BIO421 | General Botany: Tissues & Growth

Plants transitioned to terrestrial life approximately 420 million years ago, leading to specialized tissues and organs.
All flowering plants (angiosperms) possess leaves, stems, and roots, which may be modified for various functions.
No plant species has entirely lost the evolutionary presence of roots, stems, or leaves.
Flowering plants are categorized under the Division Magnoliophyta, with key groups including basal angiosperms, eudicots, and monocots.
Plant bodies can be classified as primary (herbaceous) or secondary (woody).

Parenchyma
- Composed of cells with thin primary walls; metabolically active and mostly alive at maturity.
- Forms a mass known as parenchyma tissue, crucial for storage and metabolic functions.
Chlorenchyma
- A type of parenchyma involved in photosynthesis, characterized by light-permeable thin walls allowing CO2 and light access to chloroplasts.
Glandular Parenchyma
- Specialized cells that secrete substances such as nectar, fragrances, mucilage, resins, and oils.
Transfer Cells
- Facilitate short-distance transport of materials through large plasma membranes equipped with molecular pumps.
Phloem Parenchyma
- Stores nutrients and is metabolically less expensive to build because of thin walls.
Collenchyma
- Consists of cells with both thin and thickened primary walls, providing support and plasticity, commonly found beneath the epidermis or supporting vascular bundles.
Sclerenchyma
- Features thick, lignified secondary walls, typically dead at maturity, providing structural support. It includes:
- Conductive Sclerenchyma (tracheary elements like tracheids and vessel elements) for water transport.
- Mechanical Sclerenchyma (fibers and sclereids) for additional support.

Phyllotaxy: The arrangement of leaves on the stem.
- Types:
  - Alternate: One leaf per node.
  - Opposite: Two leaves per node.
  - Whorled: Three or more leaves per node.
Orientation variations of phyllotaxy include:
- Distichous: Two rows of leaves.
- Decussate: Four rows of leaves.
- Spiral: Leaves arranged spirally along the stem.

Each leaf axil contains a bud; however, many remain dormant.
The apical meristem's health is crucial; if it is damaged, dormant axillary buds become active and can develop branches.