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To be able fully to appreciate trees, their mode of life, their enemies and their care, one must know something of their structure and life requirements.

STRUCTURE OF TREES

Among the lower forms of plants there is very little distinction between the various parts—no differentiation into root, stem, or crown.

Often the lower forms of animal and vegetable life are so similar that one cannot discriminate between them. But as we ascend in the scale, the various plant forms become more and more complex until we reach the tree, which is the largest and highest form of all plants.

The tree is a living organism composed of cells like any other living organism. It has many parts, every one of which has a definite purpose. The three principal parts are: the stem, the crown, and the root.
Tree Major Parts


THE STEM

If we examine the cross-section of a tree, we will notice that it is made up of numerous rings arranged in sections of different color and structure.
Growth Rings
The central part is known as the pith.

Around the pith comes a dark, close-grained series of rings known as the heartwood, and outside the heartwood comes a lighter layer, the sapwood.
Pith, Heartwood, Sapwood, Cambium, and Bark
The cambium layer surrounds the sapwood and the bark covers all. The cambium layer is the most important tissue of the tree and, together with part of the sapwood, transports the water and food of the tree. It is for this reason that a tree may be hollow, without heart and sapwood, and still produce foliage and fruit.



THE CROWN

The crown varies in form in different species and is developed by the growth of new shoots from buds.
Tree Crown
The bud grows out to a certain length and forms the branch. Afterwards it thickens only and does not increase in length. New branches will then form from other buds on the same branch.

This explains in part the characteristic branching of trees.

Directions

Study the lesson for one week.

Over the week:

  • Read the lesson.
  • Review the synopsis.
  • Recite aloud the vocabulary words and their definitions.
  • Learn the concepts.
  • Complete the enrichment activities.
  • Study the review questions.

Synopsis

This lesson looks at the stem (trunk) and the crown (leaves and branches) of the tree. A cross-section of the stem reveals the pith, heartwood, sapwood, cambium, and bark.

Vocabulary

Stem: The above-ground stalk (technically axis) of a vascular plant.
Trunk: The usually single, more or less upright part of a tree, between the roots and the branches.
Crown: The top part of the tree, including the branches off the main trunk and the leaves.
Root: The part of a plant, generally underground, that anchors and supports the plant body, that absorbs and stores water and nutrients.
Pith: The soft, spongy substance in the center of the stems of many plants and trees that stores and transports nutrients throughout the plant.
Heartwood: The dead wood nearer the heart of a stem or branch, generally darker in color than the sapwood due to stored sugar, dyes, and oils.
Sapwood: The living wood just under the bark of a stem or branch that carries water and nutrients and is generally lighter in color than the heartwood.
Cambium: A layer of cells between the xylem and the phloem that is responsible for growing new growth rings.
Bark: The exterior covering of the trunk and branches of a tree.

Concepts

HEARTWOOD VS SAPWOOD

  1. Heartwood is at the inner 'heart' of the tree, sapwood is the outer layer.
  2. Heartwood is dead, sapwood is still living.
  3. Heartwood is older, sapwood is younger.
  4. Heartwood is often darker as it is filled with stored sugar, dyes and oils.
  5. Sapwood is often lighter, is the 'xylem,' and carries water and nutrients up from the roots to the leaves.
  6. Sapwood turns into heartwood as the tree grows.
  7. Heartwood holds less moisture and is more resistant to decay - making it better for furniture.

Point out the heartwood, the sapwood, the pith, and the bark in the image

Enrichment

Activity 1: Narrate the Lesson

  • After reading or listening to the lesson, narrate the lesson aloud using your own words.

Activity 2: Study the Lesson Pictures

  • Study the lesson pictures and describe how they relate to the lesson.

Activity 3: Take a Nature Walk

  • Bring a small sketchbook and embark on a nature walk.
  • Seek out a cross-section of a tree trunk to sketch, such as a stump.
  • Sketch out the cross-section including the pith, heartwood, sapwood, and bark.

Activity 4: Complete a Field Book Entry   

After your nature walk, complete page 29 in 'Science Field Book for Fourth Grade.'

Review

Question 1

What is the largest and most complex form of all plants?
1 / 7

Answer 1

The largest and most complex form of all plants is the tree.
1 / 7

Question 2

What are the three major structural parts of the tree?
2 / 7

Answer 2

The three major structural parts of the tree include the roots, the trunk, and the crown.
2 / 7

Question 3

What two major parts make up the tree crown?
3 / 7

Answer 3

Branches and leaves make up the tree crown.
3 / 7

Question 4

Which is older - sapwood or heartwood?
4 / 7

Answer 4

Heartwood is older.
4 / 7

Question 5

Which carries water and nutrients from the roots to the crown - sapwood or heartwood?
5 / 7

Answer 5

Sapwood carries water and nutrients from the roots to the crown.
5 / 7

Question 6

Which is in the center or heart of the tree - sapwood or heartwood?
6 / 7

Answer 6

Heartwood is in the center or heart of the tree.
6 / 7

Question 7

Which is older and tends to be darker - sapwood or heartwood?
7 / 7

Answer 7

Heartwood tends to be older and darker.
7 / 7

  1. What is the largest and most complex form of all plants? The largest and most complex form of all plants is the tree.
  2. What are the three major structural parts of the tree? The three major structural parts of the tree include the roots, the trunk, and the crown.
  3. What two major parts make up the tree crown? Branches and leaves make up the tree crown.
  4. Which is older - sapwood or heartwood? Heartwood is older.
  5. Which carries water and nutrients from the roots to the crown - sapwood or heartwood? Sapwood carries water and nutrients from the roots to the crown.
  6. Which is in the center or heart of the tree - sapwood or heartwood? Heartwood is in the center or heart of the tree.
  7. Which is older and tends to be darker - sapwood or heartwood? Heartwood tends to be older and darker.

References

  1. 'Studies of Trees' by Jacob Joshua Levison. gutenberg.org/ebooks/16116. n.p.
  2. 'Wood.' Wikipedia. en.wikipedia.org/wiki/Wood#Heartwood_and_sapwood. n.p.

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