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Global Forests -
Little Known or Interesting Factoids About Trees and Tree Physiology

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Karen Rockoff is the only ISA certified
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                     Karen Rockoff  Arborist  - TDA Certified

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Tree Identification - Parts of a Tree

(Terms appearing in Bold Print may be found in the (Glossary of Tree Terms) at the bottom of this page 


Leaves provide trees with all their food because they turn sunlight into food energy. Chlorophyll makes this energy transformation possible.  Leaves also make the oxygen in the air that we breathe.

Chlorophyll is a pigment found in the cells of leaves which is formed only in the presence of light and is the substance that colors plants green.  Chorophyll is contained in chloroplasts and has the property of capturing light energy.

The process of Photosynthesis (the process by which plants make sugar from sunlight, water, and carbon dioxide):

        Sunlight shines through the top of the leaf and reaches the next layer of cells.  The light energy is     trapped by the chlorophyll in the chloroplasts.  In the chloroplasts, a process that uses water changes the light energy into a kind of chemical energy. This chemical energy is stored in the chloroplasts.

        The chloroplasts use the chemical energy to make food.  Air enters the leaf through the stomata and moves into tiny spaces around the food-making cells in the leaf. Carbon dioxide from the air passes through the cell walls and membranes of the cells.  Carbon dioxide enters the chloroplasts where the previously stored chemical energy converts the carbon dioxide into sugar.

        Tubes in the plant carry sugar from the leaf cells to other parts of the plant, such as roots, stems, and fruits.   Cells in these parts of the tree store some of the sugar.

From Illustrations From  Discover Science, Scott, Foresman, & Co., 1993


There are three main parts to a leaf:
The base which is the point at which the leaf is joined to the stem.
The stalk or petiole is the thin section joining the base to the lamina - it is generally cylindrical or semicircular in form.
The lamina or leaf blade is the wide part of the leaf

Leaves can be of many different shapes:
Primarily, leaves are divided into simple - a single leaf blade with a bud at the base of the leafstem; or compound - a leaf with more than one blade.  All blades are attached to a single leafstem.  Where the leafstem attaches to the twig there is a bud.


Simple Leaf

Compound leaf

Leaves may be arranged on the stem either in an alternate arrangement - leaves that are staggered or not placed directly across from each other on the twig; or in an opposite arrangement - 2 or 3 leaves that are directly across from each other on the same twig.

Leaf Arrangement

The margin (the edge of a leaf) may be entire, singly-toothed, doubly-toothed, or lobed.

Simple Leaves - Margin Structure



Compound leaves may be palmate - having the leaflets arranged round a single point like fingers
on the palm of a hand; or pinnate - when the leaves are joined on the two sides of the stalk, like the
vanes of a feather.

Compound Leaves


 (Leaf diagrams adapted from Fifty Trees of Indiana, Purdue University, Department of Forestry and Conservation)


The form of leaves is related with all their functions and their environment.  In addition to photosynthesis, the leaf also carries out all the other exchanges with the atmosphere.  It is through the leaf that the plant "breathes" (absorbs oxygen and gives off carbon dioxide plus energy) and transpires.  Epidermic tissues in the leaf contain stomata - microscopic openings like valves which regulate opening or closing, permitting or preventing transpiration, through which the plant loses the major part of the water it absorbs so as to allow further absorption by the roots.  In most plants the stomata are located on the underside of the leaves.  Their function is regulated so that plants living in dry climates have a substantially smaller number of them than those in humid climates, where they are numerous and prominent.  Where humidity is low the stomata may actually be recessed or partly protected by soft hairs which can prevent excessive transpiration.

  Flowers ~ Fruits and Seeds 

All trees produce flowers of some kind.  The main parts of a generalized flower are diagramed below.  Flower parts occur in a standard arrangement of 4 whorls around the flower stem, or pedicel or pedicuncle.  The outermost whorl is the calyx whose job is to protect the developing flower.  The calyx is usually green and its separate parts (sepals) are what we would recognize as the outside covering of a bud, as in a rose.  As the flower opens, the sepals are pushed apart by the petals.

The whorl of petals is collectively called the corolla.  Petals are usually bright-colored to attract pollinators to visit flowers.  Inside the petals, the next whorl consists of the male parts of the flowers, the stamens.  The stamen's job is to make pollen.  Tiny, microscopic pollen grains carry sperm from flower to flower.  Stamens have two components: filaments and anthers.  Filaments are thread-like structures like the filaments in a light bulb, that support the anthers out from the flower base.  The pollen grains are produced in the sac-like anthers, which open in intricate ways to release pollen.

A generalized flower would also have female parts as the center whorl.  These are known as the pistil or carpel.  Like stamens, they are made of parts:  the style extends from the center of the flower and supports the stigma, the sticky surface on which the pollen adheres during pollination.  At the base of the carpel in the center of the flower is the ovary, where eggs are borne.

This is a generalized description; in nature, there are many variations on the general theme.  Some plants have separate sexes, so that an individual bears only flowers with male (stamens) or femal (carpels) parts, not both.  Some flowers have colorful sepals, some have no petals, some have elaborate stamens that look like petals.  Different species also may have different numbers of parts in each whorl.


Illustration by Jan Glimn-Lacy, Indiana Native Plant and Wildflower Society (INPAWS)

Life Cycle of Flowering Plants
Illustration from Discover Science, Scott, Foresman, & Co., 1993


Different trees produce different kinds of seeds.  Some produce seeds in a fleshy covering - a fruit or berry, while other trees produce seeds tucked into the folds of cones or catkins.  Other trees produce seeds with wings as well as some produce seed inside nuts or pods.


Seed Types
Adapted from Fun With Science: Trees and Leaves,
Rosie Harlow and Gareth Morgan, Warwick Press, 1991

Tree seeds vary greatly in size - some of the largest trees have the smallest seeds.  Tree fruits in various forms aid in the dispersal of seeds.  Fleshy fruits are eaten by animals, from whose bodies the seeds may later be dropped.  Winged fruits are spread by wind.  "Seed trees" left after lumbering will reforest the land.

Conifers (pine and fir trees) make their seeds in cones.  Pollen cones make pollen and the pollen spreads through the air like dust.  Seed cones are sticky and the pollen grains stick to a seed cone.  Tubes then grow from the pollen grains into egg cells in the cone.  A sperm enters an egg cell and fertilizes the egg.  Each fertilized egg cell grows into an embryo and is housed in a seed.


Life Cycle of Conifers
From Discover Science, Scott, Foresman, & Co., 1993


Twigs and Buds

Like a branch, a twig's job is to support and transport.  Twigs support the leaves which have the job of making food.  Because leaves need to collect the Sun's rays to make food, they must be held up as high as possible by the twigs.  Twigs also transport water to the leaves and sugars from the leaves, using tiny tubes.


Tree Twig
From Fun With Science: Trees and Leaves,
Rosie Harlow and Gareth Morgan, Warwick Press, 1991


The photograph (left) and the diagram (right) show the open bud scales with new twig and
leaves emerging.  Both from Fun With Science: Trees and Leaves,
Rosie Harlow and Gareth Morgan, Warwick Press, 1991.


Glossary of Tree Terms

Abscission layer - layer of cells that forms at the base of each leaf petiole where it is attached to the twig when the veins that carry fluids into and out of the leaf gradually close off.

Alternate - leaves that are staggered or not placed directly across from each other on the twig.

Anthers - sac-like component of a flower where pollen grains are produced.  The anthers open to release pollen.

Anthocyanins - pigments in plants responsible for pink and purple colors.

Bark - outward covering of the tree.

Base - where the point at which the leaf is joined to the stem.

Broadleaf - A tree with leaves that are flat and thin and generally shed annually.

Calyx - the outermost whorl of sepals whose job is to protect a developing flower.  It is usually green and is what we would recognize as the outside covering of a bud.

Cambium - layer which forms across and between primary bundles where each year cells in this layer divide and grow.  As the cambium divides, wood and bark cells form.

Carotenoids - pigments in plants responsible for yellow and orange colors.

Carpel - the female part of the center whorl of a flower.  Also known as the pistil.

Chlorophyll - the green pigment in plants that absorbs energy from sunlight necessary for photosynthesis.

Chloroplast - the organelle in the cytoplasm of plant cells where chlorophyll is stored.

Compound - a leaf whose blade is divided into distinct leaflets.

Conifers - cone-bearing trees where the seeds are present in cones or catkins.

Corolla - the whorl of petals of a flower.

Deciduous - shedding all leaves annually.

Evergreen - trees with needles or leaves that remain alive and on the tree through the
winter and into the next growing season.

Fertilization - joining of a sperm to an egg cell. Results in an embryo which triggers development of a seed.

Filaments - thread-like structures that support the anthers out from the flower base.

Heartwood - the inner part of the wood; also called duramen.

Lamina - the wide part of the leaf; also called the leaf blade.

Leaflet - one of the subdivisions of a compound leaf.

Opposite - 2 or 3 leaves that are directly across from each other on the same twig.

Ovary - The inner part of carpel or pistil where eggs are borne.

Palmate - having leaflets radiating out from a central point.

Pedicel (Pedicuncle) - the flower stem.

Petals - outer part of a flower; protects the inside parts of a flower.

Petiole - thin section of leafstalk joining the base of the leaf to the lamina; generally is cylindrical or semicircular in form.  Also called the stalk.

Phloem - a protective layer made up of tiny tubes that transport the sugars from the leaves to the rest of the tree.

Photosynthesis - the process by which plants make sugar from sunlight, water, and carbon dioxide.

Pinnate - having leaflets on both sides of a common axis.

Pistil - Female part of a flower; also known as the carpel.

Pollination - the movement of pollen from a stamen to a pistil by pollinators (birds or insects).

Provascular tissue - bundles of cells in young tree shoots.

Root hairs - threadlike extensions that grow from a plant root and takes in water and minerals from the soil.

Roots - anchors the tree to the soil and absorbs water and soil minerals.

Sapwood - the outer part of the wood; also called alburnum.

Senescence - death of a leaf triggered by an increase in the enzymes that promote the breakdown of plant cells.  Begins when shorter days and cooler temperatures occur.

Sepals - the separate parts of the flower calyx  that is the outside covering of a bud.

Simple - a single leaf blade with a bud at the base of the leafstem.

Stamen - the male part of a flower that makes pollen.

Stigma - The sticky surface of a flower pistil on which pollen adheres during pollination.

Stomata - openings in a leaf through which gases and water enter or leave.

Style - extending from the center of a flower, it supports the stigma where pollen adheres during pollination.

Tannins - pigments in plants responsible for brown colors.

Xylem - the main part of the tree trunk made up of tiny tubes which transport water and minerals from the roots up the trunk and branches to the leaves.

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