In this article we will discuss about the anatomy of lycopodium. Also study the strobilus, arrangement of sporangia, L.S. strobilus and spores of lycopodium.
Cut thin transverse sections of stem, leaf and root by inserting the material in pith, stain in safranin- fast green combination, mount in glycerine and study- under microscope.
1. Internally, the stem (Fig. 227) consists of a superficial epidermis, a broad cortex and a central stele or vascular cylinder.
2. Epidermis is the outermost layer, usually with the thick cutinized outer walls.
3. Stomata are also present in the epidermis.
4. Cortex is broad, homogeneous throughout or divided into three concentric zones, i.e., outer and inner zones of elongated sclerenchymatous cells and middle zone of large thin-walled parenchymatous cells. In the species, where cortex is homogeneous, it consists of parenchymatous cells.
5. An ill-defined endodermis marks off the stele from the cortical region.
6. Inner to the endodermis are present one to three layers of thin-walled cells constituting the pericycle.
7. Next to the pericycle is present the stele.
8. In general, the stele is protostele, but it varies in different species as well as in different portions of the same plant.
9. In L. serratum the stele is actinostele, in which xylem has radiating ribs and the phloem is present in isolated masses alternating with the xylem (Fig. 228 A). In L. volubile, plectostele is present, in which xylem and phloem are lying in the form of alternating plates (Fig. 228D.)
But in Lcernuum, mixed protostele is present, where the xylem is present in irregularly scattered groups embedded in a ground mass of phloem (Fig. 228C).
10. The xylem consists of protoxylem and metaxylem with the former being exarch and consisting of spiral or annular tracheids, and the latter consisting of scalariform tracheids.
11. Phloem consists of sieve tubes, sieve plates and phloem parenchyma with no companion cells.
12. Many leaf traces are present.
13. Cambium is absent and, therefore, the secondary tissues are absent.
1. It consists of cuticle, epidermis, spongy parenchyma and the central vascular strand (Fig. 229).
2. Epidermis is single-layered and covered with cuticle.
3. Stomata are present on both the surfaces of the leaf.
4. Inner to the epidermis is present the undifferentiated mesophyll tissue having intercellular spaces.
5. In the centre is present a single median concentric vascular bundle. Xylem is surrounded by a zone of phloem and may or may not be further surrounded by the endodermis.
6. Xylem consists of annular or spiral tracheid’s, and phloem consists of sieve cells and phloem parenchyma.
1. Anatomically, the root consists of epidermis, cortex and stele.
2. The epidermis gives rise to many root hairs.
3. The cortex is several cells in thickness, and outer few layers often become heavily sclerified.
4. The stele is monarch, diarch or triarch with one, two or three protoxylem groups
5. In some cases the same root is diarch in one portion and tetrarch in the other
6. The xylem is C- or U-shaped (Fig. 230) having the protoxylem at the tips of the ‘C’ or ‘U’.
7. Single mass of phloem lies between the points of ‘C’ or ‘U’.
Study the strobilus, arrangement of sporangia, L.S. strobilus and spores by cutting sections and with the help of permanent slides:
1. Fertile region is represented by strobili (Fig. 231), present at the apices of the branches.
2. In the species of sub-genus Urostachya, nearly each leaf of the plant is a sporophyll, but the species belonging to sub-genus Rhopalostachya the leaves of the apices of the branches are the sporophylls and bear sporangia.
3. Aggregation of sporophylls is called a strobilus.
4. Each strobilus has a strobilus axis (Fig. 233).
5. On the strobilus axis the sporophylls are arranged spirally.
6. On the adaxial side of each sporophyll is present a sporangium.
7. The sporangium is reniform, kidney-shaped or sub-spherical, and varies in diameter from 1 to 2.5 mm.
8. A sporangium is raised on a short and massive stalk.
9. Lycopodium is homosporous, i.e., all spores are of the same type.
10. Spores in the sporangium are arranged tetrahedrally. On germination, they develop into prothalli.
11. Each spore has a triradiate ridge (Fig. 234), and is enclosed within a thin or thick spore wall. The latter consists of two layers. The inner layer is granular and the outer layer is made up of concentric lamellae.
12. The spore wall may be smooth or variously sculptured. Each spore is uninucleate and the cytoplasm contains few chloroplasts.