General characters of Gymnosperm:
- The plants are well developed, woody trees having true root, stem and leaves. Herbaceous or annuals habit is not found in gymnosperms. Trees are xerophytes.
- The root system is a well developed tap root system. In some plants like Cycas, the secondary roots become coralloid due to association with algae, and in Pinus the roots form association with fungi called mycorrhiza. 3.
- Stem is aerial, erect and woody. It is well branched. Cycas, however, has unbranched stem.
4. Leaves are usually of two types i.e., dimorphic, the scale leaves and the green leaves. Scale leaves are microphyllous, small, brown and non photosynthetic. The green leaves may be simple or compound and are megaphyllous. In Pinus the leaves are long needle like.
- Leaves may have parallel or dichotomous venation.
Anatomical characters
- Xerophytic features like thick cuticle, sunken stomata and resin/latex ducis and transfusion tissue are seen.
- The stem has a ring of vascular bundles which are conjoint, callateral and open.
- Xylem is made up of tracheids and xylem parenchyma. Vessels are absent except in the order Gnetales.
- Phloem consists of sleve tubes and phloem paranchyma. Vessels are absent.
- Secondary growth occurs and annual rings are seen.
- Secondary wood is manoxylic (ie., soft and parenchymatous) in Cycas but pycnoxylic in pinus.
- The vascular bundles of petioles and lamina are diploxylic i.e., centripetal and centrifugal xylem.
- Mesophyll of leaf may be differentiated into palisade and spongy parenchyma in Cycas.
Reproductive Structures
- All gymnosperms are heterosporous i.e., two types of spores are formed, the microspores and megaspores.
- Microspores develop in large numbers in microsporangia which occur on the ventral side of microsporophyll.
- Many microsporophylls are aggregated in the form of a male cone. Male cones of Cycasare large woody and may be up to 60 cm. long.
- Megaspores occur singly in megasporangia also called ovules. The ovules occur onmegasporangia which are aggregated in the form of female cones.
- Sporangial development in ensporangiate type.
- Male and female cones may develop on the same plant i.e., monoecious (Pinus) or on different plants i.e., dioecious (Cycas).
Male Gametophyte
- Microspores are unicellular and haploid structures. They may be winged in Pinus.
- Development of microspore starts in the microsporangium but continues even afterpollination and is completed in the pollen chamber of ovule.
22. Male gametophyte consists of 1-2 prothallial cells, a stalk cell, a body cell and a tube cell.
- Male gametes are naked, non motile but motile in Cycas and Ginkgo. Ovule and Female Gametophyte
- Ovules are generally Orthotropous.
- Ovule or megasporangium consists of nucellus surrounded by a thick integument. So, ovules are unitegmic but bitegmic in Ephedra.
- A single large megaspore mother cell becomes prominent in the nucellus, it undergoes meiosis to form four haploid megaspores. Three of them die and the surviving one expands, undergoes free nuclear division to form the female gametophyte or endosperm.
- Two or more archegonia develop in each ovule. No archegonia are formed in Gnetales. 28. Each archegonium has a neck and venter. A non motile female gamete called egg develops in each archegonium.
- Pollination and Fertilization.
29. is done by wind..
- Pollen are deposited on the micropyle of the ovule where they enter the ovule and are deposited in the pollen chamber.