In this article we will discuss about the anatomy of pteridium.
Cut thin transverse sections of root, rhizome, rachis and pinnule with the help of a sharp razor,double stain them with safranin-fast green combination, mount in glycerine and study under low and high powers of your microscope.
Anatomy of Root:
1. It is circular in outline and has three distinct regions, namely epiblema, cortex and vascular cylinder (Fig. 251).
2. Epiblema is the outermost layer of thin-walled ceils, from some of which develop unicellular hairs.
3. Cortex is quite extensive and divisible into outer cortex and inner cortex. The outer cortex is parenchymatous while the inner cortex is sclerenchymatous.
4. Inner to the cortex is present a single-layered endodermis followed by one or two-layered pericycle. Casparian strips are present on the radial walls of the cells of the endodermis.
5. Vascular cylinder exhibits radial, diarch and exarch conditions. Two large centrally located metaxylem tracheids with groups of protoxylem elements on their both sides constitute the xylem. On both the sides of the xylem plate is present the phloem.
Anatomy of Rhizome:
1. It appears like that of a biconvex lens in outline in transverse section. It is differentiated into epidermis, hypodermis, ground tissue and stele (Fig. 252).
2. Epidermis is single-layered, and its cells are thickly cuticularised.
3. Epidermis is followed by sclerenchymatous hypodermis. The hypodermal cells often show pitted walls. Some parenchymatous cells interrupt the continuity of the hypodermis on lateral sides of rhizome.
4. Ground tissue is parenchymatous and present below the hypodermis. Starch grains remain filled in the cells of the ground tissue.
5. The stele changes in structure according to the age of the rhizome. It is protostelic in very young rhizome and ectophloic siphonostelic in rhizome of the plant of about 2-3 weeks old. The rhizomes show dictyostelic condition in mature plants.
6. Dicnostele consists of meristeles arranged in two rings. Two sclerenchymatous bands separate both the rings of meristeles. Each meristele (Fig. 253) has its own endodermal layer followed by uni-or bilayered pericycle. The pericycle is parenchymatous. In the centre of each meristele is present the xylem which remains completely surrounded by phloem?
Anatomy of Rachis:
1. It is hemispherical or horse-shoe shaped in outline, and differentiated into epidermis, hypodermis, ground tissue and stele (Fig. 254).
2. Epidermis is thickly cuticularised and single- layered.
3. Hypodermis is sclerenchymatous, 2 to 3-layered and present below the epidermis.
4. Ground tissue follows the hypodermis. It is well developed and parenchymatous.
5. The stele is U-shaped or horse-shoe shaped and present in the ground tissue. A single-layered endodermis followed by a few-layered pericycle surround the stele. In the centre of the stele is present a massive xylem. Metaxylem is situated in the centre and protoxylem at two of its ends. Phloem is filled in between peicycle and xylem.
6. The nature of the stele, however, varies with the maturity of the rachis. The stele is U-shaped in younger parts. At a level, slightly above the base, the stele gets divided into two well-developed meristeles. Many meristeles are present in the mature part of the rachis.
Anatomy of Pinnule:
1. It is divisible into a midrib region and the wings.
2. Single-layered upper and lower epidermis is present. Some stomata are present in the lower epidermis.
3. In the region of the wings, mesophyll is present in between two epidermal layers. It is divisible into palisade and spongy parenchyma (Fig. 255). Palisade is present towards the upper epidermis whereas spongy parenchyma is present close to the lower epidermis. The cells of the spongy parenchyma are loosely arranged. Chloroplasts are present in these cells. The intercellular spaces of the spongy parenchyma open into the stomata.
4. The midrib region contains a centrally located concentric vascular bundle and compactly arranged parenchyma. A parenchymatous bundle sheath surrounds the vascular bundle which consists of centrally located xylem surrounded by phloem.
Sporophyll, Sorus and Sporangium:
Cut sections of the fertile pinnule containing sori (sporophyll) on its lower surface, stain in safranin, mount in glycerine and study under microscope:
1. Sori (groups of sporangia) are present on the lower or abaxial side of the fertile pinnule (sporophyll, Fig. 256A). They are present along the margins. The sporangia form a continuous or confluent linear sorus called coenosorus.
2. Indusium or a layer of indusial flap protects the sorus. Mixed sporangia are present in each sorus, and their development is leptosporangiate.
3. A mature sporangium is differentiated into a stalk and a capsule. The stalk is long, slender and consists of three rows of cells (Fig. 256B, C).
4. The capsule is globular or biconvex. A single- layered thick sporangial jacket is present. Some thick-walled cells in a ring form the annulus. A few thin-walled cells of the ring represent stomium. 32 or 64 spores are present inside the capsular wall.
5. Pteridium is homosporous, i.e., all spores are similar in shape and size. Each spore is uninucleate and has a bilayered wall. The intine is thin while the exine is a thick layer.
Prothalius (Young):
1. Young prothallus is a dark-green, heart-shaped structure consisting of single-layered sheet of cells (Fig. 257).
2. In the central region of the lower side of prothallus are present several rhizoids which attach the prothalius to the substratum.
3. Middle region of the prothallus is several cells thick.
4. Several antheridia and archegonia are present. Several multi-flagellate antherozoids are present in each antheridium. Archegonia develop near the apical notch of the prothallus.
5. Each archegonium consists of a neck and ventre. The neck is 5-7 cells in height and encloses a binucleate neck canal cell. A small venter canal cell and a large egg are present in the venter.