GYMNOSPERMS

INTRODUCTION Gymnosperms (Gymno: naked, sperma= seed) include simpler and primitive plants. They are characterised by the presence of naked ovules, borne unprotected on the surface of the megasporophylls. Gymnosperms are sometimes called as phanerogams without ovary.

GENERAL CHARACTERISTICS Most of the living gymnosperms are evergreen trees or shrubs with xerophytic  adaptation.  The main plant body is sporophytic and is differentiated into root, stem and leaves. The stem is usually erect, profusely branched (Unbranched in Cycas) and woody. Sometimes, as in Zamia, it is tuberous. Presence of leaf scars on the stem is a characteristic feature of gymnosperms.

GENERAL CHARACTERISTICS The plant possess well developed tap root system. Roots of some have symbiotic relationship with blue green algae (Coralloid roots of Cycas) or fungi (e.g. mycorrhizal roots of Pinus).

GENERAL CHARACTERISTICS CYCAS PINUS ZAMIA

LEAVES The leaves are usually dimorphic. The foliage leaves are green, simple, needle shaped or pinnately compound. Scaly leaves are usually minute and deciduous. The leaves are well adapted to withstand extremes of temperature, humidity and wind due to following features. -Needle like leaves reduces surface area. -Thick cuticle. -Sunken stomata.

LEAVES

REPRODUCTION Main plant body is sporophyte and heterosporous. It produces haploid microspores and megaspores. The spores are produced in sporangia that are born on sporophyll. The sporophylls are arranged spirally along an axis forming compact strobili or cones. The male and female cones or strobili may be borne on the same tree (Pinus) or on different trees(Cycas). Strobili bearing microsporophylls and microsporangia are called male strobili or male cone.

STROBILI

MALE CONE (STAMINATE CONE) REPRODUCTION MALE CONE (STAMINATE CONE) FEMALE CONE (OVULATE CONE) Male cones are usually short-lived. Microsporangia develop on the abaxial side of the microsporophylls. The number of sporangia persporophyll varies from two  to many. Microspores develops into a male gametophyte generation which is much reduced and is confined to only a limited number of cells..This reduced gametophyte is called a pollen grain. Development of pollen grains takes place within the micrsporangia. The cones bearing megasporophyll with megasporangia (ovules) are called as female cone. In megasporangia, the mega spore mother cell divides meiotically to form four haploid megaspores.  One of the megaspore develops into a multicellular female gamerophyte that bears two or more archegonia.

REPRODUCTION

REPRODUCTION Strobili bearing microsporophylls and microsporangia are called male strobili or male cone. The pollen are released from the microsporangium and are carried with air current to the ovules.  After fertilization, zygote develops into embryo and ovules into seeds. The seeds are naked.

LIFE CYCLE OF PINUS

ECONOMIC IMPORTANCE Edible seeds Ornamental Timber Paper Drug- Ephedrine Fibre board Essential oil Resins- Turpentine