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Botany

1. BOTANY B.Sc. B.Ed. Part II Paper 1- Diversity of Seed Plants Unit 3 -2.6 General features of Gymnosperms

2. PAPER –I: Diversity of Seed Plants (Gymnosperms- Cycas , Pinus , Ephedra )

3. Gymnosperms Spermatophyta - seed bearing plants 2 sub-divisions Gymnosperms (Naked seed) and angiosperms Phenerogams without ovary Originated in palaeozoic era and were dominant during the Jurassic and Cretaceous periods of mesozoic era Members of several primitive groups of gymnosperms ( Cycadofilicales , Bennetitales , Cordaitales ) are extinct today and only their fossils are known There are about 70 genera and 725 species of living gymnosperms Other groups like Cycadales , Ginkgoales , Coniferales and Gnetales represented by both living and fossil members

4. Characteristic Features of Gymnosperms 1-Most of the living gymnosperms are Evergreen trees or shrubs with xerophytic adaptations 2-Plant body is sporophytic and is differentiated among root, stem and leaves 4- The stem is usually erect, profusely branched ( unbranched in Cycas ) and woody, sometimes tuberous ( Zamia ) 6- The leaves are usually dimorphic -The foliage leaves are green, simple, needle shapes or pinnately compound while scaly leaves are usually minute and deciduous In Ephedra , only scale leaves are present 3- Tap root system. Some texa roots have symbiotic relationship with algae ( Coralloid roots of Cycas ) or fungi ( mycorrhizal root of Pinus ) 5-Presence of leaf scar on the stem is the characteristic feature of gymnosperms 7- The roots are di to polyarch

5. 10- The xylem consists of only tracheids and xylem parenchyma . Vessel are absent except Gnetales 11- The phloem consists of sieve tube and phloem parenchyma . However, companion cells are absent 12- The stem shows distinct secondary growth and conspicuous annual rings are present in the wood 14- The leaves have thick cuticle and sunken stometa 15- The mesophyll of the leaves may be undifferentiated ( Pinus and Cedrus ) or differentiated into pallisade and spongy parenchyma ( Cycas ) 16-Most of gymnospermic leaves do not have lateral veins and the lateral translocation of nutrients takes place by transfusion tissue 8- In the cortex of stem, tanniniferous cells are frequently present 9- The young stem has a ring of colleteral and open vascular bundle 13- The wood may be manoxylic ( Cycas ) or pycnoxylic ( Pinus )

6. 17- They are heterosporous ; mega and microsporangia occur on mega and micro sporophyll respectively which usually aggregate to form compact strobili or cones 18- The cones are usually monosporangiate (Unisexual), but in some species bisporangiate cones occur ( Ephedra foliata ) 19- Male cones are usually short lived. Microsporangia develop on the abaxial side of the microsporophylls The number of sporangia per sporophyll varies from two ( Pinus ) to many ( Cycas ) The development of sporangia is eusporangiate 20-The female cones are formed by the aggregation of megasporophylls They are persistent on the plants for several years 21- The mega sporophyll may be similar to normal foliage leaves ( Cycas ) or are cauline ( Pinus ) 22-The megasporangium (Ovule) is a naked structure on the megasporophyll 23-The ovules are orthotropous and unitegmic ,but are bitegmic in Gnetales 24-The ovular integument is differentiated into three layers ; outer and inner are fleshy while middle is stony

7. 25- The microspores are liberated at various stage of development of male gametophyte; 3 celled stage in Cycas , 4 celled stage in Pinus , 5 celled stage in Ephedra Male gametes are non-motile with exception of Cycas and Ginkgo 26- The number of archegonia in a female gametophyte is variable; several archegonia in Cycas while only two in Pinus The archesporium of Gnetum is represented by ovum only 27- The archegonium has single egg and a Venter canal cell, neck canal cells are absent 28- Pollination is direct;pollen grains come in direct contact with ovule Pollen are deposited in pollen chambers where they germinate. All gymnosperms are wind pollinated 29-Fertilization is siphonogamic and pollen tube may function as haustorial ( Cycas ) and sperm carrier ( Pinus ) 30-The zygote is formed after fertilization is the mother cell of sporophytic generation

8. 31-The development of embryo is meroblastic , the embryo develop from a part (basal) of the zygote 32- The development of endosperm takes place before fertilization , hence haploid in nature 33-With few exception ( Gnetum , Welwitschia ), there are three nuclear divisions in the early stage of embryo development The embryo is endoscopic ; shoot apex is directed opposite to the micropyle 34- There is marked tendency of polyembryony 35- The polyembryony may arise by fertilization of more than one eggs or by division of zygote (cleavage polyembryony ) but only one embryo attain maturity 36- The naked ovule develops into seed and integument forms seed coat 37- the number of cotyledon in a seed is one or two in Cycas and many in Pinus 38- The seed has short or long dormant period and then it germinate to form a new sporophytic body

9. 39- The seed represent three phases in the life cycle of the gymnosperms; 1- integument and nucellus represent mother sporophytic phase (first sporophytic phase), 2-endosperm gametophytic phase , 3- embryo next sporophytic phase 40- There is distinct alternation of generation . The diploid sporophytic phase is dominant while haploid gametophytic phase is reduced

10. Next class Affinities of gymnosperms