Q.9. Describe the external and internal features of Lycopodium.
Rerlated Question-
Q. Describe the internal structure or anatomy of stem of Lycopodium. (2012)
Q. Describe the internal structure of root of Lycpodium. (2011)
Q. Describe the structure of stem of Lycopodium. (2008)
Q. Draw a labelled diagram of stem of Lycopodium showing plectosele. (2004)
Q. Describe the different type of protosteles found in the stem of Lycopodium. (2002)
Ans. Morphology of the plant: -
The sporophytic plant body consists of slender and branched stem numerous small leaves and dichotomously branched roots.
Prizel (1900) divided genus Lycopodium into two sub-genera.
(A) Urostachya: - Erect stem and branches example : L. phlegmaria, L. selago, L. serratum
(B) Rhopalostachya: - Prostrate stems with upright branches example : L. cernuum, L. clavatum.
Stem: - Branching of stem in urostachya is dichotomous and in Rhopalostachya it is, partly dichotomous and partly monopodial. The stem and its branches are thickly,covered with spirally arranged leaves.
Leaves: - The leaves develop in whorls or spirally arranged. The leaves are of two types - vegetative whose function is photosynthesis and spore bearing called sporophylls. The vegetative leaves are simple, small, sessile, lens-shaped with broad base. The margins are serrate. The spore bearing leaves are broad and closely crowded to form strobilus. Leaf has single unbranched mid rib.
Roots: - Adventitious and arise all along the underside of stem in acropetal manner. The branching is dichotamous. No lateral branching.
Anatomy (Internal structure) of stem: - Cross section of Lycopodium stem shows the following structure: -
Epidermis: - Epidermis the outermost layer is one cell in thickness. The outer walls of the epidermal cells are cutinized. Stomata are present in the epidermis.
Cortex: - Epidermis is followed by cortex. Cortex may be homogenous i.e. made up of on type of cells parenchymatous or sclerenchymatous but usually to cortex has three distinct zones (a) Outer several layers sclerenchymatous zone (b) middle zone of parenchymatous cell. No intercellular space. (c) Inner zone of thick-walled sclerenchyatous cells.
Endodermis: - Cortex is followed by single layered endodermis. Endodermis may not be well defined but shows characteristic casparian thickening on the radial walls. Inner to endodermis is pericycle one to many layered.
Stele: - The centre portion of stem is occupied by a single large protostele. The xylem is star shaped and shows peculiar radiating arms. The protoxylem points are at the tip of the star shaped arms. The phloem is, present in between the xylem bands. This condition of protostele is plectostele.
However the stele in the stem of Lycopodium varies from species to species and presents a very good example of the presence of different types of protosteles. Usually three type of steles are seen in the stem of Lycopodium.
(A) Actinostele: - Xylem forms radiating arms from the centre. In btween arms lies the phloem. Example L, serratum, L. selago.
(B) Plectostele: - Xylem and phloem lies in parallel bands. Plate like appearance example : L. volubile, L. clavatum.
(C) Mixed Protostele: - Here xylem patches, are found as irregular scattered groups mixed with phloem. Example : L cernuum
Leaf: - The internal structure of leaf shows outermost layer of epidermis with thin walled cells. A thick layer of cuticle is present and stomata are present. Mesophyll does not show differentiation of tissues. Vascular bundle is single, concentric amphicribal in nature. Protoxylem and Metaxylem are not differentiated.
Root: - T.S. of Lycopodium root shows following structures:
1. Epidermis: - It is single layered outermost, made up of thin walled cells, unicellular root hairs are also present.
2. Cortex- It is broad, present below the epidermis, multilayred and parenchymatous, the outer cortex is sclerenchymatous.
3. Stele- It is diarch in which xylem is ‘C’ shaped; On both the ends of metaxylem protoxylem is seen. Actually there are seven to ten patches of protoxylem are corresponding metaxylem often unite in the center presenting a stellate form with the phloem between the rays. Stele is surrounded by well defined endodermis.
Q.10. With the help of diagrams only, describe the life cycle of Lycopodium. (2005, 07, 12)
Ans.
