Chapter 25 The Shoot: Primary Structure and Development

shoot

which consists of the stem and its leaves, is the aboveground portion of the plant that is familiar to us.

principle functions of stem

support and conduction

phytomeres

repeating units of leaf and bud

leaf primordia

Lateral outgrowths from apical meristem; control differentiation of procambium in stem. Develop into leaves.

bud primordia

develop into lateral shoots.

apical meristem

denotes only the part of the shoot lying distal to, or above, the youngest leaf primordium. The meristem at the apex of a root or shoot, but in this case the shoot.

shoot apex

includes the apical meristem together with the subapical region bearing young leaf primordia.

tunica-corpus

theory of plant development holding that embryonic tissues differentiate into outer layers, called ___1___, and an inner cell mass, called _____2_____.

tunica

consists of the outermost layer (or layers) of cells that divide anticlinally, that is, in planes perpendicular to the surface of the meristem, contributing to surface growth.

corpus

consists of a body of cells that lie beneath the tunica layers in which the cells divide in various planes and add bulk to the developing shoot

anticlinally

planes perpendicular to surface of meristem

periclinally

parallel with apical surface

central zone

In the shoot apices of angiosperms, the corpus and the portions of the tunica layers overlying the corpus constitute the so-called _____ ____ which corresponds to the promeristem of the shoot apical meristem, and is also surrounded by the peripheral zone

peripheral zone

originates partly from the tunica (L1 and L2 layers) and partly from the corpus, whose origin can be traced to the L3 layer

pith meristem

To the inside of this ring and just beneath the central zone is the ____ ____ in which cell divisions are relatively infrequent, making the central zone analogous to the quiescent center of the root apical meristem, but with an incredibly mitotically active peripheral zone.

intercalary meristem

a meristematic region between two more highly differentiated regions

interfascicular regions

parenchymatous regions (portion of vascular cylinder separated bynarrow ground parenchyma) that interconnect the cortex and the pith.

pith rays

interfascicular regions are also called ____ ____.

herbaceous

nonwoody stems

closed vasclar bundles.

vascular cells in whch all the procambial cells mature and the potential for further growth within the bundle is lost. Closed vascular bundles are usually entirely surrounded by a sheath composed of sclerenchyma cells.

open vascular bundles

Vascular bundles that do give rise to a cambium

leaf traces

The extensions from the vascular system in the stem toward the leaves

leaf trace gaps

the wide interfascicular regions, or gaps of ground tissue, in the vascular cylinder located above the level where leaf traces diverge toward the leaves are called ___ ___ __

stem bundle

A leaf trace extends from its connection with a bundle in the stem - a ____ ____, - to the level at which it enters the leaf

sympodium

A stem bundle and its associated leaf traces are called a _____

branch traces

Buds commonly develop in the axils of leaves, and their vascular system is connected with that of the main stem by _____ _____.

phyllotaxis

The arrangement of leaves on a stem

spiral

one leaf at each node forming spiral aroud the stem

Alternate (distichous)

In other plants with a single leaf at each node, the leaves are disposed in two opposite ranks, as in the grasses. This type of phyllotaxis is called _____

opposite

In some plants the leaves are formed in pairs at each node, and the phyllotaxis is said to be ______.

spiral

If each successive pair of leaves is at a right angle to the previous pair, the arrangement is termed _____

whorled

have three or more leaves at each node

blade/lamina

an expanded portion of the leaf

petiole

a stalklike portion of a leaf

stipules

Scalelike or leaflike appendages called _____ develop at the base of some leaves

sessile leaf

Many leaves lack petioles and are said to be ______, like trillium.

sheath

In most monocots and certain eudicots, the base of the leaf is expanded into a _____ which encircles the stem.

simple leaves

the blades are not divided into distinct parts but can be deeply lobes.

compound leaves

The blades of _____ _____ are divided into leaflets, each usually with its own small petiole

rachis

In pinnately compound leaves, the leaflets arise from either side of an axis, the _____, like the pinnae of a feather. (The _____ is an extension of the petiole.) The leaflets of a palmately compound leaf diverge from the tip of the petiole, and a _____ is lacking.

mesophytes

plants that require an environment that is neither too wet nor too dry

hydrophytes

plants that require a large supply of water or grow wholly or partly submerged in water

xerophytes

plants that are adapted to arid habitats

mesophyll

the ground tissue of the leaf

palisade parenchyma

A leaf tissue composed of columnar chloroplast-bearing parenchyma cells with their long axes at right angles to the leaf surface. usually located on the upper side of the leaf

spongy parenchyma

A leaf tissue composed of loosely arranged, chloroplast-bearing cells. usually located on the lower side of the leaf

veins

The mesophyll of the leaf is thoroughly permeated by numerous vascular bundles, or ____, which are continuous with the vascular system of the stem

netted venation

veins are arranged in a branching pattern, with successively smaller veins branching from somewhat larger ones.

parallel venation

veins that extend along the long axis of the leaf. These veins may be almost equal in size or they may vary in size, with larger veins alternating with smaller ones.

minor veins

veins embedded in mesophyll tissue. role in the collection of photosynthates (organic compounds produced by photosynthesis) from the mesophyll cells.

major veins

veins associated with ribs. as the minor veins increase in size, their primary function changes from collection of photosynthates to transport of photosynthates out of the leaf, and become major veins.

bundle sheath

Layer or layers of cells surrounding a vascular bundle; may consist of parenchyma or sclerenchyma cells, or both.

bundle-sheath extensions

A plate of ground tissue extending from a bundle sheath of a vein in the leaf mesophyll to the upper or lower epidermis, or both; may consist of parenchyma, collenchyma, or sclerenchyma.

Kranz anatomy

Plants that utilize this pathway typically possess a distinctive _____ ______, consisting of two photosynthetic cell types. These are the bundle sheath (bs) cells, which surround the vascular centres, and the mesophyll (mp) cells, which surround the bs cells.

bulliform cells

Large epidermal cells present in longitudinal rows in grass leaves; believed to be involved in the mechanism of rolling and unrolling or folding and unfolding of the leaves. Also called motor cells.

founder cells

the group of cells from which leaf primordia and root primordia are initiated.

abscission

The dropping off of leaves, flowers, fruits, or other plant parts, usually following the formation of an abscission zone.

abscission zone

The area at the base of a leaf, flower, fruit, or other plant part containing tissues that play a role in the separation of the plant part from the plant body.

separation layer

consists of relatively short cells with poorly developed wall thickenings that make it structurally weak.

protective layer

composed of heavily suberized cells is formed, further isolating the leaf from the main body of the plant before the leaf drops.

leaf scar

a scar left on a twig when a leaf falls

transition region

The region in the primary plant body showing transitional characteristics between structures of root and shoot.

homeotic mutations

A mutation that changes organ identity so that the wrong structures appear in the wrong place or at the wrong time.

homeotic genes

Genes affecting floral organ identity.

tendrils

A modified leaf or part of a leaf or a modified stem forming a slender, coiling structure that aids in support of the plant's stems; found only in some angiosperms.

cladophylls

A branch resembling a foliage leaf.

tuber

An enlarged, short, fleshy underground stem, such as that of the potato.

stolons

A stem that grows horizontally along the ground surface and may form roots, such as the runners of a strawberry plant. Also called a runner.

rhizomes

A more or less horizontal underground stem.

bulb

large bud consisting of a small, conical stem with numerous modified leaves attached to it.

corm

A thickened underground stem, upright in position, in which food is accumulated, usually in the form of starch.