In this article we will discuss about the anatomy of riccia with the help of a suitable diagram.
Internally, as revealed in a cross section, the thallus shows two distinct zones (Fig. 2.2C, D); an upper assimilatory zone and lower storage zone. The chlorophyllous cells of assimilatory zone reveal two types of tissue organizations.
In a more common type of organization (Fig. 2.2C), the chloroplast-rich assimilatory cells are stacked over one another, forming a filament which serves as a column of air chamber. The uppermost cells of assimilatory filaments lack chloroplasts and together form a loose epidermis. A number of air chambers, are in fact long vertical canals, each chamber is bound by four or more epidermal cells.
In a less common type of organization, the assimilatory cells form a loosely arranged network; enclosing large air spaces (Fig. 2.2D). Such thalli are spongy as that of R. crystallina (Fig. 2.2E). The air chambers arise schizogenously; by the splitting of internal cell walls. The splitting may begin from below and extend upwards or it can be the other way round.
The storage zone is made up of non-chlorophyllous cells, which are compactly arranged parenchymatously. These cells are full of storage products; starch can be easily detected in these cells on treatment with iodine. The lowermost cell layer of this zone forms the lower epidermis, some of the central cells of the epidermis elongate to form rhizoids, whereas marginal cells in an organized way divide to form scales.