Chapter 14: Shoots and Stems

The protoderm forms from the...

...L1 of the peripheral zone.

Periderms replace the...

...epidermis

The procambium and ground meristem of the cortex develop form the...

...peripheral zone

The ground meristem in the pith develops from the...

...pith meristem.

Vascular Cambium

A cylinder (continuous ring) of lateral meristematic tissue in woody plants that adds layers of secondary vascular tissue called secondary xylem (wood) to the inside and secondary phloem to the outside. Forms from divisions within the procambium and the pericycle.

Cork Cambium

A cylinder of meristematic tissue in woody plants that replaces the epidermis with thicker, tougher cork cells. As soon as the vascular cambium becomes active (producing secondary growth), this region will begin division.

Bundle Cap

A layer of sclerenchyma or thickened parenchyma cells at the tip of a vascular bundle.

Lenticel

A small raised area in the bark of stems and roots that enables gas exchange between living cells and the outside air. Allow gas exchange (no water exchange) through the periderm. Analogous to stomates in the epidermis.

Eustele

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

Resin Duct

A tubelike intercellular space lined with resin-secreting cells (epithelial cells) and containing resin.

Deciduous

A type of perennial growth in which the organism has leaves that die and fall in the cold season.

Evergreen

A type of perennial growth in which the organism has leaves that persist for two or more seasons.

Siphonstele

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

Bark

All tissues external to the vascular cambium, consisting mainly of the secondary phloem and layers of periderm. Does not develop growth rings like wood because the primary and old secondary phloem get crushed as a result of secondary growth.

Peripheral Zone

An external region within the shoot apical meristem containing rapidly dividing derivatives which form axillary structures like leaves. Outer parts of L1, L2, and L3. This region is very mitotically active. These cells originate partially from the tunic layers and the corpus.

How do the outer tissues keep pace with the growing xylem core?

Anticlinal divisions in the vascular cambium increase circumference to fit the expanding inside. Dilation of phloem rays. Formation of new periderms. Vascular cambium is growing and increasing in diameter, but it is not the outermost material so it pushes everything else out which may cause gapes and gaps in the phloem and cortex.

Sclerenchyma Fibers

Appear in the primary phloem after elongation stops to form a bundle cap.

Sapwood

Area in plants that surrounds heartwood and is active in fluid transport.

Why do we see rings?

Because of density differences in the wood produced early in the growing season vs let in the growing season.

Corpus

Beneath the tunica layer(s); first layer undergoes periclinal divisions; the rest of the structure divides in various planes to add bulk.

Fascicular Cambium

Cambium that develops within the vascular bundles in the stem of a plant.

Internal Elongation

Can take place simultaneously along all the internodes at once, or separately, depending on the species. In some species, elongation occurs uniformly along the entire length of the internode. In other species, elongation can occur in a wave pattern that starts at the base of the internode and progresses upward. In grasses, elongation occurs only at the base of the internode from an area that remains meristematic called an intercalary meristem.

Anticlinal Divisions

Cell divisions that are perpendicular to the adjacent layer of cells. So, what you get is columns of cells adjacent to one another. Fill in the gaps.

Periclinal Divisions

Cell divisions that occur parallel to the tissue or organ surface. As a result, we get rows of cells stacked one over the other. Add more length.

Cork cells

Cells produced by the cork cambium. They are dead at maturity when functional, their inner walls (lamellaea) are lined with wax and suberin (waterproof) an may become lignified.

Protoderm

Comprised of the outermost tunica layer (L1).

Procambium

Comprised of the peripheral zone. The vascular cambium is derived from strads of this region.

Zea mays stem

Corn, maize; monocot stem.

Lateral Buds

Develop into lateral shoots in subsequent growing seasons creating a branching crown.

Springwood

Early wood; less dense (wider cells, thinner walls). For rapid conduction of water. Lighter in color.

T or F? The shoot apical meristem has a cap.

False

Leaf Primordia

Fingerlike projections along the flanks of a shoot apical meristem, from which leaves arise.

Primary Xylem

Formed at root and shoot apex early in development, they form vascular bundles in leaves and young stems for water transport. These structures develop from the procambial cells adjacent to the pith.

Central Zone

Forms in the center of the apical meristem after it becomes established. This area consists of the corpus and overlapping tunica layers. Like the promeristem in roots, this area will become relatively inactive, dividing infrequently. This area is analogous to the quiescent center of a root apical meristem. This region is surrounded by a ring of cells that are very mitotically active (peripheral zone).

Parenchyma

Fundamental tissue composed of thin-walled living cells that function in photosynthesis and storage. Found in the cortex, pith, and other regions of the stem. It contains chloroplasts for photosynthesis. As these cells expand during differentiation, they create intercellular spaces which allow for gas exchange. Some of these cells in the pith undergo programmed cell death to create a hollow center in the stem.

Fusiform Initials

Give rise to conducting cells of the seconday xylem and phloem. Cells within the vascular cambium that produce elongated cells such as trocheids, vessel elements, fibers, and sieve-tube members. They are vertically oriented and run up and down the stem.

Ray Initials

Give rise to the parenchyma cells of the secondary xylem and phloem. Cells within the vascular cambium that produce xylem and phloem rays, radial files that consist mostly of parenchyma cells. They are horizontally oriented and run radially out from the center of the stem. Slightly elongated or square-ish.

Bud Primordia

Growth from the apical meristem that will eventually become a bud (an embryonic shoot, often protected by young leaves). Develops into lateral shoots.

Secondary Growth

Growth produced by lateral meristems, which thickens the roots and shoots of woody plants. Results from activities of vascular cambium and cork cambium.

Vine

Herbaceous; stem climbing (tendrils, holdfast, or adventitious roots) or twining.

Cell Differentiation

In plant shoots, this process occurs from the outer most portions of the procambial strands inward toward a center line.

Cortex

In plants, region of ground tissue just inside the root through which water and minerals move. Composed of collenchyma and parenchyma.

Phelloderm

In the stems of woody plants, a thin layer of cells located between the outer cork cells and inner cork cambium. They are less numbers and resemble cortical parenchyma. These cells will replace the cortical cells. They lack suberin and lignin in their lamellaea.

Pith Meristem

Inside peripheral zone & below central mother cell zone; gives rise to pith.

What happens to the cortex once the cork and phelloderm have been produced in large amounts?

It disappears

Summerwood

Late wood; more dense (narrower cells, thicker walls). Less likely to cavitate. Darker in color.

Annual

Lives for one year/season, reproduces, then dies.

Perennial

Lives for several to many years/seasons.

Biennial

Lives for two years/seasons, reproduces, then dies.

Tropical Trees

Many trees exhibit continuous cambial activity. No stopping and starting of activity of the vascular cambium. May lack growth rings entirely because of sufficient rainfall year round. May be hard to age.

Do roots develops from designated bud regions?

No; they can establish almost anywhere along a mature root (region of maturation or higher) as long as the correct hormonal signals are given.

Ruptured Epidermis

Occurs as the periderm develops. Results when there is more cork than phelloderm.

Shoot Development

Occurs at the apex which produces both leaves and new lateral buds.

Heartwood

Older xylem near the center of a woody stem that no longer conducts water. Tends to be darker because it is xylem that has stopped functioning.

Tunica

Outermost layer(s) of initial cells; cells usually divide anticlinally.

Leaves

Photosynthetic tissue. These are formed at designated areas along the shoot called nodes and lateral buds are most often located just above the attachment points of leaves.

Vascular Bundle

Plant stem structure that contains xylem and phloem tissue. Composed of bundle cap, primary phloem, vascular cambium, and primary xylem.

Outer Bark

Protective layers of mostly dead cork cells that cover the outside of woody stems and roots. Cork or one or more older periderms.

Phytomeres

Repeating units of leaf and bud that occur along a stem. Each consists of a leaf, node, internode below, and the lateral bud above the internode.

Inner Bark

Secondary living phloem, tissues of the cortex, phelloderm, and cork cambium.

Wood

Secondary xylem all inside the vascular cambium. Growth rings develop here due to the accumulation of secondary xylem.

Herb

Stems are not persistent; dies back to the ground at the end of the growing season.

Stems

Support for leaves and reproductive parts and conduction.

Shoot

The aboveground parts of the plant. Includes stems and leaves. Established during embryogenesis. This structure is considered more complex than roots.

Plumule

The embryonic shoot with an apical meristem found at the very tip. The part of a plant embryo that will, when mature, become the leaves. Consists of the epicotyl and leaf/leaves.

Intercalary Meristem

The growth region at the base of grass leaves that causes internodes to elongate.

Tunica-Corpus Organization

The organization of shoot apical meristems. The two regions are distinguished by the type of cell division that occurs within them.

Pericycle

The outermost layer of the vascular cylinder of a root, where lateral roots originate. contributes to the formation of the vascular cambium.

Protophloem

The part of the primary phloem that differentiates early, while adjacent cells are still elongating. These are stretched during elongations of the internode and are often destroyed.

Metaphloem

The part of the primary phloem that differentiates late, after adjacent cells have completed their elongation.

Protoxylem

The part of the primary xylem that differentiates early, while adjacent cells are still elongating. These are stretched during elongations of the internode and are often destroyed.

Metaxylem

The part of the primary xylem that differentiates late, after adjacent cells have completed their elongation.

Ground Meristem

The portion that becomes the cortex region and part of the pith are produced by the peripheral zone. The rest of this region that forms all or most of the pith is produced from the pith meristem.

Periderm

The protective coat that replaces the epidermis in plants during secondary growth. Formation follows the initiation of secondary xylem and phloem by the vascular cambium. Replaces the epidermis as the protective covering on woody stems and roots. Includes the cork, cork cambium, and phelloderm. The first periderm usually arises from a cortical cell layer just beneath the epidermis.

Protostele

The simplest type of stele, consisting of a solid column of vascular tissue. Solid core; phloem surrounds xylem. In primitive seed plants, whisk ferns, club mosses and ferns.

Root vs. Shoot Stele

The stele of roots is usually completely filled by a solid core of vascular tissue. The stele in shoots consists of vascular tissue that occurs in discrete strands embedded within ground tissue. The vascular bundles can be found in rings or scattered throughout the stem.

Internodes

The stem segments between nodes. Once the new stalk is produced, new cell divisions and growth in this region causes it to lengthen, making is discernible from the leaf bearing nodes.

Monocot Stem

The vascular bundles occur in multiple rings of bundles OR scattered throughout the ground tissue. Ground tissue is NOT separate into cortex and pith. Found in monocots and herbaceous eudicots.

Derivatives

These cells are produced by the apical meristem and will partially differentiate into cells of the three primary meristems based on their location within the plant. The primary structure of stems is a result of the differentiation of the three primary meristems.

Herbaceous Eudicots and Monocots

These plants do not form secondary growth. In these plants, the pro cambium fully differentiates into xylem or phloem. These plants have vascular bundles that lack a vascular cambium and are considered to be "closed vascular bundles". It is common for a closed bundle to be completely surrounded by a bundle sheath of sclerenchyma fiber cells.

Epidermis

This structure constitutes the outer body wall of the plant. The shoot epidermis is usually a single cell layer in thickness and is made primarily of unspecialized epidermal cells.

Most eudicots have apices consisting of...layers.

Three; 2 tunica and one corpus.

Interfascicular Region

Tissue region between vascular bundles in a stem. Also called a pith ray.

T or F? In plants with secondary growth, a layer of procambial cells between phloem and xylem will remain meristematic forming the vascular cambium.

True

T or F? Redifferentiated parenchyma in the pith rays makes the vascular cambium a continuous ring going throughout the stem.

True

T or F? Shoots do not contain the three defined regions of division, elongation, and maturation that are present in roots.

True In roots, cell elongation prodded division immediately and the two occur at a relatively constant rate. In shoots, cell division happens first and proceeds quickly to make the new shoot.

T or F? More secondary xylem is produced than secondary phloem and it is more sturdy.

True The primary phloem is pushed outward and its thin-walled cells are destroyed. Only its associated fibers remain.

Pith Ray

Undifferentiated parenchyma cells between vascular bundles, connecting the cortex with the pith. These cells allow for lateral movement throughout the stem. In plants with secondary growth, some of the interfascicular parenchyma will dedifferentiate into part of the vascular cambium.

Shoot Apical Meristem

Undifferentiated tissue at the apex of the shoot that gives rise to the organs of the shoot. This region divides rapidly to produce several phytomeres in succession. Cells remain partially differentiated along the new stalk so that nodes and internodes are indistinguishable.

Eustele with Discrete Bundles

Vascular bundles are arranged in a cylinder. Cortex and pith are distinct and connected by wide interfascicular regions. Most common but NOT in monocots.

Primary Phloem

Vascular tissues originating from apical meristem growth (food transport). This structure develops from the cells of the procambial strand that are adjacent to the cortex region.

Siphonostele-Like Eustele

Vasculature is a continuous cylinder around a central pith. Narrow interfascicular region. Not very common.

Collenchyma

When present, it exists as a continuous cylinder go a few cell layers underneath the epidermis which gives support as the stem elongates.

Liana

Woody vine; secondary growth.

Shrub

Woody; several stems from the base. Less than 25' tall.

Tree

Woody; usually one main stem, usually more than 25' tall; much secondary growth.

Vascular cambium can increase in circumference by...divisions.

anticlinal This helps it stretch to fit the growing xylem core. Fills in the gaps between initial cells so there are no empty spaces.

Secondary xylem and phloem are produced by...divisions of the vascular cambium.

periclinal