CHAPTER 23 Plant Diversity.

CHAPTER 23 Plant Diversity

Section #1 The Evolution of Plants
Plants Overcame Obstacles to Living on Land A. The Earth is believed to be 4.5 billion years old. Scientists think that life on Earth began about 3.5 billion years ago. Fossil records indicate that nothing lived on LAND until about 440 Million years ago. Life was confined to the sea for the first 3 billion years of Earth’s existence.

B. Scientists feel that living things stayed in the seas to avoid the intense solar radiation that was coming from the sun. At this time there was no protective ozone layer in the atmosphere.

C. With the advent of photosynthesis in Earth’s oceans, oxygen gas began to accumulate in the atmosphere. Some of this oxygen was converted to ozone. This ozone created a protective layer in the Earth’s atmosphere that shielded the Earth’s surface from much of the harmful solar radiation, allowing organisms to live on land instead of in the water.

D. Both plants & fungi probably evolved from multicellular protists
D. Both plants & fungi probably evolved from multicellular protists. Multicellularity enabled plants to develop the complex structures that have helped them be successful on land. E. Before these descendants of the earliest plants could thrive in terrestrial habitats, they had to overcome three obstacles:

1) They had to be able to absorb minerals from rocky surfaces.
a. Mutualistic associations similar to mycorrhizae have enabled the first plants to absorb minerals from the rocky surfaces. b. Mycorrhizae are symbiotic relationships between fungi & the roots of some plants. Plants provide carbohydrates and fungi absorb phosphorus and other minerals that plants need. c. 80% of all living plant species form mycorrhizae today.

2. They had to be able to conserve water.
a. First plants lived near oceans, where water was abundant. To live further away they had to develop a way to conserve water. b. Plants developed a watertight outer covering called a CUTICLE (waxy layer) c. Although a cuticle seals in moisture, it also seals out the gases a plant needs for photosynthesis & cellular respiration.

d. The problem was solved with the formation of specialized pore cells called stomata. A pair of specialized epidermal cells called guard cells border each stoma and control its size by expanding and contracting

3. They had to have a way to reproduce on land.
a. The male gametes (sperm) of aquatic plants were able to swim to fertilize the female gametes. The gametes of plants that live on land needed to be able to move in an environment where water is not abundant. In addition, they have to be protected from drying out while being transferred.

b. The eggs of the first plants were surrounded by jackets of cells to prevent drying, and a film of water was required for a sperm to swim to an egg & fertilize it. c. Today, mosses, ferns, and several other groups of primitive plants still reproduce in this way.

d. In more advanced plants, the sperm are enclosed in multicellular pollen grains that keep them from drying out. This allows them to be transmitted to female gametes by wind or animals rather than by water

II. A Vascular System Enabled Plants to Thrive on Land
A. One of the most important changes in the structure of plants that occurred as they adapted to land was the development of an efficient way to move water and other materials through the plant body.

B. In order to survive in environments that have a limited water supply, most plants need an efficient “plumbing” system to carry water from their roots up to their leaves and carry carbohydrates from their leaves down to their roots.

C. These plumbing systems consist of specialized strands of hollow cells connected end to end like a pipeline (see Fig pg. 522) D. The tissues that transport water and other materials within a plant make up the vascular system. The word vascular is derived from the Latin word vasculum, meaning “vessel” or “duct”

E. In the dominant group of plants today, the cells of the vascular system run from near the tips of the roots to the tips of the stems and into the leaves. Not all plants have efficient vascular systems, however. Of the twelve phyla of living plants on Earth today, three either have no vascular system or have only very simple vascular tissue. The nine remaining plant phyla have well-developed vascular systems

F. Non Vascular Plant Phyla
Hepatophyta (Liverworts) – 6,000 species. Simplest plants; small, having a dominant gametophyte with a flattened or “leafy” body that lacks vascular tissue, a cuticle, stomata, roots, stems, and leaves.

Anthocerophyta (Hornworts) 100 species
Small, with a flattened, dominant gametophyte that has stomata but lacks vascular tissue, roots, stems, and leaves

Liverwort & Hornwort Liverwort Hornwort

Bryophyta (Mosses) 10,000 species
Small: most have simple vascular tissue, a sporophyte consisting of a bare stalk and a spore capsule, and a dominant, “leafy” green gametophyte that lacks roots, stems, & leaves.

G.Vascular Plant Phyla 1) Psilotophyta (Whisk ferns) 21 species
Seedless, with a small, independent gametophyte and a dominant sporophyte that is highly branched and has tiny leaves but is not differentiated into roots and stems

Sphenophyta (Horsetails) 15 species
Seedless, with a small, independent gametophyte and a dominant sporophyte consisiting of roots and ribbed and jointed stems with soft needlelike leaves at the joints.

Whisk Ferns & Horsetails

Lycophyta (Club Mosses)1,000 species
Seedless, with a small independent gametophyte and a dominant, mosslike sporophyte with roots, stems, and leaves.

Pterophyta (ferns) 12,000 species
Seedless, with a small, independent gametophyte and a dominant sporophyte consisting of roots, horizontal stems, and leaves called fronds; spores are produced in clusters of sporangia on lower surfaces of leaves.

Club Moss & Ferns

Coniferophyta (Conifers) 100 species
Gymnosperms with palm-like leaves; produce male and female cones on separate plants

Cycadophyta (Cycads) 100 species
Gymnosperms with palmlike leaves Produce male and female cones on separate plants

Ginkgophyta (Ginkgo) 1 species
Gynmosperm deciduous tree with fanlike leaves; produces conelike male reproductive structures and uncovered seeds on separate individuals

Gnetophyta (Gnetophytes) 70 species
Gymnosperms; diverse group of shrubs and vines

Conifer, Ginkgo, Gnetophyte, Cycad

Anthophyta (Flowering Plants) 250, 000 species
Angiosperms (seed plants with tiny gametophytes, a large sporophyte, and ovules enclosed by an ovary); a very diverse group including trees, shrubs, vines, and herbs that produce flowers and fruits.

Angiosperms – flowering plants

III. Plants Evolved With Alternation of Generations
A Plants evolved with a distinctive pattern of development in their life cycles. B. Among many algae, the zygote is the only diploid (2n) cell, and it undergoes meiosis immediately after fertilization (zygotic meiosis) to form haploid (n) cells. C. In early plants, however, meiosis was delayed. The zygote divided by mitosis to produce many diploid cells that persist for a long portion of the life cycle.

D. As a result, plants developed alife cycle in which a multicelled haploid individual that produces gametes, the gametophyte, alternates with a multicelled diploid individual that produces spores, the sporophyte.

E. The pattern among life cycles in which a haploid individual alternates with a diploid individual is called Alternation of Generations. F. As plants evolved, however, a fundamental difference arose between the life cycles of the simpler, nonvascular plants and those of the more complex, vascular plants:

1) In the nonvascular plants (mosses & liverworts), the gametophyte generation is the dominant (most noticeable ) generation. 2) In the vascular plants (ferns, gymnosperms, & angiosperms), the sporophyte generation is dominant. In fact, the very tiny gametophytes of most vascular plants grow within tissues of the sporophytes

1. In the nonvascular plants (mosses & liverworts), the gametophyte generation is the dominant (most noticeable) generation. 2. In the vascular plants (ferns, gymnosperms, & angiosperms), the sporophyte generation is dominant. In fact, the very tiny gametophytes of most vascular plants grow within tissues of the sprophytes.

IV. The First Plants Lacked a Vascular system
A. The first plants to successfully make the transition to living on land probably had no vascular system for transporting materials throughout their bodies. All materials had to be transported by osmosis and diffusion, which greatly limited the maximum size of the plant.

B. Only two phyla of living plants, the liverworts (Hepatophyta) and hornworts (Anthocerophyta) completely lack a vascular system. The members of these two groups have historically been grouped with the mosses and are still frequently referred to as “bryophytes”.

However, botanists no longer think that these three groups of relatively simple plants are directly related to one another. C. The genus Marchantia is a common liverwort seen in Fig on pg. 525. D. The word “wort” meant “herb” in Old English.

E. The name liverwort dates back to the Middle Ages, when it was thought that plants resembling certain body parts might contain substances that could cure diseases of those body parts.

While the shape of some liverworts resembles a liver, the dominant gametophyte of most liverworts consists of simple leaflike and stemlike structures.

G. Gametes are formed by mitosis in separate multicellular structures.
F. Projections called rhizoids help anchor liverworts to the surfaces on which they grow. G. Gametes are formed by mitosis in separate multicellular structures. 1) Archegonia produce eggs 2) Antheridia produce sperm

H. When water is available, the sperm swim to a nearby archegonium and fertilize the egg within it. The resulting zygote grows into a very tiny diploid sporophyte.

V. Mosses Have Simple Vascular Tissue
A. The mosses (phylum Bryophyta) include many species in which a central strand of specialized conducting cells distributes water and carbohydrates throughout the plant. These conducting strands make up what is called vascular tissue

This tissue is very simple in bryophytes because the conducting cells lack thickened walls
B. Because their vascular tissue is so simple, mosses are still grouped with the liverworts and hornworts, and all three groups are considered to be nonvascular plants.

C. The three phyla of nonvascular plants share an important similarity
C. The three phyla of nonvascular plants share an important similarity. Their life cycles, represented in fig.23-7 on pg. 526, are dominated by the gametophyte generation. The archegonia and antheridia of mosses are produced on separate gametophytes.

D. The moss sporophyte consists of a bare stalk that supports a spore capsule, or sporangium, in which haploid spores are produced by meiosis

VI. Vascular Plants Are Characterized by Several Features
A. The first vascular plants appeared approximately 430 million years ago, but only incomplete fossils of these plants have been found. B. The earliest known vascular plants for which there are relatively complete fossils are Rhynia and Cooksonia. (See Fig on pg. 527

C. Today, vascular plants occupy almost all terrestrial habitats except those perpetually covered by ice and snow. Unlike the nonvascular plants and the earliest vascular plants, many modern vascular plants grow very tall. D. All vascular plants are distinguished by the following features:

1) A Dominant Sporophyte --- In contrast to nonvascular plants, the life cycles of vascular plants are dominated by a diploid sporophyte that is much larger than the gametophyte.

2) Specialized Conducting Tissue –
a) Phloem --- Relatively soft-walled cells that conduct carbohydrates away from the areas where they are made b) Xylem – Hard-walled cells that transport water and dissolved minerals up from the roots.

3) Distinctive Body Form--
a) SHOOT – Above ground structures, including the stem and leaves. b) ROOT – Below ground structures c) MERISTEM – Zones of actively dividing cells that produce plant growth.

Section #2 The Evolution of Seeds

I. First Vascular Plants Lacked Seeds
A. The first forests were composed vascular plants that did not produce seeds. B. Like the nonvascular plants, ferns, and other seedless vascular plants have swimming sperm and require a film of water for fertilization. Forests of these plants flourished in the warm, humid climate of the late Paleozoic era

C. In these forests, plenty of water was available for successful reproduction.
D. Ferns are the most abundant and most familiar group of seedless vascular plants today. Though they are found throughout the world, ferns are most abundant in the tropics.

E. Many ferns are small, measuring only a few centimeters in diameter
E. Many ferns are small, measuring only a few centimeters in diameter. However, some of the largest living plants are tree ferns that can have trunks more than 24 meters tall and leaves up to 5 meters long.

F. The fern life cycle, illustrated in Fig
F. The fern life cycle, illustrated in Fig , represents an intermediate stage in the revolutionary change that took place in plant life cycles. Remember, the life cycles of nonvascular plants are dominated by a gametophyte that supports a smaller, dependent sporophyte.

G. In ferns and other seedless vascular plants, however, the sporophyte is dominant, and the gametophyte is smaller, independent, and self-sufficient.

H. The fern gametophyte is a thin, heart-shaped photosynthetic plant that lives in moist places and is usually no more than 1 cm in diameter.

I. Fern gametophytes produce eggs in archegonia and sperm in antheridia, both of which are located on the lower surface of the plant. In ferns, the archegonia and antheridia are produced by the same individual. In other seedless vascular plants, the male and female structures are produced by separate gametophytes.

J. When a film of water is available, sperm are able to swim to eggs and fertilize them.
K. Fern sporophytes consist of roots, horizontal underground stems called rhizomes, and long, often highly divided leaves called fronds. Clusters of spore-producing sporangia form on the lower surfaces of fronds.

II. First Seed Plants Were Gymnosperms
A. Seeds apparently arose only once among the vascular plants, as the plant life cycle continued to shift toward a more dominant sporophyte generation and a more reduced gametophyte generation.

B. Of the 5 phyla of living seed plants, four are collectively called gymnosperms. The word gymnosperm comes from the Greek words gymnos, meaning “naked” and sperma, meaning “seed,” and refers to the fact that gymnosperm seeds do not develop within a fruit.

C. First appearing about 380 million years ago, gymnosperms were the first seed plants.
D. The flowering plants, or angiosperms, evolved from gymnosperms and make up the fifth phylum of seed plants. The word angiosperm comes from the Greek words angeion, meaning “case” and sperma, meaning “seeds” and refers to the fact that angiosperm seeds develop within a fruit.

E. First appearing between 150 and 200 million years ago, angiosperms are the most recently evolved of all plant phyla. F.. As Fig illustrates, the gametophytes of seed plants have become highly reduced during the course of evolution.

1) Developing from spores that are produced within the tissue of the sporophyte individuals, the gametophytes of seed plants are entirely dependent upon those sporophyte individuals for nutrients and water.

2) Seed plants produce two kinds of gametophytes:
a) A very tiny male gametophyte, or microgametophyte, that produces sperm. b) Arelatively large female gametophyte, or megagametophyte, that produces eggs.

3) Thus, the spores that produce the microgametophytes are called microspores and those that produce the megagametophytes are called megaspores.

a) A pollen grain, which consists of only a few haploid cells surrounded by a thick protective wall, is a mature microspore that contains a microgametophyte.

b) Each megagametophyte develops from a megaspore within an ovule, a multicellular structure that is part of the sporophyte. If the inside of an ovule is fertilized, the ovule and its contents becomes a seed.

G. Wind, insects, or other animals transport pollen grains to the female reproductive structures that contain ovules. The transportation of pollen grains from a plant’s male reproductive structures to a female reproductive structure of a plant of the same species is called pollination.

H. When a pollen grain reaches a female reproductive structure, the pollen grain cracks open. A pollen tube then grows from the pollen grain to an ovule and enables a sperm to pass directly to an egg. I. Thus, in seed plants there is no need for a film of water during the fertilization process.

III. Most Living Gymnosperms are Conifers
A. Members of the most familiar phylum of gymnosperms are trees that produce seeds in cones and thus are called conifers.

1) Phylum Coniferophyta includes cedar, cypress, fir, hemlock, pine, redwood, spruce, and yew trees.
a. The tallest living vascular plants, the giant redwoods of coastal California and Oregon, are conifers.

b. One of the biggest redwoods, a giant sequoia (Sequoia gigantea) named after General Sherman of the Civil War, stands more than 80 m tall and measures 20 m around its base. c. Some individuals of another, much smaller species of conifer, the bristlecone pine (Pinus longaeva) that lives in the Rocky Mountains, are more than 5,000 years old– the oldest trees in the world!

2) Most conifers have needle-like leaves that are an adaptation for limiting water loss. Conifers are often found growing in seasonally dry regions of the world, including the vast taiga forests of the northern latitudes

B. The Life cycle of a Conifer (Fig. 23-14 pg. 533)
1. Conifers form two kinds of cones which can be seen in Fig a. Seed cones produce ovules on the surface of their scales. At the time of pollination, the scales of a seed cone are open, exposing the ovules

b) Pollen cones produce pollen grains within sacs that develop on the surface of their scales. The pollen grains of conifers are small and light, and they are carried by wind to seed cones.

2. In pines and some other conifers, each pollen grain has a pair of air sacs that help to carry it in the wind. Because it is very unlikely that any particular pollen grain will be carried to a seed cone of the same species, a great many pollen grains are needed to ensure that at least a few succeed in pollinating the species’ seed cones. For this reason, pollen cones produce huge quantities of pollen grains.

3) When a pollen grain lands near the ovule on a scale of a female cone, a slender pollen tube grows out of the pollen grain and into the ovule. Thus, the pollen tube delivers a sperm to the egg inside the ovule.

4. Fertilization occurs when the sperm fuses with the egg, forming a zygote that is the beginning of a new sporophyte generation.

5) Instead of growing directly into an adult sporophyte (a tree)– just as you grow directly into a n adult from a zygote– the zygote first develops into a small embryo and then becomes dormant.

6) While its further growth is postponed, the zygote and the sporophyte tissues that surround and protect it form a seed.

C. Other Gymnosperms (Fig. 23-15 pg. 533)
1. Cycads (Phylum Cycadophyta), the dominant land plant during the Jurassic period, have short stems and palmlike leaves and are still widespread throughout the tropics.

2) The only living species of ginkgo (Phylum Ginkgophyta), the maidenhair tree (Ginkgo biloba), has fan-shaped leaves that are shed in the autumn.

3) The gnetophytes (Phylum Gnetophyta) are all very unusual
3) The gnetophytes (Phylum Gnetophyta) are all very unusual. Welwitschia mirabilis, perhaps the most bizarre of all plants, is a gnetophyte that grows in the harsh Namib Desert of southwestern Africa.

IV. What is a seed? A. By providing the offspring of plants with several survival advantages, seeds have had an enormous influence on the evolution of plants on land.

B. As you can see in Fig , a seed is a sporophyte plant embryo surrounded by a protective coat. The hard cover of a seed is called the seed coat.

C. Formed from the sporophyte tissue of the parent plant, the seed coat protects the embryo and other tissues in the seed from drying out. D. In addition to their role in protecting a plant embryo, seeds have enabled plants to become better adapted to living on land in at least three other respects:

1) Dispersal—Seeds enable the offspring of plants, which are anchored in one place by their roots, to be dispersed to new locations. Many seeds have appendages, such as wings, that help wind, water, or animals carry them away from their parent plant.

The dispersal of a plant’s offspring prevents the parent and offspring from competing with each other for water, nutrients, light, and living space. Seed dispersal also facilitates the migration of a plant species to new habitats.

2) Nourishment– Most kinds of seeds have abundant food stored in them
2) Nourishment– Most kinds of seeds have abundant food stored in them. Playing a role similar to that of the yolk in an egg, this food supply is a ready source of energy for a plant embryo as it starts its growth. Thus, seeds offer a young plant nourishment during the critical period just after germination when the seedling must establish itself.

3) Dormancy-- Once a seed has fallen to the ground, it may lie dormant for many years. When conditions are favorable, particularly when moisture is present, the seed will begin to grow into a young plant.

By remaining dormant until conditions improve, seed enable plants to postpone development during unfavorable conditions such as a drought or a cold period. Thus, seeds aid in synchronizing the growth of a new plant with the season of the year.

The Evolution of Flowers
Section #3 The Evolution of Flowers

Angiosperms Achieved Evolutionary Success On Land
A. 90% of all living plants—more than 250,000 species of trees, shrubs, herbs, fruits, vegetables, and grains—are angiosperms.

B. Virtually all of your food comes directly or indirectly from angiosperms. In fact, more than half of the calories that humans consume come from just three species of angiosperms: 1. rice 2. corn 3. wheat

II. What is a Flower A. Flowers are the reproductive organs of angiosperms. B. Many flowers are sophisticated structures that are adapted to enable insect pollination: 1) Bright colors attract the attention of insects

2) Nectar, which is a sugary secretion of many flowers, induces insects to enter a flower.
3) Pollen-bearing structures coat the insects with pollen while they are visiting a flower. 4) Then, when the insects visit another flower, they carry the pollen into that flower.

C. The basic structure of a flower, seen in Fig. 23-18 pg
C. The basic structure of a flower, seen in Fig pg. 536, consists of the four concentric whorls (circles) of appendages described below: 1) Calyx – The outermost whorl of a flower, derived from the Greek word kalyx, meaning “cup”. The calyx is made of the sepals, which are modified leaves that protect the flower from damage while it is a bud.

2) Corolla– Aname derived from the Latin word corona, meaning “crown”
2) Corolla– Aname derived from the Latin word corona, meaning “crown”. The corolla consists of the petals, which are also modified leaves. The petals are often colored or scented to attract pollinators.

3) Androecium– The word comes from the Greek words andros, meaning “male”, and oikos, meaning “house”. The androecium produces the microgametophytes (pollen grains). It is made up of one or more stamens, which consist of slender, threadlike filaments that are each topped by a pollen-containing sac called an anther.

4) Gynoecium– The term comes from the Greek words gyne, meaning “female” and oikos, meaning “house”. The gynoecium houses the ovules, in which the megagametophytes develop. It consists of one or more pistils that are found in the center of a flower.

The pistil is made of three parts:
a. Ovary– The swollen lower portion that houses the ovules. b. Style– A slender stalk that rises from the ovary. c. Stigma – The swollen, sticky tip of the style where pollen lands.

D. Flowers may or may not have all four whorls
1. A flower that has all four whorls of appendages is called a Complete flower. 2. If a flower has both a gynoecium and an androecium, it is a perfect flower. 3. Many flowers lack either a gynoecium or an androecium and are called imperfect flowers. 4. Incomplete flowers are those that lack any one of the four whorls

III. Flowering Plants Coevolved With Animals
A. Insects do not visit flowers at random. Instead, certain insects are attracted by particular flowers. Insects and plants have coevolved so that certain insects specialize in visiting particular kinds of flowers.

B. An insect recognizes a particular color pattern and searches for flowers with that pattern. As a result, a particular insect carries pollen from the flowers on one individual to the flowers of another individual of the same species. This specificity is the key to successful insect pollination, making it much more effective than wind pollination.

1. bees are the most numerous insect pollinators.
a. Today, there are over 20,000 species of bees. b. Bees locate sources by odor first, then by color. They are usually attracted to yellow or blue flowers. These flowers often have lines of dots that guide the bee to the location of the nectar.

c. While inside a flower, bees become coated with pollen
c. While inside a flower, bees become coated with pollen. This coating is far from accidental. Most of the bees visiting flowers actively seek the pollen, which is rich in protein for their larvae.

2. Butterflies tend to visit flowers that have “landing platforms” on which they can perch. These flowers are typically tube-shaped and filled with nectar that they can reach by uncoiling a long, hose-like mouthpart. 3. Flies pollinate flowers that smell like rotting meat.

4. Moths, which visit flowers at night, pollinate white, heavily scented flowers that are easy to locate in dim light.

C. Many angiosperms are pollinated by animals other than insects.
1. Red flowers are typically visited by hummingbirds. Birds, which have keen vision, have a poor sense of smell. Knowing this, it is not surprising that red flowers usually lack a strong odor.

2. Certain angiosperms have large, heavily scented, and pale-colored flowers that open at night. These flowers are pollinated by another nighttime visitor, bats.

D. Some angiosperms have reverted to wind pollination, a characteristic of their ancestors. Examples include oaks, birches, and grasses

IV. Double Fertilization Provided Large Food Reserves in Seeds
A. Unlike the seeds of gymnosperms, the seeds of angiosperms develop a highly nutritious tissue, called endosperm, that originates at the same time that an egg is fertilized. 1. In some angiosperms (corn & wheat) the endosperm is still present in mature seeds.

2. In other angiosperms ( beans & peas) the endosperm is completely transferred into the embryo by the time the seed is mature. The food reserves are then stored in the embryo’s fleshy, leaflike cotyledons (seed leaves).

B. The angiosperms are divided into two classes based on the number of cotyledons in their seeds.
1. Dicots (class Dicotyledones) have two cotyledons. They typically have flower parts in multiples of four or five, netlike veins, and vascular bundles arranged in a ring.

2. Monocots (class Monocotyledones) have only one cotyledon
2. Monocots (class Monocotyledones) have only one cotyledon. They typically have flower parts in multiples of three, parallel veins, and vascular bundles scattered throughout the cortex.

C. Figure on page 539 shows how the angiosperm embryo and endosperm originate at fertilization. 1. The microgametophytes of seed plants contain two sperm cells. 2. In most gymnosperms, one of these sperm dies.

3. In angiosperms, however, both sperm fuse with certain cells of the megagametophyte.
a. One sperm fuses with the egg, forming the zygote. b. The other sperm fuses with the haploid nuclei of the two other cells produced by meiosis, forming a triploid (3n) cell that gives rise to the endosperm.

4. The term double fertilization is used to describe the process by which two sperm fuse with cells of the megagametophyte to produce both a zygote and the endosperm.

V. Fruits Enabled Efficient Seed Dispersal
A. A fruit consists of a mature ovary that contains one or more seeds and often includes other flower parts. B. Animals, which aid in pollination because they are attracted to and obtain nourishment from flowers, also aid in seed dispersal.

1. many mammals and birds are attracted to and eat fruits that are fleshy and tasty.
2. As fruits ripen, they often change from green and odorless to brightly colored and sweet smelling. 3. The mature seeds within such ripe fruits are often resistant to chewing and digestion.

C. Most fruits, however, are not eaten by animals.
1. Some are specialized for sticking to an animal’s fur 2. Others are adapted for floating on wind currents or water.

CHAPTER 23 Plant Diversity.

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