Here is a compilation of essays on ‘Gymnosperms’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Gymnosperms’ especially written for school and college students.
Essay on Gymnosperms
Essay Contents:
- Essay on the Introduction to Gymnosperms
- Essay on the Plant Body of Gymnosperms
- Essay on the Classification of Gymnosperms
- Essay on the Life Cycle of Gymnosperms
Essay # 1. Introduction to Gymnosperms:
Greek philosopher Theophrastus was the first to employ the term Gymnosperms, to describe plants with naked seeds. The epithet gymno means naked and sperma means seed. This was to separate these plants from flowering plants—angiosperms—in which the seeds are enclosed in an ovary. The epithet angio means closed.
Gymnosperms are evergreen plants, mainly trees, and are a major component of temperate forests. These are valued for their timber, resins, essential oils, drugs and edible nuts. Newspaper industry is dependent on the soft wood of conifers. Gymnosperms of the past are a source of the present-day coal industry.
Moreover, gymnosperms with their vide range of shapes, colours and texture are valued by garden lovers. Ginkgo, a highly unusual non- flowering plant, is worshipped in Buddhist temples of Japan and China.
There is a wide range in the forms of gymnosperms. Zamia pygmaea, as the name suggests, is the smallest, with its leaves only 5 cm long, and Sequoia semipervirens, the California redwood, is tallest among trees, reaching a height of 112 meters with a girth of 15 M, taller than a 35-storey building.
The plants have well-developed taproot system. There are coralloid roots in Cycas and mycorrhizic roots in Pinus, with xylem elements ranging from diarch to polyarch, but without vessels.
Leaves of gymnosperms are micro- as well as mega-phyllous, ranging in size from minute scales in Ephedra, to acicular needle-like in Pinus and large pinnate leaves of Cycas attain a size of up to 2 meters. An important feature of gymnosperm leaf is transfusion tissue. The mesophyll is differentiated into palisade to spongy parenchyma in Cycas and undifferentiated in Pinus.
Vascular cylinder in stem is made up of open-collateral endarch bundles with secondary growth. Secondary xylem is marked with an absence of vessels, save for some plants, and comprise exclusively of tracheids. The wood formed is manoxylic or pycnoxylic. The former is sparse as against the latter which is dense and forms the main bulk of the stem. Manoxylic wood is of no importance, whereas pycnoxylic wood provides the timber of commerce.
Essay # 2. Plant Body of Gymnosperms:
The plant body of a Gymnosperm is a sporophyte the dominant generation which originates or generation of a seed and ends up producing more seeds (Fig. 14.1).
Save for Cycas where ovules are borne on megasporophylls, in rest of plants the reproductive structures are in cones or strobili, either male (staminate) or female (ovulate).
An ovule is a new structure in gymnosperms it is the precursor of female gametophyte to bear female sex organs – archegonia or simply the archegonial cells.
Essay # 3. Classification of Gymnosperms:
1. Chamberlain (1935) divided the group into two classes: cycadophytes (Cycas) and coniferophytes.
2. Arnold (1948) recognized three classes: cycadophyta (Cycas), coniferophyta, conifers, (Pinus) and chlamydospermatophyta (Ephedra and Gnetum).
3. Pant (1957) raised these classes to three divisions.
4. Sporne (1974) recognized three classes.
5. Gifford & Foster (1989) have recognized seven divisions- progymnospermophyta, pteridospermophyta, cycadophyta, cycadeophyta, ginkgophyta, coniferophyta and gnetophyta.
These classifications differ in respect of different genera.
Cycadales:
Cycadales are a group of true gymnosperms with naked seeds, borne on sporophylls. The plants have retained ciliated sperms, a characteristic of lower plants. Not related to any other group of plants, cycadales actually represent a transitional stage between ferns and gymnosperms. Thus, it is not surprising that these plants exhibit a number of very primitive features in their morphology and life cycle.
This group has been in existence for at least 200 million years. It comprises 11 genera, five of which: Dioon, Ceratozamia, Zamia, Chigua and Microcycas belong to the western hemisphere and the rest (Cycas, Macrozamia, Lepidozamia, Encephalartos, Stangeria and Bowenia) occur in the eastern hemisphere.
Coniferales:
Coniferales, the cone-bearing plants, are the largest group of woody perennial gymnosperms without or with two types of branches, long and dwarf shoots, dimorphic leaves, scales and needles and mycorrhizic roots. The wood is pycnoxylic and cones are compact. Pollen grains are winged. Conifers are the tallest trees, Sequoia semipervirens is 112 metre high and an oldest tree is Pinus aristata, over 400-year-old, in mountain forest of California.
Ephedrales:
Ephedrales, with a single family called Ephedraceae and a single genus Ephedra, is known for its jointed stems and double fertilization (a characteristic of flowering plants, angiosperms). The plant is also known for its alkaloid, ephedrine.
Gnetales:
Monotypic genus, Gnetum represents the order with about 40 species. It is widely distributed in tropics and subtropics. The genus is confined in moist tropical forests of Amazon basin, West Africa, India, South China and Malaysia. G. gnemon is cultivated in Malaysia for its edible seeds. Most of Gnetum species are lianes, climbers on trees, in rainforests. G. trinerve is apparently parasitic.
In India there are five species of the genus.
G. ula, a woody climber with branches of swollen nodes, is widely distributed extending from Western Ghats to Khandala, evergreen forests of Coorg (Kerala), Nilgiris (Godawari district of Andhra and some parts of Odisha).
G. contractum, a scandent shrub, is found in Kerala, Nilgiri Hills and Coonoor district of Tamil Nadu.
G. montanum, a climber, with smooth slender branches, swollen at nodes occurs in Assam, Sikkim and Odisha.
G. latifolium, a climber, with its variety macropodum occurs in Andaman and Nicobar Islands and var funiculare occurs in Andaman.
G. gnemon is a tree, while its variety brunonianum is a slender shrub. It is restricted to Lushai Hill, Naga Hills and Golaghat area of Assam. Another variety, griffithi, a shrubby plant, is restricted to Sibsagar, Naga Hills and Kungaba areas of Assam.
Essay # 4. Life Cycle of Gymnosperms:
Major events/stages in the reproductive cycle of a gymnosperm are specified (Fig. 14.2).
Since gymnosperms are basically temperate plants there is little activity in the development of reproductive structures during winter. This activity is, however, resumed in summer and for females it is so in autumn. Contrary to it in plants growing in tropics or subtropics such as Cycas and Ephedra the development of ovule is a continuous process, synchronous with the development of male cones.
Exceptionally, in Ephedra the reproductive cycle is of 3-4 months, whereas in other plants this cycle is of 1-year, 2-years or 3-years.
