Plant Growth and Development

Plant Science/Horticulture I

Instructor: Mr. Dixon

VEGETATIVE PLANT PARTS

UNIT OBJECTIVE

After completion this unit, students should be able to match terms and definitions and identify the parts of a plant.

Students should also be able to list functions of plant parts and name the root systems.

Terminology

I. Terms & Definitions

Node--The part of a stem where a leaf is attached

Internode--The part of stem between two nodes

Bud--An embryonic shoot of a plant

Leaf scar--A scar left on the stem when a leaf falls

Vascular bundle scar--A spot within a leaf scar left by the vascular bundles when a leaf falls

Terminology

Monocot--Plant having one seed leaf (cotyledon) as in cereals and corn

Dicot--Plant having two seed leaves (cotyledons) as in beans and peas

Vascular bundle--A strand of tissue containing xylem and phloem enclosed by a sheath of cells

Xylem--Vascular tissue that transports water and minerals from the root system to the leaves

Phloem--Vascular tissue that conducts food from the leaves to regions of growth or storage

Terminology

Pistil--Seed bearing organ of a flower, composed of the ovary, style and stigma

Stamen--Part of the flower producing the pollen; composed of the filament and anther

Fertilization--Union of the male (pollen) nucleus with the female (egg) cell

Pollination--Transfer of pollen from the anther to the stigma

Embryo--The young plantlet within the seed; the germ

Terminology

Radicle--The embryonic root

Hypocotyl--The part of an embryo between the cotyledons and the radicle. The Stem: Usually emerges before the leaves.

Plumules--The part of the embryo above the cotyledons.

Bean Seed Cross section

Germination of Seeds

Proper temperature. Water. Water is always needed to allow vigorous metabolism to

begin. It is also sometimes needed to leach away a germination inhibitor within the seed. This is especially common among desert annuals. The inhibitor is often abscisic acid (ABA).

Oxygen. A preceding period of dormancy (often). The seeds of many

temperate-climate angiosperms will germinate only after a prolonged period of cold. An inhibitor within the seed (probably abscisic acid - ABA) is gradually broken down at low temperatures until finally there is not enough to prevent germination when other conditions become favorable. This mechanism is of obvious survival value in preventing seeds from germinating during an unseasonably warm spell in the autumn.

Correct photoperiod (often).

Germination in Dicots

The primary root emerges through the seed coats while the seed is still buried in the soil.

The hypocotyl emerges from the seed coats and pushes its way up through the soil. It is bent in a hairpin shape - the hypocotyl arch - as it grows up. The two cotyledons protect the epicotyl structures - the plumule - from mechanical damage.

Once the hypocotyl arch emerges from the soil, it straightens out. This response is triggered by light. The cotyledons spread apart exposing the epicotyl, consisting of two primary leaves and the apical meristem

In many dicots, the cotyledons not only supply their food stores to the developing plant but also turn green and make more food by photosynthesis until they drop off.

Germination in Dicots

Bean Germination Steps

Pea Germination Steps

Sectional views of a corn kernel

per. = pericarp, end. = endosperm, sc. = scutellum, col. = coleoptile, pl. = plumule, rad. = radicle

Cross Section of Corn

Germination in Monocots

When grass seeds, e.g. corn (maize) or oats (shown here), germinate

the primary root pierces the seed (and fruit) coverings and grows down;

the primary leaf of the plant grows up. It is protected as it pushes up through the soil by the coleoptile - a hollow, cylindrical structure.

Once the seedling has grown above the surface, the coleoptile stops growing and

the primary leaf pierces it.

Germination in Monocots

Corn Germination Steps

Corn Germination Con,t

Corn Germination

Visible Corn Germination

Day Four

Day Four Con’t

Primary parts of a plant

II.Primary parts of a plant

A. Roots

B. Stem

C. Leaves

D. Flowers