Roots

Do not move More than ½ of plants resources go into roots Can account for 80% of biomass Move nutrients into food chain

Kinds of Roots: Taproot Fibrous Roots Radicle Main taproot (dicots) Branch roots Taproot system Fibrous Roots Mostly monocots Extensive root network Adventitious roots

Function and Structure of Roots Functions: (1) Anchorage (2) Storage (3) Absorption (4) Conduction Structure: Root Tip = root apical meristem Root Cap Sub-apical Region Zone of cellular division Zone of cellular elongation Zone of cellular maturation Mature Region = primary tissues

Layers of Root: Superficial to Deep Epidermis One cell thick with thin or no cuticle Covers all, but not root cap Lack stomata, have root hairs Cortex Composed of ground tissue Largest part of root Consists of three concentric layers

Cortex continued: Hypodermis Storage Parenchyma Endodermis Suberized Store starch, many cells, very thick Lots of intercellular spaces Endodermis Cells very tight together No spaces Cylinder all through root Contains Casparian Strip = composed of lignin and suberin

Casparian Strip Blocks water and nutrient movement Material must pass through cells of endodermis to reach vascular tissues

Stele Pericycle Vascular Tissue (see later) Pith All tissues inside cortex, within endodermis Three types Pericycle Meristematic Forms lateral branch roots that form endogenously Vascular Tissue (see later) Pith

Root Vascular Tissues Protostelic Siphonostelic Lobed solid core of xylem Phloem in notches Most dicots Siphonostelic Tissues form rings Xylem and phloem alternate Most monocots, some dicots

Factors Controlling Root Growth and Dispursement: Temperature Light Gravity Soil chemistry Genetics Other organisms Root – Soil Interface

Economic Importance of Roots Modified Roots Storage Propagation Aeration Movement Nutrition Parasitism Mycorrhizae Nodules Aerial roots Economic Importance of Roots

Monocot Stem Cross Section Lack vascular cambium in mature forms. Vascular bundles embedded throughout tissue.