Biological Diversity 6

BIOLOGICAL DIVERSITY: SEED PLANTS
Table of Contents
Gymnosperms are Seed Plants | Cycads | Ginkgos | Conifers | Gnetales | Angiosperms are Flowering
Plants | Flowers | Trends in Plant Evolution | Learning Objectives | Terms | Review Questions | Links
Gymnosperms are Seed Plants | Back to Top
Gymnosperms have seeds but not fruits or flowers. Gymnos means naked, sperm means
seed: thus the term gymnosperm = naked seeds. Gymnosperms developed during the
Paleozoic Era and became the dominant seed plant group during the early Mesozoic Era,
as shown in Figure 1. The ancestors of gymnosperms were some now-extinct type of
heterosporous fern or related group. There are 700 living species of gymnosperms
placed into four divisions: conifers (such as pines and spruce), cycads (such as the sago
palm, Cycas revoluta), ginkgos (the maidenhair tree, Ginkgo biloba), and gnetophytes
(such as Mormon tea, Ephedra).
Figure 1. The fossil records of some protist and plant groups. The width of the shaded space is
an indicator of the number of species. Image from Purves et al., Life: The Science of Biology,
4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman
(www.whfreeman.com), used with permission.
Gymnosperms are undoubtedly the group from which the angiosperms developed, although, as
Charles Darwin noted in Origin of Species, which group "remains an abominable mystery".
Numerous gymnosperm groups have been proposed as flowering plant ancestors over the past
century.
Cycads | Back to Top
Cycads are placed in the Division Cycadophyta. They retain several fern-like features, notably
pinnate leaves and circinate vernation. However, they usually produce cones of
nonphotosynthetic reproductive structures, a distinctively unfernlike feature. Cycads, like all
seed plants, are also heterosporous, unlike the ferns which are all homosporous. Cycad cones are
unisexual, in fact the plants producing them are dioecious, having separate male and female
plants. Cycads also produce free-swimming sperm (a feature found only in ginkgoes among
living seed plant groups).
Cycads were much more prominent in the forests of the Mesozoic than they are today.
Presently, they are restricted to the tropics. Zamia floridana is the only cycad occurring natively
in the continental United States. Several species of Cycas, notably C. revoluta (shown in Figure
2), are commonly encountered cultivated plants in warm, moist areas. Cycas revoluta leaves are
often used in Palm Sunday services in some churches, both for their feathery appearance and
ease of obtaining from local greenhouses.
Figure 2. Cycas revoluta from Hawaii, Top: female cones bearing large, orange seeds. Image
from http://www.botany.hawaii.edu/faculty/carr/images/cyc_rev_f.jpg; Bottom: male cone
bearing numerous pollen-producing sporangia. Image from
http://www.botany.hawaii.edu/faculty/carr/images/cyc_rev_m.jpg.
Ginkgos | Back to Top
The ginkgoes also were a much more prominent group in the past than they are today. The sole
survivor of this once robust and diverse group is Ginkgo biloba, the maidenhair tree shown in
Figure 3. Extensively used as an ornamental plant, Ginkgo was thought extinct in the wild until
it was discovered growing natively in a remote area of China. Ginkos are dioecious, with
separate male and female plants. The males are more commonly planted since the females
produce seeds that have a nasty odor. Pollination is by wind. Recently, Ginkgo has become the
current herbal rave, although scientific studies have debunked the claim that the herbal
supplement made from ginkgoes improves memory. I think.
Figure 3. Ginkgo biloba, close-up of young shoot. Image from
http://www.dinoworld.net/ginkgo.JPG.
Precise systematic placement of the ginkgoes has yet to bet determined. Ginkgoes have motile
(swimming) sperm, a rarity among living seed plants (only ginkgoes and cycads have this
feature today), although the vegetative anatomy of ginkgoes is more conifer-like (long shoot and
short shoot morphology discussed below; structure of their wood). Ginkgoes, like the cycads,
are dioecious, and also have similar seed features to cycads.
Plants possibly allied to the modern ginkgoes have been found in Permian-aged and later rocks.
These plants have been classified in the leaf-genera Ginkgoites (shown in Figure 4) and Baiera,
although recent studies suggest these genera are really morphological variants and that the
modern genus Ginkgo should be used to include these fossils. During the Mesozoic ginkgoes
were worldwide in their distribution and important elements in the gymnosperm forests that
dominated the land.
Figure 4. Ginkgoites leaf from the Triassic of North Korea. Although this fossil is not the
typical fan shape of most modern ginkgo leaves, modern ginkgoes do produce leaves of this
general shape. Image from http://www.dges.tohoku.ac.jp/museum/fosgal19.html.
Conifers | Back to Top
The conifers remain a major group of gymnosperms that include the pines, spruce, fir, bald
cypress and Norfolk Island Pine (Araucaria). The division Pinophyta contains approximately
550 species of conifers. The conifers are cone producing trees and shrubs that usually have
evergreen needle-like leaves. Needles have a thick cuticle, sunken stomates, and a reduced
surface area. The conifers, as a group, are well adapted to withstand extremes in climate and
occur in nearly all habitats from the equator to the subpolar regions. The taiga biome consists
largely of various conifer species.
Auracarias
Members of this group of conifers have numerous small, scale-like leaves spiraling around their
stems. Araucaria, a major genus that gives its name to the group, is a common ornamental
because of the symmetry and beauty of its growth form. The monkey puzzle tree, shown in
Figure 5, is a species of Araucaria.
Figure 5. Image of Araucaria sp. Note the large female comes at the tips of branches. Image
from http://www.botany.hawaii.edu/faculty/carr/images/araucar_sp3.jpg.
The fossil record of Auracarias and similar plants is quite good. The fossil genus
Auracarioxylon that grew in Arizona during the Triassic Period comprises the largest group of
petrified wood in the Petrified Forest National Park of Arizona.
Taxodiaceae: Sequoias and more
Members of this group include some of the largest trees, and have been significant members of
the forests of the world since the Mesozoic. Sequoia, shown in Figure 6, and Sequoiadendron
are major genera in this group.
Figure 6. Top: Habit photograph of Sequoia sempervirens. Note the tall, woody stem with
leaves borne at the top of the stem. Image from
http://www.botany.hawaii.edu/faculty/carr/images/seq_sem_hab.jpg. Bottom: Close-up of
Sequoia sempervirens leaf and cone. Image from
http://www.botany.hawaii.edu/faculty/carr/images/seq_sem_cu.jpg.
The Pine Life Cycle
Pines have an interesting life cycle, shown in Figure 7, that takes two years to complete. Not all
seed plants have such a long time span to complete their life history: some flowering plants
manage to do it in as little as a few weeks.
The sporophyte, as in all other vascular plant groups, is the dominant, photosynthetic part of the
life cycle: when you are holding pine needles in your hand you are holding sporophyte parts.
Pines have specialized reproductive structures in which meiosis occurs: pine cones. Pollen
grains are produced in the male cones, and contain the male gametophyte (which consists of
only a very few cells). Pollen released from the male cones is carried by wind to the female
cones, where it lands. The cones close and the next year the pollen grain germinates to produce
a pollen tube that grows into the female gametophyte. The sperm cell (from the pollen grain)
and egg cell fuse, forming the next generation sporophyte. The sporophyte develops into an
embryo encased within a seed. The seed is later released to be transported by the wind to where
(hopefully) it lands and germinates. If you have seen a large pine tree you realize there are
hundreds or more female cones on such a tree. Pine pollen has been noted to travel great
distances from the plant that produced it, if the wind is strong enough. To aid this transport pine
pollen has two air sacs, and thus is quite distinctive, as shown in Figure 8.
Figure 7. The pine life cycle. Note: to view these four segments in correct sequence you will need to increase
your browser window width as much as possible. Images from Purves et al., Life: The Science of Biology, 4th
Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with
permission.
Figure 8. Pine pollen from 38,000 year old sediments in the White Mountains of eastern
Arizona. Image from http://www.smu.edu/geology/palynolab.htm.
Gnetales | Back to Top
The Gnetales, shown in Figure 9, are an odd group: they have some angiosperm-like features
but are not themselves angiosperms. Cladistic analyses support placement of the gnetales (or
some portion of them) as outgroups for the flowering plants. Three distinctive genera comprise
this group: Welwitschia, Gnetum, and Ephedra. Ephedra occurs in the western United States
where it has the common name "Mormon tea". It is a natural source for the chemical ephedrine,
although there is no evidence the Mormons in Utah (where the plant is extremely common) ever
used it for tea. Welwitschia is limited to coastal deserts in South Africa, although fossil leaf,
cuticle and pollen evidence indicates plants of this type were widespread during the Mesozoic
Era. Welwitschia is noted for its two long, prominent leaves. Gnetum has leaves that look
remarkably like those in angiosperms, as well as vessels in the xylem, generally considered an
angiosperm characteristic.
Figure 9. Representative gnetalean plants. Top: Ephedra female plant. Image from
http://www.botany.hawaii.edu/faculty/carr/images/eph_sp_f.jpg. Middle: Welwitschia mirabilis
habit shot of a cultivated specimen. Image from
http://www.botany.hawaii.edu/faculty/carr/images/wel_mir.jpg. Bottom: Gnetum gnemon habit
shot showing pinnate leaves bearing female strobili. Image from
http://www.botany.hawaii.edu/faculty/carr/images/gne_gne.jpg.
Among the gnetalean plants, Ephedra is perhaps the best known. One folkloric name for the
plant is "Mormon tea". This is a misnomer as there appears little or no evidence that members
of a religion that bans stimulants such as caffeine ever brewed a tea from the plant. However,
the plant does produce the drug ephedrine, a stimulant lately linked to deaths of athletes.
Welwistchia is a very bizarre plant natively growing only in the coastal deserts of South Africa.
The plant produces two long leaves and a crown of reproductive cones rimming a brown, central
body. Pollen resembling Welwitschia has been found in many parts of the world, indicating a
formerly more widespread distribution of this enigmatic plant.
Angiosperms are Flowering Plants | Back to Top
Flowering plants, the angiosperms, were the last of the seed plant groups to evolve, appearing
during the later part of the of the Age of Dinosaurs (the beginning of the Cretaceous, 140
million years ago). All flowering plants produce flowers. Within the female parts of the flower
angiosperms produce a diploid zygote and triploid endosperm. Fertilization is accomplished by a
variety of pollinators, including wind, animals, and water. Two sperm are released into the
female gametophyte: one fuses with the egg to produce the zygote, the other helps form the
nutritive tissue known as endosperm.
The angiosperms (angios = hidden) produce modified leaves grouped into flowers that in turn
develop fruits and seeds. There are presently 235,000 known living species. Most angiosperms
also have larger xylem cells known as vessels that improve the efficiency of their vascular
systems.
Whence came the angiosperms? This was Darwin's "abominable mystery". Clearly angiosperms
are descended from some group of Mesozoic-aged gymnosperm seed plant....but which one?
Click here to view an online lab exercise in phylogeny and try to figure things out!
The classical view of flowering plant evolution suggests early angiosperms were evergreen trees
that produced large Magnolia-like flowers. Click here to view an illustration of suggested paths
of floral evolution. However, this view has recently been contradicted by the oldest fossil yet
found, a 140 million year old plant found by David Dilcher and his associates.
The angiosperms underwent an adaptive radiation during the Cretaceous, and for the most part
escaped the major extinctions at the end of the Cretaceous.
Flowers
| Back to Top
Flowers are collections of reproductive and sterile tissue arranged in a tight whorled array
having very short internodes. Sterile parts of flowers are the sepals and petals. When these are
similar in size and shape, they are termed tepals. Reproductive parts of the flower are the stamen
(male, collectively termed the androecium) and carpel (often the carpel is referred to as the
pistil, the female parts collectively termed the gynoecium). Lily flowers (shown in Figure 10)
demonstrates these concepts.
Figure 10. Flower of lily (Lilium) illustrating a complete flower. The image is reduced from
gopher://wiscinfo.wisc.edu:2070/I9/.image/.bot/.130/Angiosperm/Lilium/Flower_dissection/Flower.
Follow that link to view a larger image of this flower.
Flowers may be complete, where all parts of the flower are present and functional, or
incomplete, where one or more parts of the flower are absent. Many angiosperms produce a
single flower on the tip of a shoot (like the lily pictured in Figure 10, or tulips). Other plants
produce a stalk bearing numerous flowers, termed an inflorescence, such as is seen in many
orchids. Many flowers show adaptations for insect pollination, bearing numerous white or
yellow petals. Others, like the grasses, oaks, and elms, are wind pollinated and have their petals
reduced and often inconspicuous.
Angiosperm Life Cycle
Flowering plants also exhibit the typical plant alternation of generations, shown in Figure 11.
The dominant phase is the sporophyte, with the gametophyte being much reduced in size and
wholly dependant on the sporophyte for nutrition. The is not a unique angiosperm condition, but
occurs in all seed plants as well. What makes the angiosperms unique is their flowers and the
"double fertilization" that occurs. Technically this is not double fertilization, but rather a single
egg-sperm fusion (fertilization proper) plus a fusion of the second of two sperm cells with two
haploid cells in the female gametophyte to p[produce triploid (3n) endosperm, a nutritive tissue
for the developing embryo. More details on this aspect of the flowering plants are available in
the FLOWERING PLANT REPRODUCTION: Fertilization and Fruits chapter.
Figure 11. Life cycle of corn, a typical monocot angiosperm. Note the formation of endosperm
by "double fertilization". Images from Purves et al., Life: The Science of Biology, 4th Edition,
by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with
permission.
Angiosperm Systematics | Back to Top
The flowering plants, the division Magnoliophyta, contain more than 235,000 species, six times
the number of species of all other plants combined. The flowering plants divide into two large
groups, informally named the monocots and the dicots. The techjnical names for these groups
are the class Magnoliopsida for dicots and the class Liliopsida for monocots.
The dicotyledons are in the class Magnoliopsida and have these features: either woody or
herbaceous, flower parts usually in fours and fives, leaves usually net-veined, vascular bundles
arranged in a circle within the stem, and produce two cotyledons (seed leaves) at germination.
Prominent dicot families include the mustards, maples, cacti, peas and roses. Several dicot
families are noteworthy because of the illegal drugs (shown in Figure 12) derived from them:
the Cannabinaceae (marijuana) and Papaveraceae (poppies from which opium and heroin are
derived). Erythroxylum coca (in the dicot family Erythroxylaceae) is the plant from which the
illegal drug cocaine is extracted.
Figure 12. Some dicot plants bused for making illegal drugs. Top: Erythroxylum coca, left
image, the plant that is the source of cocaine, from
http://www.drugs.indiana.edu/graphics/photographs/cocaine1.gif, right image, cocaine, from
http://www.drugs.indiana.edu/graphics/photographs/cocaine3.gif; Bottom left, Cannabis
sativa, the marijuana plant; image from
http://www.drugs.indiana.edu/graphics/photographs/marij6.gif, right: Papaver somniferum,
the opium poppy being harvested; image from
http://www.drugs.indiana.edu/graphics/photographs/opium7.gif.
Not all dicot plants are misused to produce illegal drugs. Notable dicot families with legitimate
uses include the pea family, which includes the crop plants beans, clover, and peas as well as
many ornamental landscape plants such as Acacias. Beans are an excellent source of nonanimal
protein as well as fiber. Another dicot of enormous use is cotton, Gossypium, shown in Figure
13. Chocolate and cola are products of the plant family Sterculiaceae. Coffee is produced from
Coffea arabica, a plant in the family Rubiaceae, while tea comes from Camelia sinensis
(Theaceae), a plant native to China.
Figure 13. Economic dicots. Top: Gossypium sp., cotton., image from
http://botit.botany.wisc.edu/images/401/Magnoliophyta/Magnoliopsida/Dilleniidae/Malvaceae/Gossypium/Cotton_boll_leaves_MC.html;
Bottom: Capsicum annuum, the chili pepper; Image from http://www.botany.hawaii.edu/faculty/carr/images/cap_ann_233.jpg.
The class Liliopsida has plants that are herbaceous (a majority are, only palms and bamboo
stand out as monocot trees), flower parts are in threes, leaves are usually parallel-veined,
vascular bundles are scattered within the stem, and produce one cotyledon (seed leaf) at
germination. Monocot families include lilies, palms, orchids, irises, and grasses.
The monocot family Poaceae (known previously as the Gramineae) includes the grasses such as
corn, oats, wheat, rye, and rice that are staple food products as well as ornamental plants such as
crabgrass and tiff grass. The importance of this plant family to modern civilization cannot be
overstated, as the first six plants mentioned in the previous sentence provide 75% of our food,
either directly as food we eat or indirectly as food for animals we eat.
Trends in Plant Evolution | Back to Top
Several evolutionary trends within the plant kingdom have been noted. The monophyletic
nateure of this kingdom is not in dispute, with the first major division being between vascular
and nonvascular plants. Wihin the vascular plants we see increasing changes in the relationship
between sporophyte and gametophyte, culminating in flowering plants.
Developing from green algal ancestors, plants show a trend for reduction of the complexity,
size, and dominance of the gametophyte generation. In nonvascular plants the gametophyte is
the conspicuous, photosynthetic, free-living phase of the life cycle. Conversely, the angiosperm
gametophyte is reduced to between three and eight cells (hence it is very inconspicuous) and is
dependent on the free-living, photosynthetic sporophyte for its nutrition.
Plants also developed and refined the root-shoot-leaf axis with its specialized conducting cells
of the xylem and phloem. The earliest vascular plants, such as Cooksonia and Rhynia, were little
more than naked (unleafed) photosynthetic stems. Some plants later developed secondary
growth that produced wood. Numerous leaf modifications are known, including "carnivorous"
plants such as the Venus flytrap, as well as plants that have reduced or lost leaves, such as
Psilotum and the cacti.
A third trend is the development of the seed to promote the dormancy of the embryo. The seed
allows the plant to wait out harsh environmental conditions. With the development of the seed
during the Paleozoic era plants became less prone to mass extinctions.
The fourth trend in plant evolution is the encasing of a seed within a fruit. The only plant group
that produces true fruit is the flowering plants, the angiosperms. Fruits serve to protect the seed,
as well as aid in seed dispersal.
Table 1. Plant classification.
Division
Bryophyta
Characteristics
nonvascular plants, gametophyte
dominanted life cycle
naked photosynthetic stems, no
leaves, free-sporing
microphyll leaves, sporangia in
Lycophyta (the
strobili; more significant in the
club mosses)
Paleozoic
Sphenophyta megaphyll leaves, sporangia in
(=
tight cones; plants with jointed
Equisetophyta; stems; more significant in the
the horsetails) Paleozoic
Psilophyta
Examples and Uses
mosses, liverworts, hornworts
Psilotum nudum, Tmesipteris;no commercial uses
Lycopodium, a homosporous plant, Selaginella, a
heterosporous plant; no commercial uses except as
ground cover in some areas
Equisetum, the scouring rush or horsetail; no
commercial applications
Filicophyta
(ferns)
megaphyll pinnately compound
leaves, sporangia on underside of
leaves, clumped in sori; leaves
arise by circinnate vernation
(uncoiling to look initially like a
crozier or sheperd's crook)
Ornamental plants such as the Boston fern; tree ferns;
commercial applications as ornamentals; ecologically
important plants in some areas of the world
Cycadophyta
(the cycads)
long, pinnately compound
megaphyll leaves with a leathery
feel arising from soft woode4d
stems by circinnate vernation; new
leaves arise as a crown or whorl;
reproduction by seeds produced in
female cones, pollen produced in
male cones
Cycas revoluta, a common ornamental known as the
Sago palm;Zamia floridana, only cycad native to the
48 contiguous United States; commercial uses as
ornamental plants
Ginkgophyta
(the ginkoes)
fan shaped, usually bilobed leaves
on a woody tree with long anmd Ginkgo biloba, the maidenhair tree; commercial uses
short shoot anatomy; seeds
as ornamental plants and allegedly as a memory aid in
produce a foul odor when mature; herbal form
pollen elliptical, monoaperturate
needle-like or scale-like leaves
with thick cuticles and sunken
stomata; soft wooded plants; seeds
Coniferophyta lacking fruit, dispersede from
hardened cones; pollen can be
bisaccate (Pinus) or lacking sacs
(Taxodium)
living plant group most closely
related to flowering plants; vessels
in some members of group;
Gnetophyta
reproductive structures close to
flowers; pollen elliptical eith
usually one aperture
flowering plants (angiosperms)
that encase their seeds within a
ripened ovary wall known as a
fruit; fruits may be dry or fleshy,
single or multiple; two major
Magnoliophyta
classes the monocots and dicots;
xylem may include vessels as well
as tracheids; range from
herbaceous annuals to periennel
trees
Pinus(wood, resin, pine straw, pine nuts, paper); Taxus
(yew) a natural source for the anticancer drug taxol;
Douglas fir (wood); ornamental plants
Ephedra (Mormon tea) source of ephedrine; Gnetum;
Welwitschia have no commercial uses
Monocots: cereal grains form staple of economy and
diet; palms are used in many places as building
material; ecologicalimpact as pioneer species in
disturbed habitats;
Dicots: food crops such as beans, peas; fibers from
cotton used to make clothing and paper; illegal drugs
such as marijuana, cocaine, heroin; legal products such
as chocolate, tea, and coffee; Nicotiana leaves make
tobacco a dangerous legal "drug"; ornamental plants
Learning Objectives | Back to Top
Be able to compare and contrast the characteristics of seed, nonseed, and nonvascular plants. To do
this complete the table below.
Characteristic
Nonvascular Plants Nonseed Plants Seed Plants
Dominant Phase of Plant Life Cycle
Swimming Sperm
Pollen Tube
Pollen or Spores
Homospory or Heterospory or Mixed
Examples of Plants in this Group
Be able to list the uses of some common gymnosperm plants, such as pines and ginkgoes.
Be able to list some of the uses of flowering plants.
It has been stated that the ancestor of flowering plants most likely was a gnetalean plant (or at least a
plant closely related to them). What evidence supports this?
How might the fact that a species in monoecious or dioecious affect your decision to use it as a crop
plant? As a landscape plant?
Terms | Back to Top
androecium angiosperms Auracarioxylon carpel
cones
conifers
cycads
dioecious
endosperm
Ephedra
fertilization ginkgoes
Gnetales
Gnetum
gymnosperms gynoecium homosporous internodes
Mesozoic Era Paleozoic Era petals
pistil
pollen grains pollen tube
sepals
sporophyte stamen
Welwitschia zygote
Review Questions | Back to Top
1. Endosperm tissue is unique to which of these groups? a) cycads; b) conifers; c) flowering
plants; d) ferns
2. Seed plants have ___. a) pollen grains with male gametophytes developing on the inside;
3.
4.
5.
6.
b) female gametophytes developing inside an ovule retained on the sporophyte; c) roots; d)
all of these
Which of these plants is not a gymnopserm? a) corn; b) pine; c) redwood; d) ginkgo
Which of these plants is not a flowering plant? a) corn; b) wheat; c) lily; d) douglass fir
Cycads and ginkgoes were important plants to the world's terrestrial ecosystems during the
____. a) Paleozoic era; b) Cenozoic era; c) Mesozoic era; d) precambrian
The presence of long shoot/short shoot anaytomy characterizes which of these pants? a)
Ginkgo; b) Cycas; d) Zamia; d) ferns
Answers: 1. c; 2. d; 3. a; 4. d; 5. c; 6. a;
Links | Back to Top
Non-Flowering Plant Family Access Page Sorted by family on the non-flowering plants. Thumbnail
photos are linked to larger versions. This site is a great educational resource maintained by Gerald D.
Carr.
Encyclopedia of Plants Scientific and common names for garden plants.
The Botanical Society of America The official website of the plant folks.
Cycad Pages This Australian website is a great stepping stone for more information about a favorite
plant group of mine: cycads. This page is maintained by Ken Hill of the Royal Botanic Gardens
Sydney and Dennis Stephenson of the New York Botanical Garden.
Ginkgo biloba History, uses, and other information about this living "fossil tree" whose leaves are
essentially unchanged since the Tertiary period.
The Ginkgo Pages Cor Kwant has produced a great resource on a fascinating plant. A great resource
for images and information!
Gymnosperm Database Christopher J. Earle has developed a nifty resource for digging deeper into the
gymnosperms. A series of links from this page take you into images and descriptions of the various
gymnosperm groups.
Erythroxylum: The Coca Plant This ethnobotanical page, by April Rottman, describes the systematics
and uses of the plant as well as its product, cocaine.
Barley: The Versatile Crop This page, part of a series of ethnobotanical leaflets, is by Bryan Young,
and describes the natural history and economic uses of barley, the 4th most important crop.
All text contents ©1995, 1999, 2000, 2001, 2003, 2004, by M.J. Farabee. Use of text for educational
purposes is encouraged.
Back to Table of Contents
Email: mj.farabee@emcmail.maricopa.edu
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