An organism's structure can be studied completely underT two branches of biology- morphology and anatomy. Morphology deals with the study of form, size, colour, structure and relative position of various parts of the organisms. It indicates the structural adaptations of organisms to their environment.
WHAT IS MEANS BY PLANT MORPHOLOGY
The angiosperms are the most diverse and wide-spread of all plant groups. Depending on their habitat they can be classified as hydrophytes, mesophytes and xerophytes. The various habitats show modifications in their morphology. Plant morphology includes study of root, stem, leaves,flowers, fruits and seeds and their modifications.
MORPHOLOGY OF ROOT
Root is an important vegetative part of the plant mainly responsible for nutrition and support. Root develops from radicles of seed. It is the descending, non-green, underground, positively geotropic and negatively phototropic part. Roots are absent in some angiosperms, e.g., Utricularia, Ceratophyllum, Cuscuta, Wolffia, Balanophora, etc.
Stem is the aerial part of the plant which develops from plumule. It is the ascending portion of the plants which is positively phototropic and negatively geotropic. It bears nodes, internodes and buds. It holds the plants upright and performs the function of storage. It transports the
absorbed water and minerals from the roots to different parts of the plant. Sugar synthesised in leaves is transported to the roots by stem.
MORPHOLOGY OF LEAF
Leat is a green, flattened outgrowth of the plant arising from the node of the stem and is specialized to perform photosynthesis. An axillary bud is often present in the axil of the leaf. A leaf is known as the kitchen of the plant or food factory of the plant because it perform: photosynthesis.
Abundant stomata present on the leaves make them the major seats of transpiration. Leaves of some plants help in vegetative propagation and protection by modifying themselves into different forms. A typical leaf consists of three parts, leaf base, leaf stalk or petiole and leaf blade or lamina.
Leaf base (hypopodium) is the lowermost part of the lea and is joined to the node of the stem. Different types of leaf bases are pulvinus, sheathing and decurrent. In pulvinus leaves, leaf base in swollen and leaf is easy to pluck due to weak attachment with stem, e.g., mango, pea, gram, banyan, etc. Sheathing leaf base forms a sheath around the stem portion above the node. It may be amplexicaul(completely sheathing) or semi-amplexicaul.
Decurrent leaf base is a wing that covers the upper part of the node.In some plants leaf base consists of small appendages on both sides, these are called stipules. The leaves having stipules are termed as stipulate while the leaves without stipules are called exstipulate. Mainly stipules perform the function of protection of leaves.
Petiole (Mesopodium) is a cylindrical or sub cylindrical smooth or grooved stalk of the leaf which connects the lamina with the stem. Leaf having petiole is called petiolate and when it is absent, it is called sessile.Lamina (epipodium) or leafblade is green, flattened part of
leaf performing the important functions of photosynthesis,transpiration and respiration. In the middle of lamina, a thick midrib is present extending from petiole to the apex. The midrib produces thinner lateral veins, which in turn, give rise to still thinner veins or veinlets and as a result a net like structure is visible in the lamina.
Venation
The arrangement of veins and veinlets on the lamina of the leaf is called venation. In parallel venation the veins run parallel to each other. Generally found in monocotyledons and rarely in some dicotyledonous leaves. E.g., Eryngium, Calophyllum, etc. In reticulate venation the main vein forms a number of branches and gives rise to a net like structure in the leaf. It is generally found in dicots and rarely in monocots. E.g., Smilax, Alocasia, Dioscorea,etc.
Phyllotaxy
Phyllotaxy means the arrangement of leaves on the true stem and its branches. The arrangement of leaves are of three types: alternate, opposite and whorled arrangement.In alternative (spiral) arrangement only one leaf is borne on a node and the leaves of the adjacent nodes roughly lie towards the opposite side, eg, shoe flower, mango, mustard, tobacco, etc. In the opposite arrangement, a node gives rise to two leaves, arranged opposite to each other. In Whorled type of arrangement more than two leaves are formed from each node, which are e.g., Alstonia, Nerium, Vangueria, etc.
Types of leaves
Depending upon the incision of lamina, leaves are of two types, i.e., simple and compound. These two types are further subdivided into two types each
MORPHOLOGY OF INFLORESCENCE
Inflorescence is the arrangement of flowers on the floralaxis (peduncle) which may be positioned either on the tip of stem branches, i.e., terminal e.g.,Crotalaria. in leaf axils, i.e., axillary, e.g., Petunia. in between the floral axis, i.e., intercalary, e.g, Callistemon.
Depending upon the growth pattern of peduncle an inflorescence may be cymose, racemose or mixed.In racemose type, main axis of inflorescence has an indefinite (indeterminate) growth and it gives rise to (lateral or axillary) flowers in an acropetal order, i.e The youngest flower is at the apex while the oldest is at the base of the peduncle. In cymose inflorescence the growth of the main axis is limited and the rachis or peduncle apices are terminated by flower (no further elongation of the axis). Mixed inflorescence has combination of cymose and racemose characters, e.g., cymose umbel, thyrsus (main branching 15 racemose and lateral branching is cymose). Special types of inflorescences are basically cymose but ultimately it is modified to form a special appearance.Various subtypes of these four viz. cymose, racemose, mixed and special inflorescence are discussed in the flowchart
MORPHOLOGY OF FLOWER
lower is a modified condensed shoot of limited growth which bears floral leaves that carTy on sexual reproduction and give rise to seeds and fruits. Peduncle is the stalk of a solitary flower or inflorescence. In an inflorescence stalk of a Single nower 1s known as pedicel. The tip of the pedicel is called thalamus or torus or receptacle.Thalamus 1S formed by the condensation of internodes of the floral axis.
Actinomorphic towers can be cut into two equal parts in any plane, eg, bolanum. Zygomorphic flowers can be cut into two equal parts in only one plane, e.g, PIsum. Asymmetric flowers cannot be cut into two equal parts in any plane, e.g., Canna.
There are two lower whoris of accessory or non essentialorgans (calyx and corolla) and two upper whorls of reproductive or essential organs (androecium and gynoecium). Flowers possessing both androecium and gynoecium are termed bisexual. Unisexual flowers possess either only androecium or gynoecium.
Affower poSsessing superior ovary 1s known as hypogynous while a flower possessing inferior ovary 1s epigynous. A perigynous flower possesses half-inferior and half- superior ovary. In pentamerous flower each whorl especially calyx and corolla possesses 5 units. In trimerous
and tetramerous flowers each whorl possess 5 and 4 units,respectively.
Calyx
The outermost or the first accessory whorl of flower consisting of sepals is called calyx. It may be polysepalous (calyx with free sepals) and gamosepalous (calyx with Fused sepals). They protect floral organs during bud' stage.
Corolla
The second whorl of a flower consisting of petals is called corolla. Corolla are brightly coloured and attract insects For pollination and protect the inner essential whorls from injury. Corolla with free petals is a polypetalous corolla.Corolla with fused petals is a gamopetalous corolla. Shape
of polypetalous corolla are cruciform, caryophyllaceous,rosaceous and papilionaceous.
In monochlamydeous flowers when a single accessory whorl is present (with no distinction between sepal and petal), the whorl is described as perianth. Unit of perianth or individual member of perianth is known as tepal. The mode of arrangement of sepals or petals or even sepals in a flower bud is called aestivation. When their margins are not overlapping it is valvate aestivation. When of the total number, one is completely out, one is completely in and the rest are in and out, it is imbricate aestivation. In descending imbricate aestivation the standard petal
is large and overlaps the two wing petals which in turn overlap the two keel petals. It is technically known as vexillary aestivation. When of the total number, two are completely out, two are completely in and the rest is in and out, it is quincuncial aestivation. In contorted or twisted aestivation all sepals or petals are in and out.
Androecium
The third whorl of the flower or the first essential whorl of the flower, composed of stamens is called androecium. A sterile stamen is called staminode. A typical stamen consists of a stalk called filament, a connective and an anther. While the connective links the two anther lobes, the anther produces the pollen. The stamens of an androecium may be free or exhibit cohesion or
adhesion.
When stamens are partially or completely fused among themselves, such a condition is known as adelphi. Stamens may be monadelphous, e.g., Hibiscus, Abutilon, Crotolaria, etc, diadelphous, e.g., Pisum (pea), Indigofera, tephrosia, Clitoria, etc, polyadelphous, e.g., Bombax, syngenesious, e.g., Tridax, Helianthus (sunflower) or Synandrous, e,g. Cucurbita, Coccinia. When stamens are adhered to either sepals or petals the conditions are known as epipetalous and epipetalous, respectively. Episepalous, e.g., Quisqualis indica, epipetalous, e.g., Solanum, Leucas, Vinca, etc. When two stamens are long and two are short as in labiatae, acanthaceae, etc. the condition is said to be didynamous. In tetradynamous condition four stamens are long and two are short, e.g., cruciferae.
Gynoecium
A typical gynoecium (pistil) may consist of one or more units known as carpels. A carpel is differentiated into basal ovule(s) containing a part called ovary, a middle elongated or short style and the pollen receiving terminal structure called stigma. A gynoecium with free carpels is known as apocarpous, while one with fused carpels is known as syncarpous. The swollen part of the ovary where the ovules are attached is called placenta. Arrangement of placentae in ovaries is known as placentation which may be marginal, basal, axile, free central or parietal. In marginal placentation placentae are present along the ventral suture, found in monocarpellary ovary, e.g., family fabaceae. In basal type the placenta is located on the floor of the locule of the ovary, e.g., Tridax, Helianthus (sunflower), etc. In axile placentation placentae are located along the axis of the ovary, but partitioned by radial septae, e.g Hibiscus, Tribulus, Allium cepa (onion), etc. In free-central type, lacunae are located along the axis of the ovary as in axile placentation, but are not partitioned by radial septae, e.g Dianthus. In parietal type, two or more placentae are longitudinally located on the inner side of the ovary wall, e.g., Cucurbita, Cucumis, Raphanus (radish), Brassica (mustard), etc.
MORPHOLOGY OF FRUIT
A fruit can be defined as a matured ovary or ovaries, with or without seeds together with any accessory structure closely associated with them. True fruits develop only from the ovary and other floral parts do not take part in its development. Fruits formed by some other parts of flower are known as false fruits or pseudocarp fruits. E.g., apple in which fruit consists of swollen thalamus enclosing mature ovary. Parthenocarpic fruits or seedless fruits, are fruits which are formed without fertilization e.g., banana. Mature wall of the ovary after ripening is called pericarp. It has three layers.
Pericarp
Outermost layer - Epicarp (skin of fruit)
Middle layer-Mesocarp (may be thin and membranous in orange, hard and stony in plums,
fleshy and juicy in mango, etc.
Innermost layer - Endocarp (thin and membranous)
Classification of different kinds of fruit
Fruits are classified into various types according to the structure of pericarp, mode of dehiscence and the ovary from which they have developed. These types of fruits are discussed in brief in the following flow chart.
MORPHOLOGY OF SEED
Morphologically, seed (ripened ovule) is the integumented, mature, megasporangium which is developed from fertilized ovule and is with an embryo (future plant, enclosed by seed coat). In bitegmic ovules (with two distinct layers) outer, thick hard, leathery seed coat is called
testa (if one seed coat is present, then it is also called testa) and the inner thin, papery layer is called tegmen. Fused pericarp and testa With the help of a stalk called funicle, a seed is attached to the fruit wall (pericarp) and the point of attachment is called hilum. Raphe is the part of the funicle that is fused with the seed coats or integuments. Chalaza is that region from which the seed coats originate. Micropyle 1s a small opening or pore, present just below the hilum.Kernel is obtained by removing the seed coat and it mainly consists of the embryo. Kernel may also contain endosperm (reserve food; present in endospermic or albuminous seeds like cereals, castor, coconut, etc.) a special type of nutritive tissue. In albuminous or non-endospermic seeds like gram, pea, mustard, etc., endosperm is fully consumed by the embryo.
There is one cotyledon, 1n monocotyledonous angiosperms and two cotyledons, in dicotyledonous angiosperms. Over the narrower end of the seed a brownish pad is found which is called caruncle. Below the seed coat a very thin membrane is found over a kernel called perisperm (the persistent nucellus). Below perisperm there is a large, white, swollen and oily mass found called endosperm. The outer covering of endosperm separates the embryo by a proteinous
layer called aleurone layer. Cotyledon is shield-shaped and called scutellum in monocotyledonous seed. 2-4 protective layers are found over plumules which are called coleoptiles. Such protective layers over radicals are called coleorhiza.
DISPERSAL OF FRUITS AND SEEDS
For better growth of plants, it is needed that seeds reach
places distant from the parent plant. Dispersal is important as it prevents overcrowding at a place thus decreases competition between seedlings for nutrients, etc. Besides, it results in wide distribution of various plant species thus invasion of new habitats. Various methods of seed and fruit
SEMI-TECHNICAL DESCRIPTION OF A FLOWERING PLANT
For ease of study, identification and classification it is necessary to describe a flower in semi technical language. Description of a flowering plant in semi technical language is done using various morphological features. The symbolic representation of the flower just like a chemical formula is