Adult plant of Lycopodium represents saprophytic phase of life cycle. It completes to life cycle by gametophytic phase. Thus there are two phases of life cycle of Lycopodium the saprophytic and gametophytic which alternate with each other showing alternation of generation and the saprophytic phase is dominant over gametophytic phase. saprophytic plant body has definite leaf, root and stem, plant reproduces by minute unicellular structures called spores produced in special sac like structures called sporangia.
Sporophytic generation:
It is generation by spore formation. Fertile region in most cases is represented by strobili borne in pairs at apices of erect elongates stalk like branches the podia. Strobilus is made up of central axis on which the sporophylls are closely arranged. Sporophylls are similar to sterile leaves and differ in various species. Sporophylls usually rise in pairs. On inner side of each sporophyll in sigle kidney shaped sporangium is produced which bears the spores. All the sporangia are alike non sepiate sac like with short stalk and large number of spores. All spores are similar in size and shape i.e. they are homosporous in nature.
Development of sporangium and spores:
A group of superficial cells of sporophyll develop and function as sporangium initial cell i.e. the development is of eusporangiate type. These cells undergo further divisions and each of them divides into a large central and peripheral cells. The central cells divide periclimically and form a row of three cells the middle one form archesporium. By further division there forms three layered thick sporangial wall the inner most layer of which forms tapetum. Central cell also divides and forms a group of cells as archesporium, the cells of which form spore mother cells, which undergo reduction division and form tetrads of haploid spores which are all similar i.e. homosporous.
Gametophyte generation:
Spores are the units of gametophytic generation as the production of spores marks the end of diploid sporophytic generation and the beginning of haploid gematophyte. Spores are minute unicellular structures produced in large number and all are uniform in size and shape i.e. homosporous. Spores remain surrounded by two distinct walls the inner initine and outer exine. Spores get liberated from sporangium by transverse slit which divides sporangium into two valves which remain united at the base. Spores are carried by wind and germinate when ever they find the favourable conditions.
Germination of spore and development of gametophyte (Prothallus):
In Lycopoduim cernum the spores germinate within few days. The spore which is the unit of gametophytic generation germinates into prothallus. During germination of spores, the exine opens by three valves and intine corners out in the form of spherical vesicle.
This divides by transverse wall into an inner basal cell which gives small less shaped rhizoidal cell and an outer cell which develops as an apical cell and forms two rows of segments. Apical cell divides to form 4 to 5 called gametophyte. Further development of gametophyte takes place only when microhizal fungus infect it. This fungus enters through rhizoidal cell. After this the apical cell cuts off a group of mestermetic cell which after further division form a multi-cellular structure the prothallus. Mature prothallus consists of outer layer of epidermis followed by multilayered cortex. Prothallus is monoecious (bisexual) and sex organs are borne on upper surface of prothallus. The male and female reproductive organs are known as antheridium and archegonuim.
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