GYMNOSPERM
1.Gymno= naked Sperma = seeds that means these are the plants with naked seeds which originated during late palaeozoic era & flourish well during mesozoic era ( age of dinosaurs).These are cone bearing plants grow in cold climate in snow warmer climate group is cycads. The main plant body is sporophyte which is differentiated into true root stem and leaves.
2.Root : Tap root system is present.
Stem : It is erect aerial solid woody &branched (unbranched in cycads).
3.Plants are vascular They possess Xylem & Phloem arranged in vascular bundle. Secondary growth is present . Vessel are absent in xylem and campanion cells are absent in phloem.Exception is Gnetales where vessel are present.
4.Gymnosperm are heterosporous.
Male microspores and female megaspore born inside sporangia. These two types of sporangia are born on leaf like structure called sporophyll , Microsporangia on microsporophyll and megasporangia on megasporophyll .
Sporophyll are usually arranged in compact structure called cones or strobilli ( male and female cones) Male cone are short lived and female cones are long lived. The female cone remain attached on the plant for several years till the maturity or ripening of seeds.
5.Microsporangia produces numerous pollen gains. The pollination is anemophilous .Ovules are orthotropous remain on megasporophyll surrounded by integuments which encloses nucellus and female gametophyte contain egg.
Pollen grain germinate inside ovule generative cell produces two male gamete & these gametes reaches upto the egg cell by pollen tube .One of male gamete fertilize the egg and form diploid zygote.
6.Fertilization occur by siphonogamy ( through pollen tube) but in cycads the pollen tube function as haustorium & fertilization occur by zoodiogamy.
7. Diploid zygote develop into embryo and ovule become seed the embryo gets its nutrition from endosperm ,Seeds are naked that means they do not occur inside fruit .
•Gymnosperms are adapted to land conditions because :
•1.Vascular tissue is present.
•2.Cambium in vascular tissue for secondary growth so bark is produced.
•3.Pollen grain production in large no. to ensure anemophily.
•4.Development of female gametophyte inside ovule.
•5.Formation of seed to protect the embryo in it.
•6.No need of external water for fertilization.
Cycads : This is the group of gymnosperm known as reptiles of plant kingdom or Panda of vegetable kingdom because the are become endangered species due to over exploitation.
They are strictly dioecious. The sperm of cycas is largest in the plant kingdom.
Conifers : It is the largest group in gymnosperms .
coniferns have largest plant on earth that is
Sequoidendron giganteum. & the oldest living plant Pinus longavea 3000years old.
•Economic importance of gymnosperms:
•1. Stem of seeds of cycads yield sago starch.
2. Seeds of Pinus gerardiana are used as dry fruit called chilgoza.
3.Species of Ephedra yield alkaloids called ephedrine for cough, asthma & bronchitis.A gum from Cycas rumphii & Cycas circinalis is known to treat tumor. Taxol is anticancer drug obtained from Taxus.
4.Resin obtained from gymnosperms used in waterproof paints sealing wax etc.
5.Tannins obtained from bark of Tsugo candensis is a phenolic compound.