2024 BOT 121 leaf-stem-root morphology.pdf

Botany department contribution

1. BOT 121: Introductory Biology of Pharnerogams
Taiye R. Fasola Ph.D
Professor of Botany
University of Ibadan, Nigeria

2. THE LEAF: TYPES
According to the petiole:
Petiolated(Stalked)
Sessile.(Unstalked)
Petiolatedleaves are those that have a petiole. This
can be different in length from one plant to another.
Sessileleaves do not possess a petiole. The blade
expands itself directly from the stem.

4. External Features of a Leaf
For plant identification purposes, the shape of the leaf margin, leaf tip and leaf
base are key features to note. A leaf begins at the lateral or auxiliary bud.

5. Functions
To compete for light for photosynthesis, i.e., the manufacture of sugars
Evapotranspirationfrom the leaves moves water and nutrients up from the
roots.
Small openings on the leaf, known asstomata,regulate moisture and gas
exchange (water and carbon dioxide) and temperature (cooling effect as water
vapor escapes through stomata).
Horticultural uses
Aesthetic qualities
Feed and food
Mulch and compost
Plant identification
Propagation from cuttings
Summer cooling (Evaporative cooling accounts for 70-80% of the shading
impact of a tree.)
Wildlife habitat
Wind, dust and noise reduction

6. Leaf blade–Flattened part of the leaf
Petiole–Leaf stalk
Stipules –Leaf-like appendages at the base of the leaf.
Leaf Arrangement on Stems
Alternate–Arranged in staggered fashion along stem
Opposite–Pair of leaves arranged across from each other on stem
Whorled–Arranged in a ring
Rosette–Spiral cluster of leaves arranged at the base (or crown)

7. Leaflet Arrangement on Petiole
Simple –Leaf blade is one continuous unit
Simple leavesshow an undivided blade or, in case it has divisions,
they do not reach the midrib.
Compound–Severalleafletsarise from the same petiole
Compound leaveshave a fragmented blade, with divisions reaching
the midrib. Sometimes each one of these fragments is similar to a
single leaf. They are calledleaflets.
Pinnately compound–Leaflets arranged on both sides of a common rachis
(leaf stalk), like a feather (mountain ash)
Palmately compound–Leaflets radiate from one central point
Double pinnately compound–Double set of compound leaflets
Leaf Arrangement on Petiole.

9. According to the edge:
Entire leaveshave a smooth margin.
Sinuate leaveshave little curves with smooth edges like waves.
Dentate leaveshave little teeth at the margin.
Serrate leaveshave little bent teeth like those of a saw.
Lobed leaves have divisions that do not arrive the center of half blade.
According to the shape of the blade:
Elliptic leaves: remembering to a ellipse. 2 or 3 times longer than wide
Lanceolate leaves: spear-shaped. Gradually extending at base and lessening to the apex.
Acicular leaves: needle-shaped. Severally longer than wide; ending sharply at the apex.
Ovate leaves: egg-shaped. Wider at the base than the apex.
Cordate leaves: heart-shaped. More extended at base than ovate type and with a notch
Hastate leaves:halberd-shaped. Remembering that old fashioned weapon/ combination
between a spear and a battle-ax. Wider at base but with lobes ending sharply.
linear leaves:strip-shaped. Several times longer than wide. Not pointed at the apex like
in the acicular type.

10. According to the veins:
•Parallel-veined leaves: the veins run at the
same distance to each other, like in canes.
•Pinnate leaves: There is a main nerve, called
midrib, from which the other nerves derive,
remembering a plume.
•Palmate leaves:The nerves diverge from the
main point such as the fingers do in the palm
of the hand.

13. According to the arrangement along the stem:
•alternate:springing one per node at different
levels of the stem.
•opposite:two per node, facing opposite sides
of the stem.
•whorled:Several leaves disposed at the same
level around the stem.
•rosulateforming a rosette, like a ring around
the stem.

14. Types of Compound Leaves
There are two types of pinnate compound leaf:
Paripinnate imparipinnate

15. Bipinnate
Twice pinnate:The leaflets are also divided into leaflets

19. Pinnate (odd):Leaflets are attached along an extension of the petiole
called a rachis; there is a terminal leaflet and therefore an odd number
of leaflet
Pinnate (even):Leaflets are attached along an extension of the petiole
called a rachis; there is an even number of leaflets.
Palmate:Leaflets are attached to the
tip of the petiole
Note:Sometimes identifying a "leaf" or "leaflet" can be confusing. Look at the
petiole attachment. A leaf petiole attaches to the stem at a bud node. There is
no bud node where leaflets attach to the petiole.

21. XEROPHYTE, MESOPHYTE AND HYDROPHYTE
XEROPHYTE
Plants that live in conditions where water is scare (for example in the desert)
MESOPHYTE
Land plants living in environment with moderate amount of moisture.
HYDROPHYTE
A plant adapted to grow in water.
•Scale-like –Mature leaves common on most junipers and arborvitae
•Awl-shaped–Juvenile leaves common on some junipers
•Linear-shaped–Narrow flat needles of spruce, fir, and yews
•Needle-like–In pine, the single, bundle,or cluster of needles makes a rounded shape
Modified Leaves
Adhesive disc–Modified leaf used as an attachment mechanism, sometimes
referred to as a holdfast. (Boston ivy)
Bract–Specialized, often highly colored leaf below flower that often serves to
lure pollinators. (Poinsettia, dogwood)
Thorn–Modified leaf (barberry, pyracantha)
Tendril–Modified sinuous leaf used for climbing or as an attachment
mechanism (Virginia creeper, peas, grapes)

30. 1.According to presence/absence of petiole, leaves are either: i…………………….. ii
……………...
2.In pinnate evenness or oddness, compound leaves areeither:i……………………
ii……………….
3.Fix as appropriate in leaf (opposite, kidney,stalk, inequilateral, obovate, needle) for the
following:
iReniform………………… ii, Decussate……………………… iii, Petiolule………………
iv,oblique …………………… v, inverse ovate………………… vi, acicular…………………

31. Stem Morphology
Plantstems,whetheraboveorbelowground,arecharacterizedbythepresenceofnodesand
internodes
Nodesarepointsofattachmentforleaves.Leavesoftenconsistofathinregionthatattachesto
thestem(thepetiole)Thestemregionbetweentwonodesiscalledaninternode.Anaxillary
budisusuallyfoundintheaxil—theareabetweenthebaseofaleafandthestem—whereitcan
giverisetoabranchcalledanaxillaryshoot.Theshootapexatthetipshootcontainstheshoot
apicalmeristemsurroundedbydevelopingleavescalledleafprimordia.Leavesareattachedto
theplantstematareascallednodes.Aninternodeisthestemregionbetweentwonodes.
StemcouldbeherbaceousorwoodyPrimarygrowthoccursattheapicaltipsofthestemby
virtueoftherapidlydividingmeristematictissueintheseregionsofthestem.
Secondarygrowthisactuallytheincreaseinthethicknessofthestembyvirtueofthelateral
meristemsandthisisabsentintheherbaceousplants.

32. Thegrowingapexofthestemiscoveredbynumerous,tiny,developingleavesandiscalledtheapicalbud.Buds
alsoariseintheaxilsofleaves;theyaretermedaxillaryorLateralbuds.Thesebudsgiverisetobranchesor
flowers.
Plantshavebeenclassifiedonthebasisoftheheightandstrengthofstemandtheirlife-span.
Herbsaresmallplantswithasoftstem.
Medium-sizedplantswithwoodystemsthatbranchesprofuselyfromthebaseandattainabushyappearanceare
calledShrubs.
Treeshaveastoutandtalltrunkwithprofusebranching.
Plantswhichcompletetheirlifecyclewithinoneseasonaretermedannualssuchasagriculturalcrops
Biennialscompletetheirlifecycleintwoseasons
Plantsthatusuallysurviveforanumberofyearsaretermedperennials.

35. Whatisastem?
Thestemisthepartoftheplantthatgrowserectlyabovethegroundintheoppositedirectiontotheroot.The
stemshowsnegativegeotropism,whichmeansthattheygrowintheoppositedirectiontogravity.Itusuallyextends
abovegroundlevelservesasasupporttoovercomegravity,butdifferentsecondarystemsarebornfromitthat
endholdingleavesandflowersinplace.Howevertherearesomestemsthatcannotsupporttheweightofthe
plantandremainatgroundlevel(theyarenoterect),otherswithstemsthatclimbsurfaces.verticalandevensome
withaquaticstems.Fewstemsarealsofoundundergroundandareconsideredtobestem
modifications.
The stem may have specialized functions, such as the storage of nutrients in tubers or the presence of
tendrils in some climbing plants
Thus, its two main functions are the support and transport of nutrients and substances between roots
and leaves

36. FunctionsofStem
Itsupportsandholdsleaves,flowers,andfruits.
Thestemallowstheleavestoarrangeinawaythattheyareabletoreceivedirectsunlightinorderto
efficientlyperformphotosynthesis.Thearrangementandpositionofleavesalsoallowforgasexchange.
Thexylemandphloempresentinthevascularbundlesofstemsconductwaterandmineralsacrosstheplant.
Stemsbearflowersandfruitsinapositionthatfacilitatestheprocessesofpollination,fertilization,and
dispersionofseeds.
Somestemsundergomodificationtostorefoodandwater.Example:succulents.
Fewgreenstemscontainchloroplastsandarecapableofcarryingoutphotosynthesisaswell.
Somestemsaremodifiedtocarryoutvegetativepropagationwhichisaformofasexualreproductionseenin
plants.

37. What are the functions of stems?
Stemsareimportantforplantsbecausetheyareresponsiblefortransportingwaterandnutrientsthroughouttheplant.
Additionally,stemsareresponsibleforphotosynthesis,stemelongation,andfloraldevelopment.
Theprimaryfunctionofstemsistotransportwaterandnutrients.Thewaterandnutrientsaretransportedfromthe
rootstotheleaves,andthentotheflowersandfruit.Thisisnecessaryfortheplanttogrowandproducefood.
Stemsarealsoresponsibleforphotosynthesis.
Stemelongationisanotherimportantfunctionofstems.Itallowstheplanttogrowtallerandproducemoreleaves.
Flowerdevelopmentisalsodependentonstems.Theflowersarethereproductiveorgansofplants,andtheyare
responsibleforproducingseeds.
Unlikeleavessheddingindeciduousplants.Stemsarenecessaryforplantsurvival.Ifaplantlosesitsstem,itwill
notbeabletotransportwaterandnutrients,anditwilleventuallydie.”

40. Primary or main functions:
1. It supports and holds leaves, flowers and fruits.
2. Leaves are borne on stem in such a fashion that they are able to carry on the important
function efficiently just like to receive the light and to carry on the gaseous exchange.
3. The stem conducts the water and minerals from roots to leaves and fruits.
4. Stem bears flowers and fruits in position to facilitate the processes of pollination and
fertilization.
Secondary or Accessory functions:
1. Perennation
2. Storage of food
3. Photosynthesis
4. Vegetative propagation
5. As climbers

43. Therearethreetypesofstem:Undergroundstem,AerialstemandSub-aerialstem.
Undergroundstem:
Stemsofsomeplantsremaininthegroundandservethefunctionofperennationandstorage
offood.Theyproduceaerialshootsannually.Theyresemblerootssuperficiallybutare
distinguishablebythepresenceofscaleleavesandbudsatnodes.Suchstemalsoactasa
meansofvegetativepropagation.Themodifiedundergroundstemsarethefollowing:
(i)Rhizome:
Itisathickened,prostrate,undergroundstemhavingdistinctnodesandinternodes,scalyleaves
atthenodes,axillaryandterminalbudspresent;maybebranchedorun-branched;sometimes
adventitiousrootsalsoarise,e.g.Ginger.
(ii)Tuber:
Theundergroundstembecomesenlargedatthegrowingtipsbytheaccumulationofstoredfood,
commonlystarch,tubersareproducede.g.Potato.Theeyesofpotatoarenodesateachofwhich
1-3budsareproducedintheaxilsofsmallscalylikeleaves.

45. (iii) Bulb:
Bulb is a short underground stem with fleshy leaf base called scales. Stem is very much reduced and becomes disc
like.
(iv) Corm:
Corm is short, thick and un-branched underground stem with stored food material. It grows vertically and covered by
thin sheathing leaf bases of dead leaves called scales. The corm bears buds at their nodes. These buds are responsible
for giving off adventitious roots. Corm serves the functions of food storage, vegetative propagation and perennation.
Corm is more or less rounded in shape or often somewhat flattened from top to bottom
2. Sub –aerial stems:
As its name suggests, aerial stems include all those that rise above ground level. Lower buds of the stem in
some plants grow out into short, lateral branches.

46. (i) Runner:
It grows prostrate in all directions above the soil level. Nodes bear scale leaves. It has a creeping stem with long
internodes. On the lower sides, nodes bear adventitious roots. Runner develops from the axils of lower leaves of
aerial stem which sends slender horizontal branches in the form of runners. When older parts of plant die, the
branches separate from parent plant and form independent plants
(ii) Stolon:
They are a type of creeping stem typical of plants capable of creating roots through which other plants will
develop. It is a slender lateral branch which appears from the lower part of main axis. This lateral branch grows
aerially for some distance andbecomes arched and finally touches the ground to give rise to new shoot with the
help of its terminal bud. It also bears roots to get fixed with the soil
(iii) Offset:
Offset is more shorter and thicker. It is usually found in aquatic plants like water hyacinth and Pistia. It bears a cluster
of leaves near the water or ground level and gives adventitious roots inside water or ground from all nodes, e.g.
Pistia.
(iv) Sucker:
Like the stolon the sucker is also a lateral branch but it grows obliquely upwards and gives rise to a new
plants e.g. Mentha.

47. Culm

51. 3. Aerial stems:
These modified aerial stems perform unusual functions. Different forms of these stems are the
following (Fig. 4.8 i-v):
(i) Stem tendril:
It is a leafless, spirally coiled branch formed in some climbers and helps them in climbing
neighboring objects; they may be modification of axillary bud
(ii) Stem thorn:
Stem thorn is a hard, straight and pointed structure; it is a defensive organ; also helps in climbing;
originates from axillary or terminal bud
(iii) Pylloclade:
It is a green, flattened or cylindrical stem which takes the form and function of leaf. It contains
chlorophyll and is responsible for carrying on photosynthesis. It bears succession of nodes and
internodes at long or short intervals. Phyllocladesare found in xerophytic plants where the leaves
either grow feebly or fall off early or modified into spines e.g. Opuntia,

53. (iv) Cladode:
Phylloclade with one or two internodes is called cladode e.g. Asparagus. In Asparagus cladodes
are needle-like, slightly flattened green structures which appear in cluster in the axil of a scaly
leaf. Main stem bears leaf spines at its nodes. A scale leaf is found just above the spine. Every
branch on main stem bears only scale leaves. In the axil of scale leaves cluster of cladodes appear
(v) Bulbil:
Bulbil is the modification of vegetative or floral bud. It is swollen due to storage of food. It can
function as an organ of vegetative propagation
•Definition
•Phyllodereferstoaflatexpandedpetiolethatreplacesthebladeofafoliageleaf,fulfillsthe
samefunctions,andisanalogoustoacladophyll.
•Phyllocladereferstoaflattenedstemorbranch(suchasacactusjoint)thatfunctionsasaleaf.
Meanwhile,cladodereferstoshootsystemsinwhichleavesdonotdevelop;instead,thestems
becomeflattenedandassumethephotosyntheticfunctionsoftheplant.

54. Trailing stem:
This is a weak stem spreading on the ground without rooting at the nodes.
It is of three types
i, Prostrate -flat on the ground eg basella
ii, Decumbent –lying on the ground but with apex ascending eg Tridax
iii, Diffuse –trailing stem with many spreading branches eg Boerhaavia

56. Erectstems
Theuprightonesareallthosestemsthatnotonlyriseabovegroundlevel,butalsotheyremaininan
uprightpositionwithoutneedinganysupport.Allthoseplantsthatareerectontheirownhavesucha
stem.Someofthistype,toavoidbeingeaten,havedevelopedthorns,asisthecasewithrosebushes.
Thereisaspecialtypeofcylindricalstemwithverymarkedknotsthatiscalledcane,whichispresentin,
forexample,wheat.
Creepingstems
Thecreepersareallthosestemsthat,despiterisingabovegroundlevel,donothavethenecessary
consistencyeithertoovercomegravityortosupporttheplant'sownweight.Thus,thestemstaysat
groundlevel.Andinsteadofgrowingvertically,itgrowsvertically.Anexamplewouldbethecarrotplant.
An example would be the carrot plant.
1.3, for example, strawberries.

57. Ficklestems
Thevolubleonesarestemsthat,likethecreepers,donothaveenoughstrengthtokeeptheplantuprightontheirown.
However,astheyneedmorelight,theymustreachhigherareas.Andwhentheycan't,whattheydoiswrap
themselvesaroundthestemofanotherplant(oranartificialstructuresimilartoastem)andgoupinaspiral.An
exampleisthebell.Normally,whenthestemiswrappedaroundanartificialsupport,suchasanironbarorany
similarobject,thestemiscalledatendril.
Climbingstems
Climbersaresimilartofickleinthesensethattheyneedtoreachhigherareasbutcannotstanduprightontheirown.
However,climbers,insteadofcoilingonanotherstem,havetheabilityto,astheirnamesuggests,climbavertical
surface,ascanbeawall.Aclearexampleisthebougainvillea.tanduprightheiown.However,climbers,insteadof
coilingonanother

58. 2Tuber2.Undergroundstems
Asitsnamesuggests,undergroundstemsarethosethatdevelopbelowgroundlevel,thatis,underground.Themain
typesarethefollowing:
Bulbs
Thebulbsareatypeofshortstemspresentnexttotherootsandwithleaves,whichserveasastoreforstarch.These
leavesareattachedtothemainstem,whichisobviouslyunderground.Theclearestexampleisonions.
Tubers
Thetubersarestemssimilartobulbs,althoughtheydifferinthesensethatthestarchisnotstoredintheleaves,butin
thestemitself.Aclearexampleispotatoes.
Rhizomes
Rhizomesarestemsthatgrowparalleltothesurfaceofthesoil,althoughtheydosojustbelow.Isaboutstemsof
greatthicknessandthatareusuallyedible.Anotheroftheircharacteristicsisthatwiththearrivalofthewarm
months,theydevelopshootsthatgrowoutwards.Twocharacteristicexamplesarebambooandginger.

62. Answer
Verified
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Hint: The subaerial stem is a stem that remains partly in air and partly underground. It is
also known as ‘Creeper'.
Complete answer: The runner is a subaerial stem modification with a long internode and
a creeping stem. The nodes give rise to axillary buds, aerial branches, adventitious roots,
and scaly leaves. The aerial branches arising from the nodes can detach itself to develop
into a new plant. It also helps in the vegetative propagation of plants. It can be seen in
Cynodon(lawn grass), Oxalis (wood sorrel), Centella, etc.
Additional Information:
Some other kinds of the modified subaerial stem are-
1. Sucker-This subaerial stem arises from the base of the stem that lies beneath the
ground. After running horizontally under the ground for some distance it obliquely comes
out to give new branches and roots. It is seen in Chrysanthemum, Banana, Mentha,
strawberry, pineapple, etc.
2. Stolon-This weak subaerial stem arises from the base of the stem. It grows in the air
for a while and after that bends downwards to touch the ground. There it gives rise to a
new shoot and adventitious roots. It can be seen in Jasmine, Colocasia, Vallisneria, etc.
3. Offset-This subaerial stem is short and bears one internode only. After originating
from the leaf axil, it grows a little horizontally and then produces a rosette of leaves
above and roots below. It can be seen in Pistia(water lettuce), Eichhomia(water
hyacinth), etc.

65. Thereare2principaltypesofbranching:
A.LateralandB.Dichotomous.
A.Lateralbranching.Whenbranchesareproducedlaterally,i.e
fromthesidesofthemainstem,thebranchingiscalledlateral.
Thismayracemoseorindefiniteandcymoseordefinite.
1.Racemosetype:
Thestemcontinuestogrowbytheterminalbudandgivesoff
brancheslaterallyinacropetalsuccessioni.ethelowerbranches
areolderandlongerthantheupperones.Branchingofthistype
isalsocalledmonopodialbecauseitbearsasinglecontinuous
axisegCasuarinaisconicalorpyramidalshaped
2.Cymosetype
Theterminalbuddoesnotcontinuetogrowbutlowerdown,the
mainstemproduceslateralbranchesthatgrowvigorouslythan
theterminalone.Themainstemgrowthisdefinite.

66. Cymose branching are of three kinds, viz. Uniparous,
Biparous and Multiparous.
1. Uniparous Cyme. If in the cymose type, only one lateral
branch is produced at a time. This also known as monochasial.
Otherwise called sympodial(syn, together or united; pod-foot)
because of the succession of daughter axes fused together in the
cause of plant’s development. It has two distinct forms:
a, Helicoid or one-sided cyme. When successive lateral
branched develop on the same side, forming a sort of helix
b, Scorpioidor alternate-sided cyme. When successive lateral
branched develop on alternate sides, forming a zigzag.
2.Biparous Cyme:

67. 2. Biparous Cyme:
If in the cymose branching branching, two lateral axes develop at the
same time, it is called biparous or dichasial.
How is this different from dichotomy?
3. Multiparous Cyme.
If more than two branches develop at the same time, the branching is
said to be multiparous or polychasial
B. Dichotomous branching
When the terminal bud bifurcates, i.e divides into two, producing two
branches in a forked manner, the branching is termed dichotomous.

72. PLANT ROOTS
What is the root of a plant?
The roots of plants are their warehouses and serve three primary
functions:
-they anchor the plant
-absorb water and minerals for use by the plant
-storefood reserves.
Depending on the plant’s needs and environment, certain parts of the
root system may become specialized.

73. How Do Roots in Plants Develop?
In most cases, the beginning of the roots in plants are found in the embryowithin the
seed. This is called a radicleand will eventually form the primary root of a young plant
whilePlumuleis the part of the seed embryo that grows into a shoot.The primary root will
then evolve into one of the two main types of roots in plants: a taproot system or a
fibrous root system.
Taproot–In the taproot system, the primary root continues to grow into one main trunk
with smaller root branches emerging from its sides. Taproots can be modified to serve as
carbohydrate storage, as seen in carrots, or to grow deeply in search of wateras those
found in mango.
Fibrous–The fibrous system is another of the types of roots in plants. Here, the radicle
dies back and is replaced by adventitious(fibrous) roots. These roots grow from the
same cells as the plant stem and are generally finer than tap roots and form a dense
matbeneath the plant. Grassis a typical example of a fibrous system. The fibrous roots
in plants like sweet potatoesare good examples of the types of roots in plants that are
used for carbohydrate storage.

74. Fibrous root systems, common in monocots, have many very thin roots spread
out under the surface and form a mat of roots underground.
Keeping their roots close to the surface means they may lose some stability
provided by the deep tap root, however the large number of roots firmly secure
the plant to ground.
Plant species with fibrous roots such as grasses are also great at stabilizingthe
soil and preventing erosion.
The extensive root system provides excellent exposure to nutrients and water in
the soil.
Root hairs
Plant rootsare important for securing the plant to the soil but the majority of
nutrient uptake occurs near the tip of the root. Here a large number of root hairs
grow; very fine roots with large surface area to volume ratio. By having a large
surface area and low volume it increases the efficiency of absorption of
minerals and water.

75. Fibrous Root System:
-Characterized by having a mass of similarly sized roots.
-The radicle from a germinating seed is short lived and is replaced by adventitious roots.
-Adventitious roots are roots that form on plant organs other than roots.
-Most monocots have fibrous root systems.
-Some fibrous roots are used as storage; for example sweet potatoes form on fibrous roots.
-Plants with fibrous roots systems are excellent for erosion control, because the mass of roots
cling to soil particles.

79. Characteristics of Tap Root:
•It develops directly from the radicle and grows vertically downwards.
•Only one main root that grows from the end of the stem is called the primary root.
•The primary root gives out branches of secondary and tertiary roots.
•The lateral roots of the taproot are called secondary and tertiary roots.
•It is very thick, straight, and goes deepinto the soil.
•Very fine hair like structures on the root, known as the rootlets or root hair.
•There is a root cap on the tip of the root that protects the root cap.
Examples of Tap roots:bean, hibiscus, mustard, carrot, beetr

81. What are the different types of root systems?
Plants have three types of root systems:
1.) taproot, with a main taproot that is larger and grows faster than the branch roots
2.) fibrous, with all rootsabout the same size
3.) adventitious, rootsthat form on any plant part other than the roots.
What are the major roles of a root system?
The first root that comes from a plant is called the radicle. A root's four major functions
are 1) absorption of water and inorganic nutrients, 2) anchoringof the plantbody to
the ground, and supporting it, 3) storageof food and nutrients, 4) vegetative
reproduction and competition with other plants.
What type of root system do monocots have?
A taproot system is one in which the primary rootbecomes the main rootof the plant
with minimal branching consisting of secondary, smaller lateral roots. The taproot
system occurs in dicot plants and is one of the basis of distinguishing these plants from
the monocotswhich havefibrous roots

82. The following points highlight the five main parts of a typical root. The parts are:
1.RootCap
2.Growing Point or MeristematicZone
3.Region or Zone of...
-Zone of Cell Division -this is the location of the apical meristem
(~0.5 -1.5 mm behind the root tip).Cells derived from the apical meristem add to the
primary growth of the root.
-Zone of Cellular Elongation -the cells
derived from the apical meristem increase in length in this region.Elongation occurs
through water uptake into the vacuoles.This elongation process shoves the root tip
into the soil.
-Zone of Cellular Maturation -the cells begin differentiation.In this region one finds
root
hairs which function to increase water and nutrient absorption.In this region the
xylem cells are the first of the vascular tissues to differentiate.

83. Root Structures and Their Functions:
Root Cap: root tips are covered and protected by the root cap.
The root cap cells are derived from the root cap meristem that pushes
cells forward into the cap region.
Root cap cells differentiate first into columella cells.
Columella cells contain amylopasts that are responsible for gravity detection.
These cells can also respond to light and pressure from soil particles.
Once columella cells are pushed to the periphery of the root cap, they differentiate into
peripheral cells.
These cells secrete mucigel, a hydrated polysaccharide formed in the dictyosomes that
contains sugars, organic acids, vitamins, enzymes, and amino acids.
Mucigel aids in protectionof the root by preventing desiccation.
In some plants the mucigel contains inhibitors that prevent the growth of roots from
competing plants.
Mucigel also lubricates the root so that it can easily penetrate the soil.
Mucigel also aids in water and nutrient absorptionby increasing soil: root contact.
Mucigel can act as a chelator, freeing up ions to be absorbed by the root.
Nutrients in mucigel can aid in the establishment of mycorrhizae and symbioticbacteria.

84. Based on Mechanical Functions
Some roots get modified to provide strength and protection to the plant, based on which
roots are classified into the following types:
1)Prop roots: These are adventitious roots that arise from the aerial branches of trees
and help in their additional support. Examples: Banyan tree, rubber plant,
2) Stilt roots: They are obliquely growing adventitious roots thatdevelop from the
lower nodes of the stem to give stability to the plant. Examples: Sugarcane, maize,
sorghum,Pandanus, andRhizophora.
3) Buttress roots: Thehorizontalplank-like aerial, adventitious roots that develop at the
base of the stem to give additional support to the plant.
Examples:TerminaliaandSalmalia.

88. -Prop roots are pillar like roots which give support to heavy stem branches. For
example banyan (Ficusbenghalensis).
-Stilt roots are stout oblique roots which arise in circular whorls from the lower
nodes of the stem and enter the soil and become stronger.
-They protect the plants against wind. For example sugarcane (Saccharum
officinarum), maize (Zeamays)

89. Stilt roots

91. Types of Root Modifications
Roots of some plants undergo a change in their shape and structure to perform specialized
functions, other than the basic ones. The different types of those modifications are listed below:
Based on Physiological Functions
Sometimes roots are modified to perform the basic chemical and physical processes needed by
the plant to grow and survive, based on which roots are classified into the following types:
1) Storage roots: They become fleshy to store reserve food materials. Examples: Radish,
carrot, beet,Mirabilis, andEchinocystis
2) Aerial roots: Also called epiphytic roots, they are found above the ground and helps
plants to absorb moisture from the air. Examples: Mangroves, banyan trees, common ivy,
and poison ivy.
3) Assimilatory roots: Also called photosynthetic roots, they are green roots which prepare
food for the plants byphotosynthesis. Examples:Taeniophyllum,Trapa,andTinospora.

92. Based on the origin of the adventitious root, they are further classified into:
a) Fibrous Roots
They are slender, branched, bushy roots that grow directly from the stem of the plant. Fibrous
roots are formed from moderate branching of the taproot and do not penetrate deep into the soil.
Examples: Grass, rice, wheat, maize, and banana.
b) Foliar Roots
They arise naturally fromleaf veinsor petioles due to some injury on the leaf. The injured region
develops new buds called foliar buds, which later give rise to these roots for new plants to grow.
Sometimes, artificial application ofplant growthhormones can also stimulate the plant to
develop new foliar buds from the region where it is applied.
Examples: Pogostemon, rubber plant,Bryophyllum, andBegonia.
c) True Adventitious Roots
Lateral buds that arise from parts of the stem (at the nodes and internodes) are called true
adventitious roots.
Examples: Aerial roots of a banyan tree, stilt roots of sugarcane, and clasping roots of the money

94. Napiform roots
The plant contains agreat taproot, which has evolved to be able to store reserve
nutrients and other vital substances. Therefore, they are very thick roots and, in addition,
many of them are edible

95. Fasciculated roots
Also calledatypical or fibrous root. In this type of roots there is no main root, so all the
branches are equally important and can reach similar sizes. It is one of the most
common types of roots in gardening plants.

96. Aerial roots
It is another of thetypes of parasitic plant rootsthat grows downward and can lead to
strangling the host plant. In this other post you can see more about Air Plants: types,
names and care.

97. Fulcreas roots or stilts
This type of roots is known asFulcreas roots, wading roots, or stilts. These start from
the base of the trunk or stem before reaching the ground, and grow from there,
extending into the ground, even passing through water, so that a part of them is visible.
They usually have themlarge trees, which need greater stability due to the environment
in which they develop

111. Adventitious roots are very similar to fibrous roots.Roots forming from other parts of the
plant except radicle are called adventitious roots.They can grow underground or aerial. An
aerial root grows above the ground and absorbs nourishment directly from the air.
Usually, adventitious roots may originate from any nodes, internodes, stem or the branch or even
from the leaf. Examples of adventitious root:orchids, banyan tree, mangroves etc.
Adventitious roots can be further subdivided into different categories based on the location and
shape of the swollen parts.
Buttress roots areaerial extensions of lateral surface rootsand form only in certain species.
Buttress roots stabilize the tree, especially in shallow saturated soils, thereby resisting toppling.
Buttress rootsare aerial extensions of lateral surfacerootsand form only in certain
species.Buttress rootsstabilize the tree, especially in shallow saturated soils, thereby
resistinguttresses orbuttress roots(laterally or vertically compressed and flattened plank
likerootsnear the trunk)
Stilt roots areadventitious rootsthat emerge from the base of stem nodes. They grow
downwards till they reach the soil substratum. Typically, they support the weaker stems
mechanically.

112. Buttress root

113. Buttress root

115. Theroot cap,or calyptra, has the functions of protecting the delicate stem cells within the root
tip, and of receiving and transmitting environmental signals to theThe root cap, however,
follows neither of these principles. While new root cap cells are constantly produced by root
cap stem cells in an indeterminate fashion, the size and cell number of the root cap are
determinate (Barlow, …root capplays a vital role in gravity perception in plants. It protects
the root from environmental stress. It enables the downward growth of the root. It …Now we
will find a smallcap-like structure is fitted at eachroottip; this is calledroot-cap.Root-
capsprotect theroottips from being damaged due to friction with soil particles …

119. Pneumatophore
s

120. Prop roots

121. Stilt roots

122. Prop roots

123. Prop Roots:
1. Prop roots develop from the upper part of the stem, especially the
horizontal branches.
2. The roots are quite long.
3. Prop roots pass down into the soil in a vertical position.
4. They provide support to the plant like pillars or poles.
5. Young prop roots are hygroscopic.
6. Prop roots are quite thick and massive.
7. They can replace the trunk or main stem.

124. Stilt Roots:
1. Stilt roots develop from the basal nodes of the main stem.
2. They are comparatively short.
3. The roots develop obliquely at an angle to the stem.
4. Stilt roots provide support like ropes of a tent or pole.
5. Young stilt roots are non-hygroscopic.
6. Stilt roots are comparatively little thick or massive.
7. Main stem is seldom replaced.
Examples: Maize. Sugarcane.

125. 1.The three primary functions of roots are:
i,………………………….......... ii,……………………………….. iii,…………………………
1.Mucigelsecreted in root cap has three functions:
i,………………………….......... ii,……………………………….. iii,…………………………
1.List modified roots that provide support in plants:
i,………………………….......... ii,……………………………….. iii,…………………………
1.Fix the most appropriate (carrot, breathing, atypical/fibrous root)that best describe the
following in root:iFasciculated………………………………………….
ii, Napiform…………………………… iii, pneumatophore……………… …………….
1.Fix the most appropriate word (hydrophytes, mesophytes, halophytes and xerophytes)that
best fit the following in plants:iDessert……………………
ii,Bog…………………………… iii, Highsalinity ……………… ……………. iv,moderate
dryness/wetness ………..…………….
2.List four features of survival in xerophytic plants: i, …………………………..…………
ii,………………………………… iii,…………..……………………… iv,
…………..……………

126. Theplantstructureofhydrophytesisnotwelldeveloped,whiletheplantstructuresof
mesophytesandxerophytesarewelldevelopedintorootsandshoots.
Hydrophyteslackacuticle;mesophytescontainathincuticle,whilexerophytes
containathickcuticle.
Moreover,hydrophytescontainlong,finedissectedpetioles,andmesophytescontain
large,broad,andgreenleaves,whilexerophytescontainsmall,fleshyleaves.
Hydrophyteslackstomata,andmesophytescontainstomataonleaves,while
xerophytescontainveryfewstomata.
Inbrief,hydrophytes,mesophytes,andxerophytesarethreetypesofplantsthatshow
adaptationstotheamountofwatertheyhave.Hydrophytesliveinwater,andtheir
plantstructureisnowwell-developed.Theylackcuticlesandcontainlong,fine,
dissectedpetioles.Inaddition,theylackstomata.Ontheotherhand,mesophyteslive
inmoderateconditionsofwater.Therefore,theycontaincuticlesandlarge,broad,
greenleaves.However,mesophytescontainstomata.Incomparison,xerophyteslive
inenvironmentswithverylowamountsofwater.Therefore,theycontainathick
cuticleandcontainveryasmallernumberofstomata.Theleavesofxerophytesare
smallandfleshy.