2.3 Plant Organ System - Roots
2.4 Plant Organ System - Stems
2.5 Plant Organ System - Leaf
2.6 Plant Organ System - Flower
2_Parts-of-a-Plant
Parts of a Plant
Overview
Common ash (Fraxinus excelsior), a deciduous broad-leaved (angiosperm tree)
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Introduction
Learning Objectives
- Describe the angiosperms or flowering plants.
- Identify the root & shoot system of a plant.
- Differentiate between a monocot and a eudicot plant.
- Describe the external structure of roots and various modifications of the roots.
- Describe the external structure of the stem and various modifications of the stem.
- Explain the external structure of a typical leaf.
- Define phyllotaxy.
- Differentiate between simple and compound leaves.
- Describe the internal structure of a typical dicot leaf.
- List and describe the parts of a typical angiosperm flower.
- Differentiate between perfect and imperfect flower flowers.
- Differentiate between complete and incomplete flowers.
- Differentiate between monoecious and dioecious plants.
Key Terms
androecium - the sum of all the stamens in a flower
angiosperms - a group of seed-bearing plants that produce flowers and fruits
anther - sac-like structure at the tip of the stamen in which pollen grains are produced
bract - modified leaf associated with a flower
bulb - a modified underground stem that consists of a large bud surrounded by numerous leaf scales
calyx - whorl of sepals
carpel - a single unit of the pistil
complete flower - flower with all four parts, sepals, petals, stamens, and carpels
compound leaf - a leaf in which the leaf blade is subdivided to form leaflets, all attached to the midrib
corm - rounded, fleshy underground stem that contains stored food
corolla - a collection of petals
dicot - (also, eudicot) related group of angiosperms whose embryos possess two cotyledons
dioecious - describes a species in which the male and female reproductive organs are carried on separate specimens
filament - thin stalk that links the anther to the base of the flower
guard cell - paired cells on either side of a stoma that control the stomatal opening and thereby regulate the movement of gases and water vapor
gynoecium - (also, carpel) structure that constitutes the female reproductive organs
imperfect flower - a flower that only carries either male or female reproductive organ
monocot - a related group of angiosperms that produce embryos with one cotyledon and pollen with a single ridge
monoecious - describes a species in which the male and female reproductive organs are on the same plant
ovary - a chamber that contains and protects the ovule or female megasporangium
palisade mesophyll - an area of a typical dicot leaf comprising column-shaped tightly packed parenchyma cells found underneath the upper epidermis
perfect flower - a flower that carries both male and female reproductive organs
petal - modified leaf interior to the sepals; colorful petals attract animal pollinators
phyllotaxy - arrangement of leaves on a stem
pistil - a fused group of carpels
pistillate flower - a flower that only carries female reproductive organs
pneumatophore - roots participating in gas exchange
rhizome - a modified underground stem that grows horizontally to the soil surface and has nodes and internodes
root - belowground portion of the plant that supports the plant and absorbs water and minerals
runner/stolen - a modified stem that runs parallel to the ground and can give rise to new plants at the nodes
sepal - a modified leaf that encloses the bud; the outermost structure of a flower
simple leaf - leaf type in which the lamina is completely undivided
spongy mesophyll - an area of a typical dicot leaf comprising large air spaces and loosely packed irregularly shaped parenchyma cells found underneath the palisade parenchyma cells
staminate flower - a flower that only carries male reproductive organs
stem - aboveground portion of the plant; consists of nonreproductive plant parts, such as leaves and stems, and reproductive parts, such as flowers and fruits
stigma - the uppermost structure of the carpel where pollen is deposited
style - long, thin structure that links the sigma to the ovary
Introduction
Plants are as essential to human existence as land, water, and air. Without plants, our day-to-day lives would be impossible because, without oxygen from photosynthesis, aerobic life cannot be sustained. From providing food and shelter to serving as a source of medicines, oils, perfumes, and industrial products, plants provide humans with numerous valuable resources.
When you think of plants, most of the organisms that come to mind are vascular plants. These plants have tissues that conduct food and water, and most of them have seeds. Seed plants are divided into gymnosperms and angiosperms. Gymnosperms include the needle-leaved conifers—spruce, fir, and pine—as well as less familiar plants, such as ginkgo and cycads. Their seeds are not enclosed by fleshy fruit. Angiosperms, constitute seed plants with flowers, also called flowering plants. They include broadleaved trees (such as maple, oak, and elm), vegetables (such as potatoes, lettuce, and carrots), grasses, and plants known for the beauty of their flowers (roses, irises, and daffodils, for example).
While individual plant species are unique, all share a common structure: a plant body consisting of stems, roots, and leaves. They all transport water, minerals, and sugars produced through photosynthesis through the plant body in a similar manner. All plant species also respond to environmental factors, such as light, gravity, competition, temperature, and predation.
Angiosperms or flowering plants
From their humble and still obscure beginning during the early Jurassic period, the angiosperms—or flowering plants—have evolved to dominate most terrestrial ecosystems (Figure 1.2.1). With more than 300,000 species, the angiosperm phylum (Anthophyta) is second only to insects in terms of diversification.
The success of angiosperms is due to two novel reproductive structures: flowers and fruits. The function of the flower is to ensure pollination, often by insects, as well as to protect a developing embryo. The colors and patterns on flowers offer specific signals to many pollinating insects or birds and bats that have coevolved with them. For example, some patterns are visible only in the ultraviolet range of light, which can be seen by insect pollinators. For some pollinators, flowers advertise themselves as a reliable source of nectar. Flower scent also helps to select pollinators. Sweet scents tend to attract bees and butterflies and moths, but some flies and beetles might prefer scents that signal fermentation or putrefaction. Flowers also provide protection for the ovule and developing embryo inside a receptacle. The function of the fruit is seed protection and dispersal. Different fruit structures or tissues on fruit—such as sweet flesh, wings, parachutes, or spines that grab—reflect the dispersal strategies that help spread seeds.
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Diversity of Angiosperms
Diversity of Angiosperms
Within the angiosperms are three major groups: basal angiosperms, monocots, and dicots. Basal angiosperms are a group of plants that are believed to have branched off before the separation of the monocots and dicots, because they exhibit traits from both groups. They are categorized separately in most classification schemes. The basal angiosperms include Amborella, water lilies, the Magnoliids (magnolia trees, laurels, and spice peppers), and a group called the Austrobaileyales, which includes the star anise. The monocots and dicots are differentiated on the basis of the structure of the cotyledons, pollen grains, and other structures. Monocots include grasses and lilies, and the dicots form a multi-branched group that includes (among many others) roses, cabbages, sunflowers, and mints.
Monocots
Plants in the monocot group are primarily identified by the presence of a single cotyledon in the seedling. Other anatomical features shared by monocots include veins that run parallel to and along the length of the leaves, and flower parts that are arranged in a three- or six-fold symmetry. True woody tissue is rarely found in monocots. In palm trees, vascular and parenchyma tissues produced by the primary and secondary thickening meristems form the trunk. The pollen from the first angiosperms was likely monosulcate, containing a single furrow or pore through the outer layer. This feature is still seen in modern monocots. The vascular tissue of the stem is scattered, not arranged in any particular pattern, but is organized in a ring in the roots. The root system consists of multiple fibrous roots, with no major taproot. Adventitious roots often emerge from the stem or leaves. The monocots include familiar plants such as the true lilies (Liliopsida), orchids, yucca, asparagus, grasses, and palms. Many important crops are monocots, such as rice and other cereals, corn, sugar cane, and tropical fruits like bananas and pineapples (figure 1.2.2 a, b, c).
Eudicots
Eudicots, or true dicots, are characterized by the presence of two cotyledons in the developing shoot. Veins form a network in leaves, and flower parts come in four, five, or many whorls. Vascular tissue forms a ring in the stem; in monocots, the vascular tissue is scattered in the stem. Eudicots can be herbaceous (not woody) or produce woody tissues. Most eudicots produce pollen that is trisulcate or triporate, with three furrows or pores. The root system is usually anchored by one main root developed from the embryonic radicle. Eudicots comprise two-thirds of all flowering plants. The major differences between monocots and eudicots are summarized in table 2.1. However, some species may exhibit characteristics usually associated with the other group, so the identification of a plant as a monocot or a eudicot is not always straightforward (figure 1.2.2. d, e, f).
Characteristic | Monocot | Eudicot |
Cotyledon | One | Two |
Veins in Leaves | Parallel | Network (branched) |
Stem Vascular Tissue | Scattered | Arranged in a ring pattern |
Roots | Network of fibrous roots | Taproot with many lateral roots |
Pollen | Monosulcate | Trisulcate |
Flower Parts | Three or multiple of three | Four, five, multiple of four or five and whorls |
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Plant Organ System - Roots
In plants, just as in animals, similar cells working together form a tissue. When different types of tissues work together to perform a unique function, they form an organ; organs working together form organ systems. Vascular plants have two distinct organ systems: a shoot system and a root system. The shoot system consists of two portions: the vegetative (non-reproductive) parts of the plant, such as the leaves and the stems, and the reproductive parts of the plant, which include flowers and fruits. The shoot system generally grows above ground, where it absorbs the light needed for photosynthesis. The root system, which supports the plants and absorbs water and minerals, is usually underground. Figure 1.2.3 shows the organ systems of a typical plant.
Roots
The roots of seed plants have three major functions: anchoring the plant to the soil, absorbing water and minerals, transporting them upwards, and storing the products of photosynthesis. Some roots are modified to absorb moisture and exchange gases. Most roots are underground. Some plants, however, also have adventitious roots, which emerge above the ground from the shoot.
Types of Root Systems
Root systems are mainly of two types (figure 1.2.4). Dicots have a taproot system, while monocots have a fibrous root system. A tap root system has a main root that grows down vertically, from which many smaller lateral roots arise. Dandelions are a good example; their tap roots usually break off when trying to pull these weeds, and they can regrow another shoot from the remaining root. A tap root system penetrates deep into the soil. In contrast, a fibrous root system is located closer to the soil surface and forms a dense network of roots that also helps prevent soil erosion (lawn grasses are a good example, as are wheat, rice, and corn). Some plants have a combination of tap roots and fibrous roots. Plants that grow in dry areas often have deep root systems, whereas plants growing in areas with abundant water are likely to have shallower root systems.
Root Modifications
Root structures may be modified for specific purposes. For example, some roots are bulbous and store starch. Aerial roots and prop roots are two forms of aboveground roots that provide additional support to anchor the plant. Tap roots, such as carrots, turnips, and beets, are examples of roots that are modified for food storage (figure 1.2.5).
Epiphytic roots enable a plant to grow on another plant. For example, the epiphytic roots of orchids develop spongy tissue to absorb moisture. The banyan tree (Ficus sp.) begins as an epiphyte, germinating in the branches of a host tree; aerial roots develop from the branches and eventually reach the ground, providing additional support (figure 1.2.6). In screwpine (Pandanus sp.), a palm-like tree that grows in sandy tropical soils, aboveground prop roots develop from the nodes to provide additional support.
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Plant Organ System - Stems
Stems are a part of the shoot system of a plant. They may range in length from a few millimeters to hundreds of meters, and vary in diameter, depending on the plant type. Stems are usually above ground, although the stems of some plants, such as the potato, also grow underground. Stems may be herbaceous (green & soft) or woody in nature. Their main function is to provide support to the plant, holding leaves, flowers, and buds; in some cases, stems also store food for the plant. A stem may be unbranched, like that of a palm tree, or it may be highly branched, like that of a magnolia tree. The stem of the plant connects the roots to the leaves, helping to transport absorbed water and minerals to different parts of the plant. It also helps to transport the products of photosynthesis, namely sugars, from the leaves to the rest of the plant.
Plant stems, whether above or below ground, are characterized by the presence of nodes and internodes (figure 1.2.7). Nodes are points of attachment for leaves, aerial roots, and flowers. The stem region between two nodes is called an internode. The stalk that extends from the stem to the base of the leaf is the petiole. An axillary bud is usually found in the axil—the area between the base of a leaf and the stem—where it can give rise to a branch or a flower. The apex (tip) of the shoot contains the apical meristem within the apical bud.
Stem Modifications
Some plant species have modified stems that are especially suited to a particular habitat and environment (figure 1.2.8). A rhizome is a modified stem that grows horizontally underground and has nodes and internodes. Vertical shoots may arise from the buds on the rhizome of some plants, such as ginger and ferns. Corms are like rhizomes; except they are more rounded and fleshier (such as in gladiolus). Corms contain stored food that enables some plants to survive the winter. Stolons are stems that run almost parallel to the ground, or just below the surface, and can give rise to new plants at the nodes. Runners are a type of stolon that runs above the ground and produces new clone plants at nodes at varying intervals: strawberries are an example. Tubers are modified stems that may store starch, as seen in the potato (Solanum sp.). Tubers arise as swollen ends of stolons and contain many adventitious or unusual buds (familiar to us as the “eyes” on potatoes). A bulb that functions as an underground storage unit is a modification of a stem that has the appearance of enlarged fleshy leaves emerging from the stem or surrounding the base of the stem, as seen in the iris.
Some aerial modifications of stems are tendrils and thorns (figure 1.2.9). Tendrils are slender, twining strands that enable a plant (like a vine or pumpkin) to seek support by climbing on other surfaces. Thorns are modified branches appearing as sharp outgrowths that protect the plant; common examples include roses, Osage orange, and devil’s walking stick.
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Plant Organ System - Leaf
Leaves are the main sites for photosynthesis: the process by which plants synthesize food. Most leaves are usually green, due to the presence of chlorophyll in the leaf cells. However, some leaves may have different colors, caused by other plant pigments that mask the green chlorophyll. The thickness, shape, and size of leaves are adapted to the environment. Each variation helps a plant species maximize its chances of survival in a particular habitat. Usually, the leaves of plants growing in tropical rainforests have larger surface areas than those of plants growing in deserts or very cold conditions, which are likely to have a smaller surface area to minimize water loss.
Structure of a Typical Leaf
The structure of a leaf is more complex than meets the naked eye. A leaf typically has a leaf blade also called the lamina, which is also the widest part of the leaf. Some leaves are attached to the plant stem by a petiole. Leaves that do not have a petiole and are directly attached to the plant stem are called sessile leaves. Small green appendages usually found at the base of the petiole are known as stipule(s). Most leaves have a midrib, which travels the length of the leaf and branches to each side to produce veins of vascular tissue. The edge of the leaf is called the margin. Figure 1.2.10 shows the structure of a typical eudicot leaf.
Within each leaf, the vascular tissue forms veins. The arrangement of veins in a leaf is called the venation pattern. Monocots and dicots differ in their patterns of venation (figure 1.2.11). Monocots have parallel venation; the veins run in straight lines across the length of the leaf without converging at a point. In dicots, however, the veins of the leaf have a net-like appearance, forming a pattern known as reticulate venation. One extant plant, the Ginkgo biloba, has dichotomous venation where the veins fork.
Leaf Arrangement
The arrangement of leaves on a stem is known as phyllotaxy. The number and placement of a plant’s leaves will vary depending on the species, with each species exhibiting a characteristic leaf arrangement. Leaves are classified as either alternate, spiral, or opposite. Plants that have only one leaf per node have leaves that are said to be either alternate—meaning the leaves alternate on each side of the stem in a flat plane—or spiral, meaning the leaves are arrayed in a spiral along the stem. In an opposite leaf arrangement, two leaves arise at the same point, with the leaves connecting opposite each other along the branch. If there are three or more leaves connected at a node, the leaf arrangement is classified as whorled.
Leaf Form
Leaves may be simple or compound (figure 1.2.12). In a simple leaf, the blade is either completely undivided—as in the banana leaf—or it has lobes, but the separation does not reach the midrib, as in the maple leaf. In a compound leaf, the leaf blade is completely divided with the formation of leaflets (that may have a stalk), as in the locust tree, attached to the main axis or midrib in a simple leaf. This main axis is also called a rachis. A palmately compound leaf resembles the palm of a hand, with leaflets radiating outwards from one point. Examples include the leaves of poison ivy, the buckeye tree, or the familiar houseplant Schefflera sp. (common name “umbrella plant"). Pinnately compound leaves take their name from their feather-like appearance; the leaflets are arranged along the midrib, as in rose leaves (Rosa sp.), or the leaves of hickory, pecan, ash, or walnut trees.
Internal Structure of a leaf
The outermost layer of the leaf is the epidermis; it is present on both sides of the leaf and is called the upper and lower epidermis, respectively. Botanists call the upper side the adaxial surface (or adaxis) and the lower side the abaxial surface (or abaxis). The epidermis helps in the regulation of gas exchange. It contains stomata (figure 1.2.13): openings through which the exchange of gases takes place. Two guard cells surround each stoma, regulating its opening and closing.
The epidermis is usually one cell layer thick; however, in plants that grow in very hot or very cold conditions, the epidermis may be several layers thick to protect against excessive water loss from transpiration. A waxy layer known as the cuticle covers the leaves of all plant species. The cuticle reduces the rate of water loss from the leaf surface. Other leaves may have small hairs called trichomes on the leaf surface. Trichomes help to deter herbivory by restricting insect movements, or by storing toxic or bad-tasting compounds; they can also reduce the rate of transpiration by blocking air flow across the leaf surface (figure 1.2.14).
Below the epidermis of dicot leaves are layers of cells known as the mesophyll, or “middle leaf.” The mesophyll of most leaves typically contains two arrangements of parenchyma cells: the palisade parenchyma and spongy parenchyma (figure 1.2.15). The palisade parenchyma (also called the palisade mesophyll) has column-shaped, tightly packed cells, and may be present in one, two, or three layers. Below the palisade parenchyma is loosely arranged cells of irregular shape. These are the cells of the spongy parenchyma (or spongy mesophyll). The air space found between the spongy parenchyma cells allows gaseous exchange between the leaf and the outside atmosphere through the stomata. In aquatic plants, the intercellular spaces in the spongy parenchyma help the leaf float. Both layers of the mesophyll contain many chloroplasts. Guard cells are the only epidermal cells to contain chloroplasts.
Like the stem, the leaf contains vascular bundles composed of the xylem and phloem (figure 1.2.16). The xylem consists of tracheids and vessels, which transport water and minerals to the leaves. The phloem transports the photosynthetic products from the leaf to the other parts of the plant. A single vascular bundle, no matter how large or small, always contains both the xylem and phloem tissues.
Leaf Adaptations
Coniferous plant species that thrive in cold environments—like spruce, fir, and pine—have leaves that are reduced in size and needle-like in appearance. These needle-like leaves have sunken stomata and a smaller surface area, which are two attributes that aid in reducing water loss. In hot climates, plants such as cacti have leaves that are reduced to spines that, in combination with their succulent stems, help to conserve water. Many aquatic plants have leaves with wide lamina that can float on the surface of the water, and a thick waxy cuticle on the leaf surface that repels water.
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Plant Organ System - Flower
Flowers are the sexual reproductive parts of a plant. Flowers are modified leaves, or sporophylls organized around a central receptacle. Although there is a remarkable variation in the appearance of flowers, virtually all flowers contain the sepals, petals, carpels, and stamens. A complete flower must have all four structures, otherwise, it is called an incomplete flower.
The peduncle typically attaches the flower to the plant body. A whorl of sepals(collectively called the calyx) is located at the base of the peduncle and encloses the unopened floral bud. Sepals are usually photosynthetic organs, although there are some exceptions. For example, the corolla in lilies and tulips consists of three sepals and three petals that look virtually identical. Petals, collectively the corolla, are located inside the whorl of sepals and may display vivid colors to attract pollinators. Sepals and petals together form the perianth. The sexual organs—the female gynoecium and male androecium —are located at the center of the flower. Typically, the sepals, petals, and stamens are attached to the receptacle at the base of the gynoecium, but the gynoecium may also be located deeper in the receptacle, with the other floral structures attached above it.
As illustrated in figure 1.2.17, the innermost part of a perfect flower is the gynoecium, the location in the flower where the eggs will form. The female reproductive unit consists of one or more carpels, each of which has a stigma, style, and ovary. The stigma is the location where the pollen is deposited either by wind or a pollinating arthropod. The sticky surface of the stigma traps pollen grains, and the style is a connecting structure through which the pollen tube will grow to reach the ovary. The ovary houses one or more ovules, each of which will ultimately develop into a seed. Flower structure is very diverse, and carpels may be singular, multiple, or fused. (Multiple fused carpels comprise a pistil.) The androecium, or male reproductive region, is composed of multiple stamens surrounding the central carpel. Stamens are composed of a thin stalk called a filament and a sac-like structure called the anther. The filament supports the anther, where the microspores are produced by meiosis and develop into haploid pollen grains, or male gametophytes.
Most angiosperms have perfect flowers, which means that each flower carries both stamens and carpels (figure1.2.17), for example lilies. Many flowers are called imperfect since they are either staminate (with only male reproductive structure) or carpellate flowers (with only female reproductive structure).
In monoecious plants, male (staminate) and female (pistillate/carpellate) flowers are separate but carried on the same plant, which can mature simultaneously or at different times (dichogamous) to ensure cross pollination, Sweetgums (Liquidambar spp.) and beeches (Betula spp.) are monoecious (figure 1.2.18). Family Rosaceae (rose) include many plants that show dichogamy. Monoecious plants also include many plants that produce bisexual flowers. In dioecious plants, male and female flowers are found on separate plants. Willows (Salix spp.), poplars (Populus spp.), papaya and asparagus are dioecious.
Despite the predominance of perfect flowers, only a few species of angiosperms self-pollinate. Both anatomical and environmental barriers promote cross-pollination mediated by a physical agent (wind or water), or an animal, such as an insect or bird. Cross-pollination increases genetic diversity in a species.
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Attributions
Biology 2e by Clark Mary Ann, Douglas Matthew, Choi Jung. OpenStax is licensed under Creative Commons Attribution License V 4.0
Glossary
adventitious root - an above-ground root that arises from a plant part other than the radicle of the plant embryo
apical bud - bud formed at the tip of the shoot
apical meristem - meristematic tissue located at the tips of stems and roots; enables a plant to extend in length
axillary bud - bud located in the axil of a leaf, area of the stem where the petiole connects to the stem
bark - the tough, waterproof, outer epidermal layer of cork cells
bulb - modified underground stem that consists of a large bud surrounded by numerous leaf scales
Casparian strip - waxy coating that forces water to cross endodermal plasma membranes before entering the vascular cylinder, instead of moving between endodermal cells
collenchyma cell - elongated plant cell with unevenly thickened walls; provides structural support to the stem and leaves
companion cell - phloem cell that is connected to sieve-tube cells; has large amounts of ribosomes and mitochondria
compound leaf - a leaf in which the leaf blade is subdivided to form leaflets, all attached to the midrib
corm - rounded, fleshy underground stem that contains stored food
cortex - ground tissue found between the vascular tissue and the epidermis in a stem or root
cuticle - waxy covering on the outside of the leaf and stem that prevents the loss of water
dermal tissue - a protective plant tissue covering the outermost part of the plant; controls the gas exchange
endodermis - a layer of cells in the root that forms a selective barrier between the ground tissue and the vascular tissue, allowing water and minerals to enter the root while excluding toxins and pathogens
epidermis - a single layer of cells found in plant dermal tissue; covers and protects underlying tissue
fibrous root system - type of root system in which the roots arise from the base of the stem in a cluster, forming a dense network of roots; found in monocots
ground tissue - plant tissue involved in photosynthesis; provides support, and stores water and sugars
guard cells - paired cells on either side of a stoma that control the stomatal opening and thereby regulate the movement of gases and water vapor
intercalary meristem - meristematic tissue located at nodes and the bases of leaf blades; found only in monocots
internode - region between nodes on the stem
lamina - leaf blade
lateral meristem - also called secondary meristem, meristematic tissue that enables a plant to increase in thickness or girth caused by the vascular cambium and cork cambium
lenticel - opening on the surface of mature woody stems that facilitates gas exchange
meristem - plant region of continuous growth
meristematic tissue - tissue containing cells that constantly divide; contributes to plant growth
node - point along the stem at which leaves, flowers, or aerial roots originate
palmately compound leaf - leaf type with leaflets that emerge from a point, resembling the palm of a hand
parenchyma cell - most common type of plant cell; found in the stem, root, leaf, and in fruit pulp; site of photosynthesis and starch storage
pericycle - outer boundary of the stele from which lateral roots can arise
periderm - outermost covering of woody stems; consists of the cork cambium, cork cells, and the phelloderm
permanent tissue - plant tissue composed of cells that are no longer actively dividing
petiole - stalk of the leaf
phyllotaxy - arrangement of leaves on a stem
pinnately compound leaf - leaf type with a divided leaf blade consisting of leaflets arranged on both sides of the midrib
pith - ground tissue found towards the interior of the vascular tissue in a stem or root
primary growth - growth resulting in an increase in length of the stem and the root; caused by cell division in the shoot or root apical meristem
rhizome - modified underground stem that grows horizontally to the soil surface and has nodes and internodes
root cap - protective cells covering the tip of the growing root
root hair - hair-like structure that is an extension of epidermal cells; increases the root surface area and aids in absorption of water and minerals
root system - belowground portion of the plant that supports the plant and absorbs water and minerals
runner - stolon that runs above the ground and produces new clone plants at nodes
sclerenchyma cell - plant cell that has thick secondary walls and provides structural support, usually dead at maturity
sessile - leaf without a petiole that is attached directly to the plant stem
shoot system - aboveground portion of the plant; consists of nonreproductive plant parts, such as leaves and stems, and reproductive parts, such as flowers and fruits
sieve-tube cell - (sieve-tube members in angiosperms) phloem cell arranged end to end to form a sieve tube that transports organic substances, such as sugars and amino acids
simple leaf - leaf type in which the lamina is completely undivided or merely lobed
sink - growing parts of a plant, such as roots and young leaves, which require photosynthate
source - organ that produces photosynthate for a plant
stele - inner portion of the root containing the vascular tissue; surrounded by the endodermis
stipule - small green structure found on either side of the leaf stalk or petiole
stolon - modified stem that runs parallel to the ground and can give rise to new plants at the nodes
tap root system - type of root system with a main root that grows vertically with few lateral roots; found in dicots
tendril - modified stem consisting of slender, twining strands used for support or climbing
thorn - modified stem branch appearing as a sharp outgrowth that protects the plant
tracheid - xylem cell with thick secondary walls that helps transport water
translocation - mass transport of photosynthates from source to sink in vascular plants
transpiration - loss of water vapor to the atmosphere through stomata
trichome - hair-like structure on the epidermal surface
tuber - modified underground stem adapted for starch storage; has many adventitious buds
vascular bundle - strands of plant tissue made up of xylem and phloem
vascular stele - strands of root tissue made up of xylem and phloem
vascular tissue - tissue made up of xylem and phloem that transports food and water throughout the plant
venation - pattern of veins in a leaf; may be parallel (as in monocots), reticulate (as in dicots), or dichotomous (as in ginkgo biloba)
vessel element - xylem cell that is shorter than a tracheid and has thinner walls
whorled - pattern of leaf arrangement in which three or more leaves are connected at a node