Lab 11 Seed Plants

Lab 11
Seed Plants: Whole Plant and Vegetative Structure

In this lab session the overall pattern of seed plant structure will be examined followed by a detailed examination of the vegetative (non-sexually-reproductive) areas of these plants. The term vegetative does not preclude reproductive capabilities for these plant areas. The term "vegetative propagation" indicates the development of a whole plant from one of these areas (the leaf, stem, or root) rather than from a seed that has resulted from sexual reproduction. Indeed, some seed plants such as bananas have completely lost their seed producing ability and only reproduce by vegetative propagation. The term "vegetable" refers to root, stem, and leaf foods.

In studying plant structure, primary emphasis here will be placed on the angiosperms although it should be remembered that gymnosperms are also seed plants. Angiosperms are divided into two subclasses, Monocotyledonae and Dicotyledonae. Characteristics of these two subclasses are as follows.

Dicots	Monocots
1. Two seed leaves (cotyledons	1. One seed leaf (cotyledon)
2. Leaves are net veined	2. Leaves have parallel veins
3. Vascular bundles in stems arranged in a circle	3. Vascular bundles in stems scattered

4. Flower parts in fours or fives or multiples	4. Flower parts in threes or multiples
5. Seed chambers in fruit in fours or fives or multiples	5. Seed chambers in fruit in threes or multiples
6. Fibrous root system	6. Tap root system

The characteristics above should be learned and noted where applicable in this and following labs and lecture (see figure 1). Note that these are general characteristics and that there are many examples where they will not apply. The dicots are the most abundant of the two and are considered to be the most ancient by many. Most of the monocots are herbaceous. Dicots exist as herbaceous or woody.

Question 1: What does the term vegetative mean?

Question 2: What is meant by vegetative propagation?

Question 3: If all the apple trees in the world were killed but we still had some apples, could apple trees be reproduced? Explain.

Question 4: If all banana trees were killed, could banana trees be reproduced. Explain.

Question 5: From your own experience, give an example of vegetative propagation.

Question 6: What is a vegetable?

Question 7: What two classes of plants are seed plants?

Question 8: What does the term herbaceous mean?

Question 9: Would you expect to see trees having parallel veined leaves? Explain.

LAB OBJECTIVES:
To learn the basic anatomy both internal and external of herbaceous and woody seed plants with special emphasis on the vegetative plant regions.

PROCEDURE:

I. Whole Plant: Observe live plants and figure 2 for aid in identification of the following plant parts.
Define and/or give the function of the following plant parts:
a. flower:

b. leaf blade:

c. petiole:

d. node:

e. internode:

f. stipule:

g. stem:

h. root:

i. leaf axil:

j. lateral bud:

   II. Leaves
        A. Internal Structure
            1. Mesophytic Leaves: Mesophytic plants are those plants that are adapted for environments characterized by moderate climate and rainfall. The majority of plants in our area fit this description. Adaptations in leaf structure of these types of plants reflect their moderate environment, and to us these are "typical" leaves.

Obtain the slide labeled "Ligustrum (Privet) leaf". Scan the slide using the 10X objective and examine figure 3. Using the 10X objective or the 40X objective identify all leaf structures labeled.

Define and/or give the function of the following leaf structures:
a. cuticle:

b. epidermis:

c. mesophyll (spongy and palisade):

d. vein:

e. guard cells:

f. stoma:

2. Xerophytic Leaves: Xerophytic plants are those plants that are adapted for environments that are dry. To these plants water conservation is an utmost consideration for survival. This is quite apparent in the structure of their leaves.

Obtain the slide labeled "Pinus leaf". Using the 10X objective and 40X objective, locate the structures labeled in figure 4.

Question 11: Define xerophytic.

Question 12: List all differences in structure between a "typical" leaf and a pine needle.

B. External Structure
One of the characteristics used most extensively in identification and classification of plants is the external appearance of leaves. Leaves show great variety in size, shape, complexity vein patterns, margins, bases, etc. Your instructor will provide information and complexity comparisons, such as simple opposite, simple alternate, compound, etc. Also note the differences between parallel and net veined leaves.

III. Apical Meristem: Apical meristems are the growing tips of stems and roots where plants elongate and grow in width (primary growth).

A. Stem Apex
Obtain the slide labeled "Coleus stem tip". With the aid of figure 5, using the scan and 10X objectives, note the terminal apical meristem with projections arising from its margins. These protuberances are developing leaves, leaf primordia. In the axils of the leaf primordia small masses of meristematic tissue cells, bud primordia, can be observed. Under certain circumstances the bud primordia develop into branches of the stem. Note that the cells of the stem change in appearance as you move down the stem. These are meristematic cells which give rise to the mature tissues of the stem. Two basic areas can be seen; the single layer of cells covering the apical meristem is called the tunica. The mass of cells beneath it is called the corpus.

Question 13: Define apical meristem.

B. Root Apex
Obtain the slide label "Alium root tip". With the aid of figure 6 study the rooot using the 4x objective, beginning at the tip end. Covering the tip is a root cap composed of a rather loose mass of cells. Whereas roots grown in water show a loosely textured cap, a similar root grown in soil would have a more restricted one. In the soil some of the cells would be crushed and left along the side of the root. This root cap protects the rest of the young root as the tip is forced through the soil. Behind the cap there is a smooth region, the cells of which are small and have a dark appearance. This is the apical meristem "Region of Division". This apical meristem forms new cells, including the root cap. The addition of the new cells account for some of the elongation of the root. Behind the Region of Division the cells begin to elongate and may show a slight differentiation. This is the "Region of Elongation" and is responsible for most of the increase in length. Behind this is the "Region of Differentiation" where many root hairs are located. While the cells are differentiating internally, the root hairs form externally thus establishing the great absorbing surface of the plant roots. As one follows up into the older part of the root, all the cells become mature and complete the primary development of the root. The three regions have no exact lines of demarcation separating them; they merge into one another. The region of differentiation may be lacking on your slide. Obtain a slide of radish root tip to see root hairs. Also examine plastomounts of root systems.

Question 14: Define
a. region of division:

b. region of elongation:

c. region of differentiation:

d. root cap:

IV. Stems: The stem is the major support organ of a plant. It is also responsible for transporting nutrients, minerals, and water between roots and leaves. There are two basic patterns of internal stem structure, and these patterns are one of the characteristics used to classify plants as being either monocots or dicots.

A. Dicot Stem - Herbaceous
Examine a slide of a cross section through the stem of a buttercup (Ranunculus) using all powers. This non-woody stem shows the typical pattern of a circular arrangement of vascular bundles. Refer to figure 7. The first layer of cells is the epidermis, and is covered with a waxy cuticle which prevents water loss. The next region of the sterm toward the center is a layer of many cells in thickness, the cortex, usually composed of parenchyma cells, but some stems collenchyma cells. The area in the center of the stem is the pith, and it is composed of parenchyma cells or tissue. The remaining tissue is the vascular tissue which is a ring of vascular bundles. A closer examination of the individual bundles shows new cell types. The outer part of the bundle is called the bundle cap. The tissue adjacent to the bundle cap is the phloem. The large-celled tissue of the bundle is the xylem, containing vessels, tracheids, and parenchyma cells. The vessels function to conduct water throughout the plant. The vessels and tracheids are dead cells with thick, lignified secondary walls. The cavity, called the lumen, is large and is the site of water movement.

Question 15: What is a vascular bundle?

B. Monocot Stem
Re-examine the corn stem slide, a typical monocot. See figure 8 and label the structures your instructor points out.

Question 16: What is different about the way vascular bundles are arranged in monocots and dicots?

C. Dicot Woody Stems
The young woody stem is similar to that of herbaceous stems in that the regions are the same. However, the amount of primary xylem, vascular cambium, and primary phloem is greater, and they form a complete cylinder. With the growth in diameter of the woody stem, two regions show considerable change. The active cambium builds up more secondary tissues; and because of the resulting increase in diameter, the outer part of the stem becomes modified.

1. Study a cross section of a young woody stem of Tilia (basswood) or similar stem. Refer to figure 9. Three general regions of the stem can be identified: the pith in the center; the thick band of xylem or wood surrounded by the thin vascular cambium; the bark, all tissues outside the vascular cambium. If these sectors are studied more closely, the following can recognized: the xylem is made up of annual rings, each ring made up of spring wood (larger vessels) and summer wood (smaller xylem cells); the vascular cambium; the phloem made up of the conducting cells (sieve tubes) and thick-walled strengthing fibers (sclerenchyma); cork layers; and the vascular rays. Vascular rays are composed of conducting cells lying at right angles to the long axis of the stem. They are living parenchyma cells that are initiated by the vascular cambium and extend through the corresponding annual growths of the xylem and phloem

Question 17: What is the relationship between spring wood, summer wood, and annual rings?

2. Examine the blocks of wood provided for you. Note the dark central area of each block. This dark area is filled with gums and resins, does not necessarily conduct substances, and is called the heartwood. The lighter colored wood external to the heartwood is called sapwood, and actively conducts substances between the leaves and roots.

Question 18: Define:
a. heartwood:

b. sapwood:

c. bark:

3. Note examples of winter twigs. Refer to figure 10 and label the structures your instructor addresses.

V. Roots
The root is the major absorbing organ of the plant, and roots anchor the plant. In many plants, carrots for example, it also serves as a food storage organ.

A. Typical Internal Structure
Obtain a cross section of Rannunculus, a common dicot root. Refer to figure 11.

The epidermis is the outer layer of cells. Directly underneath is the relatively wide layer of thin-walled cells constituting the cortex. This layer of parenchyma cells extends completely around the root, and most of the cells have conspicuous starch grain stored in them. The innermost layer of cortex is the endodermis, one cell in thickness and with many of the cells showing thickened walls. The pericycle lies just underneath the endodermis and is one or two cells in thickness. The cells are larger than those of the endodermis and are the area from which branch roots develop. In the center of the section there is a solid core of xylem cells. Phloem tissue lies between the arms of the xylem. For convienience, all primary tissues within, but not including, the endodermis are collectively called the stele.

Question 18: Where is food stored in a root?

Question 19: The root epidermis is not coated with a waxy cuticle. Why?

Question 20: What is the stele of a root?

B. External Structure: Refer to figure 12 and plastomounts showing various types of roots.

Figure 1: Monocots vs. Dicots