Lesson 5 - Root and Stem

Stellar Theory

well known concept pertaining to the phylogeny of the form of the vascular system in its axis

Stele

the core of the plants axis (stem and root)

Protostele

has a solid cylinder of vascular tissues in the center of the axis surrounded by the cortex

haplostele, actinostele, and plectostele

types of protostele

Haplostele

xylem is circular mass

Actinostele

xylem margin is not smooth; it undulates.

Plectostele

xylem not one mass; series of plates

Siphonostele

vascular tissues occuer as a hollow cylinder with a ground tissue or pith at the core

eustele (dicots)

one ring of vascular bundled surrounding a pith

Atactostele (monocots)

Scattered vascular bundle arrangement

Ectophloic siphonostele, Amphiphloic siphonostele, and Dictyostele.

other types of stele

collateral, bicollateral, concentric, and radial bundle

vascular bundle arrangement

Collateral bundle

Phloem on one side (abaxial) and xylem on the other (adaxial)

Bicollateral bundle

phloem on both side of the xylem

Amphicribral and Amphivasal

type of concentric bundle

Amphicribral

xylem in the middle surrounde by phloem

Amphivasal

phloem in the middle surrounded by xylem

Radial bundle

primary xylem and primary phloem strands are separated from each other by nonvascular tissues and they are situated on alternate radii of an axis.

Root

Anchorage, storage, absorption, and conducion.

radicle

embryonic root

tap root, secondary root, and adventitious root

classification of roots

tap root

primary, derived from radicle.

secondary root

arising from primary root or its branches. originates from the pericycle.

Adventitious root

Arising from another plant part

Root tip

the end 1 cm of a root contains young tissues that are divided into the root cao, thr quiescent center and the sub-apical region.

Root cap

Covers and protects the delicate root tip.

Root cap

the cells are derived from the root cap meristem that pushes cells forward into the cap region. These cells secrete mucigel

Mucigel

Aids in protection of the root by preventing desiccation.

Zone of cell division

primary griwth if the root

Zone of cellular elongation

The cells derived from the apicl meristem increase in length in this region

Zone of cellular maturation

Distinguished by eohemeral root hairs

Quiescent center

“to rest”. A region of inactive cells, they function to replace the merismatic cells of the root cap meristem.

Epidermis

derived from the protoderm and surround the young root one cell layer thick

Cortex

storage pf parenchyma cells

Endodermis

the innermost layer of the cortex

Casparian strip

forces water and the dissolved nutrients to pass through the symplast, thus allowing the cell membrane to control absorption by the root.

symplast

living portion of the cell

pericycle

a cylinder of parenchyma or sclerenchyma cells that lies just inside the endodermis and is the outermost part of the stele of plants.

pericycle

strengthen the stem, provides protection for the vascular bundles, and gives rise to the branch roots.

Haustorium

root of parasitic plant specialized in absorbing the food and nutrints from its host.

Contractile roots

adventitious roots that pull the bulb deeper into the ground as it grows.

Stem

Is a collection of integrated tissue arranged as nodes and internodes

Stem

Supports the leaves, stores minerals, and treansports water and solute between roots and leaves.

Epidermal tissue, Vascular tissue, and Ground tissue

stem is made up of three tissues:

Epidermal tissue - stem

the walls are thickened and civered with a thin waterproof layer called the cuticle.

Vascular bundle - stem

consists of three main tissues - xylem, phloem, and cambium.

Ground substance

Cortex. This region comprises the collenchyma, parenchyma, and endodermis.

Ground substance

It is sutuated to the inside of the epidermis.

Pith

Occupies the large part of thin-walled parenchyma cells with intercellular air spaces.

Heart wood

Older, nonconducting rings of xylen at the center of the tree’s trunk or root.

Sapwood

Outer ring of xylem that still transports sylem sap.

Bulb storage

short underground structure composed of overlaapping fleshy leaves (scales) and knob (stem).

Rhizomes

Horizontal underground stems

Tubers

Are rhizome that enlarge at the ends

Corm

Vertical, fleshy, underground stem that acts as a vegetative reproductive structure.

Runners/Stolon

Underground stems that form another individual plant tip

Thorns

sharp pointed stems

Offsets

Small plant growing at the base of larger one trough a horizontal branch.

Tendril, cladophyll, leaves (modified as spines)

Types of modified stems