Plant Physiology




Basic Botany for Beginners

Don't know your petiole from your stolon? Start here!

Important Plant Parts: The Basics

Stems

Structural support for plants-both above ground and under the ground. Stems can be thought of as the scaffolding or the skeleton of the plant. They transport water, minerals and sugars. Stems are made up of xylem vessels which carry the water and minerals and phloem tubes with carry food.

You may also hear:

Rhizome - a special type of stem that grows along, or just beneath, the soil surface-similar to stolons. Useful for propagation.
Spur - short, stubby fruiting branches.
Stolon - a special type of stem that grows along the ground. Mint and strawberries, for example, grow stolons known as "runners" which send roots down into the soil and produce new plants.
Vine - another specialized type of stem that is long and trailing and often need support from another plant or structure.

Leaves

The light harvesting part of the plant and main area of transpiration (giving water back to the atmosphere) and CO2 absorption. The blade of the leaf is the main light harvesting portion. The mini stalk that links the leaf to the stem is called a petiole. Note, some species of plants don't produce petioles and the leaves appear to emerge directly from the stem.

Diagram: Close-up of Leaf Parts

Leaves have a tough, protective outer skin called theepidermis. The epidermis contains a waxy, water-proofing substance calledcutin. This is responsible for keeping the leaf hydrated so the leaf doesn't dry out in the sun or under grow lights. Plants dynamically produce more cutin in response to brighter light and less when they are in shade. This is why you must take care when moving your plants from low or moderate light environment to an area of higher light intensity. Do it gradually over a few days so that your plants have time to up their cutin levels.

The epidermis also contains some special valve-like cells calledguard cells. They are capable of opening and closing and regulate the flow of water and gas exchanges through the leaf. When the guard cells are open, tiny entrances into the inner part of the leaf are revealed calledstoma. When stoma are open this means the leaf is working well-oxygen and water vapor are being released and carbon dioxide is being absorbed from the air. But the stoma will only open if the environmental conditions are good. Hot, dry weather, for example, will cause the guard cells to close the stoma up because of the threat of dehydration.

Roots

If all is well below the surface, all should be well above. Roots absorb and store water and nutrients. They also serve to physically anchor the plant in the soil or growing media.

Diagram: Close-up of Root Structure

Think of roots in terms of primaries ("leader" roots, thicker) and laterals (aka secondary, branching.) Both serve to essentially explore the soil or growing media to help the plant above exploit the resources (moisture and minerals) available. Growing out of the lateral roots are tiny root hairs which actually do the vast majority of the feeding. The primary and lateral roots serve to translocate moisture and nutrients up to the plant.

A layer known as the Casparian strip regulates the types of minerals the root absorbs.

Flowers

Flowers are all about one thing-sex! Female 'pistils' catch male pollen released from sacs called "anthers." Pollen is usually transferred by wind, birds or insects. Normally, the pollen fertilizes the eggs in the ovules and these eggs develop into seeds. And life, as they say, goes on!

Diagram: Close-up of Flower Parts

An individual plant flower may contain male pollen or female ovule (pollen catchers) or, in some cases  both in the same flower! At a plant level, some species produce male and female flowers on the same plant, and some produce solely "male" and "female" plants (dioecious - coming from the Greek for "two households.") The Kiwi vine (Actinidia deliciosa) is dioecious, producing separate male and female vines that need to be planted adjacent to each other in order to produce fruit.