Chapter 7
Plant Organs: Stems
CHAPTER OUTLINE
Stem structure and function
A woody twig exemplifies the external structure of all stems
Stems of herbaceous eudicots and monocots
Focus On: Tree-Ring Analysis
Plants and the Environment: The Deforestation of Tropical Rain Forests
Plants and People: The Importance of Wood
CHAPTER OBJECTIVES
1. Describe three functions of stems
2. Relate the functions of each tissue in an herbaceous stem.
LECTURE OUTLINE
I. What are the three main functions of stems?
II. Describe the external structure of a woody twig.
D. What are lenticels and what is their function?
III. What tissues are found in herbaceous eudicot stems?
A. Where is the epidermis located?
1. Does the epidermis have a cuticle?
C. What is the arrangement of the vascular bundles as seen in a cross section of the
stem?
1. How are the xylem and phloem arranged in relation to each other?
2. What are the functions of the xylem and phloem, respectively?
F. How does the eudicot root differ from the eudicot stem?
IV. How does the arrangement of the tissues in monocot stems differ from that of eudicots?
A. How are the vascular bundles arranged?
B. Where are fibers usually found?
C. Do monocot stems have distinct cortex and pith?
D. Can monocots produce secondary growth?
V. What kinds of plants have secondary growth?
A. What are the two structures that produce secondary growth?
B. What changes occur in the young stem when secondary growth begins?
1. What happens to the primary xylem and phloem?
F. Where does the cork cambium arise?
1. What kinds of cells does it produce?
2. What are the functions of the cork cell layer?
3. What is the function of the cork parenchyma?
1. What is the cellular explanation for annual rings?
2. What is the difference between springwood and late summerwood?
3. How can information from the size and number of annual rings be used?
J. How do knots form?
K. In what ways are forests ecologically important?
VI. What are the characteristics of vines?
A. What is the difference between an herbaceous vine and a liana?
B. In what habitats are vines most frequently found?
VII. How is asexual reproduction accomplished in flowering plants?
A. Although rhizomes grow underground, how can you tell they are stems? Give an
KEY TERMS
annual rings, p. 141
apical meristem, p. 131
axillary buds, p. 131
bud, p. 131
ground tissue, p. 133
hardwood, p. 140
heartwood, p. 139
internode, p. 131
ray, p. 138
rhizome, p. 146
runner, p. 147
sapwood, p. 139
TEACHING TIPS
1. To emphasize the difference between primary and secondary growth, ask students the
2. Three-dimensional models are useful to help students comprehend the arrangement of
3. Bring in grocery store and garden examples whenever appropriate, such as sugar cane,
potato, iris rhizome, strawberry runner, vines, etc.
trees and lumber products.
6. Take a short field trip to look at the plants on your campus. Apply as much of the
descriptive terminology as possible.
7. Many medicines are based on plant chemicals. Some of these which come from