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21-1 Plants Invade the Land

Section Objectives

Describe some of the adaptations to survive on land.

First Land Plants

Entire lives were designed around an aquatic environment. All process that ensured survival took place in water.
Fossil record tells little of the early stages of development.
Long slow process. Two groups evolved 450 to 500 million years ago.
One group developed into the Phylum Bryophyta (brigh-oh-FIGHT-uh)
Includes the mosses, liverworts, and hornworts.
Other group evolved into the Phylum Tracheophyta (tray-kee-oh-FIGHT-uh)
Includes ferns and the rest of the higher plants.

Demands of Life on Land

Advance	Green Algae	Bryophytes	Tracheophytes
Development of the root-stem-leaf vascular system	nonvascularized body (thallus) that may be variously shaped no leaves, shoots, or roots	no vascular system leaflike structures are present, but lack any vascular tissue	early vascular plants are naked, rootless vascularized stems later vascular plants develop vascularized leaves, then roots
Reduction in the size of the gametophyte generation	wide range of life cycles, some gametophyte dominant, others sporophyte dominant	sporophyte generation dependant on gametophyte generation for food; gametophyte is free-living and photosynthetic	progressive reduction in size and complexity of the gametophyte generation, leading to its complete dependence on the sporophyte for food in angiosperms, 3 celled male gametophyte and a (usually) 8 celled female gametophyte
Development of seeds in some vascular plants	no seeds	no seeds	seed plants retain the female gametophyte on the sporophyte
Spores/Pollen	spores for resisting environmental degradation	Spores that germinate into the gametophyte generation	Spores that germinate into the gametophyte generation or spores that have the gametophyte generation develop within themselves

Some of the requirements for living on land.
Land plant cells need a constant supply of water. Delivered to all their cells.
Land plants must protect the plant from evaporation to the atmosphere.
That part of the land plant making food must be exposed to as much sunlight as possible.
Land plants need rigid support to hold leaves up to the sun.
Land plants take up water and nutrients in roots, but make food in leaves.
Land plants must transport water and nutrients upward and products of photosynthesis downward.
Land plants must exchange water and carbon dioxide with the environment without losing too much water in the process.
Land plants must be able to reproduce in environments that lack standing water in which sperm may swim.
Land plants young zygote must be protected from drying out.
Bryophytes have partially solved these problems, but must remain moist most of the time.
Tracheophytes have evolved towards complete independence from water.

21-2 The Mosses, Liverworts and Hornworts

Section Objectives

Identify the characteristics of the three main groups of bryophytes
Describe some adaptations shown by the Bryophytes that enable them to survive on land.
Identify patterns of reproduction in Bryophytes.

Have life cycles that involve alternation of generation between a haploid gametophyte and a diploid sporophyte.

Need water for reproduction.

Most abundant in swamps, marshes, near streams, and in rain forests.

Some are miniature evergreen trees other a soft green carpet.

Moss plants you observe in the woods are mostly haploid moss gametophytes growing close together.

Has thin upright shoot, that looks like a stem with tiny leaves.

Since it lacks tubes that conduct water and other substances, these are NOT true leaves and stems.

From the base of the shoot grow a number of thin tiny branches called rhizoids that penetrate into the ground and act like roots to securely anchor the plant.

Physical Characteristic of Bryophytes

Lack water conducting tubes that are found in higher plants
Water passes from cell to cell by osmosis in Bryophytes.
This works well for short distances. Keep them from growing tall.
Lack a protective surface covering to keep water from evaporating from their cells.
If surrounding air is dry, they lose water rapidly.
Lack true roots, which collect and transport nutrients & water.
Have rhizoids that anchor them to the ground.
Have motile sperm that must swim through water to fertilize eggs.

Alternation of Generation

At the tip of the sporophyte are reproductive structures, similar to algae.
One structure called the antheridium (an-ther-IHD-ee-uhm) produces sperm cells.
Another structure called the archegonium (ahr-kuh-GOH-nee-uhm) produces eggs.
Reproductive of mosses are designed to protect the gametes from drying out.
Some species of mosses have both types of reproductive structures on one gametophyte.
Mosses can sexually reproduce only when standing in water. Sperm must swim.
When zygotes germinates, it produces a diploid sporophyte.
As it grows, sporophyte is supplied with water and nutrients by the gametophyte.
Moss sporophytes cannot live independently of gametophyte
Mature sporophyte has a foot stuck in the gametophyte
Haploid spores are produced by meiosis.
Spores ripen and dispersed by wind and water.
Spore lands, germinates and grows into a tangled mass of green filaments called protonema.
As it grows it forms rhizoids that grow into the ground and shoots that grow into the air.

21-3 The Ferns and the First Vascular Plants

Section Objectives

Recognize the importance of vascular tissue to land plants.
Identify the characteristics of club mosses and horsetails.
Discuss ways in which ferns resemble other land plants.
Describe alternation of generations in ferns.

Members of the phylum Tracheophyta are "true" land plants. They have freed themselves from dependence on wet environments.

Vascular tissue are specialized tissue for the transportation of nutrients and the products of photosynthesis.

Xylem tissue is associated with the movement of water.

Phloem tissue is associated with the movement of nutrients and the products of photosynthesis.

Tracheid cells carry water from roots in the soil to the leaves in the air. (Phylum named after these cells)
Have thick, strong cell walls that strengthen stems and help stand up against the pull of gravity
True roots have vascular tissue gathered in a central area of the root that is called the vascular cylinder.
True leaves contain one or more bundles of vascular tissue gathered into veins.
True leaves have a waxy covering called a cuticle.

Club Moss and Horsetails

Are the only living descendants of the ancient types of land plants

Lycopodium (ligh-koh-POH-dee-uhm) the common club moss looks like a miniature pine tree. (9cm)

Equisetium (ehk-wih-SEET-uhm) grows about 1 meter high.
Commonly called horsetail, or scouring rush.
Stems contain crystals of silica, abrasive.
Have true leaves, stems, and roots.
Leaves of horsetails are arranged in whorls at joints along the stem.

Physical Characteristics of Ferns

Have true vascular tissue, strong roots, creeping or underground stems called rhizomes, and large leaves called fronds.
Most abundant in wet, or at least seasonally wet, habitat around the world.

Alternation of Generation in Ferns

Plants recognized as ferns are diploid sporophytes.
Sexual reproduction requires the presence of standing water for the motile sperm to swim.

Fern sporophytes produce haploid spores on the underside of their fronds.
Spores are produced inside tiny containers called sporangia.
Sporangia group in large clusters called sori.
When conditions are right the spores germinate into haploid gametophytes.
First grow rootlike rhizoid, then into heartshaped green structure called a prothallium (proh-THAL-ee-uhm).
Antheridia and archegonia, which produce gametes, are found on the underside of the prothallium.
When the antherium are mature, sperms are released.
Fertilization can occur when both the ground and the prothallium are covered with a thin film of water.
Diploid zygote produced by fertilization immediately begins to grow into a new sporophyte plant.
Sporophyte plant can live for several years. Rhizomes survive winter and sprout new fronds each spring.

21-4 Where Mosses and Ferns Fit into the World

Section Objective

Describe ways in which certain characteristics of mosses make these plants useful to people.
List ways in which ferns are used by people.

Are well adapted to certain environments.
Some are grown in gardens for decorative purposes.
Mosses are frequently added to garden soils.
Peat moss and/or sphagnum moss.
Were used by Indians to treat burns and bruises.
Sphagnum moss is used to add flavor to Scotch whiskey
Few eaten by man.

LOWER VASCULAR PLANTS

All are Kingdom Planate.

All have Chlorophyll a & b, starch, and cellulose.

All are oogamous and sporic.

	WHISK FERNS	CLUB MOSSES	*Selaginella*	HORSETAILS	FERNS
DIVISION	Psilotophyta	Lycopodophyta	Lycopodophyta	Equisetophyta	Pteridophyta
EXAMPLES	Psilotum	Lycopodium	Selaginella	Equisetum	Pteridium
STEM	cylinder exarch radial	ribbons exarch amphiphloic	cylinder exarch radial	bundles endarch radial-reverse bicollateral	bundles mesarch amphiphloic (bicollateral)
"LEAF"	enation	microphyll	microphyll	microphyll	megaphyll
"ROOT"	rhizoid	root	root	root	root
SPORANGIUM	axil of enation; synangium	axil of microphyll; (strobilus)	axil of microphyll; strobilus	under sporangiophore; strobilus	underside of megaphyll; sori
SPORES	Homosporous Wind	Homosporous Wind	Heterosporous Wind	Homosporous Wall Elaters	Homosporous (Heterosporous) Annulus
GAMETOPHYTE	Heterotroph Fungi	Heterotroph Fungi	Heterotroph Stored matter	Autotroph	Autotroph
GAMETANGIA	All have archegonia (neck, venter) and antheridia (sterile jacket)
GAMETES	All have sessile egg and flagellate sperm