(External & Internal Structures) plants (External & Internal Structures) (Part 1)

Shoot system Root system leaf blade axillary bud petiole node vascular tissue shoot apical meristem terminal bud internode Shoot system vascular tissue Root system root tip root hair root cap root apical meristem dermal tissue ground tissue vascular tissue

ROOTS

Types of root systems Tap root system Fibrous root system

Primary Root System Primary Root Secondary Root Tertiary Root

Fibrous Root System The primary root is lost and is replaced by numerous adventitious roots arising from the lower part of the stem. These roots are fibrous in appearance , that is, they are slender in form and are more or less equally prominent

The Root Tip Elongation region Meristematic region Root cap Cells in this region increase in size, particularly in length The Root Tip Meristematic region Actively dividing cells in various stages of mitosis Root cap Produces mucigel for protection, lubrication, water and nutrient absorption

Three primary meristems Protoderm outermost primary meristem – gives rise to epidermis. Ground Meristem store food and uptake of minerals Procambium gives rise to stele – central cylinder of vascular tissue where xylem and phloem develop Quiescent Zone slower or no cell division

Maturation region characterized by the presence of root hairs is made up of primary tissues that develop from transitional meristems of the elongation region Protoderm epidermis Ground meristem cortex pericycle phloem Procambium vascular cambium xylem

Root hairs Increase the surface area for the absorption of water

Young dicot root epidermis cortex vascular cylinder Exarch - tetrarch Stele - actinostele

cortex endosperm with casparian strip pericycle xylem phloem vascular cambium

lateral root arising from pericycle xylem phloem endodermis with casparian strip cortical parenchyma uncutinized epidermis with root hair

Lateral roots develop from the pericycle primary root xylem lateral root Lateral roots develop from the pericycle

Monocot root epidermis cortex endodermis pericycle pith xylem phloem root hairs

Exarch polyarch Stele actinostele

Modified Roots

For Support - Brace roots Aerial roots arising from the main stem which penetrates the ground Corn (Zea mays) Pandan (Pandanus odoratissimus)

For Support - Prop roots Aerial roots arising from the branches which penetrates the ground Banyan tree (Ficus indica) Mangrove (Rhizophora sp.)

For Support – Clinging roots Aerial roots which adhere to some kind of support English ivy (Hedera helix)

For Support - Buttress Plant-like extensions from the lower part of the stem Ficus sp.

Adventitious buds in root For Reproduction Adventitious buds in root Bog Yellowcress (Rorippa palustris)

For Protection Screw pine (Pandanus tectorius) Presence of spines

For Photosynthesis Green aerial roots Vanda sp.

For Food Storage enlarged, fleshy and succulent roots White Radish (Raphanus sativus) Carrot (Daucus carota)

For Aeration development of pneumatophores – roots with spongy tissues protruding above the ground Mangrove (Rhizophora sp.)