15.2 Gymnosperms

Gymnosperms (gymnos = naked; spermos = seed) represent a primitive group of seed-bearing plants (spermatophytes) in which the seeds are naked (i.e., without the covering of a fruit wall) . This is because in gymnosperms, a closed carpel (ovary) is not formed. The ovules are directly borne on open carpellary leaves (megasporophylls) and hence they are "naked". These develop into naked seeds after fertilization. The term ’gymnosperms’ was first used by Theophrastus in 300 B.C. in his book, Enquiry into Plants.

Gymnosperms were most abundant and widely distributed during the mesozoic era. However, they form only a small part of the present day vegetation. There are about 70 genera and 725 species of gymnosperms distributed in tropical and temperate regions. Most of these are the conifers, which are comparatively better-represented today. Others include the cycads and the Ginkgo tree.On the Indian sub-continent, these are found in the form of the coniferous forests in the Himalayas.

1. The life cycle shows heteromorphic alternation of generations.

2. Gymnosperm plants are more advanced than pteridophytes but are more primitive than angiosperms.
   
   

3. A diploid plant body (sporophyte) is mostly a tree with well developed roots, stem and leaves.

4. Two types of reproductive leaves are present: microsporophylls that produce microspores and megasporophylls that produce megaspores.

5. The gametophytes are greatly reduced, microscopic and dependent on sporophyte plant body.

6. The ovules as well as the seeds are naked.

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Table of Contents

15.0 - Introduction
15.1 Pteridophyta : General Account
15.2 Gymnosperms
15.3 Angiosperms : Dicotyledons
15.4 Angiosperms : Monocotyledons
15.5 Vascularization
15.6 Development of seed habit
15.7 Development of Flower and Fruit

Chapter 16