Plant Morphology and Anatomy (Botany 07101) PDF

Fundamentals of plant morphology and anatomy (Botany 07101) Prepared by Dr. Ahmed Gomaa Mabrouk Gad  Stem morphology Stem: It is the main structural axes of vascular plants, it supports leaves, flowers and fruits. It develops from the seed plumule Stem charact...

Fundamentals of plant morphology and anatomy (Botany 07101) Prepared by Dr. Ahmed Gomaa Mabrouk Gad  Stem morphology Stem: It is the main structural axes of vascular plants, it supports leaves, flowers and fruits. It develops from the seed plumule Stem characteristics Stem develops from the plumule and epicotyl of the embryo. It is generally an aerial and ascending part of the plant axis. Its apex bears a terminal bud for growth in length. It bears nodes and internodes. The stem nodes bear leaves. The young stem is green and is thus has the ability to make photosynthetic. In the mature state, it bears flowers and fruits. Stem branches and leaves develop exogenously. Hair, if present, is generally multicellular. Stem is positively phototropic and negatively geotropic. Q: Lateral organs of the stem are…… (1) Endogenous in origin (2) Exogenous in origin (3) Both (4) None of the previous  Stem primary function Stem bears leaves, flowers and fruits. It conducts water and minerals from the roots to the leaves, flowers, and fruits. It also transports food, manufactured by the leaves to the roots, fruits and other storage organs of the plant. It adds new cells, tissues, and organs, which are required for the continued functioning of the plant because of the presence of terminal bud.  Stem secondary functions 1- A large number of plants store food and water in their underground stems like rhizomes of ginger, corms (colocasia ) and tubers (e.g., potato). The stem of sugarcane which stores sugar in it. 2- The stems of several succulent plants store water. 3- The underground stems such as rhizomes, corms, tubers, etc. perform the function of perennation (tiding over unfavorable growing period). 4- In many plants, stems serve as a means of vegetative propagation as in the case of runner (e.g., grass), stolons (e.g., strawberry), offsets and underground stems (e.g., mint, Potato, etc.). Q: Which of the following is an underground stem? (1) Ginger (2) Sweet potato (3) Radish (4) Turnip 5- The stems of some weak-stemmed plants may be modified into tendrils (e.g., Grapevine), thorns and hooks to help them in climbing. 6- The stem of some plants is modified into thorns, phylloclades and cladodes to reduce transpiration. 7- The stem thorns act as organs of defense and protect the plant from wandering animals. 8- The stem in younger state and when modified into phylloclades and cladodes, performs the function of photosynthesis. 9- The stem when modified into a flower performs the function of sexual reproduction.  DIFFERENT FORMS OF STEM In most plants, stems grow above the soil surface. These are called aerial or epiterranean stems. The aerial stems of some plants trail or creep on the ground. They are called sub-aerial or subepiterranean stems. In some plants, the stems grow in the soil. Such stems are called underground or subterranean stems. The aerial stems or epiterranean stems are of three types: Reduced Erect Weak 1. Reduced stems (short stems): The stem is reduced to a small disc above the base of the root. Nodes and internodes are not distinct, and leaves arise crowded together on the stems. Such leaves appear to arise directly from the root and are called radical leaves, such as radish, turnip, carrot, etc. A reduced discoid, flattened stem is found in some free-floating aquatic plants such as Lemna, spirodela and Wolffia etc. The underground structures called bulbs found in such as onion and garlic also possess a reduced and non-green stem. 2. Erect stems: These are the most common type of aerial stems. The stems are strong enough to remain erect or upright without any external support. The erect stem is of the following types: Culm: Erect, unbranched, cylindrical, hollow, nodes visible as rings and swollen. Stems are joined at nodes, e.g., bambo (family Gramineae). Caudex: Erect, unbranched, cylindrical stem. On the stem, scars of fallen leaves are visible, e.g., coconut date palm.  Excurrent: The main stem is thicker than the branches, tapers towards the apical part, branching is acropetal. The appearance of the tree is just like a cone. Decurrent or deliquescent: The main stem is short, and branching does not follow any definite manner and spread more laterally than vertically. At the stem top, the branches appear like a crown. The tree appears dome shaped, e.g., banyan 3. Weak stems: These are thin, delicate, and slender stems, which cannot stand erect. Therefore, they require support to expose their leaves and reproductive organs. The weak stems may climb up support or grow prostrate on the ground. Thus, they are of two types: upright and prostrate. A. Upright weak stems: These are weak stemmed plants, which climb up support to expose their foliage and reproductive organs. The upright weak stems are of two types: twiners and climbers. Twiners: These have long, flexible, and sensitive stems. The stem can coil around support like a rope  Climbers: These have weak and flexible stems, which climb up a support with the help of certain clasping or clinging structures. Accordingly, climbers are of four types: ⚪ Root climbers: The stem cling to the support by adventitious roots like plant (Pothos) ⚪Tendril climbers: Tendrils are highly sensitive structures, specialized, thread- like structures, which can coil around a support, and help the weak stemmed shoot to climb up the support. When in contact with a support, the side of the tendril, which is opposite to that in contact grows more rapidly. This results in the coiling around the support and gives a firm grip for climbing. Q: A thin spirally coiled structure sensitive to contact is……(1) Stem (2) Root (3) Tendril (4) Root hair  ⚪ Scramblers or ramblers: These are weak stemmed plants that climb up the support with the help of thorns , prickles etc. Thorns are obtained from shoots. Spines are obtained from leaves and prickles are derived from the epidermis.  Sub-epiterranean stems Also called prostrate or weak stems. These weak stems spread on the ground for exposing their leaves and reproductive organs. Types of sub-aerial or sub-epiterranean stems: 1- Runners: The sub-aerial weak stem and their slender lateral branches grow horizontally along the soil surface. Adventitious roots arise from nodes and nodes bear new tuft of leaves. Runners serve as means of vegetative propagation. The nodes bear scale leaves and axillary buds e.g., (lawn grass). 2-Stolon: They are elongated, horizontal or arched runners with long internodes like runners, these are slender axillary branches, which develop adventitious roots on coming in contact with the soil. Each stolon has one or more nodes possessing scale leaves and axillary buds. The axillary buds may either form a secondary stolon or may grow up as an erect short aerial stem. Stolons also propagate vegetatively, e.g., jasmine, strawberry 3- Sucker: These are sub-aerial, non- green branches that arise from the underground base of the aerial shoot or crown and runs parallel to the soil surface up to short distance then emerges out of the soil obliquely. These sub-aerial branches are shorter and stouter than the runners. Each sucker has one or more nodes with scale leaves and axillary buds. The axillary buds can also sprout into new shoots. A sucker also bears adventitious roots at the nodes, e.g., mint, etc. 4- Offset : These are one internode long, stout, slender and condensed runner found in rosette plants at the ground or water level. An offset arises from an axillary bud at the base of the cluster of leaves. It runs horizontally and terminates in a bud at a short distance that develops into adventitious roots and a rosette (cluster) of leaves, e.g., (water lettuce), (water hyacinth), etc.  How to differentiate between underground stem and a root? Underground stems appear root like in their appearance, but they can be distinguished from roots by (i) Absence of root caps (ii) Absence of root hair (iii) Presence of terminal bud (iv) Presence of nodes and internodes (v) Presence of foliage or scale leaves on the nodes (vi) Presence of buds in the axils of scale leaves (vii) Exogenous branching Q: How to differentiate between underground stem and a root?  TYPES OF UNDERGROUND STEMS 1. Stem tuber: Fleshy, swollen, rounded or oblong distal portions of underground axillary or adventitious branches that arise from the underground basal nodes (present on tubers). Underground axillary or adventitious branches are termed as stolons. The tips of these branches become enlarged in the form of tubers, due to the accumulation of surplus food material manufactured by the aerial shoots. Stem tubers are covered over by corky skin having lenticels for aeration. Each tuber possesses several spirally arranged depressions called eyes. Each eye represents a node that has a scale leaf in the form of a ridge. Each eye contains 1–3 dormant buds. The stem tuber lacks adventitious roots, such as potato What is the eye of potato? (i) A xillary bud (ii)A ccessory bud (iii)A dventitiousbud (iv)A picalbud 2. Rhizome: It is fleshy, horizontally growing, perennial, underground stem which continues to grow for an indefinite period producing new leaves or shoots during favourable conditions. The aerial leaves or shoots wither or die on the approach of unfavourable conditions and are replaced by the new ones on the arrival of next favourable period. A rhizome bears nodes and internodes. The nodes bear scale leaves that protect axillary buds. It also bears adventitious roots on the nodes and on the lower side Examples are ginger, banana The new banana plant develops from— (1) Rhizome (2) Sucker (3) Stolon (4) Seed 3. Corm: It is a vertically growing, thick, fleshy usually unbranched spherical or sub-spherical underground stem. It bears several circular nodes with scales, which represent thin sheathing bases of fallen dead leaves. The nodes bear axillary buds and adventitious roots. Corms take part in perennation. They develop aerial shoots from their buds during favourable period. The aerial shoots manufacture food and store the same in their bases, where new corms are formed. The new corms may appear either above or on the side of the old ones. The aerial shoots die of during the unfavourable season. The old corms generally shrivel due to utilization of the stored food in forming the new aerial shoot in the next favourable season 4. Bulb: It is an underground spherical structure that possesses a reduced discoid stem and several fleshy, sheathing bases (usually called scales), enclosing a terminal bud. Discoid stem bears fibrous adventitious roots. Tunicate or laminate bulbs: These have fleshy scales arranged concentrically. Each scale completely envelops the younger one within it. The outer scale becomes dry and membranous forming a protective covering called as tunic. Simple tunicate bulb: In this type of bulb, the fleshy scales represent leaf bases in the outer region and scale leaves in the central part. The bulb is covered with a whitish or pinkish tunic, e.g., (onion), (Tulips).  Compound tunicate bulb In this type, the fleshy scales represent axillary buds. Each axillary bud has its own tunic. These fleshy buds are called bulblets or cloves. The concentric rings of tunicate bulblets are in turn surrounded by overlapping tunics, garlic Atunicate or scaly imbricate bulbs These bulbs lack tunic or covering sheath. The fleshy scales are narrow and overlap one another on the margins only. Such a bulb is never a compact body, e.g., (lily).  MODIFICATIONS OF AERIAL STEMS In some plants, stems undergo an extreme degree of modifications and depict specific appearances to perform certain special functions besides the normal functions. How to recognize stem modification? By observing the following: - The presence of axillary bud - Origin-exogenous - Presence of nodes and internodes - Occurrence of occasional branching - Presence of scale or reduced leaves - Formation of flowers - Internal structure. - types of vascular bundle.  Types of aerial stem modification 1. Stem Tendrils: These are thin, thread- like sensitive, leafless structure which coil around a support and help the plant in climbing. Stem tendrils can be branch or unbranched. Branched stem tendrils may bear scale leaves in the region of forking. Stem tendrils are of the following types - Axillary bud tendril : Axillary bud modifies into a tendril, e.g., (passion flower). - Apical bud tendril : The apical bud gets modified into a tendril. The growth of the axis is continued by successive lateral axillary buds on either side of the axis. Thus, a sympodial axis is formed, and the tendrils are opposite to leaves such as grapevine. 2. Stem Thorns : These are modified axillary buds, which have lost the capacity for growth. These are stiff , woody, sharp and pointed. Reduce transpiration Prevent browsing by animals Stem thorns of are curved and help in climbing Q: The prickles of rose are…… (1) Modified leaves (2) Modified stipules (3) Exogenous in origin (4) Endogenous in origin 3. Phylloclade These are green flattened or cylindrical stem or branches, which appear leaf like, and have taken over the function of photosynthesis in the absence of normal green leaves. The true leaves fell of soon after their appearance or reduced to scales or spines to reduce transpiration. Phylloclades are succulent due to storage of water, food and are of unlimited growth. Phylloclades are characteristics of some xerophytic plants such as cacti. 4. Cladodes :These are green cylindrical or flattened stem branches of limited growth (usually one internode long). They have taken over the function of photosynthesis from leaves. The true leaves are reduced to scales and spines to reduce transpiration. The cladodes arise in the axils of scaly or spiny leaves at the nodes on the normal stem.  MORPHOLOGY OF LEAF Leaf is a flattened, lateral outgrowth, which is borne exogenously on the node of a stem or its branches and bears bud in its axil. Green colour due to the presence of chlorophyll and is the chief photosynthetic organ of the plant. Parts of a leaf (i) leaf base or hypopodium, (ii) petiole or mesopodium (iii) lamina or leaf blade or epipodium.  Leaf Characteristics It is borne on the node of the stem in acropetal order. It is exogenous in origin. It often bears axillary bud. The leaf does not bear an apical bud or regular growing point. A leaf is differentiated into three parts, leaf base, petiole and lamina. The leaf base may possess two lateral outgrowths called stipules. The lamina is traversed by prominent streaks called veins.  1. Leaf Base (Hypopodium) Leaf base is the lowermost part of the leaf, by which the leaf is joined to the node of the stem or its branch. Usually, it protects a small bud in its axil. Leaf base is often indistinguishable from the petiole. In many leguminous plants, it is swollen. The swollen leaf base is called pulvinus. It is responsible for sleep or shock movements of certain plants (e.g., Mumosa pudica). In several monocot plants (e.g., cereals, grasses, etc.) the leaf base is broadened, clasps and forms a sheath like structure around the stem at the node. Such a leaf base is called a sheathing leaf base. When the leaf base surrounds the stem partially, it is called semi amplexicaul. When the leaf base surrounds the stem, it is called amplexicaul. Stipules: In many plants, the leaf base possesses two lateral outgrowths, called stipules. They protect leaf primordia. The stipules vary in size and form and can be free or fused. The fused stipules cover and protect leaves in the bud In pea and wild pea, the stipules are large and green to take part in photosynthesis. They are called foliaceous stipules. In Acacia and Zizyphus the stipules are modified into spines to reduce transpiration. They also protect the plant from grazing animals. Such stipules are called spiny stipules. In Smilax, the stipules are modified into tendrils to help the plant in climbing. They are called tendrillar stipules. 2. Petiole (Mesopodium): It is a cylindrical or sub cylindrical stalk of the leaf. It raises the lamina above the stem to provide maximum exposure to light for photosynthesis. In some plants, the leaves are without petioles, such leaves are called sessile leaves. The leaves with petioles are called petiolate leaves. Q: The broad part of a leaf is — (1) Leaf base (2) Petiole (3) Lamina (4) All 3- Lamina (leaf blade or Epipodium): It is green, expanded portion of the leaf. It is the main site of photosynthesis and also helps in exchange of gases. Lamina is interspersed with a number of veins and veinlets which transport water and food. They also provide rigidity to the lamina and keep the latter expanded. There are one or more prominent veins in the lamina. They are called midribs or mid-veins.  Types of Leaves Leaf Duration: Based on the life span, leaves are of three types: Caducous (Fugacious): Leaves falling down soon after their appearance Deciduous (Annual): Leaves falling of simultaneously at the end of growing season, leaving the plant leafless. The phenomenon is called leaf fall. Persistent (Evergreen): Leaves live for more than one season. They fall down individually at different times. Plants with persistent leaves are called evergreen.  The veins are the conducting channels for water, minerals and organic food. Veins also provide firmness to the lamina and keep it expanded. The lamina has one or more prominent veins termed as midribs, which arise from the petiole. Midrib (prominent/main vein) gives rise to lateral veins that traverse the entire lamina. The veins and veinlets are more prominent on the undersurface of the lamina in dorsiventral leaves Venation The arrangement of veins and veinlets in the lamina of the leaf Reticulate Venation: The veins arising from the midrib, branch and re-branch to form a network of veins, this network is reticulate venation. It is a characteristic feature of the leaves of dicot plants. Based on the number of main veins or midribs in the lamina, reticulate venation has two sub-types: (i) Pinnate or Unicostate Reticulate Venation: The lamina has a single principal vein or midrib extending from base to the apex. It produces lateral veins. Lateral veins branch and re-branch into veinlets forming a network-like structure, e.g., leaf of Banyan, Mango, etc (ii) Palmate or Multicostate Reticulate Venation: The lamina has more than one prominent or principal veins arising from the tip of the petiole and reaching either the apex or margin of the lamina. They give rise to lateral veins and further to veinlets. It has two forms: Convergent: The principal veins converge towards the apex of the lamina Divergent: The principal veins diverge towards the margin, e.g., Castor.  2. Parallel Venation :The veins arising from main veins run parallel to each other towards the margin or the apex of the lamina. The veinlets are inconspicuous and reticulation or network of veinlets is absent. Parallel venation is characteristic of the leaves of monocot plants. Parallel venation is of two sub- types. (i) Pinnate or Unicostate Parallel Venation: The lamina has a single prominent vein or midrib running from the base to the apex of the lamina. It gives of lateral veins that run parallel toward the margin of the lamina, (banana). Types of Parallel Venation A. Unicostate parallel venation of banana; B. Multicostate convergent of bamboo; C. Multicostate divergent venation of Fan Palm  (ii) Palmate or Multicostate Parallel Venation The lamina has several principal veins arising from the base and running towards the apex or margin of the lamina. The main veins do not branch further. (a) Multicostate parallel venation has two forms Convergent: The principal veins converge towards the apex, e.g., bamboo, grass. Divergent: The principal veins diverge towards the margin Fan palm. 3. Furcate Venation : The veins give of dichotomous branching. The finer branches do not form reticulum. Furcate venation is common in ferns. Among higher plants, it is found in Circaeaster plant Thank you