In this article we will discuss about the anatomy of sphagnum with the help of a suitable diagram.
The stem grows by means of an apical cell with three-cutting faces.
The leaves are distinctive in lacking a midrib and an orderly disposition of two types (Fig. 4.6A) of cells:
(a) Narrow and elongate chlorophyllous cells, and
(b) Polygonal large hyaline cells which are devoid of cell contents.
These cells have thickening bands and pores. Leaves on the main stem are different in size, shape and structure than those on branches. The stem leaves have little or no chlorophyll, their hyaline cells lack pores and thickenings. The leaves present on branches are made up of a network of elongate chlorophyllous cells, 5 or 6 of which surround one hyaline swollen porose dead cell.
In a cross section of mature leaf (Fig. 4.6B) there is an alternation of large and dead hyaline cell and wedge-shaped chlorophyllous cell.
Internally, the main stem is differentiated into three distinct zones (Fig. 4.6E, G). The cortical cells are hyaline and often have thickening bands and pores, as in hyaline cells of leaf, for absorption and retention of water. In species with submerged stems the cortical cells are unmodified normal cells.
The axial cylinder is made up of outer layer of small pigmented thick-walled cells and a central mass of somewhat enlarged cells. The pigmented cells have various shades. Bright colours of Sphagnum plants are due to these pigmented cells and the light passing through colourless cortical cells.
The branches are characterized by one-layered cortex (Fig. 4.6F). The axial cylinder is similar to the main stem. In some species the cortical cells are of two types. There is conspicuous elongation of some of the cortical cells into a long narrow structure with a curved neck and an opening. These modified cells resemble a retort; hence the name retort cells (Fig. 4.6C, D). In species having cortical cells with thickenings and pores, the retort cells are missing.
