ABC Hypothesis

A model of flower formation identifying three classes of organ identity genes that direct formation of the four types of floral organs.

Blade

1. The flattened portion of a typical leaf.

Cuticle

A waxy covering on the surface of stems and leaves that prevents desiccation in terrestrial plants.

Differentiation

The process by which a cell or group of cells become specialized in structure and function.

Endodermis

In plant roots, the innermost layer of the cortex that surrounds the vascular cylinder.

Ground Tissue System

Plant tissues that are neither vascular nor dermal, fulfilling a variety of function, such as storage, photosynthesis, and support.

Growth

An irreversible increase in size or biomass.

Guard Cells

Two cells that flank the stomatal pore and regulate the opening and closing of the page.

Indeterminate growth

A type of growth characteristic of plants, in which the organism continues to grow as long as it lives.

Internode

A segment of a plant stem between the points where leaves are attached.

Lateral Meristem

A meristem that thickens the roots and shoots of woody plants. The vascular cambium and cork cambium are lateral meristems.

Lateral Root

A root that rises from the pericycle of an established root.

Leaf

The main photosynthetic organ of vascular plants.

Leaf Primordium

A finger-like projection along the flank of a shoot apical meristem from which a leave arises.

Lenticel

A small raised area in the bark of stems and roots that enables gas exchange between living cells and the outside air.

Morphogenesis

The cellular and tissue-based process by which and animal body takes place.

Node

A point along the stem of a plant at which plants are attached.

Organ

A specialized center of body function composed of several different types of tissues.

Pattern formation

The development of a multicellular organism organism's spatial organization, the arrangement of organs and tissues in their characteristic places in three-dimensional space.

Root Cap

A cone of cells at the tip of a plant root that protects the apical meristem.

Root Hair

A tiny extension of a root epidermal cell, growing just behind the root tip and increasing surface area for absorption of water and minerals.

Root System

All of a plant's roots, which anchor it in the soil, absorb and transport minerals and water, and store food.

Stoma

A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant.

Tissue

An integrated group of cells with a common structure, function, or both.

Vein

In plants, a vascular bundle in a leaf.

Xylem

Vascular plant tissue consisting mainly of tubular dead cells that conduct most of the water and minerals upward from the roots to the rest of the plant.