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Chapter 6 classification of plants and plant anatomy.

ABSTRACT

Many benefits are associated with plants; however, to classify them, you must have a better understanding of their anatomy. In this chapter you will learn how to classify plants and recognize their various parts and functions. Classifying plants is an important task that many years ago was accomplished using two main categories. Scientists today group plants by using similarities among them for classification into eight general groupings. Scientific classification and morphology will be defined in this chapter, and you will learn why common names and Latin polynomials were never accepted as the standard for classifying plants. The binomial nomenclature system developed by Linnaeus for classifying plants is also discussed and you will learn about the nine groups used for botanical classification. You will then explore why cultivar identification is important and discover the different ways cultivars are identified today. You will see an example of botanical classification using the "Delicious" apple, including both major and minor taxa. This is followed by a discussion of the different stages of the plant's life cycle and the principal vegetative and reproductive structures. The last portion of this chapter discusses seeds and seed germination.

Objectives

After reading this chapter, you should be able to

* explain why we classify plants and describe the two main categories used to classify plants in early systems. list and explain the eight ways in which scientists group plants by using similarities between them for classification.

* define scientific classification and morphology and explain why common names and Latin polynomials were never accepted as the standard for classifying plants.

* explain binomial nomenclature and list and explain the nine groups used for botanical classification. explain why cultivar identification is important and describe commonly used methods for identifying cultivars today.

* provide the major and minor taxa for the "Delicious" apple as an example for botanical classification. discuss the different phases of the plant's life cycle, including juvenile or vegetative phase, reproductive or mature phase, and the senescence phase.

* discuss the basic vegetative parts of the plant, including leaves, stems, and roots.

* discuss the reproductive parts of the plant, including flowers and fruits.

* discuss seeds and seed germination.

Key Terms

alternate leaf

arrangement

angiosperm

annual

anther

apical meristem

axillary bud

biennials

bract

bud scale

calyx

cambium

complete flower

compound leaf

cortex

cultivar

dead heading

deciduous perennial

deciduous plants

dicots

dicotyledonae

dry fruit

epidermis

epigeous seed

germination

evergreen perennial

evergreen plants

fertilization

fibrous root system

filament

filicinae

fleshy fruit

fruit

germination

gymnosperm

hardy plants

herbaceous perennial

herbaceous plant

hypogeous seed germination

incomplete flower

imperfect flower

internode

juvenile or vegetative stage

leaf apex

leaf base

leaf blade

leaf covering

leaf margin

leaf scar

leaflet

lenticel

midrib

modified root

monocots

monocotyledonae

morphology

node

nonwoody plant

opposite leaf arrangement

ovary

perennials

perfect flower

petals

petiole

phloem

photosynthesis

pistil

pith

pollination

primary root

reproductive or mature phase

respiration

root cap

root hairs

scientific classification

scout

secondary root

seed

senescence

sepals

simple leaf

stamens

stigma

stomata

style

taproot system

taxon (taxa)

taxonomy

tender plants

tendril

terminal bud

terminal bud scale scar

transpiration

veins

vernalization

viable

whorled leaf arrangement

woody plant

xylem

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INTRODUCTION

In this chapter, you will learn how to classify plants by better understanding their anatomy. Plants are classified for identification and cataloguing purposes as well as to overcome language barriers and better understand plant origins and plant relationships. Early systems of classification simply categorized plants as either harmful or useful. Today, plant classification has become much more complex. Scientists use similarities among plants to classify or break down plants into eight characteristics: kind of stem, size of plant, stem growth form, kind of fruit, life cycle, foliage retention, temperature tolerances, and number of cotyledons. Scientific classification uses the morphology of plants as a means of plant classification. In 1753, Linnaeus established a simple yet elegant scientific classification system called binomial nomenclature, which is still used today. Plants can be broken down into major and minor taxa. A taxa is a group name applied to organisms that make up a hierarchy within a formal system of classification; for example, kingdom is a taxa. The botanical classification system is commonly used for horticultural crops: the major taxa starts with kingdom followed by division or phylum, class, subclass, order, and family; the minor taxa starts with genus followed by species and cultivar.

The plant's life cycle can be broken down into three phases: the juvenile or vegetative phase, reproductive or mature phase, and senescence, which is ultimately followed by death. The juvenile phase is characterized by exponential increases in size and the inability to flower. The mature phase is characterized by changes that enable the plant or organ to express its full reproductive potential. The senescence phase involves deteriorative changes, which are natural causes of death.

To classify plants properly, you should be familiar with the plant's leaves, stems, and roots, which make up the primary vegetative structures of the plant. The main function of the leaf is to produce food for the entire plant through photosynthesis. Leaves have several basic parts that can help you identify plants: the petiole, leaf blade, midrib, veins, leaf margin, leaf apex, leaf base, leaf covering, and stomata. The leaf form, apexes, margins, and bases are most commonly used to identify plants. The pattern of leaf attachment to stems--including opposite, alternate, and whorled arrangements--is another way to classify plants. Modified leaves, which include bracts and tendrils, have also been used to identify plants. Stems can also be used to classify plants. The basic parts of the stem are the terminal bud, bud scale, terminal bud-scale scar, axillary bud or lateral bud, node, internode, leaf scar, and lenticel. The internal anatomy of the stem is also used to classify plants by these key anatomical features: cambium, xylem, phloem, and pith. Modified stems, which include stolons, rhizomes, tubers, corms, and bulbs, are specialized stems used for storing food reserves and for reproducing.

The primary function of the root is to absorb water and nutrients to sustain plant life. The key parts of the root are the primary root, secondary root, root hairs, and root cap. The two different classes of roots used to classify plants are plants with a tap root system and plants with a fibrous root system. Some plants also have modified roots, which serve as a reserve food system; for example, a sweet potato is a modified root that is vastly different from an Irish potato, which is a modified stem.

The major function of the flower (Figure 6-1) is to attract pollinators and to produce fruit and seed. Flowers are commonly used to classify plants because they come in a variety of sizes, shapes, and colors. A typical flower contains the following parts: sepals (calyx), petals, stamens (filament, anther), and pistils (stigma, style, and ovary). The four classes of flowers--complete, incomplete, perfect, and imperfect--can be used as means of classifying plants. Another means of classification is through the use of fruits that can be fleshy or dry.

At the end of this chapter, you will learn that in order for germination to occur the seed must be viable, be exposed to the proper environmental conditions, and be able to overcome primary dormancy. The four stages of seedling germination include the imbibition of water, formation or activation of enzyme systems, breakdown of storage food reserves, and emergence of the radicle from the seed. At the conclusion of this chapter, you will learn the two common forms of seed germination: epigeous and hypogeous.

HOW PLANTS ARE CLASSIFIED AND NAMED

Before you begin to classify plants, it is important to understand why they are classified. Plants are classified for many reasons, the first being that identifying plants is important. Second, after a plant is identified, it can be catalogued for future reference. Third, the classification of plants overcomes language barriers because when plants are scientifically classified and named, the plant retains that same name all over the world (unlike common names that can be very different within the same country or even the same state). Fourth, by classifying plants, we can better understand their origins. Fifth, classifying plants helps uncover the relationship among plants, which is useful information when growing different types of plants together for the benefit of each.

The early systems used for classifying plants simply determined whether plants were harmful or poisonous and should not be eaten or whether they were useful and could be used for food, spices, medicinal purposes, construction, transportation, and communication (Janick, 1986).

Today, scientists use similarities among plants to break them down into the following eight groups.

Kind of Stem

Stems can be broken down into two basic categories: woody or nonwoody (herbaceous). The woody plant (shrubs, trees, and others) produces wood and has buds, which survive above ground level during the winter months. The nonwoody or herbaceous plant has soft, nonwoody stems. Nonwoody or herbaceous plants typically include turfgrasses, herbs, ground covers, and flowering plants.

Size of the Plant

The overall size of the plant at maturity is commonly used to classify and name plants. Plants may be dwarf, which exhibit shortened internodes, or they can be standard size with normal internode lengths.

Stem Growth Form

The stem growth form is based on how the stem stands in relation to the ground. For example, an erect stem is vertical with respect to gravity, whereas a creeping habit stem grows horizontal with respect to gravity. A plant that grows along the ground and then climbs (such as an ivy plant) when it comes in contact with an obstacle has a climbing habit (Figure 6-2).

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Kind of Fruit

The characteristic of the fruit is another means of classifying plants. For example, fruits are classified as fleshy if they are soft and succulent (such as a peach) or dry if they are hard and have a low water content (such as a walnut).

Life Cycle

As shown in Figure 6-3, plants can be designated as annuals, biennials, or perennials. Annuals are plants that germinate from seed, grow to full maturity, flower, and produce seeds in one growing season; in other words, these plants go from seed to seed in one season (for example, a marigold). To extend the flowering period for annuals, a process known as dead heading is commonly used. Dead heading refers to removing dead or dying flowers from annuals so the plant continues to live and bloom longer. Biennials are plants that complete their life cycle in two growing seasons, such as lettuce. Biennial plants require a vernalization period in order to flower. Vernalization refers to using cold treatment to induce flowering. Perennials are plants that may be herbaceous or woody and live for more than two growing seasons. There are three types of perennials.

* Herbaceous perennials. The tops die and roots live throughout the winter months.

* Deciduous perennials. The root systems and stems live throughout the winter months.

* Evergreen perennials. The root system, stems, and leaves live throughout the winter months.

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Foliage Retention

When (or if) a plant loses its leaves is also a characteristic commonly used to classify and name plants. Deciduous plants lose their leaves during a portion of the year, usually the winter months. Evergreen plants hold their leaves all year.

Temperature Tolerances

How plants handle temperature is also used to classify and name plants. Tender plants such as tomatoes and peppers cannot tolerate cool weather. Hardy plants such as broccoli and chrysanthemums are less sensitive to temperature extremes than tender plants.

Number of Cotyledons and Venation

The number of cotyledons (seed leaves) and type of leaf venation is commonly used to classify and name plants. Dicot plants are characterized by two cotyledons and have reticulate leaf venation. Monocot plants are characterized by one cotyledon and have parallel leaf venation.

SCIENTIFIC CLASSIFICATION

Scientific classification uses the morphology of plants (the plant's form and structure) as a means of classification and names plants based on the International Code of Botanical Nomenclature. Using common names for plants was inadequate as a means of classification because of the major problems that arise as a result of language and plant differences throughout the world. Differences in common names can also occur within in the same country and even within the same state. For example, a common name used in upper New York state can have a different meaning at another location such as New York City. Latin polynomials were also found inadequate because they were too long, cumbersome, and difficult to use.

In 1753, Linnaeus published the Species Plantarum (a two-volume work), which presented the binomial nomenclature system for plant classification that is commonly used today. An example of the binomial nomenclature system is Brassica oleracea L. 'Union'. In this example the first word is the genus (Brassica) followed by the species (oleracea) (L.), authority, in this case, Linneaus and cultivar (Union). When using the binomial nomenclature system, the genus and species are either underlined or italicized with the first letter in the genus capitalized and the species all lowercase. Many binomials also indicate an authority, which is the person involved in the discovery, description, and naming of the plant.

Botanical Nomenclature

To better understand botanical nomenclature, you should be familiar with the following terms: Taxonomy. The study of scientific classification and nomenclature. Taxon (taxa). A group name applied to organisms that make a hierarchy within a formal system of classification.

Botanical Classification

The following is the botanical classification system (Table 6-1) commonly used for horticultural plants.

Major Taxa

1. Kingdom--Plants or animals

2. Division or Phylum

Tracheophyta includes most horticultural plants. Other phylums include Spermatophyta, Pteridophyta, Thallophyta, and Bryophyta.

3. Class

Filicinae: Ferns G ymnosperms: Primarily evergreen trees, usually have naked seeds born in cones.

Angiosperms: Flowering plants and seeds develop in fruits.

4. Subclass

Dicotyledonae (Dicot): Has two cotyledons and reticulate leaf venation, such as a bean plant.

Monocotyledonae (Monocot): Has only one cotyledon and parallel leaf venation, such as corn.

5. Order

6. Family: Plants are grouped based on natural plant relationships using structural and cultural similarities.

Minor Taxa

7. Genus: Plants are grouped based on morphology and genetic, biochemical, and molecular relationships.

8. Species: Plants are grouped with even greater refinements than the genus but are still grouped based on morphology and genetic, biochemical, and molecular relationships.

9. Cultivar: Horticulturists are generally interested in the botanical variety, form, biotype, and clone; when any of these are intentionally cultivated, they are referred to as a cultivar--cultivated variety (for example, a "Delicious" apple). The term cultivar has replaced the older term variety to avoid confusion with the taxonomic term. In a taxonomic sense, a variety means a botanical variety.

Cultivars

When a grower puts a lot of time and effort into establishing a cultivar, the grower must establish ownership to prevent patent infringements. Cultivars can be distinguished by the following characteristics:

* Flower. Size, shape, and number of the different floral parts.

* Fruit. Flesh types, color, size, and shape.

* Vegetative parts. Buds, bark color, size, and hardiness.

In today's society, patents and ownership are very important; therefore, using more precise methods of identifying a cultivar are even more critical. Methods used to establish patents and ownership in addition to the preceding are as follows:

* Chemical taxonomy and biochemistry uses proteins, anthocyanins, and other specific chemicals as fingerprints to identify cultivars.

* Molecular evidence uses the Polymerase Chain Reaction (PCR) for DNA analysis.

These tools are necessary to protect patents and resolve infringement disputes. Patent holders may also employ a scout to buy plants at various outlets and run analyses of these plants to determine whether the plants are being used legally.

THE PLANT'S LIFE CYCLE

As stated previously, the plant's life cycle has three phases with varying characteristics.

Juvenile or Vegetative Phase

In the initial period of growth, the apical meristem, which is the primary growing point of the stem, will not typically respond to internal or external conditions to initiate flowers. The juvenile phase of development exhibits exponential increases in size and the inability to shift from vegetative to reproductive maturity leading to the formation of flowers. In addition, juvenile plants have specific morphological and physiological traits. Examples of morphological traits include the following:

Leaf shape. Hedra helix, or ivy, in the immature stage has five lobes, whereas in the mature stage it has none. The ivy commonly seen around college campuses is mostly immature; it is actually fairly hard to find plants in the mature stage (Figure 6-4).

Thorniness. Young growth in Juniperus virginum has thorns, whereas older growth does not.

[FIGURE 6-4 OMITTED]

Examples of physiological traits during the juvenile stage include vigorous plant growth, disease resistance, and a greater ability to regenerate roots and shoots (Arteca, 1996).

Reproductive or Mature Phase

This phase refers to qualitative changes that allow the plant or organ to express its full reproductive potential. Both genetic and environmental conditions determine when plants enter this phase.

Senescence

This phase involves internally controlled deteriorative changes, which are natural causes of death. Changes that occur during senescence include the following:

* Decreases in chlorophyll, protein, nucleic acids (RNA/DNA), and photosynthesis.

* Changes in plant hormones--some increase while some decrease.

* When the senescence phase is complete, abscission occurs.

THE PLANT'S VEGETATIVE STRUCTURES

The leaves, stems, and roots make up the primary vegetative structures of the plant. They take part in growth processes that are essential to the plant's survival.

Leaves

The main function of a leaf is to manufacture food for the plant through photosynthesis. Photosynthesis refers to a series of chemical reactions in which carbon dioxide and water are converted in the presence of light to carbohydrates (sugar) and oxygen. The simplified equation for photosynthesis is as follows:

6C[O.sub.2] + 6[H.sub.2]O[right arrow][right arrow][right arrow][right arrow][C.sub.6][H.sub.12][O.sub.6] + 6[O.sub.2]

[FIGURE 6-5 OMITTED]

Both light and chlorophyll are essential to photosynthesis. The two major photosynthetic enzymes found in plants are ribulose-bisphosphate carboxylase (Rubisco) and phosphoenolpyruvate carboxylase (PEP-Carboxylase). Carbon dioxide and other gases enter and exit the leaf through tiny pores in the leaf's surface called stomata (Figure 6-5). Another important function carried out by the leaf is transpiration, which is the loss of water from the leaf in the form of water vapor. Respiration is another important function carried out by the leaf; this process uses sugars made during photosynthesis and breaks them down into simpler molecules (such as [H.sub.2]O and C[O.sub.2]) that are used as energy for plant growth and development.

Parts of Leaves

Leaves consist of several basic parts that help identify them. The major parts of a simple dicot leaf are listed here (Figure 6-6):

* Petiole. The leaf stem or stalk that attaches the leaf to the stem.

* Blade. The flat thin part of the leaf.

* Midrib. The largest vein located in the middle of the leaf.

* Veins. Used to transport water and nutrients throughout the plant. The different leaf-venation patterns found in plants can be parallel, pinnate, or palmate (Figure 6-7).

* Leaf margin. The outer edge of the leaf blade, which can be lobed, smooth, toothed, or various combinations of the three.

* Leaf apex. The tip of the leaf blade, which can be pointed, rounded, or a variety of other shapes.

* Leaf base. The bottom of the leaf blade, which can be rounded, pointed, or a variety of other shapes.

* Leaf covering. Various leaf coverings include hairy versus not hairy, waxy versus not waxy, and others.

* Stomata. The tiny openings in the leaf blade in which gases enter and exit the leaf; they can be located on the leaf's top, bottom, or both.

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Leaf forms, apexes, margins, and bases are commonly used to identify plants (Figure 6-8).

Two Basic Types of Leaves

The simple leaf consists of one blade per petiole, such as found on an oak leaf (Figure 6-9). The compound leaf has two or more leaflets, such as found on a potato leaf (Figure 6-10). The main difference between a leaf and a leaflet is the position of the axillary bud, which is located at the base of the entire leaf; leaflets do not have axillary buds.

Patterns of Leaf Attachment to Stems

Differences in how leaves are attached to stems are commonly used as a means of plant identification. Leaves are attached to stems in three major patterns, as shown in Figure 6-11.

* Opposite. The opposite pattern occurs when two leaves are directly across from each other.

* Alternate. The alternate pattern occurs when leaves are staggered along the length of the stem.

* Whorled. The whorled pattern occurs when three or more leaves are attached to the same portion of the stem.

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Modified Leaves

Modified leaves are commonly mistaken for other plant structures such as flowers or stems. To illustrate this point, examples of modified leaves are provided as follows:

* Bracts. Leaves located just below the flower, for example, the poinsettia and dogwood (Figure 6-12).

* Tendrils. Appendages produced by certain vines that wrap around a support and allow them to climb, for example, the grape (Figure 6-13).

[FIGURE 6-12 OMITTED]

Stems

Stems can be used to identify plants with some practice. The stem has several important functions:

* Support. Stems are used to support leaves, flowers, and fruits.

* Transport. Stems contain important transport systems, including the xylem for transporting water and minerals, and the phloem for transporting manufactured food.

* Photosynthesis. Stems can be used to manufacture food, but to a lesser extent than the leaves.

* Storage organ. Stems can act as a storage organ for food; an example of this is the Irish potato.

Basic Parts of the Stem

The basic parts of the stem are illustrated in Figure 6-14 and described here.

* Terminal bud. The bud is positioned at the tip of the stem and contains an undeveloped leaf, stem, flower, or mixture of all.

* Bud scale. The bud scale is a tiny leaf-like structure that covers the bud and protects it.

* Terminal bud-scale scar. The terminal bud-scale scar is left when the terminal bud begins growth in the spring; it represents one year's growth.

* Axillary or lateral bud. The axillary bud is located along the side of the stem below the terminal bud.

* Node. The node is the point along the length of the stem where leaves or stems are attached.

* Internode. The internodal region is located between the nodes.

* Leaf scar. The leaf scar is left when the leaf drops.

* Lenticel. The lenticels are tiny pores located in the stem and are used for gas exchange; an example of a tree with conspicuous lenticels is the cherry tree (Figure 6-15) (Esau, 1965).

[FIGURE 6-13 OMITTED]

[FIGURE 6-14 OMITTED]

[FIGURE 6-15 OMITTED]

Internal Anatomy of Stems

Within the stem, the water, nutrients, and food made during photosynthesis are transported throughout the plant and stored for later use. The internal anatomies of a monocot (has one cotyledon and parallel leaf venation) and dicot stem (has two cotyledons and reticulate leaf venation) are shown in Figure 6-16. The following are key anatomical features found in stems:

* Epidermis. The outer layer of plant parts.

* Cortex. Primary tissue of the stem or root, which is located between the epidermis and the vascular region.

* Cambium. The cambium is an area where new plant cells are formed. When grafting, the cambium layers must match for the graft union to be successful.

* Xylem. The xylem is composed of tiny tubes that transport water and nutrients up from the roots to other parts of the plant. The annual rings in a tree are made up of xylem.

* Phloem. The phloem is composed of tiny tubes that transport manufactured food and carbohydrates from the leaves down to other parts of the plant, such as the roots and shoots.

* Pith. The pith is located in the center portion of the stem where food and moisture are stored.

[FIGURE 6-16 OMITTED]

Modified Stems

In addition to standard stems, there are also modified stems used for storage of reserves and for reproduction. Examples of modified stems are shown in Figure 6-17 and listed here:

* Stolon--strawberry.

* Rhizomes--asparagus or iris.

* Tubers--Irish potato.

* Corms--gladiolus.

* Bulbs--onions, tulips.

[FIGURE 6-17 OMITTED]

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Roots

The major function of the root is to absorb water and nutrients to sustain plant life. In addition, roots act as storage organs for carbohydrates and provide anchor and support for the top portion of the plant. The first structure to emerge from a germinating seed is the root. The key parts of the root are shown in Figure 6-18 and described here:

* Primary root. The primary root is the main root that first emerges from the seed. Starting from the tip of the primary root, there is the root cap, just behind the root cap is the area of cell division, followed by the area of cell elongation, and then the area of cell differentiation.

* Secondary root. The secondary root arises from the primary root.

* Root hairs. Root hairs are single cells that absorb the greatest amount of water and minerals. Improper handling during transplanting can cause the loss of many root hairs, which decreases the plant's water uptake and results in transplant shock.

* Root cap. The root cap is located at the tip of the root and consists of several layers of cells that protect the root as it grows through the soil.

Different Classes of Root Systems

The two major classes of root systems are shown in Figure 6-19 and described here.

* Taproot system. The taproot system has a primary root that grows down from the stem with only a few secondary roots; both carrots and dandelions are examples.

* Fibrous root system. The fibrous root system has a large number of small primary and secondary roots; potato plants and grasses are examples.

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Modified Roots

Modified roots serve as a reserve food-storage system; an example of a modified root is a sweet potato (Figure 6-20). Be careful not to be confused the modified-root sweet potato with the modified-stem Irish potato.

REPRODUCTIVE PARTS OF THE PLANT

The reproductive parts of the plant are the flowers, which are pollinated and fertilized to produce the fruits.

Flower

The main function of flowers is to attract pollinators and to produce fruit and seed. Flowers come in a variety of sizes, shapes, and colors to achieve their main function. In addition to their main function, flowers are commonly used for plant identification and produced commercially for their beauty and fragrance.

Parts of the Flower

A typical flower consists of four major parts, as shown in Figure 6-21 and described here:

* Sepals. The sepals are green, leaf-like structures located beneath the petals. The calyx is the term used to describe all the sepals on one flower. The calyx is used for protection. For example, some plants have calyx that contain spines, which deter animals from feeding on them.

* Petals. The petals are the brightly colored portions of the flower that are used to attract pollinators.

* Stamens. The stamens are the male reproductive part of the flower. The stamen consists of a filament that supports the anther, which produces the male sex cells.

* Pistils. The pistils are the female reproductive part of the flower. The pistil consists of the stigma, which is the sticky surface for collecting pollen; the style, which is the tube that connects the stigma and ovary; and the ovary, which contains ovules or eggs.

[FIGURE 6-21 OMITTED]

Pollination is the transfer of pollen grains from the anther to the stigma. This should not be confused with fertilization, which occurs when the male sex cell fuses with the egg cell to form a new plant.

Four Classes of Flowers

Flowers can be broken down into four different classes.

* Complete flower. The complete flower contains all four major flower parts: sepals, petals, stamens, and pistils.

* Incomplete flower. The incomplete flower lacks one or more of the major flower parts.

* Perfect flower. The perfect flower contains both stamens and pistils.

* Imperfect flower. The imperfect flower lacks either stamens or pistils; an example of a plant containing this type of flower is corn.

Fruits

Fruits are formed after the flower has been pollinated and fertilized. The definition of a fruit is a mature ovary of a flowering plant. There are two types of fruits:

* Fleshy fruit. The fleshy fruit (such as a tomato) has soft fleshy material with or without seeds enclosed.

* Dry fruit. The dry fruit (such as a sunflower) has seeds enclosed in a hard fruit wall.

SEEDS AND SEED GERMINATION

A seed is a mature fertilized egg that is contained in the fruit. Seeds can be dispersed by the wind (dandelions) (Figure 6-22), stuck to the fur of animals, or spread in other ways. Dicots store their reserve food in cotyledons, whereas monocots store their food in the endosperm.

Seed Germination

The germination process is a series of events whereby the seed embryo goes from a dormant state to an actively growing state. For seed germination to occur, the following criteria must be met:

* The seed must be viable, which means that the embryo is alive and capable of germination.

* The seed must be exposed to appropriate environmental conditions. Primary dormancy must be overcome in the seed.

Three stages of seedling germination are as follows:

* Imbibition of water. This is the active uptake of water by the seed.

* Formation or activation of enzyme systems. After the seed is hydrated, preexisting enzymes are immediately available for breaking down storage reserves, and new enzymes are produced for the breakdown of additional reserves.

* Breakdown of storage products for use during germination. Preexisting and newly formed enzymes break down food reserves, which are used for the germination process.

[FIGURE 6-22 OMITTED]

The first visible sign of seed germination and growth is the emergence of the radicle followed by growth of the seedling.

The following are two common forms of seed germination.

* Epigeous seed germination. The hypocotyl elongates and brings the cotyledons above ground (for example, cherry) (Figure 6-23a).

* Hypogeous seed germination. The epicotyl emerges and the cotyledons remain below the soil surface (for example, corn) (Figure 6-23b).

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SUMMARY

The classification of plants has come a long way from the times of our ancient ancestors, who only had two main categories for classifying plants, namely as harmful or useful. Today, scientists group plants in eight ways based on plant similarities for their classification. That botanical classification breaks plants down into nine distinct categories.

Cultivar identification is important, especially when communicating with others. Knowledge of basic plant anatomy, including vegetative (leaves, stems, and roots) and reproductive (flowers and fruits) plant parts, together with understanding the plant's life cycle is important in plant classification as well as in maximizing the plant's potential uses.

Review Questions for Chapter 6

Short Answer

1. What are five reasons for classifying plants?

2. What were two categories used for the classification of plants in early systems?

3. What are eight ways scientists group plants for classification?

4. Why were Latin polynomials and common names found to be inadequate?

5. What group is responsible for the naming of plants today?

6. Give an example of the binomial nomenclature system.

7. List the nine categories used for botanical classification and provide an explanation for each.

8. Why is cultivar identification important, and what are some ways commonly used to distinguish between cultivars?

9. Provide the major and minor taxa of the "Delicious" apple.

10. Name and explain the three major phases of a plant's life cycle.

11. What is the main function of a leaf ?

12. What are the two major photosynthetic enzymes found in plants?

13. List the nine major parts of a simple leaf.

14. Distinguish between a leaf and a leaflet.

15. Give two examples of a modified leaf.

16. What are the four major functions of a stem?

17. List the eight parts of the stem.

18. What are four examples of a modified stem?

19. What are the three major functions of the root?

20. Draw a root system and designate the area of differentiation, area of cell elongation, and area of cell division.

21. What are two types of root systems?

22. Provide an example of a modified root.

23. What are the three major functions of flowers?

24. Provide the four major parts of a typical flower and, where applicable, give additional parts associated with each.

25. What are two types of fruits?

26. Where is food stored in monocot and dicot seeds?

27. Provide three factors required for seed germination to occur. After these requirements are met, what are the three phases of seed germination?

Define

Define the following terms:

woody plant

herbaceous plant

annual

biennials

vernalization

perennials

deciduous plants

evergreen plants

monocots

dicots

taxonomy

taxon (taxa)

gymnosperm

angiosperm

apical meristem

senescence

photosynthesis

transpiration

stomata

respiration

cambium

xylem

phloem

pith

root hairs

sepals

calyx

petals

stamens

pistil

pollination

fertilization

fruit

seed

epigeous seed germination

hypogeous seed germination

True or False

1. Removing dead or dying flowers from annuals so the plant will continue to bloom for a longer period of time is known as dead heading.

2. Vernalization is a cold treatment used to make certain plants flower.

3. Angiosperms usually have naked seeds born in cones.

4. Latin polynomial nomenclature is commonly used to classify plants.

5. Gymnosperms are a class of flowering plants that develop their seeds in fruits.

6. C[O.sub.2] enters the leaf through tiny pores called stomata.

7. One of the major photosynthetic enzymes in plants is ribulose-diphosphatase.

8. Fertilization is the transfer of pollen grains from the anther to the stigma.

9. Pollination occurs when the male sex cell fuses with the egg cell to form a new plant.

10. A perfect flower contains both stamens and pistils.

11. An imperfect flower lacks either sepals and petals.

12. Dicots store their food in a specialized group of tissues called the endosperm.

13. Epigeous germination occurs when the epicotyl emerges and cotyledons remain below the soil surface.

14. Hypogeous germination occurs when the epicotyl emerges and cotyledons remain below the soil surface.

15. Monocots store their food in the cotyledons.

Multiple Choice

1. Why do we classify plants?

A. Overcome language barriers

B. Better understand the relationship between plants

C. Catalog plants

D. All of the above

2. Most horticultural crops are in the division (phylum)

A. Bryophyta.

B. Pteridophyta.

C. Thallophyta.

D. None of the above.

3. The annual rings of a tree are made up of

A. Xylem.

B. Phloem.

C. Pith.

D. Cambium.

4. Which of the following is the major function of the pith?

A. Stores food and moisture in the center portion of the stem

B. Transports water and nutrients

C. Moves manufactured food and carbohydrates

D. All of the above

5. Which of the following is the major function of the xylem?

A. Stores food and moisture in the center portion of the stem

B. Transports water and nutrients

C. Moves manufactured food and carbohydrates

D. All of the above

6. Which of the following is the major function of the phloem?

A. Stores food and moisture in the center portion of the stem

B. Transports water and nutrients

C. Moves manufactured food and carbohydrates

D. All of the above

Fill in the Blanks

1. The other term for a nonwoody plant is --.

2. Horticulturists are generally interested in the botanical variety, form, biotype, and clone. When any of these are intentionally cultivated, they are referred to as a --.

3. Linnaeus established a clear and concise method for classifying plants called --.

4. Both -- and -- conditions determine when plants flower.

5. The -- is an area where new cells are formed and is the layer between the xylem and phloem.

Matching Questions

Match the terms with the appropriate label on the diagram (some terms may be used twice).

Terms: Phloem (A), xylem (B), cambium (C), pith (D), monocot (E), dicot (F)

[ILLUSTRATION OMITTED]

Activities

You now understand basic plant anatomy and how plants are classified. This knowledge enables you to explore additional ways in which plants are classified. In this activity, you will evaluate other ways plants are classified. Your activity is to search the Internet for different sites that present information on the botanical classification of plants. In addition to the Internet, check with your local library for potential reference books that have information on plant classification. From the Internet and/or the library, find the answers to the following questions:

What other forms of botanical classification do these references contain and how similar are they to the ones presented in this chapter?

Which form of botanical classification in your opinion is the easiest to follow?

What is the Web site address or the textbook where you found the information contained in this activity?

References

Arteca, R. N. (1996). Plant growth substances: Principles and applications. New York: Chapman & Hall.

Esau, K. (1965). Plant anatomy. New York: John Wiley and Sons.

Janick, J. (1986). Horticultural science (4th ed.). San Francisco, CA: W.H. Freeman.
TABLE 6-1 CLASSIFICATION OF A DELICIOUS APPLE PLANT USING
HORTUS THIRD

MAJOR TAXA
  Kingdom              Plant
  Division (Phylum)    Tracheophyta
  Class                Angiospermae
  Subclass             Dicotyledonae
  Order                Rosales
  Family               Rosaceae (same family as rose or strawberry)

MINOR TAXA
  Genus                Malus
  Species              pumila (domestica)
  Cultivar (variety)   Delicious
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Author:Arteca, Richard N.
Publication:Introduction to Horticultural Science
Geographic Code:1USA
Date:Jan 1, 2006
Words:6214
Previous Article:Chapter 5 the relationship between horticulture and the environment.
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