Q.7. Describe the economic importance of Pteridophyta. (2013)
Ans. In comparison with the gymnosperms and angiosperms, the pteridophytes are ecomically not so important. The chief economic importance of the pteridophytes is that their fossil remains contributed to the coal deposits of the world. The most important petridophytes concerned in coal formation were the lepidodendrons, sigillarias and their relatives, and ferns.
The members of the Lycophyta have limited economic values. Plants of Lycopodium and Selaginella are commercially used by florists for decorative
purposes during the pooja festival and christmas season. Some important species of Lycopodium and Selaginella that are grown for ornamental purposes include Lycopodium clavatum, L. complanatum, L. selago, Selaginella caesea. S. wildenovii and S. kraussiana. The spores of certain species of Lycopodium
are used in making fireworks and in the preparation of drug pills. During drought conditions, the plant Selaginella lepidophylla becomes dried and curls up into a ball like structure. On availability of moisture, the ball uncurls and its branches become green and lie flat on the soil. Due to this habit, this plant is commonly called resurrection plant and is sold in the market as a novelty. The corms’ of Isoetes are eaten by ducks, and other aquatic animals Many of the ancient lycophytes constituted an important part of coal, e.g., lepidodendrids, sigillarians and others.
Plants of Equisetum accumulate large quantities of silica, particularly in their epidermal cell walls. The silicons deposit gives to the shoots a harsh texture, and on this account, the plant was formerly used for cleaning and polishing metal pots, pans and floors. For this reason, the plant has been given the name of “scouring rush”. Some species of. Equisetum, accumulate minerals (including gold) in their bodies. On account of this ability, these plants are used indicators of minerals in the soil in which they grow. Equisetum arvens is used in the preparation of diuretic, haemostatic and haemopoietic drugs. Like the Lycophyta, the dead bodies and spores of ancient Sphenophyta contributed to the formation of coal during Carboniferous.
Filicophyta (ferns) are of economic use in the following ways. Ferns are extensively cultivated in gardens and greenhouses because of their attractive foliage that are used by people in bouqiets and floral decorations. They young leaves and starch-rich rhizomes of certain ferns (bracken and ostrich fern) are eaten by some persons in some places. The rhizome of male fern (Dryopteris Julixmas) is used as an anthelmintic for the cure of tepeworm, liver flukes and other parasites inhabiting the digestive tract. Notholaena aurea, a xerophytic fern is used for the relief to stomach pain and cough. In some places, Marsilea plant is used in the preparation of a medicine that soothens the nervous system. The sporocarps of some species of Marsilea, e.g., M. salvatrix and M. drumondii, are edible Epidermal hairs from some species of ferns are used as a stuffing in pillows and mattresses. The fibrous roots of Osmunda spp. are used as a medium for growing the epiphytic plants suct as orchids. The water fern, Azolla, is cultivated commercially, since this plant harbours symbiotic cyanobacteria, that fixes atmospheric nitrogen. It plays an important role in maintaining the fertility of rice padi by fixing the nitrogen. The chief economic importance of the Filicophyta is the contribution of its fossil members to coal formation.
Q.8. Describe the life cyc1e of Lycopodium.
Ans. Systematic position: -
Division - Pteridophyta
Class - Lycopsida
Order - Lycopodiales
Family - Lycopodiaceae
Genus - Lycopodium
Lycopodium is a widely distributed, genus with about 200 species. In India it has been reported from the Eastern himalayas. It grows in moist shady places. L. phlegmaria grows as an hanging epiphyte. The plant of Lycopodium are commonly known as “creeping pines”, “trailing pines” and “clubmosses”. They occurs in variable climatic conditions.
Two generation are distinct in the life cycle of Lycopodium.
1. Sporophytic generation: - Plant body diploid and dominant.
2. Gametophytic generation: - It is haploid, partly or wholly subterranean.
The Sporophyte: - The vegetative plant body differentiated into root, stem and leaves. It is the dominant phase.
Stem: - Simple, unbranched but usually dichotomously or monopodially branched. Stem is erect in L. selago and prostrate in Anatomically the stem is differentiated into outer layer epidermis, broad cortex and a cental stele. The cortex is usually three layered i.e., outer sclerenchymatous, middle parenchymatous and inner sclerenchymatous. Endodermis is not well defined but pericycle is of one or more layers enclosing phloem and xylem. Different species of Lycopodium show different type of steles such as actinostele, plectostele and mixed protostele.
Leaves: - Lycopodium is homophyllous with simple, small, sesile and lans-shaped, spirally arranged in pairs. Each leaf has a single unbranched mid-rib. Heterophylous rare but it is shown by L. volubile and L.complanatum.
Anatomically the leaf has a single outer epidermis with stomata. Mesophyll is chlorenchymatous with cells having inter cellular spaces. Vascular bundle is medion with xylem surrounded by phloem. Endodermis is absent.
Root: - Roots are adventitious, branched with endogenous origin. In a cross section root shows a single superficial layer of epidermis with root hairs in pairs. Cortex is broad with outer thick wall and inner of thin walled cells. Stele diarch but may be tetrarch to hexarch in some cases. Xylem ‘C’ shaped or ‘U’ shaped.
In most of the species definite strobiliare present but in L. selago sporophylls are not organised into strobili.
Sporangium: - Each sporophyll has a kidney shaped, orange coloured, shortly stalked sporangium on the upper adaxial surface or in its axil. The sporangium is three layered containing mass of sporogenous tissue. The sporangium shows eusporangiate development i.e. it develops from a group of cells. Sporogenous cells produce spores after meoisis from spore mother cells. These are all similar i.e. homosporous. Dehiscence of sporangium is by transverse opening.
Spores: - Spore represent the first cell of gametophytic generation. Spore remain surrounded by two layered outer exine and inner intine. Spore has a single nucleus, reserve food and cytoplasm with few chloroplast.
The spores on germination produce different type of prothalli in different species. The different type of prothalli formed are as follows:
(i) In Lycopodium cernuum: - A topical species, the prothallus grows on the surface of ground. The basal portion is buried in the soil and is non-green. The upper part of prothallus has green leafy lobes. The sex organs are found between the green lobes. Endophytic mycorrhiza is present.
(ii) In Lycopodium clavatum: - A creeping species the prothallus is found completely underground. The sex organs develop on upper flat surface.
(iii) In Lycopodim phlegmaria: - The epiphytic species, the prothallus develops just below humans or rotting bark of trees. The prothallus has a central body with many colourless filamentous branches. The sex organs develop on the upper surface branches.
(a) Sex Organs: - The prothalli are usually monoecious (bisexual) and sex organs are usually borne on the upper surface or prothallus. The male and female reproductive organs are know as antheridium and archegonium respectively.
(b) Antheridium: - The mature antheridium is partly or totally embedded in the prothallus. The antheridum consists of a single layered jacket enclosing an oval mass of androcytes (anthrozoid mother cell). The androcytes develop fusiform biflagellate antherozoids.
(c) Archegonium: - The archegonium is also found embedded in prothallus tissue but it has projecting neck. Each archegonium has 4-8 neck canal cells, a ventral canal cell and an egg.
(d) Fertilization: - Fertilization takes place as usual in the presence of water. The neck canal cells and the ventral canal cell disintegrate and come out exuding citric acid and citrates which probably attract the antherozoids. Only one antherozoid fertilise the egg that develops into the zygote.
(e) The young sporophyte: -
Zygote represents the first sporophytic generation. The zygote develops into an embryo having a upper suspensor cell and a lower embryonic cells. The suspensor cell elongates may be one to three celled and functions like that of selaginella. The embryonic cells by division from in octant with tier of four cells such. The tier adjacent to suspensor from the food, whiledistal develops into remaining protion of the sporophyte. However, the stem, a single cotyledon and primary roots develop from the distal tier. The embryo later assumes the form of adult plants.
In some species, the zygote develop into massive globose structure protocorm specially formed from the distal tier. It is from the protocorm that later on stem and cotyledon originate. The protocorm has been considered to be of great morphological significance. Treube has formed the protocorm theory for such protocorm.