In this article we will discuss about the structure of Pogonatum with the help of diagrams.
External Features of Pogonatum:
The gametophyte is perrenial, differentiates into a rhizomatous basal portion and aerial upright shoots (Fig. 6.54A). The basal portion bears numerous rhizoids. The rhizoids are multicellular, elongated, thick-walled with oblique septa and are twisted together in a rope-like manner to form strong cable-like strings.
The aerial shoot may be unbranched or branched, composed of a central axis, covered with spirally arranged leaves (Fig. 6.54A, B). In the lower part of the upright stem, the leaves are very small, scaly and much paler in colour. While, in the upper part of the stem, the leaves are comparatively larger with broad sheathing bases.
The upper part of these large leaves extend into a narrow brown or deep red coloured limb having serrated margins. The leaves are provided with a thick midrib and two laterally extended thin and narrow wing-like lamina (Fig. 6.54C).
Internal Features of Pogonatum:
Stem (Axis):
A T.S. of the stem shows an epidermis, the cortex and the central cylinder consisting of elongated leptoids and hadrom cylinder (Fig. 6.55). The epidermis is the outermost covering of the stem, composed of thick- walled cells. The epidermis is broken up giving an irregular outline of the stem by the interruption of a number of leaf bases.
The cortex is differentiated into two zones, the outer cortex and the inner cortex. The outer cortex is composed of deeply coloured, 3-5 layered chlorenchymatous cells. The inner cortex is made up of thin-walled parenchymatous cells, full of starch.
Many leaf-traces are present in the outer part of the inner cortex, comprising of a small group of thick-walled cells. Next to cortex, a zone called leptoid is present which is comprised of elongated living cells, devoid of starch. This zone is comparable to the sieve tubes of the higher plants. There is a zone of leptoid cells interspersed with starch-containing cells, called leptoid mantle.
The central zone of the stem is called hadrom cylinder, comprised of two types of cells: the elongated thick- walled cells with protoplasts, called stereides, and thin-walled cells, devoid of protoplasts, called hydroids.
Leaf:
The upper surface of the midrib is completely covered by parallel vertical plates of cells, called lamellae (Fig. 6.54C, D). This is comparable to the gills of Agaricus fungi. Each lamella consists of 4-8 cells (Fig. 6.56). All the cells, except the terminal one contain chloroplasts.
The terminal cell is larger than the remaining cells of the lamellae (Fig. 6.56). In some species (viz. P. microstromium), terminal cells split into two conical cells. The lower epidermis forms a distinct layer, comprised of thin-walled cells.
