In this article we will discuss about the anatomy of anthoceras with the help of a suitable diagram.
The thallus of Anthoceros is several layers thick but it lacks a definite midrib. In a thallus all cells are thin-walled (Fig. 3.2B). On the ventral surface of the thallus are smooth colourless rhizoids. Stomata-like pores occur on the undersurface. On the undersurface of thallus are seen small dark bluish-green spots; which are colonies of cyanobacterium Nostoc.
On the under surface of thallus, very early in development, are formed cavities (Fig. 3.2A). It is due to the breakdown of cells and their replacement by mucilage. With the maturity of thallus, the mucilage in these cavities dries out resulting in air-filled chamber.
The cyanobacterium Nostoc entering through mucilage pore forms a colony in these cavities (Fig. 3.2A). The cyanobacterium-hornwort association is symbiotic; the thallus supplies carbohydrate to the cyanobacterium and the latter in turn adds to nitrate nutrition by fixing atmospheric nitrogen.
Each cell of a thallus contains a single large chloroplast (Fig. 3.2B). The chloroplast of a superficial cell is larger than others and is lens-shaped. Each chloroplast encloses a body of 25-50 discrete units, the pyrenoid. The nucleus lies opposed to chloroplast, usually near the pyrenoid body.
At times, the chloroplast gets folded to enclose the nucleus as well as pyrenoid. A single chloroplast per cell with its associated pyrenoid is unique to Anthoceros and unknown in any other bryophyte. Some species of Anthoceros have variable number of chloroplasts per cell. In A. pearsoni there are two chloroplasts in the inner cells and in A. halli their number may be even four.
The growth of thallus is due to a single wedge-shaped apical cell of four cutting faces or a marginal meristem, where each cell has four cutting faces- dorsal, ventral and two lateral.
