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KENYATTA
UNIVERSITY
INSTITUTE OF OPEN DISTANCE & e-LEARNING
IN COLLABORATION WITH
SCHOOL E.G. SCHOOL OF PURE & APPLIED SCIENCES
DEPARTMENT OF BOTANY
SBT 102
PLANT MORPHOLOGY AND ANATOMY
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EDITED BY:
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TABLE OF CONTENTS
LECTURE ONE
INTRODUCTION TO THE STUDY OF PLANT MORPHOLOGY
AND ANATOMY
1.0 Introduction
We welcome you to the study of morphology and anatomy. This unit is one of
the core units in the field of botany. The study will mainly deal with the group
of plants called the vascular plants or tracheophytes. In this we shall look at
both the external morphology and internal anatomy of representative organs of
plants.
1.1 Objectives
By the end of this lesson you should be able to:
 Define the term “plant morphology”
 Distinguish the groups of plants, which comprise the tracheophytes or
vascular plants.
 Distinguish between a cross section (or transverse section) from a
longitudinal section of a plant organ such as a stem or root.
 Identify the anatomical and morphological features that distinguish
the angiosperms from the pteridophytes and gymnosperms.
1.2 content
1.2.1 The meaning of Plant Morphology and Anatomy
The term plant morphology refers to the form of plants. This is with r4egard
to the different plant organs, such as sterns, leaves, roots and flowers.
The term plant anatomy is particular used to refer to the internal structure of
plant organs, such as stems, roots, leaves and flowers. To be able to study
the internal anatomy of a plant organ you will require to cut cross sections
(or transverse sections) of the particular organ. Some times it is also
necessary to cut longitudinal sections of the plant organ. Such sections are
then viewed or examined under the light compound microscope in order to
see the distribution of the various cell types and tissues. Permanent stained
slides may also be used.
When examining a specimen under a microscope please start by using the
low power of the microscope. Under this power you should be able to see
the general layout or distribution of tissues. To see cell details you have to
switch to the medium power. Generally the use of the high power should be
done under adequate instruction.
1.2.2 A classification of vascular plants (or Tracheophytes)
As indicated earlier in the lesson we shall deal mainly with the morphology
and anatomy of the vascular plants. In view of his it will be useful to
familiarize yourselves with the classification of the major group of plants.
(a) Non seed plants
Pteridophytes
The classification include the sub divisions:
(i)
(PSILOPSIDA (spore bearing)
Mainly occurring in fossil form but a few living genera are found e.g.
Psilotum.
(ii)
LYCOPSIDA – tracheid and spore bearing
Including living genera, such as:
Lycopodium – Clubmosses e.g.
Lycopodium clavatum
Phylloglossum
Selaginella.
(iii)
SPHENOPSIDA
Largely extinct, with only one living genus Equisetum.
(iv)
PTEROPSIDA
This is the largest subdivision of the vascular plant (Tracheophytes).
It includes:
a) The ferns (Filicinae)
- Spore producing (non seed)
- With tracheids.
b) Seed plants – Phanerogams
Gymnosperms
Seed borne on scales (naked seeds) and having tracheids in the xylem.
Angiosperm or flowering plants.
Seeds borne inside a fruit (fruit wall) and having xylem vessels.
Angiosperms are 2 kinds:
Monocotyledonous plants e.g. maize, grass etc.
Characterized by having:
- One cotyledon
Scattered vascular bundles in the stem.
Dicotyledonous plant e.g. Bean, sunflower etc.
Characterized by having 2 cotyledons
Vascular bundles arranged in a ring in the stem.
In the evolution of the plants it has been suggested that there was a gradual
movement from water onto land. This necessited the development of a
vascular system of the tracheids and xylem vessels. This system provides
channels for the conduction of water and dissolved solutes from the soil to
the leaves. This development led to the 3 groups of plants that may be listed
as:
1. Pteridophytes
2. Gymnosperms
3. Angiosperms
referred to above
1.3 Questions
1. Outline the classification of the vascular plants.
2. What special anatomical development helped the movement of plants
from water onto land?
1.3.3. The Morphology and anatomy of Lycopodium clavatum
Morphology
Lycopodium species including L. clavatum, grow as creepers on the ground.
The creeping stem bears leaves and at intervals produces vertical shoots to
form strobili (or cones). Each fertile leaf in a strobilus bears a single large
sporangium containing spores. The shoot of Lycopodium clavatum is
dichotomously branched.
IMAGE
FIG 1.0) a diagram of Lycopodium calavatum, showing leaves and rhizoids
and dichotomous branching
Anatomy
A transverse section of the stem of Lycopodium clavatum, as shown in figure
1.1. shows the following features:
- A wide layer of cortex.
- An endodermis encompassing the vascular system.
- A vascular system consisting mainly of xylem and phloem.
- The xylem is made up of tracheids, Fig. 1.1
IMAGE
FIG. 1.1 Diagram of transverse section of Lycopodium stem/rhizome
showing the distribution of tissues. It is to be noted that the vascular systems
is at the center, with phloem being found in between army of xylem.
1.3.4 Morphology AND ANATOMY OF PTERIDIUM AQUILINUM
We shall here briefly look at the morphology and anatomy of the more
common fern, bracken fern (Pteridium aquilinum)
In Kenya this fern commonly found growing on red acidic soil of the
highlands.
It is a persistent weed
It is to be noted that the sporophyte i.e. the spore-producing plant is the
conspicuous plant. This plant has its stem growing
Underground in the form of a rhizome, which produces roots and aerial
shoots at intervals, as shown in Fig, 1.2
IMAGE
1.2 Diagram of Bracken fern (Pteridium aquilinum) consisting of the
sporophyte generation with a rhizome, aerial shoot or frond bearing
sori on the under side that contain spores. The rhizome bears roots.
The mature plant produces spores contained in sori Fig. 1.3. Such sori are
borne on the underside of the leaves fronds Fig. 1.2. The spore bearing
leaves are known as the sporophylls.
IMAGE
Fig. 1.3 A cross section of a single sorus of Bracken fern containing
sporangia on the under side of the leaf. The sorus has a protective shield
called the indusium.
A transverse section of the rhizome of Pteridium aquilinum, Fig. 1.4 (a)
shows Dictyostele. This is a system in which there are separate vascular
bundles. The xylem here is made up of tracheids, Fig. 1.4 (b).
IMAGE
Fig. 1.4 (a) Diagram of a transuerse section of stem/rhizome of Bracken fern
(Pteridium aquilinum) showing inner and outer vascular bundles with
intervening sclerenchyma the xylem consists of tracheids.
Characteristics Features of Tracheids
(i)
Tracheids are dead cell elements
(ii)
The walls of tracheids are very thick
(iii)
The walls have pits
(iv)
Tracheids have tapering ends, fig. 1.4 (b)
IMAGE
Fig 1.4 (b) A longitudinal section of several tracheids showing their
characteristic features of thick walls, tapering ends and possession of pits.
Tracheids strengthen the plants.
1.3.5 The life cycle of the Bracken fern (Pteridium aquilinum)
as noted before the vegetative plant is the sporophyte, which bears/ produces
spores. When the spores are shed from the sori and fall on warm moist soil
they germinate. A colour less rhizoid grows which serves to absorb water
and mineral salts from the soil. Through repeated cell division a prothallus is
formed Fig. 1.5.
IMAGE
Fig. 1.5 Diagram of a fern prothallus underside showing male and
female organs and rhizoids.
The prothallus develops into a heart shaped structure. The growing point is
located at the notch end. On the lower surface of the prothallus rhizoids are
formed towards the tapering end.
The reproductive structure/organs are found on the lower surface of the
prothallus. These consist of several female organs, archegonia at the notch
end and the male organs i.e., antheridia located amongst the rhizoids at the
tapering end, Fig. 1.5.
Each archegonium contains an egg (ovum). The antheridia produce
antherozoids which swim in water and reach the archegonia. One of the
antherozoids unites with the egg in the archegonium resulting in a zygote,
which is diploid.
Through repeated cell division of the zygote an embryo is formed which
develops a root and stem/shoot and a frond (leaf). As a result a sporophyte
plant is established, Fig. 1.6.
IMAGE
Fig. 1.5 Diagram of a fern prothallus underside showing male and
female organs and rhizoids.
Activity
1. Make a labeled drawing of the transverse section of the rhizome of the
bracken fern (pteridium aquilinum).
2. Give a well illustrated account of the anatomical features of a tracheid.
3. Collect two or three type types of pteridophytes and dry them by pressing
them between newspaper sheets mount them, and label the morphogical
features.
Summary
You will now have realized that morphology and anatomy is a basic field of
study for a botanist. It provides information on the structure of the plant. We
have noted that the vascular plants have structures that strengthens them as well
as providing a system for conduction of water and solutes from the soil to the
leaves. This is due to elements such as tracheids and xylem vessels. [it has also
been noted that the sporophyte plant is the more prominent phase while the
gametophyte much smaller in size. The sporophyte is haploid (n) while the
gametophyte is diploid (2n)].
Definition of key words
Morphology – refers to form
Tracheophytes or vascular plants – plants with vascular elements such as
tracheids and vessels of the xylem.
Pteridophyte – first group of truelly terrestrial plants e.g. fern.
Gymnosperm – group of seed plants whose seeds are not coloured by any
structure (naked).
Angiosperm – group of plants whose seeds are contained in fruit.
Sporophyte – vegetative plant bearing spores.
Gametophyte – plant producing gametes
Strobilus – a collection of leaves called sporophylls bearing sporangia.
Sporangium – a structure containing spores
Sorus – a structure, which houses spores and found in pteridophytes.
Prothallus – a heart shaped structure bearing both archegonia and antheridia
on the underside. It constitutes the gametophyte of a pteridophyte.
Gametophyte – gamete bearing phase of a plant.
Gamete – male and female cells which unite during fertilization, e.g. Egg or
ovum and antherozoid.
Pit – an opening in the wall of a tracheid or vessel.
Gametophyte – a gamete producing plant that is generally haploid and
produce the gametes by mitosis.
REFERENCES
 Esau, K. 1960. Anatomy of seed plants.
 Esau, K. Plant Anatomy
 Fahn, A. 1974 Plant Anatomy
 Foster, A. S. Comparative Morphology of Vascular plants.
 Fuller, H.J. and O. Tippo. 1949, College Botany.
 Sporne, K.R. The Morphology of Angiosperms. The structure and
evaluation of flowering plants.
 Steeves, T.A. 1989, Patterns in plant development.
LECTURE TWO
THE EXTERNAL MORPHOLOGY OF THE GYMNOSPERMS AND
THE ANGIOSPERMS.
2.1 INTRODUCTION
In lesson 1, we looked at the introduction to the study of Plant Morphology and
Anatomy. In unit 2 or lesson 2, we are going to describe the external
morphology of the gymnosperms and the angiosperms. These are the seed
bearing plants. The study will include the shoot system and root system.
Differences between the external morphology and the organs of the
gymnosperms will be highlighted.
2.2 OBJECTIVES
By the end of this lesson, you should be able to:
 Describe the external morphology of stem, branch, leaf and bud of
an angiosperm (monocotyledon and dicotyledon)
 Describe the external morphology of the root of an angiosperm.
 Distinguish the external morphology of the leaves of
gymnosperms from those of angiosperms.
 Describe the external morphology of the specialized stems, such
as the rhizomes, stem tubers and bulbs.
 Identify the different types of roots, such as, the taproots,
secondary roots, fibrous roots, aerial roots and proproots.
 Draw the external morphology of specimens during practical work
sessions.
2.3 A STUDY OF EXTERNAL MORPHOLOGY OF SEED BEARING
PLANTS (ANGIOSPERMS AND GYMNOSPERMS)
In this study we would like to start by looking at the more familiar plants
and later proceed to the less familiar ones. In view of this we suggest that we
first look at the external morphology of the Angiosperm plants (flowering
Plants). These comprise of the monocotyledonous and dicotyledonous
plants.
2.3.1 the external Morphology of the angiosperm plant and its organs.
The development of the embryo into a seeding.
Following fertilization which in an ovule is through the union of an egg
(ovum) and the male gamete, a zygote is formed. Through repeated cell
division of the zygote a young embryo is formed. In the case of
dicotyledonous plant, such an embryo may be illustrated in an opened
soaked bean seed Fig. 2.1.
In the practical session you should note, draw and label the following
features:
 Testa or seed coat
 Two cotyledons
 The embryo held between the two cotyledons
 The embryo consists of
(i)
2 plumule leaves
(ii)
an axis (or rudimentary stem) and
(iii)
a radicle
IMAGE
Fig. 2.1 (a) The structure of a soaked opened up bean seed showing a
young embryo two cotyledons and a seed coat or testa.
Under suitable conditions of adequate moisture, oxygen concentration and
temperature the bean seed will germinate. The radicle will protrude and
grow down wards while the two plumule leaves and the axis will grow
upwards to form the hypocotyls and epicotyl of the young seedling. The
radicle will give rise to the root system consisting of a tap root and
secondary roots, as shown in Fig. 2.1 (b).
IMAGE
Fig. 2.1 (b) A young bean seedling showing 2 foliage leaves, 2 cotyledons, a
shoot apex, an epicotyl, a hypocotyls, tap root apex and secondary roots
(lateral roots).
In the practical session you should draw and label the various features of a
dicotyledonous seedling.
The young seedling eventually grows into a mature vegetative plant.
2.3.1.2 The shoot system
Such a mature plant will have a shoot system comprising of :
 The stem with nodes, internodes dormant axillary buds, apical or
terminal bud.
 Lateral branches.
 Foliage leaves, as shown in Fig. 2.1 (c)
By virtual of processing of chlorophylls the shoot carries out the all
important function of photosynthesis and therefore production of food for
the plant.
IMAGE
Fig. 2.1 (c) The external morphology of a dicotyledonous flowering plant
showing the main organs: stem, nodes, internodes, foliage leaves, axillary
buds, shoot apex, a lateral branch, a flowering shoot, tap root, lateral roots
and root apex.
Specially modified organs of the shoot system, such as the stem and leaves
may perform special functions as explained below.
2.3.1.2.1 Specialized stems
We shall describe to you some examples of specialized stems as follows:
2.3.1.2 The stem tubers
A good example of stem tubers are the Irish/English potato plant (Solanum
tuberosum) tubers which store large quantities starch. This is an important
crop.
The Irish potato tuber is identified as an underground stem. In the practical
session you should make drawings of Irish potato tuber to show the
following features, as illustrated in Fig. 2.2 (a)
 Tiny, leaf scales
 Eyes or dormant axillary buds
IMAGE
Fig.2.2 (a) An Irish potato tuber (Solanum tuberosum) showing ‘eyes’ or
dormant auxiliary buds and tiny leaf scales.
Other forms of underground stems are rhizomes bulbs and corns. These also
store food stuffs.
Bulbs e.g. Onions
The bulb of the onion consists of a small stem which bears many fleshy
leaves. Axillary buds develop in the axils of the leaves as shown in fig.2.2.
IMAGE
Fig. 2.2 (b) A longitudinal section (L.S) of an onion bulb showing the
compact underground stem, fleshy leaves an adventitious roots.
2.3.1.2 Structures on the surface of stems
Various structures may occur on the stem as outlined below:
Hairs – the stem surface of a herbaceous plant may bear hairs, which are
outgrowths of epidermal cells.
Stipules: which are small projections at the junction of leaf petiole with the
stem.
Spines: which may be modified twigs or leaves.
Woody stems and twigs of trees and shrubs have structures as follows:
Lenticels: which are tiny pores/openings which facilitate an exchange of
gases between inner tissues of the stem and outside atmospheric air.
Leaf scars: which are the marks left when leaf stalks fall off from the stem or
twig.
Bundle scars: which are the broken ends of the vascular bundles.
Bark; as the woody stems grow and increase in diameter (girth) the smooth
outer bark splits. As a result the surface of the stem becomes rough, old bark
peel off in the course of time.
2.3.1.2.3 FOLIAGE LEAVES
Leaves of dicotyledonous plants
Types of leaves
There are three types of leaves, as follows:
 Simple leaves
 Compound leaves, and
 Complex leaves
Simple leaves
A typical simple leaf of a dicotyledonous plant consists of a leaf blade and a
leaf stalk (Petiole). In some plants the simple leaf may not have a leaf stalk
in which case it is said to be sessile leaf. The point of attachment of the leaf
to the stem is called the node as shown in Fig. 2.3 (a). some leaves have
stipules which are small projections at the juncture of the petiole and the
stem.
IMAGE
Fig. 2.3 (a) Showing a simple leaf with an entire margin
A simple leaf may have a serrated or lobed leaf blade, as in Fig. 2.3 (b) and
Fig. 2.3 (c) respectively.
IMAGE
Fig. 2.3 (b) Showing a simple leaf with a serrated margin e.g. Hibiscus
sp.
IMAGE
Fig. 2.3 (c) Showing a simple palmately lobed leaf e.g. Trimfeta sp.
The plastochron
The plastochron is the period between the successive initiation of leaves or
two pairs of leaves on the stem.
Modified leaves for special functions.
There are several types of modified leaves as follows:
 Spines and thorns
In the cactuses the leaves have become modified into thorns or spines. This
is an adaptation for the reduction of the rate of transpiration.
 Water storage leaves
Certain plants growing in the arid and semi-arid areas, such as the Aloe
have thick leaves containing mucilaginous colloidal materials which hold
water firmly.
 Tendrils
In some plants some of the leaves are modified into tendrils which are used
for climbing, e.g. the garden pea.
 Leaves of insectivorous/carnivorous plants.
Examples: The pitcher plant
The Venus fly – trap plant
The sundew (Drosera rotundifolia)
Other leaf types
- Succulent leaves – thick and fleshy
- Sclerophyllous foliage leaves
Produce more sugars by photosynthesis than are used in their own
construction
- Soft, flexible and edible.
- Thorns, prickles, spines – in cacti are modified leaves protect the
plant.
- Tendrils – leaves modified partly or completely as tendrils. Used to
help the plant in climbing by curling tightly around an object to
support weak stems.
- Reproductive leaves e.g.bryphyllum
Plantlets sprout on edge of leaves.
Floral leaves (bracts) specialized leaves found at the basis of flowers
or flower stacks e.g. Poisentia – brightly coloured floral bracts around
the small flowers.
Uses of leaves
- Shade
- Food – cabbages
- Spices – thyme, oregano
- Dyes – red from henna
- Cordage fibres for ropes ogave (sisal) hats, bags, thatching huts –
makuti.
- Oils – essential voldutile oils
- Medicinal e.g cocaine as anesthetic
- Tobacco
- Intoxicants – marijuana, miraa
- Beverages – tea.
These plants which grow in swampy habitats become deficient of certain
essential elements. They use specialized mechanism to trap small insects
which they digest in order to obtain the deficient elements or nutrients.
THE LEAVES OF MONOCOTYLEDONOUS PLANTS
These are characterized by having:
 A leaf sheath instead of a leaf stalk (petiole).
 Parallel venation in the leaf blade as shown in Fig. 2.4.
IMAGE
Fig. 2.4 A portion of the stem of the maize of the maize plant showing two
nodes, a leaf shealth around the internodes and parallel vein leaf.
Roots
The roots of a plant collectively form the root system.
Types of Roots
 The Tap Root system: dicotyledonous particularly/trees, shrub and
herbs have a tap root system, which bear secondary roots.
 The Fibbrous Root system: fibrous roots are particularly common.
 Monocotyledonous plants, particularly the grass family plants (cereals),
These roots are numerous and grow shallowly in the soil, see Fig.
IMAGE
Fig.2.5: Showing fibrous roots of a grass plant.
Functions of roots
There are two main functions of roots.
1. The anchorage of the plant in the soil, and
2. The absorption of water and dissolved minerals salts.
2.3.1.3 The various regions of a growing root
A growing root is charactersized by having the following regions:
(i)
The Root Cap.
This is an apical cap-like tissue whose main functions is to protect the
delicate meristematic region immediately behind it. the root cap produces
new cells to replace the cell worn out or destroyed as the root tip is bruised
by rocks and soils particle. Position of the rock cap is shown in Fig. 2.6.
IMAGE
Fig. 2.6 Diagram of a root showing the various regions
(ii)
The Root Apical Meristem
This region is enclosed by the root cap. It is a region in which new cells are
produced through division of the meristematic cells.
(iii)
The Region of Cell Elongation
This is the region behind the root apical mersitem. In this region all the cells
greatly elongate.
(iv)
The Root hair region
This is a region noted for bearing root hairs. These are epidermal cells which
grow laterally and serve for the absorption of water and dissolved mineral
salts.
(v)
The mature region
In this region the cells are mature and have undergone differentiation to
carry out various functions and no longer elongate.
Table 2. External differences between stems and roots of angiosperms
Stems
Roots
1. Stem of most plants are
Roots are positively geotropic
negatively geotropic (gravitopic)
grow upward
2. Stems have well developed nodes
and internodes
Roots do not have nodes and
internodes
3. Branches of stems arise externally Root branches or secondary roots
from axillary buds on the surface
arise internally from the pericycle.
of stems
4. The growing apices stems are
covered only by bud scales
5. The characteristic appendages of
stems are leaves and flowers.
The growing apices of roots are
covered by root caps.
The characteristic appendages of
roots are root hairs.
6. Vascular cambium produces same True pith absent, but may have pithsecondary xylem & phloem
like parenchyma in center.
Pith present
2.3.2. The external morphology of the Gymnosperm plant
gymnos – naked
sperma – seed
We have spent a considerable amount of time on the external morphology of
the angiosperms and we wish now to look at the gymnosperms.
Gymnosperms are seed plant whose seeds are born exposed and therefore
not contained in a fruit as in the case of the angiosperms.
The gymnosperm tree, such as the pine tree, is the sporophyte since it bears
spores.
2.3.2.1 The classification of Gymnosperms
The gymnosperms fall into three orders, as outlined below:
1. Order Cycadales (Cycads or Sago palms) Examples Cycas revoluta and
Encepharlatos.
These two examples are native to Australia and South Africa. They have
been introduced to Kenya in the course of time.
Slow growing plants of the tropics.
Morphological characteristics of Cycades.
(i)
They have unbranched stems
(ii)
The stems have large pith
(iii)
They have pinnate leaves.
(iv)
They have very huge female cones, particularly in the case
Encepharlatos.
Slow-growing plants of the tropics and sub-tropics.
Dioecious with massive male and female strobili born on different plants.
IMAGE
Fig. 2.6 A diagram of encepharlatos plant bearing a huge female cone.
2. Order Ginkgoales.
This consists of only one living genus i.e. Ginkgo and one species bibola,
making Ginkgo bibola. It is sometimes referred to as the maiden hair tree.
Ginkgo bibola tree grows to a sizeable tree of up to 80ft. in height. The stem
is woody. The leaves are fan-like in shape. A female plant has several
strobili borne at the summit of short stalks, Fig. 2.7 (a) A male tree bears
several male strobili, Fig. 2.7 (b) Thus Ginkgo bibola tree is dioecious (male
and female reproductive organs borne on separate trees).
IMAGE
Fig. 2.7 (a) Showing female strobili on a leafy shoot of Ginkgo bibola
IMAGE
Fig. 2.7 (b) Showing male strobili on a leafy shoot of Ginkgo bibola
3. Order Coniferales
This is the most economically important order, with large trees such as:
The pine tree (Pinus patula)
The cedar tree (Cedrus sp.)
The cypress tree (Cupressus sp.)
The podo tree (Podocarpus sp.)
The coniferous trees are an important source of:
- Timber for building construction
- Timber for furniture making
- As well as for firewood
Characteristics of coniferales
1. They have needle – shaped leaves
2. The leaves are evergreen
3. They are either trees or shrubs. There are no herbs.
4. They are monoecious, i.e. male and female cones are borne on the same
plant (although some are dioecious with male and female strobili on
different plants.
5. The leaves are simple and need-like.
4.gnetales
2.3.2.2 Characteristics of Gymnosperms.
1. They have seed borne on ovuliferous scales and exposed (there is no fruit
wall).
2. They have tru roots stems and leaves.
3. The sporophyte plant is a big tree or shrub there are no herbs.
4. Water is not required as a medium of transport of the male gametes
(Spermatozoa) in achieving fertilization.
5. Have tracheid xylem elements instead xylem vessels found in
angiosperm.
6. The phloem has sieve tubes but have no companion cells.
7. They have starminate (male) cones and ovulate (female) cones on
separate plants, i.e. they are dioecious, while others are monoecious.
2.3.2.3 THE REPRODUCTIVE STRUCTURES
Male and Female cones of the pine.
The pine tree e.g. Pinus patula is one of the economically important
coniferous trees. It bears male and female cones on the same plant.
The female cones bears woody scales each of which has 2 ovules at the early
stages. After fertilization 2 winged seeds are formed. When the cones dry up
the scales open up and the 2 winged seeds may be dispersed by the wind,
Fig. 2.8
IMAGE
Fig. 2.8 showing a small portion of a female cone with opened up female
scales bearing 2 winged seeds.
2.4 Questions
1. Give an illustrated account of the external morphology of a young bean
seedling.
2. Give a brief description of two types of specialized stems. Illustrates your
answer with labeled diagrams.
2.5 Activity
1. Make a study to determine he phyllotaxy of five identified
dicotyledonous plants from you local area. Collect leafy shoots of the
plants selected, press them and mount them on paper. Identify the plants
with a common name and a botanical name (Genus and species), where
possible.
2. Make a collection of plants showing or having
- a tap root system
- a fibrous root system
Press the roots then mount on paper and label the specimens
3. Briefly describe two main features that distinguish the gymnosperms
from the angiosperms.
2.3.2.4 Main differences between Gymnosperms and Angiosperms
1. The gymnosperms have seeds borne (exposed) on woody ovuliferous
scales unlike in the case of the seeds of angiosperms that are found in
a fruit, confined or covered by a fruit wall.
2. The xylem of gymnosperms has tracheids while xylems of
angiosperms has vessels. Both types of elements are for strengthening
the plant.
3. The xylem vessels of angiosperms have open end walls, which
facilates the conduction of water up the plant.the tracheids of
gymnosperms have no end wall perforations.
4. There are companion cells associated with phoem sieve tubes in
angiosperms, but no companion cells are to be found in gymnosperms.
5. Most gymnosperms, particularly among he conifers have needle
shaped evergreen leaves unlike the leaves of angiosperms.
2.6 SUMMARY
In lesson 2 we have looked at the external morphology of the seed plant; i.e.
the angiosperms and the gymnosperms. This has been done with regard to
the shoot system and the root system.
For shoot system of the angiosperms the following have been highlighted:
- Structures on the surface of stem.
- Special stems e.g. Tubers, rhizomes and bulbs.
- Leaves: simple, compound and complex leaf venation. Leaf
arrangement and phyllotax (assignment)
For the roots of Angiosperms the following was highlighted.
- Types of root systems.
Tap root, fibrous and special roots,
- The various regions of the root.
For the Gymnosperms the following was highlighted
- The classification of the gymnosperms,
- Characteristics of gymnosperms
- (The reproductive structures male and female cones of the pine)
- Leaf morphology.
The main differences between gymnosperms and angiosperms was also
highlighted.
2.7 REFERENCES
 Esau, K. 1960. Anatomy of seed plants.
 Esau, K. Plant Anatomy
 Fahn, A. 1974 Plant Anatomy
 Foster, A. S. Comparative Morphology of Vascular plants.
 Fuller, H.J. and O. Tippo. 1949, College Botany.
 Steeves, T.A. 1989, Patterns in plant development.
 Weier, T.E., C.R. Stocking and M. G. Barbour 1974. Botany. An
introduction to plant Biology.
LECTURE THREE
3.0 MERISTEMS AND THEIR ROLE IN THE GROWTH OF
PLANTS
3.1 INTRODUCTION
In lesson 1 and 2 we mainly described the morphology of plants without going
into how plant cells are formed. In unit 3 we wish to introduce to you the study
of the meristems in plants.
In the early stages of the development of the embryo of a plant all the cells are
able to divide. But later the further development cell division becomes
restricted to particular parts of the plant. These are the parts with cells that
divide and constitute meristematic tissues or simply meristems.
3.2 OBJECTIVES
By the end of this unit you will be able to:
 Define what a meristem is.
 Describe the main features of a plant cell
 Describe the different types of meristems
 Describe the characteristics of metistematic cells.
 Distinguish the different theories concerning the shoot and root apical
organization.
 (Explain what “totipotency” is)
 Explain the difference between “differentiations” and “de-differentiation”
 Describe the different tissues of the stem and root which result from the
activities of the meristems.
3.3 DEFINITION
meristems are the regions of a plant whose cells keep on dividing i.e regions
in which undifferentiated cells divide.
3.4 THE PLANT CELL
Before going into the study of the meristematic tissues of plants we would
like to describe the main structural features of the plants cell.
MISSING PAGES
3.6 THE CLASSIFCATION OF MERISTEMS.
The classification of the meristems is based on several criteria. The most
important of these are:
3.6.1 Their position or location in the plant body
These include:
(i)
The apical meristems of the shoot and the root.
These are also called the terminal meristems which occur at the growing
apices of the shoots and the roots.
The apical meristem of the shoot is more complex that the apical meristem
of the root because it is involved in the initiation of leaf primordial and the
lateral branches of the stem. In addition there is no structure equivalent to
the root cap found at the shoot apex.
The promeristem
The distal part of the apical meristem is referred as the promeristem, in
which literally all the cells divide. In the peripheral region the cells remain
meristematic, and give rise to:
 The epidermis
 The cortex
 The leaf primordial
 The procambium which in turn give rise to the vascular tissue, as shown
in Fig. 3.2.
IMAGE
Fig. 3.2 Diagram of a longitudinal section of a dicotyledon shoot apex
showing the promeristem region.
Theories concerning the shoot and the root apical organization.
There are three theories which have been proposed to explain the shoot and
the root apical organization in plants. These are:
a) The shoot Apical Cell Theory
This theory was proposed by Nageli in 1858. it postulated the existence of a
single cell at shoot apex of pteridophyte called Equisetum (horse tail). The
single apical cell is also found in other pteridophytes such as the aquatic fern
Marsilea.
The apical cell is shaped like an inverted pyramid or a tetrahedron as shown
in Fig. 3.3, The apical cell cut off cells along three planes.
IMAGE
Fig. 3.3 a diagram of a longitudinal section of the shoot apex of a fern
showing the apical single cell.
b) The Tunica Corpus theory
This theory was proposed in 1924. the apices can be divided into two
regions of dividing cells, i.e. The tunica on the outside and the corpus on the
inside as shown in Fig. 3.4.
IMAGE
Fig. 3.4 A diagram of longitudinal section of shoot apex of a
dicotyledonous plant showing a 2-layered tunica and the corpus.
The tunica consists of one or two layers of cells. It has been shown that the
cells of the tunica divided anitclinally i.e., approximately at right angles to
the dome, on the other cells in the corpus divide periclinally i.e,
approximately in a plane parallel to the dome.
The tunica corpus theory of the shoot and the root apical organization has
proved more acceptable than the histogen theory.
c) The histogen theory.
This theory was proposed by Hanstein in 1870. the theory postulated that the
shoot and root apices consisted of 3-super imposed cell layers (or histogens)
which through cell division gave rise to specific regions of the plant body.
The 3 layers are shown in Fig. 3.5.
IMAGE
Fig. 3.5 A diagram of a longitudinal section of a shoot apex showing the 3
layers or histogens i.e. The dermatogen, periblem and plerome.
The dermatogen
This is the outermost layer of cell whose division gives rise to the epidermis.
The periblem
This is the region occurring between the dermatogen and the plerome. Cells
of the periblem divide to give rise to the cortex of stem and the mesophyll
cells of the leaf.
Fig. 3.6 shows the three layers of cells in the case of root apex.
As in the case of shoot apex, the dermatogen of the root gives rise to the
epidermis. The periblem gives rise to the cortex. But the plerome gives rise
to vascular system and the pith.
IMAGE
Fig.3.6 A diagram of a longitudinal section of root apex showing the
dermatogen, periblem, plerome and the root cap.
(ii)
The lateral meristems
There are three types of lateral meristems:
The fascicular (vascular) cambium
This is found in the vascular bundles, occurring between the phloem and the
xylem, as in Fig. 3.7 (a)
IMAGE
(a) Primary tissues
IMAGE
(b) Portion of stem showing cork cambium and interfasicular cabium.
Fig. 3.7 A diagram of a transverse section of a dicotyledonous stem showing
fascicular cambium (a) and interfascicular cambium (b) as well as the
formation of cork (Phellem) from cork cambium (phellogen).
The interfascular cambium
This is the cambium formed during the process of secondary thickening of a
dicotyledonous stem. Some of the parenchyina cells in the medullary ray
region between the vascular bundles undergo de-differentiation and become
meristmematic. The interfascicular cambium links up with the fascicular
cambium to form a continuous ring of cambium. This cuts off cells on the
inside which become xylem, i.e. secondary xylem. This results in an increase
in the diameter of the stem (an increase in girth). In big trees annul rings of
xylem/wood form. This constitutes what is known as secondary growth.
Cork cambium (or phellogen)
Cork cambium or phellogen arises fro the outer cortex cells of shrubs and
trees through the process of de-differentiation to form a meristematic ring of
cells. These cork cambium cells divide periodically. The outer daughter cells
differentiate to become cork cells (or phellem) Next round of cell division
cuts off cells on the inside which differentiate to form the phelloderm as
shown in Fig. 3.7.
The cork so formed is impervious to water and is therefore useful to the
plant.
(iii)
The intercalary meristems
This type of meristems is found in the form of a band at the region where the
leaf sheath joins the stem in a monocotyledonous plant, particularly among
the members of family Graminae, Fig. 3.8 This meristem contributes to the
elongation of the internoded.
IMAGE
Fig. 3.8 a diagram showing the intercalry meristem of a Graminae plant
such as maize or grass.
3.6.2 The stage of the development of the plant which the meristems
appear.
On the above basis the meristems fall into two categories.
 The primary meristems: these are the meristems which develop directly
from the embryonic cells, e.g. the fascicular cambium.
 The secondary Meristems: these are formed when cells of the already
differentiated tissues de-differentiate and become capable of cell
division. Examples are cork cambium (Phellogen) and the
interfascicular cambium already referred before.
3.7 Questions
1. Briefly describe the main structural features of a plant cell. Illustrate you
answer with a labeled diagram.
2. What are the characteristics of the meristematic cells?
3.8 Activity
Collect from the field shoot apices of 3 different monotyledonous plants and 3
different dicotyledonous plants. Cut longitudinal sections of these apices and
examine them with a hand lens and also under the microscope (medium power).
Identify and draw the main features.
3.9 Summary
In this unit we have looked at:
 The main structural features of a typical plant cell.
 Different types of meristems and how they function.
 The theories concerning plant shoot apical organization.
 Totipotency, differentiation and de-differentiation and their significance.
3.10 References
 Esau, K. 1960. Anatomy of seed plants (1962 edition)
 Esau, K. Plant Anatomy
 Fahn, A. 1974 Plant Anatomy
 Foster, A. S. Comparative Morphology of Vascular plants.
 Fuller, H.J. and O. Tippo. 1949, College Botany.
 Steeves, T.A. 1989, Patterns in plant development.
 Weier, T.E., C.R. Stocking and M. G. Barbour 1974. Botany. An
introduction to plant Biology.
LECTURE FOUR
THE MAIN TYPES OF CELLS AND TISSUES FOUND IN PLANTS
4.1 Introduction
In the previous lesson we looked at meristems and the way they divide to give
new cells. In this lesson we look at the different types of cells and the tissues
they form. This is useful because as one studies the anatomy of plant organs
such as the stems, roots, leaves and flowers, one constantly comes across one or
the other of these cell types and tissues. We shall also find out that these tissues
carry out specific functions.
4.2 Objectives
By the end of this unit you should be able to:
 Describe the characteristics of the palisade, collenchyma, sclerenchyma
(sclereids and fibres), epidermis, cork, sieve tubes and companion cells.
 Explain the tissues that these cells and elements give rise to and their main
functions.
4.3 The main types of plant cells.
The following are the main types of cells in plants.
4.3.1 Parenchyma cells.
The parenchyma cell is structurally the simplest cell in a plant Fig 4.1 (a).
the parenchyma cells are characteristically isodiametric, with thin cell walls
and they are living cell with active protoplasts. The cell walls are composed
of cellulose. Parenchyma cells occur in both the simple and the complex
tissues of plants e.g. in the stem pith (simple tissue) and xylem (complex
tissue).
The parenchyma cells play the role of water storage, photosynthesis as in the
case of leaf mesophyll and the storage of food materials such as sugars and
proteins. They are capable of differentiating and becoming meristematic
whereby they divide repeatedly resulting to wound healing.
IMAGE
Fig. 4.1 (a) T/S parenchyma
IMAGE
Fig. 4.1 (b) TS Collenchyma
4.3.2 Collenchyma cells.
Collenchyma cells are living cells which are characterized by uneven
thickening of the cell walls. The cells tend to be more thickened at the
corners. Collenchyma cells occur in the stems cortex of herbaceous and are
positioned just below the epidermis; Fig. 4.1 (b) Collenchyma cells are
absent from the root of monocotyledons except in some cases. The
collenchyma cells provide support, particularly to herbaceous plants. The
uneven thickening of the cell walls is due to uneven deposition of cellulose,
hemicellulose and pectic substances. The mature collenchyma form a strong
flexible tissue.
4.3.3 Sclerenchyma cells
There are two types of sclerenchyma cells:
The sclereids.
The sclereids are characterized by having thickened lignified cell walls
which may have pits. At maturity the sclereids lose their protoplast and
therefore die off. The sclereids are dimensionally isodiametric,slightly
elongated or irregularly shaped Fig. 4.2. The main function of sclereids is to
provide support.
IMAGE
Fig. 4.2 Sclereid
The other type of the sclerenchyma cells are the fibres. The fibres are also
thick walled like the sclereids, but differ from the sclereids in that they are
slender and much elongated, and posses pits Fig. 4.3 (a,b). at maturity the
fibres just like the sclereids are dead wood fibres. They have heavier cell
wall thickening with greater lignification.
IMAGE
IMAGE
Fig. 4.3 (b) L.S. of a wood fiber
4.3.4. Epidemal cells.
The epidermis is normally made up of a single layer of cells and it is the
outermost tissue in the plant at the primary stage of growth. The outer wall
of the epidermal cells is much thickened by the deposition of cutin to form a
cuticle Fig. 4.4. this chemical substance, cutin is a waxy water proof
substance secreted by the protoplasm of the epidermal cells and serves to
reduce cuticular transpiration. The epidermal cells, with the exception of the
guard cell have no chloroplasts. The other role of the epidermal cells is to
provide protection against mechanical injury, excess heat or cold and attack
by parasitic fungi and bacteria. Apart from the guard cells other specialized
epidermal cells include those that become trichomes and root hairs.
IMAGE
Fig. 4.4 TS Leaf.
4.3.5. Xylem tracheids and vessels.
The xylem tracheids and vessels are cells which have very much thickened
walls for the purpose of providing mechanical strength to the plant as well as
water conduction. Te characteristics of the tracheids have already been dealt
with in lesson 1, Fig. 1.4 (b) in view of this, in the present lesson we shall
only indicate the characteristics of xylem vessels, which are only found in
the angiosperms.
Xylem vessels.
In the evolution of plants it is thought that the tracheid which is found in the
pteridophytes and the gymnosperms gave rise to the xylem vessel. This
entailed a slight shortening, and widening as well as the perforation of the
end walls. So the xylem vessels are characterized by having a greatly
thickened cells wall and perforated end walls.
Xylem vessels which have undergone secondary thickening show different
ways of thickening. In a longitudinal section of the stem of a dicotyledonous
plant the following are the forms of secondary thickening that might be
observed as in Fig. 4.5.
(i)
Annular thickening – the first to occur, Fig 4.5 (a)
(ii)
Spiral or helical thickening which in the order of their formation
(ontogenetically) follow annular thickening, Fig. 4.5 (b).
These two types of thickening i.e. Annular and spiral thickening, are mainly
found in the protoxylem. In the later formed xylem vessels i.e. the
metaxylem the vessels are much larger and bands of thickening are much
wider giving a ladder like pattern of thickening called the scalariform
thickening. Fig. 4.5 (c) Xylem vessels formed later during secondary
thickening show a reticulate type of thickening. Fig 4.5 (d).
IMAGE
IMAGE
Xylem vessels, like the tracheids have pits in their thickened cell walls.
There are two types of pits, simple pits and bordered pits, fig. 4.6 c, d. a
simple pit pair has primary wall and secondary wall, and a pit aperture. The
area of the pits is uniform throughout its depth Fig. 4.6 (a). in a bordered pit
the secondary wall rises around the pit. The membrane is thicker at the
center than at the ends, fig. 4.6 (b). The area of the pit is unequal, being
broader towards the original wall and narrower towards the original cavity of
the cell.
IMAGE
IMAGE
4.3.6 Phloem sieve tubes and companion cells.
Phloem conducts food from leaves to all parts of the plant. It is made up of
sieve cells in the lower vascular plants and sieve tubes and companion cells
in angiosperms Fig. 4.7. Sieve tubes are made up of sieve elements
connected at the ends with perforated characteristic areas called sieve plates.
The pores are surrounded by a colourless substance called callus. The sieve
cells of lower vascular plants can quickly accumulate callus to block pores.
During an active season like spring in temperature climates, the callus
dissolves. Ferns and conifers have sieve areas scattered all over cell wall.
Sieve tube cell walls are thin and are made up of cellulose. Sieve tubes are
associated with parenchymatous cells called companion cells. Companion
cells have a nucleus and cytoplasm and each is connected to the sieve tube
through a pore.
IMAGE
Fig. 4.7 LS of a sieve tube and companion cells.
4.3.7 Cork cells
In lesson three we came across the type of meristem called cork cambium or
phellogen which we saw produces cork cells on the outerside.
The following are the characteristics of cork cells:
 Their cell walls are greatly thickened with cellulose, and
hemicelluloses.
 These cell walls are also heavily suberized through the deposition of a
substance known as suberin.
 The cells walls are also lignified by the deposition of a substance called
lignin.
 Cork cells, particularly as a result of being heavily suberized are
impervious to water, and therefore check excessive water loss. Cork
forms the outer bark of stems and roots of woody plants. These are
plants which have undergone secondary thickening.
4.4 Types of plant Tissues.
A tissue is a group of cells with common origin, structure and function.
Permanent plant tissues may be classified into two types as follows:
 Simple Tissues
Simple tissues comprise of one type of cells e.g. pith which consists of
parenchyma cells only. Thus simple tissue is homogeneous in its
composition.
 Complex tissues
Complex tissues are made up of several different types of cells e.g., xylem.
In other words a complex tissue is heterogenous in its composition.
We shall give more details about each one of the above two types of tissues:
4.4.1 Types of simple tissues
There are several types of simple tissues, as follows:
The epidermis
This is made up of the epidermal cells, and as noted earlier this is a
protective tissue
The parenchyma tissue
This is made of parenchyma cells and is characteristically found occurring in
the cortex, pith and medullary rays of the dicotyledon stem.
The parenchyma tissue also occurs in the cortex of the stems of the
monocotyledonous plants. Parenchyma is also found in the cortex of the
root.
The collenchyma tissue.
This is found in many dicotyledonous stems, just below the epidermis,
forming part of the cortex. It provides the plant with mechanical strength.
The sclerenchyma tissue.
This tissue is made up of two types of elements, i.e. sclereids and fibres.
Sclereids.
Sclereids has been shown to occur in the pith of gymnosperms such as
Podocarpus. Sclereids or sclerotic cells also occur among leaf mesophyll,
and in some fruits, and seed coats of leguminous seeds. Sclereids cause the
hardening of the seed coats.
Fibres.
Fibres have been shown to completely enclose each vascular bundle
resulting in a bundle strand. In the dicotyledonous plant fibres are
particularly found in the vascular tissue. In the flax plant (Linum
usitatissimum) there is a preponderous presence of phloem fibres bordering
on the phloem (between the phloem and the cortex).
Fibres are economically important in the production of ropes and cords.
Another plant that produces phloem fibres is jute (Corchorus capsularis).
4.4.2 Types of complex Tissues
Complex tissues are made up of more than one type of cells which work as a
unit. They are two kinds: xylem and phloem, both of which are conducting
and strengthening tissues of plant.
We shall now give some details of the composition, structure, location and
functions of these two complex tissues.
Xylem
The xylem is a major component of the vascular bundle of the stem of both
dicotyledonous and monocotyledonous plants. In a collateral vascular bundle
the xylem occurs towards the pith separated from the phloem by the vascular
cambium. Fig. 4.8 (a).
Some plants have what are known as the bicollateral vascular bundles. An
example of such plants is the herbaceous of cucumber, A bicacollateral
vascular bundle Fig. 4.8 (b) has two sets of phloem, one on the outside
towards the cortex and the other on the inside towards the pith.
IMAGE
Phloem
Phloem is composed of sieve tubes, companion cells, phloem parenchyma
and phloem fibres. The primary function of this complex tissue is
conducting of food to growing regions and storage organs. Phloem cells are
living as opposed to the xylem tracheids and vessels which are dead. As
explained earlier in this lesson, the composition of the phloem elements is
variable between the lower vascular plants and angiosperms.
4.5 Question
What structural features and call specialization are associated with basic
functions of the complex tissues in angiosperms?
4.6 Activity
Apart from water and food conducting tissues, secretory tissues are also
important in plants. Read and write notes on the various types of secretory
structures, their functions in plant and any economic importance to man.
4.7 Summary
There are two types of tissues in plants, simple and complex.
Simple tissues include:
 Parenchyma cells. These are thin walled cells which perform various
functions, e.g. food storage and photosynthesis. They are capable of
differentiating (they can change activities).
 Collenchyma cells. These are thick walled living cells thickened at the
corners with cellulose and pectin substances, they give mechanical support
to the plant.
 Sclerenchyma cells. These are lignified cells which provide mechanical
support.
Complex tissues include:
Xylem: these include tracheids and vessels composed of dead cells and are used
for transport of water. Phloem consists of living cells, sieve cells, sieve tubes
and companion cells for conduction of food from leaves to all parts of the plant.
4.8 References
 Esau, K. 1977. Anatomy of seed plants 2nd ed. New York. Wiley.
 Fahn, A. 1982 Plant Anatomy. 3rd ed. New York. Pergamon press.
 Rost, T. L. et al, 1984. A brief introduction to plant Biology 2nd ed. New
York. Wiley.
 Dutta, A.C. 1979. Botany for degree students 5th ed. Calcutta. Oxford
University press.