Question

describe the anatomy of thallus of Marchantia.full description of mark 5​

Answer 1

Answer:

A section (V.T.S.) of the thallus shows three distinct regions viz., the epidermal region, the photosynthetic region, and the storage region.

1. The Epidermal Region:

It consists of a well- defined upper (dorsal) and lower (ventral) epi­dermis. The epidermis is formed of quadrate cells containing a few chloroplastids. An air chamber of schizogenous origin (Fig. 6.9A) is present just below the polygonal area.

The air chambers are connected with the outside atmosphere by a barrel-shaped air pore situated at the center of the polygon (Fig. 6.9A). The air pore is formed by 4 to 8 superimposed tiers of cells, and each tier composed of 4 or 5 cells (Fig. 6.9C).

The cells of the lowermost tier project inwards giving a star- shaped appearance to the pore when view from the above (Fig. 6.9D).

The lowermost ventral layer is the lower epi­dermis, which bears scales and rhizoids

2. The Photosynthetic Region:

The upper dor­sal epidermis contains a few chloroplastids. The air chamber is demarcated from others by single layered partitions of cells containing chloroplas­tids. Simple or branched filaments formed of cells in horizontal row full of chloroplastids arise from the floor of the air chamber.

These horizon­tal row of cells form the main photosynthetic tissue of the Marchant

3. The Storage Region:

 The ventral tissue lies immediately below the air chambers forms the storage region. It is a compact zone comprised of several layers of thin-walled, polygonal paren­chymatous cells devoid of chloroplasts. This region is thick in the center and gradually tapers towards the margin

However, most of the cells of the storage region contain starch grains or protein granules and some isolated cells contain large oily bodies or mucilage

The midrib of the thallus is made up of cells elon­gated tangentially showing reticulate thickening.

Explanation: