Q.19. Describe the structure of rhizophore of Selaginella. (2008)
Related Question-
Q. Describe the nature of rhizophore of Selaginella. (2011)
Q. Rhizophore is a stem or root. Describe in brief. (2009)
Ans. Anatomy of Rhizophore: -
According to Harvey Gibson (1902) and Uphof (1920) The internal structure of rhizophore is very much similar to root but it differs in certain points which are as follows :
1. Epidermis: - It is the outermost, single layered and consists of thick walled cells. It is cuticularized and without root hairs.
2. Cortex: It is broad and divided into outer and inner cortex e.g., The outer cortex is sclerenchymatous which forms the hypodermis. The inner cortex is parenchymatous.
3. Endodermis : It is single layered and is present below the cortex.
4. Pericycle : It is also single layered and is situated below the endodermis.
5. Stele: It is protostele. The central solid core of xylem is surrounded by phloem. The xylem is monarch and exarch.
Morphological Nature of Rhizophore: - There are three views regarding the nature of the rhizophore.
1. Van Tieghem, Harvey Gibson and Uphof (1920) consider rhizophores as roots, because -
(a) They are positively geotropic,
(b) They have no leaves,
(c) They exhibit root-like internal features. The rhizophores always have monostelic stelar organisation, even when the stems are polystelic.
2. According to Pfepper, Trueb, Bruchmann, Velonovsky, Worsdell and Troll, the rhizophores have been regarded as stem-like structure because -
(a) They are exogenous in origin,
(b) They are devoid of root caps and root hairs,
(c) they are formed always from ‘angle meristems’ which are present between the two branches of the stem, and
(d) They can be developed into leafy shoots under controlled experimental conditions (Bruchmann and Williams, 1937).
3. According to Bower and Goebel, the rhizophore is neither a root nor a shoot but is an ‘organ sui-generis’.
Q.20. Differentiate between the roots Lycopodium and Selaginella. (2006)
Ans. Difference between the roots of Lycopodium and selaginella.
Q.21. With the help of labelled diagrams only describe the life-cycle of Selaginella.
(2006, 08)
Ans.
Q.22. Describe the alternation of generation in selagine11a.
Ans. Alternation of generation in Selaginella: -
In Selaginella two types of generation found (1) Sporophyte and (2) Gametophyte. The sporophyte plant body is differentiated into, rhizophore stem, leaves and strobilus. The strobilus bears two types of sporangia (Heterosporous) microsporangia and megasporangia. Inside the microsporangium, haploid microspores are produced after reduction division and inside the megasporangia haploid (n) megaspores are produce after reduction division. The micro and megaspores upon germination give rise to male and female gametophytes on which antheridia and archegonia are developed. After fertilization diploid (2n) zygote is formed. The zygote undergoes numerous divisions to form an embryo which develops into the sporophyte plant of Selaginella.