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

z

Germination of Seeds zProper temperature. zWater. 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).abscisic acid zOxygen. zA 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. abscisic acid zCorrect photoperiod (often).

Germination in Dicots zThe primary root emerges through the seed coats while the seed is still buried in the soil. zThe 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. zOnce 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 apical meristem zIn 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 z

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 zWhen grass seeds, e.g. corn (maize) or oats (shown here), germinate zthe primary root pierces the seed (and fruit) coverings and grows down; zthe primary leaf of the plant grows up. It is protected as it pushes up through the soil by the coleoptile - a hollow, cylindrical structure. zOnce the seedling has grown above the surface, the coleoptile stops growing and zthe primary leaf pierces it.

Germination in Monocots

Corn Germination Steps

Corn Germination Con,t z

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