§ Seeds can be found everywhere!
§ Gymnosperms - bear their seeds directly
in the surfaces of cones
► conifers such as pines and spruces
► cycads which are palmlike plants
► ginkgoes
► gnetophytes
§ Angiosperms - (flowering plants) bear
their seeds within a layer of tissue that protects the seed.
► grasses
► flowering trees and shrubs
► all wildflowers and cultivated flowers
Reproduction
Free From Water
§ Seed plants have alternation of generations but DO NOT require water for fertilization
of gametes
Cones
and Flowers
§ The gametophytes of seed plants grow and mature within the sporophytes structure
v Cones are the seed-bearing structures
of gymnosperms
v Flowers are the seed-bearing structures
of angiosperm
Pollen
§ A pollen grain contains the entire male
gametophyte
§ The pollen grain is carried to the female gametophyte by wind, insects,
birds, small animals, or sometimes even bats.
§ Pollination is the transfer of pollen from the male gametophyte to the female gametophyte.
Seeds
§ A seed is an embryo of a plant that is encased in a protective
covering and surrounded by a food supply.
§ An embryo is the early developmental stage of the sporophyte plant.
§ The seed coat surrounds and protects the embryo and keeps
the contents of the seed from drying out.
v Some seed coats are textured so they stick to fur.
v Some are contained in fleshy tissue that are eaten and dispersed
by animals
§ After fertilization, the zygote contained within a seed grows into
an embryo.
§ When the embryo begins to grow, it uses nutrients from the stored
food supply.
§ Seeds can survive droughts, bitter cold, or extreme heat and grow when conditions
are right.
Gymnosperms-Cone
Bearers
§ The most ancient surviving plant
§ All reproduce with seeds that are exposed or commonly known as the "naked seed" plants
Gnetophytes
§ The reproductive scales of these plants are clustered into cones.
§ Vascular system closely resembles those of angiosperms
v Ephedra is a genus of desert shrubs which is the source of the drug ephedrine a decongestant.
v Welwitschia has huge leathery leaves which spread across the ground and is found in the Namibian desert.
Cycads
§ Palmlike plants that reproduce with large cones
§ Huge forests of cycads thrived when dinosaurs roamed Earth
§ Now, they can be found growing in tropical and subtropical places such as Mexico,
the West Indies, Florida and parts of Asia, Africa and Australia
Ginkgoes
§ Today, only one species lives that being the Ginkgo
biloba
§ It may be one of the oldest seed plant species alive today.
§ Ginkgo trees were cultivated in China
and planted around temples.
§ They are now planted in urban settings because of their toughness and resistance to
air pollution.
Conifers
§ more than 500 species of conifers
§ Phylum includes pines, spruces, firs, cedars, sequoias, redwoods, and yews.
§ Some can live for more than 4000 years and grow to more than 100 meters in height.
Ecology
of Conifers
§ Thrive in a wide variety of habitats - on mountains, in sandy soil, and in cool, moist
areas such as the temperate rain forest of the Pacific Northwest.
§ Conifer leaves are adapted to dry conditions and are long and thin. (pine needles)
§ This unique shape reduces the surface area from which water can be lost to evaporation
§ The leaves also have a thick, waxy layer to conserve water
§ The openings of leaves that allow for gas exchange are located in cavities below the
surface to reduce water loss
§ Most conifers are "evergreens" because they retain their leaves all year long.
§ The needles remain on the plant for 2-14 years
§ As older needles fall off, they are replaced by new ones so the trees never become
bare.
