Root Structure and Function Penetration of Soil Gravitropism Downward Growth Water and Mineral Intake Conduction (Xylem and Phloem) Storage of Materials Branching Anchorage

Notice how the growing zone has no root hairs or lateral roots! Growth among soil particles would result in shear forces. Zone of Maturation - cell differentiation Protoderm Ground Meristem Provascular Zone of Cell Elongation - cell expansion Zone of Cell Division - new cells by mitosis Root Cap - penetration, padding

Mucilage Slough Cells

Root Tip Senses Gravity Auxin Hormone Produced Auxin Accumulates on Lower Growth Inhibited on Lower… Relative to Upper Root Curves Downward Gravitropism Root Hairs Increase Surface Area Root Hairs Secrete Acid (H + ) H + Cation Exchange w/Minerals Mineral Uptake into Roots Water and Mineral Uptake

Dicot Mature Root Structure - Anatomy Epidermis Cortex Vascular Cylinder Ranunculus acris - buttercup

What does all of this autumn color (leaf senescence) have to do with roots?

Root Vascular Cylinder and Cortex Ranunculus acris - buttercup Cortex Endodermis Xylem Phloem Pericycle

Root Anatomy: Dicot Root Cross Section Epidermis - root hairs, mineral and water intake Cortex - storage, defense Endodermis - selective mineral uptake Pericycle - lateral root formation (periderm) Vascular Cambium - makes 2° tissues Phloem - CH 2 O delivery from leaves Xylem - conduct water and mineral upwards Casparian strips in radial walls One Vascular Cylinder (Phloem + Cambium + Xylem)

Monocot Root Cross Section Smilax-catbrier Pith

How is this section different? Smilax - catbrier

A closer look… What do these features tell you? Starch Cutin/Suberin Mitochondria Sieve Tube Element Companion Cell Vessel with Lignin Xylem Parenchyma Lignified Pith Parenchyma

What is the Pericycle doing? Root Cap Zone of Cell Division Growing out through cortex In fibrous root systems, there is much lateral root formation. Here you can see two root apices initiating from the pericycle. Notice their connection to the ridges of xylem

In shrubs like this tea plant (Camellia sinensis), the root system will be more tap root than fibrous root. Notice the diameter of this tap root compared to this mans waist! But shrubs also generally have some compromise for uprooting forces…feeder roots extending laterally.

Tropical soils are nutrient poor. Roots must traverse the surface for minerals, so roots grow on the surface (no tap root). So, to keep this tall baobab tree standing upright, the roots grow in diameter but only in the vertical dimensions to form ridge roots…called buttress roots. My wife here is as large as I am so you can see these roots are a meter tall! These roots inspired gothic cathedral architects to design buttress walls.

Pandanus utilis - screw pine Prop roots such as these inspired flying buttresses.