Botany Tutorial

8/6/2019 Botany Tutorial

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BASIC BOTANY, PHYSIOLOGY, AND ENVIRONMENTAL EFFECTS ON PLANT GROWTH

In order to gain a working knowledge of horticulture, it is necessary tounderstand the structure and function of plants and the environmentalfactors that affect plant growth. In the greatly diversified kingdom of

plants, all flowering plants have certain structures and functions incommon. These similar ities are the basis for this chapter.Higher flowering plants are divided into two groups, monocotyledons(monocots) and dicotyledons (dicots). Although monocots and dicots aresimilar in many ways, differences with respect to number of seed leaves,number of flower parts, leaf vein pattern, and root structure exist. Inaddition, physiological dissimilarities exist which, for example, resultin different responses to herbicides.

BOTANY: PLANT PARTS AND FUNCTIONS

The parts of a plant can be divided into two groups, sexual reproductiveparts and vegetative parts. Sexual reproductive parts are those involvedin the production of seed. They include flower buds, flowers, fruit, and seeds.The vegetative parts include leaves, roots, leaf buds, and stem. Although thevegetative parts are not directly involved in sexual reproduction, theyare often used in asexual or vegetative forms of reproduction, such ascuttings.

PRINCIPAL PARTS OF A VASCULAR PLANT

STEMS

Stems are structures which support buds and leaves and serve as conduitsfor carrying water, minerals, and sugars. The three major internal partsof a stem are the xylem, phloem, and cambium. The xylem and phloem arethe major components of a plant's vascular system. The vascular systemtransports food, water, and minerals and offers support for the plant.Xylem tubes conduct water and minerals, while phloem tub es conduct food.

The vascular systems of monocots and dicots differ. While both containxylem and phloem, they are arranged differently. In the stem of amonocot, the xylem and phloem are paired into bundles; these bundles aredispersed throughout the stem. But in the stem of a dicot, the vascular

system forms ring s inside the stem. The ring of phloem is near the barkor external cover of the stem and is a component of the bark in maturestems. The xylem forms the inner ring; it is the sapwood and heartwoodin woody plants. The difference in the vascular system of the two groupsis of practical interest to the horticulturist because certainherbicides are specific to either monocots or dicots.

The cambium is a meristem, which is a site of cell division and active growth.It is located between the xylem and phloem inside the bark of a stem andis the tissue responsible for a stem's increase in girth, as it producesboth the xylem and phloem tissues. Stems may be long, with greatdistances between leaves and buds (branches of trees, runners onstrawberries), or compressed, with short distances between buds or

leaves (fruit spurs, crowns of strawberry plants, dandelions).Stems can be above the ground like most stems with which we arefamiliar, or below the ground (potatoes, tulip bulbs). All stems must


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have buds or leaves present to be classified as stem tis sue.

DIVERSIFIED STEM DEVELOPMENT

Above-ground modifications

A crown is a region of compressed stem tissue from which new shoots areproduced, generally found near the surface of the soil. A spur is acompressed fruiting branch. A runner is a type of stolon. It is aspecialized stem that grows on the soil surface and forms a new plant atone or more of its nodes. A branch is a stem which is more than one year old.

Below-ground modifications

A rhizome is a specialized stem which grows horizontally at or just belowthe soil surface and acts as a storage organ and means of propagation insome plants. A tuber is an enlarged portion of an underground stem.A corm is a compressed stem with reduced scaly leaves. A bulb is composed

of a short stem plate, closely spaced buds, and fleshy leaves.An area of the stem where leaves are located is called a node. Nodes areareas of great cellular activity and growth, where auxiliary buds developinto leaves or flowers. The area between nodes is called the internode.The length of an internode may depend on many factors. Decreasingfertility will decrease internode length. Internode length varies withthe season. Too little light will result in a long internode, causing aspindly stem. This situation is known as stretch or etiolation. Growthproduced early in the season has the greatest internode length.Internode length decreases as the growing season nears its end.Vigorously growing plants tend to have greater internode lengths thanless vigorous plants. Internode length will vary with competition fromsurrounding stems or developing fruit. If the energy for a stem has to be

divided between three or four stems, or if the energy is divertedinto fruit growth, internode length will be shortened.

Modified Stems:

Although typical stems are above-ground trunks and branches, there aremodified stems which can be found above ground and below ground. Theabove-ground modified stems are crowns, stolons, and spurs, and thebelow-ground stems are bulbs, corms, rhizomes, and tubers.

Above-ground stems:

Crowns (strawberries, dandelions, African violets) are compressed stemshaving leaves and flowers on short internodes.Spurs are short, stubby, side stems that arise from the main stem andare common on such fruit trees as pears, apples, and cherries, where theymay bear fruit. If severe pruning is done close to fruit-bearing spurs,the spurs can revert to a long, nonfruiting stem.A stolon is a horizontal stem that is fleshy or semi-woody and lies alongthe top of the ground. Strawberry runners are examples of stolons.Remember, all stems have nodes and buds or leaves. The leaves onstrawberry runners are small, but are located at the nodes, which areeasy to see. The nodes on the runner are the points where roots beginto form. The spider plant has stolons. Below-ground stems such as thepotato tuber, the tulip bulb, and the iris rhizome are underground stems

that store food for the plant. The tuber, like any other stem, has nodesthat produce buds. The eyes of a potato are actually the nodes on thestem. Each eye contains a cluster of buds.


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Rhizomes are similar to stolons, but grow underground. Some rhizomes arecompressed and fleshy such as those of iris; they can also be slenderwith elongated internodes such as bentgrass. Johnsongrass is a hated weedprincipally because of the spreading capability of its rhizomes.Tulips, lilies, daffodils, and onions are plants that produce bulbs -shortened, compressed, underground stems surrounded by fleshy scales(leaves) that envelop a central bud located at the tip of the stem. If

you cut through the center of a tulip or daffodil bulb in November, youcan see all the flower parts in miniature within the bulb. Many bulbsrequire a period of low-temperature exposure before they begin to send upthe new plant. Both the temperature and length of this treatment are ofcritical importance to commercial growers who force bulbs for holidays.Corms are not the same as bulbs. They have shapes similar to bulbs, butdo not contain fleshy scales. A corm is a solid, swollen stem whosescales have been reduced to a dry, leaf-like covering.Some plants produce a modified stem that is referred to as a tuberous stem.Examples are tuberous begonia and cyclamen. The stem is shortened,flattened, enlarged, and underground. Buds and shoots arise from thecrown and fibrous roots are found on the bottom of the tuberous stem.

In addition, some plants such as the dahlia and the sweet potato producean underground storage organ called a tuberous root, which is oftenconfused with bulbs and tubers. However, these are roots, not stems, andhave neither nodes nor internodes.

Stems are commonly used for plant propagation. Above-ground stems can bedivide d into sections that contain internodes and nodes. They arereferred to as cuttings, and will produce roots to form a new plant.Below-ground stems are also good propagative tissues: rhizomes can bedivided into pieces; b ulbs form small bulblets at the base of the parentbulb; cormels are miniature corms that form under the parent corm ; andtubers can be cut into pieces containing eyes and nodes. All of these willproduce new plants.

It may sometimes be difficult to distinguish between roots and stems, butone sure way is to look for the presence of nodes. Stems have nodes;roots do not.

Types of Stems. A shoot is a young stem with leaves present. A twig is astem which is less than one year old and has no leaves, since it is stillin the winter-dormant stage. A branch is a ste m which is more than oneyear old, and typically has lateral stems. A trunk is a main stem of awoody plant. Most tree s have a single trunk.

Trees are perennial woody plants, usually have one mail trunk, and areusually more than 12 feet tall at maturity.

Shrubs are perennial woody plants, may have one or several main stems, and areusually less than 12 feet tall at maturity.

A vine is a plant which develops long, trailing stems that grow along theground unless they are supported by another plant or structure. Sometwining vines circle their support clockwise ( hops or honeysuckle) whileothers circle counter-clockwise (pole beans or Dutchman's pipe vine).Climbing vines a re supported by aerial roots (English ivy or poison ivy),slender tendrils which encircle the supporting obj ect (cucumber, gourds,grapes, and passion-flowers), or tendrils with adhesive tips (Virginia

creeper and Japanese creeper).

Texture and Growth of Stems. Woody stems contain relatively large amounts


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of hardened xylem tissue in the central core, and are typical of mosttree fruits and ornamental trees and shrubs.

A cane is a stem which has a relatively large pith (the centralstrength-giving tissue of stem) and usually lives only one or two years.Examples of plants with canes include rose, grape, blackberry , andraspberry.

Herbaceous or succulent stems contain only small amounts of xylem tissueand us ually live for only one growing season. If the plant is perennial,it will develop new shoots from the root.

Plants are classified by the number of growing seasons required tocomplete a life cycle. Annuals pass through their entire life cycle fromseed germination to seed production in one growing season, and then die.

Biennials are plants which start from seeds and produce vegetativestructures a nd food storage organs the first season. During the firstwinter, a hardy evergreen rosette of basal leaves pers ists. During the

second season, flowers, fruit, and seeds develop to complete the lifecycle. The plant then dies. Carro ts, beets, cabbage, celery, and onionsare biennial plants. Hollyhock, Canterbury Bells, and Sweet William arebienni als which are commonly grown for their attractive flowers.

Plants which typically develop as biennials may, in some cases, completethe cycle of growth from seed germination to seed production in only onegrowing season. This situation occurs when droug ht, variations intemperature, or other climatic conditions cause the plant tophysiologically pass through the e quivalent of two growing season, in asingle growing season. This phenomenon is referred to as bolting.

Perennial plants live for many years, and after reaching maturity,

typically produce flowers and seeds each year. Perennials are classifiedas herbaceous if the top dies back to the ground each winter and newstems grow from the roots each spring. They are classified as woody ifthe top persists, as in shrubs or trees.

Stems as Food. The edible portion of cultivated plants such as asparagusand k ohlrabi is an enlarged succulent stem. The edible parts of broccoliare composed of stem tissue, flower buds, and a fe w small leaves. Theedible part of potato is a fleshy underground stem called a tuber.Although the name suggests otherwise, the edible part of the caulifloweris proliferated stem tissue.

LEAVES

Parts of a Leaf. The blade of a leaf is the expanded, thin structure oneither side of the midrib. The blade is usually the largest and mostconspicuous part of a leaf. The petiole is the stalk which supports theleaf blade; it varies in length, and may be lacking entirely in somecases where the leaf blade is described as sessile or stalkless.

The principal function of leaves is to absorb sunlight for the

manufacturing of plant sugars in a process called photosynthesis. Leavesdevelop as a flattened surface in order t o present a large area forefficient absorption of light energy. The leaf is supported away from the


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stem by a stem- like appendage called a petiole. The base of the petioleis attached to the stem at the node. The small angle formedbetween the petiole and the stem is called the leaf axil. An active ordormant bud or cluster of buds is usually lo cated in the axil.

The leaf blade is composed of several layers. On the top and bottom is alayer of thickened, tough cells called the epidermis. The primary function

of the epidermis is protection of leaf tissue. The way in which the cellsin the epidermis are arranged determines the texture of the leaf surface.Some leaves have hairs that are an extension of certain cells of theepidermis. The African violet has so many hairs that the l eaf feels likevelvet.

Part of the epidermis is the cuticle, which is composed of a waxysubstance called cutin that protects the leaf from dehydration andprevents penetration of some diseases. The amount of cutin is a directresponse to sunlight, increasing with increasing light intensity. For thisreason, plants grown in th e shade should be moved into full sunlightgradually, over a period of a few weeks, to allow the cutin layer to build

and to protect the leaves from the shock of rapid water loss or sunscald.The waxy cutin also repels water and can shed pesticides ifspreader-sticker agents or soaps are not used. This is the reason manypesticide manufacturers i nclude some sort of spray additive to adhere toor penetrate the cutin layer.

On the underside of leaves, some epidermal cells are capable of openingand clo sing. These cells guard the interior of the leaf and regulate thepassage of water, oxygen, and carbon dioxide throu gh the leaf. Theseregulatory cells are called guard cells. They protect openings in the leafsurface called stoma. The opening and closing of the cells is determinedby the weather. Conditions that would cause large water losses fr omplants (high temperature, low humidity) stimulate guard cells to close.

Mild weather conditions leave guard c ells in an open condition. Guardcells will close in the absence of light.

The middle layer of the leaf is the, mesophyll and is located between theupper and lower epidermis. This is the layer in which photosynthesisoccurs. The mesophyll is divided into a dense upp er layer, called thepalisade, and a spongy lower layer that contains a great deal of airspace, called the parenc hyma layer. The cells in these two layers containchloroplasts which are the actual site of the photosynthetic process.

LEAF PARTS

Types of Leaves. A number of rather distinct types of leaves occur onplants. Leaves commonly referred to as foliage are the most common andconspicuous, and, as previously stated, serve a s the manufacturingcenters where the photosynthetic activity of the plant occurs. Scaleleaves or cataphylls are found on rhizomes and are also the small,leathery, protective leaves which enclose and protect buds. Seed leaves,or cotyledons, are modified leaves which are found on the embryonic plantand commonly serve as storage organs. Spines and tendrils, as found onbarberry and pea, are specialized modified leaves which protect the plantor assist in supporting the stems. Storage leaves, as are found inbulbous plants and succulents, serve as food storage or gans. Otherspecialized leaves include bracts, which are often brightly colored. The

showy structures on dogwoods and poinsettias are bracts, not petals.

Venation of Leaves. The vascular bundles from the stem extend through the


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peti ole and spread out into the blade. The term venation refers to thepatterns in which the veins are distributed in the blade. Two principaltypes of venation are parallel-veined and net-veined.

Parallel-veined leaves are those in which there are numerous veins whichrun essentially parallel to each other and are connected laterally by minute,straight veinlets. Possibly the most common type of parallel-veining is that

found in plants of the grass family where the veins run from the base tothe apex of the leaf. Another type of parallel-venation is found inplants such as banana, calla, and pickerel-weed, where the parallelveins run laterally from the midrib. Parallel-veined leaves occur onplants which are part of the monocotyledon group.

Net-veined leaves, also called reticulate-veined, have veins which branchfrom the main rib(s) and then subdivide into finer veinlets which thenunite in a complicated network. This system of e nmeshed veins gives theleaf more resistance to tearing than most parallel-veined leaves.Net-venation may be eit her pinnate or palmate. In pinnate venation, theveins extend laterally from the midrib to the edge, as in apple, cherry

and peach. Palmate venation occurs in grape and maple leaves, where theprincipal veins extend outward, lik e the ribs of a fan, from the petiolenear the base of the leaf blade. Net-veined leaves occur on plants whichare pa rt of the dicotyledon group.

TYPES OF VENATION

Leaves as a Means of Identifying Plants. Leaves are useful in identifyingspec ies and varieties of horticultural plants. The shape of the leafblade and the type of margin are of major importa nce as identifyingcharacteristics. Simple leaves are those in which the leaf blade is asingle continuous unit. A compound leaf is composed of several separate

leaflets arising from the same petiole.

A deeply lobed leaf may appear similar to a compound leaf, but if theleaflets are connected by narrow bands of blade tissue, it may beclassified as a simple leaf. If the leaflets have separ ate stalks and,particularly, if these stalks are jointed at the point of union with themain leaf-stalk, the leaf is conside red to be compound. Some leaves maybe doubly compound, having divisions of the leaflets.

Shape of the leaf blade: The following are some common shapes which arefound in leaves and leaflets.

Linear: Narrow, several times longer than wide; approximately the samewid th throughout. Lanceolate: Longer than wide; tapering toward the apexand base. Elliptical: 2 or 3 times longer than wide; tapering to an acuteor rounded ape x and base. Ovate: Egg-shaped, basal portion wide;tapering toward the apex. Cordate: Heart-shaped, broadly ovate; taperingto an acute apex, with the base turning in and forming a notch wherethe petiole is attached.

Shape of the leaf apex and base:The following are common shapes found in leaves.

Acuminate: Tapering to a long, narrow point.Acute: Ending in an acute angle, with a sharp, but not acuminate, point.

Obtuse: Tapering to a rounded edge.Sagittate: Arrowhead-shaped, with two pointed lower lobes.Truncate: Having a relatively square end.


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Leaf margins: Studying leaf margins is especially useful in theidentification of certain varieties of fruit plants.

Entire: A smooth edge with no teeth or notches.Serrate: Having small, sharp teeth pointing toward the apex.Dentate: Having teeth ending in an acute angle, pointing outward.

Crenate: Having rounded teeth.Sinuate: Having a pronounced sinuous or wavy margin.Incised: Margin cut into sharp, deep, irregular teeth or incisions.Lobed: Incisions extend less than halfway to the midrib.Cleft: Incisions extend more than halfway to the midrib.

Leaf arrangement along a stem: The various ways leaves are arranged alonga stem are also used to help identify plants. Rosulate arrangement is onein which the basal leaves form a rosette ar ound the stem with extremelyshort nodes. Opposite leaves are positioned across the stem from eachother, two leaves at each node. Alternate or spiral leaves are arrangedin alternate steps along the stem with only one leaf at eac h node.

Whorled leaves are arranged in circles along the stem.

Leaves as Food. The leaf blade is the principal edible part of severalhorticultural crops including chive, collard, dandelion, endive, kale,leaf lettuce, mustard, parsley, spinach, and Swiss chard. The ediblepart of leek, onion, and Florence fennel is a cluster of fleshy leafbases. The petiole of the leaf is the edible product in celery and rhubarb.In plants like Brussels sprout, cabbage, and head lettuce, the leaves -in the form of a large, naked bud - are the edible product.

BUDS

A bud is an undeveloped shoot from which embryonic leaves or flower partsarise . The buds of trees and shrubs of the temperate zone typicallydevelop a protective outer layer of small, leat hery, bud scales. Annualplants and herbaceous perennials have naked buds in which the outer leavesare green and s omewhat succulent.

Buds of many plants require exposure to a certain number of days below acritic al temperature (rest) before they will resume growth in the spring.This time period varies for different plants. The flower buds offorsythia require a relatively short rest period and will grow at thefirst sign of warm weather. Many peach varieties require from 700 to1,000 hours of temperatures below 45F (7C) before they will resume growth.D uring rest, dormant buds can withstand very low temperatures, but afterthe rest period is satisfied, buds b ecome more susceptible to weatherconditions, and can be damaged easily by cold temperatures or frost.

A leaf bud is composed of a short stem with embryonic leaves, with budprimordia in the axils and at the apex. Such buds develop into leafyshoots. Leaf buds are often less plump and more po inted than flower buds.

A flower bud is composed of a short stem with embryonic flower parts. Insome c ases, the flower buds of plants which produce fruit crops ofeconomic importance are called fruit buds. This terminology isobjectionable because, although flowers have the potential for developinginto fruit, this development may never occur because of adverse weather

conditions, lack of pollination, or other unfavorable circumstances. Thestructure is a flower bud, and should be so designated since it may neverset fruit. Types of Buds. Buds are named for the location which they


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inhabit on the stem surface. Terminal buds are those which are located atthe apex of a stem. Lateral buds are borne on the sides of the stem. Mostlateral buds arise in the axis of a leaf and are called axillary buds. Insome instances, more tha n one bud is formed. Adventitious buds are thosewhich arise at sites other than in the terminal or axillary posi tion.Adventitious buds may develop from the internode of the stem; at the edgeof a leaf blade; from callus tissue at the cut end of a stem or root; or

laterally, from the roots of a plant.

Buds as Food. Enlarged buds or parts of buds form the edible portion ofsome h orticultural crops. Cabbage and head lettuce are examples ofunusually large terminal buds. Succulent axillary buds of Brussels sproutsbecome the edible part of this plant. In the case of globe artichoke, thefleshy basal por tion of the bracts of the flower bud are eaten along withthe solid stem portion of the bud. Broccoli is the most import anthorticultural plant in which edible flower buds are consumed. In thiscase, portions of the stem as well as small l eaves associated with theflower buds are eaten.

ROOTS

A thorough knowledge of the root system of plants is essential if theirgrowth, flowering, and fruiting responses are to be understood. Thestructure and growth habits of roots have a pronounce d effect on the sizeand vigor of the plant, method of propagation, adaptation to certain soiltypes, and response to cultural practices and irrigation. The roots ofcertain vegetable crops are important as food.

Roots typically originate from the lower portion of a plant or cutting.They possess a root cap, have no nodes, and never bear leaves or flowers

directly. The principal functions of roots are to absorb nutrients andmoisture, to anchor the plant in the soil, to furnish physical support forthe stem, and to serve a s food storage organs. In some plants, they maybe used as a means of propagation.

Types of Roots. A primary (radicle) root originates at the lower end ofthe embryo of a seedling plant. A taproot is formed when the primary rootcontinues to elongate downward into the soil an d becomes the central andmost important feature of the root system, with a somewhat limited amountof secondary branching. Some trees, especially nut trees like pecan, havea long taproot with very few lateral or f ibrous roots. This makes themdifficult to transplant and necessitates planting only in deep,well-drained soil. The ta proot of carrot, parsnip, and salsify is theprincipal edible part of these crops.

A lateral, or secondary, root is a side or branch root which arises fromanother root.

A fibrous root system is one in which the primary root ceases to elongate,lead ing to the development of numerous lateral roots, which branchrepeatedly and form the feeding root system of the plant. A fibrous rootis one which remains small in diameter because of a lack of significantcambial activity. On e factor which causes shrubs and dwarf trees toremain smaller than standard trees is the inactivity of the camb ium

tissue in the roots.

If plants that normally develop a taproot are undercut so that the taproot


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is s evered early in the plant's life, the root will lose its taprootcharacteristic and develop a fibrous root system. This is donecommercially in nurseries so that trees, which naturally have tap roots,will develop a compact, fibrous root sys tem. This allows a higher rate oftransplanting success.

The quantity and distribution of plant roots is very important because

these two factors have a major influence on the absorption of moistureand nutrients. The depth and spread of the roots is dependent on theinherent growth characteristics of the plant and the texture and structureof the soil. Roots w ill penetrate much deeper in a loose, well-drainedsoil than in a heavy, poorly-drained soil. A dense, compacted laye r inthe soil will restrict or stop root growth.

During early development, a seedling plant absorbs nutrients and moisturefrom the few inches of soil surrounding it. Therefore, the early growthof most horticultural crops which are seeded i n rows benefits from bandapplications of fertilizer, placed several inches to each side andslightly below the seeds.

As plants become well-established, the root system develops laterally andusual ly extends far beyond the spread of the branches. For mostcultivated crops, roots meet and overlap between the rows. The greatestconcentration of fibrous roots occurs in the top foot of soil, butsignificant numbers of lat erals may grow downward from these roots toprovide an effective absorption system several feet deep.

Parts of a Root. Internally, there are three major parts of a root. Themeristem is at the tip and manufactures new cells; it is an area of celldivision and growth. Behind it is the zone of elon gation, in which cellsincrease in size through food and water absorption. These cells, byincreasing in size, push the root through the soil. The third major root

part is the maturation zone, in which cells undergo changes in order to become specific tissues such as epidermis, cortex, or vascular tissue. Theepidermis is the outermost layer of cells surrounding the root. Thesecells are responsible for the absorption of water and minerals dissolvedin water. Cortex cells are involved in the movement of water from theepidermis and in food storage. Vascular tissue is lo cated in the centerof the root, and conducts food and water.

Externally, there are two areas of importance; root hairs are found alongthe m ain root and perform much of the actual work of water/nutrientabsorption. The root cap is the outermost tip of the root, and consists ofcells that are sloughed off as the root grows through the soil. The rootcap covers and protec ts the meristem.

Roots as Food. The enlarged root is the edible portion of severalvegetable cr ops. The sweet potato is a swollen root, called a tuberousroot, which serves as a food storage area for the plant . Carrot, parsnip,salsify, and radish are elongated taproots.

FLOWERS

The sole function of the flower, which is generally the showiest part ofthe pl ant, is sexual reproduction. Its attractiveness and fragrance have

not evolved to please man, but to ensure the continuance of the plantspecies. Fragrance and color are devices to attract pollinators - insectsthat play an i mportant role in the reproductive process.


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Binomial nomenclature is the scientific system of giving a double name toplant s and animals. The first, or genus name, is followed by adescriptive, or species, name. Modern plant classificati on, or taxonomy,is based on a system of binomial nomenclature developed by the Swedishphysician, Carl von Linne (Li nnaeus). Prior to Linnaeus, people had triedto base classification on leaf shape, plant size, flower color , etc. None

of these systems proved workable. Linnaeus's revolutionary approach was tobase classification on the f lowers and/or reproductive parts of a plant,and to give plants a genus and species name. This has proven to be thebest system, since flowers are the plant part least influenced byenvironmental changes. For this reason, a knowle dge of the flower and itsparts is essential to plant identification.

Parts of the Flower. As the reproductive part of the plant, the flowercontain s the male pollen and/or the female ovule plus accessory partssuch as petals, sepals, and nectar glands.

Sepals are small, green, leaf-like structures on the base of the flower

which p rotect the flower bud. The sepals collectively are called thecalyx.

Petals are highly colored portions of the flower. They may contain perfumeas w ell as nectar glands. The number of petals on a flower is often usedin the identification of plant families and genera. The petalscollectively are called the corolla. Flowers of dicots typically havesepals and/or petals in multiples of four or five. Monocots typically havethese floral parts in multiples of three.

The pistil is the female part of the plant. It is generally shaped like abowli ng pin and located in the center of the flower. It consists of thestigma, style, and ovary. The stigma is located at the top, and is

connected to the ovary by the style. The ovary contains the eggs, whichreside in the ovules. After th e egg is fertilized, the ovule developsinto a seed.

The stamen is the male reproductive organ. It consists of a pollen sac(anther ) and a long, supporting filament. This filament holds the antherin position so the pollen it contains may be dis bursed by wind or carriedto the stigma by insects or birds.

Types of Flowers. If a flower has a stamen, pistils, petals, and sepals,it is called a complete flower. If one of these parts is missing, theflower is designated incomplete.

If a flower contains functional stamens and pistils, it is called aperfect flo wer. (Stamen and pistils are considered the essential parts ofa flower.) If either of the essential parts is lacking, the flower isimperfect.

Pistillate (female) flowers are those which possess a functional pistil(s)but lack stamens. Staminate (male) flowers contain stamens but no pistils.

Because cross-fertilization combines different genetic material andproduces st ronger seed, cross-pollinated plants are usually moresuccessful than self-pollinated plants. Consequently, more plantsreproduce by cross-pollination than self-pollination.

As previously mentioned, there are plants which bear only male flowers(stamina te plants) or bear only female flowers (pistillate plants).


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Species in which the sexes are separated into stam inate and pistillateplants are called dioecious. Most holly trees are dioecious; therefore, toobtain berries, it is necessary to have a female tree. Monecious plantsare those which have separate male and female flowers on the s ame plant.Corn plants and pecan trees are examples. Some plants bear only maleflowers at the beginning of the growing season, but later develop flowersof both sexes; examples are cucumbers and squash.

How Seeds Form. Pollination is the transfer of pollen from an anther to astig ma. This may occur by wind or by pollinators. Wind-pollinated flowerslack showy floral parts and nectar since t hey don't need to attract apollinator. Flowers are brightly colored or patterned and contain afragrance or nectar whe n they must attract insects, animals, or birds. Inthe process of searching for nectar, these pollinators will transf erpollen from flower to flower.

The stigma contains a chemical which excites the pollen, causing it togrow a l ong tube, down the inside of the style, to the ovules inside the

ovary. The sperm is released by the pollen grain and f ertilizationtypically occurs. Fertilization is the union of the male sperm nucleus(from the pollen grain) an d the female egg (in the ovule). Iffertilization is successful, the ovule will develop into a seed.

Types of Inflorescences. Some plants bear only one flower per stem andare cal led solitary flowers. Other plants produce an inflorescence, aterm which refers to a cluster of flowers and how t hey are arranged on afloral stem. Most inflorescences may be classified into two groups,racemes and cymes.

In the racemose group, the florets, which are individual flowers in an

inflores cence, bloom from the bottom of the stem and progress toward thetop. Some examples of racemose inflorescence inclu de spike, raceme,corymb, umbel, and head. A spike is an inflorescence in which manystemless florets are attach ed to an elongated flower stem, or peduncle,an example being gladiolus. A raceme is similar to a spike except theflorets are borne on small stems attached to the peduncle. An example of araceme inflorescence is the snapdrago n. A corymb is made up of floretswhose stalks, pedicels, are arranged at random along the peduncle in sucha way that the florets create a flat, round top. Yarrow has a corymbinflorescence. An umbel is similar except that the ped icels all arisefrom one point on the peduncle. Dill has an umbel inflorescence. A head,or composite, infloresce nce is made up of numerous stemless florets whichis characteristic of daisy inflorescence.

In the cyme group, the top floret opens first and blooms downward alongthe ped uncle. A dischasium cyme has florets opposite each other along thepeduncle. Baby's breath inflorescence is an example. A helicoid cyme isone in which the lower florets are all on the same side of the peduncle,examples being freesia and statice inflorescences. A scorpioid cyme is onein which the florets are alternate to each other along the peduncle.Examples are tomato and potato inflorescences.

Parts of fruit: Fruit consists of the fertilized and mature ovules calledseed s and the ovary wall, which may be fleshy, as in the apple; or dryand hard, as in a maple fruit. The only parts o f the fruit which are

genetically representative of both the male and female flowers are theseeds (mature ovules ). The rest of the fruit arises from the maternalplant, and is therefore genetically identical to that parent. Some fruits


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have seeds enclosed within the ovary (apples, peaches, oranges, squash,cucumbers). Others have seeds that are situated on the periphery of fruittissue (corn, strawberry).

Types of fruit: Fruits can be classified as simple fruits, aggregatefruits, o r multiple fruits. Simple fruits are those which develop from a

single ovary. These include cherries and peaches (drupe), pears and apples(pome), and tomatoes (berries). Tomatoes are a botanical fruit since theydevelop from the flower, as do squash, cucumbers, and eggplant. All ofthese fruits develop from a single ovary. Other types of simpl e fruit aredry. The fruit wall becomes papery or leathery and hard. Examples arepeanut (legumes), poppy (capsule), ma ple (samara), and walnut (nut).

Aggregate fruits, such as raspberries, come from a single flower which hasmany ovaries. The flower appears as a simple flower, with one corolla, onecalyx, and one stem, but with many pistils or ovaries. The ovaries arefertilized separately and independently. If ovules are not pollinatedsuccessfu lly, the fruit will be misshapen and imperfect. Strawberry and

blackberry are also aggregate fruits with the addition of an edible,enlarged receptacle. For this reason, they are sometimes termedaggregate-accessory fruits.

Multiple fruits are derived from a tight cluster of separate, independentflowe rs borne on a single structure. Each flower will have its own calyxand corolla. Examples of multiple fruits are pin eapple, fig, and the beetseed. Multiple fruits are not common in Virginia.

Kinds of Fruit

The seed, or matured ovule, is made up of three parts. The embryo is a

miniatur e plant in an arrested state of development. Most seeds contain abuilt-in food supply called the endosperm (or chid is an exception). Theendosperm can be made up of proteins, carbohydrates, or fats. The thirdpart is the hard outer covering, called a seed coat, which protects theseed from disease and insects and prevents water from entering the seed(this would initiate the germination process before the proper time).

Parts of a Seed Seedlings. Germination is the resumption of active embryogrowth. Prior to any visual signs of growth, the seed must absorb waterthrough the seed coat. In addition, the seed must be in the p roperenvironmental conditions; that is, exposed to oxygen, favorabletemperatures, and for some, correct light. The radicle is the first partof the seedling to emerge from the seed. It will develop into the primaryroot from which root hairs and lateral roots will develop. The portion ofthe seedling between the radicle and the first leaf-like structure iscalled the hypocotyl. The seed leaves, cotyledons, encase the embryo andare usually different in shape from t he leaves that the mature plant willproduce. Plants producing one cotyledon fall into the group ofmonocotyledons or monocots. Plants producing two seed leaves are calleddicotyledons or dicots.

PHYSIOLOGY: PLANT GROWTH AND DEVELOPMENT

The three major plant functions that are the basics for plant growth and develo

pment are photosynthesis, respiration, and transpiration.


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HOW A PLANT GROWS

PHOTOSYNTHESIS

One of the major differences between plants and animals is the ability ofplant s to internally manufacture their own food. To produce food foritself, a plant requires energy from sunlight, carbon dioxide from the

air, and water from the soil. If any of these ingredients is lacking,photosynthesis, or food produ ction, will stop. If any factor is removedfor a long period of time, the plant will die. Photosynthesis literallymeans " to put together with light."

673 kcal of radiant energy Chlorophyllous cellsCARBON DIOXIDE + WATER --------------------------> SUGAR + OXYGEN6CO2 + 6H2O ----------------------------------------------->C6H12O6

+ 6O2

Plants store the energy from light first in simple sugars, such as

glucose. This food may be converted back to water and carbon dioxide,releasing the stored energy through the process called resp iration. Thisenergy is required for all living processes and growth. Simple sugars arealso converted to other sug ars and starches (carbohydrates) which may betransported to the stems and roots for use or storage, or they may be usedas building blocks for more complex structures, e.g. oils, pigments,proteins, cell walls, etc.

Any green plant tissue is capable of photosynthesis. Chloroplasts inthese cel ls contain the green pigment, which traps the light energy.However, leaves are generally the site of most food pr oduction due totheir special structure. The internal tissue (mesophyll) contains cellswith abundant chloroplasts in an arrangement that allows easy movement of

water and air. The protective upper and lower epidermis (skin) lay ers ofthe leaf include many stomata that regulate movement of the gases involvedin photosynthesis into and out of the leaf.

Photosynthesis is dependent on the availability of light. Generallyspeaking, a s sunlight increases in intensity, photosynthesis increases.This results in greater food production. Many garden crops, such astomatoes, respond best to maximum sunlight. Tomato production is cutdrastically as light intensities dr op. Only two or three varieties of"greenhouse" tomatoes will produce any fruit when sunlight is minimal inlate f all and early spring.

Water plays an important role in photosynthesis in several ways. First, itmain tains a plant's turgor, or the firmness or fullness of plant tissue.Turgor pressure in a cell can be compared to air i n an inflated balloon.Water pressure or turgor is needed in plant cells to maintain shape andensure cell growth. Se cond, water is split into hydrogen and oxygen bythe energy of the sun that has been absorbed by the chlorophyll in th eplant leaves. The oxygen is released into the atmosphere and the hydrogenis used in manufacturing carbohyd rates. Third, water dissolves mineralsfrom the soil and transports them up from the roots and throughout theplant, where they serve as raw materials in the growth of new planttissues. The soil surrounding a plant shou ld be moist, not too wet or toodry. Water is pulled through the plant by evaporation of water through theleaves (t ranspiration).

Photosynthesis also requires carbon dioxide (CO2) which enters the plantthroug h the stomata. Carbon and oxygen are used in the manufacture of


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carbohydrates. Carbon dioxide in the air is plen tiful enough so that itis not a limiting factor in plant growth. However, since carbon dioxide isconsumed in making sug ars and is not replenished by plants at a rapidrate, a tightly closed greenhouse in midwinter may not let in enoughoutside air to maintain an adequate carbon dioxide level. Under theseconditions, improved crops of roses, carnations, tomatoes, and certainother crops can be produced if the carbon dioxide level is raised with CO2

generators or, in small greenhouses, with dry ice.

Although not a direct component in photosynthesis, temperature is animportant factor. Photosynthesis occurs at its highest rate in thetemperature range 65 to 85F (18 to 27C) and decreases w hen temperaturesare above or below this range.

RESPIRATION

Carbohydrates made during photosynthesis are of value to the plant when

they ar e converted into energy. This energy is used in the process ofbuilding new tissues (plant growth). The chemi cal process by which sugarsand starches produced by photosynthesis are converted into energy iscalled respira tion. It is similar to the burning of wood or coal toproduce heat (energy). This process in cells is shown most simp ly as:

C6H12O2 + 6O2 --------------- 6CO2 + 6H2O + Energy

This equation is precisely the opposite of that used to illustratephotosynthes is, although more is involved than just reversing thereaction. However, it is appropriate to relate photosynthesis to abuilding process, while respiration is a breaking-down process.

Photosynthesis

1. Produces food.2. Stores energy.3. Occurs in cells containing chloroplasts.4. Releases oxygen.5. Uses water.6. Uses carbon dioxide.7. Occurs in sunlight.

1. Uses food for plant energy.2. Releases energy.3. Occurs in all cells.4. Uses oxygen.5. Produces water.6. Produces carbon dioxide.7. Occurs in darkness as well as light.

By now, it should be clear that respiration is the reverse ofphotosynthesis. U nlike photosynthesis, respiration occurs at night aswell as during the day. Respiration occurs in all life forms and in allcells. The release of accumulated carbon dioxide and the uptake of oxygenoccurs at the cell level. In animals, b lood carries both carbon dioxideand oxygen to and from the atmosphere by means of the lungs or gills. Inplants, there is simple diffusion into the open spaces within the leaf,

and exchange occurs through the stomata.


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TRANSPIRATION

Transpiration is the process by which a plant loses water, primarily fromleaf stomata. Transpiration is a necessary process that involves the useof about 90% of the water that enters the plant t hrough the roots. Theother 10% of the water is used in chemical reactions and in plant tissues.

Transpiration is necessary for mineral transport from the soil to theplant parts, for the cooling of plant parts through evaporation , to movesugars and plant chemicals, and for the maintenance of turgor pressure.The amount of water lost from the p lant depends on several environmentalfactors such as temperature, humidity, and wind or air movement. Anincrease in temperature or air movement decreases humidity and causes theguard cells in the leaf to shrink, o pening the stomata and increasing therate of transpiration.

Plant growth and distribution are limited by the environment. If any oneenviro nmental factor is less than ideal, it will become a limiting factorin plant growth. Limiting factors are also respon sible for the geography

of plant distribution. For example, only plants adapted to limited amountsof water can live in deserts. Most plant problems are caused byenvironmental stress, either directly or indirectly. Therefore, i t isimportant to understand the environmental aspects that affect plantgrowth. These factors are light, temper ature, water, humidity, andnutrition.

LIGHT

Light has three principal characteristics that affect plant growth:quantity, quality, and duration.

Light quantity refers to the intensity or concentration of sunlight andvaries with the season of the year. The maximum is present in the summerand the minimum in winter. The more sunlight a plant receives (up to apoint), the better capacity it has to produce plant food throughphotosynthesis. As the sunlight quantity decreases, the photosyntheticprocess decreases. Light quantity can be decreased in a garden orgreenhouse by using cheesecloth shading above the plants. It can beincreased by surrounding plants with white or reflective material, orsupplemental lights.

Light quality refers to the color or wavelength reaching the plantsurface. Sun light can be broken up by a prism into respective colors ofred, orange, yellow, green, blue, indigo, and violet. On a rainy day,raindrops act as tiny prisms and break the sunlight into these colors,producing a rainbow. Red and blue lig ht have the greatest effect on plantgrowth. Green light is least effective to plants as they reflect greenlight an d absorb none. It is this reflected light that makes them appeargreen to us. Blue light is primarily responsible for veg etative growth orleaf growth. Red light, when combined with blue light, encouragesflowering in plants. Fluoresce nt, or cool-white, light is high in theblue range of light quality and is used to encourage leafy growth. Suchlight would be excellent for starting seedlings. Incandescent light ishigh in the red or orange range, but generally produces too much heat tobe a valuable light source. Fluorescent "grow" lights have a mixture ofred and blue colors that attempts to imitate sunlight as closely as

possible, but they are costly and generally not of any g reater value thanregular fluorescent lights.


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Light duration, or photoperiod, refers to the amount of time that a plantis ex posed to sunlight. When the concept of photoperiod was firstrecognized, it was thought that the length of periods of light triggeredflowering. The various categories of response were named according to thelight length (i.e., short-day and long-day). It was then discovered thatit is not the length of the light period but the length of unin terrupteddark periods that is critical to floral development. The ability of many

plants to flower is controlled by photo period. Plants can be classifiedinto three categories, depending upon their flowering response to theduration of da rkness. These are short-day, long-day, or day-neutralplants.

Short-day plants form their flowers only when the day length is less thanabout 12 hours in duration. Short-day plants include many spring- andfall-flowering plants such as chrysanthemum and poinsettia. Long-dayplants form flowers only when day lengths exceed 12 hours (short nights).They include alm ost all of the summer-flowering plants, such as rudbeckiaand California poppy, as well as many vegetables incl uding beet, radish,lettuce, spinach, and potato. Day-neutral plants form flowers regardless

of day length. Some pla nts do not really fit into any category but may beresponsive to combinations of day lengths. The petunia will flower regardless of day length, but flowers earlier and more profusely under longdaylight. Since chrysanthemums flower und er the short-day conditions ofspring, or fall, the method for manipulating the plant into experiencingshort days is very simple. If long days are predominant, a shade cloth isdrawn over the chrysanthemum for 12 hours daily t o block out light untilflower buds are initiated. To bring a long-day plant into flower whensunlight is not prese nt longer than 12 hours, artificial light is addeduntil flower buds are initiated.

TEMPERATURE

Temperature affects the productivity and growth of a plant, depending uponwhet her the plant variety is a warm- or cool-season crop. If temperaturesare high and day length is long, cool-sea son crops such as spinach willbolt rather than produce the desired flower. Temperatures that are toolow for a wa rm-season crop such as tomato will prevent fruit set. Adversetemperatures also cause stunted growth and poor quality; for example, thebitterness in lettuce is caused by high temperatures.

Sometimes temperatures are used in connection with day length tomanipulate the flowering of plants. Chrysanthemums will flower for alonger period of time if daylight temperatures are 59F (15C). TheChristmas cactus forms flowers as a result of short days and lowtemperatures. Temperatur es alone also influence flowering. Daffodils areforced to flower by putting the bulbs in cold storage in October at 35 to40F (2 to 4C). The cold temperatures allow the bulb to mature. The bulbsare transferred to the greenho use in midwinter where growth begins. Theflowers are then ready for cutting in 3 to 4 weeks.

Thermoperiod refers to daily temperature change. Plants and producemaximum gro wth when exposed to a day temperature that is about 10 to 15higher than the night temperature. This allo ws the plant tophotosynthesize (build up) and respire (break down) during an optimumdaytime temperature, and to curt ail the rate of respiration during a

cooler night. High temperatures cause increased respiration, sometimesabove the rate of photosynthesis. This means that the products ofphotosynthesis are being used more rapidly than they are being produced.


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For growth to occur, photosynthesis must be greater than respiration.

Low temperatures can result in poor growth. Photosynthesis is slowed downat lo w temperatures. Since photosynthesis is slowed, growth is slowed,and this results in lower yields. N ot all plants grow best in the sametemperature range. For example, snapdragons grow best when nighttimetemperatur es are 55F (12C); the poinsettia prefers 62F (17C). Florist

cyclamen does well under very cool condit ions, while many bedding plantsprefer a higher temperature. Recently it has been found that roses cantolerate much lower nighttime temperatures than was previously believed.This has meant a conservation in energy for green house growers.

However, in some cases, a certain number of days of low temperatures areneeded by plants to grow properly. This is true of crops growing in coldregions of the country. Peaches are a prime ex ample; most varietiesrequire 700 to 1,000 hours below 45F (7 C) and above 32F (0C) before theybreak their rest per iod and begin growth. Lilies need 6 weeks at 33F (1C)before blooming.

Plants can be classified as either hardy or nonhardy, depending upon theirabil ity to withstand cold temperatures. Winter injury can occur tononhardy plants if temperatures are too low or if un seasonably lowtemperatures occur early in the fall or late in the spring. Winter injurymay also occur because o f desiccation (drying out) - plants need waterduring the winter. When the soil is frozen, the movement of water into the plant is severely restricted. On a windy winter day, broadleavedevergreens can become water-deficient in a few mi nutes; the leaves orneedles then turn brown. Wide variations in winter temperatures can causepremature bud brea k in some plants and consequent bud-freezing damage.Late spring frosts can ruin entire peach crops. If tempera tures drop toolow during the winter, entire trees of some species are killed by thefreezing and splitting of plant cells and tissue.

Review of Temperature Effects on Plant Growth:

Photosynthesis:Increases with temperature to a point.Respiration: Rapidly increases with temperature.Transpiration:Increases with temperature.Flowering: May be partially triggered by temperature.Sugar storage: Low temperatures reduce energy use and increase sugar storage.Dormancy: Warmth, after a period of low temperature, will break dormancy and

the plant will resume active growth

WATER

As mentioned earlier, water is a primary component of photosynthesis. Itmainta ins the turgor pressure or firmness of tissue and transportsnutrients throughout the plant. In maintaining turgor pressure, water isthe major constituent of the protoplasm of a cell. By means of turgorpressure and other changes in t he cell, water regulates the opening andclosing of the stomates, thus regulating transpiration. Water alsoprovides the pressure to move a root through the soil. Among water's mostcritical roles is that of the solvent for minerals moving into the plantand for carbohydrates moving to their site of use or storage. By itsgradual evaporatio n from the surface of the leaf near the stomate, water

helps stabilize plant temperature.

Relative Humidity is the ratio of water vapor in the air to the amount of


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water the air could hold at a given temperature and pressure, expressed asa percent. For example, if a pound of ai r at 75F could hold 4 grams ofwater vapor and there are only 3 grams of water in the air, then therelative humidit y (RH) is :

RH = water in the airwater the air could hold (at constant temperature and pressure)

so, RH = 3/4 = .75 expressed as a % = 75%

Warm air can hold more water vapor than cold air; therefore, if the amountof water in the air stays the same and the temperature increases, therelative humidity decreases.

Water vapor will move from an area of high relative humidity to one of lowrela tive humidity. The greater the difference in humidity, the fasterwater will move.

The relative humidity in the air space between the cells within the leafapproa ches 100%; therefore, when the stomate is open, water vapor rushesout. As the vapor moves out, a cloud of hig h humidity is formed aroundthe stomate. This cloud of humidity helps slow down transpiration and coolthe leaf . If air movement blows the humid cloud away, transpiration willincrease as the stomata keep opening to balance the humidity. CrossSection of a Leaf Dots Represent Relative Humidity

NUTRITION

Many people confuse plant nutrition with plant fertilization. Plantnutrition r efers to the needs and uses of the basic chemical elements in

the plant. Fertilization is the term used when these mater ials aresupplied to the environment around the plant. A lot must happen before achemical element supplied in a fer tilizer can be taken up and used by theplant.

Plants need 17 elements for normal growth. Carbon, hydrogen, and oxygenare fou nd in air and water. Nitrogen, potassium, magnesium, calcium,phosphorous, and sulfur are found in the soil. T he latter six elementsare used in relatively large amounts by the plant and are calledmacronutrients. There are eight other elements that are used in muchsmaller amounts; these are called micronutrients or trace elements. The micronutrients, which are found in the soil, are iron, zinc, molybdenum,manganese, boron, copper, cobalt, and chl orine. All 17 elements, bothmacronutrients and micronutrients, are essential for plant growth.

Most of the nutrients that a plant needs are dissolved in water and thenabsorb ed by the roots. Ninety-eight percent of these plant nutrients areabsorbed from the soil solution and only about 2% are actually extractedfrom the soil particles by the root. Most of the nutrient elements areabsorbed as charged io ns, or pieces of molecules (which are the smallestparticle of a substance that can exist and still retain the characteristics of the substance). Ions may be positively charged cations ornegatively charged anions. Positive and negative are equally paired sothat there is no overall charge. For example, nitrogen may be absorbed asnitrate (NO3-) whic h is an anion with one negative charge. The potassium

ion (K+) is a cation with one positive charge. Potassium nitrate (K+NO3-)would be one nitrate ion and one potassium ion. However, calcium nitrate(Ca++(NO3-)2) would have tw o nitrate ions and one calcium ion because the


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calcium cation has two positive charges.

The balance of ions in the soil is very important. Just as ions havingopposite charges attract each other, ions having similar charges competefor chemical interactions and reactions in the environm ent. Some ions aremore active than others or can compete better. For example, both calcium(Ca++) and magnesium (M g++) are cations with two charges, but magnesium

is more active. If both are in competition to be absorbed, the ma gnesiumwill be absorbed. This explains why the results of a soil test mayindicate that, while there is suffi cient calcium in the soil, the plantmay still exhibit a calcium deficiency because of an excess of the moreactive magn esium. What may be expressed as a deficiency in onemicronutrient may really be caused by an excess of another.

In order for the ions to be easily absorbed, they must first be dissolvedin the soil solution. Some combinations of ions are easily dissolved, suchas potassium nitrate. When other ions combine, they may precipitate orfall out of solution and thus become unavailable to the plant. Many of themicronutrients f orm complex combinations with phosphorous and calcium and

precipitate out of the soil solution so the nutrien ts cannot be easilytaken up by the plant. The pH, which is a measurement of acidity oralkalinity, greatly affects these chemical reactions. If the soil pH isextremely high (alkaline), many of the micronutrients precipitate out ofthe solution and are unavailable to the plant. When the soil pH isextremely low (acid), some of the micronutrients become extremely solubleand ion levels may become high enough to injure the plant. The effect ofpH varies with the ion, the types of ions in the soil, and the type ofsoil. Therefore, not only is the amount of the nutrient importa nt, butalso the soil pH.

Adequate water and oxygen must be available in the soil. Water isrequired for nutrient movement into and throughout the roots. Oxygen is

required because the mineral ions must be move d into the root cellsacross their membranes. This is an active absorption process, utilizingenergy from respira tion. Oxygen is not transported to roots from theshoot. Without adequate oxygen from the soil, there is no energ y fornutrient absorption. This also stops active water absorption in which thewater flows into the cell due to the higher concentration of nutrientsthat were actively absorbed.

Anything that lowers or prevents the production of sugars in the leavescan low er nutrient absorption. If the plant is under stress due to lowlight or extremes in temperature, nutrient deficienc y problems maydevelop. The stage of growth or how actively the plant is growing may alsoaffect the amount of nu trients absorbed. Many plants go into a restperiod, or dormancy, during part of the year. During this dormancy, fewnutrients are absorbed. Plants may also absorb different nutrients just asflower buds begin to develop.

Nutrients transported from the root to the cell by the vascular systemmove int o the cell through a cell membrane. There are three differentways this happens. First, an entire molecule or ion p air may move throughthe membrane. If the cell is using energy or active transport to absorbthe ions, then only o ne of the ions in the pair is pulled into the cell.The other will follow to keep the number of positive and negative cha rgeseven. Most anions (negative ions) are actively absorbed.

The second way of keeping the charges inside the cell balanced andabsorbing a new ion is to exchange one charged ion for another ion withthe same charge. A hydrogen ion (H+) is often released so that the cell


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can absorb another positive ion such as potassium (K+). Since this is asimple, passive exchange, absorption energy may not be required. Cationsmay be absorbed by this passive method.

Both of the methods mentioned above may be passive or active. However, thethir d method, the carrier system, is always active absorption, requiringenergy. Scientists have discovered that wit hin the cell membrane there

are specialized chemicals that act as carriers. The carrier, throughchemical chang es, attracts an ion from outside the cell membrane andreleases it inside the cell. Once the ion is inside the cell, it isattached to other ions so that it does not move out of the cell. Complexchemical reactions are involved in the entire process. Although nutrientscan be absorbed passively, research has shown that active absorption musttake place i f the plant is to grow and be healthy. The factors wediscussed earlier about absorption by the root are also true forabsorption by the cell. A quick review of some of the factors that affectnutrient absorption: type of ion, soil pH, s olubility of ion pairs,water, soil oxygen, sugar supply, plant stress, and temperature.

Foliar Absorption: A Special Case. Under normal growing conditions,plants ab sorb most nutrients, except carbon, hydrogen, and oxygen, fromthe soil. However, some nutrients can also be absorb ed by the leaves ifthey are sprayed with a dilute solution. The factors that affectabsorption by the cell are stil l important because the nutrient mustenter the cell to be used by the plant. Care must be taken that theconcentration of the nutrient is not too high or the leaf will be injured.Also, the leaf is covered by a thin layer of wax called the cu ticle thatthe nutrient must get around or through before it can enter the cell.

MACRONUTRIENT OUTLINE

Nitrogen (N)Absorbed as NO3-, NH4+Leaches from soil, especially NO3-Mobile in plant.

Nitrogen excess:Succulent growth, dark green color, weak spindly growth, few fruits,may cause brittle growth especially under high temperatures.

Nitrogen deficiency:Reduced growth, yellowing (chlorosis), reds and purples may intensify withsome plants, reduced lateral breaks. Symptoms appear first on older growth.

Action notes:In general, the best NH4+/NO3- ratio is 1/1.High NH4+ under low sugar conditions (low light) can cause leaf curl.Uptake inhibited by high P levels.N/K ratio extremely important.Indoors, best N/K ratio is 1/1 unless light is extremely high.In soils with high CHO/N ratio more N should be supplied.

Phosphorus (P)Absorbed as H2PO4-, HPO4-Does not leach from soil readilyMobile in plant.

Phosphorus excess:Shows up as micronutrient deficiency of Zn, Fe, or Co

Phosphorus deficiency:Reduced growth, color may intensify, browning or purpling in foliage in someplants, thin


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stems, reduced lateral breaks, loss of lower leaves, reduced flowering.Action notes:

Rapidly "fixed" on soil particles when applied under acid conditions fixedwith Fe, Mg and Al. Under alkaline conditions fixed with Ca.Important for young plant and seedling growth.High P interferes with micronutrient absorption and N absorption. Used inrelatively small amounts when compared to N and K. May leach from soil

high in bark or peat.

Potassium (K)Absorbed as K+ leaches from soil.Mobile in plant.

Potassium excess:Causes N deficiency in plant and may affect the uptake of other positiveions.

Potassium deficiency:Reduced growth, shortened internodes, marginal burn or scorch (brown leafedges), necrotic (dead) spots in the leaf, reduction of lateral breaksand tendency to wilt readily.

Action notes:N/K balance is important.High N/low K favors vegetative growth; low N/high K promotes reproductivegrowth (flower, fruit).

Magnesium (Mg)Absorbed as Mg++.Leaches from soil.Mobile in plant.

Magnesium excess:Interferes with Ca uptake.

Magnesium deficiency:Reduction in growth, marginal chlorosis, interveinal chlorosis (yellow

between the veins) in some species. May occur with middle or lowerleaves, reduction in seed production, cupped leaves.

Action notes:Mg is commonly deficient in foliage plants because it is leached and notreplaced. Epsom salts at a rate of 1 teaspoon per gallon may be used 2times a year. Mg can also be absorbed by leaves if sprayed in a weaksolution. Dolomitic limestone can be applied in outdoor situations torectify a deficiency.

Calcium (Ca)Absorbed as Ca++ moderately leachable.Limited mobility in plant.

Calcium excess:Interferes with Mg absorption. High Ca usually causes high pH whichthen pre cipitates many of the micronutrients so that they becomeunavailable to the plant.

Calcium deficiency:Inhibition of bud growth, death of root tips, cupping of maturingleaves, we ak growth, blossom end rot of many fruits, pits on rootvegetables.

Action notes:Ca is important to pH control and is rarely deficient if the correct pHis maintained. Water stress, too much or too little, can affect Carelationships within the plant causing deficiency in the locationwhere Ca was needed at the time of stress.

Sulfur (S)Absorbed as SO4-.


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Leachable.Not mobile.

Sulfur excess:Sulfur excess is usually in the form of air pollution.

Sulfur deficiency:S is often a carrier or impurity in fertilizers and rarely deficient.It may be also absorbed from the air and is a by-product of combustion.

Symptoms are a general yellowing of the affected leaves or the entireplant.

Action notes:Sulfur excess is difficult to control.

MICRONUTRIENT OUTLINE

The majority of the micronutrients are not mobile; thus, deficiencysymptoms ar e usually found on new growth. Their availability in the soilis highly dependent upon the pH a nd the presence of other ions. Theproper balance between the ions present is important, as man y

micronutrients are antagonistic to each other. This is especially true ofthe heavy metals whe re an excess of one element may show up as adeficiency of another. If the pH is maintained at the proper level and afertilizer which contains micronutrients is used once a year, deficiencysymp toms (with the exception of iron deficiency symptoms) are rarelyfound on indoor plants. Many of the micronutrients are enzyme activators.

Iron (Fe)Absorbed as Fe++, Fe+++.

Iron deficiency:Interveinal chlorosis primarily on young tissue, which may become white.Fe deficiency may be found under the following conditions even if Fe is

in t he soil:Soil high in Ca, poorly drained soil, soil high in Mn, high pH, high P,soil high in heavy metals (Cu,Zn), oxygen deficient soils or whennematodes attack the roots.

Fe should be added in the chelate form; the type of chelate neededdepends u pon the soil pH.

Iron toxicity:Rare except on flooded soils.

Boron (B)Absorbed as BO3-

Boron excess:Blackening or death of tissue between veins.

Boron deficiency:Failure to set seed, internal breakdown, death of apical buds.

Zinc (Zn)Absorbed as Zn++.

Zinc excess:Appears as Fe deficiency. Interferes with Mg.

Zinc deficiency:"Little leaf," reduction in size of leaves, short internodes,distorted or puckered leaf margins, interveinal chlorosis.

Copper (Cu)

Absorbed as Cu++, Cu+.Copper excess:

Can occur at low pH. Shows up as Fe deficiency.


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Copper deficiency:New growth small, misshapen, wilted. May be found in some peat soils.

Manganese (Mn)Absorbed as Mn++.

Manganese excess:Reduction in growth, brown spotting on leaves. Shows up as Fe

deficiency. Found under acid conditions.Manganese deficiency:

Interveinal chlorosis of leaves followed, by brown spots producing acheckered red effect.

Molybdenum (Mo)Absorbed as MoO4-.

Molybdenum deficiency:Interveinal chlorosis on older or midstem leaves, twisted leaves(whiptail).

Chlorine (Cl)

Absorbed as Cl-.Chlorine deficiency:Wilted leaves which become bronze then chlorotic then die; club roots.

Chlorine toxicity:Salt injury, leaf burn, may increase succulence.

Cobalt (Co)Absorbed as Co++.Needed by plants recently established.Essential for Nitrogen fixation.Little is known about its deficiency or toxicity symptoms.

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