TABLE OF CONTENTS
LABORATORY EXERCISES:
Laboratory Exercise #1
Relationships in Taxonomy.................................5
Laboratory Exercise #2
The Microscope...........................................13
Laboratory Exercise #3
The Cell.................................................23
Laboratory Exercise #4
The Root.................................................29
Laboratory Exercise #5
The Stem.................................................35
Laboratory Exercise #6
The Leaf.................................................43
Laboratory Exercise #7
Tissue Culture...........................................53
Laboratory Exercise #8
Flowers, Pollination and Fruit...........................57
Laboratory Exercise #9
Seed and Seed Germination................................63
Laboratory Exercise #10
Photosynthesis...........................................71
Laboratory Exercise #11
Plant Genetics...........................................77
REFERENCES....................................................85
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LABORATORY EXERCISE #1
RELATIONSHIPS IN TAXONOMY
INTRODUCTION:
The grouping of organisms into some meaningful hierarchy is an on-going
task.
Some students miss the relationships evident in this hierarchy and
just memorize the taxonomic groupings. It is difficult to commit such
groupings to memory and the memorized set of terms is quickly forgotten and
usually leaves the student with little general knowledge.
However, once
relationships become evident and established, classification becomes easier
and the student will “see” more of the environment and the plants within it.
PART I: THE TAXONOMIC KEY
Because of the predominance of morphologists (scientists who study the
form of plants and animals) among the early biologists concerned with
taxonomy, the great bulk of criteria used for identifying plants and animals
is their form.
While in some respects this narrow view of species
determination by morphological characteristics is declining in importance
among biologists, the use of such criteria will continue for a long time to
come.
However, such criteria are much easier for the casual student of
botany to use because a plant’s form can be readily seen. Physiological or
embryological characteristics can only be used after much research.
For any plant or animal, there may be hundreds, even thousands, of
characteristics which appear to differentiate it from all other organisms.
Experience has shown, however, that most of these are not critical in
determining the species; usually only a few characteristics are valuable in
this respect.
The beginning taxonomist, however, may be overwhelmed by all
of these characteristics and find it difficult to concentrate on the few
critical ones.
Plant keys are most useful in overcoming this problem.
By using a
series of choices concerning the characteristics of the plant, the student
only needs to concentrate on those given.
Other variations may be
conveniently forgotten unless they are stated in the key.
A key is a device for easily and quickly identifying an unknown object
such as a species of plant. The user is given a series of choices, usually
between two statements. By always taking the correct choice, one arrives at
the name of the unknown object.
Keys based on successive choices between only two statements are known
as dichotomous keys and are usually preferred to those with more than two
choices. Each set of mutually exclusive statements is called a couplet.
The following are examples of two types of dichotomous keys. The basic
concepts are the same, but it is important to be familiar with both types
since both are in use.
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INDENTED KEY:
1.
Fruit a group of achenes; flower not spurred
2. Petals none
3. Sepals usually 4: involucre none........................Clematis
3. Sepals usually 5: involucre present..................... Anemone
2. Petals present ..........................................Ranunculus
1. Fruit a group of follicles, flowers spurred
4. Flowers regular...........................................Aquilegia
4. Flowers irregular........................................Delphinium
BRACKET KEY:
1.
1.
Fruit a group of achenes: flowers not spurred........................2
Fruit a group of follicles: flowers spurred..........................4
2. Petals none.......................................................3
2. Petals present...........................................Ranunculus
3. Sepals usually 4: involucre none..............................Clematis
3. Sepals usually 5: involucre present............................Anemone
4. Flowers regular: spurs 5..................................Aquilegia
4. Flowers irregular: spur 1................................Delphinium
PART II: EXERCISES
Exercise 1.
Taxonomic Grouping of the Kingdom.
Taxa
Western Rhododendron
Cascade Huckleberry
Domain
Kingdom
Subkingdom
Superdivision
Division
Class
Subclass
Order
Family
Genus
Species
Eukarya
Plantae
Tracheobionta
Tracheophyta
Magnoliaphyta
Magnoliopsida
Dilleniidae
Ericales
Ericaceae
Rhododendron
macrophyllum
Eukarya
Plantae
Tracheobionta
Tracheophyta
Magnoliaphyta
Magnoliopsida
Dilleniidae
Ericales
Ericaceae
Vaccinium
deliciosum
(vascular plants)
(seed plants)
(flowering plants)
(dichots)
a.
Write the scientific name of the Western Rhododendron.
b.
Write the scientific name of the Cascade Huckleberry.
Remember the genus and species must be underlined. Notice that the
genus is always capitalized, but the species name is not.
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Exercise 2.
Natural System of Classification.
Using the bracketed dichotomous key at the end of this lab and the
conifers provided, classify each specimen one at a time.
Read each couplet
as a unit. If you answer “yes” to the first statement, go to the couplet
number indicated; if a name appears, you have identified your specimen.
If
your answer to the first statement of the pair is “no”, then go to the second
statement of the couplet. Your answer must be a “yes”. If you cannot give a
positive answer to the second statement either, you are off track. Return to
the beginning of the key and start over, being careful to read each statement
accurately and to examine your specimen carefully.
Follow the key, step by step, until you reach a name at the end of a
line. That is the name of your conifer specimen. After you have identified
a specimen, write the number of the specimen, the name (following proper
format for genus and species), and the proper sequence of couplet numbers you
used to identify your specimen on a separate sheet of paper.
Take another
conifer and begin with the first couplet again. You must always begin with
the first couplet. Identify a total of five conifers and hand in your
findings and specimens at the end of lab today. By the time you finish you
should be familiar with the workings of a dichotomous key.
Exercise 3. Artificial System of Classification.
The artificial system is designed for convenience and is based on the
plants form or ultimate use. In horticulture, there are five major factors
which can be used in classifying a plant (see factors listed below).
1. Water Content
a. Succulent – plant tissues that hold a lot of water.
b. Herbaceous – soft, green tissues, containing little wood.
c. Woody – dense tissues containing wood in stems and roots.
2. Form
a. Turf grasses – lawn grasses that spread by horizontal stems.
b. Groundcovers – low growing plants for erosion control or to cover
areas.
c. Ferns – herbaceous deciduous or evergreen plants growing from the
center to form a rosette of fronds.
d. Herbaceous Perennials – soft tissue perennials that die back to
the ground every year and regenerate from the roots.
e. Shrubs – woody plants that grow to 15’ of less and are multistemmed.
f. Trees – woody plants that grow larger than 15’ and have a trunk.
g. Vines – herbaceous or woody plants that need support to grow
upright.
3. Leaf Retention
a. Deciduous – sheds all leaves at the end of the growing season.
b. Evergreen – leaves are not shed yearly.
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4. Length of life Cycle
a. Annual – completes life cycle in one year or less.
b. Biennial – completes life cycle over two years, first year:
vegetative, green growth, second year: flower, fruit and
seed production.
c. Perennial – plants that live three years or more. Can be
herbaceous or woody plants.
5. Ability to Survive Environmental Extremes*
a. Tender - Low tolerance of freezing temperatures.
b. Semi-hardy – hardy under normal winter conditions, but are easily
killed by extremes in cold weather
c. Hardy – plants that are resistant to, or tolerant of frost and
freezing temperatures
* Determine the ability to survive by comparing each plant’s listed
zone(s) to Portland’s climate or zone (Sunset - Zone 6, or USDA - Zone 8). A
plant that is hardy to Portland would include Sunset Zone 6 in their
description. If it lists Zone 7 or higher, it is semi-hardy, and if it lists
Zone 8 or higher, then it is tender.
Choose ten out of the following plants, list the five factors in order,
and state the subcategory which would best describe the plant. The best
source of information for this exercise is Sunset – Western Garden Book.
Turn in this take home assignment at the end of lab, in two weeks.
Example:
Acer rubrum (Red Maple)
Water Content – Woody
Form – Tree
Leaf Retention – Deciduous
Length of Life Cycle – Perennial
Ability to Survive – Hardy
PLANTS FOR THE ARTIFICIAL KEY:
Abies balsamea ‘Nana’
Acer circinatum
Adiantum aleuticum
Arctostaphylos uva-ursi
Buddleia davidii
Camellia sasanqua
Camellia japonica
Campanula isophylla
Crassula ovata
Daphne cneorum
Fuchsia magellanica
Ficus benjamina
Iberis umbellata
Ilex aquifolium
Metasequoia glyptostroboides
Penstamon rupicola
Poa pratensis
Primula auricula
Primula x polyantha**
Rhododendron occidentale
** Note the “x” in front of the second name. The “x” indicates that
polyantha is the name of this hybrid.
This Primula is a hybrid, not a
species.
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KEY TO SOME COMMON NATIVE CONIFERS IN OREGON
1a.
1b.
Leaves not scale-like..................................................2
Leaves scale-like, almost completely covering the branches............25
2a.
2b.
3a.
3b.
Leaves 2 to 5 in a cluster (pines).....................................4
Leaves many in whorls on spur branches.................................9
4a.
4b.
5a.
5b.
6b.
7b.
8b.
9b.
10b.
11b.
Cones slender, 6-10 in. long.......................Pinus monticola
Western White Pine
Cones huge, 11-20 in. long; southern species
with range limit in Lane County..................Pinus lambertiana
Sugar Pine
Leaves angled in cross-section, evergreen trees(not native).......Cedrus
True Cedars
Leaves flatter, deciduous trees.......................Larix occidentalis
Western Larch
10a.
11a.
Leaves 3 in a cluster..............................Pinus ponderosa
Western Yellow Pine
Leaves 5 in a cluster (white pines)..............................7
Cones rounded, 1-3 inches long; bark silvery to white;
high altitude species...................................Pinus albicaulis
White Bark Pine
Cones elongated, over 6 inches long; bark grey; species
of middle altitudes....................................................8
8a.
9a.
Leaves 2 in a cluster............................................5
Leaves 3-5 in a cluster (yellow pines)...........................6
Bark thick, not flaking off in scales; coast species......Pinus contorta
var. contorta - Shore Pine
Bark thin, flaking off in scales; mountain species........Pinus contorta
var. murrayana - Lodgepole Pine
6a.
7a.
Leaves in clusters or whorled on spur branches,
needle-like, 2-8 inches long.....................................3
Leaves not in clusters; growing separately......................10
Leaves tapering to a point like thorns; basal part
grown tightly to the branchlet, and covering the branchlet;
½ or less inches long..........................................11
Leaves linear (not tapering), may be pointed or notched;
½ to 2 inches long.............................................13
Leaves with terminal free part
less than ¼ inch long..........................Sequoiadendron giganteum
Giant Sequoia
Leaves with terminal free part ¼ inch or more,
leaves with glands on back; cone fleshy..............................12
12a.
12b.
Low, more or less prostrate shrub..............Juniperus communis
Common Juniper
Usually a tree.............................Juniperus occidentalis
Western Juniper
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13a.
13b.
Leaves when falling, leave a circular scars on branchlet.............14
Leaves when fall, do not leave circular scars........................19
14a.
14b.
15a.
15b.
Leaves grey-green (glaucous), with whitish bands or
lines (stomata) on both upper and lower surfaces.....................16
Leaves dark green and shiny above, white lines
lacking above, notched at tip........................................18
16a.
16b.
17a.
17b.
18b.
19b.
Leaves in flat sprays, the leaves on upper
surface twig shorter; odor of leaves strong.........Abies grandis
Grand Fir
Leaves not in flat sprays, upper row of needles point
noticeably toward end of twig; deeply grooved
on upper surface.................................. Abies amabilis
Silver Fir
Leaves stiff, prickly pointed, leaving distinct
brown pegs on branchlet when falling.................................20
Leaves more flexible.................................................21
20a.
20b.
21a.
21b.
Branchlets glabrous (not hairy); leaves often twisted
at the short petiole-like base to form flattish sprays;
needles usually blue-green.........................Abies concolor
White Fir
Leaves not glabrous............................................17
Leaves grooved above, flat beneath; resin canals
deeply embedded; high mountain species.................Abies lasiocarpa
Alpine Fir
Abies procera
Noble Fir
Leaves ridged above and below, almost 4-angled in
cross section........................................Abies x shastensis
Shasta Red Fir
18a.
19a.
Scar smooth , not raised above the bark; cones erect...........15
Scar somewhat raised above the bark; cones hanging with
conspicuous 3-toothed bracts................Pseudotsuga menziesii
Douglas Fir
Leaves 4-angled in cross section;
high mountain species............................Picea engelmanii
Engelmann Spruce
Leaves indistinctly 4-angled; coastal species....Picea sitchensis
Sitka Spruce
Leaves sharply pointed at apex.......................................22
Leaves abruptly pointed or even rounded at apex......................23
22a.
22b.
Leaves with distinct short petioles
falling singly; cone is berry-like...............Taxus brevifolia
Western Yew
Leaves sessile (no petiole); whole branchlets often
falling, rather than separate leaves.........Sequoia sempervirens
Redwood
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23a.
23b.
Leaves ¾ to 1 ¼ inches long; spirally arranged
around branch.....................................Pseudotsuga menziesii
Douglas Fir
Leaves ¼ to ¾ inches long............................................24
24a.
24b.
25a.
25b.
Stomata (light lines) on under surface only;
leaves flat, 2-ranked, forming flat sprays;
cones 1 inch or less long......................Tsuga heterophylla
Western Hemlock
Stomata on both surfaces of leaves; leaves keeled
above or convex, spreading from branchlets
in all directions; cones 1 ½ to 3 inches long...Tsuga mertensiana
Mountain Hemlock
Branchlets cord-like, circular in cross section; leaves
tapering to a point, like thorns(rough to touch).....................26
Branchlets flat; leaves in twos or fours.............................28
26a.
26b.
Leaves with terminal free part
less than ¼ inch long....................Sequoiadendron giganteum
Giant Sequoia
Leaves with a terminal free part ¼ inch or more,
leaves with glands on back; cone fleshy........................27
27a. Low, more or less prostrate shrub.....................Juniperus communis
Common Juniper
27b. Usually a tree....................................Juniperus occidentalis
Western Juniper
28a. Leaves in whorls of 4; cones elongated,
scales widely divergent when mature:
bark scaly and reddish.......................Calocedrus decurrens
Incense Cedar
28b. Leaves opposite (discussate); cone scales peltate
or overlapping, not divergent..................................29
29a.
29b.
Cones oblong to ovate; cone scales overlapping; branchlets
usually more than 1/12 inch broad; underside of each
fresh leaf with white butterfly pattern;
branches drooping.........................................Thuja plicata
Western Red Cedar
Cones globular; cone scales peltate (umbrella shaped);
branchlets less than 1/12 inch broad.................................30
30a.
30b.
Branchlets smooth to the touch, tips of scale leaves
lie flat on twig; white X’s on surface of each fresh leaf;
branches arranged in horizontal plane....Chamaecyparis lawsoniana
Port Orford Cedar
Branchlets rough to the touch, due to tips of scale leaves
turning slightly outward; branches drooping;
no white X’s on undersurface; species of high mountains
north of Mt. Jefferson; bark shredding in long strips
.......................................Chamaecyparis nootkatensis
Alaska Cedar
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LABORATORY EXERCISE #2
THE MICROSCOPE
INTRODUCTION:
Before looking at cells and tissues, it is important to learn to use
the microscope correctly and efficiently. A little extra time spent learning
the parts and methods now will make future laboratory work much easier.
Exercise 1. Proper Handling and Parts of the Microscope.
a. Obtain a compound microscope from the metal cabinet under your lab
table.
When moving the microscope from one area to another, the
microscope should always be held in an upright position with one hand
holding the arm and the other hand holding the base.
See Diagram 1
below.
Diagram 1. Correct method of carrying a microscope.
b. Compare your microscope to Diagram 2.
With the aid of Table 1,
familiarize yourself the names and functions of each of the indicated
parts.
c. Locate the ocular lens and each of the four objective lenses.
Raise
the nosepiece using the coarse adjustment knob.
You will be able to
see the number on each of the objective lenses easier this way.
1. Find the magnification of the ocular and objective lenses.
ocular
_____________________
magnification
scanning power (shortest)_____________________
magnification
low power
_____________________
magnification
high power
_____________________
magnification
oil immersion* (longest) _____________________
magnification
* In order to use this lens, a drop of oil must be placed on the slide
to ensure a sharp focus. We will not use this lens.
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2. As the image passes through the scanning objective lens, it is
magnified 4 times (4x).
This larger image then passes through
the ocular lens where it is magnified 10 times more (10x). Thus
the total magnification with the scanning power is 40x (or
4 x 10 = 40x).
3. Compute the total magnification for each of the following lens
systems:
scanning power
_____________________
magnification
low power
_____________________
magnification
high power
_____________________
magnification
oil immersion
_____________________
magnification
Diagram 2. The parts of a typical compound microscope.
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PART NAME
FUNCTION
A
ocular (eyepiece).........................Used to view specimen and
further magnifies image.
B
body tube.................................Conducts image of specimen
from objective to ocular lens
C
arm.......................................Connects lens systems with
base of microscope.
D
objective.................................Contains lens to magnify
image of specimen.
E
slide with specimen.......................Object to be studied.
F
slide clip attachment.....................Holds slide securely
in place for viewing.
G
stage.....................................Holds slide.
H
fine adjustment...........................Used for precise,
final focusing.
I
coarse adjustment.........................Used for rapid,
initial focusing.
J
base......................................Supports microscope.
K
high power objective......................Gives highest magnification
(without oil immersion).
L
diaphragm.................................Regulates amount of light
passing through aperture.
M
aperture..................................Allows light to pass through
stage, illuminating specimen.
N
light source..............................Illuminates specimen.
O
light switch..............................Turns light on and off, as
well as adjusting intensity
of light.
P
slide adjustment knob.....................Moves slide on the stage so
different parts of the
specimen may be viewed.
Table 1. Parts and functions of a compound microscope.
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Exercise 2. Using the Microscope.
In using the compound microscope, there are certain steps that should
be carefully followed in order to make a complete study of the specimen on
the slide.
These steps will also prevent accidents to the lens system and
working parts.
It is important to carry out these steps in the order
indicated even after you are experienced in using the microscope.
a. Before using the microscope, clean the ocular and objective lenses with
lens paper. NEVER USE ANYTHING BUT LENS PAPER.
b. Raise the nosepiece using the coarse adjustment.
Turn the nose piece
until the scanning power objective (the shortest objective) is in
place.
c. Adjust the light source to get the maximum amount of light.
The
circular area you can see though the microscope is called the field.
d. Open the diaphragm to maximum capacity.
This is the largest aperture.
e. Place a prepared specimen slide on the stage. To insert the slide in
the clips properly, squeeze together the two upright tabs on the left
of the clip attachment. This rotates the left bar allowing the slide
to be inserted in the holders.
See Diagram 3.
Once the slide is in
place directly on the stage, slowly release the upright bars.
Diagram 3. Slide clip attachment.
f. As you are looking at the slide from the side (not through the
oculars), position the specimen directly over the aperture.
To do
this, use the slide adjustment knobs below the stage on the right side.
One knob moves the slide from right to left, one forward and backward.
(There is a knob at the same position on the left side of the
microscope. This is the condenser adjustment and should not be turned.)
g. While looking at the objective (not through the oculars), turn the
coarse adjustment until the scanning power objective is about 5/8 inch
from the slide.
The nosepiece will automatically come to a stop at
this point.
View through the oculars and slowly rotate the coarse
adjustment until the specimen is in focus.
Then rotate the fine
adjustment until the object is in the sharpest possible focus.
h. Since these microscopes have a binocular body (two oculars), the
eyepieces will need to be adjusted to your individual needs.
First,
use the thumb wheel to adjust the eyepieces to the distance between
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your eyes.
See Diagram 4.
The distance is correct when the focus
becomes sharper and three dimensional vision is achieved.
Diagram 4. Binocular head.
To adjust for the differences in vision between your eyes,
specimen into the sharpest possible focus with the fine
using the right eyepiece only. Then using the left eyepiece
the knurled collar until the specimen is in sharp focus. Do
the fine adjustment knob during the latter procedure.
bring the
adjustment
only, turn
not adjust
i. At this point, you may need to readjust the diaphragm.
It should be
emphasized that even though you can see the object, it is important to
open and close the diaphragm while looking through the microscope to
determine whether you can see the object better or more clearly with a
different amount of light.
j. If the low power objective is needed, move the slide until the object
is in the exact center on the lighted field.
Then, without changing
the coarse or fine adjustments, rotate the nosepiece until the low
power objective is in place.
Complete the focusing with the fine
adjustment, and readjust the diaphragm, if needed. You do not need to
readjust the eye pieces.
k. If high power is needed, move the slide until the portion of the object
to be studied is in the exact center of the low power field. Looking
at the slide (not through the oculars), slowly turn the nosepiece until
the high power objective is in place, making sure that you do not crush
the slide.
(You can look at the distance between the slide and the
objective to see if they will touch, you can feel it touching, or if
the slide is a wet mount, you can see the water under the cover slip
move if the objective touches the slide.) Make sure you are using the
high power objective, not the oil immersion lens.
If the high power
objective cannot be moved into place without touching the slide, ask
your instructor for assistance.
This microscope is parfocal, which means that if it is in focus on low
power, it should also be in focus on high power. Focus again with the
fine adjustment and readjust the diaphragm.
NEVER USE THE COARSE
ADJUSTMENT WITH THE HIGH POWER OBJECTIVE.
The longest objective, the oil immersion lens, will not be used in this
course.
If you wish to use it for a particular study, ask your
17
instructor for directions. DO NOT USE THE OIL IMMERSION LENS IN PLACE
OF THE HIGH POWER OBJECTIVE.
l. After using the microscope, turn the scanning power objective into
position. Remove the slide and clean the stage. If you are finished,
return the microscope to its storage space using the correct carrying
technique.
CAUTION:
DO NOT ATTEMPT TO ADJUST PARTS OF THE MICROSCOPE THAT WERE NOT
DISCUSSED ABOVE.
IF A PART IS NOT WORKING PROPERLY, REPORT IT TO YOUR
INSTRUCTOR. DO NOT ATTEMPT TO REPAIR IT.
Exercise 3.
Preparing a slide for observation.
Diagram 5 illustrates the procedure for making a slide using the wet
mount technique. The object to be observed is placed in a drop of water on a
slide and covered with a clean cover slip.
It is important that the cover
slip be held at a 45 degree angle against the slide and moved up against the
water before dropping it into place.
This minimizes the number of air
bubbles that will be trapped under the cover slip. If you get any water on
the underside of the slide or on the edges, dry it off before placing the
slide on the stage. Water on the stage will make moving the slide difficult
during observation.
a. Prepare a wet mount slide of any of the objects on the demonstration
table. Many will need to be sliced into as thin a section as possible.
The thinner the specimen, the better view you will have through the
microscope.
b. View the specimen under the scanning, low and high powers.
Draw a
portion of the specimen in the circle below and indicate the
magnification you used for that drawing.
The circle represents the
total lighted field at that power.
c. Depth of focus. When using the higher power you will notice that it is
not possible to get the entire specimen in focus at one time as you
could with scanning power.
When you focus on the top of the object,
the middle and bottom are out of focus, so you have to change the fine
adjustment to see the entire object.
This is because the depth of
focus (the depth of the specimen which can be in sharp focus) is very
thin on high power, but thicker on scanning.
As the magnification
increases, the depth of focus decreases.
________________ X
18
Diagram 5. Preparation of wet mounts.
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Exercise 4.
The Dissecting Microscope.
The other microscope you will be using in this course is the binocular
dissecting microscope.
This type of microscope also has a double objective
system arranged in such a way as to render a stereoscopic, three-dimensional
image.
a. Obtain a dissecting microscope from the cabinet at the back of the room
and compare it to Diagram 6.
Diagram 6.
The dissecting microscope.
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b. Notice that the distance between the oculars can be adjusted.
Pull
them apart or push them together until you have them adjusted to the
correct position for your eyes.
Your microscope has one ocular on
which the focus can be adjusted. Look through the nonadjustable ocular
first, and with your other eye closed, obtain a clear focus on some
object in the usual manner. Then open the other eye, close the first,
look through the adjustable ocular and rotate the milled cuff around it
until you obtain a clear image.
c. Since the magnification of the dissecting microscope is lower than that
of the compound microscope, the working distance is greater; hence much
larger objects can be examined.
The dissecting microscope has two
objectives of different magnifications mounted on a revolving turret.
1. What is the magnification of the oculars?
2. What is the
nosepiece?
magnification
of
each
objective
found
on
the
3. What is the lowest possible magnification?
4. What is the
microscope?
Exercise 5.
highest
possible
magnification
of
the
dissecting
Practice with the dissecting microscope.
a. Obtain a leaf or other specimen from the demonstration area and place
it on the stage of the dissecting scope. You do not need to mount it
on a slide.
b. Adjust the illuminator to discover whether you get a clearer view of
the object with or without illumination from beneath.
Light passing
through an object is transmitted light, while light going from the
illuminator directly to the object and bouncing off the object up into
the microscope is reflected light. One of the decisions a microscopist
must make is whether to use transmitted or reflected light.
1. Which form of light was used with the compound microscope?
Whether you use reflected light or transmitted light, or both together
depends, of course, on the size and opacity of your specimen. If you
decide to use reflected light, it is well to remember that the
illumination must usually be more intense since more of the light is
lost by scattering before it reaches the microscope lenses.
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LABORATORY EXERCISE #3
THE CELL
INTRODUCTION:
You are going to observe the material used over 340 years ago which led
to the use of the term cell. You will then look at two types of living plant
cells, pollen grains and protozoa.
Exercise 1.
Cork Cell.
a. Obtain a small piece of cork.
This material came from the bark of a
tree, but is no longer living tissue.
b. Use a sharp razor blade and carefully cut as thin a sliver as is
possible. Prepare a wet mount slide using the directions in Diagram 5.
c. Examine the cork specimen with scanning, low and high powers of your
microscope.
Observe the cells along the edge where the section is
thinnest.
1. Describe the appearance of the cork cells.
2. Draw a few cork cells.
The circle indicates the total lighted
field in the microscope.
Note the magnification that you are
using for your drawing on the line below the circle.
________________ X
3. Does a cork cell look like it is living?
23
Why or why not?
Exercise 2.
Onion Cell.
The cell is the fundamental unit of any living organism.
The living
part of the cell includes all the organelles inside the cell membrane, but
not the cell walls of plant cells.
Therefore, if the cell is living you
should be able to see some organelles inside the cell.
The cork cell was
nonliving because it contained only a cell wall. The inside was empty.
a. Place a drop of Lugol’s solution on a clean slide.
The Lugol’s
solution contains iodine which stains organelles in the onion cell
an amber color making them easier to observe.
b. Use forceps to pull the transparent epidermis (skin) from the inner
curved part of the surface of the onion.
c. Carefully spread the epidermis strip in the Lugol’s solution.
overlapping or wrinkling
Avoid
d. Apply a cover slip.
e. Examine the preparation with the scanning, low and high powers.
f. Identify the following components of the
(components in bold type are easily seen):
onion
epidermal
cell
Nucleus – located centrally or along the cell’s periphery (it
will be oval shaped and stained light brown)
Nucleoplasm – the interior of the nucleus.
Nucleolus – tiny body within the nucleoplasm (faintly evident)
Nuclear membrane – the boundary around the nucleus.
Cytoplasm – a narrow, lightly stained band situated along the
cells periphery. Strands of cytoplasm may “lace” the vacuole.
Cell membrane – the outer boundary of the cytoplasm, which
adheres to the cell wall.
Cell wall – the rigid wall surrounding these cells.
g. Draw an individual onion cell and label the parts listed above.
________________ X
24
Exercise 3.
Elodea Cell.
a. Prepare a wet mount of a mature Elodea leaf. Take a small leaf from
the growing tip of the plant. Place the entire leaf flat on a drop
of water on a clean slide. Apply a cover slip.
b. Examine the cells throughout the leaf with the scanning, low and
high powers. Cells that are not dark green will be best for initial
observations. Recall that all three-dimensional objects have depth
as well as width and length. Choose an individual cell and focus
continually up and down with the fine adjustment knob.
1. Is there a difference in appearance among the upper, middle and
lower levels of focus?
2. Is the green color found equally throughout the cell or is it
located in packets?
c. Identify the following parts of the cell.
Nucleus – a very pale olive-brown oval located next to the cell
wall. In many cells it will be difficult to locate.
Scan over
the specimen and try to find a nucleus in one of the cells.
Cytoplasm – clear fluid inside the cell.
Vacuole – a large clear sac in the center of the cell. It will be
necessary to focus on the middle level of the cell to see an area
which is clear and lacks chloroplasts.
Cell wall – the rigid wall surrounding these cells.
(The cell
membrane will be invisible because it is cemented to the cell
wall.)
Chloroplasts – these are the tiny green packets of chlorophyll
that are found in the cytoplasm.
They give the leaf its green
color
and
are
responsible
for
making
food
(through
photosynthesis) for the plant.
d. Draw and label a microscopic view of one Elodea cell.
________________ X
25
e. Focus carefully up and down through the Elodea leaf.
Note the
overlapping of cells and determine the number of cell layers that
comprise the leaf’s thickness. Repeat at two or three locations.
1. How many cell layers are characteristic?
f. The chloroplasts of some cells may now appear to be moving. It is
actually the cytoplasm that is in motion, a phenomenon known as
cyclosis (or cytoplasmic streaming).
Exercise 4.
Pollen Grains.
Pollen grains are cells specialized for reproduction.
They usually
have a hard, opaque (does not allow light to pass through) cell wall.
Therefore, when you observe them through the microscope, you will only see
the outside of the cell wall.
a. Obtain a prepared slide of mixed pollen grains. This slide has been
stained with various chemicals to make the details of the cell wall
more apparent. Pollen is not this color in nature.
b. Observe the specimens at scanning, low and high powers.
c. Draw three different kinds of pollen grains in the circle below.
________________ X
26
Exercise 5.
Protozoa.
These are small, one celled organisms found in the soil or in pond
water. The majority of these organisms are neither animals nor plants, but
protozoa. They belong to the kingdom Protista.
a. With a dropper, place one drop of pond water on a clean slide. Try
to get a bit of decayed grass or scum, because this is the food
source for the protozoa.
b. Place a cover slip over the drop of pond water. Wipe off any excess
water on the cover slip or on the underneath side of the slide.
c. Observe the specimens on scanning, low and high powers.
(These
little critters are very fast moving; catching them on the move
requires patience and quickly moving from scanning up through the
different powers to get a closer look.)
d. Draw one of the organisms you see in the space below.
________________ X
27
28
LABORATORY EXERCISE #4
THE ROOT
INTRODUCTION:
The root is the vegetative organ of the plant that usually grows
totally or partially embedded in the soil. Substances from the soil, which
are essential for growth and development of the plant, are obtained through
the root or root system. Roots function as follows:
1. to anchor the plant to the soil;
2. to absorb and conduct water and dissolved nutrients to other
parts of the plant;
3. to store food products, especially starch;
4. and in some cases to initiate vegetative reproduction.
Most plants have a system of roots rather than a single root. The most
common types of root systems are; the fibrous root system (grasses and corn);
the taproot system (dandelions, some trees, carrots and turnips); the
fascicled or tuberous root system (dahlias and sweet potatoes).
Roots may also be classified according to their origin: primary roots
develop from the seed; secondary roots arise as outgrowths from other roots;
and adventitious roots emerge from stems and leaves.
Exercise 1. Observation of Root Systems.
Obtain live and/or preserved specimens of corn, bean, carrot and dahlia
(or sweet potato) plants from the back table in lab. Observe each plant and
fill in the tables below for their root system and origin.
PLANT
Fibrous
Table 4-1. ROOT SYSTEM
Taproot
Fascicled
Primary
Table 4-2. ROOT ORIGIN
Secondary
Adventitious
Bean
Corn
Carrot
Dahlia or
Sweet Potato
PLANT
Bean
Corn
Carrot
Dahlia or
Sweet Potato
29
a. Are the roots on the corn and bean of uniform diameter or are they
tapering?
b. What is the advantage to their shape?
c. Is there any particular pattern or regularity to the branching of the
roots? If so, describe the pattern.
d. Do you observe any evidence of leaves on the roots? If so, describe
them.
e. Do you observe any evidence of chlorophyll in the root cells?
Exercise 2.
The Root Tip.
The root grows in length by the action of a few meristematic cells at
the root tip. Water and minerals are absorbed within the first two to five
millimeters of the root. It is important, therefore, to examine the root tip
with these functions in mind.
a. Examine a prepared microscope slide of an onion (Allium sp.) root tip
and complete the following diagram.
Identify the five parts of the
root tip and fill in the typical cells, putting in as much detail as
you are able to see.
Diagram 7. Allium root tip.
30
Exercise 3.
Observation of a living root tip.
Place a young radish or oat seedling on a slide and observe it with a
dissecting microscope.
From your observations on this exercise and the
previous one, answer the following questions.
a. Are the root hairs present at the very end of the root?
b. Locate the thimble shaped root cap.
arranged?
How are the cells of the root cap
c. What is the function of the root cap?
Locate the meristematic region. This is the region in which new cells
are formed continuously by cell division. Just above the meristematic region
is the region of cell elongation.
d. How do these cells compare in shape with the meristematic cells?
e. In what way does the elongation of these cells affect the relative
position of the meristematic region in the soil?
About a millimeter or so behind the root tip is the region of
maturation or differentiation. In this area, you might see evidence of some
mature tissues.
f. In what area are the root hairs formed?
g. Are all the root hairs the same length?
h. Do they contain nuclei?
i. Cytoplasm?
Make a labeled drawing of the root tip of the radish or oat seedling
and identify as many of the regions as possible.
________________ X
31
Exercise 4.
The Dicot Root.
Observe a slide of a cross-section of a buttercup (Ranunculus sp.)
root. Beginning from the outside of the section and progressing toward the
center, locate the following tissues.
Epidermis - This is the outermost layer of cells.
a. Root hairs may or may not be present in this cross-section of the
root. Why?
Cortex – The cortex is a broad layer of parenchyma cells with numerous
intercellular spaces. Cortical parenchyma cells often contain dark blue
or black stained bodies.
b. What are these bodies and what is their function?
Endodermis – The endodermis is a layer of mostly thick-walled cells,
one cell layer thick, which forms a boundary between the cortex and
vascular cylinder or stele.
c. What is the possible function of the endodermis in roots?
Xylem – The xylem is located in the center of the stele. The cells of
the xylem are usually arranged in an X or cross pattern with four xylem
“points”. The cells, which are dead, are often stained red.
d. What is the major function of xylem in the root?
Phloem – The less conspicuous patches of phloem cells are located
between the “points” of xylem tissue. Phloem cells are smaller, thinwalled cells, which contain cytoplasm, and therefore living. Phloem is
usually stained green.
e. What is the major function of phloem tissue?
Pericycle – Located between the phloem and the endodermis is a band of
cells, one to several cells wide, called the pericycle. Certain cells
of this tissue retain their ability to undergo cell division and give
rise to lateral or branch roots. The cork cambium of older roots also
is derived from cells of the pericycle, as well as part of the vascular
cambium of the root.
Vascular Cambium – Parenchyma tissue is found between the phloem and
the xylem tissue.
As the root ages some of these cells become
meristematic and eventually give rise to the vascular cambium. You may
see some early divisions of the cambium in these slides.
32
f. Identify and label the diagram below with the parts of the root
indicated in bold type on the previous page.
Diagram 8.
Buttercup (Ranunculus sp.) root.
33
Exercise 5.
Origin of lateral roots.
Observe the slide illustrating the origin of lateral roots.
a. What layer of cells gives rise to the secondary root?
b. Through what tissues does the secondary root grow before emerging into
the soil?
34
LABORATORY EXERCISE #5
THE STEM
INTRODUCTION:
This lab studies the external structure of woody stems and grasses.
The internal anatomy of an herbaceous dicot stem will be observed as well as
woody dicots and gymnosperms.
PART I:
THE MORPHOLOGY OF STEMS
The stem is one of the three basic vegetative organs (stem, root and
leaves) of higher plants, and functions in several ways:
1. By the activity of specialized tissues, the stem produces leaves and
floral structures, and furnishes mechanical support for these organs.
2. The stem functions in the conductive or transport system of the plant,
conducting water and minerals via xylem to all above ground parts of
the plant, and translocation of food materials via phloem from the
aerial parts to the root system.
3. The stem may serve as a storage reservoir for food materials, water and
minerals.
4. Vegetative reproduction is initiated by the stem or portions of it.
In your experiences, you have seen plant stems that are green
(indicating the presence of chlorophyll) and fleshy. Stems fitting this
description are called herbaceous. Stems with a high water content, and very
watery are called succulent.
In contrast, woody stems are devoid of
chlorophyll (at least during the later stages of growth), hard, and persist
from a few to several hundred growing seasons and therefore are perennial.
Plants living in different growing conditions show a variety of stem
forms.
We generally think of a stem as being an upright aerial structure.
However, some plants have stems which normally are prostrate on the surface
of the soil called stolons (bent grass) or above ground as runners
(strawberries and spider plants); others have stems which normally grow
beneath the soil surface called rhizomes and are mistaken for roots (iris and
quack grass); and still others have stems that twine around other plants for
support (beans and honeysuckle) or grow appendages that curl around supports
called tendrils (passion vine).
Adaptations of stems such as prickles and
thorns protect plants from predators in the environment.
Other modifications of stems include; tubers, enlarged underground
storage structures (potatoes); corms, short fleshy underground stems (crocus
and gladiolus); and bulbs, flattened stems with leaf scales attached (onions
and daffodils).
35
Exercise 1.
Observation of stems.
a. Horse Chestnut (Aesculus sp.) stem
Identify, label, and give the definition of the following structures on
the horse chestnut stem:
1.
Terminal bud (apical)
2.
Terminal bud scales
3.
Terminal bud scale scars
4.
One year’s growth
5.
Axillary bud (lateral)
6.
Leaf scar
7.
Vascular bundle scar
8.
Node
9.
Internode
10. Lenticel
Diagram 9.
Horse Chestnut (Aesculus sp.) stem
36
b. Pear (Pyrus sp.) stem
Identify and label the following structures on the pear stem:
1. Fruit spur (branches with very short internodes)
2. Terminal bud (apical)
3. Terminal bud scale scars
4. One year’s growth
5. Axillary bud (lateral)
6. Node
7. Internode
Diagram 10.
Pear (Pyrus sp.) stem
c. Corn (Zea sp.) stem
Identify and label the following structures on the corn stem:
1. Node
2. Internode
3. Leaf sheath
Diagram 11. Corn (Zea sp.) stem
37
Exercise 2.
Structure of fleshy stems.
Examine the living stems of Coleus, and geranium (Pelargonium sp.).
Look for the following:
Apical bud – The terminal or apical bud is located at the tip of the
stem.
Axillary bud – Lateral buds are located on the stem below the apical
bud.
Branches – Some of the Coleus plants exhibit branching along the stem.
Nodes and internodes – The node is that part of the stem from which
leaves arise, and may be characterized by a swollen area in the stem.
That area of the stem connecting two adjacent nodes is known as the
internode.
a. What is the position of the axillary buds in relation to the closest
leaves?
b. Is a bud associated with the base of a branch? If not, why?
c. Using a ruler, measure the internodes down one stem. Where are the
internodes the shortest? Longest?
d. From your observations, in what part of the plant would you conclude
that growth (cell division and elongation) is occurring?
e. Look closely at the stem.
PART II:
Do you see any lenticels?
THE ANATOMY OF STEMS
Exercise 3.
Anatomy of a apical bud.
Obtain a compound microscope and a prepared slide of a Coleus stem tip.
Focusing on scanning or low power, locate the dome-shaped shoot apex in the
longitudinal section.
Using your textbook, locate and give the definitions
of the following areas of the apical bud:
a. Apical meristem
b. Leaf primordia
c. Axillary bud primordia
d. Internode
e. Node
38
Exercise 4.
Anatomy of a herbaceous dicot stem.
Obtain a prepared slide of a sunflower (Helianthus sp.) stem.
Begin
your examination of the stem cross-section from the outside of the stem
toward the center. Use your handout as a guide.
Epidermis – The epidermis consists of a single layer of cells, which
enclose the stem.
Note that these cells are all about the same size
and shape.
In young herbaceous stems the epidermal cells secrete a
waxy substance that forms a covering over the outside of the epidermis.
This thin waxy layer is called a cuticle.
a. What is the probable function of the cuticle?
Cortex – The first few cells layers beneath the epidermis consists of
collenchyma tissue. Collenchyma cells have thickened cellulose walls
and function as a mechanical or strengthening tissue.
Cortical
parenchyma lies adjacent to the collenchyma. Cortical parenchyma cells
are larger in diameter and have thinner walls than collenchyma. Open
areas between the cells of the cortex are called intercellular spaces.
Cells of the cortex may contain chloroplasts and function in
photosynthesis, or they may lack pigmentation and serve as storage
cells. In some plants such as sunflower, latex ducts are found in the
cortex.
Latex ducts appear as empty spaces surrounded by one or two
layers of smaller, more regularly shaped cells.
Vascular tissue – The
conductive tissues, the
closest to the center
predominantly red-stained
stem.
vascular tissue consists of two types of
xylem and the phloem.
Xylem tissue lies
of the stem and is distinguished by the
cells: phloem is toward the outside of the
b. What is the function of the phloem tissue?
c. What is the function of the xylem tissue?
Vascular Cambium – The vascular cambium is a zone of meristematic cells
located between the xylem and the phloem tissue.
In young stems the
cambium appears to be one or two layers of thin-walled, brick-shaped
cells. These cells are small and regular in appearance. In very young
stems, the cambium is restricted to vascular bundles, but as the stem
ages, parenchyma cells between the vascular bundles (or pith rays)
become meristematic, resulting in a continuous vascular cambium.
d. What function does the vascular cambium serve in stems?
39
Pith – The center of the stem is occupied by this parenchymous tissue.
These are the large cells with thin walls and numerous intercellular
spaces. Pith cells probably aid in short-term food storage after which
the cell contents disintegrate and the walls only contribute to support
the stem.
Pith Rays – Pith rays are extensions of parenchyma tissue between the
vascular bundles.
e. Identify and label the parts of the stem (indicated in bold
letters above) for the following diagram.
You should know the
function of each of these parts.
Diagram 12.
Cross-section of an herbaceous dicot stem (Helianthus sp.)
40
Exercise 5.
Anatomy of a woody dicot stem.
The pith, composed of thin-walled parenchyma cells, is located in the
center of the stem.
The major portion of the stem is made up of xylem
tissue.
In the three-year old slide of Tilia the xylem will consist of
concentric rings or annual rings of irregular shaped, relatively thin-walled
vessels, and more uniformly shaped thick-walled, fiber-like cells.
In any
one annual ring, the larger vessels or spring wood, are closer to the pith
than the smaller sized vessels and fibers of the summer wood.
The ordered
arrangement of different shaped cells allows one to delineate a year’s
growth.
Immediately outside the xylem or wood are several layers of flattened,
brick-shaped, very thin walled living cells (stained bluish-green). This is
the cambial zone.
One layer of cells of this zone is called the vascular
cambium.
The phloem tissue lies adjacent to and just outside of the vascular cambium.
Phloem is made of concentric plates, each composed of sieve tube elements,
companion cells and fibers.
The cork is usually represented by the outermost layer of tissue after
the first year’s growth. Cells in the outer portion of the cortex give rise
to the cork cambium. Cork cells are produced toward the outside of the stem
by the cork cambium.
a. Study a prepared slide of a cross-section of a basswood (Tilia sp.)
three-year old stem.
Identify and label all the parts given in bold
type above for Diagram 13 below.
Diagram 13.
Partial cross-section of a woody dicot stem (Tilia sp.)
41
Exercise 6.
Cross-section of a dicot stem.
Examine a wood block cut from an oak, ash or maple.
The small dark
colored tissue in the center of the stem is the pith and/or xylem tissue
where resins and toxins are deposited and called the heartwood. The light
colored area is the sapwood or water conducting xylem tissue. Annual rings
may be visible in the heartwood/sapwood portion of the stem. An annual ring
represents the amount of xylem tissue produced in one growing season.
The
outer rind completely surrounding the stem is the bark. Bark is composed of
functional phloem tissue, the cork, and the cork cambium.
Exercise 7.
Anatomy of a gymnosperm stem (Pinus sp.).
a. Study a prepared slide of a cross-section of pine stem, noting the
similarities and differences with the previous herbaceous and woody
dicot stems.
Diagram 14.
Cross-section of an older pine stem.
42
LABORATORY EXERCISE #6
THE LEAF
INTRODUCTION:
Almost all the food for terrestrial animals and plants is derived from
the functions of the green leaf.
Leaves are the structures that capture
energy from the sun and turn it into stored chemical energy in the form of
simple sugars and other complicated molecules. This in turn, supplies energy
for man and other animals. Much of life is directly related to and dependent
upon this energy conversion and storage by green leaves.
Therefore, it is
important that we understand the structure and functions of the green leaf.
This
lab
studies
the
green
leaf
both
macroscopically
and
microscopically. The outer features of the leaf are discussed in relation to
the adaptive advantages that these structures have for the leaf in performing
its basic function as an organ for photosynthesis.
The inner structure of
the leaf is also examined with the same relationship in view. Operation of
the stomata is discussed and demonstrated. Modifications in leaf form and
structure are related to environment and growth habit.
PART I:
THE MORPHOLOGY OF LEAVES
Exercise 1. Leaf Parts.
Leaves are perhaps the most conspicuous parts of plants.
They are
always borne on stems. The part of the stem to which a leaf is attached is
called a node.
The upper angle which the leaf makes with the stem at its
point of attachment is called the axil of the leaf.
The presence of an
axillary bud is always seen at this location, although the bud may be so
immature that it is not visible to the unaided eye or it may be covered by
the sheath of a leaf base.
a. Answer the following questions using Diagram 15.
1. List 3 structures that a compound leaf has that a simple leaf does
not.
2. A leaflet can be distinguished from a simple leaf blade because a
leaflet would never have an ______________________ at the base of
the petiolule.
3. Identify the function of the following structures:
a) Leaf blade
b) Midrib and veins
c) Petiole
43
d) Stipule
e) Axillary Bud
f) Rachis
g) Petiolule
h) Leaflet
A. Simple leaf.
Diagram 15.
Exercise 2.
B. Compound leaf.
Simple and compound leaves.
Types of Leaves.
Collect one sample of each of the following leaf types.
Use the
diagrams in our textbook to assist you with each category. Tape each leaf on
a sheet of paper and correctly identify each with its description listed
below. Hand in the assignment by the end of lab, in two weeks.
a. Simple leaf
b. Pinnately compound leaf
c. Palmately compound leaf
g. Broadleaf evergreen
h. Needle leaf evergreen
i. Scale leaf evergreen
d. Leaf showing parallel venation
e. Leaf showing pinnate venation
f. Leaf showing palmate venation
j. Leaves arranged oppositely on stem*
k. Leaves arranged alternately on stem
l. Leaves arranged whorled on stem
* Leaf arrangement on stems or phyllotaxy, requires you find a stem
with leaves attached to show whether it is opposite, alternate, or whorled.
Be sure your samples show this!
44
PART 2:
THE ANATOMY OF LEAVES
Exercise 3.
Section of a Leaf.
Study a prepared slide of the cross-section of a leaf, compare your
slide to the diagram below and locate the labeled structures.
Diagram 16.
A cross-section of Ligustrum (Privet) a broadleaf evergreen.
Next to each of the following structures, cell types and tissues listed
below, identify their function.
a. Cuticle
b. Epidermis
c. Palisade mesophyll
d. Spongy mesophyll
e. Guard cells
f. Stomata or stoma
g. Substomatal chamber
45
h. Intercellular space
i. Vein or vascular bundle
j. Xylem
k. Phloem
l. Chloroplasts
Exercise 4.
The epidermis.
Study
the
microscopically.
surface
of
the
leaf
of
the
Wandering
Jew
plant
a. Prepare a slide by breaking the top surface of the leaf and carefully
peeling back the lower layer with forceps.
Mount a small section of
the lower leaf epidermis in water and cover with a cover slip.
Diagram 17.
Wandering Jew leaves.
b. Sketch a few of the cells in the space below.
________________ X
46
c. Answer the following questions.
1. Are there any openings in the surface layer (epidermis) of the leaf?
2. Why is water lost from the plant?
3. What are the advantages of transpiration to the plant?
4. What are the disadvantages of transpiration to the plant?
d. Label the diagram below as indicated by the arrows.
Diagram 18.
Lower epidermis of a leaf.
47
Exercise 5.
Transpiration.
Transpiration is the process by which water vapor is lost from the
aerial parts of plants, principally through the stomata and the lenticels
(tiny holes in the epidermis or bark of the stem).
Study the data outlined
in Table 2. below. Construct a graph in the grid provided on the next page.
Plot the data as points and connecting lines, using different colors
representing transpiration and evaporation.
After completing the graph
answer the questions at the end of the exercise.
Table 2.
Transpiration from leaves.
48
TRANSPIRATION / EVAPORATION GRAPH
a. Does there appear to be a relationship between the amount of water lost
from the plant and the time of day?
b. If you answered the above question yes, what environmental factor(s)
might help explain this relationship?
c. List several environmental factors which would increase the rate of
transpiration from the plant.
49
Exercise 6.
Stomata.
Using the information in Table 3., answer the questions below.
NUMBER OF STOMATA*
(Average number per square millimeter of leaf surface)
SCIENTIFIC NAME
COMMON NAME
Elodea
Betula alba
Hydrangea arborescens
Syringa vulgaris
Pinus strobus
Castalia odorata
Avina sativa
Zea mays
Brassica oleracea
Populus deltoides
0
Birch
Smooth Hydrangea
Common Lilac
White Pine
White Water Lily
Oats
Corn
Cabbage
Cottonwood
* From:
UPPER SURFACE
0
0
0
0
142
460
25
94
141
89
237
25
330
0
0
23
158
226
131
Developmental Plant Anatomy, by R.A. Popham.
Table 3.
LOWER SURFACE
1952
Number of leaf stomata.
a. Elodea is a common water plant used in aquariums.
lacking in stomata entirely?
b. Why would birch, hydrangea
undersurface of the leaves?
and
lilac
have
Why would it be
stomata
only
on
the
c. Why do you think the water lily would have stomata only on the upper
leaf surface?
d. Explain why oats would have an approximately equal number of stomata on
both sides of the leaf?
50
e. Why do you think corn, cabbage and cottonwood have more stomata on the
underside of the leaves?
Exercise 7.
Abscission Layer.
Answer the following questions using Diagram 19 and your observations
of deciduous plants.
Diagram 19.
Abscission layer – a leaf petiole in longitudinal section.
a. Define the term “abscission”.
b. At what time of the year would you expect the abscission layer to form?
c. At what time would you expect the abscission layer to function?
d. What would you surmise is the adaptive value of the abscission layer?
51
Exercise 8.
Summary.
a. Can you think of any reason why cells should be elongated to form the
palisade layer?
b. Beneath the palisade layer is the spongy layer, characterized by large
intercellular spaces.
Of what advantage to the leaf is such a
structural organization?
c. In which cells would most of the photosynthesis occur?
answer.
Explain your
d. Is there any evidence for the presence of supporting and/or conducting
cells in the leaf? What are the functions of a vein?
e. Would you expect the leaf or the stem to carry on more photosynthesis?
Explain your answer.
52
LABORATORY EXERCISE #7
TISSUE CULTURE
INTRODUCTION:
Plant tissue culture is a method of asexual reproduction through "cloning”.
A small piece or explant, of the desired plant is placed on an agar medium
which promotes cell multiplication and differentiation. As new plants develop,
they are transplanted to a normal potting mix.
The concept of tissue culture is based on the theory of cell totipotency.
The theory states that regardless of their location, all cells in a plant
contain a full complement of genes. Each cell, therefore, is capable of forming
a whole new plant identical to the original.
Since all the plants produced are identical to the original, tissue
culture techniques are ideally suited to mass propagation of named hybrids
that will not breed true through seeds. Tissue culture also makes possible
the production of disease-free plants. The method is currently being used in
research on genetic engineering of plants, in which a single plant cell can
be genetically modified and grown into a mature plant having new
characteristics.
The agar medium on which the plants are grown is composed of inorganic
salts, vitamins, hormones, sugar and agar. The salts provide all the
essential nutrients for plant growth; that is, they act as the fertilizer.
Vitamins and hormones enhance shoot production, root, growth, cell division
and differentiation. Sugar is used as an energy source because there may be
too little light or not enough chlorophyll present to carry on normal
photosynthesis. Agar is a gelatin-like substance which supports and holds the
explant in place. The exact composition and proportions of the amendments
will vary with the different species of plants to be grown.
The agar is an ideal growth medium for bacteria and fungi. Since
bacteria and molds will grow extremely fast, contamination usually proves
fatal to the explant. These two contaminants are found in the air, on the
skin and clothing; in short, everywhere. The only way to kill bacteria and
fungi is to use heat and pressure, conditions found in the normal home
pressure cooker. All the tubes of medium have been pre-sterilized.
The biggest single factor to success with tissue culture is the
prevention of contamination from sources other than the agar medium.
Therefore, much of the work has to be done under as sterile conditions as
possible. In this case, a transfer case will be used to minimize air-borne
contamination. The case should be cleaned thoroughly with 70% ethanol before
use.
The work area should be located away from drafts. Fans and air
conditioners should be turned off as they can stir up dust and increase
contamination. The area around the transfer case should be cleaned with soap
and wiped with a bleach solution. Wear short sleeves or a lint-free lab coat
when performing the work.
53
Make sure all the needed items are within reach. Equipment you will
need each time include sterile petri dishes, forceps, scalpels, ethanol,
sterile distilled water, sterile paper towels, a wastebasket and a container
to hold discarded solutions. Know the steps you will follow before you start
work.
Instruments are sterilized by placing them in a beaker of ethanol until
needed. To remove the ethanol, dip the instrument into the sterile water and
proceed. When finished with an instrument, wipe plant debris on a paper towel
and return the instrument to the ethanol. Be sure that "dirty" operations are
not performed over "clean" or sterile items.
Exercise 1. Preparation of the explant. (Sterile technique not required)
a. Use the younger leaves near the center of the plant as their cells will
be more likely to have retained their totipotency. Refer to Diagram 20.
as you read the following steps.
b. Remove the young leaves, leaving a length of petiole (leaf stalk)
attached to each. Put them in a small beaker and cover with the
antioxidant solution. This solution will prevent browning of the
tissues. The leaves should remain in the antioxidant solution for 20
minutes to one hour.
c. Pour off the antioxidant solution and cover the leaves with 10% sodium
hypochlorite (bleach) to which has been added one drop of detergent.
The detergent acts as a wetting agent and allows the entire surface of
the leaf to be exposed to the bleach. This will disinfest the leaf of
any surface bacteria, fungi, mites or small insects. Put some parafilm
over the top of the beaker and shake the solution with the leaves in it
for 5 minutes.
d. Pour off the bleach solution and replace it with 70% ethanol. Swirl the
ethanol and leaves for 30 seconds.
e. Place the leaves in a beaker with sterile water, being careful not to
contaminate the explant.
Exercise 2. Preparation of the explant. (Sterile technique required)
a. Go to the sterile work area to proceed. Be sure you have all the
equipment you will need within reach. Be sure your hands and forearms
have been thoroughly washed with soap and water before proceeding.
b. With sterile forceps, remove the leaves from the jar and place each
leaf, underside up, on a sterile paper towel. Return the forceps to the
ethanol. The paper towels will provide sterile work surfaces for
trimming the leaves. Resterilize your instruments after trimming the
leaves.
c. Remove the scalpel and forceps from ethanol and dip in sterile water.
Open a sterile paper towel and place on the work space. While holding
the leaf by its petiole, cut off both sides and the ends (cut the end
with the petiole last), leaving a rectangle of leaf with the midvein
running through it. Cut the rectangle into sections perpendicular to
the midvein and about 0.5 to 1 cm wide. Wipe any debris from your
instruments and return them to the ethanol.
54
Exercise 3. Culturing. (Sterile technique required)
a. Remove the top from a tube of multiplication medium, and with forceps
place the leaf sections in the medium so the midvein is perpendicular
to the medium surface and half the section is sticking into the medium.
Place no more than 3 sections in each tube. Take care not to let your
hands touch the rim of the tube.
b. Place the cultures under artificial light (or indirect natural light)
and maintain them at 24 to 27 degrees C. throughout. Ideally, the
photoperiod should be 16 hours of light and 8 hours of darkness. In no
case should direct sunlight be used as this will probably kill the
cultures. The light intensity requirements increase with each stage:
Stage
Stage
Stage
Stage
I
II
III
IV
100 foot-candles
100 - 300 foot-candles
300 - 3000 foot-candles
2000 - 5000 foot-candles
c. When the leaf segments have been in culture for 2 weeks with no
contamination, Stage I has been successfully completed. Contaminated
cultures should be removed as soon as contamination appears. Autoclave
contaminated tubes before opening or discarding. If no autoclave is
available, use a pressure cooker set at 15 lb. pressure for 15 minutes.
Exercise 4. Subculturing. (Sterile technique required)
a. After about six weeks, primordia (tiny green bumps) will begin to
appear on the leaf sections and will grow into tiny plantlets. At this
time (Stage II) the leaf can be removed from the culture tube, cut into
smaller pieces, and placed on fresh multiplication medium to initiate
greater numbers of plantlets. Some can be left to mature into large
plantlets. These larger plantlets can be separated and placed on fresh
multiplication medium, but as plantlet size increases, so does the
length of time required to initiate new multiplication. The larger
plantlets (1.5 cm tall) should be transferred to pre-transplant medium
to form roots (Stage III), or transplanted directly into potting medium
(Stage IV).
b. Make all transfers in your sterile work area, following the procedures
described
above.
Re-sterilize
instruments
often
to
prevent
contamination of cultures.
Exercise 5. Transplanting
a. Thoroughly moisten and mix potting medium and allow to stand overnight.
Mix the potting medium again before using. Place the pots in a tray and
loosely fill them with medium. Do not pack.
b. Large plants that have been selected to bypass pre-transplant medium
and/or plants that have been rooted in the pre-transplant medium should
be brought from the sterile work area to a sink. Rinse under lukewarm
running water until all the agar that was attached to the plantlet is
removed. (These media will support the growth of bacteria and fungi
that may kill the tender plantlet.)
55
c. Place one plantlet in each pot and gently press potting medium around
it. Keep moist by adding water to the tray and allowing plants to soak
up water from the bottom. About once a week, water with quarter
strength liquid fertilizer that contains equal portions of nitrogen,
phosphate and potash. The first few weeks it may be necessary to cover
the tray with a piece of clear plastic or plastic wrap. This can
gradually be removed as the plants become hardened off, or acclimated
to their new surroundings.
Diagram 20.
Procedure for tissue culturing African Violets.
56
LABORATORY EXERCISE #8
FLOWERS, POLLINATION AND FRUIT
INTRODUCTION:
Our flowering plants in the Division - Magnoliaphyta (Angiosperms)
are of great bi ological and eco nomic importance. Their biological
importance lies in the fact they are the primary producers in food chains and
webs on land.
By far the most economically important plants for man are the flowering
plants. They serve as our main source of food, either directly through crops
or indirectly through livestock and certain other animals. Not only do
angiosperms play an important part in providing man with the three basic
necessities of life - food, clothing and shelter - they also provide a variety of
other useful products such as drugs, rubber, cork, dyes, oil, perfumes and waxes.
Exercise 1. Parts of a flower.
The flower and all its parts originated from modified leaves. Flowers
are important to the species and to man because of their role in seed
production. Many flowers are large and the plants are cultivated for
ornamental value. Other flowers are very small and inconspicuous as to
escape notice by one not searching for them. Many flowers have such a
distinct morphology that they are used in plant taxonomy.
a. Obtain a flower, and with the help of Diagram 21 on the next page,
locate the following parts on your flower:
1. Sepals are modified leaves and are the outermost structures of
the flower. They are typically green, although they may be
colored. In some cases, they may not be present.
2. Petals lie to the inside of the sepals and are often brightly
colored. Both the sepals and petals are attached to the enlarged
end of the branch, the receptacle.
3. Carefully remove the sepals and petals. In the center of the
flower locate a stalk-like structure. This is the female part of
the flower, the pistil. It is composed of a swollen base, the
ovary, which contain the unfertilized ovules or eggs, and an
elongated style that is terminated by a sticky stigma. More than
one pistil may be present in a flower.
4. Find several stamens that surround the pistil. These are the male
parts of the flower and consist of a terminal capsule, the anther,
attached to a slender filament.
57
Diagram 21.
Parts of a flower.
b. In the space below, make a sketch of your flower
labeling all the parts indicated above in bold type.
identifying
and
c. The ovary contains one or more ovules. These may be seen if the ovary is
cut lengthwise and examined with a dissecting microscope. Using a razor
blade cut the ovary lengthwise and lay the opened ovary on the stage. Tiny
white objects, the ovules, should be visible. These will develop into
seeds if fertilized. Make a sketch of the longitudinal section of the
ovary and the ovules in the space below.
________________ X
58
d. Remove a ripened anther (one that has split and pollen is spilling out)
from your flower. Drag the anther across the slide to deposit some
pollen, and prepare a wet mount. Examine the slide with a compound
microscope and locate the pollen grains. Make a sketch of the pollen
grains in the space below.
________________ X
Exercise 2. Inflorescences.
a. Choose ten of the following plants and determine which type of
inflorescence each produces, and whether it opens flowers from the bottom
up (indeterminate) or the top down (determinate). Use pictures in seed
catalogs, your own experience, Sunset - Western Garden Book, or if the
flowers are in bloom, the specimens in class to help you. Diagram 22 on
the next page will help to determine the inflorescence type. Hand in the
assignment at the end of lab, in two weeks.
COMMON NAME
SCIENTIFIC NAME
Dill
Snapdragon
Jack-in-the-Pulpit
Milkweed
Birch
Caraway
Chrysanthemum
Lily of the Valley
Coralbells
Red Hot Poker
Hoop Petticoat Daffodil
Gayfeather
Lupine
Skunk Cabbage
Lady's Slipper
Garden Penstemon
Cherry
Rhododendron
Willow
Common Lilac
Anthum graveolens
Antirrhinum majus
Arisaema triphyllum
Asclepias tuberosa
Betula spp.
Carum carvi
Chrysanthemum frutescens
Convallaria majalis
Heuchera sanguinea
Kniphofia uvaria
Narcissus bulbocodium
Liatris spicata
Lupinus ‘Russell Hybrids’
Lysichiton americanum
Paphiopedilum spp.
Penstemon x gloxinoides
Prunus spp.
Rhododendron spp.
Salix spp.
Syringa vulgaris
59
INFLORESCENCE INDET/DET
I.
Indeterminate
1a.
1b.
1c.
Simple Spike
Spadix
Catkin
II.
2.
3.
4.
Raceme
Corymb
Panicle
Diagram 22.
5. Head
6a. Umbel
6b. Compound Umbel
Inflorescence Types.
60
Determinate
7. Solitary
8a. Cyme
8b. Compound Cyme
I.
Simple Fruits
A. Fleshy
1. Pome
(apple)
2. Drupe (cherry)
3. Berry (tomato)
Hesperidium (orange)
Pepo
(cucumber)
B. Dry – Indehiscent
4. Samara (maple)
5. Achene (sunflower)
6. Nut
(pecan)
7. Grain (corn)
8. Schizocarp (geranium)
Diagram 23.
I.
Simple Fruits
B. Dry – Dehiscent
9. Legume
(pea)
10. Capsule (cotton)
11. Silicle (shepherd’s purse)
12. Silique (mustard)
13. Follicle (milkweed)
II.
Aggregate Fruit (14. blackberry)
III. Multiple Fruit
Fruit types.
61
(15. mulberry)
Exercise 3.
Fruits.
Select any ten of the fruits on the demonstration table. Use Diagram 23.
on the previous page to determine the type of fruit you have. On a separate
sheet of paper record the name of the fruit, whether it is simple, aggregate,
or multiple, whether it is fleshy or dry, and if fleshy - the specific type of
fruit, or if dry - whether it is dehiscent (splits) or indehiscent (doesn’t
split) and name the specific type of fruit. Hand in the assignment at the end
of lab today.
Exercise 4 . Hybridizing. (A hands-on demonstration)
Hybridizing is used by plant breeders to develop new varieties of plants
that are not currently in existence. The basic steps used in hybridizing are
outlined below and will be demonstrated by your instructor.
a. Select two plants which show obvious differences: flower color, leaf
color, mature plant size, leaf size, growth habit. Record the name and
description of each plant as completely as possible for your records and
label the plants used.
b. Examine the stigmas of several flowers of one plant with a hand lens.
Choose one flower whose stigma appears to be shiny, sticky and free of
pollen. With scissors, carefully remove the petals and stamens from the
flower you have chosen. Take care not to get any pollen on the stigma.
Leave the flower attached to the plant. This will be the seed parent.
c. Choose a stamen from a flower on the second plant. This will be the pollen
parent. The anther should appear "dry" and full of pollen. Remove the
stamen with tweezers and brush the anther over the stigma you selected.
Examine the pollinated stigma with a hand lens. It should be covered with
pollen.
d. Label the flower you have pollinated with the names of the parent plants
(both stigma and pollen donors). Print your name and date clearly with a
waterproof pen on a piece of masking tape. Fasten the tape securely, but
carefully, around the flower stem so as not to damage it. Bag the
flower with small paper bag to allow the ovary and ovules to develop
without contaminating the stigma with another source of pollen.
e. In a few weeks to months seed will develop within the bag.
When
fully dry and ripe, harvest the seed and germinate using a seed flat
prepared according to plant specifications.
Your seed will then
develop into plants that are potted up and observed to see if any
have the needed characteristics.
At this point the plant breeder
rogues out the plants unsuitable and keeps those that exhibit the
characteristics sought after.
In this way, a plant breeder can
continually produce plants that may yield the quality that is most
desired.
62
LABORATORY EXERCISE #9
SEEDS AND SEED GERMINATION
INTRODUCTION:
Seeds are formed following fertilization, or the union of sperm and egg in
the ovary of a flower. The angiosperm seed consists of the embryo surrounded by
the remains of the endosperm and a seed coat. In this lab we will look at the
anatomy of seeds and the factors that go into the germination of seed.
PART I: SEED ANATOMY
Exercise 1 . Anatomy of a bean seed.
a. Examine a dry bean seed. Locate the following structures indicated in bold
type.
1. The tough outside covering is the seed coat.
2. Near the center of one edge is a large scar formed when the fertilized
ovule becomes ripened, and the seed breaks from the ovary. This scar is
the hilum.
3. At one side of the hilum a tiny opening in the seed coat is visible.
This is the micropyle, where the pollen tube entered the ovule.
b. Label the following diagram with the parts indicated in bold type.
Diagram 24. External view of a lima bean.
63
c. Obtain a bean seed that has been soaked approximately one hour. Remove the
seed coat and locate the following structures indicated in bold lettering.
Note that the seed can be separated into two halves. These are
cotyledons or seedling leaves; they are part of the embryo.
the
The remainder of the embryo can be observed at one end of the seed between
the two cotyledons. The embryo consists of four parts: the cotyledons,
the epicotyl (the part above the attachment to the cotyledons), the
hypocotyl (the part below the point of attachment), and the radicle (the
terminal portion of the hypocotyl).
1. What evidence is there that the epicotyl will form the stem and
leaves?
2. What part of
hypocotyl?
the
plant
do
you
think
will
develop
from
the
3. What part
radicle?
the
plant
do
you
think
will
develop
from
the
of
4. On the Diagram below, label the cotyledon, epicotyl, hypocotyl
and radicle.
Diagram 25. Internal structure of a bean.
64
d. Scrape the inner surface of the cotyledons of the bean. Add a drop of
Lugol's solution on the scraped area.
1. Is the Lugol's test for starch positive or negative?
2. What appears to be the role of the cotyledons in the development of
the bean seed?
Exercise 2.
Anatomy of a corn seed.
Corn is a familiar example of a monocot seed. Technically the grain of
corn is a fruit. It is a one-seeded fruit in which the ovary wall and the
remains of the integuments are so intimately connected as to appear fused.
Any seed encased in an ovary is a fruit.
a. Obtain a soaked corn seed. Note that one side of the corn seed has an
indentation. The embryo is located on this side inside the seed. Take a
razor blade and cut the seed longitudinally down the center with the
embryo side up.
1. The hard tissue above the white area and away from the base (where
the seed was attached to the cob) is the endosperm. This is the
yellow portion. The remainder of the seed is the embryo which
appears white.
2. The epicotyl is directed away from the base, and the hypocotyl and
radicle directed toward the base. Both the epicotyl and hypocotyl
are enclosed in a sheath of tissue. The remainder of the embryo is a
single cotyledon.
b. Locate and label the following structures within the diagram below:
endosperm, epicotyl, hypocotyl, cotyledon, seed coat and radicle.
Diagram 26. Internal structure of corn seed.
65
PART II: SEED VIABILITY
Three major factors influence seed germination. They are (1) seed
viability; ( 2 )
seed dormancy; and ( 3 )
environmental conditions. If
germination is to occur, certain conditions must be met in regards all three.
( 1 ) The seed must be viable; that is, the embryo must be alive and capable of
growth; (2) any dormancy conditions within the seed which may chemically or
physically prevent germination must have disappeared or been eliminated; and (3)
the seed must be exposed to favorable environmental conditions of moisture,
temperature and oxygen. (Some seeds also require light or darkness.)
The U. S. Federal Seed Act requires that all lots of seed entered in trade must
be tested for their viability beforehand. The most commonly used test is the
Germination Percentage Test. Another is the Tetrazolium Test. Both can be
done in the laboratory.
The germination percentage is the percentage of seed tested that
produces normal seedlings under optimal conditions. When you buy a package or
a lot of seed, the information on the label will usually include the minimum
germination percentage. In licensed laboratories the germination percentage test
is done using 400 seeds. For classroom accuracy, you can use only 100 seeds of
any one type divided into lots of 25. The total germination of the four lots
is the new germination percentage.
Exercise 3. Germination Percentage Test.
a. Select one package of seed, such as lettuce Lactuca sativus,
spinach Spinacia oleracea, corn Zea mays, beans Phaseolus vulgaris,
marigold Calendula officinalis, etc. on the back table.
Note the date
on the package.
b. Work in groups of four students. Any four students will test 100 seeds
(or the number present in the package if less than 100) of one type of
seed. All materials and the work area must be as clean as
possible to reduce contamination with fungi. Obtain a beaker containing
a bleach disinfectant made of 9 parts water and 1 part commercial
bleach. This gives a solution of about 0.5 percent sodium hypochlorite.
c. Soak the seeds in the bleach for 5 to 10 minutes. While the seeds are
soaking, each student should soak two paper towels; one in the bleach
solution to wipe the table work area clean, and another in distilled
water for preparation of the seeds.
d. Each student prepares 25 seeds as follows. (1) Take the moistened paper towel
and spread it out. (2) Space five seeds along one side of the towel
and fold the edge over the row of seeds. (3) Space another row of
five seeds and roll the first fold over them. Continue adding rows. Do
not make tight rows. Five rows are needed. (4) Tie the rolls at each end
with a string or twist tape. You have now made a "rag-doll tester".
(5) Put the rag-doll testers in plastic bags and store in a warm
place at about 21 degrees C. or 77 degrees F. Make certain the
testers do not dry out during the germination period.
e. After 7 - 12 days unfold the testers and count the number of seeds
that have germinated. Compute the germination percentage for each
seed species tested.
Record the results in Table 9-1.
Some will
unavoidably be lost due to fungal and/or bacterial contamination.
66
Plant Name
(date of package)
Number of
Seeds Tested
Table 9-1.
Number of Seeds
Germinated
Germination
Percentage
Germination percentage results.
Exercise 4. Tetrazolium Test.
This is a quick test for viability. It simply determines if the embryo
in the seed is alive or dead. It is done by testing the respiration of the
seed. Viable seeds respire and can change colorless tetrazolium dyes into a
red color.
The test is not foolproof and therefore is not legal for
germination labeling on seed packets.
In research, however, it is valuable
because it can determine if a dormant seed is viable whereas germination
tests cannot.
a. Select 5 seeds each of corn and pinto beans that have been soaked in
water overnight in the dark. With a razor blade, cut each seed in half
and place the cut surface on a filter paper in a petri dish. Have one
dish for corn seed and another for beans.
b. Saturate the papers with 0.1 percent tetrazolium chloride.
dishes aside for 30-60 minutes in the dark.
Set the
c. Examine the seeds for any red coloration. Any of the following results
indicates a viable seed:
embryo entirely red: embryo mostly red:
endosperm also red. Dead seeds are indicated by pink embryos or embryo
remaining white. Record your results below as a percent viability.
Number of Seeds
Tested
Number of Seeds
Viable
Percent Viability
Corn
Beans
Table 9-2.
Tetrazolium percentage test results.
67
PART III:
SEED DORMANCY
Seed dormancy is the failure of seed to germinate even though optimal
environmental conditions exist.
It is due to physical, physiological or
chemical barriers within the seed.
In most wild and even cultivated plants
this is of value. For example, it is very common for seeds to be produced at
the end of the summer or early fall.
Conditions at this time are often
perfect for germination, but if germination took place there would not be
time for much seedling growth before the first killing frost.
It is,
therefore, a survival advantage to the species if its seeds remain dormant at
this time.
Seed dormancy is caused by many factors, but three very common ones
are: (1) impermeable seed coat, (2) dormant embryo, and (3) chemical
inhibitors within the seed. The easiest of these to demonstrate is dormancy
due to an impermeable seed coat.
Exercise 5.
Dormancy due to an impermeable seed coat.
Impermeable seed coats prevent water absorption.
Without water, the
seed’s reserve foods are not hydrolyzed (made soluble) and the digestive
enzymes are not activated, so the embryo cannot grow.
a. Select two Honey Locust (Gleditsia triacanthos) pods and extract 20
seeds.
b. As a group of four students: (1) scarify 10 seeds by using a razor
blade to chip the seed coat until an opening is visible, wrap them in a
rag-doll tester. (2) Leave an equal number of seeds intact and wrap in
a separate tester. (3) Label the testers and store them in a plastic
bag in a warm (21 degrees C.) place for five to seven days.
Make
certain the testers do not dry out during the germination period.
c. After five to seven days, unfold the testers and count the number of
seeds that have germinated. Compute the germination percentage. Record
in Table 9-3 below.
Number of Seeds
Tested
Number of Seeds
Germinated
Germination
Percentage
Scarified Seeds
Intact Seeds
Table 9-3. Honey Locust germination results.
PART IV:
ENVIRONMENTAL CONDITIONS INFLUENCING SEED GERMINATION
Exercise 6.
Oxygen requirements for germination.
a. Select 20 dry bean seeds.
b. As a group of four students: (1) Prepare two rag-doll testers as per
class procedure, each with 10 seeds. (2) Thoroughly soak both testers.
(3) Place one tester in a Zip-lock bag and seal after removing as much
68
air as possible. (4) Place the second tester in another bag and seal
with as much air inside as possible. (5) Set both bags in a warm place
for five to ten days.
c. After five to ten days, unfold the testers and answer the questions
below.
1. Has germination occurred in the bag with minimal air supply?
2. How about the bag with adequate air supply?
3. What is the gas that promotes germination?
Exercise 7.
Temperature as a factor in seed germination.
The experienced gardener living in the North Temperate Zone knows that
one doesn’t have to wait until the really warm days of summer to set out the
seeds of all the different vegetables in the garden.
Some can be planted
earlier than others. Different plants have different minimum temperatures at
which their seeds will germinate.
For instance, peas Pisum sativum and
turnips Brassica rapa can be planted outdoors six weeks before the average
last freeze date of winter: lettuce Lactum sativa can be planted five weeks
before the average last freeze date of the winter: and spinach Spinacia
oleracea and beets Beta vulgaris, three weeks.
However, for cucumbers
Cucumis sativus, green peppers Capsicum frutescens var. grossum, pumpkins
Curcurbita pepo, and watermelons Citrullus vulgaris you must wait two weeks
after the average last freeze date before planting, and for sweet corn Zea
mays, about three weeks after the last average freeze date.
a. Obtain 20 seeds of peas, turnips, or cabbage and prepare them for
germination in rag-doll testers. Put 10 seeds in each tester, label and
date it.
b. Do the same for 20 seeds of cucumber, green pepper, eggplant or sweet
corn.
c. As a group of four students: (1) Store one tester of each type of seed
in a plastic bag in a refrigerator maintained about 10 degrees C. (50
degrees F).
Store another set of each type in some warm place or a
germination chamber if one is available.
d. Between one and two weeks later, check the rag-doll testers to observe
whether or not germination has occurred.
The days required for
germination under optimum conditions are listed in the Table 9-4., and
these should be consulted and used as a time guide for making your
observations. Record your findings in Table 9-4.
69
Plant
Cabbage
Standard
Germ. Days
@ Optimum
Temperature
6-9
Pea
7-10
Turnip
5-10
Cucumber
7-10
Green
Pepper
10-14
Eggplant
10-21
Sweet
Corn
Observed
germination
time @ Low
Temperature
Germination
Percentage
Observed
germination
time @ High
Temperature
Germination
Percentage
5-12
Table 9-4.
The effect of temperature on seed germination.
70
LABORATORY EXERCISE #10
PHOTOSYNTHESIS
Exercise 1.
Carbon dioxide as a factor in photosynthesis.
Carbon dioxide is a gas found in our atmosphere. It is produced by the
burning of fuels and is a by product of cellular respiration.
In this
exercise you are to determine the effect of photosynthesis on carbon dioxide.
a. Obtain 3 test tubes and add approximately 9 cm of water.
b. To each tube add 10 drops of phenol red and shake gently.
As CO2 dissolves in water it forms carbonic acid. As the carbonic acid
increases in the water it lowers the pH.
Phenol red is an indicator of a
change in pH. At a low (acidic) pH, phenol red is yellow in color. As the
pH rises, the color will change back to red.
c. Using a soda straw, bubble your breath gently through the solution in
Tubes 1 and 2 just until the solution changes color from red to
yellow. As you bubble your breath through the solution, the CO2 you
exhale forms carbonic acids.
This lowers the pH causing the color
change.
d. Tube 3 will remain the control.
e. Put a sprig (small shoot) of healthy, green Elodea into Tube 1.
sure the entire sprig is below the surface of the solution.
Make
f. Place all three tubes in a bright light for at least 30 minutes to an
hour. Note any color changes and then answer the following questions.
1. Describe the color change in Tube 1.
2. Why did the solution in Tube 1 change color?
3. Describe the color change (if any) in Tube 2.
4. What happened to the CO2 in Tube 1?
5. What happened to the color of the solution in Tube 3?
71
Exercise 2.
Radiant Energy.
The energy of the sun is called radiant energy. As the radiant energy
strikes and object, such as a leaf, it may be reflected, absorbed, or
transmitted as the following diagram shows.
The energy reflected from the
leaf is really the light bouncing off the leaf that enables you to see it.
If you hold a leaf up to the light and you see light passing through the
leaf, you are seeing the transmitted light. The only light you cannot see is
the absorbed light.
Diagram 27.
Fate of light striking a leaf.
a. Using a green coleus plant and Diagram 27. above, answer the questions
below.
1. What color is the reflected light?
2. What color is the transmitted light?
3. How much of the total light striking a leaf is reflected?
4. How much is transmitted?
5. What is the total amount of light absorbed by the leaf?
6. How much of the total amount of light striking a leaf is actually
absorbed
by
the
chlorophyll
and
therefore,
available
for
photosynthesis?
72
Exercise 3.
The structure of white light.
Light is refracted (bent) into its separate wavelengths.
The various
wavelengths have different colors and are referred to as the visible
spectrum.
Complete this exercise by using the spectroscope with a bright
light. List the colors of light you see in the order in which you see them.
Using the scale on the spectroscope, label each color on the spectroscope
with its correct wavelength.
Diagram 28.
Colors of the spectrum.
a. Which has a longer wavelength, violet or red light?
b. Which has a greater energy, violet or red light?
Exercise 4.
Absorption of light by chlorophyll.
Review your lecture notes and answer the following questions.
a. What wavelengths
chlorophyll?
of
light
b. What wavelengths of light
reflected by chlorophyll?
would
would
you
you
expect
expect
to
to
be
be
transmitted
c. What is the relationship between the wavelengths
chlorophyll and those most active in photosynthesis?
73
absorbed
absorbed
by
and
by
Exercise 5.
Chlorophyll and other factors in photosynthesis.
Obtain all the materials before you begin.
in the experimental area.
Carefully conduct your work
Materials:
a. Variegated Coleus leaf
b. Boiling water
c. Hot plate
d. 75% alcohol
e. Petri dish
f. Lugol’s iodine solution
g. 100 ml beaker
Examine the leaves of the variegated Coleus.
Make a sketch below of
the leaf and indicate the distribution of chlorophyll (green), carotene
(orange), xanthophylls (yellow) and anthocyanins (red). (The presence of the
carotenes and xanthophylls may be masked by the chlorophyll.)
One can tell whether or not photosynthesis has occurred in a leaf by
extracting the pigments and testing for starch. Starch will be present only
in those areas where photosynthesis has occurred.
a. Place a leaf in a 100 ml beaker. Add just enough water to cover the
leaf.
Boil for 2 minutes to kill the tissue and weaken the cell
walls.
b. Pour off the water and add just enough alcohol to cover the leaf.
Using a hot plate boil the leaf for a few minutes until the pigments
are extracted, or until the leaf turns whitish. Be careful – alcohol
is flammable!
c. Test for the presence of starch by placing the leaf in a Petri dish
and flooding with Lugol’s solution. Allow a minute for the iodine to
penetrate the leaf.
If the starch is present the tissue will turn
purple to black in color indicating the photosynthetic area.
Carefully remove the leaf from the beaker and place it flat on a paper
towel to see the colors more clearly.
d. Make a sketch of the leaf indicating photosynthetic and nonphotosynthetic areas in the space provided and answer the questions on
the next page.
Sketch of
Untreated leaf
Sketch after
boiled in water
Sketch after
boiled in alcohol
74
Sketch of leaf
treated with Lugol’s
1. If starch is an indication
required for photosynthesis?
of
photosynthesis,
what
pigments
are
2. What pigments are not required for photosynthesis?
Anthocyanins
violet colors in
chlorophyll, but in
as radishes, beets,
Exercise 6.
(antho = flower, cyano = blue) produce red, blue and
plants and are not found in the chloroplasts with
the vacuole. They give the familiar color to such plants
grapes, cherries, plums, geraniums, tulips and roses.
Separation of leaf pigments by paper chromatography.
Prepare a leaf extract by grinding leaves in a small volume of acetone.
This can be done with a mortar and a pestle. By using paper chromatography,
you can separate the different pigments out of the leaf extract.
a. Obtain a small vial and add to it a small amount of solvent (about 1
cm in depth). The solvent is a mixture of 95 parts petroleum ether
and 5 parts acetone. Stopper the vial and set it aside.
b. Obtain a strip of filter paper that is long and narrow enough to fit
inside the vial and crease it lengthwise.
c. With a toothpick, apply a few drops of the leaf extract to the
filter paper strip about 2 cm from one end. Allow the spot to dry.
Two or three repeated applications to the same spot will be needed.
The spot must be dry before you proceed to the next step.
d. Insert the paper into the vial.
Do not permit the extract on the
paper to be moistened directly by the solvent. Stopper the vial and
set it aside.
e. In a few minutes, you will see the pigments begin to separate. As
the solvent passes through the paper, the various pigments become
dissolved in it and move up the paper at different rates.
f. Examine the chromatography at frequent intervals.
If the pigment
separation continues too long, some of the pigments will be
superimposed on each other near the top of the strip.
The five pigments that separate out into their respective colors are:
1.
2.
3.
4.
5.
Chlorophyll a – blue-green color
Chlorophyll b – pale green color
Xanthophyll
– pale yellow
Carotene
– orange yellow
Anthocyanin
- red
g. Sketch the chromatograph in the margin, showing the position and
general appearance of the pigments. Label each pigment line.
75
Exercise 7.
The effect of CO2 concentration.
No other single factor has a greater effect on photosynthesis than the
carbon dioxide level in the air.
Approximately 0.03 percent of the
atmosphere is composed of carbon dioxide. That is a very small amount and if
it were not constantly renewed, plants could use up all available carbon
dioxide in 20 years.
The concentration remains fairly constant, however,
because the ocean releases great amounts of CO2 daily.
In addition, all
living things release CO2 as a by-product of respiration.
The burning of
fossil fuels (gas, oil, and coal) and the decay of organic matter add to the
CO2 reservoir.
It has been estimated that if the CO2 levels were increased by 13
times, the photosynthetic process would increase 400-500 percent.
However,
the long term effect on plants at this high concentration is not known. It
is known, however, that high CO2 levels decrease the plant’s ability to take
in oxygen. Thus a plant might be able to make great quantities of food, but
could not break down that same food to release the energy for its own use.
Carbon dioxide in the air lets light pass through to warm the earth,
but doesn’t let the heat escape again. It is similar to the effect you get
when you leave the windows of your car closed on a warm day. The car will
certainly heat up! As the concentration of atmospheric CO2 increases (which
it is doing, due to the increased burning of fossil fuels) the temperature of
the earth would increase also. An increase of about 4 degrees F. could melt
the polar ice caps and significantly change the climate all over the earth.
This increase in the earth’s temperature due to increased atmospheric CO2
concentration is known as the “greenhouse effect”.
a. What effect does increasing the CO2 level in the air have on plants in
general?
b. Where would you expect to find higher CO2 levels, near cities or in
rural areas? Why?
c. If one could increase the CO2 in the air, what other factors might
limit the amount of photosynthesis?
d. What possible
effect” have?
effect(s)
on
photosynthesis
76
could
the
“greenhouse
LABORATORY EXERCISE #11
PLANT GENETICS
INTRODUCTION:
Knowledge of the science of genetics enables plant breeders to develop
new strains of ornamental and crop plants.
It also helps the amateur to
experiment with plants on a smaller scale to develop new flower colors, plant
forms, hardiness ratings, and drought or disease resistant strains.
Exercise 1.
Homologous chromosomes.
Study the following Diagram 29.
With
readings, complete the questions listed below.
Diagram 29.
our
class
Homologous chromosomes.
a. Define homologous chromosomes.
b. Which of the above chromosomes form homologous pairs?
c. Define allele.
d. Define locus.
77
discussion
and
e. Identify at least 5 allelic pairs.
f. Define homozygous.
g. Define heterozygous.
h. List 3 homozygous allelic pairs.
i. List 2 heterozygous allelic pairs.
Exercise 2.
Allele combinations.
The determination of the different combinations of alleles resulting
from meiosis is most important to understanding the mechanism of genetics.
Study the following example before proceeding.
Two methods of gamete
determination are outlined. Choose and follow one.
Remember! Each gamete may contain only one representative of each gene
pair, but must contain one from each pair.
78
a. What different gene combinations would result from meiosis of a cell
containing the following genes?
1. Aa
_____
_____
2. BB
_____
_____
3. AAbb
_____
_____
4. AaBB
_____
_____
5. AaBb
_____
_____
_____
_____
6. AaBbCc _____ _____ _____
(for the expert!)
_____
Exercise 3.
_____
_____
_____
_____
Probability.
Probability is the mathematical science that tries to predict the
“chances” of an event occurring.
In the formation of gametes, probability,
expressed as a genetic ratio, is used to predict the “chance” that a specific
character allele will appear.
Probability is defined as the total number of favorable events divided
by the total number of events.
Probability
=
Total number of favorable events
Total number of events
There are two rules of probability:
1. If an event is going to occur, the probability is one. If an event
is not going to occur, the probability is zero. In other situations
the probability is expressed as a fraction between zero and one.
2. The probability of two or more independent events occurring is the
product (or multiplication) of their individual probabilities.
For example:
A.
What is the probability of a die stopping with the “two” face
up?
Answer = 1
6
B.
(only one “two” face on a die)
(total possible faces on a die)
When rolling dice, what is the probability that both dies
will have the “two” face up?
Answer:
=
1
6
X
1
6
=
1
36
79
a. Express the following probabilities as fractions.
1. What is the probability of a die stopping with the “four” face up?
2. What is the probability of a ten-sided die stopping with the “two” face
up?
3. What is the probability of an A gamete from an AA parent?
4. What is the probability of an A gamete from an Aa parent?
5. What is the probability of an a gamete from an Aa parent?
6. What is the probability of an ab gamete combination coming from an AaBb
parent?
7. What is the probability, if two coins are tossed in the air that they
will both come up heads?
8. Suppose in a certain city one girl in two is blonde. Also suppose that
one girl in three is slim. What is the probability that the next girl
passing will be blonde and slim?
80
Exercise 4.
Monohybrid cross.
Monohybrid crosses involve hybridizing plants looking at only one
characteristic (in this case seed color), to determine the genotype of the
parents and offspring.
Genotype is the actual genetic make up of a plant,
the actual allelic combination within the plant; whereas phenotype is the
outward characteristic (yellow or green seed color) exhibited due to the
dominance of one trait over another. Using the information in the following
genetic diagrams, determine the F2 generations genotype and phenotype.
Parents (P1)
Offspring (F1)
Phenotype
Yellow
X
Genotype
YY
X
Gametes
(Y)
Genotype
Green
yy
(y)
Yy
Phenotype
Yellow
a. Now if you take the offspring (F1) generation from the above cross and
cross them again [as the Parents (P2) generation below], what would you
get as genotypes for the offspring (F2) generation? Fill in the blank
spaces in the Punnett Square to answer the question.
Parents (P2)
Phenotype
Genotype
Gametes
Yellow
X
Yellow
Yy
X
Yy
(Y) (y)
(Y) (y)
Offspring (F2)
Y
Y
y
YY
y
1. What is the genotypic ratio? _______________________________________
2. What is the phenotypic ratio? ______________________________________
b. In the P2 cross above, if only 2 offspring are produced, what is the
probability that:
1. Both will be yellow?
2. Both will be green?
3. That one will be yellow and one will be green?
81
Exercise 5.
Monohybrid cross problem.
The gene for tallness in plants is dominant to the gene for dwarfism.
If a homozygous tall plant is crossed with a dwarf plant, what will be the
phenotypes and genotypes of the offspring?
Exercise 6.
Dihybrid cross.
Dihybrid crosses involve looking at two different characteristics (in
this case, purple vs. yellow flowers and smooth vs. wrinkled seeds) to
determine the genetic make up of both the parents and progeny by the
phenotypic ratios exhibited.
a. Perform the following genetic cross: PpSs X PpSs
P
p
S
s
=
=
=
=
purple flowers
yellow flowers
smooth seeds
wrinkled seeds
1. What types of gametes can the female produce?
contains one and only one gene from each pair.
Eggs (female gametes): _____
Pollen (male gametes):
PS
_____
Ps
_____
pS
Be sure each gamete
_____
ps
2. Fill in the Punnett Square below with the outcome of this cross.
PS
PS
Ps
pS
ps
82
3. Of the 16 offspring, how many would you expect to be:
Purple, smooth
_____
Purple, wrinkled
_____
Yellow, smooth
_____
Yellow, wrinkled
_____
4. What is the probability of one of the offspring being homozygous
dominant for both traits?
Exercise 7.
Incomplete Dominance.
In petunias, the red flower color (R) is incompletely dominant to white
(W).
If two pink petunias were crossed, what would be the phenotypic and
genotypic ratio of the offspring? (Begin by determining the genotype of the
pink parents!
Then use a Punnett square to determine the genotypes of the
offspring.)
83
84
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
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
Biology Experiences 101, 102 and 103. Portland Community College.
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Botany. Holt, Rinehart and Winston, New York, 1977.
Barden, J.A., R.G. Halfacre and D.J. Parrish: Plant Science. McGraw-Hill,
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Capon, Brian: Botany for Gardeners. Timber Press, Portland, OR, 1990.
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Rice, L.W. and R.P. Rice, Jr.: Practical Horticulture. Prentice Hall,
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85