Question

Describe the structure of Pteris prothallus.

Answer 1

Hint: Pteris is an example of Pteridophyta that are the spore bearing most primitive vascular plants. They are commonly called vascular cryptogams and they are divided into four classes- Psilopsida, Lycopsida, Sphenopsida, and Pteropsida.

Complete answer:
The gametophyte stage in the life cycle of the fern or other Pteridophytes is called prothallus. It is also used to describe the young gametophyte of the peat moss.

The spores after germination develop into the prothallus which is an inconspicuous structure. The spores after germination develop into rhizoid and a filamentous structure called the prothallial cell. This prothallial cell has an apical cell divide and a small structure called prothallus. It is a dorsiventral and flat structure.

It is generally heart-shaped and consists of a number of rhizoids on the ventral surface. It has a thick layer of cells towards the centre and a single layer of cells at the margin. It can be green and photosynthetic or non-green and saprotrophic in the nutrition.

The female and male sex organs i.e. archegonium and antheridium develop near the notch and the central region respectively.

Note: Pteris is a homosporous fern that shows the alternation of generations. Its sporophytic stage which is also called as the fern forms spores in the sori of the leaves by meiosis. These haploid spores then divide by mitosis and develop into the gametophytic stage i.e. the prothallus. The prothallus then develops male and female gametes in antheridium and archegonium that fertilize and fuse to form the diploid zygote.