apparatus

procambium

where do the vascular tissues form from

- Endarch pattern

- Protoxylem (first-formed primary xylem) is closer to the center of the axis

- Direction of maturation: centrifugal (younger outside)

Primary xylem differentiation

2ndary growth

- Responsible for increase in girth (diameter)

- Allows for much greater size and volume

- Great commercial value (wood and wood products)

- partially procambium

- IF parenchyma that dedifferentiates (mature --> meri)

kaya di siya TRUE secondary meristem

origin of vascular cambium

2ndary phlo and xy

products of vascular cambium

fascicular cambium + interfascicular cambium = vascular cambium

1. Development commences at the fascicular cambium (procambium in the vasc bundles)

2. Secondary xylem and phloem are produced by the fascicular cambium

3. The interfascicular regions begins to develop a cambium (interfascicular parenchyma --> interfascicular cambium thru dedifferentiation)

4. A widening band of secondary vascular tissue results.

5. The ring of secondary tissue is Complete. The interfascicular and fascicular cambia together form a vascular cambium

development of vascular cambium

does not activate, thus does not produce new phloem or xylem tissues

IF cambium in herbaceous stems

cell grows in volume; periclinal

- New xylem cells are formed inwardly

- New phloem cells are formed outwardly

activity of functional vascular cambium

- cortical parenchyma

- parenchyma of 1 and 2 phloem

origin of cork cambium (phellogen)

cork (phellem) outside, phelloderm inside

products of cork cambium (phellogen) to form periderm

- secondary tissue

- replaces epidermis in roots and stems

- consists of phellem, phellogen, and phelloderm

periderm definition

- corky tissues

- non-living suberized cells to lessen water loss

- produced by the cork cambium (phellogen) to outside of stem

- produced more than phelloderm

phellem (cork) definition

- parenchyma-like cells

- produced toward inside of stem by the cork cambium (phellogen)

Phelloderm definition

1. increase in diameter of the stem occurs due to activity of vascular cambium

2. causes the protective epidermis to crack and split open

3. layer of cork cambium forms outside of the phloem

4. cylinder of cork cambium increases in diameter as stem increases in diameter

Forming the Periderm

As the layers of cells outside the vascular cambium die, they are sloughed off as bark

bark definition

epidermis, cork, cork cambium, phelloderm, cortex, and phloem

In the young stem the bark contains

cork, cork cambium, phelloderm, and phloem

In the old stem the bark contains

a. Cortical cells just under the epidermis become meristematic

b. Produces a layer 1-2 cells thick of cork cambium called phellogen

cork formation in the young stem (1 year old or less)

- Cork cells are flattened and cell walls contain suberin, a waxy substance

- new cambium forms because the former phellogen dies as it is crushed by expanding xylem

- forms in the outer region of the still-living phloem

- reforms every ~ 1 to 4 years depending upon the species of tree

cork in old stems (more than 1 year old, generally 3-4 years)

- cork is generally impervious to fluids and gases

- Special structures for gas exchange required to provide oxygen to the living cells of the secondary growth region, loose arrangement of cells

Lenticels definition

composite of dead phloem cells and old periderm layers (aging of bark)

rhytidome definition

- active in spring and tapers in summer, ceasing in fall

- determine age of stem because texture of spring and summer cells is different

growth/annual rings

larger vessels (larger diameter compared to to tracheids), more porous, fewer and smaller rays

spring/early wood

denser, smaller cells, thicker walls

summer/late wood

gymnosperm (conifers) bc it has resin ducts and only tracheids

gymnosperm or angiosperm?

- dump site for tree's waste prod.

- can rot away, leaving a hollow core filled with a variety of substances (oils, gums, resins, tannins)

- darker, denser more durable

- support a tree

heartwood definition

- functioning xylem toward the exterior

- usu. light, pale & weak

sapwood definition

softwood

Conifers (gymnosperms) are often any called

pine, spruce, fir, cypress, redwood

examples of conifers

- only tracheids, no vessels

- minimal parenchyma (appears more uniform)

- prominent bordered pits along their walls

conifers/softwood description

- conifers

- lined by a ring of parenchyma cells.

- defense mechanism

Resin ducts (or canals)

- Comprised of vessels, fiber and parenchyma rays

- Frequently referred to as hardwood (but has no real meaning in terms of strength)

- Larger diameter vessels, and more numerous fibers

dicot/angiosperm wood description

oak, maple, birch, mahogany

dicot/angiosperm wood examples

- Most monocots are small and herbaceous

- Generally lack secondary growth bc no vascular cambium

Secondary Growth in Monocots

Aloe, Agave, Yucca, Dracaena, Cordyline

Woody monocots with secondary-like growth

ground tissue and entire vascular bundles

what does novel cambium produce sa inner side

- "Novel cambium"

- Derived from parenchyma of the cortex

Secondary thickening meristem; anomalous secondary growth

Cortical parenchyma

what does novel cambium produce sa outer side

hindi dumaan sa meristematic stage, bale mature tissue --> new tissue

why else is secondary thickening meristem not considered true secondary growth

Primary thickening meristem

where does STM arise from

Primary thickening meristem

closer to shoot apex of palms (cocomt) so may "wood-like" structure

- u wont see 2ndary xy but many vascular bundles

- wide procambium region

- much vascular parenchyma

Secondary thickening meristem ng palms