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Seed Plants I: Seed Plants without Flowers (Gymnosperms) (Division…
Seed Plants I: Seed Plants without Flowers (Gymnosperms)
Gymnosperms
have "naked ovules"
4 divisions of living
Cycadophyta
Coniferophyta
Ginkgophyta
Gnetophyta
ovules located on flat sporophylls (ex.=pine cones)
Division Progymnospermophyta
progymnosperms
extinct
evolution of vascular cambium
no seeds or ovule precursors
orders
Archaeopteridales
heterosporous reproduction
planated branch systems with spirally arranged simple leaves
seeds not produced
Aneurophytales
1* xylem was protostele
vascular cambium and 2* growth
evolution of seeds
magasporangium surrounded by integument
hole in integument called micropyle that allowed sperm to swim to egg
pollen chamber at top of megasporangium
one viable megaspore and three aborted
Division Pteridospermophyta
seed ferns
woody plants with fern-like foliage and seeds instead of sori
rays in wood were many cells thick
distinctive radial plates in cortex
Division Cycadophyta
#
Cycads
trunk w/ bark and persistent leave bases
seed cones and pollen cones on separate plants
stems similar to seed ferns
#
mostly tropical
Division Coniferophyta
#
conifers
have both pollen cones and seed cones
(ex.) pines
long shoots= where tiny papery leaves occur
short shoots=produce needle leaves
simple cones
pollen cones; single, short unbranched axis
compound cones
seed cones
consist of shoot with axillary buds
short axis bears cone bracts (instead of sporophylls)
each bract has axillary bud that bears megasporophylls
in modern conifers, megasporophylls fuse to form an ovuliferous scale
fertilization
zygote does not immediately form embryo
suspensor pushes other cells into megagametophyte
cells called proembryo develop into embryo
Division Cycadeoiophyta
Cycadeoids
all extinct
almost identical to cycads
differ from cycads in differentiation of stomatal complexes and leaf trace organization
Division Ginkgophyta
#
Maidenhair tree
contains single living species
stout trunk w/ many branches
wood lacks vessels & axial parenchyma
Division Gnetophyta
three groups of enigmatic plants
gymnosperms with vessels in their wood (unusual)
pollen cones compound
