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DEPARTMENT OF BIOLOGICAL SCIENCES
PLANT FORM AND FUNCTION (HBZB201)
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PLANT FORM AND FUNCTION ()
PLANT FORM AND FUNCTION introduces the student to morphology and anatomy in relation to
physiological processes (in particular acquisition of water and ions, photosynthesis, growth and
development, ecology and survival), especially under stressed conditions. The student is guided through
the course by structured lectures and discussions preceding relevant practical classes in the laboratory or
in the field to achieve competence in technical skills. The course focuses on functional morphology and
anatomy of organs. It includes the following topics.
Growth form and morphology of plants
Modified organs and their functional aspects
Cells and tissues and their development and organisation
Root primary structure and development
Stem primary structure and development
Secondary growth structure in eudicots
Leaf form, structure and adaptation
Flower structure, development and diversity
Reproductive anatomy
Fruit structure, development and classification
Seed development, structure and germination
Seedling morphology
COURSE OBJECTIVES
The course is intended to provide necessary background to modules in plant sciences, especially Systematic
Botany, Evolutionary Botany, Applied Botany, Forensic Botany, Pollination and Reproductive
Biology, Plant Ecology and Plant Eco-physiology. At the close of the course, students are expected to be
able to:
 understand the structure of plants at cell, tissue and organ and whole organism levels
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recognise and be able to describe features of plant anatomy
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relate structure to function and adaptation
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use microscopy to investigate cell and tissue features of plants
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critically read literature in the field of plant anatomy, morphology and functional
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reflect in written form on their mastery of topics covered during the course
CONTINUOUS ASSESSMENT
A practical course assessment (PCA) mark will be drawn from selected practicals. Students will be notified
during the course of the practical (attendance to all practicals is obligatory) whether a particular practical is
under assessment or not. A theory course assessment mark (TCA) will be drawn from written assignments
and tests. All written assignments must be submitted in time.
Essays should be well researched. Ample time is given for assignments. There is, therefore, no justification
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for preparing an assignment a night before the morning deadline (marking of hurriedly prepared work is
irritating!). Copying from other students is unpardonable and attracts a penalty. Guidelines to essay writing
are given at Part 1 (the door is open for any consultation). Assignments handed late will not be marked.
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PRACTICAL 1
FORM AND MODIFIED ORGANS
INTRODUCTION
Angiosperms and gymnosperms (higher tracheophytes) include some of the most complex and
diversified plants. Angiosperms by far represent the dominant extant group, and are more varied
and complex than gymnosperms
Approximately 250 000 species of angiosperms are known to science. An estimated 200 000 of
these are eudicotyledons, and 50 000 are monocotyledons. Angiosperms, especially those from the
tropics, show remarkable diversity in habit, morphology, anatomy and physiology. They are of
outstanding economic importance, being a primary source of food, many durable hardwoods and
drugs.
The National Botanic Garden contains a large assemblage of plant species from different
ecosystems of tropical southern Africa. It thus provides a unique opportunity for the study of
variation among plants. Close to 2 000 species grow naturally or are in cultivation in the Garden.
This huge collection includes aquatic species as well as species from the driest habitats of southern
tropical Africa, Asia, South America and Australia.
OBJECTIVES
1. To study variation in growth form and habit among flowering plants
2. To study morphological variation among aquatic, mesophytic and xerophytic plant groups
3. To study form modification among plant species
4. To relate form to function to adaptation
PROCEDURE
Plants evolved varied growth habits adapted to different environments. They grow as annuals,
biennials, short-lived perennials or long-lived perennials. Growth is either monopodial or
sympodial. Among typical savannah species, monopodial growth tends to be dominant in early
growth but is later overtaken by sympodial growth.
1. From NAMED examples among terrestrial species:
i)
Which features characterise annual and perennial habit?
ii)
Which features characterise dominant monopodial and sympodial growths?
2. Some features are characteristic of aquatic plants.
a. Observe the general features of aquatic plants?
b. Study some submerged macrophytes.
i.
Based on NAMED examples, shortly describe morphological characters of the stem
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and leaves of submerged macrophytes.
Based on NAMED examples, shortly describe morphological characters of the
floating leaf.
3. Plants from arid environments are characterised by modified organs associated with water
storage or reduced water loss.
a. Comment on parallels in body form between two arid genera, Cactus and Euphorbia
(Note that the two genera have no common ancestry).
b. Briefly comment on leaf form of the genus Acacia.
c. Suggest the form of leaf modification in genus Aloe and comment on its significance.
4. Examine the aerial roots in genera Ficus and Pandanus. Explain the functional significance
of this type of root?
5. Examine thorns and leaf prickles in some NAMED species. Comment on their evolutionary
origin and functional significance.
6. From the Tropical Rain Forest area,
a) Study the habit of two genera, Musa and Strelitzia.
i)
Comment on the leaf form. Examine the “stem” and explain why it is considered a
false stem?
b) Study the external leaf structure of any three NAMED species.
i)
Make sketches of the leaves. Identify the distinctive features of the leaves and
explain their functional significance.
Back at the lab, complete your practical write-up and hand it for marking.
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PRACTICAL 2
PLANT GROSS FORM
INTRODUCTION
Angiosperms generally produce true roots, stems, leaves, flowers and fruits. The plant body thus
consists of two basic parts: the root system and the shoot system. The root system is commonly
below ground, and often consists of a taproot and lateral branch roots. Sometimes (depending
on the species) there is no taproot, and the root system is adventitious. The root system may be
modified into various functional structures (bulbs, nodules, etc.). The shoot system is often above
ground (of course with some exceptions). It consists of a stem, together with leaves, flowers and
fruits which are commonly attached to the stem at the nodes. In between any two nodes are
internodes. The stem may be modified into various functional structures. At the tip of the plant
is the terminal bud which contains the actively dividing meristems. The leaf may be attached to
the stem through a petiole (commonly eudicotyledons) or a leaf sheath (monocotyledons).
Leaves are variously arranged on the stem. The blade of the leaf may be divided into leaflets
(compound leaf), or it may be undivided (simple leaf). At the base of the petiole, small lateral
outgrowths (stipules) may be found. Between the stem and the petiole (leaf axial) lies the
axillary bud.
OBJECTIVES
1. To study shoot and root morphology
2. To compare features of dicotyledons and monocotyledons
PROCEEDURE
You are provided with material of eudicot and monocot plants.
1. Study the shoot system from the provided material.
a) Make sketch diagrams of the stem, and (where present) label the following structures: stipule,
axillary bud, terminal bud, node, internode, leaf scar, vascular bundle scar and lenticels.
b) Make a sketch diagram of the leaf, and label the following structures: leaf margin, lamina,
tip, midrib, lateral vein, and (where present) petiole, pulvinus, rachis, pinna, auricle and
ligule.
c) Which major stem and leaf morphological characters distinguish eudicotyledons from
monocotyledons?
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d) State the functional significance of a compound leaf in a xerophytic environment?
e) Examine the various types of modified stems on display:
i.
Potato tuber (a fleshy underground stem). The potato on display shows some “eyes”.
State the functional role of the “eye”?
ii.
Onion bulb. Explain why the bulb is not a true stem.
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iii.
iv.
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Corm (a short, thick stem that grows vertically underground). Explain how this
structure differs from a stem bulb. State which structures are found in the corm, but
not in the bulb. State the significance of these structures.
Rhizome (a horizontal underground stem) - State two functions associated with this
structure.
Stolon (a horizontal, above ground stem) – Explain how this structure differs from a
rhizome. State its functional significance.
2. Study the root system from the provided material.
Characterise the root system in each case and relate it to environmental adaptation.
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PRACTICAL 3
TISSUES OF THE PLANT BODY
INTRODUCTION
The plant includes three major organ systems (roots, stems and leaves) that function in concert to
maintain the supply of resources to all parts of the plant body. To allow for growth, new cells are
added at specific locations (meristems) throughout the plant body. These new cells are initially
unspecialised, but then mature into different tissue and cell types. Each organ is composed of three
different tissue systems (dermal, ground and vascular). The following are some of the major
tissues of the angiosperm plant: meristem, parenchyma, colenchyma, sclerenchyma, dermal and
vascular. Compared to gymnosperms, angiosperms have much more complex tissue structures.
Also, among angiosperms are considerable differences in tissue organisation between
eudicotyledons and monocotyledons.
Variation in structure and organisation of tissues has taxonomic and evolutionary significance.
Considerable variation in tissue organisation is also found among different organs of the same
plant. This variation is best studied at primary growth stage.
OBJECTIVES
1. To study structure and organisation of tissues in stems and roots of angiosperms at primary
growth stage
2. To compare and contrast root anatomy in monocotyledons and eudicotyledons at primary
growth stage
3. To compare and contrast stem anatomy in eudicotyledons and monocotyledons at primary
growth stage
PROCEDURE
Roots and stems arise from apical meristems. The meristem of the root, however, does not occur at
the extreme tip, but just behind it. The tip of a root is covered by a thimble-like structure, the root
cap. For several millimetres behind the root cap, the root is smooth, representing the zone of
elongation - a region of undifferentiated tissue. Root hairs are found immediately behind the zone
of elongation.
A. Cut a thin cross-section of a piece of a petiole of a young bean leaf that has been kept in dye
overnight. Place it in a watch glass and observe it using a dissecting microscope. Draw the
cross section, and label the dermal, ground and vascular tissue systems.
B. Using a dissecting blade, carefully cut a paper-thin cross section of the petiole material and
make a wet mount. Using the compound microscope, identify the vascular, collenchyma
(with unevenly-thickened primary cell walls), parenchyma and sclerenchyma (xylem vessel
elements with evenly-thickened lignaceous secondary cell walls) tissues. Draw and label a
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few cells of each tissue type.
C. Eudicot stem structure
Eudicot stems have a distinct ring arrangement of vascular bundles. In the Phaceolus
vulgaris (the common bean) stem, the ground tissue system is separated into two areas, the
pith and cortex (towards the outside, between the epidermis and the vascular bundles).
Closely study the prepared slide of the bean stem cross-section.
i)
ii)
Make a Low Power diagram of a whole section to show the distribution of tissues.
Make a High Power drawing of a representative section and label the following.
Epidermis
Cortex with EXODERMIS (single layer of cells beneath the epidermis), PARENCHYMA
(note intercellular spaces and starch grains) and ENDODERMIS (note the thickened
walls)
Vascular system comprising of PERICYCLE (a single layer of cells); XYLEM (triarch
or tetrarch, noting the smaller, outer protoxylem vessels and the larger, inner
metaxylem vessels); PHLOEM (patches of cells alternating with xylem);
PARENCHYMA (between xylem and phloem).
Study the prepared slide of a Cucurbita stem. Locate the xylem (with lignified secondary walls that
stain red). Identify, draw and label protoxylem and metaxylem vessel elements. Next, locate the
phloem. Identify sieve-tube member with a porous sieve plate and the associated companion cells.
Draw and label these tissues.
D. The monocotyledon primary root
T/S of Zea mays (MAIZE)
a) Make a Low Power diagram of a whole section to show the distribution of tissues.
b) Make a High Power drawing of a representative section. Note and label the following:
i)
epidermis ( a single layer of cells surrounding the entire root);
ii)
cortex (the ground tissue, composed of several cell types whose primary function is
that of support, storage, secretion, and a variety of other functions):
EXODERMIS (several layers below the epidermis);
PARENCHYMA (bulk of cortex)
ENDODERMIS (with U-shaped thickening on radial walls, and at intervals
with some passage cells)
ii)
vascular system, comprising:
PERICYCLE
XYLEM (polyarch, note the protoxylem and metaxylem)
PHLOEM (alternating with xylem)
PITH parenchymatous cells (rest of the cells in between the vascular
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bundles)
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E. Comparing the T/S of a eudicot stem to that of a monocot
1. Make a Low Power diagram and a High Power drawing of a representative section of the stem in
each case.
2. Draw up a comparison table between monocot and eudicot roots and stems, emphasising the
diagnostic characters.
F. Anomalous conditions in eudicot and monocot stems
1. Make a Low Power diagram and a High Power drawing of a representative section of the stem of
Oryza (a monocotyledon). In which features does the structure differ from that of maize?
2. Make a Low Power diagram and a High Power drawing of a representative section of the stem of
Cucurbita (a dicotyledon). In which features does the structure differ from that of Phaseolus?
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PRACTICAL 4
LEAF STRUCTURE
INTRODUCTION
Leaves are the primary photosynthetic organs of the plant, although occasionally stems, roots, or
floral parts may assume photosynthetic functions. The functional efficiency of leaves is directly
related to external form (size, shape, arrangement, orientation, etc.) and internal structure
(anatomy). Thus, leaves may be furnished with a large surface area and an optimal orientation for
maximum capture of light, numerous intercellular spaces for efficient exchange of gases, and large
vascular supply for the maintenance of optimal moisture levels and efficient translocation of
photosynthetic products. The upper and lower epidermis may be covered with a waxy cuticle to
minimise water loss, with stomata providing the only pathway for gases. Leaves of eudicotyledons
are usually dorsiventral (upper and lower mesophyll layers differentiated) and divided into an upper
palisade parenchyma and lower spongy parenchyma.
OBJECTIVES
1. To compare and contrast leaf anatomy between ferns (pteridophytes) and higher plants
2. To compare and contrast leaf anatomy between eudicots and monocots
3. To compare and contrast leaf anatomy among angiosperms from different habitats
PROCEDURE
1. Make High Power drawings of representative sections of a pteridophyte leaf specimen. How
does the leaf structure differ from that of the angiosperm material provided?
2. Make High Power drawings of representative sections of eudicot and monocot leaf
specimens provided. Draw up a table to compare and contrast monocot and eudicot leaves,
emphasising on diagnostic characters.
3. Make High Power drawings of sections of the aquatic and arid leaf specimens provided.
Draw up a list of features characteristic of each leaf type. List any significant differences
between the two specimens and between each specimen and a typical dicotyledon leaf.
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PRACTICAL 5
LEAF FORM AND STRUCTURE
INTRODUCTION
Leaves are the primary photosynthetic organs of the plant, although occasionally stems, roots, or
floral parts may assume photosynthetic functions. The functional efficiency of leaves is directly
related to external form (size, shape, arrangement, orientation, etc.) and internal structure
(anatomy). Thus, leaves may be furnished with a large surface area and an optimal orientation for
maximum capture of light, numerous intercellular spaces for efficient exchange of gases, and large
vascular supply for the maintenance of optimal moisture levels and efficient translocation of
photosynthetic products. The upper and lower epidermis may be covered with a waxy cuticle to
minimise water loss, with stomata providing the only pathway for gases. Leaves of eudicots are
usually dorsiventral (upper and lower mesophyll layers differentiated) and divided into an upper
palisade parenchyma and lower spongy parenchyma.
OBJECTIVES
3.
4.
5.
6.
To compare and contrast leaf morphological characteristics of angiosperm plants
To compare and contrast leaf anatomy among groups of plants
To compare and contrast leaf anatomy of eudicots and monocots
To compare and contrast leaf anatomy under different environmental conditions
PROCEDURE 1 (LEAF MORPHOLOGY)
Examine the leaf material on display and be sure to note the morphological differences
Identify and briefly characterize the structures/features printed in BOLD below.
Note whether the leaves are simple or compound, and if compound if they are pinnately or
palmately compound. Also note their shape and insertion on the stem.
Leaves can be divided into two distinct regions: blade or lamina (the expanded portion of the leaf),
and petiole (the stalk). The blade can also be divided into leaf base (towards
the petiole) and apex. The leaf may be sessile on the stem. Leaves may be
simple or compound (each blade being pinna -pl. pinnae).
Pinnately compound leaves can be once, twice or even three times
pinnately-compound (see fern specimen on display). Leaflets can be differentiated from
leaves by the presence of an axillary bud in the axil formed where a true leaf meets the
stem. Axillary buds are absent from the axils where leaflets are joined to a rachis.
Leaves, or leaflets as the case may be, also have characteristic
arrangements of vascular tissue, the so-called "veins" of the leaf. Most eudicots have either a
pinnate venation in which secondary or lateral veins arise from a primary vein or a palmate
venation in
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which several (or more) major veins originate from a common point. A third type of
venation, parallel venation, is typical of many monocots.
Leaves also exhibit differences in overall shape of the blade, ranging from scale or needle-like to
linear and lanceolate to elliptic and orbicular. The leaf base can be acute, obtuse, rounded,
cordate or peltate. Another important feature of leaf blades is the type of margin (leaf edge) they
possess. If there are no indentations of any kind along the margin the blade is said to be entire.
Alternatively, the margin may be variously toothed (i.e. serrate, dentate or crenate).
Leaves can be inserted along the stem in an alternate, opposite or whorled fashion. The point at
which a leaf attaches to the stem is a node and the region of the stem between two adjacent nodes is
an internode. In many plants there is a stipule at each node along the stem. Depending on the
particular plant, the stipule may be attached either to the leaf base or directly to the stem. Stipules
vary greatly in shape and size and can be minute and deciduous (i.e. falling away) or persistent and
enlarged, sometimes to such an extent that they become the major photosynthetic organ. Also
associated with each leaf/node is an axillary or lateral bud. In addition to lateral buds, there are
also terminal buds at the tip of the shoot. Both types of buds are meristematic. Lateral buds result
in new branches (and possibly flowers).
PROCEDURE 2 (LEAF INTERNAL STRUCTURE)
From the provided slides:
4. Make High Power drawings of representative sections of the eudicot and monocot leaves.
Draw up a table to compare and contrast monocot and eudicot leaves, emphasising on
diagnostic characters.
5. Make High Power drawings of sections of aquatic and xerophytic leaves. Draw up a list of
features characteristic of each leaf type. List the major differences between the aquatic leaf
and the xerophytic leaf.
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PRACTICALS 6
FLOWER STRUCTURE, MODIFICATION AND DEVELOPMENT
INTRODUCTION
Angiosperms and gymnosperms have seeds as dispersal units. The two groups differ from each
other in the extent to which the megaspore (ovule) is exposed at time of pollination. Whereas in
gymnosperms the pollen grain has direct access to the ovule, in angiosperms the ovule is enclosed
within modified megasporophylls (carpels). Hence, the pollen grain has to penetrate the carpelary
tissue before reaching the ovule for fertilisation.
The angiosperm flower is homologised with the vegetative shoot, and individual parts of the flower
with leaves. The flower is hypothesised to be an assemblage of sterile and fertile parts borne on an
axis (receptacle). Sterile parts are petals and sepals. Reproductive parts are stamens
(microsporophylls) and carpels (megasporophylls). The arrangement of floral parts on the axis and
the relationship of parts to each other are highly variable. This variation is of particular significance
to reproductive biology, and is important in taxonomic and phylogenetic studies of angiosperms.
Modification of the flower has occurred in relation to mode of pollination. In primitive flowers,
floral parts are usually large and of an indefinite number. Advanced flowers have fewer floral parts
and of a definite number. A high degree of reduction in floral parts is seen among grasses where
many have imperfect flowers consisting of either stamens or pistils. The grass family (Poaceae) is
hypothesised as representing the apex of one evolutionary line in the monocotyledons.
The angiosperm anther usually contains four elongated cavities (pollen sacs) in which pollen grains
are produced. Examination of the cavities at young stage shows microspore mother cells (each of
which divides and develops into microspores). Meiotic division followed by mitotic division
produces pollen grains. The grains are transferred to the stigma during pollination.
The ovary may contain one or more ovules, each ovule arising separately from the placenta as a
minute dome-shaped projection (the nucellus). There soon develops the integuments, which cover
the nucellus, except for a small opening, the micropyle. Within the nucellus, a single large cell, the
megaspore mother cell, soon appears and through meiotic division, megaspores are produced.
Germination of the pollen grain and subsequent development of the pollen tube lead to fertilisation.
OBJECTIVES
1. To study the basic floral structure as represented by the genus Aloe
2. To study floral structures in highly modified flowers
7. To compare and contrast floral structure in provided plant taxonomic groups
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4. To study anatomical details of microsporogenesis and megasporogenesis and events leading to
fertilisation in the angiosperm flower
PROCEDURE 1
Study the flower material provided. Note the type of inflorescence.
a. Dissect Flower A, and draw a half flower. Label all parts. Briefly comment on the structure
of the flower. Note primitive and derived characters of the flower, and comment on the
united corolla and the petaloid perianth. Separately, make thin sliced cross sections of the
andoecium and gynaecium. Draw and label all parts. Make a wet-mount slide of pollen grains.
Observe at High Power and draw a single pollen grain.
b. Dissect and draw a half flower from Flower B and label all parts. Briefly comment on the
structure of the flower. Compare the flower structure from that of Flower A. Relate the
structure to mode of pollination. Provide a floral diagram and formula for Flower B.
c. Dissect Flower C and label all parts. Provide a floral formula for the flower. Relate
structure to function, and comment on the mode of pollination.
d. From the provided slide, make a High Power drawing of a partial cross section of a
microsporangium of Lilium species. Label the following: epidermis, parietal layer, outer
tapetum, sporogenous tissue, microsporocytes (if present) and inner tapetum. Observe
the same structures from material of Gossypium arboreum for comparison.
e.
From the provided slide, make a Low Power diagram of a longitudinal section of a
developing ovule of a Lilium species. Label the following: outer and inner integuments,
micropyle, nucellus, procambium, chalazal region, and positions of egg cell and
antipodal cells.
f.
Observe the path of a pollen tube from a longitudinal section of an ovule of Gossypium
arboreum from the provided slide. Note the following: pollen tube, micropyle, egg cell,
synergid and antipodal cell.
PROCEDURE 2
a. Microsporogenesis
From the provided inflorescences of two species, D and E, pick young flower buds at different
stages of development, and maintain them in separate vials. Fix the freshly picked buds in Carnoy’s
fluid (100% ethyl alcohol and glacial acetic acid in the proportion of 3:1, Johansen 1940) for 24
hours at 40 C. Wash the fixed material in two series of 70% alcohol. Carefully remove the young
anthers and stain them overnight in HCL-Carmine stain (Snow 1963) at 600C. Wash the stained
tissues in 70% ethyl alcohol and store in same until needed. Squash the material in 45% acetic acid
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and observe under High Power light microscopy. Make a comparative study of microsporogenesis
in the two species.
c. Megasporogenesis
From the provided young inflorescences of Species A and B, pick flower buds at different stages of
development. Maintain the young buds in different vials. Fix the freshly picked flower buds in
Karpechenko’s modified Navashin’s fluid (Johansen 1940) and store in same until needed. Wash
and dehydrate the preserved material in concentration series of alcohol (70%, 90%, 95% and
100%). Embed the material in paraffin wax. Section the material on a microtome at 10-14
micrometres. Stain the sectioned tissue in safranin and fast green. Make into permanent mounts.
Study the slides under High Power light microscopy. Provide detailed descriptions on type, shape
and orientation of ovules.
References
JOHANSEN, D.A. (1940). Plant microtechnique. McGraw-Hill, New York.
SNOW, R. (1963). Alcoholic hydrochloric acid-carmine as a stain for chromosomes in squash
preparations. Stain Technology 38: 9-13.
UZINATTO, V.A., PAGLIARINI, M.S. & VALLE, C.B. (2008). Evaluation of
microsporogenesis in an interspecific Brachiaria hybrid (Poaceae) collected in distinct
years. Genetics and Molecular Research 7: 424-432.
MENDES-BONATO, A.B., PAGLIARINI, M.S., FORLI, F., VALLE, C.B. & PENTEADO,
M.I.O. (2002). Chromosome number and microsporogenesis in Brachiaria brizantha
(Gramineae). Euphytica 125: 419-425.
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PRACTICAL 7
FRUIT STRUCTURE AND DISPERSAL
INTRODUCTION
After pollination, the flower withers. Some or all of the floral parts other than the ovary (or ovaries
in the case of flowers with apocarpous gynoecium) are shed. The ovary persists and develops into a
fruit (a modified gynoecium that encloses seeds until they are ripe). Two processes are involved in
fruit formation: development of ovules into seeds, and modification of the ovary wall into fruit wall
(pericarp). The floral receptacle may be involved in the formation of the mature fruit as in
Anacardium occidentale (CASHEW).
The structure of the fruit largely determines the method of seed dispersal. Fruit structure also
provides useful characters for the classification of flowering plants. A number of characters
determine the structure of a fruit:
 whether the ripe fruit is dry or succulent;

whether it splits at maturity to release the seeds, or remains closed becoming the dispersal unit;

whether it contains one or more seeds;

whether it is a product of one or more carpels, and in the latter case, how many carpels;

whether the fruit is a product of a single flower, or an inflorescence (as in Ficus); and

whether the fruit is a product of a superior or inferior ovary.
Should seeds germinate directly beneath or near the parent plant, there is likely to be intense
competition and only a few of the seedlings may survive. On the other hand, when seeds are
dispersed, more seedlings are likely to survive, and the area colonised by the progeny is extended.
This also minimises the effect of seed predation. Seeds may be dispersed on their own or as part of
the fruit. Seed-bearing plants have varied mechanisms for dispersal. These may be divided into four
categories: dispersal by wind, dispersal by water, dispersal by animals, and self-dispersal. Seed and
fruit structures determine mode of dispersal.
OBJECTIVES
1. To study fruit structure and infer type of flowers from which the fruit developed
2. To classify fruits
3. To study structures of fruits and seeds that are important in dispersal, and to infer mode of
dispersal from fruit and seed structure
PROCEDURE 1
The structure of a fruit is best understood from the original floral structure. Any presence of
accessory structures is likely to obscure the true nature of the fruit at mature stage. This renders the
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fruit difficult to classify.
In general, all fruits may be classified into three major groups:
i.
simple fruits, developed from a single (simple or compound) pistil and consisting of single
matured ovary, together with any accessory structures associated with the ovary;
ii.
aggregate fruits, developed from a single flower with many separate pistils and consisting
of a number of mature ovaries aggregated as a unit on a common receptacle, together with
any accessory structures; and
iii.
multiple fruits, developed from an entire inflorescence and consisting of all the matured
ovaries of several flowers grouped into a single mass, together with any accessory
structures.
You are provided with fruit material.
a) Dissect the provided citrus and peach fruits into halves. Study and draw the sectioned material
and label the following: exocarp, mesocarp, endocarp and seed. What are the fundamental
differences between the two fruits?
b) Study fruit structure from the rest of the provided material. In each case, state (with reasons)
whether the fruit is from a single flower (and whether from simple or compound pistil) or from
an inflorescence.
c) State and shortly describe any accessory floral structure(s).
d) Attempt a classification of the fruits.
PROCEDURE 2
Wind-borne seeds and fruits are characterised by any of the following: winged structures, bladderlike structures, light weight, hairy structures. Water borne seeds and fruits are characterised by any
of the following: buoyant structures, water resistant coverings, lightweight coverings. Selfdispersed seeds are usually associated with fruits with explosive devices, or satures. The following
are some of the characters of animal dispersed seeds or fruits: fleshy and edible, with small hard
seeds; fleshy and edible with large inedible seeds; seeds or fruits with structures adhering to hair
and clothing; sticky seeds.
1. You are provided with six fruits.
a) Study the specimens and note the structures of dispersal.
b) In each case, suggest the mode of dispersal.
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PRACTICAL 8
SEED STRUCTURE AND SEEDLING MORPHOLOGY
INTRODUCTION
The seed is the seat of partial development of the new sporophyte, the embryo. It plays a major role
in providing continuity between generations in seed plants. The angiosperm seed develops from the
ovule as a result of double fertilisation. In the mature seed, the embryo is protected by the
surrounding seed coat and supplied with stored nutrients. Seeds have a greater survival chance than
spores. The capacity to produce seeds has made seed plants dominant over spore-bearing plants.
A true seed is a matured ovule containing an embryo and stored nutrients, with the integuments
differentiated as protective seed coat or testa. Although no two species of seeds are exactly alike in
all features, seeds resemble each other in that they are ripened ovules consisting of similar parts.
Furthermore, they all serve functions of dissemination, protection and reproduction.
After a more or less prolonged dormancy caused by various internal and external factors, seeds
germinate under appropriate conditions. Morphological features of the seedling vary among
different species.
OBJECTIVES
1. To study features of a mature seed in monocots and eudicots
2. To study seedling morphology in monocotyledons and dicotyledons and to assess the type of
germination among species
PROCEEDURE
Seed structure differs between eudicots and monocots. It also differs between endospermous and
non-endospermous seeds. In both monocots and eudicots, germination may be hypogenous
(cotyledon(s) remaining underground), or epigenous (cotyledon(s) brought above ground).
1. Make a longitudinal dissection of a soaked seed of Zea. Apply a drop of iodine to the cut
surface of each half. Wait a few moments for the colour reaction to occur. The darkly coloured
region is the endosperm. The lightly coloured area is the embryo. Draw and label all structures,
and outline their functions.
2. Dissect into half a soaked seed of Arachis. Draw and label all structures, and outline their
functions.
3. Study the morphology of emerging seedlings of Vigna, Arachis, Zea and Allium. Draw the
Arachis and Zea seedlings. Label all parts.
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4. List the morphological differences among the four species, and relate them to type of seed and
type of germination.
sk ( September 2016)
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