Plant Structures I
Objective
The purpose of this lab is to introduce you to some terms and basic
concepts related to the plant body. Knowledge of plant structures
(anatomy/morphology) will aid you in plant identification and propagation. You
will also gain an understanding of functions related to vegetative plant structures.
Introduction
The body of a seed plant consists of a root system and a shoot system.
The root system, in most plants the below ground part, includes all the roots.
The shoot system, the above ground part, contains all the stems and leaves.
Roots, stems and leaves are generally referred to as the vegetative parts and the
flowers the reproductive parts (covered in Plant Structures II).
Moncots versus Dicots. There are two major groups of flowering plants,
the dicots (dicotyledons) and the monocots (monocotyledons). Dicots are those
plants having two cotyledons in the seed, monocots have one. Cotyledons are
food storage organs in the seed. Other important differences between monocots
and dicots are in figure 1.
Important Terms
Cotyledons If present, are the first leaves of a plant and are modified for food
storage; may constitute the largest part of the embryo within the seed. The
cotyledons are the first appendages of the stem above the root system.
Leaf Leaves consist of 2 parts (figure 3 and 6):
Blade – The expanded flat portion. In some dicots, the blade is lobed or
divided into a number segments, called leaflets. In monocots it is
relatively narrow, parallel-sided and flat (figure 3).
Petiole – A stalk that attaches the blade to the stem (figure 3).
Sheath – Only in monocots. The base of the blade. It partially or
completely encloses the stem.
Leaf veins In dicots the veins form a meshwork throughout the blade. The
meshwork is called net venation. In monocots the veins run parallel to the leaf
margin – parallel venation (figures 1, 5 and 6).
Axil The angle formed between the stem and the upper side of the petiole
(figures 3 and 6).
Axillary or Lateral Bud A bud in the axil (figure 3). It will produce a leafy
branch or a flower or both. In many dicot plants these axillary buds develop
protective scales and become dormant for a period of time.
Terminal or Apical Bud The bud at the top of the main stem or at the end of
each branch (figure 3). Its growth produces more stem and leaves.
Node The place on the stem where a leaf occurs (figure 3).
Internode The segment of stem between any two nodes (figure 3). Stem
elongation is primarily due to elongation of the internodes.
Root In dicots there is one main root, the primary or tap root, and lateral roots.
The primary root originates from the seed radicle. Monocots generally have a
fibrous root system with many equal-sized roots growing in many different
directions. Fibrous root systems are usually more shallow-growing than tap root
systems.
Dicot Versus Monocot
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Figure 1. Comparison of Dicots and Monocots (Peffley et.al, 1999).
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Figure 2. Vascular Tissue.
Monocots
Dicots
Cotyledons
Flower Parts
Stem Characteristics
Leaf Venation
Vascular System
Representative Plant
Figure 3. Monocot and dicot differences. Monocots have one cotyledon in
the seed (A), scattered vascular bundles in the stem (B), and parallel leaf
venation (C). Dicots have two cotyledons in the seed (D), stem vascular
tissue in a single ring (E), and netted leaf venation (F). (Adapted from
Principles of Horticulture Teaching Manual).
Figure 4. Parts of a Stem. (A) A simple complete leaf showing stem relationship. (B) Distribution of tissue systems in the seed plant
(Peffley et.al, 1999).
© Kendall/Hunt Publishing Company
Stem Anatomy
Leaf Anatomy
Opposite
Two nodes opposite
each other on the stem,
one leaf arising from
each node
Alternate
Each node has
one leaf
Whorled
One node producing
three or more leaves
Basal
Leaves originating in a
cluster at the stem’s
base
Figure 5. Leaf Arrangement (adapted from Principles of Horticulture Teaching
Manual).
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Figure 6. Types of Leaves and Venation Patterns (Peffley et.al, 1999).
© The Botany Coloring Book
Figure 7. Leaf Structure, Venation, and Margin Types (Young, 1982).
© The Botany Coloring Book
Figure 8. Types of Compound Leaves (Young, 1982).
© Kendall/Hunt Publishing Company
Figure 9. Variation in Leaf Form (Peffley et.al, 1999).
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Figure 10. Variations in Leaf Margins and Tips (Peffley et.al, 1999).
Specialized Stems
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Figure 11. Types of Specialized Stems – Aerial (Peffley et.al, 1999).
Figure 12. Types of Root Systems (Peffley et.al, 1999).
© Kendall/Hunt Publishing Company
Name:_______________________________________Date:________________
Plant Structures I Worksheet and Questions
Part I
Different vegetative structures will be placed around the classroom. Answer the
following questions. You may use your lab book.
1.
What type of leaf margin is this?
2.
What type of leaf arrangement is this?
3.
Is this a simple or compound leaf?
4.
What type of venation is this?
5.
What type of leaf shape is this?
6.
Is this a simple or compound leaf?
7.
What type of leaf arrangement is this?
8.
What type of leaf tip is this?
9.
Is this a monocot or dicot?
10. Is this a monocot or dicot?
Part II
Answer the following questions.
1. What function(s) does the root have?
2. What function(s) does the stem have?
3. What is the function of the leaves?
4. What is the function of the cotyledon(s)?
5. Why are the leaves and stems of the plant green? Does the green color
tell you anything about their function? (If yes, what?)
6. What were the different types of roots seen and how do they differ?