noticed insects embedded in a transparent substance called amber which preserves the extinct forms. What is amber? Which group of plants produces Amber? Amber is a plant secretion which is an efficient preservative that doesn’t get degraded and hence can preserve remains of extinct life forms.
The amber is produced by Pinites succinifera , a Gymnosperm. In this chapter we shall discuss in detail about one group of seed producing plants called Gymnosperms . Gymnosperms (Gr. Gymnos = naked; sperma= seed) are naked seed producing plants.
They were dominant in the Jurassic and Cretaceous periods of Mesozoic era. The members are distributed throughout the temperate and tropical region of the world . . General characteristic features • Most of the gymnosperms are evergreen, woody trees or shrubs.
Some are lianas ( Gnetum ) • The plant body is sporophyte and is differentiated into root, stem and leaves. • A well developed tap root system is present. Coralloid roots of Cycas have symbiotic association with blue green algae. In Pinus the roots have mycorrhizae.
• The stem is aerial, erect and branched or unbranched ( Cycas ) with leaf scars. • In conifers two types of branches namely branches of limited growth (Dwarf shoot) and Branches of unlimited growth (Long shoot) is present. • Leaves are dimorphic, foliage and scale leaves are present. Foliage leaves are green, photosynthetic and borne on branches of limited growth.
They show xerophytic features. • The xylem consists of tracheids but in Gnetum and Ephedra vessels are present. • Secondary growth is present. The wood may be Manoxylic (Porous, soft, more parenchyma with wide medullary ray - Cycas ) or Pycnoxylic (compact with narrow medullary ray- Pinus ).
• They are heterosporous. The plant may be monoecious ( Pinus ) or dioecious ( Cycas ). • Microsporangia and megasporangia are produced on microsporophyll and megasporophyll respectively. • Male and female cones are produced.
• Anemophilous pollination is present. • Fertilization is siphonogamous and pollen tube helps in the transfer of male nuclei. • Polyembryony (presence of many embryo) is present. The