Botany 110 Week 2 (Stems, Leaves, Flowers and Seeds)

Function of Stems

1. Support

2. Transport

3. Producing Food

4. Producing more stems

Apical Meristem

Contributes to an increase in stem length, is dormant before the growing season.

Leaf Primordia

Tiny embryonic leaves that develop into mature leaves

Vascular Cambium (Cambium, Vascular Bundle)

Narrow bands of cells between the primary xylem and primary phloem may become vascular cambium. Cells produced by VC become components of secondary phloem and xylem.

Deciduous

Lose all leaves annually. Have dormant axillary buds with leaf scars bellow

Cotyledons

Seed leaves attached t embryonic stems. (Store food for seedling)

Dicotyledons (Dicots)

Flower plants that develop from seeds having two cotyledons. (Beans)

Monocotyledons (Monocots)

Flower plants that develop from seeds with a single cotyledon (Corn)

Herbaceous Dicots

Have discrete vascular bundles arranged in a cylinder

Woody Dicots

Secondary xylem, one year’s growth is of xylem = annual ring

Monocotyledonous Stems

No vascular cambium, xylem, or phloem is present throughout the stem.

Rhizomes (Stem)

Horizontal stems that grow below-ground and have long to short internodes (Irises, Ferns and Grasses)

Runners (Stem)

Horizontal stems that grow above the ground and have long internodes. (Strawberry)

Stolons (Stem)

Produced beneath the surface of the ground and tend to grow in different directions. (Irish Potato)

Tubers (Stem)

Swollen, Fleshy, underground stem that stores food. (Irish potatoes eyes of potato are nodes)

Bulbs (Stem)

Large buds surrounded by numerous flashy leaves, with a small stem at the lower end. Store food. (Onions, lilies, Tulips)

Corms (Stems)

Resemble bulbs, but composed almost entirely of stem tissue with papery leaves. Store food. (Gladiolus and Crocus)

Cladophyll (Stem)

Flattened, leaf-like stems (Prickly pear cactus and some orchids)

Function of the leaf

1. Photosynthesis

2. Storage

3. Transpiration

Photosynthesis

Trapping and storing of energy in sugar molecules that are constructed from water and carbon dioxide

Stomata

Tiny pores on the lower surface of leaves (carbon dioxide enters through here, water vapor and oxygen diffuse out)

Guard Cells

Control water loss by opening or closing pore of stomatal apparatus

Simple Leaves

Leaves with a single blade.

Compound Leaves

Arrangement of veins in a leaf that is divided into multiple leaflets that attach to a single petiole.

Pinnately Veined Leaves (Compound Leaves)

Main mid-vein included within enlarged midrib.

Palmately Veined Leaves (Compound Leaves)

Several primary veins fan out from base of blade

Monocot Leaf Venation

Primary veins parallel (Parallel Venation)

Diocot Leaf Venation

Primary veins diverge in various ways. (Netted)

Phyllotaxy

Arrangement of leaves on the stem.

1. Alternate- one leaf per node

2. Opposite- Two leaves per node

3. Whorled- Three or more leaves at a node

Epidermis

A single layer of cells covers the entire surface of the leaf. Devoid of chloroplasts, coated with cuticles.

Storage Leaves

Succulent leaves are modified to store water. These leaves are often fleshy to store carbohydrates. Have parenchyma cells with large vacuoles.

Reproductive leaves

1. Walking ferns have new plants at the leaf tips

2. Air plants have tiny plants along leaf margins

Floral leaves (bracts)

At the base of flower stalks, often brightly colored. Poinsettias.