Morphology and Anatomy of Plant Body - Leaf (Folium) PDF

Morphology and anatomy of plant body… continue Leaf (Folium) Definition of the plant leaf The leaf may be defined as a lateral outgrowth on the stem, characterized by its flattened form, thin texture, the presence of chlorophyll and having buds or branches in its axil. ...

Morphology and anatomy of plant body… continue Leaf (Folium) Definition of the plant leaf The leaf may be defined as a lateral outgrowth on the stem, characterized by its flattened form, thin texture, the presence of chlorophyll and having buds or branches in its axil.  Types of leaves Prophylls (fore leaves): the first leaf born on a branch, and it is simple in form and structure. Foliage leaves: the ordinary green leaves. Scale leaves: occur on all subterranean stems and on some aerial ones. They are thin, membranous and devoid of chlorophyll. Bracts: leaves having a flower in their axils. Floral leaves: include the colored sepals, petals, the stamens and carpels. Cotyledons (Seed leaves).  FOLIAGE LEAVES The foliage leaves are green in color due to the presence of chlorophyll. In autumn, the leaves may acquire different color. The yellow and the orange colors are due to the pigments, xanthophyll and carotene respectively. The red color is due to the pigments xanthocyanins.  The leaves may be cauline when they are spread apart on elongated aerial stem or radical when they are crowded together about the top of the root, at the level of the ground or just above it.  Duration of leaves Persistent: when live for one year or more, thus the plant is described as evergreen. Deciduous: when falling in autumn, thus the plant bears no expanded leaves during winter.  Phyllotaxis It is the distribution of the leaves on the stem. They may be: Alternate or Spiral: when the leaves are inserted singly at the node regularly. Opposite: when the leaves are inserted in pairs at each node opposite to each other. Whorled or Verticillate: when 3 or more leaves are inserted at each node. A complete leaf is composed of three parts: Lamina or Blade Stalk or petiole Base: It is the part of the leaf by which it is attached to the stem and is slightly enlarged.  Stipules They are lateral outgrowth developed in the leaf base for protection of the young axillary buds and assist in photosynthesis. When the stipules are present, the leaf is described as stipulate. When absent, it is exstipulate.  Petiole or leaf-stalk: It serves to carry the lamina away from the stem and conducts materials to and from the lamina. When it is present, the leaf is described as petiolate, while when absent, it is sessile.  The lamina or leaf blade: Usually green in color, flattened, rarely needle- shaped. It may be: Simple: Consists of a continuous, undivided surface Lobed or divided: cut up into a number of lobes, connected together by an undivided portion. Compound: Completely segmented into a number of separate leaflets.  COMPOUND LEAVES Compound leaves consists of 2 or more leaflets, either coming out from the top of the petiole or arranged on a central axis called rachis, which is continuous with the petiole and corresponds to the midrib of the simple leaf. They may be are:  Binate: with 2 leaflets only. Ternate: with 3 leaflets, 2 lateral and 1 terminal. Palmate: with 5 or more leaflets coming out from the top of the petiole. Pinnate: with several leaflets arranged on the rachis. It may be; o Paripinnate: With even number of leaflets in 2 rows, 1 on either side of the rachis. o Imparipinnate: the leaflets are odd in number and terminate with a single leaflet.  SIMPLE LEAF Shape Venation Apex Surface Margin Texture Base  Shape When the lamina has nearly the same width: o Filiform: thread like. o Acicular: needle-shaped. o Linear: flat, long and very narrow. o Oblong: flat and wide with edges parallel near the middle. When the lamina has the widest part near the base: o Lanceolate: like linear but wider below the middle. o Ovate: like the outline of an egg. o Cordate: heart-shaped. When the lamina has the widest part near the apex: o Obcordate: reversed heart-shaped. o Obovate: reversed egg-shaped. o Spathulate: flat like a spoon. When the lamina is symmetric Orbicular: circular. Elliptical: wide in the middle and symmetrically narrow and rounded at base and apex. Oval: broadly elliptical.  Apex Acute: when the 2 sides of the margin form an acute angle at the tip. Acuminate: more tapering apex into a point and is longer than in acute. Obtuse: blunt or rounded. Recurved: curved backwards. Mucronate: acute apex, terminating in a sharp horny point called apiculus. Emarginate: with apical notch or incision.  Margin Entire: even and smooth. Revolute: rolled back. Crenate: numerous rounded lobes. Dentate: having teeth, pointed straight outwards. Serrate: having sharp teeth directed towards the apex.  Base Symmetric: equal on both sides of midrib. Asymmetric: unequal on both sides of midrib. Decurrent: when the base continuous downwards as wings along the petiole.  Venation Parallel: several veins run side by side parallel with each other. Reticulate: veins form network.  Surface Upper surface of the leaf is usually dark green while the lower is paler. Midrib is usually prominent on the lower surface. It may be: Smooth: when wrinkled. Punctate: when dotted with projections from oil glands. Glabrous: when free from hairs. Pubescent or hairy: when covered with short hairs.  Texture Membranous: very thin. Papery: thin like paper. Coriaceous: thick and leathery. Succulent: thick and fleshy. Microscopical Structure of the Leaf The midrib region consists of the epidermis, cortical tissue, and vascular system. The lamina region consists of epidermis and mesophyll. The epidermis is a protective layer; it may contain stomata or trichomes. Trichomes or hairs, they are either covering (nonglandular) or glandular trichomes.  Mesophyll It is usually differentiated into: Palisade: cylindrical, columnar cells, perpendicular to the epidermis. Spongy tissue: closely packed chlorenchyma. According to the disposition of the mesophyll, the leaf is described as: Isobilateral: symmetric mesophyll showing palisade layer on both upper and lower epidermises. Dorsiventral: asymmetric mesophyll, showing only 1 palisade beneath the upper epidermis.  Cortical tissue: Present mainly in the midrib. It may be formed wholly of parenchyma or collenchyma or of both. Vascular system: Vascular system consists of phloem towards the lower surface of the leaf and xylem towards the upper surface. Medullary rays may be visible, traversing the xylem and the phloem in the form of radiating lines.  Trichomes or hairs Non-Glandular (covering) Trichomes Glandular Trichomes  Non-Glandular (covering) Trichomes They may be unicellular or multi-cellular. Unicellular: formed of 1 cell Multi-cellular: formed of more than 1 cell o Uniseriate: formed of 1 row of cells o Biseriate: formed of 2 rows of cells. o Pluriseriate: formed of many rows of cells. o Stellate: radiating unicellular. o Peltate: very short stalk with a plate-like structure of closely joined cells. o Candelabra: uniseriate axis branching into numerous unicellular hairs.  Glandular Trichomes Uniseriate stalk and Unicellular or Multi-cellular head. Biseriate stalk and biseriate head or composite glandular head. Pluriseriate stalk and a head with numerous, mostly 8, radiating cells. Branched stalk: each branch ending in a head.  Stomata According to the characters and arrangement of the surrounding epidermal cells, stomata are classified into:  Paracytic or Rubiaceous (parallel-celled): the stomata are surrounded by 2 subsidiary cells, having their long axes parallel to the osteole. Diacytic or Caryophyllaceous (cross-celled): the stomata are surrounded by 2 subsidiary cells having long axes perpendicular to the osteole. Anisocytic or Cruciferous (unequal-celled): the stomata are surrounded by usually 3 subsidiary cells, 1 of which is distinctly smaller than the others. Anomocytic or Ranuculaceous (irregular-celled): the surrounding cells have no special arrangement