Q.14. Compare the sporophyte of Marchantia and Anthoceros on the basis of : (i) Origin of sporogenous tissue (ii) Capsule wall and (iii) Extent of dependency of the gametophyte. (2012)
Ans. Marchantia and Anthoceros: -
On the basis of Sporogonous Tissue
On the basis of Capsule Wall
On the basis of Extent of Dependency on the Gametophyte
Q.15. Describe the structure of sporophyte of Anthoceros. (2012)
Ans. The mature sporophyte or sporogonium is an erect cylindrical structure consists of expanded or builonus foot and smooth slender, erect cylindrical; capsule which may project 2 to 3 centimetre-but sometimes upto 15 cm, above the surface of gametophytic thallus. The foot absorbs food from gametophyte. The capsule in made up of seveal tissue. It has a central column of strile cells, the columella, surrounded by the sporogenous tissue which consists of spores and elaters. The wall of capsule is 4 to 5 layered, with an outer of epidemis which have stomata.
Q.16. Draw only the labelled diagram of T-S of thallus of Anthocerous. (2012)
Ans.
Fig. - T.S. of Thallus of Anthoceros
Q.17. Describe the importance of Anthoceros sporophyte from the evolutionary point of view.
Ans. Importance of Anthoceros Sprophyte from the Evolutionary point of View: -
Anthoceros is a member of Bryophyte. The sporophyte of Anthoceros is well developed and advanced due to this, it shows some evolutionary tendencies. Some well developed characters of Anthoceros sporophyte as follows -
(1) Physiological Independence -
(a) Anthoceros sporophyte contain photosynthetic tissue due to this itself syizthesize its food.
(b) Foots are fully developed.
(c) Stomata present on the external layer of Sporophyte.
Thus, the sporophyte of Anthoceros is independence. If it has rhizoids or root then it could absorb water from the ground and pass their life independently.
(2) Conducting Region: -
The presence of well developed columella (a central sterile portion) developed from the central endothecium suggests the begining of the formation of conducting region.
(3) Continuous growth of Sporophyte -
Due to the presence of meristematic tissue in the lower region of the capsule the growth of sporophyte occurs continuously. This character of sporophyte is analogous to Pteridophyte plants.
(4) Increased amount of sterile tissue: -
A major portion of Anthoceros sporogonium consists of sterile tissue such as foot, capsule wall, columella and pseudoelasters. The increased amount of sterile tissue, therefore, suggests the beginning of formation of sporophytic plant body as in higher plants.
(5) Reduced nature of Gametophyte -
This character is also similar to higher plants (Angiosperms). Thus, the sporophyte of anthoceros is more developed and fully independence. Its sporophyte is also similar to some rootless Psilophytes. Thus, the Anthoceros is link between Bryophytes and Pteridophytes.
(6) Better distribution of Spores: -
In Anthoceros, there is gradual formation of spores which means better distribution of spores and regular supply of nutrition to them. This character again resembles with Pteridophytes.
Q.18. What do you understand by alternation of generation? Explain it in the life cycle of Anthoceros. (2012)
Ans. Life cycle of Anthoceros: -
(i) The gametophytic generation (haplophase) begins with the production of haploid spores by reduction division.
(ii) The spores germinate into thallus, the main component of the gametophytic generation. The thallus as well as all the structures produced or it vegetative reproductive bodies (persistent apices, tubers, gemmae), sexual reproductive organs (antheridia, archegonia) all have ‘x’ no of chromosomes.
(iii) The gemetophyte has the capacity to grow, propagate and multiply indefinitely and is the dominant phase.
(iv) With the fertilization of the egg and production of zygote (which is diploid), the sporophyte generation starts. It is represented by sporogonium.
(v) Sporogonium, though endowed with capacity to grow by the action of intermediate meristem, does not have the same capacity, to propagate, multiply as we see in the case of gametophytic generation. The entire tissue of sporogonium (cells of foot, meristematic zone, wall of capsule, columella, archesporium and its products i.e. spore mother cells, pseudoelaters) are all diploid.
(vi) The sporogonium, however, remains attached to the thallus and derives its nutrition from the thallus by the foot. The lower part of the sporogonium is protected by an envelope or collar of the gametophytic tissue i.e., haploid tissue (the involucre).
(vii) The spores mother cell is the last generation of sporophyte, and undergoes meiosis to form 4 meiospores.
(viii) The two generations (or phases) the sporophyte and the gametophyte-occur regularly one after the other. The life cycle thus exhibits regular alternation of generations.
Q. 19. Describe the thallus structure and habitat of Anthoceros. (2005)
Ans. Thallus Structure and Habitat of Anthoceros: -
The plant body is small, dark green, dorsiventral and distinctly spongy thallus. The thalli may be arranged in overlapping small rosettes 0.5 to 1.5 cm. in diameter.
The dorsal surface of the thallus may have flat lobed lamellae imparting a velvety appearance. There is no conspicuous mid rib. The ventral surface of the thallus bears large number of unicellular and smooth walled rhizoids. The tuberculate rhizoids, scales and mucilage hairs are absent. Several large, opaque, more or less rounded, dark bluish green patches of Nostoc colonies can be seen with the naked eyes on the ventral surface of the thallus. The sporophytes are formed prominently during September and October.
Occurence: -
The species of Antheros are found in all temperate parts of the world. In India, this genus is represented by 25 species, which are found in moist and shady places of hills and plains. The species frequently occur, on moist rocks, moist shady walls and along the bank of rivers and streams. Some species of Anthroceros are also found on decaying wood.