origin of seeds late devonian, 360 mya seed = embryo + food + protective coat advantage: protection...
TRANSCRIPT
origin of seeds
• late Devonian, 360 mya• seed = embryo + food + protective
coat• advantage:• protection from desiccation• wait for good conditions• own food to get started
reproductive adaptations of seed plants
• gametophytes smaller• female gametophyte retained on
parent sporophyte• male gametophyte transports
sperm• water not required for fertilization• seeds are means of dispersal
2 types of seed plants
• 1. Gymnosperms “naked seeds”– seeds exposed (on cones)
• 2. Angiosperms “vessel seeds”– seeds inside fruits
gymnosperm life cycle
• heterospory w/2 types of cones:• 1) small cones w/microsporangia• microspores develop into pollen• pollen = immature male gametophyte• reduced in size—no antheridia• whole gametophyte travels (pollination)• fertilization without water
gymnosperm life cycle
• 2) large cones have megasporangia• megasporangium protected by
integuments• ovule = megasporangium +
integuments• seed = mature ovule• integuments become seed coat• megaspore stays in megasporangium
gymnosperm seedexample: Pine
•
embryo (2n)
female gametophyte (n)
seed coat (2n)
embryo is new sporophytefemale gametophyte is stored food
pine life cycle
• 3 years to make seed
• pollination & seed dispersal by wind
gymnosperms--cycads
• prominent w/dinosaurs• today 11 genera 130 sp • tough leaves• look like ferns• but have cones w/seeds• roots assoc. w/cyanobacteria• plants defended by toxic compounds
gymnosperms--Ginkgo
• only genus in group Ginkgophyta• thought extinct• good urban tree• stinky seeds• veins dichotomously
branched
gymnosperms--Gnetophyta3 very different genera, 70 sp
• 1) Ephedra • desert• “mormon tea”• ephedrine
gymnosperms--Gnetophyta
• 2) Gnetum• tropical vine• flat leaves
gymnosperms--Gnetophyta
• 3) Welwitschia mirabilis• Namib desert, 2 leaves, ~1500 yrs
old
gymnosperms--conifers
• very successful. 50 genera, 550 sp• most evergreen• needle leaves adapted for drought
– small surface area, thick cuticle– stomata sunken in valleys
Taxodium distichum bald cypress
Heron Pond, Cache River State Natural Area , S IL
deciduous
relative of redwoods & sequoias
•oldest plants•Bristlecone Pines 4600 years old
gymnosperms--conifers
• most massive plants• Giant Sequoia 26 m circumference,
(8.3 m diameter!) 3000 years old• tallest living plants• Coast Redwoods 367 ft tall,
600-800 yrs old• Watterson Towers only 281 ft
types of growth
• primary growth (up or down):shoot & root apical meristems
• secondary growth (out): cambium— meristem makes shoot & root thick
secondary growth
• vascular cambium:– xylem to inside, phloem to outside
• wood is secondary xylem• cork cambium makes cork to
outside• bark = cork + phloem
– everything outside of vascular cambium
tree rings: seasonal changes in xylem cell size
dendrochronology
• tree rings date historical events• similar patterns in neighboring trees• overlap rings: to get complete
record• need consistent rings• regular wet &
dry cycles
Plant tissue culture Fig 38.14
• plant cells are totipotent:– any cell can grow into whole new plant
• new plant is clone (same genes)• examples: leaf cutting, Wollemi Pine• callus = undifferentiated tissue (wound) • develops roots and shoots• balance of hormones required• biotech: insert gene into callus