Q.12. Write Economic and Ecological importance of sphagnum.
Ans. Economic importance: -
1. It has exceptionally high capacity of retaining the water and can withhold water two hundred times more of its own dry weight (Dittmer, 1964). That is why the plants are used in providing moisture to seed beds, to packed material of bulbs, seedling, cutting etc.
2. The plant secretes acid and has germicidal properties.
3. The plant were used in surgical dressings, in place of cotton. The sphagna are popularly called moss cotton.
4. The peats are sued as fuel.
5. Paraffin acetic acid, peat tar and ammonia are formed as by-products of peat obtained for industrial uses.
Species of Sphagnum both alive and air-dried have been widely used as indicators of both atmospheric and aquatic pollutions.
Ecological importance: -Sphagnum is of great ecological importance. As it establishes itself on the shore of a lake it gradually extends inwards and grows over water. The surface of water in the lake is finally completely covered. The Sphagnum plants are interwined so as to give the apperance of solid soil from the surface. Such areas are called the quacking bogs. Sometimes seed plants (hydrophytic) grow on the bog. The moss plants gradually die and settle to the bottom. In the course of long periods of time these swamps, ponds and lakes, which were sterile sheets of water, become filled with partially decomposed, old parts of this moss and other hydrophytic plants. Finally these areas are converted into solid soil. The constantly accumulated debris raises the surface level. The moss and the other hydrophytic angiosperms gradually disappear. They are replaced by forest growth of mesophytic type. In this way Sphagnum moss modifies the landscape in regions with small lakes and ponds.
Anthoceros
Q.13. Describe in detail the life cycle of Anthoceros. (2008)
Ans. Life Cycle of Anthoceros: -
The life cycle of Anthoceros consists of two generations:
I. The Gametophytic Phase: -
Structure of Thallus: - The gametophyte of Anthoceros is a dorsiventral plate like thallus. It is somewhat lobed of a radially disected which may result
in irregular dichotomous branching. The thallus remain attached to substratum by means of rhizoids which are only of one type i.e. smooth walled. The tuberculated rhizoids scales and midrib are absent.
The dorsal surface of the thallus may be smooth (A.laevis) or rough with ridges (A. fusiformis) or velvety with many flat’ leaflike, lobed lamella (A. crisulus). The ventral surface of the thallus bears numberous smooth walled rhizoids.
Reproduction: - It may take place either vegetatively or by sexual means.
Vegetative reproduction: - It may take place by the following methods -
(i) By Death and Decay: - By death and decay of the older portions of thallus, the young one are separated apart which lead an independent life and grow into adult plant.
(ii) By gemmae formation: - In some species the gemmae formation take place which on seperation forms the new thallus.
(iii) By tubers formation: - In some species e.g. A. tuberosus, A thalli, A. himalayensis, A laevis, etc. tubers arise on the thallus during unfavourable conditions. They get detached from the thallus and give rise to plant.
(iv) By persistant Apecies: - In few species e.g. A. fusiformis the apices of gametophyte are capable of resisting under unfavourable conditions.
Sexual reproduction: - The sexual reproduction is of highly advanced oogamous type, brought about by means of definite male (antheridium) and female (archegonium) reproductive organs. Usually the Anthoceros is homothallic or monoecious but in few species it may be heterothallic or dioecious.
Male Reproductive Organs: -
Antheridium develops on the dorsal surface of gametophyte cell
increases in size and divide by pericilinal division into inner antheridial initial and outer sterile roof cell. The antheridial initial divides into a primary antheridial cell and primary stalk cell.
In certain species of Anthoceros, the antheridial initial may divide by vertical divisions and each daughter cell develops into an antheridium. Thus a single antheridial chamber may have two or more antheridia in it.
The mature antheridium has a spherical body with a long stalk. The roof of the antheridia brust irregularly and absorbs water and swell and ultimately break, thus exposing the antherozoids.
Female Reproductive Organs: -
The female reproductive organs in Anthoceros are archegonia, the archegonia are also embeded in the dorsal surface of thallus. Any cell for dorsal surface of thallus behaves as archegonial initial cell and functions directly as primary archegonial cell. The cover initial divide by vertical wall and form four cover cell. The primary neck canal cell divides and redivides and give rise to four to six neck canal cells. The primary venter cell divides transversly to form Venter canal cells egg. The mature archegonium is a flask shaped structure.
Fertilization: -
The water medium is essential for fertilization. When the archegonium is fully mature its neck canal cells and venter canal cell disorganise forming a mucilage substance which absorbs water, thus creating a pressure that bring about the opening of the cover cell. Motile antheorzoids enter through this opening and ultimetly one sperm fuses with egg forming a diploid oospore or zygote.
II. The Sporopytic Phase: - The zygote is the first cell or sporophytic generation. It germinates to produces sporophytic plant body. The sporogonium of anthoceros is elongated rod shaped and differentiated into foot, intercalary meristematic zone and capsule.
The foot is massive, bulbous, inverted cup shaped and embeded in gametophytic tissue of thallus. Its superficial cells-are haustorial which absorb water and nutrients form the gametophyte. The intercalary meristematic zone is situated between foot and capsule. The cells of this zone are in continuous state of dimension. They add new cells towards the upperside with the result the sporogonium is long lived show all differential stages in capsule. The capsule is long slendor and errect. It looks like horn and hence the popular name of the genus is ‘horn worts’ The capsule has outer 4-5 layered wall.
Dehiscence of Capsule and liberation of Spore: - The capsule when dried is brown or black in colour and by the loss of water and hygroscopic movements of pseudoelaters the capsule get twisted and the wall of capsule ruptures and the spore get liberated free.