Structure Of The Grass Plant PDF

STRUCTURE OF THE GRASS PLANT Objectives Students should be able to: identify the vegetative and reproductive parts of grass. Explain the functions of the various parts of the grass Structure  Vegetative parts Root system Stolons Rhizomes Culms...

STRUCTURE OF THE GRASS PLANT Objectives Students should be able to: identify the vegetative and reproductive parts of grass. Explain the functions of the various parts of the grass Structure  Vegetative parts Root system Stolons Rhizomes Culms Leaves Leaf blade Leaf sheath Ligule Root System Used to anchor the plant Absorbs water and nutrients Stores reserve nutrients Roots can develop to 2m deep and 2m wide in sandy soils. Hard soils with massive structures restrict accessibility of nutrients and water to plants. Stolons and Rhizomes Many grasses grow as compact tufts but others produce runners which grow horizontally and root at each node. If the runners are above the ground they are termed stolons and they are rhizomes if they occur beneath the ground. The nodes of stolons produce green leaves, while small brown scale-like leaves are produced at the nodes of rhizomes. Culms A culm is the upright stem in the middle of a shoot Consist of internodes and nodes from which the leaves grow They are solid at the nodes and often hollow throughout the internode area. In some grasses the internodes of the culm are very short until the culm elongates for flowering. Culms range from unbranched (simple) to many-branched. Leaves The grass leaf is an elongated structure arising at the node and consisting of 3 parts which are: leaf blade(Lamina), leaf sheath and ligule Leaf blade Used for photosynthesis, is longitudinal and has parallel veins. Can be of different length and breadth depending on the species Can be open, rolled or folded. Leaf sheath It is a modified leaf base and originates at the node and it encloses the internode. It strengthens the culm and protects the growth zone of the internode. Ligule Found between leaf blade and leaf sheath, against the culm  Function of ligule is not certan but it is thought to prevent water, insects and other organisms from entering the sheath to prevent damage. Ligule can be a membrane, a ring of hairs or a membrane with a hairy margin Ligule type is a useful identification character as it is relatively constant within a genus. Some grasses may lack ligules e.g. Echinochloa crus-galli (Barnyard Grass). Many grasses have translucent, membranous ligules whereas others have ligules fringed with hairs or in the form of a rim of hairs Types of ligules  Reproductive parts Inflorescence (Flower head) It is the flowering portion of a plant An inflorescence includes all the structures above the last leaf of the culm or base Each inflorescence consists of a number of spikelets, which contain very small flowers, arranged on branches or the main axis.  Types of inflorescence There are three main grass inflorescence types Spike Raceme Panicle Panicles are of different types True panicles False panicles Digitate panicles Only one species of grass has no visible inflorescence structure, the Kikuyu  Spike and raceme They are single unbranched inflorescence and are similar. Difference between spike and raceme A Spike is a group of flowers arising from the main stem, without individual flower stalks (sessile). A Raceme is a flower spike where the flowers have stalks of equal length, and the tip of the stem continues to grow and produce more flowers.  Panicles True Panicles Panicles are branched inflorescences with a primary axis(central axis) giving rise to branched secondary axis False Panicles Branched inflorescences that have racemes or group of racemes and various spathes. Digitate Panicles Inflorescences with two or more branches all arising from the same point are digitate, or if the branches arise from almost the same point subdigitate. Panicle False Panicle Digitate Panicle  Spikelets Flower bearing parts of the plant Their main function is to produce seeds and disperse them Have uniform structure within a genus , therefore used for identification of grass at genus level Vary in form but 2 main groups can be distinguished: 1) Those with a single floret 2) Those with numerous florets Single and multi-flowered spikelets Identification key