Definition: The kidney shaped sporangia growing in a group on the ventral surface of a fern leaf are called fern sori.
Position: They are situated on both sides of the midrib of matured leaf from the ventral surface.
Season: Usually, sori are found to grow in the late spring or in early summer.
Colour: At the beginning, they are green, later they turn into brown colour.
Origin: On the ventral surface of the leaf, sori start growing from the special meristematic tissue or placenta.
Structure: In each sorus, numerous sporangia are present A membrane covers the sporangia called inducium
Internal structure of sporangium: Each fern sporangium comprises of two main parts
(I) Stalk &
(I) Stalk: It is a multicellular and slender, rod like structure growing from placenta.
Fig: T.S. of fern sorus
- The oval shaped swollen part, situated at the tip of the stalk is called capsule.
- Its wall is composed of a one celled layer. These cells almost cover the capsule. This cellular layer is known as annulus.
- All the remaining cells other than annulus are thin layered which form an incomplete ring. These cells are called stomium.