Stephen P. Broker
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I. Introduction.
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Lesson 1: (2-3 days) Introduction to the study of plant evolution—evolution the unifying theory of biology. (a review, making use of slides & photographs)
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II.The Concept of Time
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Lesson 2: Preparation of an Earth Calendar
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(2 days)
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Lesson 3: Plant Migration Time
(1 day)
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III. The Concept of Change Geological History
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Lesson 4: (1 day) Ecological Change (a brief review of the effects of wind, waves, erosion, volcanic action, earthquakes)
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Lesson 5: Preparing a Chart of the Geological Periods (2 days)
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IV. The Diversity of Life The Major Divisions of Plants
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Lesson 6: Slides: The Diversity of Plant Life (Set #1) (2 days)
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Lesson 7: Preparing Herbarium Specimens
(2 days)
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Lesson 8: A Trip to an Herbarium
(1 day)
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V. Paleobotanical Evidence The Formation of Fossils
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Lesson 9: The Stiles Clay Pits 7,000 Year Old
(2 days) Plant Remains
Lesson 10: How Fossils are Formed
(1 day)
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VI. An Overview of Plant Evolution
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Lesson 11: (1-2 days) Language used in the study of plant evolution (Slides: The Yale Peabody Museum of Natural
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History The Paleobotany Collection) (Set #III) Lesson 12: Slides: Plant Evolution The Fossil Evidence
(3 days) (Set #II)
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Lesson 13: The Teaching Collection of Fossil Plants
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Lesson 14: (3 days) Comparing a Carboniferous Forest with a present day Deciduous Hardwood Forest. (Trip to a local Hardwood Forest)
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VII. Conclusion.
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Lesson 15: Review and Evaluation of Unit
(1 day)
Sample Lesson Plans
Preparing Herbarium Specimens
(materials: vasculum (optional); garden clippers; notebook; plant press; herbarium sheets; Elmer’s glue; needle & thread; labels; field guide to trees.)(Suggested trees: Red oak, White oak, Sugar maple, Silver maple, Elm, Beech, Ginkgo)
Procedure:
More than 250,000 different species of plants have been named and described by botanists, and estimates of the total number of plant species on earth run to 800,000 or more. Obviously, many plants in various parts of the world have not yet been properly described. Botanists have developed a system for preserving and describing plants collected in the field. Specimens are located and the different parts of the plant are removed for drying. Large structures, such as wood samples, fruits, and cones, are usually just stored in boxes. Smaller, flat structures. including branches and leaves. receive more specific treatment.
You will be following procedures for collecting and preparing plant specimens. The ‘herbarium sheets’ which you make will be useful to others in identifying and describing plants.
A. Collecting specimens from trees.
(In the field . . .) Select one of the trees in the area and describe the appearance of the tree. Make note of the following: height, overall shape of tree, diameter of trunk near ground level, color and appearance of bark, position of branches. Make simple sketches or drawings of the tree or its parts. These drawings will be helpful to you when you return to the laboratory to identify the tree. Collect a leaf sample from the tree, looking for a small branch which has leaves in good condition (not chewed up or damaged). Do not select leaves which are very large or very small for the tree. Also collect any fruit, cone, or nut samples that may be found on the tree. If you have a vasculum, put the leaf samples inside it to help prevent drying out.
B. Pressing the leaves.
A stem with 2 to 4 good leaves on it is best to use. Place the sample in a spread out position between the sheets of newspaper, which in turn go between sheets of blotter paper and corrugated cardboard. When your specimens and those of the others have been put in the press, it is strapped together tightly. Herbaria usually prop the plant presses over enclosed hot plates to speed the drying process. . . . After 1 2 days, check the specimens for dryness and flatness.
C. Preparing the herbarium sheets.
Herbarium sheets come in a standard size 12” x 17”. Place your dried specimen on the paper. gluing it to the paper with small amounts of Elmer’s glue. If the branch is somewhat thick, it may be necessary to sew it onto the sheet at several points. This is a technique which requires an amount of skill, but give it your best try. Use the guidebook and your notes from the field to identify the specimen. Record the following information on the label: Date, Record No., Location, Description. Common Name, Botamical (Latin) Name. Family, Collected by———.
The Stiles Clay Pit of Hamden, Connecticut
(Laboratory materials:
Walks and Rides in Central Connecticut and Massachusetts
, Longwell & Dana; Stiles Corp. bricks; Diagram: The Stiles Clay Pit (cross section); prints of Stiles Clay Pit; sample material from the different levels of the pit; tree stump (3,500 5,000 yr. old); samples of matted leaves; chemicals: HNO3 (dil) and glycerin.)
Procedure:
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1. Read Longwell & Dana, “To The Clay Pits And Brickyards Of Quinnipiac Valley,” pp. 120-122, the day before the lab period.
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2. Define the following word:
varves
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3. Compare the 75 yr. old brick from Stiles Brickyards with the newly-made brick. In what ways do they differ in appearance? The brickyards operated from 1854 until 2-3 yrs. ago.
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4. Study the cross sectional diagram of the pit. At what depths would you expect to find semi-fossilized plant parts?
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5. In the room are jars containing samples gathered from depths of 1, 6, 14, 17, and 20 feet. Describe the color & appearance of each sample; describe briefly any plant parts in each jar.
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6. Study the peat layer from the pit. How thick is this layer in the pit? Spend the next 5 minutes removing plant matter from the peat, trying not to break the leaves, etc.. Describe what you remove & compare it with herbarium sheets for
Spartina
,
Phragmites
, and
Typha
. a) write common names for each of these plants; b) can you identify any of the fragments?
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7. Examine the section of hemlock stump & count the tree rings to determine the age of the tree when it died. Stumps & logs from the pit were not found in upright positions, but rather lying on their sides. What does this tell you about where the trees were growing and how they got into the area of the pit?
8. Obtain a sample of matted leaves. These leaves were found at a depth of 13 1/2 ft., as shown on the diagram. Using scalpel or tweezers, pry into the edae of the leaf mat & expose a clean-looking inner surface of leaves. Repeat 2-3 times, until you have a thin layer of matted leaves. Now soak the leaves in dilute nitric acid to separate off individual leaves for study. (NOTE TO THE TEACHER: CAUTION HNO3 is a very caustic chemical & must be handled carefully. If your students are not experienced in handling acids, perform this step prior to class.) When the individual leaves are loose, gently lift them out, rinse in water, & set them aside. Did any seeds float to the surface? If so, save them. Make sketches of 3 of the leaves. Compare the leaves & sketches to the ff. herbarium sheets: American beech; Sugar maple; Buttonwood; American elm; birch sp.; White oak; Basswood. Pay particular attention to the overall shape of the leaf & the pattern of leaf veins. Can you now identify any of the leaves isolated from the leaf mat? Are they in any way different from the corresponding herbarium specimens? Carefully transfer any whole separated leaves to the glycerin container & clean up all laboratory materials.
Plant Evolution: The Fossil Evidence (Slide Set II & worksheet)
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slides #1,2: Fossil hunting. These people are searching layers of sedimentary rock for plant fossils.
How do you think these rock layers were formed
?
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slide #3: Fig Tree microfossils. This stratum of rock in South Africa is one of the oldest known formations of rock on earth, dated to 3.2 billion yrs. ago.
Describe the microfossils contained in this rock
.
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slide #4: Gunflint chert, stromatolytes. Stromatolytes are believed to be the fossilized evidence of plant growth from many millions of yrs. ago. This stromatolyte may have been produced by the growth of bluegreen algae, simple photosynthetic plants. The rock is 2.0 billion years old.
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slide #5: Gunflint chert, spore-like bodies & filaments of blue-green algae.
How old was the earth at this time
?
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slide #6: Reconstruction Middle Devonian plants. This slide shows the way a forest of 375 million yrs. ago may have looked. This & the ff. slides are of plant life from the Paleozoic, Mesozoic, & Cenozoic Eras, which span the past 570 million yrs. These more recent times are much better known than the Precambrian time of the first several slides.
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slide #7: Devonian alga. By the Devonian period a variety of simple plants lived on land. Water plants, such as algae, continued to be successful, though. This alga is one example of a Devonian thallophyte.
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slide #8:
Psilophyton
. This vascular plant from 390 million yrs. ago is important because of the branching that arises from the main stem. It is a more complex type of branching than earlier plants had.
What is a vascular plant
?
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slide #9: Devonian lycopod,
Archaeosigillaria
. This plant is of a different type from
Psilophyton
.
What structures
did the plant have that Psilophyton lacked?
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slide #10:
Archaeopteris
. This plant is called a progymnosperm. It was one of a group of plants which gave rise to the gymnosperms, of which many examples are alive today.
Name some plants which have needles
.
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slides 11-13: Reconstruction Carboniferous forest. We will compare this 300 million yr. old forest with one of today. First, let’s take a closer look at the plants growing here.
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slides 14-19:
Lepidodendron
reconstruction, cast & mold, roots, cones. This lycopod (club moss) was a tree which grew to be 100 ft. tall.
Describe the bark of the tree. What caused the diamond-shaped ‘scars’ on the tree
?
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slide #20:
Sigillaria
reconstruction.
In what ways was this club moss similar to Lepidodendron
?
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slides 21-24:
Calamites
reconstruction, stem anatomy foliage. This plant is a giant arborescent sphenopsid, or horsetail, which grew to 30 ft. or more.
What
does the word “arborescent” mean? (Hint: Arbor Day) The club mosses & horsetails reproduced by spores, not seeds.
What other plants, living
today, produce spores?
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slides 25,26:
Sphenophyllum
, reconstruction & fossil. Unlike the plant
Calamites
, this horsetail is an herbaceous plant.
What does “herbaceous” mean
?
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slide #27:
Equisetites
, Stuttgart Germany.
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slides 28,29:
Psaronius
, reconstruction & foliage. These leaves (fronds) are very similar to those of some present day plants.
Name the plants
.
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slides 30,31:
Medullosa
reconstruction & foliage. This fern-like plant produced seeds.
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slides 32,33:
Cordaites
reconstruction & foliage. The tree shown here is a forerunner of today’s conifers.
In what ways are its leaves different from conifer leaves, however
?
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slide #34: Reconstruction Mesozoic Era.
Name the types of plaits shown in this reconstruction
.
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slide #35: Specimen Ridge, Yellowstone National Park.
These are among the best-known fossil plants. What are they
?
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slides #36,37: Petrified tree, cross section of wood. What
are you able to see in this fossil?
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slide #38: a mid-Jurassic
Ginkgo
fossil foliage.
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slide #39:
Metaseguoia
, a fossil conifer.
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slide #40:
Proaraucaria
, fossil cones. Gymnosperms are plants with “naked seeds.”
Where in the cone are the seeds located
?
Why are they called “naked”
?
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slide #41:
Pinus
fossil, the cone.
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slides #42-45:
Cycadeoidea
, reconstruction, trunk, polished lateral cross section, longitudinal section, collecting cycadeoids. This extinct plant lived 150 million years ago. The Peabody Museum at Yale has one of the finest collections of cycadeoid fossils in the world.
Can you tell the difference between the leaf scars & the scars left by the reproductive organs
?
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slide #46: Reconstruction Tertiary forest.
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slide #47: tree cast, Oregon cascades.
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slides #48-50: angiosperms:
Astranium
,
Sassafras
,
Ulmus.
Flowering plants have been the dominant plants on earth for 100 million years or so.
What type of reproductive structure is produced by a flower
? Fossils are produced as compactions, compressions & impressions, casts & molds.
What type of fossil is the Ulmus leaf
?
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slides #51, 52: Generalized climatic zones, Late Eocene-Early Oligocene & Late Oligocene Early Miocene.
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slide #53: Cartoon, “South America Secedes” (continental drift)
The Earth Calendar
In order to improve one’s perspective on the magnitude of geologic time, a special earth calendar is devised. The entire 4.8 billion year history of the earth is condensed into one calendar year. The following events can then be plotted:.
January 1 the formation of the earth
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April 1 chemical evolution is occurring
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April 8 the oldest known biological cells appear
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May 1 the prokaryotic cell
Eobacterium
Fig Tree formation, Transvaal, South Africa
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July 1 the first primitive photosynthetic organisms (filamentous blue-green algae) Gunflint Iron Formation, western Ontario (Gunflint chert)
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October 15 in addition to filamentous blue-green algae, there are green algae (the first eukaryotic cells) Bitter Springs Formation, Northern Territory, Australia
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November 18 beginning of the Paleozoic Era. End of the Precambrian
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November 18-22 sudden and dramatic appearance of diverse marine plant and animal life
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December 1 first (Vascular) land plants
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December 4 the diversification of lycopsids. first leaves. advent of the seed and of arborescence.
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December 6-10 the Pennsylvanian lowland coal-swamp forests (carbonif.)
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December 10 seed ferns become extinct
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December 11-14 extensive Permian extinctions (arborescent lycopsids and sphenopsids disappear).
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December 17-21 the Jurassic: conifers, seed ferns, and cycads dominate
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December 21-26 the Cretaceous: dominance of the gymnosperms. Cycadeoids become extinct. First angiosperms appear.
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December 23 angiosperms begin dominance over all other plant types.
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December 25 the modern angiosperm genus
Platanus
traces back this for
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December 30-mid Dec 31 the Miocene: diversification of herbs
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December 31 7:24 P.M. the appearance of man (Richard Leakey’s KNM-ER1470,
Homo habilis
)
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December 31 8:18 P.M. many subtropical plants of North America become extinct.
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December 31 11:58.40 P.M. varved red clay has been deposited along the Quinnipiac River Basin.
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December 31 11:59.14 P.M. sedimentation of coarse gray sand above the New Haven red clay.
(figure available in printed form)
(figure available in printed form)