29 plants ii text

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The evolutionary view of origin of plants!

• For more than the first 3 billion years of Earth’s history

– The terrestrial surface was lifeless

• Since colonizing land

– Plants have diversified into roughly 290,000 living species

– Researchers have identified green algae called charophyceans as the closest relatives of land plants


Genetic Evidence

• Comparisons of both nuclear and chloroplast genes

– Point to charophyceans as the closest living relatives of land plants

Chara, a pond organism

(a)10 mm

Coleochaete orbicularis, a disk-shaped charophycean (LM)

(b)

40 µm

Figure 29.3a, b


Defining the Plant Kingdom

• Systematists

– Are currently debating the boundaries of the plant kingdom

Plantae

Streptophyta

Viridiplantae

Red algae Chlorophytes Charophyceans Embryophytes

Ancestral algaFigure 29.4


Derived Traits of Plants

• Five key traits appear in nearly all land plants but are absent in the charophyceans

– Apical meristems

– Alternation of generations

– Walled spores produced in sporangia

– Multicellular gametangia

– Multicellular dependent embryos


APICAL MERISTEMSApicalmeristemof shoot

Developingleaves

100 µm

Apical meristems of plant shoots and roots. The light micrographs are longitudinal sections at the tips of a shoot and root.

Apical meristemof root

Root 100 µmShoot

Figure 29.5

• Apical meristems and alternation of generations

Haploid multicellularorganism (gametophyte)

Mitosis Mitosis

Gametes

Zygote

Diploid multicellularorganism (sporophyte)

Alternation of generations: a generalized scheme

MEIOSIS FERTILIZATION

2n2n

n

n

nn

nSpores

Mitosis

ALTERNATION OF GENERATIONS


• Walled spores; multicellular gametangia; and multicellular, dependent embryos

WALLED SPORES PRODUCED IN SPORANGIA

MULTICELLULAR GAMETANGIA

MULTICELLULAR, DEPENDENT EMBRYOS

SporesSporangium

Longitudinal section ofSphagnum sporangium (LM)

SporophyteGametophyte

Sporophyte and sporangium of Sphagnum (a moss)

Female gametophyte

Archegoniumwith egg

Antheridiumwith sperm

Malegametophyte

Archegonia and antheridia of Marchantia (a liverwort)

EmbryoMaternal tissue

2 µm

Wall ingrowths

Placental transfer cell

10 µm

Embryo and placental transfer cell of Marchantia

Figure 29.5


• Fossilized spores and tissues

– Have been extracted from 475-million-year-old rocks

Fossilized spores. Unlike the spores of most living plants, which are single grains, these spores found in Oman are in groups of four (left; one hidden) and two (right).

(a)

Fossilizedsporophyte tissue. The spores were embedded in tissue that appears to be from plants.

(b)

Figure 29.6 a, b


• Whatever the age of the first land plants

– Those ancestral species gave rise to a vast diversity of modern plants

Table 29.1

An overview of land plant evolution

Land plants can be informally grouped based on the presence or absence of vascular


Bryophytes(nonvascular plants) Seedless vascular plants Seed plants

Vascular plants

Land plants

Origin of seed plants(about 360 mya)

Origin of vascular plants (about 420 mya)

Origin of land plants(about 475 mya)

Ancestralgreen alga

Ch

aro

ph

ycea

ns

Liv

erw

ort

s

Ho

rnw

ort

s

Mo

sse

s

Lyc

op

hyt

es(c

lub

mo

sses

, sp

ike

mo

sses

, q

uil

lwo

rts)

Pte

rop

hyt

e (f

ern

s, h

ors

etai

ls,

wh

isk

fern

)

Gym

no

sper

ms

An

gio

sper

ms


• The life cycles of mosses and other bryophytes are dominated by the gametophyte stage

• Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants

– Liverworts, phylum Hepatophyta

– Hornworts, phylum Anthocerophyta

– Mosses, phylum Bryophyta


• The life cycle of a moss

Maturesporophytes

Youngsporophyte

Malegametophyte

Raindrop

Sperm

Key

Haploid (n)Diploid (2n)

Antheridia

Femalegametophyte

Egg

Archegonia

FERTILIZATION

(within archegonium)Zygote

Archegonium

Embryo

Femalegametophytes

Gametophore

Foot

Capsule(sporangium)

Seta

Peristome

Spores

Protonemata

“Bud”

“Bud”

MEIOSIS

Sporangium

Calyptra

Capsule with peristome (LM)

Rhizoid

Maturesporophytes

Spores develop intothreadlike protonemata.1

The haploidprotonemataproduce “buds”that grow intogametophytes.

2 Most mosses have separatemale and female gametophytes,with antheridia and archegonia,respectively.

3

A sperm swimsthrough a film ofmoisture to anarchegonium andfertilizes the egg.

4

Meiosis occurs and haploidspores develop in the sporangiumof the sporophyte. When thesporangium lid pops off, theperistome “teeth” regulategradual release of the spores.

8

The sporophyte grows along stalk, or seta, that emergesfrom the archegonium.

6

The diploid zygotedevelops into a sporophyte embryo withinthe archegonium.

5

Attached by its foot, thesporophyte remains nutritionallydependent on the gametophyte.

7

Figure 29.8


• Bryophyte gametophytes

– Produce flagellated sperm in antheridia

– Produce ova in archegonia

– Generally form ground-hugging carpets and are at most only a few cells thick

• Some mosses

– Have conducting tissues in the center of their “stems” and may grow vertically


Bryophyte Sporophytes

• Bryophyte sporophytes

– Grow out of archegonia

– Are the smallest and simplest of all extant plant groups

– Consist of a foot, a seta, and a sporangium

• Hornwort and moss sporophytes

– Have stomata


• Bryophyte diversityLIVERWORTS (PHYLUM HEPATOPHYTA)

HORNWORTS (PHYLUM ANTHOCEROPHYTA) MOSSES (PHYLUM BRYOPHYTA)

Gametophore offemale gametophyte

Marchantia polymorpha,a “thalloid” liverwort

Foot

Sporangium

Seta

500

µm

Marchantia sporophyte (LM)

Plagiochiladeltoidea,a “leafy”liverwort

An Anthoceroshornwort species

Sporophyte

Gametophyte

Polytrichum commune,hairy-cap moss

Sporophyte

Gametophyte

Figure 29.9


“Tolland Man,” a bog mummy dating from 405–100 B.C. The acidic, oxygen-poor conditions produced by Sphagnum canpreserve human or other animal bodies for thousands of years.

Ecological and Economic Importance of Mosses

• Sphagnum, or “peat moss”

– Forms extensive deposits of partially decayed organic material known as peat

– Plays an important role in the Earth’s carbon cycle

GametophyteSporangium attip of sporophyte

Livingphoto-syntheticcells

Dead water-storing cells

100 µm

Closeup of Sphagnum. Note the “leafy” gametophytes and their offspring, the sporophytes.

(b)

Sphagnum “leaf” (LM). The combination of living photosynthetic cells and dead water-storing cells gives the moss its spongy quality.

(c)

Peat being harvested from a peat bog(a)

Figure 29.10 a–d

(d)


• Ferns and other seedless vascular plants formed the first forests

• Bryophytes and bryophyte-like plants

– Were the prevalent vegetation during the first 100 million years of plant evolution

• Vascular plants

– Began to evolve during the Carboniferous period


Life Cycles with Dominant Sporophytes

• In contrast with bryophytes

– Sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern

– The gametophytes are tiny plants that grow on or below the soil surface


Sporophyte dominance

• The life cycle of a fern

Fern sperm use flagellato swim from the antheridia to eggs in the archegonia.

4

Sporangia release spores.Most fern species produce a singletype of spore that gives rise to abisexual gametophyte.

1 The fern sporedevelops into a small,photosynthetic gametophyte.

2 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanismspromote cross-fertilizationbetween gametophytes.

3

On the undersideof the sporophyte‘sreproductive leavesare spots called sori.Each sorus is acluster of sporangia.

6

A zygote develops into a newsporophyte, and the young plantgrows out from an archegoniumof its parent, the gametophyte.

5

MEIOSIS

Sporangium

Sporangium

Maturesporophyte

Newsporophyte

Zygote

FERTILIZATION

Archegonium

Egg

Haploid (n)Diploid (2n)

Spore Younggametophyte

Fiddlehead

Antheridium

Sperm

Gametophyte

Key

Sorus

Figure 29.12


• Vascular plants have two types of vascular tissue (Xylem and phloem)

• Xylem

– Conducts most of the water and minerals

– Includes dead cells called tracheids

• Phloem

– Distributes sugars, amino acids, and other organic products

– Consists of living cells


Evolution of Roots

• Roots

– Are organs that anchor vascular plants

– Enable vascular plants to absorb water and nutrients from the soil

– May have evolved from subterranean stems


Evolution of Leaves

• Leaves

– Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis

• Leaves are categorized by two types

– Microphylls, leaves with a single vein

– Megaphylls, leaves with a highly branched vascular system


• According to one model of evolution

– Microphylls evolved first, as outgrowths of stems

Vascular tissue

Microphylls, such as those of lycophytes, may have originated as small stem outgrowths supported by single, unbranched strands of vascular tissue.

(a) Megaphylls, which have branched vascular systems, may have evolved by the fusion of branched stems.

(b)

Figure 29.13a, b


Sporophylls and Spore Variations

• Sporophylls

– Are modified leaves with sporangia

• Most seedless vascular plants

– Are homosporous, producing one type of spore that develops into a bisexual gametophyte


• All seed plants and some seedless vascular plants

– Are heterosporous, having two types of spores that give rise to male and female gametophytes


Classification of Seedless Vascular Plants

• Seedless vascular plants form two phyla

– Lycophyta, including club mosses, spike mosses, and quillworts

– Pterophyta, including ferns, horsetails, and whisk ferns and their relatives

• Ferns

– Are the most diverse seedless vascular plants


• The general groups of seedless vascular plants

LYCOPHYTES (PHYLUM LYCOPHYTA)

PTEROPHYTES (PHYLUM PTEROPHYTA)

WHISK FERNS AND RELATIVES HORSETAILS FERNS

Isoetesgunnii,a quillwort

Selaginella apoda,a spike moss

Diphasiastrum tristachyum, a club moss

Strobili(clusters ofsporophylls)

Psilotumnudum,a whiskfern

Equisetumarvense,fieldhorsetail

Vegetative stem

Strobilus onfertile stem

Athyrium filix-femina, lady fern

Figure 29.14


The Significance of Seedless Vascular Plants

• The ancestors of modern lycophytes, horsetails, and ferns

– Grew to great heights during the Carboniferous, forming the first forests

• The growth of these early forests

– May have helped produce the major global cooling that characterized the end of the Carboniferous period

– Decayed and eventually became coal


• Seeds changed the course of plant evolution

– Enabling their bearers to become the dominant producers in most terrestrial ecosystems

Figure 30.1


• The reduced gametophytes of seed plants are protected in ovules and pollen grains

• In addition to seeds, the following are common to all seed plants

– Reduced gametophytes

– Heterospory

– Ovules

– Pollen


Advantages of Reduced Gametophytes

• The gametophytes of seed plants

– Develop within the walls of spores retained within tissues of the parent sporophyte


• Gametophyte/sporophyte relationships

Figure 30.2a–c

Sporophyte dependent on gametophyte

(mosses and other bryophytes).

(a) Large sporophyte and small, independent gametophyte (ferns and other seedless

vascular plants).

(b)

Microscopic femalegametophytes (n) in

ovulate cones(dependent)

Sporophyte (2n),the flowering plant

(independent)

Microscopic malegametophytes (n)inside these parts

of flowers(dependent)

Microscopic malegametophytes (n)

in pollen cones(dependent) Sporophyte (2n)

(independent)

Microscopic femalegametophytes (n)inside these parts

of flowers(dependent)

Reduced gametophyte dependent on sporophyte (seed plants: gymnosperms and angiosperms).

(c)

Gametophyte(n)

Gametophyte(n)

Sporophyte(2n)

Sporophyte(2n)


Heterospory: The Rule Among Seed Plants

• Seed plants evolved from plants that had megasporangia

– Which produce megaspores that give rise to female gametophytes

• Seed plants evolved from plants that had microsporangia

– Which produce microspores that give rise to male gametophytes


Ovules and Production of Eggs

• An ovule consists of

– A megasporangium, megaspore, and protective integuments

Figure 30.3a

(a) Unfertilized ovule. In this sectional view through the ovule of a pine (a

gymnosperm), a fleshy megasporangium is surrounded by a

protective layer of tissue called an integument. (Angiosperms have two

integuments.)

Integument

Spore wall

Megasporangium(2n)

Megaspore (n)


Pollen and Production of Sperm

• Microspores develop into pollen grains

– Which contain the male gametophytes of plants

• Pollination

– Is the transfer of pollen to the part of a seed plant containing the ovules


• If a pollen grain germinates

– It gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule

Figure 30.3b

(b) Fertilized ovule. A megaspore develops into a multicellular female gametophyte. The micropyle,the only opening through the integument, allows

entry of a pollen grain. The pollen grain contains amale gametophyte, which develops a pollen tube

that discharges sperm.

Spore wall

Male gametophyte(within germinating

pollen grain) (n)

Femalegametophyte (n)

Egg nucleus (n)

Dischargedsperm nucleus (n)

Pollen grain (n)Micropyle


• Pollen, which can be dispersed by air or animals

– Eliminated the water requirement for fertilization


The Evolutionary Advantage of Seeds

• A seed

– Develops from the whole ovule

– Is a sporophyte embryo, along with its food supply, packaged in a protective coat

Figure 30.3c

Gymnosperm seed. Fertilization initiatesthe transformation of the ovule into a

seed,which consists of a sporophyte embryo, a

food supply, and a protective seed coat derived from the integument.

(c)

Seed coat(derived fromIntegument)

Food supply(female

gametophytetissue) (n)

Embryo (2n)(new sporophyte)


• Gymnosperms bear “naked” seeds, typically on cones

• Among the gymnosperms are many well-known conifers

– Or cone-bearing trees, including pine, fir, and redwood


• The gymnosperms include four plant phyla

– Cycadophyta

– Gingkophyta

– Gnetophyta

– Coniferophyta


• Exploring Gymnosperm Diversity

Figure 30.4

Gnetum

Ephedra

Ovulate cones

Welwitschia

PHYLUM GNETOPHYTA

PHYLUM CYCADOPHYTA PHYLUM GINKGOPHYTA

Cycas revoluta


• Exploring Gymnosperm Diversity

Figure 30.4

Douglas fir

Pacificyew

Common juniper

Wollemia pine

Bristlecone pine Sequoia

PHYLUM CYCADOPHYTA


Gymnosperm Evolution

• Fossil evidence reveals that by the late Devonian

– Some plants, called progymnosperms, had begun to acquire some adaptations that characterize seed plants

Figure 30.5


• Gymnosperms appear early in the fossil record

– And dominated the Mesozoic terrestrial ecosystems

• Living seed plants

– Can be divided into two groups: gymnosperms and angiosperms


A Closer Look at the Life Cycle of a Pine

• Key features of the gymnosperm life cycle include

– Dominance of the sporophyte generation, the pine tree

– The development of seeds from fertilized ovules

– The role of pollen in transferring sperm to ovules


Figure 30.6

Ovule

Megasporocyte (2n)

Integument

Longitudinalsection of

ovulate cone

Ovulatecone

Pollencone

Maturesporophyte

(2n)

Longitudinalsection of

pollen cone

Microsporocytes(2n)

Pollengrains (n)

(containing malegametophytes)

MEIOSIS

Micropyle

Germinatingpollen grain

Megasporangium

MEIOSIS

SporophyllMicrosporangium

Survivingmegaspore (n)

Germinatingpollen grain

ArchegoniumIntegumentEgg (n)

Femalegametophyte

Germinatingpollen grain (n)

Dischargedsperm nucleus (n)

Pollentube

Egg nucleus (n)FERTILIZATION

Seed coat(derived from

parentsporophyte) (2n)

Food reserves(gametophyte

tissue) (n)

Embryo(new sporophyte)

(2n)

Seeds on surfaceof ovulate scale

Seedling

Key

Diploid (2n)Haploid (n)

• The life cycle of a pine

A pollen cone contains many microsporangia held in sporophylls. Each microsporangium

contains microsporocytes (microspore mothercells). These undergo meiosis, giving rise to

haploid microspores that develop into pollen grains.

3

In mostconifer species,

each tree hasboth ovulate

and pollencones.

1

A pollen grainenters throughthe micropyle

and germinates,forming a pollentube that slowly

digeststhrough the

megasporangium.

4

While thepollen tube

develops, themegasporocyte

(megasporemother cell)

undergoes meiosis,producing four

haploid cells. Onesurvives as amegaspore.

5

The female gametophytedevelops within the megaspore

and contains two or threearchegonia, each with an egg.

6

By the time the eggs are mature,two sperm cells have developed in the

pollen tube, which extends to thefemale gametophyte. Fertilization occurs

when sperm and egg nuclei unite.

7

Fertilization usually occurs more than a year after pollination. All eggs

may be fertilized, but usually only one zygote develops into an embryo. The

ovule becomes a seed, consisting of an embryo, food supply, and seed coat.

8

An ovulate cone scale has twoovules, each containing a mega-

sporangium. Only one ovule is shown.

2


• The reproductive adaptations of angiosperms include flowers and fruits

• Angiosperms

– Are commonly known as flowering plants

– Are seed plants that produce the reproductive structures called flowers and fruits

– Are the most widespread and diverse of all plants


Characteristics of Angiosperms

• The key adaptations in the evolution of angiosperms

– Are flowers and fruits


Flowers

• The flower

– Is an angiosperm structure specialized for sexual reproduction


• A flower is a specialized shoot with modified leaves

– Sepals, which enclose the flower

– Petals, which are brightly colored and attract pollinators

– Stamens, which produce pollen

– Carpels, which produce ovules

Figure 30.7

Anther

Filament

Stigma

Style

Ovary

Carpel

Petal

ReceptacleOvule

Sepal

Stamen


Fruits

• Fruits

– Typically consist of a mature ovary

Figure 30.8a–e

(b) Ruby grapefruit, a fleshy fruitwith a hard outer layer andsoft inner layer of pericarp

(a) Tomato, a fleshy fruit withsoft outer and inner layers

of pericarp

(c) Nectarine, a fleshyfruit with a soft outerlayer and hard inner

layer (pit) of pericarp

(e) Walnut, a dry fruit that remains closed at maturity

(d) Milkweed, a dry fruit thatsplits open at maturity


• Can be carried by wind, water, or animals to new locations, enhancing seed dispersal

Figure 30.9a–c

Wings enable maple fruits to be easily carried by the wind.

(a)

Seeds within berries and other edible fruits are often dispersed

in animal feces.

(b)

The barbs of cockleburs facilitate seed dispersal by

allowing the fruits to “hitchhike” on animals.

(c)


The Angiosperm Life Cycle

• In the angiosperm life cycle

– Double fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovule

– One sperm fertilizes the egg, while the other combines with two nuclei in the center cell of the female gametophyte and initiates development of food-storing endosperm

• The endosperm

– Nourishes the developing embryo


• The life cycle of an angiosperm

Figure 30.10

Key

Mature flower onsporophyte plant

(2n)

Ovule withmegasporangium (2n)

Female gametophyte(embryo sac)

Nucleus ofdevelopingendosperm

(3n)

Dischargedsperm nuclei (n)

Pollentube

Male gametophyte(in pollen grain)

Pollentube

Sperm

Survivingmegaspore

(n)

Microspore (n) Generative cell

Tube cell

Stigma

OvaryMEIOSIS

MEIOSIS

Megasporangium(n)

Pollengrains

EggNucleus (n)

Zygote (2n)

Antipodal cellsPolar nuclei

SynergidsEgg (n)

Embryo (2n)

Endosperm(food

Supply) (3n)

Seed coat (2n)

Seed

FERTILIZATION

Haploid (n)

Diploid (2n)

Anther

Sperm(n)

Pollentube

Style

Microsporangium

Microsporocytes (2n)

GerminatingSeed

Anthers contain microsporangia.Each microsporangium contains micro-

sporocytes (microspore mother cells) thatdivide by meiosis, producing microspores.

1 Microspores form

pollen grains (containingmale gametophytes). Thegenerative cell will divide

to form two sperm. Thetube cell will produce the

pollen tube.

2

In the megasporangiumof each ovule, the

megasporocyte divides bymeiosis and produces four

megaspores. The survivingmegaspore in each ovule

forms a female gametophyte(embryo sac).

3

After pollina-tion, eventually

two sperm nucleiare discharged in

each ovule.

4

Double fertilization occurs. One spermfertilizes the egg, forming a zygote. The

other sperm combines with the two polarnuclei to form the nucleus of the endosperm,

which is triploid in this example.

5

The zygotedevelops into an

embryo that ispackaged alongwith food into aseed. (The fruit

tissues surround-ing the seed are

not shown).

6

When a seedgerminates, the

embryo developsinto a mature

sporophyte.

7


Angiosperm Evolution

• Clarifying the origin and diversification of angiosperms

– Poses fascinating challenges to evolutionary biologists

• Angiosperms originated at least 140 million years ago

– And during the late Mesozoic, the major branches of the clade diverged from their common ancestor


Fossil Angiosperms• Primitive fossils of 125-million-year-old

angiosperms

– Display both derived and primitive traits

Figure 30.11a, b

Carpel

Stamen

Archaefructus sinensis, a 125-million-year-old fossil.

(a)

Artist’s reconstruction of Archaefructus sinensis

(b)

5 cm


An “Evo-Devo” Hypothesis of Flower Origins

• In hypothesizing how pollen-producing and ovule-producing structures were combined into a single flower

– Scientist Michael Frohlich proposed that the ancestor of angiosperms had separate pollen-producing and ovule-producing structures


Angiosperm Diversity

• The two main groups of angiosperms

– Are monocots and eudicots

• Basal angiosperms

– Are less derived and include the flowering plants belonging to the oldest lineages

• Magnoliids

– Share some traits with basal angiosperms but are more closely related to monocots and eudicots


• Exploring Angiosperm Diversity

Figure 30.12

Amborella trichopoda Water lily (Nymphaea “Rene Gerard”)

Star anise (Illicium floridanum)

BASAL ANGIOSPERMS

HYPOTHETICAL TREE OF FLOWERING PLANTS

MAGNOLIIDS

Am

bo

rell

a

Wat

er l

ilie

s

Sta

r an

ise

and

rel

ativ

es

Mag

no

liid

s

Mo

no

cots

Eu

dic

ots

Southern magnolia (Magnoliagrandiflora)


• Exploring Angiosperm Diversity

Figure 30.12

Orchid(Lemboglossum

fossii)

MonocotCharacteristics

Embryos

Leafvenation

Stems

Roots

Pollen

Flowers

Pollen grain withone opening

Root systemUsually fibrous(no main root)

Vascular tissuescattered

Veins usuallyparallel

One cotyledon Two cotyledons

Veins usuallynetlike

Vascular tissueusually arranged

in ring

Taproot (main root)usually present

Pollen grain withthree openings

Zucchini(Cucurbita

Pepo), female(left) and

male flowers

Pea (Lathyrus nervosus,

Lord Anson’sblue pea), a

legume

Dog rose (Rosa canina), a wild rose

Pygmy date palm (Phoenix roebelenii)

Lily (Lilium“Enchant-

ment”)

Barley (Hordeum vulgare), a grass

Anther

Stigma

Californiapoppy

(Eschscholziacalifornica)

Pyrenean oak(Quercus

pyrenaica)

Floral organsusually in

multiples of three

Floral organs usuallyin multiples of

four or fiveFilament Ovary

EudicotCharacteristics

MONOCOTS EUDICOTS


Evolutionary Links Between Angiosperms and Animals

• Pollination of flowers by animals and transport of seeds by animals

– Are two important relationships in terrestrial ecosystems

Figure 30.13a–c

(a) A flower pollinated by honeybees. This honeybee is

harvesting pollen and nectar (a sugary solution secreted by

flower glands) from a Scottish broom flower. The flower has a tripping mechanism that arches

the stamens over the beeand dusts it with pollen, some ofwhich will rub off onto the stigmaof the next flower the bee visits.

(c) A flower pollinated by nocturnal animals. Some angiosperms, such as this cactus, depend mainly on

nocturnal pollinators, including bats. Common adaptations of such plants include large, light-colored,

highly fragrant flowers that nighttime pollinators can locate.

(b) A flower pollinated by hummingbirds.The long, thin beak and tongue of this

rufous hummingbird enable the animal to probe flowers that secrete nectar deep within floral tubes. Before the hummer leaves, anthers will dust its beak and

head feathers with pollen. Many flowers that are pollinated by birds are red or

pink, colors to which bird eyes are especially sensitive.


Products from Seed Plants

• Humans depend on seed plants for

– Food

– Wood

– Many medicines

Table 30.1


Threats to Plant Diversity

• Destruction of habitat

– Is causing extinction of many plant species and the animal species they support

Documents

29 plants ii text