Morphology1

• The description of the diverse forms of life on earth was made only by observation – through naked eyes or later through magnifying lenses and microscopes
• This description is mainly of gross structural features, both external and internal
• Observable and perceivable living phenomena were also recorded as part of this description
• Before experimental biology or more specifically, physiology, was established as a part of biology, naturalists described only biology
• Biology remained as a natural history for a long time
• The detailed description was utilised in the later day reductionist biology where living processes drew more attention from scientists than the description of life forms and their structure
• The description became meaningful and helpful in framing research questions in physiology or evolutionary biology
• For convenience, the description of morphological and anatomical features is presented separately for plants and animals
• Katherine Esau

  Born in Ukraine in 1898, studied agriculture in Russia and Germany, received doctorate in 1931 in United States, reported that the curly top virus spreads through a plant via the food-conducting or phloem tissue, her book Plant Anatomy published in 1954 took a dynamic, developmental approach designed to enhance one's understanding of plant structure and had an enormous impact worldwide, elected to the National Academy of Sciences in 1957, received the National Medal of Science from President George Bush in 1989
• When Katherine Esau died in the year 1997, Peter Raven, director of Anatomy and Morphology, Missouri Botanical Garden, remembered that she 'absolutely dominated' the field of plant biology even at the age of 99
• The wide range in the structure of higher plants will never fail to fascinate us

  
• Angiosperms show a large diversity in external structure or morphology, but are all characterised by presence of roots, stems, leaves, flowers and fruits
• We need to know standard technical terms and standard definitions, as well as possible variations in different parts, found as adaptations of the plants to their environment
• The underground part of the flowering plant is the root system while the portion above the ground forms the shoot system
• Tap root system

  Primary root which grows inside the soil, bears lateral roots of several orders
• Fibrous root system


  Primary root is short lived and replaced by a large number of roots originating from the base of the stem
• Adventitious roots


  Roots arising from parts of the plant other than the radicle
• Functions of the root system

  • Absorption of water and minerals from the soil, providing a proper anchorage to the plant parts, storing reserve food material and synthesis of plant growth regulators
• Root cap

  Thimble-like structure that protects the tender apex of the root
• Region of meristematic activity


  Cells are very small, thin-walled and with dense protoplasm, divide repeatedly
• Region of elongation

  Cells undergo rapid elongation and enlargement, responsible for the growth of the root in length
• Region of maturation

  Cells differentiate and mature, some epidermal cells form root hairs that absorb water and minerals
• Modifications of root

  • Tap roots of carrot, turnips and adventitious roots of sweet potato get swollen and store food, prop roots of banyan tree, stilt roots of maize and sugarcane, pneumatophores of Rhizophora
• Stem

  Ascending part of the axis bearing branches, leaves, flowers and fruits, develops from the plumule of the embryo, bears nodes and internodes
• Functions of the stem

  • Spreading out branches bearing leaves, flowers and fruits, conducting water, minerals and photosynthates, storage of food, support, protection and vegetative propagation
• Modifications of stem

  • Underground stems of potato, ginger, turmeric, zaminkand, Colocasia for storage and perenation, stem tendrils for climbing, thorns for protection, flattened or fleshy cylindrical stems in arid region plants, underground stems of grass and strawberry for spread and vegetative propagation, lateral branches in banana, pineapple and Chrysanthemum
• Leaf

  Lateral, generally flattened structure borne on the stem, develops at the node and bears a bud in its axil, consists of leaf base, petiole and lamina

  
• Venation

  Arrangement of veins and veinlets in the lamina, reticulate (network) or parallel
• Simple leaf


  Lamina is entire or when incised, the incisions do not touch the midrib
• Compound leaf


  Incisions of the lamina reach up to the midrib breaking it into a number of leaflets
• Pinnately compound leaf


  A number of leaflets are present on a common axis, the rachis, which represents the midrib of the leaf
• Palmately compound leaf

  Leaflets are arranged like the fingers of a hand on the end of the petiole
• Leaves of dicotyledonous plants generally possess reticulate venation, while parallel venation is the characteristic of most monocotyledons

  
• A bud is present in the axil of petiole in both simple and compound leaves, but not in the axil of leaflets of the compound leaf
• Palmately compound leaf


  The leaflets are attached at a common point, i.e., at the tip of petiole
• Phyllotaxy


  The pattern of arrangement of leaves on the stem or branch

  
• Types of phyllotaxy

  • Alternate
  • Opposite
  • Whorled
• Alternate phyllotaxy


  A single leaf arises at each node in alternate manner
• Opposite phyllotaxy


  A pair of leaves arise at each node and lie opposite to each other
• Whorled phyllotaxy


  More than two leaves arise at a node and form a whorl