Morphological Study
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The abundance of plants and their size from bacteria to huge trees make it difficult to study their morphological characters. Classification of plants has solved the problem to a greater extent. Still it is impossible to define precisely the plant body as made up of certain parts only.
MORPHOLOGICAL STUDY
The abundance of plants and their size from bacteria to huge
trees make it difficult to study their morphological characters. Classification
of plants has solved the problem to a greater extent. Still it is impossible to
define precisely the plant body as made up of certain parts only. Plants
exhibit vividness in several respects.
The details of morphological characters of these plant
organs are as under.
Morphology of Bark
The bark (in commerce) consists of external tissues lying
outside the cambium, in stem or root of dicotyledonous plants. Following are
the tissues present in bark:
Cork (phellum), phellogen and phelloderm (collectively known
as periderm), cortex, pericycle, primary phloem and secondary phloem.
In Botany, the bark consists of periderm and tissues lying
outside it, i.e. cork, phellogen and phelloderm.
Methods
of collection of barks
Bark is generally collected in spring or early summer
because the cambium is very active and thinwalled and gets detached easily.
Following are the methods of collection of barks.
1.
Felling method: The fully grown tree is cut down near the ground level by an axe. The
bark is removed by making suitable longitudinal and transverse cuts on the stem
and branches. The disadvantages of this method are (a) the plant is fully
destroyed and (b) the root bark is not utilized.
2.
Uprooting method: In this method, the stem of definite age and diameter are cut
down, the root is dug up and bark is collected from roots, stems and branches.
In Java, cinchona bark is collected by this method.
3.
Coppicing method: The plant is allowed to grow up to certain age and diameter. The
stems are cut at a certain distance from ground level. Bark is collected from
stem and branches. The stumps remaining in the ground are allowed to grow up to
certain level; again the shoots are cut to collect the bark in the same manner.
Cascara bark and Ceylon cinnamon bark are collected by this method.
Morphology
of bark
The following features may be used to describe the
morphology of bark.
1.
Shape: The shape of the bark depends upon the mode of cuts made and the extent and
shrinkage occurred during drying.
a)
Flat: When the large piece of the bark is
collected from old trunk and dried under pressure, the bark is flat, e.g.
Quillaia and Aarjuna barks.
b)
Curved: Here, both the sides of the bark are
curved inside, e.g. Wild cherry, Cassia and Cascara barks.
c) Recurved: Both sides of bark are curved outside, e.g. Kurchi bark.
d)
Channelled: When the sides of bark are curved
towards innerside to form channel, e.g. Cascara, Cassia and Cinnamon barks.
e) Quill: If one edge of bark covers the other edge, it is called quill,
e.g. Ceylon, Cinnamon and Cascara barks.
f) Double quill: Here, both the edges curve inward to form double quill, e.g.
Cinnamon and Cassia barks.
g)
Compound
quill: When the quills of smaller
diameter are packed into bigger quills, it is called compound quills. Compound
quills are formed to save the space in packing and transportation, e.g.
Cinnamon bark.
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1.
Outer surface:
a)
Smooth:
When development of cork is even, e.g. Arjuna bark.
b)
Lenticels: They are transversely elongated holes
formed on outer surface because of lateral pressure, e.g. Wild Cherry and
Cascara barks.
c)
Cracks
and fissures: They are formed due to increase in diameter, e.g. Cinchona bark
d)
Longitudinal
wrinkles: They are formed because of shrinkage of soft tissues, e.g. Cascara
bark.
e)
Furrows:
If troughs between wrinkles are wide, it is called furrows, e.g. Cinchona
calisaya bark.
f)
Exfoliation:
Sometimes the cork of bark flakes off exposing cortex, e.g. in Wild cherry
bark.
g)
Rhytidoma:
It is composite dead tissue consisting of alternate layers of cork, cortex
and/or phloem, e.g. Quillaia and Tomentosa barks. Sometimes it is removed
during peeling.
h)
Corky
warts: They are the small circular patches, found sometimes in old barks, e.g.
in Cinchona succirubra and Ashoka
barks.
i) Epiphytes: Such as moss, lichen and
liverwarts are sometimes seen in bark, e.g. Cascara bark.
2.
Inner surface: The colour and condition of inner
surface is of
diagnostic value.
a)
Striations:
When parallel longitudinal ridges are formed during drying, it is called
striations; it may be fine or coarse, e.g. Cascara bark.
b)
Corrugations:
They are the parallel transverse wrinkles formed due to longitudinal shrinkage,
e.g. Cascara bark.
3.
Fracture: The appearance of exposed surface of trans-versely broken
bark is called fracture. Different types of fracture, their descriptions and
examples are given in table.
Table : Various types of fracture of bark
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Histology
of barks
The bark shows
following microscopical character: (i) Tabular, radially arranged
cork cells, may be suberised or lignified (e.g. in Cassia bark), (ii)
Thin-walled cellulosic parenchymatous phellogen and phelloderm, (iii)
Collenchy-matous and/or parenchymatous cortex, (iv) Parenchymatous or
scleranchymatous pericycle; may contain band of stone cells and fibres, (v)
Primary phloem which is generally crushed, e.g. in Cascara and Arjuna and (vi)
Secondary phloem consisting of sieve tubes, companion cells, phloem parenchyma,
phloem fibres and stone cells. Phloem fibres are thick walled, lignified, e.g.
in Cinchona and Cascara; stone cells are thick, lignified with narrow lumen,
e.g. Kurchi and Cinnamon barks; sometimes branched stone cells are seen in Wild
cherry bark, (vii) Thin walled, living radially elon-gated medullary ray cells
which are uni-, bi- or multiseriate and straight or wavy, (viii) Starch,
calcium oxalate, oil cells, mucilage, etc., are often present in cortex.
Morphology of Roots
Root is a downward growth of the plant into the soil. It is positively geotropic and hydrotropic. Radicle from the ger-minating seed grows further into the soil to form the root. It produces similar organs. Root does not have nodes or internodes. Branching of the root arises from the pericyclic tissues. Roots are covered by root caps or root heads.
[A] Functions of roots
1. Roots fix the plant to the soil and give mechanical support to the plant body.
2. Roots absorb water and the minerals dissolved in it from the soil and transport them to the aerial parts where they are needed.
3. At times, the root undergoes modification and per-forms special functions like storage, respiration, repro-duction, etc.
[B] Various parts of a root
A typical underground root exhibits the following parts:
a) Root cap: The tip of the root is very delicate and is covered by root cap. Root cap protects the growing cells and as and when it is worn out it is replaced by the underlying tissues immediately.
b) Region of cell division: The next layer of tissue lying immediately after the root cap towards the stem is the meristematic tissue producing new cells, known as region of cell division or growing region.
c) Region of elongation: The newly formed cells in the growing region grow further by elongation in this region resulting in the increase in the length of the root.
d) Region of root hairs: Above the region of elonga-tion is the region of root hairs wherein the root hairs, the unicelluar, tubular outgrowths formed by the epiblema are formed. They are responsible for strengthening the hold of root into the soil and also for the absorption of water.
e) Region of maturation: It is located above the region of root hairs. It does not absorb anything, but is mainly responsible for the absorbed material by roots. The root branches or the lateral roots are produced in this region.
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[C] Types of roots
There are two types of root systems:
a) Tap root system or primary roots and
b) Adventitious roots.
Tap root system: The radicle grows into the soil and forms main axis of the root known as tap root. It grows further to produce branches in the acropetal manner known as secondary roots which further branches to give tertiary roots. These are all true roots. This system is characteristic of dicotyledons.
Adventitious root system: The roots that develop from any
part of the plant other than radicle are termed as adventitious roots. They may
develop from root base nodes or internodes. This type of root system is found
in monocots and in pterido-phytes.
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I. Modification for storage of food: This type of modifi-cation is shown
by both the types of roots, i.e. tap roots and adventitious roots. They store
carbohydrates and are used during early growth of successive season.
i.Tap roots show the following three
types of modifica-tions:
a)
Conical:
These are cone-like, broader at the base and tape-ring at the tip, e.g. carrot.
b)
Fusiform:
These roots are more or less spindle shaped, i.e. tapering at both the ends,
e.g. radish.
c)
Napiform:
These are spherical shaped and very sharply tapering at lower part, e.g. beat
and turnip
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ii. Adventitious root show the following types of
modi-fications. They store carbohydrates but do not assume any special shape.
a)
Tuberous
roots: These get swollen and form single or isolated tuberous roots which are
fusiform in shape, e.g. sweet potato, jalap, aconite.
b)
Fasciculated
tuberous roots: When several tuber-ous roots occur in a group or cluster at the
base of a stem they are termed as fasciculated tuberous roots as in dahlia,
asparagus.
c)
Palmated
tuberous roots: When they are exhibited like palm with fingers as in common
ground orchid.
d)
Annulated
roots: The swollen portion is in the form of a series of rings called annules
as in ipecacuanha.
II. Modifications for support: Plant develops special aerial roots to offer additional support to the plant by way of adventitious roots.
a) Clinging or Climbing roots: These types of roots are developed by plants like black pepper for support or for climbing purposes at nodes.
b) Stilt roots: This type of root is observed in maize and screw-pine, which grow vertically or obliquely downwards and penetrate into soil and give addi-tional support to the main plant.
c) Columnar roots: In certain plants like banyan, the additional support is given by specially developed pillars or columnar roots. They even perform the function of regular roots.
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III. Modifications for special functions:
a) Respiratory roots or pneumatophores: The roots of the plant growing in marshy places on sea-shores due to continuous water logging are unable to respire properly. They develop some roots growing against the gravitational force (in the air) with minute openings called lenticels. With the help of lenticels they carry on the exchange of gases. They look like conical spikes around the stems. This type of root is observed in case of plants called mangroves found in creeks, i.e. avicinnia.
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b) Sucking roots or Haustoria: The plants, which are total parasites on the host, develop special type of roots for the purpose of absorption of food material from, the host. These roots neither possess root caps nor root hairs, and are known as sucking roots, e.g. cuscuta, striga and viscum.
c) Photosynthetic roots: Aerial roots in some cases, specially in leafless epiphytes become green in colour on exposure to sunlight and perform photosynthesis and are known as photosynthetic roots as in case of Tinospora cardifolia.
d) Epiphytic or Assimilatory roots: The plants which grow on the branches or stems of the plants without taking any food from them are called epiphytic and the roots developed by them are the epiphytic roots. They consist of the following:
i. Clinging roots with which they get fixed with the host and
ii. Aerial roots which hang freely in the air, which are normally long greenish white in colour and absorb moisture from the atmo-sphere with the help of porous tissue. These roots are devoid of root caps and root hairs. They carry on photosynthesis. These are developed in the plants growing in humid atmosphere. Bulbophyllum, uanda are the examples of this type.
e) Nodulated roots or root tubercles: The plants belonging to leguminosae family develop nodules or tubercles. These are formed by nitrogen fixing bacteria and getting carbohydrates from the plants. Roots and bacteria are symbiotic to each other. These swellings developed by roots are nodulated roots.
Uses
of roots
1)
Source
of food and vegetables: Most of vegetables constitute roots only, i.e. radish,
turnip, beet, carrot, etc. They are rich sources of vitamins or their
precursors. Some of them like sweet potato and tapioca are rich in starch, and
hence are consumed as food.
2)
Various
types of medicinally important drugs are obtained from roots.
Morphology of Stems
The plumule develops to form the stem. Thus stem is an
aerial part of the plant. It consists of axis and the leaves. Stem has got the
following characteristics:
a. It is ascending axis of the plant and
phototropic in nature.
b. It consists of nodes, internodes and
buds.
c. It gives rise to branches, leaves
and flowers.
d. Stems may be aerial, sub-aerial and
underground. Depending upon the presence of mechanical tissues, the stems may
be weak, herbaceous or woody.
Weak stems: When the stems are thin and long, they are unable to stand erect, and hence may be one of the following types:
a) Creepers or Prostate stem: When they grow flat on the ground with or without roots, e.g. grasses, gokharu, etc.
b) Climbers: These are too weak to stand alone. They climb on the support with the help of ten-drils, hooks, prickles or roots, e.g. Piper betel, Piper longum.
c) Twinners: These coil the support and grow further. They are thin and wiry, i.e. ipomoea.
[B] Herbaceous and woody stems: These are the normal stems and may be soft or hard and woody, i.e. sunflower, sugarcane, mango, etc.
1) Produce leaves and exposes them
properly to sunlight for carrying out photosynthesis.
2) Conducts water and minerals from
roots to leaves and buds.
3) Foods produced by leaves are
transported to nongreen parts of the plant.
4) Produce flowers and fruits for
pollination and seal dispersal.
5) Depending upon the environment it
gets suitably modified to perform special functions like storage of foods,
means of propagation, etc.
1.
Underground
modifications of stems
Underground modifications of stems are of the following
types:
1) Rhizome
2) Tuber
3) Bulb
4) Corm.
1. Rhizomes: Grow horizontal under the soil. They are thick and are characterized by the presence of nodes, internodes and scale leaves. They also possess bud in the axil of the scale leaves, e.g. ginger, turmeric, rhubarb, male fern, etc.
2. Tubers: Tubers are characterized by the presence of ‘eyes’ from the vegetative buds which grow further and develop into a new plant. Tubers are the swollen underground structure of the plant, e.g. potato, jalap, aconite, etc.
2. Bulb: In this case, the food material is stored in fleshy scales that overlap the stem. They are present in the axils of the scales, and few of them develop into new plant in the spring season at the expense of stored food material in the bulb. Adventitious roots are present at the base of the bulb. The reserve food material formed by the leaves is stored at their bases, and the new bulbs are produced next year, e.g. garlic, squill and onion.
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3. Corm: Corms are generally stout, and grow in vertical direction. They bear bud in the axil of the scaly leaves, and these buds then develop further to form the new plant. Adventitious roots are present at the base of the corm, e.g. saffron, colchicum, dioscorea, etc.
II. Sub-aerial modifications of stems:
These include (1) Runner, (2) Stolon, (3) Offset and (4) Sucker.
1. Runner: These creep on the ground and root at the nodes. Axillary buds are also present, e.g. strawberry, pen-nywort.
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. Stolon: These are lateral branches arising from the base of the stems which grow
horizontally. They are character-ized by the presence of nodes and internodes.
Few branches growing above the ground develop into a new plant, e.g.
glycyrrhiza, arroroot, jasmine, etc.
3. Offsets: These originate from the axil of the leaf as short, thick horizontal branches and
also characterized by the presence of rosette type leaves and a cluster of
roots at their bottom, e.g. aloe, valerian.
4. Sucker: These are lateral branches developed from underground stems. Suckers grow
obliquely upwards, give rise to a shoot which develop further into a new plant,
e.g. mentha species, chrysanthemum, pineapple, banana, etc.
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III.
Aerial modification of stems
As the name indicates they grow into the air above the soil
to a certain height, as follows:
1. Phylloclades:
At times, the stem becomes green and performs the function of leaves.
Normally this is found in the plants growing in the desert (xerophytes).
Phylloclades are characterized by the presence of small leaves or pointed
spines, e.g. opuntia, ruscus, euphorbia,
etc.
Cladode is a type of phylloclade with one
internode, i.e. asparagus.
2.
Thorns and prickles: This is another type of aerial
mod-ification meant for protection. Thorns are hard, pointed, straight
structures, such as duranta, lemon, etc. Prickles and thorns are identical
in function. Prickles get originated from outer tissues of the stem. Thus, they
are superficial outgrowths. Prickles are sharp, pointed and curved struc-tures.
They are scattered all over the stem. Rose, smilax can be quoted as examples of
the same.
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1. Stem
tendrils: In certain
plants, the buds develop into tendrils for the purpose of support. Terminal buds in
case of vitis, axillary bud in case of passiflora are suitable examples.
4. Bulbils: These are modifications of floral buds meant for vegetative propagation, such as Dioscorea and Agave.
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Uses
of stems
Depending upon the structural and chemical contents, stems
are used for various purposes.
1.
Underground
stems in their various forms are either used as food spices or for culinary
purposes like, potato, amorphophalus, colocasia, garlic, ginger and onion.
2.
Jowar,
rice and other stems are used as fodder.
3.
Stems
of jute, hemp and flax as sources of industrial fibres used for various
purposes.
4.
Sugarcane
stems are used as source of sucrose while latex from stems of Hevea brasiliensis is used as rubber.
5.
Woods
from stems of several plants are used as drugs like quassia, guaicum,
sandalwood, etc.
6.
The
stems of several plants are injured to produce gums for their multiple
industrial uses like gum-acacia, gum-tragacanth, gum-sturculia, etc.
Morphology of Leaves
Leaves are flat, thin green, appendages to the stem, contain-ing supporting and conducting strands in their structure. They develop in such a way that older leaves are placed at the base while the younger ones at the apex.
A typical angiospermic leaf consists of the following parts:
a) Leaf base or hypopodium: By means of which it is attached to the stem.
b) Petiole: It is the stalk of leaf with which leaf blade is attached to the stem. It is also known as mesopodium. It may be present in leaf or may be absent in leaf. Leaves with petiole are called petiolate, and those without petiole sessile. They may be short or long and cylindrical. Sometimes, it is flattened as in the case of lemon. Then it is described as winged petiole. In some plants the petiole undergoes modification to form the tendrillar petiole which helps the plant to climb, e.g. clematis. In few aquatic plants it enlarges to form the swollen petiole by enclosing air and thus keep the entire plant floating over the water. In few other cases, the petiole enlarges to such an extent to form the leaf like structure as in Australian acacia and is known asphyllode.
c) Lamina or Leaf blade: The flat expanded part of the leaf is lamina or leaf blade (Epipodium). Lamina may be thick as in xerophytic leaves or thin as in hydrophytes or intermediate as in mesophytes.
d) Stipules: These are the two small outgrowths found at the base of the leaf, to protect the axillary bud. Leaves may or may not have stipules. Leaves with stipules are described as stipulate, while those without stipules are described as ex-stipulate.
Some stipules perform special functions and hence are put into following types:
1. Tendrillar stipules: The stipules get modified into coiled, tendrils helping the plant to climb, i.e. Indian sarsaparilla (Smilax microphylla).
2. Foliaceous stipules: In case of plants with compound leaves some of the leaflets get converted into tendril and the stipules expand to form the flat surface and carry on photosynthesis, i.e. Lathyrus or pisum.
3. Bud stipules: Scaly stipules of the Ficus sp. are charac-teristic, which protect the terminal vegetative bud. With the development and unfolding of the leaf the bud stipule falls off.
4. Spiny stipules: In some plants, the stipules get converted into spines and help against browsing animals as in the case of Acacia and Zizyphus.
There are five types of stipules which are as under:
1. Free lateral: These are free and located on either side of the leaf as in China rose.
2. Adnate: When the stipules unite with the petioles forming wing like structure are known as adnate stipules, i.e. Groundnut, rose, etc.
3. Inter-petiolar: When stipules are located in between the two petioles of two leaves as in ixora.
4. Axillary: When two stipules unite becoming axillary to the leaves.
5. Ochreate stipules: These form a hollow tube around the stem as in Polygonum
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Before considering the further anatomical details of the leaves, it is very essential to know the basic difference botanically between the leaf and the leaflet which is as under:
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[B] Shape of the lamina of leaves
Various shapes of the leaves are due to various types or shapes of lamina. It may be one of the following:
1. Acicular: Needlelike, i.e. pinus.
2. Subulate: With acute apex and recurved point, i.e. Ephedra sinica.
3. Linear: When it is long, narrow and flat, i.e. Grasses.
4. Oblong: Broad leaves with two parallel margins and abruptly tapering apex, i.e. Banana.
5. Lanceolate: Which look like lance or spear shaped, e.g. nerium, senna.
6. Ovate: Egg shaped or broad base and narrow apex, e.g. China rose, Buchu.
7. Obovate: Broad apex and narrow base, e.g. Jangali-badam.
8. Obcordate: Inversely heart shaped, i.e. base is narrow but apex is broad, e.g. Oxalis.
9. Spathulate: Like spatula or spoon shaped as in calen-dula and drosera.
10. Cuneate: Wedge shaped as in pista.
11. Cordate: Heart shaped, i.e. betel.
12. Sagittate: Arrow shaped such as in arum.
13. Hastate: When the two lobes of sagittate leaf are directed outwards as in ipomoea.
14. Reniform: Kidney shaped, i.e. Indian pennywort.
15. Auriculate: When the leaf has got ear like projections at the base.
16. Lyrate: When it is lyre shaped or the blade is divided into lobes with large marginal lobe, i.e. radish mustard.
17. Runcinate: With the lobes convex before and straight behind, pointing backward like the teeth of the double saw, i.e. dendelion leaf.
18. Rotund (Orbicular): When the blade is circular or round, e.g. lotus.
19. Elliptical or oval: When the leaves are narrow at the base and apex but broad in the middle such as guava, vinca, etc.
20. Peltate: When the lamina is shield shaped and fixed to the stalk by the centre.
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[C]
Leaf margins
Leaf margin may be of the following types:
1. Entire: When it is even and smooths, i.e. senna, eucalyptus.
2. Sinuate or wavy: With slight undulations like Ashok.
3. Crenate: When the teeth are round as in digitalis.
4. Dentate: Toothed margin, teeth directing outwards such as margosa, melon.
5. Serrate: When it is like the teeth of the saw such as rose, China rose, etc.
6. Ciliated: It is fringed with hairs.
7. Biserrate: Lobed serrate margin.
8. Bicrenate: Lobed crenate margin.
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[D] Leaf apices
The apex of the leaf may be one of the following kinds:
1. Obtuse: Rounded tip, i.e. banyan.
2. Acute: When it is pointed to form acute angle, but not stiff, i.e. hibiscus.
3. Acuminate: Pointed tip with much elongation, peepal.
4. Recurved: When the apex is curved backward.
5. Cuspidate: With spiny tip like date palm.
6. Mucronate: Rounded apex ending abruptly in a short point i.e vinca, ixora.
7. Retuse: Broad tip with slight notch, i.e. pistia.
8. Emarginate: When tip is deeply notched as in bambinia.
9. Tendrillar: Tip forming a tendril such as Gloriosa— superba.
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[E] Leaf bases
The lower extremity of the lamina of the leaf may exhibit one of the following shapes:
a) Symmetrical: Equal as in vasaka.
b) Asymmetrical: Unequal as in senna or datura.
c) Decurrent: As in digitalis.
d) Cordate: As in betel.
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[F] Leaf surface
It may be of the following types:
a) Glabrous: When surface is smooth and free of hair or any outgrowth, i.e. vasaka, datura.
b) Rough: When harsh to touch, digitalis.
c) Hairy: When covered with hairs.
d) Glutinous: When covered with sticky substance, tobacco.
e) Glaucous: When covered with waxy coating, castor.
f) Pubescent: Covered with straight, short hair, i.e. senna.
[G] Types of leaves
Taking into consideration the nature of the lamina of the leaves, they are classified into two main groups:
1. Simple leaves and
2. Compound leaves.
1. Simple leaves: A leaf which has only one leaf blade or lamina is called a simple leaf. It may be stipulate or exstipulate, petiolate or sessile, but always possess axillary bud in its axil. It may have an undivided lamina or may be lobed, e.g. vasaka, digitalis, eucalyptus, datura, carica, castor and argemone.
2. Compound leaves: A compound leaf consists of more than one leaf blade or the lamina, the compound leaf is divided into several segments called leaflets or pinnae, e.g. senna, tamarind, acacia.
Compound leaves have been further classified as (a) pinnate compound leaves and (b) palmate compound leaves.
a) Pinnate compound leaves: These are sub-classified as under depending upon the number of rachis (an axis bearing the leaflets in pinnate compound leaf is known as rachis):
1. Unipinnate compound leaves: Wherein only one rachis bearing the leaflets is present. When an even number of leaflet is present, it is known as paripinnate, e.g. tamarind, gul mohor; if the number of leaflet is odd, it is described as imparipinnate, e.g. rose, margosa, etc.
2. Bipinnate compound leaves: It consists of primary rachis and secondary rachis. The secondary rachis only bears the leaflets, e.g. acacia.
3. Tripinnate compound leaves: These contain primary, secondary and even tertiary rachis. Tertiary rachii only bear the leaflets as in moringa, oroxylon.
1. Decompound
leaf: Wherein
compound leaf is much divided irregularly as in coriander, carrot, anise, etc.
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b) Palmate compound leaves: In this type the leaflets are born
by the petiole of the leaf.
Depending upon the number of leaflets in a compound palmate
leaf they are further divided as:
1. Unifoliate
compound leaf: Lemon.
2. Trifoliate
compound leaf: Bael,
wood apple.
3. Multifoliate
compound leaf: Bombax,
alstonia.
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[H]
Venation
The arrangement of veins in the lamina or leaf blade is
known as venation. Veins are nothing but vascular bundles. Water and minerals
absorbed by roots is conveyed to various parts of leaf by veins and the food
synthesized by leaf by way of photosynthesis is translocated to other parts of
plant through veins only. Veins also offer strength, support and shape to the
lamina of the leaf. The prominent vein in the centre of the leaf is known as
midrib. In the flower-ing plants two types of venations exist: (1) Reticulate
and (2) Parallel.
1.
Reticulate venation: This type of venation is
character-ized by the fact that many veins and veinlets in the lamina of the
leaf are arranged in the form of network or reticulars. This type of venation
is characteristic to dicotyledonous leaves. It is further sub-classified as:
a)
Unicostate-reticulate
venation: Where
the leaf contains only one midrib and several veins are given out on both the
sides to form the network such as henna, eucalyptus, peepal, etc.
b)
Multicostate-reticulate
venation: In
this type many veins of equal strength arise from the end of the petiole. Each vein
further branches to give rise to veinlets that form the network. The veins may
be convergent (meeting at the apex) or divergent (diverge towards the margin)
as in castor, carica and cucurbita.
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2. Parallel venation: In this type the vein and veinlets in leaf blade are arranged parallel to one another. It is char-acteristic to monocotyledonous plants with few exceptions like dioscorea and sarsaparilla.
Like reticulate venation, it may also be unicostate parallel venation or multicostate parallel venation as under:
a) Unicostate parallel venation: Wherein the leaf consists of only one midrib running from apex to the petiole of the leaf. The veinlets and veins arise parallel to one another on each side as in banana and canna.
b) Multicostate parallel venation: In case of multicostate parallel venation many number of main veins of equal strength arise from the tip or the petiole and run parallel to each other. It may be convergent as in case of several grasses and bamboo or divergent as in case of fan palm.
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[I] Phyllotaxy
It is the mode of arrangement of leaves on the stem. Since the leaves are the chief organs of photosynthesis they must be exposed to sunlight favourably. This is done by arranging the leaves in systematic manner. Following are the various types of phyllotaxy:
1. Alternate or spiral: This phyllotaxy is characterized by the presence of one leaf at each node and all leaves together make a spiral path on the axis, i.e. tobacco, mustard and sunflower.
2. Opposite: When two leaves are placed at the same node and are opposite to one another. This is farther divided into two:
a) Opposite decussate: In this type a pair of leaves of one node is at right angles to the pair of leaves at the next node such as maddar, sacred basil, vinca.
b) Opposite superposed: When one pair of leaves is placed above the other exactly in the same plane, i.e. Rangoon creeper, ixora.
3. Whorled: When more than two leaves are present in a single node and are arranged in a circle as in nerium, alstonia.
4. Leaf mosaic: In this type, the leaves are so arranged that there will not be any overshading and all the leaves are exposed properly. The older leaves have longer petiole while younger leaves have short petiole and are placed in the space left by the older leaves. It recalls the arrangement of glass bits in a mosaic and hence the name, e.g. Oxalis and acalypha.
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[J] Modifications of Leaves
Under the functions of leaves, it is stated that leaves have to perform two types of functions, i.e. primary functions and secondary functions. Under the primary function, leaves are known to perform three main functions like photosynthesis, gaseous exchange and transpiration. The secondary functions which the leaf has to perform are support, protection, storage of food material etc.
To perform these secondary functions the leaf under-goes structural and physiological changes called modifica-tions. There are at least five types of leaf modifications known.
1. Leaf tendrils: Leaves get modified into slender, coiled and wiry structures as seen in Lathyrus peas and gloriosa for support to the plant.
2. Leaf spines: For the sake of protection certain leaves get converted into spines as seen in Aloe, argemone, acacia, etc.
3. Phyllode: Petiole gets modified to flat leaf-like phyl-lode to reduce the transpiration, e.g. Australian acacia.
4. Scale Leaves: In ginger and potato they protect the terminal buds, while in onion and garlic they store food material.
5. Pitcher and bladder: These are specially developed modifications of leaves to capture and digest insects in case of carnivorous plants, e.g. Utricularis Bladder wort and Nepenthes.
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Morphology of Flowers
The flower is actually a modified shoot meant for
produc-tion of seeds. It consists of four different circles (whorls) arranged
in a definite manner. A flower is built up on stem or pedicel with the enlarged
end known as thalamus or receptacle.
The four whorls of the flowers can be described as under:
1. Calyx: It is the outermost whorl of flower
and is gen-erally green in colour, the individual member of which is called
sepal.
2. Corolla:
It is the second whorl of flower and
is either white or
bright coloured, each member of which is known as petal.
3. Androecium:
It is the third circle of flower and
con-stitutes the male part. The individual component is called stamen and each
stamen consists of filament, anther and connective.
4.Gynoecium:
This is the fourth circle of the
flower and constitutes
the female part. Each component is known as carpel or pistil and is made of
stigma, style and ovary.
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When all the four whorls, are present in a single flower, it
is described to be a complete flower, absence of any one of them describes it
as incomplete flower. A flower is described to be hermaphrodite or bisexual
when it contains stamens and carpels. Absence of any one of them describes it
as unisexual flower. When calyx and corolla in a flower are similar in colour
and shape, then both of them (calyx and corolla) together are called Perianth,
i.e. garlic, onion, asperagus.
When a flower is divided into two equal parts by any
ver-tical section passing through the centre, then it is described as regular
or symmetrical or actinomorphic flower as in ipomoea, rose, datura and shoe
flower. But when it cannot be divided equally into two parts by one vertical
section, then it is described as irregular or asymmetrical or zygo-morphic
flower.
When the stamens arise from petals instead of thalamus, the
petals are called epipetalous. When the stamens get united with gynaecium the
structure is known as gynaste-mium. The union of stamens among themselves is
known as cohesion. When the filaments of stamen get united to form a single
bundle, it is known as monoadelphous. When it forms two bundles, it is known as
diadelphous. When anthers get united to form a column (but filaments are free),
the stamens are known as syngenesious. When ovary consists of only one carpel,
it is said to be monocarpellary and when it contains more than one carpel, it
is said to be polycarpellary. When the carpels in ovary are free, the ovary is
described as apocarpous and when they are united it is known as syncarpous.
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Arrangement
of Floral Parts on Thalamus
Depending upon the arrangement of floral parts on thala-mus, the flowers may be of three types.
i. Hypogynous flower (Superior ovary): Herein the thalamus is conical, flat, convex and stamens, sepals and petals are arranged at base and ovary at the apex, e.g.: brinjal, china rose, mustard, etc.
ii. Perigynous flowers (Half-superior Ovary): Thala-mus is flat, sepals and stamens grow around the ovary. The flowers are said to be perigynous as in Rose, Strawberry peach.
iii. Epigynous flower (Inferior ovary): The thalamus is fused with ovary wall, calyx, corolla, stamen appear at the top and the gynaecium at the bottom as in Sunflower, cucumber, apple, etc.
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Placentation
The type of distribution of placentae in the ovary is called placentation. They are of the following types.
1. Marginal: It is characteristic to monocarpellary ovary and placentae arise on ventral suture, e.g. bean and pea.
2. Axil: It is characteristic to polycarpellary syncarpous, bilocular or multilocular ovary. Ventral sutures of each carpel meet at the centre and each of them have marginal placentation, e.g. onion, china rose, ipomoea.
3. Parietal: It is characteristic to polycarpellary syncarpous ovary and the placentae develop on the ventral suture but the ovary is unilocular as in papaya and cucurbita.
4. Free Central: It is characteristic to polycarpellary syn-carpous ovary, which is unilocular. Ovules arise on the central axis, but it is not connected with the peripheral wall, e.g. Dianthus, saponaria, portulacca.
5. Basal: It is characteristic to polycarpellary and unilocular ovary. Only one ovule is present and it arises from its base as in sunflower.
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Pollination
Pollination is the process of transference of pollen grains from the anther of a flower to the stigma of the same flower or another flower of the same or allied species. Pollen grains are produced by bursting the anther and are carried by various agencies to the stigma.
The agencies may be insects of various types, wind or even water. There are two types of pollination, i.e.
a) Self-pollination or autogamy and (b) cross pollination or allogamy.
a) Self-pollination: There are two types of self-pollina-tion, i.e.
Homogaxny: In this case the anthers and stigmas of a flower mature at the same time.
Clestogamy: It is found in flowers which never open or in the underground flowers of Commeline bengalensis.
(b) Cross-pollination: Pollination through the agency of insects, animals (such as snails, bats, squirrels, birds and even human being) wind and water is cross-pollination
Pollination by insects is known as entomophily. To attract various insects, plants adapt different means such as colour, nectar and scent. Entomophilous pollination is very common in plants.
Morphology of Inflorescence
Plant bear flowers either solitary or in groups. The flowers which are large and showy are normally borne solitary, but which are not so prominent and are small, occur in group or bunches.
The form of natural bunch of flowers in which they occur is called inflorescence. Depending upon the type of branching various forms of inflorescences are known. The axis on which the flowers are arranged is known as peduncle while the stalks of flowers are known as pedicels.
Types of Inflorescences
Following are the types of inflorescences:
(A) Racemose or indefinite inflorescence:
1. Raceme: In this type of inflorescence the peduncle is long. Flowers are stalked and born in acropetal succession and peduncle has indefinite growth and goes on produc-ing flowers as in mustard, radish, dwarf gold mohor, etc. When the main axis is branched and the lateral branches bear the flowers, it is said to be Compound raceme or panicle or branched raceme as in gul mohor, peltopho- rum, yuchr, etc.
2. Spike: This is similar to raceme, with sessile flowers as in Rangoon creeper, vasaka. A branched spike of polyanthes and terminalia species is known.
3. Spadix: In this inflorescence the peduncle is short with numerous small unisexual flowers, which are sessile and covered with boat shaped bract known as Spathe, i.e. banana, arum, palms and coconut are the example of compound spadix.
4. Catkin: A spike with unisexual sessile flowers on long peduncle as in mulberry and oak.
5. Umbel: Axis is shortened and bears flowers at its top which are having equal stalk and arranged in centripetal succession. A whorl of bracts is present at the base of inflo-rescence as in coriander, caraway, cumin, fennel, etc.
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6. pikelet: It is present in family Graminae characterized by small and branched spikes. Spikelets are provided with two bracts at the base known as glumes, and bracteole called palea.
7. Corymb: Peduncle is short, flowers bracteate, bisexual oldest flower is lower most and youngest at apex. Lower-most has longest stack and youngest has shortest, lying at same level.
8. Capitulum or Head: In this type flattened and expanded peduncle is present, called as receptacle. Base of receptacle is covered with bracts. The flowers are small and sessile (florets). Flowers towards the periphery are older, while at the centre, they are younger and open later. Two types of flowers are present, i.e. ray florets (strap shaped) and disc florets (tubular shaped), e.g. zinnia, cosmos, sunflower.
9. Capitate: Inflorescence similar to umbel type, except the flowers are sessile, i.e. acacia.
(B) Cymose inflorescence: In this type the growth of the main axis or peduncle is stopped by producing the flower. The order of opening is centrifugal. Its types are as under:
1. Solitary cyme: In this type the inflorescence ends in a single flower as in datura, capsicum, China rose, etc.
2. Uniparous or monochasial cyme: In this type, axis ends in a flower only; one branch arises just behind and ends in a flower. Uniparous depending upon the type of branching is again subdivided into (a) Hellicoid uniparous and (b) Scorpioid uniparous.
Hellicoid uniparous is characterized by branching on one side only, while scorpoid uniparous cyme by branch-ing on alternate side.
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3. Biparous or Dichasial cyme: This type of inflores-cence is characterized by the end of main axis in a flower, which is followed by two lateral branches ending in flowers again. Actually this is a true cyme as in case of ixora, teak,
jasmine, etc.
4. Multiparous or Polychasial: The main axis ends in a flower and numbers of flowers are produced laterally in
the same manner, i.e. in nerium, calotropis, etc.
5. Special type: In this type hypanthodium (like peepal and fig), verticillasters (sacred basil, mentha, coleus blumi) cymose-umbel (onion) are included. Each of them has its special characters not covered in any type described above.
Morphology of Seeds
The seed is a fertilized ovule and is a characteristic of Phanerogams. Parenchymatous body of the ovule known as nucellus contains embryo-sac in which fertilization of pollen cells takes place giving rise to embryo. The seeds are characterized by the presence of three parts known as embryo, endosperm and seed coat.
Seed coat
It is the outermost layer of the seeds providing necessary protection to the embryo lying inside the seed. In case of dicotyledonous seeds normally, it is hard and may contain two layers; the outermost thick layer is known as testa while the inner one which is thin is known as tegumen. In monocotyledonous seeds, it is thin or even may be fused with the wall of the fruit.
Embryo
It is the main part of the seed. It consists of an axis having apical meristem for plumule, radicle the origin or root and adhered to it are one or two cotyledons, differentiating the plants as monocot or dicot.
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Endosperm
It is the nutritive tissue nourishing the embryo. It may be present or may not be present in the seed. Depending upon the presence or absence the seeds are classified as under:
1. Endospermic or albuminous seeds.
2. Nonendospermic or exalbuminous seeds.
3. Perispermic seeds.
1. Endospermic or albuminous seeds: In this seed, the part of the endosperm remains even up to the germination of seed and is partly absorbed by embryo. Therefore, seeds are known as endospermic seeds as in colchicum, isabgol, linseed, nux vomica, strophamthus, wheat and rice.
2. Nonendospermic or exalbuminous seeds: During the development of these seeds, the endosperm is fully absorbed by embryo and endosperm, and is not represented in the seeds; hence, they are known as nonendospermic, e.g. sunflower, tamarind, cotton and soyabean.
3. Perispermic seeds: Herein the nucleus develops to such an extent that it forms a big storage tissue and seeds are found to contain embryo, endosperm, perisperm and seed coat; e.g. pepper, cardamom, nutmeg, guinea grains.
Seeds are characterized by the following descriptive terms:
a) Hilum: This is the point of attachment of seed to its stalk.
b) Micropyle: It is the minute opening of the tubular structure, wherefrom water is provided for the ger-mination of seeds.
c) Raphe: Raphe is described as longitudinal marking of adherant stalk of anatropous ovule.
d) Funicle: It is the stalk of the ovule attaching it to the placenta.
e) Chalza: This is the basal portion of ovule where stalk is attached.
Special features of seeds
Sometimes, apart from the regular growth of seeds, addi-tional growth is visible in the form of appendages which attribute to their special features. They are described as:
i. Aril: Succulent growth from hilum covering the entire seeds as in nutmeg (mace) and yew seeds.
ii. Arillode: Outgrowth originating from micropyle and covering the seeds as in cardamom.
iii. Arista (awn): Stiff bristle-like appendage with many flowering glumes of grasses and found in strophanthus.
iv. Caruncle: A warty outgrowth from micropyle, i.e. castor, croton, viola moringa.
v. Hairs: Gossypium and calotropis are examples of this type of outgrowth.
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Functions of Seeds
Seed performs the following functions:
1. Reproduction, i.e. it germinates into new plant.
2. Spread of the species.
3. Species and varieties do not come to an end by suc-cessive formation of seeds by plant. Thus seeds are ‘means of perennation’
Morphology of Fruits
Phanerogams are said to be matured when they reach the flowering stage. The ovules of the flowers after fertilization get converted into seeds, whereas the ovary wall develops further to form the protective covering over the seed, which is known as fruit. In botany, this particular coating is also called pericarp.
Pericarp consists of three different layers, one after the other as:
1. Epicarp: The outermost coating of the pericarp and may be thin or thick.
2. Mesocarp: A layer in between epicarp and endocarp, and may be pulpy or made up of spongy parenchy-matous tissue.
3. Endocarp: The innermost layer of the pericarp, may be thin or thick or even woody.
It is not necessary that the fruits should have seeds. If the ovules do not fertilize, the seedless fruits are formed. Depending upon the number of carpels present in the flowers, and other structures, the fruits fall into (1) simple fruits, (2) aggregate fruits and (3) compound fruits.
Simple fruits
Formed from the single carpel or from syncarpous gynoe-cium. Once again depending upon the mesocarp, whether it is dry or fleshy, they are classified as dry fruits and fleshy fruits. Dry fruits are further sub-classified into dehiscent and indehiscent fruits.
Aggregate fruits
These fruits get formed from many carpels or apocarpous gynoecium, e.g. raspberry.
Compound fruits
In this particular case many more flowers come together and form the fruits, e.g. figs, pineapple.
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False fruits
Sometimes it so happens that apart from the ovary and the other floral parts like thalamus, receptacle or calyx grow and form the part of the fruit, known as false fruit or pseudo-carp. Following are the few examples of pseudocarp in which other parts of the flower forming important part of the fruits are shown in the bracket. Strawberry (thalamus), cashew nut (peduncle and thalamus), apple (thalamus), marking nut (peduncle) and rose (thalamus)
I. Dehiscent capsular fruits:
1. Legume or pod: It is a dry monocarpellary fruit devel-oping from superior ovary, dehiscing by both the margins,
i.e. senna, tamarind, pea.
2. Capsule: It is a dry one to many-chambered fruit, developing from superior or poly carpellary ovary dehisc-ing in various forms, i.e. cardamon, cotton, datura, lobelia,
colchicum, digitalis, poppy.
3. Follicle: Similar to legumes and dehisces at one margin only, i.e. rauwolfia, anise, calotropis.
4. Siliqua: A dry, two-chambered fruit, developing from bicarpellary ovary, multiseeded. It dehisces from base upwards as in radish mustard, etc.
II. Indehiscest fruits:
1. Achene: A dry, one-chambered, one-seeded fruit devel-oped from superior monocarpellary ovary. Pericarp is free of seed coat, i.e. clemantis, rose.
2. Caryopsis or grain: Small, dry, one-seeded fruits, developing from simple pistil, pericarp fused with seed coat as in maize, rice, bamboo.
3. Nut: Dry, one-seeded fruits developing from superior ovary, pericarp hard and woody, i.e. areca nut, marking nut, cashew nut.
4. Samara: Dry, one- or two-seeded, winged fruit from superior bi- or tricarpellary ovary, i.e. dioscorea, shorea, etc.
5. Schizocarp: These are further divided into two sub-classes.
(i) Lomentum: In this type of pod of legume is parti-tioned into one-seeded compartments as observed in acacia, ground nut, cassia fistula.
(ii) Cremocarp: Dry, two-chambered fruit, developing from an inferior bicarpellary ovary. Splitting into two, indehiscent one-seeded pieces are called mericarps, i.e. coriander, cumin, fennel, dill, etc.
Fleshy fruits:
1. Drupe (Stone fruit): A fleshy one or more seeded fruit, with pericarp well differentiated into epicarp, fleshy mesocarp and hard endocarp as in mango, olive, coconut, etc.
2. Berry: A fleshy, many-seeded fruit developed from superior, single carpel, i.e. tomato, guava, grapes, banana.
3. Pepo: Pulpy, many-seeded fruit developing from one- or three celled inferior ovary, i.e. cucumber gourd, colocynth, water melon.
4. Pome: Fleshy, one- or more-celled syncarpous fruit. Fleshy, part is thalamus, while actual fruit lies inside, e.g. apple, pear.
5. Hesperidium: A superior, many-seeded fleshy fruit endocarp forming chambers; epicarp and mesocarp fused to form skin, e.g. orange, lemon.
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Uses of fruits
1. Apart from the main source of food grains, i.e. wheat, jowar, fruits are also used for their high sugar value, minerals and vitamins.
2. Fleshy fruits like, papaya, mango, apple are used com-mercially as source of pectin.
3. Bayberry wax and olive oil are obtained industrially from fruits only.
4. Several fruits like chilies, black pepper caraway and cumin are used on large scale for the preparation of spices.
