Duckweed, Seed’s Structure - General Botany | BSB 251, Study notes of Biology

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Botany BSB 251Botany BSB 251

T. Michael Dodson T. Michael Dodson

http://www.okpond.com/images/aquatic%20veg%20pic/duckweed.jpeg

DuckweedDuckweed

http://botit.botany.wisc.edu/images/veg/Wetlands_I_Plants/Lemna_minor_Duckweed_VK.html http://commons.wikimedia.org/wiki/File:Alligator_(Alligator_mississippiensis)_im_Duckweed.jpg

SeedsSeeds

• StructureStructure

• (^) Seed Coat (testa) -Seed Coat (testa) - formed from theformed from the

integuments integuments

• (^) EndospermEndosperm – nutritive tissue/food storage– nutritive tissue/food storage
• (^) Embryo sporophyteEmbryo sporophyte
• (^) HilumHilum – place where funiculus attached– place where funiculus attached
• (^) MicropyleMicropyle – opening of ovule– opening of ovule

SeedsSeeds

• (^) Embryo sporophyteEmbryo sporophyte
  • (^) CotyledonsCotyledons - Food storage organs that function as- Food storage organs that function as first seed leaves. (embryonic leaves) first seed leaves. (embryonic leaves)
  • (^) Hypocotyl (root axis)Hypocotyl (root axis) - Stem below attachment point.- Stem below attachment point. (with root apical meristem) (with root apical meristem)
  • (^) EpicotylEpicotyl (shoot axis)(shoot axis) - Stem above cotyledon. (with- Stem above cotyledon. (with shoot apical meristem) shoot apical meristem)
  • (^) PlumulePlumule - Embryo shoot.- Embryo shoot.
  • (^) RadicleRadicle - Stem tip- Stem tip developing into a root. developing into a root.

SeedsSeeds

• Structure of CaryopsisStructure of Caryopsis

• (^) Scutellum (cotyledon)Scutellum (cotyledon)
• (^) Coleorhiza – sheathes radicleColeorhiza – sheathes radicle
• (^) Coleoptile – sheathes plumuleColeoptile – sheathes plumule

GerminationGermination

• GerminationGermination is the beginning or resumptionis the beginning or resumption

of seed growth. of seed growth.

• (^) Seed must be viable.Seed must be viable.
  • (^) Some require period of dormancy.Some require period of dormancy.
    • (^) ScarificationScarification
    • (^) inhibitorsinhibitors
  • (^) After RipeningAfter Ripening
• (^) Favorable Environmental FactorsFavorable Environmental Factors
  • (^) Imbibe waterImbibe water

LongevityLongevity

• (^) Viability of most seeds is significantly extendedViability of most seeds is significantly extended when the seeds are stored under conditions of when the seeds are stored under conditions of low temperatures and kept dry. low temperatures and kept dry. - (^) Cucurbitaceae – viable for severalCucurbitaceae – viable for several

years years

• (^) Liliaceae – 2-3 yearsLiliaceae – 2-3 years
• (^) A few species produce seeds withA few species produce seeds with

no period of dormancy. no period of dormancy.

• (^) ViviparyVivipary