Q.16. Draw a labelled diagram of longitudinal section of female prothallus of Selaginella. (2004,07, 12)
Ans.
Q.17. Describe the morphological and anatomical features of Selaginella.
Related Question-
Q. Write short notes on ;
(i) Distinguishing features of Selaginella.
(ii) T.S. Selaginella stem.
Q. Describe the internal structure of stem of Selaginella. (2012, 13)
Q. Describe the internal structure of root of selaginella. (2012)
Q. In which pteridophytic plant does trabeculate occur ? Explain internal structure of that part. (2006, 09)
Q. Draw labelled diagram of transvers section of stem of Selaginella. (2005)
Ans. Selaginella is a evergreen delicate herd. The plant body is sporophytic in nature and shows considerable morphological variations. Mostly the plant body is prostrate, creeping along the surface of the soil (S.kraussiana) others are suberect (S. trachyphylla) or erect (S.ergthropus). It may also climb by means of rhizophore (S. alligans). Selaginella can be divided into two sub-genera by Hieromymus 1900.
A. Homeophyllum: - Includes about 50 species with uniform leaves spirally arranged. They are monostelic (S. rupestris).
B. Heterophyllum: - It includes large number of species with dorsiventral symmetry and two types of leaves with prostrate plant body. (S.lepidophylla) (S.kraussiana) The plant body has stem, leaves, rhizophore and root.
Enternal features or morphogical features: - Go through Q.15
Anatomy of stem: - A transverse section of stem shows different parts :
1. Epidermis: - It is the outermost layer. The cells of epidermis are elongated and prosenchymatous and have their outer walls cuticularised. The stomata are absent.
2. Cortex: - It is situated below the epidermis. The outer part consists of Thick-walled, lignified cells forming a sclerenchymatous hypodermis, while the cells of the inner cortex are thin-walled green cells usually without intercellular spaces.
3. Endodermis - The endodermis is not continuous. The endodermal cells are radially elongated which are called trabeculae. The trabeculae connects the cortex, and the pericycle. In between the trabeculae clear air spaces are present.
According to Parihar (1977) - during the formation of trabeculae from endodermis, in the beginning single layered endodermis surrounds the stele. Then the endodermal cells detach laterally and elongate in the axis to the stele and thus the trabeculae are formed. Presence of characteristic casperian strips on the radial walls of trabeculae is an indication of their endodermal origin.
4. Pericycle: - It is single layered which is present outside the phloem.
5. Stele: - The number of stele is variable in different species of Selaginella. Most species have a well developed stele which is a protostele with two lateral protoxylem groups. In some species, the vascular arrangement of the stem is a siphonostele. The two protoxylem groups lie at the ends of the oval mass of metaxylem, so the stem is diarch and exarch. Various stelar modifications are found in the different species of selaginella. In species with dorsiventral stems, e.g., s. chrysocaulos, S. martensii and S.chrysorrhizos, there is a single stele (monostele) in the stem and in others two, three or more separate steles are present.
The xylem may be polyarch with a number or protoxylem groups. In S. spinulosa, the stem may have endarch xylem instead of exarch.
The stele becomes solenostelic by the appearance of a central pith, and further in the upright stems, it is broken up into many meristeles.
6. Xylem: - In monostelic condition, the xylem is diarch and exarch but in bistelic condition it is monarch and exarch. Both the protoxylem points are situated in opposite direction.
7. Phloem: - The phloem consists of smaller cells with densed protoplasm and completely surrounds the central core of xylem in each stele.
Antaomy of Leaf: -
The transverse section of leaf shows small and simple structures. The epidermal cells (upper and lower) are thin walled and contain chloroplasts (chlorenchymatous), stomata are many and restricted to the ventral surface near mid rib only. The differentiation of mesophyll into the palisade and spongy parenchyma is not very clear. Each cell contains a single chloroplast. The midrib consists of vascular strand which is concentric on outline. It consists of central xylem surrounded by phloem and endodermis.
Anatomy of Root: -
Anatomically the root consists of centrally placed stele surrounded by cortex and epidermis.
1. Epidermis: - It is the outermost and single layered. On the epiblema unicellular root hairs are present.
2. Cortex: - Below the epiblema a thin-walled parenchymatous cortex is found.
3. Endodermis: - It is not well developed except in few species like S.densa, S. rubella etc. An endodermis is present limiting the cortical region. It is followed by the pericycle.
4. Pericycle: - It is 1-3 layered in different species.
5. Stele: - The stele is a protostele, consisting of exarch and monarch xylem. The phloem surrounds, the xylem strand but there are no sieve tubes opposite the protoxylem. There is only one protoxylem group which is peripheral in position.
Q.18. Write short notes on ligule in Selaginella. (2005)
Related Question-
Q. Describe the stucture and function of ligule. (2013)
Ans. In Selaginella leaves are ligulate. The ligule is a structure differentiated early in the ontogeny of a leaf. A mature ligule is a tongue to fan-shaped and more than one cell in thickness, except at the apex. Its base consists of a cup-shaped sheath whose cells are tublar in shape and without protoplast when mature. In S. karaussiana the sheath cells-have a casparian strip similar to that of endodermal cells. Immediately adjoining the sheath is the glossopodium, a hemispherical mass of thin walled cells with greatly vacuolate protoplast. The remaining cells of the ligule are more or less cubical and densely filled with protoplasms. The function, of ligule is controversial. Many workers consider its as water absorbing or water secreting organ and prevent the undue drying of the stem apex and the leaves by keeping them moist.