%here are t&o groups o# seed producing plants' gymnosperms and gymnosperms and angiosperms. angiosperms . •
"roduce seeds. (ascular tissue) xylem #or xylem #or &ater and mineral transport and phloem #or phloem #or dissolved sugars.
*ametophyte is very reduced and totally dependent on the sporophyte.
eterosporous) microspores and megaspores.
GYMNOSPERMS %here are about 72+ species #ound in all terrestrial habitats grouped into #our divisions ,phyla-. %hey have great economic importance) lumber' paper' chemicals. I. CARACTERISTICS O! GYMNOSPERMS 1. ood oody y trees trees and and shrub shrubs. s. 2. /ylem /ylem made made o# o# trac trache heids ids.. 3. Seeds Seeds are are borne borne'' e0pos e0posed' ed' in cone cones s ,megas ,megastrob trobilus ilus-. -. 4. "ollinat "ollinated ed by by &ind' &ind' seldom seldom by by insect insects. s. !. Singl Single e #ertili #ertili$at $atio ion) n) sperm sperm egg egg
. Most ar are monoe"io#s) monoe"io#s ) male and #emale organs on the same individual.
II. CONIPEROPYTA or CONIPEROPYTA or coni#ers %here are about !!+ species o# coni#ers. Many coni#ers produce resin$ a resin$ a comple0 mi0ture o# organic compounds that protect the plant #rom insect and #ungal attac. •
esin is stored in resin ducts in the roots' stem' leaves and cones'
Cone bearing gymnosperms' e. g. pines' #irs' cypresses' etc. 5eaves are needles or scale6lie' rarely broad %ena&ion is %ena&ion is parallel and open. 8 male cone is called mi"ros&ro'il#s ' and contains the mi"rosporangia that mi"rosporangia that produce mi"rospores through mi"rospores through meiosis that &ill develop into mi"rogame&ophy&es ,pollen grains-. %he #emale cone is called the megas&ro'il#s' megas&ro'il#s ' &hich produce megasporangia in megasporangia in each o# &hich a megaspore is megaspore is produced through meiosis and &ill develop one megagame&ophy&e. megagame&ophy&e . 8n egg &ill #orm &ithin the megagame&ophy&e . "ollination is by &ind. No&e( Study the life cycle of pine and learn the terminology. Pages 572 - 574.
III. CYCADOPYTA or CYCADOPYTA or cycads 9mportant in the %riassic ,24:6213 m .y. a-' &hich is called sometimes the 8ge o# Cycads . Most species are e0tinct. %here are about 14+ living species in tropical and subtropical parts o# the &orld. Cy"a)s are Cy"a)s are palm or #ern6lie plants &ith compound leaves and simple seed cones. %he are )ioe"io#s) )ioe"io#s ) plants are either male or #emale. %hey have a very large motile sperm &ithin the pollen grain but do not need &ater #or pollen transport. "ollination is by air and in some cases by ants.
I*. GIN+GOPYTA or GIN+GOPYTA or gingoes %here is a single species o# gingo alive today. 9t is native to China &here it has been under cultivation #or centuries. 9t has been #ound in the &ild in only t&o locations. *ingoes are dioecious and have #lagellated sperms. "ollination is by air and seeds are borne e0posed rather than in cones. 9t is commonly planted in 8merican cities because it is very resistant to pollution.
*. GNETOPYTA %he gnetophytes consists o# three genera and about 7+ species. 8 group o# rare plants plants that share share some traits traits &ith angiosperm angiosperms. s. • •
;##icient &ater conducting cells in the 0ylem called vessel elements. eproductive structures resemble #lo&ers.
ANGIOSPERMS %here are about 23!'+++ species o# #lo&ering plants. %his is the dominant group in terrestrial habitats. oins the t&o polar polar nuclei nuclei #orming the the triploid ,3n,3n- nutritive tissue called called the endosperm. See figure 27-12, page 51, for details. Seeds develop #rom the ovule #ollo&ing #ertili$ation. %he ovary enlarges and #orms the #ruit. 9n some instances other tissues also enlarge and become part o# the #ruit. Fruits serve t&o purposes) protect the seed and aid in dispersal o# the seeds.
E*OLTION O! SEED PLANTS "rogymnosperms appeared about 37! million years ago in the Devonian. • • •
they reproduced by spores. had megaphylls. &oody tissue o# secondary 0ylem similar to modern gymnosperms.
%heir reproductive structures appear to be intermediate bet&een those o# spore producing plants and seed plants. coni#ers "rogymnosperms seed #erns cycads and possibly gingoes Seed producing plants appeared in the Devonian' about 3+ m. y. a. ?y the end o# @urassic' 1:+ million years ago' several lines o# gymnosperms e0isted &ith #eatures that resembled those o# #lo&ering plants. Di##erent groups o# seed plants apparently appeared independently several times. 8ngiosperms 8ngiosperms probably probably arose #rom #rom ancient gymnosperms. gymnosperms. %hey must have been dicots' dicots' &hich &hich then gave rise to monocots. %he oldest #ossil record o# angiosperms is pollen #rom the Cretaceous' about 13+ m. y. a. %he oldest #lo&er #ossil is 12+ m.y.a. ?y late Cretaceous angiosperms had began to replace gymnosperms as the dominant group o# land plants. Many angiosperm species apparently arose #rom changes in chromosome number.
COMPARISON COMPARISON O! GYMNOSPERMS AND ANGIOSPERMS . *AM=