*gymnos means naked and sperma means seed, hence gymnosperm are those plants in which the ovules are not enclosed by any ovary wall.
* it includes medium size trees,tall trees and shrubs.
*SEQUOIA is the tallest tree among gymnosperm.
*it generally posses tap root
*PINUS root has association of fungus called mycorrhiza
*CYCUS root is coralloid and has association with cyanobacteria which helps in nitrogen fixation.
*stem are unbranched in CYCUS and branched in PINUS,CEDRUS.
*leaves may be simple or compound.
*in conifers , the needle like leaf reduce the surface area, their thick cuticle and sunken stomata also help to reduce water loss.
*gymnosperms are heterosporous, they produce microspore and megaspores.
*spores are produced within sporangia that are borne on sporophylls, which are arranged spirally along an axis to form lax or compact or strobili or cones. *the cone bearing microsporophylls and microsporangia are called male strobili.
* male strobili produces pollen grain
*the cone bearing megasporophylls and megasporangia are called female strobili.
* in PINUS , male and female cones develops on same tree.
*in CYCUS,male and female cones develops on different tree.
*megaspore mother cell(MMC) differentiate from one of the cell of nucellus, nucellus is protected by ovule, the ovule clustered to form female cone. this MMC develops 4 megasporangium one of which develops into multicellular female gametophyte bear two or more archegonia or female sex organ.
* male and female gametophyte do not have free living existance, they remain wthin sporangia.
*after fertilization zygote develops into an embryo and the ovules into seeds, seeds are not covered.
CYCAS
PINUS
GINKGO
* it includes medium size trees,tall trees and shrubs.
*SEQUOIA is the tallest tree among gymnosperm.
*it generally posses tap root
*PINUS root has association of fungus called mycorrhiza
*CYCUS root is coralloid and has association with cyanobacteria which helps in nitrogen fixation.
*stem are unbranched in CYCUS and branched in PINUS,CEDRUS.
*leaves may be simple or compound.
*in conifers , the needle like leaf reduce the surface area, their thick cuticle and sunken stomata also help to reduce water loss.
*gymnosperms are heterosporous, they produce microspore and megaspores.
*spores are produced within sporangia that are borne on sporophylls, which are arranged spirally along an axis to form lax or compact or strobili or cones. *the cone bearing microsporophylls and microsporangia are called male strobili.
* male strobili produces pollen grain
*the cone bearing megasporophylls and megasporangia are called female strobili.
* in PINUS , male and female cones develops on same tree.
*in CYCUS,male and female cones develops on different tree.
*megaspore mother cell(MMC) differentiate from one of the cell of nucellus, nucellus is protected by ovule, the ovule clustered to form female cone. this MMC develops 4 megasporangium one of which develops into multicellular female gametophyte bear two or more archegonia or female sex organ.
* male and female gametophyte do not have free living existance, they remain wthin sporangia.
*after fertilization zygote develops into an embryo and the ovules into seeds, seeds are not covered.
CYCAS
PINUS
GINKGO
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