Plant Morphology PDF

PLANT MORPHOLOGY  MORPHOLOGY is the branch of botany that deals with the external features of plants. The plant body consists of the ROOTS, STEMS and LEAVES. The roots along with their branches (lateral roots) form the root system. The stem with the leaves form the shoot system. ...

PLANT MORPHOLOGY  MORPHOLOGY is the branch of botany that deals with the external features of plants. The plant body consists of the ROOTS, STEMS and LEAVES. The roots along with their branches (lateral roots) form the root system. The stem with the leaves form the shoot system.  Habitats of Plants The surroundings where the plants grow. Strongly related to the morphology, anatomy and physiology of plants. Plants are classified according to their habitats into: 1- MESOPHYTES The plants living in a fairly and continuously moist habitat. e.g. crop plants as vicia faba(broad bean), Zea mays (corn), Triticum sativum (wheat),…… 2- XEROPHYTES The plants living in dry conditions. e.g. desert plants as Alhagi and the cactus plants. 3- HYDROPHYTES Plants living in extreme moist conditions. They may be floating, submerged or fixed to the mud. 4- HALOPHYTES Plants growing in salt marches or saline soils. 4- MANGROVES Groups of trees or shrubs living at the intertidal regions at the tropic and sub-tropic regions. They are characterized by the presence of respiratory (breathing) roots. 6- EPIPHYTES Plants hanging on another plant for support and not for parasitism. They are usually short plants that have clinging roots (for fixing themselves on the host plant in order to reach sufficient sunlight). Their roots are also capable of absorbing water, either rain water or even air humidity water. 7- Parasites They draw nourishment from other organisms by haustoria. They may be totally parasites (having no chlorophyll-no green color) or semi-parasites(having chlorophyll and capable of performing photosynthesis if their host is not available). 8- CARNIVOROUS or INSECTIVOROUS PLANTS Living in soils deficient in nitrogen and gain their requirements of nitrogen from the flesh of insects or small animals. Plants are either: 1- Annuals Plants which complete their life cycle in one season or one year. They flower once in their life cycle. e.g. maize, wheat, beans,….. 2- Biennials Plants which complete their life cycle in two seasons or two years. They grow vegetatively in one season and form flowers and seeds in the second season. e.g. onions and carrots. 3- Perennials Plants living for more than two years. They may be Herbs…with no woody parts above the soil Shrubs…..not exceeding 1.5 m above the ground and not having trunk. Trees……woody plants with unbranched trunk at the base. Trees and shrubs are either evergreen or deciduous (shed their leaves during one season).  ROOT SYSTEM The root is the underground portion of the plant. It has +ve geotropism. Functions of roots: 1- support…..fixation of the plant to the soil. 2- Absorption of water and dissolved minerals. 3- Conduction of the absorbed water and minerals to above-ground plant parts. 4- Storage of food in some plants such as carrots, radish and turnip. 5- Other functions such as respiration in respiratory roots. ROOT ZONES The root of a plant is not divided into nodes and internodes and is distinguishable into five regions: 1- root cap (calyptra)….function in protecting the meristematic cells. The cells of this region are mucilagenous to help penetrating into the soil particles. They are continuously replaced as they are destroyed due to friction with soil particles. 2- meristematic region….cell division 3- region of elongation 4- region of root hairs…where maximum water absorption occurs. This region is almost absent in hydrophytes and well-developed in xyrophytes. 5- permenant region….where lateral roots originate. Lateral roots are endogenous while root hairs are exogenous. They have acute angles to the main root. ORIGIN of ROOTS There are two types of roots according to their origin: 1- Tap roots…….originate from the embryo and is persistent. 2- Adventitious roots…….Originate from the stem, leaf or other organs and is short-living. Modifications of roots 1- Storage or tuberous roots Swollen due to storage of reserved food. They are either: A- Tap roots…named according to their shape, either conical (e.g. carrots), fusiform (e.g. raddish) or napiform (e.g. turnip and beetroot) B- Adventitious (e.g. sweet potato) 2- Fibrous roots Common in Graminae They are fine, thread-like and slender. 3- Prop roots Develop from the lower nodes of stem. Growing downwards into the soil. Their aerial part is thick and unbranched. Inflexible. Function mainly for aerial support to keep the stem erect against wind action. When they reach the soil, they also act for absorption. E.g. zea mays and sugarcane. 4- Aerial roots They may arise from some branches of Ficus benghalensis trees and some epiphytes. They hang down from the stem. They have special spongy tissues called velamen of many layers replacing the root epidermis and used to absorb moisture from atmosphere. 5- Pillar roots When the aerial roots reach the soil surface, they penetrate and grow rapidly in the soil and used for the absorption of water and minerals. They become thick and act for supporting the horizontal branches from which they originate. E.g. Ficus benghalensis. 6- Respiratory roots They grow in water-logged soil where the aeration is bad. They grow upwards and are covered with pores called lenticles which facilitate the exchange of gases between the root and atmosphere. 7- Haustoria roots Specialized roots formed by parasitic plants. E.g cuscuta plant which parasitizes Trifolium and Orobanche plnt which parasitizes Vicia faba 8- Contractile roots They develop from some bulbs, corms or rhizomes. They are long, straight, thick and fleshy. They contract and pull the plant down to a lower depth where water is more available or to avoid crowding and competition with other plants for water.  Many plants engage in symbiosis with microorganisms. Two important types of these relationships are 1) with bacteria such as Rhizobium, that carry out biological nitrogen fixation, in which atmospheric nitrogen (N2) is converted into ammonium (NH4). 2) with mycorrhizal fungi, which through their association with the plant roots help to create a larger effective root surface area. Both of these mutualistic relationships enhance nutrients uptake.  Though nitrogen is plentiful in the Earth's atmosphere, relatively few plants host nitrogen fixing bacteria, so most plants rely on nitrogen compounds present in the soil to support their growth. These can be supplied by added plant residues, nitrogen fixing bacteria, animal wastes, or through the application of fertilizers.  STEMS Functions of stem: 1- The green parts of stems undergo photosynthesis. 2- Exchange of gases through stomata. 3- Conduction of soil solution absorbed by roots to branches and leaves through xylem vessels. 4- Conduction of manufactured food from leaves to all plant parts through phloem. 5- Used in vegetative reproduction. e.g. potatoes. 6- Could be modified for other functions such as storage e.g. potatoes and taro )‫ القلقاس‬Colocasia esculenta(. Mode of Growth 1- Erect stems They grow upwards and have enough mechanical support. They may be trees, shrubs or herbs. 2- Weak stems They can not grow upwards by their own because they do not have enough mechanical tissues. They are long and have rapid growth and may be: A- climbing by tendrils ‫المحاليق‬ B- twining C- Prostrate ‫زاحفة‬ the stem extends in all directions and has only one root system e.g. watermelon D- Runner ‫جارية‬ The shoots and roots develop at every other node e.g. strawberry Stem modifications a- Modification of aerial parts Succulent stems….modified to store water, common in xerophytes  Leafy stems….modified to increase the photosynthetic surface Spiny stems……modified to reduce water loss through evaporation and for protecting the plant against animals. B- Modification of subterranean parts Rhizomes…..underground stem, differentiated into nodes and internodes, the terminal bud develops into an aerial shoot and the lateral buds complete the plant growth (sympodial branching). Axillary (lateral) buds at the axils of scaly leaves at the nodes, these buds develop aerial shoots upwards and adventitious fibrous roots downwards. e.g. Cynodon dactylon ‫النجيل‬  Bulbs….has a discoid dwarf stem carrying fibrous roots, outer leaves are scaly and red or golden yellow, inner leaf bases are fleshy and are used for food storage. e.g. onions  Tubers…swollen underground stems with stored food, it has eyes which are depressions representing the stem nodes, each eye is surrounded by scaly leaves with axillary buds. e.g. Solanum tuberosum (potatoes) Corms….also swollen with stored food, differentiated into nodes and internodes with brown leathery scales (for protection) and axillary buds at different stages of development at the nodes. e.g. Colocasia  LEAVES Functions of leaves: 1- They undergo photosynthesis because they contain chlorophyll. 2- Exchange of gases between the atmosphere and plant tissues. 3- Protection of buds from the environmental conditions. Summer buds are protected by green leaves while winter buds are protected by brown scaly leaves. 4- could be modified to perform other functions as in bulbs (food storage), succulent leaves (water storage), insectivorous plants (catching insects), spines (protection) and tendrils (climbing). Morphological description of leaves includes several points: Leaves arrangement Leaves composition Leaf base (stipules) Leaf petiole Leaf margin Leaf apex Veination Blade Modifications  Leaves arrangement on stem Alternate Parallel Arrangement Opposite Decussate Whorled  Ordinary Exstipulate Leafy Leaf Base Stipulate spiny hairy stipuleoles  Alternate Parallel Petiole Opposite Decussate Whorled  Linear Tubular Ovate Palmate Spatulate Blade Elliptical Cordate Lanceolate Reniform Hastate  Acute Acuminate Apex Obtuse Emarginate  Entire Dentate Margin Serrate Lobate  Longitudinal Parallel Transverse Veination Pinnate Reticulate Palmate  Paripinnate Simple Composition Pinnate Imparipinnate Compound Palmate Bipinnate  SEED GERMINATION Conditions necessary for seed germination: 1- Internal factors a) Viability (ability of the seed to germinate under favorable conditions) and longivity (the life span of the seed). Storage of seeds in cold dry conditions keeps them vital for longer times. b) Dormancy of the seed Dormancy is due to: Incomplete development of embryo Hardness of the testa Some seeds of parasitic plants can not grow away from their hosts. 2- External factors a) Presence of water….softens the testa and activates the protoplasm and hydrolytic enzymes b) Presence of oxygen….for respiration of the embryo c) Temperature…..Each species has three main temperatures for germination: minimum, optimum and maximum Seeds are named according to season of germination to winter seeds or summer seeds. d) Light and dark conditions…..seeds are either light seeds(+ve photoblastic), dark seeds (-ve photoblastic) or indifferent seeds (non- photoblastic). Changes occuring during germination 1- Physical changes……swelling of the seed and rupture of the testa due to imibition of water. 2- Biochemical changes….hydrolysis of complex compounds into simple ones by hydrolytic enzymes (e.g. amylase (for starch), proteases (for proteins) and lipases (for lipids). This is followed by translocating the simple compounds to the growing regions and are used to produce energy through respiration. 3- Biotic changes….growth of plumule into the shoot and radicle into the root. Structure of the seed 1- Seed coat (testa) 2- Embryo….consists of: a) The embryo axis b) The plumule c) The redicle d) The cotyledones 3- The storage tissue (endosperm)…..seeds are either exendospermic (no endosperm-food is stored in the cotyledons) or endospermic (food is stored in special tissues outside the cotyledons )