Q.1. Give the important characters of Gymnosperms. (2010)
Ans. Gymnosperms (gymno = naked; sperma = seeds), as evident from their name are naked seeded plants with their ovules freely exposed on open megasporophylls unlike aniosperms which bear them enclosed within closed megasporophyll.
In contrast, the angiosperms or flowering plants develop their ovules and seeds within a closed ovary.
The members of Gymnosperms form a bridge between the Pteridophytes on one hand like Cycas possess ciliated male gametes (a feature of pteridophytes); as well as with Angiosperms as they do not possess independent Gametophytic generations and produce seeds due to the permanent retention of megaspores in the megasporangia.
Characteristic features of Gymnosperms: -
1. They are all woody, perenial forms.
2. They are xerophytic in habit.
3. The stele is siphonostelic type and the vascular cylinder is made up of collateral mesarch bundles.
4. The xylem is formed of tracheids and phloem is of sieve tubes and phloem parenchyma.
5. There is well marked secondary growth by the activity of primary cambium.
6. The conferales stem after secondary growth have a dense and more xylem (wood) known as Pycnoxylic while the cycadales have less developed wood known as monoxylic.
7. The reproductive organs are known as cones, which are normally unisexual.
8. The females cones are long lived structures.
9. The ovules are orthotropous and unitegmic (one integument only).
10. The ovule are not enclosed inside ovary.
11. The pollination of direct, i.e., pollen grain directly come in contact of ovule.
12. The nucellus remain present below the integment, and is sporophytic in nature.
13. Within nucellus the female gametophyte (endosperm containing two or more archegonia) remain present. The archegonium does not have neck canal cells.
15. The proembryo differentiates into three zones; outer rosette or haustorial, middle suspensor and the basal embryonal cells.
16. Presence of polyembryony.
Q.2. Give an account of the recent classification of Gymnosperm. Give an account of the classification of Gymnosperm which you consider to be most - satisfactory.
Related Questions -
Q. Give the classifications of gymnosperms proposed by various scientists.
Ans. Classification of Gymnosperms: -
1. Tippo (1942) - He has divided Gymnosperms in to two sub-classes and it was further divided in to order -
Class 1. Cycadophyte
Order -
1. Cycadofilicasles 2. Cycadales 3. Bennetittales
Class - 2 Coniferophytae
Order -
1. Ginkgoales 2. Coniferales 3. Cordiatales 4. Gnetales
2. Sahni and Raizada (1960) - The view of discovery of new Gymnosperms order Pentoxyleae. They classified Gymnosperms as follows:
3. Coulter and Chamberlain (1917) divided the gymnosperms directly into seven orders : Cycadofilicales, Bennettitales, Cycadales, Cordaitales, Ginkgoales, Coniferales and Gnetales. Chamberlain (1934) divided the gymnosperms into two class which were further subdivided into following order :
(A) Class - Cycadophyta - It is characterized by unbranched and stumpy stems, leaves large and pinnately divided, male cones large and compact with simple sporophylls that bear large ovules; stems have with cortex and manoxylic wood. It includes three orders -
1. Cycadofilicales - It includes all extinct forms.
2. Cycadeoidales - It includes both living and one extinct forms.
3. Cycadales - It includes both living and extinct forms.
(B) Class - Coniferophyto - The stems are profusely branched and the foliage gives cone-like, appearance; leaves simple; male and female strobilli are compact and bear complex sporophylls; wood is pycnoxylic. It includes 4 orders:
1. Corditales - Extinct order.
2. Ginkgoales - It includes extinct and one living representative.
3. Coniferales - Includes both extinct and living genera.
4. Gnetales - In includes extinct and living genera.
4 D.D. Pant (1957) divided the gymnosperms into three divisions each of which is further divided into classes and orders. Pant’s classification is as under -
5. Andrew (1961) divided the gymnosperms into six divisions:
7. Takhataijan, Cronquist and Zimmermann (1966) proposed a different classification in which they included the gymnosperms in a separate division which they called Pinophyta. It was further divided into subdivisions, classes and subclasses as follows:
