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CHAPTER 29: PLANTS
LECTURE OUTLINE
29.1 Evolutionary History of Plants
Plants are vital to human survival. Our dependence on them is nothing less than absolute. The
evolution of plants is marked by four events: protection of a multicellular embryo, evolution of
vascular tissue, evolution of the seed, and evolution of the flower.
Alternation of Generations
All plants have a life cycle that includes alternation of generations. In this life cycle, two
multicellular individuals alternate, each producing the other. The two individuals are the
sporophyte (diploid) and the gametophyte (haploid). Plants differ as to which generation
is dominant or more conspicuous.
29.2 Nonvascular Plants
The nonvascular plants lack vascular tissue. They do not have true roots, stems, and leaves. The
gametophyte is the dominant generation.
Liverworts
Liverworts exist in two types: those with a flat, lobed thallus, and those that are leafy.
Mosses
Mosses live in a variety of environments. Most can reproduce asexually by
fragmentation. The life cycle of a moss is shown in Figure 29.5.
Adaptations and Uses of Nonvascular Plants
Mosses are capable of living on stone walls and on rocks. Accumulated moss that does
not decay in areas such as bogs, called peat or bog moss, can be used as a fuel.
29.3 Seedless Vascular Plants
Vascular tissue in these plants consists of xylem, which conducts water and minerals up from the
soil, and phloem, which transports organic nutrients from one part of the plant to another.
Vascular plants usually have true roots, stems, and leaves. The sporophyte is the dominant
generation. Some vascular plants do not produce seeds.
Whisk Ferns
The resemblance of its life cycle to that of a fern suggests that the whisk fern is actually a
fern devoid of leaves and roots.
Club Mosses
The club mosses are common in moist woodlands of the temperate zone, where they are
known as ground pines. The majority of club mosses live in the tropics and subtopics,
where many of them are epiphytes.
Horsetails
Horsetails thrive in moist habitats around the globe. The stems of horsetails are tough
and rigid because of silica deposited in their cell walls.
Ferns
Ferns are the largest group of plants other than the flowering plants, and they display
great diversity in form and habitat.
Life Cycle, Adaptations, and Uses of Ferns
The life cycle of a typical fern is shown in Figure 29.11. People use ferns in a
decorative manner. Wood from tropical tree ferns often serves as building
material.
29.4 Seed Plants
The gymnosperms and angiosperms are seed plants. Seeds contain a sporophyte embryo and
stored food within a protective seed coat. The survival value of seeds largely accounts for the
dominance of seed plants today. Seed plants are heterosporous, meaning that they have two types
of spores, and they produce two kinds of gametophytes.
Gymnosperms
The life cycle of a gymnosperm is shown in Figure 29.12. Most gymnosperms are conebearing plants.
Conifers
The better-known gymnosperms are evergreen, cone-bearing trees called
conifers.
Adaptations and Uses of Conifers
Conifers are adapted to cold, dry weather. Conifers supply much of the
wood used to construct buildings and to manufacture paper.
Other Gymnosperms
Cycads have large, finely divided leaves growing in clusters at the top of the
stem. Ginkgoes are represented today by only one surviving species, the
maidenhair tree. The three living genera of gnetophytes don’t resemble one
another.
Angiosperms
Angiosperms, the flowering plants, are an exceptionally large and successful group of
plants. The seed develops from an ovule within an ovary, which becomes a fruit.
Therefore, angiosperms produce covered seeds.
Monocots and Eudicots
Most flowering plants belong to one of two classes: monocots or eudicots.
The Flower
The parts of a flower include the sepals, petals, stamens, and carpels, attached to
the receptacle in whorls. The stamen consists of an anther and a filament. The
carpel consists of the ovary, style, and stigma.
Life Cycle, Adaptations, and Uses of Flowering Plants
The life cycle of a flowering plant is shown in Figure 29.17. Sexual
reproduction in flowering plants is dependent on the flower, which
produces both pollen and seeds. Some species have windblown pollen,
and others rely on pollinators such as bees, wasps, flies, butterflies,
moths, beetles, and even bats. Fruits aid in the dispersal of seeds