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CHAPTER 22: SEED PLANTS I: SEED PLANTS WITHOUT FLOWERS ("…
CHAPTER 22: SEED PLANTS I: SEED PLANTS WITHOUT FLOWERS ("GYMNOSPERMS")
Concepts
becoming seed plants
megaspore is retained
megagametophyte develops in sporangium
microspore transported by wind
not water
embryo uses capacity of previous sporophyte
lignophytes
woody plants with vascular cambium that divides longitudinally
spermatophytes
seed plants
gymnosperms
naked ovules
located on flat sporophylls
angiosperms
flowering plants
carpels
fruits
Division Pteridospermophyta: Seed Ferns
Seed Ferns (extinct)
woody plants with fern-like foliage that bore seeds
three-ribbed protostele
long-lived vascular cambium
longer and wide tracheids
manoxylic wood
soft, spongy, paranchymatous wood
leaves
similar to true ferns
bore seeds
megasporangium was large with vascular tissue
vascularized integument
Division Cycadeoidophyta: Cycadeoids
Cycadeoids (extinct)
almost identical to cycads
#
individual cones contain both microsporophylls and megasporophylls
Division Ginkgophyta: Maidenhair Tree
single extant species
Ginkgo biloba
looks like a large dicot tree
but coniferous wood
broad leaves like dicots
but dichotomously branched veins like seed ferns
short shoots and long shoots
reproduction is dioecious and gymnospermous
but no cones
Division Gnetophyta
Gnetum
vines and small shrubs with broad leaves
Ephedra
tough shrubs and bushes
Welwitschia mirabilis
short, wide stem with only two leaves
gymnosperms with vessels in wood
compound pollen cones and seed cones
spindle-shaped pollen
Division Progymnospermophyta: Progymnosperms
Progymnosperms (extinct)
megaphyllous leaves
vascular cambium
unlimited growth potential
produces secondary xylem and secondary phloem
cork cambium
no seeds
Aneurophytales
from shrubs to large trees
vascular cambium and secondary growth
protostele primary xylem
little webbing
not yet leaves
Archaeopteridales
trees
abundant wood and secondary phloem
siphonostele (pith)
spirally arranged simple leaves
megaphylls
heterosporous
terminal sporangia
megaspore released
Evolution of Seeds
integument
layer of tissue surrounding megasporangium
micropyle
hole that permits sperm
pollen chamber
space at top of megasporangium protected by telomes
microspores
pollen grains
Division Cycadophyta: Cycads
stout trunks with pinnately compound leaves
look like ferns or young palms
stem similar to seed ferns
#
only have small amount of wood
leaves do not bear ovules
seed cones and pollen cones instead
dioecious
pollen cone
microsporophyhlls with clusters of microsporangia
seed cones
pinnately compound megasporophylls
6-8 large ovules
Division Coniferophyyta: Conifers
moderate to gigantic trees
redwoods
pines
leaves
simple needles or scales
perennial
venation
simple
transfusion tissue
no vessels or sieve tubes
pollen cones and seed cones
Pines
#
Wood
monopidial
one main trunk bearing branches
wood is exclusively tracheids
annual rings
rays
resin canals
cork cambium
Shoots
long shoots
tiny papery leaves
short shoots
long needle leaves
in axils
Cone
pollen cones
simple cones
single short unbranched axis
bears microsporophylls
gametophytes shed as pollen
seed cones
compound cones
shot with axillary buds
bears cone bracts (leaves)
axillary bud
bears megasporophylls
fuse laterally forming ovuliferous scale
zygote
suspensor
pushes other cells deep into megagametophyte
proembryo
other cells
develop into enbryo
