Q.11. Describe spore producing organs and development of sporangium in Lycopodium spore producing organs.
Related Question-
Q. Write short note on strobilus in Lycopodium.
Q. Describe development of sporangium and spores in Lycopodium.
Q. Describe the structure of sporangium and spore of Lycopodium.
(2008, 11)
Q. Describe the structure of cone (strobilii).
Ans. Strobilus: -
The asexual reproduction takes place by spores, which are small and unicellular. The spores are produced in sac like sporangia, which are borne on adaxial surface of sporophylls. These sporophylls are grouped together into distinct cone or strobili. In L. clavatum the strobili are borne in pairs at the apices of erect, elongated stalk like branches. The strobilus is made of central axis on which the sporophylls are closely arranged. The sporophylls are similar to sterile leaves and differ in various species. The sporophylls usually arise in pairs. On the inner side of each S.porophyll a simple kidney shaped sporangium is produced which bears the spores.
Sporangia: - Sporangia are found singly on the upper surface of the Sporohylls near the base or less commonly grow from the stem close to the leaf base. It has two parts (a) stalk and (b) capsule. Sprangia are similar in structure and contain large number of similar one type of spores (homosporous).
Development: - The development of the sporangium is of Initial cell eusporangiate type. Each sporangium develops from a transverse raw of superficial group of cells on the upper surface of sporophylls. The Initial cell divide repeatedly to produce a three layered wall. The inner most layer is called tapetum and its function is nourishment of developing spores. The central mass is the archesporium arranged in three tangential rows of twelve cells each. The archesporial cells give rise to spore mother cells or sporocytes. The spore mother cell undergoes meiosis reduction division to form of tetrads of haploid spores.
The mature sporangium is remiform with a short stalk. The sporangium opens by a tangential slit and the spores are dispersed with the help of wind.
Each spore is yellow in colour marked with a triradiate ridge. The spores are minute measuring 0.03-0.05 mm in diameter, unicellular structures produced in large number and all uniform in size and shape i.e., homosporous. The spores remain surrounded by two distinct walls, the inner intine and outer exine.
Q.12. Describe the morphological nature of protocorm in Lycopodium. (2009)
Related Question-
Q. What is Protocorm ? Discuss its morphology. (2007)
Ans. Protocorm: -
In species with green and surface living prothalli eg. L.cernuum and L. inundatum the tier of the four cells next to the suspensor in the sporophyte develops a foot which consists of a few cells only. The cells of the other tier instead of developing immediately into the first leaf and stem, undergo division in different planes and break through the prothallial tissue forming an extra prothallial massive, globose and tuberous structure termed as protocorm. It is composed of undifferentiated mass of parenchymatous cells. The protocorm develops rhizoids on the lower surface by means of which it attaches itself to the soil. On its upper surface a cylindrical green outgrowth termed as protophyll appears and then as the protocorm slowly grows further protophylls appear in an irregular manner. A mycorrhizal fungus grows inside this structure. The protocorm remains in this condition for sometime and then a stem apex becomes organized which will produce the normal type of sporophytic body.
Morphological Nature of Protocorm: -
(1) Protocorm is considered as an undifferentiated primitive stage of sporophyte which was present in all pteridophytes but has disappeared in most existing pteridophytes.
(2) It is also considered by some as an occasional adaptation to meet the strain of sporophytic development under special conditions.
(3) According to Holloway the protocorm is a specialized structure that helps the young sporophyte in perennating the dry season and it has no phylogenetic significance.
(4) Some others hold that it is carbohydrate / nitrogen ratio which is responsible for the development of swellings of the meristematic tissue in the embryo. If embryo gets a normal supply of C/N ratio no swellings in the embryo is recorded. If embryo gets high supply of C/N ratio the protocormous outgrowths develop.
Q.13. Write short note on different types of prothalli found in Lycopodium.
Related Question-
Q. Describe various types of prothalli of Lycopodium. (2006)
Ans. The gametophyts or prothalli of Lycopodium show great variation in form and structure in different species. The prothalli can be ordered in three inter grading types and can be distinguished as follows:
(1) The First Type of Prothallus: -
This type of prothallus is found among the tropical species eg. L.cernuum and in some temperate species eg. L. inundatum. The prothallus is usually smaller, annual, partly aerial and partly underground. The rhizoids arise from the lower buried portion. This underground tuberous part always contains a characteristic endophytic fungus, which inhabits a definite region of the body. The upper aerial part is conspicuously lobed and bears antheridia and archegonia at the bases ao the green lobes.
(2) The Second Type of Prothallus: -
This type of prothallus is found in many creeping species. eg. L. clavatum and L.obscurum. The prothalli are yellowish brown or nearly colourless, underground, non green and tuberous structures. Their length varies from one to two cms and may be top shaped as in L. clavatum or carrot shaped. Long rhizoids usually arise from the lower surface of the prothallus. A vertical longitudinal section of the mature prothallus shows an outer epidermis from the cells of which arise rhizoids. The outer cortex is parenchymatous whereas the inner cortex is filled by mycorrhizal fungus. The central region consists of parenchymatous storage tissues. The top of the prothallus of L. clavatum is lobed and the antheridia the archegonia and the growing embryos are located on these lobes.
(3) The Third Type of Prothallus: - This type of prothallus is found among the epiphytic species of the Lycopodium eg. L.phlegmaria. The prothalli are saprophytic and grow on trunks just below the surface of humus. There is central, small and tuberous body from which extend a number of colourless, slender and cylindrical arms on whose surfaces are developed the antheridia and archegonia. The endophytic fungus is present.
L.selago shows the presence of the both the first and second types of prothalli. If the spores germinate soon after their liberation and grow on the surface, they give rise to an aerial prothallus in which the chlorophyll is formed in the apical region. If the spores grow below the soil surface the prothallus formed is of subterranean type. It lacks chlorophyll.
(4) Nutrition of Prothallus: - It shows remarkable mode of nutrition. The cells of the cortical region and the pollisade tissue remain filled with endophytic fungus and these form a mycorrhizal association with the cells of prothallus. The association is considered symbiotic. The fungus enters soon after the germination of spore. It’s fungus fail to enter then the gametophyte never develops more than five cells.
Q.14. Describe the economic importance of Lycopodium. (2011)
Ans. Economic Importance of Lycopodium: -
Lycopodium is an important genus on the economic point of view. Spores of L. clavatum are used in making skin softening powders. Some species, are used as kidney stimulant. Some species like-L. obscurum are used for, ornamentation on X- mas and other festivals. Spores of Lycopodium are highly inflammable, thus used in manufacturing of fire works. Spores of some species are used in making medicinal tablets.