How Is The Sporophytic Generation Dominant In The Life Cycle Of Adiantum?


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Life cycle of Adiantum shows heteromorphic alternation of generations.

The diploid sporophyte produces, in summer, a number of structures, the sori (singular Sourus).

The sori occur on the surface of the margins of the fertile pinnules.The margin of each pinnule is bent over the sorus to form a false indusium.The sori are green, but when rip they become dark brown. The leaves bearing sporangia are called sporophyllus.

Structure of Sporangium:
Each sporangium is slightly flattened, biconvex body (capsule) bone on a multi stalk. The capsule wall consists of a single layer of flat thin walled cells. The edge of the capsule is made up of two parts, the annulus and the stomium.The annulus occupies three fourth of the edge and remaining one fourth is the stomium. Annular cells have their radial and inner walls thickened the stomial cells are thin walled.

Inside the sporangia haploid spores are formed by reduction division (meiosis) from diploid spore mother cell. The annulus of the sporangium contracts in dry weather, the stomial cells being thin walled rupture and spores are dispersed by wind. When a spore falls on a damp soil, it germinates at a suitable temperature and produces a haploid gametophyte or prothallus.

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