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Seed Plants
Chapter 27
Seeds are ‘better’ than spores
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Seed contains a multicellular young plant
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Seeds contain a food supply
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After germination the plant is nourished until selfsufficient
Seeds are protected by a seed coat
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Root, stem, and at least one leaf are already formed
Seeds live for extended periods at a reduced metabolism
until conditions for germination are adequate
Seed plants are the dominant plants in most
terrestrial ecosystems
Major characteristics of seed plants
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Vascular tissue: xylem and phloem
Alternation of generations
Two groups based on seed structures
Gymnosperms
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An ovary wall does NOT surround the ovule
Pine, spruce, fir, hemlock, gingko
Angiosperms
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Produce seeds within a flower/fruit
Very diverse group
Gymnosperms
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Name means ‘naked seed’
Seeds are totally exposed or carried on the
scales of cones
The ovary wall does not surround the ovule
Four phyla:
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Conifers
Ginkgo and cycads
Gnetopytes
Conifers
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Largest and most familiar group
Pines, spruces, firs, hemlocks
All are woody
Leaves are needles and usually evergreen
Most are monoecious
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Separate male and female reproductive parts (cones) on the
same plant
Wide range – from arctic to tropics
Used for building materials, resins, and
landscaping/decorating
Conifer species,
clockwise from
top-left:
Western red cedar,
Douglas fir, spruce,
and lodgepole pine.
The conifer life cycle
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Male cone – pollen cone
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Female cone – seed cone
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Produce pollen grains – each with 4 cells and large air sacs
Pollen grains are spread by wind
Larger and more noticeable
Pollination – occurs in the spring
Fertilization – occurs about 15 months after
pollination; seeds take another few months to mature
Other gymnosperms
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Cycads:
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Ginkgo:
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Most ancient species are now extinct
Dioecious – separate male and female plants
Only one living species
Leaf extract has been used to increase blood flow to the
brain and may aid memory
Gnetophytes:
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Have more efficient water conducting cells
Ephedrine – stimulates the heart and raises blood pressure
Clockwise from top left:
Cycad, gingko,
gnetophyte
Angiosperms
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Most successful plants today
Very important to humans
Divided into two classes:
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Monocots – have a single seed leaf
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Herbaceous
Narrow leaves with parallel veins
Flower parts in multiples of 3
Dicots – have two seed leaves
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Either herbaceous or woody
Broad leaves with net venation
Flower parts in multiples of 4 or 5