Morphology of Flowering Plants PDF

# Morphology of Flowering Plants ## Plant Morphology - Flower - Fruit - Stem - Leaf - Shoot system - Node - Internode - Bud - Primary root - Root system - Secondary root ## Morphology of Root ### Characteristics 1. Root is defined as the descending part of the plant axis. 2. It is positively ge...

# Morphology of Flowering Plants ## Plant Morphology - Flower - Fruit - Stem - Leaf - Shoot system - Node - Internode - Bud - Primary root - Root system - Secondary root ## Morphology of Root ### Characteristics 1. Root is defined as the descending part of the plant axis. 2. It is positively geotropic. 3. It is positively hydrotropic. 4. It is negatively phototropic. 5. It develops from the radicle of the embryo during seed germination. 6. Roots are generally non-green and cylindrical. 7. They produce only similar organs i.e. secondary and tertiary roots 8. They do not show nodes and internodes ## Root Development - The radicle is the first root produced at germination. - Rapid cell division takes place at the apical meristem, then root hairs production and subsequently the lateral root developed from pericycle. - Lateral roots growth from the primary root. **Diagram Legend:** - Protoxylem Pole - Metaxylem - Phloem - Pericycle - Endodermis - Cortex - Epidermis - Lateral Root Growth - Apical Meristem - Root Cap ## Embryonic Root or Radicle - **Diagram:** Shows a close-up image of a seed with the radicle emphasized, followed by two images of seedlings with the radicle elongated. ## Morphology of Root ### Regions of the Root: 1. **Region of root cap** - The tender apex of the root is protected with a multicellular cap-like structure called root cap. - The cells of the root cap secrete mucilage for lubricating the passage of the root through the soil. - In many hydrophytes like *Pistia* and *Eichhornia*, the root cap is replaced by a root pocket. 2. **Region of cell division or meristematic region** - It is a small region about 1mm in length. - This is the growing part of the root and is protected by the root cap. - It is made up of thin-walled, compactly arranged meristematic cells which have the power of division. - This region helps in longitudinal growth by the addition of new cells. 3. **Region of elongation** - It lies just above the meristematic region. - The cells of this region are newly formed and they elongate rapidly. This increases the length of the root. - The cells of this region help in the absorption of mineral salts. 4. **Region of root hair or root absorption** - Surface of this area is covered with numerous root hairs. - The cells of the outer layer known as piliferous layer or epiblema produce root hair. - The root hairs are elongated, single-celled, tubular structures which remain in contact with soil particles. - The root hairs increase the surface area of absorption. - They are short-lived and are replaced by new root hairs after every 10 to 15 days and is responsible for absorption of water. 5. **Region of maturation or cell differentiation** - It forms the major part of the root. - The outermost layer of this region has thick-walled impermeable cells. - The enlarged cells undergo differentiation to form different types of primary root tissue like cortex, endodermis, xylem, phloem, etc. This region helps in fixation of the plant body into the soil and also in conduction of absorbed substances. - Lateral roots also develop from this region of the root. ### Functions of the Root - **Primary:** - The normal functions of the roots are fixation or anchorage of the plant body into the soil (substratum), absorption of water and minerals from the soil, and conduction of absorbed materials up to the base of the stem. - **Secondary:** - In some plants, roots perform certain special functions, and such roots undergo necessary modifications. Some roots become fleshy or swollen for the storage of food materials e.g. carrot, radish, asparagus, sweet potato, Dahlia, etc. - After becoming green, some roots manufacture food by photosynthesis e.g. *Tinospora*, *Trapa*, *Orchids* etc. - Some roots help in the exchange of gases (respiration) e.g. *Rhizophora*, *Sonneratia* etc. - In parasitic plants like *Cuscuta*, adventitious roots penetrate the host stem to obtain food and water. - Sometimes roots also take part in vegetative reproduction e.g. sweet potato. - Aerial roots absorb moisture from the air e.g. *Orchids*. Thus modified roots perform different functions. ### Types of Roots **Tap Roots or True Roots:** - Develops from the radicle of an embryo during seed germination is called a true root or tap root. - The main root is called a primary root. - Its branches of first order are called secondary roots, and branches of secondary order are called tertiary roots and so on. - The main root along with its branches forms a tap root system e.g. *Mustard* (Brassica), *Sunflower* (Helianthus) etc. - Presence of a tap root system is a characteristic feature of dicotyledonous plants. - The tap root normally grows vertically downwards to a lesser or greater depth, while secondary and tertiary roots grow obliquely downwards or some grow horizontally outwards. - All lateral branches are produced in acropetal succession, i.e. the older and longer branches are near the base, and the younger and shorter ones are near the apex of the main root. **Adventitious Root System:** - A root that develops from any other part other than the radicle is known as an adventitious root. - Such roots may develop from the base of the stem, nodes or from leaves. - In monocots, the radicle is short-lived, and from the base of the stem, a thick cluster of all equal-sized roots arises. This is known as the adventitious root system e.g. *Maize*, *wheat*, *sugarcane*, etc. - It is also known as a fibrous root system as the adventitious roots of grasses (monocots) look like fibers. - Fibrous roots do not grow very deep into the soil. ## Modifications of the Root ### Modifications of Tap Root 1. **Storage of food:** - The tap root (primary) becomes fleshy and swollen due to the stored food. - The secondary roots remain thin. - Hypocotyl (embryonic region between cotyledons and radicle) may also join the tap in storing food. - The stem is reduced and discoid in the beginning and bears radical leaves. - The swollen tap root acquires some typical shape and is accordingly classified into the following three types: - **Fusiform root:** The storage root which is swollen in the middle part and tapers towards the base and apex is called fusiform root e.g. radish (*Raphanus sativus*). - **Conical root:** The storage root which is broader at the base and gradually tapers towards the apex is called conical root e.g. *carrot* (*Daucus carota*). - **Napiform root:** The storage root which is much swollen, almost spherical and abruptly tapers around the apex is called napiform root e.g. *beet* (*Beta vulgaris*). 2. **Respiration:** - Plants growing in saline swamps, marshy places and salt lakes are called halophytes. - Many halophytes develop special kinds of roots called respiratory roots or pneumatophores. - Roots of these plants do not get air for respiration as the soil is waterlogged. As a result, absorption of minerals is affected. - Such plants produce special roots from the underground roots of the plant near the soil, which grow vertically upwards i.e. negatively geotropic and come out of the soil in the form of conical spikes. - They occur in large numbers around the tree trunk and are provided with pores called lenticels. - The lenticels help in gaseous exchange required for respiration. - e.g. *Rhizophora*, *Avicennia*, *Sonneratia*, *Heritiera* (vern or sundri) etc. ### Modifications of Adventitious Root 1. **Storage of food:** - **Simple tuberous roots:** These roots become swollen and do not assume a definite shape. They are always borne singly. These roots arise from the nodes of the stem and enter in the soil e.g. *sweet potato* or *shakarkand* (*Ipomoea batatas*). - **Fasciculated tuberous roots:** A cluster of adventitious roots of some plants become thick and fleshy due to the storage of food. These are known as fasciculated tuberous roots, as there are many tuberous roots at the base of the stem. E.g. *Dahlia* and *Asparagus*. 2. **Mechanical Support:** - **Prop roots:** These roots arise from horizontal branches of trees like *Banyan tree* (*Ficus benghalensis*) and grow vertically downward till they penetrate the soil. Secondary growth occurs in these roots, so that they become thick and act like pillars to provide mechanical support to the heavy branches. - **Climbing roots:** Climbing plants like *piper* produce roots from their nodes, by means of which they attach themselves to some support or climb over it. e.g. *money plant* (*Pothos*), *kali mirch* (*Piper nigrum*), *pan* (*Piper betel*). - **Stilt roots:** These roots normally arise from a few lower nodes of a weak stem in some monocots, shrubs and small trees. They grow obliquely downwards and penetrate the soil and provide mechanical support to the plant. In plants like *maize*, *sugarcane*, *bajra* and *jowar*, the roots grow in whorls. After penetrating the soil they provide support to the plant. In *screwpine* or *Pandanus*, these roots arise only from the lower surface of the obliquely growing stem to provide support. These roots bear much folded multiple root caps. 3. **Special Functions:** - **Epiphytic roots:** Some plants like orchid grow perched on the horizontal branches of big trees in the forest to get sunlight. Such plants have green leaves and can photosynthesize. These plants are called epiphytes. Epiphytes develop special aerial, hanging roots called epiphytic roots. These roots are spongy due to the presence of a special tissue called velamen, which is situated outside the cortex. The cells of velamen tissue are hygroscopic, have porous walls and with the help of velamen tissue these roots absorb moisture from the atmosphere e.g. *Venda*, *Dendrobium*, etc. These roots fulfill the need of water in epiphytes, as they do not have normal roots penetrating the soil to absorb water. These roots are also called assimilatory roots, as they are greenish-white in color, have chloroplast and can photosynthesize up to a certain extent. - **Sucking roots or Haustoria:** These are highly specialized and microscopic roots, developed by parasites to absorb nourishment from the host. In partial parasites like *Viscum album*, they penetrate only xylem elements of the host to absorb water and minerals. In total parasites like *Dodder* or *Cuscuta* (Amarvel), they establish a connection with the vascular strand of the host and suck food directly from phloem and water and minerals from the xylem. Such roots are called parasitic roots, sucking roots or Haustoria. ### Summary of Root Modifications | MODIFICATIONS | Type | Description | |---|---|---| | **Underground** | Rhizome | Prostrate, dorsiventral thickened brownish stem which grows horizontally under the surface of the soil. | | | | Sympodial: Growth of rhizome takes place horizontally with the help of the lateral bud. | | | | Monopodial: Growth of rhizome takes place horizontally with the help of the terminal bud. | | | Tuber | Swollen ends or tips of special underground branches due to the storage of food. | | | Bulb | Condensed, disc-like underground stem which doesn’t store food. | | | | Tunicated Bulb: fleshy scale leaves surround the apical bud in the form of concentric rings. | | | | Scaly Bulb: fleshy scale leaves partially overlap each other by their margins. | | | Corm | Short, stout, fleshy, upright and thickened underground stem. | | **Sub - aerial** | Runner | Special, narrow, green, horizontal or prostrate branches which develop at the base of erect shoots called crowns. | | | Stolon | Slender lateral branch that arises from the base of the main axis. | | | Offset | Commonly called the runner of aquatic plants. | | | Sucker | Runner-like non-green branch which develops from the axil of a scale leaf in the underground part of the stem. | | **Aerial** | Tendril | Modification of a stem in which the axillary bud modifies to form a thin, wiry, and highly sensitive structure called tendril. | | | Thorn | Hard, pointed usually straight structure produced by modification of an axillary bud. | | | Phylloclade | Stem which gets transformed into leaf-like structure. | | | Cladode | Green branches of limited growth which have taken up the function of photosynthesis. | | | Bulbil | Axillary bud becomes fleshy and rounded due to storage of food. | ## Morphology of Stem ### Characteristics - The aerial part of the plant body is collectively described as a shoot system. - The main axis of this shoot system is called the stem. - Stem can be defined as the ascending part of the plant axis, which develops from the plumule. - It is usually negatively hydrotropic, negatively geotropic and positively phototropic. - It bears a terminal bud and axillary buds in the axils of leaves, for growth. - It is differentiated into nodes and internodes. - At the nodes, it produces dissimilar organs such as leaves and flowers and similar organs such as branches, exogenously i.e. originate from outer tissue. - The young stem is green and capable of performing photosynthesis. ### Buds - **Vegetative buds:** The buds which develop into branches are called vegetative buds. - **Apical buds:** located at the apex of the stem. - **Axillary buds:** located in the axils of leaves. - **Accessory buds:** located on the sides or above the axillary buds. - **Adventitious buds:** located at areas other than nodes. - **Floral buds:** The buds which develop into flowers are called floral buds. ### Functions of Stem - The primary functions of the stem are to produce and support lateral appendages such as branches, leaves, flowers and fruits, conduction of water and minerals to different parts of shoots, and transport food to all plant parts. - Stem may, however, get modified to perform additional or functions such as storage of food and water, proliferation and propagation, procuring support for climbing, perennation i.e. to tide over unfavorable conditions, synthesis of food (photosynthesis). ### Modifications of Stem | MODIFICATIONS | Type | Description | |---|---|---| | **Underground** | Rhizome | Prostrate, dorsiventral thickened brownish stem which grows horizontally under the surface of the soil. | | | | Sympodial: Growth of rhizome takes place horizontally with the help of the lateral bud. | | | | Monopodial: Growth of rhizome takes place horizontally with the help of the terminal bud. | | | Tuber | Swollen ends or tips of special underground branches due to the storage of food. | | | Bulb | Condensed, disc-like underground stem which doesn’t store food. | | | | Tunicated Bulb: fleshy scale leaves surround the apical bud in the form of concentric rings. | | | | Scaly Bulb: fleshy scale leaves partially overlap each other by their margins. | | | Corm | Short, stout, fleshy, upright and thickened underground stem. | | **Sub - aerial** | Runner | Special, narrow, green, horizontal or prostrate branches which develop at the base of erect shoots called crowns. | | | Stolon | Slender lateral branch that arises from the base of the main axis. | | | Offset | Commonly called the runner of aquatic plants. | | | Sucker | Runner-like non-green branch which develops from the axil of a scale leaf in the underground part of the stem. | | **Aerial** | Tendril | Modification of a stem in which the axillary bud modifies to form a thin, wiry, and highly sensitive structure called tendril. | | | Thorn | Hard, pointed usually straight structure produced by modification of an axillary bud. | | | Phylloclade | Stem which gets transformed into leaf-like structure. | | | Cladode | Green branches of limited growth which have taken up the function of photosynthesis. | | | Bulbil | Axillary bud becomes fleshy and rounded due to storage of food. | ## Morphology of Leaf ### Characteristics - Leaf is a thin, expanded, green structure. - The green color of the leaf is due to the presence of chlorophyll pigment. - It is exogenous in origin. - It is borne on the stem at the node. - An axillary bud is often present in the axil of each leaf. - It has limited growth. - It does not possess an apical bud or a regular growing point. ### Parts of a Leaf 1. **Leaf base or hypopodium:** - The part of the leaf attached to the stem or branch is known as the leaf base. - It may assume different shapes in different plants. - In some leguminous plants, the leaf blade may become swollen which is called pulvinus. - In monocots, the leaf base expands into a sheath covering the stem partially or completely. - Leaves of some plants possess a pair of lateral outgrowths at the base, on either side of the axillary bud. These outgrowths are called stipules, and such leaves are called stipulate leaves. - The leaves without stipules are called ex-stipulate leaves. Stipules are usually green. - The main functions of stipules are to protect the bud and carry out photosynthesis. 2. **Petiole or mesopodium:** - Petiole is the part of the leaf connecting the lamina with the branch or stem. - Leaves that possess petiole are called petiolate, and leaves without petiole are called non-petiolate or sessile leaves. - Petiole is usually cylindrical but may be hollow (Papaya), tubular or flattened. - The function of the petiole is to raise the lamina to expose it to more light and air and to help in conduction. 3. **Lamina or epipodium:** - This is the largest, most important, green and flattened part of the leaf. - It plays a vital role in photosynthesis, gaseous exchange and transpiration. - The leaf is known as dorsiventral when its ventral surface is structurally different from the dorsal surface, e.g. dicotyledonous leaves. - The leaves having both similar surfaces are called isobilateral. Such leaves are found in monocot plants. ### Leaf Venation - The arrangement of veins and veinlets in the lamina is known as venation. - The veins are, in fact, conducting strands of lamina. - They are concerned with the conduction of water, mineral salts and food and form the structural framework of the lamina. - **Reticulate venation:** When the veins and veinlets form a network, it is called reticulate venation. Here the midrib is centrally placed, and veins and veinlets remain distributed laterally. It is found in dicotyledonous plants. - **Unicostate:** With a single mid-vein (e.g. Mango). - **Multicostate:** With two or more prominent veins (e.g. Zizyphus). It may be convergent or divergent. - **Parallel venation:** In this type of venation, veins in lamina run almost parallel to one another. It is found commonly in monocotyledonous plants. - **Unicostate:** e.g., Banana, Canna. - **Multicostate:** e.g., Grass, rice, bamboo, etc ### Types of Leaves - **Simple leaf:** Simple leaves are those in which a single leaf blade or lamina is present, e.g., Mango, Peepal, Papaya, etc. - **Compound leaf:** Compound leaves are those in which the leaf blade or lamina is divided into a number of segments known as leaflets or pinnae. The leaflets never bear axillary buds in their axil. - **Pinnately compound leaves:** In this type, the leaflets are present laterally on a common axis called rachis, which represents the midrib of the leaf (e.g. Gold mohur, Cassia). - Unipinnate - Bipinnate - Tripinnate - Decompound - **Palmately compound leaves:** All the leaflets of the palmately compound leaves are attached at a common point, i.e. at the tip of the petiole, like fingers of the palm. - Unifoliate - Bifoliate - Trifoliate - Quadrifoliate - Multifoliate ### Phyllotaxy - Phyllotaxy is the arrangement of leaves on the stem and branches. - **Alternate phyllotaxy:** In this type, a single leaf arises at each node. The leaves arise laterally on the stem or branches, e.g., Sunflower, Mango, China rose, Mustard etc. - **Opposite phyllotaxy:** In this type, two leaves arise from each node in opposite directions. - **Decussate:** When one pair of the leaf is placed at a right angle to the next or lower pair of the leaf, it is said to be opposite decussate phyllotaxy. e.g., Calotropis, Ocimum, etc. - **Superposed:** In this type, all the pairs of leaves on the stem are arranged one above the other, e.g., Jamun, Guava, etc. - **Whorled or verticillate phyllotaxy:** In this type, more than two leaves arise from each node and form a whorl around it. e.g., *Nerium*, *Alstonia* ### Modifications of Leaves - **Leaf spines:** In some xerophytic plants like *Opuntia*, the entire leaf gets modified into a small, stiff, pointed structure called spine to check transpiration. Sometimes only a part of the leaf, such as stipules, get modified into spines, to protect plants from grazing animals, e.g., *Zizyphus* and *Acacia*. - **Leaf tendrils:** In certain plants having weak stems, the entire leaf or a part of it gets modified into an elongated, thin, cylindrical, coiled, wiry, sensitive structure known as a tendril. These tendrils help the plant to climb up on some support. - In *wild pea* (*Lathyrus*), the entire leaf is tendrillar. - In *sweet pea* (*Pisum sativum*), terminal leaflets are tendrillar. - In *Gloriosa*, only the leaf apex modifies into a tendril. - In *Smilax*, stipules become tendrillar. - **Leaf hooks:** In *Bignonia unguis-cati* (Cat's nail), the terminal three leaflets get modified into three stiff curved and pointed hooks which look like cat's nails. They cling to the bark of trees (support) and help the plant for climbing. *Bignonia* is an elegant hook-climber. - **Phyllode:** In some plants, the petiole becomes flat, green and leaf-like and performs photosynthesis. This is known as phyllode. For example, in *Acacia auriculiformis*, the normal leaf is bipinnately compound and falls off soon. The petiole gets modified into phyllode. This is xerophytic adaptation to reduce transpiration. ### Summary of Leaf Modifications | MODIFICATIONS | Type | Description | |---|---|---| | **Venation** | Reticulate | When the veins and veinlets form a network. | | | | Unicostate: With a single mid-vein. | | | | Multicostate: With two or more prominent veins. | | **Venation** | Parallel | When these veins run almost parallel to one another. | | | | Unicostate: With a single mid-vein. | | | | Multicostate: With two or more prominent veins. | | **Types** | Simple | A single leaf blade or lamina is present. | | | Compound | The leaf blade or lamina is divided into a number of segments known as leaflets or pinnae. | | | | Pinnately compound: Leaflets present laterally on a common axis called a rachis. | | | | Palmately compound: Leaflets attached to a common point at the tip of the petiole. | | **Phyllotaxy** | Alternate | A single leaf arises at each node. | | | Opposite | Two leaves arise from each node. | | | | Decussate: One pair of the leaf is placed at a right angle to the next or lower pair. | | | | Superposed: All the pairs of leaves on the stem are arranged one above the other. | | | Whorled | More than two leaves arise from each node and form a whorl around it. | | **Modifications** | Spine | Entire leaf or a part of the leaf gets modified into a small, stiff, pointed structure. | | | Tendril | Entire leaf or part of it gets modified into an elongated, thin, cylindrical structure. | | | | Whole leaf | | | | Terminal leaflet | | | | Apex | | | | Stipules | | | Hook | Terminal leaflets modified into hooks. | | | Phyllode | Petiole becomes flat, green, and leaf-like and performs photosynthesis. |